Comparing charateristics of the partial laminar and clasp dentures. Errors and complications using clasp prosthesis.
Treatment of patients with defects of dentitions by removable dentures
Carious disease and its complications, non carious lesions of hard tissues of a teeth, diseases of parodontium, inflammation diseases of jaws of odontogenous and non-odontogenous parentages, malocclusion, trauma, tumors are often result to integrity disturbance of dentitions. In 70% and more people in age 40-50 years has that defects. The arisen disturbance of integrity of dentition— irreversible process, that’s why defects of dentition should to know like heavy affect of formed dental-jawsystem, because there are Arise and develop pathological conditions with typical symptomatic.
|
Laminar denture with fixing clasps on the lower jaw (not leaning). |
Clasp denture on lower jaw at combined defects of dental arch.
Elimination of the arisen defect in dentitions, remove of inflammatory and destructive processes, the prevention of the further deformationare reached by prosthetics. It is based on load possibility of parodontium of basis teeth within their endurance at the expense of available physiological reserves. Using in this process dentures was divide on three main groups.
1. Bridge dentures, leaning more often on a teeth, limiting defect and transferring a load by theirperiodontium (that is more physiological path).
2. Partial removable dentures which can divideon leaning and non-leaning. Removable dentures, perceiving a load and transferring it by the admixed path, both through a periodontium of a basic teeth, and through tissues, not fitted for a load (alveolar processes), are called as leaning. Them concern all clasp prosthesesand removable prothesis, in which construction there are adaptations which allowing to transfer pressure the admixed path.
3. laminardentures with fixing clasps which transferring a chewing pressure only on alveolarprocesses, body of jaws and palatum (on the tissues of denture’s field, not adaptive to a load, are called as non-leaning).
The earliest kind of prostheses, used for elimination of defects of dentitions, the most widespread and almost completely (to 95-98%) restore a chewingeffectively, are a bridge-like dentures.
Except bridge, at defects of dentitions often using a removable dentures, that is it is possible to tell that with augmentation of defect of the indicationto using fixing dentures arenarrowed, and removable dentures — extend.
Construction of the modern removable denture. Every removable denture has itself constructive features, defined position and in size of defect, amount of remain teeth, condition of their hard tissues and parodontium, condition of covered a prosthetic field mucosa, safety of alveolar process, expression of hard palatum and other anatomical features.
Despite a variety of existing constructions there are can find partsrepeated in all types of removable dentures. It is necessary to carry to them: basis, fixed mechanisms(clasps) and artificial teeth. In the arch denture (except basis, fixed elements)has also an arch and it processes.
Laminardenture consists of leaned to alveolar process basis, the body of jaw, artificial teeth which restore an integrity of dentition, and claspsor other mechanical attachments which fixing a denture on natural teeth.
The main feature of lamellar dentures with fixedclasps is their locating on the non chewing pressure tissues. That’s why it can’t to reach such size like at bridge prothesis when the chewing pressure transferred by most natural path (through periodontium of teeth). Hence, the functional valueor chewing effectively of removable laminarnon-leaning dentures is much less then in bridges. If it at bridges is 90-95%, than at laminar is 25-30% and not much more than 40%. And the main case ofsuch difference is perception of pressure by non-specialized tissue.
The pressure of basis on the tissues which are under prosthetic field and not fitted for its perception causes their atrophy. There is a raised desquamation of an epithelium. It breaks endurance of a mucosa to external borings, therefore in it often there is a chronic inflammatory process. The part of denture which adjacentto the necks of teeth and gingival margin causes a nearly-neck caries and gingivitis with formation of a dento-gingival pathologicalpocket. Fixing denture clasps are constantly slipping on a surface of a crown of a tooth owing to denture immersingin mucosa at a load and homingsin a starting position at it removing. Owing to this the enamel is traumatizing, appear a hyperesthesia, quite oftenand caries.
But removable dentures have an advantage before a fixed bridges in it’s hygiene.
Considering disadvantages of both dentures which remove defects of dentitionsit’s evolution move at the path of removability saving and reduction of denture basis, uniform distribution ofchewing pressure between mucosa ofdenture area and teeth at simultaneous augmentation of fastnessand functional value of denture. If reduce the basis removable lameinar denture than specific pressure will be enlarged (pressureon unit of mucosa of denture area). How it can be compensative? Redistribute the part of a load from mucosa to teeth. This tendency has led to occurrenceto leaning denture.
The questions about construction of basis and other elements of partial removable dentures were given a lot of attention during all period of dentistry development. Along with difficult constructions of a leaningdentures are offered also simple.
In ancient times people were tried to restore the lost teeth. The material for making dentures were been the natural teeth which loss before and processed in appropriate path and teeth of different animals. Such teeth became attached by thread or golden wire to the adjacent natural teeth and, of course, they functional values were been small. The most ancient of found teeth were made from gold. These works cause our surprise as expediency of the device and durability of manufacturing. Etruscans were able to fix the loosened teeth and replace the loosed. Romans borrowed much at Etruscan and indenture technique followed by its way. Throughout many centuries the prosthetics of teeth remainsalmost at the same level, as in the ancient time. And only in begin of XVIII century dental prosthetics were begun to passfrom handicraftsmen to dentists.
One of the first scientists which open the new ways in dental prosthetics was Pyer Foshar. In 1728 he for the first time has published the book «the Treatise about a teeth» in which in detail described various waysof manufacturing and strengthening of artificial teeth. The material for his dentures were been thebull’s or elephant’s bone. Separate teeth Foshar were strengthened for the adjacent by means of the waxed silk thread. The full denture on the upper jaw he strengthened by means of springs. Foshar were made also and a pin teeth by the naturalor cut them from the bone. All this dentures were made by himselfmanually. Further Foshar covered the teeth by a golden plate, because the artificial teeth were turned yellowat the time. Then on this plate he begins to put a layer of white enamel like the natural teeth color. It has suggested on idea the latest inventors to the manufacturing dentures fully from porcelain.
In 1756 Wilhelm Pfaff begins to take out casts from jawsby the wax and on them to cast plaster models. It has served as thebig jerk to denture development, because before the dentures were sharpen «on the eye».
The developer of the porcelain teeth is the druggist from Sent-Germen Dushato. In 1774 he made fully denture with all teeth from fusible porcelain.
Later the French surgeon Fuku has replaced fragile fusible porcelain on refractory. After this the Parisiandoctor Fontsy in 1808 begins to manufacturing separate front teeth from refractory porcelain and also has supplied them behind with a small hooks from platinum (crampons). All this lifted prosthetics on higher step.
In 1834 the master of dentistry and obstetrics Joseff Hall published his book «Popularity administrateabout importance themes of dentistry». In this work he was first which describe «Clasps dental prosthetics». Being based on its this report consider as a founder of modern partial removable dentures. He has research a construction ofdenture on the hooks which was covering the teeth and, thanks toelasticity of material, the denture can be frequentative to put in andto put out. This removable partial denture was opposed non removable.
With dentistry development has increased as well number of produced dentures. In this connection the problem of a cheap material becomes the most actual. Cutting dentures from the bone was required a big expense of the time, but the stamped gold plates was too expensive.
That’s why the scientists try to find the cheapest material for manufacturing the dentures.
The new era in prosthodontics development was an introduction in dentistry the rubber.Vulcanized rubber into the dentistry practice for the first time has been entered in the fifties XIX century by American Putram, and in 1854Nink for the first time has made of it f denture. Since thus the denture basis begin to manufacturing from the rubber, fixing in itporcelain teeth. Such denture was a not just esthetic, but has the most functional quality. By it can be good to chew a food. It was a perfect basis material in these times, and rubber dentures taken a wide distribution.
Simultaneous with the dentures from the rubber in this period was manufactured a basis plates which fixed in the mouth by the clasps.
In 1916 Kummer has offered the bugel denture construction.
Most authors was try to improve already available claspsor to invent new.
Absolutely new construction of basis for dentures was gives E.E. Gaffner (1937, 1942). He has suggested making crowns with nearly-neck prominences for clasps. For this author hasespecially constructed planimetric forceps and also has offereda methodic of making of these prominences. Such prominencesare interfering the shift of clasps in a direction to the root and by that take up a part of chewing pressure. These crowns are founded a wide using in the dental prosthetics. They are easy makes and especiallyvaluable in the partial removable denture.
Interested method of fixing dentures on the roots has given Arnold (1962). Fixation of denture by his method was goes by theway of fixing about the root of tooth the spherical buttonwhich casted from the metal and cemented in the root.
In 1952-1961 Kemeny has offered to fixing the partial removable dentures with using the dento-alveolar clasps(img. 357, 409). This clasps was manufactured from the basis plastic, and in frontal site — from the transparent plastic. The dentures with these fixating elements Kemeny has named retential. Additional coverage of vestibular surface of alveolar process was supplya good stabilization of denture, promotes reductionof vertical loading and amortization the horizontal pushes. At choose the constructions of partial removable denture before the dentist the first of all arise a question about the way of its strengthening in the oral cavity. Effective way of fastening is one of the conditions which provide a good functionalquality of the denture. For fixation the partial removable dentures are resort to the adhesion help, anatomical retention, and artificial mechanic devices: clasps, pelots (one of the types of non-clasps fixation), telescopic crowns and other.
B.E. Lemberk in 1940 has described manufacturing of denture, occupyingaverage position between bugel and lamellardentures. The similar construction of partial removable dentures for upper jaw, which have advantages about thearch dentures, offered in 1951 I.V. Ithighyn. These dentures have all main details of arch denture, except an arch. She has replaced by the plastic intersection, connecting the denture’s parts and placed on a margin of average and back third of tooth.
Principal components ofpartial removable lamellar denture are the basis (plastic or metal), artificial teeth by other materials and every possible mechanical devices for fixation.
The basis of denture. The basis (basic) of removable lamellar denture is the plate from plastic or metal on which fixating the artificial teeth and devicesfor holding it in the mouth. The basis of denture was placedon the alveolar process of lower jaw, and on the upperbesides also and on the palatum. Chewing pressure from the artificial teeth is transferred through it on the mucosa ofdenture field.
With the basis of denture is bounded the series of negative phenomenon. He has causes the disturbance of the tactile, gustatory and thermoesthesia, covering the hard palatum. Simultaneouslycan be observed the disturbance of speech, self-cleaning of the oral cavity mucosa, its irritation, sometimes occurrence the vomitive reflex. In places of adhere the denture to the natural teeth can arising gingivitis with formation ofpathological pockets.
For uniform distribution of chewing pressureon subject tissues the basis of removable denture should to possess sufficient durability, elasticity and minimal plasticity. From hygienic reasons the basis should be manufactured from the material which little adsorbs the components of the oral fluid and foodstuff, easy cleaning by the usual agents which intended for tooth care. The greatestdistribution has received special basis plastics. Its basis is a polymers of an acrylic group which difference by entered co-polymers and excipients. Also has next basis plastic: etacryl, phtorax, bak-rel, acrel, acroneel, transparent plastic.
But the last list of basis plastics not always allow to made the removable dentures of sufficient durability, especially in the hard clinical cases. Also using the metal alloys: stainless steel for the basis removable dentures manufacturing by the method of stamping and cobalt-chromium alloy (CHA) — for casted alloy. The precious metal alloys, ext. on the golden basis, isn’t using for this purpose, because they isn’t have much durability like the non-precious metals, very expensive, and the main — it’s have too many weight.
Thickness of the plastic basis (in average) – 2 mm, that is it is peer to a thickness of the plate of the basis wax. Metal basis at the mostly durability has a smaller thickness — from 0,2 to 0,6 mm. By this case, and also by better heat conductivity, the patients are better carry metal basis, quickly adapting to it at the case of exact conformity of an internal basis relief to the mucosa relief whichis reached by precision moulding of cobalt-chromiumalloy on the fire-resistant models and it’s very hard to receive the metal basis by stamping. The domestic industry does not deliver preparations from sheet stainless steeland presses for manufacturing thestamped metal basises, that’s why it’s not using in our time. Ubiquitous introduction of high-pitched fusion of alloysand precision moulding on a compensation fire-resistance models allow to use these more progressive constructions.
Plastic basises of a removable dentures have various shades of a pink color which is defined by color of an initial powder (etacryll, acrell, phtorax) or by amount of entered stain (acronyll). It is publishing also transparent basis plastic which usingin persons with allergy on the stain for manufacturing dento-alveolar clasps with purpose of taking the esthetic effect.
Size of the denture basis depend from quantity of saved teeth, degree of atrophy of alveolar process, expressions of the crestof the hard palatum, torus presence on it, pliabilityof the mucosa and others. If safeties of teeth lower, than basis is bigger. The good terms for denture fixation(high alveolar process, expressed crestof the hard palatum or increase of quantity of clasps) allow decreasing the denture basis.
Removable dentures
|
|
|
There are a lot of cases when patients are partially toothless and it is impossible to set a fixed denture. So we have to offer them removable dentures of two types: fully removable (if a patient is completely toothless) or partially removable (if a patient is partially toothless). Removable dentures may be laminar and clasp (arched or supported). In the latter a metal arch substitutes for a significant part of a plastic base.
Removable dentures have different characteristics.
Clasp dentures produce masticating load not only on the gum and bone tissue of jaws but also on attachments by means of special rests that may be made of metal or plastic.
Removable dentures have different characteristics. Clasp dentures produce masticating load not only on the gum and bone tissue of jaws but also on attachments by means of special rests that may be made of metal or plastic. Removable laminar dentures are supported only by the alveolar ridge. To improve the fixation of them in the oral cavity we use dentures with a soft functional edge and achieve close and comfortable joint even under heavy load. But you should bear in mind that a removable denture will never be attached in the oral cavity as good as a fixed one.
If you are against removable dentures but have lost most of your teeth you will be offered implants. Unfortunately, there are few people affording it for medical contraindications or high cost. Cheer up! We have different kinds of removable dentures (made of nylon, durable soft plastic, with a soft functional edge, silicon liners, telescopic crowns, attachments and etc.). Take your time to extract the left teeth even if they are decayed. They caot be attachments for a bridge but helpful for a partially removable denture (dentures with telescopic crowns and attachments). These dentures will be supported not only by your gum but also by roots of the left teeth.
1. Partial denture: A prosthesis that replaces one or more, but not all of the natural teeth and supporting structures. It is supported by the teeth and/or the mucosa. It may be fixed (i.e. a bridge) or removable.
2. Removable partial denture (RPD): A partial denture that can be removed and replaced in the mouth by the patient.
3. Interim denture (provisional; temporary): A denture used for a short interval of time to provide:
a. esthetics, mastication, occlusal support and convenience.
b. conditioning of the patient to accept the final prosthesis.
4. Retention: Resistance to removal from the tissues or teeth
5. Stability: Resistance to movement in a horizontal direction (anterior-posteriorly or
medio-laterally
6. Support: Resistance to movement towards the tissues or teeth
7. Abutment: A tooth that supports a partial denture.
8. Retainer: A component of a partial denture that provides both retention and support for
the partial denture
B. Treatment Objectives
1. preserve remaining teeth and supporting structures
2. restore esthetics and phonetics
3. restore and/or improve mastication
4. restore health, comfort and quality of life
C. Alternatives to RPD’s (Treatment Options – Important for Informed Consent)
1. No Treatment (Shortened Dental Arch)
– Most patients can function with a shortened dental arch (SDA)
– Requires anterior teeth + 4 occlusal units (symmetric loss) or 6 occlusal units
(asymmetric loss) for acceptable function (opposing PM =1 unit, opposing molars
= 2 units)
– RPD doesn’t usually improve function if minimal occlusal units present
2. Fixed partial denture – requires abutments at opposite ends of edentulous space, more expensive than RPD, must grind down abutments, flexes and can fail if too long.
3. Implant supported prosthesis – most costly, closest replacement to natural dentition, less costly over long term
4. Complete denture (if few teeth left, with poor prognosis); if replacement of missing
teeth is very complex or costly
D. Indications for RPD’s
1. lengthy edentulous span (too long for a fixed prosthesis)
2. no posterior abutment for a fixed prosthesis
3. excessive alveolar bone loss (esthetic problem)
4. poor prognosis for complete dentures due to residual ridge morphology
5. reduced periodontal support of remaining teeth (won’t support a fixed prosthesis)
6. cross-arch stabilization of teeth
7. need for immediate replacement of extracted teeth
8. cost/patient desire considerations
Treatment Sequence for Partial Dentures
If an RPD is part of planned Treatment:
PLAN THE RPD BEFORE BEGINNING ANY OTHER TREATMENT
• Survey, tripod, heights of contour
• Draw design on surveyed cast
• Design approved before any treatment started:
o Affects direct restorations
o Can influence need for/preparations for crowns
o Insures RPD can be completed successfully
o NO EXCEPTIONS
CLINICAL STEPS
1. Diagnosis, Treatment Plan, Hygiene
2. Diagnostic Casts
3. Draw design & list abutment modifications on Prosthesis Design page
4. Instructor Approval
5. Complete Phase 1 treatment
6. Abutment modifications
7. Preliminary impression to check abutment modifications
8. Crown or Fixed partial denture’s for removable partial denture abutments (if necessary)
9. Final Framework Impression (must include hamular notches/retromolar pads for distal extension removable partial dentures
10. Make two casts
11. Draw design on 2nd cast
12. Instructor approval/corrections
13. Complete RPD Framework Prescription (instructor signature required)
a. Second poured cast with design sent to Lab with 1st pour
14. Inspect wax-up
15. Framework Adjustment
16. Altered Cast impression, if needed
17. Try-in with teeth in wax
18. Process, deliver to patient
E. Components of a Partial Denture
a. Major Connector: The unit of a removable partial denture that connects the parts of one side of the dental arch to those of the other side. It’s principal functions are to provide unification and rigidity to the denture.
b. Minor Connector: A unit of a partial denture that connects other components (i.e. direct retainer, indirect retainer, denture base, etc.) to the major connector. The principle functions of minor connectors are to provide unification and rigidity to the denture.
c. Direct Retainer: A unit of a partial denture that provides retention against dislodging forces. A direct retainer is commonly called a ‘clasp’ or ‘clasp unit’ and is composed of four elements, a rest, a retentive arm, a reciprocal arm and a minor connector.
d. Indirect Retainer: A unit of a Class I or II partial denture that prevents or resists
movement or rotation of the base(s) away from the residual ridge. The indirect retainer is usually composed of one component, a rest.
e. Denture Base: The unit of a partial denture that covers the residual ridges and supports the denture teeth.
Denture margins on the upper jaw.
From the vestibular part:on the transitive cord level, bypassing bridles and cords of the mucosa closely to the oral side.
From the oral side:at the frontal natural teeth having on the level of бугорковof teeth, without blocking them. In the molars and premolars area on the 2/3 level of the crowns height. In the presence of a torus it’s should to block by basis with correspond isolation of a site. Trying not to dilate the torus margins on a model the torus is outlined by circular line. In the future denture in the torus area from the gingival side of the denture will be a small thick which allow a denture not to rest on a torus.
Distal marginof the denture to round in the spaces between last molars. Distal border of the denture will represent a line spent at once behind last molar teeth of a jaw.
Denture margins on the mandible.
From the vestibular side:by the transitive cord level, bypassing mucosa bridles and cords closely to the oral side.
From the oral side:to block all remain teeth on the 2/3 from the crowns height. The lingual margin of the denture passes on the transitive cord, having corresponding cut for the lingual bridle in the form of a semilunar cutting.
After the model is outlined, starting the wax template manufacturing with the occlusial platens. They are need for defining the condition of the central occlusion at the patient in the clinic by the doctor and fix it which help the dental-technique to plaster the models in the articulator in the central occlusion position.
Templates and patens are making from the basis wax. The wax is issued in the plates diameter 20×10 sm. Preliminary cutting the plate on the square of the outlined zone on the model. On the lower jaw the plate should to fold double. The next step is warming up the wax plate over the torch or the spirit-lamp flame (for the lower jaw – the wax plate fold double, in warmed up by a part, then again warming up the folded double plate); the back side to the warmed big fingers is press to the gingival surface of the model. Surplus of wax on the borders is cutting by the warmed spatula. The wax basis is fixing by the wire to prevent the deformation in the oral cavity. Cutting 4-6 sm of the wax diameter 0.8 sm, bend horseshoe-like by the oral cavity part form of the alveolar process, try on the wax template, for it. The wire taking by a tweezers and warming over a torch. After, the wire piece smoothly to lover in the wax outside of template at the basis of the alveolar process from the pallatinal side. The wax template is ready.
Further start to manufacturing the occlusial platens. The warmed wax plate rolling down in the platen and stack in a free site from a teeth. The platen should be monolithic, height 1-1,5 sm, width 1 sm; based at the average of the alveolar process, stuck densely together with the wax basis (should to spend the warm spatula on the inner and outer surface of platen for it). Theplatensgiveasmoothsurface. The distal platen’s sites are making it the form of a bias. In the presence of a natural teeth the platens making on the 2-3 mm higher than teeth level.
The finished wax templates with the occlusal platens on the models transfer to the clinic. The dentist is defining the central occlusion.
The next step of the partial lamellar dentures manufacturing is casting models in the articulator.
The articulator represents the simulator of the vertical movements of the lower jaw (opening and closing the mouth). It is consists from the upper and lower frames, axis which fastening this frames, articulator high pin which help to regulate the height of the occlusion. The articulator is helping to statement the teeth on existing antagonists, and also to fix the central occlusion.
Surpluses of the gypsum cut off from the models so that the pin of height of an articulator rested against a platform and didn’t interfere with the connection and disconnection of the articulator. On socle parts of the models do notches crosswisely for the better gypsum fixation. The lower frame of an articulator moistenswithwater.
Get mixed up gypsum and impose it on a smooth table surface and immerse in it the lower frame of an articulator. After add a small layer of gypsum and putting the models on it which fixing it so the overage line of the models is coincided with the overage line of an articulator in the central occlusion position. Further the layer of gypsum imposing on a lower jaw model and omit the upper frame of an articulator. Gypsum compare so that it has covered with an equal layer a framework of the model and articulator. After the gypsum will fall asleep, models will be plastered in an articulator in the central occlusion position.
After an articulator opening the occlusal platens are deleting, correct wax templates and start to partial lamellar denture manufacturing.
As is it shows any partial lamellar denture consist of a three parts: basis, artificial teeth and clasp system.
Clasp system is fixing denture attachments which hold it in the oral cavity at the chewing and non-chewing movements. Clasps are sectioned by a material: on the plastic and metal.
Teeth on which settle down a clasp are called as basic. If connect basic teeth a conditional line we will receive a clasp line. If in denture has one basis tooth so that denture fixation called dotted, if two (one clasp line) – linear. If exist two cross clasp lines – fixation is plane (it’s the most optimal fixation type for the partial lamellar dentures). The clasp lines are subdivided on: sagittal (in front back or on the contrary) and transversal (on the right in front – back at the left or on the contrary).
Fully-casted basis-keeping clasps are not using at the partial lamellar prosthetics. Theirdestinyisbugeldentures.
Methodic of fix metal clasps manufacturing is next. On tooth on which the clasp will be located modeling the fixing clasp from the wax that the main part of a clasp were lay more low than the equator line (the most convex part of tooth). The clasp termination was blunted (to do not traumatize the soft tissues) and deduce a little (no more than 1 mm) above an equatorial line. The clasp accurately take out from the model and give it to the moulding. The moulded clasp fitting, hot spatula paste in wax.
The most widespread for this type dentitions is wired clasps. They are simply in manufacturing and enough functionally. The wired clasps has three parts: the process (fixed in the plastic part of clasp), the body (springing part of clasp) and the shoulder (located on the tooth part of clasp).
The wired round clasp manufacturing is next. In the beginning select a clasp from a set or cut off by scissors for metal a part of wire length 2-2.5 sm.
The clasp manufacturing begins with sharpening of the extremity of a wire by a file. Keeping the wire by a left arm, bend forcepses a clasp shoulder adjusting it to a vestibular surface of a tooth. Further at the straight angle from top to bottom bend a wire creating a body of clasp. Then follows the third flexure – unbend a process on the center of alveolar process in a denture basis depth.
The process flatten out on an anvil (if it’s the flat clasp then flatten full clasp) and make the notches by a file on the process for the better fixation in a plastic.
Plastic clasps are casting from the wax like it’s sown on an image.
After manufacturing the clasps on all teeth on which it need, begin the artificial teeth fixation.
All artificial teeth, which using for the fixation at the partial lamellar denture, subdivide on the plastic and porcelain.
Let’s try to understand the plastic teeth fixation. That’s teeth are issued by factory in sets (or by 28 teeth, or separately sets front and side teeth). The plastic teeth are differing by a form, color and design.
Teeth need to be picked up in the beginning depending on defect size, color and form of remain teeth.
At the tooth fitting in the beginning it is necessary to give width by cutting it on the polishing-motor or by milling cutter on a handpiece by dentitechnical a part of plastic. Further fitting it gingival part, on height, watching that the gingival part settet down in a gum and didn’t press the wax. The next step in teeth fitting is specification of a parity of plastic tooth with antagonists.
The right fitted tooth must:
– the vertical axis of tooth must to coincide with the alveolar process overage;
– each tooth (except lower central incisors and second upper molar) should to have two antagonists and it contact should to be the maximal (decently) on full chewing surface;
– the neck of an artificial tooth should to be on the natural tooth level;
– the plastic teeth are located decently to each other, fitting is making without trems and diastemas.
The porcelain teeth in the past were popular enough for the partial lamellar dentures using. They are much more cosmetic then a plastic teeth, more strongly the last. But at the same time a plastic teeth was chemically bridged with the basis of denture (they are manufactured from the one type materials), and the porcelain just by a retention (special attachments presence for fixation in the porcelain teeth).
Fitting of the porcelain teeth is next.
Teeth steals up depending on defect size, color and form of the remain teeth.
Requirements which present to that porcelain tooth same that to the plastic. Fitting features:
– at the porcelain teeth sharpening should to preserve the crampons from grinding;
– the cylindrical form crampons to bend downward and aside at right angle;
– between the teeth and alveolar crest of the model should to be lumeot less than 1-2 mm.
Have the cases when in cosmetic goals recede from these fitting teeth rules, and put the teeth on “sharpening”. At this method the requirements to present tooth the same. Features of fitting on “sharpening”: at the expressed alveolar process the frontal teeth installing on sharpening, that is ahead of alveolar process, grinding off them so each artificial tooth densely adjoined by neck part to the gingival margin of the alveolar process.
After the clasp fixation fixing the artificial teeth, the model of future denture giving in an articulator to the clinic. Dentist checking correctness of selection of a teeth, correctness of the fixing and defining of the central occlusion, flexure or equipment of the clasps. In case of errors in previous steps in common with doctor making a relocation of teeth, to lower or to raise one or group of teeth, clasp position managing.
After begin modeling of the denture basis. At the necks of front teeth the vestibular surface of an artificial gum modeling with the small round prominence above the roots and the cambers which imitating relief of the alveolar process. Gingival margin at the side teeth from neck side modeling with the prominent crest. It is necessary to consider and release the stagnation places of mucosa to preserve the denture dropping at the mouth opening.
On the lower jaw denture the gingival surface in the front teeth area is modeling to create a relief that so at teeth biting don’t disturbance the occlusion and don’t be the thickness. Configuration of the gingival part of a denture should to repeat the features of patient palatum configuration including the palatinal cords. Margin transition of a denture by “A” line should to be a uniform thickness and it’s shown “on is not present”.
The denture basis margins rounding, making a smooth by a hot spatula; the margins should to repeat the margins of neutral zone.
On the lower jawat the expressed bridle of a lower lip and buccal bridle the margins of an artificial gum modeling with their tension at the mouth opening (it’s necessary that the denture margin lagged behind an attachment place of bridle on the 1-1.5 mm). In the side teeth region from the vestibular side modeling a bends for cheeks which is promotes a fixation of denture and correct participation in chewing act.
The lingual surface of basis in the sublingual process region the front teeth make a slightly bending for a free adhering and movement of end of tongue. In the side teeth area modeling a sublingual processes more thickness, with a bends in the average part, which in will be located the side surfaces of tongue.
The basis margins of the lower jaw denture is bend and also observe their dimensions according to the planned model margins by a doctor. The back margins of denture are locating on the back-molar triangle on the inside surface of the lower jaw branch.
Lead off on the basis margin the hot spatula to bond the basis to gypsum. After that easy blows of a hammer beat off models from an articulator. In the presence of auxiliary model it deletes. Start to replace the denture basis from wax to plastic.
Plastic polymerization is carried out in a ditch under the influence of temperature and pressure.
As is it shown we have a three casting methods of model in the ditch. Direct (when in the lower part of ditch remaining the clasps, artificial teeth and the model), reverse (when the plastic teeth and clasps are moved at the lower part of ditch) and combined (when the clasps remain on the model, but a teeth moving to the upper part of ditch). At the partial lamellar denture manufacturing can be all three paths.
Clinical and laboratory stages of the construction
of the bar prostheses out of the model.
CLINICAL
1. Taking of 2 working and 1 auxiliary impressions.
LABORATORY
1. Casting of the plaster model from the auxiliary impression and 2 super-plaster models by the working impressions.
2. Construction of the bite rim.
CLINICAL
II. Determination of the central occlusion.
LABORATORY
1. Preparation of the model in the surveyor
2. Drawing of the bar prosthesis pattern
3. Plastering of models in the occludator
4. Modeling of the prosthesis framework.
5. Replacement of wax with the metal.
6. Processing of the framework after casting, adjustment to the model.
CLINICAL
III. Fitting of the bar prosthesis framework.
LABORATORY
The final processing of the framework. Covering with protective coatings.
Positioning of the teeth.
CLINICAL
IY. Fitting of the teeth.
LABORATORY
Replacement of wax of the bases with plastic.
Processing and polishing of the prosthesis
CLINICAL
Y. Fixation of the prosthesis in the oral cavity.
YI. Correction of the prosthesis
After appropriate preparation of the model and its marking in the surveyor, modeling of the bar prosthesis framework is made. The model and rubber dams are covered with the thin layer of vaseline so that wax would not adhere to the metal.
Modeling is started with clasps and then the model itself. To remove one-piece wax framework from the model more easily, each modeled part should be preliminarily removed. The standard matrix “Formodent” or ready-made wax blanks are used for modeling.
While modeling of the framework it is necessary to watch on the uniform thickness of the components. The clasp arms are modeled taking into account the mechanical trimming (adjustment) after casting.
The finished modeled bar prosthesis is checked for the removal from the model and cast from the metal.
The trimming of the cast framework on the model requires carefulness and accuracy. The framework adjusted to the model is checked in the oral cavity and the necessary corrections are made.
Before insertion of the artificial teeth, it is necessary to determine the size of the base, whose size depends on the extension of the dentition defects. The more teeth are absent, the larger must be the base. In absence of one or two teeth with presence of the distal support the base size depends on the extension of the absent teeth, configuration of the toothless part of the alveolar process, degree and compliance of the soft tissues as well as the method of connection of the base with clasps.
In absence of the distal support on the upper jaw (1, 2 class according to Kennedy) the prosthesis base must overlapthe tuber maxilla. The area of the base in absence of the remaining support depends on the degree of atrophy of the alveolar process. If it is atrophied, the base area increases. The base size also depends on the degree of compliance of the mucous membrane, if its size is 0.6-1.2 mm, and then the base area must be increased. The base border of the bar prosthesis is a neutral zone – a place of transfer of the fixed mucosa into the mobile. The base must go around the frenulum of the upper and lower lips as well as the fold on the upper jaw behind the premolars. On the lower jaw the base goes around the intermaxillary tuber, but on the side of the oral cavity the base edge must not reach the floor of the oral cavity by 2 mm. The base border on the model is drawn by the pencil. In the bar prosthesis it is desirable that the mucous membrane of the alveolar processes would fit closely the plastic base, but not the metal of the framework. It is associated with simplicity of its construction and possibility of correction of the base, if need be.
The artificial teeth, selected by colour can be porcelain and plastic. Plastic teeth are more frequently used for lightness of construction; however, they are rapidly erased, as a result of which occlusion is lowered and the abutment teeth are overloaded. When teeth are positioned, the base with the teeth is modeled.
After this, the doctor checks position and construction of the bar prosthesis in the clinic. After checking the framework with the base is removed from the model. The wax base is modeled and thoroughly stuck on the model. Plastering is made in a combined manner. Natural teeth, clasps and arches are accurately closed by the plaster roll.
When plastering of the cuvette is finished and plaster is hardened, wax is removed by the boiling water, the cuvette is cooled and packing of plastic begins. The teeth are degreased and lubricated with the tampons moistened in the monomer. Packing is made in the cold cuvette, when plastic matures. If the cuvette was pressed badly and there will be opening between its halves, filled with the layer of plastic, then occlusion will be increased by the thickness of this layer. So packing should be checked. A sheet of cellophane is placed on one half of the cuvette; it is pressed, then the cuvette is opened, excess plastic is cut off and cellophane is removed. The cuvette is again pressed to t complete joining of its edges. The plastic is polymerized according to the instruction.
The cooled cuvette is opened, the prosthesis is pushed out from the cuvette in the special press, thoroughly cleaned from plaster, excess plastic is cut off, and the prosthesis is processed and polished.
At present it is preferable to construct the bar prostheses on the fireproof models.
Clinical and laboratory stages of the construction of the
bar prostheses on the model.
CLINICAL
1. Taking of 2 working and 1 auxiliary impressions.
LABORATORY
1. Casting of the plaster model from the auxiliary impression and 2 super-plaster models by the working impressions.
2. Construction of the bite rim.
CLINICAL
II. Determination of the central occlusion.
LABORATORY
3. Preparation of the model in the surveyor
4. Drawing of the bar prosthesis pattern
5. Plastering of models in the occludator
6. Preparation to the duplication of the model
7. Duplication of the model
8. Modeling of the prosthesis framework.
9. Replacement of wax with the metal.
10. Covering of the framework with protective coatings.
11. Positioning of the teeth.
CLINICAL
III. Fitting of the bar prosthesis (positioning of the teeth).
LABORATORY
Replacement of wax of the bases with plastic.
Processing and polishing of the prosthesis
CLINICAL
IY. Fixation of prosthesis in the oral cavity
After the preparation of the bar prosthesis in the surveyor and its preparation to duplication the construction of the fireproof model is started. The fact is that in this method the bar is modeled on the model and during casting it is not removed from it. Usual plaster or superplaster model burns down at the temperature of casting (more than 1000°). Therefore it is necessary to prepare, to copy (to duplicate) the working model from the refractory material.
After the preliminary preparation the model should be moistened, if duplication is made with the aid of the duplicating gel. It is best of all to soak the model in water at the temperature of 38°C for 15-20 min, till disappearance of bubbles on the plaster surface.
Heating to 38°C has 2 reasons:
1. Saturation of the model is more rapid in the warm water.
2. The duplicating gel will not thicken immediately on the cold metallic surfaces, which are present on the crown model during filling with the warm duplicating mass.
The moistening model should be dried by napkin, not by compressed air. Air pressure may contribute to detachment of the glued wax. The prepared model should be fastened on the base of the duplicating cuvette before pouring gel. The classical duplicating cuvette has a base made of the rubber and a frame of aluminum. For fixation of the model in the cuvette plasticine-like paste or soft wax is used in the center. The layer of gel around the model must have maximally flat thickness; otherwise there may be distortion of the negative form because of uneven cooling and shrinkage. The cuvette frame is mounted after fixation of the model.
The gels – reversible thermoplastic materials utilized for duplication approximately consist of 70% of water. They are composed of agar-agar and sticky gelatin with the additions of glycerin and mineral substances. Agar-agar is the basic component of the hydro-colloidal impression material. The gel has unstable properties because of its composition.
It is better to melt the gel at 95°C or according to the recommendation of the manufacturer in constant stirring; it preserves fluidity during cooling to the operating temperature of 48-52°C. Before melting it is necessary to cut gel down to pieces in order to avoid partial overheating. It greatly harms the material. Only enameled dishes or dishes of stainless steel are used for melting.
The duplicating gel has the following properties:
1. Precise reproduction of all details, because of its fluidity;
2. Good elasticity, the ability to return to the initial state, if we carefully removal the control model from the mould;
3. Repeated use;
4. Low price.
However, the gels have the drawbacks, which are especially visible in their misapplication:
1. Natural raw material is especially sensitive to heating. During repeated melting the basic substances are lost, so that good properties of the material gradually disappear. This process of decomposition can be slowed down with the addition of the new material. The regeneration of too strongly decomposed gel is impossible.
2. Constant evaporation occurs because of the high amount of water. Good properties of the mass can be preserved only when this loss will be compensated. Therefore the gel should be prepared in the closed apparatuses with the mixer and adjustable temperature with the aid of the thermostat. This is better than use the open dishes and manual mixing – the duplicating gel begins to shrink immediately because of the loss of water, as soon as the control model is taken out from the mould. In using the open flame or electric stove for melting the duplicating mass, the gel must be melted on the water bath.
3. The gel does not have resistance at the moment of break. Only well prepared model can be taken out from the cuvette without damage of the negative.
4. The water, which forms part of the duplicating gel, influences the solidified packing masses. It may result in the change in the form, which cannot be taken into account.
5. It is not possible to obtain precise plaster duplicate with the aid of the gels for duplication, since glycerin in its composition prevents the consolidation of plaster. But new modern materials appear at the market without such negative properties.
6. Shrinkage begins during cooling of still liquid mass from 50°C to 8-10°C in the running water or in the special apparatus. It may be regulated by “directed” cooling.
But the problem remains unsolved when the metal components of crowns and bridges – abutments are duplicated. The explanation is simple: the duplicating gel giving shrinkage during cooling is removed from the smooth metal surface, since metal has another thermal conductivity than plaster.
Before pouring the duplicating mass on the model, it is necessary to check the gel temperature with the aid of the thermometer even in the device for duplication. Liquid mass must slowly flow into one of the openings in the upper part of the cuvette. The jet must not get onto wax components. The slowly rising mass covers and fills in all forms and structures of the model.
The filled cuvette must be cooled in the air, until the mass thickens as jelly. This is easily checked by fingers in the openings for filling. The exposure time is very important so that the thickening of the model would occur. Shrinkage of the gel must be regulated so that the gel would not be scaled from the model. If we begin cooling sharply, then external walls will thicken first and they will begin to absorb internal liquid content to compensation the mass shrinkage. Thus the gel will scale from the model. As a result of these processes the distorted negative is obtained. If the cuvette bottom is made of aluminum, then it transfers heat very rapidly. The model stands on the bottom, the effect of cooling increases, if the base stands on the legs. In this case the cuvette bottom can be cooled more effectively by room air or water. Thus, the gel in the upper part of the cuvette must thicken last, so the cuvette frame must be made of the material, which conducts heat badly for example, plastic.
After the duplicating gel, which filled the form, was cooled during 20-30 min at the room temperature, the cuvette may be placed in the water or on the special cooling device. For complete hardening of the duplicating mass the running water of 8-10°C is sufficient in the subsequent 30-45 min. In this case the cuvette must not be completely immersed in the water. It is better that only two thirds of its height is washed by water. On this phase of cooling the gel must first be cooled in the remote area and harden where the model is located. It is possible to exclude inaccuracies because of the erroneously directed shrinkage by limiting the water level. Then the plaster model is extracted from the gel, and the negative is filled up with fireproof mass.
The reversible thermoplastic masses have some disadvantages, namely inaccurate reproduction of the form of the duplicated metal components. It may result in the inexact fit of the fixing elements on the crowns. There are fluid silicone masses for duplication at the market, which compensate many drawbacks in the gels. Two components are mixed up thoroughly in the ratio of volumes according to instructions, and further stages of work are the same as with duplicating gels.
Advantages of silicones:
1. Silicones reproduce form and relief very accurately. The problem of duplicating metal components with the aid of these masses can be considered solved;
2. The model must not be soaked;
3. Approximately in 45 min, beginning with mixing, the negative form is ready for use;
4. A repeated filling is possible, first of all with plaster for the control model;
5. There is no reaction between the material of the form and packing mass.
It is only related to silicones.
The duplicating masses on the base of polyester react in other way. High price of the gel masses and single application are the drawbacks. There may be smallest savings to 25% if we cut silicone having been used and put it round the base of the plaster model in the cuvette before duplication. Savings are also possible with the use of the special dosing device for the silicone materials. It allows to dose precisely a quantity of the mass and mix up the components of silicone evenly without the air inlet.
The fireproof model must maintain the heating temperature up to 1400-1600° without being deformed and without changing.
Usually the fireproof mass consists of the mixture of the refractory thinly grinding stocks, which are mixed up with water. 100-120 g of the powder is necessary for one ceramic model. A precise quantity of attachments can be determined, if the weight of dry plaster model is multiplied by 1.7. A quantity of water per 100 g of the powder depends on the composition of the fireproof mass and as it is indicated in the instruction.
A definite quantity of the powder is poured into the rubber flask. Fill it the measured quantity of water and mix with a spatula. After mixing the mass together with the cup is placed on the vibration table, after that its surface becomes bright.
Pouring of the fireproof mass in the impression is also made on the vibration-table with the subsequent application of vacuum. The cuvette with the impression is placed on the vibration-table, it is turned on. Place the fireproof mass on the edge of impression so that small portions of it flowed and evenly fill cavities; it protects the model from formation of the pores. The entire process of the model casting lasts for 2- 3 min. However, after this method of filling there are still small pores, which do not give smooth surface.
For elimination of the gas bubbles from the molding compound and consolidation of the model, it is placed in the reservoir, from which the air is pumped out. Low vacuum contributes to the suction of the air from the compound. The process of degassing lasts for 4-5 min, after that the vibration table is turned off. The model begins to harden in 10-12 min after filling. It is at this time it is necessary to remove the sprue cup from the cuvette.
The final hardening of the model begins in 40-45 min. After this, the model is released from the duplex mass.
After hardening the models of the fireproof mass are fragile; therefore they should be extracted carefully – cut the duplex mass in parts in order not to injure the model. After the model release from the duplex mass it should have a smooth bright surface without pores and be the precise copy of the original. For strengthening of the fireproof models, they undergo drying in the cabinet drier at a temperature of 200-250° for 30 min. From the dry-air cabinet the model is placed in wax heated to 150° for its fixation for 10 sec.
The impregnation of the models with a fixing agent is achieved in the electrothermal device, which is a bath with 1 liter of capacity with electrical heating and the heat-control device.
After finishing duplication we obtain a fireproof model with the bar prosthesis framework applied onto it. After this, we start modeling.
In modeling the prosthesis framework on the fireproof model, wax should fit the surface of the fireproof model and have sufficient plasticity.
Special matrices on the silicone basis (Formodent) should be used. The shape and size of the prosthesis components should correspond to the construction of the prosthesis, value of the working load and depend on the properties of the poured alloy. The sprue basin is made in the bottom of the fireproof model, which gives the smooth filling of the mould with liquid metal.
In making the sprue system it is necessary to provide the rational arrangement of the sprues in order to avoid the appearance of the incorrect direction of metal jet and its strike against the mould wall. In some parts of the metal casting it is necessary to provide the installation of additional compensating balls from wax; for complete filling of the casting mold the sprues should be of appropriate diameter and length.
For obtaining the wax components of the deepening of the plate, Formodent is covered with casting wax. After thickening the excess of wax is removed from the plate surface by the sharp heated dental spatula. Wax component is easily extracted from the silicone plate during its small bend.
During casting of wax components the silicone form is not lubricated.
Long components are shortened by knife; separate parts are connected with the aid of molten wax.
The preparation of the model of the prosthesis framework begins with the application of the thin plate of heated wax onto the fireproof model and it is pressed out thoroughly, attaining its tight fit to the surface. It cannot be always achieved by application of the plate onto the entire surface of the model. Such difficulties are frequently encountered in the area of the abutment teeth. In such cases thin wax is applied first by separate parts onto the abutment teeth, the edges of the applied wax are fixed by a hot spatula to the least critical places of the model. Then clasps are modeled.
In the clasp installationwe are guided by the guide line bearing in mind that the rigid part of the clasp should be located above this line, and the flexible part –below it.
The arch of the upper prosthesis is modeled from the zoned wax strip of semioval section, while the arches of the lower prosthesis – from the same strip of semicircular section. Moreover, the width of these wax strips must be 1.5 times less than the designed width of the arch. For example, if the width of the upper arch in the final formulation must have6 mm, then the zoned wax strip of 4 mm in width is placed on the base from thin wax. At the junction of this strip with the wax base the edge of its each side are widen by 1.5 mm by fusing elastic model wax. Thus, the arch obtains a three-layered modeling. It is very important as usual volumetric shrinkage of wax makes 0.1-0.15% per each degree of the temperature interval from 8 to 20°C.
In modeling the saddle of the prosthesis framework attention should be first of all paid to the strong joint of the clasp frame with this part and did not prevent
loose fit of the prosthesis by its direction, moving away for a sufficient distance from the neck of the abutment tooth. Saddle parts must have smooth taper to the prosthesis arch without the formation of acute angles and other irregularities, which can cause inconveniences for the tongue and become the retention place for the food remnants.
The modeled prosthesis together with the sprue system is directed to casting and is cast together with the model. After casting the framework does not require fitting and checking in the clinic.
Positioning of the teeth and further stages do not differ from those in construction of the bar prostheses by the method of removal from the model.
After fabrication of the master cast, the laboratory will perform the following steps in the fabrication of the removable partial denture framework:
1. Place wax blockout in undercuts on the master cast:
– below heights of contour
– minor connector & lingual plate embrasures
– soft tissue undercuts (if necessary)
2. Place relief on the master cast:
– under gridwork
– over free gingival margin
– under mandibular major connector
3. Duplicate master cast in refractory material, which will withstand casting temperatures
4. Wax-up framework according to design on secondary cast using prefabricated patterns
5. Invest refractory cast, solder wrought wire clasps
6. Burnout wax, cast in a chrome cobalt or other alloy
7. Finish & polish, return to dentist
Partial Denture Framework Adjustment
Even the best partial denture frameworks do not fit perfectly in the mouth. Stewart Rudd and Kuebker have stated that up to 75% of all frameworks may not fit the mouth on the day of insertion. Since clasp tips are designed to fit passively into a specified undercut, any discrepancy in seating of the partial denture framework will cause the direct retainers to become active, thereby causing orthodontic movement of the teeth. For this reason, frameworks must be adjusted intraorally. This is accomplished most easily when the denture base is not attached to the framework. Metal framework try-in should be accomplished as soon after the framework is
returned from the laboratory to minimize changes that occur due to tooth migration.
Pre-clinical Inspection and Adjustment
Ensure that the partial denture has been fabricated as designed. The dental laboratory should never change the framework design without consulting the dentist. Conversely, errors in framework design caused by inaccurate drawing on casts or omissions in laboratory prescriptions are the fault of the dentist. The framework should fit the master cast. If it does not, it will probably not fit intraorally. Replace the framework on master cast as little as possible to prevent abrasion (in case a remake is necessary). The framework should be assessed using the following
criteria:
1. Rest seats should be fully seated (adequate support)
2. Reciprocal arms and proximal plates should be contacting the cast
3. Linguoplates and maxillary palatal major connectors should be in intimate contact
with the cast (food impaction)
4. Major and minor connectors should be an adequate distance from abutment
teeth (hygiene). Adjust, if possible, or have lab adjust or remake framework
5. Major and minor connectors should be of proper proportions (rigidity, hygiene).
Note especially that cingulum rests should not be carried into embrasures and that
embrasure minor connectors for distal extensions should not be in contact with the
more anterior tooth (unless it has a rest seat preparation). Adjust, if possible, or
have lab adjust or remake framework.
6. Butt joints should be adequate for acrylic resin (slightly undercut). Adjust, if
possible, or have lab adjust or remake framework
7. Clasps should be of uniform taper
8. Proper gridwork should have adequate relief
9. Finish and polish of the framework should be adequate – no evidence of pits,
nodules and scratches in the metal. Eliminate sharp edges that might impinge on
the oral mucosa.
Check framework with an instructor prior to making adjustments. These adjustments should proceed the patient’s clinical appointment for framework adjustment. Heatless stones, diamond burs, Brasseler E-Cutter burs, carborundum disks and coarse stones may be used to make adjustments to the major and minor connectors. Remove and replace the framework on the master casts as few times as possible. In this way, it will not be severely abraded should a remake of the framework be necessary.
Clinical Adjustment (Fit)
Binding against one or more of the abutment teeth can cause inadequate seating of a framework. The area(s) of binding cannot be located without the use of an indicating
medium. Several media can be used for this purpose:
1. Spray type Powders (Occlude): A small amount is sprayed in an even continuous layer over ALL tooth-contacting portions of the framework. The advantage of this medium is that it is thin and accurate and is not easily displaced from the framework. The material can get quite thick if over-sprayed. Teeth, tissues and the framework must be dry to prevent the pigment bleeding and making reading of the indicator difficult. A disadvantage of this technique is that it provides only two-dimensional assessment of fit.
2. Disclosing wax (Kerr): A small amount of wax is removed from the jar and placed on a mixing pad. A warmed instrument (#7 wax spatula, PKT waxing
instrument, etc.) is used to pick up and melt a portion of the wax. The melted wax is applied in an even coat over ALL tooth-contacting portions of the
framework. The wax is allowed to gel prior to placement in the mouth. The advantage of this medium is that it provides three-dimensional assessment of fit.
Areas of burn-through indicate possible areas of binding, and the thickness of the remaining wax indicates how far the rest of the framework is from contact with
the teeth. A disadvantage of wax is that it can stick to teeth or be wiped away easily if the framework is seated improperly.
3. Silicone impression materials or indicating medium:
These materials can also be used as three-dimensional indicators. A disadvantage of elastic materials is that they can tear or pull off the framework. In addition,
time is required for set of the materials. In this regard the silicone fit-checking media are more useful since they have shorter working times.
Use of Indicating Media
1. Attempt to place framework intraorally. If gross resistance to placement is felt, remove and coat with indicating medium. If the framework seats, ask the patient
if they feel the framework pulling on any teeth. The latter sensation will be caused by active engagement of abutment teeth. Inquire as to the overall comfort
of the framework.
2. Remove the framework and coat it with indicating medium. Align the framework over the abutment teeth and use finger pressure over rest seats along
the path of insertion. DO NOT PLACE PRESSURE OVER GRIDWORK OF DISTAL EXTENSIONS as this will fulcrum the framework. If gross resistance
to seating is encountered, remove and inspect for areas of burn-through. Have an instructor inspect the framework. Relieve areas of binding as indicated.
Repeat until seating is achieved. The master cast can be inspected for areas of abrasion that may indicate areas of gross binding as well.
3. Once the denture can be seated, coat with media and seat along the path of insertion again. Use firm even pressure over the rest seats and or indirect
retainers. A mirror handle can be used for seating purposes. Use care in removing the framework, as removal along the wrong path of insertion will
change the markings with displaceable media (wax & spray media).
4. Use caution in adjusting the framework. The clinician must differentiate between normal and abnormal contacts. Guiding planes normally will exhibit long
vertical areas of contact, but broad areas of complete burn-through may indicate a binding contact on the guiding plane. Similarly, the retentive tip of direct
retainers will normally exhibit burn-through, but active clasp retention must be eliminated after the framework is fully seated. Therefore, the first step in
adjustment is to ensure complete seating. The most common areas that interfere with seating are:
1. under rests
2. rigid portions of direct retainers (e.g. above the survey line)
3. interproximal portions of linguoplate major connectors
4. interproximal minor connectors
5. shoulder areas of embrasure clasps
Experience is required to differentiate betweeormal and excessive marking of the indicator medium. Therefore it is wise to consult with an instructor regarding
proposed changes prior to adjustment. Adjustments can be made with small round diamond burs, white stones or rubber abrasive points, depending on the
position and extent of binding. Do not use excessive force or the framework may be bent. Heat generation is one of the reasons major adjustments are made prior to acrylic placement (i.e. the heat would melt the acrylic).
5. Completely remove any media contaminated with metal grindings and place fresh media. Repeat this procedure until full seating is achieved. At this point a thin,
even film of media should be observed under rests and indirect retainers. The wax or silicon media will have a greyish hue from the underlying metal. The feel
of the denture upon seating will change from a grating or snapping sensation to one of a gliding sensation. Normal adjustment of a framework should take no
longer than 20 minutes.
6. Check for soft tissue impingements using pressure-indicating paste. Remove a small portion from the jar, and place it on a mixing pad. Use a stiff-bristled brush
to spread a thin layer over the tissue surfaces of the major connector, and infrabulge clasps. Leave streaks in the paste. Place intraorally with moderate
pressure and remove. Relieve any areas of marked burn-through. If streaks are left in the paste, this indicates no contact with the tissues. Adjust or leave accordingly. Maxillary palatal connectors should exhibit broad even contact with the palate.
7. If the framework cannot be adequately adjusted, it should be remade. In some cases this decision may be made at the pre-clinical inspection stage. Make this
determination early, so that time will allow for a new impression to be made. Determine if the casting fits similarly on the cast and in the mouth. If it does not, the final impression was most likely inaccurate and should be remade. If the casting does fit similarly, the discrepancy may be due to laboratory errors. In many cases abrasion of the master cast will require re-making of the final impression as well. If the pre-clinical inspection leads the dentist to believe a remake is a possibility, a new custom tray should be made prior to the patient appointment in anticipation of the need for a new impression.
Occlusal Adjustments to the Framework
Since most frameworks are be fabricated on unmounted casts there are usually occlusal interferences present on rests and indirect retainers. These should be adjusted at this time.
Vertical dimension should remain unchanged by a removable partial denture in almost all instances. The framework should not interfere with normal centric and eccentric contacts of the maxillary and mandibular teeth. Contacts should be identical with and without the framework in the mouth.
Mark occlusal contacts with thin articulating paper and remove the framework for
adjustment. The highly polished metal surfaces do not mark well with articulating paper so that the opposing occlusion should be checked for heavy contacts. Diamond burs, heatless stones, Shofu coral stones or cross cut Brasseler lab burs will most readily remove interferences. DO NOT FORGET TO LOCATE AND ADJUST EXCURSIVE INTERFERENCES.
When maxillary and mandibular frameworks are being adjusted, they should be adjusted individually, then placed in the mouth together to eliminate interferences between the frameworks. Occlusal rests or indirect retainers that have inadequate thickness (< 1.5 mm) after adjustment will be subject to fatigue and possible fracture. The latter situation may occur due to inadequate preparation (i.e. not considering opposing occlusion) or subsequent extrusion of teeth. If the teeth have extruded, the entire framework will most likely not fit. If occlusal interferences exist that will excessively thin the rests, the rest seat preparation may have to be deepened and a new impression taken, or an opposing cusp or framework element may have to be reduced. Reduction of opposing cusps should be performed as a last resort to save an otherwise acceptable framework.
Occlusal interferences should not normally occur on retentive clasp arms if proper
treatment planning has been followed. However, if the opposing occlusion is not
considered at the time of mouth preparations, it is possible that occlusal contact may occur on a retentive arm. If this contact is minor, the opposing cusp may be reduced. Again, reduction of opposing cusps should be performed as a last resort to save an otherwise acceptable framework. If the interference is gross, the tooth surface should be recontoured (i.e. lower height of contour) and a new impression taken. IN NO INSTANCE SHOULD A RETENTIVE ARM BE RELIEVED, since this will affect its flexibility and resistance to fracture.
Special Adjustments for Distal Extension Cases:
In most cases distal extension cases will be designed with relatively short occluso-gingival guiding planes to allow for release of the abutments during tissueward movement of the denture base. However, there are some cases where teeth are tipped and a long guiding plane is the only type of guiding plane that can be placed. In these instances, “physiologic relief” of the framework should be used to provide release. With this technique the distal guiding planes, minor connectors and linguoplates are coated with alcohol and rouge (not wax or silicone). The framework is placed intraorally and placed under hyperfunction by pressing over the distal extension gridwork. The framework is removed and the guideplanes and other rigid metal contacts, which could torque the tooth, are relieved in areas of burn-through. Relief should be provided so that marks remain in only the occlusal one third of the guiding planes.
Finishing and Polishing of Adjusted Surfaces
All adjusted surfaces should be smoothed and brought to a high polish. This is imperative, since even well finished frameworks have been shown to enhance intraoral plaque adhesion. Dedco green knife-edge wheels for chrome cobalt alloys will remove scratches and bring the adjusted surface to a high shine quickly. Additionally, Dedco blue clasp polishers or any other carborundum-impregnated points can be used to finish the chrome cobalt alloy. A final polish can be placed using a tripoli on a bristle brush and rouge on a small diameter cloth wheel. Use care not to snag the cloth wheel on sharp edges of the framework (to prevent injury to yourself). Remove traces of the polishing compounds with soap and water and a toothbrush.
Preclinical Inspectationof frmework
1. Check accuracy of the framework as designed
2. Framework should fit master cast If it does not, probably will not fit Intraorally
3. Rest seats should be fully seated
4. Contacting Cast:
a) Superior portion of lingual plates
b) All maxillary major connectors
c) Minor connectors
5.Adequate distance from abutments (hygiene)
6. Butt joint junction slightly undercut for acrylic resin (FINISH LINE)
7.Direct Retainers
1– Retentive arms • Clasps have uniform taper
2– Reciprocal arms,
3– Proximal plates
8.Finish and Polish
Highly polished
• No pits, nodules, scratches
• No sharp edges -injure mucosa
Solution:
Adjust or have lab adjust or remake framework
Clinical adjustment
No tissue contact
The metal framework tried in the mouth to verify the fit. Notice that the underside of the framework in the areas where teeth are to be placed is not in contact with the tissue.
1. Incomplete seating
Most common interferences:
– Under rests
– Rigid portions of direct retainers
– Interproximal portions of lingual plates
– Interproximal minor connectors
– Shoulder areas of embrasure clasps
Indicating Medium
Rouge & Alcohol
Aerosol • Sprays
Disclosing Wax
Silicone
Rouge & Alcohol
Advantages
Thin & accurate
Disadvantages
– Not easily displaced
– Can dissolve in saliva
– Difficult to remove
– Can’t tell how far from seating
Disclosing Wax
Advantages
Sets immediately
Inexpensive
Shows how far from seating
Disadvantages
Can stick to teeth
Silicone
Advantages
Minimal distortion
Disadvantages
• More expensive
• Sets relatively slowly (2 min)
• Can tear or pull off the framework
Prior to imposing clasp dentures in the mouth it is necessary to look at it carefully, paying attention to the surface that is adjacent to the mucosa, which should be smooth and polished.
After insertion of the removable denture, further correction is needed in most cases. It is explained by different degree of the mucous membrane compliance of the prosthetic bed and impossibility to take this factor into consideration while constructing removable dentures. Every dentist should carry out these additional stages.
The following inspection of the patient should be made the next day. Asking the patient the dentist gets to know his complaints and condition. Both in presence or absence of complaints the oral mucosa should be thoroughly examined. It is necessary to control the occlusion once more and correct its drawbacks. The pain in the alveolar process is often of uncertain localization and occurs in uneven distribution of the masticatory pressure.
At first, the patient’s complaints are thoroughly analyzed including complaints on phonetic, esthetic and functional character (bad fixation in biting or mastication), pain (in conversation, during meal), etc. Special attention should be paid to the pain syndrome determining its character, localization, degree. At first the dentures are inspected in the mouth without taking them out. Attention is paid to the character of occlusion relationship, degree of fixation and stabilization of the dentures. The drawbacks found are eliminated by correction of the occlusion contacts, activation of the retaining elements. Then the prosthetic bed is thoroughly inspected. The revealed areas of hyperemia of the mucous membrane, erosion or ulcer are outlined by the chemical pencil and transferred on the denture base, and then they are ground off. At present our industry manufactures a special indication paste. This paste is applied to the area of the damaged mucous membrane and covered with a denture. It leaves exact visible trace on the base indicating the area which needs correction. The contrast between a lot of patient’s complaints and absence of visible, pathological changes of the mucous membrane indicates that the patient might not wear the similar constructions of the dentures . The patient is told about complexity and individuality of the adaptation process to the removable dentures and explained the rules of their wearing.
There is no common opinion among the specialists as to removal of the dentures during night sleep. On one hand, removal of the removable dentures at night when there are separateteeth in the mouth with affection of the supporting apparatus may result in their injury and quick loss. On the other hand, permanent compression of the vessels of the submucous layer by the denture base may lead to disturbance of the tissue trophicity and enhancement of the atrophic processes. Therefore the dentist should select the most optimal variant in every case.
While treating patients with the aid of removable dentures there may be complications due to dentist’s and technical mistakes or side effects of the denture materials. In this case the patients may have the following typical complaints: unsatisfactory denture fixation, speech dysfunction, pain or burning sensation, breakdown of some denture elements, esthetic defects.
Unsatisfactory fixation (stabilization) of the removable denture may be a consequence of a number of causes: atypical shape of the abutment teeth, incorrect localization of the retainers as to the examination line, drop of the removable plate denture of the upper jaw with porcelain masticatory teeth; sagittal localization of the clamp line; dotted fixation; denture balance on the upper jaw due to sharply marked torus and absence of isolation; taking of compression impression in the atrophic mucous membrane; incorrect position of the artificial teeth in all phases of all kinds of occlusion. The abutment teeth in clasp fixation of the removable dentures must have well-expressed equator and sufficient height of the crown, otherwise the artificial dentures on them should be constructed beforehand, without plastic covering as the latter is worn out in time and retention is worsened. In case the abutment teeth are of atypical shape, e.g. triangular or of reverse cone restored with fillings on the vestibular side or affected by a wedge-shaped defect, they should be covered with crowns.
Unsatisfactory fixation of the removable plate denture may be associated with incorrect position of the retention part of the retainer as to the medium survey line, i.e. it is near to the masticatory surface or comes under the line by less than 0.25 mm in depth. To prevent atrophy under the removable dentures with unfavorable state of fixation (dotted, sagittal unilateral) it is necessary to use light plastic masticatory teeth instead of porcelain one, if possible, using telescope system of fixation – a bar of Rumpel – Dolder, clip attachments, intraroot magnets, functional formation of the base borders. It is undesirable to extract the remaining teeth on the upper jaw, especially in II and IV type of the mucous membrane by Suppley; they are devitalized, shortened to the level of the gingival margin and intraroot attachment is used: clip – in stable root, without atrophy of the parodont; magnetic – in the mobile root with signs of the parodont affection. Such additional fixation in combination with the functional formation the denture base borders contributes to improvement of its stabilization to prevent its drop (in cough, sneezing, etc).
The toxic effect of the plastic base of the removable denture on the mucous membrane may be due to bad quality of plastic polymineralization and , as a result, excessive presence of free monomer, which exerts the toxic influence. On examination of the patient there is hyperemia of the mucous membrane of the prosthetic bed but it is not of local but of the diffuse character. To eliminate increased content of the monomer there are proposed different methods of depolymineralization – repeated thermoprocessing in the cuvette, ultraviolet, ultrasound irradiation.
Hypersensitivity of the patients to the acrylic resin, which is used for removable denture base as well as to the dyes, is encountered quire frequently. Such complication cannot be considered dentists’ or technician’s mistake as it is associated with a side effect of the removable dentures, especially of the plate type.
The denture should not be dropped. In case of its breakdown the patient should go to the dentist immediately. Clasps, especially wire, may become weakened in time; therefore patients should consult a dentist once or twice a year to their straightening. In 3-4 years the denture should be changed. During the first three days after insertion the patient should visit the dentist. The follow up continues till the dentist is sure of the patient’s adaptation to the denture. Some specialists recommend the patients to refer to the dentist in case of development of pain. It is a mistake resulting in serious complications.
Pain is tolerated in different ways. Some people experience pain in considerable size of the decubital ulcer as a feeling if discomfort, the others develop pain in the slightly marked decubital ulcer, and the pain is so bad that the patient cannot sleep. In most cases ulcers heal forming a cicatrix that deforms the transition fold resulting in complicated prosthesis. Pains may disappear after correction of the artificial teeth occlusion.
The transition fold should be thoroughly examined ion the upper jaw, in the area of the alveolar tubers and the line “A”. The decubital ulcers located behind the alveolar tuber, at the site of transition of the hard palate into the soft one cause pains in swallowing. On the lower jaw the sublingual space needs careful examination starting from the tongue root to its frenulum. The decubital ulcers in the sublingual space interfere with the tongue movements, and the decubital ulcers of the lip frenulum – movements of the lips and cheeks. In some cases it helps the dentist in seeking the causes of pain.
Vomiturition is associated with irritation of the mucous membrane of the soft and rarer hard palate. Shortening the denture borders always gives a good result. Only in some cases it is difficult to struggle with this reflex. The patient is the best helper in struggle with this reflex. It may be suppressed by training.
DENTURE TROUBLESHOOTING
Overextension of Denture Borders
Slight overextension is preferred to slight underextension.
Remember, however, overextension is prejudicial to denture retention.
To examine the lower denture for overextension:
· Instruct patient to protrude tongue slightly until the tip rests upon the lower lip
· Place your index fingers on the occlusal surfaces of the lower teeth to determine if the lower denture remains firmly seated on the denture-supporting structures
If the denture lifts, consider 3 possiblities:
· Overextension in the region of the genioglossus muscle (contracts w/ forward movement of the tongue to dislodge denture) Anterior portion of denture lifts
· Overextension in the region of the premolar-molar area (denture dislodges by contraction of mylohyoid) Entire denture lifted from position
· Overextension of the extreme distolingual border of the lower denture (dislodgement of the forward movement of the retromylohyoid curtain) Entire denture dislodged from position and moved forward
To test buccal and labial flanges of the lower denture for retention, cheeks and lips are drawn outward. Keep index finger of the other hand on occlusal surface of the teeth on the same side. If denture lifts, border may be overextended.
Test buccal and labial flanges of the upper denture for retention the same way except hold index finger of the opposite hand in contact with palatal vault
Wharton’s (submaxillary duct)
· Occasionally a lower denture can cause complete or partial closure of Wharton’s duct
· This is clinically manifest by enlargement of the submaxillary gland
· The gland will usually return to normal soon after removal of the denture
· If mild duct closure, mild discomfort often disappears by itself during the adjustment period
· Sometimes a reduction of the lingual flange thickness, without disturbing the border, gives relief (avoid excessively reducing the border)
Faulty Vertical Dimension
- One of the most common denture faults
- Always check for this regardless of how remote the patient’s complaint may be
- Vertical Dimension is a combination of relaxed muscles, lips at rest, varying freeway space, harmony between lower and middle 1/3 of the face, ability to speak without bite rims contacting, tongue room for making the “th” sound, satisfaction of the patient’s tactile sense, and a consistent rest position measurement
- Two types of patient’s need a freeway space far in excess of the 2 – 3 mm generally recommended
- The patient accustomed to occluding in a very over-closed relationship for a long period of time (not a good idea to open a patient 10 – 12 mm all in one operation – important to rely on patient judgement, too)
- The mouth breather – lower jaw has been in an opened relationship for a long period of time (a tactile closure into soft wax is a good way to determine the vertical dimension in this case)
- In these 2 instances, don’t try to get proper VDO by subtracting 3 mm from rest position
- Determine the vertical component of centric occlusion which meets the requirement of the case, without regard to the extent of freeway space
- A good way to check VDO (provided the upper incisors are set in a normal position) = Push the lower lip with your index finger with the joints in centric occlusion. If the lower lip tends to slide under the incisors instead of impinging on them the VDO is generally opened too far ( however, horizontal overlap may do the same thing)
- The “th” sound is a good phonetic cue to correct vertical dimension.
- When the patient says words beginning with “th” his tongue should pop forward between the bite rims. If the VDO is excessive, the forward movement of the tongue, is restricted by the height of the rims or set teeth
Speech Problems
It takes patients from 2 – 3 weeks to accustom themselves to dentures, so it is difficult to judge this early on, but some things to think about are:
- Patients are adaptable and generally will correct speech difficulties (not directly related to technical error) within 2 or 3 weeks, so most patients can be assured they will get past the difficulty
- The pronunciation of the letter “s” is the most common speech problem; the patient may even have involuntary hissing or whistle. This can be caused by:
- Rugae area too thick or too thin or the maxillary anterior teeth may be set too far lingually. If the patient has a heavy anterior ridge and the denture is thick, the rugae area should be thinned to allow more space for air to escape. If the anterior ridge is small and thin, likely too much air is escaping and wax on the palatal surface should correct the problem (autopolymerizing resin can then be added if the wax shows this to be an effective correction). If the maxillary anterior teeth are set too lingually, they must be reset or you may try heavy festooning just lingual to the teeth. If these remedies don’t work, sometimes adding a median ridge will help.
- Inability to speak clearly may be due to the lack of tongue room posteriorly on the mandibular denture.
- Overextension of the upper denture onto the soft palate results in speech difficulties, as the patient has to make a conscious effort to keep the denture in position when talking.
Physiologic Failures
- Weight loss can affect denture fit. Clothes get loose; dentures can get loose
- Patients with diabetes or periodontal disease are subject to rapid loss of supporting structures when dentures are inserted and should be forewarned of frequent re-fittings
- Malignant growths can cause dentures to be ill-fitting
- Sometimes patients just can’t successfully wear dentures; check to see if they are using good denture “tricks” such as tightening the corners of the mouth against the lower flange when the mouth is opened wide, trying to chew in an up and down motion with a minimum of lateral excursion, and keeping the tongue low and well forward in the mouth to stabilize the lower denture.
Mucosal Irritations
- Frenum impingement is common; the upper frenae need the most room to move
- Mucosal soreness is often seen on the buccal surface of the R and L maxillary tuberosities. Careful adjustment of the tissue surface of the denture in this area usually solves problem. The size of the ulceration will correlate to the size of the prominence in the denture, ie pointed, or broad and shallow.
- Sharp, bony projections should be removed prior to denture construction, but only remove the sharp point; avoid extensive aveolectomy!
- To relieve a sore spot on the mucosa, it must be correlated exactly with the corresponding spot on the denture that is causing the trouble – try marking the area with a Thompson stick and transferring it to the denture
- Expect to have adjustments with a flat or concave ridge and forewarn your patient
Sialorrhea (hypersalivation)
- May be a short-term major problem; patient may actually refuse to wear denture
- Usually lasts only a few days and gradually tapers off to normal
- Dentist must maintain calm, kind attitude and offer emotional support
- Physiologic symptoms noted are a flow of blood through the salivary glands and their excessive stimulation
- Etiology is emotional stress, pain in the oral cavity, reflex stimulation by the dentures, or a combination
- Causes arising from the dentures are:
- Incorrect centric jaw relation registrations
- Excessive VDO
- Overextension of denture borders
- Pain and excessive pressure on the oral mucosa
- Pressure upoerves
- Excessive stimulation of the salivary glands from the denture acting as a foreign body
- Excessive thickness of the dentures restricting the tongue in its static state, as well as in function
- The patient’s anxiety about possible failure of the dentures
- Treatment options:
- Small doses of opiates or atropine sulfate for the first day may be desirable
- Kind, sympathetic treatment with understanding and reassurance are essential (this alone may effect the cure)
Xerostomia
- Possible causes:
- Insertion of new dentures
- Diabetes
- Chronic infection
- Drugs (antianxiety, antidepressant, antihistamine, antihypertensive, diuretic, decongestant, antiparkinsonism, antipsychotic, anorexiant)
- Biological aging
- Sjogren’s Syndrome
- Vitamin deficiencies
- Stress and depression
- Treatment:
- Address etilogic factors
- Prescribe a balanced diet rich in vitiamins and essential minerals
- Moisturizing gel such as Oralbalance
- Saliva substitutes
- Sugar free candy to stimulate saliva production
Stomatopyrosis (burning mouth)
- This is a tough one!
- Affects menopausal and post-menopausal women more than men
- Etiology is unknown in many cases
- Definite psychological component in many cases (All the articles I’ve read suggest this)
- Onset often connected with major adverse life event
- Possible causes
- Systemic/ oral disease (candida, fissured tongue, geographic tongue, foliate papillitis, carcinoma-burning is localized vs. more widespread as in BMS-burning mouth syndrome)
- Nutritional deficiencies
- Emotional disturbances (this is a big one)
- Allergy (very small percentage due to this! Another type of denture acrylic probably will not work; could be due to excess monomer)
- May be neuralgia—consider help from neurology department
- Treatment:
- All systemic sources of inflammation (i.e. candida) should be eliminated
- All sources of local irritation and undue pressure by the dentures should be thoroughly eliminated
- Centric relation should be checked and double-checked. A new centric occlusion that is in harmony with centric relation should be established. The dentures should be remounted on an adjustable articulator to correct occlusal disharmony.
- Border extension and stability of the dentures should explored with utmost care
- When indicated, hormones should be administered
- Balanced diet rich in vitamins and minerals should be prescribed
- Psychotherapy by a psychiatrist (in order for this to work, the dentist must be fully acquainted with the past history of the patient)
- Don’t undertake or continue the treatment of burning mouth unless you are sure of the utmost confidence and cooperation of the patient.
- Reassurance is an important factor
- Some patients just need to know they don’t have a malignancy and therefore don’t insist on any type of treatment
Action of the Denture as a Foreign Body
- Some patients experience hypersalivation and some xerostomia (not due to technical problems with the denture; consider other things first)
- You may also see considerable redness of the palate not associated with pain or discomfort
- Disturbances that complete dentures cause as a foreign body are usually within the limits of tolerance of the tissues. Re-adaptation of the mucosa to a newly established physiologic pattern is the rule. Everyone is different, however, and it is impossible to predict these type of reactions and may be difficult to manage them – no good answers here.
Contraindications to a Denture Reline
- Unresolved TMJ dysfunction and myofacial pain
- Unsuccessful resolution of inflamed tissue caused by pathologic basal seat on mucosa
- Malposition of artificial teeth that results in unfavorable mechanics, poor phonetics and unacceptable/esthetics
- Multiple-fractured and severely worn artificial teeth (cause of this should be determined!)
- Unfavorable occlusal plane that produces a poor appearance
- Artificial teeth that are grossly malpositioned in relation to the residual alveolar ridge
- A vertical dimension that must be increased more than 3 mm
- A vertical dimension that is too great
