Statement of teeth in partial removable prostheses. Checking the design of partial dentures. Modeling base partial denture. Preparation of wax reproductions to gypsuming in a cuvette.
Artificial teeth
Artificial teeth are made from either acrylic resin or porcelain. The quality of acrylic teeth has improved greatly in recent years and porcelain teeth are no longer commonly used.
Two types of posterior cusp form are produced by manufacturers of artificial teeth:
• Anatomical teeth – may have different cuspal angulations, e.g. 20°, 30° or 40° cuspal angle; 20° cuspal angle teeth are commonly used for complete dentures.
• Zero-degree teeth (flat-cusped, cuspless) – are said to be indicated for cases with flat alveolar ridges or where there is great difficulty recording CR.
Research has not provided evidence to support commonly held views on advantages and disadvantages of artificial tooth form. For example, while it is possible that selection of artificial posterior teeth, such as cusped rather than cuspless, may have a marginal effect on chewing efficiency, other factors, in particular retention and stability of the dentures, have far more effect.
False Teeth and Teeth Dentures
Temporomandibular Joint issues, a pain in the head or ear, and problems with jaw movement can all be symptomatic of issues with teeth spacing. This issue arises when the removed teeth leave gaps, which are in turn filled in by the remaining teeth as they move for placement. This occasionally results in the above mentioned symptoms, and often with an aesthetically unappealing appearance. This can be resolved with partial dentures. Fake teeth are usually matched to the normal teeth, and the color, size and shape is matched to the same teeth as precisely as possible. The dentures are comfortable and with proper dental care and hygiene can function just like normal, healthy teeth.
Classification of Teeth Dentures
Two types of partial dentures exist, and they are commonly prescribed depending on how healthy the teeth around the gaps are. Fixed Partial Dentures, or dental implant bridges, are installed by attaching artificial teeth straight to the gum tissue or jaw, through a dental implant bridge. They bear a strong resemblance to real teeth and are more comfortable, making them more viable. On the other hand, cleaning them is more difficult, and they only function with healthy teeth. Inflammation, oral problems and bad breath can also affect them, and the procedure is usually pricy. Removable Partial Dentures, or removable dental bridges, can be placed and taken out whenever the wearer chooses. Consisting of a metal frame with metal clasps, resin base material and artificial teeth, these dentures are preferable to individuals with injured or diseased teeth. Removable partial dentures can be made of different materials, utilized for denture teeth support. Flipper Partial Dentures are the cheapest ones, featuring Acrylic utilized for the pink plastic denture base, to which false teeth are connected to. Clasping wrought wire is fixed into the base and utilized for clasping the normal teeth. Placement can be performed right after the tooth is taken out, but is not a permanent solution. Cast Metal Partial Dentures consist of cast metal, and are more stable due to its alteration of the original teeth surface for fitting purposes. It is not as obvious as the Flipper variety, and is much more durable due to its chrome cobalt construction. As the soft oral tissues are never contacted by the dentures, there is no risk of soft spot irritation. Flexible Framework Partial Dentures are the most modern of these types of dentures. In place of the metal and the pink acrylic base a pink nylon-like material is utilized. This material does not break, and is utilized for clasp construction as well, lending them even more invisibility inside the mouth. They lean on the gums, like the metal ones. A Nesbit Partial Denture is created to exchange one or several lost rear teeth, and can only be made from a flexible framework material variety. While a risk of swallowing this denture by accident is present, due to its flexibility it rarely causes damage. The teeth are fixed with metal clasps, and as there is no teeth support, this can lead to large amounts of pressure to the clasped teeth, making it an unpopular choice. The Cusil Partial Denture is a hole-ridden full denture that gives the natural teeth that remain an opportunity to go through these holes. There is a rubber gasket lining that holds the teeth. This type is unsuitable for persons with teeth that are distributed evenly, but more recommended to the opposite case.
It is a sad fact of aging that eventually, teeth begin to fall out or experience problems requiring them to be extracted. Even before old age sets in, trauma or gum disease may cause a handful of teeth to need to be removed. When this happens, there are a number of different options one can take. Artificial teeth have advanced rapidly, to a point where in many cases they are indistinguishable from real teeth.
The history of artificial teeth is extremely long, with humans having made fake replacements for lost teeth at least since the 7th century BCE, when the Etruscans created dentures with the teeth from dead humans and animals. This style of dentures, although somewhat morbid, was actually very popular well into the 19th century. Although these teeth, since they were no longer alive, did deteriorate quickly, they were also easy to make and quite cheap, so remained accessible even after other options became available.
Artificial teeth are important even before the entire mouth is empty of teeth, and even if enough teeth remain to eat, simply because with large empty spaces the other teeth may drift or fall in on each other. For this reason, single replacement artificial teeth have become an important part of modern dentistry, and it is rare in the modern age to see someone with adequate dental coverage who has a large gap in their teeth. There are three main classes that artificial teeth fall into: dentures, bridges, and implants. Early artificial teeth were all of the dentures variety, while both bridges and implants are more modern inventions.
Dentures are essentially artificial teeth that are attached to some sort of base, usually either made of metal or plastic. Dentures can either be temporary, partial, or full. Temporary dentures are used when teeth are first removed, while the jaw is still healing, as an intermediate step to full dentures. Partial dentures are used when a few teeth are missing, and are usually attached via metal hooks to the natural teeth that are adjacent to the opening. Full dentures are used when all of the teeth in either the top or bottom row of the mouth are gone, and are stuck to the roof of the mouth with saliva in the case of upper dentures, or kept in place by the muscles of the mouth and tongue in the case of lower dentures.
Dentures require a fair amount of upkeep, and many people find them difficult to adjust to. As the mouth muscles weaken with age, it can be difficult to keep them in place, and some people rely on adhesives to assist in this. Dentures also need to be removed at night, and cleaned regularly, to ensure proper oral health. They can also cause soreness, and may exhaust the muscles of the mouth and tongue, slurring speech until the body adjusts.
Bridges are a much less drastic type of artificial teeth, which can be used when only a tooth or two is missing from the mouth. These are artificial teeth that are directly attached to adjacent teeth, usually by means of crowns on those teeth. Bridges are usually made of metal orporcelain, and since they are cemented in place, they cannot be removed.
Implants are even more permanent than bridges, and in many ways are looked at as the ultimate in artificial teeth. A metal rod is placed into the jawbone, and that rod holds an artificial tooth directly, without the need of a denture plate or crowns. Implants can last ten to twenty years, and offer a secure connection for dentures or bridges that can’t otherwise be achieved. Although a fairly invasive surgical procedure, as the technology advances implants are becoming ever more popular.
In the past, false teeth made with porcelain were generally preferred over false teeth made from plastic due to their greater durability and esthetics. However, in recent years, new generation biomaterials have resulted in the development of very wear-resistant false teeth made from plastic.
Clinically, the esthetics of plastic and porcelain denture teeth is nearly comparable, with good quality false teeth made from porcelain still being the standard for esthetics. However, the majority of dentures today probably are fabricated with false teeth made from plastic. For all practical purposes, the cost of porcelain and false teeth made from plastic are about the same.
While porcelain and plastic teeth are competitive with regards to durability, and to a lesser extent, esthetics and wear, there are other factors that may favor the selection of one type of tooth over another.
Some Selection Factors for False Teeth
Balanced bite and force transmission:
Denture bite (called occlusion) changes due to the constantly changing jawbone (called alveolar bone) upon which a denture rests, and, to varying degrees, uneven tooth wear resulting from use. Unless a denture is evaluated and its occlusion adjusted to a uniform and even contact (called balanced bite or balanced occlusion) at regular intervals, denture occlusion will become unbalanced.
Since false teeth made from porcelain are more wear-resistant, their occlusion will not become significantly self-altered by wear, as will false teeth made from plastic. However, when alveolar bone changes cause an unbalanced occlusion, the resulting biting forces from false teeth made from porcelain will be unevenly transmitted to underlying supporting alveolar bone. Frequent tissue refitting of the denture usually eliminates or lessens this problem.
Porcelain denture teeth tend to transmit the impact of biting forces to the alveolar ridge with greater intensity than that transmitted by plastic teeth in an unbalanced tooth contact situation. Some practitioners are of the opinion that this greater force, especially when uneven as in an unbalanced occlusion, may be damaging to the alveolar ridges and could result in accelerated bone loss.
Therefore, unless denture occlusion is checked and balanced on a regular basis, false teeth made from plastic would probably be a preferred choice over false teeth made from porcelain.
Bone loss:
If a person has lost a great deal of supporting alveolar bone and their gum tissue is not of a sturdy type, then plastic denture teeth might be a better choice. These teeth are more forgiving of excessive forces developing from habits such as clenching, grinding, and tapping or “clacking” of teeth, which seems to be more prevalent among older individuals. Plastic teeth do not transmit forces to underlying bone as intensely as false teeth made from porcelain.
Noise:
If false teeth made from porcelain are vigorously used or sometimes habitually tapped together, a “clacking” sound can be heard. Plastic teeth will muffle this sound and be quiet during normal function or habit jaw motions (called parafunction).
Which Type of Tooth Is Best?
If a person has been successfully wearing dentures with false teeth made from porcelain, then they should probably continue with false teeth made from porcelain. These teeth will not wear as fast as false teeth made from plastic, and the relationship between upper and lower jaws will tend to stay normal for a longer time than with false teeth made from plastic.
Regardless of which type of tooth is selected, the success of the selection is strongly based upon regularly checking dentures for proper balanced occlusion and fit on regular intervals.
If a denture is going to be worn against opposing natural teeth, then false teeth made from plastic should be selected because false teeth made from porcelain, being harder, could excessively wear natural teeth away.
After a thorough examination and frank discussion of what a person wants from wearing a denture, a licensed dentist can effectively discuss which type of tooth would best meet a particular individual’s unique needs and desires.
Tooth Strength
Because false teeth made from porcelain are extremely hard in comparison to false teeth made from plastic, they tend to chip and crack more easily. For this reason, when dentures having false teeth made from porcelain are brushed and cleaned, they are generally handled over a sink filled with water or over a towel. Should the denture accidentally fall, the water or towel would help break the fall and hopefully reduce tooth breakage.
Requirements For Good Artificial Teeth:
§ They should have good appearance.
§ They should be indistinguishable from natural teeth in shape, colour and translucency.
§ Good attachment between the artificial teeth and denture base.
§ Artificial tooth and base material should be compatible i.e. introduction of artificial teeth into the base should not affect the base material.
§ Should be of low density in order that they do not increase the weight of denture unduly.
§ Artificial teeth should be strong and tough to resist fracture.
§ Hard enough to resist abrasive forces in mouth during cleaning.
§ They should allow grinding with a dental bur so that adjustments to the occlusion can be made by dentists at the side chair.
ARTIFICIAL TEETH – GENERAL DISCUSSION
A. DEFINITION:
Denture teeth are artificial substitutes for the coronal portions of the missing teeth. They are usually made of porcelain or plastic. Porcelain denture teeth contain various retentive devices such as platinum-iridium pins and diatoric holes, to secure them to the acrylic denture base.
B. PURPOSE:
To select the proper anterior and posterior denture teeth which will fulfill the esthetic and functional requirements of the patient.
C. INSTRUMENTS and MATERIALS:
1. Occlusion and contour rims
2. Tooth mold and shade guides
3. Flexible ruler
4. Large hand mirror
D. PROCEDURE:
1. The maxillary anterior denture teeth are selected according to size, shape, shade and material.
a. Size:
Insert the maxillary baseplate and occlusion rim that was used to establish the tentative vertical dimension and centric relation. If the occlusion rim lacks retention, it is advisable to use a denture adhesive. With the patient’s facial musculature relaxed, indicate the midline of the face on the labial aspect by inscribing a line parallel to the mid-sagittal plane of the head with a #7 spatula. This line usually bisects the philtrum of the upper lip. It does NOT ALWAYS coincide with the labial frenum.
Establish the level of the high lip line on the occlusion rim by asking the patient to smile broadly. This will aid in the determination of the tooth length. The width of the six maxillary anterior teeth is determined by using the following methods: 1) by dropping a perpendicular from the lateral surface of the ala of the nose. This indicates the center of the cuspid. 2) By marking the corner of the mouth with the lips relaxed on the contour rim with the #7 spatula. This indicates the distal of the cuspid. 3) By dropping a perpendicular line midway between the ala of the nose and the pupil of the eye and marking it with the #7 spatula on the contour rim. This may also indicate the distal of the cuspid. These guides are used as a starting point for the selection of the maxillary anterior teeth. Variations may be made to suit the esthetic and biomechanical requirements of the patient.
b. Shade
The shade may be selected according to the facial skin coloration or complexion and the age of the patient. The shade should be selected iatural light or a proper color-corrected light substitute (not the unit light). Select two or three of the most suitable shades for the patient from the shade guide of the manufacturer of the teeth to be used. Consult with the patient as to which shade will be tried initially. The large hand mirror will aid the patient in the determination.
c. Shape
The shape or mold of the artificial anterior tooth is selected by studying the contour of the face and by the sex of the patient. Some studies have shown an esthetic harmony between the contour of the face and the contour of the inverted maxillary central incisor. This harmony does not always exist in regard to natural teeth but it does provide a guide to selection of artificial teeth. Those who follow the system divide the face into square, tapering, or ovoid and various combinations of these. One denture tooth manufacturing company groups its artificial teeth according to this plan. It will be found that most faces fall into the tapering with modification group. Another company divides its teeth according to flat or curved labial surfaces.
Consult the manufacturer’s mold guide, using the information obtained thus far. Select one or more molds that conforms to the shape, length (from the high lip line), and width of six anterior teeth as measured on a curve (distal of cuspid to distal of cuspid lines marked on wax rim). Make your final selection the one that most suits your particular patient. Record the mold number in the patient’s chart.
2. The mandibular anterior teeth:
Remove the maxillary contour rim and place it on the articulator. Study the relationship of the facial contour of the maxillary rim to the mandibular alveolar ridge. In the average mouth where there is slight to moderate horizontal overlap, the mold suggested by the manufacturer which corresponds to the maxillary anteriors may be used. If the mandible is retruded, it will be necessary to select a narrower mold of lower incisors. If the mandible is in protrusive relation, it will be necessary to select a larger width mandibular incisor. The degree of horizontal overlap affects the relative widths of the maxillary and mandibular anteriors because the radius of the curvature of the arches varies. In order to achieve functional anterior occlusion, the correct corresponding width must be used. In addition, it may be desirable to incline the incisors labially or lingually.
Troubleshooting and Adjusting the Framework
Introduction
It is best to wait until the framework is fabricated and adjusted intraorally before securing jaw relation records. Expect frameworks to require selective grinding along guiding planes and clasp shoulders before seating. Teeth do drift. If every frame fit without adjustments, you can be almost certain the laboratory is overblocking your cases with what becomes serious food trap zones. We recommend disclosing agents (chloroform-rouge or Occlude) to identify prematurities. Also, be certain that there is no opposing occlusion on the framework itself, not even on the rests. If further reduction of the framework may weaken the metal too much, then the opposing tooth enamel should be reduced and polished as necessary. Bending clasps is not recommended, but when necessary, a three-prong plier should be used.
Common Metal Framework Problems
The following are common metal framework problems and possible solutions:
• Frame fits cast but not the oral cavity
– Distorted master impression. Remake case.
– Abutment teeth have drifted. Place self-cure resin blocks into the mesh area for
temporary occlusion and have the patient wear the frame for several days. Hope
for orthodontic-like positional movement.
• Frame pops up before a complete insertion is accomplished
– Too much retention. Reduce height of contour on teeth.
– Inflexible retentive clasps. Thin and taper the clasp toward the tip.
– Rigid parts of the framework, i.e., major connector, bracing clasp, or guide plate
are in harsh premature contact with teeth. Reduce frame thickness and/or height
of contour of teeth. Also, check the cast for signs of abrasion and adjust the
framework accordingly.
• Teeter-totter of framework
– Locate the fulcrum point with rouge-chloroform and reduce frame and/or tooth.
– Distal extensions only. Expect a slight posterior downward rock on a distal
extension frame. Essentially, you are usually observing mucosal compression
under the small tissue stop. If your impression was accurate, the resin saddle will
not allow this rocking after processing. If the posterior downward rock persists at
delivery, then consider a reline. If the downward rock at framework try-in is
gross, make an altered cast impression.
• Bent major connector
Section the major connector (usually a lingual bar) at the bend. Replace each part
into the oral cavity properly and make a full arch over impression. Pour a stone
cast and send to the laboratory for a weld repair.
– Distorted master impression. Remake case.
• Broken cast-type clasp
– Place clasp part and framework correctly in the mouth. Dura-lay the parts
together. Take a full arch impression pulling the framework with it. Pour cast
and send it to the laboratory for weld.
– Consider the above except have the laboratory place a retentive wrought clasp
into the adjacent resin base or weld the wrought clasp to the framework.
– Remake the case if the above fail.
Determining Maxillo-Mandibular Relations and Tooth Selection
Introduction
The occlusion rim is now attached to the well-fitting framework. The rim is made entirely of wax since an acrylic baseplate would require extra work to remove from the framework later on.
In general, the procedures for recording jaw relations for removable partial dentures are similar to those described for complete dentures. If the casts can be related to each other in unmistakable centric occlusion by means of the remaining teeth, then vertical, connecting lines may be drawn across the facial surfaces of occluding teeth at widely separated points. When insufficient or improperly related natural teeth do not make accurate cast relationship possible, the use of wax occlusion rims with a recording material (polyvinylsiloxane or Aluwax) must be used. After the casts have been related to each other with the registration, this relationship should be checked clinically against the patient’s natural occlusion. To make this comparison, it is necessary to trim the registration so that only the indentations of the tips of the opposing cusps remain.
Choosing the Teeth
The choice of tooth form (anatomic vs. nonanatomic), tooth material (plastic vs. porcelain), and occlusal arrangement (centric relation/centric occlusion and eccentric movements) depends primarily on the type of opposing dentition and partial denture support.
Statment of teeth
Statment of teeth with tight feet of tooth neck to the gums from vestibular side. Mostly is used for anterioir group of teeth.
Statment of teeth on fake gums
Statment of teeth from plastic
Grinding of the teeth on the motor
Groups of defects
First group
Second group
Borders of partial removable dentures
While choosing the constructions of the partial removable denture the dentist faces the problem of its fixation in the oral cavity. The effective method of fixation is one of the conditions of good functional quality of the denture. There are different methods of partial removable denture fixation, such as adhesion, anatomical retention, and artificial mechanic devices: clasps, Flange, telescopic crowns, etc.
The mechanic devices (retainers) are of the main use in fixation of the removable dentures.
The retainers are divided into direct and indirect. Direct retainers are placed on the tooth and prevent vertical displacement of the denture. They include clasps, all kinds of attachments. According to the place of positioning retainers are divided into intracrown and extracrown. Some attachments are related to the former and clasps to the latter.
Kinds of clasps. The clasps are subdivided by different signs: the way of making (wire, cast); by the shape of the profile intersection (circular, semicircular, strip); by the degree of the tooth clasp and their amount (one-arm, two-arm, mesiodistal (proximal grip), double, multisection); by function (retention, supported); by the method of connection with the denture base (rigid, semirigid, spring, articulated (pivot).
Indirect retainers prevent falling out of the denture. Continuous clasps, processes, rests may play their role.
The amount of the abutment teeth and their localization is of great importance for denture fixation.
The clasp line. The line that connects the abutment teeth on which the clasps are placed is called a clasp line. Its direction depends on the position of the abutment teeth. When the abutment teeth are located on one side of the jaw the clasp line is of sagittal direction, in contralateral position of the abutment teeth it is of transversal or diagonal direction.
When one tooth is used as an abutment, the denture fixation is called punctuate, two teeth – linear, three and more teeth – plane. The punctuate fixation is the least beneficial as all pushes of the denture during the functional load fall on the parodont of one teeth resulting in its overload.
The harmful effect of the clasps on the abutment tooth parodont may be significantly reduced by using the points of anatomical retention for denture fixation (alveolar processes or their parts, maxilla tubers, palatal torus, internal oblique lines).
The linear fixation. From the point of view of statics this fixation is more expedient than the punctuate one. Only in case of choice one has to make a sagittal clasp line unbeneficial as to firmness of the abutment teeth and the denture. For example, there are two lateral teeth left on the upper jaw – the first molar and first premolar. The clasp line will be sagittal in this case. In other words, while making the clasp line we should aim at the denture parts being on either side of it, i.e. the clasp line should be the axis of the denture rotation (transversal on the lower jaw and diagonal – on the upper jaw). Nevertheless even expedient linear consolidation has quite significant drawbacks as to effect on the firmness of the teeth. During the masticatory pressure the denture moves lever-like in different directions. The strength of this movement is measured by the length of the lever arm. The arm is equal to the pendendicular reestablished from the middle of the clasp line, i.e. the line that connects the middle of the abutment teeth. The larger the lever arm, the greater the strength of the masticatory pressure, the more is the overturning effect on the abutment teeth.
Plane fixation.To prevent the tooth from the rotation force another force should counteract, it is the centre of counteraction. The plane fixation provides it when there is system of levers that have centers of rest (support). Depending on the centers of rest there may be triangular, quadrangular and more systems.
The make the denture stable it is necessary that resistance should be more than the rotation force during mastication. That’s why abutment strong multiroot teeth are chosen as the center of support. By using their firmness as a positive factor for prosthesis and by using a large amount of teeth for transmission of masticatory pressure we achieve the denture equilibrium.
The clasp system may be considered satisfactory if it meets the following requirements:
1. makes equal fixation on all abutment teeth;
2. excludes turnover or rotation of the denture;
3. does not elevate the height of occlusion (interalveolar) on the occlusion rest;
4. disturbs the esthetic norms minimally;
5. does not form traumatogenic occlusion.
At present the orthopedists have different constructions of clasps at their disposal; it allows them to fix dentures in the oral cavity even under very difficult conditions using natural teeth as abutment. The clasp was first used by Mouton in 1764. The problem is to use such system of clasps that fix the denture but does not exert a harmful influence of the abutment teeth allowing to preserve the dentition. At the same time we should solve the problem of prevention of fast atrophy of the alveolar process by correct distribution of pressure falling on the denture between the abutment teeth and tissues of the prosthetic bad. From this point of view fixation of the partial removable denture is a complex biomechanical problem.
Most clasps have both advantages and disadvantages. It is art to know where, when and in what order to place this or that clasp. It includes the study of clinical peculiarities of the tissues and organs of the oral cavity as well as mechanic properties of the clasps and method of their interaction. Therefore there are a lot of different constructions of clasps.
Before speaking of the clasp role it is necessary to understand such notions as supporting, stabilizing and fixation function.
The supporting function is transfer of the masticatory pressure via the supporting elements of the clasp onto the teeth that prevent subsidence of the denture and overload of the tissues of the prosthetic bed.
The stabilizing function prevents lateral displacement.
The fixation function means prevention of denture slipping off from the prosthetic bed.
Most perfect types of clasps fulfill all three functions simultaneously, for example, three-arm or compound clasp. This or that function prevails in other clasps, for example, retainers. A wire clasp is an example of this.
The retainers. There are three main parts in the construction of any retainer: arm, body and extension.
The circular wire retainers are more commonly used in the partial plate plaster dentures. The clasp arm is a spring part that encircles the tooth crowns and is placed directly in the area between the equator and neck. It should tightly fit the surface of the abutment tooth, reproducing its shape and has high elastic properties. Gapping only in one point may lead to highly increased pressure density in movement of the denture and cause necrosis of the enamel. Destruction of the enamel of the abutment tooth often results from irregular distribution of pressure due to gapping of the clasp. The clasps should be passive, i.e. do not cause pressure on the tooth when it is not under pressure.
To prevent this one clasp arm should fix the denture and the other – to resist it, i.e. to prevent its displacement into this or that side (reciprocal effect).
The word “articulation” has borrowed from anatomy where is it designates a joint, but many authors are put in this word a various maintenance. In our dentistry greatest distribution has received a definition of this term given by A.J.Catz: articulation is every possible positions and movements of a lower jaw in relation to the upper carrying out by the chewing muscles.
This definition of articulation include itself not just a chewing movement, but also and it’s moving during conversation, yawning and others. For practice purposes the most convenient to define an articulation as a chain of variants of an occlusion replacing each other. Such definition is more concrete because cover only chewing movements of a lower jaw which studying is very important to designing the articulators.
Occlusion is a closure of dentitions in the whole or separate group of teeth during a smaller or larger interval of time.
Thus an occlusion survey as an articulation special case is one of it’s moments.
Distinguish four basic types of an occlusion: central, frontal and lateral (right and left).
Central occlusion is a closing of the teeth at the maximal amount of a contact points(pic. 1).
Central occlusion signs: — average face line coincides with a passing line between central incisors;
– articulate heads settle down on a clivus of an articulate hillock at its basis.
Thus it becomes perceptible simultaneous and uniform reducing of the chewing and temporal muscles on both sides.
At the frontal occlusion occurs a promotion of the lower jaw forward. It is reached by bilateral reduction of lateral pterygoid muscles.
Frontalocclusionsigns:
— average line of face coincides with a average line occur between incisors;
— articulate heads at the frontal occlusion moved forward and located at the apex of the articulate hillocks.
Lateral occlusion arising at the lower jaw moving to the right (right occlusion) or to the left (left occlusion).
Lateralocclusionsigns:
— at the lower jaw displacement to the right on the displacement side the articulate head remain at the basis of the articulate hillock, slightly rotating. On the left side an articulate head located at the apex of the articulate hillock;
— the right lateral occlusion accompanied by reduction of a lateral pterygoid muscle by opposite (left) side and on the contrary – left lateral occlusion by the same name muscle reduction by the right side.
Condition of relative rest of a mandible.
Out of chewing and conversation dentitions are usually opened, because a lower jaw is downy and between the frontal teeth have a lumen in size of 1-6 mm. At the jaw hanging down the muscles are a little stretched that causes a boring of the proprioceptors.
Artificial teeth statement in the partial lamellar dentures has making with anatomical reference points.
Anatomical reference points for the artificial teeth statement are:
– Nearby standing teeth
– Teeth-antagonists
– Crest of a alveolar process
– Between-alveolar lines
– Form of the teeth arches
– Average face line
– Bridles of lips
– Form of the alveolar process
– Pupillary line
– Line of a line
– Incisors margin level
The artificial teeth statement are making in the articulators that is providing corresponding accuracy of reproduction of various occlusal parties. For a correct locating of a artificial teeth make them pre-sharpening (the form of an alveolar crest, height of teeth, a locating of a shoulder of a clasp, occlusal contacts).
Angle of a saggital articulate way.
The angles of a saggital articulate way of the natural (a) and artificial (б) teeth.
Three-points Bonville connection. а — Benett angle; б — Bonville triangle
Side occlusion Central occlusion
Artificial teeth statement in the partial lamellar dentures
Artificial teeth on basis can be putted be two ways: on sharpening (when the artificial teeth putted to the without teeth alveolar process) and on the artificial gum (when the artificial teeth putted on the basis of denture). For example, at well or moderately expressed toothless alveolar process of the upper jaw in the frontal part and the truncated upper lip the artificial teeth are expedient to put on sharpening. At the moderately expressed alveolar process or it’s sharp atrophy in combination with long upper lip it is necessary to give presence to the teeth statement on the artificial gum. Careful estimation of the in- and out-mouth features (atrophy degree of the alveolar parts, length of lips, degree of denudation of an alveolar process and the teeth at smiling) allow to choose a correct method of the artificial teeth statement and maximally individualized it having departed from the standards which making the artificial teeth (visible at smiling) more natural.
The longitudinal and cross-section sizes, design of the artificial teeth are defining first of all the form of the patient’s face in a fullface and in a profile, extent of defect of a dentition and between-alveolar space. At the well expressed alveolar process should to use the artificial teeth with a small curve of neck, and also at the considerable atrophy of the alveolar part – with a more expressed curve.
At the artificial teeth statement in the frontal part first of all pay attention to atrophy degree of the alveolar process. At a small and in regular intervals enough atrophied alveolar part the artificial teeth should to be dilated in a at-neck area with a slightly oblique surfaces from the inside. If alveolar part (process) in a frontal part is well saved but narrow then it is necessary to give a presence to the artificial teeth narrowed in at-gum part and considerably cut from the inside.
At the artificial teeth statement in a frontal part the greatest difficulties arise at the place disadvantage for teeth statement, sharply expressed undercuts at teeth (which limiting defect), to the pear-like form of a vestibular clivus of the alveolar part of a jaw and color choosing.
Place disadvantage for the artificial teeth statement can be compound with a dentitions deformation when the teeth, which limiting defect, are moving to the site of extracted teeth. The same situation arises at the teeth extraction with anomalies. If orthodontic correcting of the displaced teeth is impossible then the better way is, the first, grinding of the contact surfaces of teeth which block the standard teeth size statement and, the second, careful artificial teeth statement in so-called stratification which imitates a dense teeth position. Thus for achievement of good esthetic effect it is necessary to use for statement the artificial teeth of the same size, as a natural. Besides, it is possible to combine a method of preliminary preparation of the teeth limiting defect of a dentition with dense statement of the artificial teeth by stratification.
Sharply expressed undercuts on the teeth limiting visible at a smile defect of a dentition look especially ugly at statement of the artificial teeth on an artificial gum. To improve an esthetics in this situation it is possible by statement of the artificial teeth on sharpening by undercut reduction at grinding the most acting surface of tooth or use so-called inclined, or rotary, ways of introduction of a denture when the undercut will be filled by a basis material. In this case application dilated and thick edge of an artificial gum closing an undercut or defect of a toothless alveolar part is also useful.
At the pear-like form of a toothless alveolar part the usual way of introduction is impossible without preliminary grinding the plastic filling an undercut. Change of a way of introduction of a denture can frame additional undercuts in the field of lateral teeth that also will demand excision of superfluous plastic. However it in turn can lead to deterioration of bracing of a denture. The shorting of basis from the labial part or statement of the artificial teeth on sharpening can be the question decision.
Special problem at statement of the artificial teeth is the reconstruction of beauty, depth and variability of color of natural teeth. The best conditions for color selection consider bright day illumination. For this patient it is necessary to bring to a window and to switch off artificial illumination. In doubtful cases it is necessary to choose hardly more dark teeth which after grinding will look lighter. This results from the fact that the basic colorgenerate zone in acrylic teeth is located just with grinding part. Sharped tooth loses the most part of painting plastic and looks is more light. At its excessive grinding can appear through, for example, a metal skeleton which should be masked preliminary by opacker.
At selection of frontal porcelain teeth it is necessary to pay attention to depth of incisor overlapping. At deep overlapping select teeth with cross-section located crampons, established more close to a neck. It will promote conservation of durability of fastening of porcelain tooth in basis of a denture. At appreciable overlapping of thr frontal teeth it is necessary to give preference to the plastic artificial teeth.
The lateral artificial teeth are choosing with according to extent of defect and size of a between-alveolar distance.
A false tooth is any substitute for a tooth that has been lost or is severely damaged and required restorative work. They can take a number of forms and are secured in the mouth using a variety of techniques. Dentures are the most well known form of false teeth but they are not the only ones available.
False teeth have come a long way since people in pre-Modern Italy first started using human and animal teeth to replace their lost teeth. Modern false teeth tend to be made out of acrylic but porcelain is still used in some cases because of its superior chewing ability.
Dentures are still popular because they are relatively cheap and can be removed, but increasingly patients are opting for more permanent solutions like dental implants or dental crowns. You can find more information about different solutions for tooth loss on this website. Whichever one you choose, modern false teeth are incredibly realistic and are able to be fitted far more conveniently than they used to be.
Perhaps even more importantly, you can find information in these pages about how to avoid situations where you might need dentures, dental implants or dental crowns. Accidents are unavoidable and can happen to anyone but there are simple things you can do to give your teeth the best chances of being healthy. After all, it is preferable not to find yourself in the situation where you actually require one of these procedures!
Read on to find a host of information about different types of false teeth, how they work and in which situations they tend to be required.
False teeth
Replacements for decayed or lost teeth have been produced for a few thousand years. The Etruscans (people from the ancient country of Etruria in western Italy) made skillfully designed false teeth out of ivory and bone. These false teeth were secured in the mouth by gold bridgework as early as 700 B.C. Unfortunately, the skills and artistry that went into these efforts were lost until the 1800s.
During medieval times, the practice of dentistry was largely confined to tooth extraction. Replacement and repair were seldom considered. Gaps between teeth were expected, even among the rich and powerful. Queen Elizabeth I of England (1533-1603) filled the holes in her mouth with cloth to improve her appearance in public.
When hand-carved false teeth were installed, they were tied in place with silk threads. If not enough natural teeth remained to tie the dentures to, anchoring false ones was difficult.
Dentures
People who wore full sets of dentures had to remove them when they wanted to eat. Upper and lower plates fit poorly and were held together with steel springs. Because the sets were not anchored, they could spring suddenly out of the wearer’s mouth. Even George Washington (1732-1799) suffered terribly from tooth loss and ill-fitting dentures. The major obstacles to progress were finding suitable materials for false teeth, making accurate measurements of a patient’s mouth, and getting the teeth to stay in place. These problems began to be solved during the 1700s.
Porcelain
Since antiquity, the most common material for false teeth was animal bone or ivory, especially from elephants or hippopotami. Human teeth were also used, pulled from the dead or sold by poor people from their own mouths. These kinds of false teeth soon rotted, turning brown and rancid. Rich people preferred teeth of silver, gold, mother of pearl, or agate.
In 1774 the French pharmacist Duchateau enlisted the help of the prominent dentist Dubois de Chemant to design hard-baked, rot-proof porcelain (a hard, white ceramic) dentures. De Chemant patented his improved version of these “Mineral Paste Teeth” in 1789 and took them with him when he emigrated to England shortly afterward. The single porcelain tooth held in place by an imbedded platinum pin was invented in 1808 by the Italian dentist Giuseppangelo Fonzi. Inspired by his dis-like of handling dead people’s teeth, Claudius Ash of London, England, invented an improved porcelain tooth around 1837.
Porcelain teeth came to the United States in 1817 via the French dentist A. A. Planteau. The famous American artist Charles Peale (1741-1847) began baking mineral teeth in Philadelphia, Pennsylvania, in 1822. Commercial manufacture of porcelain teeth in the United States was begun, also in Philadelphia, around 1825 by Samuel Stockton. In 1844 Stockton’s nephew founded the S. S. White Company, which greatly improved the design of artificial teeth and marketed them on a large scale.
Porcelain is no longer used because better materials have been developed. Today, dentures are made from either plastic or ceramic. These materials can be tinted to match existing teeth and look more like real teeth than ever before.
False Teeth: Plastic vs. Porcelain – Discover The Difference
Doctor
In the past, false teeth made with porcelain were generally preferred over false teeth made from plastic due to their greater durability and esthetics. However, in recent years, new generation biomaterials have resulted in the development of very wear-resistant false teeth made from plastic.
Clinically, the esthetics of plastic and porcelain denture teeth is nearly comparable, with good quality false teeth made from porcelain still being the standard for esthetics. However, the majority of dentures today probably are fabricated with false teeth made from plastic. For all practical purposes, the cost of porcelain and false teeth made from plastic are about the same.
While porcelain and plastic teeth are competitive with regards to durability, and to a lesser extent, esthetics and wear, there are other factors that may favor the selection of one type of tooth over another.
Some Selection Factors for False Teeth
Balanced bite and force transmission:
Denture bite (called occlusion) changes due to the constantly changing jawbone (called alveolar bone) upon which a denture rests, and, to varying degrees, uneven tooth wear resulting from use. Unless a denture is evaluated and its occlusion adjusted to a uniform and even contact (called balanced bite or balanced occlusion) at regular intervals, denture occlusion will become unbalanced.
Since false teeth made from porcelain are more wear-resistant, their occlusion will not become significantly self-altered by wear, as will false teeth made from plastic. However, when alveolar bone changes cause an unbalanced occlusion, the resulting biting forces from false teeth made from porcelain will be unevenly transmitted to underlying supporting alveolar bone. Frequent tissue refitting of the denture usually eliminates or lessens this problem.
Porcelain denture teeth tend to transmit the impact of biting forces to the alveolar ridge with greater intensity than that transmitted by plastic teeth in an unbalanced tooth contact situation. Some practitioners are of the opinion that this greater force, especially when uneven as in an unbalanced occlusion, may be damaging to the alveolar ridges and could result in accelerated bone loss.
Therefore, unless denture occlusion is checked and balanced on a regular basis, false teeth made from plastic would probably be a preferred choice over false teeth made from porcelain.
Bone loss:
If a person has lost a great deal of supporting alveolar bone and their gum tissue is not of a sturdy type, then plastic denture teeth might be a better choice. These teeth are more forgiving of excessive forces developing from habits such as clenching, grinding, and tapping or “clacking” of teeth, which seems to be more prevalent among older individuals. Plastic teeth do not transmit forces to underlying bone as intensely as false teeth made from porcelain.
Noise:
If false teeth made from porcelain are vigorously used or sometimes habitually tapped together, a “clacking” sound can be heard. Plastic teeth will muffle this sound and be quiet during normal function or habit jaw motions (called parafunction).
Which Type of Tooth Is Best?
If a person has been successfully wearing dentures with false teeth made from porcelain, then they should probably continue with false teeth made from porcelain. These teeth will not wear as fast as false teeth made from plastic, and the relationship between upper and lower jaws will tend to stay normal for a longer time than with false teeth made from plastic.
Regardless of which type of tooth is selected, the success of the selection is strongly based upon regularly checking dentures for proper balanced occlusion and fit on regular intervals.
If a denture is going to be worn against opposing natural teeth, then false teeth made from plastic should be selected because false teeth made from porcelain, being harder, could excessively wear natural teeth away.
After a thorough examination and frank discussion of what a person wants from wearing a denture, a licensed dentist can effectively discuss which type of tooth would best meet a particular individual’s unique needs and desires.
Tooth Strength
Because false teeth made from porcelain are extremely hard in comparison to false teeth made from plastic, they tend to chip and crack more easily. For this reason, when dentures having false teeth made from porcelain are brushed and cleaned, they are generally handled over a sink filled with water or over a towel. Should the denture accidentally fall, the water or towel would help break the fall and hopefully reduce tooth breakage.
Porcelain or Plastic Denture Teeth?
Lots of people with dentures, or those who learn that they need dentures, often wonder which is the best choice; plastic or porcelain. This used to be a relatively easy question to answer because most dental professionals opted for the long wearing porcelain fixtures. Today, however, there have been so many advancements in the world of plastics that the decision gets a bit tricky. For instance, there are now dental-safe plastics with the durability of porcelain, and which can look just as good as real teeth.
The solution isn’t found by purchasing the cheapest options either because the advancement of manufacturing allow both options to actually be priced within the same general ranges as well. This leaves a dental patient with the dilemma of having to choose the appropriate materials for their particular conditions.
Fortunately, a good dental professional will offer the kind of useful advice and guidance necessary for making the proper choices. For instance, they will always alert their patients to the condition of their “alveolar bone” which is also referred to generally as the jaw bone. This is a major factor in the decision making process because this bone is highly affected by the materials selected.
Consider that someone ieed of dentures will be missing several, if not all, of their adult teeth. The absence of the roots of the teeth means that the jawbone might be easily compromised, and that it will begin to experience bone loss at a faster pace than it would have with the teeth in place. When you add the kind of strong pressures that biting creates, it can lead to a huge amount of pressure on the jawbone – particularly with a material as hard as porcelain.
This is one reason that a dental professional will recommend that a patient opt for plastic. The dentist would also make this same recommendation if a patient did not have a lot of sturdy gum tissue remaining over their jaws as well. This is because there would be very little “padding” between the rigid porcelain dentures and the underlying bone.
Finally, it is usually only the dentist who understands the changing bite patterns of their patient. They can review their records and charts to determine if they have patterns that indicate habits such as bruxism or clenching of the teeth. If such a condition exists the dentist will usually recommend the plastic dentures at that time too.
1. Selection of artificial teeth
2. GOALS FOR THE SELECTION OF ARTIFICIAL TEETH Construct a denture to : Function well Allow pt: speak normally Esthetically pleasing Will not abuse the natural tissues
3. TOOTH SELECTION STAGES ANTERIOR TEETH SELECTION(ATS) POSTERIOR TEETH SELECTION
4. ANTERIOR TEETH SELETION (ATS) SELETION CRITERIA: Selection of tooth size Selection of tooth shape (Form) Selection of tooth colour ( shade) Selection of tooth material
5. Selection of tooth size Size has three dimensions: Mesio – distal width Occluso – gingival height Facio – lingual thickness
6. GUIDES FOR THE SELECTION OF ANTERIOR TEETH SIZE Pre – Extraction guides Post – Extraction guides
7. PRE-EXTRACTION GUIDES FOR THE SELECTION OF TOOTH SIZE Diagnostic casts: most reliable guide Helps to duplicate pt: original teeth shape, size & positional arrangement . Especially useful in immediate dentures.
8. PRE-EXTRACTION GUIDES FOR THE SELECTION OF TOOTH SIZE Photographs: Provide information on width & form of teeth (rarely on color). Usefulness depends on the extent of teeth visibility Human size photographs are more valuable Digitization of images make computer assisted vision possible.
9. PRE-EXTRACTION GUIDES FOR THE SELECTION OF TOOTH SIZE 3 . RADIOGRAPHS: helps in size & form selection Need compensation for magnification Distortion of radiographic image is an inherent problem. 4. EXTRACTED TEETH: Excellent guide for tooth size & form selection. Not a good guide to select shade of teeth. 5. Previous Dentures:
10. POST-EXTRACTION GUIDES FOR THE SELECTION OF TOOTH SIZE GUIDES TO DETERMINE THE TOOTH WIDTH Size of the face: Anthropometric Measurements Bi-zygomatic width Cranial circumference Ratio of cranial circumference to the combined upper anterior six teeth width is 10:1.
11. GUIDES TO DETERMINE THE TOOTH WIDTH 3 . CORNER OF THE MOUTH: Line drops over the max: rim from corner of the mouth at rest, corresponds to the distal surface of the canine. 4. ALA OF THE NOSE: A vertical line dropping from the ala of the nose usually passes along through middle of canine.
12. GUIDES TO DETERMINE THE TOOTH OCCLUSO-GINGIVAL HEIGHT HIGH LIP LINE: 2 . INTER-ARCH SPACE:
13. GUIDES TO DETERMINE THE TOOTH FACIO- LINGUAL THICKNESS Thicker teeth should be prefer. Can be rotated & space out to give more realistic appearance. Allow more depth while setting the teeth.
14. SELECTION OF TOOTH FORM Shape/form of artificial teeth is three dimensional. Therefore teeth has got three important forms, FACIAL FORM LATERAL /PROXIMAL FORM AN INCISAL FORM
15. FACIAL FORM Leon Williams Theory: Face form corresponds to facial form of inverted Central incisor. Similarly, Face form corresponds to arch form. Face form can be categorized into three primary forms; Square form Tapering form Ovoid form
16. LATERAL /PROXIMAL FORM & AN INCISAL FORM Lateral face form determine the lateral form of the artificial teeth Lateral face form can be categorized into; Straight convex
17. Selection of tooth colour ( shade) Colour of an object is recognized when a light of a particular wavelength is reflected off an object & then falls on the retina of the eye
18. Properties of colour Colour has got the three important qualities: HUE: Particular variety of colour(red, green,etc) Determined by the wavelength of reflected light. Shorter the wavelength, the closer the hue is to the violet portion. longer the wavelength, the closer the hue is to the red portion.
19. Properties of colour CHROMA: Amount of colour. Canine is more saturated then other anterior teeth. VALUE: Represent amount of black or white. The brightness depends on the amount of light energy reflects/transmits by an object. TRANSLUCENCY: Represents the amount of light transmits through an object. Predominant in the area of incisal edges &/or proximal surfaces
20. FACTORS EFFECTS THE COLOUR OF NATURAL TEETH AGE: As age progresses teeth become more opaque . WEAR: Teeth looks more glossy, smooth & prone to stain. GENDER: Females have more whiter teeth. DEMINERALIZATION: teeth gets more prone to staining. STAINS: Both extrinsic & intrinsic stains effects the actual shade of the natural standing teeth . POSITION OF TEETH IN DENTAL ARCH: Canine is having more saturation of a specific hue .
21. SHADE REPLICATION Process of replicating the colour of adjacent teeth in an artificial prosthesis, having following steps: SHADE MATCHING PHASE: a) visual shade matching’ b) Instrumental colour analysis. 2. SHADE DUPLICATION PHASE:
22. FACTORS INFLUENCE THE APPERANT COLOUR OF AN OBJECT Physical properties of an object. Nature of the light. Subjective assessment of an observer.
23. SHADE SELECTION FOR EDENTULOUS PATIENT PRE_EXTRACTION GUIDES: Not particularly helpful for shade selection, Photographs Extracted teeth
24. SHADE SELECTION FOR EDENTULOUS PATIENT POST-EXTRACTION GUIDES: COLOUR OF THE EYES & HAIRS Little correlation exist (Hallarman). Hair colour is unreliable. Black eye individuals have darker teeth shade SKIN COLOUR: Fair skinned individuals can be given with lighter shades. Lighter shades on Darker skinned individual look more conspicuous.
25. POST-EXTRACTION GUIDES: DENTOGENIC CONCEPT: Concept proposed by FRUSH & FISHER. Has got the great impact on selection of teeth. Teeth selected according to this concept consider the following factors in the given order. GENDER: FEMALES HAVE, Delicate look accorded by rounding the point angles & avoiding the sharp angles in the contour of the teeth. Select the small lateral incisors Set the lateral incisor at higher level than centrals.
26. DENTOGENIC CONCEPT: 2 . PERSONALITY: Patient can have VIGOROUS or DELICATE personality Vigorous look can be given by, Selecting wider centrals Wearing the centrals & canine Selecting the darker shade Sharp line & point angles Delicate personality can be created by , More paler teeth Rounded contours.
27. DENTOGENIC CONCEPT: AGE: Aged appearance can be given by, Wearing the incisal edges. Proximal wear can also be incorporated. More of the cervical portion visible to give gingival recession appearance. Select darker shade. Age characterized molds are also available.
28. Posterior tooth selection
29. CONSIDERATIONS FOR THE SELECTION OF TEETH Masticatory function Preservation of ridge Denture stability Soft tissue health Esthetics
30. SELECTION CRITERIA FOR POSTERIOR TEETH Colour Mesiodistal width Buccolingual width Occlusogingival length Cuspal inclination Material selection
31. SELECTION CRITERIA FOR POSTERIOR TEETH COLOUR SELECTION: The upper premolars & mesiobuccal half of the 1 st molar are usually visible during smile. Canine are the darkest teeth Premolars & molars should be slightly lighter in shade than canine. The difference should not be too much obvious.
32. SELECTION CRITERIA FOR POSTERIOR TEETH 2. Mesio-Distal width selection: Mesio-distal width is dictated by the length of mand: residual ridge from the distal of the canine to retro-molar pad. Arrangement of three post: teeth is more often the norm & will reduce the potential for the placement of the 2 nd molar too far posteriorly. Max: post: teeth that extends too close to the post: border of max: denture may cause cheek biting.
35. SELECTION CRITERIA FOR POSTERIOR TEETH 5. CUSPAL MORPHOLOGY SELECTION: Based on cuspal morphology posterior teeth can be classified into: Non-anatomical teeth Anatomical teeth Combination of anatomic & non-anatomic teeth
36. CUSPAL MORPHOLOGY SELECTION: NON–ANATOMICAL TEETH Also known as Flat or Monoplane or Cuspless or Zero degree teeth. Historically, HALL ( 1929) was the 1 st person to design cuspless teeth called “INVERTED CUSP TEETH.” “ TRUE-KUSP” design by Myerson in 1929. “ CHOPING BLOCK” by Nelson in 1934. “ NON-LOCK by Swenson in 1939. “ VITALLIUM OCCLUSAL” by Hardy in 1946. Introduced in order to reduce lateral forces acting on the denture. Balanced occlusion Can be obtained by introducing “Balancing ramps”. .
37. NON–ANATOMICAL TEETH INDICATIONS: Flat ridge cases Abnormal jaw relation case Where difficulty is faced in recording the centric relation. Where balanced occlusion is not planed.
38. NON–ANATOMICAL TEETH ADVANTAGES: Freedom of occlusal movements from centric to eccentric jaw positions. Elimination of lateral forces that can destabilized the denture. When denture settling take place due to denture abuse no cuspal interference occur. DISADVANTAGES: Not esthetically pleasing. Difficult to balance Reduced masticatory efficiency
39. ANATOMICAL TEETH Can be classified on the bases of cuspal inclines. Cuspal inclines vary from 20 degree to 45 degree. INDICATIONS: Good ridge form with sufficient retention & support. Where balanced occlusion is planed. Where possible to record & transfer the centric relation with accuracy.
40. ANATOMICAL TEETH ADVANTAGES: Easier to balance Better masticatory efficiency Reduced chewing cycles Better esthetics
41. COMBINATION OF ANATOMIC & NON-ANATOMIC TEETH This concept was proposed by payne in 1941, called “ LINGUALIZED OCCLUSION.” Lingualized scheme use upper anatomical & lower either semi or nonanatomical teeth molds. The max: lingual cusp set into the lower central fossa ( MOTAR & PESTLE) The mand: buccal cusp kept out of the max: central fossa. Occlusion can be balanced by introducing the “compensating curves”.
42. EXAMPLES OF LINGUALIZED INTEGRATION MOLDS Mayerson Lingualized Integration( MLI). Gysi’s cross bite posterior.( 1927) French’s Modified posteriors.(1935) Max Pleasure Scheme.(1937) Vita Linguoform.
43. LINGUALIZED OCCLUSION ADVANTAGES: This concept provides maximum intercuspation. Absence of deflective contacts. Adequate cuspal height for selective grinding. Natural & pleasing appearance. Can be used in pt: where recording the CR is uncertain. Occlusion can be balanced .
44. 1. Acrylic resin teeth INDICATIONS: When there is opposing natural dentition. When opposing dentition has got the gold crowns or inlays. Where there is reduced interarch space. Where occlusal adjustment is required.
45. MATERIAL SELECTION FOR ARTIFICIAL TEETH 1. Acrylic resin teeth 2. Porcelain teeth
46. 1. Acrylic resin teeth INDICATIONS: When there is opposing natural dentition. When opposing dentition has got the gold crowns or inlays. Where there is reduced interarch space. Where occlusal adjustment is required.
47. Acrylic resin teeth ADVANTAGES: Inexpensive Easy to grind & adjust Absorb the occlusal stresses Does not wear the opposing natural teeth. Bond chemically to denture base. Self adjusting & polishing. Softer impact sound DISADVANTAGES: Wear easily Loss of VD because of wear. Stains with time. Shearing efficiency with time.
Wax pattern manufacturing
The wax pattern of the removable partial denture is manufactured following the profiles imprinted on the model: the wax pattern of the main connector, made of red wax (so that it’s thickness is twice as normal), the wax pattern of the saddles and the wax pattern of the Ackers circular clasps, made of blue wax.
Injection bars are required for the sensitive areas of the framework that are placed on the areas that are not visible in the finite piece.
A large central shaft is also necessary in order to connect with the main connector, through which the initial injection takes place.
Unlike the pattern of a metallic framework, the patterns of the clasps, occlusal rests and lingual bar were made 50% thicker.
Because the wax pattern of the metal-free framework has to be 50% thicker than that of a metallic framework, pink wax is used for wax-up. In order to produce patterns of the saddles, wax plates were adapted on the cast according to the hallmarks and circular retentive holes were cut along them.
The lingual bar was made by the same wax, achieving a half-pear shape with an optimal dimension. Wax-up of the saddles and lingual bar was made using a special wax, easy to wash away, following the hallmarks. Preformed wax patterns were adapted to the hallmarks with an adhesive solution. Blue wax was used to drop wax-up the patterns of the circumferential clasps.
Once the pattern of the framework is ready, it is stabilized by sticking the margins to the cast.
3.5 Investing the wax pattern
Spruing the framework was performed using five minor sprues of 2.5 mm calibrated wax connected to one major sprue.
Wrapping the wax pattern frame of the removable partial denture
After surface-tension reducing solution is applied to the wax pattern, it is invested in a vaseline insulated aluminum flask. Class III hard stone is used as investment. About 250 g gypsum paste is poured into one of the two halves of the flask and the duplicated cast containing the spruing of the framework pattern is centrally dipped base-face down
Insulation of the investment
When the investment is set, the gypsum surface is insulated and the second half of the flask is assembled. About 400 g of the same hard stone is prepared and poured into the upper chamber of the flask, covering thoroughly the wax pattern and sprues.
After the gypsum sets the flask is submerged in warm water in a thermostatic container.
The two halves of the flask are than disassembled and the wax is boiled out using clean hot water.
The mold is then insulated using a special agent which is applied in a single layer on the gypsum surface. The surface of the mold is given a shining aspect by treating the gypsum surface with light curing transparent varnish.
Dentures, or false teeth, are fixed or removable replacements for teeth. Tooth replacement becomes necessary when the tooth and its roots have been irreparably damaged, and the tooth has been lost or must be removed. Dentists have long known that a missing permanent tooth should always be replaced or else the teeth on either side of the space gradually tilt toward the gap, and the teeth in the opposite jaw begin to move toward the space.
There are several standard forms of tooth replacement in modern dentistry. A full denture is made to restore both the teeth and the underlying bone when all the teeth are missing in an arch. A smaller version is the fixed partial denture, also known as a fixed bridge, which can be used if generally healthy teeth are present adjacent to the space where the tooth or teeth have been lost. The partial is anchored to the surrounding teeth by attachment to crowns, or caps, that are affixed to the healthy teeth. A removable partial denture is used to replace multiple missing teeth when there are insufficient natural teeth to support a fixed bridge. This device rests on the soft tissues of the jaws, and is held in place with metal clasps or supports. Dental implants are the latest tooth-replacement technology. They allow prosthetic teeth to be implanted directly in the bones of the jaw.
History
Historically, a variety of materials have been used to replace lost teeth. Animal teeth and pieces of bone were among the earliest of these primitive replacement materials. Two such rudimentary false teeth (probably molars) were found wrapped in gold wire in the ancient Egyptian tomb of El Gigel. In the last few hundred years, artificial teeth have been fashioned from natural substances such as ivory, porcelain, and even platinum. These comparatively crude prototypes of earlier times were carved or forged by hand in an attempt to mimic the appearance and function of natural teeth. Such early denture workmanship is exemplified by George Washington’s famous wooden teeth.
Modern technology has offered considerable advances in the materials used to make artificial teeth and improved techniques for affixing them in the mouth. Synthetic plastic resins and lightweight metal alloys have made teeth more durable and natural looking. Better design has resulted in dentures that provide more comfortable and efficient chewing. In the 1980s technology was developed to create the next generation of dentures, which are permanently anchored to the bones in the jaw. These new dentures, known as dental implants, are prepared by specialized dentists called denturists.
Raw Materials
Teeth
Most artificial teeth are made from high quality acrylic resins, which make them stronger and more attractive than was once possible. The acrylic resins are relatively wear-resistant, and teeth made from these materials are expected to last between five and eight years. Porcelain is also used as a tooth material because it looks more like natural tooth enamel. Porcelain is used particularly
for upper front teeth, which are the most visible. However, the pressure of biting and chewing with porcelain teeth can wear away and damage natural teeth. Therefore, porcelain teeth should not be used in partial dentures where they will contact natural teeth during chewing.
Mounting frame
Artificial teeth are seated in a metal and plastic mount, which holds them in place in the mouth during chewing. The mount consists of a frame to provide its form and a saddle-shaped portion that is shaped to conform to the patient’s gums and palate. This design allows for comfort and optimizes the dentures’ appearance. Frames are typically constructed of metal alloys such as nobilium or chromium. The latest generations of plastic materials used in dentures are virtually indestructible and can be easily adjusted or repaired with a special kit at the dentist’s office. These materials are also ultra lightweight and can eliminate problems in patients who are allergic to acrylic materials or who are bothered by the metallic taste left by a metal frame.
Design
Every individual’s mouth is different, and each denture must be custom designed to fit perfectly and to look good. The latest methodology used in denture design, known as dentogenics, is based on research conducted in Switzerland in the early 1950s, which developed standards for designing teeth to fit specific smile lines, mouth shapes, and personalities. These standards are based on such factors as mouth size and shape, skull size, age, sex, skin color, and hair color. For example, through proper denture design, patients can be given a younger smile by simply making teeth longer than they normally would be at that patient’s age. This rejuvenation effect is possible because a person’s teeth wear down over time; slightly increasing the length of the front teeth can create a more youthful appearance.
The Manufacturing
Process
1. The manufacturing process begins with a preliminary impression of the patient’s mouth, which is usually done in wax. This impression is used to prepare a diagnostic cast. While making the impression, the dentist applies pressure to the soft tissues to simulate biting force and extends the borders of the mold to adjacent toothless areas to allow the dentures to better adapt to the gums.
2. Once an appropriate preliminary cast has been obtained, the final cast is cast from gypsum, a stone-like product. The final mold is inspected and approved before using it to manufacture the teeth.
3. After the mold has been cast, it is filled with acrylic resin to form the denture. The mold is prepared with a release agent prior to adding the resin to ensure that the hardened acrylic can be easily removed once the process is completed. A sheet of separating film between the acrylic and the model is also helpful in this regard. The denturist then mixes the appropriate resin compounds in liquid form. Upon drying, the resin hardens to a durable finish.
4. This resin mixture is packed into the mold, while a vertical vise packs it tightly. At this point the model can be inspected to ensure it is filled properly, and if necessary additional resin can be added. Instead of vice packing, certain types of acrylic may be poured into the mold. This method is more prone to air bubbles than hand packing.
5. Once the mold is packed to the denturist’s satisfaction, it is heated to initiate the chemical reaction which causes the resin to harden. This part of the process may take up to eight hours.
6. After the heating is done and the mold has cooled, the mold is broken apart so the denture may be removed.
7. The denture is then put in the model of the patient’s mouth to ensure that it fits and that the bite is good. Because of the number of processing steps there may be a slight discrepancy in the fit. Usually just a minor grinding and smoothing of surfaces is all that is necessary to make the denture fit correctly.
At this point, if the denture is the removable type, it is ready for use. Implants require additional preparatory steps before they can be used. The denturist must drill the appropriate holes in the jaw bone and attach an anchor. After three to six months, when the hole has healed and the anchor is set in place, a small second surgical procedure is necessary to expose the implant and connect a metal rod to it that will be used to hold the crown or bridge. Finally, the replacement tooth is attached to the rod, where it is held firmly in place.
Quality Control
Good quality control is critical to ensure the denture fits and looks natural in the patient’s mouth. No two dentures will be alike; even two sets of dentures made for the same person will not be exactly alike because they are manufactured in custom molds that must be broken in order to extract the denture. After the molding process is completed, the fine details of the denture are added by hand. This step is necessary to ensure the teeth look natural and fit properly.
The quality of the denture’s fit can be controlled in two ways. Relining is a process by which the sides of the denture that contacts the gums are resurfaced. Such adjustments are necessary because the dental impressions used to make dentures cause the gums to move. As a result new dentures may not fit properly. Also, over time bone and gum tissues can shift, altering the fit of the denture. Rebasing is used to refit a denture by replacing or adding to the base material of the saddle. This process is required when the denture base degenerates or no longer extends into the proper gum areas. Most patients require relining or rebasing approximately five to eight years after initial placement of the dentures.
