Slip-cast bridge dentures

Slip-cast bridge dentures. Dental bridge constructions, designs and techniques. The laboratory technique of dental slip-cast bridge denture design.

 

Іndications for use of bridge prostheses in orthopedic treatment of patients with defects of dentitions. Choice of their construction is determined mainly by the following factors: size and topography of the defect, its localization, the state of hard tissuesand by periodontal abutment teeth and their antagonists, as well as occlusal relationships.

Defects of dentitions are commonly divided into small ones (in case of absence from 1 to 3 teeth on the jaw), medium (in case of absence from 4 to6 teeth) and big ones in case of absence of more than 6 teeth). Indications for use of fixed prosthesis arebounded edentulous spaces, theseare dentitions bounded on both sides with teeth. Depending on extent and topography of the defect (quantity of removed teeth and a functional quality of the rest) it is determine the possibility of using non-removable dental prostheses.

 Non-removable prostheses are used for treatment in the following cases:

1) loss of one or four incisor;

2) loss of canine;

3) loss of one or more premolars;

4) the loss of two premolars and the first molar;

5) permissible loss of two premolars on one side of the jaw, the first and the second molars with preserved and well-developed third molar.

 

 

 Bounded edentulous spaces  are not always an indication for making non-removable types of prostheses. For example, the absence of the canine, two premolars and one molar on one or two sides of the jaw is also considered a bounded edentulous space. However, in case of such extended defects the use of non-removable prosthesis is contraindicated.

Many years of clinical observation and study of mastication physiology determined that grinding and chewing food is done by 2-3 teeth of the upper and lower jaws. Therefore, for replacement of defect of 2 lateral teeth it is enough to  fix a bridge prosthesis on 2 healthy teeth. If the defect is formed from the loss of more than 2 teeth, the prosthesis can also have two abutments (a molar and a canine). This position applies only to the side teeth and a canine, located at the junction of two differently functionally oriented groups of teeth.

 

 

Clinical stages of making solid-cast bridge prostheses include:

1.               Preparation of the abutment teeth with preliminary retraction.

2.               Getting the primary and secondary impressions.

3.               Determination or fixation of occlusion.

4.               Fitting the frame of bridge prosthesis.

5.               Fixing bridge prosthesis.

Comparative characteristic of the bridge prostheses (swaged and cast)

The figure schematically presents the construction of the soldered bridge prosthesis constructed from the stainless steel, on which three sections are isolated: crown 1, solder 2 and the cast intermediate part 3 of the dental prosthesis.

 

 

     The case, from which the crown 1 was constructed, was stretched and then swaged. The artificial teeth 3 were obtained by casting. The place of junction between the crown 1 and intermediate part 3 was filled with the solder 2; therefore the structure of all sections was not identical. The most unsatisfactory of three sections indicated is the solder.

     The solder testing as to the strength of junction of the soldered parts carried out in the Research Institute of nonferrous metallurgy as early as the 30s showed that the solder possessed satisfactory mechanical properties, although it was unstable to the effect of even weak acids.

     At the same time the literature data analysis of the results of experimental studies and clinical observations on the study of effect of different solder alloys on the biological medium, gives grounds to assert that the solder does not meet the requirements, to the dental prostheses, which are in the biological medium, as to physicomechanical properties.

 

 

     The main drawbacks of the solders are their low stability to the corrosive destruction in the oral cavity, electro-potential difference with the soldered metals, as well as change of the structure of the soldered metal during the process of soldering.

     This specifies a number of the positions, which have a negative nature.

     1. There is a formation of metal oxides in the oral cavity of people using soldered prostheses of chromium nickel steel. Depending on the nature of saliva, composition of other metal ware, being in the oral cavity (prostheses, metallic fillings, inlays) as well as individual peculiarities of the organism, the formation of oxides may have the more or less expressed character.

     Blackening of the sites of soldering or presence of the sharply outlined spots on the steel prosthesis surface is evidence of the presence of such oxides. In this case a quantitative increase of the micro cells in the saliva and the formation of salts of heavy metals are noted in the oral cavity of people using such prostheses, which adversely affects the secretory function of the stomach. The mechanism of effect of metal oxides on the organism during the electrolytic dissociation in the oral cavity is still studied insufficiently; however, their nonphysiological state is completely obvious and incompatible with the principles of preventive medicine.

     2. The pathologic state, which was called the phenomena of galvanism, develops in the oral cavity of those, who use soldered prostheses, which are associated with a potential difference and can appear both in presence of different metals or alloys and as a result of heterogeneity of one alloy.

Both factors, which specify a potential difference, can develop in presence of soldered bridge prostheses, since these prostheses consist of different alloys – chrome-nickel steel and solder, and the structure of each of these alloys acquires heterogeneous nature during the process of their manufacture.

 

 

While conducting the metallographic examination of the soldered bridge prostheses of chrome-nickel steel, it is revealed that even during thorough observance of technology along the contact line there are many nonsoldered sections. There are micropores in the layer of solder dividing them. Although the decrease of the thickness of the solder layer provides more durable junction of the soldered parts, however, it does not improve the alloy structure at the site of their junction, but in this case a quantity of micropores in the solder layer even increases. The two-phase structure of steel is observed both in the crown and in the intermediate part. There are sections of metal with the precipitation of chromium carbides on the margins of the metal grains.

 

 

 

It is impossible to improve the alloy structure by heat treatment (recrystallization), since the prosthesis should be heated to the temperature of 1, 000-1,100⁰C, and this will lead to deformation and separation of its parts.

But if we examine the clinical stages of construction of swaged-soldered prostheses, they included up to 5 visits of the patient to the dentist:

1 visit: Preparation of the teeth and taking of the impressions for constructing the swaged – soldered crowns.

2 visit: Fitting of the swaged crowns and their trimming as well as taking of the impressions for constructing soldering of the intermediate parts of the prosthesis (cast teeth).

3 visit: Fitting of the unpolished swaged – soldered constructions of the bridge prostheses and their trimming.

4 visit. Fitting of the polished swaged – soldered constructions of the bridge prostheses and constructions with their subsequent fixation.

5 visit. In spraying of the dental prostheses – the prosthesis construction takes from 20 to 30 days.

 

Thus, analyzing the aforesaid it is possible to make the following conclusions, namely:

1. At present the swaged crowns and soldered bridge prostheses do not meet the necessary modern requirements as the methods of swaging do not ensure the precise construction of the crown.

2. Presence of different alloys and metals in the soldered bridge prosthesis leads to the phenomenon of galvanism in the oral cavity.

3. Breakdown occurs very frequently at the site of soldering of the dental prosthesis elements.

4. The technical process of construction of different elements of the swaged- soldered dental prosthesis provides for the use of the strong acids.

 

EVALUATION OF THE WHOLE CAST PROSTHESES

– Construction of the wax reproduction of the component (wax pattern);

– Installation of sprues and creation of the casting block;

– Preparation of the mixture, utilized for formation of the covering layer of model;

– Coating of the wax reproduction of the component with a covering mass;

– Construction of the casting form;

– Melting of wax from the casting form with the subsequent drying and burning of the casting form;

– Melting of the dental alloy with the subsequent filling of the molten metal in the casting form;

– Cooling of the casting with its subsequent release from the molding mass and sprues;

– If necessary thermal processing of the cast components;

– Polishing, fitting, etc

     The sequential and thorough fulfillment of the construction stages of the dental prosthesis components enumerated above by the casting method of the cast models is the guarantee of a high quality of the cast component of the prosthesis, which can be achieved only by thorough fulfillment of the enumerated points in accordance with the existing procedures.

     Besides, the clinical stages of the whole cast construction of the dental prostheses in comparison with the clinical stages of the swaged – soldered construction of the dental prostheses requires only 3 visits, namely:

1 visit: Preparation of the teeth, taking of the impressions for constructing temporary protective constructions and fixation of the temporary protective constructions.

2 visit: Fitting of the polished whole cast constructions and fixation of the prosthesis.

3 visit. In spraying of the dental prostheses – the prosthesis construction takes from 3 to 5 days.

Thus, from the comparative analysis of the dental prosthesis construction by the method of swaging with the subsequent soldering and the casting method it is possible to make the following conclusions:

1. Obtaining dental prostheses by the casting method allows to get more uniform properties of the metal of the dental prosthesis, which allows to exclude electrochemical processes in the oral cavity;

2. The dental prostheses allow to compensate most fully the dentition defect, since cast crowns are more precise, they tightly cover the tooth neck and do not traumatize the gum tissue;

3. The dental prostheses are reliably protect by aesthetical coverings from the plastics or ceramic metal.

4. The mechanical strength and chemical stability of the dental prostheses increases, and, therefore, the period of their service.

5. Introduction of the technology of casting into dental practice allows to reduce the number of both clinical and laboratory stages in construction of whole cast bridge prostheses, which makes it allows to increase the quality of the dental prostheses.

6. Technology of construction of the whole cast bridge prostheses does not provide for the use of the strong chemical substances (acid, alkali, etc), which allows to improve the working conditions of the dental technicians.

7. In organization of the proper and qualitative training of the technician- caster, construction of the dental prostheses by the casting method by the cast models allows to increase several times productivity and effectiveness of work of the dental technicians.

 

4. Content of the theme.

Bridge prostheses.

     Bridge prostheses are most common category of prostheses in partial included defects of the dentitions.

     The dental arch consists of two symmetrical halves and in loss of one of them another one can take its function. It is considered that the periodontium of each tooth, because of the special reserve possibilities, is capable of maintaining dual masticatory load. The construction of any bridge-shaped prosthesis is based on this principle, when two and more crowns bear intermediate part, body on themselves, which compensates the defect of the absent tooth or teeth. When the tooth load, i.e., width of the intermediate part is more than the reserve possibilities of the periodontium of the teeth, on which abutment crowns are located, it will give arise to physiological irritation, the injury, which will lead to the teeth loosening.

     The loss of teeth on one of the jaws frequently leads to the reconstruction of the bone tissues of the alveolar processes, protrusion of the teeth- antagonists on the opposite jaw, contributing to the formation of block in the sagittal direction (Popov -Godon phenomenon). To prevent these phenomena it is necessary to make bridge prostheses as early as possible with the restoration of the lost function of the dentition.

     All bridge prostheses can be divided regarding the material into: plastic, metallic, combined. Metallic and combined dentures are also divided into: soldered (at first supporting crowns are made, then the intermediate part, later on all elements are soldered by the solder) and whole cast (at first all parts of the prosthesis are made of wax, and then wax is substituted by the metal by the method of precision casting). The soldered bridge prostheses become the thing of the past, preserving the major advantages – cheapness, easiness of construction, abrading of insignificant quantity of hard tissues of the teeth. The whole cast prostheses with the wide acceptance of precision casting and its significant development acquire greater popularity in dentists and dental technicians.

The following postulate is the more generalized formulation of indications to the bridge prosthesis: the partial defects of the dentition when the sum of the coefficients of the masticatory effectiveness of supporting teeth according to Agapov is more or equal to the sum of the coefficients of the masticatory effectiveness of the absent teeth.

Coefficients of masticatory effectiveness according to Agapov:

Teeth       1   2   3   4   5   6   7	Total
the upper 2   1   3   4   4   6   5 jaw	25 un.
the lower 2   1  3   4   4   6   5 jaw	25 un.

 

By Oxman

Teeth       1   2   3   4   5   6   7   8	Total
the upper 2   1   2   3   3   6   5   3 jaw	25 un.
the lower 1   1   2   3   3   6   5   4 jaw	25 un.

 

Kennedy’s classification and classification by Kulazhenko.

Kennedy’s classification by classes:

1 bilateral end defect of the dentition.

2 unilateral end defect of the dentition.

3 intermediate defect in the lateral parts of the dentition.

4 intermediate defect in the region of the anterior part.

 

CLASSIFICATION BY V.I.KULAZHENKO

I class.The defect of the dentition is limited by one tooth – the continuous shortened dentition without the distal support (according to Kennedy – II class).

II class. Two defects, limited by two teeth – the shortened dentition with the bilateral defects without the distal support (according to Kennedy – I class).

III class.Two defects, limited by three teeth – bilateral defects, limited by three teeth, one defect without the distal support (on Kennedy – II class, I sub-class).

IV class.Two defects, limited by four teeth – bilateral defects with the distal supports (by Kennedy – III class, I subclass).

       In the presence of additional defects besides basic ones – these cases make the subclass of the basic class. The absence of front teeth with the presence of the lateral ones is also II class, but with the distal support, hence the construction of the denture will be another in this case.

All classifications proposed are characterized only by topography of the dentition.

     Local and general influence of defects on the organism. This pathology leads to the disturbance of the mastication function and it is the cause for cosmetic defects, produces a change in the person’s appearance, and loss of the last pair of the antagonists makes the person look older than his age. The loss of even one tooth leads to changes in the whole dentition: the teeth, which limit defect, displace, without having antagonists, they rise from the alveoli. (V.O.Popov, 1862, Godon, 1865).

     Displacement of the teeth does not develop in the intact dental arch and the healthy periodontium, there is a so-called “articulatory equilibrium”. The displacement of the teeth prevents the protection of each tooth on the side of its neighbor.

     The partial defects of the dentition lead to development of various forms of the maxillodental system pathology, which are manifested not only in a change of the position of separate teeth and dentitions, but also in the incorrect bite, modification of the alveolar processes and mucous membrane.

     The alveolar processes become atrophied at the place of the absent teeth and are hypertrophied on some part with the teeth, which have the antagonists. Changes in the height of occlusion occur as a result of the increased dental abrasion on the large area.

     The teeth, which do not have antagonists, may cause injury and inflammation of the mucous membrane of the alveolar processes of the opposite jaw. Complete or partial edentia is reflected both in the functional and the morphological changes in the temporal- mandibular joint. Atrophic- degenerate processes develop; there are changes in the gastrointestinal tract.

     The disturbances of the mastication result in changes in the functional activity of the salivary glands. Thus, prosthesis of the dentition defects is a preventive measure for preventing different changes of the local or general nature.

 

Both crowns and most bridges are fixed prosthetic devices. Unlike removable devices such as dentures, which you can take out and clean daily, crowns and bridges are cemented onto existing teeth or implants, and can only be removed by a dentist.

A crown is used to entirely cover or “cap” a damaged tooth. Besides strengthening a damaged tooth, a crown can be used to improve its appearance, shape or alignment. A crown can also be placed on top of an implant to provide a tooth-like shape and structure for function. Porcelain or ceramic crowns can be matched to the color of your natural teeth. Other materials include gold and metal alloys, acrylic and ceramic. These alloys are generally stronger than porcelain and may be recommended for back teeth. Porcelain bonded to a metal shell is often used because it is both strong and attractive.

Dentist may recommend a crown to:

·                        Replace a large filling when there isn’t enough tooth remaining

·                        Protect a weak tooth from fracturing

·                        Restore a fractured tooth

·                        Attach a bridge

·                        Cover a dental implant

·                        Cover a discolored or poorly shaped tooth

·                        Cover a tooth that has had root canal treatment

A bridge may be recommended if you’re missing one or more teeth. Gaps left by missing teeth eventually cause the remaining teeth to rotate or shift into the empty spaces, resulting in a bad bite. The imbalance caused by missing teeth can also lead to gum disease and temporomandibular joint (TMJ) disorders.

Bridges are commonly used to replace one or more missing teeth. They span the space where the teeth are missing. Bridges are cemented to the natural teeth or implants surrounding the empty space. These teeth, called abutments, serve as anchors for the bridge. A replacement tooth, called a pontic, is attached to the crowns that cover the abutments. As with crowns, you have a choice of materials for bridges. Your dentist can help you decide which to use, based on the location of the missing tooth (or teeth), its function, aesthetic considerations and cost. Porcelain or ceramic bridges can be matched to the color of your natural teeth.

Before either a crown or a bridge can be made, the tooth (or teeth) must be reduced in size so that the crown or bridge will fit over it properly. After reducing the tooth/teeth, your dentist will take an impression to provide an exact mold for the crown or bridge. If porcelain is to be used, your dentist will determine the correct shade for the crown or bridge to match the color of your existing teeth.

Using this impression, a dental lab then makes your crown or bridge, in the material your dentist specifies. A temporary crown or bridge will be put in place to cover the prepared tooth while the permanent crown or bridge is being made. When the permanent crown or bridge is ready, the temporary crown or bridge is removed, and the new crown or bridge is cemented over your prepared tooth or teeth.

 Indications and clinical-laboratory techniques of slip-cast bridge denture construction.  

The prognosis of fixed partial denture pontics will be compromised if mechanical principles are not followed closely. Mechanical problems may be caused by improper choice of materials, poor frame­work design, poor tooth preparation, or poor occlu­sion. These factors can lead to fracture of the pros­thesis or displacement of the retainers. Long-span posterior FPDs are particularly susceptible to me­chanical problems. Inevitably, there is significant flexing from high occlusal forces and because the displacement effects increase with the cube of the span length. Therefore, evaluating the likely forces on a pontic and designing accordingly are important. For example, a strong all-metal pon­tic may be needed in high-stress situations rather than a metal-ceramic pontic (Fig. 3-24), which would be more susceptible to fracture. When metal-ceramic pontics are chosen, extending porcelain onto the occlusal surfaces to achieve better esthetics should also be carefully evaluated. In addition to its potential for fracture, porcelain may abrade the op­posing dentition if the occlusal contacts are on enamel or metal.

 AVAILABLE PONTIC MATERIALS

Some fixed partial dentures are fabricated entirely of metal, porcelain, or acrylic resin, but most use a combination of metal and porcelain. Acrylic resin-veneered pontics have had limited acceptance be­cause of their reduced durability (wear and discol­oration). The newer indirect composites, based on high inorganic-filled resins and the fiber-reinforced materials, have revived interest in composite resin and resin-veneered pontics.

Metal-ceramic Pontics. Most pontics are fabri­cated by the metal-ceramic technique. If properly used, this technique is helpful for solving com­monly encountered clinical problems. A well-fabricated metal-ceramic pontic is strong, easy to keep clean, and looks natural. However, mechanical failure (Fig. 3-25) can occur and often is attribut­able to inadequate framework design.

1.     The framework must provide a uniform ve­neer of porcelain (approximately 1.2 mm).
Excessive thickness of porcelain contributes to inadequate support and predisposes to eventual fracture.  This is often true in the cervical portion of an anterior pontic. A reliable technique for ensuring uni­form thickness of porcelain is to wax the fixed prosthesis to complete anatomic con­tour and then accurately cut back the wax to a predetermined depth.

2.     The metal surfaces to be veneered must be smooth and free of pits. Surface irregularities will cause incomplete wetting by the porcelain slurry, leading to voids at the porcelain metal interface that reduce bond strength and increase the possibility of mechanical failure.

3.    Sharp angles on the veneering area should be rounded. They produce increased stress con­centrations that can cause mechanical failure.

4.  The location and design of the external metal-porcelain junction require particular atten­tion. Any deformation of the metal frame­work at the junction can lead to chipping of
the porcelain. For this reason, oc­clusal centric contacts must be placed at least
1.5 mm away from the junction. Excursive ec­centric contacts that might deform the metal-
ceramic interface must be watched carefully.

Resin-veneered Pontics. Historically, acrylic resin-veneered restorations had deficiencies that made them acceptable only as longer-term provi-sionals. Their resistance to abrasion was lower than enamel or porcelain, and noticeable wear occurred with normal toothbrushing. Further­more, the relatively high surface area/volume ratio of a thin resin veneer made dimensional change from water absorption and thermal fluctuations (thermocycling) a problem. Because no chemical bond existed between the resin and the metal framework, the resin was retained by mechanical means (e.g., undercuts). Continuous dimensional change of the veneers often caused leakage at the metal-resin interface, with subsequent discoloration of the restoration.

Nevertheless, there are certain advantages to us­ing polymeric materials instead of ceramics: they are easy to manipulate and repair and do not re­quire the high-melting range alloys needed for metal-ceramic techniques. Recently introduced in­direct composite resin systems have resolved some of the problems inherent in previous indirect resin veneers. These new-generation indirect resins have a higher density of inorganic ceramic filler than tra­ditional direct and indirect composite resins. Most use a post-curing process that results in high flex-ural strength, minimal polymerization shrinkage, and wear rates comparable to those of tooth enamel In addition, improvements in the bond be­tween the composite resin and metal 39 may lead to a reappraisal of resin veneers.

Fiber-reinforced   Composite   Resin   Pontics.

Composite resins can be used in fixed partial den­tures without a metal substructure A substructure matrix of impregnated glass or polymer fiber provides structural strength. The physical properties of this system, combined with its excellent marginal adaptation and esthetics, make it a possible metal-free alternative for FPDs, although long-term clinical performance is not yet known.

ESTHETIC CONSIDERATIONS

No matter how well biologic and mechanical prin­ciples have been followed during fabrication, the patient will evaluate the result by how it looks, es­pecially when anterior teeth have been replaced. Many esthetic considerations that pertain to single crowns also apply to the pontic. Several problems unique to the pontic may be en­countered when attempting to achieve a natural appearance.

THE GINGIVAL INTERFACE

An esthetically successful pontic will replicate the form, contours, incisal edge, gingival and incisal embrasures, and color of adjacent teeth. The pon­tic’s simulation of a natural tooth is most often be­trayed at the tissue-pontic interface. The greatest challenge here is to compensate for anatomic changes that occur after extraction. Special attention should be paid to the contour of the labial surface as it approaches the pontic-tissue junction to achieve a “natural” appearance. This cannot be accomplished by merely duplicating the facial contour of the missing tooth, because after a tooth is removed, the alveolar bone undergoes resorption and/or remod­eling. If the original tooth contour were followed, the pontic would look unnaturally long incisogingi-vally. To achieve the illusion of a natural tooth, an esthetic pontic must deceive observers into believing they are seeing a natural tooth.

 The modified ridge-lap pontic is recommended for most anterior situations; it compensates for lost buccolingual width in the residual ridge by over­lapping what remains. Rather than emerging from the crest of the ridge as a natural tooth would, the cervical aspect of the pontic sits in front of the ridge, covering any abnormal ridge morphology resulting from tooth loss. Fortunately, because most teeth are viewed from only two dimensions, this relationship remains undetected. A properly designed, modified ridge-lap provides the required convexity on the tissue side, with smooth and open embrasures on the lingual side for ease of cleaning. This is difficult to accomplish. Clinically, many pontics are seen with less than optimal contour, re­sulting in an unnatural appearance. This can be avoided with careful preparation at the diagnostic waxing stage. Sometimes the ridge tissue must be surgically reshaped to enhance the result.

Iormal situations, light falls from above, and an object’s shadow is below it. Unexpected lighting or unexpectedly placed shadows can be confusing to the brain. Because of past experience, the brain “knows” that a tooth grows out of the gin­giva, and it therefore “sees” a pontic as a tooth un­less telltale shadows suggest otherwise. Special care must be taken when studying where shadows fall around natural teeth, particularly around the gingi­val margin. If a pontic is poorly adapted to the residual ridge, there will be an unnatural shadow in the cervical area that looks odd and spoils the illusion of a natural tooth. In additional, re­cesses occurring at the gingival interface will collect food debris, further betraying the illusion of a natural tooth.

When appearance is of utmost concern, the ovate pontic, used in conjunction with alveolar preserva­tion or soft tissue ridge augmentation, can provide an appearance at the gingival interface that is virtu­ally indistinguishable from a natural tooth. Because it emerges from a soft tissue recess, this pontic is not susceptible to many of the esthetic pitfalls previ­ously described for the modified ridge lap pontic. However, in most cases, the patient must be willing to undergo the additional surgical procedures that an ovate pontic requires.

INCISOGINGIVAL LENGTH

Obtaining a correctly sized pontic simply by dupli­cating the original tooth is not possible. Ridge re­sorption will make such a tooth look too long in the cervical region. The height of a tooth is immediately obvious when the patient smiles and shows the gingival margin. An abnormal labiolingual position or cervical contour, however, is not imme­diately obvious. This fact can be used to produce a pontic of good appearance by recontouring the gingival half of the labial surface. The observer sees a normal tooth length but is un­aware of the abnormal labial contour. The illusion is successful.

Even with moderately severe bone resorption, obtaining a natural appearance by exaggerated con­touring of the pontics may still be possible. In areas where tooth loss is accompanied by excessive loss of alveolar bone, however, a pontic of normal length would not touch the ridge at all.

One solution is to shape the pontic to simulate a normal crown and root with emphasis on the ce-mentoenamel junction. The root can be stained to simulate exposed dentin. Another ap­proach is to use pink porcelain to simulate the gin­gival tissues. However, such pontics then have considerably increased tissue contact and require scrupulous plaque control for long-term success. Ridge-augmentation procedures have been successful in correcting areas of limited resorption. When bone loss is severe, the esthetic result ob­tained with an RPD is often better than with an FPD.

MESIODISTAL WIDTH

Frequently, the space available for a pontic will be greater or smaller than the width of the contralat­eral tooth. This is usually due to uncontrolled tooth movement that occurred when a tooth was re­moved and not replaced.

If possible, such a discrepancy should be cor­rected by orthodontic treatment. If this is not possi­ble, an acceptable appearance may be obtained by incorporating visual perception principles into the pontic design. In the same way that the brain can be confused into misinterpreting the relative sizes of shapes or lines because of an erroneous interpreta­tion of perspective, a pontic of abnormal size may be designed to give the illusion of being a more natural size. The width of an anterior tooth is usually identified by the relative positions of the mesiofacial and distofacial line angles, and the over­all shape by the detailed pattern of surface contour and light reflection between these line angles. The features of the contralateral tooth should be duplicated as precisely as possible in the pontic, and the space discrepancy can be compen­sated by altering the shape of the proximal areas.

The retainers and the pontics can be proportioned to minimize the discrepancy. (This is another situation in which a diagnostic waxing procedure will help solve a challenging restorative problem.)

Space discrepancy presents less of a problem when posterior teeth are being replaced because their distal halves are not normally visible from the front. A discrepancy here can be managed by duplicating the visible mesial half of the tooth and adjusting the size of the distal half.

PONTIC FABRICATION

AVAILABLE MATERIALS

Over time, several techniques for pontic fabrica­tion evolved. Prefabricated porcelain facings were very popular for use with conventional gold al­loys. As use of the metal-ceramic technique in­creased during the 1970s, prefabricated facings lost their popularity and essentially disappeared. Al­though an acceptable substitute, custom-made metal-ceramic facings never gained widespread acceptance. (Fig. 3-38).

Most pontics are now made with the metal-ceramic technique, which provides the best solution to the biologic, mechanical, and esthetic challenges encountered in pontic design. Their fabrication, however, differs slightly from the fabrication of in­dividual crowns. These differences will be empha­sized in the ensuing paragraphs.

METAL-CERAMIC PONTICS

A well-designed metal-ceramic pontic provides easy plaque removal, strength, wear resistance, and esthetics (see Fig. 3-38, D). Its fabrication is rela­tively simple if at least one retainer is also metal-ceramic. The metal framework for the pontic and one or both of its retainers is cast in one piece. This facilitates pontic manipulation during the succes­sive laboratory and clinical phases. In the discus sion that follows, it will be assumed that either or both of the retainers are metal-ceramic complete crowns. When this is not the case, an alternate ap­proach is recommended.

Anatomic Contour Waxing. For strength and esthetics, an accurately controlled thickness of porcelain is needed in the finished restoration. To ensure this, a wax pattern is made to the final anatomic contour. This also permits an assessment of connector design adequacy and the relationship between the connectors and the proposed configu­ration of the ceramic veneer.

Armamentarium

•    Bunsen burner

•    Inlay wax

•    Sticky wax

•   Waxing instruments

Cotton cleaning cloth

•    Die-wax separating liquid

•    Zinc stearate or powdered wax

•    Double-ended brushes

•   Cotton balls

Fine-mesh nylon hose

Step-by-step Procedure

1.     Wax the internal, proximal, and axial surfaces of the retainers.

2.  Soften the inlay wax, mold it to the approxi­mate desired pontic shape, and adapt it to the ridge. This is the starting point for subse­quent modification. Alternatively (and per­haps preferably), an impression may be madeof the diagnostic waxing or provisional
restoration. Molten wax can then be pouredinto this to form the initial pontic shape. Pre­fabricated pontic shapes are also available as a starting point.

3.  If a posterior tooth is being replaced, leave the occlusal surface flat because the occlusion is best developed with the wax addition tech­nique.

4.  Lute the pontic to the retainers and, for addi­tional stability, connect its cervical aspect di­rectly to the master cast with sticky wax. Then wax the pontic to proper axial and oc­clusal (or incisal) contour.

5.  Complete the retainers and contour the prox­imal and tissue surfaces of the pontic for the desired tissue contact. The pontic is now ready for evaluation before cut-back.

 Evaluation. The form of the wax pat­tern is evaluated and any deficiencies are corrected. Particular attention is given to the connectors, which should have the correct shape and size. The connectors provide firm attachment for the pontic so it does not separate from the retainers during the subsequent cut-back procedure.

Cut-back

Arm amentarium

•    Bunsen burner

•    Waxing instruments

•    Cut-back instrument

•    Scalpel

•    Thin ribbon saw blade or sewing thread

•    Explorer

Step-by-step Procedure

1.  Use a sharp explorer to outline the area that will be veneered with porcelain. The porcelain-metal junction must be placed suf­ficiently lingual to ensure good esthetics.

2.  Make depth cuts or grooves in the wax pat­tern.

3.  Complete the cut-back as far as access will allow with the units connected and on the mas­ter cast.

4.  Section one wax connector with a thin ribbon saw (sewing thread is a suitable alternative) and remove the isolated retainer from the master cast.

5.  Finish the cut-back of this retainer, making sure there is a distinct 90-degree porcelain-metal junction.

6.  Reflow and finalize the margins. The pontic is held in position by the other retainer dur­ing this procedure.

7.     Refine the pontic cut-back where access is im­
proved by removal of the first retainer.

8.  Reseat the first retainer, reattach it to the pontic, section the other connector, and repeat the
process.

9.   Sprue the units and do any final reshaping

as needed.

10.   Invest and cast.

NOTE: When one connector of a three-unit FPD is to be cast and the other soldered, the cast connec­tor should be sectioned first when the foregoing procedure is followed. The gingival surface of the pontic should be cut back in the metal rather than in the wax, because the tissue contact will help stabi­lize the pontic. Access is difficult, and it is easy to break the fragile wax connector.

Metal Preparation Armamentarium

•    Separating disk

•    Ceramic-bound finishing stones

•    Sandpaper disks (nonveneered surfaces only)

•    Rubber wheel (nonveneered surfaces only)

•    Round carbide bur (no. 6 or 8)

•    Airborne abrasion unit (with 25 um aluminum
oxide)

Step-by-step procedure.

1.  Recover the castings from the investment and prepare the surfaces to be veneered.

2.  Finish the gingival surface of the pontic. Do not overreduce this area.

Evaluation. Less than 1 mm of porcelain thick­ness is needed on the gingival surface, because once it is cemented, the restoration will be seen from the facial rather than from the gingival. Excessive gin­gival porcelain is a common fault in pontic frame­work design and may lead to fracture and poor ap­pearance.

To facilitate plaque control, the metal-ceramic junction should be located lingually. Then tissue contact will be on the porcelain and not on metal, which retains plaque more tenaciously.

Porcelain Application. Many of the steps for porcelain application are identical to those in indi­vidual crown fabrication. There are some features peculiar to pontic fabrication, how­ever, and these will be emphasized.

Armamentarium

•   Paper napkin

•   Glass slab

•   Tissues or gauze squares

•   Distilled water

•   Glass spatula

•   Serrated instrument

•   Porcelain tweezers or hemostat

•   Ceramist’s brushes (no. 2, 4, or 6)

•   Whipping brush

•   Razor blade

•   Cyanoacrylate resin

•   Colored pencil

•   Articulating tape

•   Ceramic-bound stones

•   Diamond stones

•   Diamond disk

Step-by-step Procedure

1.  Prepare the metal and apply opaque.

2.  Apply cervical porcelain to the gingival sur­face of the pontic and seat the castings on the master cast. A small piece of tissue paper adapted to the residual ridge on the cast by moistening with a brush will prevent porce­lain  powder from sticking to the stone.
(Cyanoacrylate resin or special separating agents can be used for the same purpose.)

3.  Build up the porcelain with the appropriate distribution of cervical, body, and incisal shades. The tissue paper will act as a matrix for the gingival sur­face of the pontic.

4.  When the porcelain has been condensed, sec­tion between the units with a thin razorblade. This will prevent the porcelain from pulling away from the framework as a result of firing shrinkage. A second application  of porcelain will be needed to correct any defi­ ciencies caused by firing shrinkage. Such ad­ditions usually are needed proximally and
gingivally on the pontic.

5.  Apply a porcelain separating liquid (e.g., Vita Modisol*) to the stone ridge so that the addi­tional gingival porcelain can be lifted directly from the cast as in the fabrication of a porce­lain labial margin.

6.  Mark the desired tissue contact and contour the gingival surface to provide as convex a surface as possible. The pontic is now ready for clinical evaluation and soldering proce­dures, characterization, glazing, finishing, and polishing.

Evaluation. The porcelain on the tis­sue surface of the pontic should be as smooth aspossible. Pits and defects will make plaque control difficult and promote calculus formation. The metal framework must be highly polished, with special care directed to the gingival embrasures (where ac­cess for plaque removal is more difficult).

ALL-METAL PONTICS

Pontics made from metal require fewer laboratory steps and are therefore sometimes used for posterior FPDs. However, they have some disadvantages (e.g., their appearance). In addition, investing and casting must be done carefully be­cause the mass of metal in the pontic is prone to porosity as the bulk increases. A porous pontic will retain plaque and tarnish and corrode rapidly.

SUMMARY

Designs that allow easy plaque control are especially important to a pontic’s long-term success. Minimiz­ing tissue contact by maximizing the convexity of the pontic’s gingival surface is essential. Special con­sideration is also needed to create a design that com­bines easy maintenance with natural appearance and adequate mechanical strength. When the appro­priate design has been selected, it must be accurately conveyed to the dental technician.

There are subtle differences between metal-ceramic pontic fabrication and the fabrication of other types of pontics. Under most circumstances, the metal-ceramic technique is used because it is straightforward and practical. However, it requires careful execution for maximum strength, appear­ance, and effective plaque control. Alternative pro­cedures may sometimes be helpful, particularly when gold alloys are used for the retainers.

 

 

What types of metals are used to make crowns?

Crowns (all-metal and porcelain-fused-to-metal) are made using specific types of dental alloys. No pure metals are used for crowns, not even gold. This is because the physical properties of dental alloys are superior.

The classification of dental alloys.

Here’s the formal classification system that is used to categorize dental alloys.

1) High noble alloys (Precious metals)

This group of alloys has a composition that is over 60% noble metal (gold, palladium and/or platinum), of which more than 40% must be gold.

These metals constitute the “gold standard” of dental alloys; all others are compared to them. High noble alloys are the easiest type of metal to work with (for both the dentist and dental laboratory) and create the most predictable bond with porcelain.

2) Noble alloys (Semiprecious metals)

These alloys have a noble metal content that is, at minimum, over 25%.

3) Non-noble (Nonprecious metals)

These alloys are also referred to as base metals. Their noble metal content is less than 25%. They often contain large percentages of nickel, chromium or beryllium. 

Why should I care what metal is used to create my dental crown?

There are several reasons why the type of dental alloy that is used to fabricate your dental crown should be important to you. Some of these reasons will affect you directly. Others will be more of a concern to your dentist, or the dental laboratory that makes it.

A) Color – Dental alloys can be white or yellow.

In those cases where an all-metal dental crown is being placed, you might have a preference as to whether it should have a yellow (like gold) or silver (“white”) coloration. The alloy’s composition determines its color.

 

B) Costs – High noble metal alloys cost more.

The “noble” dental metals are gold, platinum and palladium. These metals are pricey. And the greater the percentage of them found in the composition of an alloy, the greater its cost will be. With some applications, the overall cost between using a high noble or base metal alloy might be small. But in the case of an all-metal crown for a large molar, it might be a consideration.

 

C) Dental plan and insurance policy limitations.

If some type of dental plan is paying a part of your bill, you might check to see if there are any limitations as to the type of metal that can be used for crowns. The policy might state that they do not cover the cost of high noble alloys. Or the level of coverage might change based on the type of alloy that is used.

 

D) Some people have metal allergies.

Studies report that about 10% of the female population and 5% of the male have an allergic response to nickel, chrome and/or beryllium alloys. These metals are often found in the composition of nonprecious dental alloys.

 

E) The physical properties of the alloy are an important consideration.

 

 

Dentists and dental laboratories often have a set opinion about which types of dental alloys they will consider working with. This is because their goal is getting the job done right, the first time. They know that any difficulties or problems experienced will just end up costing them money. So, if choosing a certain type of alloy makes getting a positive result more likely, then that’s the one they are probably going to want to work with.

Advantages of precious dental alloys.

In general, dentists and dental labs prefer to work with high noble alloys. These metals are easiest to cast, provide the most accurate fit on the tooth, offer some degree of malleability (so the fit of the metal can be adjusted, if needed), and offer the most predictable bond with porcelain.

 

 

 

 

Finishing lines:

Is the final margin that separate between the prepared axial tooth surface and the remaining unprepared tooth surface.

Requirements of finishing line:

1.                It must be clear, well defined and smooth, so it can be reproduced on working model.

2.                It must be continuous from one surface to another.

3.                Whenever possible the finishing line should be placed on sound tooth structure.

Position of finishing line:

1.                With the level of free gingival margin.

2.                Supra gingival finishing line,: its better to place the finishing line supragingivally for the following reasons:

A.   Easily to be prepared without trauma to the soft tissues.

B.   Easy to be prepared and finished by dentist.

C.   Patient can keep it clean easily.

D.   Impression is easily made and can be removed without tearing or deficiency.

 

3.                Subgingival finishing line: indicated in

A.   Esthetic.

B.   Caries or filling at the area of finishing line.

C.   To increase retention of short teeth.

Types of finishing line:

1.                Feather edge (knife edge).

2.                Chamfer.

3.                Shoulder.

4.                Bevel shoulder.

The selection of certain type of finishing line depends on:

1.                The materials used to construct the restoration.

2.                The position of the tooth.

3.                The tooth aspect to be prepared.

Feather edge (knife edge):

In this type all convexities coronal to the margin are removed only, its mostly unacceptable but it was advocated already before the development of high speed cutting instruments and improvement of impression materials and techniques, this type of margins lack strength, difficult to locate on the cast and difficult to fabricate the wax pattern, however it provide the best marginal seal and it’s the most conservative type.

Chamfer finishing line:

This type is prepared with a tapered round ended fissure diamond bur, its regarded as the line of choice for most veneer cast metal restorations and lingual margins of porcelain fused to metal restoration. It has been shown to exhibit the least stress.

 

Shoulder finishing line: 

This is the best choice for jacket crowns; the wide ledge provides resistance to occlusal forces and minimizes stresses that might lead to fracture of the restoration, and its less conservative. This finishing line is prepared with flattened end tapered diamond fissure bur. Its very well defined finishing line so it’s easily detected on the cast.

 

Shoulder with bevel:

In this type we create a bevel on the end margin of unprepared tooth structure, this lies between the prepared and unprepared tooth structure and is very critical area. This type of finishing line is recommended for extremely short walls, since the axial walls of this type is nearly parallel to each other so enhances retention. This type of finishing lines is used for porcelain fused to metal and full cast veneer with acrylic facing.      

 

 

 

 

 

 

Types of crowns:

1. Full metal (veneer) crown:

This provides better retention and resistance because all the axial surfaces of the teeth are included in the preparation.

Indication:

1.                Posterior abutment teeth with excessive caries.

2.                As retainer on tooth receive clasp (posterior teeth).

3.                High caries index.

4.                Necessity of maximum retention and strength.

Contraindication:

1.                Teeth located in the appearance zone.

2.                 Low caries index.

Advantage:

1.                Strong.

2.                More conservative and easy to prepared.

3.                Provide more retention and resistance compared to partial veneer crowns.

Disadvantage:

1.                Poor esthetic.

2.                Tarnish and corrosion, so it needs prophylactic measures.

3.                Difficulty to test the vitality of the abutment teeth.

 

Steps of preparation:

Depth orientation grooves must be prepared on the surface of the tooth to act as guide or reference to determine when sufficient amount of tooth structure is removed, without these grooves we may remove much or less tooth structure or we loss time in repeated checking.

 

 1. The preparation for a full veneer crown is begun with the occlusal reduction. By accomplishing this step first, the occlusso gingival length of the preparation can be determined. The potential retention of the preparation can then be assessed, and auxiliary features can be added if necessary there should be 1.5 mm clearance on the functional cusps and about 1.0 mm on the non functional cusps. A No. 170 taper fissure bur or a round-end tapered diamond is used to place the grooves on the ridges and in the primary grooves of the occlusal surface. If there is already sonic clearance with the opposing tooth because of malpositioning or fracture of the tooth being prepared, do not make the grooves as deep.

The tooth structure remaining between the orientation grooves is removed to accomplish the occlusal reduction then smooth any roughness left by the grooves. Keeping the occlusal surface in the configuration of the geometric inclines that make up the occlusal surface of any posterior tooth after that a wide bevel is placed on the functional cusp again using the No. 170 buy or rounded tapered diamond. The functional cusp bevel placed on the buccal inclines of mandibular buccal cusps and the lingual inclines of maxillary lingual cusps after completion of occlusal surface preparation we should check the occlusion of the patient in centric and eccentric positions of jaw relationship.

 

2. Buccal surface: because of the anatomy of the buccal surface of the lower posterior teeth, this surface should be divided into two parts: gingival two thirds and occlusal one third for the gingival two thirds we should place a (DOG) in the center of this surface parallel to the long axis of the tooth and by moving the bur mesially and distally following the inclination of the surface so this surface prepared. For the occlusal one third a (DOG) is placed in the center of this area by placing the bur 45 degree with the long axis of the tooth and by moving the bur with the curvature of the surface to be prepared. This type of preparation is called two plane preparation or two steps

preparation The two plane preparation is done on the buccal surface of the lower molar and the palatal surface of the upper molar.

3. Lingual surface :the (DOG) is placed in the middle parallel to the long axis of the tooth and by moving the bur mesially and distally so we complete the reduction, this type of preparation is done in one plane as it is indicated for the lingual lower and buccal upper molar and premolar teeth.

4. Proximal surfaces: we start with a fine tapered diamond fissure bur (needle type) to open and remove the contact area carefully without touching the adjacent tooth because caries will be developed in the damaged surface later on, because we are going to create a rough surface in addition to removing the outer layer of enamel which is saturated with fluoride. The bur should be rested on the prepared tooth itself and by moving the bar up and down the contact will be removed, finally any sharp angle should be removed to prevent fracture due to stress concentration, sometimes seating groove is placed in the buccal surface of the lower and the palatal surface of the upper molar teeth which act as a guide during placement of the crown, to prevent the rotation of the restoration, increase the surface area of preparation so it enhance the retention and the resistance, finally it improves the seating of crown as it let the escape of the excess cement during cementation.

 

2-Full metal crown with facing

It is a full metal crown having the labial or buccal surface covered by a tooth colored materials (acrylic, Porcelain), it combines the strength of full metal crown and the cosmetic effect of the tooth colored material, and it is not a conservative type of crown since it includes excessive tooth preparation to provide enough space for the metal and the facing material in addition to that there is excessive contact with the gingival tissue when the margin of the crown is placed close or below the gingival margin ,it can be used on anterior and posterior teeth

Indication:

1.                Improvement of esthetics (carious teeth, malposed teeth, peg shaped lateral incisor, discolored teeth).

2.                Fracture of tooth without pulp exposure.

3.                Teeth with large filling.

4.                As a bridge retainer especially in long span bridge.

5.                Endodontically treated teeth with sufficient remaining tooth structure.

Contraindications:

1.                Teeth with large pulp.

2.                Teeth with short crown.

3.                Patient with poor oral hygiene.

Advantage:

1.                It combines the strength of full metal crown and the cosmetic effect of the tooth colored material.

2.                Natural appearance can be closely matched by good technique and if desired through characterization of the restoration with internally or externally applied stains.

 

Disadvantages:

1. Requires significant tooth reduction to provide sufficient space for the restorative    materials.

2. Increases the potential for periodontal disease.

3. Because of the glasslike nature of the veneering material, a metal-ceramic crown is subject to brittle fracture (although such failure can usually be attributed to poor design or fabrication of the restoration).

 

 

Preparation

1. Preparation for posterior teeth

We should follow the same principles as in full metal crown as in the full metal crown with one exception only, by doing a deep reduction on the buccal surface to provide enough space for the metal and the facing material and also to gain bulk for proper shade of the final crown The finishing line is shoulder on the buccal surface and chamfer all around the remaining tooth aspects.

2. Preparation for anterior teeth

A. Incisal edge reduction:

We started by basing a depth orientation groove of 2 mm in the center of the of the incisal edge and by using a fissure bur placed with the palatal inclination of the incisal edge, this edge will be reduced (in the lower anterior teeth the bur should be placed with the labial inclination to follow the anatomy of the tooth) the 2mm reduction of the incisal edge is to provide a space for the facing material and metal to get a better translucency of the incisal edge.

B. Preparation of the labial surface:

This surface should be divided into two parts, gingival and incisal, for the gingival part a DOG of 1.5 mm is placed in the gingival part parallel to the longitudinal axis of tile tooth and by moving the bur mesially and distally this part will be reduced, while for the incisal reduction we place a DOG with the inclination of this area since the preparation if done without inclination we may have pulp exposure.

C. Lingual surface preparation:

For the cingulum area a DOG of 0.5 mm depth is placed in the center of the cingulum area parallel to the longitudinal axis of the tooth and by following the inclination of the tooth this area will be reduced The remaining axial lingual surface should he reduced using a wheel diamond bur, we must keep in mind not to remove or over reduce the junction between the cingulum and the axial and the remaining part of the lingual axial surface if not we may create a conical shape preparation which will lead to lack of retention and resistance, finally we should smooth and round the lie angle to facilitate the next steps of crown construction.

Why we do the two steps preparation on the lower buccal, upper palatal surfaces of the posterior and labial surfaces of anterior teeth:

1.                To follow the anatomy and the inclination of the tooth and not to disturb the surface geometry.

2.                To increase the surface area this will give increase in retention and resistance of the final restoration.

3.                To avoid hitting of the pulp chamber during preparation.

4.                To give enough space for the restorative material so this will enhance the structural durability other vise we will have bulky restoration, bulky facing or poor shade of the tooth.

 

 

 

 

Dental Bridge or Pontic or Fixed Bridge or Fixed Partial Denture is a custom-made fake tooth or false teeth or prosthetic device used to replace missing teeth, that is permanently placed between your natural healthy teeth or dental implants. Usually two tooth crowns (tooth caps, “caps”) are holding it in place that are cemented onto your teeth on each side of the false teeth. These two anchoring teeth are called abutment teeth.

Fixed bridges or pontics or prosthetic devices used to replace missing teeth cannot be taken out of your mouth compare with removable partial dentures.

The teeth to be crowned (abutment teeth) are prepared in a very specific way (filing down the tooth to make room for crowns and bridge) by a dentist. Records are given to a dental technician to fabricate the dental bridge, which can then be inserted at another dental appointment.

The main advantages of dental procedures and solve dental problems  with the indirect method of teeth restoration:

·                    you do not need to be in the dental chair

·                    use of materials that require intense heat to be processed with superior mechanical properties, such as gold and natural looking porcelain

·                    produce a restoration of much higher quality

 

Indication to Restore with a Dental Bridge

 

Re-establish your smile

·                    Bring back your ability to properly chew

·                    Help improve speech

·                    Preserve the shape of your face

·                    Distribute the forces in your bite properly by replacing missing teeth

·                    Limit remaining teeth from drifting out of position

·                    Correct some bite problems

·                    Reduce the risk of gum disease

 

Before

 

After

 

CLINICAL TECHNIQUE

 

The clinical techniques for using this class of metal-ceramic materials are the same as conventional metal-ceramic systems, which can be a benefit over many of the all-ceramic systems on the market. Teeth can be prepared with any traditional margin design, but for truly esthetic metal-ceramic restorations, a shoulder preparation that allows for the creation of a 1-mm porcelain margin is preferred. Ideally, a minimum of a 270° or 360° shoulder preparation on teeth in the anterior region facilitates optimal esthetics. Facial reduction can be slightly less than conventional metalceramics as the granular gold surface of Captek gives a light scattering effect that improves the perception of depth in the restoration. Generally, an overall facial thickness of 1.2 mm to 1.3 mm gives a highly esthetic result. Accepted tissue management and impression making procedures should be followed. The author prefers polyether impression material (Impregum™, 3M™ ESPE™, Minneapolis, MN).

 

 

Diagram of ideal preparation for maximum esthetics for metal-ceramic restorations.

 

 

1 st laboratory step

Production of metal skeleton is very hard process, its better to see one time, that  ten times read.

 

 

 

 

 

 

Any construction starts with the model. This time with sectional model.

 

The working surface is covered by the compensation varnish, which serves to compensate for the space under the cement and partial shrinkage of the metal after casting. The varnish is covered to the whole teeth but leave 1 mm near the border preparation to better clossing of metal edge.

 

 

The gypsum stamps is covered with isolated fluid.

 

 

We are doing the cap with submersible wax, the thickness is 0,4 mm.

 

 

 

 

 For fixing the intermediate part  of the prosthesis we put on sticky wax (0,7 mm) to make a place for  future ceramics.

 

 

There are different companies that produce the standart wax form for the composition.

 

We put the intermediate part  of the prosthesis on the model

Composition elements are connected.

 

 

 

The superfluous wax removed from the stamp. The material easily remove under preparation line.

 

 

We put wax on the thin parts of the stamp. We need to do that on the model, especially if we are doing the correction of the shape.

 

 

 

  On the next step we are forming  the garland and put some wax  on the neck part of the cap.

We correct the form of . Its width varies between ± 1 mm.

 

A view of the finished element. The wax composition  is collected.                                                                          

 

 

 

The casting system (3-5 mm long)  set in the most convenient place for further cutting. The companies recomed the thickness of casting system 3 mm.

 

We stick the casting system to the compositoin. We connect the interdental spaces.

 

 

 

On our days there are different types of waxes, the  main condition for all are small contraction, certain hardness and stickiness.

From the correct placement the composition in the casting form depends the density of the metal.

The carcass after the casting cuts from the casting system. We mark and remove places which trouble putting on and out the carcass.

 

 

 

 

 

We polish the places where casting system was. We finish the neck part of the crown.                                                                                                                                         

We control the thickness of the carcass. The construction should not be thinner 0.3 mm.

 

 

2 laboratory step

 

The finished carcass. The surface should not have sharp edges or wedges

Before putting ceramics on it, we  wash with oxide aluminum oxide with 150-250 microns, and with pressure 4-6 Bar.

 

On this slide we see the first layer  of  putting opaque (powder).

The layer should be the minimum thin and thoroughly rub into the surface of metal.

 

The second layer of opaque. Its much more thicker than first. Its better to use  glass cane with the round end.

 

The view of burned model.Its important that opaque have a smooth and straight surface. If there are any defects on the surface we need to polish it, but very carefully with the diamond  and cover that parts with opaque again.

 

 

 

 

The first step in the production process is putting the matherial that allow to get the necessary saturation of color

in the thin parts of the construction.   That’s why we put it near the neck of the teeth and in the area of  fissures on the occlusual surface, also on the oral surface of the incisors.

 

 

Then with the dentine color we form the midle platen. He helps to see the height of the teeth and direction of the teeth. The  prosthesis controls in the articulator in the position of central and lateral oclusion.

 

Now we model the messial and distal platen of buccal surface ot the teeth with the same dentine color.

 

The construction controls in the articulator

 

                The view of ceramics after burning.

 

 

 

The steps of putting enamel is the same like dentine.

The view after the burniong.

 

 

We fit the work on the model.

The tracing paper must easily pass over the teeth and leave the mark, as you can see on the picture.

 

 

We polish the surface with backed diamond boron.

 

 

We do the first separation with rough disc

We do the finished separation with disc (0,15 mm) with middle abrasive and polish the proximal parts of the teeth.

 

It is necessary to provide the smooth surface, that contact with gums.

we polish the chewing surface with balls from baked diamond  and carbide boron.

 

 

We control the bridge in the articulator.

 

3 laboratory step

The we do the work with glazing . We need to put the glaze with the thin layer on the teeth.

 

The view of the work after glazing.