EVALUATION

When the laboratory procedures have been completed, the restoration is ready to be evaluated in the patient’s mouth before final finishing and cementation. The completed prosthesis is cleaned either ultrasonically or with a steam cleaner to remove any residual polishing compound and then disinfected. Metal castings need to be evaluated in terms of proximal contacts, margin integrity, stability, internal fit, external contours, occlusion, and surface finish.

Metal-ceramic restorations often require two evaluations: a metal evaluation stage, followed by reevaluation after the esthetic veneer has been applied. At the metal evaluation appointment, the margin integrity, stability, occlusion, and substructure design are evaluated. Especially important at this appointment is the assessment of the cut-back area. Minor adjustments can be made: for instance, by extending the veneering surface slightly interproximally to enhance the appearance of the completed prosthesis. During the subsequent bisque evaluation, marginal integrity and stability are reassessed to determine whether any distortion has occurred during porcelain firing. Proximal contacts are also evaluated during this stage, as are porcelain contours, stability, and the shade, texture, and glaze. For fixed dental prostheses (FDPs), tissue contact of the pontics and the location and shape of connectors need careful assessment; otherwise, tissue irritation may occur. Primarily because of the inevitable inaccuracies that result during the indirect technique and the high degree of precision needed for a successful fixed prosthesis, only rarely does the restoration not require some chairside adjustment.

Interim Restoration and Luting Agent

The interim restoration is removed by gently positioning hemostats or a Backhaus towel clamp on the buccal and lingual surfaces and rocking it gently in a buccolingual direction to break the seal of the interim luting agent. Special band removers (Fig. 30-1) may also be used. Most of the luting agent or interim cement adheres to the interim restoration when it is taken out of the mouth. Any remaining cement should be loosened from the prepared tooth surface with an explorer, followed by careful application of a water-pumice mixture^* in a prophylaxis cup. Slow speed and relatively light pressure are essential. Polishing the preparation is undesirable because it may lessen retention. The preparations are rinsed with water and air spray, and after drying, the area is inspected. All residual luting agent must have been removed, because even a very small particle of interim cement can prevent a casting from seating completely.

Fig. 30-1 Hemostat (A), Backhaus towel clamp forceps (B), and Baade-type band remover (C).

Proximal Contacts

The location, size, and tightness of a restoration’s proximal contacts should resemble those of the natural teeth. Typically, textbooks refer to contacts that allow unwaxed floss to “snap” through “relatively easily.” Although this is not a very scientific definition, the use of floss is a convenient method for comparing the contacts with other contacts between adjacent teeth in the arch. If the floss does not pass, the contact is excessively tight; if it goes through too easily, food impaction may result (Fig. 30-2). The use of shim stock (thin Mylar film) is probably a more reliable indicator of proximal contact. The ideal contact should allow for positional stability of the abutments and adjacent teeth, as well as easy maintenance of the supporting structures. Most patients give reliable information as to a tight proximal contact when asked whether they “feel as though they have a seed between their teeth,” provided that a local anesthetic has not been administered. A deficient contact is easily overlooked but invariably results in discomfort as food becomes impacted.

Fig. 30-2 Deficient mesial contact, which could allow food to become impacted.

Excessive tightness

All-metal restorations

If a tight contact prevents the seating of an all-metal restoration, adjustments are readily made with a rubber wheel. The satin finish produced helps identify where binding occurs, because a shiny spot (Fig. 30-3) appears where adjustment is necessary.

Fig. 30-3 Identifying the location of a tight proximal contact. The metal is given a matte finish by grinding with a rubber wheel. A shiny mark is formed where the contact is excessive.

When a contact is too tight, the restoration is removed from the mouth, adjusted, and then reevaluated intraorally. The dentist must remember to allow a small degree of excessive tightness for polishing. When both proximal contacts of a crown are excessively tight, the dentist should make adjustments on an alternating basis, verifying whether additional material needs to be removed before proceeding with further adjustments.

Porcelain restorations

A tight proximal contact in unglazed porcelain is easily adjusted with a cylindrical stone. The area of contact (Fig. 30-4) can be identified with red pencil or thin marking tape.

Fig. 30-4 The location of tight porcelain contacts can be identified with thin marking tape.

After glazing, a slight change in the contact may be observed because of the pyroplastic surface flow that occurs during firing. If adjustment of a glazed restoration is needed, it can be repolished with diamond-impregnated silicone points, pumice, or diamond-polishing paste.

Deficiency

All-metal restorations

A gold casting with a deficient proximal contact can usually be corrected by soldering (Fig. 30-5). The procedure is simple and can be performed in the dental office in a matter of minutes. However, soldering a proximal contact should not be routinely necessary. After soldering, the restoration requires repolishing.

Fig. 30-5 Adding a proximal contact with gold solder. A, Armamentarium. B, Roughening the deficient proximal surface. C, Adding antiflux (graphite or rouge/turpentine) to the margin. D, Segment of solder positioned with paste flux. E, Heated over a Bunsen burner flame until the solder just melts. F, Proximal contact readjusted.

Armamentarium (see Fig. 30-5A)

• Soldering tweezers

• Gold solder

• Paste flux

• Bunsen burner

• Antiflux

• Polishing armamentarium

Step-by-step procedure

1. Roughen the deficient area with a disk (see Fig. 30-5B).

2. Protect the margin of the casting with a graphite pencil (or another suitable antiflux) (see Fig. 30-5C).

3. Coat a small piece of solder with flux and position it on the previously roughened surface (see Fig. 30-5D).

4. Hold the casting with the soldering tweezers in a properly adjusted flame of the Bunsen burner to position the solder at the height of the reducing portion of the flame (see Fig. 30-5E).

5. Observe the solder carefully as it heats up. As the solder starts to fuse, it rapidly spreads. With a little practice, the casting can be tipped to help the solder flow in the desired direction. The casting is then immediately removed from the flame.

6. Pickle the casting, and adjust the proximal contours with disks (see Fig. 30-5F) before repolishing and cleaning.

Porcelain restorations

A deficient proximal contact in porcelain requires additional firing. At the bisque stage, this is time consuming, but adding additional porcelain is not a problem. However, if a restoration has been completely finished, glazed, and characterized at the time the deficient contact is discovered, a lower fusing “add-on” or correction porcelain can be used to solve the problem (Fig. 30-6).

Fig. 30-6 Correction of a defective proximal contour with low-fusing, add-on porcelain (A). B, Applying the porcelain. C, Corrected proximal contours. D, Fired restoration.

These correction porcelains are a mixture of body porcelain and overglaze with additional modifiers to produce a maturation temperature as low as 850° C (1562° F). Minor corrections can thus be made with little risk of dimensional change in any other part of the restoration. Major corrections should be made by performing an additional firing with the conventional body and incisal powders, although there are limits to the number of times a restoration can be fired if devitrification is to be avoided (see Fig. 24-36B).

Margin Integrity

The completed restoration should go into place without binding of its internal aspect against the occlusal surface or the axial walls of the tooth preparation; in other words, the best adaptation should be at the margins. If the indirect procedure is handled properly, there should be no noticeable difference between the fit of a restoration on the die and that in the mouth.

Several techniques have been used to detect where a casting binds against an occlusal or axial wall, including disclosing waxes, a suspension of rouge in turpentine or acetic acid, air abrasion to form a matte finish surface, powdered sprays, water-soluble marking agents (Fig. 30-7), and special elastomeric detection pastes. However, none has proved to be entirely satisfactory. Most techniques are rather messy and time consuming and should not be needed on a routine basis.

Fig. 30-7 Water-soluble marking agent.

Nevertheless, elastomeric paste (Fig. 30-8) has some advantages. The material is similar to a silicone impression material and is obtained as a two-paste system. Its viscosity is similar to that of the final luting agents, and so it can be used not only to identify unwanted internal contacts but also to assess adequate marginal fit. The degree of clinically acceptable marginal opening (i.e., the discrepancy unlikely to have an adverse effect on the prognosis) is hard to define. Margin integrity has been the subject of many laboratory and clinical evaluations. Obviously, to limit dissolution of the luting agent, the thickness of the cement film at the margins should be kept minimal. Through careful technique, a marginal gap width of less than 30 μm can be obtained consistently.^1,2

Fig. 30-8 A, Elastomeric detection paste, recommended for evaluating the internal surface of a restoration. B, The interference is seen as a perforation in the film of silicone material, which can be marked with a colored pencil. Note: The residual film of silicone should be thoroughly removed before cementing the restoration.

(B, Courtesy of Dr. J. H. Bailey.)

Assessment

Figure 30-9 illustrates some of the possibilities that may be encountered in verifying margin integrity. The presence of a small ledge does not necessarily mean that the restoration must be remade. It may merely require additional finishing where accessibility allows.

Fig. 30-9 Assessing margin integrity with an explorer. A, An overhang. B, A ledge. C, An open margin.

A sharp explorer moved from restoration to tooth and from tooth to restoration can be used in evaluating the marginal adaptation. If resistance is encountered in both directions, a gap or open margin exists, and its cause must be determined. If the gap is the result of an excessive proximal contact or of residual interim luting agent that prevents the casting from being seated, corrective action can be easily taken and the situation remedied. However, an obviously inaccurate restoration should be quickly rejected. Trying to “make it fit” should be avoided, because a new impression is a better use of time.

Finishing

Subgingival margins are not accessible for finishing in the mouth. They must be finished on the die. Because clinical examination of subgingival margins is not always easy, a precementation radiograph may be justified.

Supragingival margins are generally finished with the casting seated on the tooth. White stones and cuttle disks rotating from restoration to tooth structure should result in a suitably finished margin (Fig. 30-10), which, if the casting is properly adapted, is virtually undetectable with the tip of a sharp explorer.³

Fig. 30-10 Supragingival margins allow access for finishing the restoration directly on the tooth. A and B, Fine-grit white stone lubricated with petroleum jelly. C, Rubber point. D, Completed restoration.

Accessible margins can also be burnished during the cementation procedure before initial setting of the cement.⁴ However, the less accessible proximal margins are the critical ones in terms of prognosis. They are the most common site of recurring caries and periodontal disease, and they can neither be evaluated readily nor finished easily. It has also been demonstrated^5,6 that correcting a poorly fitting cast restoration with finishing procedures is not possible.

Occlusion

After the restoration has been seated and the margin integrity and stability are acceptable, the occlusal contact with the opposing teeth is carefully checked. The criteria for these relationships, both static and dynamic, have been discussed in Chapters 4 and 18. Any undesirable eccentric contacts as well as centric interferences must be identified. Minor adjustment of eccentric contacts may be needed if a semiadjustable (as opposed to a fully adjustable) articulator is used.

Evaluation and adjustment

Armamentarium

• Hemostats

• Miller forceps

• Marking ribbon or tape

• Thin Mylar shim stock

• Diamond rotary instruments

• White stones

Only restorations in supraocclusion can be adjusted. For those that are out of occlusion, there is no satisfactory solution other than remaking (if in metal) or adding porcelain and refiring (if a metal-ceramic restoration).

Step-by-step procedure (Fig. 30-11)

1. Before seating the casting, assess the contact relationship between maxillary and mandibular teeth. The most convenient way to do this is to cut a narrow strip of Mylar shim stock, hold it in hemostats or forceps, and have the patient open and close with the strip between opposing teeth. A “tug” can be felt on the strip, indicating occlusal contact (Fig. 30-12). Ideally, contact should be as evenly distributed as possible, but it is not uncommon to find one or more areas of relatively light contact between opposing teeth.

2. Seat the restoration, have the patient close, and reassess the contacts. The new restoration should hold the shim stock and yet not alter the existing tooth relationships. If a discrepancy is detected, a decision must be made whether this can be adjusted intraorally or whether a remount procedure is necessary.

3. Mark any interferences that are detected. Have the patient close on articulating ribbon or tape.

4. Adjust the marked interferences with the diamond rotary instrument or white stone, always checking the thickness of the casting with calipers before an adjustment is made. On occasion, adjusting an opposing cusp rather than cementing a restoration that is too thin may be the preferred method, although performing such adjustment at the tooth preparation stage is recommended. Explaining the procedure and its rationale to the patient before grinding an opposing tooth is essential. Options, such as increasing occlusal clearance by repreparing the tooth, should be presented to the patient before proceeding.

5. Be careful not to misinterpret occlusal markings. Note that a true interocclusal contact leaves a mark with a clean center (like a bull’s-eye), but a false contact leaves a smudge. Marking ribbon or tape is useful for helping determine the location of an interference. Shim stock, however, is a more reliable indicator than ribbon or tape for confirming the presence or absence of an occlusal contact and should be used to evaluate the result when the end point is reached.

6. Use two colors of ribbon for the different types of movement. Excursive movements and interferences are first marked in one color (e.g., green). Then a different color (e.g., red) is inserted for centric contacts. Any excursive interferences (i.e., green marks not covered by red) are adjusted with the diamond or white stone.

Fig. 30-11 Evaluating and adjusting the occlusion. A, Refinement on the articulator before evaluation. B, Testing the occlusal relationship with shim stock and marking with tape. Typically, some adjustment is needed, especially in more complex treatments, but this should not be extensive unless an error has been made. C, After adjustment, the occlusal contacts should always be verified with shim stock because ribbon markings can be misinterpreted.

Fig. 30-12 A, Use Mylar shim stock to identify presence or absence of occlusal contacts. B, Use articulating tape to identify the location of occlusal contact.

An alternative technique requires the use of an airborne particle abrasion unit with aluminum oxide (Fig. 30-13). A matte finish is obtained on the occlusal surfaces of the casting in question, and the patient is asked to close. Where shiny marks appear, an adjustment is made. This technique, however, presents the following disadvantages:

1. Differentiating between centric and excursive contacts is not possible.

2. The technique is more time consuming.

3. It is applicable only to cast-metal occlusal surfaces.

Fig. 30-13 Occlusal prematurities can be identified by giving the casting a matte finish with an air-abrasion unit. A and B, The prematurities appear as shiny areas.

(Courtesy of Dr. M. T. Padilla.)

Gross occlusal adjustment involving dental porcelain is better done in the bisque stage, because interferences are more easily marked on a bisque surface than on glazed porcelain. Minor adjustments are needed after glazing because of the pyroplastic flow of the porcelain.⁷ After adjustment, the porcelain can be polished with silicone wheels or diamond-polishing paste.

Remount

If there is a need for significant occlusal adjustment, a remount procedure⁸ may be recommended. It is typically used when extensive restorative dentistry has been performed, and it serves to convey the relationships of the restorations and teeth to the dental laboratory (Fig. 30-14). Detailed adjustments can then be made in an organized manner. Any inaccuracy (e.g., slight tooth movement, previous mounting discrepancies, or small dimensional change inherent with the indirect process) can be compensated for relatively easily, thus reducing the amount of chair time needed for precementation adjustment.

Fig. 30-14 A and B, Accurate transmission of occlusal relationships to the laboratory should be the rule when a careful technique has been followed. If discrepancies occur, they are often better corrected by a remount procedure in the laboratory.

Intraoral occlusal refinement is limited because of visibility and access difficulties. Laboratory adjustments offer optimum access and visibility and the opportunity to evaluate lingual contact relationships.

The remount procedure consists of making an impression of the castings in the patient’s mouth, with an occlusal index in place. The index is made with reinforced resin or impression plaster and provides the opportunity to accurately reposition the castings back into the impression after it has been removed from the patient’s mouth. A new definitive cast can then be fabricated. To enable easy removal of the castings from the newly fabricated definitive cast, resin is usually poured into the castings, after which the rest of the impression is poured in conventional type IV stone (Fig. 30-15). The cast can then be articulated with a conventional facebow transfer and occlusal registration techniques (see Chapter 2).

Fig. 30-15 Cross-sectional schematic of the remount procedure.

Armamentarium (Fig. 30-16)

• Impression trays (A)

• Irreversible hydrocolloid (B)

• Rubber bowl and spatula (C)

• Interim luting agent (D)

• Petrolatum (E)

• Autopolymerizing resin (F)

• Stiff wire (e.g., coat hanger wire) (G)

• Zinc oxide–eugenol (ZOE) occlusal registration paste (H)

• Inlay wax or light-bodied reversible hydrocolloid (I)

• Facebow transfer equipment

• Centric relation recording

Fig. 30-16 Armamentarium for a remount procedure.

Step-by-step procedure (Fig. 30-17)

1. Use autopolymerizing resin (e.g., custom tray resin) to make an occlusal index of the restorations on the definitive cast. Reinforce the index with stiff wire. The index should not extend beyond the occlusal table of the restored teeth, and its thickness must not be greater than 5 mm. It should fit the cast passively.

2. Grind the occlusal aspect of the index until only shallow indentations of the cusp tips remain.

3. Seat the restorations on the prepared teeth (see Fig. 30-17B). To prevent dislodgment, use a small amount of interim luting agent mixed with petrolatum. FDPs that have yet to be assembled can be stabilized with autopolymerizing resin applied by the brush-bead technique (see Fig. 28-24).

4. After the fit of the index has been verified, cover the surfaces of the restorations with a thin coating of petrolatum, and apply ZOE registration paste to the occlusal aspect of the index. Then seat it in the patient’s mouth. As an alternative, impression plaster can be used (see Fig. 30-17C).

5. Make an orientation impression over the index and the restorations with an elastomeric impression material in a stock tray, making sure the index is not displaced (see Fig. 30-17D).

6. Make a conventional opposing impression if no restorations were made for that arch. If restorations have been made for both arches, repeat the procedure described previously.

7. Remove the restorations from the mouth, replace the interim restorations, and reschedule the patient.

8. Clean the internal aspects of the restoration of any residual cement or debris, reseat the restoration in the index, and apply a thin coating of petrolatum.

9. Cover the margins of the restoration with wax or soft lining resin. As an alternative, reversible hydrocolloid impression material can be applied around them with a syringe. Note: Crowns with long retentive axial walls can be partially filled with reversible hydrocolloid to aid in their subsequent removal.

10. Pour the internal surface of the casting with autopolymerizing resin or low-fusing metal, adding retention (see Fig. 30-17E). American Dental Association type IV stone can be used, but the casting must be lubricated carefully; special care must be taken to prevent fracture when the casting is removed.

11. Complete the maxillary cast (see Fig. 30-17F).

12. Make a new centric relation record at the occlusal vertical dimension and articulate the cast (see Fig. 30-17G).

13. Save the index to confirm accuracy after the occlused remount is poured.

Fig. 30-17 Remount technique. A, A maxillary arch is prepared for metal-ceramic crowns and fixed dental prostheses. B, The metal framework is evaluated clinically; a remount procedure is needed. C, Impression plaster is used to register the location of each unit. D, The registration is picked up with an elastomeric material. E, Restorations are lubricated, and soft lining resin is painted around them. Their internal surfaces are filled with hard resin. Acrylic chips provide retention for the soft resin. Small wood screws are inserted into the hard acrylic, which are also for retention. F and G, The remainder of the cast is poured and articulated in the usual way.

(Courtesy of Dr. J. H. Bailey.)

This completes the remount procedure. The restoration can now be reassessed and adjusted in the dental laboratory. Although a remount procedure is not routinely needed, it may be advantageous with an extensive restoration to reduce the amount of chair time required for occlusal adjustment.

Ceramic Restorations

Ceramic restorations need certain additional steps during evaluation to satisfy esthetic, biologic, and mechanical requirements. Achieving an esthetic result depends on the contour of the restoration, surface characterization, and color match.

Contouring

Armamentarium (Fig. 30-18)

• Flexible diamond disk

• Porcelain grinding wheel

• Ceramic-bound stones

• Diamonds

Fig. 30-18 Armamentarium for porcelain adjustment.

When contouring a restoration that is to be evaluated during the bisque stage, it should be moistened first with water or saliva. The moist surface reflects light in the same manner as the glazed restoration.

Step-by-step procedure

1. Check the proximal contact relationship (adjust as necessary), and verify the marginal fit of the restoration.

2. Verify the contour of the gingival third, and make any necessary adjustments. Excessive bulk in this area is a common fault and is often associated with periodontal disease (Fig. 30-19). When adjustment of porcelain is needed, the porcelain and metal should not be ground simultaneously, because small metal particles may be transferred to the porcelain, causing discoloration and a black spotty appearance after the restoration has been glazed. If grinding both porcelain and metal simultaneously is absolutely necessary, the direction of grinding should be parallel to the metal-ceramic junction (Fig. 30-20). A thin, flexible disk provides good access to reduce any overcontoured interproximal area (Fig. 30-21).

3. Identify and adjust any occlusal interferences on the posterior teeth. As mentioned, porcelain occlusal contacts need readjustment after glazing because of the pyroplastic flow of porcelain.

4. On anterior teeth, establish the proper position and shape of the incisal edge. This is a key step in achieving good esthetics and function. Unfortunately, it is hard to obtain in the laboratory because the soft tissues of the patient’s lips and cheeks are not present on the articulator. A stone cast of a well-adjusted interim restoration (made from the diagnostic cast or waxing procedure) helps the technician because it can be duplicated when the porcelain is applied. However, as a general rule, the restoration should be tried in the patient’s mouth with the incisal edges slightly longer than intended; their shape should be refined in the mouth.

Fig. 30-19 A, Periodontal disease associated with excessively contoured restorations. B and C, Teeth reprepared to allow appropriate facial contours. D, Correct emergence profile established in restoration. E, Clinical adaptation verified. F, Note tissue response to new restorations. G, Appropriate embrasure form allows plaque control.

Fig. 30-20 If it is necessary to grind at the metal-porcelain junction, the stone should be held perpendicular to the junction. Otherwise, metal particles may contaminate the porcelain.

Fig. 30-21 Adjusting the axial contour.

If too much adjustment is made, the incisal porcelain layer will be ground away, and the esthetic effect will be spoiled. Incisal edge position is important in obtaining good esthetics and function. Specific criteria for what constitutes “normal” are hard to define, but an average of 1 to 2 mm of the clinical crown should be visible on maxillary central and lateral incisors when the upper lip is relaxed. Additional help in contouring the incisal edges can be obtained by looking at the patient’s smile and listening to speech characteristics. Ideally, the incisal edges of the maxillary anterior teeth follow the curvature of the lower lip when the patient smiles.⁹ Ordinarily, the incisal edges of the lateral incisors (Fig. 30-22) are 1 to 2 mm shorter than the central incisors, which may touch the internal aspect of the lower lip when it is relaxed.

5. Evaluate the negative space, the name given to the shape of the incisal embrasures¹⁰ (see Chapter 1). Proper embrasures (Fig. 30-23) significantly enhance the apparent separation between restorations, whereas their absence draws attention to the prosthesis and reveals its artificial nature (see Fig. 30-23C). Similarly, when viewed from the incisal aspect, interproximal embrasures should be as narrow and deep as possible to enhance the shadows between components of the fixed prosthesis. If these are absent, even the casual observer will recognize the teeth as artificial.

6. Have the patient enunciate the consonants. F sounds are particularly helpful because they are made with the incisal edge of the maxillary central incisors touching at the junction of the moist and dry surfaces of the vermilion border of the lower lip (“wet-dry line”).¹¹

7. Mark the line angles directly on the porcelain restoration in the bisque stage with a colored pencil, and compare these to the line angles of adjacent and contralateral teeth. Red pencil is preferred because blue or black pencil may discolor the porcelain. The position of the line angles is probably one of the more critical procedures for achieving good esthetics because the line angles delineate the shape of the tooth to an observer. (Line angles on wax patterns are discussed in Chapter 18.) By superimposing normal line angle distribution over teeth that are otherwise too large or too narrow,¹² creating the impression that the left and right sides are identical is possible (Fig. 30-24) (see Chapter 23).

8. Evaluate the overall contour to see that it matches the shape of the adjacent teeth. With experience, most operators quickly develop an appreciation for evaluating “normal” contours and detecting areas that need correction. Moistening the teeth and observing light reflections may help. It also helps to have the patient stand up to be checked at normal conversational distance, as opposed to the extreme closeup of a dental examination.

Fig. 30-22 Typical incisal edge position.

(From Monteith BD: A cephalometric method to determine the angulation of the occlusal plane in edentulous patients. J Prosthet Dent 54:81, 1985.)

Fig. 30-23 A and B, Properly shaped incisal embrasures. C, Inadequate embrasures. Note the unnatural look.

Fig. 30-24 Insufficient mesiodistal space is available for the right maxillary lateral incisor. By creation of an apparent overlap, the pontic is given the illusion of normal anatomic proportions.

Surface texture characterization

When the contour of the restoration has been finalized, the next goal is to duplicate the surface detail of the patient’s natural teeth.

Armamentarium

• Diamond disk

• Carborundum stones

• Diamond stones

Step-by-step procedure

1. Dry the teeth, and examine their surfaces carefully. Perikymata and defects can be simulated by grinding the porcelain with a diamond stone of appropriate texture. (Be careful not to overemphasize such details.) Flat or concave areas reflect light in a characteristic manner, producing highlights (Fig. 30-25).

2. Copy the details and carefully blend them with the adjacent area. In general, the effort should aim at generating textures that follow the principal curvatures of the normal anatomic form of the tooth, in order to result in optimal perception of the characterized surface.

3. Similarly, mimic any vertical defects with careful grinding.

4. Be careful to avoid “overcharacterizing” restorations, which is a common error (Fig. 30-26).

Fig. 30-25 A, Restoration texture should closely match natural enamel. B, Sharp grooves should not be cut into the ceramic surface because these “trap” light. A curved surface looks more natural and results in either converging or diverging reflections.

Fig. 30-26 The texture of these metal-ceramic units has been overemphasized, which has led to an artificial appearance.

On occasion, altering the apparent size of a restoration by these techniques may be possible. A smooth tooth appears larger than one that is identical in size but has intensive surface texture characterization.

CHARACTERIZATION AND GLAZING

The surface luster or degree of gloss of a porcelain restoration depends on the autoglazing procedure (see Chapter 24). Both time and temperature must be carefully controlled. During a glazing firing, the surface layers of porcelain melt slightly, coalescing the particles and filling in surface defects.

The restoration should not be glazed in a vacuum, because included air may be drawn to the surface and result in bubbling (Fig. 30-27). Because air-fired glazing furnaces are relatively compact and inexpensive, some dentists prefer to glaze porcelain restorations in the operatory. This is particularly convenient if surface stains are to be used. The glazing step is straightforward; the degree of glaze depends on furnace temperature and how long the restoration is held at that temperature. Excessively glazed anterior teeth look unnatural. The patient should moisten the restoration because saliva affects its appearance. A dry crown looks misleadingly underglazed. Underglazing and refiring a restoration is better than overglazing it. If a restoration is not sufficiently glazed, it will retain more plaque and may be more liable to fracture. After glazing, the metal surfaces of the restoration are polished.

Fig. 30-27 A bubble that surfaced immediately before the evaluation stage. These types of defects must be addressed before delivery of the prosthesis.

An alternative to glazing is to polish the porcelain surfaces of the restoration.¹³ This provides greater control of the surface luster and distribution than glazing.¹⁴ For example, having a higher gloss on the cervical area and a lower gloss on the incisal area is possible. This is not possible with glazing because the entire crown is subjected to the same time-temperature combination.

Polishing dental ceramics has long been advocated as an expedient way of restoring luster after adjusting by grinding. A number of commercially available polishing kits are available for this purpose. If used correctly (i.e., without omitting the successively finer grits), most are capable of producing smooth porcelain surfaces.^15,16 As an alternative, the use of finishing wheels followed by pumice is satisfactory.¹⁷ More recently, ceramists have advocated polishing as a way to improve luster control. To achieve the precise degree and distribution of luster required, the porcelain is polished rather than glazed.

Despite the esthetic advantages of polishing, there is concern whether the strength of a polished restoration might be reduced or its abrasiveness increased. Glazing has been cited as strengthening a dental restoration,¹⁸ presumably because it causes a reduction of the flaws that initiate fracture. However, polishing also reduces flaws, and in laboratory studies, polishing has not been found to result in reduced physical properties, in comparison with glazing.^19-23 Laboratory studies have shown that polished porcelain is no more abrasive than glazed porcelain.²⁴ However, unpolished porcelain is much more abrasive on opposing enamel and is more plaque retentive than is polished or glazed porcelain.

External Color Modification and Characterization

Stuart H. Jacobs

The accomplishment of a perfect color match by using the basic shades supplied in the porcelain kits, without the need for chairside modification, is the goal of all dental ceramists. However, there are difficulties and inaccuracies inherent in the technique. There are also difficulties in duplicating the appearance of a patient’s tooth without the patient’s actually being present in the dental laboratory. These problems make perfect shade matching very difficult to achieve routinely. In many situations, a restoration that does not blend well with the adjacent teeth can be improved by simple chairside color modification or characterization procedures.²⁵ These are done concurrently with final glazing, and it is therefore recommended that restorations be tried in the patient’s mouth contoured but unglazed (bisque stage).

Armamentarium

• Porcelain furnace (a small air-fired furnace is suitable for the operatory) (Fig. 30-28).

• Clean glass slab

• Sable hair brush

• Distilled water

• Tissue

• Stain kit

Fig. 30-28 Ney Miniglaze/2 glazing furnace.

A number of stain kits are available from porcelain manufacturers, and most contain a fairly wide range of colors. The stains themselves are highly pigmented surface colorants that contain a small amount of glass, allowing the color to fuse into the porcelain surface.

Available characterization kits are illustrated in Figure 30-29. They come in various colors. Additional colors can be made by mixing the stains with each other; the color intensity can also be toned down with a colorless porcelain.

Fig. 30-29 A, The IPS Stain and Shade kits. B, The Akzent Stain Kit.

(A, Ivoclar Vivadent, Amherst, New York; B, Courtesy of Vident, Brea, California.)

Step-by-step procedure

The application of stain has advantages and disadvantages. One advantage is that the dentist or technician can modify the shade after a restoration is completed with the patient present. The greatest disadvantage is that the color can be applied only to the surface, and so it is ineffective in producing characterizations that look realistic (i.e., deep within the tooth). Also, if surface characterization is applied excessively,²⁶ it can cause a loss of fluorescence in the finished restoration, as well as an increase in the metameric effect (shade mismatch is more apparent under some lighting conditions). Furthermore, a characterized crown is slightly rougher than an autoglazed one,²⁷ and the stain will eventually wear away under normal toothbrushing^28,29 (10 to 12 years).

Three aspects of characterization may be used singly or in combination to achieve a natural appearance: shade modification (increasing the chroma, changing the hue, or reducing the value); specific characterization (e.g., hypocalcified areas or cracks); and special illusions of form or position (Fig. 30-30).

Fig. 30-30 Characterization and glazing technique. A, The colored stains are mixed to a stiff consistency on a suitable palette. B, Applying the stain. Often the procedure is repeated, or modifications are made after removal from the mouth. C, White stain is used to mimic hypocalcification. D, Stain with increased chroma is used for proximal coloration. E, A thin brown check line is made by painting a line of stain on the porcelain. This is reduced to the desired width by wiping a clean brush on each side of it. F and G, Stain is dried to a chalky consistency in front of the furnace muffle. H, Characterized and glazed restorations after firing.

(A, Courtesy of Dr. G. W. Sheen.)

1. Mix the stain with the liquid provided in the kit (normally a glycerin-water mixture) to a creamy, stiff consistency (see Fig. 30-30A). If the mixture is too thin, it runs over the restorations and pools in certain areas. An even coat is essential for producing the best results.

2. Before applying the stain, thoroughly clean the restoration with steam. Apply stain to the restorations with the clean moist sable brush (see Fig. 30-30B). When moist, the brush becomes easier to draw to a point, and application of the stain is greatly facilitated.

3. When the effect has been created, make a note of which stain was used and where. This procedure usually must be duplicated because absolute cleanliness is essential; in addition, placing a unit in the mouth without some contamination is difficult. Removing the restorations without smudging is also difficult.

4. Take the restorations out of the mouth, wash them, and re-create the characterization (see Fig. 30-30C to E).

5. After the characterization is complete, transfer the restorations to a firing tray, and place it in front of the muffle of the furnace until the stain is dry and the surface appears chalky white (see Fig. 30-30F and G).

6. Remove the prosthesis, and examine it to ensure that no stain has run inside.

7. Remove any excess with a dry brush, and place the crown in the furnace.

8. Increase the heat to the maturation temperature of the porcelain, and hold it there according to the degree of glaze required (see Fig. 30-30H).

9. Remove the restorations, allow them to cool, and retry them in the patient’s mouth.

Shade modification (see Chapter 23)

When a porcelain shade is being altered with external stain, certain limitations must be considered, particularly because surface characterization causes a loss of fluorescence and increases the effect of metamerism. It cannot be used to make major corrections or compensate for gross errors.

When the correctness of shade is assessed, simulating the appearance of glazed porcelain is necessary. This can be done by painting on some of the liquid provided in the stain kit. It may also help to paint the adjacent natural tooth to prevent dehydration during the characterization procedure, which would increase the value of the tooth.

Chroma and hue adjustment

Increasing the chroma (saturation) is one of the simplest shade alterations to achieve.³⁰ The addition of yellow stain increases the chroma of a basically yellow shade, whereas adding orange has the same effect on a yellow-red shade. When an alteration in hue is necessary, pink-purple moves yellow toward yellow-red, whereas yellow decreases the red content of a yellow-red shade. These are the only two modifications that should be necessary, because the hue of a natural tooth always lies in the yellow-red to yellow range.

A metal-ceramic restoration that has too high a chroma is difficult to modify. Choosing a shade with a lower chroma is always better, because a lower chroma can be altered easily. Using the complementary color of a restoration reduces its chroma: Yellow requires purple-blue and orange requires blue or blue-green. However, the addition of these stains lowers the value of the restoration and increases the metameric effect; it is rarely successful in practice.

Value adjustment

Value can be reduced by adding a complementary color (see Fig. 23-1). Violet is used on yellow restorations and has the added effect of increasing the translucency. Gray is not encouraged because it tends to reduce translucency and makes the surface cloudy.

Attempting to increase the value is generally less successful, although value can be increased if the dominant color added has a higher lightness ranking. For example, a crown can be stained with white, but opacity will be greatly increased.

Characterization

Characterization is the art of reproducing natural defects, and it can be particularly successful in making a crown blend with the adjacent natural teeth. In general, defects should be reproduced to a slightly lesser extent on the restoration than as they appear on the natural teeth. The temptation to overcharacterize is strong but must be resisted.

Characterization looks slightly more natural and is more permanent if applied intrinsically during the buildup of the restoration (see Chapter 24) rather than by subsequent extrinsic application.³¹ However, communicating the exact characterization needed to the laboratory may be difficult; therefore, copying natural defects at chairside may be more practical.

Hypocalcified areas

These are produced with white stain and may be some of the easiest and most commonly made modifications.

Proximal coloration

Many natural teeth exhibit proximal characterization. By reproducing this in the restoration, the dentist is able to create the illusion of depth and separation and is also able to tone down excessive opacity at the cervical area. The stains used are brown and orange. They are applied lightly to the proximal area and extended slightly onto the buccal surface apical to the contact. Proximal coloring is particularly useful in creating the illusion of separate units of an FDP.

Enamel cracks

This characterization is better if done intrinsically, although it can be added extrinsically. A linear vertical crack interrupts the light transmission across the tooth surface, causing a shadow. Thus, both the highlight and the shadow of the crack must be simulated for an authentic result.

The highlight is developed with white and yellow mixed in the ratio of 4 : 1, and gray stain is used for the shadow. A thin line is drawn with a brush in the desired area with the white and yellow stains. Then a thin line of gray is placed distal to the first line to create the illusion of a shadow.

Stained crack line (Fig. 30-31)

Cracked enamel stains quickly on natural teeth. An orange-brown mixture applied in as thin a line as possible will effectively simulate a crack.

Fig. 30-31 Thin brown check lines have been added to enhance the appearance of this prosthesis.

Exposed incisal dentin

This is usually seen on the mandibular incisors of older patients and is caused by enamel wear. The incisal edge should be “cupped out,” with orange and brown colorants used to reproduce the dentinoenamel junction.

Incisal halo

Translucent incisal edges are more common on the incisors of younger patients. Often, although the incisal area is translucent, the edge is totally opaque. This may be difficult to reproduce internally. A mixture of white and yellow stains in the ratio of 4 : 1 is placed in the linguoincisal area, with an extension just onto the labial area, to produce the halo effect.

Translucency

Translucency can be mimicked with violet stain, although the results are usually disappointing in comparison with those achieved with correct application of the incisal porcelain. For optimum results, both labial and lingual surfaces should be coated. Decreasing the translucency is accomplished by adding the dominant hue over the labiolingual surface.

Special illusions

Form and position are undoubtedly the most important factors in achieving an attractive result. However, restoring the original form may not always be possible. Loss of supporting tissue, the size of a pontic space, or a poor occlusal position may impede the attempt.

An FDP pontic may be very long because of loss of supporting bone. Simulating a root surface can partially improve the appearance. The root extension is contoured for length and width, and then an orange-brown mixture is placed over the extension. Pink stain can be used to simulate gingival tissue, but results are better with pink body porcelain.

Recommended characterization procedures are summarized in Table 30-1.

Table 30-1 CHARACTERIZATION PROCEDURES

SUMMARY

When a restoration is evaluated in the mouth, the proximal contacts are assessed first, followed by margin integrity, stability, and occlusion. Minor occlusal discrepancies can usually be adjusted intraorally. For extensive prosthodontic treatment, a remount procedure may be needed, which will reduce the chair time needed to achieve an optimum occlusal scheme in the restoration.

With a metal-ceramic restoration, proper contouring of the porcelain in the cervical third is crucial for facilitating maintenance of health of the supporting structures. Proper shaping of the gingival and incisal embrasures, along with contouring and characterization, significantly improves the esthetic result. Small corrections and subtle changes can be made with surface stains.

GLOSSARY^*

antiflux \ăn′tē-flŭks′\ n: materials that prevent or confines solder attachment or flow

¹cast·ing \kăs′tng\ n (14c): something that has been cast in a mold; an object formed by the solidification of a fluid that has been poured or injected into a mold

²cast·ing \kăs′tng\ vt: the act of forming an object in a mold—see VACUUM C.

characterization: to characterize by application of unique markings, indentations, coloration and similar custom means of deliniation on a tooth or dental prosthesis thus enhancing natural appearance

char·ac·ter·ize \kăr′ak-ta-rīz\: to distinguish, individualize, mark, qualify, singularize, or differentiate something

emergence profile \-mûr′jens proōfīl\: the contour of a tooth or restoration, such as a crown on a natural tooth or dental implant abutment, as it relates to the adjacent tissues

extrinsic coloring \k-strn′sk kŭl′or-ng\: coloring from without; applying color to the external surface of a prosthesis

glaze \glāz\ vb glazed \glāzd\; glaz·ing \glaōzng\ vt (14c) 1: to cover with a glossy, smooth surface or coating 2: the attainment of a smooth and reflective surface 3: the final firing of porcelain in which the surface is vitrified and a high gloss is imparted to the material 4: a ceramic veneer on a dental porcelain restoration after it has been fired, producing a nonporous, glossy or semi-glossy surface—see NATURAL G., OVERGLAZE

intrinsic coloring \n-trn′zk, -sk kŭl′ar-ng\: coloring from within; the incorporation of a colorant within the material of a prosthesis or restoration

line angle \līn ang′gal\: the point of convergence of two planes in a cavity preparation

natural glaze \năch-ar-al, năch′ral glāz\: the production of a glazed surface by the vitrification of the material itself and without addition of other fluxes or glasses

o·ver·glaze \oōvar-glāz\ adj (1879): the production of a glazed surface by the addition of a fluxed glass that usually vitrifies at a lower temperature

pig·ment \pg′mant\ n (14c): finely ground, natural or synthetic, inorganic or organic, insoluble dispersed particles (powder), which, when dispersed in a liquid vehicle, may provide, in addition to color, many other essential properties such as opacity, hardness, durability, and corrosion resistance. The term is used to include an extender, white or color pigments. The distinction between powders that are pigments and those that are dyes is generally considered on the basis of solubility—pigments being insoluble and dispersed in the material, dyes being soluble or in solution as used

primary colors (additive) \prī′mr′ē, -ma-rē kŭl′erz ăd′-tv\: three colored lights from which all other colors can be matched by additive mixture. The three must be selected so that no one of them can be matched by mixture of the other two. Generally, red, green, and blue are used. Additive primaries are the complements of the subtractive primaries

primary colors (subtractive) \prī′mr′ē, -ma-rē kŭl′erz sab-trăk′tv\: colors of three colorants or colored materials which, when mixed together subtract from one another, resulting in black or a very dark neutral color. Subtractive primaries are generally cyan, magenta, and yellow

remount cast \rē-mount′\: a cast formed of a prosthesis for the purpose of mounting the prosthesis on an articulator

remount procedure \rē-mount′ pra-sē′jur\: any method used to relate restorations to an articulator for analysis and/or to assist in development of a plan for occlusal equilibration or reshaping

remount record index \rē-mount′ rk′ard n′dks′\: a record of maxillary structures affixed to the mandibular member of an articulator useful in facilitating subsequent transfers

speaking space \spē′kng spās\: the space that occurs between the incisal or/and occlusal surfaces of the maxillary and mandibular teeth during speech

¹stain \stān\ n (1583) 1: a soiled or discolored spot; a spot of color in contrast to the surrounding area 2: a preparation used in staining 3: in dentistry, the discoloration of a tooth surface or surfaces as a result of ingested materials, bacterial action, tobacco, and/or other substances. This may be intrinsic, extrinsic, acquired, or developmental

²stain \stān\ vb (14c) 1: to suffuse with color 2: to color by processes affecting chemically or otherwise the material itself 3: in dentistry, to intentionally alter restorations through the application of intrinsic or extrinsic colorants to achieve a desired effect, best termed characterization or to characterize a restoration