Pontic Space

One function of an FDP is to prevent tilting or drifting of the adjacent teeth into the edentulous space. If such movement has already occurred, the space available for the pontic may be reduced and its fabrication complicated. At this point, creating an acceptable appearance without orthodontic repositioning of the abutment teeth is often impossible, particularly if esthetic appearance is important. (Modification of abutments with complete-coverage retainers is sometimes feasible.) Careful diagnostic waxing procedures help determine the most appropriate treatment (see Chapters 2 and 3). Even with a lesser esthetic requirement, as for posterior teeth, overly small pontics are unacceptable because they trap food and are difficult to clean. When orthodontic repositioning is not possible, increasing the proximal contours of adjacent teeth may be better than making an FDP with undersized pontics (Fig. 20-3). If there is no functional or esthetic deficit, the space can be maintained without prosthodontic intervention.

Fig. 20-3 Careful planning is always necessary in deciding how to restore an undersized pontic space where orthodontic treatment is not practical. A, In this patient, individual crowns of increased proximal contours were preferred to a partial fixed dental prosthesis with undersized pontics. Excellent plaque control had been demonstrated, and the design provided the optimum occlusal relationship. B, Here two small pontics were used to replace the missing maxillary teeth.

Residual Ridge Contour

The edentulous ridge’s contour and topography should be carefully evaluated during the treatment planning phase. An ideally shaped ridge has a smooth, regular surface of attached gingiva, which facilitates maintenance of a plaque-free environment. Its height and width should allow placement of a pontic that appears to emerge from the ridge and mimics the appearance of the neighboring teeth. Facially, it must be free of frenum attachment and be of adequate facial height to sustain the appearance of interdental papillae.

Loss of residual ridge contour may lead to unesthetic open gingival embrasures (“black triangles”) (Fig. 20-4A), food impaction (Fig. 20-4B), and percolation of saliva during speech. Siebert² classified residual ridge deformities into three categories (Table 20-1 and Fig. 20-5):

There is a high incidence (91%) of residual ridge deformity after anterior tooth loss³; the majority of these are Class III defects. Because patients with Class II and III defects are frequently dissatisfied with the esthetics of their FDPs,⁴ preprosthetic surgery to augment such residual ridges should be carefully considered.

Fig. 20-4 Loss of residual ridge contour, leading to unesthetic open gingival embrasures (A) and food entrapment (arrow) (B).

Table 20-1 INCIDENCE OF MAXILLARY ANTERIOR RESIDUAL RIDGE DEFECTS

Fig. 20-5 Residual ridge deformities as classified by Siebert.² A, Class O, no defect. B, Class I defect. C, Class II defect. D, Class III defect.

Surgical Modification

Although residual ridge width may be augmented with hard tissue grafts, this is usually not indicated unless the edentulous site is to receive an implant (see Chapter 13).

Class I defects

Soft tissue procedures have been advocated for improving the width of a Class I defect; however, because Class I defects are infrequent and are not esthetically challenging, surgical augmentation of ridge width is uncommon. Paying careful attention to interim pontic contour helps the operator identify patients who would benefit from surgery. In the roll⁵ technique, soft tissue from the lingual side of the edentulous site is used. The epithelium is removed, and the tissue is thinned and rolled back upon itself, thereby thickening the facial aspect of the residual ridge (Fig. 20-6). Pouches may also be prepared in the facial aspect of the residual ridge⁶ into which subepithelial^7,8 or submucosal⁹ grafts harvested from the palate or tuberosity may be inserted (Fig. 20-7).

Fig. 20-6 The roll technique for soft tissue ridge augmentation. A, Cross-section of Class I residual ridge defect before augmentation. B, Epithelium removed from palatal surface. C, Elevation of flap, creating a pouch on the vestibular surface. D, The flap is rolled into the pouch, enhancing ridge width.

Fig. 20-7 The pouch technique for soft tissue ridge augmentation. A and B, Split-thickness flap is reflected. C, Graft material placed in the pouch increases ridge width. D, Flaps sutured in place.

Class II and III defects

Unfortunately, few soft tissue surgical techniques can increase the height of a residual ridge with predictability. The interpositional graft^2,10 is a variation of the pouch technique, in which a wedge-shaped connective tissue graft is inserted into a pouch preparation on the facial aspect of the residual ridge. The epithelial portion of the wedge may be positioned coronally to the surrounding epithelium if an increase of ridge height is desired (Fig. 20-8A and B). The onlay graft is designed to gain ridge height^2,11 but also contributes to ridge width, which makes it useful for treating Class III ridge defects (Fig. 20-9). It is a thick “free gingival graft” harvested from partial- or full-thickness palatal donor sites. Because the amount of height augmentation can be only as thick as the graft, the procedure may have to be repeated several times to reestablish normal residual ridge height. Although the onlay graft has greater potential for increasing ridge height than does the interpositional graft, its survival is greatly dependent on revascularization, which requires meticulous preparation of the recipient site. Therefore, it is more technique sensitive than the interpositional graft. In fact, connective tissue grafts have been demonstrated to achieve approximately 50% more ridge volume gain 3.5 months after surgery than do free gingival grafts in single-tooth residual ridge defects.¹²

Fig. 20-8 An interpositional graft for augmentation of ridge width and height. A, Tissue reflected. B, Graft positioned and sutured in place.

Fig. 20-9 An onlay graft for augmentation of ridge width and height. A, Presurgical view of Class III residual ridge defect with abutment teeth prepared. B, Recipient bed prepared by removing epithelium. C, Striation cuts are made in connective tissue to encourage revascularization. D, Onlay graft is sutured in place., E, An interim partial fixed dental prosthesis with open embrasures is placed immediately to allow adaptation of tissue during healing. F, Cast with Class III residual ridge defect; the lateral incisor was unrestorable. G, Donor site for graft. H, Graft sutured in place. I, Augmented ridge. J and K, Final restoration with improved contours.

Gingival Architecture Preservation

Although the degree of residual ridge resorption after tooth extraction is unpredictable, resulting deformities are not an inevitable occurrence. Preservation of the alveolar process can be achieved through immediate restorative and periodontal intervention at the time of tooth removal. By conditioning the extraction site and providing a matrix for healing, the pre-extraction gingival architecture, or “socket,” can be preserved.

Preparing the abutment teeth before the extraction is the preferred technique. An interim FDP can be fabricated indirectly, ready for immediate insertion. Because socket preservation is dependent on underlying bone contour, the extraction of the tooth to be replaced should be atraumatic and aimed at preserving the facial plate of bone. The scalloped architecture of interproximal bone forming the extraction site is essential for proper papilla form, as are facial bone levels in the prevention of alveolar collapse. If bone levels are compromised before or during extraction, the sockets can be grafted with an allograft material (hydroxyapatite, tricalcium phosphate, or freeze-dried bone).^13-15

Immediately after preparation of the extraction site, a carefully shaped interim FDP is placed (Fig. 20-10A and B). The tissue side of the pontic should be an ovate form, and, according to Spear,¹⁶ it should extend approximately 2.5 mm apical to the facial free gingival margin of the extraction socket (Fig. 20-10C and D). Because the soft tissues of the socket begin to collapse immediately after the tooth extraction, the pontic causes tissue blanching as it supports the papillae and facial/palatal gingiva. The contour of the ovate tissue side of the pontic is critical and must conform to within 1 mm of the interproximal and facial bone contour to act as a template for healing. Oral hygiene in this area is difficult during the initial healing period, and so the interim restoration should be highly polished to minimize plaque retention. After approximately 1 month of healing, oral hygiene access is improved by recontouring the pontic to provide 1 to 1.5 mm of relief from the tissue. When the gingival levels are stable (approximately 6 to 12 months), the final restoration can be fabricated (Fig. 20-10E).

Fig. 20-10 Alveolar architecture preservation technique. A, Atraumatic tooth extraction. B, Cross-section view of the immediate interim partial fixed dental prosthesis, demonstrating ovate pontic form. C, Interim restoration. Note the 2.5-mm apical extension of the ovate pontic. D, The seated interim restoration should cause slight blanching of interdental papilla. E, Interim restoration 12 months after extraction. Note the preservation of interdental papilla.

(Courtesy of Dr. F.M. Spear and Montage Media, Mahwah, New Jersey.)

Techniques involving orthodontic extrusions have also been employed to preserve ridge form before extraction. In these proactive methods, light forces are used to extrude the teeth destined to be extracted. As the teeth are extruded, apposition of bone occurs at the root apex, thereby filling the socket with bone as the tooth is slowly extracted orthodontically. First employed to avoid ridge augmentation and gain vertical ridge height before immediate implant placement,¹⁷ the orthodontic extrusion technique has been used successfully to maintain ridge contour before treatment with conventional FDPs (Fig. 20-11). In addition to the additional time and expense of orthodontic treatment, because the teeth to be extracted must continuously be adjusted as they are extruded, previous endodontic treatment is necessary.

Fig. 20-11 Orthodontic extrusion to preserve alveolar architecture. A, Pretreatment (note gingival crest height discrepancy between the maxillary central incisors). B, Orthodontic extrusion. C, Pre-extrusion and post-extrusion radiographs. Red line denotes reference point; blue and yellow lines denote change in gingival crest height. D, Post-extraction evaluation of interim restoration with ovate pontics. E, Gingival architecture immediately prior to pression. F, Final restoration.

Although maintenance of the residual ridge after extraction is admirable, socket-preservation techniques are technically challenging and require frequent patient monitoring and conscientious hygiene on the part of the patient. Even when the procedure is performed meticulously, success is unpredictable because of the variability in patients’ healing response. Additional surgical augmentation of the ridge may still be necessary for some patients.

Sanitary or Hygienic Pontic

As its name implies, the primary design feature of the sanitary pontic allows easy cleaning, because its tissue surface remains clear of the residual ridge (Fig. 20-12A). This hygienic design permits easier plaque control by allowing gauze strips and other cleaning devices to be passed under the pontic and seesawed in a shoeshine manner. Disadvantages include entrapment of food particles, which may lead to tongue habits that annoy the patient. The hygienic pontic is the least “toothlike” design and is therefore reserved for teeth seldom displayed during function (i.e., the mandibular molars).

Fig. 20-12 A, Sanitary pontic. B and C, Modified sanitary pontic. D, Placement of the pontic, close to the ridge, has resulted in tissue proliferation (arrow).

A modified version of the sanitary pontic has been developed¹⁸ (Fig. 20-12B and C). Its gingival portion is shaped like an archway between the retainers. This geometry allows increased connector size while decreasing the stress concentrated in the pontic and connectors.¹⁹ It is also less susceptible to tissue proliferation that can occur when a pontic is too close to the residual ridge (Fig. 20-12D).

Saddle or Ridge Lap Pontic

The saddle pontic has a concave fitting surface that overlaps the residual ridge buccolingually, simulating the contours and emergence profile of the missing tooth on both sides of the residual ridge. However, saddle or ridge lap designs should be avoided because the concave gingival surface of the pontic is not accessible to cleaning with dental floss, which leads to plaque accumulation (Fig. 20-13). This design deficiency has been shown to result in tissue inflammation¹ (Fig. 20-14).

Fig. 20-13 A, Cross-section view of ridge lap pontic. B, The tissue surface is inaccessible to cleaning devices.

Fig. 20-14 A and B, Partial fixed dental prosthesis (FDP) with a ridge-lap (concave) gingival surface. C, When it was removed, the tissue was found to be ulcerated. D, The defective FDP was recontoured and used as an interim restoration while the definitive restoration was being fabricated. Within 2 weeks the ulceration had resolved.

Modified Ridge Lap Pontic

The modified ridge lap pontic combines the best features of the hygienic and saddle pontic designs, combining esthetics with easy cleaning. Figures 20-15 and 20-16 demonstrate how the modified ridge lap design overlaps the residual ridge on the facial side (to achieve the appearance of a tooth emerging from the gingiva) but remains clear of the ridge on the lingual side. To enable optimal plaque control, the gingival surface must have no depression or hollow. Rather, it should be as convex as possible from mesial to distal aspects (the greater the convexity, the easier the oral hygiene). Tissue contact should resemble a letter T (Fig. 20-17) whose vertical arm ends at the crest of the ridge. Facial ridge adaptation is essential for a natural appearance. Although this design was historically referred to as ridge-lap,^20,21 the term ridge-lap is now used synonymously with the saddle design. The modified ridge lap design is the most common pontic form used in areas of the mouth that are visible during function (maxillary and mandibular anterior teeth and maxillary premolars and first molars).

Fig. 20-15 Modified ridge lap pontic. A, Partial fixed dental prosthesis (FDP) partially seated. B, FDP seated.

Fig. 20-16 Three-unit partial fixed dental prosthesis replacing the maxillary lateral incisor. A, To facilitate plaque control, the lingual surface is made convex. B, The facial surface is shaped to simulate the missing tooth.

Fig. 20-17 Tissue contact of a maxillary partial fixed dental prosthesis (FDP) should resemble the letter T. This FDP is viewed from the gingival aspect.

Conical Pontic

Often called egg-shaped, bullet-shaped, or heart-shaped, the conical pontic (Fig. 20-18) is easy for the patient to keep clean. It should be made as convex as possible, with only one point of contact at the center of the residual ridge. This design is recommended for the replacement of mandibular posterior teeth, where esthetic appearance is a lesser concern. The facial and lingual contours are dependent on the width of the residual ridge; a knife-edged residual ridge necessitates flatter contours with a narrow tissue contact area. This type of design may be unsuitable for broad residual ridges, because the emergence profile associated with the small tissue contact point may create areas of food entrapment (Fig. 20-19). The sanitary or hygienic pontic is the design of choice in these clinical situations.

Fig. 20-18 A and B, A pontic with maximum convexity and a single point of contact with the tissue surface is the design easiest to keep clean. C, Evaluating the contour of three possible pontic shapes (1, 2, and 3). Contour 3 is the most convex in area B but is too flat in area A. Contour 1 is convex in area A but is too flat in area B. Contour 2 is the best. D, An all-metal partial fixed dental prosthesis with a conical pontic, suitable for replacement of a mandibular molar.

Fig. 20-19 A, Conical pontics may create food entrapment on broad residual ridges (arrow). B, The sanitary pontic form may be a better alternative.

Ovate Pontic

The ovate pontic is the most esthetically appealing pontic design. Its convex tissue surface resides in a soft tissue depression or hollow in the residual ridge, which makes it appear that a tooth is literally emerging from the gingiva (Fig. 20-20). Careful treatment planning is necessary for successful results. Socket-preservation techniques should be performed at the time of extraction to create the tissue recess from which the ovate pontic form will emerge. For a preexisting residual ridge, soft tissue surgical augmentation is typically required. When an adequate volume of ridge tissue is established, a socket depression is sculpted into the ridge with surgical diamonds or electrosurgery. In either case, meticulous attention to the contour of the pontic of the interim restoration is essential when the residual ridge that will receive the definitive prosthesis is conditioned and shaped.

Fig. 20-20 Ovate pontic. A, Partial fixed dental prosthesis (FDP) partially seated. B, FDP seated.

The ovate pontic’s advantages include its pleasing appearance and its strength. When used successfully with ridge augmentation, its emergence from the ridge appears identical to that of a natural tooth. In addition, its recessed form is not susceptible to food impaction. The broad convex geometry is stronger than that of the modified ridge lap pontic, because the unsupported, thin porcelain that often exists at the gingivofacial extent of the pontic is eliminated (Fig. 20-21). Because the tissue surface of the pontic is convex in all dimensions, it is accessible to dental floss; however, meticulous oral hygiene is necessary to prevent tissue inflammation resulting from the large area of tissue contact. Other disadvantages include the need for surgical tissue management and the associated cost. Furthermore, an additional evaluation appointment is typically necessary to achieve an esthetic result. The socket depression, with its pseudopapillae, requires the support of the interim ovate pontic and will collapse when the interim restoration is removed before an impression is made. To compensate for this three-dimensional change in the socket that occurs during the impression, it is necessary to scrape the cast in this area to ensure positive contact and support of the pseudopapillae with the definitive pontic. Because these adjustment are made somewhat arbitrarily, it may also be necessary to make revisions to the tissue surface of the pontic (reshaping or porcelain additions) at the evaluation phase.

Fig. 20-21 The ovate pontic design eliminates the potential for unsupported porcelain in the cervical portion of an anterior pontic.

Ridge Contact

Pressure-free contact between the pontic and the underlying tissues is indicated to prevent ulceration and inflammation of the soft tissues.^1,22 If any blanching of the soft tissues is observed at evaluation, the pressure area should be identified with a disclosing medium (e.g., pressure-indicating paste) and the pontic recontoured until tissue contact is entirely passive. This passive contact should occur exclusively on keratinized attached tissue. When a pontic rests on mucosa, some ulcerations may appear as a result of the normal movement of the mucosa in contact with the pontic (Fig. 20-22). Positive ridge pressure (hyperpressure) may be caused by excessive scraping of the ridge area on the definitive cast (Fig. 20-23). This was once promoted as a way to improve the appearance of the pontic-ridge relationship. However, because of the ulceration that inevitably results when flossing is not meticulously performed, the concept is not recommended^1,23,24 unless followed as previously described for an ovate pontic.^22,25 Although ovate pontics maintain positive tissue contact to support the pseudopapillae, healthy mucosa can be maintained, provided that the contact to the mucosa is tight but noncompressive and the gingival portion of the pontic is regularly cleaned.²⁶

Fig. 20-22 Pressure inevitably leads to ulceration.

Fig. 20-23 Soft tissue blanching at evaluation indicates pressure.

Oral Hygiene Considerations

The chief cause of ridge irritation is the toxins released from microbial plaque, which accumulate between the gingival surface of the pontic and the residual ridge, causing tissue inflammation and calculus formation.

Unlike removable partial dental prostheses, FDPs cannot be taken out of the mouth for daily cleaning. Patients must be taught efficient oral hygiene techniques, with particular emphasis on cleaning the gingival surface of the pontic. The shape of the gingival surface, its relation to the ridge, and the materials used in its fabrication influence ultimate success.

Normally, where tissue contact occurs, the gingival surface of a pontic is inaccessible to the bristles of a toothbrush. Therefore, excellent hygiene habits must be developed by the patient. Devices such as proxy brushes, pipe cleaners, Oral-B Super Floss,^* and dental floss with a threader are highly recommended (Fig. 20-24). Gingival embrasures around the pontic should be wide enough to permit oral hygiene aids. However, to prevent food entrapment, they should not be opened excessively. To enable passage of floss over its entire tissue surface, tissue contact between the residual ridge and pontic must be passive.

Fig. 20-24 The patient must be instructed in how to clean the gingival surface of a pontic with floss.

If the pontic has a depression or concavity in its gingival surface, plaque accumulates, because the floss cannot clean this area, and tissue irritation²⁷ follows. This is usually reversible; when the surface is subsequently modified to eliminate the concavity, inflammation disappears (see Fig. 20-14). Therefore, an accurate description of pontic design should be submitted to the laboratory, and the prosthesis should be checked and corrected if necessary before cementation. Prevention is the best solution for controlling tissue irritation.

Pontic Material

Any material chosen to fabricate the pontic should provide good esthetic results where needed: biocompatibility, rigidity, and strength to withstand occlusal forces; and longevity. FDPs should be made as rigid as possible, because any flexure during mastication or parafunction may cause pressure on the gingiva and cause fractures of the veneering material. Occlusal contacts should not fall on the junction between metal and porcelain during centric or eccentric tooth contacts, nor should a metal-ceramic junction occur in contact with the residual ridge on the gingival surface of the pontic.

Investigations into the biocompatibility of materials used to fabricate pontics have centered on two factors: (1) the effect of the materials and (2) the effects of surface adherence. Glazed porcelain is generally considered the most biocompatible of the available pontic materials,^28-30 and clinical data^23,31 tend to support this opinion, although the crucial factor seems to be the material’s ability to resist plaque accumulation³² (rather than the material itself). Well-polished gold is smoother, less prone to corrosion, and less retentive of plaque than an unpolished or porous casting.³³ However, even highly polished surfaces accumulate plaque if oral hygiene measures are ignored.^34,35

Glazed porcelain looks very smooth, but when viewed under a microscope, its surface shows many voids and is rougher than that of either polished gold or acrylic resin³⁶ (Fig. 20-25). Nevertheless, highly glazed porcelain is easier to clean than other materials. For easier plaque removal and biocompatibility, the tissue surface of the pontic should be made in glazed porcelain. However, ceramic tissue contact may be contraindicated in edentulous areas where there is minimal distance between the residual ridge and the occlusal table. In these instances, placing ceramic on the tissue side of the pontic may weaken the design of the metal substructure, particularly with porcelain occlusal surface (Fig. 20-26). If gold is placed in tissue contact, it should be highly polished. Regardless of the choice of pontic material, patients can prevent inflammation around the pontic with meticulous oral hygiene.³⁷

Fig. 20-25 Scanning electron micrographs of glazed porcelain (A), polished gold (B), and polished acrylic resin (C).

(Microscopy by Dr. J. L. Sandrik.)

Fig. 20-26 Four pontic designs in descending order of strength, based on cross-sectional diameter of the metal substructure. When vertical space is minimal, design 4 (porcelain tissue and occlusal coverage) may be contraindicated.

Occlusal Forces

Reducing the buccolingual width of the pontic by as much as 30% has been suggested^38,39 as a way to lessen occlusal forces on, and thus the loading of, abutment teeth. This practice continues today, although it has little scientific basis. Critical analysis⁴⁰ has revealed that forces are lessened only when food of uniform consistency is chewed and that a mere 12% increase in chewing efficiency can be expected from a one-third reduction of pontic width. Potentially harmful forces are more likely to be encountered if an FDP is loaded by the accidental biting on a hard object or by parafunctional activities such as bruxism, rather than by chewing of foods of uniform consistency. These forces are not reduced by narrowing the occlusal table.

In fact, narrowing the occlusal table may actually impede or even preclude the development of a harmonious and stable occlusal relationship. Like a malposed tooth, it may cause difficulties in plaque control and may not provide proper cheek support. For these reasons, pontics with normal occlusal widths (at least in the occlusal third) are generally recommended. One exception is if the residual alveolar ridge has collapsed buccolingually. Reducing pontic width may then be desired and would thereby lessen the lingual contour and facilitate plaque-control measures.

Available Pontic Materials

Some FDPs are fabricated entirely of metal, porcelain, or acrylic resin, but most consist of 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 (see Chapter 27), 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, is easy to keep clean, and looks natural. However, mechanical failure (Fig. 20-28) can occur and often is attributable to inadequate framework design. The principles of framework design are discussed in Chapter 19, but the following points are emphasized in this chapter:

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 (Fig. 20-29). 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 (Fig. 20-30).

2. The metal surfaces to be veneered must be smooth and free of pits. Surface irregularities cause incomplete wetting by the porcelain slurry, which leads 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 (Fig. 20-31). 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 evaluated carefully.

Fig. 20-28 Failure resulting from improper laboratory technique.

Fig. 20-29 Failure of unsupported gingival porcelain.

Fig. 20-30 A, Waxing to anatomic contour and controlled cut-back are the most reliable approaches to fabricating a satisfactory metal substructure (B).

Fig. 20-31 Failure caused by occlusal contact across the metal-ceramic junction.

Resin-veneered pontics

Historically, acrylic resin-veneered restorations had deficiencies that made them acceptable only as longer term interim restorations. Their resistance to abrasion was lower than that of enamel or porcelain, and noticeable wear occurred with normal toothbrushing (Fig. 20-32). 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 (i.e., undercuts). Continuous dimensional change of the veneers often caused leakage at the metal-resin interface, with subsequent discoloration of the restoration.

Fig. 20-32 Wear of an acrylic resin-veneered prosthesis.

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. Indirect composite resin systems introduced since the 1990s 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 do traditional direct and indirect composite resins. Most are subjected to a post-curing process that results in high flexural strength, minimal polymerization shrinkage, and wear rates comparable with those of tooth enamel.⁴¹ In addition, improvements in the bond between the composite resin and metal⁴² may lead to a reappraisal of resin veneers.

The Gingival Interface

An esthetically successful pontic replicates 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 incisogingivally (Fig. 20-33). To achieve the illusion of a natural tooth, an esthetic pontic must deceive observers into believing they are seeing a natural tooth.

Fig. 20-33 Correct incisogingival height is critical to esthetic pontic design. A, Esthetic failure of a four-unit partial fixed dental prosthesis (FDP) replacing the right central and lateral incisors. The pontics have been shaped to follow the facial contour of the missing teeth, but because of bone loss they look too long. B, The replacement FDP. Note that the gingival half of each pontic has been reduced. Esthetic appearance is much improved. C, This esthetic failure is the result of excessive reduction. The central incisor pontics look too short.

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 structure 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, which results in an unnatural appearance. This can be avoided with careful preparation at the diagnostic waxing stage (see Chapter 3). Sometimes the ridge tissue must be surgically reshaped to enhance the result.

In normal situations, light falls from above, and an object’s shadow is below it. Unexpected lighting or unexpectedly placed shadows (Fig. 20-34) 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 in studying where shadows fall around natural teeth, particularly around the gingival margin. If a pontic is poorly adapted to the residual ridge, there is an unnatural shadow in the cervical area that looks odd and spoils the illusion of a natural tooth (Fig. 20-35). In addition, recesses at the gingival interface collect food debris, further betraying the illusion of a natural tooth.

Fig. 20-34 Optical illusion. A and B are identical except that one image is upside down. Most people make different three-dimensional interpretations of each photograph, interpreting one as a negative impression and the other as a positive cast. (Verify the illusion by turning the book.) The interpretation is based on how shadows fall; in normal situations, objects are seen illuminated from above.

Fig. 20-35 A pontic should be interpreted as “growing” out of the gingival tissue. The second premolar pontic in the four-unit partial fixed dental prosthesis (A) is successful because it is well adapted to the ridge; however, the pontic for the first premolar is evident because of its poor adaptation to the ridge, which creates a shadow. B, Shadows around the gingival surface (arrow) spoil the esthetic illusion.

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 that of a natural tooth. Because it emerges from a soft tissue recess, this pontic is not susceptible to many of the esthetic pitfalls applicable to 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 makes such a pontic look too long in the cervical region. The height of a tooth is immediately obvious when the patient smiles and shows the gingival margin (Fig. 20-36). 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 (see Fig. 20-36). The observer sees a normal tooth length but is unaware of the abnormal labial contour. The illusion is successful.

Fig. 20-36 A, A pontic should have the same incisogingival height (H) as the original tooth. B, Correctly contoured pontic. C, Incorrectly contoured pontic. (The dotted lines in B and C show the original tooth contour.) The shelf at the gingival margin may trap food and create an esthetically unacceptable shadow.

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 cementoenamel junction. The root can be stained to simulate exposed dentin (Fig. 20-37). Another approach is to use pink porcelain to simulate the gingival tissues (Fig. 20-38). 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 a partial removable dental prosthesis is often better than with an FDP.

Fig. 20-37 It is difficult without surgical augmentation to fabricate an esthetic fixed prosthesis for a patient with extensive alveolar bone loss. A to D, One approach is to contour the crowns normally and shape and stain the apical extension to simulate exposed root surface.

(A and B, Redrawn from Blancheri RL: Optical illusions and cosmetic grinding. Rev Asoc Dent Mex 8:103, 1950.)

Fig. 20-38 Partial fixed dental prosthesis replacing maxillary left central and lateral incisors. This patient had lost significant bone from the edentulous ridge. A and B, Appearance of the prosthesis was enhanced with the use of pink porcelain between the pontics to simulate gingival tissue. The patient has been able to maintain excellent tissue health through the daily use of Oral-B Super Floss.

Mesiodistal Width

Frequently, the space available for a pontic is greater or smaller than the width of the contralateral tooth. This is usually because of 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 (Fig. 20-39), 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 (Fig. 20-40) 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 helps solve a challenging restorative problem.)

Fig. 20-39 Optical illusions. A, The authors are the same size. B, The lines are straight. (Tilt the book to verify this.) C, Kitaoka’s “Rotating Snake” Illusion. Look at this one close up. Rotation of the “wheels” occurs in relation to eye movements. On steady fixation the effect vanishes.⁴⁴

(A, Modified from Shepard RN: MindSights. New York, WH Freeman, 1990; C, © Akiyoshi Kitaoka 2003, reproduced by permission.)

Fig. 20-40 An abnormally sized anterior pontic space can be restored esthetically by matching the location of the line angles and adjusting the interproximal areas. Large (A) and small (B) pontic spaces. Dimension a should be matched in the replacement.

(Redrawn from Blancheri RL: Optical illusions and cosmetic grinding. Rev Asoc Dent Mex 8:103, 1950.)

Space discrepancy presents less of a problem when posterior teeth are being replaced (Fig. 20-41) 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.

Fig. 20-41 When replacing a posterior tooth (A), duplicate the dimension of the more visible mesial half of the adjacent tooth. Narrow (B) and wide (C) pontic spaces.

(Redrawn from Blancheri RL: Optical illusions and cosmetic grinding. Rev Asoc Dent Mex 8:103, 1950.)

Available Materials

Over time, several techniques for pontic fabrication have 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. Table 20-3 summarizes the various techniques (Fig. 20-42).

Table 20-3 AVAILABLE PONTIC SYSTEMS

Fig. 20-42 A, Eight-unit partial fixed dental prosthesis (FDP) with porcelain facings. B and C, This three-unit posterior FDP has been fabricated by post-ceramic soldering of a metal-ceramic facing to conventional gold. D, Metal-ceramic FDP with a modified ridge lap pontic (canine) that appears to emerge from the gingiva.

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 are emphasized in the ensuing paragraphs.

Metal-Ceramic Pontics

A well-designed metal-ceramic pontic allows for easy plaque removal, strength, wear resistance, and good esthetics (see Fig. 20-42D). 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 then cast in one piece. This facilitates pontic manipulation during the successive laboratory and clinical phases. In the following discussion, it is assumed that either one or both of the retainers are metal-ceramic complete crowns. When this is not the case, an alternative approach is necessary.

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 enables an assessment of connector design adequacy and the relationship between the connectors and the proposed configuration of the ceramic veneer (see Chapter 28).

Armamentarium (Fig. 20-43)

• 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

Fig. 20-43 Waxing armamentarium.

Step-by-step procedure

1. Wax the internal, proximal, and axial surfaces of the retainers as described in Chapter 18.

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 made of the diagnostic waxing or interim restoration. Molten wax can then be poured into this to form the initial pontic shape. Prefabricated pontic shapes are also available as a starting point (Fig. 20-44).

3. If a posterior tooth is being replaced, leave the occlusal surface flat, because the occlusion is best developed with the wax addition technique outlined in Chapter 18.

4. Lute the pontic to the retainers and, for additional stability, connect its cervical aspect directly to the definitive cast with sticky wax. Then wax the pontic to proper axial and occlusal (or incisal) contour (Fig. 20-45).

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.

Fig. 20-44 Prefabricated wax pontics.

Fig. 20-45 Luting the pontic to the retainers.

Evaluation

The form of the wax pattern is evaluated (Fig. 20-46), 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 that it does not separate from the retainers during the subsequent cut-back procedure.

Fig. 20-46 Anatomic contour wax patterns.

Cut-back

Armamentarium

• 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 (Fig. 20-47A). The porcelain-metal junction must be placed sufficiently lingually to ensure good esthetics.

2. Make depth cuts or grooves in the wax pattern (see Chapter 19 and Fig. 20-47B).

3. Complete the cut-back as far as access allows, with the units connected and on the definitive cast.

4. Section one wax connector with a thin ribbon saw (sewing thread is a suitable alternative), and remove the isolated retainer from the definitive cast (Fig. 20-47C).

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 improved 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 in the manner described in Chapter 22.

When one connector of a three-unit FDP 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 helps stabilize the pontic. Access is difficult, and it is easy to break the fragile wax connector.

Fig. 20-47 Cut-back procedure for a three-unit anterior partial fixed dental prosthesis. A, Delineating the porcelain-metal junction. B, Wax patterns cut back for porcelain application. C, A ribbon saw is used to section the 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 μm aluminum oxide)

Step-by-step procedure

1. Recover the castings from the investment and prepare the surfaces to be veneered as described in Chapter 19 (Fig. 20-48).

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

Fig. 20-48 Metal substructure ready for airborne particle abrasion and oxidation.

Evaluation

Less than 1 mm of porcelain thickness is needed on the gingival surface, because once it is cemented, the restoration is seen from the facial rather than from the gingival side. Excessive gingival porcelain is a common fault in pontic framework design and may lead to fracture and poor appearance (see Fig. 20-29).

To facilitate plaque control, the metal-ceramic junction should be located lingually. Then tissue contact is on the porcelain and not on metal, which retains plaque more tenaciously.⁴³

Porcelain application

Many of the steps for porcelain application are identical to those in individual crown fabrication (see Chapter 24). There are some features peculiar to pontic fabrication, however, and these are emphasized.

Armamentarium (Fig. 20-49)

• 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

Fig. 20-49 Armamentarium for porcelain application.

Step-by-step procedure

1. Prepare the metal and apply opaque as described in Chapter 24 (Fig. 20-50).

2. Apply cervical porcelain to the gingival surface of the pontic, and seat the castings on the definitive cast. A small piece of tissue paper adapted to the residual ridge on the cast by moistening with a brush prevents 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 (as described in Chapter 24) with the appropriate distribution of cervical, body, and incisal shades. The tissue paper acts as a matrix for the gingival surface of the pontic.

4. When the porcelain has been condensed, section between the units with a thin razor blade. This prevents the porcelain from pulling away from the framework as a result of firing shrinkage. A second application of porcelain is needed to correct any deficiencies 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 (see Chapter 24).

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, character-ization, glazing, finishing, and polishing (see Chapter 28, Chapter 29 and Chapter 30).

Fig. 20-50 Porcelain application. A, Substructure ready for opaquing. B, Opaque application. C, Body porcelain application. D, The porcelain after the first firing.

Evaluation

The porcelain on the tissue surface of the pontic should be as smooth as possible (Fig. 20-51). Pits and defects 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).

Fig. 20-51 Metal-ceramic pontic replacing a lateral incisor.

All-Metal Pontics

Pontics made from metal (Fig. 20-52) require fewer laboratory steps and are therefore sometimes used for posterior FDPs. 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 retains plaque and tarnishes and corrodes rapidly.

Fig. 20-52 All-metal partial fixed dental prostheses.