Fixed Dental Prostheses for Anterior and Posterior Teeth
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Irena Sailer, prof dr med dent
Fixed dental prostheses (FDPs) were traditionally constructed as a metallic framework veneered with a tooth-colored ceramic. In recent years, heightened esthetic expectations of both clinicians and patients have created the demand for prostheses fully constructed from ceramics. The first all-ceramic fixed partial dentures exhibited promising outcomes in anterior regions. However, in the posterior region all-ceramic prostheses suffered from high fracture rates within a few years of clinical service.1 It became obvious that the ceramics used at that time, more specifically glass-ceramics and glassinfiltrated ceramics, did not exhibit sufficient strength for this kind of application. The replacement of posterior teeth by means of ceramic FDPs was not recommended until the development of the high-strength ceramic zirconia.2 Today the replacement of both anterior and posterior teeth can be accomplished successfully with different types of zirconia-based reconstructions as long as the material-specific requirements of zirconia are fulfilled. Zirconia has excellent material properties (strength and toughness) that exceed the properties of other types of ceramics. Still, it is a brittle material, as are most ceramics, and must be handled with care and attention to detail. The success of the zirconia-based FDPs is highly dependent on selection of appropriate clinical indications and careful attention to the clinical and technical procedures best suited for this material. If these factors are considered and the user has knowledge of the physical properties of this material, both resin-bonded and conventional FDPs with zirconia frameworks can be considered a very good treatment option in a variety of clinical situations.
Cantilevered All-Ceramic Resin-Bonded FDPs Resin-bonded FDPs are a minimally invasive treatment option for the replacement of single teeth. Originally, resin-bonded prostheses were developed for the replacement or splinting of periodontally compromised anterior teeth.3 Subsequently, application of this type of restoration was extended to the premolar and molar regions.4
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Fixed Dental Prostheses for Anterior and Posterior Teeth
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The first kind of resin-bonded FDP was constructed utilizing metal-ceramic technology. Unfortunately, debonding of these FDPs occurred frequently; this type of restoration, therefore, was solely considered to be an interim restoration for short to medium terms of clinical service times, usually up to 2 years. During the last 40 years, significant modifications of the materials and the design have improved outcomes, resulting in increased use of the resin-bonded prosthesis as a medium- to long-term treatment alternative. New resin cements with improved bonding capacity to various types of materials have reduced the debonding rates. In addition, the development of a minimally invasive preparation design encompassing an increase in surface area for the bonding and vertical grooves for retention has led to significant improvement in the survival and success rates of resin-bonded prostheses.5 Most interestingly, the use of ceramics instead of metal as framework material has greatly improved the clinical outcomes of resin-bonded prostheses. Long-term studies of all-ceramic resin-bonded FDPs have demonstrated very good outcomes with low or no incidence of debonding.6 The ceramic frameworks, in addition, have dramatically improved the esthetic outcomes of the prostheses (Fig 7-1). 120
b Fig 7-1 (a) Metal-based framework for a resin-bonded FDP. Note the grayish discoloration of the mesial part of the abutment tooth and the small dimensions of the retainer (thickness of 0.5 mm) and the connector (cross section of 6.0 mm2). (b) Glass-ceramic resin-bonded FDP framework (Empress I, Ivoclar Vivadent). No discoloration of the abutment tooth occurs. Note the pronounced framework dimensions needed in the connector area (cross section of 16.0 mm2). The minimum retainer thickness for this kind of FDP is 0.8 mm. (c) Zirconia resinbonded FDPs combine the best of both types of resinbonded FDP shown in a and b; they share the toothlike color of glass-ceramic frameworks and the minimal dimensions of retainers (thickness of 0.5 mm) and connectors (cross section of 6.0 mm2) in metal-ceramic frameworks.
Because of these improvements, all-ceramic resin-bonded FDPs may be considered a permanent solution in a number of different clinical situations today. Several factors influence the choice among single-tooth implants, conventional fixed partial dentures, and all-ceramic resin-bonded FDPs for the replacement of single missing teeth: • Age and general medical health of the patient • Health of the teeth adjacent to the edentulous area (presence or absence of restorations, caries, etc) • Position of the teeth adjacent to the edentulous area (straight or tilted, convergent or divergent roots) • Anatomical situation of the edentulous ridge (presence or absence of supporting bone and soft tissues, ridge defects) • Compliance of the patient • Patient’s interest in surgical procedures and financial situation Clinical success rates for all-ceramic resin-bonded FDPs can be expected to be similar to those for other treatment options, provided that the clinical situation and site are indicated for this type of reconstruction.
Cantilevered All-Ceramic Resin-Bonded FDPs
Clinical indications General indications, advantages, and limitations Resin-bonded prostheses are mostly indicated for patients in the following categories: • Adolescents and young adults with congenitally missing teeth or teeth lost to trauma, which cannot be replaced with single implants due to the age of the patient • Patients with narrow single-tooth edentulous spaces not suitable for the placement of implants • Patients with a missing single tooth and healthy adjacent teeth who are not willing to undergo implant surgery • Patients with medical contraindications to implant surgery To select the best restoration for any given clinical situation, the advantages and disadvantages of the various treatment options need to be considered. The main advantage of the resin-bonded FDP is the minimal invasiveness. Significantly less tooth structure is removed for a resin-bonded prosthesis than for other types of tooth-borne restorations.7 Another important advantage of the resin-bonded FDP is the low patient morbidity associated with the clinical treatment, most specifically compared to implants. Finally, the treatment time is shorter and the costs are lower for resin-bonded prostheses than for conventional fixed partial dentures or implants.8 This specific advantage is increasingly important for patients today. However, the resin-bonded FDP has some limitations that have to be considered. The literature indicates that the survival rates of metal-ceramic resin-bonded FDPs are lower than those of single-tooth implants or conventional FDPs. Systematic reviews of the literature estimated that resin-bonded prostheses have a 5-year survival rate of only 87.7%,9 whereas the corresponding survival rates of singleimplant crowns and conventional FDPs were much higher, 97.2%10 and 94.4%,11 respectively. However, these low survival rates seem only to be valid for the traditional metalceramic resin-bonded FDPs. The outcomes of all-ceramic resin-bonded prostheses are considerably better.6 As an example, cantilevered resinbonded FDPs made out of glass-infiltrated alumina exhibited a survival rate of 94.4% after 10 years.6 This specific ceramic is not in routine use any more due to the development of improved ceramics such as zirconia. Cantilevered zirconia resin-bonded FDPs performed even better than the ones constructed with glass-infiltrated alumina. Excellent results for the zirconia resin-bonded FDPs
were recently published, showing a survival rate of 100% at 3 and 4 years of service.12,13 Although these first reports are very positive, more clinical data are needed to support the findings.
Specific indications: Anterior region Another factor to be considered in the choice between different treatment options is the region of the jaw in which a tooth needs to be replaced. Replacement of incisors. All-ceramic resin-bonded pros theses are mainly indicated in anterior regions for the replacement of maxillary and mandibular incisors. In these regions the forces occurring during function are rather low. The maximal loading forces reported for incisor regions range between 108 and 382 N.14,15 For reconstructions in these regions, ceramics with a fracture resistance exceeding the maximal load are needed. The fracture resistance of leucite-reinforced glass-ceramic reconstructions (eg, Empress 1, Ivoclar Vivadent) ranges from 160 to 330 N, while the fracture resistance of lithium disilicate–reinforced glass-ceramic (eg, Empress 2, Ivoclar Vivadent) ranges from 260 to 280 N.16 Reconstructions made of a lithium disilicate glass-ceramic (ie, e.max Press and e.max CAD, Ivoclar Vivadent) exhibit a fracture resistance of 907 to 986 N.17 The fracture resistance of zirconiabased reconstructions can reach 1,620 N.18 Furthermore, laboratory studies of cantilevered resin-bonded prostheses made of glass-infiltrated alumina or zirconia showed fracture resistance values ranging from 270 to 290 N.19,20 With respect to stability, all of the types of ceramics discussed so far are appropriate for anterior resin-bonded FDPs. For weaker types of ceramics, such as glass-ceramics, the desired stability of the reconstruction has to be provided by increasing the framework thickness in the retainer and connector areas. This increase in thickness may cause overcontouring and, as a consequence, esthetic and hygienic issues. Zirconia framework dimensions (retainer and connector) can be designed more similarly to the dimensions of metallic frameworks.21 The choice of the ceramic for an anterior resin-bonded FDP is based on the following factors: • Amount of vertical and horizontal interocclusal space in the abutment tooth and pontic regions • Minimally required dimensions for the framework and the connector for the different types of ceramics • Color and shade of the teeth adjacent to the area to be restored
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Fixed Dental Prostheses for Anterior and Posterior Teeth
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Fig 7-2 (a) Palatal view of a canine in a model. The red area indicates the region of the central occlusal contact and the region loaded during canine guidance; the blue area indicates the region below the load during occlusion and function, the area that is useful for the retention of the prosthesis. (b) Contact point in centric occlusion. In this area adequate space for the retainer and connector of the prosthesis must be provided by preparation design. (c) A minimum of 0.5 mm of preparation is recommended in the region of the centric occlusion contact area, if frameworks have to be extended to that area. (d) Fracture of a zirconia ceramic resin-bonded prosthesis. This occurred because there was insufficient space for the framework in the region of the centric occlusion contact point, leading to the need for adjustments and thereby weakening of the zirconia framework.
Replacement of canines. In contrast to the incisor area, the replacement of canines with all-ceramic resin-bonded prostheses may be critical because of the type of load that occurs during function in the canine regions. During the occlusal and lateral movements of the jaws, high tensile load is transmitted to the retainer and/or the connector area of the resin-bonded FDP.19,22 This may increase the risk for fracture or debonding of the resin-bonded FDP during canine guidance (Fig 7-2). Consequently, the dimensions of the retainer and connector have to be increased in the canine region, and sufficient space has to be provided by a more invasive abutment tooth preparation. If there is a lack of space and/or enamel, a metal-ceramic resin-bonded prosthesis should be preferred. 122
Site-specific requirements. In general, the clinical success of the all-ceramic resin-bonded FDPs is highly dependent on careful selection of the appropriate patient and site. Anterior resin-bonded FDPs have the following sitespecific clinical prerequisites: • Overjet greater than 0.5 to 1.0 mm to allow sufficient space for a retainer • Overbite less than 1.0 to 1.5 mm to provide sufficient area for the bonding • Centric occlusal contacts located in incisal third, to leave sufficient area for the retainer The choice of the most appropriate abutment tooth for the anterior resin-bonded prosthesis is based on the pala-
Cantilevered All-Ceramic Resin-Bonded FDPs
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Fig 7-3 (a) The palatal surface of the central incisors is rather flat. (b) The palatal surface of the canine is rounded. Canines, therefore, allow for better retention of the framework because of the wraparound shape of the palatal surface.
Fig 7-4 Posterior metal-ceramic resin-bonded prosthesis. Note the visibility of the gray metal framework.
tal or lingual space offered in centric occlusion and on the shape and size of the palatal or lingual surface (Fig 7-3). Two factors have to be evaluated in order to choose the most appropriate abutment tooth: • Size of the palatal or lingual surface area that can be used for the bonding • Shape of the palatal or lingual surface—ideally oval or round to allow a wraparound design of the retainer (see Fig 7-3b) For example, for the replacement of a lateral incisor, a canine may be more suitable as abutment tooth than a central incisor. The flat palatal surfaces of central incisors may compromise the minimally invasive abutment tooth preparation design (see the section, “Clinical procedures”) and may complicate the positioning of the FDP during the cementation (see Fig 7-3a).
Specific indications: Posterior region Because of the high load occurring in posterior regions, posterior metal-ceramic resin-bonded FDPs were used exclusively until recently23 (Fig 7-4). Metal frameworks provide a high level of stability; however, their gray color may result
in esthetic compromises in posterior regions (see Fig 7-4). Furthermore, the difficulties associated with the bonding of metal to the tooth have a negative impact on posterior resin-bonded prostheses. The debonding rates of posterior resin-bonded FDPs (22.8%) have been shown to be higher than those of anterior prostheses (18.4%).9 In general, the published outcomes of posterior metalceramic resin-bonded FDPs are controversial. While some studies report posterior resin-bonded FDPs to have low rates of complications,24–26 others show the contrary.23,27 Altogether a meta-analysis of the published data indicated that more problems were associated with posterior than anterior metal-ceramic resin-bonded FDPs.9 This type of restoration was and still is only recommended as a longterm provisional solution. To date, very little information is available on the clinical outcomes of posterior all-ceramic resin-bonded FDPs. A recent retrospective study of cantilevered resin-bonded prostheses of lithium disilicate glass-ceramic showed very promising outcomes in the posterior region and a 5-year survival rate of 100%.28 Fractures did not occur in this investigation. Furthermore, no debonding of the posterior glassceramic resin-bonded FDPs occurred in this study. Still, a number of open questions have to be answered before this type of reconstruction can be recommended as 123
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Fixed Dental Prostheses for Anterior and Posterior Teeth Fig 7-5  (a and b) Possible design of a glass-ceramic resin-bonded prosthesis, including a mesial inlay to restore the tooth defect.
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Fig 7-6 (a) Design of a zirconia ceramic resin-bonded prosthesis fabricated according to the techniques developed for metalceramic resin-bonded FDPs. (b) Fracture and debonding have occurred 9 months after placement of the FDP. This type of prosthesis, therefore, cannot be recommended.
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a long-term solution. One question is whether or not all-ceramic resin-bonded FDPs provide sufficient stability for use in posterior regions for longer periods of time. The mean occlusal force at posterior teeth was found to be approximately 400 N.29 Considering the aforementioned fracture resistance values of the different types of ceramics, it seems that both lithium disilicate glass-ceramics and zirconia ceramics might be indicated as framework materials (Figs 7-5 and 7-6). Still, long-term data for this type of restoration are very limited. Randomized clinical studies are needed to test whether or not posterior all-ceramic resin-bonded FDPs 124
can be recommended as a long-term, predictable solution in the future. Furthermore, the most suitable ceramic and the ideal design for posterior resin-bonded prostheses need to be elucidated.
Relative contraindications Resin-bonded FDPs can be problematic because of lack of space or malpositioning of the abutment teeth in patients with deep bite or a crowded dentition. In these situations, orthodontic pretreatment should be performed to provide the conditions required for resin-bonded FDPs (see Fig 7-16).
Cantilevered All-Ceramic Resin-Bonded FDPs
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Fig 7-7 (a) Two-retainer metal-ceramic resin-bonded prosthesis replacing the maxillary right central incisor, shown at the 10-year recall visit. The patient had observed a recently increasing discoloration of the maxillary left lateral incisor. The loosening of the retainer on the right lateral incisor, however, was not noticed at the recall visit. (b) Brownish discoloration of the abutment tooth, indicating the presence of secondary caries beneath the retainer. (c) Radiograph showing secondary caries in the marginal areas of the metallic retainer.
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Other relative contraindications to all-ceramic resinbonded FDPs are parafunctional habits and bruxism. Affected patients need to be informed about the increased risk for fracture or debonding of the all-ceramic resin-bonded prostheses. Finally, if the esthetics of the abutment tooth are poor (ie, it is discolored or has an unesthetic shape or size) a complete crown with a cantilever may be a better treatment option than a resin-bonded prosthesis because the complete-coverage design can positively influence the esthetics of the abutment tooth.
Absolute contraindications The following clinical situations represent absolute contraindications to all-ceramic resin-bonded prostheses: • Absence of more than one tooth (multiple pontics) • Enamel deficiency (eg, amelogenesis imperfecta) • All other types of enamel defects (eg, severe erosions or abrasions) • Caries or extensive restorations on abutment teeth
Design of the FDP: Multiple versus single retainer The FDPs designed for the first patients treated with allceramic resin-bonded prostheses had two or more abutment teeth. This design was recommended to increase the bonding area and the geometric retention. Today, though, it has been well documented that the outcomes of singleretainer, cantilevered resin-bonded prostheses are significantly better than those of prostheses with two or more retainers.30 The major problem with the multiple-retainer prostheses is that unnoticed loosening of one retainer may occur, leading to high risk for secondary caries beneath the loose retainer (Fig 7-7). The most likely cause of this problem is the differing periodontal mobility of the abutment teeth that are splinted by the prosthesis. As the splinted teeth move in different directions, shear tensile strain occurs in the areas of the retainer and connector. In the case of metal frameworks, the most vulnerable area is the bonding interface between the framework and the tooth. As a consequence, debonding is the most likely problem to occur. Multiple125
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Fixed Dental Prostheses for Anterior and Posterior Teeth retainer resin-bonded prostheses showed higher rates for debonding and lower survival rates than cantilevered metal-ceramic resin-bonded FDPs.30 In all-ceramic resin-bonded prostheses, the most vulnerable area is the connector area. Under tensile load occurring during the differing movement of the splinted abutment teeth, tensile stress cumulates in the connectors, inducing an increase in risk for fracture of one of the connectors. In clinical investigations, multiple-retainer anterior all-ceramic resin-bonded FDPs suffered from fractures of one the connectors, whereas cantilevered resin-bonded FDPs exhibited no fractures and had a very high 10-year survival rate of 94.4%.6 Hence, the number of retainers has a significant effect on the outcomes of all-ceramic resin-bonded FDPs. The change in design from two or more retainers to cantilevered might also be reason for the lower complication rates reported for posterior resin-bonded prostheses in more recent studies.24–26 Furthermore, no fractures were reported for cantilevered posterior all-ceramic resinbonded FDPs.28 Thus, metal-ceramic and all-ceramic resin-bonded FDPs should be designed as one-retainer, cantilevered prostheses.
• No or low risk for discoloration of the abutment teeth by the retainer • Highly esthetic outcomes
Choice of materials
Advantages of glass-ceramic • A large number of different shades are available. • Color selection is relatively easy. • Procedures for the adhesive cementation are well established in daily clinical practice.
All-ceramic versus metal-ceramic resin-bonded FDPs Ceramic frameworks for FDPs have several advantages over metal frameworks. Metal-ceramic resin-bonded FDPs offer excellent material stability; however, a number of problems have been associated with the metal. Most important, the retention of the metal-ceramic resin-bonded retainer to the tooth continues to be a clinical problem. A number of techniques for chemical or morphologic improvement of the bonding were introduced, such as the use of nonprecious alloys, chemical etching, or silica coating.5 Despite these improvements, debonding rates remain a real clinical problem. Furthermore, in the anterior region, the esthetics of metal-ceramic resin-bonded prostheses is problematic because of the possible display or shadowing of the metallic retainers on the abutment teeth. Finally, ceramics are biologically advantageous over metals because the metals used for the resin-bonded FDPs most frequently are nonprecious alloys.31,32 Ceramics offer the following advantages over metals as a choice of framework material: • Higher biocompatibility • Lower corrosion rates • Lower allergenic potential 126
Metal-ceramic resin-bonded FDPs are indicated in situations where the FDP will be subjected to a very high load or there is very little interocclusal space for the retainer. In all other situations, all-ceramic resin-bonded FDPs should be preferred.
Clinical criteria for choice of ceramic Different types of ceramics have been used for the fabrication of resin-bonded prostheses, including reinforced glassceramics, glass-infiltrated alumina, and densely sintered zirconia.6,28 The choice of the ideal ceramic for the individual patient is mainly based on the space available for the retainer and the connector and the color of the adjacent teeth. The literature indicates that all previously mentioned types of ceramics may be used with good success; hence, the choice of the ceramic can be based on factors other than just the material stability.
Disadvantage of glass-ceramic • Larger dimensions of the framework are needed for clinical stability. Advantages of zirconia • Material stability is very high. • Framework dimensions are similar to those of metallic frameworks. • Different framework shades are available. Disadvantages of zirconia • Adhesive cementation may be more difficult; specific resin cements are needed.33 • Fabrication procedures are costly; computer-aided design/ computer-assisted manufacture (CAD/CAM) technology is needed.
Technical criteria for choice of ceramic As mentioned previously, the relevant dental technical criteria for the choice of the material for the resin-bonded FDP are the color and translucency of the teeth and the space available for the retainer and the connector. Other impor-
Cantilevered All-Ceramic Resin-Bonded FDPs Fig 7-8 (a) Clinical situation of a patient with very translucent, slightly chromatic teeth. Glass-ceramic resin-bonded FDPs may be used for the replacement of the right and left lateral incisors. (b) Glass-ceramic resin-bonded FDPs (e.max Press, Ivoclar Vivadent). Note the pronounced thickness in the retainer and connector areas.
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Fig 7-9 (a) Clinical situation in a patient with bright and rather opaque teeth. A zirconia ceramic resin-bonded prosthesis is indicated for the replacement of the maxillary right central incisor. (b) The zirconia framework can be fabricated with thinner dimensions in the retainer and connector areas.
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tant factors in the choice are the access to fabrication technology (eg, CAD/CAM) and the personal experience of the dental laboratory technician. In general,
• Zirconia ceramic resin-bonded FDPs are superior to glassceramics for patients with limited interocclusal space and with opaque bright teeth (Fig 7-9).
• Glass-ceramic resin-bonded FDPs are indicated for patients with large vertical and horizontal space and translucent and/or chromatic teeth (Fig 7-8).
One important technical requirement for zirconia ceramic resin-bonded prostheses is the adequate preparation of the abutment tooth to fulfill the demands of the CAD/CAM fabrication of the frameworks. 127
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Fixed Dental Prostheses for Anterior and Posterior Teeth
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Fig 7-10 (a) Analysis of horizontal space in centric occlusion. A minimum of 0.5 mm is required for zirconia. (b) Analysis of vertical space in centric occlusion. A minimum of 3.0 mm is required for zirconia.
Clinical procedures Analysis of the clinical situation and diagnostics Meticulous treatment planning encompasses the choice of the appropriate patient and indication with respect to the load, the amount of space for the FDP retainer/connector (Fig 7-10), and the choice of the most appropriate abutment tooth with respect to the area available for the bonding.
Conditioning of the pontic site For the conditioning of the soft tissues of the pontic site, flowable composite resin can be applied to the provisional prosthesis. The composite resin is applied primarily to the palatal/lingual part of the provisional tooth, leaving space in the labial and interproximal regions for optimal soft tissue shaping. After the application of the resin, the removable provisional prosthesis is placed back in the mouth. Slight blanching of the surrounding tissues is expected with the application of localized pressure. After 1 to 2 weeks, additional resin should be applied for further conditioning to achieve the desired gingival form in the pontic site (Fig 7-11).
Abutment tooth preparation The goal of treatment with a resin-bonded prosthesis is to be as minimally invasive as possible. However, clinical experience clearly shows that a minimal retentive preparation of the abutment tooth is advantageous for long-term success.23,34 Various types of preparations have been suggested over the years with the aim to provide a path of insertion and a geometric resistance form of the resin-bonded FDP abutment tooth. Most of the preparation designs encompassed vertical grooves, boxes, or slots, occlusal rests, and reduction of
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the palatal or lingual surfaces to provide a path of insertion.5 With the introduction of all-ceramic resin-bonded prostheses, a completely new design for the preparation was presented.34 This design included a proximal veneer preparation, which was adapted to the needs of the glassinfiltrated ceramics. More recently, a minimally invasive preparation adapted to the properties of zirconia and its CAD/CAM fabrication procedures was introduced.14 The minimally invasive preparation design for anterior zirconia-based resin-bonded FDPs includes preparation of a mesial and a distal vertical groove plus a tiny slot at the palatal or lingual cingulum region (Fig 7-12). Proximal grooves provide mechanical resistance of the framework to dislodgment, reducing the stress at the cement-substrate interface when under functional load. Clinical studies have shown that the clinical incidence of debonding was reduced when resin-bonded FDPs included abutment tooth preparation.35 Unfortunately, there is still no agreement on the preparation design for posterior zirconia-based all-ceramic resin-bonded FDPs. As mentioned earlier, the posterior all-ceramic resin-bonded FDP as such is still considered experimental. A significant clinical benefit of the minimally invasive preparation with grooves and ball-shaped rest is the simplification of adhesive cementation. With the defined path of insertion, the FDP can securely be positioned during cementation. For long-term provisional resin-bonded pros theses involving no preparation of the abutment tooth, hooks made of resin or metal can be used as an aid for the positioning of the prosthesis during cementation (Fig 7-13). To summarize, a minimally invasive retentive preparation is recommended for resin-bonded FDPs that are planned as a definitive treatment option. Pretreatment diagnostic planning should encompass use of the study casts for thorough planning of the least invasive yet most retentive tooth preparation for each patient’s situation.
Cantilevered All-Ceramic Resin-Bonded FDPs
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Fig 7-11  (a) Clinical site for resin-bonded prosthesis to replace the maxillary lateral incisor, prior to the conditioning of the pontic area. (b and c) For conditioning the pontic, flowable composite resin is applied to the provisional prosthesis, primarily to the gingival part of the provisional tooth. Adequate space is left in the labial and interproximal regions for optimal soft tissue health. (d) Removable provisional prosthesis in place, after the application of the resin. The slight blanching of the surrounding tissues indicates the application of localized pressure. (e) Incisal view of the preparation and the shaped pontic area prior to the impression. Conditioning has been achieved within two visits over 3 weeks. (f ) Virtual model of the prosthesis area (Cadent iTero, Align Technology). The shape of the pontic area enables the ideal virtual design of the framework.
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Fig 7-12  (a and b) Demarcation of mesial and distal grooves by means of a separating diamond bur (Universal Prep Set, diamond D3, Intensiv) within the enamel. The mesial groove is located slightly behind the proximal contact zone and is defining the path of insertion. (c and d) Finalization of the mesial and distal grooves in enamel with a veneer prep diamond (Universal Prep Set, diamond D 18 GS), ensuring the appropriate size and taper for CAD/CAM zirconia frameworks. (e) Preparation of the ball-shaped rest in the area of the cingulum with a round diamond bur (Universal Prep Set). (f ) Digital impression of the finalized preparation for the design of the CAD/CAM zirconia framework. (g) Zirconia ceramic resin-bonded prosthesis displaying the grooves and the ball-shaped rest.
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Cantilevered All-Ceramic Resin-Bonded FDPs
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d Fig 7-13  (a and b) Composite resin retainer for the positioning of the no-preparation resin-bonded prosthesis. (c and d) Metallic retainers for the positioning of the no-preparation resin-bonded prosthesis.
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Fixed Dental Prostheses for Anterior and Posterior Teeth
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e Fig 7-14  (a) The digital impression of a tooth preparation using Cadent iTero provides the STL file. (b) The framework shape and extension are defined. (c) The virtual framework designed using CARES (Straumann). (d) The milled white-stage zirconia framework is sintered. (e) The framework is checked on the CAD/CAM digital resin master cast.
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Cantilevered All-Ceramic Resin-Bonded FDPs
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Fig 7-15 (a) Isolation of the area of interest with rubber dam. The pontic zone is covered, which may cause problems with the seating of the prosthesis. Alternatively, rubber dam may be cut out in the pontic zone. (b) Thorough cleaning of palatal surface of the abutment tooth with pumice.
Technical fabrication procedures Technical fabrication begins with a digital impression of the tooth preparation, which will provide a standard tessellation language (STL) file that can be sent to the dental laboratory technician via the Internet (Fig 7-14a). In the laboratory, the framework shape and extension are defined before the retainer, connector, and pontic of the zirconia framework are designed (Fig 7-14b). The virtually designed framework is checked and approved by the technician before the data are sent to the centralized milling center (Fig 7-14c). After the milling of white-stage zirconia, the framework is sintered to full density in a sintering furnace (Fig 7-14d). The fit of the framework is checked on the CAD/ CAM digital resin master cast (Fig 7-14e). Subsequently the framework is veneered with conventional zirconia veneering ceramics.
Cementation of resin-bonded FDPs Clinical procedures for lithium disilicate glass-ceramic For the cementation of lithium disilicate glass-ceramic resinbonded FDPs, dual-curing bisphenol glycidyl methacrylate (bis-GMA)–based resin cements (eg, Variolink II, Ivoclar Vivadent) are recommended.36 Preparation of the clinical site • Placement of rubber dam • Thorough cleaning of the palatal or lingual surface with pumice • Etching of the palatal or lingual surface of the abutment tooth with phosphoric acid • Application of bonding agent in accordance with the manufacturer’s instructions
Preparation of the resin-bonded FDP • Etching with hydrofluoric acid • Silanization • Application of bonding agent • Application of dual-curing resin cement Positioning of the resin-bonded prosthesis, removal of excess cement, and light curing are performed according to the manufacturer’s recommendations.
Clinical procedures for zirconia For the cementation of zirconia ceramic resin-bonded FDPs, specific phosphate monomer–containing resin cements (eg, Panavia 21, Kuraray) and specific silanes (eg, Clearfil Porcelain Bond Activator, Kuraray) have to be used, because conventional bis-GMA resin cements do not chemically bond to zirconia.33 Preparation of the clinical site • Placement of rubber dam • Thorough cleaning of the palatal or lingual surface with pumice • Etching of the palatal or lingual surface of the abutment tooth with phosphoric acid • Application of ED Primer (Kuraray) Preparation of the resin-bonded FPD • Cleaning with alcohol and sandblasting (30-µm aluminum oxide, 2-bar pressure, from a 10-cm distance) • Silanization • Application of a chemically curing resin cement The resin-bonded FDP is positioned, excess cement is removed, and glycerin (Oxyguard, Kuraray) is applied until setting is completed (Fig 7-15). 133
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d Fig 7-15  (cont) (c) Etching of the abutment tooth by means of phosphoric acid. Subsequently primer (ED Primer) corresponding to the resin cement (Panavia 21 TC) will be applied. (d) Application of the resin cement on the framework. Pretreatment of the framework involves silanization with a corresponding silane (Clearfil Porcelain Bond Activator). (e) Removal of excess cement while the prosthesis is securely held in place and application of glycerin gel (Oxyguard).
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Clinical example A 16-year-old adolescent girl is missing her maxillary right central incisor because of posttraumatic endodontic complications (Figs 7-16a and 7-16b). Because of her age, a resinbonded prosthesis is considered the treatment of choice. Crowding of the anterior teeth and the deep, steep bite contribute to the complication that insufficient space is available for a resin-bonded prosthesis (Fig 7-16c). Orthodontic pretreatment is planned to provide the ideal clinical condition for either a resin-bonded prosthesis or a single implant (Fig 7-16d). When the tooth is removed, an extensive bone and soft tissue defect is revealed (Fig 7-16e). Bone
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and soft tissue augmentation are performed for ridge preservation (Fig 7-16f ). After healing of the ridge, orthodontic treatment is initiated. The crowding of the teeth is corrected, and sufficient horizontal and vertical space is provided for placement of a resin-bonded prosthesis on the maxillary left central incisor (Figs 7-16g and 7-16h). The soft tissue is conditioned into the shape of an ovate pontic by means of a removable provisional prosthesis (Figs 7-16i and 7-16j). After tooth preparation and impression procedures, a zirconia ceramic resin-bonded prosthesis is made, and nopreparation veneers made of resin are used to improve the shape and esthetic appearance of the right lateral incisor (Figs 7-16k to 7-16o).
Cantilevered All-Ceramic Resin-Bonded FDPs
a
b
Fig 7-16  (a and b) Initial situation showing the affected maxillary right central incisor and posttraumatic endodontic complications. (c and d) Crowding of the anterior teeth and a deep, steep bite can be managed with orthodontic pretreatment.
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d
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e
f
g
h
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Fig 7-16  (cont) (e and f ) After removal of the tooth, the extensive bone and soft tissue defect is managed with bone and soft tissue augmentation. (g and h) Orthodontic treatment corrects the crowding of the teeth and provides sufficient horizontal and vertical space for the resin-bonded restoration. (i and j) The removable provisional prosthesis is used to condition and shape the soft tissue for an ovate pontic. (k) The zirconia ceramic resin-bonded prosthesis.
k
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Cantilevered All-Ceramic Resin-Bonded FDPs
l
m
n
o Fig 7-16  (cont) (l) No-preparation veneers. (m) Adhesive cementation of the resin-bonded prosthesis with Panavia 21 TC and of the no-preparation resin veneers with a bis-GMA resin (Tetric Classic, Ivoclar Vivadent). (n and o) Appearance after finalization of the restorations.
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Conventional All-Ceramic FDPs Conventional all-ceramic fixed partial dentures have become a viable treatment alternative to metal-ceramic FDPs and are utilized in anterior and posterior regions in daily practice today. The interest in all-ceramic FDPs was greatly affected by the introduction of zirconia as a framework material in the early 1990s. In contrast to ceramic FDPs utilizing glass-ceramic or glass-infiltrated alumina, reconstructions constructed of zirconia are able to withstand very high loads and are, therefore, applicable in different clinical indications. Because zirconia cannot be processed with traditional dental technical techniques, new CAD/CAM procedures developed over the last few years have made zirconia a viable alternative to metal-ceramic and weaker all-ceramic systems. These computerized methods of fabricating frame足 works, including the digital design of frameworks and the milling of prefabricated zirconia blanks, have overcome a number of initial challenges and have significantly evolved since their introduction. Today, zirconia ceramic FDPs and the CAD/CAM procedures required to fabricate them have become part of daily practice.
Indications and clinical research outcomes Zirconia ceramic FDPs have been in routine clinical use for more than 10 years, and their outcomes have been the subject of numerous studies. When zirconia was first introduced, zirconia ceramic FDPs exhibited very good clinical stability, but there were significant problems with the accuracy of the frameworks. As a consequence, a number of early clinical studies reported marginal discrepancies of the reconstructions and subsequent high incidence of secondary caries. High rates of loss of the reconstruction, caused by biologic complications, were therefore reported.37 The problems with accuracy were mainly associated with the early CAD/CAM procedures, which were either in a prototype stage38 or needed further refinement of the software or the processing.39 Another, clinically related explanation was that, initially, knowledge about the ideal type of tooth preparation for the new computerized manufacturing was lacking. The preparation guidelines for metal-ceramic reconstructions first had to be adapted and modified to conform to the specific needs of CAD/CAM and zirconia. These issues seem to be greatly reduced or even overcome today. Awareness of the requirement for adequate abutment tooth preparation by the clinician along with steady improvements in CAD/CAM systems have led to an
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increase in the accuracy of fit of zirconia frameworks.39 As a consequence, fewer biologic complications of zirconia ceramic FDPs are being reported today. Today, the clinical survival rates of anterior and posterior zirconia ceramic FDPs are similar to those of traditional metal-ceramic FDPs. The mean cumulative 5-year survival rate of zirconia ceramic FDPs was 94% in a recent systematic review.37 The same rate reported for metal-ceramic FDPs was 94%.11 More recent randomized controlled clinical trials of zirconia ceramic and metal-ceramic FDPs also show no differences in the survival rates of the two types of reconstruction.40 These positive results are valid both for anterior and posterior regions of the jaws. However, they are limited to short-span FDPs (three- to four-unit). It has been shown that long-span zirconia ceramic FDPs (five units or more) have a higher risk for failure due to catastrophic fracture.37
Technical complications: Chipping of the veneering ceramic Recently concerns have been raised with respect to chipping of the zirconia veneering ceramic (Figs 7-17 and 7-18). This complication occurs significantly more often with zirconia ceramic than with metal-ceramic FDPs41 and is found in all types of available zirconia framework materials, systems, and veneering ceramics.37 Numerous basic studies have been performed with the aim to solve the problem of chipping of zirconia veneering ceramic. Yet despite improvements of the framework support, the physical properties of the zirconia veneering ceramics, and the firing procedures, this significant clinical challenge with the zirconia ceramic FDPs has not been solved yet. More research and further modifications will be necessary to reduce rates of chipping in the future. Otherwise, zirconia ceramic FDPs will only be applicable as an alternative to metal in very specific clinical situations. In a number of investigations, chipping of the zirconia veneering ceramic was found at nonfunctional cusps (eg, the lingual cusps of mandibular molars).40,42 In this region, no or only minimal load should be expected, because these cusps are not in centric occlusion. In the presence of excursive contacts during function, however, shear loading of the veneering ceramic may occur at the nonfunctional cusps. It may be assumed that one additional factor influencing the risk for chipping is the type and direction of occlusal or functional load on the veneering ceramic. Occlusion and function lead to wear of the veneering ceramic, which significantly increases the risk for chipping, as has been shown in clinical studies.28,43 Scanning electron microscopic evaluations of zirconia-based ceramic
Conventional All-Ceramic FDPs
a
b
Fig 7-17  (a) Ceramic chipping at the buccal cusps of zirconia ceramic maxillary first and second premolar crowns. (b) There is a close relationship between the chipped areas and the occlusal contacts in centric occlusion.
2 mm
Fig 7-18  Ceramic chipping at the distolingual cusp of a pontic on a mandibular posterior zirconia ceramic prosthesis (original magnification ×100). (Reprinted from Sailer et al40 with permission.)
FDPs with chipping demonstrate the association between chipped and fractured areas and the occlusal and functional contact areas. Chipping of the zirconia veneering ceramic remains a significant clinical problem. Basic and clinical studies are needed to analyze the aforementioned observations in more detail. This is a significant research challenge because
there are so many variables involved, including preparation design, design of the zirconia framework, laboratory procedures, and chairside procedures to adjust the occlusion and polishing. Until this issue is solved, patients have to be informed about the risk of chipping, and the clinical indications for this type of reconstruction have to be weighed against other options. 139
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Clinical and technical considerations in the selection of material Anterior regions In the anterior region, different types of ceramics can be used as framework material, because the load in this area is rather low. In this region, the choice of restorative material can mainly be based on esthetic factors. The first generation of veneering ceramics for zirconia exhibited poor esthetics because their high translucency led to show-through of the bright white framework (see the article by Sailer et al38 on zirconia veneering ceramics). In the past few years, zirconia veneering ceramics have significantly improved.44 Furthermore, zirconia can be colored to match the shade of the reference teeth before veneering or can be delivered with different grades of translucency. The choice of the ideal restorative material is based on: • The color of the substrate (dentin or core material). • The space available as a result of the tooth preparation. • Preferences in cementation techniques. Fixed partial dentures constructed of glass-ceramics are indicated when: • The dentin of the abutment teeth is not discolored. • The color of adjacent (reference) teeth is warm and chromatic. • Sufficient vertical and horizontal space is available for the connectors (three-unit FDP: cross section of 16.0 mm2). • Clinical prerequisites for good adhesive cementation (good dentin quality and low amount of saliva) are present. • Low loads will be transmitted at occlusion and function. Fixed partial dentures constructed of zirconia ceramic are indicated when: • Dentin is not discolored or lightly discolored. • The color of adjacent teeth is bright and whitish. • Sufficient vertical and horizontal space is available for the core (minimal thickness of 0.5 mm) and the connectors (three-unit FDP: cross section of 6.0 to 9.0 mm2). • Clinical prerequisites for adhesive cementation are present. Alternatively, self-adhesive cements or glass-ionomer cements may be used. • Low to medium loads will be transmitted at occlusion and function. In patients with high occlusal loads (parafunctions or bruxism), metal-ceramic FDPs should be preferred. 140
Posterior regions In posterior regions where high loading forces occur, zirconia is the “ceramic of choice” today for patients or clinicians desiring all-ceramic rehabilitations. Other types of reinforced ceramics, like lithium disilicate glass-ceramics (eg, e.max Press or CAD), may alternatively be considered in the future; however, the incidence of fracture of these prostheses is reportedly higher than that associated with zirconia.6 Furthermore, the dimensions of the framework have to be adapted to the requirements of this glass-ceramic to provide sufficient strength. Therefore, each posterior site has to be evaluated with respect to the expected load and available space, and connector sizes recommended by the manufacturers must be followed. Furthermore, the site needs to be judged with respect to the CAD/CAM requirements. For CAD/CAM frameworks, specific requirements for the shape and taper of the abutment teeth need to be considered at the abutment tooth preparation.45 In situations where high loads are expected, metal-ceramic FDPs are more typically indicated.
Clinical procedures Analysis of the clinical situation and diagnostics The restorative team of clinician and the dental technician has to evaluate each individual clinical situation with respect to the different framework materials. With respect to CAD/CAM zirconia frameworks, the team should consider the following factors (Fig 7-19): • The length of the FDP: Is it suitable for the available size of the ingots? • The axial height of the abutment walls: Do they allow for the required dimensions of the FDP connectors? • The condition of the abutment teeth: Can undercuts be avoided? • Occlusion and function: Is there a risk for chipping of the veneering ceramic?
Universal tooth preparation The design of the abutment tooth preparation has a significant influence on the outcomes of all-ceramic reconstructions. Most specifically, the accuracy of the CAD/CAM zirconia framework is influenced by the preparation.45 To provide the ideal prerequisites for all types of materials and fabrication techniques, use of a universal tooth preparation
Conventional All-Ceramic FDPs
Fig 7-19 Clinical situation after abutment tooth preparation, displaying the factors to consider with respect to CAD/CAM zirconia frameworks.
a
Fig 7-20 Universal tooth preparation of nondiscolored and discolored abutment teeth, allowing for both all-ceramic and metal-ceramic crowns.
b
Fig 7-21 (a and b) The labiolingual width of the incisal edge is crucial for CAD/CAM feasibility. Sharp-edged preparations might not be transferrable to the frameworks because of the large size of the milling instruments.
(Universal Prep Set, Intensiv) is recommended for crowns and FDPs. The universal tooth preparation fulfills the following criteria (Fig 7-20): • Marginal shoulder: 1.0-mm, located equigingivally or 0.5 mm or less subgingivally • Total occlusal convergence: 10 to 12 degrees • Axial reduction: 1.5 mm or greater
• Incisal or occlusal reduction: 1.5 to 2.0 mm • Minimal labiolingual width of the incisal edge of anterior teeth: 1.0 mm (Fig 7-21) • Buccolingual reduction of the occlusal surface: 30 degrees • Height of axial walls: 3.0 to 4.0 mm • Smoothed and rounded line angles and edges • No undercuts in splinted multiunit reconstructions
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Impression techniques: Conventional versus digital Recently, multiple optical and digital impression systems have been introduced as alternatives to the conventional impression. With these systems, the intraoral condition is digitized, and the scan is sent to the dental laboratory via the Internet. Based on these data, the dental technician can order a master cast, which is fabricated from resin in a centralized production facility. Alternatively, based on the same data, a zirconia framework is virtually designed and sent to another centralized production facility for milling. Today veneering of the frameworks is performed manually. It is very likely, though, that in the future the veneering will be done by CAD/CAM techniques as well using prefabricated glass-ceramic ingots. Furthermore, monolithic zirconia reconstructions may also be recommendable in the future. The entirely digital method of fabricating zirconia ceramic FDPs is still very new, and the benefits and limitations of the optical and digital impressions compared to those of traditional impressions are currently being analyzed. CAD/ CAM fabrication of the frameworks, however, is well established.
Clinical example A patient presented with a posterior prosthesis extending from the mandibular left first premolar to first molar (Fig 7-22a). Secondary caries at the first molar abutment required removal of the prosthesis (Fig 7-22b). After removal of the caries, a composite resin core is built up on the first molar, and the teeth are prepared for a digital impression (Fig 7-22c). Retraction cords are placed according to the techniques used for conventional impressions, and the site is pretreated with a scanning powder (Figs 7-22d and 7-22e). A digital impression is performed, and the virtual
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model is delivered to the dental technical laboratory via the Internet (Figs 7-22f and 7-22g). In the laboratory, a virtual framework is designed by means of specialized software, combining crown copings with a preshaped pontic chosen from a virtual tooth library (Fig 7-22h). One significant advantage of CAD/CAM manufacturing is the inherent quality control. Before the framework data are sent for production, the desired thickness of the framework and the connectors have to be approved as defined by the manufacturer (Figs 7-22i to 7-22k). The zirconia framework and a centrally fabricated resin master cast are delivered to the dental laboratory for veneering and finalization (Fig 7-22l). The zirconia ceramic prosthesis is completed and cemented in place (Figs 7-22m and Fig 7-22n).
Cementation of high-strength ceramic FDPs Specific phosphate monomer窶田ontaining primers and cements are needed for adhesive cementation of zirconia ceramic FDPs.46 The resin cement best documented in the literature for use with zirconia is Panavia 21.47 This resin cement exhibits very high bond strengths but is technique sensitive because of its hydrophobic nature. More recently, less technique-sensitive self-adhesive resin cements with phosphate monomers were introduced; among these, RelyX Unicem (3M ESPE) performs very well in combination with zirconia.48 Interestingly, in clinical studies, conventional cementation of zirconia ceramic FDPs with resin-reinforced glassionomer cement did not negatively influence the outcomes compared to the results of studies testing with adhesive cementation.43,49 As a consequence, in situations in which adhesive cementation may be impaired (in the posterior region or in the presence of high saliva flow), conventional cementation of zirconia ceramic FDPs can be recommended.
Conventional All-Ceramic FDPs
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b
d
f
c
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g
Fig 7-22  (a and b) The posterior prosthesis extending from the mandibular left first premolar to first molar must be removed because of secondary caries at the first molar abutment. (c) The caries is removed and a composite resin core is built up on the first molar. (d) Retraction cords are placed in preparation for the digital impression. (e) The site is pretreated with a scanning powder. (f ) The digital impression is completed with a Lava Chairside Oral Scanner (3M ESPE). (g) The virtual model.
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References
Conclusion All-ceramic FDPs are a widely used alternative to metalceramic prostheses for different indications. Resin-bonded prostheses fabricated of glass-ceramic or zirconia ceramic are a recommendable, minimally invasive treatment option for the replacement of missing incisors. The clinical requirements for these FDPs, however, have to be considered for each individual patient, and meticulous pretreatment diagnostics and planning must be performed. All-ceramic full-arch prostheses can only be recommended if zirconia is used as ceramic framework material. The high rates of chipping of the veneering ceramic are still a clinical problem. For this reason, zirconia ceramic full-arch prostheses are not an equally successful alternative to metal-ceramics today. These all-ceramic prostheses should, therefore, only be recommended in specific clinical situations or for patients who are willing to accept this risk. Future developments and improvements are needed to improve the outcomes of zirconia ceramic FDPs.
Acknowledgments Master Dental Technician Vincent Fehmer, chief dental technician for the Clinic for Fixed and Removable Prosthodontics and Dental Material Science of the University of Zurich, is gratefully acknowledged for his high expertise and important contribution of sections on technical criteria and technical fabrication procedures.
Fig 7-22 (opposite page) (h) The virtual framework is designed in the laboratory. (i to k) Quality control ensures the thickness of the framework and the connectors are approved as defined by the manufacturer prior to production. (l) The zirconia framework and a centrally fabricated resin master cast. (m and n) The finalized zirconia ceramic prosthesis is cemented in place.
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