The all‐ceramic,inlay supported fixed partial denture. Part 1. Ceramic inlay preparation design: a literature review

The effect of cavity design is a controversial and underrated factor in the clinical success of ceramic inlays and inlay supported prosthesis. Many articles and studies have been conducted into the advantages and disadvantages of isolated aspects of preparation design, but lacking is a review of the most relevant papers which bring together a consensus on all the critical features. Hence, a review and analysis of cavity depth, width, preparation taper and internal line angles is warranted in our attempts to formulate preparation guidelines that will lead to clinically successful, all‐ceramic inlay restorations and ceramic inlay supported prosthesis.     

Fracture Resistance of Three Ceramic Inlay‐Retained Fixed Partial Denture Designs. An In Vitro Comparative Study

Purpose: The fracture resistance of ceramic inlay‐retained fixed partial dentures (CIRFPDs) was studied. Materials and Methods: Thirty CIRFPDs were constructed using ice zircon milled ceramic material. Specimens were divided into three groups, 10 specimens each, according to the abutment preparation: inlay‐shaped (occluso‐proximal inlay + proximal box), tub‐shaped (occluso‐proximal inlay), and proximal box‐shaped preparations. Each group was then subdivided into two subgroups of five specimens each, according to the span of the edentulous area representing a missing premolar or molar. All specimens were subjected to a fracture resistance test. Results: CIRFPDs with inlay‐shaped retainers showed the highest fracture resistance values for missing premolars and molars. CIRFPDs with box‐shaped retainers showed lower fracture resistance values. Statistical analysis revealed a significant difference between the three tested CIRFPD designs. There was a statistically significant difference between CIRFPDs constructed for the replacement of molars and those constructed for the replacement of premolars. The CIRFPD constructed for the replacement of molars gave lower fracture resistance values with the three tested designs. All the fracture resistance values obtained in this study were superior to the assumed maximum mastication forces. Failure mode was delamination and chipping of the veneering material. Conclusions: There was a statistically significant difference between the three designs of CIRPFDs tested. There was a statistically significant difference between CIRFPDs constructed for the replacement of molars than those constructed for the replacement of premolars. The CIRFPDs constructed for the replacement of molars gave lower fracture resistance values with the three tested designs. All fracture resistance values obtained in this study were superior to the assumed maximum mastication forces.     

The Effect of Incorporation, Orientation and Silane Treatment of Glass Fibers on the Fracture Resistance of Interim Fixed Partial Dentures

Fracture of interim fixed partial dentures (FPD) is of important concern to the dental surgeon, especially with long-span fixed partial dentures or areas of heavy occlusal stress. Polymers used in interim FPDs, reinforced with glass fibers have shown to have a positive effect on the fracture resistance of interim FPDs. Since little research has been done on the influence of silane treated glass fibers on the fracture resistance of interim FPDs, this study was conducted to evaluate the effect of silane treatment of glass fibers on the fracture resistance of interim FPDs and its correlation with the position of fiber reinforcement and length of the span of the interim FPD. Interim FPDs were fabricated from an autopolymerizing polymethyl methacrylate (PMMA) resin. Seven FPDs were made in each group. The FPDs in the control group were unreinforced, and in the other groups the FPDs were reinforced either with non silane treated glass fiber or with silane treated glass fiber. The fibers were placed in two different locations in the FPDs. Three length of span of FPDs were tested. The load was applied to the FPD by a steel ball placed in the center of the pontic space. One Way Anova, Two Way Anova, Studentized range test (Scheffe’s). Results showed that the load required for fracturing the unreinforced FPDs varied from 272 to 998 N. Mean fracture load of reinforced FPDs varied from 536 to 1642 N. One-way analysis of variance showed that the position of fibers and the silane treatment fibers significantly affected the fracture load. The results of this study suggested that the silane treatment of glass fibers had a marked improvement in the fracture resistance of FPDs as compared to untreated glass fibers. Selective placement of the glass fibers at the undersurface of the pontic and the occlusal surface of the interim fixed partial denture showed more increase in the fracture resistance as compared to the randomly distributed glass fibers. The glass fiber reinforcement is effective in increasing the fracture resistance with the effectiveness most evident in interim FPDs with long spans. With increase in the length of span of interim fixed partial denture the fracture resistance was shown to decrease significantly in all the groups.     

Reliability and Failure Modes of Implant‐Supported Y‐TZP and MCR Three‐Unit Bridges

Purpose: Chipping within veneering porcelain has resulted in high clinical failure rates for implant‐supported zirconia (yttria‐tetragonal zirconia polycrystals [Y‐TZP]) bridges. This study evaluated the reliability and failure modes of mouth‐motion step‐stress fatigued implant‐supported Y‐TZP versus palladium‐silver alloy (PdAg) three‐unit bridges. Materials and Methods: Implant‐abutment replicas were embedded in polymethylmethacrylate resin. Y‐TZP and PdAg frameworks, of similar design (n = 21 each), were fabricated, veneered, cemented (n = 3 each), and Hertzian contact‐tested to obtain ultimate failure load. In each framework group, 18 specimens were distributed across three step‐stress profiles and mouth‐motion cyclically loaded according to the profile on the lingual slope of the buccal cusp of the pontic. Results: PdAg failures included competing flexural cracking at abutment and/or connector area and chipping, whereas Y‐TZP presented predominantly cohesive failure within veneering porcelain. Including all failure modes, the reliability (two‐sided at 90% confidence intervals) for a “mission” of 50,000 and 100,000 cycles at 300 N load was determined (Alta Pro, Reliasoft, Tucson, AZ, USA). No difference in reliability was observed between groups for a mission of 50,000. Reliability remained unchanged for a mission of 100,000 for PdAg, but significantly decreased for Y‐TZP. Conclusions: Higher reliability was found for PdAg for a mission of 100,000 cycles at 300 N. Failure modes differed between materials.     

In Vitro Exploration and Finite Element Analysis of Failure Mechanisms of Resin‐Bonded Fixed Partial Dentures

Purpose: The purpose of this study was to explore the debonding mechanisms of two‐unit cantilevered and straight and bent three‐unit fixed‐fixed resin‐bonded fixed partial dentures (RBFPDs) and to measure the failure loads needed for debonding. Materials and Methods: Failure load tests were performed using Bondiloy beams simulating both cantilevered and fixed‐fixed RBFPDs, luted onto flat‐ground buccal surfaces of bovine teeth with RelyX ARC, Panavia F2.0, and UniFix resin cements. The failure loads were recorded, and the debonded surfaces of both the enamel and the restorations were examined for details of interest. Finite element analysis (FEA) was used to calculate the stress concentrations within the cement layers at failure. Results: Simulated two‐unit cantilevered and straight three‐unit fixed‐fixed RBFPDs showed a significantly higher failure load than the simulated three‐unit fixed‐fixed RBFPDs with a curved appearance. The FEA models revealed the magnitude and stress locations within the cement layer, resulting in an explanation of the different failure modes. Conclusions: The low failure loads for the three‐unit bent fixed‐fixed RPFPDs, compared with their straight counterparts and the two‐unit cantilevered RBFPDs, indicate that clinically a reserved attitude needs to be maintained with regard to three‐unit fixed‐fixed RBFPDs spanning a clearly curved part of the dental arch. The FEA results make it clear which part of the tooth restoration interface is subject to the highest stress levels, making it possible to design abutment preparations that avoid high interfacial stresses to help prevent debonding.     

Effect of Veneering Techniques on Color and Translucency of Y‐TZP

Purpose: This study compared the color parameters and total luminous transmittance of disc specimens by different veneering techniques in order to examine the effect of veneering technique on esthetics of yttria‐stabilized tetragonal zirconia polycrystalline (Y‐TZP) all‐ceramic restorations. Materials and Methods: Thirty disc specimens (10‐mm diameter, 0.50 ± 0.01 mm thick) were fabricated of IPS e.max ZirCAD core material, and ZL1 IPS e.max ZirLiner (0.10‐mm thick) was layered. The specimens were randomly divided into three groups (n = 10/group). Group ZP (fully anatomical technique) was veneered 0.60 mm by heat‐pressing IPS e.max ZirPress fluorapatite glass‐ceramic ingots; Group ZC (traditional layering technique) was veneered 0.60 mm by condensing and sintering IPS e.max Ceram low‐fusing nano‐fluorapatite veneering porcelain; Group ZPC (cutback technique) was veneered by partially pressed ingots and subsequently layered 0.30 mm with veneering porcelain. Color parameters (L*, a*, b*) and total luminous transmittance (τ) of zirconia core discs and core and veneer specimens were measured with ShadeEye NCC dental colorimeter and spectrophotometer, respectively. Color saturation (C*ab) and color difference (ΔE) were calculated using color difference formula. One‐way analysis of variance (ANOVA) combined with a Tukey multiple‐range test were used to analyze the data (α= 0.05). Results: As to ZP, ZPC, and ZC groups, the value of a* increased (?1.35 ± 0.07, ?0.64 ± 0.06, ?0.36 ± 0.05, respectively) (p < 0.05); b* decreased (27.01 ± 0.07, 25.48 ± 0.11, 23.28 ± 0.25, respectively) (p < 0.05); and C*ab decreased (27.04 ± 0.08, 25.49 ± 0.11, 23.28 ± 0.25, respectively) (p < 0.05). L* value and total luminous transmittance were highest in ZP group (87.53 ± 0.48, 1.64 ± 0.03, respectively), and lowest in ZPC group (82.14 ± 0.18, 1.47 ± 0.01, respectively) (p < 0.05). Conclusions: Y‐TZP all‐ceramic restoration veneered by fully anatomical technique was the most transparent and lightest, while restorations veneered by cutback technique were the least translucent and the darkest.