Digital workflow for monolithic and veneered zirconia and metal-ceramic posterior fixed partial dentures: A five-year prospective randomized clinical trial.

Purpose To evaluate and compare the survival, success rates, and biological and technical complications of three-unit posterior monolithic and veneered zirconia and metal-ceramic (MC) posterior fixed partial dentures (FPDs) fabricated using a digital workflow and computer-aided design and computer-aided manufacturing (CAD/CAM) over a 5-year follow-up.Methods Ninety patients in need of three-unit posterior FPDs were randomized to receive monolithic zirconia (MZ), veneered zirconia (VZ), and MC restorations (n = 30 each). Teeth preparations were scanned using an intraoral scanner, and restorations were milled and cemented with resin cement. Clinical performance and periodontal parameters were assessed at baseline and yearly up to 5 years after insertion. Data analysis was performed using the Kaplan-Meier method, Friedman test, and Wilcoxon signed-rank test with Bonferroni correction and Mann-Whitney U test.Results The 5-year survival rates of the MZ, VZ, and MC FPDs were 87%, 97%, and 100%, respectively (P = 0.04). Most complications were biological in nature. Only one MZ FPD fractured 58 months after placement. All the restorations were assessed as satisfactory at each recall. Differences were found in the gingival index score over time in the VZ and MC groups. The margin index remained stable throughout the follow-up period in both zirconia groups.Conclusions The results of this study suggest that using a digital workflow to fabricate posterior FPDs is an adequate treatment option and that monolithic zirconia could be a viable alternative to metal-ceramic or veneered zirconia. However, further long-term studies are necessary to provide stronger evidence in patients with bruxism.

Influence of Digital Technologies and Framework Design on the Load to Fracture of Co-Cr Posterior Fixed Partial Denture Frameworks.

PURPOSE: To compare the load to fracture of cobalt-chromium (Co-Cr) 3-unit posterior fixed partial denture (FPD) frameworks manufactured by conventional and digital techniques and to evaluate the influence of the framework design on the fracture load. MATERIAL AND METHODS: Eighty 3-unit Co-Cr posterior FPD frameworks were fabricated with two designs: intermediate pontic (n = 40) and cantilever (n = 40). Each design was randomly divided into four groups (n = 10): casting, direct metal laser sintering, soft metal milling, and hard metal milling. After thermal cycling, all specimens were subjected to a 3-point bending test until fracture. Data were statistically analyzed using one-way ANOVA, Welch and Brown-Forsythe test, Ryan-Einot-Gabriel-Welsch F and Tamhane T2 post hoc test, Student's t test, and Weibull statistics (α = 0.05). RESULTS: Significant differences (p < 0.001; F = 39.59) were found among intermediate pontic frameworks (except between laser sintering and hard metal milling), and cantilevered frameworks (F = 36.75) (except between laser sintering and hard metal milling, and casting and soft metal milling). The cantilever groups showed load to fracture values significantly lower than those of the intermediate pontic (p < 0.001; F = 28.29). The Weibull statistics corroborated the results. CONCLUSIONS: Hard metal milling and laser sintered frameworks exhibited the highest load to fracture values. However, all tested frameworks demonstrated clinically acceptable load to fracture values. The framework design directly affected the fracture load, with drastically lower values in cantilevered frameworks.

Adhesion to Zirconia: A Systematic Review of Surface Pretreatments and Resin Cements.

This systematic review aims to evaluate the different pretreatments of the zirconia surface and resin cement in order to determine a valid operative protocol for adhesive cementation. Methodologies conducted for this study followed the Prisma (Preferred Reporting Items for Systematic Reviews and Meta-Analysis) guidelines. An electronic search was performed in four databases. The established focus question was: "What type of surface conditioning method is the one that obtains the best adhesion values to zirconia over time by applying a resin cement?" Forty-five relevant papers were found to qualify for final inclusion. In total, 260 different surface pretreatment methods, mainly combinations of air-abrasion protocols and adhesive promoters, were investigated. Altogether, the use of two artificial aging methods, three types of cement and four testing methods was reported. The results showed that mechanicochemical surface pretreatments offered the best adhesive results. Self-adhesive cement and those containing 10-MDP obtained the best results in adhesion to zirconia. Artificial aging reduced adhesion, so storage in water for 30 days or thermocycling for 5000 cycles is recommended. A standardized adhesive protocol has not been established due to a lack of evidence.

Fracture Load of Metal, Zirconia and Polyetheretherketone Posterior CAD-CAM Milled Fixed Partial Denture Frameworks.

The aim of this study was to investigate the load to fracture and fracture pattern of prosthetic frameworks for tooth-supported fixed partial dentures (FPDs) fabricated with different subtractive computer-aided design and computer-aided manufacturing (CAD-CAM) materials. MATERIALS AND METHODS: Thirty standardized specimens with two abutments were fabricated to receive three-unit posterior FDP frameworks with an intermediate pontic. Specimens were randomly divided into three groups (n = 10 each) according to the material: group 1 (MM)-milled metal; group 2 (L)-zirconia; and group 3 (P)-Polyetheretherketone (PEEK). The specimens were thermo-cycled and subjected to a three-point bending test until fracture using a universal testing machine (cross-head speed: 1 mm/min). Axial compressive loads were applied at the central fossa of the pontics. Data analysis was made using one-way analysis of variance, Tamhane post hoc test, and Weibull statistics (α = 0.05). RESULTS: Significant differences were observed among the groups for the fracture load (p < 0.0001). MM frameworks showed the highest fracture load values. The PEEK group registered higher fracture load values than zirconia samples. The Weibull statistics corroborated these results. The fracture pattern was different among the groups. CONCLUSIONS: Milled metal provided the highest fracture load values, followed by PEEK, and zirconia. However, all tested groups demonstrated clinically acceptable fracture load values higher than 1000 N. PEEK might be considered a promising alternative for posterior FPDs.

Influence of Implant Connection, Abutment Design and Screw Insertion Torque on Implant-Abutment Misfit.

BACKGROUND: An accurate fit at the implant-abutment interface is an important factor to avoid biological and mechanical complications. The aim of this study was to evaluate the marginal misfit at the implant-abutment interface on external and Morse taper connection, with straight and angulated abutments under different insertion torque loads. MATERIALS AND METHODS: A total of 120 implants were used, 60 with external connection (EC) and 60 with Morse taper connection (IC). Straight (SA) (n = 60) and angulated abutments (AA) (n = 60) were randomly screwed to each connection at different torque levels (n = 10 each): 10, 20 and 30 Ncm. All specimens were subjected to thermal and cyclic loading and the misfit was measured by scanning electron microscopy. Data were analyzed with one-way ANOVA, t-test and Kruskal-Wallis test. RESULTS: Significant differences (p < 0.001) were found between connections and abutments regardless of the torque applied. Morse taper connections with straight and angulated abutments showed the lowest misfit values (0.6 µm). Misfit values decreased as torque increased. CONCLUSIONS: The misfit was affected by the type of connection. The type of abutment did not influence the fit in the Morse taper connection. The higher the tightening torque applied the increase in the fit of the implant-abutment interface.

Effect of Thermomechanical and Static Loading on the Load to Fracture of Metal-Ceramic, Monolithic, and Veneered Zirconia Posterior Fixed Partial Dentures.

PURPOSE: To evaluate the influence of static (not preloaded) and thermomechanical loading on the load to fracture of metal-ceramic, monolithic and veneered zirconia computer-aided design/computer-aided manufacturing (CAD/CAM) posterior fixed partial dentures (FPDs). MATERIALS AND METHODS: One hundred standardized specimens with 2 abutments screwed onto a platform were prepared from stainless steel to receive a posterior 3-unit FPD with an intermediate pontic. Specimens were randomly divided into 5 groups (n = 20): Metal-ceramic (control group), Lava Zirconia system, Vita In-Ceram YZ, IPS e.max ZirCAD, and Lava Plus. Half of the specimens of each group (n = 10) underwent no preloading, and the other half were subjected to thermomechanical loading in a masticatory simulator, and then all FPDs were loaded until fracture using a universal testing machine at a 1 mm/min crosshead speed. The load to fracture of the veneering ceramic and the load to fracture of framework (total fracture) were recorded for each specimen. Data were statistically analyzed using 2-way ANOVA, Tukey's HSD post-hoc test, Student's t test, and Weibull statistics, α = 0.05. RESULTS: Significant differences were recorded between the metal-ceramic and veneered zirconia groups for the veneering ceramic load (p < 0.001; f = 36.62; f = 57.76) in no preloading and thermomechanical loading subgroups, respectively, but no differences were observed between the static and thermomechanical loading conditions. No differences were observed among the veneered zirconia groups. For the total load to fracture, significant differences were observed according to the material (p < 0.001; f = 500.8), between the metal-ceramic and Lava Plus group and the other zirconia groups in no preloading subgroup, and between metal-ceramic and the other groups (p < 0.001; f = 303.33) in thermomechanical loading subgroup. For the type of preloading, significant differences were observed (p = 0.02; f = 5.24) between the Lava Plus group and the other groups. Thermomechanical loading significantly decreased the fracture load of the Lava Plus group (p = 0.005). The Weibull statistics corroborated the results. CONCLUSIONS: Monolithic zirconia restorations provided the highest load to fracture values among the zirconia groups tested; however, the results indicate that they must be used in the oral environment with caution, because their load to fracture was influenced by the aging simulation.