Fatigue resistance of 3D printed anatomic post-and-core after mastication simulation.

STATEMENT OF PROBLEM: Rigid post-and-core systems have traditionally been used in the restoration of endodontically treated teeth and are regarded by many as the standard treatment. Flexible materials, including nanoceramic resins, are being increasingly implemented as post-and-core systems, but data supporting their use are lacking. PURPOSE: The purpose of this in vitro study was to compare the fatigue resistance of conventional cast metal and nanoceramic 3-dimensionally (3D) printed resin post-and-core systems with teeth without posts. MATERIAL AND METHODS: Thirty freshly extracted human maxillary premolars were endodontically treated and divided into 3 subgroups (n=10) according to the restorative procedure: cast metal post-and-core (CM), nanoceramic 3D printed resin post-and-core (3DR), and without a post (0P). The CM post-and-core group was fabricated conventionally, while the 3DR group was printed using a 3D resin printing material. For the 0P group, the teeth were restored with a composite resin foundation after root canal obturation. Complete coverage 3-mol% monolithic zirconia restorations were cemented on all specimens. The specimens were exposed to simultaneous mastication simulation (1.2 million cycles) and thermocycling (10 000 cycles at 5 ºC to 55 ºC) and analyzed based on the failure of specimens. Data were analyzed using the Kruskal-Wallis survival analysis and the Wilcoxon rank sum test (α=.05). RESULTS: The Kruskal-Wallis test indicated statistically significant differences among the cycles needed to reach failure for each of the 3 groups (P<.001). At 1.2 million cycles, there were no CM failures. The 3DR group failed at a median value of 950 000 cycles, while the 0P group failed at a median value of 222 500 cycles (P<.001). CONCLUSIONS: All the endodontically treated teeth that received CM survived the 1 200 000 simulated mastication cycles. Both 3DR and 0P specimens fractured at the crown cervical third during mastication simulation.

Survivability and fracture resistance of monolithic and multi-yttria-layered zirconia crowns as a function of yttria content: A mastication simulation study.

OBJECTIVE: To compare four different types of monolithic zirconia crowns in terms of survival rate and fracture resistance after thermocycling and/or thermo-mechanical loading in a chewing simulator. METHODS: Partially stabilized zirconia (PSZ) crowns with fiber-reinforced resin die assemblies (n = 80) were fabricated using: multi-yttria-layered 5Y-PSZ/3Y-PSZ, multi-yttria-layered 5Y-PSZ/4Y-PSZ, monolithic 4Y-PSZ, and monolithic 3Y-PSZ as control (n = 20). Half of the samples in each group were subjected to thermo-mechanical loading under 110 N, 1.4 Hz, 1.2 million cycles with simultaneous thermocycling (10,000 cycles, 5-55°C). The other half were subjected to thermocycling alone. The samples were loaded to failure to measure their fracture resistance. The data were analyzed using by two-way ANOVA and Tukey's HSD post-hoc test (α = 0.05). RESULTS: All specimens survived the aging protocols. The yttria content significantly affected the fracture resistance of the crowns (p < 0.0001). The mean fracture resistance, from highest to lowest: 3Y-PSZ, 4Y-PSZ, followed by the two multi-yttria-layered systems. The mean difference between the two multi-yttria-layered systems were not statistically significant (p = 0.98). The mechanical loading protocol did not affect the mean fracture resistance within each group (p = 0.18). CONCLUSIONS: Within each group, there was no difference in fracture resistance after thermocycling alone and thermo-mechanical loading. However, increasing the yttria concentration at the occlusal third of the crown decreased its fracture resistance. CLINICAL SIGNIFICANCE: The term "monolithic zirconia" alone without specifying the actual yttria content is misleading. This term represents different materials with different mechanical properties. The yttria content has an inverse relationship with the fracture resistance of zirconia crowns. The fracture resistance of multi-layer zirconia crowns is determined by the amount of the weaker zirconia phase at the occlusal part of the restoration rather than enforced by the stronger zirconia at the cervical part of the crown.

Anatomic CAD-CAM post-and-core systems: A mastication simulation study.

STATEMENT OF PROBLEM: Few studies have investigated the differences among various post-and-core systems under mastication simulation. Comparing these systems while simulating the clinical environment should provide a more accurate assessment of their performance. PURPOSE: The purpose of this in vitro study was to evaluate the fatigue resistance of conventional cast metal and prefabricated fiber post systems with computer-aided design and computer-aided manufacture (CAD-CAM) prefabricated nonmetal post-and-core systems. MATERIAL AND METHODS: Forty freshly extracted human maxillary premolars were endodontically treated and divided into 4 subgroups (n=10) according to the material: cast metal, zirconia, fiber-reinforced composite resin, prefabricated fiber post. The post-and-core materials were manufactured either conventionally or milled with CAD-CAM technology. All specimens were exposed to simultaneous mastication simulation (1.2 million cycles) and thermocycling (10 000 cycles at 5 °C to 55 °C) and analyzed based on failure of specimens. Data were analyzed by using the Kaplan-Meier survival analysis and Cox-regression (α=.05). RESULTS: Both cast metal and zirconia post-and-core groups had similar fatigue resistance (P>.05) but significantly higher fatigue resistance than the fiber-reinforced groups (P<.05). Fiber-reinforced composite resin and prefabricated fiber post did not survive the mastication simulation, fracturing between 504 000 and 752 000 cycles, with fractures occurring in the cervical portion of the tooth. CONCLUSIONS: Cast metal and zirconia post-and-core systems had improved physical properties with high resistance to fatigue when compared with fiber-reinforced post-and-core systems.

A Digital Approach to Improved Overdentures for the Adolescent Oligodontia Patient.

OBJECTIVE: The use of overdentures for treatment of oligodontia in adolescent patients using conventional techniques has described limitations. The aim of the case report is to demonstrate the use of CAD (Computer Aided Design) CAM (Computer Aided Manufacture) technology to produce an esthetic monolithic polymethylmethacrylate prosthesis that is retentive and stable on insertion. CLINICAL CONSIDERATIONS: Adolescent oligodontia patients are typically not suitable candidates for dental implant therapy. Overdentures provide interim or definitive restorative advantages. Given the important esthetic, psychological, and social functions of the prosthesis, an important therapeutic goal for the overdenture prosthesis is esthetics. A CAD-CAM approach to overdenture manufacture can provide a highly esthetic, strong, and retentive prosthesis. CONCLUSIONS: CAD-CAM manufacture of monolithic acrylic overdentures offer several advantages that include (1) improved planning and clinical communication, (2) high fidelity manufacture, (3) improved flexural strength, impact strength, and porosity, (4) improved prosthesis integrity and durability (due to the monolithic design), (5) CNC control of occlusal contacts, (6) high esthetic potential due to quality of bulk material and iterative design, and (7) archival nature of the digital prosthesis. CAD-CAM manufacture of monolithic overdentures is a viable approach to completing high value esthetic management of the adolescent oligodontia patient. CLINICAL SIGNIFICANCE: This case report identifies a new way to utilize CAD CAM technology to produce an improved overdenture for the oligodontia patient. It will be of interest to many and underscores the fundamental principles of smile design transfer to the digital environment. (J Esthet Restor Dent, 2016).

Effect of Finishing and Polishing on the Surface Roughness of Four Ceramic Materials after Occlusal Adjustment.

PROBLEM: Intraoral occlusal adjustment of ceramic restorations can create a significant increase in surface roughness that can produce wear of the opposing dentition. PURPOSE: To compare the surface roughness of glazed and polished monolithic ceramics with the surface roughness produced by different intraoral polishing systems on adjusted monolithic ceramics. MATERIALS AND METHODS: Milled ceramic discs (10 mm diameter × 2 mm thickness) were manufactured and distributed according to the following groups (n = 10): BruxZir (glazed and polished), Zenostar (glazed and polished), IPS Empress CAD, and IPS e.max CAD. Surface roughness, expressed as arithmetic average height (Ra ), was measured using atomic force microscope and profilometer before and after adjustment and polishing with the following intraoral polishing systems: BruxZir and Dialite ZR (for BruxZir), Zenostar and Dialite ZR (for Zenostar), and OptraFine and Dialite LD for IPS Empress CAD and IPS e.max CAD. Mean and standard error for each material and polishing system were calculated. T-test, one-way ANOVA, and Bonferroni post hoc tests were used to analyze data. RESULTS: BruxZir zirconia presented smoother surfaces with Dialite ZR system compared to BruxZir system, Zenostar zirconia shown smoother surfaces with Zenostar system compared to Dialite ZR system and IPS Empress CAD and IPS e.max CAD presented smoother surfaces with OptraFine system in comparison to Dialite LD system. CONCLUSION: All materials presented smoother surfaces at baseline than after adjustment and polishing. CLINICAL SIGNIFICANCE: This paper reveals the results of an in vitro study that provides information to clinicians regarding which intraoral polishing system will produce a smoother surface after the adjustment and polishing of IPS Empress CAD, IPS e.max CAD, BruxZir and Zenostar ceramic materials. (J Esthet Restor Dent 28:382-396, 2016).

Lithium disilicate: the restorative material of multiple options.

As dentistry continues to evolve, new technologies and materials are continually being offered to the dental profession. Throughout the years restorative trends and techniques have come and gone. Some material developments have transformed the face of esthetic dentistry, while other initial concepts have already phased out and disappeared. Today, all-ceramic restorations continue to grow in the area of restorative dentistry, from pressed-ceramic techniques and materials to the growing use of zirconia, and new materials that can be created from CAD/CAM technology. This article will explore new uses for the all-ceramic material known as lithium disilicate, and the use of a digital format to design and process this material in new and exciting ways. An overview of the material as well as unique clinical procedures will be presented.

Comprehensive Rehabilitation for a Permanent Tooth Anodontia Patient Using an Integrated Digital Approach.

Agenesis of the permanent dentition is rare. This report describes a 20-year-old woman with 19 deciduous teeth, a single permanent mandibular premolar, and other physical traits associated with ectodermal dysplasia. The patient demonstrated esthetic parameters associated with maxillomandibular alveolar insufficiency, and her chief complaints were directed toward esthetics and the potential impact of restorative choices on function. Three typical options for restoration include overdentures, removable partial dentures, or implant-supported prostheses replacing her natural dentition. This report illustrates a fully integrated digital approach to treatment planning, the fabrication of a computer-aided design/computer-assisted manufacture surgical guide and provisional restoration, guided implant placement, and definitive restoration using monolithic zirconia implant-supported fixed dental prostheses. The lifelong management of this rehabilitation is an acknowledged challenge.

Ingot selection for aesthetic restorations using contemporary pressed ceramics.

Accurate communication among the patient, clinician, and laboratory technician is critical to the development of a functional, aesthetic restoration. The use of pressed ceramic restorations has provided a durable, consistent alternative for full-coverage crowns, veneers, onlays, and short-span fixed partial dentures. This article discusses the importance of proper ingot selection in the fabrication of aesthetic restorations and in the realization of patients' expectations for smile design. Ceramic ingots are available in a variety of colors and opacities that provide the clinician and laboratory technician with the latitude to select an ingot that will ultimately ensure patient satisfaction.