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STATEMENT OF PROBLEM: The properties of commercially pure titanium are better than those of cobalt chromium alloys in various ways. However, casting pure titanium is challenging because of its high melting point and chemical reactivity. Because of excellent mechanical strength, a titanium alloy, Ti-6Al-4V, has been commonly adopted, but the aluminum and vanadium ions released may be cytotoxic. PURPOSE: The purpose of the present study was to evaluate a new titanium alloy, Ti-7.5Mo, developed by the National Cheng Kung University for casting removable denture frameworks. The casting success rate, porosity, and guide plane or rest fit were compared among frameworks cast with Ti-7.5Mo alloy and pure titanium for 3 types of edentulism. MATERIAL AND METHODS: Ti-7.5Mo alloy and pure titanium were used to cast frameworks for Kennedy Class I and II and completely edentulous conditions, with 5 frameworks for each condition. Wax patterns of the frameworks were designed and fabricated by using computer-aided design and computer-aided manufacture (CAD-CAM) technology to ensure their geometrical consistency. They were then invested with aluminum oxide-based material and cast. The castings were examined with microcomputed tomography (µCT) for porosity, and fit was evaluated from the thickness of a vinyl polyether silicone material at the guide plane or the rest by using an optical microscope. The casting was determined to be successful if the frameworks were complete. The porosity and fit were statistically evaluated by using 2-way ANOVA (α=.05). RESULTS: Using pure titanium, the casting success rate was 80%, with only 64% of the major connectors in the deficient castings being complete. The µCT images showed that the percentage of casting defects in Ti-7.5Mo castings was one-third of the pure titanium castings. Furthermore, internal voids were detected in the clasps of the pure titanium castings, while the Ti-7.5Mo castings had few defects in the minor connectors and no radiographically detectable defects in the clasps. The fit analysis demonstrated smaller gaps over both guide planes and rests in the Ti-7.5Mo castings. CONCLUSIONS: Ti-7.5Mo alloy had better castability than pure titanium. Based on the results, Ti-7.5Mo alloy is suitable for dental casting and may provide better performance.
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Background/purpose: Nowadays, zirconia-based framework has been used for longspan or full-arch fixed dental prostheses (FDPs). This study aimed to evaluate the effect of pontic distribution on marginal and internal gaps of five-unit anterior zirconiabased DPs. Materials and methods: Right maxillary central incisor and second premolar were selected as terminal abutments and three different edentulous conditions with one nonterminal abutment were simulated. Marginal and internal gaps in each zirconia-based samples(n = 10) were examined by computer-aided replica technique. Five regions, including marginal gaps at mesial or distal finishing line, internal gaps at the mesial or distal axial wall, and occlusal surface, were statistically analyzed (α = .05). Results: Most of marginal gaps and internal gaps at axial wall were clinically acceptable, but larger at occlusal surface. For the three experimental groups, clinically accepted percentage with qualified gaps were less than 30%.There were statistical differences at axial wall over pontic side and marginal gaps over non-pontic side between groups (P<0.05). For sum of gaps of all abutments in each group, statistical differences were found at marginal and axial wall (P < 0.05). As for those on terminal and non-terminal abutments, statistical differences were found on second premolar (P < 0.05). Conclusion: Except for occlusal surface, the overall marginal gaps and internal gaps at axial wall of five-unit anterior zirconia-based FDPs with different pontic distribution were clinically acceptable. However, the percentage with qualified gaps were low (<30%). Greater gaps were noted when adjacent pontic existed. Different pontic size and distribution with curvature had an influence on the gaps.
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BACKGROUND/PURPOSE: Clinically, PMMA resin is extensively used for fabricating provisional FPDs. However, fracture often occurs due to the unsatisfactory mechanical strength, especially within connectors of long-span provisional FPDs. The purpose of this study is to evaluate the fracture load of fiber-reinforced provisional FPDs with various pontic span lengths, and to identify the most suitable span length for fiber-reinforced long-span provisional FPDs. MATERIALS AND METHODS: Fifty-six provisional FPDs with various pontic span lengths were fabricated. Seven samples from each group were reinforced with glass fibers. Unreinforced counterparts served as control. The samples were fixed on the abutments after thermocycling and then received a fatigue test. Subsequently, they were mechanically loaded until fracture, and the initial fracture load and fracture patterns were recorded. Statistical analysis, including two-sample t-test, one-way, two-way ANOVA, Tukey-Kramer HSD post hoc analysis and χ2 test were used to evaluate mechanical performance. RESULTS: The mean fracture load of FPDs with 14 mm pontic span length is significantly higher than the other lengths. The fracture load of each reinforced group is significantly higher than each counterpart control. There is no interaction between two variables, pontic span and fiber reinforcement. With fiber reinforcement, the fracture patterns were altered from catastrophic fracture to bent or partial fracture. But, the fracture patterns were not affected by pontic span. CONCLUSION: The fracture load of acrylic FPDs decreases significantly when pontic span length is greater than 17 mm. Adding glass fibers into long-span provisional FPDs can significantly improve the fracture resistance and fracture patterns.