Castability of a Ti-7.5Mo alloy for fabricating frameworks for removable partial dentures

Yung-Chung Chen; Min-Chieh Chang; Wen-Yu Hsiao; Yen-Chun Chen

doi:10.1016/j.prosdent.2021.10.014

Castability of a Ti-7.5Mo alloy for fabricating frameworks for removable partial dentures

J Prosthet Dent. 2023 Oct;130(4):646-653. doi: 10.1016/j.prosdent.2021.10.014. Epub 2021 Dec 16.

Authors

Yung-Chung Chen¹, Min-Chieh Chang², Wen-Yu Hsiao³, Yen-Chun Chen⁴

Affiliations

¹ Assistant Professor, School of Dentistry & Institute of Oral Medicine, College of Medicine, National Cheng Kung University, Tainan, Taiwan, ROC; Chief, Division of Prosthodontics, Department of Stomatology, National Cheng Kung University Hospital, College of Medicine, National Cheng Kung University, Tainan, Taiwan, ROC. Electronic address: yc_chen@mail.ncku.edu.tw.
² PhD student, Department of Biomedical Engineering, National Cheng Kung University, Tainan, Taiwan, ROC; Adjunct visiting staff, Division of Prosthodontics, Department of Stomatology, National Cheng Kung University Hospital, College of Medicine, National Cheng Kung University, Tainan, Taiwan, ROC.
³ Engineer, R&D Department, Joy Medical Devices Corporation, Kaohsiung, Taiwan, ROC.
⁴ Engineer, R&D Department, Joy Medical Devices Corporation, Kaohsiung, Taiwan, ROC; Adjunct assistant Professor, School of Dentistry, Kaohsiung Medical University, Kaohsiung, Taiwan, ROC.

PMID: 34920871
DOI: 10.1016/j.prosdent.2021.10.014

Abstract

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.