Abstract
The objective of this study was to evaluate the retention force of T-bar clasps made from commercially pure titanium (CP Ti) and cobalt-chromium (Co-Cr) alloy by the insertion/removal test simulating 5 years use. Thirty-six frameworks were cast from CP Ti (n=18) and Co-Cr alloy (n=18) with identical prefabricated patterns on refractory casts from a distal extension mandibular hemi-arch segment. The castings were made on a vacuum-pressure machine, under vacuum and argon atmosphere. Each group was subdivided in three, corresponding to 0.25 mm, 0.50 mm and 0.75 mm undercuts, respectively. No polishing procedures were performed to ensure uniformity. The specimens were subjected to an insertion/removal test and data was analyzed statistically to compare CP Ti and Co-Cr alloy in the same undercut (Student's t-test for independent samples) and each material in different undercuts (one-way ANOVA) (p=0.05). Comparisons between materials revealed significant differences (p=0.017) only for the 0.50-mm undercut. No significant differences (p>0.05) were found when comparing the same material for the undercuts. It may be concluded that for different undercuts, both Co-Cr alloy and CP Ti had no significant differences for T-bar clasps; CP Ti showed the lowest retention force values when compared to Co-Cr alloy in each undercut, but with significant difference only for the 0.50-mm undercut; and both materials maintained the retentive capacity during the simulation test.
Highlights
Since the introduction of lost-wax casting, various metals have been tested for the fabrication of removable partial denture (RPD) frameworks
Despite the improvements made to Co-Cr alloys and the fact that these alloys are the most used for casting RPD metallic frameworks, the search for a material with the ideal properties for fabricating RPD remains a matter of concern and the use of titanium for the production of cast RPD framework has gradually increased [1,2,3,4]
For commercially pure titanium (CP Ti), there were no significant differences (p>0.05) for the tested undercuts, there was a slight increase in retention force for the 0.50-mm and 0.75-mm undercuts, and a slight decrease for the 0.25-mm undercut during the simulation test
Summary
Since the introduction of lost-wax casting, various metals have been tested for the fabrication of removable partial denture (RPD) frameworks. On the past few years, various materials have been tested for RPD casting and, especially over the last decade, several studies have highlighted the advantages of titanium and titanium alloys, and have investigated their possible use in the fabrication of RPD metallic frameworks [4,5,6,7,8,9]. In addition to its remarkable biocompatibility, the low modulus of elasticity is another property that makes titanium more resilient and, more similar to gold alloys. This property allows for placing clasps in larger retentive areas, without applying excessive loads to abutment teeth during denture insertion and removal, favoring esthetics [10,11]. More studies are necessary to investigate the permanent deformations, which are one of the most common mechanical complications that affect denture clasps due to the possibility of causing loss of denture retention and stability [12]
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