ABSTRACT
Aims: Resistance form of full metal-ceramic crown is an important feature that determines longevity of these restorations. This study evaluated the resistance form of full metal-ceramic prepared with four different design features. Materials and Methods: An acrylic tooth was prepared with 20° total occlusal convergence (TOC) angle, 2.5 mm of occlusocervical dimension and a shoulder finishing line. This design lacked resistance form. The crown preparation was subsequently modified by preparing Mesial Occlusal Distal isthmus, placing occlusal inclined plane, and reducing TOC. Four metal dies from these designs were constructed by lathe machine and then 10 metal copings were fabricated for each preparation. Metal coping were cemented on metal dies with temp-bond cement. Force was applied at 45° from lingual to buccal direction with universal testing machine. Statistical analysis used: The data were evaluated by Kruskal-Wallis and non-parametric Mann-Whitney test. Results: All features increased resistance form when compare to control group. However, reduce TOC group showed greatest value of resistance. Conclusion: Within the limitation of this study, reducing the tapering of occlusocervival dimension is the most effective way in increasing resistance form, although, other features were also effective.
ABSTRACT
Wear resistance of artificial teeth has an important role in denture longevity. The purpose of this in vitro study was to evaluate wear resistance of four brands of artificial teeth. In this in vitro study four brands of artificial teeth, including Apple, Yaghoot, Glamour and Ivoclar were used. Ten maxillary first premolars were selected from each set and were fixed in autopolymerizing acrylic resin. Wear test was performed for 1000 and 2000 cycles. Heights of the teeth were measured under a light microscope before and after wear cycles. Data were analyzed by ANOVA and Duncan tests [? = 0.05]. ANOVA showed that mean wear rate of the teeth in both 1000 and 2000 cycles had significant differences [p value < 0.001]. According to Duncan test, except for Apple and Yaghoot, other groups had significant differences with each other [p value2 = 0.314], [p value1 = 0.289]. It was concluded from the results of the present study that wear rate of Ivoclar teeth was significantly lower than that in other groups. Glamour, Yaghoot and Apple teeth showed the highest rate of wear, respectively
ABSTRACT
Mean bar failure in overdenture-supported implant has been reported to be 3.97 percent; even this low failure rate is unacceptable for patients because of its cost compared with complete denture. The aim of this study was to assess stress distribution in different points of the bar of overdenture-supported implants by finite elements analysis. In this descriptive study, stress distribution on the bar of mandibular overdenture was evaluated by the finite elements analysis [FEA]. Implants in two canine areas were connected to each other by one bar at the distance of 2 mm from the lining tissue of the edentulous ridge. Then the vertical force applied to the left first molar increased gradually from 0.5 to 50 N and stress distributions were recorded at different points of the bar. By increasing the force up to 6.06 N, stress was uniformly distributed over the bar, but with greater force stress was focused on the border of the middle third and the force application third. This pattern of stress distribution continued parallel with an increase in the force. Failure is higher at the border area between the middle third of the bar and the third near the applied force due to maximum stress; therefore, reinforcement of the bar at this area is suggested