Effect of cement type on the color attributes of a zirconia ceramic

PURPOSE: This in vitro study evaluated the effects of four different cements on the color attributes of a zirconia ceramic. MATERIALS AND METHODS: 40 zirconia ceramic disk specimens (0.5 mm thickness, 10 mm diameter, 0.1 mm cement space) were fabricated by a computer-aided design and computer-aided manufacturing system. The specimens were divided into 4 groups of 10 specimens and cemented to composite substrates using four different cements including: Glass Ionomer, Panavia F2.0, Zinc Phosphate, and TempBond. The L*, a*, and b* color attributes of the specimens were measured before and after cementation by a spectrophotometer. Additionally, ΔE values were measured to determine color changes for the groups and then compared with the perceptional threshold of ΔE = 3.3. Repeated Measures ANOVA, Tukey Post Hoc, Bonferroni, One-way ANOVA, and One-sample t-test tests were used to analyze the data. All tests were carried out at the 0.05 level of significance. RESULTS: Statistically significant differences were detected in the ΔE values for Zinc Phosphate (P<.0001) and TempBond (P<.0001) groups. However, there were no statistically significant differences in this respect for Glass Ionomer (P=.99) and Panavia F2.0 (P=1) groups. The means and standard deviations of the ΔE values for Glass Ionomer, Panavia F2.0, Zinc Phosphate, and Tempbond groups were 2.11±0.66, 0.94±0.39, 5.77±0.83, and 7.50±1.16 Unit, respectively. CONCLUSION: Within the limitations of this study, it was concluded that Zinc Phosphate and Tempbond cements affected the color attributes of the tested zirconia ceramic beyond the perceptional threshold. However, Glass Ionomer and Panavia F2.0 cements created acceptable color changes.

The combined effect of dismantling for steam sterilization and aging on the accuracy of spring-style mechanical torque devices

PURPOSE: This study aimed to assess the combined effect of dismantling before sterilization and aging on the accuracy (+/-10% of the target torque) of spring-style mechanical torque devices (S-S MTDs). METHODS: Twenty new S-SMTDs from two different manufacturers (Nobel Biocare and Straumann: 10 of each type) were selected and divided into two groups, namely, case (group A) and control (group B). For sterilization, 100 cycles of autoclaving were performed in 100 sequences. In each sequence, 10 repetitions of peak torque values were registered for aging. To measure and assess the output of each device, a Tohnichi torque gauge was used (P<0.05). RESULTS: Before steam sterilization, all of the tested devices stayed within 10% of their target values. After 100 cycles of steam sterilization and aging with or without dismantling of the devices, the Nobel Biocare devices stayed within 10% of their target torque. In the Straumann devices, despite the significant difference between the peak torque and target torque values, the absolute error values stayed within 10% of their target torque. CONCLUSION: Within the limitations of this study, there was no significant difference between the mean and absolute value of error between Nobel Biocare and Straumann S-S MTDs.

effect of implant position on retention and stability of mandibular implant-supported overdentures

The standard of treatment of edentulous people is implant retained overdenture. The aim of this study was to compare the effect of different implant location [ABDE, 6AE6, 6BD6] on the retention and stability of mandibular implant overdenture with ball attachment. An experimental study was designed. An acrylic resin model of edentulous mandible with six implant in the location of first molars, first premolar and between lateral incisor and canine on the left and right side was fabricated. A metallic overdenture was fabricated precisely adapted to the model and attached to a Zwick testing machine [crosshead speed of 51 mm/min]. The ball attachments were screw in three ways. First the balls in ABDE, then ball in 6AE6 and then balls in 6BD6 position were screwed. Dislodging tensile forces were applied in three vertical, oblique, anterior-posterior directions for each sample. For each of these three situations, five tests were done. The maximum dislodging force was measured. Normal distributions of data were analyzed with Shapiro-Wilk test. Levene test analazed the variances. A Three-way ANOVA test was employed followed by Tukey's test. The amount of vertical load is significantly higher than the oblique and Ant-post load [P<0.001]. The amount of ant-post load is signifivantly higher than the oblique load [P<0.001]. The average of MDF is significantly higher in 6BD6 position [P<0.001]. This average is also signifivatnly lower in ABDE position [P<0.001]. The amount of measured force in ABDE and 6BD6 position was the least and the most respectively [ABDE=64.51 N and 6AE6=66.06 N]. Vertical and oblique dislodging force are the minimum and maximum measured forces respectively [mean vertical= 87.95 N, mean Lateral= 48.1 N and mean Ant.Post= 63.5 N] Lateral and Ant.Post dislodgment values are higher in 6BD6 and 6AE6 respectively. In vertical dislodgment the retention values in the most in 6BD6 position. Vertical retention in higher than lateral and Ant.Post retentions. The more posterior position the distal implant the more the retention and stability