ABSTRACT
Demand for implant supported overdentures has increased due to the problems of conventional dentures. Despite the high success rate of implants, implant failure remains a major challenge. Implant overload can cause cortical bone loss and implant failure. Using finite element analysis, this study aimed to find the best design and type of attachments causing minimum stress in the alveolar bone. The geometrical model of the mandible was produced using computed tomography [CT] data and three ITI implants were placed in the midline and the location of the first premolar teeth. All conditions were simulated using finite element software. Three bar-ball, bar and ball attachments were considered to support the overdenture. Maximum von Mises stress was calculated in the supporting bone in different overdenture designs. The results showed that the greatest amount of stress in bone was around the upper thread and the neck of the implant. The ball and the bar-ball attachments applied the most and the least amount of stress to the bone around the implant, respectively. Maximum stress was applied to the ball attachment in the bar-ball design. The maximum amount of movement was in bar-ball attachment. The bar-design decreased the stability of overdenture, as well as the stress in the peri-implant bone. Ball design increased concentration of stress in bone around the implant and increased the stability of overdenture
Subject(s)
Denture, Overlay , Dental Stress Analysis , Denture Retention , Mandible , Finite Element AnalysisABSTRACT
Enamel wear is among the main disadvantages of ceramic restorations. Recently, use of full zirconia crowns without dental porcelain has been suggested. The aim of this study was to compare the effect of feldspathic porcelain and zirconia on the wear of natural teeth. In this experimental study, 22 zirconia specimens were fabricated; out of which, 11 specimens were polished and chosen as zirconia specimens while the remaining 11 were used to fabricate porcelain specimens. A total of 22 natural human teeth were also obtained. The natural teeth were photographed by a stereomicroscope in a fixed position and the distance from the cusp tip to a reference point was measured. Next, 11 teeth opposed zirconia and the remaining 11 opposed porcelain specimens in a chewing simulator and subjected to 120,000 masticatory cycles. The teeth were photographed again and the greatest difference between the before and after values was recorded. The mean [ +/- standard deviation] wear rate was 153.8 +/- 95.68 and 306.3 +/- 127.74, in the zirconia and porcelain groups, respectively; and the two groups had a statistically significant difference in this respect [P=0.007]. The mean wear was significantly lower in teeth opposing zirconia than in those opposing feldspathic porcelain
ABSTRACT
Statement of Problem: The increase in the use of metal-ceramic restorations and a high prevalence of porcelain chipping entails introducing an alloy which is more compatible with porcelain and causes a stronger bond between the two. This study is to compare shear bond strength of three base-metal alloys and one noble alloy with the commonly used VMK Master Porcelain
Materials and Method: Three different groups of base-metal alloys [Ni-cr-T3, Super Cast, and VeraBond] and one group of noble alloy [X-33] were selected. Each group consisted of 15 alloy samples. All groups went through the casting process and change from wax pattern into metal disks. The VMK Master Porcelain was then fired on each group. All the specimens were put in the UTM; a shear force was loaded until a fracture occurred and the fracture force was consequently recorded. The data were analyzed by SPSS Version 16 and One-Way ANOVA was run to compare the shear strength between the groups. Furthermore, the groups were compared two-bytwo by adopting Tukey test
Results: The findings of this study revealed shear bond strength of Ni-Cr-T3 alloy was higher than the three other alloys [94 MPa or 330 N]. Super Cast alloy had the second greatest shear bond strength [80. 87Mpa or 283.87 N]. Both VeraBond [69.66 MPa or 245 N] and x-33 alloys [66.53 MPa or 234 N] took the third place
Conclusion: Ni-Cr-T3 with VMK Master Porcelain has the greatest shear bond strength. Therefore, employment of this low-cost alloy is recommended in metalceramic restorations
ABSTRACT
The infection transmission by impression to the laboratory is growing concern for clinicians and laboratory technicians. This study aimed to compare the self-antibacterial effect of six irreversible hydrocolloid impression materials [Iralgin, Xantalgin, Tropicalgin, Hydrogum and Orthoprint] and oral flora microorganisms. In this experimental set-up, 108 irreversible hydrocolloid specimens including alginate disks with 1 mm thickness, 5 mm diameter and 30 +/- 2 mg weight, and 18 sterile paper disks as negative control specimens [totally 126 specimens] were prepared. These specimens were transferred to Staphylococcus aureus [Group 1], Pseudomonas aeruginosa [Group 2] and Candida albicans [Group 3] fresh microbial environments. After 48 hours incubaction in37 degrees Celsius, the maximum growth inhibition zone diameters were recorded. Statistical analysis was performed by ANOVA or Friedman test. No zone of inhibition was observed around the control specimens. Iralgin and Tropicalgin specimens had significant growth inhibition on Group 1. Tropicalgin more than Iralgin and Iralgin more than the other specimens significantly inhibited Group 2 microorganisms. Plastalgin specimens had significant growth inhibition on Group 3 [P<0.05]. Some of the investigated alginates had self-antibacterial effects; however, disinfection of impressions with other techniques are still inevitable