A comparative survey on the increased fracture resistance of amalgam restored teeth using three types of Glass Ionomer as adhesive liners

Statement of Problem: Because dental amalgam does not adhere to tooth structure, using adhesive cements in amalgam-bonded restorations have been increased. Purpose: The goal of this in-vitro study was to compare the effects of three types of glass ionomer as adhesive liners as well as varnish liner in increasing fracture resistance of teeth restored with amalgam. Materials and Methods: Seventy extracted human maxillary premolars were selected and MOD cavities were prepared on them excluding ten intact teeth as positive control group and ten cavity prepared teeth without restoration as negative control group. All the prepared teeth were then restored with spherical amalgam (gs.80) with one of the following liners silver alloy glass ionomer liner, conventional glass ionomer liner, varnish liner, resin-modified glass ionomer and resin-modified glass ionomer with delayed light curing. The teeth were stored in 37C distilled water for 7 days and were then loaded under compressive strength using an Instron testing machine. The force required to fracture teeth were recorded and the data were analyzed statistically using ANOVA and Tukey HSD tests. Results: Statistically significant differences were observed in fracture resistance between restored and non-restored samples. Comparisons between groups attributed significant effects to resin-modified glass ionomer in increasing fracture resistance of amalgam restored teeth (P<0.05). In most specimens, one cusp was separated from tooth structure whereas amalgam remained bonded to the intact cusp. Conclusion: According to these findings, resin-modified glass ionomer put a statistically significant effect in fracture resistance of amalgam-restored teeth

Comparison of Fracture Strength of Endodontically Treated Teeth Restored with Two Different Cast Metallic Post Systems

Statement of Problem: Endodontically treated teeth are more prone to fracture. The post and core are often used to provide the necessary retention for prosthetic rehabilitation. Objectives: The purpose of this study was to: 1) compare the fracture strength of endodontically treated teeth restored either with Nickel-Chromium (Ni- Cr) post or Non- Precious Gold-color alloy (NPG) post compared to the control group and 2) evaluate the fracture site in each group. Materials and Methods: In this experimental study, endodontic treatment was carried out for 45 extracted maxillary premolars. The specimens were divided into 3 groups (n=15). Group1: restored with NPG post and core, group2: restored with Ni-Cr post and core, and group 3, no post and core were used after endodontic treatment and the access cavity was filled with amalgam. Failure force was recorded in Newton when root or remaining coronal structure fracture was occurred. Data were analyzed using one-way analysis of variance (ANOVA), Student t-test and Tukey HSD test to compare the three groups. Results: There was a statistically significant difference among all groups (P<0.05). Fracture resistance of the teeth restored by NPG posts was significantly higher than those restored by Ni- Cr (P<0.001). Results showed that the fracture mainly occurred in the root of the teeth restored with Ni- Cr and NPG post while fractures occurred in the core portion of the teeth restored with amalgam. Conclusions: The findings of the present study indicated that the fracture strength of the teeth without using cast post and core was significantly lower than the teeth restored with cast post and core. Also the teeth restored by NPG post had a significantly higher fracture resistance than Ni-Cr posts

Wear Resistance of Acrylic Resin Teeth against Porcelain and Natural Teeth

Statement of Problem: The effect of porcelain surface on the antagonist acrylic teeth has not been widely studied. Objectives: This study aimed to investigate the effect of polished porcelain, glazed porcelain, and natural teeth (as the control group) on the acrylic resin teeth. Materials and Methods: In this experimental-laboratory study, a total of 60 specimens of glazed and polished porcelain, natural teeth, and acrylic resin teeth were prepared; in groups of 15 samples each. The denture teeth specimens were examined in terms of tooth wear against glazed or polished or enamel surfaces. After the abrasion test using the polishing machine, the wear of each sample was measured based on the weight lost by a digital scale. The wear surfaces of acrylic teeth were observed by SEM to evaluate the wear characteristic. The data were analyzed using Independent Sample t-test. Results: The glazed and polished porcelain teeth abraded the denture teeth significantly more than the natural teeth (P=0.001). Although there was not a significant difference between the glazed and polished porcelain (P=0.059), the polished porcelain caused less tooth wear than the glazed porcelain. Conclusions: According to the results of this study, glazed porcelain caused less tooth wear on denture teeth than both of the polished porcelain and natural teeth