[Colorimetric evaluation of cercon zirconia and metal ceramic restorations in two thicknesses of veneering porcelain]

The aim of this study was to evaluate the effect of zirconia and base metal cores on the color of restorations. Furthermore, the effect of different backings on the color of cercon zirconia was evaluated. The specimens were Cercon zirconia and metal ceramic discs with "high Au" and "base metal" alloys. Cercon zirconia discs were veneered with veneering shade of A2 and two thickness of porcelain [0.7 mm, 1.2 mm]. There were 3 discs in each group. Metal ceramic discs were made of "nickel-chromium" alloy [Verobond] and "high Au" alloy [World 89] and two shades [A2, A3.5] and two thicknesses of veneering porcelain. 3 types of backing [high Au, nickel-chromium and A3 shade composite] were made for Cercon zirconia discs. Spectrophotometric evaluation of zirconia discs [on 3 backings] and metal ceramic discs was done. One-way ANOVA and Tukey tests were used for data analysis. There were no significant differences between the amounts of L*, a*, b* for Cercon zirconia on different backings [P>0.05]. In comparison between different core groups, a* was significantly higher in metal ceramic groups compared with that of zirconia groups [P<0.05]. Cercon zirconia can completely mask the underlying backing

Shear bond strength of a ceromer to noble and base metal alloys

The improvement of the physical and chemical properties of resins as well as great advances achieved in the field of chemical bonding of resin to metal has changed the trend of restorative treatments. Today the second generation of laboratory resins have an important role in the restoration of teeth. The clinical bond strength should be reliable in order to gain successful results. In this study the shear bond strength [SBS] between targis [a ceromer] and two alloys [noble and base metal] was studied and the effect of thermocycling on the bond investigated. In this experimental study, alloys samples were prepared according to the manufacturer. After sandblasting of bonding surfaces with 50|u AI2o3 Targis was bonded to the alloy using Targis I link. All of the samples were placed in 37°C water for a period of 24 hours. Then half of the samples were subjected to 1000 cycles of thermocycling at temperatures of 5°C and 55°C. Planear shear test was used to test the bond strength in the Instron machine with the speed rate of 0.5mm/min. Data were analyzed by SPSS software. Two-way analysis of variance was used to compare the bond strength among the groups. T test was used to compare the alloys. The influence of thermocycling and alloy type on bond strength was studied using Mann Whitney test. P<0.05 was considered as the limit of significance. The studied alloys did not differ significantly, when the samples were not thermocycled [P=0.136] but after thermocycling a significant difference was observed in SBS of resin to different alloys [P=000.1]. Thermal stress and alloy type had significant interaction, with regard to shear bond strength [P=0.003]. There was a significant difference in SBS before and after thermocycling in noble alloys [P=0.009], but this was not true in base metals [P=0.29]. Maximum SBS [19.09 Mpa] belonged to Degubond 4, before thermocycling. Minimum SBS [8.21 Mpa] was seen in Degubond 4 after thermocycling. The effect of thermocycling in reducing bond strength of resin to metal depends on the type of alloy. The noble metal studied is significantly affected by thermal tensions

relationship between corresponding upper buccal cusp distance [IBD] and Gothic arch width, inter-condylar width [ICH] and inter-upper canine distance [ICD] in an Iranian population

The aim of this study was to assess the relationship between corresponding upper buccal cusp distance [IBD] with Gothic arch width, inter-condylar width [ICW] and inter-upper canine distance [ICD] in an Iranian population. In this cross sectional investigation, subjects consisted of 42 adults with intact dentitions and class I occlusion, with no history of orthodontic treatment and TMJ disorders. Study casts were made from alginate impressions taken from maxillary teeth. Gothic arch tracing was performed and arbitrary hinge axes were determined on both sides. The distance between these points was recorded as the inter-condylar width [ICW] using a facebow. The Gothic arch width, ICW, LBD and LCD were measured by a vernier caliper. Pearson correlation test was used for statistical analysis [P