[ effect of porcelain veneer and coloring pigments on microtensile bond strength of a zirconia ceramic]

The bond strength between veneer ceramics and zirconia frameworks is the weakest component in the layered ceramics. Due to the possible effect of adding pigments to the core materials on the bond strength between core and veneer as well as the introduction of new ceramic materials in dentistry, the aim of this study was to compare the zirconia core-veneer microtensile bond strength using two ceramic veneers with or without coloring the core. In the experimental study, 12 disc-shaped specimens were fabricated using a manually aided design- manually aided manufactured [MAD/MAM] zirconia core [Zirkonzahn]. Two veneering ceramics of Ceram Kiss and Zirkonzahn ICE were also used to veneer the specimens. Half of the zirkonzahn discs were remained white and the others were colored by shade A2. Then, the discs were cut into microbars [30 for each group] and the microtensile bond strength of the core-veneer was calculated. The specimens were assessed using scanning electron microscopy [SEM] and the data were analyzed using two-way ANOVA and Student's t-test. Significant differences with respect to veneer layer were found [P<0.001]. No significant differences were seen among colored and uncolored cores [P=0.69]. According to the apparent effect of veneering ceramics on the core-veneer bond strength, careful selection of these agents is essential to achieve adequate bond strength between core and veneer to prevent delaminating and chipping failures of zirconia veneered restorations

Evaluation of solubility of modelling plastic in contiguity of ethanol and plasticizer

In patients with complete denture, some clinicians have used modelling plastic impression compound [MPIC] along tissue conditioner [TC] materials simultaneously. Little information is available on the composition of these materials and the interaction between them. The purpose of this study was to evaluate the influence of two components of MPIC on the structure and chemical composition of TC. In this experimental study, MPIC specimens were provided in 25x2 mm discs. Specimens were randomly divided into three groups and were immersed in ethanol 70%, plasticizer [dibutyl phthalate] and a mixture of them [ethanol 70% and dibutyl phthalate]. All of the discs were weighed with a digital balance before and 2, 4, 6 and 24 hours after immersion. Values were analyzed by non parametric Kruskal-Wallis [alpha= 0.05] and SPSS 16 for Windows [SPSS Inc., Chicago, IL] was used for statistical analysis. Statistical analysis indicated significant differences among all groups [p>.05]. Dibutyl phthalate [DBP] had high impact on the solubility of MP, while the mixture of dibutyl phthalate [DBP] and ethanol demonstrated the highest impact

[Discrepancy measurements of copings prepared by three casting methods and two different alloys, on ITI implants]

An important criterion of success assessment of implant-supported prostheses is marginal fit. Vertical and horizontal discrepancy can result in loosing of the prosthetic screw, crestal bone resorption, peri-implantitis and loss of osseointegration. Despite careful attention to waxing, investing, and casting, marginal discrepancies are inevitable. The aim of this study was to evaluate the marginal gap and overhang in three casting methods with two different alloys in ITI implants. In this experimental in vitro study 48 analog abutments were randomly divided into six groups as follows: 1] burn out cap + BegoStar, 2] impression cap+ BegoStar, 3] conventional wax up + BegoStar, 4] burn out cap + Vearbpond2, 5] impression cap + Verabpond2, 6] conventional wax up+ Verabond2. Waxing was done in 0.7 mm thickness verified by a digital gauge and a putty index was made for all groups. Reamer was used for correction of the finish line after casting in all groups. Castings were seated on analog abutments and embedded in acrylic resin. Specimens were sectioned by isomet instrument and polished and cleaned by ultrasonic cleaner for 10 min. The marginal gap and overextended margins of castings were examined under a Scanning Electron Microscope [SEM] [X200]. The mean gap and margin overextension were calculated for each group. Data were analyzed by multivariate analysis and Bonferroni post-hoc test with p<0.05 as the level of significance. No significant difference in gap size was observed among the three casting methods with two alloys [P=0.56]. The marginal gap was not different in the studied casting methods [P=0.092]. Gold alloy crowns showed lower marginal gaps compared to base metal alloy crown [P<0.001]. No significant difference in overhang size was observed among casting methods with two alloys [P=0.093]. Base metal alloy crowns showed less overhang compared to gold alloy crowns [P<0.001]. There was a significant correlation between overhang and use of impression cap in base metal alloys [P<0.001]. Based on the results of this study, vertical discrepancy of frameworks made with gold alloy were less than those made with base metal alloy. Base metal alloy demonstrated less overhang. Conventional wax up or using burn out caps reduced less horizontal discrepancy