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PURPOSEThe aim of this study was to evaluate the effects of abutment diameter, cement type, and re-cementation on the retention of implant-supported CAD/CAM metal copings over short abutments.MATERIALS AND METHODSSixty abutments with two different diameters, the height of which was reduced to 3 mm, were vertically mounted in acrylic resin blocks with matching implant analogues. The specimens were divided into 2 diameter groups: 4.5 mm and 5.5 mm (n=30). For each abutment a CAD/CAM metal coping was manufactured, with an occlusal loop. Each group was sub-divided into 3 sub-groups (n=10). In each subgroup, a different cement type was used: resin-modified glass-ionomer, resin cement and zinc-oxide-eugenol. After incubation and thermocycling, the removal force was measured using a universal testing machine at a cross-head speed of 0.5 mm/min. In zinc-oxide-eugenol group, after removal of the coping, the cement remnants were completely cleaned and the copings were re-cemented with resin cement and re-tested. Two-way ANOVA, post hoc Tukey tests, and paired t-test were used to analyze data (α=.05).RESULTSThe highest pulling force was registered in the resin cement group (414.8 N), followed by the re-cementation group (380.5 N). Increasing the diameter improved the retention significantly (P=.006). The difference in retention between the cemented and recemented copings was not statistically significant (P=.40).CONCLUSIONResin cement provided retention almost twice as strong as that of the RMGI. Increasing the abutment diameter improved retention significantly. Re-cementation with resin cement did not exhibit any difference from the initial cementation with resin cement.

In post-core crown restorations, the significant mismatch between stiffness of artificial crowns and dental tissues leads to stress concentration at the interfaces. The aim of the present study was to reduce the destructive stresses by using a class of inhomogeneous materials called functionally graded materials (FGMs). For the purpose of the study, a 3-dimentional computer model of a premolar tooth and its surrounding tissues were generated. A post-core crown restoration with various crown materials, homogenous and FGM materials, were simulated and analyzed by finite element method. Finite element and statistical analysis showed that, in case of oblique loading, a significant difference (p < 0.05) was found at the maximum von Mises stresses of the crown margin between FGM and homogeneous crowns. The maximum von Mises stresses of the crown margin generated by FGM crowns were lower than those generated by homogenous crowns (70.8 vs. 46.3 MPa) and alumina crown resulted in the highest von Mises stress at the crown margin (77.7 MPa). Crown materials of high modulus of elasticity produced high stresses at the cervical region. FGM crowns may reduce the stress concentration at the cervical margins and consequently reduce the possibility of fracture.

Aim and Objective. Impression materials and stone casts are the main sources of cross-contamination and transmission of dental infections between dental offices and laboratories. Both Surfosept (alcohol-based) and Deconex® (quaternary ammonium compound) are biocompatible solutions that have superior antimicrobial properties against bacteria, fungi, and viral envelope. Considering the influence of disinfection substances on the dimensions of impression materials, this study aimed to compare the effect of Surfosept and Deconex® 53 on the accuracy and dimensional stability of the Panasil® dental addition silicone material. Materials and Methods. This in vitro study was performed on 30 dental casts. The samples were divided into one control group and two experimental groups to be disinfected with Surfosept (1%) and Deconex® 53 (2%) using a sequential sampling method (10 per group). The impressions in the experimental groups (i.e., Surfosept and Deconex® 53) were rinsed and dried; then, the disinfectant was sprayed on the impressions and remained for 30 seconds before pouring with stone. In the control group, the impressions were only rinsed and dried and were poured in 10 minutes. Cast dimensions were measured by a profile projector device, and the mean values obtained from the experimental groups were compared with those of the control group. Results. There were no significant differences among the groups regarding the height of the resulting dies without undercut ( P = 0.62 ). Moreover, there was no significant difference among the groups regarding the distance between the two dies ( P = 0.77 ). However, the diameter of the dies with undercut and without undercut was different significantly among the control and experimental groups ( P < 0.005 ). Conclusion. In general, no significant difference was encountered between dimensional stability and accuracy of the dental impressions using Surfosept and Deconex® 53 in this study.

Background and Aim: Several methods are available for intraoral repair of chipped porcelain restorations by composite resin. Also, there is still controversy regarding the best method of porcelain repair in terms of bond strength and cost effectiveness. This study aimed to compare three methods of porcelain surface treatment on shear bond strength (SBS) of composite to porcelain. Materials and Methods: This in vitro, experimental study was conducted on 30 porcelain blocks with a metal base in three groups. In group 1, porcelain surface was etched with hydrofluoric (HF) acid and silanized. After the application of bonding agent, several composite increments with 2mm thickness were applied on the porcelain surface. In group 2, porcelain surface was sandblasted with 50µaluminum oxide particles, etched and silanized. In group 3, grooves with 2mm length and 0.5 mm depth were created on the porcelain surface. The surface was then etched and silanized. Bonding agent and composite were then applied. The samples were then mounted in acrylic resin, stored in water for one week and subjected to thermocycling. The SBS was then measured using a universal testing machine. The SBS data were compared among the three groups using one-way ANOVA. Results: The mean SBS was 9.13±6.09, 12.71±9.82 and 11.44±7.37 MPa in groups 1-3, respectively. No significant difference in bond strength was noted among the three groups (P>0.05). Conclusion:No significant difference exists among the three surface treatment methods evaluated in this study in terms of SBS of composite to porcelain.