ABSTRACT
OBJECTIVES: It is difficult to achieve adhesion between resin cement and zirconia ceramics using routine surface preparation methods. The aim of this study was to evaluate the effects of CO2 and Er:YAG laser treatment on the bond strength of resin cement to zirconia ceramics. MATERIALS AND METHODS: In this in-vitro study 45 zirconia disks (6 mm in diameter and 2 mm in thickness) were assigned to 3 groups (n = 15). In control group (CNT) no laser treatment was used. In groups COL and EYL, CO2 and Er:YAG lasers were used for pretreatment of zirconia surface, respectively. Composite resin disks were cemented on zirconia disk using dual-curing resin cement. Shear bond strength tests were performed at a crosshead speed of 0.5 mm/min after 24 hr distilled water storage. Data were analyzed by one-way ANOVA and post hoc Tukey's HSD tests. RESULTS: The means and standard deviations of shear bond strength values in the EYL, COL and CNT groups were 8.65 +/- 1.75, 12.12 +/- 3.02, and 5.97 +/- 1.14 MPa, respectively. Data showed that application of CO2 and Er:YAG lasers resulted in a significant higher shear bond strength of resin cement to zirconia ceramics (p < 0.0001). The highest bond strength was recorded in the COL group (p < 0.0001). In the CNT group all the failures were adhesive. However, in the laser groups, 80% of the failures were of the adhesive type. CONCLUSIONS: Pretreatment of zirconia ceramic via CO2 and Er:YAG laser improves the bond strength of resin cement to zirconia ceramic, with higher bond strength values in the CO2 laser treated samples.
Subject(s)
Adhesives , Ceramics , Lasers, Gas , Resin Cements , WaterABSTRACT
Low fracture resistance is one of the most important disadvantages of all-ceramic restorations. The aim of the present study was to assess the effect of convergence angle and change in copping thickness related to it on fracture resistance of all ceramic crowns. This study was an experimental study in which 30 brass dies were fabricated as crowns with a height of 5.5mm, base diameter of 6.2mm and marginal thickness of 1.2mm in the following design: [10 shoulder 90° -" Convergence 6°], [20 shoulder 90° - Convergence 12°]. With a special index, 0.6mm thickness acrylic cores were made on 20 dies [10 with 6° convergence, 10 with 12° convergences]. With the 6° index and 12° dies, 10 cores were made with the thickness of 0.6mm+difference in thickness of 6° and 12° convergence angle. Cores were casted with IPS e.max porcelain of core and veneered with another index with parallel cylindrical wall and then cemented with Panavia F2 on the brass dies. After storage in distilled water of 37°c for 24 hours, the specimens were placed in compressive test ring within an Instron universal testing machine and loaded in the center of occlusal surface with a 4mm diameter stainless steel ball. An axial preload of 20N was applied followed by a compressive load until fracture occurred. The data were analyzed with one way analysis of variance [ANOVA]. Average fracture load in 6° convergence angle and 0.6mm core thickness was 1951.40N, in 12° convergence angle and 0.6mm core thickness, it was 2798.46N and in 12° convergence angle and 0,6mm+additional core thickness because of increase in convergence angle, it was 3151.05N. The results revealed no significant difference in the fracture load between two core thickness but fracture load of 12° convergence angle was significantly greater than 6° [P<0.001]. Copping thickness didn't affect the fracture load of all ceramic crowns but increase in convergence angle increased the fracture load significantly
ABSTRACT
Finite elemental analysis is an efficient technique for investigating biomeehanical interactions of different implant designs. The purpose of this study was to investigate the effect of cylindrical and tapered implants with different degree of tapering and similar lengths on the stress and strain distribution in the bone and implant. One cylindrical and five types of tapered implants with degrees of tapering from 0.02 to 0.16 were modeled to this study. The implant material was grade IV titanium and abutment was grade ELI titanium. The bone model used comprised of compact and spongious bone assumed to be homogeneous, isotropic and linearly elastic. With increased degree of implant tapering, the von Mises stress and strain increased in the bone. However, at the neck of implant, the most sensitive area, with increase in degree of tapering, both stress concentration and strain decreased. The lowest stress and strain were generated in the most tapered implant. Based on the results, cylindrical screw implant generated the lowest maximum von Mises stress in cortical bone and tapered implant type 5 with highest taper degree generated the highest maximum von Mises stress