Bond Strength of Resin Cement and Glass Ionomer to Nd:YAG Laser-Treated Zirconia Ceramics.

PURPOSE: To investigate the effect of neodymium-doped yttrium aluminum garnet (Nd:YAG) laser irradiation on the surface properties and bond strength of zirconia ceramics. MATERIALS AND METHODS: Forty-eight zirconia ceramic pieces (4 × 4 × 1 mm3 ) were divided into four groups according to surface treatment as follows: two control groups (no treatment) for resin bonding (CRC) and glass ionomer (GI) bonding (CGC); two laser treatment groups (Nd:YAG irradiation, 3 W, 200 MJ, 10 Hz, 180 µs) for resin bonding (LRC) and GI bonding (LGC). The ceramics in the control groups and the laser groups were distinguished by the application of different cements (resin cement and GI). Following surface treatments, the specimens were cemented to human dentin with resin cement and GI. After bonding, the shear bond strength (SBS) of the ceramic to dentin was measured, and the failure mode of each specimen was analyzed using a stereomicroscope. A one-way ANOVA compared the average bond strength of the four groups. Pairwise comparisons among the groups were performed using the Games-Howell test. The level of significance was set at 0.05. RESULTS: The means (± standard deviation) of SBS values in the CRC, CGC, LRC, and LGC groups were 3.98 ± 1.10, 1.66 ± 0.59, 10.24 ± 2.46, and 2.21 ± 0.38 MPa, respectively. Data showed that the application of the Nd:YAG laser resulted in a significantly greater SBS of the resin cement to the zirconia ceramics (p < 0.001). The highest bond strength was recorded in the LRC group. In the CRC group, 75% of the failures were of the adhesive type, compared with 66.7% and 83.3% in the LRC and LGC groups, respectively. In the CGC group, all failures were adhesive. CONCLUSIONS: Pretreatment of zirconia ceramic via Nd:YAG laser improves the bond strength of the resin cement to the zirconia ceramic. GI cement does not provide sufficient bond strength of zirconia ceramics to dentin.

Effect of tightening torque on the marginal adaptation of cement-retained implant-supported fixed dental prostheses.

BACKGROUND: The final position of the abutment changes with the amount of tightening torque. This could eventually lead to loss of passivity and marginal misfit of prostheses. The aim of this study was to evaluate the effect of three different tightening torques on the marginal adaptation of 3-unit cement-retained implant-supported fixed dental prostheses (FDPs). MATERIALS AND METHODS: Two implants (Straumann) were inserted in an acrylic block so that one of the implants was placed vertically and the other at a 15° vertical angle. A straight abutment and a 15° angulated abutment were connected to the vertically and obliquely installed implants, respectively, so that the two abutments were parallel. Then, 10 cement-retained FDPs were waxed and cast. Abutments were tightened with 10, 20, and 35 Ncm torques, respectively. Following each tightening torque, FDPs were luted on respective abutments with temporary cement. The marginal adaptation of the retainers was evaluated using stereomicroscope. FDPs were then removed from the abutments and were sectioned at the connector sites. The retainers were luted again on their respective abutments. Luting procedures and marginal adaptation measurement were repeated. Data were analyzed by ANOVA and least significant difference tests (α = 0.05). After cutting the FDP connectors, the independent samples t-test was used to compare misfit values (α = 0.05). RESULTS: Following 10, 20, and 35 Ncm tightening torques, the marginal discrepancy of the retainers of FDPs significantly increased (P < 0.05). There was no significant difference between the marginal discrepancies of these two retainers (P > 0.05). The marginal gap values of angulated abutment retainers (ANRs) were significantly higher than those of the straight abutment after cutting the connectors (P = 0.026). CONCLUSION: Within the limitations of this study, the marginal misfit of cement-retained FDPs increased continuously when the tightening torque increased. After cutting the connectors, the marginal misfit of the ANRs was higher than those of the straight abutment retainers.

Effects on shear bond strength and the enamel surface with an enamel bonding agent.

INTRODUCTION: The purpose of this study was to evaluate the shear bond strength of orthodontic brackets and the effect of an enamel bonding agent (EBA) on enamel surface after debonding. METHODS: Seventy-five extracted maxillary premolars were collected and randomly divided into 3 groups of 25. The enamel cracks were surveyed with a stereomicroscope. In the first group, 1 layer of EBA was applied before the adhesive resin. In the second group, 2 layers of EBA were used; in the third group, no EBA was used. Bonding was followed by incubation for 48 hours at 37 degrees C and thermocycling for 1000 cycles. Debonding was performed with a shear force. The surfaces of the teeth were evaluated, and the length, depth, direction of cracks, and adhesive remnants on the enamel surface were recorded. Data were analyzed by using analysis of variance and paired samples t tests. RESULTS: There were no significant differences between the shear bond strengths (P = 0.341) of the 3 groups, or in the direction, length, and depth of the cracks before and after debonding (P > 0.05). There was a significant increase in the number of cracks after debonding in the 3 groups (P < 0.05). The evaluation of adhesive remaining on the surface of the teeth indicated that most bond failures occurred at the resin-bracket interface. CONCLUSIONS: The use of EBA does not enhance bond strength or provide greater protection to the enamel surface during debonding.