Journal of Dental Medicine

Background and Aim: Cementation is one of the most critical steps of the porcelain restoration technique. However, limited information is available concerning the bond strength of current ceramic bonding systems. The aim of this study was to evaluate the shear bond strength of three dual-cure resin cements to IPS-Empress2 ceramics.

Materials and Methods: In this experimental study, 30 pairs of IPS-Empress 2 ceramic discs were fabricated with 10 and 8 mm diameters and 2.5 mm thickness. After sandblasting and ultrasonic cleaning, the surfaces of all specimens were etched with 9% hydrofluoric acid for 60 seconds. Then, the three groups of 10 bonded specimens were prepared ceramic bonding resin systems including Panavia F2, Variolink II and Rely X ARC. After storage in 37±1c water for 24 hours and thermocycling in 5c and 55c water for 500 cycles with 1-minute dwell time, the shear bond strengths were determined using Instron machine at speed of 0.5mm/min. Data were analyzed by One Way ANOVA test. For multiple paired comparisons, the Tukey HSD method was used. The mode of failure was evaluated by scanning electro microscope (SEM). P<0.05 was considered as the limit of significance.

Result: Significant differences were found between different cement types (P<0.05). Variolink II provided the highest bonding values with IPS-Empress2. A combination of different modes of failure was observed.

Conclusion: Based on the results of this study, according to the highest mode of cohesive failure, Variolink II seems to have the strongest bond with IPS-Empress2 ceramics.

Background and Aim: Debonding is the most common failure type of fiber posts. This in vitro study aimed to evaluate the bond strength of 3 different fiber posts cemented with a resin luting agent in three regions of prepared post spaces after being subjected to termocycling.

Materials and Methods Thirty six mandibular first premolars were sectioned at the cemento-enamel junction and were treated endodontically. After one week the post spaces were prepared and roots were divided into 3 groups of 12 specimens according to the post types (D.T.Composipost, D.T.White, D.T.Light). Sealbond Cement Dual II was used in all groups. One day after cementation, specimens were subjected to 3500 thermal cycles (5^oC/55^oC). Each root was then embedded in acrylic resin and sectioned perpendicular to long axis. Three 1-mm tick segments from apical, middle and cervical thirds were prepared. Push out test was performed. Data were analyzed with 2-way ANOVA (P<0.05). All root segments and dislodged posts were observed with stereomicroscope to figure out their failure modes.

Results: The post type had no significant effect on bond strength (p=0.08). However bond strength at the coronl segment was higher than the other segments (p=0.005). Mixed mode was the mostly occurred failure mode with D.T.Composipost and D.T.Light but with D.T.White, the mostly occurred failure mode was adhesive between the post and cement.

Conclusion: Different fiber posts have relatively similar bond strength to root dentin, bond strength at the coronl segment was higher than the other segments.

Background and Aims: Since a large marginal opening allows more plaque accumulation, gingival sulcular fluid flow and bone loss, microleakage, recurrent caries and periodontal disease, marginal fit is of great importance in fixed restorations. The aim of this study was to compare the marginal fit of zirconium-based all ceramic (Cercon) frameworks, made by two different approaches (Direct and Wax-up scanning).

Materials and Methods: An abutment analog, with 5.5 mm width and height, was selected as an experimental model. Twenty all ceramic cores were made for this model (10 specimens per each group). In the first group (Direct), experimental models were scanned directly using Computer Aided Design/Computer Aided Manufacturing (CAD/CAM). The core was then designed with the aid of a computer and machined. In the second group (Wax-up or CAM) a wax-up pattern was made on the experimental model and then scanned and milled from Cercon blocks. The marginal discrepancy of each specimen was recorded using a stereomicroscope (SZX9, Olympus, Japan) and digital camera (Mode TK, C1380E, JVC, Japan) and then measured by Adobe Photoshop CS software. The data were analyzed using T-test.

Results: Mean marginal discrepancy of Direct group (85.2±3.95 µm) was significantly less than that of Wax-up group (120.2±6.91 µm).

Conclusion: Improved marginal fit of zirconia ceramics was found with the direct model scanning compared with that of Wax-up scanning using CAD/CAM.