Effect of Die Spacer Thickness on the Microshear Bond Strength of CAD/CAM Lithium Disilicate Veneers

Abstract

Aim. The aim of this study was to compare the microshear bond strength of ceramic veneers with digital die spacer settings at 20, 40, and 100 µm. Materials and Methods. Eighteen milled lithium disilicate microdiscs (IPS e.max CAD, Ivoclar Vivadent) were divided into three groups (n = 6) according to their digital die spacer settings: group A = 20 µm, group B = 40 µm, and group C = 100 µm. Six randomly selected sound maxillary premolars received three microdiscs each. Each microdisc was 1 mm in diameter and 1 mm in height. The buccal surfaces of the premolars were prepared with a 0.5 mm depth in enamel. After cementation, the specimens were thermocycled for 2,500 cycles between 5 and 55°C. Microshear bond strength testing was performed using a universal testing machine until bonding failure. Failure modes were evaluated using a stereomicroscope. Statistical analyses included one-way ANOVA, Tukey’s post hoc test, and chi-square test with a 5% alpha error and 80% study power. Results. The mean microshear bond strength values were calculated in MPa for group A = 31.91 ± 12.41, group B = 29.58 ± 5.03, and group C = 13.85 ± 4.12. One-way ANOVA ( p ≤ 0.05 ) showed a statistically significant difference in microshear bond strength among the three groups. Tukey’s post hoc test showed significant differences between groups A and C ( p = 0.004 ) and between groups B and C ( p = 0.011 ). The failure modes were presented as cohesive, adhesive, and mixed failures. Chi-square test indicated that the failure mode distribution was not significantly different among the three groups ( p = 0.970 ). Conclusion. Higher digital die spacer settings decrease the microshear bond strength of CAD/CAM lithium disilicate veneers.

Effect of cement film thickness on the microshear bond strength of CAD/CAM lithium disilicate bonded to cervical and mid-coronal enamel

“…Polyether impression material (Impregum Soft, 3M ESPE, GmbH, Neuss, Germany) was then coated on the roots and the tooth was returned in its acrylic block to mimic the periodontal ligament. Any excess was removed using a sharp blade (8,15) .…”

“…With a high-speed handpiece and depth limiting and tapered diamond burs of medium grit (Microdont, Monsey, NY, USA), a 0.5-mm depth preparation into the enamel of the buccal surface was performed. A stereomicroscope was used to ensure that no dentin was exposed (8,15) . An extraoral scanner (Vinyl scanner, Smart optics Sensortechnik, GmbH, Bochum, Germany) was used to scan the tooth surfaces.…”

“…The intaglio surfaces of the microdiscs were coated with a single layer of adhesive, which was then thinned with an air syringe for 5 seconds. The surfaces of the microdisc are so small that it was necessary to use a digital light microscope (Inskam 307, Shenzhen, China) to view their fitting surfaces before the application of conditioning materials and the adhesive (8) .…”

“…Two layers of universal adhesive (Single Bond Universal Adhesive, 3M ESPE, St. Paul, MN, USA) were applied onto the etched enamel surfaces and rubbed for 20 seconds. The adhesive was then evenly distributed using an air spray to form a shiny and homogeneous film (8) .…”

“…However, among those studies only a few have included the factor of cement thickness in this particular context (8)(9)(10) . Cement thickness is of crucial importance in the longevity of a restoration as it is the link between the ceramic-cement-tooth substrate triplex.…”