Influence of Different Preparation Designs on Fracture Resistance of Full-Coverage Occlusal Veneers After Thermo-Mechanical Aging Simulation

Abstract

Aim: To evaluate the fracture resistance maxillary molars restored with lithium disilicate glass-ceramic (LDG) occlusal veneers with two preparation designs. Subjects and methods: Twenty extracted maxillary molars were assigned to two groups (n = 10). In group 1 (GROUP S), the teeth received a preparation for a conservative fullcoverage occlusal veneer restoration with a 90 rounded shoulder margin. In group 2 (GROUP c), were prepared with a minimally invasive chamfer. LDG restorations (IPS e.max CAD) were obtained with the Cerec 3 CAD/CAM system and luted with Variolink II cement. After thermo-mechanical aging (120,000 cycle with vertical movement 1mm, horizontal movement 3mm and frequency 1.6Hz), All the samples were individually mounted on the Instron testing machine with a load cell of 5 KN and fracture test was done by compressive mode of load applied occlusally using a metallic rod with spherical tip (5.6 mm diameter) at cross-head speed of 1mm/min. The load required to fracture was recorded in Newton and tabulated to be statistically analyzed. The fractured specimens were examined to detect the mode of failure. Results: The fracture resistance of samples with chamfer finish line (2453.2 N ± 104.83) was higher than the values of samples with shoulder finish line (2440.6 N ± 119.36) but with no statistical significant difference (p value > 0.05). Most of the observed specimens exhibited restorable fractures. Conclusion: This study demonstrated similar satisfactory performance of the two considered preparations designs for occlusal veneer with lithium disilicate glass-ceramic. Conclusion: A new minimally invasive occlusal veneer preparation with marginal chamfer exhibited encouraging fracture resistance that were comparable to those of a standard conservative preparation for the restoration of molars with CAD/CAM lithium disilicate occlusal veneers.

Impact of Two Different Designs and Materials on Fracture Resistance of Occlusal Veneers (In Vitro Study)

“…(23,24) Fracture resistance test was chosen in our study as it played a crucial role in determining the longevity of the restorations. (21) Regarding the effect of the preparation design on fracture resistance of occlusal veneers in our study, the type of the preparation design had non-significant effect and that might be because the point of loading during fracture resistance test was centralized on specimens away from the finish line. (25) Our results agreed with Abdelhameed et al (2018) (5) and Emam Z and Aleem N. (2020) (7) who found that there was no effect of the preparation design on occlusal veneers fracture resistance .…”

“…(17) For standardization of occlusal veneer restorations, CAD/CAM technology was used to standardize the thickness and the anatomy of the restorations and to avoid laboratory errors. (21) Adhesive resin cement was chosen in our study as it was found that all ceramic restorations cemented using adhesive resin cements had greater fracture resistance than those cemented using traditional cements. (22) Moreover, in our study we used total etch technique because it was reported that the use of total-etch technique enhanced the bond strength up to 28 MPa within enamel and 13-20 MPa within dentin that lead to improving the fracture resistance.…”

Effect of Minimally Invasive Posterior Veneer Preparation Designs on Failure Load and Mode After Fatigue (in-vitro Study)

“…(41) Regarding the preparation design, it was recommended to decrease the incisal part to evenly distribute the load and lower the stress levels on the veneer material. (41) In their study, Hassan et al (2020) (42) employed the Thermo Mechanical Load Cycling procedure to evaluate the maxillary molars fracture resistance repaired with occlusal veneers constructed of Lithium Disilicate Glass-ceramic. The researchers also compared the outcomes of two distinct preparation designs.…”

“…The utilization of a minimally invasive occlusal veneer preparation, along with a marginal chamfer, demonstrated encouraging fracture resistance outcomes that were comparable to those achieved with a conventional conservative preparation for the repair of molars utilizing CAD/CAM lithium disilicate occlusal veneers. (42) Zhang et al (2020). (10) analyzed different types of preparation designs in premolars, including occlusal veneers and occlusal veneers with covering on the lingual and proximal surfaces.…”