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.

Purpose: to study the influence of different preparation designs on fracture resistance and retention of CAD/CAM endocrowns. Materials and methods: Forty human mandibular molars were selected to conduct the present study. All teeth were randomly divided into 2 groups (n=20 each) according to the preparation design of endocrown, Group (1): Endodontically treated teeth without ferrule (butt joint). Group (2): Endodontically treated teeth with 1mm ferrule. All prepared teeth were restored using IPS e-max CAD endocrowns. After cementation of endocrowns all specimens were subjected to thermal cycling in automated thermocycling machine in order to mimic the intra-oral condition. Then retention was measured using material testing machine, also fracture resistance was measured using material testing machine. The recorded data were collected, tabulated and statistically analyzed. Results: Endodontically treated molar with 1mm ferrule showed high fracture resistance and retention than endodontically treated molar without ferrule. Conclusions: All obtained fracture resistance and retention values lie within the clinically accepted ranges, endocrowns with 1mm ferrule have fracture resistance and retention higher than endocrowns without ferrule (butt joint).

Statement of the problem: Ceramics and glass-ceramics are materials of choice for dental crowns due to their attractive hardness, biocompatibility, etc. However, a major problem with their usage is the observed high wear of either the opposing dental enamel or both the enamel and ceramic itself. Objective: The present study aimed at ranking and comparing the wear performance of three different ceramic systems as an indication of wear. In addition, change in surface roughness was calculated using optical surface profiler. Results: The statistically significant highest mean material's weight loss was recorded in porcelain group, whereas the statistically significant lowest mean weight loss was recorded in BruxZir group. The statistically significant greatest mean antagonist weight loss was recorded for e.max antagonist cusp, whereas the statistically significant lowest mean weight loss was recorded for BruxZir antagonist cusp.Surface roughness increased after wear procedure in all samples. Conclusions: Within the limitations of this in vitro study, monolithic zirconia and porcelain resulted in less wear depth to human enamel compared to lithium disilicate based ceramics (e.max CAD). However, porcelain is more affected by wear compared to zirconia.

Purpose:The purpose of the current study was to evaluate marginal accuracy and color stability of lithium disilicate laminate veneer compared to hybrid ceramic veneer. Materials and Methods: Forty maxillary teeth were collected and prepared (but joint preparation) to receive a laminate veneer. They were equally sub grouped (n= 20) to receive 2 types of laminate veneers (IPS E-max CAD and vita enamic). The veneer was milled from the blocks in a CEREC 3 Machine. All veneers were cemented with resin cement. All samples had been subjected to 20000 thermal cycles which are equivalent twenty years of clinical use. Marginal gap were measured by using universal serial bus (USB) Digital microscope. Colors were measured using a reflective spectrophotometer.Marginal gap and color were measured pre and post thermo cycles. Data were tabulated and statistically analyzed. Results: For the marginal gap, the two tested materials demonstrated an acceptable value. Regarding the color stability there was color change for both groups after thermal cycling with higher mean values for Vita Enamic than E-max and that was statistically insignificant. Conclusion: The E-max veneers recorded less marginal accuracy and more color stability than Vita Enamic and they did not affected by thermo cycling. Codex : 36/1907 azhardentj@azhar.edu.eg