INTRODUCTION: CAD/CAM denture base materials are milled from pre-polymerized pucks of resin that are highly condensed. So, they provide no polymerization shrinkage eliminating its subsequent disadvantages. This technology offered improved fit, strength properties and more bio-hygienic denture bases compared with conventional processing of the denture base material. OBJECTIVES: The aim of the study was to evaluate the physico-mechanical properties of CAD/CAM denture base material and the effect of thermo-cycling on it compared with the conventional one. MATERIALS AND METHODS: The study was conducted on two parallel groups, divided according to the denture material used. Group (1) conventional PMMA (control group), group (II) CAD/CAM PMMA (study group) of 40 specimens each (16 for impact strength, 16 for flexural strength, 8 for surface roughness and grinded powder form both materials for residual monomer test). Each group was divided into 2 sub-groups: (A) No thermo-cycling and (B) Thermo-cycling, then subjected to 4 different tests, impact strength, flexural strength, surface roughness and residual monomer tests. Data were collected, tabulated and statistically analyzed. Significance level was set at 5%. Bar charts were used for graphical presentations. RESULTS: Our study revealed a highly statistically significant decrease in residual monomer of CAD/CAM PMMA material in both conditions before and after thermo-cycling when compared to conventional PMMA material, which therefore leads to enhanced impact strength and significantly reduced surface roughness after heat treatment. On the other hand, also a highly significant reduction of its flexural strength after thermocycling has been observed. CONCLUSIONS: CAD/CAM dentures with lower amount of methacrylate monomer exhibit more favourable physico-mechanical properties and they have a long-term biocompatibility even with thermal changes making them a more satisfactory as a denture base material for edentulous patients.
Yusra Muftah Saad Elfaidy, Ahmed M. Abdelhamid, Sonia M. Elshabrawy(12-2018)

Abstract Back ground: Full coverage porcelain fused to metal crowns (PFM) is commonly recommended for restoration of extensively damaged teeth. Ability of the dentist to adequately prepare teeth is necessary to achieve a proper success and longevity of these restoration. Aims: This study aimed to determine the degree of axial taper and total occlusal convergence angles (TOC) for Porcelain Fused To Metal crowns (PFM) prepared with clinically practiced values, that carried out by dental practitioners in Tripoli center, Libya. Materials and Methods: It was a descriptive, cross-sectional study design and held at Alzendah private dental laboratory, Tripoli Libya. A convenience sample (40) models of Porcelain Fused To Metal Crowns (PFM) preparations carried out by private dental practitioners were scanned by employing a 3D model scanner (Ceramill Map300, Amanngirrbach, Austria). Evaluation of the total occlusal convergence (TOC), bucco-lingual and mesio-distal convergence angles of each abutment tooth was proceeded using B&B dental software (Guide system, B&B, Italy). The degree of taper was measured on the axial walls of each crown preparation and the bucco-lingual and mesio-distal convergence angles subsequently calculated. Results: A total of 40 casts having crown preparations (15 anterior, 25 posterior). The mean convergence angles mesio-distally for all preparations was 40.29° (sd 21.8°), and for the bucco-lingual was 29.92° (sd 9.3°), with mean of TOC was 35.10°. In anterior preparations, the mean bucco-lingual convergence angle was 42.32° (sd 12.2°) compared to 24.52° (sd 15.5°) for posterior preparations (p
Dr. Khaled Omar & Abdussalam Eljabali(1-2022)

one of the main factors that affect the success of the cast crown is the accuracy of the internal and marginal fit, a well-fitting crown reduces the chance for recurrent caries and periodontal disease, whereas the space between a poorly-fitting crown and tooth preparation enables accumulation of bacterial plaque, the use of paint- on die spacing technique to produce the cement gap and subsequently to improve the seating of the cast crowns has become quite popular in the recent years. The purpose of the study is to compare the marginal gap and the internal fit produced by two paint-on die spacing materials (Manicure and paint on die spacer ). Twenty four identical stone dies were made, 12 were coated with paint- on die spacer material, and 12 were coated with nail varnish material, the dies coated with die spacer were divided into three groups (DA,DB,DC), and the dies coated with nail varnish were also divided into three groups (VA,VB,VC), groups DA and VA were coated with one layer, DB and VB were coated with two layers, DC and VC were coated with three layers, for both groups wax patterns were made and casted using the lost waxing technique and all steps were standardized, impression replicas of the casted crowns were made and sectioned by means of the impression replica technique, measurements were taken using Scanning Electron Microscope, from 4 points (marginal gap, mid-axial, axio-occlusal and mid-occlusal). There was no statistical significant difference in accuracy between crowns fabricated on die spacer coated dies and crowns fabricated on nail varnish coated dies. with the crowns fabricated on die spacer coated dies being slightly more accurate.
ABDUSSALAM ELJABALI(12-2019)