Abstract
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<0.001). Mean mesiodistal convergence anteriorly was 20.39° (sd 10.18') compared to 20.01° (sd 12.16°) posteriorly (p<0.001). Distal and buccal taper were significantly greater on posterior teeth (p<0.001) compared to anterior whereas lingual taper was greater on anterior teeth (p<0.001). Conclusions: The mean convergence angles for porcelain fused to metal crowns produced by private dental general practitioners in Tripoli, Libya, were significantly greater in bucco-lingual dimension than mesio-distal. This results exceeded the recommended guidelines proposed in the literature and it was not easy for them to achieve ideal taper results. Keywords: Porcelain fused to metal crowns, convergence angles, axial taper,