Thesis & Dissertations

Purpose: to evaluate a new experimental technique named Crown Margin Shifting "CMS", and evaluate it clinically and radiographically in comparison with crowns violating the biological width in the aim of trying to re-establish the biological width. Materials and methods: a split mouth study was done, including seven healthy patients having maxillary bilateral premolars showing a deep proximal caries violating the biological width. Each patient represented the both the control site "CS" and the study site "SS" (n = 7). The CS received a CAD/CAM monolithic zirconia with a heavy champher finish line, while the SS received the same restoration and finish line but showing CMS concept at the deep proximal finish line where a heavy rounded shoulder finish line was left exposed with a knife edge crown margin meeting the finish line. Abutment teeth were examined clinically according to the following parameters: modified plaque index "MPI", modified bleeding index "MBI", periodontal probing depth "PPD" and gingival index "GI". Clinical evaluation was done immediately at time of crown cementation then at 6 and 12 months. Radiographic evaluation using CBCT was done to measure crestal bone level at the deep proximal finish line in three positions: at the most buccal crestal bone, the middle apical crestal bone and at the most palatal crestal bone on base line, 6 and 12 months, then, marginal bone loss was calculated on 6 and 12 months. The established biological width was measured at the three examined points. Results: when comparing between CS and SS, clinical results showed that within 12 months, there was statistically significant increase in MBI, PPD and GI parameters in SS and CS up to 6 month, followed by a significant decrease up to 12 month in MBI and GI for both sites, except for PPD in CS, it continued in a non significant increase, while MPI showed no significant difference in both sites. Radiographic results revealed that MBL increased in control site up to 12 months, whereas in study site, it took place only in the first 6 months. Conclusion: within the limitation of the study, it could be concluded that CS restorations which was placed subgingivally with biological width violation showed better clinical parameters presented as improved GI with decreased MBI. SS crowns with CMS concept showed better radiographic parameters with less marginal bone loss, but added no further improvement on clinical parameters when comparing them with CS. Concluding that abutments with deep margins violating the biological width can be crowned with no need for crown lengthening or CMS modification as long as the ferrule effect is enough and good oral hygiene can be preserved. Key words: biologic width, subgingival crown margin, crown lengthening, CAD/CAM monolithic zirconia.