Deep margin elevation (DME) is a non-invasive restorative technique to relocate the deep cervical margin to a supragingival position using resin composite. This retrospective multicenter practice-based study will assess the long-term clinical performance and periodontal health of teeth restored with CAD-CAM crowns with or without DME. Patients who will receive CAD-CAM lithium disilicate (LD) crowns with or without DME between 2013 and 2023 at multiple private practices will be included. When indicated, DME will be performed using resin-based restoration. Clinical assessment of the crowns and supporting periodontal structures will be performed following the modified United States Public Health Service (USPHS) criteria. Intra-oral photographs, periapical and bitewing radiographs will be taken for further assessment by three evaluators. Kaplan Meier survival analyses will be performed.

The ethical approval to conduct this retrospective multicenter practice-based study was obtained from the Research Ethics Committee at the University of Sharjah (REC-23-09-11-01-F). The present report will complie with the STROBE guidelines for cohort studies.

Participants selection Patient records at 7 private practices in the UAE will be searched for the presence of posterior LD CAD-CAM crowns during 2013 to 2016. Inclusion criteria: adult patient and indication for crown with or without DME. Exclusion criteria: poor oral hygiene and active periodontal disease. A total of 560 eligible patients will be invited to a clinical examination.

Clinical Examination The clinical evaluation will be conducted by three calibrated independent prosthodontists. Patients will be requested to read and sign an informed consent form to participate in the study. Intraoral photographs, Periapical and bitewing radiographs will be obtained to assess the emergence profile of the DEM which should ideally reproduce the normal morphology. Both the crowned tooth and the contralateral tooth were assessed clinically for the following parameters: pocket depth (PD), BoP, and presence of plaque using a plaque indicator liquid (Mira-2 Ton Liquid, Hager & Werken; Duisburg, Germany). Bone level will be assessed by comparing a measurement from the margin of the tooth to the crest of the bone on bitewing radiographs to corresponding preoperative radiographs.

A comprehensive assessment of the restored teeth will be carried out following the modified United States Public Health Service (USPHS) criteria. The location of crown margin will be recorded clinically and radiographically to assess the association between periodontal health and margin location. The primary outcomes will be the survival rate and time to event. The secondary outcome will be the success rate. The success is defined as a crown that had remained unchanged over the observation period, while survival is defined as a crown that was in situ at the examination visit but might exhibits chipping or have been repaired. Failure will be scored for the followings: recurrent caries, loss of vitality, tooth fracture, and crown fracture.

Statistical analysis Descriptive statistics were computed with a statistical software program (IBM SPSS Statistics, v29; IBM Corp., Armonk, NY, USA). Each complication will be considered as a statistical event. The statistical testing will be 2-tailed (a=.05). The McNemar chi-squared and Fisher exact tests will be used to assess the severity of PD, BoP and plaque deposition. Odds ratios and their 95% confidence intervals will be reported. The Pearson chi-squared test for differences in proportions will be used to assess the relationship between the location of margins and the associated condition of the periodontal tissues. Kaplan-Meier survival analysis will be performed to calculate the overall crown survival and success probabilities. Cox regression models will be used to evaluate the effect of various confounding factors on the survival and success rates.

Inclusion Criteria: :

• adult patient and indication for crown with or without DME.

Exclusion Criteria:

• poor oral hygiene and active periodontal disease.