Method: An electronic search of dental literature through PubMed database was undertaken. Randomized studies, clinical controlled studies, cohort studies, case control studies, observation studies and case series were considered eligible for the study. Research was performed using following key words: “marginal gap” OR “marginal fit” OR “marginal accuracy” AND “clinical acceptable” OR “clinical acceptability”. In addition, manual research in base of MeSH terms was performed. No time interval was applied. A three-stage selection of the resulted hits was performed: titles, abstracts and finally full texts were revised respectively. The inclusion criteria were 1.literature in English; 2.single crowns; 3.marginal gap measurement; 4.micrometric measurements; 5.marginal gap clinical acceptability. The main exclusion criteria were 1.no clear experimental methods; 2.different marginal discrepancy measurements as determined by Holmes (1989) e.g. referring to internal gap, over extended crown margin, under extended crown margin or absolute marginal discrepancy; 3.studies based on tactile sensations, perception of the operator or patient satisfaction.
Result: 72 papers reporting the clinical acceptability of the marginal gap were identified; 18 met the inclusion/exclusion criteria. Study analysis showed a mean of 95.67 microns for the clinical acceptability of the marginal gap; values ranged between 39 and 200 microns. Differences were found between materials (with Porcelain Fused to Metal showing the lowest gap width) and between the various methods used for the marginal gap measurement.
Conclusion: This literature review identified an high variability of the experimental protocols, study designs and procedures completed to determine the clinical acceptability value for marginal gap of single crown prosthetic restorations. Moreover, extreme variety of the marginal gap values recorded in the literature was found. Data retrieved from the literature looks inconclusive.