Marginal and internal fit of fixed prosthodontic constructions: a literature review

Marginal fit of fixed dental prostheses is determined by the size of the gap between the margin of the restoration and finish line of the prepared tooth. The most important factors influencing marginal and internal fit of fixed dental prostheses are the material used, the type of finish line as well as peculiarities of various technique of restoration fabrication. The objective of the article is to review the literature about the marginal and internal fit of various fixed prosthetic constructions. A review of literature using Pubmed, Google Scholar, and Research Gate database was carried out and 73 articles mostly in English were selected. The keywords were “Computer-aided design, marginal gap, internal fit, marginal fit, and crown adaptation”. Clinically accepted boundary value of marginal gap is considered to be ≤100 μm. However, a number of factors such as milling machine, parameters of bur (diameter, sharpness), software, design preparation, smooth preparation margins and incorporation of rounded line angles on the tooth preparation, the type of finish line, material and fabrication method of the construction and type of impression method should be taken into consideration in order to achieve these results. The perfect marginal and internal fit are the guarantee of construction success and longevity. As a sizeable marginal opening concedes more plaque accumulation, gingival sulcular fluid flow and bone loss, following in microleakage, recurrent caries, periodontal disease and a decrease in the longevity of the prosthetics restorations. Currently used techniques of restoration manufacturing, including constructions manufactured by computer aided design/computer aided manufacturing system can provide clinically allowable marginal fit.