Method for the non-destructive three-dimensional analysis of marginal fit

Many conventional methods for the assessment of marginal fit of dental restorations are destructive due to the necessary slicing. Even if a non-destructive replica-technique is used, there still remains the immense loss of data because the silicone duplicates of the cement space have to be cut into pieces, too.

Objectives: Aim of this study was to develop a method for the non-destructive three-dimensional (3D) analysis of marginal discrepancies in dental restorations.

Methods: Sixteen human molars were prepared with a chamfer and restored with all-ceramic copings made by an experimental CAD/CAM-system. The inside of the resulting copings was digitized with a touch-probe scanner (Triclone 90, Renishaw, Gloucestershire, GB). With computer-aided analysis (Surfacer V.10.6, Imageware, Ann Arbor, MI, USA), the internal fit of the restorations as well as the marginal fit at one-hundred circumferential measuring points was determined.

Results: The comparison of a spline-curve representing the preparation line and the marginal digital data of the copings showed the absolute marginal discrepancy as defined by Holmes et al. (1989). For each point the vertical and horizontal component was calculated. For internal fit, an average of 59 µm (SD 25) and maximum discrepancies of up to 319 µm were found. The absolute marginal discrepancy showed values between 11 µm and 115 µm (mean 62 µm, SD 25). Radar charts with a benchmark of 100 µm clearly showed weather a coping would have been clinically acceptable or if the system needed further improvement.

Conclusions: The developed non-destructive method for the 3D-analysis of marginal fit has shown to be a most useful tool for analyzing and benchmarking the quality of copings. The method is independent of material or kind of a restoration. Marginal gaps that do not meet clinical requirements, even if it is just one single point, can be clearly identified.