08 November 2022

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Margin designs influence enamel, dentin removal during partial indirect preparations

By Lorenzo Breschi and Claudia Mazzitelli

Lorenzo Breschi

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Increasingly performant materials and advanced techniques have enabled the preservation of healthy tooth structure. As a consequence, it has been possible to perform more conservative treatments also in presence of extensive dental cavities, limiting more aggressive interventions such as full-crown rehabilitations. Nowadays, indirect partial restorations (IPR) are preferable to fulfill the principles of minimal invasive dentistry.

During tooth preparation for IPR, dentists can choose between different margin designs and finishing lines. However, no clear indication for the most conservative preparation design is present in literature. In a recent laboratory study, Mancuso et al. aimed to quantitatively evaluate the volumetric enamel and dentin tissue removal and the residual adhesion surface area after different preparations for IPR of a posterior tooth

Materials, methods

A micro-CT scan of a sound human molar was used to obtain STL files to print 50 tooth replicas with a 3D-printer. Teeth were prepared with the following margin designs (n=10): circumferential rounded shoulder above the dental equator, circumferential hollow chamfer above the dental equator, butt joint above the dental equator, circumferential rounded shoulder below the dental equator and circumferential hollow chamfer below the dental equator. 

After preparations, a second scan was taken and the two STL files were aligned to calculate the volume of the enamel and dentin removal and the residual adhesion surface area. The data were acquired with a quality inspection software and were statistically analyzed.

Results

Differences in dental tissue reductions were related to the margin location. No differences existed above the equator between circumferential rounded shoulder, circumferential hollow chamfer and butt joint (p=0.05). Instead, below the dental equator, the chamfer preparation resulted in a more conservative approach with the highest enamel surface area available for adhesion than the shoulder design (p>0.05). The butt joint resulted in a superior exposure of dentin.

Conclusions

Dental preparations with flat designs performed above the dental equator expose much more dentin, reducing the adhesive surface in enamel. Below the dental equator, when possible, a chamfer preparation provides a shoulder design that enables a more conservative approach.

Mancuso E, Mazzitelli C, Maravic T, Pitta J, Mengozzi A, Comba A, Baldi A, Scotti N, Mazzoni A, Fehmer V, Sailer I, Breschi L. "The influence of finishing lines and margin location on enamel and dentin removal for indirect partial restorations: A micro-CT quantitative evaluation." J Dent 2022, 127: 104334. https://doi.org/10.1016/j.jdent.2022.104334