Preparation design and milling unit impact on CAD/CAM endocrown fit

The present study evaluated the impact of tooth preparation design and chairside milling unit on the internal adaptation and marginal fit of CAD/CAM fabricated endocrowns.

Endodontically treated molars (N = 60) from a clinical research project were divided into four groups. Thirty molars received an onlay endocrown preparation and 30 molars received a shoulder endocrown preparation. The preparations were scanned and designed with Primescan (Dentsply Sirona) and 15 of each group were milled with the MC X milling machine (Dentsply Sirona) or Primemill (Dentsply Sirona) to create four clinical groups (N = 15). One in vitro group was added using the shoulder endocrown preparation and Primemill (N = 15). Polyvinylsiloxane replicas were fabricated and sectioned. Specimens were measured under a microscope at the margins and predetermined segments of the internal surface.

No significant differences in marginal fit or internal adaptation were noted in the pulpal floor, horizontal walls, or external vertical walls for the typodont shoulder endocrowns compared to clinical shoulder endocrowns. The MC X mill had significantly smaller vertical wall gaps compared to the Primemill shoulder endocrown group in the clinical model. No significant differences were found for endocrown onlays when comparing milling units. Significantly smaller marginal and pulpal floor gaps existed for shoulder endocrown preparation groups, whereas significantly smaller horizontal wall gaps existed for onlay endocrown preparation groups.

The fit of endocrown restorations obtained on a typodont preparation translated to the fit observed clinically. Both preparations and milling units are acceptable options to be used clinically, with the differences likely having no clinical impact on the longevity of the restorations.