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

This article investigates the impact of tooth preparation design and chairside milling units on the internal adaptation and marginal fit of CAD/CAM-fabricated endocrowns used to restore endodontically treated molars. Two preparation designs—shoulder endocrown and onlay endocrown—were compared clinically and in vitro, with restorations milled using two Dentsply Sirona systems: the MC X mill and the Primemill. Results showed that typodont (in vitro) shoulder endocrown fits translated well to clinical settings, and both milling units produced clinically acceptable fits, with minor differences such as smaller vertical wall gaps for the MC X mill in shoulder preparations. Shoulder endocrowns exhibited significantly smaller marginal and pulpal floor gaps, while onlay endocrowns had smaller horizontal wall gaps; however, all measured gaps were below the clinically accepted threshold of 120 µm. The study concludes that both preparation designs and milling units are viable clinical options without expected impact on restoration longevity.