Comparing Digital Reduction Guides and Free-Hand Techniques for Predoctoral Crown Preparation Accuracy

Insufficient tooth reduction compromises crown longevity and aesthetics. This study aimed to determine whether digitally designed, 3D-printed reduction guides improved crown preparation accuracy and efficiency for dental students compared to freehand preparation.

In a randomized crossover, third- and fourth-year students (N = 25) prepared typodont #8 twice-freehand and with a segmented guide (incisal, axial, and lingual components) designed per ADEX standards. Preparation quality was assessed by an independent, blinded examiner using an 11-criteria rubric (Ideal/Substandard/Critical) and digital analysis (CEREC SW 5.2). Guide usability was examined with a NASA-TLX survey.

The guided method significantly improved preparation accuracy scores by 1.12 points (p < 0.05) compared to freehand, with 64% of students achieving higher scores, and reduced preparation time by 17% (p < 0.05). Although 48% of participants rated the task difficulty as "Somewhat High" on the TLX subscale, 92% had a global NASA-TLX score < 50 (below the "High" workload threshold), indicating that the overall perceived workload remained below the "High" category and that most users found the guide easy to use.

The custom 3D-printed reduction guide significantly improved both accuracy and efficiency of anterior crown preparation among dental students. These findings support the integration of digitally fabricated guides into preclinical curricula to standardize outcomes and bridge gaps between training and practice through digital workflows.