Quantitative and Color-Coded Assessment of Crown Preparation Using a 3D-Printed Channel and Hole Guide: A Pilot Comparison With Conventional Guides.

Purpose: Crown preparation is a fundamental procedure in restorative dentistry. This study aimed to evaluate quantitative and color-coded assessment of tooth reduction using various 3D-printed tooth reduction guides in comparison to conventional guiding methods during crown preparation.

Methods: Twelve prosthodontic residents from a single prosthodontic graduate program (first year: n = 6; second year: n = 6) participated in this IRB-approved study (Yonsei University Dental Hospital IRB 2-2024-0026). Recruitment was voluntary and the participation rate was 100%. Participants provided informed consent and performed tooth preparations using four guide types: freehand, putty guide, channel guide, and hole guide. Standardized reduction parameters were provided. Maxillary and mandibular models were generated using Medit Model Builder software, and selected teeth (upper left central incisor, lower left first molar, lower right second premolar) were converted into dies. Guides were designed with a uniform 2 mm thickness for stability. The putty guide was fabricated using polyvinylsiloxane, while channel and hole guides were 3D printed. Preparations were performed with a diamond bur, and completed teeth were scanned with an intraoral scanner. Accuracy was assessed by superimposing scans onto original tooth data using 3D inspection software, with under-prepared areas analyzed in detail. Preparation times were recorded.

Results: The channel guide consistently demonstrated the highest accuracy, with the lowest mean distances in underprepared areas for all teeth. The freehand group showed the greatest variability and the highest mean distances in underprepared regions. Working time analysis showed significant differences among groups; the putty group required the longest time, while the freehand group was the most time-efficient. The channel group demonstrated moderate working times with low variability.

Conclusions: The novel channel-type guide showed potential for improving preparation accuracy. However, underprepared areas in critical regions could compromise restoration durability. While the guides had minimal impact on procedure time, further studies are needed to confirm these findings in a wider clinical context.