Harvard School of Dental Medicine

Objective: Dimensional changes in three-dimensionally (3D) printed surgical guides can occur after post- processing due to polymer relaxation, humidity, and light exposure. Such changes may reduce the accuracy of prosthetically-driven guided implant placement by altering the fit and position of the guide. This study aimed to evaluate the effect of storage conditions and time on the dimensional stability of 3D-printed surgical guides using surface deviation and angle deviation of the guide sleeves as outcome measures.

Methods: Sixty simplified surgical guide specimens were designed, printed using a HeyGears A2D 4K printer, and post-processed according to manufacturer instructions. Samples were divided into four groups (n = 15 each): Dry/UV-Blocked (DU), Dry/Ambient (DA), Wet/Ambient (WA), and Wet/UV-Blocked (WU). Each specimen was scanned immediately after post-processing (Day 0) and at subsequent time points (Days 1, 2, 5, 7, and 14) using a desktop lab scanner. STL data was analyzed in a 3D metrology software determine RMS estimate surface deviation and angle deviation relative to baseline. Normality was assessed using the Shapiro–Wilk test. Two-way repeated measures ANOVA was used to evaluate the effects of group and time, followed by Tukey post hoc testing for pairwise comparisons (α = 0.05).

Results: For RMS estimate deviation, significant main effects of group (F(3,266) = 13.20, p .001) and time (F(4,266) = 12.69, p .001) were observed, along with a significant interaction (F(12,266) = 9.42, p .001), indicating that the effect of storage condition varied over time. Tukey post hoc analysis demonstrated that the DU group exhibited significantly lower RMS estimate deviation compared DA (p = 0.0006) and WU (p .001). RMS estimate deviation values ranged from approximately 12–25 µm, with wet conditions demonstrating progressive increases over time. For angle deviation, significant main effects of group (F(3,266) = 20.18, p .001) and time (F(4,266) = 7.10, p .001) were observed, with no significant interaction (F(12,266) = 1.71, p = 0.064). Tukey post hoc analysis revealed that the DU group demonstrated significantly lower angle deviation compared to DA, WA, and WU groups (p .001), with no significant differences among the remaining comparisons.

Conclusion: Storage conditions significantly influenced the dimensional stability of 3D-printed surgical guide specimens. RMS estimate deviation demonstrated strong time-dependent changes and greater sensitivity to environmental conditions, whereas angle deviation primarily reflected overall group differences. Dry storage with UV protection provided the most stable and consistent results, while wet conditions were associated with progressive dimensional instability over time.