Transfer of Surface Relief from 3D-Printed Working Models to Injection-Moulded Composite Restorations: A Pilot Study

Background/Objectives: In the injection moulding technique, the restoration is shaped by a clear silicone index, which is itself an impression of a 3D-printed working model. The printed surface may, therefore, be the primary source of the relief seen on the finished restoration—a chain that has received little attention. This exploratory pilot study followed the surface relief along that chain. Methods: Three printed objects made from a single model resin were studied: two flat specimens differing only in layer thickness (50 µm and 150 µm) and one anatomically shaped arch model printed at 100 µm. One clear silicone index and one injection-moulded composite replica were produced from each object. Surfaces were examined by optical 3D profilometry (Zeta-20, ×20 objective), recording Sa, Sq, Sz, Ssk and Sku according to ISO 25178-2 over the whole scanned field (476 × 357 µm2) and over sub-areas of 120 × 80 µm2, three scans per flat surface and one scan per morphological field on the anatomical pair. The heights of individual layer steps were read from the instrument markers. Results: The specimen printed at 150 µm was rougher than the one printed at 50 µm (Sa 2.68 vs. 1.30 µm; Sz 45.01 vs. 25.00 µm), with non-overlapping ranges; on their replicas, this ranking was reversed. Kurtosis fell from the printed surface to its replica wherever the measurement field contained no layer step. On the anatomically shaped model, a field containing only a terrace gave almost identical values on model and replica (Sa 2.08 vs. 2.19 µm), whereas a field crossing a layer step gave Sa 22.83 vs. 33.70 µm. Two successive layer steps measured 101.5 and 104.4 µm on the model and 98.9 and 104.3 µm on the replica, each close to the nominal 100 µm layer thickness. Conclusions: These preliminary observations, obtained on one object per condition and without statistical testing, suggest that the stair-step relief of the printed working model reaches the injection-moulded composite with its height largely intact, while finer isolated features are attenuated. They are hypothesis-generating and require confirmation on replicated specimens.