Marginal and Internal Gap of Handmade, Milled and 3D Printed Additive Manufactured Patterns for Pressed Lithium Disilicate Onlay Restorations.

STATEMENT OF THE PROBLEM: On a pressed lithium disilicate restoration, the building up of a wax pattern of the future restoration is a necessary step on the fabrication process. Conventionally, a wax pattern can be produced by handmade or milled procedures; however, the development of additive manufacturing technologies allows a new fabrication method. PURPOSE: The present study measured the marginal and internal gap of handmade, milled and additive manufactured patterns for an onlay restoration. MATERIAL AND METHODS: A preparation of an onlay restoration was made on an extracted mandibular tooth. A definitive cast was fabricated from a conventional silicone impression of the prepared tooth. Three groups were established: handmade (HM), milled (ML) and additive manufactured (AM); 4 specimens per group were obtained. The marginal and internal gap of each pattern was measured on the extracted molar through a computed tomography test. Sixty measurements were done to measure the marginal gap and another 60 measurements were calculated to analyze the internal gap on each pattern on the prepared tooth. A total of 1.440 measurements were completed. Mann-Whitney and Turkey statistical tests were used for pairwise comparison. RESULTS: The mean of the marginal and internal gap was of 67.56 +/- 6.08 mum and 80.62 +/- 3.26 mum for the HM group, 85.28 +/- 2.17 mum and 96 +/- 1.97 mum for the ML group and 86.49 +/- 1.74 mum and 91.86 +/- 2.88 mum for the AM group, respectively. The HM group presented significantly lower marginal (p=0.029) and internal (p=0.029) gap compared to the ML and AM groups. There was no statistical significant difference (p=0.486) on the marginal gap between the ML and the AM groups, but the AM group, showed significantly (p=0.029) smaller internal gap than the ML group. CONCLUSIONS: All the groups presented less than 100 mum marginal and internal gap, which is a considered clinically acceptable. CLINICAL IMPLICATIONS: The three fabrication processes are viable option for manufacturing patterns for lithium disilicate onlay restorations, but the best marginal and internal fit was still obtained by the conventional handmade procedures.