Comparison of Marginal and Internal Defects of Indirect Inlay Patterns Fabricated Using Additive Manufacturing and Traditional Methods - An Ex Vivo Study.

INTRODUCTION: This study aimed at exploring clinical translation of additive manufacturing methods for fabrication of inlay restorations. MATERIALS AND METHODS: On a selected human premolar tooth sample an inlay cavity was prepared. A silicon impression of the tooth was recorded and ten die-casts were poured. Ten inlay wax patterns were fabricated using traditional method. An optical impression of the tooth model was obtained and 20 computeraided inlay designs were fabricated and optimised for additive manufacturing. Ten models were fabricated by micro-stereolithography and the other ten were fabricated using selective laser sintering. 30 inlay patterns were cast into cobalt chromium metal inlays. For 30 metal inlays, marginal and internal gaps were measured using a silicone-replica-technique, observed under a scanning electron microscope. RESULTS: The measured internal gaps were: Internal-gaps in Conventional lost wax technique (138 ± 8.7), micro-stereolithography (200 ± 7.4) and selective laser sintering (203 ± 11.8). The marginal gaps were: Conventional lost wax technique (162.12 ± 6.8), micro-stereolithography (198 ± 10.3) and scanning laser sintering (203 ± 6.6) Conclusions: The marginal gap and internal gap of a conventional lost wax technique were significantly improved compared with microstereolithography and selective laser sintering (P⟨0.05). However, according to previous criteria for maximum allowable discrepancy (100 - 200 µm) microstereolithography may represent a potential future alternative for indirect inlay fabrication.

Validating cortical surface analysis of medial prefrontal cortex.

This paper describes cortical analysis of 19 high resolution MRI subvolumes of medial prefrontal cortex (MPFC), a region that has been implicated in major depressive disorder. An automated Bayesian segmentation is used to delineate the MRI subvolumes into cerebrospinal fluid (CSF), gray matter (GM), white matter (WM), and partial volumes of either CSF/GM or GM/WM. The intensity value at which there is equal probability of GM and GM/WM partial volume is used to reconstruct MPFC cortical surfaces based on a 3-D isocontouring algorithm. The segmented data and the generated surfaces are validated by comparison with hand segmented data and semiautomated contours, respectively. The L(1) distances between Bayesian and hand segmented data are 0.05-0.10 (n = 5). Fifty percent of the voxels of the reconstructed surface lie within 0.12-0.28 mm (n = 14) from the semiautomated contours. Cortical thickness metrics are generated in the form of frequency of occurrence histograms for GM and WM labelled voxels as a function of their position from the cortical surface. An algorithm to compute the surface area of the GM/WM interface of the MPFC subvolume is described. These methods represent a novel approach to morphometric chacterization of regional cortex features which may be important in the study of psychiatric disorders such as major depression.