Wear behaviour of lithography ceramic manufactured dental zirconia.

OBJECTIVE: The study aims to evaluate the wear surface using 3D surface roughness and other material characterization of zirconia fabricated using photopolymerization based Lithography-based Ceramic Manufacturing (LCM). METHOD: LCM technology was used to fabricate zirconia specimens of size 10 × 10 × 2mm3. Scanning Electron Microscope, 3D-profilometer, X-ray Diffraction, and hardness test characterized the samples before and after wear and Coefficient of friction (COF) was monitored. RESULT: The COF was around 0.7 and did not differ much between the horizontally and vertically printed specimens. However, the surface roughness after wear for horizontally printed specimen was 0.567 ± 0.139 µm, while that for vertically printed specimen was 0.379 ± 0.080 µm. The reduced valley depth and the dale void volume were low for the vertically printed zirconia specimen, indicating lesser voids and low fluid retention. In addition, it was observed that the hardness value of the vertically printed sample was better. The scanning electron microscopic images and 3D surface profiles of the zirconia specimens depicted the surface topography and revealed the wear track. CONCLUSION: The study shows that zirconia fabricated using LCM technology possesses surface roughness of about 0.5 µm with no machining scars that are usually associated with CAD/CAM dentistry and also indicating agreement with clinically acceptable values for minimal surface roughness of dental restorations. Dental restorations using LCM fabricated zirconia redues the requirement of post-processing work flow that is part of CAD/CAM dentistry.

An in vitro comparison of the marginal and internal adaptation of ultrathin occlusal veneers made of 3D-printed zirconia, milled zirconia, and heat-pressed lithium disilicate.

STATEMENT OF PROBLEM: Whether additively produced zirconia could overcome problems with conventional computer-aided design and computer-aided manufacture (CAD-CAM) such as milling inaccuracies and provide accurate occlusal veneers is unclear. PURPOSE: The purpose of this in vitro study was to compare the marginal and internal fit of 3D-printed zirconia occlusal veneers with CAD-CAM-fabricated zirconia or heat-pressed lithium disilicate ceramic (LS2) restorations on molars. MATERIAL AND METHODS: The occlusal enamel in 60 extracted human molars was removed, with the preparation extending into dentin. Occlusal veneers at a thickness of 0.5 mm were designed and manufactured according to their group allocation: 3DP, 3D-printed zirconia; CAM, milled zirconia; and HPR, heat-pressed LS2. The prepared teeth and restorations were scanned and superimposed, and the marginal and internal adaptation were measured 2- and 3-dimensionally; the production accuracy (trueness) was also measured. The comparisons of the group medians were performed with nonparametric methods and a pairwise group comparison (α=.05). RESULTS: Three-dimensionally printed zirconia revealed median outcomes of 95 µm (margin), 252 µm (cusp), 305 µm (fossa), and 184 µm (3D internal adaptation). CAM showed median values of 65 µm (margin), 128 µm (cusp), 203 µm (fossa), and 120 µm (3D internal adaptation). The respective values for the group HPR were 118 µm (margin), 251 µm (cusp), 409 µm (fossa), and 180 µm (3D internal adaptation). Significant differences (P<.001) between CAM and 3DP (cusp, fossa, 3D internal adaptation) and between CAM and HPR (all regions) were found, with the former group showing higher accuracies. The trueness showed median discrepancies of 26 µm (3DP), 13 µm (CAM), and 29 µm (HPR) with significant differences (P<.001) for the comparisons 3DP-CAM and CAM-HPR. CONCLUSIONS: Three-dimensionally printed zirconia occlusal veneers produced by means of lithography-based ceramic manufacturing exhibit a marginal adaptation (95 µm) and a production accuracy (26 µm) similar to those of conventional methods.

Additive Manufacturing of Lithium Disilicate with the LCM Process for Classic and Non-Prep Veneers: Preliminary Technical and Clinical Case Experience.

BACKGROUND: ceramic veneers, crowns, and other types of restorations are often made using either the press heating technique or the subtractive method. The advent of lithography-based ceramic manufacturing (LCM) allows for the manufacturing of such restorations in an additive way. METHODS: this concept paper describes the first clinical experience in the application of LCM lithium disilicate restorations in vivo for the manufacturing of classic veneers for a patient with severe tooth wear. The applied restorations were analyzed in terms of their marginal fit in metrology software (Geomagic Control X, 3D Systems). Furthermore, the feasibility of 3D printing of non-prep veneers with a 0.1 mm thickness was tested. RESULTS: the classic LCM lithium disilicate veneers were tried in the mouth cavity and demonstrated adequate esthetics and a sufficient marginal fit of 100 µm. Furthermore, the non-prep veneers with a 0.1 mm thickness could be successfully printed using LCM technology and also demonstrated an adequate fit on the model in vitro. CONCLUSIONS: the described technical approach of lithium disilicate 3D printing with LCM technology may pose a valid alternative to subtractive and analog manufacturing and be a game-changing option with the use of additive chairside ceramic fabrication.

Application of high resolution DLP stereolithography for fabrication of tricalcium phosphate scaffolds for bone regeneration.

Bone regeneration requires porous and mechanically stable scaffolds to support tissue integration and angiogenesis, which is essential for bone tissue regeneration. With the advent of additive manufacturing processes, production of complex porous architectures has become feasible. However, a balance has to be sorted between the porous architecture and mechanical stability, which facilitates bone regeneration for load bearing applications. The current study evaluates the use of high resolution digital light processing (DLP) -based additive manufacturing to produce complex but mechanical stable scaffolds based on ß-tricalcium phosphate (ß-TCP) for bone regeneration. Four different geometries: a rectilinear Grid, a hexagonal Kagome, a Schwarz primitive, and a hollow Schwarz architecture are designed with 400 µm pores and 75 or 50 vol% porosity. However, after initial screening for design stability and mechanical properties, only the rectilinear Grid structure, and the hexagonal Kagome structure are found to be reproducible and showed higher mechanical properties. Micro computed tomography (µ-CT) analysis shows <2 vol% error in porosity and <6% relative deviation of average pore sizes for the Grid structures. At 50 vol% porosity, this architecture also has the highest compressive strength of 44.7 MPa (Weibull modulus is 5.28), while bulk specimens reach 235 ± 37 MPa. To evaluate suitability of 3D scaffolds produced by DLP methods for bone regeneration, scaffolds were cultured with murine preosteoblastic MC3T3-E1 cells. Short term study showed cell growth over 14 d, with more than two-fold increase of alkaline phosphatase (ALP) activity compared to cells on 2D tissue culture plastic. Collagen deposition was increased by a factor of 1.5-2 when compared to the 2D controls. This confirms retention of biocompatible and osteo-inductive properties of ß-TCP following the DLP process. This study has implications for designing of the high resolution porous scaffolds for bone regenerative applications and contributes to understanding of DLP based additive manufacturing process for medical applications.