Bridging the Gap: Subtractive Precision vs. Additive Innovation – A Head-to-Head of Milled CAD/CAM PMMA and 3D-Printed Photopolymer Resins in Modern Prosthodontics – A Review.

Abstract

Digital dentistry uses a lot of materials made of polymethyl methacrylate (PMMA) to make temporary and removable prostheses. CAD/CAM-milled PMMA blocks are made of high-molecular-weight PMMA that has already been polymerized in a factory. They have dense, even cross-linking (usually through dimethacrylates like ethylene glycol dimethacrylate), very little residual monomer, and almost no porosity because the polymerization was done at high temperature and pressure. On the other hand, 3D-printable PMMA-based photopolymer resins are liquid mixtures that contain reactive monomers (like methyl methacrylate or multifunctional dimethacrylates like EGDMA or TEGDMA), pre-dissolved PMMA oligomers or powder, photoinitiators (like TPO), inhibitors, and additives. These resins undergo layer-by-layer vat photopolymerization (SLA/DLP) and then post-curing. These differences in composition and processing cause the materials to behave differently. For example, milled CAD/CAM PMMA usually has better and more consistent mechanical properties (higher flexural strength ~100–150 MPa, better impact resistance, lower surface roughness, and better dimensional stability) because its microstructure is more homogeneous. 3D-printed resins often have lower flexural strength (usually 70–110 MPa, depending on the brand and curing), a higher chance of anisotropy, layer-line porosity if the settings aren't right, and different levels of residual monomer, but newer formulations have made them work much better. Milled materials are still the best choice for applications that need strength, but 3D printing has benefits like better handling of complex shapes, less material waste, and faster customization. Resin chemistry is always getting better, which is closing these gaps, but milled PMMA blocks are still more reliable in many clinical situations.

Keywords CAD/CAM PMMA, Milled denture base, 3D-printed resin, Photopolymer resin, Additive manufacturing, Subtractive manufacturing, Digital dentistry.