A. Occlusal Surface Reduction The goal of occlusal reduction is to provide 1.0 mm uniform reduction of occlusal Ranier M. Adarve, DMD, MS, MHPE University of Minnesota School of Dentistry 3 surface and following the contour of the tooth. Restoration: Preparation Area: Bur: Full metal crown *Occlusal reduction & functional cusp bevel: Coarse grit round end tapered diamond *Proximal axial reduction: Medium grit short needle diamond & coarse grit round end tapered diamond D, Occlusal reduction is complete. Porcelain-fused-to-metal dental crowns require a greater amount of tooth reduction (trimming) than their all-metal counterparts. T, The completed preparation. Criteria for tooth reduction. Minimum recommended clearance is 1 mm on nonfunctional cusps and 1.5 mm on functional cusps. Guiding grooves are placed for axial reduction. As is evident from the photos, the porcelain-fused-to-metal (PFM) crown prep axial walls should be slightly deeper than for zirconia or metal (1.5 mm) to accommodate 0.3–0.5 mm of metal substructure and the fused or pressed ceramic veneering material. A, Depth holes. PrepCheck ®, the revolutionary prep-marking system, promotes adequate reduction allowing ideal thickness of the final restoration and ensures superior strength and aesthetics.PrepCheck’s ® special coating marks the tooth in areas that need to be reduced. B, Occlusal depth cuts. e) Greater tooth reduction is needed. 1. 1mm (pink) commonly used for gold crowns; 1.5mm (green) commonly used for PFM crowns; 2mm (blue) commonly used … • Second plane of reduction in occlusal 1/3 prevents over-thinning of the crown >1.2 mm >1.5 mm CAD/CAM Preparations . For example, metal crowns can be as thin as 1.5 mm on their chewing surface whereas PFM crowns need to be at least 2 mm thick. The features of a preparation for a complete cast crown and the function served by each . This can be accomplished with the help of depth grooves. Complete Metal Crown – Tooth Preparation Review • A chamfer finish line that is 0.3 – 0.5 mm in depth • Axial reduction with 10 to 20 degrees of total occlusal convergence • Reduction for occlusal clearance of 1.0 – 1.5 mm • Auxiliary axial resistance form features as needed • Rounding of all line angles; 43. C, Half of the occlusal reduction is completed. Available in 3 sizes. PFM crown like: inadequate incisal or occlusal reduction, inadequate axial reduction, presence of undercuts, deficient finish line, and existence of sharp lines and/or angles. 9-3. Suggested Burs for Preparation of Full Metal Crowns / PFM / All-Ceramic Crowns . PFM #12 Occlusal Reduction • 1.5 mm • Provide Adequate Occlusal Clearance • Occlusal Planar Reduction Lingual Reduction • Remove anatomical undercut 3-degree taper ... (PFM) Crown Preparation for Posterior Teeth Full Crown Module: Learner Level 1 . Conventional 2-plane occlusal reduction for PFM crown . That being said, new ceramics such as lithium disilicate glass-ceramic and zirconia are rapidly replacing PFM. A detailed look at all aspects regarding tooth preparation can help to improve clinical results in everyday practice. E and F, Lingual chamfer and facial shoulder are prepared on half the tooth. REFERENCES The occlusal reduction should be at least 1.5 mm and preferably 2.0 mm for the same reason. The occlusal reduction must allow adequate room for the restorative material from which the cast crown is to be fabricated. Fig. Preparation of a maxillary premolar for a metal-ceramic crown. Considering the durability and somewhat aesthetics, PFM crowns have been the material of choice for single crowns and bridges for many years.