Tooth Preparation CROWNS (INC POST CORE), ONLAYS & BRIDGES • Anterior teeth should be reduced by 2.0 mm incisally. The incisal edge should be rounded and have a plateau width of at least 0.9 mm labio-lingually. Fig.1 Fig.1 • Posterior teeth should be reduced by 1.5-2.0 mm occlusally. Occlusal relief should be simple with an opening angle of no less than 12O-140° Fig.2 Fig.2 • Lateral edges should be prepared with a minimum 3° taper and no undercuts, to allow precise fitting. Fig.3 Fig.3 • Parallel sided preparations are contraindicated. • Margins should be a SHOULDER PREPARATION and be reduced by 1.0 mm, with a rounded axio-cervical line angle. Fig.4 Fig.4 • For post core type restorations, fibre posts/composite cores are the natural compliment to all-ceramic crowns. If non-precious/grey coloured metal posts are prescribed, then an opaque porcelain can be applied at the laboratory, to provide the appropriate background shade match. If the post is already in situ, a larger amount of opaceous dentine can be used in the porcelain build up and if necessary an opaque resin cement should be used. Gold post/cores do not normally require any special treatment. • Path of insertion for Lava and Cercon multiple unit restorations must allow for a cone angle of 2 x 3° on corresponding axial surfaces of abutment preps. Fig.5a,5b Fig.5a Fig.5b • All faces should be prepared in a smooth, rounded manner. • Sharp edges or excessive tapers are contraindicated. INLAYS • Preparations should have slightly divergent buccal/lingual walls. Internal angles should be rounded off. • Any undercut areas should be blocked out with glass ionomer prior to taking an impression. • Depth and width of cavity should ideally be in the order of 3.0 - 4.0mm. For deeper cavities, depth can be reduced via the application of a glass ionomer liner. • Occlusally a butt finish is recommended. VENEERS • An incisal overlap design is recommended; this design promotes long term function and optimal aesthetics. The overlap should be extended to approximately 1.0 mm lingually. Incisal reduction should be performed as indicated for anterior crowns. If a tooth is discoloured then labial reduction should be increased from 1.0-1.2mm. Proximally and cervically a defined 1.0-1.2 mm shoulder should be prepared, to accommodate the overall thickness of the veneer. • Over extension of the veneer proximally, to prevent clear path of insertion, is contraindicated. • If a significant amount of resin-modified glass ionomer or compomer is used to re-contour a tooth prep, sufficient time should be allowed to take account of any post-set expansion, prior to taking impressions for the final restoration.