GENERAL CONSIDERATIONS Technique Tips Ensure even reduction of the anatomic form. Provide enough room for the ceramic to allow adequate strength. Sharp transitions and sharp internal edges/line angles or undercuts MUST be avoided. Margins should have a pronounced chamfer or shoulder with butt joint margins. Avoid tapered margins, feathered edges or bevelled shoulders. Ensure there is an adequate path of insertion. Suggested Margin Preparation   Shoulder with rounded axio-cervical line angle, uniform circular ablation.   Chamfer preparation (with reduced mechanical support of the crown). Particularly used with reduced substructure (e.g., after repeated crowning). Common Preparation Errors Insufficiently defined and finished preparation margins. Uneven preparation limit ("gutter" preparation, vertical unevenness). Irregular marginal reduction of layers (horizontal unevenness). Wrong shape of preparation limit. Unnecessarily deep subgingival preparation. Preparation in root dentin. Poorly controlled tooth reduction. Excessive reduction, especially in the upper anterior teeth (vestibular) and premolars. Excessive incisal/occlusal reduction causing reduced retention and stability. Insufficient reduction at the palatal side of the upper anterior teeth (malfunction occlusion). Excessive taper.   Incorrect preparation of the labial surface: Preparation in one plane; therefore insufficient reduction of substance. Fracture of the crown may result due to insufficient wall thickness of the crown.   Incorrect preparation of the labial surface, risk of damage to the pulp. ANTERIOR CROWN PREPARATION Reduce lingual surface 1.5 mm at the area of centric contact (not less than 1.0 mm) and 0.8 to 1.0 mm along the remaining lingual surface. Incorporate taper of 8 to 10 degrees (never more than 12º) Tooth preparation length should reflect a 1.5 to 2.0 mm occlusal (incisal) reduction. Original position of teeth.     Preferred final position of teeth.     Actual preparation required to achieve preferred final position of teeth. ANTERIOR 3-UNIT BRIDGE PREPARATION Technique Tips Very important: Ensure there is adequate space occlusal-gingivally and buccal-lingually for interproximal joints. In the anterior region, the connector dimensions are to be 4 mm (occlusal-gingival) and 4 mm (buccal-lingual). In the premolar region, connector dimensions are to be 5 mm (occlusal-gingival) and 4 mm (buccal-lingual). Maximum pontic spans will vary from patient to patient depending on the tooth position, size, condition and arch position of the retainers. Pontic spans should not exceed 9 mm posterior to canine and 11 mm anterior to canine. Measurements for this determinant are made from the unprepared abutment surfaces next to the edentulous space. Return to In-Ceram® Crowns product page