Considerations Affecting Future Dental Health

An improperly prepared tooth may have an adverse effect on long-term dental health. For example, insufficient axial reduction inevitably results in an overcontoured restoration that hampers plaque control. This may cause periodontal disease or dental caries. Alternatively, inadequate occlusal reduction may result in occlusal dysfunction, and poor margin placement may lead to chipped enamel or cusp fracture.

Axial Reduction. Gingival inflammation is commonly associated with crowns and FPD abutments having excessive axial contours, probably because it is more difficult for the patient to maintain plaque control around the gingival margin. A tooth preparation must provide sufficient space for

Fig. 7-9. Excessive taper results in considerable loss of tooth structure (shaded area).

Minimally required clearances: Buccal cusp—1.5 mm Lingual cusp—1.0 mm Marginal ridges and fossae—1.0 mm

Fig. 7-10. An anatomically prepared occlusal surface results in adequate clearance without excessive tooth reduction. A flat occlusal preparation will result in either (1) insufficient clearance or (2) an excessive amount of reduction.

Tooth Path Withdrawal

Fig. 7-11 . To conserve tooth structure, the preparation of axial surfaces should be as uniform as possible. A, The path of withdrawal should coincide with the long axis of the tooth, which for a mandibular premolar is typically inclined 9 degrees lingually. Preparing the tooth perpendicular to the occlusal plane is a commonly seen error and results in additional tooth reduction (shadedarea). B and C, Tooth structure is conserved by uprighting a tilted FPD abutment.

Fig. 7-12. A shoulder margin (2) is less conservative than a chamfer (1).
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