Principles of Tooth Reduction for Restorations

Principles of Tooth Reduction for Extra-Coronal Restorations

• Restorations need to consider biological, mechanical, and aesthetic factors.
• Biological: Preserve tooth structure, avoid overcontouring, maintain supragingival margins, ensure harmonious occlusion, and prevent tooth fracture.
• Mechanical: Create retention and resistance forms, reduce deformation.
• Aesthetic: Minimize metal display, maximize porcelain thickness, use porcelain occlusal surfaces, and shape subgingival margins for optimal restoration.

Reduction of Sound Tooth Structure

• Biologic principles for tooth reduction focus on:
  • Preserving maximum sound tooth structure.
  • Maintaining pulp vitality.

Prevention of Damage During Tooth Preparation

• Avoid harming adjacent teeth.
• Protect soft tissues (cheeks, lips, tongue, gingiva).
• Protect the pulp.
• Pulp injury causes: Temperature (excessive pressure, high speed, type/shape/condition of the cutting instrument), coolant (air/water spray), chemical action (dental materials/luting agents), and bacterial action (left behind/gained access due to microleakage).

Protection of Adjacent Teeth

• Prepare a proximal enamel lip to prevent damage to adjacent teeth when opening proximal contacts.
• Use a matrix band to protect adjacent teeth from abrasive contact during preparation, but it should not be the only protection method. The band should be monitored effectively, as perforations could result.

Guidelines for Conservation of Tooth Structure

• Favor partial coverage restorations over complete coverage restorations to preserve more tooth structure.
• Maintain supragingival finish lines. Avoid unnecessary extension of the finish line subgingivally.
• Use a conservative finish line that facilitates sufficient bulk for the planned restoration.
• Prepare the occlusal surface anatomically. This will help maintain adequate clearance without excessive tooth reduction.

Conservation of Sound Tooth Structure (Path of Insertion)

• Path of insertion should align with the long axis of the tooth (for a mandibular molar, this is typically inclined 9-14 degrees lingually).
• Avoid perpendicular placement with the occlusal plane as this may lead to unnecessary tooth reduction.

Orthodontic Uprightening

• Orthodontic uprighting is a helpful step before reduction to achieve a more conservative preparation.

Preservation of Pulp Vitality

• Conserve as much tooth structure as possible to reduce harmful pulpal effects of procedures and materials.
• The thickness of remaining dentin is inversely proportional to the pulpal response.

Determination of Proper Tooth Reduction

• The proper amount of tooth reduction is determined by axial and occlusal reduction.

Axial Reduction

• Remove undercuts to remove any areas of potential undercut.
• Align the reduction with the path of insertion.
• Consider resistance of the restoration to deformation.
• Account for material of the intended restoration.
• Consider possible tipping or tilting of the tooth during reduction.

Occlusal Reduction

• Account for the degree of occlusal wear.
• Consider the area of occlusal contact.
• Account for overeruption of opposing teeth.

Amount of Occlusal Reduction

• Uniform reduction to produce appropriate occlusal clearance is preferred.
• Do not unnecessarily shorten the mesial walls.
• Do not reduce more than necessary to accommodate the restoration. The needed structure may not need to be cut.

Correction of Overerupted Opposing Teeth

• Correct overeruption of opposing teeth to ensure a balanced occlusion before constructing a fixed partial denture on lower arches.

Correction of Overeruption Methods

• Simple contouring of plunger cusps and topical fluoride treatment.
• Orthodontic intrusion.
• Occlusal veneers.
• Crown preparation for the overerupted tooth.
• Endodontic treatment and crowning of affected teeth.
• Extraction of overerupted teeth in certain instances.

Removal of Decay

• Remove all decay to prevent future pulp involvement and periapical pathosis.

Removal of Decay & Cavity Restoration

• Ensure no decay remains under a crown or bridge, which may result in pulp involvement, periapical pathosis, and restoration failure.

This quiz explores the principles of tooth reduction necessary for extra-coronal restorations. It covers essential biological, mechanical, and aesthetic factors to consider when performing tooth preparations. Test your knowledge on preserving tooth structure and preventing damage during procedures.