Conservative Dentistry – Part I · MU Plovdiv

11. Class I and Class II cavity preparation for composite materials – indications, critical analysis stages of preparation, retentions.

Inside: 7 sections · 1 labelled picture · 1 table · 17 flashcards · 7 min

Topic 11 of 53 in the MU Plovdiv syllabus for Conservative Dentistry – Part I (Dental Medicine, Year 3). The free AceMed note covers it in 7 sections, about 900 words (7 min of reading), with 17 flashcards.

In this note

  1. Introduction
  2. Principles of the adhesive preparation
  3. Class I and Class II designs
  4. C-factor and polymerisation shrinkage
  5. Clinical steps
  6. Main mistakes
  7. Key points

Introduction

Direct composite is now the usual material for Class I and Class II cavities in premolars and molars. Because it is bonded to enamel and dentin, the cavity no longer has to hold the filling: the preparation removes caries, gives access and is shaped to limit polymerisation-shrinkage stress. The classical (amalgam) designs are topics 6–11.

Principles of the adhesive preparation

Retention comes from micromechanical bonding – etched enamel and the hybrid layer in dentin – not from the shape of the cavity. The preparation for composite is dictated by the lesion: caries and weakened tooth are removed, and nothing more.

  • No extension for prevention: the outline stops where caries and unsupported enamel end; sound fissures are sealed, not cut.
  • No mechanical retention: no dovetail, undercuts or retention grooves. Walls need not converge occlusally; they may be parallel or slightly flared.
  • Depth set by the caries: pulpal and axial walls follow the excavated lesion, not a fixed level, and need not be flat.
  • Rounded internal angles: less stress concentration, better adaptation without voids. Use round-ended burs (pear-shaped No. 330 or 245, round-ended diamonds).
  • Minimal width: isthmus and box as narrow as the lesion and the bur allow; cusps and marginal ridges kept wherever possible.

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