Preclinics of Conservative Dental Medicine · MU Sofia

11. Class two cavities – proximo-occluso-lingual/proximo-occluso-buccal configuration.

Covers three-surface Class II cavities that extend from a proximal box and occlusal step onto the buccal or lingual surface, with the usual routes for mandibular and maxillary molars. It sets out dimensions of each part, the bur position for the extension, and the preparation sequence. A table compares MOB, DOB, DOP and MOL forms with the cusp at risk, and the note closes with cusp weakness, capping thresholds and common mistakes.

Inside: 8 sections · 3 labelled pictures · 2 tables · 17 flashcards · 11 min

Topic 11 of 53 in the MU Sofia syllabus for Preclinics of Conservative Dental Medicine (Dental Medicine, Year 3). The free AceMed note covers it in 8 sections, about 1,327 words (11 min of reading), with 17 flashcards.

In this note

  1. Introduction
  2. Definition and indications
  3. Typical configurations
  4. Outline and dimensions of each part
  5. Sequence of preparation
  6. Cusp strength and cusp capping
  7. Typical mistakes and their consequences
  8. Key points

Introduction

Proximo-occluso-buccal and proximo-occluso-lingual cavities are three-surface Class II preparations: a proximal box and an occlusal step, extended onto the buccal or lingual (palatal) surface. They are needed in molars when a carious buccal or palatal groove, pit or smooth-surface lesion lies next to a proximal lesion. Every extension takes support away from the cusp beside it, so the design decides whether that cusp survives chewing loads.

Definition and indications

The cavity is named after its surfaces, proximal first: MOB or DOB (mesio- or disto-occluso-buccal) and MOL or DOL (mesio- or disto-occluso-lingual); in the maxilla DOL is also written DOP (palatal). It remains Black's Class II, because the main lesion is proximal; the buccal or lingual part is an extension made for a second lesion. MO, DO and MOD forms and slot and tunnel designs belong to topics 8–10.

An extension is added only when the occlusal step reaches a second lesion:

  • a carious or deep, non-cleansable buccal groove of a mandibular molar, running from the central fossa over the buccal cusp ridge to the buccal pit in the middle third of the buccal surface;
  • a carious distopalatal groove of a maxillary molar – the continuation of the distal oblique groove between the mesiopalatal and distopalatal cusps, sometimes ending in a palatal pit;
  • a carious lingual groove of a mandibular molar (less common);
  • proximal caries that has spread round the buccal or lingual line angle onto the smooth surface, usually near the gingiva.

An extension is made only for caries or a deep, non-cleansable groove. A sound groove is sealed or smoothed by enameloplasty, and a pit separated from the cavity by sound tooth is prepared as a separate Class I cavity (topic 7).

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