Introduction
Class II caries starts on the proximal surface of a premolar or molar just cervical to the contact area, usually under a marginal ridge that is still intact. The classical Class II cavity (topic 8) reaches it through the marginal ridge and the occlusal surface; for small lesions, the proximal-buccal / proximal-lingual (lateral) access, the slot and the tunnel preparation sacrifice much less sound tooth.
Why keep the marginal ridge
The marginal ridge is the enamel–dentin beam joining the buccal and lingual cusps on the proximal side; with the contact area it stabilises the arch and prevents food impaction. Its loss weakens the tooth far more than an occlusal cavity: in a classic laboratory study on premolars, stiffness fell by about 20 % after an occlusal cavity, 46 % after an MO and 63 % after an MOD cavity.
Conservative Class II designs remove only the proximal lesion: the slot keeps the occlusal surface, while the lateral access and the tunnel keep both the occlusal surface and the marginal ridge.
Only lesions that need a restoration are cut: a proximal lesion confined to enamel on the bitewing is usually arrested without drilling (fluoride, sealing, resin infiltration); one clearly in dentin, or cavitated, is usually restored. The design depends on where the lesion lies:
- occlusal caries or a wide lesion → classical Class II (topics 8, 10, 11);
- sound occlusal surface, lesion just below the contact → slot;
- lesion well below the contact, towards the buccal or lingual side, open embrasure → lateral access;
- small lesion under a sound, wide marginal ridge → tunnel;
- adjacent tooth missing or being restored at the same visit → direct access from the proximal side.