The occlusal surface of a permanent molar involves pits and fissures primarily affecting the enamel and dentin within the occlusal grooves. According to Black's classification, lesions confined to these surfaces are categorized under Class I cavity preparations. This classification guides the removal of carious tissue and restoration without involving proximal surfaces. Therefore, a cavity on the occlusal surface does not extend into the interproximal areas, which are designated as Class II or other classes. Correctly classifying ensures precise removal and optimal restoration of functional anatomy.

Reference: Sturdevant's Art and Science of Operative Dentistry, 7th Edition.