Mandibular invasion by oral squamous cell carcinoma.

Forty-five specimens consisting of mandibular bone and adjacent squamous cell carcinoma were histologically investigated. In 23 of them, there was no involvement of the mandibular bone: a continuous periosteal layer separated the tumour from the bone. Tumour spread through periosteal lymphatics was not observed in any of these cases and therefore there is no reason to sacrifice bone when the tumour is not fixed to the jaw. Twenty-two specimens exhibited bony involvement. In 10 of them, the bone was eroded by an advancing tumour front. None of these cases exhibited tumour invasion into cancellous spaces, dental canal or periodontal ligament space. Tumours with this type of bony involvement are amenable to mandible-sparing surgical treatment. The other 12 exhibited diffuse growth into cancellous bone, dental canal and, if present, periodontal ligament space. Cases like these are to be operated on by removing the entire thickness of the involved mandibular part. Tumours involving bone were slightly larger than those leaving bone uninvolved. The tumours eroding bone were of a smaller size than those infiltrating bone. The differences, however, are too small to have a predictive value in treatment planning. Attention is drawn to the presence of dental epithelial rests that should not be mistaken for invading tumour nests.