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Certain aspects of malocclusion, particularly deep overbite, can be related to periodontal pathology, especially in the presence of poor oral hygiene. The authors have noted an association between deep overbite and unusual periodontal lesions. These lesions often appear on radiographs as circumscribed radiolucencies, remote from the alveolar crest and sometimes close to the apex. Gingival surface injury and food impaction may be important aetiological factors. This is illustrated in this article by a number of case studies.

This part of the series is devoted to tooth surface loss (TSL) not caused by caries or trauma. The management of this form of generalised TSL is included in this series because knowledge of occlusion is needed for both the diagnosis and, when indicated, treatment. There are, however, many other factors involved in the management of generalised TSL other than those associated with 'occlusion'. These will also be discussed.

Periodontal disease does not directly affect the occluding surfaces of teeth, consequently some may find a section on periodontics a surprising inclusion. Trauma from the occlusion, however, has been linked with periodontal disease for many years. Karolyi published his pioneering paper, in 1901 'Beobachtungen uber Pyorrhoea alveolaris' (occlusal stress and 'alveolar pyorrhoea'). (1) However, despite extensive research over many decades, the role of occlusion in the aetiology and pathogenesis of inflammatory periodontitis is still not completely understood.

A case is described where intrusion of a primary incisor resulting in apical fenestration may have occurred secondary to occlusal forces. The effects on the permanent dentition and possible aetiological factors are discussed.

A series of 46 cases of root fracture with four different patterns occurring in 51 non-endodontically treated teeth were studied. All of the patients had chewing habits which induced a unique root fracture. The results of this study suggest an additional cause of root fracture that has not been described previously. Here, the new term 'fatigue root fracture' is used to describe a fracture that results from an excessive, repetitive, heavy masticatory stress applied to a tooth. The majority (80%) of cases of this kind of fracture are vertical and occur mainly (96%) in persons over the age of 40. In addition, all the teeth affected were posterior teeth, and the majority (51%) were mandibular first molars.

Loss of alveolar bone from the edentulous jaws is a serious and common clinical problem, especially among the elderly. The retention and stability of dentures are reduced, but little is known about the pathogenesis of this bone loss. The existing data suggest that either local factors, for instance occlusal trauma, or systemic factors such as postmenopausal osteoporosis, contribute to edentulous alveolar bone resorption. This paper reviews the evidence for the aetiology of residual ridge resorption following tooth extraction.