Dens invaginatus is a developmental malformation resulting from invagination of the tooth crown or root before calcification has occurred. The presumed aetiology of this phenomenon has been related either to focal growth retardation or focal growth stimulation, or to localized external pressure in certain areas of the tooth bud (Shafer et al . 1983). The condition may occur in any deciduous or permanent tooth. The permanent maxillary incisors are the most frequently involved teeth (Bimstein & Shteyer 1976). Radiographically this anomaly demonstrates a radiopaque invagination, equal in density to enamel, extending from the cingulum into the root canal (Gotoh et al . 1979). The defects may vary in size and shape from a loop-like, pearshaped or slightly radiolucent structure to a severe form resembling a ‘tooth within a tooth’. The classification of Oehlers (1957) is as follows:

 - Type 1; an enamel invagination in the crown only.
 - Type 2; an enamel-lined invagination that invades the root but remains confined within it as a blind sac, and may communicate with the dental pulp.
 - Type 3; an invagination that extends from the crown to the apex.

An early diagnosis of such malformations is crucial. Due to abnormal anatomical configuration, an invaginated tooth presents technical difficulties in its clinical management. Various techniques for treating dens invaginatus have been reported, including conservative restorative treatment (de Sousa & Bramante 1998), non-surgical root canal treatment (Hosey & Bedi 1996), endodontic surgery (Bolanos et al . 1988), intentional replantation (Lindner et al . 1995) and extraction. The purpose of the present article is to describe a case of apical periodontitis associated with a tooth containing a dens invaginatus that healed successfully after non-surgical root canal treatment.