The aim of this study was to ascertain the age at which apical closure of the teeth occurred in dogs and to document this closure radiographically. Previously apices were reported to close between 15 and 18 months of age.
In the first study, dogs under 18 months of age which presented for general anaesthesia for any purpose had radiographs taken of the lower first molar, upper incisors and upper canine teeth. These radiographs were evaluated for stage of apical closure. Early in the study, it became apparent that the apices in all dogs older than 12 months of age were closed and the study then concentrated on dogs between six and 12 months of age.
The dogs were grouped according to age and evaluated for partial closure of the apices of all teeth or complete closure of all apices. The Fisher's Exact test was used to test for significance (P<O.05).
In dogs five to six months of age, all apices of all teeth were open. The apices of the lower first molar and upper first and second incisors were closed in all dogs seven months of age and older. The apices of the upper third incisor and canine were not closed in all dogs until 10 months of age and older. If the younger age group (5 to 6 months of age) and older age group (12 months and older) are ignored, a comparison of dogs with partial closure (some apices open, some closed) with those with full closure (all apices closed) can be made and subjected to analysis for significance using the Fisher's Exact Test and were deemed statistically significant (P = 0.003).
As these radiographs were single x-rays taken of dogs of varying age, a second study was carried out on. In this study, the upper incisors, upper canines, upper premolars, lower premolars and lower first molar of a crossbred dog were radiographed at monthly intervals until all of the apices were closed.
In this dog, the apices of the upper first incisor, upper second incisor, lower premolars and lower molars were closed at seven months of age. The apices of the upper third incisor and upper premolars were closed at eight months of age. The apex of the upper canine was closed at 9.5 months of age. These times correlate with those of the primary investigation.
The significance of these findings, which are at variance with reported closure times, becomes apparent when considering the treatment for recently fractured teeth. Fractured teeth in dogs older than 10 months of age would require intervention within 48 hours if the living tooth is to be salvaged. Endodontics can be delayed for up to two weeks post-fracture in dogs six months of age and younger with fractures of the permanent teeth as apical closure has not yet occurred. Dogs in the seven- to 10- month age group would require radiographs to be taken to ascertain the stage of apical closure before any decision could be made.