Qualitative and Quantitative Determination of Attrition and the Ensuing Tooth Migraton

Abstract

The purpose of the investigation is: A. To carry out a qualitative study of attrition, and B. To determine the mesio-distal decrease in tooth width (quantitative attrition) produced by attrition and the ensuing tooth migration if any. The following questions are dealt with; A. (1) The relation of attrition to age and sex, and (2) The distribution of attrition in the dentition. B. (1) How large is the mesio-distal reduction of the teeth produced by attrition (without loss of proximal contact)? (2) How far do the teeth migrate under the influence of attrition? The qualitative attrition is evaluated according to a scale of 0–3, in which 0 = no attrition 1 = attrition of the enamel only 2 = dentine visible on the greater part of the occlusal surface 3 = involvement of the dentine, so that the secondary dentine is exposed or the pulp cavity opened. Attrition so far advanced that one or several islets of dentine are formed is recorded as 1–2. In some cases, e.g. in the molars, attrition is not of the same degree mesially and distally. When, for example, the mesial part exhibits attrition of the enamel only (degree 1) whereas in the distal part it is so far advanced that the dentine is exposed (degree 2) attrition is recorded as 1–2. Details of the classification, as well as the error of the method, are recorded in Table 1. Quantitative attrition. The mesio-distal tooth width is found to decrease with increasing age (Table 2). An attempt is made to compute the original mesio-distal width of the teeth with the help of special indices (Table 4). These are calculated by measureing, in the individual teeth of a present-day series, the mesio-distal (m–d) and bucco-lingual (b–1) width It is possible, therefore, with the help of such indices to calculate the mesio-distal width, if the bucco-lingual width is known. A control study showed that the sum of the tooth widths calculated with the help of this index on an average only deviated 2–3 per cent from the real value. The following results were obtained: A. Qualitative attrition. (Table 6 and Figs. 3-4) (1) Attrition increases with increasing age. (2) No definite sex difference can be observed with respect to the degree of attrition. (3) In all the groups, the medial incisor is the most worn, and the third molar the least worn tooth. (4) In all the age groups, the incisors and molars of the lower jaw are more severely worn than those of the upper jaw, whereas the reverse applies to the premolars. B. Decrease in mesio-distal tooth width ad tooth migration The decrease in mesio-distal tooth dimension is calculated for the whole dental arch with the exception of the second and third molars (Table 7). Owing to effaciang of the measuring points by attrition, these calculations can be made on a very limited part of the material only. The measurements do not indicate any greater degree of over-spacing in severely worn than in unworn dentitions. When the entire crown is worn away, the roots are not, however, in contact. It is concluded that the teeth must have migrated, and an attempt is made to determine the extent of this migration in the sagittal direction. a special study is made of the upper first molar and medical incisor. The relation of the former tooth to the zygomatic bone is recorded. Comparison between the values obtained in a group with slight attrition and one with severe attrition does not disclose any significant mesial migration of the first molar. A profile-roentgenologie analysis shows, on the other hand, a smaller angle between the longitudinal axis of the upper medial incisor and the lime S–N (sella turcica–nasion) in a group with severe attrition than in a group with slight attrition. This indicates inward rotation of the medial incisors. The difference in the angle corresponds to a displacement of the edge of about 3 mm. Is is pointed out that, since attrition seems to be associated with decrease of the angle between the upper medial incisor and S–N, there is reason to believe that the angle would be still larger in unworn dentitions. If it is assumed that the angle in the unworn cranial dentitions is about 100aa, this means that, in the severely worn dentitions, the edge of the medial incisor has been displaced inwards and backwards by altogether 5–6 mm which implies that the migration of the teeth in connexion with attrition, at any rate in the upper jaw, is to be ascribed chiefly to inward rotation of the crowns of the incisors. It is suggested that the powerful muscles of the lips are responsible for the inward pressure of the crowns of the incisors.