Abstract Forty orthodontically treated patients and thirty-six persons with normal occlusions were examined for the purpose of determining whether or not there were any occlusal interferences in centric relation and habitual bite. The time lapse between the completion of treatment and the examination for prematurities in the treated patients ranged from 2 months to 6 years 5 months; the mean was 2.4 years. The mean age of the treated patients was 16.4 years, and that of the untreated patients was 16.1 years. The method of examination was similar to one described by Jankelson. The number and location of the prematurities were charted according to their position on the occlusal surfaces of the mandibular first molar, second molar, second premolar, and canine. The frequency and location of occlusal prematurities in the two groups studied showed a striking similarity. The length of time between completion of treatment and the date of the investigation was not significant with respect to the number of prematurities recorded. A glide or shift of the mandible following the initial contact of the teeth was found in 75 per cent of the treated patients and in 80 per cent of the untreated patients. Prematurities in centric relation were found in 90 per cent of the treated and 81.7 per cent of the untreated patients. Prematurities in habitual bite were found in 92.5 per cent of the treated and 94.4 per cent of the untreated patients. The mesiobuccal cusp as well as the distobuccal cusp of the second molar in the treated patients had more premature contacts in centric relation than in the habitual bite. The converse was true in the untreated patients. This, perhaps, may be related to the fact that in only four of the treated patients were the maxillary and mandibular second molars included in the mechanotherapy. On the mandibular first molar the largest number of prematurities was found on the distobuccal cusp, particularly on the buccal surface of the distobuccal cusp, in both the treated and untreated patients. A tooth positioner was worn as a retaining appliance by one half of the treated patients, who accounted for 52 per cent of the prematurities. The other half of the treated patients wore a Hawley type of retainer or no retaining appliances whatsoever. Although there was a total of 340 prematurities on the four teeth mentioned, no significant evidence of tissue damage could be observed by either visual examination or palpation. In the interest of evaluating as accurately as possible the results obtained, all patients were examined by more than one observer. When a variation in observations appeared, the examinations were repeated.