Rare and Common Variants Conferring Risk of Tooth Agenesis.

We present association results from a large genome-wide association study of tooth agenesis (TA) as well as selective TA, including 1,944 subjects with congenitally missing teeth, excluding third molars, and 338,554 controls, all of European ancestry. We also tested the association of previously identified risk variants, for timing of tooth eruption and orofacial clefts, with TA. We report associations between TA and 9 novel risk variants. Five of these variants associate with selective TA, including a variant conferring risk of orofacial clefts. These results contribute to a deeper understanding of the genetic architecture of tooth development and disease. The few variants previously associated with TA were uncovered through candidate gene studies guided by mouse knockouts. Knowing the etiology and clinical features of TA is important for planning oral rehabilitation that often involves an interdisciplinary approach.

Craniofacial morphology in 6-year-old Icelandic children.

The purpose of the study was to describe the craniofacial characteristics of 6-year-old Icelandic children, make a normative standard for children with an Angle Class I molar relationship, and compare them to those with an Angle Class II molar relationship. The material consisted of the radiographs of 363 children, 184 (50.7 per cent) boys and 179 (49.3 per cent) girls with a mean age of 6 years 7 months (range: 5 years 7 months-7 years 8 months). Twenty-two reference points were digitized and processed by standard methods with the Dentofacial Planner computer software program. The 33 variables calculated included both angular and linear. Two sample t-tests were used to study the differences between different groups. Only minimal differences could be noted between sexes in sagittal and vertical angular measurements. Linear measurements, on the other hand, were usually larger for the boys. When compared with Norwegian material of the same age group, similar trends were observed between sexes in both studies, but the Icelandic children showed slightly more mandibular prognathism and a lower mandibular plane angle. When compared with children with an Angle Class I molar relationship, children with an Angle Class II molar relationship did not have a different maxillary prognathism nor a different mandibular length. Cranial base dimensions were all significantly greater and the cranial base flexure was also significantly more obtuse in the distal group.

Remodeling of canines to the shape of lateral incisors by grinding: a long-term clinical and radiographic evaluation.

A long-term clinical and radiographic follow-up study was performed after extensive remodeling of the permanent teeth of 26 adolescent patients. The canines were ground to the shape of lateral incisors as part of the orthodontic treatment, and the patients were recalled after 10 to 15 years for clinical examinations. Grinding had been performed either unilaterally or bilaterally on 37 teeth. Unground canines or adjacent teeth served as control or reference teeth. Standardized intraoral radiographs were taken with a paralleling technique. Enamel surface replicas produced by epoxy resin in silicone impressions of the ground teeth were studied by stereomicroscopy. The long-term results were favorable. No significant color differences were observed in 36 of the 37 ground canines. Only one tooth displayed a generalized yellowish discoloration, probably the result of extensive pulp obliteration. There were no significant differences between ground and unground teeth with regard to mobility, reaction to percussion, or temperature sensitivity. Electric pulp testing revealed no statistically significant differences between test and control teeth. Radiographic changes were evident in two of the 37 ground canines. One tooth showed marked obliteration of the crown pulp, and in another tooth the pulp obliteration was almost complete. In the remaining 35 teeth no apparent differences were noted between the ground and unground teeth. In the stereomicroscope two of the ground labial surfaces showed evidence of scratches and grooves produced by the diamond instrument after more than 10 years' observation, but in all other instances the ground surfaces were indistinguishable from normal adult enamel surfaces. In conclusion, the present study has demonstrated that extensive cuspal, labial, lingual, and interproximal recontouring by the grinding of young teeth associated with orthodontic treatment can be performed without discomfort to the patients and with only minor or no long-term clinical and radiographic reactions.