Extending Genome-Wide Association Study Results to Test Classic Anthropological Hypotheses: Human Third Molar Agenesis and the "Probable Mutation Effect".

A genome-wide association study (GWAS) identifies regions of the genome that likely affect the variable state of a phenotype of interest. These regions can then be studied with population genetic methods to make inferences about the evolutionary history of the trait. There are increasing opportunities to use GWAS results-even from clinically motivated studies-for tests of classic anthropological hypotheses. One such example, presented here as a case study for this approach, involves tooth development variation related to dental crowding. Specifically, more than 10% of humans fail to develop one or more permanent third molars (M3 agenesis). M3 presence/absence variation within human populations has a significant genetic component (heritability estimate h 2 = 0.47). The evolutionary significance of M3 agenesis has a long history of anthropological speculation. First, the modern frequency of M3 agenesis could reflect a relaxation of selection pressure to retain larger and more teeth following the origins of cooking and other food-softening behaviors (i.e., the genetic drift hypothesis or, classically, the "probable mutation effect"). Alternatively, commensurate with increasing hominin brain size and facial shortening, M3 agenesis may have conferred an adaptive fitness advantage if it reduced the risk of M3 impaction and potential health complications (i.e., the positive selection hypothesis). A recent GWAS identified 70 genetic loci that may play a role in human M3 presence/absence variation. To begin evaluating the contrasting evolutionary scenarios for M3 agenesis, we used the integrated haplotype score (iHS) statistic to test whether those 70 genetic regions are enriched for genomic signatures of recent positive selection. None of our findings are inconsistent with the null hypothesis of genetic drift to explain the high prevalence of human M3 agenesis. This result might suggest that M3 impaction rates for modern humans do not accurately retrodict those of the preagricultural past. Alternatively, the absence of support for the positive selection hypothesis could reflect a lack of power; this analysis should be repeated following the completion of more comprehensive GWAS analyses for human M3 agenesis.

[Indications, feasibility and clinical experience with Vazirani-Akinozi mandibular block in limiting mouth opening and difficult anatomical conditions].

Vazirani-Akinozi technique was used in 82 patient undergoing oral surgery procedures. According to study results Vazirani-Akinozi technique was feasible in 89% of cases and particularly effective in surgical treatment of third lower molars eruption diseases complicated by inflammatory contracture. The method increases mouth opening 1.6-2.3 cm due to the soft-tissue anesthesia and partial anesthesia of masseter nerve. In case of inflammatory contracture of the jaws when inflammatory infiltration is spreading on the masseter muscle the authors recommend to use a combination of Vazirani-Akinozi and Berchet-Dubov techniques.

A review of taurodontism with new data on indigenous southern African populations.

The prevalence and degree of taurodontism (enlargement of the pulp cavity) in the mandibular permanent molars of two recent population samples from southern Africa were investigated quantitatively from lateral radiographs. The degree of occlusal wear was scored and two measures of relative pulp cavity size were recorded for each tooth. There was a significant association between increased attrition and a reduction in the size of the pulp cavity when all of the teeth were considered together, but no correlation among individual molar types within each sample. In both the Zulu (n=68 individuals) and Khoisan (n=28 individuals) samples, third molars had the highest prevalence of taurodontism and first molars the lowest. The data for Zulus are similar to those recorded for other modern populations (e.g. white and black Americans, and Israelis), whereas the Khoisan data exhibit significantly higher frequencies. An increased appreciation of the distribution of this variant in modern human populations would contribute to an understanding of its possible evolutionary significance in the human fossil record.

UK National Third Molar project: the initial report.

The National Third Molar (NTM) project was set up to assess current clinical practice in the UK concerning the management of third molar teeth. Patients were recruited from both hospital and general dental practice. During the one month study period 9248 patients with 26,577 third molars were recruited. In this report we present the findings in the 8298 patients with 25,001 third molars who were referred to hospital for assessment. Over half of all patients referred for assessment had either no extractions or a single third molar extracted. Less than a quarter of all patients referred underwent removal of all four third molars. Twenty per cent of all third molars assessed were not extracted. Of all lower third molars listed for extraction, 9574 (78%) were associated with symptoms or disease. Pericoronitis was the commonest indication for extraction and was cited in 39.5% of all extractions. Almost 70% of third molar extractions were done under general anaesthesia while less than a quarter were performed under local anaesthesia alone.