Sexual Dimorphism in the Development, Emergence, and Agenesis of the Mandibular Third Molar

Abstract

Bilateral agenesis was encountered in about 9% of the cases, with no significant sexual difference. The right and left mandibular third molars had the same pattern of development and emergence. The slight advance of girls over boys at the crown-completion stage was similar to previous observations on other mandibular teeth, particularly the second molar. The root development course of the third molar was faster in males than in females; this sexual dimorphism was much greater for retarded cases than for advanced cases. At the apex closure, the difference between median ages of males and females was 1.5 yr. Alveolar emergence tended to occur at a lower developmental stage in advanced cases compared with retarded cases.

Estimating age and the likelihood of having attained 18 years of age using mandibular third molars

“…Root stage of M3 was assessed by the second author with the aid of a magnifi er using Figure 2 (from Liversidge, 2 which are adapted from Moorrees et al 3 with added descriptions) and Levesque et al 4 (based on Demirjian et al 5 ). Kappa was calculated by re-assessment of root stages from 30 radiographs to determine reliability.…”

“…1,2,4,6-32 Three of these do not give sex-specifi c data, 20,30,32 several omit some stages 26,30 and one stage ('Ri', root initiation) has been interpolated from an illustration. 30 Two methods are detailed in Table 2 and include adapted maturity data from Levesque et al, 4 and adjusted mean age within stage from Liversidge 2 for combined groups. This adjustment was the addition of 0.33 year to the mean age within stage for the combined groups.…”

“…The 95% confi dence interval (CI) for estimated age for a single individual for each stage was calculated from the product of 1.96 and the standard deviation (SD) of mean age for each root stage. Levesque et al 4 do not give SD but this was interpolated for this paper from the cumulative curves for each stage in their illustration and calculated using the normal equivalent deviate. 33 Actual age was subtracted from dental age and mean difference (defi ned as bias), standard deviation (SD) and mean absolute difference were calculated for each method.…”

“…Six methods estimated age with bias not signifi cantly different to zero. These include maturity data from Levesque et al adapted for age estimation (see Table 2), 4 data from Spain, Turkey, China and South African Blacks [11][12][13]23 and adjusted data from the reference study (all groups combined). 2 Measures of accuracy include SD of bias as well as mean absolute difference between known and dental ages.…”

“…2 Measures of accuracy include SD of bias as well as mean absolute difference between known and dental ages. From the six methods showing little bias, the method with the lowest mean absolute difference was adjusted data for combined groups from the reference data at 1.45 years (Moorrees stages) and for Demirjian stages was the adapted maturity data from Levesque et al 4 at 1.71 years. Standard deviation of bias was very similar for all methods; the exception was a study based on a small sample.…”