Subjects of the present study were Egyptian adolescent girls (Alexandria inhabitants). As long as, it was reported in the literature that variations in growth pattern and skeletal maturation exist among different genders Soegiharto et al. (2008) [5], also maturity status of the Egyptian males was previously reported in an earlier study by Kharasa et al. (2015) [7].
The middle phalanx of middle finger (MP3) stages was evaluated according to the six modified MP3 stages, described by Rajagopal and Kansal (2002) [6], which is a modification of the original method of Hagg and Taranger (1982) [2]. This method had been evaluated and proven to be valid and reliable by several investigators (Özer et al., Pradhan et al., Perinetti et al. [8, 9, 10].
In the present study, the mean chronological age at which females reached the peak of pubertal growth spurt, as recorded by the MP3-G stage, was 11.21 ± 0.85 years. When compared with previously reported data in different population, the Egyptian girls reached their peak of pubertal growth spurt approximately 0.5–1 year earlier compared with the other ethnic groups, as in white Americans (12.28) years, Indonesian (11.77) years, Aborigines (12.4) years, Asian (Chinese) (12.5) years and Turkish (12.03) years as reported by Soegiharto et al., Grave and Brown, Chang et al., Uysal et al., [5, 11, 12, 13] respectively. On the other hand, the Egyptian girls reached their peak of pubertal growth spurt in a similar mean age with Thai girls (11.4) years, as reported by Krailassiri et al. [14].
According to Perinetti et al. (2016) [15] the MPS2 and MPS3, corresponded to MP3-FG, MP3-G stages in the present study, might be considered associated with the onset and maximum mandibular growth peak, respectively. Therefore, the optimal treatment timing with functional orthopedic treatments, especially for skeletal Class II malocclusion, would be carried out during the interval between the MP3-FG and MP3 G stages, which could take place in the Egyptian girls between the ages of 10.01–11.21 years.
However, the differences in timing of skeletal maturation between ethnic groups, might be due to factors other than genetic differences as environmental conditions, socioeconomic status, nutrition, hygiene conditions and regional climatic differences. Environmental conditions, climate differences, might be a reason that Egyptian girls, attained the skeletal maturation stage, earlier than other ethnic groups. Therefore, the results could be used when planning orthopedic treatment for Egyptian population.
Other important findings of the current study were that there was no statistically significant correlation between bone radiodensity and the pubertal stages (prepubertal, pubertal, postpubertal), but there was a statistically significant difference between bone radiodensity values at different pubertal stages. A statistically significant lowest mean value of bone radiodensity was found in the pre-pubertal group compared to pubertal and post pubertal groups. Such differences in bone radiodensity values could be interpreted in a clinically meaningful way, that there was a threshold increases in bone radiodensity associated with the occurrence of peak of pubertal growth spurt resulting in a great increase of bone radiodensity values as progress toward maturity during the adolescent growth period. This result could be comparable with the reported data that revealed an increase of BMD with aging process in both genders, with a maximal increase occurring at age of 11–12 years in girls, which was the age of puberty as reported by Nakavachara et al. [3]. Another study reported that the maximal increase of BMD occurred at age 15, 5 years in girls, Braillon et al. [16].
Although there was no statistically significant difference between mean bone density values at pubertal and post pubertal groups, the post pubertal group still had the highest mean values of bone radiodensity, indicating that a positive direct relation was evident between the bone radiodensity values and the progress toward maturity. This insignificant relation might be attributed to the wide age variability among the pubertal and post-pubertal groups.