Dental and Chronological Ages as Determinants of Peak Growth Period and Its Relationship with Dental Calcification Stages

1. INTRODUCTION

The clinical importance of evaluating skeletal maturation has long been recognized by orthodontists. However, timing of growth events is quite variable among individuals [1-3]. Many biological indicators have been assessed for evaluating developmental age including increase in body height or weight [4-6], skeletal maturation of hand-wrist [7-9], cervical vertebrae [10-13], and dental development [14-17]. Skeletal maturation assessed on hand-wrist radiographs is classically considered the best indicator of maturity and it has been found to be closely related to the growth spurt. However, because of the additional radiographic exposure needed, this diagnostic tool has evoked more concern in recent years.

Modifications in size and shape of the cervical vertebrae in growing subjects have gained interest as a biologic indicator of individual skeletal maturity [11, 18]. Cervical vertebral maturation describes the entire pubertal growth period by covering all significant phases in craniofacial growth during adolescence and young adulthood, and it is valid for both gender [10-13]. More importantly, it requires no additional x-ray exposure beyond the routine lateral cephalometric projection.

Dental maturity can be determined by the stage of tooth eruption or the stage of tooth formation. Tooth eruption is unreliable because many factors such as space available, ankylosis, and early or delayed exfoliation of primary teeth alter the eruption of the permanent successors [19, 20]. Various radiological methods have been proposed to estimate tooth formation based on the degree of calcification of the permanent teeth [21, 22]. Even if most of them show good validity, they use the unknown final length of the root as an indicator of dental age [23]. One of the most widely applied methods for ascertaining dental age is the Demirjian eight-stage system [24].This method is based on a dental age scoring system on objective criteria and relative values rather than onabsolute lengths. Considering mean differences between estimated dental ages and chronological ages [25-28] meta-analyses reveal the need to develop different estimation calculations based on local population characteristics in order to obtain accurate estimations of dental age [29].

Studies on the correlation of dental maturity described on the basis of mineralization of the entire dentition, usually produced low or no correlation coefficients between dental and skeletal age, regardless of the method of skeletal age assessment [30, 31]. In contrast, studying selected teeth rather than the whole dentition provides higher correlation coefficients between dental and skeletal maturity because the probability of accidental errors will be decreased [32-35]. The calcification stages of canines, premolars, and second molars were recommended because their maturation occurs in the pubertal growth period [32, 33, 36]. Incisors and first molars developed before the onset of the pubertal growth spurt [34] while the third molars develop after this period [37].The aims of this study were (1) to investigate the relationship between dental age, chronological age, and cervical vertebral maturation (CVM) during the peak growth period of Greek individuals and (2) to assess any relationship between the stages of calcification of canines, premolars and second molars and CVM during the same period.

2. MATERIALS AND METHODS

2.2. Assessment of Skeletal Maturity

The morphology of the second, third, and fourth cervical vertebrae was evaluated twice by the first author placing the lateral cephalometric radiograph on a conventional negatoscope (X-RAY Co., Amityville, NY, USA). The three cervical vertebrae were traced using acetate paper. Skeletal maturation of each lateral cephalometric radiograph was determined according to the CVM method [11] (Table 1).

RESULTS

The reproducibility of all the measurements was found to have high coefficient values. The coefficient of reliability was found to be .98 for the dental calcification stage assessments and .99 for the skeletal maturity assessments.

The number, corresponding chronological and dental ages for each CVM stage, for both females and males, are shown in Table 3. As skeletal maturation increased, chronological and dental ages increased accordingly (Figs. 1 and 2). Regarding gender, a consistently earlier occurrence for each skeletal maturation stage was observed for females. In the overall growth period, chronological and dental ages showed an overall high correlation for both boys (r =0.741, p<0.001) and girls (r = 0.770, p<0.001) (Fig. 3, Table 4).The strongest correlation was observed in patients with CVM Stage IV, both in males (r=0.554) and females (r=0.68).The lowest correlation was for CVM Stage III in males (r=0.433, p<0.001) and CVM Stage II in females (r=0.052, p>0.001) (Fig. 4). Paired samples t-test showed a statistically significant advanced dental age compared with chronological age for both boys (0.55 ± 1.46, p<0.001) and girls (0.78 ± 1.41, p<0.001) for all CVM stages. Apparently, around the peak growth period (CVMS II - CVMS IV), these differences were more pronounced (Table 5). Dental age accelerated by 0.68 ± 1.43 years in males (p<0.001) and 0.93 ± 1.46 years in females (p<0.001). Spearman rank order correlation coefficients between the CVM stages and the calcification stages of the four individual teeth are shown in Table 6. The second molars showed the highest and the canines the lowest correlation, respectively (p<0.001).

At CVM Stage II (Table 7), the most frequently observed dental development stages for both sexes were stages F and G for canines and premolars, respectively.

At CVM Stage III most of the subjects exhibited almost complete mandibular canine development. The first premolars were close to reaching their final stage for both sexes, while in most of our subjects, the second molars remained in stage G.

At CVM Stage IV more than 90% of the subjects exhibited completed canine and first premolar development. Regarding the second molars, only half (51.4%) of females and 76.9% of males reached stage H, respectively.

DISCUSSION

This study investigated the interrelationship between chronological and dental ages of a group of Greek children. The method used [24] has been used extensively for assessing dental maturation and DA [32, 33, 35]. The DA scoring system is based on the shape and proportion of root length, using its relative value to crown height rather than its absolute length. Thus, the panoramic distortions of the developing teeth will not affect the reliability of estimation [32]. An overall significant difference was found between chronological age (CA) and dental age (DA) in Greek individuals. On average, the Greek boys and girls were ahead of the French-Canadian children previously analyzed [24]. The secular trend in growth and development in the past decades and the ethnic disparity between Greek and French-Canadian children could be an explanation for the estimated differences [29, 38]. Even though it is easy to use and is a highly reproducible method, the eight calcification stages that describe the developing tooth are based on discernible tooth formation changes rather than dividing tooth formation into equal time intervals. This means that the times taken for a tooth to develop from one stage to the next are not identical, affecting the accuracy of age estimation. Although this sample consisted of Caucasian population, there is definitely a need for further investigation using a larger sample of Greek children in order to reach stronger conclusions.

Skeletal maturity was assessed by the CVMS method, consisting of five maturity stages defined by means of visual evaluation of the morphology of three cervical vertebrae (C2, C3, and C4) [11]. According to the present findings, skeletal maturity increased together with the increase of chronological and dental ages. The appearance of each skeletal stage is consistently earlier in females than in males. Regarding CVM stage, dental age in males tended to be more advanced than that in females. These findings are in agreement with previous investigations [14, 32, 33]. In spite of the overall high correlation coefficients between chronological and dental ages in the overall CVMS growth period, the lowest correlation was observed for CVMS III in males and CVMS II in females. Moreover, the t-test reveals statistical significant differences between these parameters around the peak growth period (CVMS II - CVMS IV). Considering that CVMS II marks the ascending portion and the CVMS III the descending portion of the growth spurt neither chronological age nor dental age seem to be reliable in the identification of the pubertal growth phase, which are the most important developmental stages to be identified in orthodontic treatment planning. Therefore, precise information about the timing of the onset of the growth spurt with the relevant clinical implications is not provided by these indices.

Apart from correlations between dental age and CVM stages, correlations between development of individual teeth and skeletal maturity stages were calculated. Calcification stages of canines, premolars, and second molars, because their maturation occurs during the pubertal growth period, were evaluated. From the present findings in Greek children, the correlation coefficients between CVMS and calcification stages of four individual teeth were high, ranging from 0.49 to 0.65 for males (p<0.001) and 0.53 to 0.72 for females (p<0.001) confirming previous investigations irrespective of the method of skeletal age assessment [17, 32-36].The strongest relationship between dental and skeletal development involved the second molars. The second molar offers an advantage over other teeth because its development tends to continue over a longer period and until a later age [27, 28, 36].

For a better understanding of the relationship between CVM indices and dental age during the pubertal growth period, percentage distributions of the studied teeth were also calculated. At CVM stage II, which represents the ascending portion of the pubertal growth spurt, most of the canines and first premolars in both attained root formation from stage F to stage G [32-34] whereas at CVM stage III, most of the canines of both sexes and 74.5% of the boys’ first premolars attained complete root formation [32-36].In this data, the second molar stage G commenced markedly at CVMS III for both sexes.

CONCLUSION

According to the results of this investigation, it can be concluded that:

• Skeletal maturity increased together with the increases in chronological and dental ages for both gender. A consistently earlier occurrence for each skeletal maturation stage was observed in females.
• Dental age was more advanced than chronological age for both boys and girls for all CVM stages. During the peak growth period, these differences were more pronounced. CVM Stages II and III mark the ascending and descending portion of growth spurt respectively, thus dental age and chronological age should not be considered as reliable tools in identification of pubertal growth spurt.
• All correlations between skeletal and dental stages were statistically significant. The second molars showed the highest correlation whereas the canines showed the lowest correlation for both sexes.
• There is a need for further investigation using a larger sample of Greek children in order to reach stronger conclusions.

REFERENCES