Original communication
Third molar development by measurements of open apices in an Italian sample of living subjects

https://doi.org/10.1016/j.jflm.2015.11.007Get rights and content

Highlights

  • Dental age estimation is crucial in clinical and forensic dentistry.

  • A sample of 975 Italian healthy children, aged between 9 and 22 years, was studied.

  • The left lower molar index (I3M) was evaluated for the purpose of age estimation.

  • Best fittings of the function I3M was generated using linear, exponential and polynomial functions.

  • The standard deviation and relative error increase with age.

Abstract

The aim of this study is to analyse the age-predicting performance of third molar index (I3M) in dental age estimation. A multiple regression analysis was developed with chronological age as the independent variable. In order to investigate the relationship between the I3M and chronological age, the standard deviation and relative error were examined. Digitalized orthopantomographs (OPTs) of 975 Italian healthy subjects (531 female and 444 male), aged between 9 and 22 years, were studied. Third molar development was determined according to Cameriere et al. (2008). Analysis of covariance (ANCOVA) was applied to study the interaction between I3M and the gender. The difference between age and third molar index (I3M) was tested with Pearson's correlation coefficient. The I3M, the age and the gender of the subjects were used as predictive variable for age estimation. The small F-value for the gender (F = 0.042, p = 0.837) reveals that this factor does not affect the growth of the third molar. Adjusted R2 (AdjR2) was used as parameter to define the best fitting function. All the regression models (linear, exponential, and polynomial) showed a similar AdjR2. The polynomial (2nd order) fitting explains about the 78% of the total variance and do not add any relevant clinical information to the age estimation process from the third molar. The standard deviation and relative error increase with the age. The I3M has its minimum in the younger group of studied individuals and its maximum in the oldest ones, indicating that its precision and reliability decrease with the age.

Introduction

Assessing dental age is important to know whether children and youths are growing properly and is especially useful in orthodontics, paediatric dentistry, forensics, and anthropology.2 For pedodontist and orthodontist, knowing child's developmental status is especially significant in diagnosis and treatment planning.3 In forensic field, dental age is mostly used in resolving issues regarding immigration and prosecution in the criminal and civil courts.4

However, a particular limitation of dental development standards is that the reliability of age estimation is not uniform from birth to adulthood. Age estimation for children up until the age of 14–15 years can be reliably assessed using both skeletal and dental development.5 In fact, up to this time, age estimation is more rewarding and accurate. As a person grows beyond these years, developmental variability increases, thus making age estimations relative imprecise during adolescence.5 Toward the end of human skeletal growth and development, only a few age-dependent features can be evaluated by morphological methods.6

The third molar is the latest tooth to initiate and complete development and therefore is the last available dental morphologic predicator of age.7, 8 The possibilities of using this tooth for assessing age are limited by the duration of its development. The third molar is more variable than for all the other maturity markers, such as the clavicle and the knee.9 In addition, the third molar is often congenitally missing and some individuals do not grow it at all. Indeed, a great variation in position, morphology, and time of formation exists.10

Dental ageing comes in two forms: calcification (tooth development) and eruption patterns.11 Third molar emergence spans the age interval of 12–22 years.11 However, radiographic analysis of third molar development expands the years of age estimation to 9–23 years as crown and root development can be studied independent of eruption.11, 12

The degree of development of this tooth may be recorded as a measure of observed tooth length,13 classified in various stages according to scores assigned to its maturation and eruption 14, or as a ratio of perceived tooth dimensions.15

Regarding to those methods based on tooth measurements, some typical features make them a precise and highly reproducible tool of registration.1, 14 Conversely, Thevissen et al.14 showed that the third molar staging and related scoring should be recommended over complicated dimensions measurements or ratio calculations for age estimation. The staging of third molar crown and root mineralization can be also accomplished easily and non-invasively through evaluation of dental radiographs. According to Olze et al.,16 the Demirjian method achieved the highest values for both the observer agreement and for correlation between the stages, as defined by the method, and chronological age. However, it is fundamental to study different ethnic groups to verify this observation or to discover differences. Interestingly, in all of the studies completed till date, an individual having third molars with Demirjian stage “H” development had very likely reached the chronologic age of 18, indicating that the use of this technique for determining the legal age of majority is valid.11, 17

In 2008, Cameriere at al. 1 developed a new method for assessing adult age based on the relationship between age and the third molar maturity index (I3M), according to measurement of the open apices of the third molar. This technique records continuous data and is based on ratios between measurements of apical pulp widths and tooth lengths. A cut-off value of I3M = 0.08 was determined to assign an individual to juvenile or adult age.1 De Luca et al.18 and Cameriere et al.19 showed that the probability that a subject positive on the test (i.e., I3M < 0.08) was 18 years of age or older was 95.6% and 90.1% respectively. In spite of these results, to date, no studies have been carried out for analysing the bias of the third molar maturity index. Liversidge and Marsden20 showed that most dental methods using M3 root formation estimate age with significant bias. The bias is, according to Liversidge et al.,21 the most useful way to quantify how good a method is at estimating age. As they noted, there is an urgent need for an evidence–based reference to address some issues such as accuracy and bias of this age marker.

The main aim of this study is to analyse the age-predicting performance of third molar in age estimation by measurements of the third molar index (I3M) on orthopantograms of living children and adolescents.

Section snippets

Sample origin

A retrospective, cross-sectional study was conducted with the analysis of panoramic radiographs (OPTs) of 975 Italian healthy subjects (531 female and 444 male) aged between 9 and 22 years. In this study, a minimum of 27 (9 years) and a maximum of 151 (13 years) individuals were studied per age and sex (Table 1). Sample scores range from 0.03 to 3.11 depending on the age group as detailed in Fig. 1.

The panoramic radiographs were collected, in the period between 2011 and 2013, at the Radmedica,

Results

In this study, the reliability of the data collection was evaluated calculating the concordance correlation coefficient (ρc) and no statistically significant difference between paired sets of measurements was detected: ρc = 1.00.

The small F-value for the gender (F = 0.042, p = 0.837) reveals that this factor does not affect the growth of the third molar. Therefore, it was not considered as a variable in the modelling process. Pearson's correlation coefficient between age and the third molar

Discussion

The third molar maturation is one of the few tools that can be used to assess age when development is nearing completion, especially during adolescence when this tooth is often the only variable age indicator left.18, 28, 29 Although the reliability of third molars in age estimation has been evaluated by several studies, consensus on the usefulness of this tooth has not been reached.5 The differences between populations, the different methodology, and the dissimilarity among observers are other

Conclusions

  • 1.

    The precision and accuracy of the I3M decreases with the age according to the values of standard deviation and relative error.

  • 2.

    As a single criterion for age estimation, the I3M is not suitable especially once the third molar's roots are fully formed and their apices closed.

  • 3.

    Once the apices are completely closed, in order to increase the accuracy of age estimation, further age markers should also be evaluated in addition to I3M.

  • 4.

    Although the great variability of the third molar, linear regression

Acknowledgements

The authors would like to thank the Radmedica, Radiologia Odontoiatrica Digitale (Rome, Italy) for their assistance in this project and their support in collecting OPTs of good quality and in anonymous way.

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