

ORIGINAL ARTICLE 

Year : 2017  Volume
: 6
 Issue : 9  Page : 611 

Linear regression formula to predict chronological age through digital orthopantomographs and canine pulp/tooth area ratio in Vidarbha population
Sweta Gandhi^{1}, Abhishek Singh Nayyar^{2}, Vaibhav Borse^{3}, KV Chalapathi^{4}, K Sudheer^{5}, Rahul A Gandhi^{2}, Neetu Punhani^{2}
^{1} Department of Public Health Dentistry, VSPM Dental College and Hospital and PostGraduate Research Institute, Nagpur, Maharashtra, India ^{2} Department of Oral Medicine and Radiology, SaraswatiDhanwantari Dental College and Hospital and PostGraduate Research Institute, Parbhani, Maharashtra, India ^{3} Department of Oral and Maxillofacial Pathology, SaraswatiDhanwantari Dental College and Hospital and PostGraduate Research Institute, Parbhani, Maharashtra, India ^{4} Department of Oral and Maxillofacial Pathology, KLR's Lenora Institute of Dental Sciences, Rajahmundry, Andhra Pradesh, India ^{5} Department of Biostatistics, University of Southern Mississippi, Hattiesburg, Mississippi, US
Date of Web Publication  2Aug2017 
Correspondence Address: Abhishek Singh Nayyar 44, Behind Singla Nursing Home, New Friends' Colony, Model Town, Panipat  132 103, Haryana India
Source of Support: None, Conflict of Interest: None  Check 
DOI: 10.4103/nnjcr.nnjcr_22_16
Context: Age is one of the essential factors of forensic odontology and is essential in establishing the identity of an individual. Estimation of the human age is a procedure adopted by anthropologists, archaeologists, and forensic scientists. Aim: The aim of this study was to develop a method for estimating the chronological age in Vidarbha population based on the relationship between age and various morphological variables of left mandibular canine tooth as obtained using digital orthopantomographs (OPGs). Subjects and Methods: Digital OPG of 200 patients was selected, and radiographic images of the left mandibular canine in each case were processed using a computeraided designing program AutoCAD2008. Regression equations were developed to estimate age from morphological variables. Results: Kappa statistics showed that the intraexaminer agreement score (κ = 0.91) was without a significant error in terms of reproducibility. Pearson's correlation coefficients between observed age and predictive morphological variables in males, females, and in the total sample population were highly significant and inversely correlated for AR (pulp/tooth area ratio) and c (pulp/root width ratio at midroot level) (P < 0.001). The participants' ages were modeled as a linear function of the morphological variables (predictors). Conclusions: There was observed a linear relationship of pulp/root width ratio at the midroot level and pulp/tooth area ratio of the left mandibular canine with chronological age in the Vidarbha population. Age of participants could, therefore, be estimated with a good degree of accuracy using regression equations.
Keywords: Age, digital orthopantomographs, linear regression formula, pulp/tooth area ratio
How to cite this article: Gandhi S, Nayyar AS, Borse V, Chalapathi K V, Sudheer K, Gandhi RA, Punhani N. Linear regression formula to predict chronological age through digital orthopantomographs and canine pulp/tooth area ratio in Vidarbha population. N Niger J Clin Res 2017;6:611 
How to cite this URL: Gandhi S, Nayyar AS, Borse V, Chalapathi K V, Sudheer K, Gandhi RA, Punhani N. Linear regression formula to predict chronological age through digital orthopantomographs and canine pulp/tooth area ratio in Vidarbha population. N Niger J Clin Res [serial online] 2017 [cited 2020 Feb 20];6:611. Available from: http://www.mdcanuath.org/text.asp?2017/6/9/6/212002 
Introduction   
Forensic odontology is the practice related to law. It can be considered as an area of specialization under dentistry and forensic medicine because knowledge of both the fields is vital for its activity.^{[1]} Age is one of the essential factors of forensic odontology and is essential in establishing the identity of an individual. Estimation of human age is a procedure adopted by anthropologists, archaeologists, and forensic scientists.^{[2]} The estimation of age at the time of death is often an important step in the identification of the human remains.^{[3]} If age can be accurately estimated, it significantly narrows down the field of possible identities that have to be compared with the remains to establish a positive identification. It is often necessary to estimate an individual's age due to certain questions related to legal requirements in a forensic context. Although several parts of the body can be used for age estimation, the poor condition of the remains, in particularly severe crashes or fires in cases of those recently dead or of moisture and burial conditions in the case of historic subjects, make many parts of the body unusable. For these reasons, the teeth are the part of the body most frequently used for identification and age estimation.^{[1]} In children, age determination from teeth is a relatively simple and accurate procedure and is based on the stages of development and eruption of teeth. However, in adults, it is a challenge to medicolegal science.^{[2]} Up to now, a multiplicity of methods has been applied to this problem including methods which analyze the various forms of tooth modification such as wear, dentin transparency, tooth cementum annulations, racemization of aspartic acid, and apposition of secondary dentin. Some of the methods are very complex and destructive and are therefore not normally used; wear and the apposition of secondary dentin, on the other hand, are the currently available nondestructive methods. Tooth wear is influenced by various external factors including masticatory function, type of food, timing and sequence of tooth eruption, tooth form, position of teeth, thickness and hardness of enamel, and predisposition to enamel hypoplasia. However, apposition of secondary dentin is a continuing, regular process which is only modified by caries and in particular, abrasion. Secondary dentin has been studied by sectioning and radiography.^{[1]} By taking into consideration these secondary changes in teeth with advancing age, various studies have been conducted to estimate the age of an individual with such research resulting in multifactorial methods helping in age estimation.^{[2]} The agerelated changes in the dentition could be divided into three categories: formative, degenerative, and histological. The formative or developmental changes are good predictors of age in the early enough years. Formative changes are subdivided into following stages: the beginning of mineralization, the completion of the crown, the eruption of the crown into the oral cavity, and completion of the root.^{[4]} Degenerative changes are also equally important for age estimation and are of significance in the advanced/late stages, wherein the other simpler and more common methods that can be used during the early developmental and eruptive phases cannot be used after a certain age in individuals. The obvious degenerative changes in adult dentitions are changes in color, attrition, and periodontal attachment level, wherein changes in color are highly variable and are closely related to the diet and oral hygiene protocols. However, all these methods require extraction, and most of them require preparation of microscopic sections of at least one tooth from each individual. The study of tooth radiographs, on the other hand, is a nondestructive and simple process which can be applied to both the living and deceased individuals, in contrast to other timeconsuming, expensive, less reliable, and destructive methods which may not be acceptable for ethical, religious, cultural, social, or scientific reasons.^{[3]} Further, procedures such as digitization of digital panoramic radiographs and computerassisted image analysis avoid the bias inherent in observer subjectivity and improve reliability, accuracy, and precision.^{[4]} Furthermore, digital radiographs taken with standard parameters for all the patients rule out the possibility of any discrepancy in between the participants. Digital radiography, in addition, has the lowest possibility of introducing an error due to the magnification factor because of an inherent low and negligible magnification factor inbuilt in their software. Furthermore, any tooth can be used to assess age; however, canine teeth are a good candidate for age estimation because they are often present in old age and are less likely than other teeth to suffer wear and tear with age and are relatively less destructive in addition, to being the singlerooted teeth with the largest pulp area, thus, being the easiest to analyze.^{[1]} Nevertheless, a number of similar studies have been conducted in the past to check the reliability of human remains in the estimation of chronological age in the deceased participants for forensic interest. Similar such studies have been conducted based on tooth measurements also, as well as the eruption age, pattern of eruption, and the assessment of the formation of teeth in specific age groups to arrive at the estimated age of the participants under study, but this study is different as it used altogether different sets of parameters and canines with similar objectives. The purpose of the present study was to assess the reliability of the method used for assessing the chronological age, based on the relationship between age and measurement of the pulp/tooth area ratio in canines, using digital orthopantomograph (OPG) and a computeraided designing program (AutoCAD2008).
Aims and objectives
The purpose of the present study was to present a method for assessing the chronological age based on the relationship between age and measurement of the pulp/tooth area ratio on singlerooted teeth using digital OPG and a computeraided drafting program, AutoCAD2008.
Subjects and Methods   
Digital OPGs of 200 patients were collected based on the following criteria.
Inclusion criteria
 Patients aged between 18 and 60 years
 Patients with the left mandibular canine fully erupted into the oral cavity
 Patients with the root of the canine fully formed.
Exclusion criteria
 Teeth with any pathology such as caries or periodontitis or periapical lesions, which would alter the surface area of the tooth
 Malaligned or rotated canines
 Canines with any prosthetic fittings and
 Missing canines.
Digital OPGs were taken as part of routine treatment that was being rendered to the patient. Participation in the study was voluntary. Relevant data including date of birth and gender were entered into the pro forma after obtaining informed consent. Ethical clearance was obtained from the Institutional Ethical Committee.
Methods
Digital OPGs of selected patients were obtained, and radiographic images of canines were processed using the computeraided designing program, AutoCAD2008. Twenty points around the edge of the tooth outline and ten points around the pulp outline of the left mandibular canine were identified [Figure 1]. Measurements of the canine tooth area and the pulp area from the radiographic images were then evaluated. The tooth length, pulp length, and root length were measured. The width of the root and pulp at three different levels: one at the level of cementoenamel junction (CEJ), second at midroot level, and the third at the level of the midpoint between the CEJ and the midroot level were measured. All measurements were carried out by a single observer. To test intraobserver reproducibility, a random sample of thirty observations from the study sample were reexamined after an interval of 1 week.  Figure 1: Orthopantomographs with measurements from different points in relation to left canine
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The following morphological variables were calculated from the above measurements:
 AR = pulp/tooth area ratio
 p = pulp/root length ratio
 r = pulp/tooth length ratio
 a = pulp/root width ratio at CEJ level
 c = pulp/root width ratio at midroot level
 b = pulp/root width ratio at midpoint level between CEJ level and midroot level.
The observed age was calculated by subtracting the date of birth from the date of the radiograph.
Statistical analysis
Statistical analysis was performed with SPSS (version 13, SPSS Inc., Chicago, USA) package. A multiple linear regression model for age estimation was developed by selecting those variables which contributed significantly to age estimation.
Results   
Kappa statistics showed that the intraexaminer agreement score (κ = 0.91) was without a significant error in terms of reproducibility. Pearson's correlation coefficients between observed age and predictive morphological variables in males, females, and in the total sample population were highly significant and inversely correlated for AR (pulp/tooth area ratio) and c (pulp/root width ratio at midroot level) (P < 0.001). The participants' ages were modeled as a linear function of the morphological variables (predictors). A multiple linear regression procedure was, therefore, applied to optimize this model. [Table 1] shows the regression analysis of the total sample, whereas [Table 2] shows the results in males and [Table 3] in females with P values that were found to be significant although among all the morphological variables tested, only AR (pulp/tooth area ratio) and c (pulp/root width ratio at midroot level) showed highly significant results. Hence, a regression model utilizing AR and c was used as shown in [Table 4] which yields the following linear regression formula to estimate the chronological age:  Table 1: Regression analysis with all morphological variables and age as the dependent variable in the total study sample (n=200)
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 Table 2: Regression analysis with all morphological variables and age as the dependent variable in males (n=100)
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 Table 3: Regression analysis with all morphological variables and age as the dependent variable in females (n=100)
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 Table 4: Regression analysis with selected morphological variables and age as the dependent variable
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For participants of unknown gender:
Age = 72.49 − 203.69 (AR) − 51.65 (c)
Similarly, the effect of gender on age estimation was also determined in the study, and it was observed that gender had no significant influence on age estimation.
Discussion   
Age is an essential factor in forensic odontology and establishing the identity of a person.^{[5],[6]} Radiography, being a nondestructive method, plays a vital role in forensic dentistry to uncover the hidden facts, which cannot be seen by means of physical examination. Dental examination and comparison between antemortem and postmortem dental records and radiographs produce results with a high degree of reliability and relative simplicity.^{[7]} In the present study, age estimation was carried out using regression equations based on pulp/tooth area ratio and pulp/root width ratio at midroot level. This was in accordance with the previous study conducted by Bosmans et al.^{[8]} with a correlation coefficient “R” that was found to be 0.99 confirming that estimating the age using pulp/tooth area ratio is relatively accurate. Previous studies have also shown that with advancing age, the size of the dental pulp cavity is reduced as a result of secondary dentin deposition so that measurements of this reduction can be used as an indicator of age. Kvaal et al. conducted a study to find a method to estimate the chronological age of an individual from measurements of size of the pulp on full mouth dental radiographs.^{[3]} They used radiographs of six different teeth  maxillary central and lateral incisors and second premolars, mandibular lateral incisors, canines, and first premolars. They tried to correlate age with various factors such as pulp/root length, tooth/root length, and pulp/root width at three different levels. They found out that the width of the pulp had a strong correlation with age.^{[9]} Later, Bosmans et al. applied Kvaal's dental age estimation method on panoramic dental radiographs, thereby avoiding the cumbersome process of taking multiple periapical radiographs.^{[8]} They also concluded pulp width to be closely associated with age in their study. In the present study, we also used panoramic radiographs, as in the study of Bosmans et al.^{[8]} and observed that estimated age was modeled as a linear function of the chronological age. Hence, this study also confirms the fact that the width of the pulp is a better indicator of the age, which is in consistence with the previous studies conducted by Kvaal et al.,^{[3]} Cameriere et al.,^{[4]} Paewinsky et al.,^{[6]} Solheim^{[10]} Singaraju and Sharada,^{[11]} and Babshet et al.^{[12]} In 1995, Kvaal et al.^{[3]} presented a method for age estimation which was based on investigation of periapical radiographs, whereas Paewinsky et al.^{[6]} verified the applicability of this method on OPG. In 2004, Cameriere et al. found a linear relationship between the pulp/root width ratio at midroot level, the pulp/tooth area ratio, and chronological age.^{[4]} The findings of the present study were consistent with this study. Cameriere et al. stated that the ratio between pulp and tooth area correlated best with age.^{[4]} With this background, they developed regression equations for age estimation using the pulp/tooth area ratios of canines from the maxilla and the mandible separately.^{[1]} In their study, Babshet et al. found that Cameriere's formula, based on the Italian population, is not as applicable to the Indian population.^{[12]} Therefore, we decided to develop regression equations for the Indian population. We used both pulp/root width ratio at midroot level and pulp/tooth area ratio in regression equations to make the equation as close to ideal as possible. Although results are promising, we cannot generalize them to other populations. Further research is thus mandated with an aim of analyzing a larger sample size from different geographic and ethnic variations, including not only age and gender but also racial and cultural parameters. This method of age estimation cannot be applied to multirooted teeth, as accurate measurements are difficult to perform in such cases. Similarly, as the curved arch of the jaw is projected onto a flat film, there will always be a certain amount of distortion when measuring the image presented there.^{[8]} To have an acceptable amount of distortion and to bring uniformity in the measurements in all the radiographs, we decided to use a particular tooth, the left mandibular canine. To compensate for the amount of distortion, we choose the tooth of study on a particular side of the radiograph, that is, we choose only the mandibular canine on the left side so that the amount of distortion is uniform in all the radiographs. Therefore, it is impending to be seen whether this distortion has any effect on accuracy of age estimation. Apart from the aforementioned limitations, the cost involved in setting up of the software is also high.
Furthermore, regression equations are not always foolproof. Linear regression is a statistical method for examining the relationship between a dependent variable and one or, more independent variables. It provides a functional relationship between two or, more related variables with the help of which the unknown values of one variable can easily be estimated or, predicted from the known values of another variable. It, also, provides a measure of errors of estimates made through the regression line. A little scatter of the observed (actual) values around the relevant regression line indicates good estimates of the values of a variable with less degree of errors involved therein. On the other hand, a great deal of scatter of the observed values around the relevant regression line indicates inaccurate estimates of the values of a variable and high degree of errors involved therein. Linear regression, also, provides a measure of coefficient of correlation between the two provided variables. Despite the above utilities, though, the technique of regression analysis suffers from numerous serious limitations. Linear regression equations assume that the cause and effect relationship between the variables remains unchanged, though, this assumption might not always hold good and hence, estimation of the values of a variable made on the basis of the regression equation may lead to erroneous and misleading results.
Summary and Conclusions   
Within the limitations of the study, it can be concluded that there is a linear relationship of pulp/tooth area ratio (AR) and pulp/root width ratio at midroot level (c) of the left mandibular canine with chronological age in the Indian population. In unknown participants, age can be estimated using regression equations based on the abovementioned variables; however, similar studies are supposed to be conducted with inclusion of population from the different parts of the world and with varying ethical, religious, cultural, and social background to validate its applicability to different sects of the world.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
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[Figure 1]
[Table 1], [Table 2], [Table 3], [Table 4]
