A Radiographic Study of Pulp Crown Dimensions of the Mandibular Deciduous Second Molar

Aim: The aim of this study was to assess the difference in crown and pulp area and dimensions of the mandibular deciduous second molar in children using digitized images of bitewing radiographs and image J®. Materials and methods: Bitewing radiographs of 48 children (24 males and 24 females) aged 3.69 to 9.46 years were assessed in a retrospective cross sectional study. Bitewings were photographed and Image J® was used to measure crown and pulp area and some linear measurements. A t-test was used to compare the difference between mean dimensions in males and females. Results: There were no statistically significant (p<0.05) differences in the area (hard tissue with pulp and without pulp area) or in the horizontal (mesial distal crown width, pulp and crown width at cervix) or vertical (mesial and distal pulp horn height to occlusal surface) dimensions of this tooth between boys and girls. Conclusions: There were no differences found in the area and linear measurements of the lower second molar between boys and girls.


Introduction
Dental pulp is integrally connected to dentine in terms of physiology and pathology, so anything that affects the pulp will affect the dentin.Both tissues embryonically share the same origin but despite this, these tissues are different in terms of conformation and structure.The pulpdentine complex is now a widely acceptable term and dentine forms the main bulk of the tooth [1].Enamel is the hardest material in all biological tissues, composing of organic and inorganic substances which cover the dentine [2].The thickness of the hard tissue surrounding the pulp in the deciduous second molar varies from one individual to another [3].
The advantage of radiology is that it is non-destructive, and precise measurement can be obtained in order to study the dimensions of the dentin-pulp complex [4].Following the discovery of X-rays in 1895, Raper introduced the bitewing radiograph technique in 1925 [5].Since then radiology has been widely used for oral tissue diagnosis, age estimation, forensic dentistry as well as dental research [6,7].Bitewings radiographs provide an excellent view of the pulp chamber but are limited as they show a two-dimensional projected images of three-dimensional object [8,9].
Although different parts of the body can be utilised for forensic identification, the tooth has the advantage of longevity in harsh environmental conditions [4].Permanent dentition pulp is given much more importance than deciduous pulp in age determination, forensic and operative dentistry [3,10,11].However a few studies describe deciduous tooth dimensions in terms of gender, ethnicity and pre and post-operative procedures [3,12].Males have larger pulp and dentine dimensions compared to females in permanent teeth [13], but this pattern has not been consistently found in deciduous teeth [3,12].Investigating the dentine and pulp dimensions of the deciduous molars in males and females will contribute to our understanding of the effect of gender on tooth size.In addition, the measurements of dimensions of deciduous teeth are of interest as a possible method to determine the gender of juvenile skeletal remains.Therefore for the determination of gender identification, canines and molars can be used due to the late exfoliation age compared with incisors [12].
The aim of this study was to measure crown and pulpal linear and area dimensions in deciduous mandibular molars using bitewing radiographs, in order to investigate differences between boys and girls.Further changes in these measurements with age were also investigated.

Study design
The design of this study was a retrospective cross sectional study of archived bitewings radiographs of the Institute of Dentistry, Queen Mary University of London.All the radiographs used in this study were of dental patients and had been obtained for diagnostic purpose at the Institute of Dentistry, Queen Mary University of London.This research was carried out during March to September 2011.

Sample
The sample size included 48 children (24 males and 24 females) aged between 3.69 and 9.46 years of age (Table 1).The children were of mixed ethnic origin consisting of British Bangladeshi, Pakistani, Indian, and Caucasian.Radiographs were selected if they were of good quality (no overlapping of teeth) and the teeth were unrestored with no caries.Both right and left mandibular second molar selected.
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Method of measurement
All measurements were carried out by the first author.The selected radiographs were photographed using a Canon Power Shot A3300 camera, tripod, and standard light box.The tripod and light box were set at a distance of 100 mm to photograph each radiograph.The images were analysed using image J ® (NIH, USA).The images were enlarged by 50% to fill the flat screen of a 19 inch computer monitor.The measurement scale was set and the actual width of the radiograph measured as 34 mm.After setting the scale, measurements were recorded in pixels.A pilot study was conducted to compare areas of the crown, measured from ten dots connected by lines or continuous outline.
Measurements of the area, linear and vertical dimensions were obtained by the first author (Figure 1).Area measurements:-Crown area was measured from the mesial dentine-enamel junction following the crown to the distal dentine-enamel following junction and connected by a straight line at the cervix level (Figure 1a).Pulp area was measured from the mesial cervix level following the outline of pulp to distal cervix level and joined by straight line (Figure 1b).Linear measurements:-Maximum bulbosity of the mesial and distal surface of the crown.Width of the pulp at the cervix level and width of the crown waist from one dentine-enamel junction to the other (Figure 1c).Vertical distances:-Distance from the tip of the distal and mesial pulp horn to the occlusal level (Figure 1d).An example of these measurements on a bitewing radiograph is illustrated in figure 2.

Intra -examiner reproducibility
Ten reference points were identified as illustrated in Figure 1e.These included area, linear and vertical measurements.Six radiographs were reexamined 2 weeks after examination by the first author and the results compared using a t-test.Analysis of results was carried out using PSAW 18 version (formerly SPSS Statistical, Statistical Package for the Social Sciences) and a comparison was carried out to assess which measurements were least variable (Table 2).

Statistical analysis
Descriptive statistics, including means, standard deviation, and standard error of mean of all area and linear data were calculated.A ttest was used to compare the means of all measurements between males and females.Statistical significance was determined at the level of 0.05 (Table 3).

Results
Table 4 shows the dental coronal pulp and hard tissue measurement from the 48 deciduous mandibular second molars studied.No statistically significant difference was observed in the width measurements of (such as mesio-distal crown width, pulp width at cervix, and crown width at cervix) between boys and girls.Further, there were no statistically differences in the height dimensions (such as mesial and distal pulp horn distance to occlusal surface of deciduous mandibular second molars) in the mesial pulp (p=0.72) and the distal pulp (p=0.45)dimensions between boys and girls.Similarly, no relationship with age was found in pulp area (p=0.06),hard tissue area (p=0.97) and the summation of pulp area and hard tissue area (p=0.96)(Table 4).Crown area 1 (mm Open Access

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Other ways of assessing deciduous tooth dimensions include from the mouth and indirectly from plaster casts.The majority of the studies were based on indirect methods [3,16,17].Hunter [18] showed that it is very difficult to use direct method for measuring the tooth dimensions due to anatomical factors.In terms of mesial distal measurements, Eswara [16] study of south Indian children found that deciduous tooth size in males was statistically different than females.Anderson [19] study of direct and indirect techniques on African American showed no statistically significant in tooth size observed among two techniques.The measurements of second molar performed on cast models by Bravo [17] on Spanish children showed no statistically significant differences between males and females.
In this study conventional radiology was used whereas Arpana [3] used the radiovisiographic images.However to our knowledge, the differences between conventional and radiovisiographic related to dimensions to vertical and horizontal dimensions and area measurements have not been assessed.The age of the subjects in this study were between 3 and 9, while Harris [12] study consisted of 3 to 6 age group and Arpana [3] used children between 4 and 7 years.
In conclusion this study has provided baseline data about the morphologic characteristics of mandibular second molar teeth showing no differences in these between girls and boys in the cohort age group studied.

Discussion
Tooth dimensions are not only important in archaeology and forensic odontology but also in operative and endodontic dentistry.Any differences found between sizes, shapes, type of tooth can be related to sample size, age of the subjects, ethnicity differences and to radiographic errors [3,14].The present study showed no statistically significant differences in horizontal and vertical linear measurements, as well as area measurements of mandibular second molar between girls and boys in this small sample aged between 3.69 and 9.46 year.
In terms of the mesio-distal crown width of deciduous second molars no significant difference was found among males and females in this study.In contrast to findings reported by Zilberman [15] and other studies [3,12].This might be due to the small sample size or to the mixed ethic groups made up of British Bangladeshi, Pakistani, Indian and Caucasian children in London.
No significant difference was found while comparing males and females in terms of pulp width and crown width at cervix in this study in agreement with findings by Arpana [3].Vertical linear measurements such as mesial and distal pulp horn distance to occlusal surface between males and females showed no significant difference in this study.
Similarly the crown and pulpal areas measured in the present study also showed no significant difference found between males and females, similar to that reported in the Arpana study [3].However there was no trend of pulp decrease seen with age observed in this study.The strength of our study was a reliable quantitative method on conventional bitewing radiographs.This was cross sectional study, a limitation of our study as other studies [16,17], as only a longitudinal study will assess the individual pulp dimensions over time for any age change.

Figure 1 :Figure 2 :
Figure 1: Tooth measurements of the deciduous second molar (A) black color area showing crown area from dentino enamel junction.(B) pulp area above dentinoenamel junction.(C) 1 and 2 distance from tip of distal and mesial pulp horns to the occlusal level.(D) 1 mesio-distal crown width, 2 crown width at cervix, 3 pulp width at cervix.(E) dots measurement method

Table 1 :
The frequency of age distribution by sex.1 males 2 females

Table 2 :
A comparison of results of the lines and points measurements.1 line 2 points Citation: Kazmi S, Anderson P, Liversidge HM (2017) A Radiographic Study of Pulp Crown Dimensions of the Mandibular Deciduous Second Molar.Int J Dent Oral Health 4(1): doi http://dx.doi.org/10.16966/2378-7090.246

Table 3 :
Results of the mean difference between area measurements (intra observer reproducibility)

Table 4 :
Results of the dimensions in males and females.