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 Table of Contents  
ORIGINAL ARTICLE
Year : 2016  |  Volume : 2  |  Issue : 4  |  Page : 213-218

Morphometric Analysis of Maxillary Central Incisor to Determine its Crown Form: A Model-based Cross-sectional Study


1 Department of Oral Pathology, Government Dental College and Hospital, Ahmedabad, Gujarat, India
2 Consultant Dental Surgeon, Bharuch, Gujarat, India
3 Department of Orthodontia, Goenka Research Institute of Dental Science, Gandhinagar, Gujarat, India
4 Consultant Dental Surgeon, Ahmedabad, Gujarat, India
5 Department of Biostatistics, National Institute of Occupational Health, Ahmedabad, Gujarat, India

Date of Web Publication9-Jan-2017

Correspondence Address:
Jayasankar Purushothaman Pillai
Department of Oral Pathology, Government Dental College and Hospital, Ahmedabad, Gujarat
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/2349-5014.197929

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  Abstract 

The size and shape of tooth crowns are morphogenetically predetermined during embryogenesis. The maxillary central incisors have contributed to sexual dimorphism, and several classifications of the form of maxillary central incisors are available in the literature. We, in the present study, aimed to analyze the mesiodistal (MD) measurements at two levels of maxillary central incisor, to determine its crown form. The study was conducted on 100 dental plaster models (50 males and 50 females). The MD dimensions at the contact area level MD_incisal (MD_I) and at the gingival papilla level (MD_G) and the gingivo-incisal height of the crown were measured in the dental models using digital Vernier caliper. The data were analyzed using SPSS version 16 statistical software. The mean values of all the three parameters measured were slightly greater for males and also for the left central incisors. There were no significant differences in all the three variables when the right and left incisors were compared. Significant differences were noted when the parameters are compared between genders. The height/width ratio of crown showed a significant difference between male and female. The value of the ratio between the two MD dimensions (MD_I and MD_G) was used to determine the crown form. The ratio between the MD dimensions at incisal and gingival area showed a significant difference between genders and no such significance was found between right and left central incisors. There is a significant difference in the form of maxillary central incisors between male and female samples and not between right and left. The MD dimensions at incisal and gingival thirds decide the form of crown.

Keywords: Crown form, maxillary central incisor, morphometric, ratio, sexual dimorphism


How to cite this article:
Pillai JP, Patel R, Banker A, Rajarajeswari J, Mishra S. Morphometric Analysis of Maxillary Central Incisor to Determine its Crown Form: A Model-based Cross-sectional Study. J Forensic Sci Med 2016;2:213-8

How to cite this URL:
Pillai JP, Patel R, Banker A, Rajarajeswari J, Mishra S. Morphometric Analysis of Maxillary Central Incisor to Determine its Crown Form: A Model-based Cross-sectional Study. J Forensic Sci Med [serial online] 2016 [cited 2019 May 22];2:213-8. Available from: http://www.jfsmonline.com/text.asp?2016/2/4/213/197929


  Introduction Top


Morphometry refers to the quantitative analysis of form, a concept that encompasses size and shape. The morphology of tooth is genetically determined, and the existence of sexual dimorphism in teeth is also a known phenomenon.[1] The morphometric analysis in tooth known as “odontometrics” has many applications in the field of anthropology, archeology, and forensics. The existence of sexual dimorphism in human dentition was revealed by several earlier investigators.[2],[3],[4] The odontometric approach is considered as a determining factor in providing sexual dimorphism in skeletal remains apart from other established methods. Thus, morphometric analysis of tooth has great significance in forensic investigations. The shape of anterior teeth, especially of maxillary central incisor, plays a major role in achieving pleasing dental and facial esthetics.[5] The difference in the measurements at two different levels in the same plane contributes to the actual shape or form of an object. In tooth also, the mesiodistal (MD) surfaces are not always parallel to each other; instead show some degree of incisogingival tapering. In this study, we aimed to measure the MD dimensions of maxillary central incisor at two levels [Figure 1] and to correlate the ratio to determine its crown form. The maxillary central incisors are centered in the maxilla, one on either side of the midline, with the mesial surface of each in contact with the mesial surface of the other. They are widest tooth MD of any anterior tooth. The MD measurement of maxillary central incisors usually measures between 8 and 9 mm at the contact area. In the mesial side, the contact area of both right and left central incisors is located at the incisal third of the crowns. The distal surface of the central incisors is more rounded, and hence, the distal contact area is somewhat at a higher level than the mesial one. With the long axis of the tooth vertical, the distance between the mesial and the distal contact areas is considered as the maximum MD diameter of the central incisor crown.[6] This MD dimension is not uniform throughout the crown length; instead, the MD surfaces appear to converge from incisal third to the cervical or gingival third. Thus, depending on the MD dimensions, taper of proximal surfaces, and location of contact areas the crown form, there is appreciable variation in central incisor crown forms. The geometrical theory of Leon Williams distinguishes three different classes of tooth form like:
Figure 1: The three metric parameters included in the study (MD-I: Mesiodistal dimension at incisal third, MD-G: Mesiodistal dimension at gingival, GI-Ht: Gingivo-incisal height of crown)

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  • Class I: characterized by the parallel or nearly parallel lines which represent the proximal surfaces for half or more than half of the length from the incisal edge
  • Class II: the lines following the proximal surfaces converge so markedly that they often meet at a point near the root apex
  • Class III: crown form is characterized by a delicate double-curved line on its distal proximal surface and sometimes, though less frequently, on the mesial surface with all surfaces of this type being more rounded and graceful than the other two types.


House and loop classified incisor shape based on the facial outline of teeth focusing on the MD and the gingivo-incisal crown contours. According to them, there are three forms of incisors: square, tapering, and ovoid. This classification is on the facial outline of crowns as well as their MD and cervico-incisal contours.[7],[8] The three classes of tooth form described by Williams closely relate to the forms classified by house and loop [Figure 2] (Class I relates to square, Class II relates to tapering, and Class III relates to ovoid).
Figure 2: The three different forms of crown of maxillary central incisor

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Variations in the MD width in right and left central incisors have been observed.[9] This reveals that the right central incisor is not the exact mirror image of the left one and vice versa. We hypothesized that the difference in the MD dimensions at the contact area level in the incisal third and at gingival third of the crown contributes to the form of the labial surface of central incisors. We performed this morphometric study on dental models as it has been proved to be more reliable method when measured using digital Vernier caliper, instead of taking measurements directly from the mouth.[10]


  Materials and Methods Top


This is a retrospective, cross-sectional, descriptive study conducted using 100 dental plaster models of undergraduate dental students of Gujarati origin at Government Dental College and Hospital, Ahmedabad, Gujarat, India. Informed consents were obtained from the subjects who included fifty male and fifty female dental students. The following inclusion criteria were followed:

  1. All subjects aged 18–23 years
  2. Well-aligned maxillary dentition without any spacing between central incisors or any crowding in the incisor region
  3. Subjects who had not undergone any orthodontic or restorative treatment
  4. Subjects whose gingival and periodontal conditions were sound without any sign of inflammation.


The subjects with the following conditions were excluded:

  1. Subjects with midline diastema
  2. Subjects with either worn out or restored maxillary central and lateral incisors
  3. Dental casts with insufficient details in the area of interest.


Based on the above criteria, the subjects were selected, and the dental casts of the willing participants were prepared. Cross-examination of the casts was done by the Principal Investigator (Jayasankar Purushothaman Pillai) to minimize the sample bias and error. On each central incisor, the MD dimensions were measured on the labial surface at two horizontal levels; one at the MD contact area level in the incisal third (MD_I) of the crown and another at the level of MD gingival papilla (MD_G) level. The greatest gingivo-incisal vertical measurement is considered as the height of the crown gingivo-incisal height (GI_Ht.). Before the measurements, the reference landmarks were marked on each models using a micro tip pencil. A digital Vernier caliper (Mitutoyo, Japan) was used to measure all the above three parameters in both right and left central incisors of the maxillary arch. All the three parameters were measured thrice on three different occasions by the same investigator (Riddhi Patel), and the results were tabulated in an Excel sheet. Statistical significance was assessed using a P value threshold of 0.05. The reliability of the measurements was assessed using Dahlberg's formula.[11] It is defined as , where di is the difference between the two measured values and N is the sample size which was remeasured to evaluate the error of measurements. A randomly selected twenty casts were remeasured by the same investigator (Riddhi Patel) for all the measurable parameters, and the values were substituted in the Dahlberg's formula. A value range of 0.15–0.25 was obtained for the measured parameters, which was considered as acceptable for our set of measured variables. The height/width ratio of the crown of maxillary central incisor and the ratio between its MD dimensions at two horizontal levels were calculated.

Statistical analysis

All measured dimensions on incisors are presented as mean and standard deviation (SD). To check statistical significance for the difference between two groups, t-test was employed unless the variable was not found in violation of normality assumption. All tests were carried out with 5% level of significance with two-sided hypothesis testing. Statistical software SPSS version 16 (SPSS Inc., Chicago, IL, USA) was used for analysis.


  Results Top


The greatest MD dimension of the maxillary central incisor at the level of contact area was 9.56 mm and 10.23 mm for right and left, respectively. [Table 1] shows the descriptive statistics on the two MD and the crown height (GI_Ht.) dimensions of maxillary right and left central incisors. The crown dimensions of the left central incisor were greater value than that of the right central incisor. The mean MD dimension at incisal third was greater for the left central incisor (8.52 mm), and the mean MD dimension at the gingival third was almost same for the right and left central incisors (7.7 mm). However, the mean difference between them was not statistically significant [Table 1]. The gender-based variations in the dimensions showed significant differences. The MD dimensions and the height of maxillary central incisor's crown were significantly higher in male samples [Table 2]. The calculated height/width ratio was same for both right and left central incisors; however, there was a significant difference in the ratio between male and female samples [Table 3] and [Table 4]. The ratio between the MD dimensions at incisal and gingival third was calculated, and the frequency distribution of the height/width ratio of the crown is depicted in [Graph 1]. The mean ratio value for right and left incisors was 1.10 and 1.11, respectively. The mean difference in the measurements between these two levels for right and left incisors was 0.74 and 0.83, respectively. The difference in the variables between right and left incisors was not found significant. The minimum ratio value for both right and left I incisors was 1.02 and the maximum value was 1.25 for the right and 1.26 for the left [Table 5]. However, those values were statistically significant between genders [Table 6]. The descriptive statistics on the differences in the three measured parameters between right and left maxillary central incisors is represented in [Table 7]. The differences in the dimensions of the parameters between male and female samples are depicted in [Table 8]. A greater difference was observed in the height of the crown (1.06 mm.), followed by the MD dimension at incisal (0.39 mm). The mean width of central incisor was nearly 89% of the height of its crown and the mean MD dimension of the central incisor at the gingival level was 90.7% of its greatest MD dimension [Graph 2].
Table 1: Descriptive statistics for mesiodistal dimensions and crown height in the right and left central incisors

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Table 2: Descriptive statistics on mesiodistal dimensions and crown height of maxillary central incisors in male and female samples

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Table 3: Descriptive statistics and comparison of height and width ratio for the right and left central incisors

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Table 4: Descriptive statistics and comparison of height and width ratio for maxillary right and left central incisors in male and female samples

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Table 5: The descriptive statistics for the ratio and differences between mesiodistal dimensions at two different levels in both right and left central incisors

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Table 6: The descriptive statistics and significance value in the ratio and differences between mesiodistal dimensions at incisal and gingival levels in male and female samples

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Table 7: The descriptive statistics of the differences in the parameter values of maxillary central incisors on the either side

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Table 8: The descriptive statistics of the differences in the parameter values of maxillary central incisors between male and female samples

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Based on our findings, we propose the following categories of MD_I/MD_G ratio to determine the crown form of maxillary central incisors.



The frequency distribution [Graph 3] of the data on ratio between MD_I and MD_G revealed 94% of our sample having ovoid form of crown, followed by square form (80%).




  Discussion Top


The tooth morphometry provides significant information related to evolution, anthropology, and forensics. The dimensions are dimorphic among gender, and it has been proved that tooth crowns are larger in men than in women.[12],[13] The size of the teeth is often expressed as the relationship between width and length, known as the height/width ratio. The height and width of the crown of maxillary central incisor are influenced by the physiological, functional, and esthetic parameters. The average height of maxillary central incisor was 11.7 mm, and its width ranged from 8.4 to 11 mm according to Magne et al.[14] Another study by Gillen et al.[15] revealed the average height of maxillary central incisor to be 10.4 mm. In our study, the mean width and height of maxillary central incisor were 8.46 and 9.54 mm, respectively. The overall width by height ratio in our case was 88% which was similar to the finding of Gillen et al. It is generally accepted that the ideal width/length ratio for the maxillary central incisor is 80%.[16] Rhee and Nahm [17] considered and measured the maximum MD widths at the incisal-most aspect (IMD) and the maximum MD width at the cervical area (CMD) and found larger width ratios (IMD/CMD) in the crowded group. In our study, we measured the MD dimensions at contact area level (MD_I) and at the gingival papilla level (MD_G) and found that MD_G was 90.7% of MD_I. The mean MD dimensions at both the levels were 8.40 mm and 7.67 mm, respectively, for right central incisor, and the difference was 0.73 mm, which was almost similar to the earlier study by Rhee and Nahm.[17] The corresponding dimensions in the left central incisor were slightly greater than the right incisor. A study by Vadavadagi et al.[18] also showed similar results. The mean height of the maxillary central incisor was greater in left central incisor, but the mean MD width at incisal and cervical area was greater for right side; whereas in our study, we found slightly higher values in the left incisors than the right one. In their study, there were no significant differences in the values obtained from the right and left central incisors; however, when the values were compared among genders, there were significant differences in them. Our study also showed similar findings. However, we also calculated the height/width ratio and the ratio between two MD dimensions. The ratio values were compared between right and left incisors and also between genders. We found significant differences in the height/width ratio between genders. A similar earlier study on Chinese population by Sah et al.[19] compared the width/height ratio of incisors and canines. In their study, there was no significant difference in the width/height ratio between genders. Similar to our study, there was no significant difference in the dimensions of right and left maxillary central incisors in theirs too. The width to height ratio in their study was 86.14% in females and 85.15% in males. In the present study, the overall width to height ratio of maxillary central incisors was 88%. Significant sexual dimorphism was noted at the MD dimension of a maxillary central incisor in a comparative study by Harris and Couch.[20] Shahid et al.[21] also have observed significant sexual dimorphism in crown width/height ratios of some maxillary anterior teeth, especially the canine. However, there was no significant sexual dimorphism with respect to maxillary central incisors. According to Mavroskoufis and Ritchie,[22] if all the three parameters such as height of crown, width of crown at incisal, and width of crown at cervical are same for both right and left central incisors, then they can be termed as “identical teeth.” They can be termed “symmetrical” if one or two dimensions had a difference not exceeding 0.2 mm. In our study, there was a mean difference of −0.12 mm for MD dimension at incisal, −0.02 mm at the gingival area, and −0.1 mm at the crown height. Although according to Mavroskoufis and Ritchie, the overall samples in our study had bilaterally symmetrical crowns, the results of their mean value were not statistically significant. In their study, the mean value for MD crown width was 8.90 mm for right incisor and 8.87 for the left central incisor. In our study, the corresponding measurements were 8.4 mm and 8.52 mm, and it was found that the MD dimensions in male were greater than those in females, which is in accordance with several other studies.[2],[3],[4] An Indian study by Kaushal et al.[23] has shown a sexual dimorphism of 3.84% and 4.52% for right and left central incisors, respectively. Similar to our findings, their study also showed higher MD mean value for left central incisor than the right incisor. A comparative study by Fernandes et al.[24] on MD measures in African, Caucasian, and Japanese population has shown significant gender difference only in African samples. For the other two ethnic groups, the difference was not as evident. A recent study [25] has shown that greater sexual dimorphism occurs in the buccolingual dimension of maxillary central incisor than its MD dimension. We, in this study, evaluated the morphometry of maxillary central incisor through a conventional method using dental models; however, investigators have used advanced technology like cone-beam computed tomography to investigate the tooth size ratio.[26] Our aim was to use the ratio values to determine the crown form of maxillary central incisor. To the best of our knowledge, there was no such study comparing the MD dimensions at incisal and gingival papilla level and using the ratio to determine the crown form. There is some degree of sexual dimorphism in the morphology of maxillary central incisors. This tooth along with mandibular canine, the most dimorphic tooth, may help in determining the gender, thus delivering its forensic significance.


  Conclusions Top


Within the limitations of the study, the following conclusions were drawn:

  • Our study provides the basis for categorizing the crown form of maxillary central incisor
  • Significant gender-based variations were observed in the MD dimensions and in the height of the crown
  • There was no significant difference in the measured parameters between right and left central incisors of the maxillary arch
  • The value of the ratio between MD_I and MD_G may be useful to determine the crown form of maxillary central incisors
  • Ovoid form of central incisor crown as determined by MD_I and MD_G values was the most common form of crown in our samples.


Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
  References Top

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    Figures

  [Figure 1], [Figure 2]
 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6], [Table 7], [Table 8]



 

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