Maxillary and mandibular anterior crown width/height ratio and its relation to various arch perimeters, arch length, and arch width groups.

OBJECTIVE: To investigate the maxillary and mandibular anterior crown width/height ratio and its relation to various arch perimeters, arch length, and arch width (intercanine, interpremolar, and intermolar) groups.
MATERIALS AND METHODS: The calculated sample size was 128 subjects. The crown width/height, arch length, arch perimeter, and arch width of the maxilla and mandible were obtained via digital calliper (Mitutoyo, Japan). A total of 4325 variables were measured. The sex differences in the crown width and height were evaluated. Analysis of variance was applied to evaluate the differences between arch length, arch perimeter, and arch width groups.
RESULTS: Males had significantly larger mean values for crown width and height than females (P ≤ 0.05) for maxillary and mandibular arches, both. There were no significant differences observed for the crown width/height ratio in various arch length, arch perimeter, and arch width (intercanine, interpremolar, and intermolar) groups (P ≤ 0.05) in maxilla and mandible, both.
CONCLUSIONS: Our results indicate sexual disparities in the crown width and height. Crown width and height has no significant relation to various arch length, arch perimeter, and arch width groups of maxilla and mandible. Thus, it may be helpful for orthodontic and prosthodontic case investigations and comprehensive management.

INTRODUCTION

Variations in tooth size, tooth morphology, and tooth size ratio have been connected with diverse ethnic foundations and occlusion statuses.[123456789] Sexual dimorphism in crown dimension has relation to humanoid sex genes and hormones and is influenced by their imbalance.[10] Hereditary and ecological factors have strong effects on human teeth.[11] Correspondingly, the teeth width/height ratio has population and ethnic variations in relation to shape.[12] These ethnic variations must be considered in treatment planning especially to address esthetic concerns.[13]

Harmonious anterior teeth with proper size and shape were one of the most influential factors contributing to a pleasant smile in orthodontic, operative, and prosthodontic management. Lombardi[14] was the first treatment providers to accentuate the status of dental proportions with different facial types. They mentioned that there was a recurring ratio noted between all teeth in relation with face from the central incisor to the first premolar. Levin[15] and Qualtrough and Burke[16] indicated that the most harmonious teeth proportion is 1:1.618 between central incisor to lateral incisor. However, conflicting reports[171819] indicated that the majority of beautiful smiles did not have these dental proportions. Several anatomic measurements have been proposed to aid in determining the correct size and shape of the anterior teeth in relation to the various facial land marks and types on various populations.[2021222324]

The authors have identified that no relative analysis of the maxillary and mandibular anterior tooth width/height ratios in relation to various arch perimeters, arch length, and arch width (intercanine, interpremolar, and intermolar) groups for the Pakistani population has been previously done.

The purpose of this study was:

To evaluate the anatomic crown width/height ratios of maxillary and mandibular anterior tooth for sexual dimorphism

To evaluate the width/height ratios of maxillary and mandibular anterior tooth in relation to various arch perimeter groups

To evaluate the width/height ratios of maxillary and mandibular anterior tooth in relation to various arch length groups

To evaluate the width/height ratios of maxillary and mandibular anterior tooth in relation to various arch width groups:

Intercanine width

Interpremolar width

Intermolar width.

MATERIALS AND METHODS

Subjects

The study was a comparative retrospective design. The oral and dental investigations were carried out with careful selection of subjects from the Pakistani population. Ethical approval was granted by the Ethics Committee of the Universiti Sains Malaysia (USM/JEPeM/140376) and informed consent was obtained from subjects. This investigation was designed and conducted according to the guidelines of Strengthening the Reporting of Observational studies in Epidemiology (STROBE), and we applied the STROBE specification in this manuscript.[25]

Sample size calculation

The sample size was calculated at a power of 80%, utilizing estimated standard deviations (SDs) of 0.60 mm,[26] a biologically meaningful mean difference of 0.3 mm, and equal sample sizes.[27] The calculated sample size was 128 subjects (64 males and 64 females with a mean age 19.4 ± 1.9 SD). The following inclusion and exclusion criteria were used.

Inclusion criteria

All patients were of Pakistani origin determined via interviews, with mutual paternities and ancestors without any multiethnic nuptials

Subjects were aged 18–24 years

Maxillary and mandibular well-aligned arches, with normal patterns of growth and development

None of the participants had undergone orthodontic treatment, with all sound erupted permanent teeth (except third molars)

Ideal occlusion with Class I molar and canine relationship with incisors according to the British Standards Institute[28]

No crowding, cross bite and spacing

Straight profile (identified by examining the profile view)

No craniofacial anomalies

No gingival or periodontal conditions or therapy that would undermine a healthy tissue-to-tooth relationship.

Exclusion criteria

Interproximal caries or restorations

Missing or supernumerary teeth

Abnormal size or morphology of teeth

Tooth wear that affected the tooth size measurements

Damage to casts.

Cross-examination of subjects was done to diminish sample bias and error; with an experienced orthodontist and dentist contributing throughout the screening sittings. Dental impressions of the upper and lower arches of each subject were obtained with alginate impression material (Zhermack Orthoprint Alginate ISO 1563-ADA 18 Italy) and poured with dental stone (Type III hard plaster quick stone China) according to the manufacturer's instructions. A total of 4325 variables were measured.

Measurement of crown width, crown height and arch dimensions

Dental models of each subject for maxillary and mandibular arches were carefully selected according to inclusion and exclusion criteria. Crown width, crown height, arch length, arch perimeter, and arch width of the maxilla and mandible were obtained via digital caliper (Mitutoyo, Japan)[29] as follows.

Crown width measurement

The mesiodistal crown diameter of the tooth was measured from anatomical contact of one tooth to another from frontal side perpendicular to the long axis of the teeth.[12]

Crown height measurement

Crown height [Figure 1] was recorded as the greatest distance on buccal/labial surface from the occlusal/incisal line to cervical line parallel to the occlusal plane.[1230]

Figure 1

Crown width and height measurement via digital caliper

Arch dimensions measurements

Arch perimeter

Arch perimeter[2931] was measured as a segmental sum of linear lines on the right and left side of the arches [Figure 2c].

Figure 2

Arch dimension measurements (a) arch width (Green color) (b) arch length (yellow color) (c) arch perimeter (Red color)

Arch length

Arch length was obtained using triangular shaped lines between the mesiobuccal cusp tips of first permanent molars and the central point between the incisors of each respective arch [Figure 2b].

Arch width of maxillary and mandibular variables

Maxillary and mandibular intercanine widths were obtained between the cusp tips

Maxillary and mandibular interpremolar widths were obtained between the cusp tips of maxillary first premolars

Maxillary and mandibular intermolar widths were obtained between the mesiobuccal cusp tips of the maxillary and mandibular first molars respectively [Figure 2a].

Arch length, arch perimeter, and arch width grouping

The subjects were further grouped as follows:

Arch length groups (small, average, and large): The numbers of subjects for small, average, and large arch length groups in the maxilla and mandible were 46, 44, and 38, respectively

Arch perimeter groups (small, average, and large): The number of subject for small, average, and large arch perimeter groups in the maxilla and mandible were 44, 45, and 39, respectively

Arch widths group (small, average, and large): The number of subject for small, average, and large arch width groups in the maxilla and mandible were 44, 45, and 39, respectively (intercanine, interpremolar, and intermolar width).

These groupings were determined based on data values of the mean ± 2SD, >2SD, and <2SD grouped in the average group, large group, and small group, respectively.[31]

Error study

Twenty percentage of dental casts were randomly selected for intraobserver errors. The time interval between the first and second readings was approximately 2 weeks. The method error (ME) was analyzed by the Dalhberg's formula:

ME = (Σ [x1 − x2]2/2[2n])1/2

Where x1 is the first measurement, x2 the second measurement and n the number of repeated measurements.[32]

Statistical analyses

The data were verified and analyzed statistically using IBM SPSS Statistics version 22.0 (Armonk, NY: IBM Corp., USA) with the confidence level set at 5% (P < 0.05) to test for significance. Independent t-tests were applied to compare mean values between males and females crown width, crown height, and crown width/height ratio in relation to all variables. Analysis of variance was applied to evaluate crown width/height ratio in relation to the arch length, arch perimeter, and arch widths groups. The post-hoc tests of Bonferroni correction were performed for differences among the groups.

RESULTS

Method error

Dahlberg's formula was used to determine the ME, which did not exceed 0.006 and 0.05 mm for the linear variables of teeth crown width and crown height, respectively. The combined errors for all of the variables were small and considered to be within acceptable limits.[32]

Sexual disparities in crown width/height ratios

Table 1 shows no significant difference for the crown width/height ratios, except the maxillary right canine (WHR13) and mandibular left central incisor(WHR31).

Table 1

Maxillary and mandibular anterior (canine to canine) sexual disparities for crown width/height ratios

Disparities in relation to arch length, arch perimeter, and arch widths groups of the maxilla

Tables 2–6 show the maxillary arch perimeter, arch length, and arch width (intercanine, interpremolar, and intermolar) groups in relation to crown width/height ratios respectively. There were no significant differences observed in relation to all groups (P ≥ 0.05). Except few variables for the intercanine and inter first molar arch width for the small versus large and average versus large group were observed (P ≥ 0.001), (P ≥ 0.01), and (P ≥ 0.05).

Table 2

Mean crown WHR of maxillary six anterior teeth in relation to various UAPG

Table 6

Mean crown WHR of maxillary six anterior teeth in relation to various UAIMWG

Disparities in relation to arch length, arch perimeter, and arch widths groups of the mandible

Tables 7–11 show the mandibular arch perimeter, arch length, and arch width (intercanine, interpremolar, and intermolar) groups in relation to crown width/height ratios, respectively. There were no significant differences observed in all groups (P ≥ 0.05).

Table 7

Mean crown WHR of mandibular six anterior teeth in relation to various LAPG

Table 11

Mean crown WHR of mandibular six anterior teeth in relation to various LAIMWG

Correlation for width/height ratio and its relation to various arch dimensions

Table 12 shows the correlation coefficients determined between the measured maxillary and mandibular crown width/height ratios values and the corresponding arch dimension groups values. There were low correlations observed for the maxillary and mandibular arches with R values ranging from 0.17 to 0.42 and 0.26 to 0.29, respectively.

Table 12

Correlation coefficients (R) and coefficients of determination (R2) between maxillary crown WHR and its relation to various arch dimensions

DISCUSSION

Current research investigates the crown width/height ratio in relation to arch perimeter, arch length, and arch width groups (intercanine, interpremolar, and intermolar) for the first time. However, Alam and Iida investigated only mesiodistal tooth size and tooth size ratio in relation to these groups via cone beam computed tomography acquisitions.[31] In orthodontic diagnosis and treatment planning, the evaluation of the tooth size and tooth size discrepancy is an essential rung and such investigation was generally determined by conventional plaster study model analysis.[33]

The clinical responsibility of the orthodontist is to visualize the macro-, mini-, and micro-esthetics and to design a pleasant smile.[343536] Current research investigates the crown width/height ratio for the very first time. These investigated norms can be used as a reference in relation to orthodontic and prosthodontic treatment of patients. There was significant difference observed in the worn and nonworn crown width/height ratio.[12] Therefore, in treatment plan, crown width/height ratio must be kept in consideration for the ideal overjet, overbite, and proper interdigitation to be achieved.

Through our study, we found out that there is significant sexual difference in the Pakistani population in the mean crown width/height ratios of maxillary and mandibular anterior six teeth (P ≥ 0.05). However, there were no significant differences observed in relation to the arch length, arch perimeter, and arch width groups (P ≥ 0.05). As study on Bangladeshi population reported no significant difference in the mean crown width/height ratios of maxillary anterior teeth between the various facial groups (P > 0.05).[24]

Our research investigated the maxillary and mandibular anterior teeth width/height ratio with ideal overjet, overbite, and proper interdigitation in relation to arch perimeter, arch length, and arch width groups (intercanine, interpremolar, and intermolar). The research results showed no significant difference in relation to these groups of ideal occlusion [Tables 3–11]. Other studies investigated the ideal occlusion in relation to maxillary and mandibular tooth size ratios and found significant differences in relation to these groups.[31] But current research found no significant difference for crown width/height ratio to various arch groups and low correlations [Table 12].

Table 3

Mean crown WHR of maxillary six anterior teeth in relation to various UALG

For the Pakistani population the tooth were investigated in mesiodistal, buccolingual, and diagonal dimension.[37]

The upshot of this study would be advantageous for both manufacturer and clinician. The current data can be used as reference, in order to create a natural pleasant esthetic smile and look. Especially during planning orthodontic, implant therapies, periodontal surgeries, and dental prosthesis procedures involving maxillary and mandibular esthetic zone. Currently, there are many manufacturers’ products of artificial teeth in various dimensions. Not all products are suitable for every person as there are variations in natural tooth size and shape from one person to another. By using the crown width/height ratio values obtained in this study, the proposed width/height, and there ratio can be calculated for each ethnic group and thus may accurately determine the ideal tooth shape and size in the esthetic zone. Therefore, such investigations are needed to be carried out in other population. Furthermore the norms will be of great value in forensic dentistry, and dental anthropology. Human teeth and arch size have lots of variations in size in relation to culture, race, and sex.[113738]

CONCLUSION

Significant sexual dimorphisms were observed in the crown width/height ratios of maxillary and mandibular anterior teeth in few variables

There were significant differences observed for crown width/height ratios of maxillary arch Intercanine and Inter first molar arch width groups (small vs. large and average vs. large)

There were no significant differences observed for crown width/height ratios of maxillary and mandibular anterior tooth in relation to:

Maxillary and mandibular arch perimeter groups

Maxillary and mandibular arch length groups

Mandibular arch width inter first premolar width groups

Mandibular arch width groups in:

Intercanine width groups

Inter first premolar width groups

Inter first molar width groups

Financial support and sponsorship

Universiti Sains Malaysia 304/PPSG/61313104 short-term grant.

Conflicts of interest

There are no conflicts of interest.

Table 4

Mean crown WHR of maxillary six anterior teeth in relation to various UAICWG

Table 5

Mean crown WHR of maxillary six anterior teeth in relation to various UAIPMWG

Table 8

Mean crown WHR of mandibular six anterior teeth in relation to various LALG

Table 9

Mean crown WHR of mandibular six anterior teeth in relation to LAICWG

Table 10

Mean crown WHR of mandibular six anterior teeth in relation to various LAIPMWG