ORIGINAL RESEARCH


https://doi.org/10.5005/jp-journals-10015-2351
World Journal of Dentistry
Volume 14 | Issue 12 | Year 2024

Tooth Size Discrepancy in Prospective Orthodontic Patients


Aparna Mohan Anitha1https://orcid.org/0000-0001-8467-5619, Mala Ram Manohar2https://orcid.org/0000-0002-6593-1856

1Department of Orthodontics and Dentofacial Orthopedics, Noorul Islam College of Dental Sciences, Kerala, India

2Department of Orthodontics and Dentofacial Orthopaedics, College of Dental Sciences, Davanagere, Karnataka, India

Corresponding Author: Aparna Mohan Anitha, Department of Orthodontics and Dentofacial Orthopedics, Noorul Islam College of Dental Sciences, Kerala, India, Phone: +91 7406620420; 9400674565, e-mail: aparnamohananitha@gmail.com

Received: 02 November 2023; Accepted: 04 December 2023; Published on: 31 January 2024

ABSTRACT

Aim: The present study was designed to investigate the anterior and overall tooth size discrepancy in patients seeking orthodontic treatment irrespective of the malocclusion in the South Trivandrum population.

Materials and methods: Good quality study models of both maxillary and mandibular arch of 55 subjects from the age of 13–30 years were selected randomly irrespective of malocclusion. A digital Vernier caliper was used to measure the mesiodistal tooth width. Bolton’s anterior ratio and overall ratio were determined.

Results: For the present study descriptive statistical analysis is being used. A clinically significant anterior discrepancy was found in only one-third, while the overall discrepancy was encountered in almost two-thirds of our sample. 69.1 and 32.7% of the sample had higher anterior and overall ratios, respectively compared to Bolton’s ratio indicating larger mandibular tooth size.

Conclusion: Mandibular anterior excess was found in more than double the subjects with maxillary excess. Clinicians should be aware of this discrepancy that may influence orthodontic treatment goals and outcomes substantially. Thus, the Bolton tooth-size index must be a primordial tool in the quotidian orthodontic diagnosis process and treatment planning.

Clinical significance: Orthodontic treatment may vary from patient to patient but once we reach the finishing stage, it’s almost similar in most of the cases. In pursuit of achieving an ideal and optimal occlusion, the orthodontic community has always looked to the six keys of normal occlusion laid down by Andrews. Unfortunately, tooth size imbalances were not critically looked at by Andrews prompting McLaughlin and Bennett to include a seventh key to address the issue of tooth size imbalances.

How to cite this article: Anitha AM, Manohar MR. Tooth Size Discrepancy in Prospective Orthodontic Patients. World J Dent 2023;14(12):1070–1074.

Source of support: Nil

Conflict of interest: None

Keywords: Bolton’s ratio, Mandibular anterior excess, Tooth size discrepancy

INTRODUCTION

The science of orthodontics has worked hard over the years to address the discrepancies in tooth size with arch length over the years. These dental discrepancies often manifest as either crowding or spacing of the teeth.1,2 The size of teeth is often attributed to a range of factors one of which includes the genetic aspect.3

In an effort to achieve an ideal and optimal occlusion, the orthodontic community has always looked to the six keys of normal occlusion put forward by Andrews.4 Unfortunately tooth size imbalances were not critically looked at by Andrews prompting McLaughlin and Bennett to include a seventh key to address the issue of tooth size imbalances.5

Bolton in 1958, studied 55 cases with normal occlusion and calculated ideal anterior and overall ratios between maxillary and mandibular teeth. He suggested that failing to identify tooth-size discrepancies makes it more difficult to achieve the ideal occlusal relationship and lengthens the course of orthodontic treatment.6,7

In nature, an ideal relation does not always exist between the upper and lower tooth material. A number of studies have reported a discrepancy in overall and anterior tooth material.818 Moreover, the extraction pattern can precipitate a discrepancy of iatrogenic nature.10 Thus, an in-depth knowledge of the effects of tooth size discrepancies is of utmost importance in the delivery of sound orthodontic treatment.

Orthodontic study casts act as an important tool in the diagnostic process which helps one assess the tooth size, shape, arch form, and occlusal symmetry.19 Orthodontic treatment modalities may be diverse and orthodontic correction may be achieved by multiple modalities. However, the orthodontic finishing phase has almost similar aims and objectives in all cases. Depending on the extent to which the initial diagnosis and treatment planning have managed to detect and address several discrepancies, the finishing phase may either be simple and straightforward or require highly complicated biomechanical solutions. Excellent orthodontic treatment result comprises ideal intercuspation, overjet, and overbite. As per a study conducted in the South Trivandrum population, it was found that the orthodontic treatment need was 53.3%; hence, this population was selected for our present study.20

The research question posed was—is there a tendency toward mandibular tooth material excess in patients being treated for correction of malocclusion in the South Trivandrum population?

The present study was designed to investigate the anterior and overall tooth size discrepancy in patients seeking orthodontic treatment irrespective of the malocclusion in the South Trivandrum population.

MATERIALS AND METHODS

The study was conducted from the study casts obtained from the Department of Orthodontics and Dentofacial Orthopedics, Noorul Islam College of Dental Sciences, Kerala, India.

ETHICAL ASPECTS

The study was begun after obtaining clearance from the Institutional Ethical Committee. The study has been approved by the Institutional Ethics Committee (CODS/785/2018–2019).

SAMPLE SIZE ESTIMATION

Based on the Aims and objective of the current study and also considering the study done by Kundi et al.,16 values of various data and parameters were calculated in a G*Power software, also other parameters were calculated by putting the following values in G*Power software as follows:

Thus, a sample size of 55 will be taken into consideration based on previous studies along with the inclusion and exclusion criteria of the study.

Sample Selection

The retrospective cross-sectional study was conducted between March and September 2020. Good quality study models of both maxillary and mandibular arch of 55 subjects of patients aged 13–30 years from the South Trivandrum were selected randomly in accordance with inclusion and exclusion criteria.

Inclusion Criteria

  • All permanent teeth are to be present from central incisors to first molars in all four quadrants.
  • Fully erupted teeth to the occlusal plane.
  • No obvious congenital craniofacial anomalies.
  • No transverse deviations such as crossbite or scissors bite.

Exclusion Criteria

  • Abnormal tooth morphology and size.
  • Prosthetically crowned teeth, extensive caries, or extensive anterior tooth fillings.

MEASUREMENT PROTOCOL

A digital Vernier caliper with sharpened edges was used to measure the mesiodistal width of the tooth. The caliper beaks were inserted from the facial aspect of the teeth and held perpendicular to the long axis of the tooth (Fig. 1). When the predetermined contact points of the teeth were made, the beaks were then gently closed. The measurements included the mesiodistal width of all the 12 maxillary and mandibular teeth from the right first permanent molar to the left first permanent molar on 55 pairs of casts. Bolton’s anterior ratio and overall ratio were determined by the following formula:

Fig. 1: Estimation of tooth size

To avoid the errors a single examiner took the measurements and did the Bolton’s analysis.

Statistical Analysis

Data was entered into Microsoft Excel 2017 edition. Statistical Packages for the Social Sciences version 21.0 was used for statistical analysis of collected data. Descriptive statistics were conducted for all the data.

RESULTS

In the present study, 69.1% of the subjects had an anterior tooth ratio greater than 77.2% or Bolton’s anterior ratio, and 27.3% had less than the same. Whereas 32.7% had an overall tooth ratio greater than 91.3% or Bolton’s overall ratio and 67.3% lesser as presented in Table 1.

Table 1: Anterior–overall tooth ratios
Anterior tooth ratio (%) Overall tooth ratio (%)
Frequency Percentage Frequency Percentage
<77.2 15 27.3% <91.3 37 67.3%
=77.2 2 3.6% =91.3 0 0%
>77.2 38 69.1% >91.3 18 32.7%
Total 55 100 Total 55 100

As presented in Table 2, the mean anterior tooth ratio was 77.76% with a minimum of 76.6% and a maximum of 81.7% having a standard deviation of 1.01 and a standard error of 0.14. The mean overall tooth ratio was 92.03% with a minimum of 87.02% and a maximum of 97.60% having a standard deviation of 2.34 and a standard error of 0.32. While comparing our study group (South Trivandrum population) with Bolton’s for anterior ratio and overall ratio, the p-value (independent t-test) was 0.87 and 0.91, respectively, which proved to be statistically insignificant.

Table 2: Anterior–overall ratios of the study group and Bolton study
Anterior ratio Overall ratio
Trivandrum population study Bolton study Trivandrum population study Bolton study
Sample size 55 55 55 55
Mean 77.76% 77.2% 92.03% 91.3%
Minimum 76.6% 74.5% 87.20% 87.5%
Maximum 81.7% 80.4% 97.60% 94.8%
Standard deviation 1.01 1.65 2.34 1.91
Standard error 0.14 0.22 0.32 0.26
Coefficient of variance 1.02 2.14 5.5 2.09
p-value (independent t-test) 0.87 0.91

*, p < 0.05 is statistically significant

As presented in Table 3, a mean anterior mandibular excess of 0.95 ± 0.82 mm was found in 40 subjects, and a mean anterior maxillary excess of 0.91 ± 0.73 was found in 15 subjects. Whereas a mean overall mandibular excess of 1.97 ± 1.56 mm was found in 37 subjects and a mean overall maxillary excess of 1.88 ± 1.21 mm was found in 18 subjects. It implies that mandibular excess was found in more than double the subjects with maxillary excess.

Table 3: Anterior–overall maxillary and mandibular excess in the study group
Anterior excess (mm) Overall excess (mm)
Mandibular excess (mm) Maxillary excess (mm) Mandibular excess (mm) Maxillary excess (mm)
N 40 15 37 18
Mean 0.95 0.91 1.97 1.88
Standard deviation 0.82 0.73 1.56 1.21
Minimum 0.1 0.2 0.2 0.3
Maximum 2.9 3.1 2.9 3.1

As per Table 3, the range for mandibular and maxillary anterior excess was 0.1–2.9 and 0.2–3.1 mm respectively whereas the range for mandibular and maxillary overall excess was 0.2–2.9 and 0.3–3.1 mm, respectively.

As per Table 4, two subjects or 5.1% had no anterior discrepancy whereas the rest of the subjects had overall tooth material discrepancy. The frequency of anterior mandibular excess is as follows:

Table 4: Frequency of anterior–overall mandibular and maxillary excess
Anterior excess Overall excess
Anterior mandibular excess (mm) Anterior maxillary excess (mm) Overall mandibular excess (mm) Overall maxillary excess (mm)
Range (mm) Frequency % Frequency % Frequency % Frequency %
0 0 2 5.1 0 0 0 0 0 0
1 0.1–1 24 61.5 10 71.4 16 47.1 5 31.2
2 1.1–2 10 25.7 4 28.6 10 29.4 7 43.8
3 2.1–3 3 7.7 0 0 8 23.5 4 25
Total 39 100 14 100 34 100 16 100

The frequency of anterior maxillary excess is as follows:

The frequency of overall mandibular excess is as follows:

The frequency of overall maxillary excess is as follows:

DISCUSSION

Black in 1902 and Neff in 1949 were the first to develop methods for measuring tooth size discrepancies. Neff developed an anterior coefficient of 1.22 by dividing the maxillary 6 by mandibular 6.11

In 1958, Bolton provided an anterior ratio of 77.2% and an overall ratio of 91.3% in what is widely referred to as the Bolton analysis. The Bolton ratios are derived by dividing mandibular teeth by maxillary teeth.6 Bolton’s ratio is considered the seventh key of normal occlusion after considering its importance.4

The present study was compared with original Bolton’s study where the sample size was 55. Therefore, the present study also restricted the sample size to 55 for the purpose of comparison. The sample was selected from a pool of prospective orthodontic patients irrespective of malocclusion to mimic a representative sample in a clinical situation. Bernabe et al. also studied a Peruvian, sample of untreated occlusion.12

The anterior and overall tooth ratios in our study were 77.76% ± 1.01 and 92.03% ± 2.34, respectively, both being higher than Bolton’s ratios, indicating a tendency toward mandibular tooth material excess. Although ours was not a normal occlusion sample, it compares well with Machado et al. worldwide trend of higher ratios.13 This could also erroneously lead to an unnecessary reduction of mandibular tooth material. This is something the clinician must keep in mind and always correlate the calculated ratios with the clinical scenario at hand.

However, our ratios were compared only to Bolton ratios as they are universally accepted; and hence, form the basis till more reliable data is available from a representative population sample.

The prevalence of tooth size discrepancies in this sample was high and serves as a sign of how important it is to perform a thorough diagnosis before orthodontic treatment. The clinical implementation of this analysis is almost always to identify the excess tooth material as it is more acceptable to equalize by reduction than by addition. However, in certain clinical situations like peg laterals, the addition may be a more esthetic solution.

Around 69.1 and 32.7% of our subjects had higher anterior and overall ratios, respectively compared to Bolton’s ratio indicating larger mandibular tooth size. Whereas 27.3 and 67.3% of our subjects had lower anterior and overall ratios indicating maxillary tooth material excess. The subjects in our sample had a higher incidence of mandibular tooth material excess. These findings are in agreement with those of a number of studies.7,8,10,12,1315

Crosby and Alexander reported that 22.9% of subjects in their study had a significantly greater anterior ratio when compared with Bolton’s ratio. They also found that there was a higher percentage of patients with anterior tooth size discrepancy than patients with such kind of discrepancies in the overall ratio.14 These findings are in agreement with our study.

Freeman et al. reported 30.6 and 13.5% of subjects presented with a significant anterior and overall tooth size discrepancy.9

Bernabe et al. found that 32.5 and 36.5% of the sample had clinically significant anterior and overall tooth size discrepancies greater than Bolton’s discrepancy.12

Araujo and Souki concluded that 56% of a total sample of 300 subjects presented with anterior tooth size discrepancies greater than Bolton’s discrepancy.8

Othman and Harradine stated that 17.4 and 5.4% of the sample had significant anterior and overall ratios greater than Bolton’s mean.15

Ibad et al. reported that the prevalence of tooth size discrepancies from Bolton’s mean were 51 and 18.8% for the anterior and the overall ratios.16

Maamar et al. reported that 18.4 and 17.3% of the subjects were found more likely to have mandibular excess in anterior and overall Bolton ratios.17

The anterior mandibular tooth material excess was in the range of 0.1–2.9 mm, with 61.5% having a discrepancy below 1 mm. The anterior maxillary tooth material excess was in the range of 0.2–3.1 mm with 71.4% having a discrepancy below 1 mm.

Mandibular anterior excess was found in more than double the subjects with maxillary excess. Freeman et al. found that the overall discrepancy could be either in the maxilla or mandible, but the anterior discrepancy was twice as likely to present as mandibular excess.9

Overall mandibular excess was in the range of 0.2–2.9 mm, with 47.1% having a discrepancy below 1 mm. and an overall maxillary excess of 0.3–3.1 mm, with 31.2% having a discrepancy below 1 mm.

According to Bolton6,7 and Proffit,18 a clinically relevant discrepancy would be around 1.5 and 2.0 mm, respectively. From the results of this study, a clinically significant anterior discrepancy was found in only one-third, while the overall discrepancy was encountered in almost two-thirds of our sample.

The research question is therefore answered thus—in patients treated for correction of malocclusion in the South Trivandrum population, there is a high tendency for mandibular tooth material excess.

Ideally, this must be detected at the time of planning the case, and the solution needs to be factored into the treatment planning to ensure the correct timing and method of resolution of the tooth size discrepancy in order to avoid increasing the treatment time and more importantly to provide an ideal post treatment occlusion which includes near ideal overjet and overbite.

A single examiner evaluated Bolton’s tooth discrepancies and κ statistics being not assessed can be considered as a limitation of the present study. Even though the sample size was considered to be adequate, future studies should include a broader range of population and evaluation of parameters to be done to produce more reliable data on this topic.

CONCLUSION

From the current study, it can be concluded that the prevalence of intermaxillary tooth-size discrepancy among the study population seems to be significant enough in a large number of patients seeking orthodontic therapy. More than half of the sample showed larger mandibular tooth size. Mandibular anterior excess was found in more than double the subjects with maxillary excess. Clinicians should be aware of this discrepancy that may influence orthodontic treatment goals and outcomes substantially. Thus, the Bolton tooth-size index must be a primordial tool in the quotidian orthodontic diagnosis process and treatment planning.

ORCID

Aparna Mohan Anitha https://orcid.org/0000-0001-8467-5619

Mala Ram Manohar https://orcid.org/0000-0002-6593-1856

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