|Year : 2021 | Volume
| Issue : 1 | Page : 29-32
A formula for estimating the mesiodistal width of permanent mandibular central incisors
Vikrant Jadhav, Meenakshi Tiwari, Vasudevan Seegavadi, Ranjit Kamble, Pallavi Daigavane
Department of Orthodontics and Dentofacial Orthopedics, Sharad Pawar Dental College, Datta Meghe Institute of Medical Sciences (Deemed to be University), Wardha, Maharashtra, India
|Date of Submission||15-Apr-2020|
|Date of Decision||22-Dec-2020|
|Date of Acceptance||25-Jan-2021|
|Date of Web Publication||29-Jul-2021|
Dr. Vikrant Jadhav
Department of Orthodontics and Dentofacial Orthopedics, Sharad Pawar Dental College, (Meghe), Wardha - 442 001, Maharashtra
Source of Support: None, Conflict of Interest: None
Introduction: A chieving acceptable occlusal contact during orthodontic treatment is very important. Tooth size ratios play a major role in the prediction of treatment outcomes. Aim: The aim of this study is to determine the mesiodistal width of missing mandibular central incisor. Materials and Methods: The study sample consisted of study casts of 300 participants in the age range of 18–30 years. Samples having a full complement of teeth with Angle's Class I molar and canine relationships, good intercuspation, normal overjet and overbite, and minimal crowding and spacing. Tooth dimensions were measured using a digital Vernier caliper. The data calculated were used for measuring schedule variance (SV) formula. Results: Based on the achieved data, SV formula is derived. Conclusion: For achieving esthetic profile, it is essential to calculate the correct mesiodistal width of the teeth. Ideal tooth proportions play an important role in achieving good occlusion at the end of orthodontic treatment.
Keywords: Mandibular central incisor, maxillary central incisor, mesiodistal width, missing incisor and digital caliper, Tonn's ratio
|How to cite this article:|
Jadhav V, Tiwari M, Seegavadi V, Kamble R, Daigavane P. A formula for estimating the mesiodistal width of permanent mandibular central incisors. J Datta Meghe Inst Med Sci Univ 2021;16:29-32
|How to cite this URL:|
Jadhav V, Tiwari M, Seegavadi V, Kamble R, Daigavane P. A formula for estimating the mesiodistal width of permanent mandibular central incisors. J Datta Meghe Inst Med Sci Univ [serial online] 2021 [cited 2021 Sep 23];16:29-32. Available from: http://www.journaldmims.com/text.asp?2021/16/1/29/322592
| Introduction|| |
The frequency of congenital missing mandibular incisor is statistically less but still is area of concern for orthodontists. Furthermore, the probabilities of missing mandibular incisor due to periodontal pathology are high. To attain of a desired occlusion and an acceptable intercuspation, proper tooth size evaluation should be done. In cases with missing mandibular incisors, determining the tooth size of the missing tooth is questionable.
There are different methods to determine the width of missing teeth. Tonn's developed a method to evaluate the width of missing maxillary lateral incisor. Ahmed et al. proposed an innovative mathematical modification of Tonn's formula for the determination of the mesiodistal width of the missing mandibular incisor. Tonn's formula required the width of all erupted incisors (maxillary and mandibular) to calculate the width of missing maxillary lateral incisor. Hence, it could not be applied if any teeth were missing. It was also time-consuming. Furthermore, this formula was derived from the Caucasian population. Hence, many authors questioned its applicability in the Indian population.,,, when the formula was applied in our population, inaccurate results were obtained. Bansal et al. just performed mathematically alteration, but the problems remained the same. Therefore, to overcome these problems, “schedule variance (SV) formula” for determining mesiodistal width of missing mandibular central incisor based on the width of maxillary central incisor for our population were derived.
The new formula is simple to use, easy to remember and does not involve all incisors for calculation.
It would benefit the patients seeking esthetic correction for replacement of missing permanent a formula for estimating the mesiodistal width of permanent mandibular central incisors. The formula can also be applied in cases of esthetic correction. This could be used by all the branches of dentistry.
| Materials and Methods|| |
The present study was carried out after the approval from the institutional ethical committee.
For the study, the potential participant was examined clinically. The following inclusion and exclusion criteria were used to select the participants.
- Participants in outpatient department with all permanent teeth fully erupted with or without third molar
- Participants with age 18–30 with Angle's Class I canine and molar relation.
- Multiple missing teeth
- Unerupted permanent teeth
- Unrestored carious teeth
- Teeth with full-coverage restoration
- Proximal wear/attrition of teeth
- Congenital defects or deformed teeth.
The informed consent was obtained from those participants who meet the inclusion criteria. A total of 300 participants were included. Following this, accurate impression of upper and lower dental arches was recorded using putty impression material. The impression was poured immediately with dental stone to minimize distortion of impression. The cast was retrieved after the dental stone was set and bases were poured and measurement was carried out on the casts.
A modified digital Vernier caliper was used to measure the mesiodistal width of the teeth. The tips of the caliper were modified to fit into the contact points of the teeth. The tips of the caliper were placed in the contact point of the tooth and the mesiodistal width of the teeth was recorded and entered into table. All the measurements were carried out in millimeters [Figure 1] and [Table 1].
The mesiodistal width of the maxillary and mandibular central incisors on both the sides was measured using a digital vernier caliper on 300 study cast. The mean and the standard deviations of the width were assessed. The proportion between the width of the maxillary and mandibular central incisor was assessed and the SV formula was derived [Figure 1].
The Institutional Ethics Committee of DMIMSDU has approved the Research work proposed to be carried out at Sharad Pawar Dental College & Hospital, Sawangi(M), Wardha. Date: 3rd April 2018 DMIMS(DU)/IEC/2018-19/7151.
| Results|| |
SV formula for missing mandibular central incisor –
SV Formula = (Mesiodistal width of both maxillary incisors/4−2)
When this formula was checked in our population we obtained the following results:
The mean of mandibular central incisor and both maxillary incisors were calculated. It was found to be: minimum 0.62 and maximum 0.92. Standard error was calculated that was 0.003 on the left side and 0.004 on the right side. Standard deviation of 0.075, average difference (error) of 0.04 in the right mandibular incisor, and error of 0.03 in the left mandibular incisor were obtained. Coefficient of variance was found to be 0.04 for the right side and for the left side, it was 0.05. Based on these mathematical values, it was possible to determine the accurate formula with minimum error for our population. The mesiodistal width of permanent mandibular incisor using combined mesiodistal width of maxillary incisors was calculated. Error was obtained similar on both sides of the arch. The error was very negligible. For more accurate results ± 0.5 to be done in results. For more accurate results ± 0.5 to be done in results.
| Discussion|| |
Missing mandibular incisors are often encountered in clinical practice. This is seen in individuals who have over-retained, impacted, submerged, and traumatically avulsed central incisors. Mandibular incisors are the fourth most common missing teeth after third molars, lateral incisors, and mandibular second premolars. Missing mandibular incisors have a psychological implication due to deprived smile and aesthetics. Thus these teeth are indicated for replacement. To achieve an optimum esthetic and functional result, it is often necessary to establish a synchronized, interdisciplinary approach with orthodontist to know correct mesiodistal width of teeth. It is difficult to estimate the widths of the missing mandibular incisors when previous dental records of the individuals are missing. This is more so in our set up as individuals rarely visit dentists at regular intervals.
According to Al Shahrani the most frequently missing permanent teeth, excluding third molars, are the mandibular second premolar (11.3%) followed by mandibular incisor (6.9%). The safe and ideal orthodontic treatment planning for individuals with hypodontia of mandibular central incisors requires the utilization of tools to diagnose the tooth size discrepancies and/or discrepancies in ideal proportions between maxillary and mandibular teeth, to achieve a perfect intercuspation. It should be considered that space closure at the region of the missing mandibular incisor leads to a tooth size discrepancy between the dental arches, commonly clinically observed as a residual overjet, and occasionally by an increased overbite, even after the achievement of ideal intercuspation of canines and premolars. However, the clinical alternatives to compensate this discrepancy and thus achieve ideal overjet and overbite are minimally invasive, either by the placement of composite resin on the mandibular incisors or by proximal stripping on the maxillary incisors. To decide this, it is very important to know the correct mesiodistal width of the teeth. Till date, mesiodistal width of central incisors was assessed on radiographs. However, magnification errors and radiation exposure have questioned the accuracy of the radiographic method. It is also true that relying on radiographic methods, orthodontist has failed to achieve correct results. Hence, there was a need to precisely plan a formula to evaluate the mesiodistal width of the mandibular central incisor. Therefore, we came up with the SV formula which will solve the problem and improve accuracy regarding treatment planning on the dental cast.
The Bolton analysis is the most often used method for such evaluation. Although widely diffused and relatively simple to use, this ratio resulted in disproportionate results which lead to unesthetic look. Missing central incisor often creates an unesthetic look with marked mobility and increase spacing with mandibular anterior teeth. Spacing increases with age and drifting of teeth in seen. Therefore, missing mandibular central incisor always create a complication for deciding whether to bring this teeth into place orthodontically or to replace it prosthetically or with an implant. Hence for deciding this, it is necessary to know the exact mesiodistal width of the teeth. It would be helpful for planning the case judiciously.
There are different methods to determine the width of missing teeth. Tonn's developed a method to evaluate the width of missing maxillary lateral incisor. There was no formula to determine the width of the mandibular incisor. Nowadays, the incidence of missing mandibular central incisor is increasing. Tonn's formula required the width of all erupted incisors (maxillary and mandibular) to calculate the width of missing maxillary lateral incisor. The SV formula used the width of maxillary incisors to calculate the width of the mandibular central incisor. This formula was simple and required minimum calculations. The problems faced by Tonn's formula were tedious calculations, and it was not derived for the right and left side. As the mesiodistal width of teeth differed on the right and left side, the applicability of Tonn's formula was not possible. Furthermore, this formula was derived from the Caucasian population. Hence, many authors questioned its applicability in the Indian population. When the formula was applied in our population, inaccurate results were obtained. Hence, it was essential to formulate the “SV formula.” The new formula is simple to use and easy to remember.
The SV formula was derived by analyzing the dental study models of 300 individuals. The mesiodistal width of the maxillary and mandibular permanent incisors were measured using a modified digital vernier caliper and tabulated. The mean and standard deviation were calculated. The dimensions of the maxillary and mandibular teeth were then compared. Based on the theory of proportions, the formula for calculating dimensions of the mandibular permanent central incisor was based on the combined width of maxillary incisors. The SV formula which was measured showed very negligible errors for our population. Average difference between the measured and estimated values of mandibular permanent central incisor was 0.05 mm when both the maxillary incisors were used. Error of 0.03 mm was observed when both the maxillary incisors were used to predict the widths of the left mandibular central incisor. Similarly, for mandibular right central incisor error was 0.04 mm. Furthermore, the difference was in the second decimal when the mandibular lateral incisors were used for predicting the mesiodistal width of the mandibular central incisor. These formulae are helpful for individuals seeking esthetic correction for the replacement of missing permanent mandibular central incisor., The formula can also be applied in cases of esthetic correction of malformed/impacted of permanent maxillary and mandibular canine. This could be used by all the branches of dentistry. This error or difference indicated the accuracy of the SV formula to predict the results.,,,,
The formula that we propose is as follows:
SV formula for missing mandibular central incisor -
SV formula = (Mesiodistal width of both maxillary incisors/4−2)
| Conclusion|| |
The success of orthodontic treatment depends on the careful approach of record taking and diagnosis. One of the important diagnostic tools is the use of the diagnostic model for the estimation of tooth size. Tooth size must be proportionate to jaw size so as to avoid tooth size arch length discrepancy. For this simple mathematical formula (SV formula) can be used as a valuable clinical aid in predicting an approximate value for the tooth. The accuracy of these formulas was checked in our population and significant results were obtained.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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