The Moyers mixed dentition space analysis method is among the most commonly used in clinical practice for detecting tooth size-arch length discrepancies. In view of reported secular trends, racial, and sex differences in tooth sizes, the purposes of this study were to evaluate the applicability of Moyers probability tables in a contemporary orthodontic population of India and to formulate more accurate mixed dentition prediction aids.
Odontometric data were collected from 300 male and 300 female subjects of Indian descent, who had fully erupted mandibular permanent incisors and maxillary and mandibular canines and premolars. We measured the mesiodistal crown widths with vernier scale dial calipers. The odontometric values obtained were then subjected to statistical and linear regression analysis.
All tooth groups showed significant differences ( P <0.001) between mesiodistal widths of male and female subjects. Regression equations for the maxillary arch (males, Y = 7.15 + 0.67X; females, Y = 7.44 + 0.65X) and the mandibular arch (males, Y = 5.55 + 0.71X; females, Y = 6.15 + 0.67X) were used to develop new probability tables on the Moyers pattern. Significant differences ( P <0.05) were found between our predicted widths and the Moyers tables at almost all percentile levels, including the recommended 75% and 50% levels.
We believe that these new prediction aids could be considered for a more precise mixed dentition space analysis in Indian children.
Every dentist who provides care for children and adolescents should be able to properly assess and manage their developing occlusions. Many malocclusions, especially crowding problems, originate in the mixed dentition period. During this critical period, the orthodontist or pediatric dentist is often asked to provide an accurate diagnosis of any developing malocclusions and an opinion on its effects, if any, on the ultimate occlusal status of the permanent dentition. One condition requiring early diagnosis and treatment is when there is a disparity between the space available in the dental arch and the space needed for the proper alignment of the unerupted permanent canines and premolars. In planning the management of these patients, the deficit of arch space must be predicted early, and the indicated preventive or interceptive procedures instituted. The mixed dentition space analysis (MDSA) is a fundamental part of an early orthodontic assessment and helps in determining any tooth size-arch length discrepancy. If a discrepancy is present, MDSA will be a useful diagnostic aid in evaluating whether the treatment plan will involve serial extractions, guidance of eruption, space regaining, proximal stripping, space maintenance, or just periodic observation of the patient.
To perform an accurate MDSA, it is vital to correctly predict the mesiodistal crown widths of the unerupted permanent canines and premolars. Two broad approaches have been used for this prediction: radiographic and nonradiographic methods. Radiographic methods require measurements of undistorted long-cone radiographic images of erupted and unerupted teeth, and also of erupted teeth on study casts. The mesiodistal widths of the unerupted canines and premolars are then estimated from multiple regression equations or graphs. Such complex methods might discourage their routine use by clinicians. Moyers proposed a simpler nonradiographic MDSA method in which the mesiodistal crown widths of the unerupted permanent canines and premolars of both arches can be predicted from the combined mesiodistal crown widths of the 4 mandibular permanent incisors by using probability tables.
The Moyers probability tables were developed at the University of Michigan based on odontometric data of American white subjects of Northwestern European descent. The accuracy of these probability tables is questionable when applied to population groups other than white people, because it has been well established in the literature that tooth sizes vary considerably between racial groups. Table I shows mesiodistal crown widths obtained from odontometric studies of various population groups. In addition, a few investigators noted a secular trend toward increased tooth sizes with succeeding generations. This implies that values used in probability tables or prediction equations developed from odontometric data of earlier generations might underestimate the tooth sizes of present-day children. Accordingly, the objectives of this study were to formulate new prediction aids (probability tables and prediction equations) that can enable a more accurate MDSA in Indian children, and to evaluate the applicability of Moyers probability tables in a contemporary Indian population.
|Study||Sex||Sample size (n)||Arch||Mean (mm)||SD (mm)|
|Jaroontham and Godfrey (Thai)||M||215||LI||23.89||1.37|
|Priya and Munshi (South India)||M||200||LI||24.88||0.36|
|Lee-Chan et al (Asian Americans)||M, F||201||LI||23.40||1.19|
|This study (Punjab, India)||M||300||LI||24.03||1.05|
|Schrimer and Wiltshire (South African blacks)||M||100||LI||23.92||1.90|
|Diagne et al (Senegalese)||M||25||LI||23.71||1.25|
|Ferguson et al (African Americans)||M, F||105||LI||23.52||1.79|
|Tanaka and Johnston (North Americans)||M, F||506||LI||23.43||1.35|
Material and methods
Dental study casts of 300 male and 300 female subjects were selected for this study from a contemporary population of India. The casts were made from dental impressions of children in various schools of Punjab state in India, after approval was obtained from their parents and teachers. The criteria for sample selection were the following.
The mandibular permanent incisors, the mandibular and maxillary permanent canines, and the mandibular and maxillary premolars were fully erupted.
There was no obvious loss of tooth material mesiodistally as a result of caries, fractures, congenital defects, or interproximal attrition.
The dental impressions and study casts were high quality and free of distortions.
The subjects had no previous history of orthodontic treatment.
All subjects had a similar ethnic background (Punjabi).
The teeth measured were the mandibular central and lateral permanent incisors, the mandibular and maxillary permanent canines, and the first and second premolars of both arches. The values obtained for the right and left canine-premolar segments in each arch were averaged, so that there would be 1 value for the mandibular canine-premolar segment and 1 value for the maxillary canine-premolar segment for each value of the combined mandibular incisors.
Measurements of the mesiodistal crown widths of the mandibular and maxillary teeth were made by using a dial caliper with a vernier scale, calibrated to the nearest 0.05 mm (Matsui Dial Caliper, Mitutoyo, Kawasaki, Japan). The tips of the calipers were precision engineered to ensure the greatest accuracy while measuring the various tooth groups.
A standardized method proposed by Moorrees and Reed was used to measure the mesiodistal crown widths. The greatest mesiodistal crown width of each tooth was measured between its contact points, with the sliding caliper placed parallel to the occlusal and vestibular surfaces. This method was reported to be highly repeatable and accurate for measuring mesiodistal crown widths by Doris et al.
Measurement reliability was checked according to a method suggested by Lundstrőm, where the same investigator measures all casts and then remeasures certain randomly selected casts. The coefficient of test-test reliability on 120 such randomly selected casts was calculated and found to be r >0.95, confirming the reliability of the measurements.
Descriptive statistics for the 3 tooth groups measured in the study (mandibular permanent incisors, mandibular canine-premolar segment, and maxillary canine-premolar segment) are presented in Table II for the sexes separately. Student t tests comparing the mesiodistal crown widths of male and female subjects showed highly significant differences ( P <0.001) in all 3 tooth groups, with males having larger teeth.
|Tooth group||Sex||Range (mm)||Mean ± SD (mm)||t value|
|Mandibular incisors||M||20.65-27.50||24.03 ± 1.05||6.92 ∗|
|F||20.40-26.15||23.48 ± 0.93|
|Maxillary canine-premolar segment||M||20.15-26.85||23.23 ± 1.07||5.84 ∗|
|F||20.05-26.25||22.75 ± 0.94|
|Mandibular canine- premolar segment||M||19.40-26.40||22.50 ± 1.09||6.11 ∗|
|F||19.50-25.70||21.99 ± 0.95|
Coefficients of correlation were calculated and standard linear regression equations of the form Y= a + b(X) derived, to evaluate the relationship between the combined mesiodistal widths of the mandibular permanent incisors (X) and the mesiodistal widths of the canine-premolar segments (Y) of each arch. Table III records the various regression parameters: correlation coefficient, regression constants ( a is the y-intercept, and b is the slope of the regression line), coefficient of determination, and standard errors of estimate (SEE).
|Sex||Canine-premolar segment||r||Constants||r 2||SEE (mm)|
This regression analysis was used to formulate new prediction equations that can be used clinically to predict the mesiodistal crown widths of the unerupted canine premolar segments (Y) when the combined mesiodistal crown widths of the 4 mandibular permanent incisors are known (X). These new prediction equations (after approximation) are shown in Table IV , along with prediction equations from some other studies. The regression equations derived in this study were used to prepare new probability tables on the Moyers pattern and are presented in Tables V and VI .
|Study||Sex||Arch||Prediction equations Y =|
|This study (Punjab, India)||M||Maxillary||7.15 + 0.67(X)|
|Mandibular||5.55 + 0.71(X)|
|F||Maxillary||7.44 + 0.65(X)|
|Mandibular||6.15 + 0.67(X)|
|Moyers (North American whites) ∗||M||Maxillary||9.73 + 0.51(X)|
|Mandibular||10.79 + 0.45(X)|
|F||Maxillary||14.17 + 0.28(X)|
|Mandibular||8.85 + 0.52(X)|
|Moyers (North American whites) ∗||M, F||Maxillary||9.23 + 0.55(X)|
|Mandibular||7.82 + 0.59(X)|
|Tanaka and Johnston (North American whites)||M, F||Maxillary||10.41 + 0.51(X)|
|Mandibular||9.18 + 0.52(X)|
|Diagne et al (Senegalese)||M||Maxillary||9.60 + 0.55(X)|
|Mandibular||5.54 + 0.72(X)|
|F||Maxillary||13.77 + 0.35(X)|
|Mandibular||8.74 + 0.56(X)|
|Lee-Chan et al (Asian Americans)||M, F||Maxillary||8.19 + 0.63(X)|
|Mandibular||7.46 + 0.62(X)|
|Jaroontham and Godfrey (Thai)||M||Maxillary||13.36 + 0.41(X)|
|Mandibular||11.92 + 0.43(X)|
|F||Maxillary||11.16 + 0.49(X)|
|Mandibular||9.49 + 0.53(X)|