Maturational changes of the normal occlusion: A 40-year follow-up

Introduction

In this study, we aimed to evaluate the changes in dental arch dimensions, tooth size, and incisor crowding in subjects with normal occlusion over a 40-year period.

Methods

A sample of 82 white subjects with normal occlusion evaluated in adolescence and early adulthood was recruited for a third evaluation in their sixth decade of life. The final sample included dental casts of 22 subjects (12 men, 10 women) obtained at mean ages of 13.3, 17.8, and 60.9 years. The following variables were measured on the digital casts: mesiodistal tooth size; clinical crown height; arch length, width, and perimeter; palatal depth; crowding; overjet; overbite; and curve of Spee. Interphase changes were evaluated using repeated measures analysis of variance, followed by Tukey tests ( P <0.05).

Results

Increases of clinical crown height in the posterior teeth and incisor crowding were found. Decreases of mesiodistal tooth size, mandibular intercanine width, arch length, arch perimeter, overbite, and curve of Spee were observed. Palatal depth increased from 13 to 17 years of age. No changes were observed for overjet.

Conclusions

Subjects with normal occlusion had changes in tooth size and alignment, overbite, and arch dimensions from adolescence to late adulthood.

Highlights

  • We quantitatively assessed the normal occlusion from 13 to 60 years of age.

  • Changes in dental arch dimensions, tooth size, and incisor crowding were assessed.

  • Tooth size and alignment, overbite, and arch dimensions changed from 13 to 60 years of age.

The unpredictability of occlusal changes with aging is a challenge for orthodontics. Craniofacial growth and development are continuous processes, and dimensional changes can occur naturally throughout life. The considerable growth during the first 2 decades of life and the dental arch changes during this period are well documented, and the literature indicates that adult craniofacial structures continue to increase in size. The study by Behrents provided evidence that craniofacial growth continues into adulthood, with greater changes observed for the soft tissues than for the skeletal tissues. Forward and downward mandibular displacement in men and backward rotation in women followed by dental compensation represented by maxillary incisor uprighting were observed. After 40 years of age, only mild changes were observed until the eighth decade of life.

The occlusion and arch dimensions are also influenced by aging. Studies of the longitudinal changes of normal occlusion were previously conducted until the third, fourth, or fifth decade of life. A remarkable decrease of intercanine width was reported. Arch length and perimeter decreased from adolescence to the fourth decade of life. Arch length decreases varied from 1.0 to 5.7 mm. A slight sexual dimorphism was observed, with greater maxillary arch length decreases in men. Overbite and overjet changes had variations. Increases in anterior crowding were greater in the mandible, compared with the maxilla. No previous studies have extended the evaluation of normal occlusal maturation to the sixth decade of life. Longer follow-ups of normal occlusion are important for providing references of natural changes for comparative studies in treated subjects. A recent review about long-term stability of orthodontic treatment reported that, despite the many articles published, few studies included an untreated control group.

In general, tooth size has an association with age. Decreases in the mesiodistal tooth size as a result of interproximal attrition with age were previously described. It was reported that a 10.5 mm of mesiodistal tooth wear was reported in the mandibular arches of primitive Australian aborigines. Mean reductions of 0.15 and 0.32 mm per tooth were described from adolescence to 50 years of age in modern people. Changes in tooth size and clinical crown height with age were not evaluated in subjects with normal occlusion, and might influence arch dimensions and smile esthetics.

Considering the above-mentioned concerns, we aimed to evaluate the changes in dental arch dimensions, tooth size, and clinical crown height in subjects with normal occlusion from 13 to 60 years of age. See Supplemental Materials for a short video presentation about this study.

Material and methods

This observational and longitudinal study was approved by the institutional research ethics committee of the University of São Paulo in Brazil (process number 43931915.4.0000.5417), and written consents were obtained from all subjects. The sample size calculation was based on preliminary statistics including the first 5 subjects of the sample. For a standard deviation of 1.47 mm for mandibular incisor irregularity and a minimal interphase difference of 1.00 mm to be detected, a sample of 19 subjects was required to provide statistical power of 80% with an α of 5%.

The initial normal occlusion sample group was obtained from 1967 to 1974 and comprised 82 white Brazilians (39 men, 43 women). Dental models and cephalometric radiographs were obtained at 13 years of age (T1) and 17 years of age (T2). At T1, all subjects had a clinically acceptable occlusion in the complete permanent dentition, dental and skeletal Class I relationships, no crossbites, normal overjet and overbite, and a maximum 2 mm of incisor crowding with no previous orthodontic treatment. From April 2015 to May 2016, the sample was recalled, and dental models were obtained (T3). Thirty-eight subjects were contacted, and 27 were enrolled. The exclusion criteria were orthodontic treatment from T1 to T3, complete tooth loss, and no dental models at any of the 3 time points. The final sample comprised 22 subjects (12 men, 10 women) assessed at 3 ages, as shown in Figure 1 . The enrollment process is also described in Figure 1 .

Fig 1
Flow chart of the enrollment process, age distribution, and tooth losses in the 47 years of follow-up.

All dental models were digitized using an R700 3-dimensional scanner (3Shape, Copenhagen, Denmark). Dental model measurements were performed using the OrthoAnalyzer 3-dimensional software (3Shape). Measurements included mesiodistal tooth size ( Fig 2 , A ), clinical crown height ( Fig 2 , B ), arch widths ( Fig 3 , A ), arch perimeter ( Fig 3 , B ), arch length ( Fig 3 , C ), palatal depth ( Fig 3 , D ), incisor crowding index ( Fig 4 , A ), overjet ( Fig 4 , B ), overbite ( Fig 4 , B ), and curve of Spee ( Fig 4 , C ). Missing teeth and prostheses were not considered for measurements.

Fig 2
Individual tooth measurements: A, mesiodistal tooth size measurement at the occlusal aspect; B, clinical crown height measured as the distance between the occlusal and cervical limits of the long-axis buccal aspect.

Fig 3
Measurement of arch size: A, intercanine, interpremolar, and intermolar widths were measured at the level of the cusp tips; B, arch perimeter was the sum of the 4 segments from the mesial aspect of the right permanent first molar to the mesial aspect of the contralateral tooth; C, arch length ( yellow arrow ) was measured on the horizontal plane from the mesial aspect of the permanent first molars to a point between the maxillary central incisors; D, palatal depth ( red arrow ) was measured from a line passing through the mesial gingival papilla of the permanent first molars to the deepest point on the palate, perpendicular to arch length.

Fig 4
A, Little’s irregularity index was measured for both arches according to the methods of Little et al and Dowling et al ; B, overbite and overjet were measured on a slice passing through the center of the maxillary right and left central incisors; the mean between the right and left sides was considered; C, curve of Spee depth was measured as the greater perpendicular distance between the buccal cusp tip of the deepest mandibular teeth and a reference plane drawn from the central incisor edge to the distal cusp tip of the second molar; the mean between right and left sides was considered.

For the error study, 1 operator (C.M.) performed all measurements, and 50% of the sample was measured twice with an interval of at least 1 month. The intrarater reliability was assessed using intraclass correlation coefficients and the Bland-Altman method.

Statistical analysis

Means and standard deviations were calculated for all measurements at T1, T2, and T3. For tooth measurements, the average of both sides was used. Kolmogorov-Smirnov tests showed normal distribution for all variables, and interphase changes were evaluated with repeated measures analysis of variance, followed by Tukey tests. Sexual dimorphism was investigated with t tests. The significance level considered was 5%. The statistical analyses were performed using Statistica software (Statistica for Windows version 11.0; StatSoft, Tulsa, Okla).

Results

Table I shows the results of the error study. All variables had excellent intrarater agreement, with intraclass correlation coefficients varying from 0.78 to 0.99. The variable with the greatest limits of agreement was maxillary intermolar width (–2.55 and 2.48).

Table I
Error study for all variables assessed with intraclass correlation coefficients (ICC) and Bland-Altman limits of agreement (95% LoA)
Variable Measurement 1 Measurement 2 Difference ICC Bland-Altman
95% LoA
Mean (SD) Mean (SD) Mean (SD) Lower Upper
Mesiodistal tooth size
Maxilla
7 9.87 (0.53) 9.93 (0.50) –0.05 (0.28) 0.85 –0.59 0.48
6 10.15 (0.39) 10.25 (0.39) –0.11 (0.13) 0.90 –0.37 0.16
5 6.76 (0.31) 6.82 (0.40) –0.06 (0.23) 0.78 –0.50 0.38
4 6.92 (0.45) 7.03 (0.49) –0.11 (0.21) 0.87 –0.52 0.31
3 7.52 (0.37) 7.57 (0.41) –0.05 (0.15) 0.92 –0.34 0.24
2 6.34 (0.41) 6.49 (0.42) –0.15 (0.20) 0.83 –0.54 0.23
1 8.48 (0.49) 8.57 (0.54) –0.09 (0.16) 0.93 –0.41 0.23
Mandible
7 10.24 (0.61) 10.31 (0.54) –0.06 (0.25) 0.90 –0.54 0.42
6 10.46 (0.63) 10.57 (0.58) –0.12 (0.17) 0.94 –0.46 0.23
5 7.15 (0.40) 7.19 (0.42) –0.03 (0.19) 0.89 –0.40 0.33
4 6.92 (0.32) 7.01 (0.33) –0.09 (0.18) 0.80 –0.45 0.27
3 6.66 (0.40) 6.75 (0.36) –0.09 (0.17) 0.87 –0.42 0.24
2 5.84 (0.30) 5.90 (0.32) –0.06 (0.14) 0.88 –0.34 0.21
1 5.33 (0.35) 5.38 (0.34) –0.05 (0.13) 0.91 –0.30 0.21
Clinical crown height
Maxilla
7 5.26 (1.57) 5.40 (1.48) –0.14 (0.23) 0.98 –0.58 0.31
6 5.79 (1.18) 5.80 (1.16) –0.01 (0.20) 0.98 –0.39 0.37
5 7.17 (1.40) 7.12 (1.40) 0.06 (0.21) 0.98 –0.35 0.46
4 8.10 (1.14) 8.13 (1.12) –0.04 (0.10) 0.99 –0.23 0.16
3 9.47 (1.14) 9.49 (1.14) –0.02 (0.13) 0.99 –0.28 0.24
2 8.42 (0.97) 8.45 (0.98) –0.03 (0.10) 0.99 –0.23 0.16
1 9.93 (1.16) 9.98 (1.19) –0.04 (0.07) 0.99 –0.18 0.10
Mandible
7 5.26 (1.23) 5.39 (1.19) –0.13 (0.36) 0.94 –0.84 0.59
6 6.31 (0.94) 6.36 (0.93) –0.05 (0.22) 0.97 –0.48 0.38
5 7.15 (1.03) 7.19 (1.06) –0.04 (0.12) 0.99 –0.27 0.19
4 8.07 (0.83) 8.09 (0.82) –0.02 (0.15) 0.98 –0.31 0.26
3 9.39 (1.03) 9.40 (1.05) –0.01 (0.11) 0.99 –0.23 0.21
2 8.41 (1.06) 8.45 (1.05) –0.04 (0.11) 0.99 –0.25 0.18
1 8.18 (1.02) 8.24 (1.02) –0.05 (0.11) 0.99 –0.27 0.17
Arch dimensions
Maxilla
3-3 width 33.26 (1.57) 33.21 (1.54) 0.05 (0.21) 0.99 –0.37 0.46
4-4 width 41.14 (2.10) 41.04 (2.07) 0.09 (0.14) 0.99 –0.18 0.37
5-5 width 47.32 (2.32) 47.27 (2.24) 0.06 (0.24) 0.99 –0.41 0.52
6-6 width 52.47 (3.01) 52.51 (3.56) –0.04 (1.28) 0.92 –2.55 2.48
Arch length 26.39 (2.15) 25.59 (2.04) –0.20 (0.40) 0.97 –0.99 0.59
Arch perimeter 72.74 (3.68) 72.99 (3.55) –0.25 (0.53) 0.98 –1.29 0.80
Crowding 0.71 (1.08) 0.76 (1.13) –0.05 (0.13) 0.99 –0.31 0.22
Palatal depth 18.01 (2.52) 18.25 (2.45) –0.24 (0.37) 0.98 –0.97 0.48
Mandible
3-3 width 25.44 (1.28) 25.49 (1.32) –0.05 (0.22) 0.98 –0.47 0.38
4-4 width 33.84 (1.91) 33.71 (1.94) 0.12 (0.30) 0.98 –0.46 0.71
5-5 width 39.82 (2.11) 39.72 (2.01) 0.10 (0.34) 0.98 –0.56 0.76
6-6 width 45.52 (3.11) 45.39 (3.23) 0.13 (0.33) 0.99 –0.51 0.76
Arch length 22.82 (1.96) 23.03 (2.05) –0.21 (0.52) 0.96 –1.23 0.81
Arch perimeter 63.81 (3.53) 63.49 (3.51) –0.18 (0.41) 0.99 –0.98 0.62
Crowding 3.69 (2.48) 3.76 (2.47) –0.07 (0.21) 0.99 –0.48 0.34
Curve of Spee 1.61 (0.68) 1.64 (0.67) –0.03 (0.34) 0.87 –0.69 0.63
Incisor relationship
Overjet 2.67 (1.08) 2.75 (1.03) –0.07 (0.29) 0.95 –0.65 0.50
Overbite 2.48 (1.23) 2.62 (1.34) –0.14 (0.26) 0.97 –0.65 0.38
7 , Second molar; 6 , first molar; 5 , second premolar; 4 , first premolar; 3 , canine; 2 , lateral incisor; 1 , central incisor; 3-3 , intercanine; 4-4 , interfirst premolar; 5-5 , intersecond premolar; and 6-6 , intermolar.

Tables II and III show the interphase changes. The aging process influenced most of the variables from T1 to T3. Mesiodistal tooth size, mandibular intercanine width, arch length, arch perimeter, overbite, and curve of Spee decreased. On the other hand, clinical crown height, incisor crowding, and palatal depth increased. Overjet and maxillary arch widths remained stable.

Table II
Interphase comparisons for tooth measurements with repeated-measures analysis of variance, followed by Tukey tests
Variable T1 T2 T3 P
Mean SD Mean SD Mean SD
Mesiodistal tooth size
Maxillary
7 10.01 A 0.48 9.95 A 0.47 9.54 B 0.43 <0.001
6 10.15 A 0.39 10.04 A 0.36 9.73 B 0.43 <0.001
5 6.91 A 0.40 6.79 A 0.37 6.44 B 0.35 <0.001
4 7.07 A 0.37 6.97 A 0.43 6.71 B 0.41 <0.001
3 7.71 A 0.40 7.68 A 0.40 7.34 B 0.43 <0.001
2 6.51 A 0.42 6.47 A 0.42 6.29 B 0.35 <0.001
1 8.41 A 0.46 8.33 A 0.48 8.09 B 0.51 <0.001
Mandibular
7 10.38 A 0.54 10.31 A 0.55 10.10 B 0.66 <0.001
6 10.78 A 0.74 10.70 A 0.70 10.29 B 0.71 <0.001
5 7.22 A 0.32 7.18 A 0.31 6.86 B 0.43 <0.001
4 7.10 A 0.37 7.03 A 0.33 6.72 B 0.35 <0.001
3 6.78 A 0.40 6.72 A 0.37 6.46 B 0.32 <0.001
2 5.91 A 0.32 5.87 A 0.29 5.69 B 0.27 <0.001
1 5.37 A 0.30 5.34 A 0.27 5.11 B 0.31 <0.001
Clinical crown height
Maxillary
7 4.09 A 0.48 4.89 B 0.47 7.31 C 1.27 <0.001
6 4.81 A 0.60 5.50 B 0.66 7.62 C 0.85 <0.001
5 5.91 A 0.57 7.00 B 0.70 8.97 C 1.00 <0.001
4 7.13 A 0.64 8.06 B 0.79 9.16 C 1.32 <0.001
3 8.28 A 1.01 9.41 B 1.11 9.78 B 1.42 <0.001
2 7.81 A 0.68 8.45 B 0.73 8.57 B 1.22 0.001
1 9.32 A 0.90 9.87 B 0.97 9.54 AB 1.33 0.027
Mandibular
7 4.43 A 0.60 5.17 A 0.81 6.57 B 1.22 <0.001
6 5.52 A 0.48 6.29 B 0.37 7.06 C 0.98 <0.001
5 6.22 A 0.53 7.11 B 0.63 7.77 C 1.30 <0.001
4 7.42 A 0.71 8.15 B 0.58 8.45 B 1.15 <0.001
3 8.53 A 0.87 9.60 B 0.84 9.63 B 1.19 <0.001
2 7.83 A 0.69 8.29 AB 0.67 8.38 B 1.28 0.016
1 8.00 0.64 8.19 0.73 7.98 1.20 0.502
Different letters indicate statistically significant differences.
7 , Second molar; 6 , first molar; 5 , second premolar; 4 , first premolar; 3 , canine; 2 , lateral incisor; 1 , central incisor.

Statistically significant at P <0.05.

Table III
Interphase comparisons for arch dimensions, crowding, and incisor relationship with repeated-measures analysis of variance, followed by Tukey tests
Variable T1 T2 T3 P
Mean SD Mean SD Mean SD
Maxilla
6-6 width 52.42 A 3.93 52.34 A 3.19 52.84 A 3.20 0.759
5-5 width 47.47 A 2.47 47.46 A 2.13 47.48 A 2.58 0.998
4-4 width 41.45 A 2.16 41.14 A 1.99 40.82 A 1.93 0.232
3-3 width 33.21 A 2.12 33.47 A 1.90 33.06 A 2.15 0.300
Length 27.38 A 1.63 26.27 B 1.72 25.17 C 2.08 <0.001
Perimeter 74.45 A 3.26 73.34 B 3.34 70.70 C 3.30 <0.001
Anterior crowding 0.37 A 0.74 0.67 A 1.08 1.49 B 1.30 <0.001
Palatal depth 16.92 A 1.93 18.66 B 2.24 19.23 B 2.56 <0.001
Mandible
6-6 width 44.74 A 3.66 45.14 A 3.26 45.44 A 2.11 0.692
5-5 width 40.14 A 2.40 40.15 A 2.53 40.89 A 3.20 0.390
4-4 width 34.39 A 2.09 34.00 A 1.81 33.78 A 2.35 0.261
3-3 width 25.50 A 1.48 25.45 A 1.52 24.76 B 1.52 0.001
Length 23.48 A 1.60 22.77 A 1.75 21.71 B 1.88 <0.001
Perimeter 64.99 A 3.52 63.99 A 2.83 62.14 B 3.12 <0.001
Anterior crowding 2.26 A 1.96 3.13 B 2.20 4.67 C 2.52 <0.001
Curve of Spee 2.02 A 0.76 1.53 B 0.64 1.16 B 0.45 <0.001
Anterior relationship
Overjet 2.81 0.66 2.36 0.72 2.75 1.19 0.071
Overbite 3.13 A 0.96 2.34 B 1.20 1.73 C 1.31 <0.001
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Dec 10, 2018 | Posted by in Orthodontics | Comments Off on Maturational changes of the normal occlusion: A 40-year follow-up
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