Introduction
Missing or peg-shaped maxillary lateral incisors can affect the mesiodistal dimensions of the dentition.
Methods
The pretreatment casts of patients with bilateral (BMLI, n = 35) or unilateral (UMLI, n = 29) missing maxillary lateral incisors or bilateral peg-shaped maxillary lateral incisors (BPLI, n = 16) were evaluated. The mesiodistal widths of all permanent teeth except the second and third molars were measured, and the sums of total and quadrant tooth widths were calculated. The results were compared with a control group (n = 32) with normal maxillary lateral incisors. A quadrant analysis was performed by comparing the quadrants with lateral incisor agenesis, peg-shaped lateral incisors, and normal lateral incisors with each other. Statistical analysis was performed by 1-way analysis of variance followed by Tukey and Tamhane tests.
Results
In the BMLI and BPLI groups, significant reductions in individual tooth widths and total tooth widths were seen. The size discrepancies were the greatest in the maxillary central incisors and decreased gradually from the incisors to the molars. Compared with the control group, the tooth-size discrepancy was more pronounced in the BPLI group followed by the BMLI and UMLI groups. Due to the variability in clinical presentations of the UMLI group, the association with the reduction of the tooth sizes was not significant. But the quadrant analysis showed that in quadrants with a missing or peg-shaped lateral incisor, the teeth were significantly narrower than in quadrants with normal incisors; this indicates the importance of the contralateral side in unilaterally affected patients during analysis.
Conclusions
Bilateral missing or peg-shaped maxillary lateral incisors were significantly associated with reduction of individual mesiodistal tooth widths as well as their total and quadrant sums. Patients with a unilaterally missing lateral incisor should be analyzed individually with quadrant analysis, since the variability in the contralateral side would affect the traditional analysis results.
Highlights
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Peg-shaped or missing lateral incisors had a narrowing effect on the dentition.
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The largest size discrepancy was noted for the maxillary central incisors.
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Quadrant analysis gives more specific results for managing missing lateral incisors, particularly in unilaterally affected cases.
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The golden ratio may be a relevant method for determining appropriate space for restoration.
In contemporary dental practice, patient-driven esthetic diagnosis and treatment planning force clinicians to focus on the smile zone, which is directly affected by the display of the maxillary anterior teeth. From the patients’ perspectives, the most common problems of maxillary anterior teeth are crowding, size and shape anomalies, proportions of each tooth, and proportions relative to adjacent teeth.
Agenesis and size or shape anomalies (peg shape) of maxillary lateral incisors are quite common, with prevalences of 1.6% to 4.9%, and can be seen unilaterally or bilaterally. Missing lateral incisors are associated with several dental and skeletal problems such as palatal impaction of maxillary canines. severity of maxillary hypoplasia in cleft patients, higher incidence of Class III malocclusion, increased rate of other permanent tooth agenesis, taurodontism and dilacerated teeth, peg-shaped contralateral incisor, and decreased mesiodistal dimensions of the dentition. On the other hand, knowledge about the associated conditions with peg-shaped lateral incisors are limited and reported as race, population, and sex differences, and 55.5% of these patients had congenital absence of the contralateral maxillary lateral incisor.
The treatment options for a missing lateral incisor are to close the space with canine substitution or to replace it with an implant or tooth-supported restoration, whereas peg-shaped lateral incisors can be restored with composite or laminate veneers. The ideal space for restoration can be determined by considering the contralateral tooth with normal dimensions in patients with a unilaterally missing lateral incisor. On the other hand, when a peg-shaped contralateral tooth is present, or when the maxillary lateral incisors are bilaterally missing or peg-shaped, the guidance of golden proportion and Bolton analysis is recommended to determine the ideal width of maxillary lateral incisor restorations. In the management of such anomalies, type of malocclusion, patient’s age, amount of space, and condition of the adjacent teeth should be considered.
Maintaining the intra-arch symmetry and achieving the ideal incisor relationship and a good posterior occlusion are challenging in patients with missing or peg-shaped lateral incisors. The orthodontic literature includes data sets reporting that the mesiodistal widths of almost all teeth are smaller in patients with missing lateral incisors. Therefore, the opened space for implants in the lateral incisor region may not be large enough (<6-7 mm) when the anterior teeth are in harmony and occlusal relationships are ideal. In addition, with a convenient space, the posterior occlusion may not be established, and the lateral incisor would be larger than the adjacent teeth, and harmony in incisor display would not be achieved.
Despite these arguments about missing lateral incisors, there is a lack of data about bilateral peg-shaped lateral incisors and their association with the changes in tooth widths. Although researchers have reported that the increased prevalence of unilateral peg-shaped lateral incisors is due to a missing lateral incisor, this is not always the case in reality. Patients having peg-shaped lateral incisors with no missing teeth may present for orthodontic treatment, but knowledge about their effects on the overall dentition is not enough for guidance to obtain the ideal treatment results.
These clinical outcomes raise 2 important questions. (1) Do the traditional tooth-width analysis methods give sufficient information about the space needed for restoration of maxillary lateral incisors? (2) What happens to the individual tooth widths and the total tooth widths in patients with bilateral peg-shaped lateral incisors? Yet, as far as we know, no authors have previously evaluated the tooth widths in patients with missing and peg-shaped maxillary lateral incisors at the same time by focusing on the affected side of the dentition.
Therefore, the aims of this study were to evaluate the association between agenesis or size discrepancy of maxillary lateral incisors and the mesiodistal dimensions of the rest of the dentition, and to analyze tooth widths in quadrants classified according to the condition of the lateral incisor. We tested 3 hypotheses. (1) The tooth widths of patients with unilateral or bilateral missing lateral incisors and bilateral peg-shaped lateral incisors are narrower than the tooth widths in patients with normal lateral incisors. (2) The widths of other teeth in the quadrants with missing or peg-shaped lateral incisors are smaller compared with quadrants with normal lateral incisors. (3) The sums of total and quadrant tooth widths of patients with missing or peg-shaped lateral incisors are smaller than those of patients with normal lateral incisors.
Material and methods
Ethical approval for this retrospective study was obtained from the ethical committee of Gazi University, Faculty of Medicine, Ankara, Turkey (77082166-302.08.01). The records of 8635 patients in the archives of Department of Orthodontics, Faculty of Dentistry, of Gazi University were reviewed. With the computer-based archive system (FileMaker Pro 11.0v1; FileMaker, Santa Clara, Calif), a search was conducted with terms “missing teeth,” “peg-shaped lateral,” and “lateral agenesis.” The records of those patients with unilateral (UMLI) or bilateral (BMLI) missing lateral incisors and bilateral peg-shaped lateral incisors (BPLI) were selected for a more detailed evaluation.
The inclusion criteria for the study groups were (1) good quality dental casts, (2) permanent dentition with all teeth between the first molars erupted, (3) no impacted teeth except third molars, (4) no agenesis or obvious shape anomalies of other teeth, (5) no craniofacial syndromes associated with abnormalities in tooth number and size (eg, ectodermal dysplasia, cleft lip and palate, amelogenesis imperfecta), and (6) no dental restorations (fillings, crowns) altering the tooth sizes.
A control group was constituted from patients with Angle Class I malocclusion with mild crowding (<3 mm); overjet and overbite within normal limits; permanent dentition with no signs of extreme wear, breakdown, or interproximal reduction in any teeth due to restorations; and normal anterior and overall Bolton ratio. Fulfillment of the inclusion criteria for the study groups was also required. The sex distribution in the control group was kept parallel to that of the study groups to minimize the effect of sex on tooth widths. Following these guidelines, the distributions of study groups are given in Table I .
| BMLI | UMLI | BPLI | Control | |
|---|---|---|---|---|
| Mean chronologic age (y) | 15.69 ± 3.14 | 13.22 ± 2.82 | 15.45 ± 2.43 | 15.42 ± 2.61 |
| Female (n) | 28 | 22 | 14 | 27 |
| Male (n) | 7 | 7 | 2 | 5 |
| Total (n) | 35 | 29 | 16 | 32 |
From the patients’ pretreatment dental casts, mesiodistal widths all teeth except second and third molars were measured in the maxilla and mandible with a high precision digital caliper, which rounded the measurements to the nearest hundredth of a millimeter. A maxillary lateral incisor was called peg-shaped if the mesiodistal width at the incisal region was smaller than the width at the cervical region. The same operator (E.B.) performed all measurements. The data about right and left sides were recorded separately, and the contralateral incisors in the UMLI group were defined as peg-shaped or normal for further analysis.
A quadrant analysis was performed to evaluate the pure effect of the size of maxillary lateral incisors on neighboring teeth. For this purpose, the study groups were combined, and the maxillary and mandibular arches were divided into 2 quadrants, right and left, including the first molar through the central incisor on the same side. Then the maxillary and mandibular quadrants were regrouped according to the maxillary lateral incisors: quadrants with a missing lateral incisor (QMLI; n = 99), with a peg-shaped lateral incisor (QPLI; n = 45), and with a normal lateral incisor (QNLI; n = 80). The schematic explanation of the analysis and digital images of the quadrants representing all possible conditions are shown in the Figure .
The sum of the tooth widths of all teeth from the first molar on 1 side through the first molar on the other side (total tooth widths) and the sum of tooth widths of the teeth in the same quadrant (quadrant tooth widths) were also calculated. Mesiodistal widths of the maxillary lateral incisors were not included in the calculations.
Statistical analysis
The data from the subjects were evaluated using a statistical software for Windows (version 16.0; SPSS, Chicago, Ill). The normality of the data was examined by Shapiro-Wilk test. The tooth widths and their sums were evaluated according to the study groups and according to the quadrants as explained in the Figure . One-way analysis of variance was used for intergroup comparisons followed by Tukey and Tamhane post-hoc tests. P < 0.05 was considered to be statistically significant.
To evaluate the intraobserver error rate, the dental casts of 35 patients were randomly selected, and tooth-width measurements were repeated 1 month after the initial analysis. The reproducibility and the strength of the measurements were evaluated by the intraclass correlation coefficient, and a coefficient of repeatability was derived according to the Bland-Altman method. A precision value was calculated by dividing the coefficient of repeatability by the mean of the first and second measurements. Precision values smaller than 10% were regarded as measurements in agreement and acceptable for reproducibility. For all variables, the intraclass correlation coefficient values were between 0.84 and 0.92, and the precision values were between 1.89% and 5.02%, which all showed good reproducibility of the first measurements.
Results
Of the 8635 patients, 162 had either missing or peg-shaped maxillary lateral incisors. However, based on the inclusion criteria, only the records of 80 patients were eligible for further evaluations. The reasons for the elimination of the records of 82 patients were impacted maxillary canines, missing second premolars, and large restorations particularly in the molar regions that potentially altered the original tooth widths. The distribution of study groups was as follows: 35 patients in BMLI group, 29 patient in UMLI group and 16 patients in BPLI group. Among the 29 patients in the UMLI group, the contralateral incisor was peg-shaped in 13 patients and normal in 16 patients.
The mean and standard deviation of each tooth’s mesiodistal width in the BMLI, UMLI, BPLI, and control groups and intergroup comparisons are given in Table II .
| 1. BMLI (n = 35) (28 F, 7 M) | 2. UMLI (n = 29) (22 F, 7M) | 3. BPLI (n = 16) (14 F, 2 M) | 4. Control (n = 32) (27 F, 5 M) | P | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Mean ± SD | Mean ± SD | Mean ± SD | Mean ± SD | 1-2 | 1-3 | 1-4 | 2-3 | 2-4 | 3-4 | |
| Maxilla | ||||||||||
| UR6 | 10.17 ± 0.50 | 10.31 ± 0.75 | 9.87 ± 0.69 | 10.38 ± 0.44 | 0.950 | 0.592 | 0.342 | 0.299 | 0.998 | 0.078 |
| UR5 | 6.58 ± 0.43 | 6.77 ± 0.54 | 6.47 ± 0.53 | 6.87 ± 0.43 | 0.383 | 0.870 | 0.059 | 0.183 | 0.828 | 0.032 |
| UR4 | 6.85 ± 0.44 | 6.97 ± 0.61 | 6.73 ± 0.49 | 7.06 ± 0.37 | 0.770 | 0.850 | 0.274 | 0.405 | 0.863 | 0.118 |
| UR3 | 7.37 ± 0.47 | 7.49 ± 0.56 | 7.20 ± 0.38 | 7.73 ± 0.34 | 0.737 | 0.595 | 0.009 | 0.181 | 0.166 | 0.001 |
| UR2 | 5.21 ± 1.06 | 4.83 ± 0.68 | 6.87 ± 0.52 | |||||||
| UR1 | 8.28 ± 0.54 | 8.60 ± 0.62 | 8.21 ± 0.63 | 8.82 ± 0.55 | 0.120 | 0.979 | 0.001 | 0.133 | 0.480 | 0.005 |
| UL1 | 8.31 ± 0.48 | 8.56 ± 0.60 | 8.14 ± 0.70 | 8.83 ± 0.59 | 0.319 | 0.765 | 0.002 | 0.098 | 0.267 | 0.001 |
| UL2 | 5.74 ± 0.92 | 4.76 ± 0.77 | 6.87 ± 0.52 | |||||||
| UL3 | 7.38 ± 0.42 | 7.44 ± 0.63 | 7.22 ± 0.39 | 7.75 ± 0.35 | 0.999 | 0.742 | 0.001 | 0.665 | 0.136 | 0.001 |
| UL4 | 6.83 ± 0.39 | 6.98 ± 0.57 | 6.69 ± 0.52 | 7.15 ± 0.38 | 0.764 | 0.924 | 0.007 | 0.415 | 0.728 | 0.025 |
| UL5 | 6.53 ± 0.44 | 6.71 ± 0.55 | 6.42 ± 0.56 | 6.83 ± 0.37 | 0.619 | 0.983 | 0.016 | 0.464 | 0.902 | 0.076 |
| UL6 | 10.14 ± 0.50 | 10.33 ± 0.69 | 9.91 ± 0.67 | 10.35 ± 0.43 | 0.793 | 0.792 | 0.367 | 0.297 | 1.000 | 0.152 |
| Mandible | ||||||||||
| LL6 | 10.84 ± 0.67 | 10.92 ± 0.59 | 10.41 ± 0.72 | 10.96 ± 0.65 | 0.948 | 0.142 | 0.878 | 0.061 | 0.998 | 0.037 |
| LL5 | 6.84 ± 0.94 | 7.19 ± 0.72 | 6.78 ± 0.52 | 7.31 ± 0.46 | 0.227 | 0.993 | 0.046 | 0.292 | 0.917 | 0.097 |
| LL4 | 6.90 ± 0.41 | 7.16 ± 0.58 | 6.72 ± 0.37 | 7.19 ± 0.40 | 0.231 | 0.598 | 0.026 | 0.020 | 1.000 | 0.002 |
| LL3 | 6.38 ± 0.43 | 6.73 ± 0.55 | 6.32 ± 0.29 | 6.63 ± 0.34 | 0.042 | 0.994 | 0.061 | 0.014 | 0.946 | 0.016 |
| LL2 | 5.65 ± 0.35 | 5.90 ± 0.50 | 5.58 ± 0.39 | 6.04 ± 0.38 | 0.078 | 0.931 | 0.001 | 0.059 | 0.541 | 0.002 |
| LL1 | 5.23 ± 0.34 | 5.45 ± 0.41 | 5.24 ± 0.42 | 5.61 ± 0.39 | 0.113 | 1.000 | 0.001 | 0.279 | 0.370 | 0.010 |
| LR1 | 5.21 ± 0.40 | 5.43 ± 0.41 | 5.17 ± 0.45 | 5.55 ± 0.46 | 0.189 | 0.984 | 0.009 | 0.205 | 0.699 | 0.022 |
| LR2 | 5.59 ± 0.35 | 5.84 ± 0.53 | 5.60 ± 0.38 | 6.02 ± 0.36 | 0.072 | 0.999 | 0.000 | 0.258 | 0.343 | 0.008 |
| LR3 | 6.40 ± 0.46 | 6.69 ± 0.50 | 6.29 ± 0.32 | 6.58 ± 0.27 | 0.109 | 0.887 | 0.260 | 0.010 | 0.889 | 0.019 |
| LR4 | 6.88 ± 0.44 | 7.11 ± 0.52 | 6.71 ± 0.42 | 7.10 ± 0.43 | 0.190 | 0.609 | 0.191 | 0.029 | 1.000 | 0.029 |
| LR5 | 6.97 ± 0.47 | 7.16 ± 0.70 | 6.80 ± 0.46 | 7.27 ± 0.50 | 0.479 | 0.749 | 0.102 | 0.158 | 0.857 | 0.031 |
| LR6 | 10.82 ± 0.72 | 10.86 ± 0.65 | 10.32 ± 0.67 | 10.88 ± 0.64 | 0.994 | 0.067 | 0.988 | 0.049 | 1.000 | 0.038 |
In the BMLI group, the mesiodistal widths of the maxillary central incisors had the largest tooth size difference compared with the control group followed by the maxillary canines. The tooth-size discrepancy tended to decrease from incisors to molars, and the sizes of the first molars were similar to those of the control group. This trend was true for the patients in BPLI group, but the dimensional differences with the control group were more pronounced.
In the mandible, the incisors were again significantly smaller than those in the control group in the BMLI and BPLI groups but to a lesser degree compared with the maxilla. Interestingly, the tooth-size differences in the premolar region were similar to the incisor region; in contrast to the maxilla, the sizes of the canines were not significantly reduced in the BMLI group. The bilateral presence of peg-shaped lateral incisors was highly associated with the reduction of tooth widths of almost all teeth in the mandible including the first molars.
On the contrary, for the UMLI group, there was no significant tooth-size difference with the control group in either the maxilla or the mandible.
The quadrant analysis of tooth widths in the maxilla and the mandible is presented in Table III .
