An Assessment of the Correlation Between Tooth Size and Agenesis of Maxillary Lateral Incisor in Subjects Undergoing Orthodontic Treatment

Background and objective Occlusion rehabilitation and restoration are difficult in subjects with congenitally missing lateral incisors, either unilaterally or bilaterally, and often lead to malocclusion and warrant replacement. The present study was conducted to assess the agenesis of maxillary lateral incisor unilaterally and bilaterally and to examine tooth size discrepancy in agenesis subjects undergoing orthodontic treatment. Materials and methods We assessed 32 dental casts of both genders (17 males and 15 females) with missing maxillary lateral incisors either unilaterally or bilaterally. Mesiodistal dimensions were measured and a comparison of tooth sizes was done for control and test groups. The data were assessed and the results were documented. Results Lateral incisors of the maxillary arch were statistically smaller in the test group compared to the control group. This was true for both males and females (p=0.001 for both). A similar finding was observed with respect to the overall study group (p<0.0001). Conclusion Based on our findings, maxillary lateral incisor agenesis plays a role in malocclusion development.


Introduction
Occlusion rehabilitation and restoration can be challenging in subjects with congenitally missing lateral incisors, either unilaterally or bilaterally. These occlusion rehabilitation problems are usually encountered by general dentists, orthodontists, and prosthodontists. The treatment choices for congenitally missing lateral incisors are mesial canine movement, fixed dental prosthesis, and implant-supported prosthesis [1].
To assess the space needed for restoration and the size of the missing lateral incisor, the lateral incisor of the contralateral side is usually used as a guide. However, a limitation of this practice is the absence or peg shape of contralateral lateral incisors in subjects with congenitally missing lateral incisors. In such cases, to determine the missing tooth size, two other methods are widely accepted and used. They include golden proportion where 62% width of the central incisor comprises the missing lateral incisor and Bolton analysis to assess the space needed for replacing the missing lateral incisor [2].
Tooth and jaw size discrepancy in both maxillary and mandibular arch can make a space of 6-7 mm insufficient for replacing the missing lateral incisor with the implant. This is mostly seen in cases with coincident midlines, ideal horizontal and vertical overlaps, and class I canine relationships [3]. Mesiodistal width of maxillary lateral incisor was found to be the most significant tooth contributing to arch size-tooth size discrepancy in comparison to buccolingual dimension as described in the published literature [4].
Genetic factors including mutations of PAX9 and MSX1 genes may lead to tooth size discrepancies and tooth agenesis. The mutation of the gene PAX9 can also lead to the formation of teeth smaller than normal. Missing lateral incisor is more commonly seen in women compared to men. Higher tooth size is usually reported in men [5].
The relationship between tooth agenesis and tooth size is not extensively studied, and data related to this is scarce in the literature. Recent data suggest that less space is needed for placing newer dental implants, thereby reducing the tooth size needed for placement. In light of this, the present study was conducted to assess the agenesis of maxillary lateral incisor unilaterally and bilaterally and to examine tooth size discrepancy in agenesis subjects undergoing orthodontic treatment.

Study design and setting
This was an observational clinical study. The study was conducted after obtaining approval from the concerned Ethical Committee (ethical approval no: ICMCH/2020/19). The study was carried out on dental casts collected from the Department of Orthodontics and Dentofacial Orthopedics. A total of 32 casts were included from both genders. There were 17 male casts and 15 female casts in the study.
All casts had unilateral/bilateral missing maxillary lateral incisors. There were 19 unilateral missing lateral incisors and 13 bilateral missing lateral incisors. The age of study subjects ranged from 11 to 42 years with a mean age of 15.78 years. For the purpose of comparison, 32 controls matched for age and sex were also included and compared against tests with missing lateral incisors.
The inclusion criteria were as follows: subjects with fully erupted teeth set except for third molars with the agenesis of unilateral/bilateral maxillary lateral incisors, and subjects with no tooth structure loss secondary to wasting diseases. The exclusion criteria were as follows: subjects with no pretreatment casts, mesiodistal restorations, and full teeth crown due to altered teeth dimensions ( Figure 1).

Methods and analysis
All the dental cast measurements were done by a single expert in the field. The mesiodistal dimensions were measured and calculated for each tooth by using a digital caliper ( Figure 2).

FIGURE 2: Vernier caliper measurements on the cast
The values were rounded off to the nearest millimeter for each tooth. All the lateral incisors were excluded from the study owing to unilateral/bilateral missing lateral incisors. Left and right tooth sizes for both the dental arches were added, and the average was considered as the tooth size variable outcome.
The comparison of tooth sizes was done for the control and test groups. Further comparison was done for gender, inter arches, and tooth number. Statistical assessment of the data obtained was performed by using the analysis of variance (ANOVA) test and the SPSS Statistics software (IBM, Armonk, NY). A p-value <0.005 was considered statistically significant.

Results
There were 19 (59.37%) unilateral missing lateral incisors and 13 bilateral missing lateral incisors. The age of the study subjects ranged from 11 to 42 years with a mean age of 15.78 years. For the purpose of comparison, 32 controls matched for age and sex were also included and compared against tests with missing lateral incisors. The demographic characteristics of the study subjects are listed in Table   The teeth dimensions were measured for all subjects in both test and control groups, and the results are summarized in Table 2.  Among females, smaller teeth were seen in the maxillary arch anterior region. In the lower arch, left mandibular lateral incisor dimensions were significantly smaller in the test group compared to males (p=0.009). Except for the lateral incisor, differences in dimensions of other teeth were insignificant. With regard to maxillary arch in females, the left canine and central incisor were significantly smaller in the test group compared to controls with respective p-values of 0.020 and 0.007. On the right side, the lateral incisor and canine were significantly smaller in the test group with respective p-values of <0.0001 and 0.02 ( Table  2).

Tooth number Groups Males (n) Dimension (mean ±SD) P-value Females (n) Dimension (mean ±SD) Group
It was observed that the lateral incisors of the maxillary arch were statistically smaller in the test group compared to the control group. This was seen in both males and females, with p-values of 0.001 and 0.0001 respectively. The same holds for the overall study group, with a p-value of <0.0001 (Table 3).  Significantly smaller dimensions of molars and premolars were seen in the male subjects in the test group compared to the control group (p=0.01) in lower first premolar. Also, in the test group, significantly smaller maxillary lateral incisors were seen on both right and left sides (p<0.0001). In males, in the mandibular arches, left central incisors, lateral incisors, and premolars were seen with respective p-values of 0.004, 0.003, and 0.01. These findings are in agreement with the studies of Garib et al. [8] in 2010 and Baidas and Hashim [9] in 2005 where similar anterior and posterior teeth discrepancies were analyzed by authors.

Group Tooth Gender Mean ±SD P-value
In the maxillary anterior region, smaller teeth were seen, and in the lower arch, a significantly smaller lateral incisor was seen in the test group (p=0.009) compared to males. Other teeth had nonsignificant differences in terms of dimension, except for the lateral incisor. In females, in the maxillary arch, the left central incisor and canine had significantly lower dimensions in the test group compared to controls, with p-values of 0.007 and 0.02 respectively. Canine and lateral incisors had significantly lower dimensions in tests compared to controls, with p-values of 0.02 and <0.0001 respectively. These results were similar to those in the study by Rosa and Zachrisson [10] in 2010 where comparable findings were described by the authors.
The study results also showed that in the maxillary arch, lateral incisors had significantly lower dimensions in tests compared to controls in both females and males (p=0.001 for both). This was similar for both the study groups (p<0.0001). These findings were comparable to the results of Othman and Harradine [11] in 2007 and Peck et al. [12] in 2002.
There is scarce literature available on the topic of this study. Our study has a few limitations, such as the small sample size. Further studies with larger sample sizes are required to gain deeper insights into the topic.

Conclusions
Within its limitations, the present study concludes that agenesis of maxillary lateral incisors in males leads to smaller posterior teeth bilaterally. In females, this agenesis leads to smaller anterior teeth in the maxilla. Irrespective of gender, maxillary lateral incisor agenesis leads to the formation of smaller and peg-shaped laterals. These findings confirm the role of maxillary lateral incisor agenesis in malocclusion development.
Our study has a few limitations, mainly the small sample size and the single-institution setting. Hence, more long-term studies involving a larger number of casts are required to reach definitive conclusions about the topic.