Inter-Incisive Index in South Bulgarians and Its Application in Aesthetic Dentistry

Background: In recent years, aesthetic dentistry has become a major focus for the public. Facial attractiveness plays a key role on modern society and the creation of harmonious smile is an aim for every dentist. The aim of this study was to dene certain values of the inter-incisive index in South Bulgarians, the sexual dimorphism and bilateral asymmetry and to verify differences of this index between Bulgarians and other Balkan populations. Materials and methods: The present study included 86 males and 83 females of Bulgarian origin living in South Bulgaria aged 20-40 years. Mesiodistal dimensions of maxillary central and lateral incisors were measured by Dentistry Sliding Vernier Caliper. We used the technique of Martin-Saller, modied by Prof. Y. Yordanov. We calculated the inter-incisive index as ratio of the mesiodistal dimension of maxillary lateral incisor to the mesiodistal dimension of the maxillary central incisor. The measurements were analyzed with SPSS 23. The level of statistical signicance was set at P< 0.05. Results: The inter-incisive index showed no statistically signicant differences between left and right side of the dental arch in both sexes. We did not nd statistically signicant differences between males and females as well. On the other hand we found statistically signicant differences in MD values of incisors between Bulgarians and other Balkan nations. Conclusion: Inter-incisive index shows no sexual dimorphism and bilateral asymmetry in South Bulgarians. This can be helpful in aesthetic dentistry, in prosthodontics and in orthodontic treatment planning.


Introduction
Facial attractiveness plays a key role on modern society and it can in uence not only self-esteem but also social opportunities, professional performance and employment prospects. In face-to-face situation a person's eyes primarily observe the other person's eyes and the area of the mouth. This means that smile aesthetics is becoming a dominant concern for patients, in particular when a dental treatment is required [1].
In recent years, aesthetic dentistry has become a major focus for the public. This trend was initiated by prosthodontists and, recently, by orthodontists. It can be said that the smile is the sum of features which comprise the lips, soft tissue (gingiva) and hard tissue (teeth). Numerous factors are related to dental aesthetics, such as the color, the shape, the size, the proportions of the teeth and the shape of the dental arch. They are in uenced by individual preferences, cultural factors, and sociodemographic factors. The selection of teeth for an edentulous patient can be di cult especially when no pre-extraction records are available. The size, form and color of the teeth must be in harmony with surrounding oral and facial structures [2]. One of the primary concerns in denture aesthetics is the selection of suitable sized maxillary anterior arti cial teeth.
Maxillary central incisors are considered to be the key teeth in smile since they are the most visible teeth during facial activity. Their size, shape, and arrangement are the most in uential factor for harmonious appearance. On the other hand, the mesiodistal dimensions of lateral incisors also play an important role in facial appearance. One of the essential elements in the aesthetic complex is exactly the contrast between the width of the central incisor and the smaller lateral incisor. The inter-incisive index is the mathematical expression of this ratio. Geometrical or mathematical relationship between teeth is an important determinant to achieve an aesthetic restorative result [3], therefore this index can be very helpful in aesthetic dentistry, prosthodontics and orthodontics.
The aim of this study was to de ne certain values of the inter-incisive index in South Bulgarians, to assess its degree of sexual dimorphism and bilateral asymmetry and to verify statistically signi cant differences in this index between Bulgarians and other Balkan populations.

Materials And Methods
The present study included 86 males and 83 females of Bulgarian origin living in South Bulgaria in the age group 20-40 years. Before starting the study, subjects were informed about the nature of the study and written informed consents were obtained. Patients were included based on the following criteria:  [4]. According to him the mesiodistal dimension is the greatest mesiodistal distance between the contact points of maxillary teeth, usually it is in the upper or middle third of coronal height. It is also termed the dental width. We calculated the inter-incisive index as ratio of the mesiodistal dimensions of maxillary lateral incisor to the mesiodistal dimensions of the maxillary central incisor. [(MD12/MD11) x100].
An ethical approval was taken for this study by the Ethics committee in Medical University-Plovdiv. Informed consents were taken from all patients involved in the study. All methods were performed in accordance with the relevant guidelines and regulations.
The measurements were analyzed with SPSS 23.0 using Student's t-test. The level of statistical signi cance was set at P< 0.05. The degree of signi cance was considered weak (P<0,05), moderate (0,01>P>0,001) or high (P<0,001). Z-test was used to compare the proportions. Results 1. We did not nd statistically signi cant differences in the inter-incisive index between left and right sides in Bulgarian men and women. (Table 1)  3. Our study did not show statistically signi cant differences in the inter-incisive index between Bulgarian and Serbian populations. There were statistically signi cant differences in mesiodistal dimension of the maxillary central incisors in favor of Serbians. (Table 3)

Discussion
Our results showed no statistically signi cant differences in the inter-incisive index between right and left sides of both sexes. This means that the ratio of the width of the lateral incisor towards the width of the central incisor is similar in both sides of the dental arch. Insigni cant bilateral asymmetries in the antimeric teeth were reported by others as well [5,6,7]. Lack of signi cant asymmetries was reported by Keith K. et al. who assessed the differences in the odontometric dimensions between left and right members of antimeric teeth in South Chinese [8]. This justi es the use of average values for the dimensions of left and right maxillary central and lateral incisors. We did not nd statistically signi cant differences in the inter-incisive index between South Bulgarian males and females which means that it showed no sexual dimorphism. These results were in accordance with Seipel [9], Moorrees [10], who reported that the most dimorphic teeth were the canines, while the maxillary incisors were the least.
Similar results were observed by Garn et al. [11] who claimed that the most dimorphic teeth were the molars, while the upper incisors were the least dimorphic.
We believe that our ndings can be useful for the prosthodontists because in treating patients with missing maxillary anterior teeth, they must determine tooth size and shape to achieve an optimal aesthetic result. If the size and shape of a replaced tooth are not in harmony with patients' face and other teeth, psychological and social problems might arise [12]. Using average values for left and right interincisive index and for males and females would considerably facilitate dentists in esthetic treatment with facets and manufactures of arti cial teeth for prosthesis.
In our study we did not nd statistically signi cant differences in the inter-incisive index neither between South Bulgarians and Serbians nor between South Bulgarians and Greeks.  [4]. He observed that the index in women is lower. This is in contrast with the results of our study according to which women show higher values (80.13%) than men (79.05%). Our results showed that values of inter-incisive index were closer to those of the Europeans (79.05%). This is in contrast with the results from Abadzhiev who observed closer values of the index in North-Eastern Bulgarians to those of the Mongoloids [13]. Examples of ethnic differences and geographic variability in tooth size have been documented and they could be related to the degree of ethnic mixing [14]. The fact that there were no signi cant differences in the inter-incisive index between Bulgarians and the two Balkan nations can be explained by geographical proximity of the countries, a decrease in racial differences due to increase of racial mixture and the common origin. Both Bulgarians and Serbians belong to the South -Slavic ethnic group.

Conclusion
Inter-incisive index can be very useful in esthetic dentistry in the treatment with facets, in prosthodontics in the treatment of edentulous patients with prosthesis and in orthodontic treatment planning. The fact that it showed no sexual dimorphism and bilateral asymmetry facilitate the dentists with use of averaged size between mesiodistal dimensions of both the incisors. Since it did not show population-speci city the index might be applicable for Serbians and Greeks as well.