One of the main reasons patients are addressing the dentist is the improving facial aesthetics. Face symmetry is considered an importance factor for facial aesthetics. Midline synchronization is considered an essential criterion for achieving harmony for facial esthetics.

A diastema is spacing or a gap in between the proximal surfaces of two adjacent teeth of 0.5 mm or more; spacing of upper or lower central incisors is frequently known as midline diastema [1] . Although commonly associated with maxillary midline diastema, such a spacing may occur between any two adjacent teeth. Most children will develop diastema during the process of normal development, and in many cases, treatment is not indicated [2] . However, maxillary midline diastemas of more than 2 mm are unlikely to close spontaneously and remain in the adult dentition [3] . Most adult patients consider a diastema, especially a maxillary midline diastema, to be unappealing [4] . Studies have shown that people consider those with diastema to be less intelligent, less beautiful, and of a lower social class [5] . Diastema may be brought about by several factors. Familial factors [4] , abnormal size, shape, or number of teeth, periodontal defects, fibrous frenum defects, and muscular defects of the tongue [6] are all possible etiologies associated with the formation of diastema. Diastema formation has proven to be a truly multifactorial anomaly [7] [8] . Several studies support the concept of a possible genetic predisposition for the maxillary midline diastema [4] [7] [9] [10] . Genetics or family tree is considered the leading risk factor for the relapse of any orthodontic treatment of midline diastema; the other important factor is the size of the diastema [11] .

Some studies concluded that maxillary midline diastema familial incidence was one of significant factors associated with the prevalence of maxillary midline diastema [7] [11] . In 2003, Gass et al. suggested that the midline diastema is inherited by an autosomal dominant mode of inheritance [10] . Diastema prevalence has been estimated between 3.7% [12] to 36.8% [13] . There was a variation of the acceptable maxillary to mandibular midline deviation, 1 - 2 mm deviation was considered to be acceptable while 2 - 4 mm was less esthetic or less acceptable, and 4 mm of deviation is considered as unaccepted [14] [15] [16] . The frequency of its occurrence and negative perceptions, it is clear that diastema is a concern for patients and practitioners. In 2007, Bernabe and Flores-Mir concluded that among young adults the maxillary anterior diastema had the most negative impact on self-perceived dental appearance [17] .

Many techniques have been demonstrated to attempt to close diastema [18] . The aim of our study was to determine the prevalence of diastema in specific social demographics in our patient population at UNLV.

Results showed that 1182 patients’ records were identified to have one of the search keywords. The socio-demographic data in Table 1 indicated that females have a higher prevalence of diastema (56.7%). Regarding age, 31.5% of the patients were between 12 - 19 years old. Ethnicity frequency calculations indicated that diastema was more among the Hispanic population (35%), followed by Caucasians (25%) and the African Americans population were 17% ( Table 1 ). Most diastema cases were in the maxillary arch (80.69%), followed by cases with diastema in both the maxillary and mandibular arch (13.49%). Most patients presented with mild diastema (60%), followed by moderate (28.7%), and then severe (11.3%) ( Figure 1 ). The chi-square analysis showed that these ethnicity results were statistically significant (p < 0.0001). Figure 2 shows some cases of different sizes of diastema.

Diastemas are frequently considered as esthetic or malocclusion problems. Once defined their etiology, different treatments can be achieved. When analyzing the present findings, results showed that the prevalence of diastema was higher in females and is of statistical significance; this comes into disagreement with the previous study, which showed a high percentage of males with diastema [20] . Diastema presence can be predicted by ethnicity. Earlier studies showed that the prevalence of maxillary midline diastema was greater in African populations than among Caucasians or Asian [21] . Another research reported that a maxillary midline diastema (MMD) occurrence among African Americans is more

than twice as in the whites or Hispanics population [22] .

The present investigation provides data that indicates that diastema is more prevalent in certain population groups, and revealed a significant difference where the hispanic population represented 35% of the patients’ population with diastema. The present results disagree with previous findings, which indicated that the prevalence of diastema, when examined by race-ethnicity, was high among African America compared to Mexican Americans and non-Hispanic whites [20] [21] .

Some cultural influences considered midline diastema as an attractive dental feature that enhance their personality and beauty; Akinboboye in 2015, revealed that most Nigerian ethnic groups considered 2 to 3 mm diastema as esthetic pleasing feature [23] ; while others consider it a dental problem that requires orthodontic or restorative intervention [1] [24] [25] [26] [27] .

Few studies reported the presence of diastema in both arch diastema; the reported percentage was 6.3% [28] ; the present investigation showed that 13.49% of the cases presented with diastema in both arches.

Facial esthetic is considered an essential factor in determining all patients’ social interactions and quality of life. To achieve a satisfactory dental esthetic, it is necessary to decide the underlying cause for the midline diastema. One of the limitations of the present study was the investigation of the presence of any family tree for the diastema case. Further research is needed to understand how ethnicity contributes to determining whether a person has diastema. Genetic studies could evaluate the lack of or presence of a gene that contributes to diastema formation. Further research may determine if diastema formation is determined during embryological development, during adolescence, or from periodontal condition.

Within the limitations of the present investigation, there was a significant relation between the presence of diastema and ethnicity. The most common type and site of diastema was mild diastema in the maxillary arch only followed by moderate diastema in both arches.

Treatment planning for diastema early in patients of certain social demographics may help avoid esthetics concerns later in life.

KC, TA and NHA planned and performed the study; KC and NHA performed literature review. KC, NHA drafted the manuscript, KC carried out the statistical analyses and interpretation of data. TA and NHA critically revised the manuscript for intellectual content. All the authors have read and approved the final manuscript.

This study was approved by the University of Nevada, Las Vegas, Biomedical Institutional Review Board and was given the status of exempt [IRB no. 1489457-1].