Dental malocclusions in the anterior sextant, in a group of Mexican patients between 3 and 14 years old.

: Aim: To evaluate the association between the frequency of malocclusions in the anterior sextant with dentition type, age, and sex. Material and methods: A descriptive, transversal and prospective study was carried out, in a convenience sample of 200 patients between 3 and 14 years old, of both sexes who attended the pediatric dentistry clinic of Dentistry Faculty from Autonomous University of Tlaxcala, Mexico. A dentist was standardized by a direct method (k =0.998, p =0.0001). Results: Crossbite and edge to edge bite were the most frequent (18% and 17% respectively), in no case the alterations in the previous sextant were related to sex, except altered overjet with age and dentition type (likelihood ratio=18,169, p =0.0001) (X 2 =18.820, p =0.0001). Conclusion: These observations highlight the importance of the diagnosis of possible alterations in the occlusion of the anterior sextant in both dentitions, in order to preventatively avoid major sequelae.


INTRODUCTION.
Occlusion refers to the relationships that are established when the teeth are in contact, both in centric occlusion (CO), as well as in protrusion and in lateral movements. At present it is conceived as a system formed by functional units such as the teeth, the temporomandibular joint and the muscles of the head and neck, which are dynamically related, a quality that allows it to adapt to the changes that are generated during body development.
When this balance is disrupted, there appear dental alterations that are characterized by any deviation from the ideal occlusion. 1- 3 The upper incisors usually cover one third of the crown of the lower teeth, since they are in a labial position between 12 and 28 degrees in relation to their lower counterparts, if a vertical line is considered as a reference. This relationship may show different variations that occur as a result of the balance exerted by the lingual, labial and perioral muscles, as well as by mandibular growth. 4- 6 The characteristics of the relationship between the anterior teeth become relevant because this relationship serves as a guide in the function of the masticatory system. Among the most frequent alterations in the anterior sextant are: overjet (horizontal overbite), in which the maxillary anterior teeth protrude and horizontally overlap the the mandibular teeth; vertical overbite, when the lingual surfaces of the upper incisors, when occluding on the buccal surface of the lower incisors, exceed the overlap in a vertical direction by more than 2mm; crossbite, either bilateral or unilateral, characterized by the inverted position, due to the fact that the lower anterior teeth are in front of their upper counterparts; open bite in which no contact is observed between the teeth of the upper anterior sextant with the lower ones; and edge-to-edge bite, defined as a type of malocclusion in the vertical and sagittal direction in which the overjet and overbite are zero, that is, the upper and lower incisors make contact on their incisal portion. 1-4,7- 10 The epidemiological profile of this event refers to the variable frequency with which the different alterations in the types of bite occur in the anterior sextant. This is because there are different factors that influence the establishment and development of dental occlusion from subject to subject, as reported by Espinal et al., 8 Bauman et al., 9 and Fontaine et al., 11 among others. Its prevalence has shown a proportion that ranges from 44.7% in Cubans 12 to 84.6% in Saudis. 13 A clear trend has not been reported in relation to which type of alteration is more frequent.
In the case of anterior open bite, Díaz et al., 12 reported that 6.3% presented this condition, while Mendoza et al., 14 reported 35.1%. A similar prevalence has been observed in anterior crossbite. Zhou et al., 15 reported this alteration in 6.8% of Chinese children with primary dentition, while Segura et al., 16 in 38.5% of a group of Cuban children. Regarding the alterations in the horizontal and vertical bite, there is no specific trend between them. [17][18][19] However, in both cases the frequency of alterations in overjet and overbite is relatively high, with altered overjet ranges of 8.8% in Chilean schoolchildren 6 up to 33.7% in Indians, 13 and overbite ranging between 19.5% in Colombians 20 to 46.9% in Nepalese. 21 The reports suggest that these alterations have been observed more frequently in females; however, in none of the cases there is evidence of an association with this variable. 3-4,8,13,21-22

Study design and participants
A descriptive cross-sectional study was carried out. The study involved a convenience sample consisting of 200 patients between 3 and 14 years old, of both sexes, treated in the spring of 2019, at the pediatric dentistry clinic of the School of Dentistry at the Universidad Autónoma de Tlaxcala, Mexico. Seventeen patients were excluded from the study because their parents did not sign the informed consent, were not present on the day of the epidemiological survey or refused to be examined.
Ethical and legal considerations of the study The study was approved by the Bioethics and Biosafety Committee of the Dental Occlusion Research unit (LIFESZ-230506), of the Zaragoza School of Higher Studies, at Universidad Nacional Autónoma de México. Parents or guardians were asked to provide informed consent in writing for their child to be included in the study. The technical standards established by the Ministry of Health of Mexico (NOM013-SSA2-200635) regarding the prevention of infection transmission were applied during the calibration of the examiner and the epidemiological survey.

Examiner Calibration
The calibration of a dental surgeon as an examiner was carried out through the direct method, a process in which the Cohen's kappa coefficient p-value was calculated in order to guarantee that said concordances were not due to chance (crossbite k=0. 998 The relevance of the epidemiological record for the registration of the clinical assessment data was designed and evaluated through a pilot test of the instrument.
Variables and clinical assessment The study variables were: age, gender, crossbite, open bite, edge-to-edge bite, malocclusion, overjet, overbite and their distribution by age, gender, and type of dentition. For the oral examination, after explaining the purpose of the study and requesting their consent for their inclusion, the patient was asked to enter the clinic accompanied by their parent or guardian. The oral examination of the patients was carried out in a dental chair, using disposable gloves, a Hu-Friedy® flat dental mirror #5, without magnification, and a Obi ® steel ruler with standard 25mm graduation, model 281509.
For the intraoral examination, the patient was asked to lie down on the dental chair and open and close their mouth until the patient was in centric occlusion; lips were separated, and the position of the jaw was verified to assess the type of bite in the anterior sextant. This procedure was carried out in groups of 30, until all patients were examined.
The diagnostic criteria considered the presence of an open, crossed, edge-to-edge bite and the presence of an altered overjet and overbite.

Statistical methods
For statistical analysis, the SPSS v.20.0 statistical package for MacOS (IBM, USA) was used. To measure the presence of alterations in the anterior sextant, frequencies and proportions were calculated. To determine the association between the presence of each alteration in the anterior sextant with gender, the Mantel and Haenszel Chi square p-value was calculated because the variables were nominally measured and the data presented in tables; except for the analysis of the association between the type of alteration in the anterior occlusion with age and the type of dentition, since in these cases the Pearson Chi-square value was calculated. Likewise, when the value observed in any of the cells was equal to or less than five, the likelihood ratio value was calculated. In all cases a confidence level of 95% was considered. The tables were designed using Microsoft® Excel v.365.

RESULTS.
The study sample consisted of 200 children with ages ranging between 3 and 14 years old, with a mean age of 8.01±2.09 years, proportionally distributed by age and gender in three groups (Table 1).
Regarding the presence of malocclusion in the anterior sextant, nine out of ten patients showed some alteration in the occlusion. Crossbite was observed in 18% of the patients, and open bite in 1.5%; this was the alteration that occurred less frequently in comparison to the other alterations. Edge-to-edge bite was observed in 17%, overjet in 23%, and overbite in 4.5% of the examined patients ( Table 2).
In relation to the distribution of cases of anterior sextant alterations according to gender, crossbite was more frequent in females than in males, a phenomenon that turned out to be similar in terms of the presence of edge-to-edge bite cases, since females showed this clinical condition more frequently. In the case of open bite, males showed a slightly higher frequency.
Regarding the distribution by age, crossbite was observed more frequently in the age group of 6 to 9, with no evidence of any relationship between these variables (likelihood ratio=0.684, p=0.693). The presence of open bite cases was almost nil, being more frequent in the age group of 6 to 9 years; however, these differences were not statistically significant (likelihood ratio=0.284, p=0.442).
This was similarly observed regarding presence of edge-to-edge bite, with the age group of 3 to 5 years presenting a greater number of cases; however, its distribution did not show statistical relevance with respect to age (likelihood ratio=0.542, p=0.536).
In relation to overjet, it was more frequent in patients between 10 and 14 years, with an increase in cases at an older age, in a highly significant manner (likelihood ratio=18.169, p=0.0001).
On the other hand, overbite was more frequent in children between 3 and 5 years old; however, these     Table 4. Frequency and percentage distribution of alterations in the dental relationship by age.
variables were not statistically related (likelihood ratio=0.654, p=0.660). In relation to the presence of malocclusions, the behavior was variable, which was not statistically relevant either (X 2 =4.058, p=0.131) ( Table 4).
Regarding the type of dentition, results were also variable. Crossbite was more frequent in the primary dentition; however, the differences observed were not significant (X 2 =0.211, p=0.900). Open bite was only observed in children with primary dentition, which is why the behavior did not show any statistical relevance (likelihood ratio=5.124, p=0.077).
Edge-to-edge bite was also observed more frequently in patients with primary dentition without statistically significance (X 2 =2.060, p=0.357).
Overjet appeared more frequently in patients with mixed dentition, resulting in a high association between this condition and the type of dentition (X 2 =18.820, p=0.0001). Overbite was more frequent in patients with primary dentition without showing evidence of any relationship between both variables (X 2 =2.744, p=0.254).
Malocclusion in the anterior sextant was more frequent in children with primary dentition; however, its distribution by type of dentition did not show any relationship between these variables (X 2 =1.957, p=0.376) ( Table 5).

DISCUSSION.
The frequency of occlusion alterations in the anterior sextant in the study population was similar to that reported by Dimberg et al., 3 and Burgos, 18 who observed a high prevalence of malocclusions and tooth discrepancies in different study populations. On the contrary, Diaz et al., 12 reported a lower percentage than that observed in this study.
The latter reveals the variability of this epidemiological event that can probably be influenced by multifactorial etiological conditions in the development of any alteration in the occlusion of the anterior sextant. There may be some genetic and exogenous factors, such as the presence of some harmful parafunctional oral habit or some systemic disease, among others. 1-3 The main variation observed in the relationship of the anterior sextant teeth was the altered overjet, whose frequency was higher than that reported by Pincheira et al., 6 and Peña et al., 20 but similar to the findings of Bauman et al., 9 and Kumari et al. 13 This may be due to the tooth replacement process during body development, hence the importance of making a timely diagnosis of the position of the teeth in order to preserve an adequate bite for optimal chewing and correct aesthetic appearance.
Open bite was the alteration that occurred less frequently in the study population in agreement with Díaz et al., 12 and Zhou et al. 15 In fact, open bite has been described as one of the malocclusions with a moderate frequency, caused by a series of habits that take place in childhood.
Regarding age, the group of 6 to 9 years presented the highest number of alterations in the anterior sextant, in agreement with that reported by Mendoza et al., 14 Segura et al., 16 and Burgos. 18 This is probably due to the fact that children at this stage of life are in a transition period based on dental replacement, a process in which the contact between the anterior teeth is slightly lost until their com-plete eruption. In relation to gender, its frequency was slightly higher in females compared to males; however, it was not significant, and the risk of presenting any type of dental alteration in the anterior sextant was similar between both genders.
The latter coincides with most of the reports that studied the distribution of this type of alterations according to the gender of the subjects examined. Results regarding the type of dentition were also variable, cross-, open-and edge-to-edge bites were more frequent in the primary dentition compared to the secondary, similar to the findings of Bhayya et al., 2 Espinal et al., 8 Zhou et al., 15 and Gálvez et al., 19 who reported considerably high frequencies of this type of alterations in populations with primary dentition.
The latter suggests the relevance of the development of any type of harmful oral habit and its influence on the appearance of any alteration in the dental relationship in the anterior sextant. Overjet occurred more frequently in patients with mixed dentition, probably due to the dental eruption process, as when there is a delay in tooth eruption, there is the risk that the occlusion may be altered, particularly in the anterior sextant due to the lack of space in the dental arch, which can lead to disharmony in the contact between the teeth.

CONCLUSION.
No association was observed between the frequency of malocclusions in the anterior sextant with the type of dentition, age and gender, except in the case of altered overjet and age.
No theoretical model was found that could explain such an association, since this condition was more likely to be observed at an older age.