Trend of traumatic crown injuries and associated factors in preschool children

The aim of this study was to assess trends in traumatic crown injuries (TCIs), their prevalence, and association with socioeconomic and clinical factors in preschool children over a 5-year period. A series of cross-sectional surveys was conducted in Santa Maria, Brazil, on children attending a National Day of Children’s Vaccination. The same protocol was used in all surveys conducted in 2008, 2010, and 2013. Clinical examinations were performed to evaluate types of traumatic crown injuries using the O’brien index. A semi-structured questionnaire was answered by the parents. It provided information about several socioeconomic factors as well as the parents’ perception of their child’s oral health. The chi-square for trends test was used to verify changes in TCI prevalence throughout the years. The association between socioeconomic and clinical factors with TCI was assessed by the Poisson regression analysis. A total of 1,640 children were examined. The prevalence of TCIs decreased significantly from 2008 to 2013 (10.12%; p < 0.001). Central incisors were the most vulnerable to injury, independent of the year. Moreover, older children and those with inadequate lip coverage were more likely to present with some traumatic dental injury (p < 0.001). prevalence of traumatic crown injuries decreased following the years, however TCI remain an important subject to consider when planning oral health policies.


Introduction
The prevalence of traumatic crown injuries (TCIs) has been evaluated in several countries; and the association with socioeconomic, clinical, and psychosocial indicators has been demonstrated in preschool children 1,2,3,4,5,6,7,8 .Data from the latest national population-based oral health study showed that 20.5% of children, aged 12 years, had TCI in at least one incisor 9 .There is no national data for TCI prevalence in preschool children; however, regional studies reported a TCI prevalence ranging from 9.4% to 41.6% 3,4,5,6,7,8,9,10 .
Studies conducted with Brazilian preschool children showed that TCI can produce a negative impact on the quality of life of children and their families 11,12,13,14 .Therefore, TCI is still considered a public dental problem due to high prevalence, impact on children's quality of life, and the high costs associated with treatment 15,16 .
In this context, oral health surveys can provide important information for planning health strategies based on trends of oral health outcomes throughout a timeline.There is national data about trends of dental caries, as well as erosive tooth wear in children 17,18 .However, for TCI, these studies are scarce.There are few studies evaluating the trends in prevalence and severity of TCI in Brazilian preschool children.The results of these cross-sectional series indicating a significant increase in the prevalence of TCI suggests that public health efforts to reduce future TCI occurrence is needed 19,20 .
Recently, a systematic review on the prevalence and trends in dental trauma in permanent teeth in Latin America and the Caribbean was conducted with 24 studies.Most were conducted in Brazil, following a cross-sectional design with school-aged children.The authors suggest that there is no change in dental trauma over time.However, when considering Brazilian studies only (excluding those up to 2000s), the review showed a decrease in the prevalence of dental trauma 21 .
There is a lack of information about the occurrence of TCI over time as well as possible predictors for its occurrence.Therefore, assessing trends of TCI would provide important information for planning and developing public healthcare promotion, with an aim to reduce oral health inequalities.The aim of this study was to evaluate the trends in TCIs and their prevalence in Brazilian preschool children from 2008 to 2013.The association with socioeconomic and clinical factors was also assessed.

Methodology
This study used data from three oral health surveys administered to preschool children, aged 0-59 months, living in the city of Santa Maria, Brazil.Santa Maria is a medium-sized city with an estimated population of 261,031 inhabitants that includes 18,420 children, aged 0-5 years 22 .The surveys were conducted using the same protocol during the National Day of Children's Vaccination in 2008, 2010, and 2013.Detailed information on the surveys has been previously described 23,24,25,26 .
In 2008, the sample calculation considered a standard error (SE) of 5%, a confidence interval (CI) level of 95%, power of 80%, design effect of 1.4, and a TCI prevalence of 41.6% 9 (10% for possible non-response rate is added).Therefore, the minimum sample size was estimated to be 410 children.In 2010, it was estimated that there was a minimum sample size of 512 participants, factoring in 95%CI, 4% SE, TCI prevalence of 31.7%, design effect of 1.4, and 10% for non-responders 24 .For the last survey performed in 2013, the same parameters were adopted excluding a previous prevalence of TCI, which was 13.3% (data from the survey conducted in 2010).After all procedures, the minimum sample size was 427 children.
Participants were systematically selected from all children who attended the National Day of Children's Vaccination in 15 health centers that are equally distributed in the five administrative regions of the city.The same health centers were used in all the surveys.The vaccination program has consistent uptake rates exceeding 97%; and the selected health centers received almost 90% of the preschool children.Each fifth child in the queue in each health center in all the years was invited to participate.If the guardian declined, the next child in the queue was invited.
Data were collected through clinical oral examinations and structured interviews.Fifteen examiners and 30 assistants participated in the study each year.A benchmark dental examiner conducted the complete examiner training as well as the calibration process before each survey.In each year of data collection, different examiners and assistants conducted clinical examinations and interviews.All examiners reached satisfactory inter-and intra-examiner reliability.Kappa values for the presence of crown fractures were calculated on a tooth-by-tooth basis.The values for intraand inter-examiner agreement ranged between 0.75 and 0.91.These values represent satisfactory intra-study reliability.
Children were individually examined while seated on a dental chair utilizing conventional dental illumination.Visual examinations were conducted with World Health Organization (WHO) periodontal probes and plane dental mirrors, using previously standardized criteria 27 .The clinical examination recorded information about TCIs using the same criteria employed in the United Kingdom Children's Dental Health Survey 28 and also utilized in previous Brazilian studies 24,29 .It includes the following criteria: 0 = no trauma; 1 = enamel fracture only; 2 = enamel-dentin fracture; 3 = enamel-dentin fracture with pulp exposure; 4 = signs of pulp involvement without signs of fracture; 5 = missing tooth due to TCI; or 6 = other TCI.Lip coverage was considered adequate when the lips covered the anterior teeth completely in the at-rest position and inadequate if any part of the crown height was exposed and visible at same position 30 .Parents and guardians, through a structured questionnaire, relayed their socioeconomic characteristics.Information provided included characteristics of the children such as age, gender, skin, color, and household income.The questionnaire was applied in 10% of the sample previously to check its feasibility.

Data analysis
Data analyses were performed using STATA 12.0 software (Stata Corp. College Station, TX, USA).The prevalence of TCI was defined as the participants having at least one type of TCI according to the dental examination.A chi-square test for trends was used to compare the prevalence of TCI through the years.Multiple logistic regression analysis was performed to evaluate the association between the outcome (prevalence of TCI) and predictors.The Backward Stepwise method was used for including or excluding the variables from the final model.All variables with a p < 0.20 on the unadjusted analysis were included in the fitting of the model; they were retained in the final model only if they presented at a p-value of <0.05 after the adjustment.

Ethics
This study was approved by the Municipal Government of Santa Maria-RS and the ethics in Research Committee of the Federal University of Santa Maria, protocol number -0270.0.243.000-09.A signed and written informed consent was obtained from the parents of all children before the study was initiated.

Results
A total of 1,640 ch ildren were en rolled.We evaluated 455, 639, and 546 children in 2008, 2010, and 2013, respectively.Most of the children were white (78.62%) and had adequate lip coverage (85.34%).All other socio-demographic variables are summarized in Table 1.The TCI prevalence was 31.7% in 2008, 13.3% in 2010, and 22.5% in 2013 (Figure 1).There was a significant decrease of 10.12% in the TCI prevalence between 2008 and 2013 (p = 0.003).
Regardless of the year, the maxillary central incisors were the most frequently traumatized teeth (Figure 2).The most common type of TCI were those involving enamel only (19.21%), and less than 1% were injuries involving the pulp (Table 2).The prevalence of TCI was associated with age, lip coverage, and the survey's year.The prevalence increased with age and was higher in those without adequate lip coverage (PR = 1.51; 95%CI 1.21-1.87).However, there was a decrease in the prevalence during the 5 years of study considering other possible confounding factors (Table 3).

Discussion
This study assessed the trends of TCI from 2008 to 2013 in a representative sample of preschool children from a medium-size cit y in Brazil.To the best of our knowledge, this is one of the few studies that evaluated the trends in TCI in primary teeth 19,20,21 .TCIs in preschool children showed a significant decrease from 2008 to 2013 (10.12%, p = 0.003).These results are in accordance with a recent systematic review that assessed studies from Latin America and the Caribbean and demonstrated a relative stability in the prevalence of TCI throughout the past decade.However, when considering Brazilian studies up to the 2000s, a trend of decrease in the prevalence of dental trauma could be observed for the permanent dentition.Although the systematic review included only studies with permanent teeth, we were able to compare our results.Other studies included in the review used the same criteria for TCI presence and were conducted in similar regions.The authors reported that the decrease could be due to more intense, preventive efforts taking place in the south and southeast regions of Brazil, the richest areas of the country 21 .
However, our results disagree with some regional trend studies conducted in a Brazilian southeastern city.Bonini et al. in 2009 reported a significant increase (p = 0.002) between 2002 and 2006 19 .
Recently, a subsequent study conducted in the same population reported an increase of TCI prevalence in a representative sample of preschool children located in the Brazilian city of Diadema between 2002 and 2012 20 .The studies used different criteria other than  the TCI diagnosis used in our study.Moreover, these were performed in different geographic regions of the country.Different cultural aspects could be the reasons for such differences.In 2004, the current public dental policy "Smiling Brazil" was created, another possible contributor.This set of actions with a goal of improving the population's oral health includes everything from prevention to complex rehabilitation 31 .Hence, the difference between the trends studies could be due to these improvements in public health in recent years because they represent different regions of the country.The decrease presented in TCI prevalence in this study could be explained by the hypothesis that children are currently adopting more sedentary lifestyles 32,33 as well as seeking early treatment for  malocclusion.According to one recent study, the traditional child activity games are being replaced by other behaviors during leisure time, including watching TV and using computers, videogames, or other electronic entertainment 33 .Furthermore, a study conducted in South Africa also reported that preschool children are spending more time in sedentary behavior than engaging in moderate-to-vigorous physical activity 34 .Sedentary behavior could be considered a protection for the development of TCI.However, we did not assess sedentary habits in our study, and further studies are necessary to assess such a hypothesis with evidence.Furthermore, the decrease in the prevalence must be considered carefully because there was an increase from 2010 to 2013 (9.2%) in our study.This increase and the short period of evaluation did not allow for an accurate trend shape.An explanation for this increase relies on information bias.Although the examiners were well trained and a standardized criterion was used, some diagnostic decisions may have changed in each year.Another possibility is that random errors occurred in the sampling process and in the short period of evaluation.However, a shorter period of evaluation was previously used 19 .It also important highlight that TCI trend studies are important since it could predict population behavior facing the outcome.Moreover, TCI impacts the quality of life of preschool children 35 .
In comparison to other studies, the majority of TCIs showed that the upper central incisors were more affected than the lateral incisors 3,19,23 .The maxillary central incisors are generally more inclined than the other teeth.They tend to be the first to receive a direct impact when the child falls, leading to a fracture in the enamel or dentin or causing major complications 24 .Crown fractures involving the enamel only were the most common type of injury in our sample (19.21%), followed by those in the enamel and dentin (2.44%).It is suggested that enamel fractures are the most common because most of the injuries are caused by a low intensity impact.The minor damage to the enamel and dentin should be assessed with caution; however, because an the seriousness of the injury could appear minor at the time of the accident, it may eventually result in pulp necrosis 36 .Nevertheless, it is interesting to emphasize that the treatment of TCIs tends to be neglected, which could affect a child's ability to eat, speak, and socialize 19 .It highlights the importance of relaying more widespread information and explanation about TCI treatment.Neglecting case resolution may result in difficult outcomes to both primary and permanent dentitions Our study showed an association between age and TCI.Older children were more likely to present TCI than their counterparts, particularly in the age group of 48-59 months (PR = 2.20, 95%CI = 1.57-3.08,p < 0.001).
In accordance with one previous study, the injuries occur in this group because they are just beginning to move independently and explore their environment with a relative lack of coordination 7 .Another positive correlation was shown between lip coverage and TCI.Those children classified without adequate lip coverage were more likely to have traumatic injuries in maxillary incisors than those with adequate lip coverage.Our results are in accordance with previous studies 3,8,37 , emphasizing the importance of anatomic predisposing factors for TCI occurrence.TCIs occur approximately twice as frequently among children with protruding incisors compared with those in children with normal occlusion 3 .Furthermore, the authors of a systematic review suggested that lip coverage and early treatment of malocclusion are important variables to consider as part of promotion of public health policies 21 .We have not evaluated overjet, and this could explain part of the association.However, a previous study reported that overjet is associated with TCI only when inadequate lip coverage is also present 38 .Some limitations must be considered.A possible underestimation of prevalence could have occurred because we used a criteria focused only on the visible signs of TCIs.Therefore, other types of TCI, such as concussion and luxation, were ignored.However, the criteria used in the surveys were consistent with previous studies, allowing for comparison 24,35 .Moreover, despite the examiners being calibrated in each survey, some small differences in diagnostic decisions may occur.It could happen because of the criteria used, which rely on visual diagnosis, excluding complementary exams.Some comparisons are not possible because there are no well-defined criteria to assess TCI.However, a recent systematic review showed that the index adopted in this study is one of the most common criteria used in Brazilian studies 21 .Another limitation was the short period of evaluation; only three points in time were used to describe our results.Further assessments over a longer period may allow us to detect more reliable effects of population changes in the trends of TCI, thereby being able to predict a better trend shape.
In conclusion, this study showed that trends of TCI in preschoolers decreased significantly between 2008 and 2013.The results are important for health sectors to implement health promotion strategies for the management of these injuries in early ages.

Figure 1 .
Figure 1.Trends in traumatic crown injuries prevalence between 2008 and 2013.Santa Maria, Brazil.p = 0.003 according to chi-square for trend test.

Figure 2 .
Figure 2. Prevalence of traumatic crown injuries in each year according the teeth.

Table 1 .
Descriptive characteristics of the sample by year.Santa Maria, Brazil.
*cut-off point used was median of the corresponding year.Median in 2013 was approximately R$1,700; 2010 was approximately R$ 1,470; and 2008 was approximately R$ 1,020.

Table 2 .
Prevalence of each type of traumatic crown injuries by year.Santa Maria, Brazil.

Table 3 .
Poisson regression of traumatic crown injuries and associated factors.Santa Maria, Brazil.
+Included in the final model for adjustment.