Noncarious cervical lesions in occlusion service patients : occlusal aspects and risk factors

Objective To evaluate the occlusal aspects of patients with and without noncarious cervical injury and identify its risk factors. Method Through a cross-sectional study, 88 patients of both sexes between 18 and 71 years old were evaluated, in Occlusion services in the cities of João Pessoa and Campina Grande. Clinical assessments were performed by a single calibrated examiner to check the occlusal aspects of patients with and without injuries, through descriptive and non-parametric analysis with 5% significance level and 95% of confidence interval. Results Parafunctional habits were identified at a frequency of 92.0% of the patients. Unilateral chewing was not associated with the presence of lesions. The side disocclusion by the canine was prevalent in the whole sample. Occlusal interference in maximal intercuspal position and in nonworking side were presented as risk factors for the higher number of lesions and their development. Wear facets were common in the premolar groups and the maxillary arch in patients with lesions. Conclusion Occlusal factors pose risks for the development and greater number of noncarious cervical lesions. Indexing terms: Dental occlusion. Functional laterality. Tooth Wear.

Patients of these services, based on a previous study 8 were in average 31.47 years old, ranging between 18-71 years old; 63.36% being female and 36.64%male; in whom 65.90% of the lesions were present, and in 34.10% they were absent, with an average of 5.28 injured teeth per patient.
The study included patients with at least 20 functional teeth), who were willing to participate.We excluded patients with periodontal disease, orthodontic, endodontic and occlusal treatment, pregnant women and patients with severe bruxism and mouth opening limitation.
The study was approved by the local ethics committee -University Hospital Lauro Wanderley-HULW CAAE 0399.0.126.000-10.For the implementation of clinical examination was used a calibrated examiner of the study previously conducted in this population 8 .
Data collection was performed by a clinical examination and specific form where variables were raised about occlusal aspects of patients with and without cervical injury.

Variables
Unilateral chewing: the patient was questioned whether this type of chewing occurred.
Parafunctional habits: the patients were asked about the presence of habits such as, teeth clenching and grinding, nail biting, lips biting, cheeks sucking, tongue sucking, biting objects resting your chin on your hand.
Lateral disocclusion: the lateral disocclusion to the left and right side was classified through the clinical examination into canine guidance (there is contact only of the upper and lower canines), Group function (premolars and upper and lower molars contact) and group partial function (there is contact only at the canine and upper and lower premolar) 13 .
Anterior guidance: it was classified through the clinical examination in anterior guidance (contact only between the anterior teeth), posterior guidance (contact only between the posterior teeth) and combined guidance (contact between the anterior and posterior teeth simultaneously) 14 .
Contact interference in maximal intercuspal position and no nonworking side: the presence of these interferences through clinical examination was observed with the aid of a double-sided articulating film (Accum-film II, Parkell-Farmingdale, USA) together with the miller clamp 15 .

INTRODUCTION
Noncarious Cervical Lesions (NCLs) are defined by the dental tissue loss in the cervical region: of teeth, without the evidence of dental caries origin [1][2][3][4] .These injuries are usually found and increasingly common practice in dental clinic.Their etiology and classification are challenging, though 4 .The action of abrasive, erosive and occlusal mechanisms may contribute to the lesion formation, making it of a multifactor source 1,[4][5][6] .
The increased consumption of fruit, sports drinks and oral hygiene habits suggest that these lesions are due to erosion and abrasive habits [6][7] .Patient of occlusion services do not present health habits associated with the presence of lesions, and only the frequency of soft drink consumption was associated with NCLs 8 .
The occlusal stress from non-axial force (lateral or oblique) on the dental element, can generate microfractures of enamel and dentin in the cervical region 1 .The occlusion as an etiologic factor of NCLs was presented in 1984 by the Tooth Bending Theory, which states that occlusal interferences cause the breakdown of enamel and dentin in the cervical region, resulting in the lesion formation 9 .
The occlusal loading and NCLs has been a subject of extensive research through studies in silico 10-12, which demonstrate high cervical stress in non-axial loading conditions on the dental element.However, it is necessary to clinically observe the behavior of these occlusal interferences and check for a possible correlation of these lesions with the occlusal factor.
Based on the above, this study aimed to observe the occlusal aspects of patients with and without noncarious cervical injury and identify its risk factors.
The hypothesis to be tested is that there is an association between occlusal factors and the presence of noncarious cervical lesions

METHODS
This research is characterized by a cross-sectional and prospective study, that is, the data obtained in this study were generated at the time it was developed.The survey was conducted with patients of the Occlusion services in the cities João Pessoa and Campina Grande.Patients of these services were the study population.A convenience sample of 88 patients was used, based on a previous study in the same services 8 .
Noncarious cervical lesions in occlusion service patients: occlusal aspects and risk factors Wear facets: were analyzed the plaster models of superior and inferior teeth of each patient.The impression was carried out in stock trays with Condensation Silicone (Perfil®, Vigodent, Rio de Janeiro, Brazil).The molds were poured with type IV plaster (Durone, Dentsply Industria e Comercio Ltda., Rio de Janeiro, Brazil) with the aid of a plaster vibrator.Once the plaster models were obtained, the occlusal anatomy of the dental elements were analyzed with the aid of a magnifying glass with 4x magnifying power (Bio-Art, São Carlos, Brazil).In order to make easier the viewing of the wear facets, they were marked on the impressions with a graphite pencil with 0.5mm diâmetro 15 .
It was used a scale present in the literature 16 to classify the facets, establishing a degree from 0 to 3. The grade 0 with no wear, grade 1 minimum wear on the tips of the cusps and occlusal surfaces, grade 2 flattening of the cusps or incisal surfaces and degree 3 total loss of contour and dentin exposure when identifiable (Figure 1).
Data were recorded in a computer program database SPSS (Statistical Package for Social Sciences) for Windows, version 15.0, and analyzed using descriptive and inferential statistics.The Chi-square test estimated the association among variables.The Cramer V coefficient identified the strength of the associations and the relative risk (odds ratio) to identify the risk factor.Guided by the compliance of the distribution of data, corroborated by Komogorov-Smirnov normallity test, which showed a normal divergent distribution of (p> 0.05).Adopted a 95% confidence interval and a significance level of 5% (p <0.05).

RESULTS
The parafunctions were identified in a prevalence of 92.0% of the patients.It was found a positive association (p = 0.040) and low correlation between clenching and the presence of NCL (V = 0.270) (Figure 2).
Unilateral chewing was prevalent in individuals with NCL presence (Figure 3), but associations found   no work side (V = 0.309) showed a moderate correlation with the presence of NCL (Table 1).Wear facets were observed in 1,751 dental elements in this study, among these 379 also had NCl lesions.It was observed among the elements without NCL that the greatest wear frequencies were in lower incisors (17.20%), lower premolars (13.63%) and the upper incisors (13.34%).The other groups showed relatively equal distribution, ranging from 10.06% (molars) to 12.68% (molars).(Figure 4).In contrast, in the number of teeth with wear and NCl lesions, those with the highest rates were lower premolars (21.11%) and upper premolars (17.68%).
The remaining dental groups have similar percentages, except the molars, which obtained a frequency of 7.12% and lower canines with 8.71%.The maxilla (53.03%) was the most affected one by the wear between these variables were not statistically significant (p = 0.110).
The lateral disocclusion standard did not correlate with the presence of lesions, although disocclusion by the canine has been prevalent in the sample.The anterior disocclusion presented a moderate correlation (V = 0.336) between presenting anterior protrusion but not having NCL.Occlusal interference in MIH (V = 0.445) and on the together with injuries in relation to the mandible (46.97%) (Figure 4).
Regarding the degree of wear on the dental elements with and without NCL, grade 0 was the prevalent one in groups of molars and premolars.Grade 1, in turn, presented equal distribution in all tooth groups.In grade 2, it was more expressive the frequency of the lower incisors, although the group of canines, showed similar proportions (14.23% to 13.14%).Finally, the degree 3 of wear was the one which reached the lower frequency compared to the other degrees of wear.Regarding the most prevalent dental group in that degree are the upper incisors (24.69%) (Table 2).
It was estimated the relative risk (Odds Ratio -OR) to show the higher number of NCLs and their development or presence for variables of interference in MI and no work side and parafunctional habits.The presence of occlusion interference in MIH increases in 26X the risk of having a higher number of lesions and in 100X the risk of having NCL.Interference in nonworking side suggest 3X or 4X the risk of having a greater number of lesions and the presence  of the same respectively.While habits do not apply as risk factors for NCLs (Table 3).

DISCUSSION
Since the publication of the classic study by Lee & Eakle 9 , in which stresses caused by excessive occlusal load would be responsible for the development of NCLs, the etiology of these lesions started to be questioned.The clinical evidence on the causal factors of NCLs are important for guiding the dentist concerning the risk variables of the same.And how he may act, guiding his patients or even taking preventive measures to avoid the appearance and progression of these lesions [2][3]6,10,15,17 .
The research results accept the hypothesis that occlusal factors were associated with the presence of NCLs, and corroborates clinical findings in literature 15,[17][18][19][20] .However, they noted that lower tension forces in lateral movements do not prevent the progression of the lesion.This result can be questioned, because even if tensions are lower, if they are not axial loads, the occlusal interference continue acting, promoting the progression of lesions.Occlusal interference in MI and next to nonworking area are risk factors for the development and a greater number of injuries corroborates the literature 18 .It is interesting to emphasize that the adequate anterior guidance is correlated to the absence of lesions, ie, patients without lesions have fewer interferences 17 .
As well as the prevalence of a normal side disocclusion in a sample that had some kind of altered occlusion, a result that goes agrees with the findings in a similar population 19 .
The occlusal factor is essecial for the development of NCLs 21 and explains their presence in the study population as well as in African patients, who had no contact with oral hygiene habits and had lesions.The occlusal loading and the supporting action of acids from drugs and feeding act together for the development of NCLs 21 .
The wear facets were found in a large number of dental elements, because they are a physiological phenomenon in the population.The combination of factors such as occlusal interferences, diet, abrasive habits, cultural habits and geographical location may influence in their frequency 16 .
However not all dental elements affected by NCL in this sample 8 showed wear facet.This study, it was not performed statistical inference of this variable for the presence of lesions.The literature suggests that wear facets do not influence the formation of NCLs 22 .Given this clinical setting, perhaps the wear facet is not a sign of the presence of an injury, however we still needed closer examination of the relationship between wear facets and NCL.
The predilection for the premolars group and maxillary arch of the wear facets on dental elements with injuries; is due to the oclusal stress 15,23 and the action of abrasion, erosion and parafunctions 16 respectively.
The prevalence of 0 degree of wear in molars and premolars is due to normal lateral excursions in the sample.The high number of grade 1 wear compared to grade 3 happened because they were samples of young adults who have not been exposed to factors that accentuate tooth loss over the time.And the frequency of degree 3 of wear facet in incisors groups might be related to the repetition of harmful habits, and because the anterior elements are mostly affected by wearing than the posterior ones 13 .
Parafunctional habits are more frequent in patients with NCL 17 , the occlusal load generated by these habits is higher than the axial loads, causing significant damage to dental tissue 12 .Some studies 15,20 deny the association of these habits to the presence of lesions.That is, as presented in this research, such habits do not mean risk for the lesions development.
Unilateral chewing was not associated with the presence of lesions, this result is also found by the literature 15 .It is possible that tensions generated during the unilateral masticatory act are not significant for the emergence of non-carious cervical lesions.Moreover, maybe the unilateral chewing is a concern much more muscular than dental.
All study participants have some kind of altered occlusion, being patient occlusion services, but not all had LCNCs 8 .Since the occlusion factor is related to the presence of injury, how to explain the absence of same in some patients?This is due to the sample is made up of young adults, which has not suffered the action of occlusal stress the right time.
As well, the sample is presented as balanced regarding lateral disocclusion, a positive factor that contributed to this result.The magnitude, duration, direction, frequency and location of occlusal loads 1.4,10-11,23-24 , are crucial to initiate and act in the progression of the lesion.And individuals where the injury was absent are considered high risk to present future lesions.
This research enables clinical aesthetic evaluation of the behavior of frontal NCL of occlusal mechanisms.
Through a controlled and estimated sample made it was possible to compare data with individuals without injury.The limitation of this study is the observation of pathology already installed, so we cannot say that occlusal factors are the initial cause of the injury; can identify them only as risk factors and correlation between variables.
Clinical research must be conducted in an attempt to observe longitudinally the development of these lesions in populations of other dental services in order to identify whether the occlusal factors are initial etiologic agents of development of these non-carious cervical lesions.As well, it is necessary to check for a possible relationship between wear facets and LCNCs.

CONCLUSION
It was concluded that the parafunctional habits like teeth clenching had a positive association but weak correlation with the presence of NCLs.Unilateral chewing was not associated with presence of lesions.Canine guidance was common throughout the sample.Occlusal interference in MI and nonworking side are risk factors for a higher number of lesions and their development.The premolars and the maxillary arch were the most affected by the wear facets and NCLs.

Collaborators
VMG FIGUEIREDO, RL SANTOS and AUD BATISTA conducted the research, collected, analyzed, discussed the data and participated in writing the article.

Figure 1 .
Figure 1.A) Analysis of plaster models with magnifying glass and graphite to mark the wear facets; B) lower model in plaster with wear facets delineated, as well as the noncarious cervical lesions.

Figure 2 .
Figure 2. Distribution of the frequency of parafunctional habits in the sample.

Figure 3 .
Figure 3. Distribution of the frequency of the Unilateral chewing in the sample.

Figure 4 .
Figure 4. Number of teeth with wear facets in the absence and presence of non-carious cervical lesion.

Table 1 .
Descriptive and inferential statistics of disocclusion pattern, occlusal interferences and the presence of NCLs.

Table 2 .
Descriptive statistics of the degree of wear facets in dental groups in the absence and presence of NCL.

Table 3 .
Relative risk in developing lesions.