Prevalence of non-carious cervical injuries and their associations with risk factors: integrative literature review

Objective: To determine the incidence of the main risk factors and also the prevalence of non-carious cervical lesions (NCCL) in relation to sex and age. Methodology: The literature search was conducted using the keywords and MeSH terms “Tooth Cervix”, “Non carious cervical lesions” and “Tooth Wear”, in the MEDLINE databases via PubMed and Scopus. Observational studies were included, which aimed to assess the relationship between sex, age and risk factors with cervical injuries. In addition, only studies in English, from the last five years, in their full version, were selected. Literature reviews, clinical cases, studies that did not include the main observation, studies that deviated from the topic and in other languages were excluded from the research. Results: 441 articles were identified, of which 17 were selected. There was no significant percentage difference between males and females, with percentages of 49% and 51%, respectively. Regarding the prevalence associated with the age group, a higher incidence was observed in the population over 65 years of age (36%). Regarding risk factors, gastroesophageal reflux, parafunctional habits, occlusal disorders and brushing problems were reported, but the acidic diet was the most incident in the literature (in 76.4% of the selected articles). Conclusion: The prevalence of NCCL increases with age, however it does not depend on sex, with an acidic diet being considered a risk factor.


Introduction
The cervical region is considered a fragile area of the tooth, since it has a fine enamel structure, with a lower content of minerals and a greater amount of proteins (Bhundia et al., 2019), thus facilitating the occurrence of tooth decay of lesions that generate the irreversible loss of tooth structure near the cementoenamel junction (Teixeira et al., 2018). Also, this area coincides with the fulcrum area of occlusal forces, a factor that contributes to the appearance of morphologically distinct lesions (Bhundia, et al., 2019).
Cervical pathologies are classified into carious lesions and non-carious lesions. While cervical carious lesions are caused by processes that involve microorganisms, non-carious cervical lesions (NCCL) have a non-bacterial multifactorial etiological cause (Aw et al., 2002), with combinations of friction, abrasion, biocorrosion and occlusal stress (Grippo et al., 2012). Cervical abrasion is a multifactorial process in which its etiologies include factors related to brushing, while friction is due to contact between teeth, most often related to clenching and/or grinding (Rajendran et al., 2019). Regarding occlusal factors, it is seen that enamel hydroxyapatite crystals rupture due to increased stress of occlusal origin (Grippo et al., 2012;Yoshizaki et al., 2017).
Biocorrosive tooth wear is defined as an irreversible loss of tooth structure caused by acidic chemical action without any bacterial involvement (Silva et al., 2001). The acid source may be intrinsic, including gastroesophageal reflux, or extrinsic, which may come from acidic diets, exacerbated by reduced salivary flow, in addition to saliva modifying effects . It is common to come across studies that prove that the prevalence of cervical lesions is increasing due to the longer exposure of teeth to risk factors associated with population aging. As consequence, maintaining the natural dentition of patients at more advanced ages exposes the teeth to risk factors for a longer period when compared to the dentition of young patients (Marochi & Queiroz, 2001). However, another study reported the high prevalence of NCCL at an early age, caused, in turn, by the increased consumption of acidic diets, which can be considered an important oral health problem .
This fact becomes even more important since advanced stages of NCCL affect not only aesthetics, but also the health and function of the stomatognathic system, and may be commonly associated with dentin hypersensitivity (HD) (Sawlani et al., 2016). Therefore, it is important to be aware of the risk factors, in addition to investigating how much each one is contributing to the evolution of each stage of the installed lesion. Recognition of the lesion at an early stage is very important to establish a correct early diagnosis and precise treatment, addressing not only therapeutic measures, but also preventive measures for the appearance of new lesions and the progression of existing ones.
Thus, the objective of this study was, through an integrative review of the literature, to determine the incidence of the main risk factors of NCCL and the prevalence in relation to sex and age.
The cervical region is considered a fragile area of the tooth, since it has a fine enamel structure, with a lower content of minerals and a greater amount of proteins (Bhundia et al., 2019), thus facilitating the occurrence of tooth decay of lesions that generate the irreversible loss of tooth structure near the cementoenamel junction (Teixeira et al., 2018). Also, this area coincides with the fulcrum area of occlusal forces, a factor that contributes to the appearance of morphologically distinct lesions (Bhundia, et al., 2019).
Cervical pathologies are classified into carious lesions and non-carious lesions. While cervical carious lesions are caused by processes that involve microorganisms, non-carious cervical lesions (NCCL) have a non-bacterial multifactorial etiological cause (Aw et al., 2002), with combinations of friction, abrasion, biocorrosion and occlusal stress (Grippo et al., 2012). Cervical abrasion is a multifactorial process in which its etiologies include factors related to brushing, while friction is due to contact between teeth, most often related to clenching and/or grinding (Rajendran et al., 2019). Regarding occlusal factors, it is seen that enamel hydroxyapatite crystals rupture due to increased stress of occlusal origin (Grippo et al., 2012;Yoshizaki et al., 2017).
Biocorrosive tooth wear is defined as an irreversible loss of tooth structure caused by acidic chemical action without any bacterial involvement (Silva et al., 2001). The acid source may be intrinsic, including gastroesophageal reflux, or extrinsic, which may come from acidic diets, exacerbated by reduced salivary flow, in addition to saliva modifying effects . It is common to come across studies that prove that the prevalence of cervical lesions is increasing due to the longer exposure of teeth to risk factors associated with population aging. As consequence, maintaining the natural dentition of patients at more advanced ages exposes the teeth to risk factors for a longer period when compared to the dentition of young patients (Marochi & Queiroz, 2001). However, another study reported the high prevalence of NCCL at an early age, caused, in turn, by the increased consumption of acidic diets, which can be considered an important oral health problem .
This fact becomes even more important since advanced stages of NCCL affect not only aesthetics, but also the health and function of the stomatognathic system, and may be commonly associated with dentin hypersensitivity (HD) (Sawlani et al., 2016). Therefore, it is important to be aware of the risk factors, in addition to investigating how much each one is contributing to the evolution of each stage of the installed lesion. Recognition of the lesion at an early stage is very important to establish a correct early diagnosis and precise treatment, addressing not only therapeutic measures, but also preventive measures for the appearance of new lesions and the progression of existing ones.
Thus, the objective of this study was, through an integrative review of the literature, to determine the incidence of the main risk factors of NCCL and the prevalence in relation to sex and age.

Eligibility Criteria
Studies that matched the following criteria were included: analytical observational studies, being case-control, cohort and cross-sectional studies that aimed to observe the prevalence of NCCL among different age and sex groups, in addition to the main associated risk factors to these groups. Filters related to the year were applied, using articles published between the years 2015 to December 2020, and the English language. Only studies in their full version were used. As exclusion criteria, literature reviews, clinical cases, studies that did not include the main observation, studies that deviated from the theme and in languages other than English were declined. Research, Society and Development, v. 11, n. 3, e57411326645, 2022 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v11i3.26645

Search strategy
An electronic search was conducted independently until December 7, 2020 to identify potential studies. The following databases were screened: MEDLINE via PubMed and Scopus. A specialist librarian (D.M.T.P.F.) guided the entire research strategy. A combination of MeSH/DECs, keywords, synonyms and free terms related to "non-carious cervical lesion" was used, with the Boolean operators OR and AND following the syntax rules for PubMed and adapted for other databases (Chart 1). Chart 1. Research strategy used for each database.

Selection of studies
After conducting the searches, all identified citations were imported into a bibliographic reference manager (online version of EndNote®, version X7; Clarivate Analytics, Philadelphia, PA, USA) to remove duplications. Subsequently, two reviewers (K.G.A., V.O.M.) independently reviewed all titles and abstracts and then applied eligibility criteria. The two reviewers' forms were compared and inconsistencies were compared by a third reviewer (M.S.T.R.). Studies that met the inclusion criteria and those with insufficient title and abstract data to determine their eligibility were selected for a full analysis.
After full-text analyzes of potentially relevant studies, those who met all selection criteria were considered eligible for this study and underwent the data extraction process.

Data extraction
Two reviewers (KGA, VOM) independently extracted the following data: author, year of publication, sample size (n), ratio of men and women with NCCL present, age and the main possible risk factors associated with NCCL most present in the studies.

Selection of studies
441 studies were identified through search strategies in the two databases (MEDLINE via PubMed and Scopus). After removing duplicates, 369 titles and abstracts were analyzed. Subsequently, 321 records were excluded because they did not meet the primary inclusion criteria, leaving 48 articles. These full texts were evaluated for eligibility, and 31 articles were excluded based on inclusion and exclusion criteria. Thus, 17 studies were included for the literature review ( Figure 1).

Prevalence of NCCL in relation to sex
According to studies by Medeiros et al. (2020), Akmal, Adimulapu and Duraisamy (2020) were male and 10 were female, without an elaborated choice criterion, only a group of patients who presented for dental treatment. In the study by O'Toole and Bartlett (2017), patients with the presence of cervical lesions with or without dentin hypersensitivity (DH) were evaluated, of which men were more prevalent with cervical lesions without HD (54%).
Swalani et al. (2016) observed a prevalence of NCCL was almost equally distributed between men and women (15:14) ( Table 1).  In the works by Ispas et al. (2016) and Yang et al. (2016), there was no difference between the sexes, as they researched the same sample number.
After analyzing the search results, the percentage of the number of men and women who had NCCL was measured.
Although females had a higher incidence of 51%, this percentage was not significant when compared to males (49%) ( Figure   2).

Prevalence of NCCL in relation to age
The only study that reported patients presenting with NCCL in the age group of 6-11 was the study by Chiriac et al. (2019), as it studied the relationship of children and the main associated risk factors at this age. In both studies by Alvarez-Arenal et al. (2019), they only presented data in relation to the age group of 12-30 years, as they studied a specific group of students with an average age of 24.5 years. In the study by Seong et al. (2018), only the age group of young adults was analyzed, as it wanted to relate which are the most frequent risk factors in this population, thus presenting a higher number exclusively in the age groups 12-30 and 31-50, with percentages of 78% and 22%, respectively. Most studies (Akmal et al., 2020;Zuza et al., 2019;Kolak et al., 2018;Seong et al., 2018;Shrestha et al., 2018;O'Toole et al., 2017, Yoshizaki et al., 2017Yang et al., 2016 andLai et al., 2015 find a higher prevalence in the age group of over 51 years (36%), followed by the age group of 31-50 years (34%), in these studies, a response to this high in these ages is explained by the possibility of being exposed to possible risk factors for a longer time (Table 2). According to the data collected in the literature search, a graph was made with the sum of the ages of each group, and a higher percentage was observed in people over 51 years old (36%) with n = 1676, followed by the group of 31 -50 years (34%) with n = 1615 ( Figure 3).

Age
Author , Figure 3. Prevalence of NCCL in relation to age.

Risk factors
According to Medeiros et al. (2020), 11.2% of the group analyzed with NCCL had a history of GER. Also  Kolak et al. (2018), frequent consumption of citrus fruits was evaluated p=0.003, which was significant for the association of NCCL. In the study by Teixeira et al.,2018 andSwalani et al. (2016), there was an association of acidic diet with cervical lesions, but did not obtain a significant p-value, p=0.746 and p=0.558 respectively. The high frequency of consumption of acidic fruits was a possible risk factor for NCCL (Yang et al., 2016). In the study by Lai et al. (2015), this risk factor was only statistically significant in the group of patients over 65 years old (p=0.009).
Parafunctional habits involve bruxism and clenching. For Medeiros et al. (2020) and Teixeira et al. (2018), there was an association of parafunctional habits between the groups studied for the appearance of cervical lesions, but it was not statistically significant, p=0.642 and p=0.606 respectively. In the study by Zuza et al. (2019) obtained a p-value of 0.018, which is a significant value for the association. According to Lai et al. (2015), bruxism was only statistically significant in the group of patients over 65 years old p=0.022.
The risk factor for occlusal disorders constitutes a set of problems that include occlusal trauma, malocclusions and occlusal interferences. In the study by Medeiros et al. (2020), an association with malocclusions was observed, but it was not statistically significant p=0.762. In Alvarez (2018), when it comes to the influence of oral hygiene factors, the analysis showed a significantly higher frequency of multiple lesions among individuals who brush their teeth once a day compared to those who brush their teeth twice or more (p = 0.005) and among patients who do not brush without knowing the type of brush they use (p = 0.006). The following relationships were analyzed: toothbrush size, brushing technique, toothpaste type, brushing force and brushing frequency, and for all they were statistically very significant with p-value <0.001 (Ispas et al., 2016). According to Yang et al. (2016), found in their study a strong correlation with the emergence of cervical lesions and brushing force <0.05 and in Lai et al. (2015) for vertical brushing technique in younger patients had a significant relationship with cervical lesions (< 0.001).

Chart 2. Main risk factors in the literature.
Source: Authors.
According to the analysis of the literature studied, the most frequent risk factors in the studies were acidic diet (13

Discussion
The objective of this integrative review was to determine the prevalence of Non-Carious Cervical Injuries (NCCL) in relation to age, sex and which risk factors are most associated with the disease. A search of publications in English and publication date in the last five years was carried out. Observational studies were searched in order to achieve this comparison between the groups of patients with and without NCCL to assess the prevalence of the disease between females and males. The age of the patients was categorized for statistical convenience as 6-11, 12-30, 31-50 and over 51 years old and their main risk factors most cited in the literature.
Although many researchers have discussed this relationship between the presence of NCCL in younger patients as a result of lifestyle, due to the search for healthier habits such as acidic food intake and physical activities, in addition to the daily stress and anxiety of modern life, causing clenching In the electronic search, this more current relationship was not found (Teixeira et al., 2020). Based on existing data, the difference between the prevalence for genders did not reach a significant percentage, on the other hand, in relation to the prevalence in relation to age, a higher percentage was observed in older patients, explained in the literature due to the longer duration of treatment exposure to risk factors. The most cited possible risk factors in the literature were gastroesophageal reflux, acidic diet, parafunctional habits, occlusal disorders and problems related to brushing. The acidic diet was the most cited factor in the literature, being more present for the appearance of these lesions, with a percentage of 76.4%.
In relation to males and females, there was a greater propensity for females, but without a significant percentage, 51% were observed. In most cases, cervical lesions are more common with increasing age, but are inaccurate in terms of sex.
However, several studies (Akmal et al., 2020;O'toole & Bartlett, 2017;Zuza et al., 2019, Kolak, et al. 2018, have reported the difference in the prevalence of cervical injury between men and women. Radentz et al. (1976) revealed that men have more injuries compared to women, with the difference between the sexes coming closer to having statistical significance. As also in the study by Akmal et al. (2020), there was a higher prevalence of cervical lesions in males (70.9%) compared to females (29.1%). The higher prevalence of cervical abrasions is often attributed to the application of greater force and longer duration of toothbrushing by men compared to women (Akmal et al., 2020). Yan and Yang (2014) cited the habit of brushing the teeth as one of the main etiological factors of cervical abrasion, mainly in terms of its technique, frequency and brittle hardness. A previous study (Turssi et al., 2019), reported a statistically significant association between abrasion and brushing habits, which includes brush change technique, frequency and time. Akmal et al. (2020) revealed that men tend to brush their teeth longer with more pressure, which explains the higher incidence of cervical abrasion in men than in women.
Other studies have reported a female predilection when it comes to cervical injuries (Shrestha & Rajbhandari, 2018;Seong et al., 2018). The difference in the distribution of NCCL between men and women can be explained by the greater masticatory force (greater occlusal loads generate greater concentrations of stress), which makes the tooth structure more susceptible to other risk factors. Interestingly, women were more likely to have NCCL with a history of HD, which may be associated with healthy oral habits or frequent intake of acidic foods and the presence of a lower pain threshold than men (Teixeira et al., 2018). However, there are some studies that show no relationship between sex and the prevalence of NCCL (Rusu et al., 2019;Yoshizaki et al., 2017;Ispas et al., 2016;Sawlani et al., 2016;Yang et al., 2016;Lai et al., 2015).
Although it had a higher prevalence in older patients, studies support the influence of age on the presence of NCCL and the idea that the onset can occur at very young ages (Chiria et al., 2019;Seong et al., 2018). A study involving Brazilians aged 40 to 60 years reported a prevalence of NCCL of 67% while a population aged 35 to 74 years in China had a prevalence of 81.3% (Smith et al., 2018;Lai et al., 2015). However, a recent clinical trial with patients aged between 18 and 40 years treated for NCCL and cervical HD at a Brazilian university revealed a prevalence of 88.1% and also suggested an increasing distribution of the disease among young people (Teixeira et al., 2018).
As demonstrated in previous studies (Kolak et al., 2018;Yang et al., 2016;Lai et al., 2015) and in this review, age may be a determining factor for the prevalence of NCCL, since older populations are probably exposed to etiological factors for a longer time than younger women. Among individuals with neck injury, most of them are in the age group of over 51 years (36%), while individuals between 12-30 years of age (20%) are the least affected with neck injury in this study, not taking into account considering the only study that approached children with NCCL with a very expressive number of participants. These results are in agreement with a study that analyzed the frequency of NCCL in patients referred to a particular dental school in which the highest frequency of patients with NCCL was recorded in the age group over 55 years (94.7%), while these injuries were less represented in the younger age group (35.2%) (Kolak et al., 2018).
The most likely reasons for such a distribution of NCCL are the cumulative effect of a large number of etiological factors over a long period of time, a greater degree of gingival recession, fewer teeth present and, therefore, greater occlusal load, loss of protective mechanisms. of natural dentition, reduction in the quality and quantity of saliva, structural and microstructural changes in enamel and dentin that are related to the aging process (Kolak et al., 2018). The etiology of NCCL is a matter of numerous controversies, it is believed that these lesions occur as a result of several mechanisms, acting alone or simultaneously. These mechanisms include: friction (abrasion and attrition), biocorrosion (chemical or electrochemical degradation) and occlusal stress, resulting in compression, bending and tension, which in turn lead to microfractures and wear of this more fragile JCE region due to its anatomy (Grippo et al., 2012).
The multifactorial nature of NCCL may be responsible for these discrepant results among the evaluated studies.
Perhaps one of the causal factors of NCCL could be acting more intensively in a given population, providing specific characteristics in each study in this review. This integrative review analyzed the main etiologic factors suspected of causing NCCL: diet, tooth brushing, medical conditions, adverse habits and occlusal forces.
The role of gastroesophageal diseases in the progression of tooth surface loss is much studied. A systematic review and meta-analyses clearly demonstrated that individuals with GER are more likely to have erosive tooth wear compared to controls without GER (Jordão et al., 2020). Alaraudanjoki et al. (2016) demonstrated that repeated or prolonged exposure of teeth to gastric acids leads to the selective dissolution of specific components of the tooth surface, causing loss of structure and dentinal hypersensitivity. The severity of tooth wear and chemical degradation of structures due to gastroesophageal reflux, for example, is correlated with disease duration and frequency, pH, acid type, salivary quality and quantity, and buffering capacity (Parkinson et al., 2010).
Regarding the acidic diet, the variables are large for each study, the concept of acidic diet encompasses many foods, such as solids, for example acidic fruits, as well as liquids, for example cola-based soda, wines, lemon "shot", and there is no standardized method in the literature to adequately evaluate an acidic diet. In a study involving male soccer players who consumed pure lemon juice on an empty stomach, an association with the presence of NCCL was observed in all of them (Medeiros et al., 2020). Other literature has shown that the consumption of citrus fruits and juices, soft drinks, alcohol and vitamin C tablets is recognized as a source of aggression to the tooth structure, which is associated with the presence of NCCL (Smith et al., 2008). According to an in vitro study, it was concluded that all acidic beverages tested in the research showed erosive potential and caused the morphological changes of the JCE in which the highest degree of damage to the JCE was found in the Red Bull®, Coca Cola® and Juice groups. orange, while the lowest grade was recorded in the samples of the white wine group (Mitic et al., 2019). Similarly, an earlier European study with a large sample of 3,187 subjects used descriptors to measure how high a patient's acid intake was (Bartlett et al., 2013) and found that fresh fruit and juice intake was positively associated to tooth wear. Thus, in the analysis of the most associated risk factors, the acidic diet had a greater number of citations, a total of thirteen articles, being quite conniving with the world literature, which makes us really believe that it plays a very important role in the development of NCCL.
For parafunctional habits, occlusal parafunction is more likely to favor the loss of tooth substance in the cervical region than physiological processes (Grippo, et al., 2012), as the magnitudes of force during bruxism are much greater than the magnitudes of force during bruxism. loads of normal functional activity (Suit, Gibbs and Benz, 1976). According to a recent study, a higher frequency of bruxism was observed in groups with NCCL than in groups without this parafunction (Zuza et al., 2019). However, it was also seen in another study that teeth grinding is considered a factor of exacerbation of NCCL, rather than a causal factor itself and that the combination of bruxism, acidic foods, consumption of drinks and abrasion can potentially lead to progression of the NCCL (Imfeld, 1996). In a Chinese study, which analyzed the prevalence of NCCL in an older population, the results indicated that elderly people who bite hard objects have a higher risk of NCCL, since biting hard objects can produce large occlusal loading forces and cause strong stress in the cervical region, which can cause tooth enamel to collapse (Lai et al., 2015). An experimental study confirmed that in abnormal occlusion, the pressure in the cervical region increases, while in normal occlusion the pressure was lower. As the tooth flexes, tensile and shear stresses are generated in the cervical region of the tooth, causing the bonds between the hydroxyapatite crystals to break, leading to the formation of cracks and eventually, thus, a new, less resistant crystal structure is formed and more easily attacked by other chemical or mechanical factors, favoring enamel loss and cervical wear (Lee & Eakle, 1996).
When dealing with occlusal disorders, it was possible to highlight this risk factor in the literature as occlusal trauma, malocclusions and occlusal interferences. This general term was chosen based on what was most often cited in the literature.
Results of a case-control study observed a greater chance of influence of premature contacts with the progression of cervical lesions (Alvarez-Arenal et al., 2019, 1). In the other, was showed that all occlusal factors that proved to be risk factors such as protrusive interferences and friction or simply having a significant association in the univariate analysis, can transmit early stress to the JCE thus initiating a NCCL, without the need for the simultaneity of other factors or situations that increase the frequency and severity of injuries with aging. These factors and situations include changes in the composition and microstructure of enamel and dentin, more frequent vertical cracks and microfractures in older enamel, greater gingival recession and bone loss with greater root surface and exposed cementum, long-term exposure to cervical stress factors and longer action time of other factors not related to the occlusion. (Alvarez-Arenal et al., 2019, 2).
The influence of brushing, which is considered an abrasion event, remains controversial on the possibility of progression of NCCL. According to some authors, under normal and proper use, brushing with toothpaste would cause minimal lifelong dentinal wear (Shellis & Addy, 2014). Other studies claim that the high prevalence of lesions on the buccal surface of the teeth automatically implies the influence of brushing on the formation of NCCL (Khan et al., 1999), which is in line with a Chinese study, in which it was found that the force of brushing was a risk factor for the presence of NCCL and in this same study, the interactive effect of the groups with heavy brushing, inadequate technique and consumption of fresh fruits at least once a day was considered an evident risk factor for patients with NCCL (Yang et al, 2016). On the other hand, a systematic review (Heasman et al., 2015) suggested that data to support the association between toothbrushing and NCCL remain largely inconclusive and that long-term projects need to be undertaken to confidently determine whether this factor consists of predisposition, or is only associated with the aforementioned alterations.
An interesting finding about the selected studies is that most showed that the multiple effects of the interaction of risk factors for the development of NCCL were evidently greater than with just a single risk factor. The interactive effects of several factors on patients may be involved in the occurrence and progression of NCCL. Thus, a comprehensive prevention and treatment strategy should consider the interactive effects of multiple risk factors, in line with the theory of the disease being multifactorial.

Conclusion
Regarding prevalence, there was a slight predilection of 2% for females and for those over 51 years of age, however, the most cited risk factor in the scientific literature was the acidic diet. The association of the diagnosis with the knowledge of the causes of the lesions makes the professional capable of transmitting necessary information for the instruction of patients susceptible to NCCL.