Association of Non-carious Cervical Lesions with Oral Hygiene Aspects and Occlusal Force

<jats:title>Abstract</jats:title>         <jats:p>One of the theories that contribute to explaining the evolution of non-carious cervical lesions (NCCLs) refers to fatigue wear, in which the concentration of stresses in the cervical region leads to the formation of microfractures in the dental tissues and progressive structure loss. However, due to a combination of factors that may cause wear, there is still uncertainty about the role of the occlusal factor as a risk factor that causes NCCLs. <jats:bold>Objectives:</jats:bold> The purpose of this case-control study was to investigate the association between the presence of NCCLs with occlusal force and other potential risk factors. <jats:bold>Materials and Methods:</jats:bold> Thirty-nine participants with NCCLs (cases) and 39 non-carrier patients (control), aged between 20 and 59 years old, were enrolled in the dental clinic of the Faculdade Integradas São Pedro (FAESA), located in Vitória, Espírito Santo State, Brazil. Information was collected through anamnesis, clinical examination, and a questionnaire addressing aspects related to tooth brushing, dentifrice, and mouthwash use. In clinical examination, patients were submitted to four measurements of occlusal force in the maxillary first premolars and maxillary first molars, using a strain gauge sensor of medium intensity, the Flexiforce (Tekscan, South Boston, MA, USA). The sensor was calibrated for the unit of measurement in Newtons (N). <jats:bold>Results:</jats:bold> Data was analyzed using a Student's t-test and multiple logistic regression, adopting the significance level of 5%. There was no statistically significant difference between the case and control groups regarding the bite force in the four measured regions. Logistic regression identified sex as a factor significantly associated with non-carious cervical lesions (p = 0.020). For the calculation of the odds ratio, the female sex presented a six-fold chance (OR = 6.082; CI = 1.332 - 27.765) higher than non-carious cervical lesions. <jats:bold>Conclusions:</jats:bold> It was concluded that females presented a higher risk factor for non-carious cervical lesions than men, whereas there was no association of occlusal strength, as well as aspects related to brushing and deleterious habits.<jats:bold>Clinical Relevance:</jats:bold> NCCLs are highly prevalent in daily clinical practices and can impact aesthetics and function, leading to hypersensitivity and impairment of oral-health-related quality of life. Gingival recession is an important clinical indicator for the presence of NCCLs.</jats:p>

section_content: Dental enamel is a highly crystalline structure composed of 96% of its constituents of mineral nature limiting the elasticity of the tissue. Dentin has a mineral content of approximately 70%, being the rest of its composition of proteins, lipids, and water that provides a certain degree of elasticity [1, 2]. One of the processes that can affect this natural interaction is dental wear, mainly in the cervical region, where the enamel is thinner, forming non-carious cervical lesions (NCCLs) which is a common condition found regularly by clinicians. 

In general, it is believed that NCCLs are not caused by a single factor, but rather by a combination of factors. NCCLs have a multifactorial origin and progression, and the contribution of these various processes is not yet well de ned in the scienti c literature. Among the processes that cause NCCLs are abrasive, corrosive, and fatigue wear. The diagnosis of NCCLs can be based on a detailed history, visual inspection, and intraoral examination [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13]. 

Based on its clinical characteristics, some NCCLs, have been labeled as abfraction lesions. This term was established by Grippo in 1991 [14], from the Latin ab = out and fractio = fracture. The abfraction hypothesis is based on the biomechanical theory that there is a concentration of tension in the cervical region caused by the exion during occlusal loading, resulting in the formation of cervical microfractures, ultimately causing the rupture between the apatite crystals of the enamel and the dentin [7, [15] [16] [17] [18]. From the clinical point of view, this lesion initially presents as minor grooves, which gradually undergo a process of fatigue wear caused by occlusal load, culminating with the formation of a wedge-like lesion, ending in thin and delicate enamel. 

When the affection progresses, radiographically it will show an increased thickening of the periodontal ligament and lamina dura. One possible explanation for these lesions is the traction forces in the region of the vestibular and palatine alveolar bone caused by oblique loads during eccentric movements. Since bone is thinner in the vestibular region, the compressive force may be more critical on the surface, promoting a vestibular bone loss accompanied by a gingival recession. This favors the progression of non-carious lesions on the buccal aspect of teeth since there is a loss of support with the loss of enamel structure in the cervical region. This is especially true in patients with decreased mucosal keratinization and ne gingival biotype [2, [18] [19] [20]. 

Abrasion consists of the wear of dental tissues through frequent contact of objects which results in mechanical wear, while erosion is the chemical loss of hard dental tissue by the action of intrinsic and extrinsic acids [21, 22]. The occlusal factor is discussed in the literature as a possible factor that may be associated with the etiology and progression of non-carious cervical lesions, usually related with occlusal trauma by lateral forces, a subject not well described in the literature [10, 16, 23, 24]. 

Since there is still a lack of information correlating certain factors such as occlusal force, deleterious habits such as biting objects, and oral hygiene habits with the progression of NCCLs, the purpose of this case-control study was to investigate the association between the presence of non-carious cervical lesions with occlusal force and other potential risk factors such as sex, brushing, age and deleterious habits.
section_name: Introduction

section_name: Materials And Methods

section_content: This study was approved by the Ethics Committee of the Faculdade Integradas São Pedro (FAESA) with the number: 850. 991 and validated by the Ethics and Research Committee of the São Leopoldo Mandic School.
section_name: Ethical aspects

section_content: The sample size was determined based on a pilot study of 15 patients. The parameters used in the calculation were: signi cance level of 5%, mean of the sample of the case group of 165. 3 N (SD 33. 8 N), mean of the control group sample of 193. 3 N (SD 41. 8 N), with 90% test power and 1: 1 sample ratio. Thus, a sample size of 39 patients was established in each group. The program used for the calculation was BioEstat 5. 0 (Instituto de Desenvolvimento Sustentável Mamirauá, Tefé, AM, Brazil). 

The participants were recruited among the patients in attendance at the dental clinics of the undergraduate course in Dentistry of the Faculdade Integradas São Pedro, FAESA, located in the city of Vitoria, ES, Brazil. 

In the case group, the patients were selected through a clinical examination performed by the same trained operator. These patients presented non-carious cervical lesions of the abfraction type located in the premolar and lower or mandibular teeth, this diagnosis was based on the clinical characteristics described by Consolaro and Consolaro (2006) [2] and Hayashi et al. (2022) [25]. According to the authors, lesions are located at the wedge-shaped cervical region and may present grooves resulting from the loss of enamel from the fractures, which can be diagnosed visually or with the aid of a very ne exploratory probe. 

The inclusion criteria for this study consisted of ASA I patients with at least 28 teeth not considering the presence of third molars, that didn't report any odontalgias, periodontal disease, and temporomandibular disorder. The exclusion criteria consisted of patients aged less than 20 years or older than 59 years, report of hallucinogenic drug use, use of drugs associated with xerostomia, and patients that reported history of anorexia bulimia and gastroesophageal re ux disease. Additional exclusion criteria included patients with current or previous orthodontic appliances, high alcohol consumption, smokers, and history of bruxism. The later was assessed using the questionnaire proposed by Pintado et al. (1997) [26], as shown in Table 1. If the patient responded positively to at least two questions in the questionnaire, they were considered ineligible to participate in the study. After assessing the location and characteristics of the abfractiontype lesions, the patient responded to a semi-structured questionnaire with questions about oral hygiene habits and deleterious habits such as biting objects (Appendix A). For the selection of patients belonging to the control group, all the exclusion criteria determined for the case group were maintained, differentiating only that for the control group patients did not present any cervical lesions.
section_name: Selection and characterization of the sample

section_content: The axial occlusal strength of both groups was measured using a strain gauge sensor of the exiforce type (Tekscan, South Boston, MA, USA) (Figure 1 ), which consists of a exible ultra-thin circuit with a thickness of 0. 208 mm. In this research, the medium intensity sensor (B201M, Tekscan, South Boston, MA, USA) was used; with sensitivity from 0 to 667 N. The active sensing area is a circle with a diameter of 0. 375 cm, located at the end of the sensor ( gure 2). The sensors are constructed of two layers of substrate, with a polyester lm. 

The measurements of the bite force were always performed in the morning between the hours 10:00 and 11:00. For standardization, each measurement was performed with the patient sitting in the dental operatory, with the device coated with plastic for biosafety control and supported by the opposing teeth ( gure 3). The patient was asked to perform the greatest clamping force possible for 2 seconds [27, 28]. 

Four measurements were performed for each patient, on both sides of the arch, in the sequence: 14, 16, 24, and 26, allowing for a 1-minute interval of rest for the patient between each region. The sensor was calibrated for unit of measurement in Newtons (N). All methods were performed in accordance with the relevant guidelines and regulations.
section_name: Assessment of axial occlusal force

section_content: The descriptive analysis was performed by means of absolute and relative frequencies, measures of central tendency, and dispersion. The comparison of bite force between the group of patients with noncarious cervical lesions (case) and without non-carious cervical lesions (control) was analyzed with a Student's t-test for independent samples. The logistic regression was used to verify if any factor had an in uence on the outcome. The likelihood ratio (OR) was also analyzed in the present study. The statistical software, SPSS Statistics version 21 (Armonk, NY, USA), was used to perform the statistical analysis.
section_name: Statistical analysis

section_content: Tables 2 and 3 describe the variables assessed in this study. Females make up 80. 8% of the total sample. The most observed type of brushing was horizontal (46. 2%). Most patients (61. 5%) brush their teeth three times a day. The type of toothpaste with abrasive particles was observed in 30. 8% of the patients, 62. 8% of patients reported the use of mouthwash which from those, 52. 0% reported daily use. Of the total sample, 32. 0% had some deleterious habit and 67. 9% used brushes with soft bristle consistency. There was no statistically signi cant difference (p = 0,188) in age when comparing the participants of the control group (mean = 31. 2 years; SD ± 11. 0 years) in relation to the case group (mean = 28. 2 years, SD ± 8. 8 years). When comparing the bite force between the case and control groups, no statistically signi cant difference was observed between them either when the measurement was conducted in the rst right upper premolar (p = 0. 724), in the upper right rst molar (p = 0. 790), in the left upper rst molar (p = 0. 964) or in the left rst molar (p = 0. 142). Table 4 shows the bite force load in premolars, molars, or overall, and did not present any statistically signi cant difference between men and women in the case group. In the control group, bite force was signi cantly higher in males, except for the rst left upper premolar, where there was no signi cant difference in bite force between males and females. If control and case patients were considered jointly, for all evaluated teeth, bite strength was signi cantly higher among men. There was no difference in the means of the bite forces between individuals of the case and control groups. Likewise, no signi cant difference was found when comparing males and females for bite force (table 5 ). Logistic regression was used to verify the association between the factors (questionnaire questions) and the outcome (patients with non-carious cervical lesions). The regression showed statistical signi cance for sex (p = 0. 020), with being female increasing the chances of having non-carious cervical lesion by 6. 1 times compared to men (table 6 ). 

Hard 0,999 0,000 0,000
section_name: Results

section_content: In the literature, there is a lack of consensus among authors regarding the role of occlusal overload in the etiology of non-carious (abfraction) cervical lesions. Among the main hypotheses that may contribute to the origin of these lesions are occlusal overload, malocclusion, horizontal forces, abrasion, and erosion. Therefore, the main purpose of this study was to investigate the association between the presence of non-carious cervical lesions with occlusal force and other potential risk factors such as tooth brushing and deleterious habits. 

In this research, the selection of patients was based on several factors that included age and number of teeth. Additionally, it was decided to include participants of 20 to 59 years of age since according to Helkimo et al. (1977) [29] for this age group, the maximum bite force remains constant, while the normal aging process past this age is known to cause loss of muscle strength and therefore yield lower occlusal forces. Additionally, patients also had at least 28 teeth in the dental arch to standardize the sample and maintain maximum bite force [30] [31] [32]. 

An important exclusion criterion was any pain reported by the patient that originated from the periodontium since according to Alkan et al. (2006) [33], patients with healthy support tissues show signi cantly greater bite force compared to patients with compromised periodontium [34]. Furthermore, patients with temporomandibular joint pain or pain at the masticatory muscles were ineligible because according to Pereira-Cenci et al. ( 2007 ) [35], the overall bite force of patients with any temporomandibular disorder is signi cantly lower. Also, the presence of pain or discomfort could limit the execution of the maximum bite force [35] [36] [37] [38]. Finally, individuals diagnosed with bruxism were also excluded from the study, as according to some authors [39] [40] [41]. 

To measure force, we selected to use a medium intensity sensor because it has a wide range (0 to 667 N), with a diameter of 0. 37 cm, which allows precision when placing intraorally, and a thickness of 0. 208 mm thus allowing the complete closing both arches during the measurement of the patient's maximum bite force. The most modern system for measuring maximum bite force is based on the action of the strain gauge's electrical resistance. This methodology can also be found in other studies [37, [42] [43] [44] [45] [46] [47]. 

Based on the results of the present study, there was no association found between the presence of noncarious cervical lesions and the mean occlusal strength measured at the rst right and left premolars and rst right and left molars. In a study by Wood et al. (2009) [20], authors also did not nd a relationship between the occlusal load and the progression or existence of non-carious cervical lesions, however, they evaluated the reduction of occlusal load through occlusal adjustments during the mandibular excursion movements [48]. 

On the other hand, the association between occlusal load and the initiation and progression of noncarious cervical lesions has been mentioned on several occasions in the literature [6]. Munari et al. (2015) [18] stated that the higher the strength concentration in the cervical area of the enamel the greater the probability of fracture [15]. Sawlani et al. (2016) [13], in a 5-year prospective clinical trial, tried to measure the relationship between NCCLs and various etiologic factors. It was concluded that the progression of NCCLs was related to occlusal load and not correlated to other factors such as a heavily acidic diet, toothbrushing techniques, and adverse oral habits [48, 49]. 

In the present study, when comparing the bite force between men and women, it was observed that in both case and control groups the mean values of bite force were higher for males. These ndings are in accordance with several studies [37, 42, 47, [50] [51] [52] [53] [54] [55], where a greater bite force was also found in men. Patients included in the present study were interrogated about their use of mouthwash, brushing habits such as frequency, hardness of bristles, type of toothpaste, and brushing technique. A signi cant association between the mentioned factors and NCCLs was not found. After NCCLs onset, other factors may in uence the progression of the lesion, including erosion. It has been pointed out in the literature [21, 24], that not only occlusion is related to NCCLs, but also chemical agents could be related to the etiology of erosion and physical factors such as abrasion. 

In the literature, Senna et al. (2012) [24], it has been a focus to associate occlusion and NCCLs, wherein this review the type of occlusion was not considered, whereas, in the present study, a physiological (nonparafunctional) occlusion was a main criterion for the inclusion criteria. Studies such as Koç (2011) [54] and Turkistani et al. (2020) [58] found no relationship between bite force and type of functional occlusion. In addition, Lee & Eakle (1984) [16] stated that the type of occlusion, when parafunctional, generates lateral forces yielding compression and traction loads larger than what natural dentition can withstand, thus suggesting that physiological occlusion is not a risk factor for NCCLs. 

In this study there was no association between bite force loads and NCCLs, therefore a prospective study is suggested since this case-control study cannot establish the cause-and-effect relationship between occlusal force and NCCLs. This is because occlusal strength may be the cause and/or consequence of NCCLs. Additionally, it would be noteworthy to evaluate additional factors such as erosion, abrasion, horizontal forces, and malocclusion and their relationship with the etiology and progression of NCCLs.
section_name: Discussion

section_content: Based on the results of this clinical study, it is concluded that females presented a higher risk for the development of non-carious cervical lesions meanwhile there was no association to occlusal force as well as other factors such as brushing technique and deleterious habits.
section_name: Conclusion

section_name: Funding Declaration

section_content: Dr. Diana Leyva del Rio has contributed in the material preparation, data analysis, review and editing of the manuscript. 

Balint Timothy Gabor Altdorfer has contributed with the statistical analysis and review of the manuscript. 

Dr. Cecilia Pedroso Turssi has contributed to the study conception and design, material preparation, data analysis, review and editing of the manuscript.

section_content: The authors have not received a grant for this project.
section_name: Funding Declaration

section_content: The study protocol and consent forms were approved by the Ethics Committee of the Faculdade Integradas São Pedro (FAESA) with the number: 850. 991 and validated by the Ethics and Research Committee of the São Leopoldo Mandic School. 

The clinicians treating patients at FAESA were told the information of this clinical research. The potential subjects were identi ed in the clinic of Prosthodontics at FAESA. The principal investigator con rmed the eligibility of these patients. 

All patients signed the consent forms and were informed of the details of the study procedures as well as potential complications. After informed consent was obtained, the occlusal bite force was registered by the device mentioned in the manuscript.
section_name: Ethics Approval

section_content: The manuscript is an original research that is not under publication consideration elsewhere and free of con ict of interest.
section_name: Con ict of interest

section_content: This is a list of supplementary les associated with this preprint. Click to download. 

AppendixA. docx
section_name: Supplementary Files