Dentine hypersensitivity and associated factors: a Nigerian cross-sectional study

Introduction Prevalence of dentine hypersensitivity (DH) may be on the increase as a result of changing lifestyles. This study aimed to assess the prevalence of DH and relative importance of associated factors in 18-35 year old Nigerians and compare to findings from a similar European study. Methods Following ethical approval, 1349 subjects from the six geopolitical zones in Nigeria participated in this cross sectional study. DH was clinically evaluated by cold air tooth stimulation, patient pain rating (yes/no) and investigator rated pain using the Schiff ordinal scale (0-3). Erosive tooth wear using the BEWE index was assessed. A questionnaire regarding the nature of the DH, erosive dietary intakes, tooth brushing habits and other factors was completed by patients. Bivariate analysis was conducted. Results 32.8% of patients reported pain on tooth stimulation and 32.9% scored ≥1 on Schiff scale for at least one tooth. Questionnaire reported sensitivity was 41.2%. There were statistically significant associations between Schiff score and clinically elicited DH (p < 0.001); and BEWE erosive tooth wear score and clinically elicited DH (p < 0.001). There were significant associations between DH and some oral hygiene practices such as brushing frequency, brush movement and brushing after breakfast. Fresh fruit and fruit/vegetable juice intake also showed significant association. Conclusion The most important risk factors of DH for this population in Nigeria appear to be the frequency and characteristics of tooth brushing. This should be considered in its prevention and management.


Introduction
Dentine Hypersensitivity (DH) is characterized by short sharp pain arising from exposed dentine in response to thermal, evaporative, tactile, osmotic or chemical stimuli that cannot be ascribed to any other dental defect or disease. It is an exaggerated response to a sensory stimulus that usually cause no response in a normal healthy tooth [1]. Other possible causes of pain that should be eliminated before a diagnosis of DH is made include fractured or chipped teeth, carious lesions, palatogingival grooves, leaky restorations and cracked cusps [2]. Dentinal pain is mediated by a hydrodynamic mechanism [3]. A pain provoking stimulus applied to dentine increases the flow of dentinal tubular fluids, this mechanically activates the nerves situated at the inner ends of the tubules. The pain thus initiated is often associated with mild to severe discomfort which often affects patients' eating and drinking habits [1], hence affecting their quality of life. It has been reported that cold stimulus is more effective in activating intradental nerves than do heat and probing [4,5]. This is supported by the observation that close to 75% of patients with DH complain of pain from cold stimuli [6]. The prevalence of DH varies from 1.34% to 98% [7,8]. Although DH may affect patients of any age group, it mostly occurs in patients who are between 30 and 40 years old [2], overall review of literature shows equal gender. Different distribution patterns have been reported [9], canines and premolars are most often affected [6,10] however, it may affect any tooth. DH condition starts with exposure of dentine by the loss of enamel and or gingival recession (with loss of cementum), this has been termed ´lesion localisation´. The exposure of root dentine secondary to gingival recession has been reported to be associated with overzealous tooth brushing [11], about 70% of people suffering from DH brush more than twice daily [12]. Not all exposed dentine is sensitive, there must be the opening of the dentinal tubule system to permit activation of the hydrodynamic mechanism by appropriate stimuli, termed ´lesion initiation´. This occurs when the smear layer and or tubular plugs are removed, which opens the outer ends of the dentinal tubules [13]. Abrasion and more importantly, dietary acid erosion may be implicated [14]. DH is more frequently encountered in patients with periodontal diseases [9,15].
Hypersensitivity has been reported to occur in about half of patients after periodontal procedures such as deep scaling, root planing and gingival surgery [16]. DH may also occur in non-carious cervical lesions especially when exposed to erosive foods and drinks. Although several risk factors leading to the exposure of dentine, tubular opening and subsequent pain have been identified, their relative importance has been controversial. DH is likely to increase in prevalence for a number of reasons; increase in life expectancy, retention of teeth throughout life, changing life styles notably diet, change from traditional African diet to western diet in urban city dwellers, and increased intake of fizzy drinks as seen in developing African countries. It was therefore the objectives of this study to determine by questionnaire combined with clinical examination the prevalence of DH and its associated factors in 18-35 years old Nigerians and to compare the findings to a similar study carried out in 18-35 years old Europeans [17]. and oral health behaviour, perception of dentine hypersensitivity including intensity, duration and origin. Following completion of the questionnaire, a clinical examination for dentine hypersensitivity, erosive tooth wear and loss of periodontal attachment was performed. All eligible teeth excluding the second and third molars were assessed for presence or absence of DH, erosive tooth wear and periodontal loss of attachment.

Methods
The exposed dentine surface of each eligible tooth was subjected to cold air stimulation by a one second application of air from the air spray of the dental unit or a triple air dental syringe from a distance of approximately 10 mm with adjacent teeth shielded. The patient´s response to the cold air stimulation was recorded by the examiner using the Schiff ordinal scale [19]: (0 = subject does not respond to stimulus, 1 = subject respond to stimulus but does not request discontinuation of stimulus, 2 = subject respond to stimulus and request discontinuation or moves away from stimulus, 3 = subject respond to stimulus, considers stimulus to be painful, and request discontinuation of stimulus). The patient was then asked whether the stimulus provoked DH or not. This procedure was undertaken for each eligible tooth in turn. Non-carious cervical lesions were evaluated using the Basic Erosive Wear Examination (BEWE) on the facial/buccal, lingual/palatal surfaces using an ordinal scale (0 = no erosive wear, 1 = early tooth loss, 2 = surface loss <50%, 3 = wear with tissue loss >50% of the surface) [20]. The location of the lesion (coronal surface, root surface or crown-root junction) was recorded.
Bivariate statistical analysis was carried out at the patient level.
Elicited sensitivity was related to several categorical variables. Odds ratios were reported in relation to the appropriate categorical variables, with 95% confidence intervals. The relationships between the measures of sensitivity i.e. DH on any tooth on cold air stimulation, Schiff score and questionnaire declared hypersensitivity; and of elicited sensitivity to tooth wear and recession were also analysed. Non-carious cervical lesions were evaluated using the Basic Erosive Wear Examination (BEWE) on the facial/buccal, lingual/palatal surfaces using an ordinal scale (0 = no erosive wear, 1 = early tooth loss, 2 = surface loss <50%, 3 = wear with tissue loss >50% of the surface) [19]. The location of the lesion (coronal surface, root surface or crown-root junction) was recorded. Bivariate statistical analysis was carried out at the patient level. Elicited sensitivity was related to several categorical variables. Odds ratios were reported in relation to the appropriate categorical variables, with 95% confidence intervals.
The relationships between the measures of sensitivity i.e. DH on any tooth on cold air stimulation, Schiff score and questionnaire declared hypersensitivity; and of elicited sensitivity to tooth wear and recession were also analysed.

Results
In all, 1349 adults were recruited. The mean number of teeth evaluated for DH in each subject was 23.7 (range [19][20][21][22][23][24]. The mean number of teeth with DH was 6.36 (range 0-18). Data analysed was based on number (n) that responded to the variable of interest in the questionnaire. Table 1 Table 2 shows that there was a statistically significant association between self-reported hypersensitivity and clinically elicited sensitivity (p < 0.001); Schiff score and clinically elicited DH (p < 0.001). This table also shows the association of elicited DH with erosive tooth wear. There were significant associations between elicited DH and erosive tooth wear (p < 0.001. There was a closer relationship between maximum BEWE score and elicited sensitivity. Table 3 shows the relationship of elicited DH to a range of subject's associated demographic factors. While Table 4 shows only subjects' associated oral hygiene and dietary factors that had significant association. Statistically significant associations were found between elicited sensitivity and some sociodemographic characteristics like age, area of residence (rural or urban), and level of education (p < 0.001). Some oral hygiene factors such as brush frequency, brush movement, brushing after breakfast were statistically associated with elicited sensitivity. Also, elicited sensitivity was statistically associated with fresh fruit intake and fruit /vegetable juice intake (p < 0.001). Other life-style factors such as smoking, use of certain medications, snoring and chewing gum did not show statistical significance (Annex 1).

Discussion
This clinical and questionnaire based cross sectional study among young Nigerian adults to determine the prevalence of DH and its associated factors, presents data among public hospital attending participants just as the European study by West et al [17]. These 2.8% [22] and in Australia 9.1% [23], the reported prevalence of the present study (32.8%) was very high. Particularly, the higher prevalence of DH recorded in this study when compared to previous clinical studies [7,21] among Nigerian population, suggest that dentine hypersensitivity may be on the increase in our environment.
The clinical prevalence of DH (32.8%, 32.9%) versus self-reported DH (41.2%) in this present study further support reports that prevalence data obtained from questionnaires based studies were often a little higher than that obtained by clinical examination [24][25][26]. It has been suggested that the majority of patients demonstrated some coping mechanisms for dealing with pain as shown by the findings of the European study where peoples' perception of their pain is less than that of clinical reporting [17]. This is contrary to the findings of the current study where peoples' perception of their pain is more than that of clinical reporting. However, a sizeable percentage (27.5%) in the present study felt that the pain intensity was ''very important'' to their lifestyle, this should be put in proper perspective when considering the treatment need for this condition and its impact on the quality of life. There was no differences in the prevalence of DH according to gender in the present study and the European study [17]. Similar studies [24][25][26] have reported the same findings, while others [27,28] have reported a female preponderance. This study finding corroborate the observation from the European study that the clinical elicited method of assessing DH correlate with the Schiff score for pain of DH. Also, there were significant associations between elicited sensitivity after stimulation and erosive wear which reinforced the similar findings reported in the European study [17]. A range of potential associated factors to DH were assessed in this study. The results showed a significant association of DH with tooth brushing frequency, and brushing after breakfast. More than 60% of participants brushed their teeth 2 or 3 times daily. These associations may also be due to the erroneous believe that the harder the tooth brush and force of brushing, the cleaner the teeth becomes. A combination of these factors will definitely lead to loss of dental hard tissue with dentine exposure. Brushing after breakfast will further enhance the hard dental tissue loss due to dietary acid challenge. In contrast to our findings, the frequency and characteristics of tooth brushing were not significantly associated with DH in the European study [17]. Rather, erosive dietary factors played significantly in the DH experienced by the young European studied [17].

Conclusion
The prevalence of DH in young Nigerian adults (18-35years) is low compared to their European counterparts. Dentine hypersensitivity may be on the increase and most important risk factors for dentine hypersensitivity among young Nigeria adult population appear to be the frequency and characteristics of tooth brushing. This should be considered in its prevention and management.

What is known about this topic
 Dentine hypersensitivity is a distinct clinical phenomenon whereby dentine is exposed and reactive;  Dentine hypersensitivity have been associated to oral hygiene and acidic dietary risk factors.

What this study adds
 Important risk factors for dentine hypersensitivity is different among populations.

Competing interests
The authors declare no competing interests.

Acknowledgements
The authors acknowledge GlaxoSmithKline Consumer Nigeria PLC for supporting this study with a grant. The funders had no role in study design, data collection and analysis, or preparation of the manuscript. Tables   Table 1: prevalence of hypersensitivity by 3 criteria   Table 2: relationship between three measures of sensitivity and of elicited sensitivity to tooth wear