Journal of Oral Rehabilitation 2006 33; 17–25
Epidemiological evaluation of the multifactorial aetiology of abfractions O . B E R N H A R D T * , D . G E S C H †, C . S C H W A H N * , F . M A C K ‡, G . M E Y E R * , U . J O H N § & T . K O C H E R ¶ *Department of Restorative Dentistry, †Department of Orthodontics, ‡Department of Prosthodontics, School of Dentistry, §
Institute of Epidemiology and Social Medicine and ¶Unit of Periodontology, Department of Restorative Dentistry, School of Dentistry, University
of Greifswald, Greifswald, Germany
SUMMARY The purpose of this study was to determine
risk indicators for the aetiology of abfractions (cervical wedge-shaped defects) on teeth using dental and medical variables obtained in a populationbased sample of the cross-sectional epidemiological ‘Study of Health in Pomerania’ (SHIP). Medical history, dental, and sociodemographic parameters of 2707 representatively selected subjects 20–59 years of age with more than four natural teeth were checked for associations with the occurrence of abfractions using a two-level logistic regression model on a tooth and a subject level. The estimated prevalence of developing abfractions generally increased with age. The following independent variables were associated with the occurrence of abfractions: buccal recession of the gingiva, odds ratio (OR) ¼ 6Æ7; occlusal wear facets of scores 1, 2 and 3, OR ¼ 1Æ5, 1Æ9, 1Æ9; tilted teeth, OR ¼ 1Æ4; inlays,
Introduction Defects in the tooth’s cervical region are commonly observed in daily practice. This usual non-carious substance loss can lead to pronounced aesthetic limitations and, in extreme cases, to tooth fractures (1). Non-carious cervical defects occur in various forms and to different extents. In addition to superficial erosions, hollows, or notches, pronounced abfractions or wedge-shaped defects manifest with a typical coronal borderline to the intact enamel (2). Further identifying characteristics of these defects include the unmistakeable wedge shape when viewing the tooth laterally, and the uniformly observed occurrence of abfractions ª 2006 Blackwell Publishing Ltd
OR ¼ 1Æ6; toothbrushing behaviour, OR ¼ 1Æ9 to 2Æ0 (two and three times a day versus once a day). First premolars had the highest estimated risk for developing abfractions, followed by the second premolars. Maxillary and mandibular teeth behaved similarly in terms of abfractions, with the exception of mandibular canines, which had a much lower estimated risk of incurring abfractions than did maxillary canines. The results of this analysis indicated that abfractions are associated with occlusal factors, like occlusal wear, inlay restorations, altered tooth position and tooth brushing behaviour. This study delivers further evidence for a multifactorial aetiology of abfractions. KEYWORDS: abfraction, non-carious cervical defect, wedge-shaped defect, toothbrushing, epidemiology, cross-sectional Accepted for publication 13 April 2005
almost exclusively on the vestibular surfaces of the teeth (3, 4). The origin of abfractions is a very contentious issue even today. Several theories explaining the origin of cervical lesions are offered: abrasion of hard dental tissue during toothbrushing, chemical erosion via exogenous and endogenous acids, and occlusal loading (4–8). A relationship between brushing technique, brushing force and the occurrence of cervical lesions has been confirmed by various authors (5, 9). Erosion in the cervical region can result from both exogenous – e.g. excessive consumption of acidic food and drink or occupational exposure to acidic vapours
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O . B E R N H A R D T et al. via inhaling – and endogenous factors, e.g. bulimia nervosa (6, 8, 10). Further, excessive occlusal loading of the teeth because of dysfunction of the masticatory system, malpositioned teeth and bruxism is thought to lead to the formation of cervical lesions. According to this theory, the tooth is elastically deformed, causing disruption of the prismatic structure at the site of least resistance, namely, the tooth cervix (4, 11). Non-axial forces on occlusal and palatal guiding surfaces of teeth in an acid environment may increase the damage at the cervical margin. This effect is called stress corrosion and is better known in the engineering field (12). In a recent in vitro study 8% of the test teeth developed abfraction-like lesions under stress and 10% sulphuric acid. None of the control teeth, that where placed in 10% sulphuric acid without occlusal loading developed such lesions (13). Some authors consider the aetiology of cervical defects to be a multifactorial process in which not just one or two but many of the processes mentioned above are involved in the genesis of non-carious hard tooth substance loss (14–17). The purpose of this study was to investigate the aetiology of non-carious cervical defects on teeth using dental and medical findings obtained in an epidemiological cross-sectional study.
Materials and methods Sample structure From the population-based cross-sectional ‘Study of Health in Pomerania’ (SHIP), 2707 subjects aged 20–59 years (mean age 40Æ6 11Æ1 years) with more than four natural teeth were chosen. The SHIP is a population-based cross-sectional study intended to systematically describe the prevalence of and risk factors for diseases common in the population of Pomerania in northern Germany. From 32 communities in the region, a random sample was drawn from residence registries, stratified by gender and age. The design of the study, recruiting of participants, and the scope of this population-based cross-sectional health survey was reported by John et al. (18). The gross sample comprised 6267 subjects with an age range of 20–79 years. The response rate of the study was 68Æ8%. Participants gave their written informed consent and the study was approved by the local ethics committee.
The study consisted of four parts: a medical and a clinical dental examination including the functional analysis, an interview and a questionnaire. In addition to a medical examination, the subjects had undergone a clinical dental examination assessing periodontal, orthodontic and cariologic data, and a clinical functional analysis. Eight experienced, calibrated dentists were the examiners. Training of the examiners and consensus discussions were carried out before the study started and took place twice a year while the study was running. Fourteen dentate volunteers were re-examined for evaluating the reproducibility of cervical defects and occlusal wear measurements. Intra-examiner reliability showed a range of Kappa values from 0Æ68 to 0Æ91 and interexaminer reliability varied from 0Æ53 to 0Æ74. For toothguided dynamic occlusion measurements in these 14 volunteers, intra-examiner reliability had a range of Kappa values from 0Æ62 to 0Æ88, and for interexaminer reliability from 0Æ58 to 0Æ79 (19).
Variables Screening for risk factors for the occurrence of abfractions included the following clinical and anamnestic data. Abfractions Visible, vestibular defects located at the cemento-enamel junction were evaluated. Defect edges had to form sharp angles (as checked with the periodontal probe PCP 11)*. The defects were recorded without gradation of lesion depth or width. The wedge shape had to be clearly discernable with a probe, even apically. Carious, erosive, or hollowed areas of hard substance loss were not counted as wedge shaped defects. Fillings in the cervical region were considered non-assessable in terms of abfractions. In subjects with four or more natural teeth, all teeth but the wisdom teeth were included in the analysis and classified according the FDI numbering system. Restorations Only those restorations were included in which the cemento-enamel junction was assessable (partial crowns, inlays, occlusal and approximal fillings). All partial crowns, inlays and fillings located on morphological occlusal surfaces were recorded independent of their contact situation. *HuFriedy, Chicago, IL, USA. ª 2006 Blackwell Publishing Ltd, Journal of Oral Rehabilitation 33; 17–25
MULTIFACTORIAL AETIOLOGY OF ABFRACTIONS Tooth elongation Teeth were defined as elongated if they protruded vertically beyond the occlusal plane, taking the sagittal and transversal compensation curve into consideration. If extensive tooth loss made it impossible to locate the occlusal plane, the criterion ‘tooth elongation’ could not be recorded and was considered not applicable. Tooth tilting Gap-adjacent and terminal teeth were evaluated for tilting in line with the dental arch and tilting towards the in- or outside of the arch. Occlusal wear Abrasion and attrition facets were registered if found on occlusal surfaces, incisal edges, or cusp apices. Occlusal dental hard-substance loss was recorded according to the method of Hugoson et al. (20) using the following gradation:
no or minimal (doubtful) enamel loss enamel loss/dentine spots loss up to one-third of the crown with obviously exposed dentine areas loss over one-third of the crown
0 1 2 3
Facets in restorations were recorded separately for all restored occlusal surfaces (fillings, inlays, partial crowns) and coded as present/absent. Recession of the gingiva Exposed portions of the buccal root surface were registered as gingival recession if the gingiva was located more than 1 mm below the cemento-enamel junction. Dynamic occlusion Tooth contacts were registered during physiological, tooth-guided mandibular movement in the regular dynamic occlusal zone. Definition of the dynamic occlusal zone: 1 Tooth-guided lateral movement of the mandible 3 mm to the right and 3 mm to the left of habitual contact position. 2 Tooth-guided protrusion movement of the mandible up to incisal edge contact of the maxillary and mandibular incisors, if this involved a distance of no more than 5 mm. Bruxism In the dental interview, the following questions were asked about bruxism: ª 2006 Blackwell Publishing Ltd, Journal of Oral Rehabilitation 33; 17–25
Do you grind your teeth? Do you clench your teeth? If yes, sometimes, often, or always? Both questions were combined in one variable in the statistical analysis. Frequency of toothbrushing The following answers were possible to the question about toothbrushing frequency: 1 Three or more times a day. 2 Usually twice a day 3 Once a day or less. Fruit juice The intake of fruit juices was also asked in the interview, with possible answers being daily intake, several times a week, once a week, several times a month, once a month, or never. Age and gender These two variables were taken from the medical interview.
Statistical procedures As tooth-related factors were to be tested in the risk analysis for the occurrence of abfractions, the patientrelated file was transformed into a tooth-related file. The advantage of this tooth-related file format consists in the ability to directly assign tooth-related characteristics to the occurrence of cervical abfractions (21). Special software for the statistical analysis of correlated data (SUDAAN 7.5.3)† was used to take into consideration the dependence among the teeth of a person. All factors assumed to influence abfractions were simultaneously examined for associations in a multivariable analysis; interactions between factors were also considered. This method delivers associations for all investigated variables with the dependent variable ‘abfraction’. These associations are expressed as odds ratios, e.g. a 1:1 ratio implies no increased estimated risk. In the model, variables become potential risk factors if the determined odds ratio clearly exceeds 1. Values between 0Æ9 and 1Æ1 yield no effect, values between 1Æ2 and 2Æ5 indicate a weak association between factor and disease/event, and the association is considered strong at values over 2Æ5 (22). †
Research Triangle Institute, Research Triangle Park, NC, USA.
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O . B E R N H A R D T et al. Table 1. Sample structure, frequency of subject-related variables (n ¼ 2707) Frequency total Variable Age groups (years) 20–24 25–29 30–34 35–39 40–44 45–49 50–54 55–59 Gender Male Female Bruxism Never Sometimes Often or always Tooth brushing Once a day Two times a day ‡ Three times a day Fruit juice Daily Several times a week Once a week Several times a month Once a month Never Abfractions 0 1–4 >4
n
%
264 321 370 375 355 352 319 351
9Æ8 11Æ3 13Æ7 13Æ9 13Æ1 13Æ0 11Æ8 13Æ0
1267 1440
46Æ8 53Æ2
Table 2. Sample structure, frequency of tooth-related variables
1836 646 225
67Æ8 23Æ9 8Æ3
Frequency within teeth with abfractions
398 2110 199
14Æ7 77Æ9 7Æ4
1040 775 229 236 149 278
38Æ5 28Æ7 8Æ5 8Æ7 5Æ5 10Æ1
1852 670 281
68Æ4 24Æ7 6Æ7
Only those factors demonstrating a significant association – corresponding to the preset level – to the presence of abfractions remained in the definitive model. A P-value of 0Æ1 was set as the acceptance level for inclusion in the model. All calculations were performed with the software programs SPSS 11Æ0‡ and SUDAAN 7Æ5Æ3.†
Results Table 1 contains the frequencies of the general characteristics of the subjects examined. A somewhat greater number of female subjects fulfilled the inclusion criteria for the risk analysis. The male:female ratio was 1:1Æ1. ‡
SPSS Inc., Chicago, IL, USA.
Out of all subjects, 23Æ9% reported sometimes clenching or grinding their teeth and 8Æ3% reported doing this often. 7Æ4 % of the subjects reported brushing their teeth three or more times a day and 14Æ7% brushed their teeth once a day or less. 24Æ7% of all subjects exhibited one to four abfractions; 6Æ7% had more than four defects. Table 2 displays the tooth-related characteristics of the groups. 5Æ3% of all teeth included in the examination exhibited abfractions. Premolars were the tooth type most frequently affected by abfractions. 26Æ9% of all teeth showed protrusion contacts, and teeth with laterotrusion contacts to the left or right
Frequency total Variable Teeth Central incisor Lateral incisor Canine First premolar Second premolar First molar Second molar Upper Jaw Lower Jaw Site Left Right Dynamic occlusion Protrusion Laterotrusion to the left Laterotrusion to the right Restoration Sound Partial crown Filling Inlay Recession Facets Degree 0 Degree 1 Degree 2 Degree 3 Facets in restorations Tooth tilting Tooth elongation
n
%
n
%
8971 8951 8912 7619 7055 5667 7029 25 347 28 857
16Æ6 16Æ5 16Æ4 14Æ1 13Æ0 10Æ5 13Æ0 46Æ8 53Æ2
261 269 389 878 569 384 99 1294 1555
9Æ2 9Æ4 13Æ7 30Æ8 20Æ0 13Æ5 3Æ5 45Æ4 54Æ6
26 599 27 605
49Æ1 50Æ9
1366 1483
47Æ9 52Æ1
14 096 10 050 10 492
26Æ9 20Æ5 20Æ1
570 658 538
20Æ6 23Æ9 19Æ5
33 510 180 19 627 8874 13 529
61Æ8 0Æ3 36Æ2 1Æ6 25Æ0
1604 14 1130 101 2198
56Æ3 0Æ5 39Æ7 3Æ5 77Æ0
16 776 25 557 11 125 746 6595 1557 1248
30Æ9 47Æ1 20Æ5 1Æ4 12Æ2 2Æ9 2Æ3
672 1350 779 48 473 130 99
23Æ6 47Æ4 27Æ3 1Æ7 16Æ6 4Æ6 3Æ5
Number of teeth ¼ 54 204, number of abfractions: 2849 (5Æ3%). ª 2006 Blackwell Publishing Ltd, Journal of Oral Rehabilitation 33; 17–25
MULTIFACTORIAL AETIOLOGY OF ABFRACTIONS were each found at a rate of about 20%. Within teeth with abfractions, only the number of laterotrusion contacts to the left was slightly higher. Of teeth with abfractions, only a slight difference according to side was discernable. 52Æ1% of abfractions were found on the right half of the mouth and 47Æ9% on the left. Almost 38% of the teeth had restorations, but only a small percentage of these were cast. Within the group with abfractions, the percentage frequency of teeth with inlays was over twice that found for the total group. 25% of all teeth and 77% of teeth with abfractions showed recessions on the buccal aspect. 31% of all teeth and 23Æ6% of teeth with abfractions had neither occlusal nor incisal facets. Compared with the group of all teeth, the group with abfractions had a higher proportion of teeth with second- and thirddegree occlusal facets and facets in restorations. In addition, teeth with abfractions also exhibited a higher percentage of elongations and tilting. Table 3 presents the significant odds ratios with 95% confidence intervals and significance levels of general and tooth-related variables which were associated with abfractions. The coefficient of determination (R2) of the model was 8%. The odds ratio for developing abfractions generally increased with age (except among 45- to 49-yr-olds). Gender-specific differences were not significant. This was also true for the parameters of dynamic occlusion, the comparison of right and left mouth halves, and the intake of fruit juices (P > 0Æ1). Recessions constitute a high odds ratio for abfractions, as also indicated by the prevalences (Table 2). Occlusal facets of scores 1 to 3 showed a significant effect on the formation of abfractions. A dose-response effect was evident for scores 2 and 3. Occlusal facets in restorations also proved significant, but the odds ratio of 1Æ2 cannot yet be considered an effect (22). Tilted teeth exhibited a 1Æ4-fold higher odds ratio for developing abfractions. Whereas fillings and partial crowns demonstrated no significant relationship, inlays were significantly associated with abfractions. Of the subject-related factors applied to the toothrelated analysis, toothbrushing behaviour was found to have a marked correlation with abfractions. The teeth of subjects who brushed two or three times a day were at about twice the estimated risk of developing ª 2006 Blackwell Publishing Ltd, Journal of Oral Rehabilitation 33; 17–25
Table 3. Odds ratios of significant variables for abfractions
Variable Age groups (years) 20–24* 25–29 30–34 35–39 40–44 45–49 50–54 55–59 Gender Male* Female Facets Degree 0* Degree 1 Degree 2 Degree 3 Facets in restorations Tooth tilting Restoration Sound* Partial crown Filling Inlay Toothbrushing Once a day* Two times a day ‡ Three times a day Bruxism Sometimes Often or always Buccal recession
Odds CI 95% CI 95% ratio lower value upper value P-value <0Æ001 1Æ49 2Æ14 2Æ12 2Æ71 2Æ31 3Æ05 3Æ37
0Æ84 1Æ39 1Æ27 1Æ66 1Æ40 1Æ83 2Æ03
2Æ64 3Æ55 3Æ53 4Æ42 3Æ82 5Æ10 5Æ59
ns <0Æ01 <0Æ01 <0Æ001 0Æ001 <0Æ001 <0Æ001 <0Æ001
1Æ01
0Æ84
1Æ21
ns <0Æ001
1Æ45 1Æ87 1Æ91 1Æ16 1Æ44
1Æ26 1Æ55 1Æ16 1Æ01 1Æ13
1Æ66 1Æ24 2Æ13 1Æ34 1Æ84
<0Æ001 <0Æ001 <0Æ01 0Æ04 <0Æ01 <0Æ01
1Æ37 0Æ98 1Æ60
0Æ65 0Æ85 1Æ14
2Æ85 1Æ13 2Æ11
ns ns <0Æ001 <0Æ001
1Æ87 2Æ07
1Æ36 1Æ32
2Æ56 3Æ24
1Æ21 1Æ16 6Æ69
1Æ00 0Æ82 5Æ66
1Æ49 1Æ54 7Æ92
<0Æ001 <0Æ001 <0Æ001 0Æ05 ns <0Æ001
*Reference group. CI, confidence interval; ns, not significant.
abfractions as the teeth of subjects who brushed once a day or less. Although bruxism was significant for abfractions, the effect was slight. Frequent bruxism was not significant. Figure 1 depicts the odds ratios of abfraction genesis by tooth type, including all variables examined. The maxillary canine was chosen as the reference tooth (odds ratio ¼ 1). Mandibular premolars had the highest odds ratio for developing wedge shaped defects, followed by the maxillary premolars. Maxillary and mandibular teeth behave similarly in terms of abfractions, with the exception of mandibular canines, which have a much lower odds ratio of incurring abfractions than do maxillary canines.
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Fig. 1. Odds ratios for abfractions of the different teeth (interactions of the upper and lower jaw), reference: upper canine (odds ratio ¼ 1).
By including the examiners in the model, significance levels or odds ratios of the independent variables were only slightly altered.
Discussion The data in the literature on the prevalence of noncarious cervical lesions are highly discrepant and are determined by defect criteria of the morphology. For instance, reviews report prevalences of 5% to 85% (23, 24). This high variance pinpoints the difficulty of defining what constitutes a non-carious cervical lesion. Due to the selection criteria (assessability of the vestibular cervical region), the prevalences listed are not representative for the assessment of tooth loss, extent of restorative/prosthetic work, etc, and serve only to describe the subjects in terms of abfractions. Clinical subdivision of cervical lesions into erosions and abfractions has been suggested and conducted by several authors (1, 23, 25). The criteria common to all were the typical wedge shape and sharply delimited borders. Prevalences of non-carious cervical defects found according to these criteria are rather comparable. For instance, Lussi et al. (1) reported an average of 3 abfractions in 19Æ1% of a group of 26- to 30-yr-old subjects and in 47Æ2% of a group of 46- to 50-yr-olds. Dawid et el. (25) examined 4367 German soldiers with average ages of 21Æ4 to 42Æ6 years and found 8% to
9Æ9% of soldiers not under stress to have abfractions, and 46Æ8% to 53Æ6% of soldiers under stress (pilots) to have them. In our study, 24Æ7% of all subjects exhibited 1 to 4 abfractions and 6Æ7% had more than 4. Other studies substantiate our finding that the number of defects per individual increases with age (26, 27). Larsson (26) detected twice the number of defects in the 41- to 55-yr-old group compared to the 26- to 40-yr-old group. Hong et al. (27) described an increase in abfraction frequency after age 20, culminating at 96Æ3% in the 51- to 66-yr-old age group. In studies with subjects grouped into several age categories, Bergstro¨m and Lavstedt (28), and Bergstro¨m and Eliasson (29) also showed that the number of cervical defects increase with age. It is difficult to construct an index appropriate for a subject-related risk analysis due to the secondary masking of abfractions by cervical fillings and crowns. Therefore, only subjects with more than 4 teeth without cervical restorations were included in the analysis. Today, it is generally accepted that multivariable analyses are preferable to bivariate analyses when screening for risk factors. Multivariable models permit better monitoring of confounding (30, 31). It is furthermore known that aggregate and nonaggregate analysis may result in different outcomes ª 2006 Blackwell Publishing Ltd, Journal of Oral Rehabilitation 33; 17–25
MULTIFACTORIAL AETIOLOGY OF ABFRACTIONS (32). The problem of aggregation and the loss of the tooth-to-tooth relation was avoided by using adequate software which takes the clustered structure of the investigated units into consideration (33). Risk indicators for abfractions were identified with a two-level logistic regression analysis. With this method, all plausible and potential risk factors were tested in the model (34). The parameters recorded in our study made it possible to determine several co- and risk indicators which support the hypotheses that toothbrushing and a high occlusal load play a role in the aetiology of abfractions. The parameter ‘intake of fruit juices’, which could support the acid-erosion theory, did not show significance. The question about the intake of fruit juices does not cover the variety of acid diets, but was thought to be highly selective for acid-erosion. Because of the limitation of the question, this result cannot be generalized. Several studies have shown that the frequent intake of acidic drinks is a predictor for the development of non-carious cervical defects (35, 36). However, in these studies also superficial erosions and hollows were included. Lussi and Schaffner (35) distinguished in their longitudinal study on progression rate and risk factors of non-carious cervical defects between erosions and wedge-shaped defects. The consumption of dietary acids was significantly associated only to erosion but not to wedge-shaped defects. In this respect our findings confirm their results since in the present study only cervical defects with sharp wedge-shaped angles were included. As with most chronic diseases, the regression model confirmed the decisive role of age as a co-factor for abfractions. From age group to age group, a dose– response effect was found, which substantiates the existence of a strong association between these two factors (22). Recessions are associated with the genesis of abfractions and must be seen as co-factors. 77% of all defects exhibited recessions, and they also showed a high odds ratio in the regression model. Volk et al. (5) described the formation of a recession as a prerequisite for the development of abfractions; however, defects bordered by enamel alone have been described without recessions (37). The increased odds ratios given occlusal facets, inlays, and tilted teeth may be evidence of a correlation between occlusal factors and abfractions. ª 2006 Blackwell Publishing Ltd, Journal of Oral Rehabilitation 33; 17–25
Occlusal facets are by definition a consequence of stressing the hard dental tissues, primarily via abrasion and attrition of the teeth (2, 15, 38). In various studies, high correlations between highergrade occlusal facets and reported bruxism have been documented (39–41). However, a combination of mechanical and chemical factors is also assumed in the origin of occlusal facets (2, 42, 43). Bruxism therefore cannot be considered the sole cause of occlusal facets. The study by Schiller et al. (44) on correlations between occlusal facets and pathological findings in the masticatory system of young adults showed – in addition to chronically more highly stressed masticatory muscles, especially the M. masseter, M. pterygoideus lateralis and medialis – that cervical defects are associated with occlusal facets. In addition to the increased odds ratios for abfractions posed by occlusal facets, this investigation found only a very weak direct association with bruxism. However, the determination of parafunctions in a brief screening is not unproblematic (45). In the German soldiers examined by Dawid et al. (25) in two categories (high and low stress potential), it was observed that abfractions occurred five times as frequently in the stressed group as in the relatively nonstressed control group. The increased estimated risk of abfractions in tilted teeth can be explained by the altered occlusal contact situation and the consequently altered force vectors (46). Braem et al. (47) found evidence of such phenomena in patients. Of the occlusally restored teeth in this study, those with inlays exhibited increased estimated risk of developing abfractions. Partial crowns comprised only a small percentage of the restorations, and the estimated risk was not increased in teeth restored with composite or amalgam. There is a paucity of data in the literature on the correlation between cervical defects and dental restorations. The results obtained by Rees (48) show a correlation between cervical defects and occlusal amalgam fillings. The author assumes that with increasing filling size, the extent of the cervical defects also increases because of weakening of the tooth. The idea that a cast restoration versus amalgam or composite filling materials has a greater influence on potential changes in tooth contacts is still considered a hypothesis, but provides a plausible explanation for the
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O . B E R N H A R D T et al. phenomenon found. Recently, experimental studies have provided evidence for the flexural stress theory via altered occlusal forces (46, 48). Indicators for a correlation between toothbrushing technique and the formation of abfractions are the frequency of toothbrushing and mouth side. Although this study recorded the frequency of toothbrushing only through a short screening question, we found it to be correlated with abfractions. Although it is not clear if this association is caused by the toothbrush alone or is based on the abrasive effect of toothpaste, earlier epidemiological studies also found correlations between heightened oral hygiene awareness and abfractions (28). Sangnes and Gjermo (9) found that those subjects who brushed more than twice a day showed a high frequency of wedge-shaped lesions. In addition, Poynter and Wright (49) observed abfractions significantly more often in patients with good oral hygiene. Addy and Hunter (50) assumed that the toothbrush alone has no or little effect on enamel and dentine. They argued that the kind of toothpaste in combination with an erosive challenge is the crucial influence for the development of erosive lesions. In the present study, no side-dependence of abfractions was found. Neither the prevalence of wedge shaped defects nor the regression model displayed a dominance of the left side of the mouth. The theory behind this observation is a higher brushing force exerted by right-handed persons on the teeth of the left side of the mouth (5, 51, 52). In conclusion the results of this risk analysis – based on a population-based subject group – indicated that abfractions are associated with occlusal factors, like occlusal wear, inlay restorations, altered tooth position and tooth brushing behaviour. Abfractions are already detectable in young adults, and the estimated risk of developing such defects increases with age. Maxillary and mandibular first and second premolars are most frequently affected by abfractions.
Acknowledgments This study is part of the Community Medicine Research net (CMR) of the University of Greifswald, Germany, which is funded by the Federal Ministry of Education and Research (grant no. ZZ9603), the Ministry of Cultural Affairs as well as the Social Ministry of the Federal State of Mecklenburg – West
Pomerania. This paper was supported by a fellowship from the Alfried Krupp von Bohlen and HalbachFoundation, Germany.
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Correspondence: Dr Olaf Bernhardt, Department of Restorative Dentistry, School of Dentistry, University of Greifswald, Rotgerberstr. 8, 17487 Greifswald, Germany. E-mail:
[email protected]
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