Epidemiology Lussi A, Ganss C (eds): Erosive Tooth Wear. Monogr Oral Sci. Basel, Karger, 2014, vol 25, pp 46–54 DOI: 10.1159/000359937
Challenges in Assessing Erosive Tooth Wear Vasileios Margaritis a · June Nunn b
a College of Health Sciences, Walden University, Minneapolis, Minn., USA; b Department of Special Care Dentistry, Dublin Dental University Hospital, Dublin, Ireland
Abstract Indices for assessing erosive wear are expected to deliver more than is expected of an ideal index: simple with defined scoring criteria so that it is reproducible, reflective of the aetiology of the condition and accurately categorizing shape, area and depth of affect, both at a point in time (prevalence) and longitudinally (incidence/increment). In addition, the differential diagnosis of erosive wear is complex, as it usually co-exists with other types of tooth wear. Therefore, a valid recording of erosive wear at an individual as well as at a population level without a thorough history with respect to general health, diet and habits is a challenge. The aims of this chapter are to describe the potential methodological challenges in assessing erosive wear, to critique the strengths and limitations of the existing erosion indices and to propose the adoption of a validated erosion index for the purpose for which © 2014 S. Karger AG, Basel it is intended.
Indices for assessing erosive wear are expected to deliver more than is expected of an ideal index: simple with defined scoring criteria so that it is reproducible, reflective of the aetiology of the condition and accurately categorizing shape, area and depth of affect, both at a point in time
(prevalence) and longitudinally (incidence/increment) [1]. In addition, the content validity is often theoretically flawed (partial vs. full-mouth recording) as can be the construct validity – for example, when there is little convergence or discriminant validity between a general index of tooth wear and aspects of erosive tooth wear only [2]. Thus arises the difficulty in selecting an index that is internationally comparable and acceptable – a dilemma that is reflected in the burgeoning number of new indices. Also, the literature on this topic is replete with terminology that is used interchangeably, especially tooth wear and erosion. In addition, the differential diagnosis of erosive wear is difficult, as it usually coexists with other types of tooth wear. Therefore, a valid recording of erosive wear at individual as well as at population level without a thorough history with respect to general health, diet and habits is challenging. The aims of this chapter are to describe methodological challenges in assessing erosive wear, to critique the strengths and limitations of the existing erosion indices and to propose the adoption of a validated erosion index for the purpose for which it is intended. Downloaded by: Karolinska Institutet, University Library 198.143.54.1 - 9/9/2015 12:11:37 AM
An ideal erosive wear index, as a valid and reliable instrument, should have the highest level of isomorphism, that is, the degree of fit between a measuring instrument and the disease or phenomenon being measured [3]. Therefore, specific quality criteria should be met in order for the researchers to provide evidence that the developed erosive wear indices are appropriate, valid and reliable. Validity Validity of an instrument reflects to what extent it measures what it is supposed to measure [2]. Although there are different types of validity, if an erosion index displays a high level of content and construct validity, significant methodological issues will have been adequately addressed. Content validity describes whether all aspects that are relevant to grasp the construct of interest have been considered at the highest possible level. Regarding an erosive wear index, the erosion of surfaces of all teeth has to be considered; therefore partial recording indicates low content validity [2]. Although the inclusion of all teeth appears to increase the content validity of an erosion index, there is still the challenge of the researcher’s subjective evaluation of the appropriateness for measuring erosive wear (face content validity) [3]. Therefore, lack of consensus between investigators regarding the clinical features of erosion may significantly affect the content validity of an instrument. For example, the morphological criteria for occlusal/incisal surfaces are not exclusively associated with erosive tissue loss [4]; thus experts in the field should reach minimum agreement as to the clinical criteria that should be included in an index. On the other hand, construct validity is established by relating the instrument to a general theoretical framework [3] and is subdivided into discriminant and convergent validity. Regarding erosion assessment, convergent validity is very difficult to confirm. The results obtained by the new instrument cannot be correlated with
the results of an established instrument that measures similar aspects and specifically erosive wear, as this established instrument simply does not yet exist. A potential solution to this may be that the new instrument could be compared to criteria/results obtained from a randomized controlled trial or other evidence-based procedure or to criteria that are determined by a minimum consensus of a panel of experts. On the other hand, an instrument possesses discriminant validity if the results of this instrument are not too highly correlated with the results of an established instrument that measures a different construct – for example, abrasive wear. In other words, this type of validity reflects the degree of differential diagnosis of the index/instrument under study. With regard to erosive wear, a potentially high correlation between tooth erosion and wedge-shaped defects might indicate insufficient discriminant validity [2]. Therefore, an ideal erosion index should include specific instead of general clinical criteria (e.g. percentage of hard tissue loss) in order to achieve the maximum discriminant validity. Both convergent and discriminant validity have to be given for a confirmation of construct validity. Sensitivity and Specificity Another significant challenge in assessing erosive wear is the achievement of the highest possible level of sensitivity and specificity of an erosion index. The sensitivity of this index indicates its ability to detect dental erosion lesions [2]. In contrast, an erosion instrument with high specificity is able to indicate the absence of dental erosion if dental erosion is not present [2]. Assessment of both sensitivity and specificity requires the comparison with a gold standard, which as mentioned earlier does not exist. Therefore, an attainable way to accomplish this comparison is the one described to confirm face validity. Reliability Reliability reflects the extent to which an instrument contains errors that appear between obser-
Challenges in Assessing Erosive Tooth Wear Lussi A, Ganss C (eds): Erosive Tooth Wear. Monogr Oral Sci. Basel, Karger, 2014, vol 25, pp 46–54 DOI: 10.1159/000359937
47
Downloaded by: Karolinska Institutet, University Library 198.143.54.1 - 9/9/2015 12:11:37 AM
Validity and Reliability Challenges
Diagnostic Criteria Challenges
As has been previously explained, specific and internationally accepted diagnostic criteria are necessary for the development of a valid and reliable erosion index. However, the validity of current diagnostic criteria for erosive wear has not been systematically studied, even though there is consensus about their definition [5]. Shallow defects located coronal from the cemento-enamel junction may predominantly occur as an effect of chronic acid exposure and most probably might be pathognomonic for dental erosion [5]. On the contrary, grooving of incisal surfaces and cupping of cusps are the most uncertain criteria because they can be an effect of various chemical and physical factors [5]. Therefore, experts in the field should reach agreement on what clinical criteria would be included in an index to exclusively record erosive wear. In order to successfully differentiate clinical diagnosis of dental erosion, having the patient’s reports about acid exposure may be helpful and could support the diagnosis ‘erosion’ [6]. However, in many cases the acid exposure lies in the past, or the patient is not aware of or does
48
not report an acid exposure. Therefore, any potential aetiological factors/criteria obtained by a thorough history should be validated and standardized in more epidemiological studies, using modern epidemiological approaches [7]. The use of exposed dentine as a diagnostic criterion is under debate. The main benefit of using this criterion is that it is generally interpreted as a relatively severe finding and therefore it may be useful for the assessment of the progression rate and for therapeutic purposes. However, studies indicate that the visual diagnosis of exposed dentine may be challenging, particularly in the cervical area [8]; thus this criterion should be avoided whenever possible, especially in epidemiological studies. Another significant challenge regarding erosive diagnostic criteria is the definition of pathological and age-related erosion; thus the use of the same erosion index for all ages could be problematic. Tooth wear of the permanent dentition, including attrition and abrasion, is expected to be more obvious at older ages. Furthermore, erosive wear as a result of chemical dissolution could become more severe at older ages because of the coexistence of other types of tooth wear [6]. This observation emphasizes the need to integrate aetiological/pathognomonic criteria in a clinical erosion index in order to reduce the false positive cases as much as possible. Erosion Indices: Benefits and Limitations
The first indices to describe this condition set out to assess the prevalence of tooth wear and, specifically, erosion of adult teeth. The earliest of these was devised by Eccles [9] and later modified with more descriptive criteria to enable the classification of the effects of erosion per se by site and severity, as graded according to the depth and area of tooth tissue involved (table 1). Smith and Knight [10] later developed an index that would assess tooth wear (tooth wear index, TWI) – again
Margaritis · Nunn Lussi A, Ganss C (eds): Erosive Tooth Wear. Monogr Oral Sci. Basel, Karger, 2014, vol 25, pp 46–54 DOI: 10.1159/000359937
Downloaded by: Karolinska Institutet, University Library 198.143.54.1 - 9/9/2015 12:11:37 AM
vations – measured either for one observer at different times (intra-examiner reliability) or between multiple examiners at points in time (inter-examiner reliability) [3]. Reliability can be relatively easily addressed if there is appropriate training and calibration of all potential examiners prior to the assessments, focusing on specific clinical criteria that must be applied in given circumstances. This training should include the detection of erosion lesions in photographs as well as in patients. The period of time between the two assessments should be fairly long – for example, 1 month – otherwise the examiners may remember their former ratings. On the other hand, if the time interval between the two assessments is too long, changes in the erosion status might affect the reliability estimates.
Table 1. Indices suggested by Smith and Knight, referring to tooth wear in general, and Eccles, including diagnostic criteria for erosive tooth wear
Score/class
Surface
Criteria
TWI according to Smith and Knight [10], 1984 0 B/L/O/I No loss of enamel surface characteristics
1
2
3
4
C
No loss of contour
B/L/O/I
Loss of enamel surface characteristics
C
Minimal loss of contour
B/L/O
Loss of enamel exposing dentine for less than one third of the surface
I
Loss of enamel just exposing dentine
C
Defect
Challenges in Assessing Erosive Tooth Wear Vasileios Margaritis a · June Nunn b
a College of Health Sciences, Walden University, Minneapolis, Minn., USA; b Department of Special Care Dentistry, Dublin Dental University Hospital, Dublin, Ireland
Abstract Indices for assessing erosive wear are expected to deliver more than is expected of an ideal index: simple with defined scoring criteria so that it is reproducible, reflective of the aetiology of the condition and accurately categorizing shape, area and depth of affect, both at a point in time (prevalence) and longitudinally (incidence/increment). In addition, the differential diagnosis of erosive wear is complex, as it usually co-exists with other types of tooth wear. Therefore, a valid recording of erosive wear at an individual as well as at a population level without a thorough history with respect to general health, diet and habits is a challenge. The aims of this chapter are to describe the potential methodological challenges in assessing erosive wear, to critique the strengths and limitations of the existing erosion indices and to propose the adoption of a validated erosion index for the purpose for which © 2014 S. Karger AG, Basel it is intended.
Indices for assessing erosive wear are expected to deliver more than is expected of an ideal index: simple with defined scoring criteria so that it is reproducible, reflective of the aetiology of the condition and accurately categorizing shape, area and depth of affect, both at a point in time
(prevalence) and longitudinally (incidence/increment) [1]. In addition, the content validity is often theoretically flawed (partial vs. full-mouth recording) as can be the construct validity – for example, when there is little convergence or discriminant validity between a general index of tooth wear and aspects of erosive tooth wear only [2]. Thus arises the difficulty in selecting an index that is internationally comparable and acceptable – a dilemma that is reflected in the burgeoning number of new indices. Also, the literature on this topic is replete with terminology that is used interchangeably, especially tooth wear and erosion. In addition, the differential diagnosis of erosive wear is difficult, as it usually coexists with other types of tooth wear. Therefore, a valid recording of erosive wear at individual as well as at population level without a thorough history with respect to general health, diet and habits is challenging. The aims of this chapter are to describe methodological challenges in assessing erosive wear, to critique the strengths and limitations of the existing erosion indices and to propose the adoption of a validated erosion index for the purpose for which it is intended. Downloaded by: Karolinska Institutet, University Library 198.143.54.1 - 9/9/2015 12:11:37 AM
An ideal erosive wear index, as a valid and reliable instrument, should have the highest level of isomorphism, that is, the degree of fit between a measuring instrument and the disease or phenomenon being measured [3]. Therefore, specific quality criteria should be met in order for the researchers to provide evidence that the developed erosive wear indices are appropriate, valid and reliable. Validity Validity of an instrument reflects to what extent it measures what it is supposed to measure [2]. Although there are different types of validity, if an erosion index displays a high level of content and construct validity, significant methodological issues will have been adequately addressed. Content validity describes whether all aspects that are relevant to grasp the construct of interest have been considered at the highest possible level. Regarding an erosive wear index, the erosion of surfaces of all teeth has to be considered; therefore partial recording indicates low content validity [2]. Although the inclusion of all teeth appears to increase the content validity of an erosion index, there is still the challenge of the researcher’s subjective evaluation of the appropriateness for measuring erosive wear (face content validity) [3]. Therefore, lack of consensus between investigators regarding the clinical features of erosion may significantly affect the content validity of an instrument. For example, the morphological criteria for occlusal/incisal surfaces are not exclusively associated with erosive tissue loss [4]; thus experts in the field should reach minimum agreement as to the clinical criteria that should be included in an index. On the other hand, construct validity is established by relating the instrument to a general theoretical framework [3] and is subdivided into discriminant and convergent validity. Regarding erosion assessment, convergent validity is very difficult to confirm. The results obtained by the new instrument cannot be correlated with
the results of an established instrument that measures similar aspects and specifically erosive wear, as this established instrument simply does not yet exist. A potential solution to this may be that the new instrument could be compared to criteria/results obtained from a randomized controlled trial or other evidence-based procedure or to criteria that are determined by a minimum consensus of a panel of experts. On the other hand, an instrument possesses discriminant validity if the results of this instrument are not too highly correlated with the results of an established instrument that measures a different construct – for example, abrasive wear. In other words, this type of validity reflects the degree of differential diagnosis of the index/instrument under study. With regard to erosive wear, a potentially high correlation between tooth erosion and wedge-shaped defects might indicate insufficient discriminant validity [2]. Therefore, an ideal erosion index should include specific instead of general clinical criteria (e.g. percentage of hard tissue loss) in order to achieve the maximum discriminant validity. Both convergent and discriminant validity have to be given for a confirmation of construct validity. Sensitivity and Specificity Another significant challenge in assessing erosive wear is the achievement of the highest possible level of sensitivity and specificity of an erosion index. The sensitivity of this index indicates its ability to detect dental erosion lesions [2]. In contrast, an erosion instrument with high specificity is able to indicate the absence of dental erosion if dental erosion is not present [2]. Assessment of both sensitivity and specificity requires the comparison with a gold standard, which as mentioned earlier does not exist. Therefore, an attainable way to accomplish this comparison is the one described to confirm face validity. Reliability Reliability reflects the extent to which an instrument contains errors that appear between obser-
Challenges in Assessing Erosive Tooth Wear Lussi A, Ganss C (eds): Erosive Tooth Wear. Monogr Oral Sci. Basel, Karger, 2014, vol 25, pp 46–54 DOI: 10.1159/000359937
47
Downloaded by: Karolinska Institutet, University Library 198.143.54.1 - 9/9/2015 12:11:37 AM
Validity and Reliability Challenges
Diagnostic Criteria Challenges
As has been previously explained, specific and internationally accepted diagnostic criteria are necessary for the development of a valid and reliable erosion index. However, the validity of current diagnostic criteria for erosive wear has not been systematically studied, even though there is consensus about their definition [5]. Shallow defects located coronal from the cemento-enamel junction may predominantly occur as an effect of chronic acid exposure and most probably might be pathognomonic for dental erosion [5]. On the contrary, grooving of incisal surfaces and cupping of cusps are the most uncertain criteria because they can be an effect of various chemical and physical factors [5]. Therefore, experts in the field should reach agreement on what clinical criteria would be included in an index to exclusively record erosive wear. In order to successfully differentiate clinical diagnosis of dental erosion, having the patient’s reports about acid exposure may be helpful and could support the diagnosis ‘erosion’ [6]. However, in many cases the acid exposure lies in the past, or the patient is not aware of or does
48
not report an acid exposure. Therefore, any potential aetiological factors/criteria obtained by a thorough history should be validated and standardized in more epidemiological studies, using modern epidemiological approaches [7]. The use of exposed dentine as a diagnostic criterion is under debate. The main benefit of using this criterion is that it is generally interpreted as a relatively severe finding and therefore it may be useful for the assessment of the progression rate and for therapeutic purposes. However, studies indicate that the visual diagnosis of exposed dentine may be challenging, particularly in the cervical area [8]; thus this criterion should be avoided whenever possible, especially in epidemiological studies. Another significant challenge regarding erosive diagnostic criteria is the definition of pathological and age-related erosion; thus the use of the same erosion index for all ages could be problematic. Tooth wear of the permanent dentition, including attrition and abrasion, is expected to be more obvious at older ages. Furthermore, erosive wear as a result of chemical dissolution could become more severe at older ages because of the coexistence of other types of tooth wear [6]. This observation emphasizes the need to integrate aetiological/pathognomonic criteria in a clinical erosion index in order to reduce the false positive cases as much as possible. Erosion Indices: Benefits and Limitations
The first indices to describe this condition set out to assess the prevalence of tooth wear and, specifically, erosion of adult teeth. The earliest of these was devised by Eccles [9] and later modified with more descriptive criteria to enable the classification of the effects of erosion per se by site and severity, as graded according to the depth and area of tooth tissue involved (table 1). Smith and Knight [10] later developed an index that would assess tooth wear (tooth wear index, TWI) – again
Margaritis · Nunn Lussi A, Ganss C (eds): Erosive Tooth Wear. Monogr Oral Sci. Basel, Karger, 2014, vol 25, pp 46–54 DOI: 10.1159/000359937
Downloaded by: Karolinska Institutet, University Library 198.143.54.1 - 9/9/2015 12:11:37 AM
vations – measured either for one observer at different times (intra-examiner reliability) or between multiple examiners at points in time (inter-examiner reliability) [3]. Reliability can be relatively easily addressed if there is appropriate training and calibration of all potential examiners prior to the assessments, focusing on specific clinical criteria that must be applied in given circumstances. This training should include the detection of erosion lesions in photographs as well as in patients. The period of time between the two assessments should be fairly long – for example, 1 month – otherwise the examiners may remember their former ratings. On the other hand, if the time interval between the two assessments is too long, changes in the erosion status might affect the reliability estimates.
Table 1. Indices suggested by Smith and Knight, referring to tooth wear in general, and Eccles, including diagnostic criteria for erosive tooth wear
Score/class
Surface
Criteria
TWI according to Smith and Knight [10], 1984 0 B/L/O/I No loss of enamel surface characteristics
1
2
3
4
C
No loss of contour
B/L/O/I
Loss of enamel surface characteristics
C
Minimal loss of contour
B/L/O
Loss of enamel exposing dentine for less than one third of the surface
I
Loss of enamel just exposing dentine
C
Defect
