Introduction 32 43 Does dentine exposure correlate with the severity of erosion? Can dentine exposure be reliably and reproducibly diagnosed? What is the interplay of factors causing tooth wear and how can other forms of tooth wear be distinguished from erosion when the wear has reached dentine? Are the parameters used for grading tooth erosion applicable to both the primary and secondary dentitions? Could symptoms of dentine hypersensitivity assist in the grading of erosive loss? Does dentine exposure correlate with the severity of erosion? For grading, the overwhelming majority of tooth wear and erosion indices use the differentiation between lesions restricted to enamel and lesions reaching the underlying dentine. The rationale for linking severity of erosion to extension into dentine probably stems from experience with dental caries and restorative procedures, but has not yet been critically discussed. It is an interesting question whether the progression of erosion from enamel into dentine has any significance in terms of disease, although it may well have a bearing in terms of treatment and, sometimes, the presence of symptoms of hypersensitivity felt by the patient. 30 6 1 Table 1 Use of the Lussi Index for grading the severity of dentine loss (in bold text) Index Score Observation Facial surfaces 0 No erosion, glazed appearance, absence of developmental ridges possible 1 Loss of surface enamel, dentine not involved 2 Erosion into dentine <50% of affected surface 3 Erosion into dentine >50% of affected surface Other surfaces 0 No erosion, glazed appearance, absence of developmental ridges possible 1 Slight erosion, rounded cusps, restorations stand proud of enamel, no dentine erosion 2 Severe erosion, more pronounced than score 1, dentine involved 13 35 41 36 26 26 17 5 25 21 33 Can dentine exposure be reliably and reproducibly diagnosed? 1 6 16 30 42 Fig. 1 Cupping of the cusp tips on the molar teeth is an early sign of erosion where extension of erosion into dentine is difficult to determine  One major problem in assessing the degree of erosion in cupping is whether or not the dentine has been exposed at the base of the lesion. Because labial and palatal enamel surfaces have a greater surface area, the observer better appreciates their surface anatomy than with a narrow cup-like lesion formed into a tooth cusp tip. Thus, grading the severity of cuppings is more difficult than perhaps it is for labial and palatal surfaces. 17 5 43 28 27 42 What is the interplay of factors causing tooth wear and how can other forms of tooth wear be distinguished from erosion when the wear has reached dentine? 24 Relevant physical forces are attrition and abrasion either from mastication or from oral hygiene procedures. Frequent exposure to dietary or gastric acid will lead to a softening of the dental hard tissues, making it easier for forces of attrition and abrasion to contribute significantly to the overall wear on the teeth. Whilst the effects of acids on enamel are relatively simple, leading to the dissolution of mineral and surface softening, the results on dentine are more complex. Chronic exposure to acids not only leads to an increasing loss of mineral but also to a progressive exposure of the organic dentine matrix, the effects of which, however, are not well known. 7 9 14 21 38 45 18 11 2 29 3 37 39 31 12 15 2 3 4 Fig. 2 Clinical case to illustrate the difficulties of attributing diagnosis of tooth wear. This example of severe tooth wear was thought to be attrition, superimposed on erosion, of the occlusal surfaces of posterior teeth and palatal surfaces of maxillary teeth  Fig. 3 Erosion of the palatal cusps of maxillary molar and premolar teeth in a patient with gastro-oesophageal reflux disease. Note that dentine is visible on the mesio-palatal cusp of the first molar tooth  Fig. 4 Typical appearance of erosion in a patient with gastro-oesophageal reflux disease showing palatal erosion of the maxillary tooth cusps and buccal erosion of the mandibular tooth cusps. The degree of tooth wear and the presence of restorations make grading difficult  Are the parameters used for grading tooth erosion applicable to both the primary and secondary dentitions? 5 3 35 36 Fig. 5 Clinical appearance of severe erosion, probably combined with other forms of tooth wear, in the deciduous dentition of a patient in whom no pathological reflux disease was recorded. The reported diet was relatively normal but erosion later appeared in the first permanent molar teeth  4 10 20 23 46 22 19 3 35 5 34 16 40 41 Could symptoms of dentine hypersensitivity assist in the grading of erosive loss? 44 44 1 In conclusion, distinctions are commonly made between erosion into enamel and erosion into dentine. Methods of scoring are derived from parameters associated more with dental caries and restorative procedures for that disease rather than specifically for tooth wear. The interplay of tooth wear factors is complex and requires further research. Classifying the severity of erosion by the area or depth of exposed dentine is difficult and poorly reproducible and, particularly with respect to the variation of enamel thickness, the amount of tissue lost often is not related to dentine exposure. There has still been very little longitudinal investigation of the significance of exposed dentine as a prognostic indicator. Further work is needed to reevaluate the explanative power of current grading procedures.