1
Introduction and the Prevalence of Tooth Wear

1.1 Introduction

There are increasing concerns over the levels of non-carious tooth surface loss being encountered amongst patients attending for routine dental examinations in general dental practice.1 Indeed due to its prevalence, it has become common practice (in at least some countries) to carry out risk assessments for the presence of tooth wear (TW) as part of the overall process of performing the accepted assessments and evaluations during a dental examination.2

Given the frequent and varied range of physical, mechanical, and chemical challenges faced by human dentition on a daily basis, the irreversible wearing-away of the dental hard tissues can be assumed to most likely occur as a result of the natural ageing process. Consequently, TW is a 'normal' physiological process and differs somewhat from a number of the other oral diseases that are also routinely screened for such as dental caries, periodontal disease or oral mucosal conditions, which are all by definition pathological processes. Difficulty may, however, be encountered in attempting to determine the clinical distinction between TW that may be considered representative of the consequences of the natural ageing process, commonly referred to as physiological wear, and an appearance worthy of a diagnostic entity. It is therefore important to consider some of the key terms and definitions in relation to the irreversible wearing-away of tooth tissue, and to further explore some of the ambiguities and confusion that surrounds the application of these terms.

The term tooth wear (TW) is a general term that can be used to describe the surface loss of dental hard tissues from causes other than dental caries or dental trauma.3 Usually, TW is subdivided into subforms, such as attrition, abrasion, and erosion, in accordance with the suspected/known aetiology. Whilst these aetiological factors can sometimes occur in isolation, clinically it is difficult (if not at times impossible) to identify a single causative factor when a patient presents with TW as the condition more often than not has a multifactorial aetiology. For this reason, the term tooth surface loss (TSL) was suggested by Eccles in 1982 to embrace all of the aetiological factors regardless of whether the exact cause of wear has been identified.4

Given the above, the authors have a preference towards a subdivision that indicates that there is a combination of factors that lead to tissue loss. Accordingly, the nature of dental wear may be broadly divided into mechanical wear and chemical wear, and both forms further subdivided into intrinsic and extrinsic, with the overall existence of four subforms, hence:

• mechanical intrinsic TW (as a result of chewing or bruxism, also called attrition)
• mechanical extrinsic TW (due to factors other than chewing and/or bruxism, also called abrasion, for example with a toothbrush)
• chemical intrinsic TW (as consequence of gastric acid, also called erosion)
• chemical extrinsic dental wear (as a result of an acidic diet, also known as erosion).

Unfortunately, there is considerable ambiguity with the application of some of the above terms (nationally and internationally) that renders effective communication between healthcare providers challenging, especially when attempting to draw comparisons between differing items of dental research.

It had been proposed by Smith et al.5 that the use of the term TSL may inadvertently imply an under-estimation of the actual extent and severity of the problem by suggesting the condition to only refer to the surface (or superficial) loss of tooth tissue (as opposed to the additional subsurface loss), which is often seen clinically, thereby failing to take into account cases of more extensive tooth tissue loss. Consequently, they have suggested that the use of the term TW be preferred where there may be inadequate evidence to strongly support the cause of wear being a result of erosion, attrition or abrasion (so as to facilitate the process of communication between dentists and with their patients).5 As a result, the authors do not recommend use of the term erosive tooth wear (as is often evidenced in many scientific publications), as this implies that erosion is the primary aetiological factor.

1.2 Physiological Wear and Pathological Wear: the Concept of Severe Tooth Wear

It has been suggested that as teeth continue to function and thus remain continually exposed to erosive, abrasive, and attritive factors, the wearing-away of tooth tissue will probably occur as an age-related phenomenon.6

A number of reports have been published describing the rates of TW progression. Lambrechts et al. have estimated the normal vertical loss of enamel from physiological wear to be approximately 18 µm for premolar teeth and 38 µm for molar teeth, respectively, per annum.7 Comparable rates of progression have been reported in a more recent study by Rodriguez et al.8 With specific reference to incisor teeth, by the means of undertaking a cross-sectional digital radiographic study to estimate the rate of incisor TW amongst 346 subjects Ray et al. have reported the average crown height of a maxillary central incisor to decrease by 1.01 mm (approximately 1000 µm) from 11.94 mm between the age of 10 years to 70 years, and for mandibular central incisor teeth, the average crown height to decrease by 1.46 mm (approximately 1500 µm) to 9.58 mm over a period of six decades (when applying the same age ranges), representing the mean annual wear rates of central incisor teeth to be in the range of 17-25 µm per year of life.9

The term physiological wear (Figure 1.1) is thus commonly applied to describe that level of TW observed which is expected for the patient's age, commensurate with normal day-to-day function.10

Historically the term pathological wear (Figure 1.2a-d) was used to relate to the presence of unacceptable wear for a particular age group based on clinical judgement and has been traditionally applied as describing a level of wear when restorative intervention may be justified. However, the use of clinical judgement clearly does not permit an accurate and consistent approach as this would require the concomitant need to define the precise 'normal levels of wear' (that should be present in differing age groups and populations), as well as the availability of a reasonably accurate and consistent method to measure the levels of wear actually present. Given the current lack of knowledge in relation to the pathogenesis of TW (with two common theories being described, one of slow cumulative progression occurring throughout life - often referred to as continual and the alternative of cyclical bursts of activity - commonly termed episodic),6 it would be very difficult to determine meaningful benchmark values for the levels of TW likely to be present amongst individuals of differing ages.6

In 2017, in an attempt to improve clarity and understating, the term pathological wear was defined in a European Consensus Statement on the Management Guidelines (for Severe Wear) as 'tooth wear which is atypical for the age of the patient causing pain or discomfort, functional problems, or deterioration of aesthetic appearance, which if it progresses, may give rise to undesirable complications of increased complexity'.11 However, ambiguity is still likely to remain for the reasons discussed above.

It has therefore been suggested that the diagnostic entity of severe tooth wear may be more appropriate when undertaking clinical assessments. The latter term has been defined as 'tooth wear with substantial loss of tooth structure, with dentine exposure and significant loss (more than or equal to one third) of the clinical crown'.11 The presence of severe wear can be used to define the highest grade of a clinical index, which in turn may be used to screen for the extent and severity of TW present, in a manner similar to other indices and monitoring tools used in clinical dentistry (Figure 1.3).

However, the use of an index based on the severity of TW observed clinically may be of limited merit in identifying treatment need. This can be illustrated by the example of the case of a young patient, seen in Figure 1.4, diagnosed with erosive pathological TW on the palatal surfaces of the maxillary central incisor teeth by virtue of the level of wear clinically present. In addition there are symptoms of sensitivity and an aesthetic impairment. However, with the absence of less than one-third clinical crown loss, severe wear (by definition) may not be present in this case, although active restorative intervention would likely be indicated. In contrast, signs of severe wear may be seen to exist in an 89-year-old (see Figure 1.5), but in this case there would be no clear indication to provide any forms of active restorative intervention.

The use of indices for TW is discussed further in Chapter 3.

1.3 The Prevalence of TW

In relation to the matter of the prevalence of TW (amongst adult dentate patients), the...