J. Dent. 1992;
Tooth wear and facial morphology A. J. R. Crothers Department of Operative
The Dental School, University
Upon Tyne, UK
ABSTRACT This review sets out to explore the relationship between tooth wear and facial morphology, with particular reference to the occlusal vertical dimension. Evidence from anthropological and archaeological investigations suggests that severe tooth wear may not only affect the teeth and occlusion, but may also have more wide ranging effects on overall dentofacial morphology. Studies on contemporary subjects confirm this finding, and the literature on the nature of these effects is reviewed. It is concluded that the adult dentofacial complex is not a static entity, but can compensate for the dental effects of wear. The consequences of this with respect to reconstruction of the worn dentition are discussed, and it is proposed that the dynamic nature of this complex may be employed to help simplify the treatment of severe tooth wear. KEY WORDS: J. Dent. 1992; 1992)
Dental wear, Occlusal vertical dimension,
13 February 1992;
18 March 1992;
accepted 30 May
Correspondence should be addressed to: Dr A. J. R. Crothers, Department of Operative Dentistry (Conservation), The Dental School, University of Newcastle upon Tyne, Framlington Place, Newcastle upon Tyne, NE2 4BW, UK.
INTRODUCTION The management of the worn dentition is becoming an increasingly common problem in the practice of dentistry in terms of both the difficulty and expense of providing a functionally comfortable and cosmetically acceptable treatment for the patient. The difficulty is compounded in that tooth wear is a condition which varies greatly in severity, and often cannot be found to have a distinct aetiology. Traditionally, non-carious loss of tooth tissue has been subdivided into attrition, abrasion and erosion, though it is now generally considered that these aspects of the wear process are not totally independent (Eccles, 1982; Smith and Knight, 1984) and consequently, the terms ‘tooth wear’ or ‘loss of tooth substance’ are now more generally used. Attrition may be defined as the gradual loss of tooth substance through tooth to tooth contact during mastication or parafunction, abrasion as the loss of tooth tissue as a result of frictional contact with substances other than teeth, and erosion as the loss of dental hard tissue through non-bacterial chemical action. Tooth tissue loss may result from any combination of these types of wear, and identification of the cause of the wear is often not possible (Klatsky, 1939; Lewis and Smith, 1973; Renson, 1975; @ 1992 Butterworth-Heinemann 0300-5712/92/060333-09
Shafer et al., 1983; Smith and Knight, 1984). The resultant effects on the dentition can be severely destructive, often necessitating extensive restorative procedures perhaps on teeth already compromised by age and previous treatment. In cases where such tooth wear has severely affected the dentition, a clinical appearance of loss of facial height is commonly observed-a feature known as ‘overclosure’. This clinical observation is supported by evidence in the literature suggesting that loss of occlusal and interproximal tooth tissue may have effects not only on the teeth themselves, but also on the dentoalveolar complex and associated structures of the face (Fishman, 1976; Krogstad and Dahl, 1985). However, such changes are difficult to assess clinically, and little quantitative and qualitative investigation into their nature has been carried out. The aim of this paper is to review these investigations, highlight the effects of tooth wear on dentofacial morphology, and thereby consider the basis behind restoration of the severely worn dentition where an alteration of facial height is required.
TOOTH WEAR Many factors may combine to produce the worn dentition and often the aetiology of the wear remains unidentified.
J. Dent. 1992;
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There is an increasing acceptance that tooth wear rarely occurs as a result of one factor alone, and that the wear observed in any individual may be the result of a combination of all possible aetiological factors over the lifetime of the dentition. The aetiological factors associated with tooth wear are many and varied, and include wear as a change associated with ageing, or due to environmental factors such as the presence of grit in primitive diets. Cultural factors such as the use of teeth as tools may be important, as may habits such as the improper use of toothbrushes. Erosive dietary factors are probably more significant in the modern subject, and abnormal tooth contacts due to bruxism or occlusal abnormalities may also produce wear. Chronic regurgitation such as in alcoholism or bulimia or the presence of disorders, of tooth structure (e.g. amelogenesis imperfecta) can produce severely destructive wear, and loss of posterior support for the occlusion or differential wear against restorative materials may also be significant. The most important consideration in the aetiology of the wear is that some or all of these factors may act concurrently. For example, attrition can occur as a result of tooth to tooth contact alone, but the quality of the diet may form an additional abrasive or erosive component to the wear (Smith, 1972, 1989). The dentition of primitive man showed marked attrition and abrasion due to cultural influences, with an unrefined diet and the use of teeth as tools both producing wear. Erosion has a particular association with abrasion and attrition in that enamel affected by an erosive agent will be more susceptible to tooth wear due to other factors, resulting in increased rates and degrees of tooth tissue loss. It is important to remember that whether the various wear factors occur concurrently or not, the overall effect on the teeth will of course be cumulative (Ten Bruggen Cate, 1968; Smith, 1972; Lewis and Smith, 1973; Eccles, 1982; Smith and Knight, 1984). Loss of posterior support for the occlusion may also act as a factor which accelerates anterior tooth wear (Basker et al., 1983; Smith and Knight, 1984; Best, 1987) and in subjects with shortened dental arches, there is greater contact between the remaining anterior teeth (Kayser, 1981). Witter et al. (1987) also suggested that increased loading of the anterior teeth occurs in shortened dental arches, but an increase in wear with decreasing tooth numbers was not confirmed. Smith (1989) commented that the concept of anterior wear due to loss of posterior teeth has not been sufficiently tested, and may be an oversimplification with little evidence existing to suggest that loss of posterior teeth increases the masticator-y activity of the anterior teeth. Reduction in the number of teeth in an individual does however imply a concentration of all possible wear influences on the remaining teeth, in addition to the redistribution of occlusal forces over a decreased occlusal surface area. Loss of tooth tissue due to abrasion from extraneous objects such as a toothbrush or wood sticks is usually easily identifiable (Johnson and Sivers, 1987), but the
appearance of worn teeth may be similar despite the cause, and where more than one type of wear is suspected it is often impossible to identify which is the primary influence. It is therefore appropriate to use a common term such as ‘tooth wear’, as this encompasses all possible forms of wear and is not misleading where any doubt as to its aetiology arises. The use of specific terms such as attrition or erosion are really only appropriate where identitication of the aetiology of any wear is possible with accuracy, and this is not always the case. Identification of the aetiological factors in tooth wear is important in the prevention of further wear, and early identification and elimination of these influences is undoubtedly a better treatment than subsequent restorations. Unfortunately, early identification is often difficult as the wear process is slow and patients may remain unaware of the effects of wear until they are well established. Indeed, a certain amount of tooth wear can be regarded as being due to normal function, providing the clinician with the difficult problem of having to distinguish between physiological and pathological tooth wear.
Tooth wear may be regarded as a physiological process, the presence of which can improve masticator-y efficiency and reduce the susceptibility of the dentition to disease and malocclusion (Murphy, 1964; Ainamo, 1972). This is certainly the situation in many species other than man, where tooth wear is required for the dentition to function fully (Berry and Poole, 1974) and this view has been extended to the human situation. Many primitive or ancient populations display extremely extensive tooth wear and it has been suggested that in such populations, all degrees of wear may be regarded as physiological. Begg and Kesling (1977) considered that advanced tooth wear and the facial morphological changes associated with it were essential for the normal development and function of the human dentition, and that many dental disorders could be attributed to the unworn cusp. Many studies of an anthropological or archaeological nature have reported an association between severe occlusal and inter-proximal wear and a lower incidence of dental disease, though this may also be related to the diet of such populations (Leigh, 1925, 1933; Campbell and Barrett, 1953; Begg, 1954; Davies and Pedersen, 1955; Beyron, 1964; Molnar, 1972; Ainamo, 1972; Galabert, 1975). In the modern dentition, severe degrees of tooth wear may not be regarded as being physiological and thus at some point the need for active treatment must be considered. The distinction between physiological and pathological tooth wear is by no means a clear one, and must be based on the circumstances under which it has occurred. Tooth wear may be associated with an underlying pathological state such as a disorder of tooth structure (Renson, 1975; Mackie and Blinkhorn, 1991) and in these circumstances it may be regarded as abnormal and in
Crothers: Tooth wear and facial morphology
need of treatment. Where wear is associated with parafunctional activity, it is much more difficult to determine whether or not the degree of wear is abnormal, (Xhonga, 1977; Colquitt, 1987) though parafunction itself is abnormal, and it is therefore reasonable to suggest that wear associated with it is pathological. In general, it is the pattern and rate of the wear together with the age and effects on the dentition of the patient which determine whether there is any need for treatment. The suggestion put forward by Berry and Poole (1974, 1976) that the concept of physiological tooth wear may justify the prophylactic reduction of tooth cusps has never been accepted, perhaps unsurprisingly in view of the destructive nature of such a procedure. Tooth wear is also found as a normal change associated with ageing (Pollmann et al., 1987) and the degree of wear present with respect to the age of the patient is a useful indicator of whether or not the tooth tissue loss is abnormal. The amount of wear increases with age, and the presence of faceting or loss of incisal edge morphology can be regarded as physiological in a young adult. Indeed, more severe wear with loss of most of the crowns of the teeth in an elderly patient may well be within physiological limits, provided function is not compromised. However, if the wear is excessive when compared with the amount of wear typical for the patient’s age, or renders the dentition susceptible to disease processes, tooth wear may be considered to be pathological. Factors such as the cosmetic and functional needs of the patient, the apparent rate of progression of the wear, the suspected aetiology, and possible loss of occlusal vertical dimension (OVD) are the best criteria upon which to base the distinction between physiological and pathological wear. It is however important to remember that if tooth wear is to be regarded as physiological in a particular situation, then any changes in facial morphology associated with it may also be regarded as physiological.
Before considering the effects of tooth wear on facial morphology, it is also necessary to take account of continuing age changes within the facial complex. This is particularly important with regard to facial height as this dimension does appear to alter with age. Facial height is measured with the teeth in occlusion and may be subdivided into upper and lower components, above and below the maxillary basal bone. Lower facial height (or OVD) could be expected to be affected by tooth wear, being the part of the face containing the dentoalveolar structures, whereas upper facial height is determined by genetic and airway considerations (Woodside and LinderAronson, 1979) and is thus less likely to be influenced by tooth wear. However, this component of face height may be influenced by any adult growth changes. Many authors have reported a continual increase in facial height throughout adult life in dentate subjects, with only small
differences between the sexes (Hrdlicka, 1936; Lasker, 1953; Baer, 1956). Tallgren (1957) demonstrated this increase, and in addition showed that the mandible adapted to the increasing facial height thus maintaining constancy of the freeway space. Thomson and Kendrick (1964) also showed an increase in facial height with age in the adult, taking place mainly in the lower part of the face. It has been suggested that this increase in vertical facial dimensions is the effect of continual tooth eruption in the absence of tooth wear (Murphy, 1959; Berry and Poole, 1976) and as such, may represent a compensatory mechanism for tooth wear. More recent studies (Forsberg, 1979; Sarnas and Solow, 1980; Behrents, 1985) suggest that the increase in adult face height with age occurs mainly in the third decade of life, with a smaller but significant increase occurring after this period. This increase appears to be mainly in the lower face, and may be accounted for in part by skeletal growth but also by the eruption of the teeth, in particular the lower incisors. This increase in lower face height with age must be taken into account when examining the facial morphology of subjects with advanced wear, and will be considered further in the context of the compensatory mechanisms which may occur in response to tooth wear.
TOOTH WEAR AND THE OCCLUSAL VERTICAL DIMENSION Restoration of the worn dentition is usually a complex and difficult problem, often complicated by a reduction of the OVD as a result of the effects of the wear. The assessment of such effects are often based on arbitrary clinical grounds, and there is considerable controversy as to the importance of such findings. It is common in case reports describing various treatment rationales for the management of advanced tooth wear for authors to note an apparent reduction in the OVD, a feature often described as overclosure (Mack and Allen, 1968; Hamilton and Whitehead, 1968; Gankerseer, 1987). This effect was investigated in detail by Tallgren (1957) who studied the changes in adult face height that occurred in association with tooth wear and found that the lower face height was markedly less in a group with advanced wear when compared to age-matched controls. Resting face height (the height of the face with the mandible in the rest position) was also studied in this investigation and a tendency for this dimension to be smaller was also observed. Resting face height is dependent on the interocclusal clearance (IOC) or freeway space, the amount of vertical space between the teeth with the mandible in the rest position, and a tendency for this dimension to be smaller was also noted. Advanced tooth wear was thus concluded to reduce the OVD, and the IOC also reduced partially, with a corresponding adaptation in the mandibular rest position. Murphy (1959) described a reduction in the OVD associated with increasing degrees of occlusal wear in a
sample of aboriginal skulls, and Begg and Kesling (1977) also described this effect in detail. Renson (1975) commented that anterior wear could produce overclosure, and Dahl and Krogstad (1975,1982,1985) observed the effects of restorative treatment on the OVD of patients with advanced attrition. The authors stated that a reduction in this dimension was clinically apparent prior to treatment and that its restoration was an accepted part of therapy. Brown (1980) accepted that loss of the OVD was inevitable in cases of advanced tooth wear, and Turner and Missirlian (1984) and Watson and Tulloch (1985) concurred with this observation. In order to investigate these apparent changes in vertical facial morphology before and after operative intervention, Dahl and Krogstad (1975, 1982, 1985) longitudinally surveyed the effects of restoring the OVD in the treatment of advanced tooth wear. Treatment was carried out by means of an anterior removable appliance followed by the provision of fixed prosthodontics, and the authors demonstrated that increasing the OVD was a well-tolerated means of providing space in which restorations could be placed. The anterior appliance was considered to have an orthodontic effect, allowing eruption of the posterior teeth as a means of increasing the OVD, with the total increase in this dimension being determined by the thickness of the appliance. The amount of space obtained was variable between subjects as all appliances were not worn for equal periods of time, and the rate at which the space was obtained appeared to be irrespective of age and sex. The authors considered that the total time that the appliance was worn was probably the most important factor in determining the amount of vertical increase in facial height that could be obtained. These observations further demonstrate that the OVD is not fixed at a particular height, but is variable and may alter in response to dental changes, or be manipulated as a part of treatment. It is an accepted clinical procedure that when the lower facial height appears to be reduced due to advanced tooth wear a trial appliance is required to test the patient’s tolerance to any restoration of the OVD (Devlin, 1985; Best, 1987; Foreman, 1988). However, Ibbetson and Setchell (1989) commented that they had yet to find a patient who was unable to tolerate such an increase. This again suggests that there is a great deal of adaptability of the dentoalveolar complex to changes in maxillomandibular relationships-a feature well recognized in the field of orthodontics (Solow, 1980). This adaptability of the dentoalveolar complex to alterations in vertical height implies that compensation for loss of OVD may occur, and if this is so, then the apparent effect of the wear on the OVD may be less than the degree of tooth tissue loss would suggest-a factor which will be discussed shortly. Russell (1987) concluded that a decrease in lower face height occurs with advancing tooth wear and that an increased IOC is often associated with this. However, the earlier work of Tallgren (1957) suggests that the increase in IOC is less than the reduction in OVD, i.e. a change in the
mandibular rest position occurs. It should also be noted that the resting position of the mandible in the dentate subject is dependent on many factors such as head posture, airway patency, tissue elasticity and muscle activity (Mohl, 1976) and as freeway space is determined by this position, the value of measuring freeway space is therefore limited when considering the effect of tooth wear on face height. Tooth wear thus appears to tend to reduce the OVD, though the effect seems to be variable between subjects and this is probably due to mechanisms which compensate for the loss of coronal tooth tissue, and the influence of these mechanisms on dentofacial morphology will be considered shortly.
TOOTH WEAR AND DENTOFACIAL MORPHOLOGY Whilst much attention has been focused in the literature on the effects of tooth wear on the OVD, less emphasis has been placed on the more widespread influences of this wear on dentofacial morphology. Early reports on tooth wear and its association with facial morphology are anthropological and archaeological in nature, studying ancient populations such as that of Ancient Egypt, Stone Age man or Aboriginal cultures (Leigh, 1925, 1933; Campbell and Barrett, 1953; Begg, 1954; Davies and Pedersen, 1955; Molnar, 1972; Ainamo, 1972; Galabert, 1975). In such populations advanced occlusal and interproximal wear is a virtually universal finding, attributed to a natural or unrefined diet and the use of the teeth as tools, such as the chewing of animal hides for use in clothing. Analysis of the occlusion and the facial morphological characteristics of such subjects has been extensively carried out, and it has been demonstrated that the effects of the loss of tooth tissue through wear are not restricted to the teeth themselves, but are also more widespread throughout the face. (Fishman, 1976; Begg and Kesling, 1977; Varrella, 1990). When such worn dentitions were compared with those without advanced tooth wear, many differences may be observed with respect to the occlusion. Features such as reversal of the buccolingual plane of occlusion, incisor uprighting, narrowing of the lower arch and the development of an edge-to-edge incisor relationship have all been described. These effects are attributed to the differential pattern of wear on individual tooth cusps, and research into the effects of tooth wear on the occlusal morphology of subjects in this type of population led to the concept of ‘attritional occlusion’. This term describes an occlusal morphology specific to the worn dentition, comprising an edge-to-edge incisal relationship, an increased occlusal surface area (through the progressive ablation of cusps), alveolar bone growth, mesial migration and continual tooth eruption to compensate for the loss of coronal tooth tissue. A reduction in arch length through interproximal wear allows for the eruption of the third molar without
crowding. The function of this specific occlusal morphology is to maintain masticator-y efficiency as the wear of the teeth progresses. The term ‘attritional occlusion’ is perhaps misleading as it implies a single aetiological factor for the wear, an assumption which is difficult to make with confidence even in the primitive dentition. However, it is reasonable to suppose that the effects of occlusal and interproximal wear on facial morphology are similar irrespective of the aetiology, and there is no evidence in the literature to indicate that this is not the case. The evidence that continual tooth eruption occurs in severe wear suggests that whereas a loss of crown height may be expected to result in an alteration of lower facial height, if eruption occurs to compensate, then effects of the wear on facial morphology become more difficult to assess. Fishman (1976) conducted a cephalometric survey of the dental and skeletal relationships to the worn occlusion, and concluded that the effects of tooth wear were not limited to the reduction of individual tooth dimensions. Incisor uprighting, arch width reduction, gonial angle reduction and a lowering of the occlusal plane within the facial complex with increasing degrees of wear were all observed in American Indian skulls. Varrella (1990) produced similar results from a population of 15th Century Finnish skulls and concluded that severe tooth wear altered the shape of the mandible to produce a reduced angle between the body and ramus (gonial angle) and consequently a smaller anterior face height. There is thus strong evidence to suggest that facial morphology may be influenced by tooth wear of this nature, but it should be noted that as most of these early studies are based on anthropological material, their relevance to the modern population is not entirely clear due to the different environment in which the wear took place. However, there are similarities between modem and primitive populations in respect of the effects of wear on the dentoalveolar complex-such as the loss of OVDand indeed any morphological adaptive mechanisms that may exist will be present in both groups. In order to provide information more relevant to a modem population, Krogstad and Dahl(l985) conducted a similar study on a group of adult Norwegians all with advanced tooth wear. Dentoalveolar and basal measurements were recorded using standardized lateral cephalometric radiographs and compared with a sample of adults without occlusal wear. Cephalometric radiography is often used in studies of this nature to identify morphological trends, and where comparative measurements are to be made, a standardized radiological and analytical technique is required to ensure accuracy. In this study, smaller values of lower face height, gonial angle and relative mandibular prognathism were recorded, and also in accordance with previous studies, upper incisor uprighting was noted. As would be expected, no differences in cranial base structure could be associated with tooth wear, as these structures are sufficiently remote from the dentoalveolar complex to be affected by such changes. The alterations in dentofacial morphology that were
Tooth wear and facial morphology
observed were attributed to increased muscle function, possibly as a result of bruxism. The role of muscle activity in the development of facial morphology has been demonstrated in children (Moller, 1966; Ingervall and Thilander, 1974) and it is reasonable to suggest that the increased muscular activity in bruxism may have some effect on facial morphology in the adult. A recent study (Crothers, 1991) investigated the craniofacial morphology associated with advanced tooth wear. Cephalometric analysis was carried out for a group of adult subjects with advanced wear for comparison with a control group without such wear. Characteristics of facial morphology were described for the groups and statistical analyses of the differences were calculated. Method error determinations showed cephalometric radiography to be an accurate and reproducible technique, and similar results to those of previous studies were obtained, though no significant difference in lower facial height was identified between the groups. However, reduced gonial and maxillary/mandibular plane angles were observed, showing that the wear had an influence on the morphology of the lower face. Compensation for the loss of tooth tissue was considered to have occurred to prevent the loss of OVD, mainly through the eruption of the lower anterior teeth. The mandible was found to be longer and more prognathic, producing an edge-to-edge incisal relationship which could not be attributed to an anterior posturing--findings which were in accordance with the previous studies. Anterior posturing of the mandible may be observed clinically in some patients with advanced tooth wear, though this is by no means always the case, and it may be that a non-postural edge-to-edge incisal relationship can develop as a result of alveolar and mandibular remodelling in response to the altered position. There is evidence that soft-tissue stretching may influence craniofacial structures (Solow and Krieborg, 1977) and this mechanism may cause such changes in mandibular morphology as a response to the anteriorly postured position, although a longitudinal survey of the development of the facial form of this type of subject would be required to examine this possibility further. This has implications for restorative treatment of severe wear in that a morphological edge-toedge incisor relationship will require an increase of the OVD to provide anterior restorations, whereas a postural incisal relationship may not require such a change. If a morphological edge-to-edge relationship does develop in some subjects, then early treatment of wear to prevent this may be indicated and the overall management of the wear is less likely to be complicated by OVD manipulation. Crothers (1991) also carried out analysis of soft-tissue facial morphology in subjects with advanced tooth wear when compared with subjects without such wear. The results revealed that the extraoral appearance of overclosure could be related in part to soft-tissue age changes, though tooth wear was considered to have an effect on upper lip profile and lower lip height. These combined differences affect facial morphology resulting in a longer
J. Dent 1992; 20: No. 6
and flatter upper lip, and a shorter lower lip with a more prognathic soft-tissue chin. The lip contact position thus becomes situated at a more inferior level, increasing the prominence of the lower incisor teeth, and all these factors combine to give an overall facial morphology which may appear overclosed even though the actual loss of OVD may be small. Thus tooth wear has effects on the whole of the dentoalveolar complex as well as on the teeth themselves. The exact mechanism by which these changes occur is poorly understood, but probably represents a morphological adaptation to an altered function. As the teeth wear, the activity of the masticatory muscles alters facial morphology and compensation occurs to accommodate the loss of clinical crown height-a feature which will be considered shortly. Cephalometric radiography shows these changes clearly, but care must be taken to ensure reproducibility of results, particularly where longitudinal or comparative studies are concerned. The clinical significance of these facial changes should however be noted. As there is a general morphological change in facial form associated with both tooth wear and the ageing process, simple restoration of the crowns of the teeth, even at an increased OVD, may not completely reverse the facial appearance of overclosure. Similarly, the long-term effects on facial form of increasing the OVD as part of restoration of the worn dentition are unclear, and whereas small increases seem to be stable, relapse in face height may occur (Dahl and Krogstad, 1985). This is not likely to be clinically relevant as the functional and cosmetic needs of the restored dentition are unlikely to be affected. The ability of the dentoalveolar complex to adapt to changes in face height either through wear or its restoration may thus be of use clinically, and the use of orthodontic techniques such as to provide space for the provision of restorations in the worn dentition may be a way to help simplify treatment of tooth wear.
TOOTH WEAR AND THE TEMPOROMANDIBULAR
The relationship between occlusion and the temporomandibular joint (TMJ) remains difficult to assess clinically and there is limited evidence that occlusal factors play a role in joint dysfunction (Wassell, 1989). The gross changes in occlusal morphology that occur in cases of advanced wear and the possible effects of the wear on the OVD may however have an influence on this joint. Moffett et al. (1964) described gross changes in condylar and glenoid fossa form associated with both loss of posterior teeth and increases in the OVD in animal experiments, demonstrating that TMJ morphology does alter with function. Mongini (1972, 1975, 1980) also demonstrated adaptive TMJ remodelling as a physiological response to altered occlusal function including tooth wear, and indeed showed that condyle remodelling could occur in response to occlusal therapy for TMJ
dysfunction. Renson (1975) considered that loss of OVD through tooth wear could result in TMJ dysfunction due to condylar repositioning, though Whittaker et al. (1985) did not find any correlation between tooth wear and condylar form or surface change in a study of archaeological material, which seems surprising in view of the above reports. Begg and Kesling (1977) did however describe a shallow glenoid fossa and a flatter head to the mandibular condyle associated with advanced wear in a similar sample, though the significance of this finding with respect to joint dysfunction in a modern population is unclear. Granados (1979) described similar changes associated with advanced tooth wear, though these were regarded as being osteoarthritic and in view of this, the author considered such advanced wear to be pathological. Thus tooth wear has an effect on the TMJ and the remodelling that occurs seems to be a response to changes in occlusal function associated with the wear. Whether or not such changes are clinically significant is less clear, and even where tooth wear is severe, if there are no TMJ symptoms, then alterations in TMJ morphology should be regarded as physiological.
COMPENSATORY MECHANISM TO TOOTH WEAR The variability of the effect of tooth wear on the OVD and the morphology of the dentoalveolar structures may be accounted for by compensatory mechanisms which may produce the wide range of variation that can be observed clinically in subjects. It has been proposed that these mechanisms compensate for loss of tooth tissue through continual wear such that the dentition is maintained in a functionally efficient state. Begg (1954) Tallgren (1957) and Murphy (1959) considered that the loss of tooth tissue was compensated for in several ways; by the continual eruption of the teeth with root lengthening through apical cemental apposition, and by continual appositional alveolar bone deposition and skeletal compensatory growth (Van der Linden and Duterloo, 1976). The evidence provided by the extensive work of Murphy suggests that compensatory mechanisms are able to prevent loss of the OVD by approximately 60%. Murphy also commented that other workers had observed an increase in facial height with age as described previously. It has been suggested that compensatory factors may continue in the absence of tooth wear, accounting for this increase in vertical facial dimensions. Berry and Poole (1974, 1976) also considered possible mechanisms of compensation for tooth wear. They proposed that the unworn cusp could be regarded as a condition associated with a relined civilized diet, and that wear was a necessary process required in order to achieve full masticatory efficiency. Three possible situations were discussed. First, where the wear was rapid, compensation was not complete and the vertical dimension of occlusion
would decrease with a consequent increase in the IOC. Secondly, where the wear was slower in developing, compensation would maintain the OVD and, thirdly, where the tooth wear was very slow or absent, the compensatory mechanisms would continue to operate and the lower anterior face height would increase with age. However, incisor eruption as a means of compensation may not always be beneficial, particularly in a preexisting Class II division 2 malocclusion where incisor eruption could cause soft-tissue damage. Finally, the authors also considered that the increase in face height with age was a feature that had become more prominent over the last two centuries, corresponding to increasing refinement of the modern diet. Russell (1987) also concurred with the idea that the degree of loss of OVD through tooth wear was a function of the rate of wear, with rapidly occurring loss of tooth tissue not allowing sufficient time for compensation to occur. Current research (Crothers, 1991) suggests that the main part of the eruptive and alveolar compensation is taken up by the lower teeth and that inferiorly directed growth of the maxilla through normal age changes forms a minor part. The evidence provided by these investigations thus may help to explain the wide range of variation in OVD that may be clinically observed when examining subjects with advanced attritional tooth wear. Certainly, where treatment of the wear is considered necessary, the variable amount of compensation that may occur suggests that the use of intermediate appliances to test alterations in OVD would be advisable.
DISCUSSION The effects of advanced tooth wear on facial morphology and the occlusal vertical dimension appear to be variable between subjects. In general, a loss of crown height through occlusal wear produces a loss of lower anterior face height, though this is not always the case. Any loss of the OVD which does occur may be less than would be expected judging by the loss of crown height due to eruptive, alveolar and skeletal compensatory mechanisms. Freeway space may be increased as a result of loss of face height, but this measurement is not a reliable indicator of either compensation for the wear or the degree of loss of OVD. The facial height of any individual subject is a balance between these compensatory mechanisms and the amount of tooth tissue lost, and the rate of wear may affect facial height in that rapid wear can occur faster than the compensatory mechanisms can manage, with a resulting loss of facial height. Ultimately, the best treatment for any wear is its early recognition and prevention, but this is an ideal which is often difficult to achieve. The distinction between physiological and pathological tooth wear in any subject is often difficult and should be based on the functional and cosmetic needs of the individual. The facial appearance of overclosure is not necessarily a problem, as it is in part due
Tooth wear and facial morphology
to the ageing process, and many individuals accept this without complaint. Indeed, alteration of the face height by the placement of restorations can modify age- and wearrelated changes but may not completely abolish the overclosed effect, and the clinician should not increase the vertical dimension excessively in an attempt to achieve this. Treatment of wear may be complex and should not be undertaken without assessment of all its effects on the dentoalveolar complex and any compensation that may have occurred. When considering the need for treatment of wear, the degree of compensation present is often difficult to assess as soft-tissue age changes and hard-tissue effects associated with tooth wear both combine to produce the appearance of overclosure. However, an estimate of the amount of compensation present would help the clinician to decide whether the OVD needs to be increased as a part of treatment, and if so by how much. This estimate may be based on the rate of wear, the degree of alveolar prominence, the amount of secondary dentine and cemental apposition, and assessment of the amount of loss of OVD and any adaptation of the mandibular rest position. Of lesser importance is an assessment of any increase in the freeway space. The ability of the dentoalveolar complex to adapt to changes in face height does however mean that the clinician has a degree of freedom to manipulate face height to facilitate the placement of restorations, and a trial appliance to test any proposed increase in this dimension is to be recommended. This may be followed by fixed restorations at the increased vertical dimension, and most patients are able to adapt to this with a minimum of difficulty. The main problem with this type of restorative approach is the large amounts of both clinical time and expense which are required to restore function and appearance. In cases where the function of the posterior teeth is not compromised by wear, or the tooth wear is confined to the anterior teeth, the most common factors determining the need for treatment are both the preservation of the remaining tooth structure and the patient’s anterior functional and cosmetic needs. In such cases, the use of a fixed or removable anterior appliance to increase the OVD (also known as the ‘Dahl appliance’) is a logical and convenient part of treatment. Current research indicates that the lower incisors erupt to occupy the space created by anterior wear, and selective intrusion of this segment, or the allowing of posterior tooth eruption to occur under the influence of this appliance, may then provide the required space for provision of anterior restorations. This form of treatment is effectively orthodontic in nature. and has the advantage of removing the need for multiple posterior restorations solely to provide space for anterior reconstruction, allowing maximum use ofwhat tooth tissue may remain. This technique is also economic in terms of both time and cost for both operator and patient, a factor that is particularly relevant in general dental practice, where tooth wear is becoming a more common problem needing a rapid, economic and minimally destructive solution.
The effects of advanced tooth wear on the temporomandibular joint remain unclear, but some altered function at the joint is possible where a decrease in the anterior facial height has occurred as a result of occlusal wear. Morphological adaptation does occur, but whether the altered form and function leads to symptoms remains controversial and each subject should be assessed individually in respect of this. Further investigation into the effects of tooth wear on the facial complex is needed, in particular with respect to the controlling mechanisms behind compensatory changes, but also how these changes develop with the progress of wear. Further investigation into the association between loss of posterior teeth and anterior wear is required, as is research into the long-term craniofacial effects of permanently altering the OVD as part of reconstruction of the worn dentition. The orthodontic approach to the provision of space for restoring worn teeth deserves particular attention as it could greatly simplify the treatment of wear in many cases. However, further research into the most effective type of appliance and how the orthodontic effects may best be controlled is still required.
CONCLUSIONS Tooth wear thus appears to have an influence on facial morphology that can affect its clinical management. Not only may the loss of clinical crown height require treatment, but the reduction of the vertical dimension of occlusion by wear must be considered. The adult dentofacial complex is not a static unresponsive entity and compensation for changes in face height may occur by skeletal growth and eruption, with the amount being very variable between individuals. The effects of ageing will also have an influence, and restorative therapy will not always eliminate the appearance of overclosure. Careful examination of the effects of the wear on the facial complex will help to assess the extent to which restoration of vertical and sagittal jaw relationships may be undertaken. However, the clinician should be aware of the great variability between subjects in respect of compensatory changes, and employ a trial appliance where alteration of the OVD is considered as a part of treatment. In general, a treatment philosophy in which simplicity of approach to tooth wear is needed, and the orthodontic approach to the provision of space for restorations fuhils this role well, helping to provide a simpler and more economic means of treating this complex and increasingly common problem.
References Ainamo J. (1972) Relationship
between occlusal wear of the teeth and periodontal health. Stand. J. Dent. Res. 80, 505-509. Baer M. J. (1956) Dimensional changes in the human head and face in the third decade of life. Am. J. Phys. Anthropol. 14, 557-568.
Basker R. M., Harrison A. and Ralph J. P. (1983) Overdentures in General Dental Practice. London, British Dental Association Publications, pp. 12-14. Begg P. R. (1954) Stone age mans dentition. Am. J. Orthod. 40, 298-312. Begg P. R. and Kesling P. C. (1977) Orthodontic Thebry and Technique, 3rd edn. London, W. B. Saunders, chap. 2. Behrents R. G. (1985) Growth In the Ageing Craniofacial Skeleton. Monograph 17. Craniofacial Growth Series. The Center for Human Growth and Development, The University of Michigan, Ann Arbor. Berry D. C. and Poole D. F. (1974) Masticatory function and oral rehabilitation. .J. Oral Rehabil. 1, 191-205. Berry D. C. and Poole D. F. (1976) Attrition: possible mechanisms of compensation. J. Oral Rehabif. 3,201-206. Best J. M. (1987) Dental treatment of a patient with severe attrition. J. Conn. State Dent. Assoc. 61, 24-28. Beyron H. L. (1964) Occlusal relations and mastication in Australia aboriginies. Acta Odontof. Stand. 22, 597-609. Brown K. E. (1980) Reconstruction considerations for severe dental attrition. J. Prosthet. Dent. 44, 384-388. Campbell T. D. and Barrett M. J. (1953) Dental observations on Australian aboriginals. Aust. Dent. .l 57, 1-14. Colquitt T. (1987) Sleep-wear syndrome. J. Prosthet. Dent. 57, 33-41. Crothers A. J. R. (1991) Craniofacial Morphology in Subjects with Advanced Dental Attrition. DDS Thesis, University of Edinburgh. Dahl B. L. and Krogstad 0. (1975) An alternative treatment in cases of advanced localised attrition. J. Oral Rehabil. 2, 209-214. Dahl B. L. and Krogstad 0. (1982) Effect of a partial biteraising splint on the occlusal face height. Acta Odontol. Stand. 40, 17-24. Dahl B. L. and Krogstad 0. (1985) Long term observations of an increased occlusal face height. J. Oral Rehabil. 12, 173-176. Davies T. G. H. and Pedersen P. 0. (1955) The degrees of attrition of the deciduous teeth and first permanent molars of primitive and urbanised Greenland natives. Br. Dent. J. 99, 35-42. Devlin H. (1985) Restoring the occlusal vertical dimension. Quintessence Int. 16, 131-134. Eccles J. S. (1982) Tooth surface loss from attrition, abrasion and erosion. Dent. Update 9, 373-381. Fishman L. S. (1976) Dental and skeletal relationships to attritional occlusion. Angle Orthod. 46, 51-63. Foreman P. (1988) Resin-bonded acid-etched onlays in two cases of gross attrition. Dent. Update 3, 150-153. Forsberg C. M. (1979) Facial morphology and ageing. Eur. J. Orthod. 1, 15-23. Galabert J. (1975) Medieval skulls-an orthodontic and cephalometric survey. Orthod. Fr. 46, 308-314. Gankerseer E. J. (1987) A new technique for the treatment of the severely worn dentition. Rest. Dent. 3, 13-22. Granados J. (1979) Influence of loss of teeth and attrition on the articular eminence. J. Prosthet. Dent. 42, 78-85. Hamilton M. C. and Whitehead F. I. (1968) The treatment of severe attrition in a young patient. Br. Dent. J. 125, 538-539. Hrdlicka A. (1936) Growth during adult life. Proc. Am. Phil. Sot. 76, 847-859. Ibbetson S. J. and Setchell D. J. (1989) Treatment of the worn dentition. Dent. Update 4,247-253, 300-307. Ingervall B. and Thilander B. (1974) Relations between facial morphology and activity of the masticatory muscles. J. Oral Rehabil. 1, 131-147. Johnson G. and Sivers M. (1987) Attrition, abrasion and erosion-diagnosis and treatment. Clin. Prevt. Dent. 9, 12-16.
Kayser A. F. (1981) Shortened dental arches and oral function. J. Oral Rehabil. 8, 457-462. Klatsky M. (1939) Dental attrition. J. Am. Dent. Assoc. 26, 73-83. Krogstad 0. and Dahl B. L. (1985) Dento-facial morphology in patients with advanced attrition. Eur. J. Orthod. 7, 57-62. Lasker G. W. (1953) The age factor in bodily measurements. Hum. Biol. 25, 50-63. Leigh R. W. (1925) Dental pathology of the Eskimo. Dent. Cosmos 67, 884-898. Leigh R. W. (1933) Notes on the stomatology and dental pathology of ancient Egyptians. J. Am. Dent. Assoc. 22, 199-222. Lewis K. J. and Smith B. G. N. (1973) The relationship of erosion and attrition in extensive tooth tissue loss. Br. Dent J. 135,400-404. Mack A. 0. and Allen D. N. (1968) Reconstruction of a severe case of attrition and abrasion. Br. Dent J. 125, 17-19. Mackie I. C. and Blinkhom A. S. (1991) Amelogenesis imperfecta: early interception to prevent attrition. Dent. Update 2, 79-80. Moffett B. C., Johnson L. C., McCabe J. C. et al. (1964) Articular remodelling in the adult temporomandibular joint. Am. J. Anat. 115, 119-142. Mohl N. D. (1976) Head posture and its role in occlusion. N.Y. State Dent. _I. 42, 17-23. Moller E. (1966) The chewing apparatus. Acta Phys. Stand. 69, (suppl. 280), 151-189. Molnar S. (1972) Toothwear and culture. Curr. Anthropol. 13, 51 l-526. Mongini F. (1972) Remodelling of the mandibular condyle in the adult and its relationship to the condition of the dental arches. Acta Anat 82, 437-453. Mongini F. (1975) Dental abrasion as a factor in remodelling of the mandibular condyle. Acta Anat. 92,292-300. Mongini F. (1980) Condylar remodelling after occlusal therapy. J. Prosthet. Dent. 43, 568-577. Murphy T. (1959) Compensatory mechanisms in facial height to functional tooth attrition. Aust Dent J. 4, 312-323. Murphy T. (1964) Reduction of the dental arch by approximal attrition. Br. Dent. J. 116, 483-510. P6llmann L., Berger F. and PCjllmann B. (1987) Age and dental abrasion. Gerodontics 3, 94-96. Renson C. E. (1975) Attrition, abrasion and erosion and the temporomandibular joint. Dent. Update 2,283-288. Russell M. D. (1987) The distinction between physiological and pathological attrition. J. Irish Dent Assoc. 33, 23-31.
Tooth wear and facial morphology
Samas H. V. and Solow B. (1980) Early adult changes in skeletal and soft tissue profile. Eur. 1 Orthod. 2, l-12. Shafer W., Hine M. and Lay B. (1983) Textbook ofOral Pathology, 4th edn. London, W. B. Saunders, pp. 318-323. Smith B. G. N. (1989) Toothwear: aetiology and diagnosis. Dent, Update 16, 204-212. Smith B. G. N. and Knight J. K. (1984) A comparison of tooth wear with aetiological factors. Br. Dent. J. 157, 16-19. Smith P. (1972) Studies in toothwear. Israel J. Dent Med. 21, 75-78. Solow B. (1980) The dento-alveolar compensatory mechanism. Br. J. Orthod. 7, 145-161. Solow B. and Krieborg S. (1977) Soft tissue stretching: a possible control factor in craniofacial morphogenesis. Stand. .I. Dent. Res. 85, 505-507. Tallgren A_ (1957) Changes in adult face height. Acta Odontol. Stand. (suppl. 24), 63-75. Ten Bruggen Cate H. J. (1968) Dental erosion in industry. Br. J. Zndust. Med. 25,249-261. Thomson J. L. and Kendrick G. S. (1964) Changes in the vertical dimension of the human male skull. Anat. Rec. 150, 209-2 14. Turner K. A. and Missirlian D. M. (1984) Restoration of the extremely worn dentition. J. Prosthet Dent 52, 467-474. Van Der Linden Frans P. G. M. and Duterloo Herman S. of the Human Den&ion, An Atlas. (1976) Development New York, Harper & Row, pp. 241-250. Varrella J. (1990) Effect of attritive diet on craniofacial morphology: a cephalometric analysis of a Finnish skull sample. Eur. J. Orfhod. 12, 219-222. Wassell R. W. (1989) Do occlusal factors play a role in temporomandibular dysfunction? J. Dent. 17, 101-l 10. Watson I. B. and Tulloch E. N. (1985) Clinical assessment of cases of tooth surface loss. Br. Dent. J. 159, 144-148. Whittaker D. K., Davies G. and Brown M. (1985) Tooth loss, attrition and the TMJ in a Romano-British population. J. Oral Rehabil. 12,407-419. Witter D. J., Van Elteren P. and Kayser A. F. (1987) Migration of teeth in shortened dental arches. J. Oral Rehabil. 14, 321-329. Woodside D. G. and Linder-Aronson S. (1979) The channelisation of upper and lower face heights compared to population standard in males between ages 6 and 20. Eur. J. Orthod. 1, 25-40. Xhonga A (1977) Bruxism and its effect on the teeth. J. Oral Rehabil. 4, 65-76.
Book Review Killey’s Fractures of the Mandible. P. Banks. Pp. 144. 199 1. Oxford, Butterworth-Heinemann. Softback, f 14.95.
This book is one of a series of concise monographs on facial fractures, first produced by Killey. The editorship has now passed to Peter Banks who has added a simple but assertive style. It is not intended as a comprehensive text but to provide a concise description of the management of mandibular fractures for the surgical trainee. In order to make the subject easy to follow, the text has been stripped of all superfluous discussion and debate and the illustrations have been kept simple. It can
be read easily in three hours. The chapters are arranged coherently, starting with aetiology and followed by clinical and radiological examination. Conventional treatment and the new bone plating systems are discussed together with postoperative management and complications. The reproduction of radiographic images is rather poor. Nevertheless, the book does achieve its prime objective in providing a wealth of practical information on fractures of the mandible. Apart from the trainee, the book will be of interest to the general surgeon, unfamiliar with mandibular trauma but who, through force of circumstance, has to treat such injuries. A copy of this book should be kept in most primary treatment units. M. McGurk