Combined dental wear and cementum analyses in ungulates reveal the seasonality of Neanderthal occupations in Covalejos Cave (Northern Iberia).

We propose for the first time the use of the combination of two high-resolution techniques, dental wear (meso- and microwear) and dental cementum analyses, to gain a better understanding of Neanderthal subsistence strategies and occupational patterns. Dental wear analysis provides information not only on ungulate palaeodiet and palaeoenvironments but also on hunting time and seasons. Dental cementum analysis allows the accurate determination of the age and season at death of a prey. Our study has focused on the Cantabrian region and has applied both methods to investigate the Mousterian faunal assemblages in Covalejos Cave. Identification of the ungulate palaeodiet reveals information on the environmental conditions of the studied region. Moreover, it may facilitate observation on the evolution of both palaeodiet and palaeoenvironment throughout the site sequence. Results show a general stability in the palaeoenvironmental conditions and in the ungulate palaeodiet throughout the Mousterian sequence; this finding may be attributed to the role of the area as a climate refuge, and slight differences in levels 8, 7 and 4 suggest long- or short-term but repeated Neanderthal occupations at different seasons in the annual cycle.

Gastro-oesophageal reflux - an important causative factor of severe tooth wear in Prader-Willi syndrome?

BACKGROUND: Prader-Willi syndrome (PWS) is the most common genetic human obesity syndrome and is characterized by hypotonia, endocrine disturbances, hyperphagia, obesity and mild mental retardation. Oral abnormalities, such as decreased salivary flow rates and extreme tooth wear, have also been described. Studies have shown a significant increase in reflux symptoms in individuals with obstuctive sleep apnoea syndrome and increased BMI, both of which are typical findings in PWS. Gastro-oesophageal reflux disease (GORD) has been identified in some individuals with PWS and is a significant intrinsic factor in dental tooth wear. The aim of this study was therefore to estimate the prevalence of GORD in adults and children and to evaluate a possible correlation between GORD and tooth wear in adults with PWS. They were all registered at the TAKO-centre. RESULTS: Twenty-nine individuals, 17 adults with a mean age of 32.6 years (range 18-48) and 12 children with a mean age of 8.8 years (range 3-17), agreed to undergo 24-hour oesophageal pH monitoring, and 90% of those enrolled managed to complete the examination. Four children and eleven adults were diagnosed with pathological gastro-oesophageal reflux, which is defined as acid exposure (pH less than 4) more than 3.6 or 4.3 percent of the time, respectively. Manometry performed in the adult group showed a pathologically high lower oesophageal sphincter pressure in four of the five individuals who had normal oesophageal pH values (pH under 4 less than 4.3% of the time). The two groups (reflux and non-reflux) were well balanced according to BMI, genotype, tooth grinding and hyposalivation. However, twice as many individuals in the reflux group as in the non-reflux group reported high consumption of acidic foods and drinks. Increased tooth wear was significantly correlated with GORD in the two groups (reflux n=6 and non-reflux n=6). CONCLUSIONS: The prevalence of gastro-oesophageal reflux is high in individuals with PWS. Tooth wear was strongly associated with GORD and acidic drinks, and both may be important aetiological factors underlying the extreme tooth wear in this group. Our data suggest a need for routine screening for GORD and dental wear in young individuals with Prader-Willi syndrome.

Role of particulate concentration in tooth wear.

Results are presented for wear tests on human molar enamel in silica particle mediums. Data for different particle concentrations show severe wear indicative of material removal by plasticity-induced microcrack formation, in accordance with earlier studies. The wear rates are independent of low vol% particles, consistent with theoretical models in which occlusal loads are distributed evenly over all interfacial microcontacts. However, perhaps counter-intuitively, the wear rate diminishes substantially at higher vol%. This is attributed to a greater proportion of lower-load microcontacts transitioning into a region of mild wear, where microcracking is suppressed. Implications of these results in relation to evolutionary biology and dentistry are explored.

Facial skeleton asymmetry and its relationship to mastication in the Early Medieval period (Great Moravian Empire, Mikulcice, 9th-10th century).

OBJECTIVES: The aim of this study was to analyse the relationship of mastication and directional asymmetry (DA) of upper facial skeleton in Early Medieval sample from the Mikulcice settlement (Czech Republic). DESIGN: The settlement is divided into two burial areas of presumably different socioeconomic status: the castle and the sub-castle. The material consisted of 193 individuals (125 castle, 68 sub-castle). The relationship of facial skeleton DA and mastication was analysed by examining tooth wear and mandibular shape by means of 3D geometric morphometrics. Tooth wear of premolars and molars was evaluated using appropriate scoring systems. 3D coordinates of 35 mandibular landmarks were scanned using MicroScribe G2X digitizing system. RESULTS: The results did not reveal any significant differences in tooth wear DA or mandible DA values between burial areas or sexes. Mandibular shape, however, differed significantly between burial areas and sexes. Directional changes of mandibular landmarks supported a right chewing side preference in the sample. Significant relationship between upper facial skeleton DA and mandible DA was recorded. CONCLUSIONS: Differences in subsistence between burial areas and sexes did not translate into differences in mandible DA and dental wear. However, mandibular shape analysis revealed prominence of areas affected by masticatory muscles in individuals from the castle. Higher consumption of tough material, such as meat, has been proposed as possible explanation. The right side was found to be preferential for chewing. The relationship between upper facial skeleton DA and mandible DA was concluded to be the result of the compensatory and adaptive function of mandible.

Worn is born: The role of the maxillo-mandibular relation in management of worn dentition.

Worn dentition, often accompanied by occlusion changes such as reduced vertical dimension, poses a big challenge to both diagnosis and treatment. Current established causes fail to explain the observed tooth wearing patterns, and the treatments based on the documented pathogeneses are often unpredictable and require frequent maintenance. From the perspective of stomatognathic system, we postulate that the role of maxillo-mandibular relation is a crucial part in the tooth wear progression patterns, and should be well addressed in treatment planning. Incompatible occlusion with the inherent tendency of maxillo-mandibular relation has a profound effect on either wearing of natural teeth or failures of restorations. With the aid of cephalometrics and analysis of occlusion it is now possible to reduce this fallacy and achieve a harmony by re-designing the occlusion. According to our treated worn dentition cases, the restoring treatment guided by the tendency of maxillo-mandibular relation showed very promising results.

Mechanical modelling of tooth wear.

Different diets wear teeth in different ways and generate distinguishable wear and microwear patterns that have long been the basis of palaeodiet reconstructions. Little experimental research has been performed to study them together. Here, we show that an artificial mechanical masticator, a chewing machine, occluding real horse teeth in continuous simulated chewing (of 100 000 chewing cycles) is capable of replicating microscopic wear features and gross wear on teeth that resemble wear in specimens collected from nature. Simulating pure attrition (chewing without food) and four plant material diets of different abrasives content (at n = 5 tooth pairs per group), we detected differences in microscopic wear features by stereomicroscopy of the chewing surface in the number and quality of pits and scratches that were not always as expected. Using computed tomography scanning in one tooth per diet, absolute wear was quantified as the mean height change after the simulated chewing. Absolute wear increased with diet abrasiveness, originating from phytoliths and grit. In combination, our findings highlight that differences in actual dental tissue loss can occur at similar microwear patterns, cautioning against a direct transformation of microwear results into predictions about diet or tooth wear rate.

Age-related changes in molar topography and shearing crest length in a wild population of mountain Gorillas from Volcanoes National Park, Rwanda.

OBJECTIVES: Great ape teeth must remain functional over long lifespans. The molars of the most folivorous apes, the mountain gorillas, must maintain shearing function for 40+ years while the animals consume large quantities of mechanically challenging foods. While other folivorous primates experience dental senescence, which compromises their occlusal surfaces and affects their reproductive success as they age, it is unknown whether dental senescence also occurs in mountain gorillas. In this article, we quantified and evaluated how mountain gorilla molars change throughout their long lifespans. MATERIALS AND METHODS: We collected high-resolution replicas of M(1)s (n = 15), M(2)s (n = 13), and M(3)s (n = 11) from a cross-sectional sample of wild mountain gorilla skeletons from the Virunga Volcanoes, ranging in age from 4 to 43 years. We employed dental topographic analyses to track how aspects of occlusal slope, angularity, relief index, and orientation patch count rotated change with age. In addition, we measured the relative length of shearing crests in two- and three-dimensions. RESULTS: Occlusal topography was found to decrease, while 2D relative shearing crest length increased, and 3D relative crest lengths were maintained with age. DISCUSSION: Our findings indicate that shearing function is maintained throughout the long lifetimes of mountain gorillas. Unlike the dental senescence experienced by other folivorous primates, mountain gorillas do not appear to possess senesced molars despite their long lifetimes, mechanically challenging diets, and decreases in occlusal topography with age.

Dust in the wind: How climate variables and volcanic dust affect rates of tooth wear in Central American howling monkeys.

OBJECTIVES: Two factors have been considered important contributors to tooth wear: dietary abrasives in plant foods themselves and mineral particles adhering to ingested food. Each factor limits the functional life of teeth. Cross-population studies of wear rates in a single species living in different habitats may point to the relative contributions of each factor. MATERIALS AND METHODS: We examine macroscopic dental wear in populations of Alouatta palliata (Gray, 1849) from Costa Rica (115 specimens), Panama (19), and Nicaragua (56). The sites differ in mean annual precipitation, with the Panamanian sites receiving more than twice the precipitation of those in Costa Rica or Nicaragua (∼3,500 mm vs. ∼1,500 mm). Additionally, many of the Nicaraguan specimens were collected downwind of active plinian volcanoes. Molar wear is expressed as the ratio of exposed dentin area to tooth area; premolar wear was scored using a ranking system. RESULTS: Despite substantial variation in environmental variables and the added presence of ash in some environments, molar wear rates do not differ significantly among the populations. Premolar wear, however, is greater in individuals collected downwind from active volcanoes compared with those living in environments that did not experience ash-fall. DISCUSSION: Volcanic ash seems to be an important contributor to anterior tooth wear but less so in molar wear. That wear is not found uniformly across the tooth row may be related to malformation in the premolars due to fluorosis. A surge of fluoride accompanying the volcanic ash may differentially affect the premolars as the molars fully mineralize early in the life of Alouatta.

Tooth wear and feeding ecology in mountain gorillas from Volcanoes National Park, Rwanda.

OBJECTIVES: Ecological factors have a dramatic effect on tooth wear in primates, although it remains unclear how individual age contributes to functional crown morphology. The aim of this study is to determine how age and individual diet are related to tooth wear in wild mountain gorillas (Gorilla beringei beringei) from Volcanoes National Park, Rwanda. MATERIAL AND METHODS: We calculated the percent of dentine exposure (PDE) for all permanent molars (M1-M3) of known-age mountain gorillas (N = 23), to test whether PDE varied with age using regression analysis. For each molar position, we also performed stepwise multiple linear regression to test the effects of age and percentage of time spent feeding on different food categories on PDE, for individuals subject to long-term observational studies by the Dian Fossey Gorilla Fund International's Karisoke Research Center. RESULTS: PDE increased significantly with age for both sexes in all molars. Moreover, a significant effect of gritty plant root consumption on PDE was found among individuals. Our results support prior reports indicating reduced tooth wear in mountain gorillas compared to western gorillas, and compared to other known-aged samples of primate taxa from forest and savanna habitats. DISCUSSION: Our findings corroborate that mountain gorillas present very low molar wear, and support the hypothesis that age and the consumption of particular food types, namely roots, are significant determinants of tooth wear variation in mountain gorillas. Future research should characterize the mineral composition of the soil in the Virunga habitat, to test the hypothesis that the physical and abrasive properties of gritty foods such as roots influence intra- and interspecific patterns of tooth wear.

Relación entre la recesión ósea y atrición en cráneos secos contemporáneos / Relationship between bone recession and attrition in contemporary dry skulls

Objetivos: El objetivo de éste estudio és observar la posible influencia de las fuerzas oclusales según el grado de atrición de las piezas dentarias sobre la altura de la cresta alveolar. Material y métodos: Se estudiaron dientes de cráneos secos de la época actual y secomparó el desgaste oclusal ó atrición (A) con la pérdida de altura de la cresta alveolar (CA) ó recesión ósea (RO) y ambos registros se relacionaron estadísticamente. Resultados: De todos los dientes estudiados 2 tuvieron grado de atrición (GA) 0, 170 grado 1, 96 grado 2 y 15 grado 3. Registrando la recesión ósea (RO) las medidas extremas promedio estuvieron entre 2,80mm y 5,30mm; la mayor RO promedio se encontró en la parte media de las caras libres (pieza 23) y la menor en distal (pieza 11). Conclusión: No hay correlación entre la recesión ósea y el desgaste oclusal ó atrición.

Aim: The aim of these work is to know the relaciònship between the bonerecessiòn and the attritiòn.Materials and methods: We taken 228 teeth belonging to 25 dry skullsof actual edge and we compare the bone recession (BR) with the occlusalwaer or attrition (A) and both to be related with a statistical analyses.Results: Of all the teeth studied, 2 had attrition degree 0, 170 degree 1,96 degree 2 y 15 degree 3. Regarding the BR the measures differ between2,80 to 5,30mm. The BR major average was in the middle of the free aspect(tooth 23) and the minor in distal (tooth 11).Conclusion: There are not correlation between bone recession andocclusal wear or attrition.

Sleep bruxism in individuals with and without attrition-type tooth wear: An exploratory matched case-control electromyographic study.

OBJECTIVES: To examine if there is a difference in possible sleep bruxism activity (SB) in subjects with or without attrition-type tooth wear. METHODS: Sixteen individuals with pronounced attritional-type tooth wear were compared with sex and aged matched controls without tooth wear by means of measurement of electromyographic (EMG) activity during a minimum of four consecutive nights of sleep. Mean age and range for the study- and control- group was 23.7 years (range 19.9-28.5) and 23.6 years (range 20.3-27.9), respectively. There were 11 females and five males in each of the two groups. The attrition group presented incisal/occlusal attrition wear into dentin and matching wear facets between opposing anterior teeth. The controls had negligible signs of incisal/occlusal wear and a minimal number of matching wear facets. RESULTS: The prevalence of both self-reported and partner-reported SB was significantly more common in the attrition group compared to the controls (P=0.04 and P=0.007, respectively). Self-reported morning facial pain was similarly more common in the attrition group (P=0.014). Maximum opening capacity, number of muscles painful to palpation, salivary flow rate and buffering capacity were not significantly different between the groups. Interestingly, none of the measures of jaw muscle EMG activity during sleep, as recorded by the portable EMG equipment, differed significantly between the attrition group and the matched controls (P>0.05). CONCLUSIONS: The results from this exploratory study suggest that there is no difference in EMG activity between subjects with and without attrition-type tooth wear. Further research is needed in order to substantiate these preliminary findings.

Does tooth wear influence ageing? A comparative study across large herbivores.

We test whether the intensity of tooth wear influences the strength of actuarial senescence across species of large herbivores. We collected from the literature data on tooth wear in the wild (measured as the slope of the regression of log-transformed M1 crown height on age), longevity (measured as the age at which 90% of individuals are dead) and two metrics of actuarial senescence in captive populations (rate of senescence between 6 and 12 years of age and Gompertz rate of senescence). Between-species differences and variation in tooth height accounted for most of the observed variation in tooth wear among large herbivores: tooth height and tooth wear were positively correlated. In contrast, tooth wear was little influenced by sex, body mass, or taxonomy. No marked between-sex differences in longevity occurred. Males senesced faster than females when tooth wear was low (for both senescence metrics), while between-sex differences in actuarial senescence when tooth wear was high depended on the metric used to measure actuarial senescence. While longevity was mostly independent of the intensity of tooth wear, we found general support for a positive relationship between both measures of actuarial senescence and tooth wear. These patterns were consistent whether hypsodonty was controlled for or not. Although varying according to sex and to the metric used for assessing actuarial senescence, our findings suggest overall that tooth wear could be positively associated with actuarial senescence among large herbivores. Further longitudinal studies focusing on changes within individuals will be required to test whether a mechanistic link between tooth wear and actuarial senescence occurs in large herbivores.

3D Simulation Modeling of the Tooth Wear Process.

Severe tooth wear is the most common non-caries dental disease, and it can seriously affect oral health. Studying the tooth wear process is time-consuming and difficult, and technological tools are frequently lacking. This paper presents a novel method of digital simulation modeling that represents a new way to study tooth wear. First, a feature extraction algorithm is used to obtain anatomical feature points of the tooth without attrition. Second, after the alignment of non-attrition areas, the initial homogeneous surface is generated by means of the RBF (Radial Basic Function) implicit surface and then deformed to the final homogeneous by the contraction and bounding algorithm. Finally, the method of bilinear interpolation based on Laplacian coordinates between tooth with attrition and without attrition is used to inversely reconstruct the sequence of changes of the 3D tooth morphology during gradual tooth wear process. This method can also be used to generate a process simulation of nonlinear tooth wear by means of fitting an attrition curve to the statistical data of attrition index in a certain region. The effectiveness and efficiency of the attrition simulation algorithm are verified through experimental simulation.

Assessment of masticatory muscle activity and occlusion time in patients with advanced tooth wear.

OBJECTIVE: Tooth wear is a basic physiological adjustment mechanism in the masticatory system. Unfortunately, it is not clear what the relationship is between the activity of the masticatory muscles and the tooth hard tissue loss (mainly enamel) in patients with advanced tooth wear. The aims of this study were (1) to compare the occlusion times and (2) to compare the EMG activity in maximal voluntary clench of the masseter and anterior temporalis muscles of patients with advanced tooth wear to the same activity of healthy volunteers. DESIGN: 50 (16F, 34M) patients and 30 (12F, 18M) age matched controls were clinically examined to assess the degree of wear (TWI). Each subject underwent electromyographic analysis (bilateral anterior temporalis, superficial masseter, anterior digastric and sternocleidomastoid muscles) and digital occlusal analysis. RESULTS: Mean values of the electrical potentials of the mandible elevating muscles during clench were higher in the study group compared to the controls. A negative correlation was found between the temporalis and masseter muscle activities during clench and the mean value of TWI (r=-0.383, p=0.009; r=-0.447, p=0.002). Occlusion time was longer in the study group compared to controls (p<0.05). CONCLUSIONS: Mandibular adductors demonstrated lower muscular activities during clenching in the tooth wear patients; however, the cause of this finding is not certain. Prolongation of occlusion time may exacerbate occlusal surfaces wear or excessive wear may prolong occlusion time.

Industrial noise and tooth wear - experimental study.

UNLABELLED: Tooth wear is a complex multifactorial process that involves the loss of hard dental tissue. Parafunctional habits have been mentioned as a self-destructive process caused by stress, which results in hyperactivity of masticatory muscles. Stress manifests itself through teeth grinding, leading to progressive teeth wear. The effects of continuous exposure to industrial noise, a "stressor" agent, cannot be ignored and its effects on the teeth must be evaluated. AIMS: The aim of this study was to ascertain the effects of industrial noise on dental wear over time, by identifying and quantifying crown area loss. MATERIAL AND METHODS: 39 Wistar rats were used. Thirty rats were divided in 3 experimental groups of 10 animals each. Animals were exposed to industrial noise, rich in LFN components, for 1, 4 and 7 months, with an average weekly exposure of 40 hours (8h/day, 5 days/week with the weekends in silence). The remaining 9 animals were kept in silence. The areas of the three main cusps of the molars were measured under light microscopy. STATISTICAL ANALYSIS USED: A two-way ANOVA model was applied at significance level of 5%. RESULTS: The average area of the molar cusps was significantly different between exposed and non-exposed animals. The most remarkable differences occurred between month 1 and 4. The total crown loss from month 1 to month 7 was 17.3% in the control group, and 46.5% in the exposed group, and the differences between these variations were significant (p<0.001). CONCLUSIONS: Our data suggest that industrial noise is an important factor in the pathogenesis of tooth wear.

Loading and composite restoration assessment of various non-carious cervical lesions morphologies - 3D finite element analysis.

BACKGROUND: The present study analysed the effects of different occlusal loading on premolars displaying various non-carious cervical lesions morphologies, restored (or not) with composites, by 3D finite element analysis. METHODS: A three-dimensional digital model of a maxillary premolar was generated using CAD software. Three non-carious cervical lesions morphological types were simulated: wedged-shaped, saucer and mixed. All virtual models underwent three loading types (100 N): vertical, buccal and palatal loading. The simulated non-carious cervical lesions morphologies were analysed with and without restorations to consider specific regions, such as the occlusal and gingival walls as well as the depth of the lesions. Data summarizing the stress distribution were obtained in MPa using Maximum Principal Stress. RESULTS: Palatal loads were responsible for providing the highest values of accumulated tensile stress on the buccal wall; 27.66 MPa and 25.76 MPa for mixed and wedged-shaped morphologies, respectively. The highest tensile values found on non-carious cervical lesions morphologies restored with composite resin were 5.9 MPa in the mixed morphology, similar to those found on sound models despite their morphologies and occlusal loading. CONCLUSIONS: The various non-carious cervical lesions morphologies had little effect on stress distribution patterns, whereas the loading type and presence of composite restorations influenced the biomechanical behaviour of the maxillary premolars.

The association between dental wear and reduced vertical dimension of the face: a morphologic study on human skulls.

OBJECTIVE: The aim of this study was to explore the relationship between dental wear and facial morphology, with particular reference to the occlusal vertical dimension, in modern human skulls. DESIGN: One hundred and three skulls (52 men and 51 women) between the ages of 20 and 50+ years old were studied. The selected skulls were from a modern period (the 17th and the 18th centuries) and included at least one entire condyle and had at least 3 posterior teeth (premolar or molar) in each quadrant to allow for dental articulation. Occlusal wear was evaluated using ordinal scale (0-4) and vertical occlusal dimension was evaluated by measuring upper facial height (UFH), lower facial height (LFH), LFH-to-UFH ratio (L-U-R) and dental wear. Based on the occlusal wear score, two groups were defined: with and without significant wear. RESULTS: Significant relation was observed between age and dental wear (P<0.01). No significant differences were found in the LFH (P=0.847) or UFH (P=0.108) between the two wear groups. In addition, no significant difference (P=0.132) was demonstrated in the LFH-to-UFH ratio between the groups. No difference was observed in the dental wear score between genders (P=0.321). CONCLUSION: Within its limitations, this study demonstrated that dental wear does not influence the vertical dimension of occlusion. Our assumption is that the dento-facial complex fully compensates for the dental effects of wear throughout life.

Dental wear: a scanning electron microscope study.

Dental wear can be differentiated into different types on the basis of morphological and etiological factors. The present research was carried out on twelve extracted human teeth with dental wear (three teeth showing each type of wear: erosion, attrition, abrasion, and abfraction) studied by scanning electron microscopy (SEM). The study aimed, through analysis of the macro- and micromorphological features of the lesions (considering the enamel, dentin, enamel prisms, dentinal tubules, and pulp), to clarify the different clinical and diagnostic presentations of dental wear and their possible significance. Our results, which confirm current knowledge, provide a complete overview of the distinctive morphology of each lesion type. It is important to identify the type of dental wear lesion in order to recognize the contributing etiological factors and, consequently, identify other more complex, nondental disorders (such as gastroesophageal reflux, eating disorders). It is clear that each type of lesion has a specific morphology and mechanism, and further clinical studies are needed to clarify the etiological processes, particularly those underlying the onset of abfraction.

Effects of dietary fracture toughness and dental wear on chewing efficiency in geladas (Theropithecus gelada).

Chewing efficiency has been associated with fitness in mammals, yet little is known about the behavioral, ecological, and morphological factors that influence chewing efficiency in wild animals. Although research has established that dental wear and food material properties independently affect chewing efficiency, few studies have addressed the interaction among these factors. We examined chewing efficiency, measured as mean fecal particle size, as a function of seasonal shifts in diet (and corresponding changes in food fracture toughness) in a single breeding population of a grazing primate, the gelada monkey, at Guassa, Ethiopia. We also measured dental topographic traits (slope, angularity, and relief index) and relative two- and three-dimensional shearing crest lengths in a cross-sectional wear series of gelada molars. Chewing efficiency decreased during the dry season, a pattern corresponding to the consumption of foods with higher fracture toughness. Older individuals experienced the most pronounced decreases in chewing efficiency between seasons, implicating dental wear as a causal factor. This pattern is consistent with our finding that dental topographic metrics and three-dimensional relative shearing crest lengths were lowest at the last stage of wear. Integrating these lines of behavioral, ecological, and morphological evidence provides some of the first empirical support for the hypothesis that food fracture toughness and dental wear together contribute to chewing efficiency. Geladas have the highest chewing efficiencies measured thus far in primates, and may be analogous to equids in their emphasis on dental design as a means of particle size reduction in the absence of highly specialized digestive physiology.

The interactions between attrition, abrasion and erosion in tooth wear.

Tooth wear is the result of three processes: abrasion (wear produced by interaction between teeth and other materials), attrition (wear through tooth-tooth contact) and erosion (dissolution of hard tissue by acidic substances). A further process (abfraction) might potentiate wear by abrasion and/or erosion. Knowledge of these tooth wear processes and their interactions is reviewed. Both clinical and experimental observations show that individual wear mechanisms rarely act alone but interact with each other. The most important interaction is the potentiation of abrasion by erosive damage to the dental hard tissues. This interaction seems to be the major factor in occlusal and cervical wear. The available evidence is insufficient to establish whether abfraction is an important contributor to tooth wear in vivo. Saliva can modulate erosive/abrasive tooth wear, especially through formation of pellicle, but cannot prevent it.