Examination of the Interproximal Wear Mechanism: Facet Morphology and Surface Texture Analysis.

Dentition is considered a dynamic system with forces that directly affect dental treatment stability and success. Understanding the biomechanical forces that influence tooth alignment is essential for both planning and performing dental treatments, as well as for anthropological and evolutionary studies. While there is currently an abundance of research on the mechanics of dental wear at the occlusal surface, the mechanics of interproximal dental wear is largely unexplored. The fretting mechanism, a wear process resulting from small-amplitude cyclic motion of 2 solid contacting surfaces, was refuted as a possible mechanism for occlusal wear but has never been considered for interproximal wear. Therefore, the aim of the current study was to reveal the biomechanical process of the interproximal wear and to explore whether the fretting mechanism could be associated with this process. Premolar teeth with interproximal wear facets were examined by 3-dimensional surface texture analysis using a high-resolution confocal disc-scanning measuring system. The unique texture topography of 3 areas in the proximal surface of each tooth was analyzed by applying 3D dental surface texture analysis. Each area showed unique texture characteristics, presenting statistically significant differences between the inner area of the facet and its margins or the surface outside the facets borders. Based on these results, we concluded that fretting is a key mechanism involved in interproximal wear.

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.

Wear Fast, Die Young: More Worn Teeth and Shorter Lives in Iberian Compared to Scottish Red Deer.

Teeth in Cervidae are permanent structures that are not replaceable or repairable; consequently their rate of wear, due to the grinding effect of food and dental attrition, affects their duration and can determine an animal's lifespan. Tooth wear is also a useful indicator of accumulative life energy investment in intake and mastication and their interactions with diet. Little is known regarding how natural and sexual selection operate on dental structures within a species in contrasting environments and how these relate to life history traits to explain differences in population rates of tooth wear and longevity. We hypothesised that populations under harsh environmental conditions should be selected for more hypsodont teeth while sexual selection may maintain similar sex differences within different populations. We investigated the patterns of tooth wear in males and females of Iberian red deer (Cervus elaphus hispanicus) in Southern Spain and Scottish red deer (C. e. scoticus) across Scotland, that occur in very different environments, using 10343 samples from legal hunting activities. We found higher rates of both incisor and molar wear in the Spanish compared to Scottish populations. However, Scottish red deer had larger incisors at emergence than Iberian red deer, whilst molars emerged at a similar size in both populations and sexes. Iberian and Scottish males had earlier tooth depletion than females, in support of a similar sexual selection process in both populations. However, whilst average lifespan for Iberian males was 4 years shorter than that for Iberian females and Scottish males, Scottish males only showed a reduction of 1 year in average lifespan with respect to Scottish females. More worn molars were associated with larger mandibles in both populations, suggesting that higher intake and/or greater investment in food comminution may have favoured increased body growth, before later loss of tooth efficiency due to severe wear. These results illustrate how independent selection in both subspecies, that diverged 11,700 years BP, has resulted in the evolution of different longevity, although sexual selection has maintained a similar pattern of relative sex differences in tooth depletion. This study opens interesting questions on optimal allocation in life history trade-offs and the independent evolution of allopatric populations.

Rate and pattern of interproximal dental attrition.

Although occlusal and interproximal attrition occur because of diverse etiology and present dissimilar features, both progress with age. The objectives of this study were to reveal the rate and pattern of development of interproximal attrition facets (PAF) with age and to compare those with occlusal attrition (OA) changes. Five-hundred and ninety-four teeth were collected from 198 skulls (of adults, 20-71 yr of age). Three mandibular teeth [first premolar (P1), second premolar (P2), and first molar (M1)] were examined for PAF size and OA rate. Interproximal attrition and OA followed similar patterns of development until subjects reached 40-45 yr of age, after which they took different paths: PAF did not increase in size and were not as large as in younger groups, regardless of facet location, whereas OA continued to progress. The PAF changes with age differed between premolars and molars, unlike OA, which presented a similar rate for all teeth studied. Although OA scores presented significantly moderate correlations with age, PAF area size demonstrated low correlations with age. Low, but significant, correlations were found between the rate of OA and that of PAF. However, PAF and OA exhibited different patterns of development with age. Premolars and molars presented dissimilar development of PAF, which is probably caused by a unique attrition pattern in the molar teeth, different morphology, and force vectors.

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.

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.

Occlusal tooth wear in Chinese adults with shortened dental arches.

To assess associations between occlusal tooth wear and shortened dental arches (SDA) in Chinese 40 years and older subjects. From a sample of 1462 urban and rural adults, those presenting with SDA (n = 150) were compared with a control group of 65 randomly selected subjects with complete dentitions (CDA). Occlusal wear was assessed using a modified Smith and Knight index - the occlusal tooth wear index (OWTI) - and analysed using multivariate (logistic) regression. There was no significant effect from SDA on severe occlusal wear (OTWI score 3 or 4: OR = 2.016; 95% CI = 0.960-4.231; P = 0.064). Higher age was associated with severe occlusal wear (P values ≤0.007) and with higher mean OTWI scores; urban had less often severe occlusal wear than rural residents (OR = 0.519; P = 0.008). Higher mean OTWI scores were associated with rural residents, except for anterior teeth. Females had lower mean OTWI score for anterior teeth (effect = -0.153; P = 0.030). Premolars in SDA had higher mean OTWI scores compared with those in CDA (effect = +0.213; P = 0.006). In SDA, more posterior occluding pairs (POPs) were associated with lower mean OTWI sores for anterior teeth (effect: -0.158; P = 0.008) and higher scores for molars (effect: +0.249, P = 0.003). Subjects with SDA or CDA presented comparable occlusal wear, but premolars in SDA tend to have higher probability for having occlusal wear. Fewer numbers of POPs were associated with more wear in anterior teeth.

Phasic jaw motor episodes in healthy subjects with or without clinical signs and symptoms of sleep bruxism: a pilot study.

BACKGROUND: To investigate the association between each clinical diagnosis criterion for sleep bruxism (SB) and the frequency of jaw motor events during sleep. METHODS: Video-polysomnography was performed on 17 healthy adult subjects (mean age, 26.7 ± 2.8 years), with at least one of the following clinical signs and symptoms of SB: (1) a report of frequent tooth grinding, (2) tooth attrition with dentine exposure through at least three occlusal surfaces, (3) morning masticatory muscle symptoms, and (4) masseter muscle hypertrophy. Episodes of rhythmic masticatory muscle activity (RMMA) and isolated tonic activity were scored visually. These variables were compared with regards to the presence or absence of each clinical sign and symptom. RESULTS: In 17 subjects, 4.0 ± 2.5/h (0.1-10.2) RMMA and 1.0 ± 0.8/h (0-2.4) isolated tonic episodes were observed (total episodes: 5.0 ± 2.4/h (1.2-11.6)). Subjects with self-reported grinding sounds (n=7) exhibited significantly higher numbers of RMMA episodes (5.7 ± 2.3/h) than those without (n=10; 2.8 ± 1.8/h) (p=0.011). Similarly, subjects with tooth attrition (n=6) showed significantly higher number of RMMA episodes (5.6 ± 3.1/h) than those without (n=11; 3.2 ± 1.6/h) (p=0.049). The occurrence of RMMA did not differ between the presence and absence of morning masticatory muscle symptoms or muscle hypertrophy. CONCLUSIONS: Clinical signs and symptoms frequently used for diagnosing SB can represent different clinical and physiological aspects of jaw motor activity during sleep.

The arrangement of the interproximal interfaces in the human permanent dentition.

OBJECTIVES: The interproximal interface (IPI) is the interface between two adjacent teeth, i.e., the site where forces are transmitted along the dental arch. We investigated the IPI arrangement of the human permanent dentition. Specifically, the IPI morphometrical characteristics were studied and interpreted within a biomechanical framework. SUBJECTS AND METHODS: A novel in vivo IPI measurement was developed based on diversity in transillumination of Polyvinyl siloxane impression of the interproximal region. The study group included 30 subjects, aged 27, ±4.0 years. Eleven parameters were examined in each of the 26 IPIs of the permanent dentition. RESULTS: The IPI showed intra-arch similarity and interarch diversity between the tooth groups. The IPI shape was predominantly oval (60-100%), yet kidney-shaped in some molars (22-40%). From incisors to molars: the IPI increased significantly (p < 0.001) in size (1.72 to 6.05 mm(2)), occupied more of the proximal wall (7.8-12%), changed its orientation from vertical to horizontal (88.66-14.80°), and was mainly located in the buccal-occlusal quadrant of the proximal wall, chiefly in the molar teeth. CONCLUSIONS: The IPI is a product of proximal wall attrition and is dictated by the mastication forces, number of cusps, and crown inclination. IPI arrangement counteracts the adverse crowding effect of the anterior component of the mastication forces. CLINICAL RELEVANCE: The IPI characteristics found in the present study provide guidelines for crown and proximal filling restorations to meet dental physiology requirements. Further, IPI determines correct tooth alignment and proximal wall stripping applied to resolve arch length deficiency.

Effect of occlusal splint therapy on maximum bite force in individuals with moderate to severe attrition of teeth.

OBJECTIVE: The purpose of the pilot study was to determine the effect of restoring lost occlusal vertical dimension (OVD) due to attrition on maximum bite force in humans. METHODOLOGY: A total of 124 subjects in age range of 25-40 years, with moderate to severe attrition, having full complement of teeth were screened according to inclusion and exclusion criteria. After consent, occlusal vertical dimension was assessed by employing mechanical and physiological methods in the experimental group and a maxillary canine guided hard splint was fabricated for each subjects fulfilling inclusion criteria and with positive consent (78). Bite force in experimental group was measured before, immediately after delivery of splint and subsequently at an interval of four, eight, and twelve weeks. Due loss during follow up, only 50 subjects could be available for bite force recording till 12 weeks. Bite force of age, gender, height and weight matched controls with no signs of attrition was also measured for comparison. RESULTS: Bite force of the experimental group was found to be significantly less than the matched controls (P=0.000) initially. After delivery of splint, bite force values increased progressively till twelve weeks. However comparison of bite force values of experimental group with control group showed no significant difference at end of eight (P=0.008) and twelve weeks (P=0.162). CONCLUSION: It was concluded that maximum bite force increases with restoration of lost vertical using splint therapy. A time period of 8-12 weeks is required to restore the maximum bite force value approximately similar to matched controls.

Determining the direction of tooth grinding: an in vitro study.

The analysis of microwear patterns, including scratch types and widths, has enabled reconstruction of the dietary habits and lifestyles of prehistoric and modern humans. The aim of this in vitro study was to determine whether an assessment of microwear features of experimental scratches placed on enamel, perpendicularly to the direction of grinding, could predict the grinding direction. Experimental scratches were placed using a scalpel blade on standardised wear facets that had been prepared by wearing opposing enamel surfaces in an electromechanical tooth wear machine. These control 'baseline' facets (with unworn experimental scratches) were subjected to 50 wear cycles, so that differential microwear could be observed on the leading and trailing edges of the 'final' facets. In Group 1 (n=28), the 'footprint' microwear patterns corresponding to the known grinding direction of specimens in the tooth wear machine were identified. Then, they were used to predict the direction of tooth grinding blindly in the same sample after a 2-week intermission period. To avoid overfitting the predictive model, its sensitivity was also cross-validated in a new sample (Group 2, n=14). A crescent-shaped characteristic observed in most experimental scratches matched the grinding direction on all occasions. The best predictor of the direction of grinding was a combined assessment of the leading edge microwear pattern and the crescent characteristic (82.1% in Group 1 and 92.9% in Group 2). In conclusion, a simple scratch test can determine the direction of tooth grinding with high reliability, although further improvement in sensitivity is desirable.

Fracture susceptibility of worn teeth.

An experimental simulation study is made to determine the effects of occlusal wear on the capacity of teeth to resist fracture. Tests are carried out on model dome structures, using glass shells to represent enamel and epoxy filler to represent dentin. The top of the domes are ground and polished to produce flat surfaces of prescribed depths relative to shell thickness. The worn surfaces are then loaded axially with a hard sphere, or a hard or soft flat indenter, to represent extremes of food contacts. The loads required to drive longitudinal cracks around the side walls of the enamel to failure are measured as a function of relative wear depth. It is shown that increased wear can inhibit or enhance load-bearing capacity, depending on the nature of the contact. The results are discussed in the context of biological evolutionary pressures.

The development of quantitative methods using virtual models for the measurement of tooth wear.

Tooth wear is an unavoidable process associated with aging. Currently, virtual three-dimensional dental models are widely used and provide an advantage for studying tooth wear. However, there are no wear assessment parameters using virtual tooth models for the quantitative analysis of wear. Therefore, the aim of this study is to develop and evaluate quantitative wear measurement parameters. Ninety maxillary and mandibular dental casts were prepared and rendered as virtual three-dimensional models. For qualitative wear scoring, Hooper's new tooth wear index (NTWI) was used. For quantitative wear measurement, virtual vectors and occlusal planes were generated with reference points. Angles, height, and distance parameters were measured from reference points, vectors or planes. Intra- and interobserver reproducibility was determined for NTWI scoring and quantitative measurements. Quantitatively measurements for all parameters were subgrouped according to age groups and NTWI score groups. The mean and standard deviation were calculated for each group. One-way analysis of variance (ANOVA) test and the coefficients test were performed on the groups. Overall, intra- and interobserver reproducibility was good for both qualitative and quantitative measurement. In the ANOVA test, angle and height parameters showed significant differences between groups, whereas distance parameters did not. Similar results were observed in the coefficients test. However, plane heights and lingual side measurement parameters of the mandible are not recommended. In conclusion, this study indicates that all angle or height parameters of the maxilla and angle or vector height parameters of the buccal side of the mandible can be used as meaningful parameters in a quantitative wear study.

An electromyographic study to assess the minimal time duration for using the splint to raise the vertical dimension in patients with generalized attrition of teeth.

BACKGROUND: To investigate the effect of restoration of lost vertical by centric stabilizing splint on electromyographic (EMG) activity of masseter and anterior temporalis muscles bilaterally in patients with generalized attrition of teeth. MATERIALS AND METHODS: EMG activity of anterior temporalis and masseter muscle was recorded bilaterally for 10 patients whose vertical was restored with centric stabilizing splint. The recording was done at postural rest position and in maximum voluntary clenching for each subject before the start of treatment, immediately after placement of splint and at subsequent recall visits, with splint and without the splint. RESULTS: The EMG activity at postural rest position (PRP) and maximum voluntary clench (MVC) decreased till 1 month for both the muscles. In the third month, an increase in muscle activity toward normalization was noted at PRP, both with and without splint. At MVC in the third month, the muscle activity without splint decreased significantly as compared to pretreatment values for anterior temporalis and masseter, while with the splint an increase was seen beyond the pretreatment values. CONCLUSION: A definite response of anterior temporalis and masseter muscle was observed over a period of 3 months. This is suggestive that the reversible increase in vertical prior to irreversible intervention must be carried out for a minimum of 3 months to achieve neuromuscular deprogramming. This allows the muscle to get adapted to the new postural position and attain stability in occlusion following splint therapy.

Clinical studies of dental erosion and erosive wear.

We define erosion as a partial demineralisation of enamel or dentine by intrinsic or extrinsic acids and erosive tooth wear as the accelerated loss of dental hard tissue through the combined effect of erosion and mechanical wear (abrasion and attrition) on the tooth surface. Most experts believe that during the last decade there has been a significant increase in the prevalence and severity of erosive tooth wear, particularly in adolescents. Even when erosive wear occurs in its milder forms, this is a matter of concern, as it may compromise the integrity of an otherwise healthy dentition in later life. The erosive wear process is complicated and modified by many chemical, behavioural and associated processes in the mouth. If interventions are to be developed it is therefore important that in vivo methods are developed to assess the outcomes of the erosion and erosive wear processes and the effects of interventions upon them. This paper discusses potential methods of investigating erosion and erosive wear in vivo and the difficulties associated with clinical studies.

Assessment of the effect of the use of laser light or dantrolene on facial muscle under occlusal wear: a Raman spectroscopic study in a rodent model.

OBJECTIVE: The aim of the present study was to use Raman spectroscopy to measure levels of CaPi in muscles under occlusal wear and treated with laser phototherapy (LPT) or muscle-relaxant therapy or both on rodents. BACKGROUND: The etiology of temporomandibular disorders is multifactorial. Malocclusion may influence the masticatory muscles, causing fatigue. A major type of fatigue is the metabolic, caused by the increased accumulation of metabolites such as inorganic phosphate. Raman spectroscopy allows nondestructive analysis of the biochemical composition of tissues. METHODS: The 30 male Wistar rats were randomly divided into three groups: occlusal wear (G-1), occlusal wear + LPT (G-2), and occlusal wear + muscle relaxant (G-3). Ten untreated animals were used for baseline data. Under intraperitoneal general anesthesia, animals of groups 1, 2, and 3 had unilateral amputation of molar cusps to simulate an occlusal-wear situation. The masseter muscle of G-2 received LPT (lambda830 nm, 4 J/cm(2), 40 mW, phi approximately 2 mm) after the procedure and repeated every other day for 14-30 days. Animals of G-3 were treated with a daily injection of dantrolene (2.5 mg/kg in 0.5 ml of H(2)O) beginning 24 h after cusp removal. Animals were killed with an overdose of general anesthetics at days 14 and 30 after cusps removal, and the ipsilateral masseter muscle was excised and divided into two parts. One part was routinely processed and underwent histologic analysis; the other was kept in liquid nitrogen for Raman spectroscopy. The mean value of the intensity of the peak 958 per centimeter was determined. RESULTS: No morphologic changes were seen. Raman analysis showed significantly less Raman intensity in the laser group at 30 days (p < 0.01). CONCLUSION: Occlusal wear did not caused morphologic alterations in the masseter muscle but resulted in changes of the levels of CaP(i) that were less compromising when the laser light was used.

Quantitative analysis of dental microwear in hadrosaurid dinosaurs, and the implications for hypotheses of jaw mechanics and feeding.

Understanding the feeding mechanisms and diet of nonavian dinosaurs is fundamental to understanding the paleobiology of these taxa and their role in Mesozoic terrestrial ecosystems. Various methods, including biomechanical analysis and 3D computer modeling, have been used to generate detailed functional hypotheses, but in the absence of either direct observations of dinosaur feeding behavior, or close living functional analogues, testing these hypotheses is problematic. Microscopic scratches that form on teeth in vivo during feeding are known to record the relative motion of the tooth rows to each other during feeding and to capture evidence of tooth-food interactions. Analysis of this dental microwear provides a powerful tool for testing hypotheses of jaw mechanics, diet, and trophic niche; yet, quantitative analysis of microwear in dinosaurs has not been attempted. Here, we show that analysis of tooth microwear orientation provides direct evidence for the relative motions of jaws during feeding in hadrosaurid ornithopods, the dominant terrestrial herbivores of the Late Cretaceous. Statistical testing demonstrates that Edmontosaurus teeth preserve 4 distinct sets of scratches in different orientations. In terms of jaw mechanics, these data indicate an isognathic, near-vertical posterodorsal power stroke during feeding; near-vertical jaw opening; and propalinal movements in near anterior and near posterior directions. Our analysis supports the presence of a pleurokinetic hinge, and the straightness and parallelism of scratches indicate a tightly controlled occlusion. The dominance of scratched microwear fabrics suggests that Edmontosaurus was a grazer rather than a browser.

An in vitro assessment of the effect of load and pH on wear between opposing enamel and dentine surfaces.

OBJECTIVE: Previous in vitro studies have described the wear characteristics of specimens in which enamel has been opposed to enamel and dentine opposed to dentine. The aim of this study was to assess the characteristics of wear between specimens in which enamel was opposed to dentine at loads simulating attrition and at pH values simulating different erosive environments. It was hypothesized that enamel would wear more slowly than dentine under all conditions. DESIGN: Opposing enamel and dentine specimens from 57 human third molar teeth were worn in electromechanical machines with various loads (32, 62 and 100 N) and lubricants (pH 1.2, 3.0 and 6.1). Tooth wear was quantified by measuring reduction in dentine volume over time using a 3D profilometer. Qualitative assessment was also carried out using scanning electron microscopy. RESULTS: Dentine wear increased with increasing load, and dentine wear was faster at pH 1.2 than at pH 3.0 or 6.1 for all loads tested. Interestingly, enamel wore more rapidly than dentine at pH 1.2 under all loads. At pH values of 3.0 and 6.1, enamel wear rates were not measurably different from zero and they were less than wear rates for opposing dentine specimens at all loads. Micrographic assessment showed extensive surface destruction of dentine wear facets due to erosion at pH 1.2. Dentine wear facets were smoother at pH 3.0 that at pH 6.1. CONCLUSIONS: When enamel wears against dentine in an acidic environment enamel will wear more rapidly at very low pH, while under less acid conditions dentine will wear faster than enamel.

[Short-term and long-term effects of occlusal rehabilitation on the co-contractration patterns of the electromyography of masticatory muscles].

OBJECTIVE: To investigate the short-term and long-term effects of occlusal rehabilitation on the co-contractration patterns of masticatory muscles of patients with extensive tooth wear. METHODS: Twenty-nine patients with severe tooth wear were selected and conducted with occlusal rehabilitation. The surface electromyography (EMG) of masseter (MM), anterior temporalis (TA) and posterior temporalis (TP) at rest position, during clenching and chewing were separately recorded in the stage of pre-treatment, 1 month after temporary restoration, 1 month after permanent restoration and long-term observation (mean 3.5 years). The Asymmetry Indexes (AI) of bilateral muscles, Activity Indexes of MM/TA, MM/TP and TA/TP were compared in each stage. RESULTS: (1) After occlusal rehabilitation, all the AIs of bilateral MM, TA and TP at rest position, during clenching and chewing showed obvious decrements. (2) In every stage of occlusal rehabilitation, all of the Activity Indexes of MM/TA at rest position, during clenching and chewing had no obvious changes. (3) The Activity Indexes of MM/TP and TA/TP during clenching and chewing significantly increased after occlusal rehabilitation. CONCLUSION: The treatment of occlusal rehabilitation can significantly improve the bilateral symmetry of masticatory muscles in patients with extensive tooth wear, and also change the coordinated EMG activity of different masticatory muscles.

Attrition, occlusion, (dys)function, and intervention: a systematic review.

OBJECTIVES: Attrition and occlusal factors and masticatory function or dysfunction are thought to be related. This study aims to systematically review the literature on this topic with the emphasis to find evidence for occlusion-based treatment protocols for attrition. MATERIALS AND METHODS: Literature was searched using PubMed (1980 to 2/2006) and the Cochrane Library of Clinical Trials with the keywords 'tooth' and 'wear'. Five steps were followed. Exclusion was based on the following: (1) reviews, case-reports, studies on non-human tooth material, and studies not published in English and (2) historical or forensic studies. Included were (3) in vivo studies. Next, studies on (4) occlusal factors, function or dysfunction [temporomandibular disorders (TMD), bruxism], or intervention, and (5) attrition were included. Two investigators independently assessed the abstracts; measure of agreement was calculated using Cohen's kappa; disagreement was resolved by discussion. Full-text articles were obtained and correlation between outcomes on occlusal factors, (dys)function, treatment, and attrition were retrieved. References in the papers included in the final analysis were cross-matched with the original list of references to add references that met the inclusion criteria. RESULTS: The search procedure revealed 1289 references on tooth wear. The numbers of included studies after each step were (1) 345 (kappa=0.8), (2) 287 (kappa=0.87), (3) 174 (kappa=0.99), (4) 81 (kappa=0.71), and (5) 27 (kappa=0.68). Hand searches through the reference lists revealed six additional papers to be included. Analysis of the 33 included papers failed to find sound evidence for recommending a certain occlusion-based treatment protocol above another in the management of attrition. CONCLUSION: Some studies reported correlations between attrition and anterior spatial relationships. No studies were found suggesting that absent posterior support necessarily leads to increased attrition, though one study found that fewer number of teeth resulted in higher tooth wear index (on the remaining teeth). Attrition seems to be co-existent with self-reported bruxism. Reports on attrition and TMD signs and symptoms provide little understanding of the relationship between the two.