Effects of enamel abrasion, salivary pellicle, and measurement angle on the optical assessment of dental erosion

The present study assessed the effects of abrasion, salivary proteins, and measurement angle on the quantification of early dental erosion by the analysis of reflection intensities from enamel. Enamel from 184 caries-free human molars was used for in vitro erosion in citric acid (pH 3.6). Abrasion of the eroded enamel resulted in a 6% to 14% increase in the specular reflection intensity compared to only eroded enamel, and the reflection increase depended on the erosion degree. Nevertheless, monitoring of early erosion by reflection analysis was possible even in the abraded eroded teeth. The presence of the salivary pellicle induced up to 22% higher reflection intensities due to the smoothing of the eroded enamel by the adhered proteins. However, this measurement artifact could be significantly minimized (p<0.05) by removing the pellicle layer with 3% NaOCl solution. Change of the measurement angles from 45 to 60 deg did not improve the sensitivity of the analysis at late erosion stages. The applicability of the method for monitoring the remineralization of eroded enamel remained unclear in a demineralization/remineralization cycling model of early dental erosion in vitro.

Effect of incisal tooth wear and restoration on interocclusal distance during Brazilian Portuguese language speech

AIM

The aim of this study was to investigate changes in interocclusal distance (IOD) during pronunciation of /m/ and /s/ sounds in Brazilian Portuguese, in patients presenting dental wear due to bruxism, before and after placement of a stabilization appliance and restorative treatment.

METHODS

Subjects were divided into a control group of 19 patients with no dental wear and an experimental group of 18 patients presenting dental wear on anterior teeth due to bruxism. A stabilization appliance was placed in each patient in the experimental group and anterior teeth were restored. A magnetic jaw-tracking device measured the interocclusal distance during pronunciation of /m/ and /s/ phonemes. Interocclusal distance for the experimental group was evaluated one week before and again immediately before the appliance was inserted and 24 hours, 7 days, 1 month and 2 months after appliance insertion. The same evaluation was performed 7 days and 1 month after restorative treatment. In the control group, the measurements were carried out at the same intervals.

RESULTS

Comparison between groups revealed a significant difference (P<0.05) in interocclusal distance for the /m/ sound at all evaluation intervals. No differences were found before and after appliance insertion and restorative treatment with either phoneme.

CONCLUSION

Stabilization appliance therapy and restorative treatment of subjects with dental wear did not change the interocclusal distance during speech of /m/ and /s/ sounds in the Brazilian Portuguese language, however, when compared with normal subjects, the IOD values were higher for the dental wear group during pronunciation of the /m/ sound.

Restoration of non-carious cervical lesionsPart I. Modelling of restorative fracture

OBJECTIVE

As a typical non-carious cervical lesion, abfraction is a common clinical occurrence which requires restorative treatment in most patients. Nonetheless, the relatively poor clinical longevity of cervical dental used for restoring abfraction lesions has been a major concern of dentists and patients. The continuing loss of hard tissue and, in turn, the low retention of the restorative materials in situ motivates an in-depth exploration of the failure mechanism of the biomaterials involved. Despite considerable biomechanical relevance, conventional application of linear static finite element analysis (FEA) does not consider the fracture failure process, nor does it provide a quantitative predictive analysis for restorative design. This paper adopts a novel Rankine and rotating crack model to trace the fracture failure process of the cervical restorations.

METHODS

In contrast to the existing linear FEA, this study presents a nonlinear fracture analysis in an explicit finite element framework, which involves an automatic insertion of initial crack, mesh updating for crack propagation and self contact at the cracked interface.

RESULTS

The results are in good agreement with published clinical data, in terms of the location of the fracture failure of the simulated restoration and the inadequacy of the dental restoratives for abfraction lesions. The success of the proposed model also demonstrates the potential for the monitoring and prediction of mechanical failure in other brittle biomaterials in a clinical situation.

Restoration of non-carious cervical lesionsPart II. Restorative material selection to minimise fracture

OBJECTIVE

It is still largely unknown as to what material parameter requirements would be most suitable to minimise the fracture and maximising the retention rate of the restoration of cervical non-carious lesions (NCCL). The present paper, as a first of its kind, proposes a radical approach to address the problems of material improvement, namely: numerical-based, fracture and damage mechanics materials optimisation engineering. It investigates the influence of the elastic modulus (E) on the failure of cervical restorative materials and aims to identify an E value that will minimise mechanical failure under clinically realistic loading conditions.

METHOD

The present work relies on the principle that a more flexible restorative material would partially buffer the local stress concentration. We employ a "most favourable" parametric analysis of the restorative's elastic modulus using a fracture mechanics model embedded into finite element method. The advanced numerical modelling adopts a Rankine and rotating crack material fracture model coupled to a non-linear analysis in an explicit finite element framework.

RESULTS

The present study shows that the restorative materials currently used in non-carious cervical lesions are largely unsuitable in terms of resistance to fracture of the restoration and we suggest that the elastic modulus of such a material should be in the range of 1GPa. We anticipate that the presented methodology would provide more informative guidelines for the development of dental restorative materials, which could be tailored to specific clinical applications cognisant of the underlying mechanical environment.

A critical review of non-carious cervical (wear) lesions and the role of abfraction, erosion, and abrasion

The terms 'abfraction' and 'abrasion' describe the cause of lesions found along the cervical margins of teeth. Erosion, abrasion, and attrition have all been associated with their formation. Early research suggested that the cause of the V-shaped lesion was excessive horizontal toothbrushing. Abfraction is another possible etiology and involves occlusal stress, producing cervical cracks that predispose the surface to erosion and abrasion. This article critically reviews the literature on abrasion, erosion, and abrasion, and abfraction. The references were obtained by a MEDLINE search in March, 2005, and from this, hand searches were undertaken. From the literature, there is little evidence, apart from laboratory studies, to indicate that abfraction exists other than as a hypothetical component of cervical wear.

Definition of erosion and links to tooth wear

Erosive tissue loss is part of the physiological wear of teeth. Clinical features are an initial loss of tooth shine or luster, followed by flattening of convex structures, and, with continuing acid exposure, concavities form on smooth surfaces, or grooving and cupping occur on incisal/occlusal surfaces. Dental erosion must be distinguished from other forms of wear, but can also contribute to general tissue loss by surface softening, thus enhancing physical wear processes. The determination of dental erosion as a condition or pathology is relatively easy in the case of pain or endodontic complications, but is ambiguous in terms of function or aesthetics. The impact of dental erosion on oral health is discussed. However, it can be concluded that in most cases dental erosion is best described as a condition, with the acid being of nonpathological origin.

Effects of Irradiation on in situ Remineralization of Human and Bovine Enamel Demineralized in vitro

The objective of this study was to evaluate the effects of irradiation and surface condition on in situ remineralization of demineralized human and bovine enamel. Specimens (n=96) obtained from 24 human molars and 24 bovine incisors were prepared. The surfaces of half of the specimens were abraded while the others remained natural. Each of the 12 human and bovine abraded and sound specimens was irradiated fractionally up to 46.5 Gy (3.1 Gy/day, 5 days/week), while the remaining samples were not irradiated. Prior to and following the demineralization (pH 5.0; 14 days) all specimens were partly covered with nail varnish (control). After in vitro demineralization 2 irradiated and 2 nonirradiated specimens were inserted into both buccal aspects of 12 intraoral appliances, which were worn by 12 persons for a period of 6 weeks. All samples were brushed twice a day with a fluoride-containing toothpaste. Mineral analyses revealed a significant influence on mineral loss (DeltaZdemin), mineral gain (DeltaDeltaZ), lesion depth (LDdemin), and lesion depth reduction (DeltaLD) of the variables 'material' and 'irradiation' (p<0.05; ANOVA). Reciprocal interactions could be observed between these two variables for DeltaZdemin, DeltaDeltaZ, and LDdemin, due to significantly reduced values found for the irradiated, abraded bovine specimens compared to the nonirradiated ones (p<0.05; Bonferroni post hoc test). It can be concluded that neither irradiation nor abrasion influenced in vitro demineralization or in situ remineralization of the human specimens, whereas abrasion hampered demineralization in irradiated, bovine specimens.

The biomechanics of abfraction

The role of occlusal loading in the development of non-carious cervical lesions is becoming increasingly prominent. It is suggested that high occlusal loads result in large stress concentrations in the cervical region of the teeth. These stresses may be high enough to cause disruption of the bonds between the hydroxyapatite crystals, eventually resulting in the loss of cervical enamel.

This article reviews the evidence to support the thesis that occlusal loading can contribute to the process of non-carious cervical tooth loss or abfraction. It also reviews the potential interactions between occlusal loading and erosion that may contribute to non-carious cervical tooth loss.

Interaction 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. 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 seems insufficient to establish whether abfraction is an important contributor to tooth wear in vivo. Saliva can modulate erosive/abrasive tooth wear through formation of pellicle and by remineralisation but cannot prevent it.

The role of erosion, abrasion and attrition in tooth wear

There is increasing clinical awareness of erosion of enamel and dentine by dietary acids and the consequent increased susceptibility to physical wear. Enamel erosion is characterized by acid-mediated surface softening that, if unchecked, will progress to irreversible loss of surface tissue, potentially exposing the underlying dentine. In comparison, dentine erosion is less well understood as the composition and microstructure are more heterogeneous. Factors which affect the erosive potential of a solution include pH, titratable acidity, common ion concentrations, and frequency and method of exposure. Abrasion and attrition are sources of physical wear and are commonly associated with tooth brushing and tooth-to-tooth contact, respectively. A combination of erosion and abrasion or attrition exacerbates wear; however, further research is required to understand the role of fluoride in protecting mineralized tissues from such processes. Abrasive wear may be seen in a wide range of patients, whereas attritive loss is usually seen in individuals with bruxism. Wear processes are implicated in the development of dentine hypersensitivity. Saliva confers the major protective function against wear due to its role in pellicle formation, buffering, acid clearance, and hard tissue remineralization. This review focuses on the physiochemical factors impacting tooth wear.

Undermining of enamel as a mechanism of abfraction lesion formation: a finite element study

Many workers have suggested that abfraction lesion formation is caused by the physical overloading of enamel. However, an alternative mechanism, involving undermining of the cervical enamel along the amelodentinal junction (ADJ), may be a more realistic explanation. The aim of this study was to examine what effect undermining of the buccal cervical enamel would have on the stress distribution in upper teeth. Two-dimensional plain strain finite element meshes of an upper incisor, canine and first premolar and the supporting periodontal ligament and alveolar bone were developed. Each tooth was loaded with an oblique 100 N load, and the nodal maximum principal stresses (MPS) along a buccal horizontal sampling plane 1.1 mm above the amelo-cemental junction was measured. A discontinuity between the cervical enamel and dentine elements was then introduced (0.1 mm wide) using gap elements. The vertical extent of this defect varied from 0.1 to 0.5 mm. The value of the MPS varied from 1.8 to 209 Mpa, and the lowest values were found for the intact teeth (range 0.6-30.3 MPa). The discontinuity caused a dramatic increase in the numerical values of the MPS, and in many instances these exceeded the known failure stress for enamel.

Simulated enamel wear during occlusal contact

PURPOSE

To investigate in vitro rates of wear for human enamel that opposes human enamel by means of two-body and three-body wear tests.

METHODS

Flattened surfaces (1000-grit) of molars and hemi-spherically prepared enamel cusps were perpendicularly opposed and loaded (75.6 N, 1.2 Hz) cyclically 100,000 times in both two- and three-body wear test conditions. Wear depths of flat enamel specimens were measured with a profilometer, and those of stylus enamel specimens were determined by a computer digitizing system at 5, 10, 25, 50, and 100 thousand cycles. Data were statistically analyzed by three-way ANOVA (P < 0.05), and differences between two-body and three-body wear data on flat and stylus enamel specimens were determined by Bonferroni-Dunn test.

RESULTS

The amount of wear after 100,000 cycles in the two-body wear test was 175.6 +/- 144.6 microm for flat enamel specimens and 199.3 +/- 72.7 microm for stylus samples. Flat enamel, three-body specimens wore 4.9 +/- 1.4 microm and the stylus samples wore 4.3 +/- 1.0 microm. The data for both flat and stylus enamel specimens subjected to the two-body test were significantly greater than those of the three-body wear test (P < 0.001).

Effects of crowding in the lower anterior segment--a risk evaluation depending upon the degree of crowding

AIM

The aim of this study was to investigate the extent to which the anterior segment is at risk of developing disease under the influence of different types of anterior crowding and whether the degree of crowding correlates with a potential risk.

PATIENTS AND METHOD

A clinical examination and cast analysis taking special account of the age and gender of 125 adult patients (63 women, 62 men) were used to determine the clinical degree of abrasion and the individual incidence of tooth infractions, tooth fractures, caries, gingivitis, periodontitis and gingival recessions (WHO-OHS method), with any correlation between the incidence of disease and the respectively calculated crowding being recorded. The diagnosis of crowding was based on the segmented arch analysis proposed by Lundström [29]. Besides evaluating the total collective, a separate evaluation was performed for the age groups 18-34 years (n = 63) and > or = 35 years (n = 62).

RESULTS

No gender-related differences in crowding were determined. Patients > or = 35 years showed significantly more crowding. An age-related increase in disease was recorded. The degree of abrasion and the individual incidence of caries did not correlate with the degree of crowding. By contrast, differences in the degree of crowding were determined in the total collective for tooth infractions (p < 0.001), tooth fractures (p = 0.004), gingival bleeding (p = 0.022), shallow periodontal pockets (p < 0.001), and gingival recessions > 3.5 mm (p < 0.001). The degree of crowding was found to correlate in the younger patients with tooth infractions (p < 0.017) and tooth fractures (p = 0.036), and in the older patients with shallow periodontal pockets (p < 0.001) and gingival recessions > 3.5 mm (p < 0.001). The incidences of disease in virtually physiologic cases of crowding (crowding < or = 2 mm, n = 31) were compared with those recorded in extreme cases of crowding (crowding > or = 5 mm, n = 30). All cases of crowding > or = 5 mm were subject to gingivitis and tooth infractions, and shallow periodontal pockets occurred three times more often and gingival recession > 3.5 mm twelve times more often. The presence of deep periodontal pockets could not be attributed to the degree of crowding.

CONCLUSION

With respect to the multifactorial etiology underlying the risk of disease of the dental hard tissue and the periodontal tissues, anterior crowding > 3 mm (threshold value) as an individual "host factor" represents a cumulative risk potential for chronic inflammatory processes whose consequences are manifest only at a higher age. This gives rise to a medical treatment indication within the framework of preventive treatment strategies.

Influence of buffering effects of dentifrices and fluoride gels on abrasion on eroded dentine

OBJECTIVE

Evaluation of abrasion resistance of eroded and non-eroded dentine brushed with experimental dentifrices and gels of varying buffering capacities.

DESIGN

One hundred and twenty human dentine specimens were distributed among six groups (A-F) according to the different buffering capacities of experimental toothpastes and gels. The dentifrices (pH: 4.5) and gels (pH: 4.5) differed in fluoride content, RDA-value and buffer capacity (given as mg KOH needed for neutralisation): (A) 0.125%F, RDA: 77, 6mg KOH; (B) 0.125%F, RDA: 125, 24mg KOH; (C) 0.125%F, RDA: 129, 12mg KOH; (D) 0%F, RDA: 81, 1.55mg KOH; (E) 1.25%F, RDA: 21, 8.5mg KOH; (F) 0.125%F, RDA: 7, 3.11mg KOH. Ten specimens were cycled through three alternating demineralisations (1% citric acid, 5min) and remineralisations (artificial saliva, 1min) including brushing abrasion in an automatic brushing machine (2 x 2000 strokes). Ten samples of each group were not eroded, but only brushed.

RESULTS

After three cycles, loss of dentine was determined by profilometry (mean +/- S.D. [microm]). Eroded samples: (A) 37.12+/-4.95; (B) 48.67+/-4.77; (C) 39.88+/-3.76; (D) 32.92+/-2.67; (E) 3.65+/-1.35; (F) 6.47+/-1.31. Uneroded samples: (A) 30.78+/-6.47; (B) 37.84+/-7.75; (C) 30.07+/-3.05; (D) 26.93+/-2.30; (E) 1.76+/-0.94; (F) 0.51+/-0.18. Analysis of variance revealed significantly higher abrasion values for the eroded compared to the non-eroded samples (P<or=0.05). Dentifrices with same pH-value, fluoride content and similar RDA-values but a higher buffering capacity exhibited significantly more abrasion than toothpastes with lower buffering capacity. Highly-concentrated fluoride gel with higher buffering capacity lead to less abrasion values compared to the gel with low fluoride concentration and low buffering capacity.

CONCLUSION

Toothbrushing abrasion behaviour of eroded dentine may be influenced by the fluoride content, RDA-value and buffering capacity of the applied dentifrice or gel.

An assessment of stress analyses in the theory of abfraction

Wedged-shaped lesions at the cemento-enamel junction of teeth have been attributed primarily to biomechanical loading forces that cause flexure and failure of enamel and dentin. This theory, termed abfraction, remains controversial. This review examined studies on mechanical properties of enamel and dentin and studies on bite forces and mastication as background information. Abfraction is based principally on a few early finite element analysis and photoelastic models showing stress concentration at the dental cervical area without actually showing enamel and dentin fracture. However, a review of more recent dental stress analyses has been contradictory. Particularly, analyses of the periodontal ligament and alveolar bone, not modeled in previous studies, have shown that those structures may dissipate occlusal loading forces from the cervical areas. In addition, some models may not fully represent intricate dental anatomy and complex occlusal function. Therefore, the key basis of the abfraction theory may be flawed.

Abrasive wear on eroded root dentine after different periods of exposure to saliva in situ

The effect of salivary exposure time on the abrasive wear of acid-eroded dentine was evaluated in situ. One-hundred and twenty bovine root dentine slabs were randomly assigned into six groups (A-F) and placed in intraoral palatal devices, which were worn by 10 volunteers for 4 d. On the first day, no erosive/abrasive procedures were carried out. On the following 3 d, erosive challenges were performed extraorally, two times per day, by immersing the device for 90 s in a soft drink. Subsequently, the group A specimens were immediately brushed (40 strokes), and the others were brushed after the following times: B, 20 min; C, 40 min; and D, 60 min. Group E specimens were only acid-eroded and those of group F were only brushed. Dentine wear was measured with a profilometer. anova and Dunnett's test showed that groups A-D did not differ statistically from the control group E but differed from the control group F. The lowest mean value was found for group F. Regression analysis was unable to show salivary effect on dentine wear reduction. The data suggest that the exposure time of saliva of up to 60 min has no effect on reducing the eroded dentine wear by toothbrushing.

[Dysfunctions of the stomatognathic system in tinnitus patients compared to controls]

AIMS OF THE STUDY

The high prevalence of ear, nose and throat symptoms in patients with temporomandibular disorders seems to depend on anatomical, functional, neuromuscular, or psychosomatic connections between both phenomena. The present study evaluates the prevalence of temporomandibular dysfunctions in tinnitus patients compared to controls.

PATIENTS AND METHODS

A total of 40 patients and 35 controls were clinically examined. The case history as well as the quality of tinnitus and its influence on the patient's life were evaluated, and psychosocial data collected by a questionnaire dealing with stress factors.

RESULTS

Tinnitus patients showed muscle tenderness in masticatory muscles as well as in other muscle groups significantly more frequently than controls. The prevalence of arthrogenous dysfunctions was not significantly different between the groups. Occlusal parameters such as instability of intercuspidation, presence of dysgnathia, and signs of parafunctions were significantly more frequent in patients than in controls. The psychosocial assessment showed some trend towards the tinnitus patients feeling more stress in society, daily life, their partnerships and at work.

CONCLUSIONS

Tinnitus correlates significantly with myogenous disorders but not with arthrogenous disorders of the temporomandibular joint (TMJ). This result supports the concept of neuromuscular and functional relationships between tinnitus and the stomatognathic system.

Noncarious cervical lesions and abfractions: a re-evaluation

BACKGROUND

The concept of abfraction is controversial. The authors present the fundamental basis of abfraction and review studies that describe the condition.

TYPES OF STUDIES REVIEWED

The authors used data on masticatory forces, enamel and dentin properties, as well as stress studies related to abfraction, for background information. They also analyzed the genesis of the abfraction theory, experimental evidence, case presentations, clinical investigations and restorative studies.

RESULTS

The theory of abfraction is based primarily on engineering analyses that demonstrate theoretical stress concentration at the cervical areas of teeth. While some recent stress studies support earlier findings, others have provided significant deviating information. Few controlled studies exist that demonstrate the relationship between occlusal loading and abfraction lesions. The role of occlusal loading in noncarious cervical lesions (as shown by clinical data) appears to be part of a multifactorial event that may not necessarily follow the proposed classic abfraction mechanism, and other mechanisms or factors may explain cervical restoration failure just as well.

CLINICAL IMPLICATIONS

There is little direct evidence supporting the theory of abfraction as the primary factor in the formation of noncarious cervical lesions. Controlled clinical trials are necessary to elucidate more fully the etiology of those lesions.

[Two-dimensional finite element stress analysis of simulating restored teeth with wedge-shaped defects under loads]

OBJECTIVE

To study the concentration of stresses at the cervix with simulating restoration of tooth defects.

METHODS

A two-dimensional finite element model of a mandible first premolar with defect from longitudinal section was developed. The model was simulatedly restored, respectively by composite resin and glass ionomer cement, and then investigated stress variation in the cervical area.

RESULTS

In the restored models, both of materials improved the concentration of stresses at the cervical area. The composite resin and the glass ionomer cement restorations made the maximum principal stresses declined respectively to 36.2 MPa and 42.5 MPa, which were close to the value of normal tooth in the deepest area of defects.

CONCLUSION

The concentration of stresses are improved in the cervical area with teeth defects restored.

Abfraction lesion formation in maxillary incisors, canines and premolars: a finite element study

Abfraction lesions are angular, wedge-shaped defects found at the cervical region of teeth and are caused by mechanical overloading initiated by cuspal flexure. Clinically, these lesions are more prevalent on the labial aspect of maxillary incisors. The aim of this study was to provide a biomechanical explanation for this clinical variation. Two-dimensional plane strain finite element models of an maxillary incisor, canine and first premolar were developed and the cervical stress profiles were examined along a horizontal plane 1.1 mm above the amelo-cemental junction. The local X (horizontal) stress on the labial/buccal side was 176.4 MPa for the incisor, 57.8 MPa for the premolar, and 3.4 MPa for the canine. Similarly, the maximum labial/buccal principal stress was 181.4 MPa for the incisor, 25.2 MPa for the premolar, and 66.8 MPa for the canine. The labial/buccal stress profile in the cervical region of an maxillary incisor was always greater than that found in an maxillary canine or premolar tooth. These findings provide a biomechanical explanation for the clinical variation seen in the prevalence of cervical abfraction lesions.

Abfraction and anisotropy--effects of prism orientation on stress distribution

This work discusses the effect of enamel anisotropy in the stress concentration at the cement-enamel junction (CEJ), a probable cause of fracture in enamel leading to abfraction. Usual simplifications when developing computer models in dentistry are to consider enamel isotropic, or that the direction of the prisms is orthogonal to either the dentine-enamel interface or the tooth outer surface. In this paper, a more refined model for the material behavior is described, based on laboratory observation and on the work of Fernandes and Chevitarese. The material description is used in a two-dimensional (2D) finite element model of the first upper premolar, and the analysis is performed for two different situations: vertical loads, typical of normal mastication and horizontal loads, dominant in bruxism. The analyses were performed using a unit load, which under the hypothesis of linear response of the tooth, allows the combinations described in the text to simulate different functional and parafunctional loads. The results indicate that a realistic enamel description in terms of mechanical properties and spatial distribution of its prisms alters significantly the resulting stress distribution. For all cases included in this study, the detailed description of prism orientation and resulting anisotropy led to improved response in terms of stress distribution, even when loading was horizontal.

Stresses at the cervical lesion of maxillary premolar--a finite element investigation

OBJECTIVES

The objective of this study was to use a three-dimensional (3-D) finite element model to investigate normal stress distribution to substantiate the tooth flexure mechanism. The study also compared the changes in the stresses by different occlusal loading sites and directions.

METHODS

The 3-D finite element analysis was used. A maxillary premolar was selected to construct the simulation model. The model was constructed step-by-step for convergence and validity. Seven load conditions for various load sites and different directions were simulated to the model.

RESULTS

The maximal principal stress and minimal principal stress distributions developed within the structures of seven load conditions were output and their stress distributions on z-plane at the vertical midline were shown. The peak tensile stress of the cervical area for various load conditions were compared and listed.

CONCLUSIONS

This study has shown that the presence of tensile stresses in the cervical region of a maxillary premolar by various loading sites and different directions. The results coincided with the stress-induced theory, hence sustaining it. The relationship of the affected factors of leverage to the development of cervical abfraction lesions, was explored.

General and oral characteristics in Rett syndrome

Rett syndrome (RS) is a neurodegenerative disorder characterized by developmental arrest of parts of the brain. It is an X chromosome-linked condition which affects females almost exclusively. Recent reports have been generated concerning the multidisciplinary management of individuals exhibiting Rett syndrome. The aim of the present report was to provide an update on the oral manifestations of the disorder. We evaluated the general and oral characteristics of RS in 13 female patients. The most frequent manifestations were stereotyped hand movements and bruxism. The treatment we carried out included the use of biteplanes and acupuncture.

A review of the biomechanics of abfraction

Loss of tooth substance in the cervical region is usually attributed to abrasion or erosion. However, the role of occlusal loading is becoming increasingly prominent. It is suggested that high occlusal loads result in large stress concentrations in the cervical region of the teeth. These stresses may be high enough to cause disruption of the bonds between the hydroxyapatite crystals, eventually resulting in the loss of cervical enamel. This article reviews the available evidence to support the thesis that occlusal loading can contribute to the process of non-carious cervical tooth loss or abfraction. It also reviews the potential interactions between occlusal loading and erosion that may contribute to non-carious cervical tooth loss.

Strain patterns in cervical enamel of teeth subjected to occlusal loading

OBJECTIVES

This study was planned to investigate the variations in strains in enamel under different patterns of occlusal loading, using three-dimensional finite element analysis (3D FEA) and strain gage measurements in extracted teeth.

METHODS

A 3D FEA model of a mandibular second premolar was used to investigate effects of occlusal load on enamel surface strains, particularly in response to oblique directions of cuspal loading. Point loads of 100 N were applied axially and at 45 degrees from the vertical on the buccal or lingual incline of the buccal cusp, either in the bucco-lingual plane or at varying mesio-distal angulations (up to +/- 20 degrees). Patterns of strain observed in the FEA model were confirmed experimentally using strain gages on extracted premolars mounted in a servohydraulic testing machine.

RESULTS

Strains predicted from the FEA model were in excellent agreement with the strain gage measurements. Strains were concentrated near the cementoenamel junction (CEJ) regardless of load direction. A vertical load on the buccal cusp tip resulted in compressive strains on the buccal surface but small tensile strains in lingual cervical enamel. Strains resulting from oblique loads on buccal cusp inclines were complex and asymmetric, with either tension or compression occurring in any location depending on the site and angle of loading.

SIGNIFICANCE

The magnitude, direction and character of strains in cervical enamel are highly dependent on patterns of loading. The asymmetric pattern of strains in buccal cervical enamel in response to oblique occlusal forces is consistent with the common clinical picture of asymmetric non-carious cervical lesions.

Different effects of nocturnal parafunction on the masticatory system: the Weak Link Theory

It is proposed that damage to the masticatory system from intense parafunction can be assessed more accurately by the Weak Link Theory. The theory predicts that the more intense and the more prolonged the forces, the more the tendency of damage to either. 1. the periodontal tissue; 2. the teeth; or 3. the orofacial structures. To test the theory, 22 subjects were selected based on reports of nocturnal bruxism. Each was assessed for masticatory system breakdown on the Russell Periodontal Index, the Helkimo Dysfunction Index, and a Tooth Wear Index. A Bruxcore (Forgione, A. 1974 J Dent Res 53:127) was used to obtain an objective score of bruxism. Five of eleven subjects with mild bruxism scored high on only one index. Significantly more subjects (ten of eleven) with moderate to severe bruxism scored high on one index only.

Brushing abrasion of eroded dentin after application of sodium fluoride solutions

The aim of the present in vitro study was to evaluate the influence of sodium fluoride solutions on brushing abrasion of eroded dentin. Dentin specimens were prepared from 60 bovine incisors. The specimens were embedded in acrylic resin, ground flat, polished and subsequently covered with tape exposing an area of 1.8 mm x 10.0 mm in the center of the exposed dentin. The samples were alternatingly stored in a demineralizing solution (5 min) and a remineralizing solution (1 min) for 5 times. The erosive soft drink Sprite light(R) served as a demineralizing solution and artificial saliva was used as a remineralizing solution. Prior to storage in artificial saliva 15 specimens were each treated for 1 min with 250 and 2,000 ppm fluoride solution, respectively. Fifteen specimens were treated with distilled water instead of the fluoride solution (= eroded controls). The remaining samples were neither eroded with the soft drink nor fluoridated (= uneroded controls). After each immersion in artificial saliva the specimens were submitted to abrasion in a toothbrushing machine. After 5 demineralization-remineralization brushing cycles the total amount of tooth wear due to erosion and subsequent abrasion was profilometrically evaluated. Statistical analysis revealed the significantly lowest wear in the uneroded controls and the highest amount of abrasion in the eroded controls. Application of the fluoride solutions increased the wear resistance of the eroded dentin specimens, showing significantly better protection by the high-concentration compared to the low-concentration solution. The susceptibility to abrasion of the eroded dentin specimens treated with the high-concentration fluoride solution did not differ significantly from the uneroded dentin samples. It is concluded that application of 2,000 ppm sodium fluoride solutions immediately before toothbrushing significantly reduces abrasion of eroded dentin in vitro.

Systemic effects of the occlusal destruction in guinea pigs

Although there is an increasing amount of information pertaining to the systemic effects of malocclusion, its mechanisms still remain unclear in many ways. This study was conducted to find out the systemic effects of the occlusal destruction in guinea pigs. The animals showed an abnormality in posture and a reversal of the T wave in electrocardiogram (ECG) about 6 days after the grinding of all molar teeth. All the animals died about 7 days after the occlusal destruction. We established the optimal condition of occlusal destruction for the induction of the above symptoms in guinea pigs: at least 6 molars, both side premolar, 1st and 2nd molar of upper jaw, because of the ease for repair. The following results were obtained: 1. The experimental group died about 5 days earlier than the fasting group. 2. The animals could not hold their head positions and dropped the head to the earth. 3. The animals died about 12 hours after the onset of postural abnormality. 4. Ninety percent of the animals with postural abnormalities showed T wave inversion on ECG. 5. None of the above symptoms occurred with bite rising. These results indicate that occlusal destruction affects head position, preventing the animals to hold their head positions and causing the head to drop to the ground. Occlusal destruction may also cause abnormality of the masticatory muscles, which control posture and modulate cardiac function via the trigeminal system. This experimental model is suitable for the analysis of the systemic effects of occlusal destruction.

Dental microwear. Morphological, functional and phylogenetic correlations

Dental wear, at first considered a pathological condition, is now regarded as a physiological mechanism of teeth adaptation to continuous masticatory stresses. Excessive wear is limited by characteristic structural adaptations of dental hard tissues showing a phylogenetic trend and specialisation. Enamel is the main tissue subjected to wear; however, advanced enamel wear exposes increasingly large areas of dentine. Enamel hardness and anisotropy are the major factors contrasting wear and microfractures. Anisotropy is mainly related to the different orientation of prism bundles (and of hydroxiapatite cristals). Enamel wear development is also related to differences in microhardness, density, mineral composition and protein distribution. Masticatory loads distributed along the enamel-dentine junction uniformly disperse in the underlying dentine. In spite of its structural characteristics, dentine is relatively isotropic by the functional point of view. Even if its lower hardness opposes less efficaciously to wear, its biomechanical characteristics successfully contrast microfractures. The study of microwear (namely the microscopic analysis of worn dental surfaces) can be made both on original surfaces and on high definition silicone-resin replicas. Scanning electron microscope observations allow identification of surface damage (microtraces) produced by different physical and chemical agents. Microwear analysis may provide indications about alimentary and non alimentary habits, masticatory biomechanics and pathological situations (e.g., bruxism).

Effect of restored and unrestored non-carious cervical lesions on the fracture resistance of previously restored maxillary premolar teeth

OBJECTIVES

The effect of non-carious cervical lesions (NCCL) on tooth fracture resistance has not previously been investigated. The aims of this in vitro study were to examine the fracture resistance of a group of extracted maxillary premolar teeth with mesio-occlusal-distal (MOD) restorations of amalgam, and restored or unrestored simulated NCCL.

METHOD

Forty sound maxillary, premolar teeth were divided at random into four groups, each of 10 teeth, which were fixed crown uppermost and long axis vertical in stainless steel moulds. Groups 1,2,3 and 4 were prepared with standardized parallel-sided MOD cavities, then restored with amalgam. Groups 1, 2 and 3 were further prepared with standardized NCCL. The NCCL in Group 1 were restored using a resin-modified polyalkenoate (glass-ionomer) cement, and the NCCL in Group 2 were restored with an adhesive composite resin system. The NCCL in Group 3 were left unrestored. The specimens were loaded compressively at 1 mm min-1 using a universal testing machine.

RESULTS

Mean fracture loads (KN) of 1.08, 1.03, 0.98 and 1.14, respectively, were recorded for Groups 1, 2, 3 and 4. Two-way ANOVA and Scheffe's Multiple Range Test showed no statistically significant difference between the groups.

CONCLUSIONS

It is concluded that the presence of a standardized NCCL in an extracted maxillary premolar tooth does not reduce the fracture resistance of the tooth when loaded compressively at 1 mm min-1. The restoration of NCCL with the materials tested did not result in an increase in the fracture resistance of the previously restored premolar teeth, when loaded compressively at 1 mm min-1.

Wear in the upper and lower incisors in relation to incisal and condylar guidance

The incisors of 85 patients were examined for tooth wear with the aim to evaluate possible association between the degree of wear and anterior guidance. Apart from clinical functional analysis electronic axiography using the system CADIAX was carried out. Anterior guidance in protrusive movement was marked on individually mounted plaster casts and scanned using a pantograph. The cephalometric analysis program CADIAS was used for the metric determination of the anterior guidance angle to the axis-orbital plane, and in order to relate the anterior guidance to the horizontal condylar inclination. The interincisal angle was included in the evaluation as a further functional angle and according to overjet and overbite there were classified typical incisor relations. Where both anterior guidance and incisor inclination and relation were in the normal range, there was an increase in incisal tooth wear in the group investigated. With reduced functional space, frequently found together with anterior deep bite, incisor wear was less extensive. While the occurrence of parafunction was shown not to be related to anterior guidance and incisor inclination and relation parafunctions were the decisive factor in the occurrence of severe incisor wear. Where anterior guidance and incisor inclination and relation are normal, the area of enamel under load is smaller and the space for bruxism larger. Parafunctional forces thus appear to result in a higher degree of wear than is found with the reduced functional space of a steep incisor position. Anterior guidance could not be evaluated as a parafunctonal inducing factor, but only as determining the wear pattern in the individual.

Ageing draft and trotter horses by their dentition

The accuracy of ageing horses by their dentition was assessed by comparing the dental features with the known dates of birth of 212 trotter horses and 189 Belgian draft horses. The horses ranged in age from two to 25 years. In both breeds it was observed that the shedding of the incisors and the appearance of the dental stars were the most reliable features for age determination. In young animals, the dental configuration was similar in both breeds. With increasing age the incisor teeth of draft horses were more liable to abrasion than those of trotter horses. The sequential changes in appearance of the permanent incisors occurred earlier in draft horses than in trotters.

[Immunochemical and immunohistochemical study of calpastatin, an endogenous calpain inhibitor, in the masseter muscle of the rabbit]

The calpains-calpastatin system (calcium-activated neutral proteases and endogenous inhibitor) seems to be, in the skeletal muscle, a fine enzymatic system of myofibrillar turnover regulation, in normal as well as pathological conditions (for ex., dystrophic muscle). The purpose of the research is to establish in qualitative and quantitative terms whether the level of calpastatin can evidence differences between a muscle in normal activity conditions and one having dysfunctional alterations experimentally induced. So the masseter muscle of rabbit in normal conditions and with experimentally modified occlusal plane has been used. Our results confirm the presence of the 68 KDa calpastatin in the masseter muscle. The presence of the inhibitor in the same subcellular structures in which the calpains have been detected (myofibrillars, sarcolemma, endomysial connective) has been confirmed. Finally, variations in calpastatin amount in the muscle of animals experimentally treated with respect to the controls have been found. Thus, calpastatin seems to act as a marker of muscle dysfunctions connected to occlusal plane alteration and to loss of vertical dimention.

The face height in adult dentate humans. A discussion of physiological and prosthodontic principles illustrated through a case report

The adaptability of the stomatognathic system to alterations in the vertical dimension is discussed based on scientific reports and clinical experience. A case is reported demonstrating the stability of a therapeutically induced increase in the occlusal vertical dimension over a 10 year period. In conclusion, it is stated that moderate alterations in the occlusal vertical dimension of patients are generally well tolerated if necessary for therapeutic measures.

Dust accumulation in the canopy: a potential cause of dental microwear in primates

Dental microwear researchers consider exogenous grit or dust to be an important cause of microscopic wear on primate teeth. No study to date has examined the accumulation of such abrasives on foods eaten by primates in the forest. This investigation introduces a method to collect dust at various heights in the canopy. Results from dust collection studies conducted at the primate research stations at Ketambe in Indonesia, and Hacienda La Pacifica in Costa Rica indicate that 1) grit collects throughout the canopy in both open country and tropical rain forest environments; and 2) the sizes and concentrations of dust particles accumulated over a fixed period of time differ depending on site location and season of investigation. These results may hold important implications for the interpretation of microwear on primate teeth.

The relation between tooth eruption and alveolar crest height in a human skeletal sample

It is commonly assumed that alveolar crest height increases with continuing tooth eruption unless affected by marginal inflammation. To test this hypothesis, the relation between eruption and alveolar crest height was examined in skulls from a sample consisting of the remains of 244 individuals from the late medieval period. The mandibular first and second molars and second premolars were analysed. The age of the skulls was determined on the basis of dental development and molar attrition. Radiographs were taken and points representing the levels of the inferior dental canal (IDC), root apices (AP), alveolar crest (AC), cementum-enamel junction (CEJ) and occlusal surface were determined on the radiographs. The level of the IDC was used as a reference not changing with age. The distances between the points were measured with a help of a computer-digitizer system. Variable IDC-AP increased with age, indicating continuous eruption of the teeth. The distance between AC and CEJ also increased while the distance between IDC and AC remained constant, showing that the alveolar crest height did not increase accordingly. The lack of inflammatory changes on the alveolar bone surface suggests that occlusal attrition may be compensated for by continuous eruption without bone growth in the alveolar margin.

Craniofacial morphology, occlusal traits, and bite force in persons with advanced occlusal tooth wear

The aim of this study was to investigate the dentofacial structure, the occlusal traits, and the bite force in subjects with advanced occlusal wear. The material comprised 54 adults, 30 men (mean = 40 years, range 16 to 61) and 24 women (mean = 28 years, range 18 to 47), most of whom had a full or near-full complement of natural teeth, and the presence of occlusal wear. Craniofacial structure was studied on lateral cephalograms. Occlusal traits were examined on study casts, these serving also for an evaluation of occlusal wear to be carried out by using an ordinal scale. Bite forces were recorded at differing force levels (maximum biting, "biting as when chewing" and "light biting") and occlusal positions. Although maximum bite force and endurance time did not differ significantly between men and women, the level of bite force was high compared with other samples. The craniofacial structure of the sample was characterized by a deviation in the vertical direction, a small angle between the mandibular-palatal planes and a small gonial angle, as compared with Swedish adult norms. No significant differences were found in anteroposterior relationships between persons with advanced wear and normal standards. The results support the hypothesis that functional hyperactivity of the masticatory system imposed increased stress on the bony structures of the craniofacial complex with possible influences on its structure.

[Functional disorders of the masticatory muscles and temporomandibular joint in pathological tooth abrasion]

Altogether 568 patients, 308 women and 260 men aged 30 to 64 with abnormal teeth abrasion were examined by clinical, anthropometric, X-ray (spot and panoramic radiography of the teeth and jaws, tomography of the temporomandibular joint), electromyography, and rheoparodontography. Pathological teeth abrasion was associated with various morphological and functional disturbances in the maxillodental system. Two types of abrasion were distinguished: with and without masticatory function disorders. The latter condition was detected in 252 (44.36%) patients. Painful dysfunction of the temporomandibular joint was observed in 66 (11.6%) patients. Three factors contribute to the pathogenesis of these functional disorders in abnormal teeth abrasion: reduction of occlusion height (interalveolar distance) and shortening of the lower third of the face, blocking of mandibular movements, lateral and distal shift of the mandible.

Bite force and dentofacial morphology in men with severe dental attrition

Patients with severely worn dentition were interviewed and clinically examined, and only those were included who had no or minimal subjective symptoms or clinical signs of craniomandibular disorder. During a 14-month screening period, only 7 patients fulfilled the inclusion criteria; all were men. Maximal bite force was measured in the molar regions and in the incisal region. Facial morphology was evaluated from lateral cephalometric radiographs, and the form of dental arches from dental casts. Average maximal bite force in the molar region was 911 N and in the incisal region 569 N. The most characteristic findings concerning bite force were the high force levels in the incisal region and an incisal/molar bite-force ratio of 63%. The facial morphology of the patients was rectangular, with an anteriorly rotated mandible, small anterior face height, and great interincisal angle. Moreover, the form of the maxillary dental arch was more rectangular than normal. The high bite forces of these patients, especially in the incisal area, can probably be explained by strong masticatory muscles and mechanically favorable skull morphology, which in its turn has been influenced by the surrounding muscles.

Vertical height differences in subjects with severe dental wear

The present study aims to determine differences in vertical facial dimensions as a result of severe dental wear. The sample consisted of 35 subjects (mean age 48.4 years) who had advanced dental wear recognized by loss of more than one-third of the estimated original incisor crown length. The control group comprised 40 subjects (mean age 26.1 years) with acceptable occlusions and no signs of severe generalized tooth wear. Lateral skull radiographs were taken for both the study sample and the control group with the mandible in the maximum retruded position, from which measurements were made using a digitizer. The results showed no significant differences for total face height (n-gn) between the groups (P > 0.05) although for the study sample, upper face height was greater (P < 0.05) and lower face height was smaller (P < 0.05). Smaller values for tooth length were found in the wear sample, with the mean differences in tooth length being 5.0 mm for upper incisors and 3.3 mm for lower incisors. The overbite was smaller in the wear sample and the lower incisor position differed from controls in this group. It is concluded that the differences in face height together with differences in lower incisor position through dento-alveolar development contribute to maintenance of total facial height, so compensating for loss of vertical height through severe dental wear.

Covariation of some factors associated with occlusal tooth wear in a selected high-wear sample

The aim of the present study was to investigate the significance of some factors associated with occlusal tooth wear in a selected high-wear Swedish sample. The material comprised 59 subjects having a mean age of 35 yr within the range 16-70 yr, the criteria for selection being a full or nearly full complement of natural teeth, and the presence of definite clinical signs of occlusal wear. A dentition wear index was derived from a tooth-by-tooth evaluation of casts. The results showed that men had significantly greater wear than women. Other factors which were found to correlate significantly with increased occlusal wear were: age, increased bite force, decreased occlusal tactile sensitivity, increased endurance time, and reduced tendency for crowding in the dental arches. In the salivary analysis, it was found that low buffer capacity and low rate of secretion were significantly correlated with high wear. Cephalometric variables shown to be correlated with increased wear were retroclination and position of maxillary incisors, and greater interincisal angle. The results from this study also suggest that the associations of attrition with certain dentoalveolar morphologic features are similar in the present contemporary sample and various noncontemporary populations.

Occlusal wear of teeth and restorative materials. A review of classification, etiology, mechanisms of wear, and some aspects of restorative procedures

This paper is a literature review of various aspects of the wear of occluding tooth surfaces. It presents classification and terminology of occlusal tooth wear, and discusses etiology and differential diagnosis. It may be difficult to differentiate among abrasion, attrition, and erosion because there is nearly always a combination of the various processes. These processes of wear are described, and the in vitro and in vivo wear of some restorative materials is discussed. Treatment of severe tooth wear is considered difficult; prophylactic measures are therefore important. Some guidelines for restorative treatment of patients with extensive occlusal tooth wear are given, with special emphasis on the type of treatment, the vertical dimension of occlusion, the space available, and choice of material for the restorations.

Oral function in dentate elderly with reduced dentitions

This study covers the characteristics of reduced dentitions in a population of elderly people. The sample consisted of 329 independently living individuals between 55 and 75 years of age. They all had one or more natural teeth and were all interviewed and investigated clinically. The findings showed that 13% of the subjects had a natural dentition with at least the first molars; 4-7 natural occlusal units (defined as 'pairs of opposing teeth that support the occlusion') occurred in 37% of the subjects; 1-4 natural occlusal units in 41% and 0 units in 9% (only anterior contacts). A removable partial denture was worn by 39% of the subjects; most of them were acrylic based dentures (61%). The percentages of restored teeth per subject were high. The need for further restorations, however, was low. Periodontal problems were uncommon; 25% of the subjects had one pocket above 5 mm; 8% had severe problems. Poor oral hygiene was present in a quarter of the cases. Most of the subjects (70%) had no pain or noises in the temporomandibular joint. Only 10% of subjects had more than one sign of craniomandibular dysfunction. Most of the subjects (85%) visit their dentist regularly and 65% had their last tooth extraction more than three years ago. A majority mentioned that they have never had problems with their dentition in the past; 50% had had no real toothache for the last five years. However, problems with food-packing were often mentioned. It can be concluded that, although the dentitions of the elderly in this population are often reduced, their dentitions are in general in good condition and few give TMJ problems.

Dental factors associated with temporomandibular joint sounds

Dental factors commonly associated with signs and symptoms of temporomandibular disorders were investigated in a group of nonpatients. A highly sensitive technique was used to establish the presence of temporomandibular joint (TMJ) sounds. In a discriminant analysis nonworking side interferences, attrition, molar contacts, horizontal range of jaw movement, and morphologic occlusion contributed significantly to the prediction of sounds. Further study of morphologic aspects of the joint and stress-related parafunctions may contribute to the understanding of the development of TMJ sounds. We concluded that TMJ sounds are a fairly common sign associated with mild deviations in certain morphologic and functional aspects of the stomatognathic system.