Finite element analysis of mechanism of cervical lesion formation in simulated molars during mastication and parafunction.
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Interproximal (approximal) grooves at the cementum-enamel junction of premolar and molar teeth have been observed in a broad range of human ancestors and related extinct species from 1.84 million years ago to the present. Many hypotheses have been presented to explain the aetiology of these grooves, though their form and positioning are most consistent with tooth-picking behaviours. This paper reviews occurrences of interproximal grooves in the cheek teeth of modern and fossil humans, evaluates hypotheses on their cause, and reports on a previously undescribed groove found in OH 60, a molar tooth from Olduvai Gorge. This specimen is among the earliest to show such grooving, and is most likely attributable to Homo erectus. It is concluded that, because interproximal grooves have been observed only on Homo teeth, they probably reflect a behaviour or behaviours unique to that genus.
The development of a standardized method of collecting data from a questionnaire and a simplified, yet relatively complete, occlusal and temporomandibular examination form has been described. The questionnaire and clinical examination form have evolved from earlier forms developed by the author1 which have been used in numerous private offices and institutions for a period of five years. These earlier forms have now been augmented and modified as a result of personal consultation with users of earlier forms and numerous clinical and academic authorites.2-27 The selection of information to be obtained through the use of the questionnaire and clinical examination forms was further influenced by the work of numerous authors.28-63 Part II of this report deals with (1) the development of a companion Data Processing Form and a method of transcribing to this form the data from the Patient Questionnaire and clinical examination forms, as well as (2) key-punch instructions consistent with data processing requirements.
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The accumulation of experimental and clinical evidence during the past decade has significantly contributed to the understanding of the role of occlusally generated tensile stress in the etiology of certain noncarious cervical lesions of teeth. More important, this knowledge has led to the understanding of the reasons why traditional restorative treatments of these stress-induced cervical lesions fail. The case of failure can be attributed to the occlusally generated stresses that are concentrated at the cervical region and result in debonding, leakage, retention failure, and, ultimately, restorative failure. With the new understanding, restorative approaches that combine chemical adhesion and restorative materials of appropriate elastic properties show promise of long-term success.
STATEMENT OF PROBLEM: Recent epidemiologic evidence suggests that tooth wear is now a significant problem in both children and adults. There is growing evidence that a major cause of severe wear in patients is regurgitation erosion due to a variety of factors including gastroesophageal reflux disease. PURPOSE: The purpose of this article is to discuss the prevalence of tooth wear in the United Kingdom. Emphasis in management should be on accurate diagnosis, and in some patients, long-term monitoring before embarking on any irreversible, interventive treatment. Even when treatment is necessary, a period of monitoring is helpful to assess the rate of progress of the wear, the effectiveness of preventive measures, and therefore the extent of the treatment necessary.
STATEMENT OF PROBLEM: Although all the processes of loss of hard tissue are important, attrition on the occlusal surfaces commands our attention. PURPOSE OF STUDY: The enamel wear rate of 18 young adults over 2 consecutive years was measured independently by volume loss and mean depth loss. Any significant differences in tooth wear resulting from gender and a clinical diagnosis of bruxism were identified. MATERIAL AND METHODS: A strict protocol for dental impressions provided epoxy models, which were digitized with a null point contact stylus. AnSur software provided a complete morphologic description of changes in the wear facets. RESULTS: The mean loss for all teeth measured was 0.04 mm3 by volume and 10.7 microns by depth for the first year. CONCLUSIONS: These numbers were approximately doubled at 2 years of cumulative wear.
STATEMENT OF PROBLEM: One of the most important physical properties of artificial teeth used in the restoration of the edentulous patient is wear resistance, and the ability of these teeth to maintain a stable occlusal relationship over time. PURPOSE: This study compared the in vitro wear of four different resin denture teeth against human enamel. MATERIAL AND METHODS: Five denture tooth samples opposing five enamel abraders were positioned in a mechanical wear testing device for two 5,000 cycle wear periods (total of 10,000 cycles) under a 13.4 N load. All tests were conducted in human saliva, and the wear was measured at the end of each test period. RESULTS: The wear of the Classic and Kenson acrylic resin denture teeth was much greater than the DB Plus and MLI composite teeth after 10,000 cycles. The wear of the KENSON denture tooth was also greater than the Classic tooth. No wear differences were found between the two composite teeth. CONCLUSIONS: The wear of DB Plus and MLI resin denture teeth was approximately 50% less than the wear of Classic and Kenson teeth when opposed by human enamel.
Vertical root fractures have been reported to occur primarily in endodontically treated teeth due to condensation forces and/or with post placement. This study describes 11 Chinese patients with 12 molars that developed vertical root fractures without endodontic or post procedures. These showed characteristics of a true vertical root fracture as confirmed after extraction. Fractured teeth showed a consistent pattern. The majority were severely attrited mandibular molars in males. All had clinically intact crowns with no or minimal restorations.
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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.
In a precise semantic sense, the most significant biomaterial in dentistry is the human tooth. How it reacts, changes and is affected during the dynamics of occlusal loading should be reexamined in light of modern technology. Much is known about the embryology, histology, biochemistry, anatomy, and the microbiology affecting teeth; however, there are areas of biomechanics, biochemistry, and bioelectricity which also affect dental hard tissues that remain largely unexplored. Technological advances enable us to use more sophisticated instrumentation to measure and quantify changes that occur during the dynamics of occlusal activity. Armed with this information, dentistry can better understand how teeth interact with restorative materials in order to increase the longevity of both.
OBJECTIVES: An 18-month follow-up clinical trial of one conventional glass-ionomer (HIFI Master Palette), three resin-modified glass-ionomers (Fuji II LC, Vitremer, 3M Exp. 155) and one polyacid-modified resin composite (Dyract) was conducted to evaluate their clinical effectiveness in Class-V cervical lesions. In addition, the interface between dentin and two resin-modified glass-ionomers and one polyacid-modified resin composite was examined by scanning electron microscopy (SEM). METHODS: After evaluation of the restorations immediately following placement (baseline), all patients were subjected to a strict recall schedule with controls at 6, 12 and 18 months. The clinical effectiveness was recorded in terms of retention and marginal integrity, clinical microleakage, caries recurrence, and tooth vitality. A chi 2-test (p < 0.05) was used to test for significant differences between materials. In case of restoration loss or special defects, a replica was made to examine the surface texture and restoration margins by SEM. In vitro, the interface was examined by SEM after an argon-ion-beam etching technique was used to enhance surface relief and disclose interfacial substructures. RESULTS: Retention appeared to be good for all the materials tested. Marginal discrepancies were localized at the incisal enamel and/or the cervical dentin margin, except for the polyacid-modified resin composite that showed most of the defects at the incisal enamel margin. None of the systems could guarantee margins free of microleakage for a long time. In vitro, the type of dentin pre-treatment defines to a great extent the morphology of the resultant interface between dentin and the restorative material tested. SIGNIFICANCE: In this clinical study, the retention rate of the tested materials was good and even excellent for some products. Perfect marginal adaptation deteriorated too fast. The marginal adaptation of the polyacid-modified resin composite at the enamel site would probably have been better by the use of selective enamel or total acid etching. Marginal sealing remains a problem. Future research should concentrate on improving the marginal adaptation and sealing capacities before a broader clinical use can be advocated.
OBJECTIVE: The purpose of this study was to evaluate the performance of a filled (OptiBond Solo) and an unfilled (Prime & Bond 2.1) "one-bottle" adhesive in Class V restorations after 18 months of clinical service. METHODS: Thirty-three patients with non-carious cervical lesions were enrolled in the study. A total of 101 lesions were restored using one of the adhesives and a hybrid composite resin. Enamel was not beveled, nor was any mechanical retention placed. The restorations were evaluated at baseline, and at 6 and 18 months after placement using modified USPHS criteria. RESULTS: Cumulative 18-month retention rates were 93.6% for OptiBond Solo and 98.0% for Prime & Bond 2.1. The difference in retention rates was not statistically significant. For OptiBond Solo, the only notable problems were interfacial staining and marginal adaptation, both of which were less than ideal in 9% of restorations. Marginal problems were slightly less frequent for Prime & Bond 2.1 restorations, but the difference was not significant. CONCLUSIONS: Both adhesives provided Class V retention rates exceeding the 18-month, full acceptance guidelines set by the American Dental Association. Any additional benefit provided by the use of a filled adhesive was not detected in this 18-month clinical trial.
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.
OBJECTIVES: Dentine hypersensitivity is a common clinical finding with a wide variation in prevalence values. The aim of this study was to establish the prevalence of dentine hypersensitivity and to examine some associated aetiological factors in a cross-sectional study of patients visiting the Periodontology and Oral Hygiene Clinic at Prince Phillip Dental Hospital, Hong Kong over a three-week period. METHODS: 226 patients were examined over a three-week period using a triple syringe to administer a blast of cold air to confirm the diagnosis of dentine hypersensitivity. Additional factors such as smoking habits, initiating stimuli, gingival recession and cervical tooth surface loss were noted. RESULTS: 153 patients were diagnosed as having dentine hypersensitivity, giving a prevalence figure of 67.7%. The commonest teeth affected were the lower incisors and the commonest initiating factor was cold drinks. CONCLUSIONS: The prevalence of dentine hypersensitivity in a hospital periodontology clinic population in Hong Kong was 67.7%.
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