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

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OBJECTIVE: The purpose of this retrospective study was to evaluate the association between cervical dentin hypersensitivity and the presence of abfractive lesions. METHOD AND MATERIALS: Written records and study casts for 250 active-care patients, selected alphabetically, were analyzed for the clinical detection of abfractive lesions and cervical dentin hypersensitivity from 1979 until 1996. Clinical diagnosis of abfractive lesions was made according to existing literature descriptions of these hard tissue lesions. Cervical dentin hypersensitivity was diagnosed when a verified positive threshold patient response was found during tooth evaluation by the air indexing method. Patient groups I and II were formed solely on the basis of the presence or absence, respectively, of a verified positive threshold patient response of cervical dentin to air. RESULTS: A significant association was found between air-indexed cervical hypersensitivity and the presence of abfractive lesions. The primary locations for both cervical hypersensitivity and abfractive lesions were the buccal surfaces of posterior teeth. CONCLUSION: This long-term retrospective study found a positive association between cervical dentin hypersensitivity and abfractive lesions. The correlative nature of this study suggests the need for further investigation.

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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.

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The term "erosion," as currently used in dentistry, is not only a misnomer but also is misleading, according to the authors. The authors highlight the critical roles of occlusal function and parafunction in the multifactorial etiology of cervical lesions and relate their significance to clinical practice. They propose a revised nomenclature for and classification of dental hard tissue lesions.

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A variety of unusual noncarious cervical lesions (NCL) are depicted that appear to negate W.D. Miller's toothbrush/dentifrice abrasion theory and demonstrate that other factors may be involved in their etiology. Confusion exists in the designation of NCL ever since G.V. Black stated in 1908 that toothbrush/dentifrice abrasion is an erosive effect. Since abrasion and erosion are two distinct activities, it is suggested that dentistry adopt the same terminology as chemical engineering in order to foster improved communication between the sciences. The term "abfraction" has been used to supplant erosion because it seems more appropriate when describing the loss of tooth substance attributable to effects of occlusal loading forces as well as the physiochemical breaking that occurs during stress corrosion. Numerous reasons, based on accepted engineering principles, indicate that NCL should be restored. It is incumbent on dentists to become cognizant of these reasons, since this would help them inform patients of the benefits to be gained by restoring such deficient areas.

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A preliminary study and hypothesis of the etiology of root caries is presented with appropriate data suggesting that biodental engineering factors (BEF) be introduced into the equation that is generally accepted in the formation of all caries. Principally, because of the rapid progression and location of root caries, BEF in addition to bacterial plaque and suitable substrate contribute to the development of these unique lesions. The dominant and most significant factors recognized by bioengineers are tooth flexure, stress concentration, stress corrosion, and piezo-electricity. All of these factors interplay during the dynamics of occlusal activity causing the loss of tooth substance. A new and revised model is being presented that provides a basis for the etiology of root caries.

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Due to the stresses resulting from biomechanical loading forces exerted on the teeth (static, as in swallowing and clenching or cyclic, as in chewing), both enamel and dentin can chip or break away. This loss of tooth substance, which shall be termed Abfraction, is dependent on the magnitude, duration, direction, frequency, and location of the forces. These abfractive lesions are caused by flexure and ultimate material fatigue of susceptible teeth at locations away from the point of loading. Clinical observation of a variety of enamel and dentin lesions due to the shapes, sizes, loci, and frequency warrants a new and distinct classification.

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