Clinical presentations of stress distribution in teeth and the significance in operative dentistry (original) (raw)
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Pract Periodontics Aesthet Dent., 2000
P ublication of one recent article that demonstrates stress distribution within tooth structure has improved clinicians' understanding of subtle compression and stress fracture presentations in teeth. 1 Until the publication of this benchmark article, numerous fracture presentations observed clinically have been difficult to explain. Strain distribution within the tooth is related to its structure. Enamel acts as a stress distributor, transferring the load vertically to the root, and horizontally via the dentinoenamel junction (DEJ) to the dentin of the crown. A thick zone (~200 µm) in the dentin at the DEJ undergoes greater stress than the central coronal dentin. Recently discovered structures within the occlusal surface of molars 2,3 indicate that conventional cavity designs are disharmonious with the tooth's natural
KB6Yz5HQJyw6PFHYPFm Stress Distribution in teeth Milicich Rainey
P ublication of one recent article that demonstrates stress distribution within tooth structure has improved clinicians' understanding of subtle compression and stress fracture presentations in teeth. 1 Until the publication of this benchmark article, numerous fracture presentations observed clinically have been difficult to explain. Strain distribution within the tooth is related to its structure. Enamel acts as a stress distributor, transferring the load vertically to the root, and horizontally via the dentinoenamel junction (DEJ) to the dentin of the crown. A thick zone (~200 µm) in the dentin at the DEJ undergoes greater stress than the central coronal dentin. Recently discovered structures within the occlusal surface of molars 2,3 indicate that conventional cavity designs are disharmonious with the tooth's natural mechanical stress distribution system. 4-7 This understanding has resulted in the development of a discipline termed microdentistry. This philosophy urges the use of modern methods of caries detection for early accurate minimal intervention in the caries process to preserve internal mechanical structures within the tooth that are vital to its long-term mechanical viability. Moiré Fringes To understand the various presentations of tooth fracture caused by the disruption of the natural stress distribution mechanism within the tooth, the significance of the Moiré fringes must be considered. To date, stress studies that utilize polarized light have generally been conducted with plastics to show stresses that occur when loads are applied. This technique is not effective in natural dentition due to their inability to transmit light, so these studies
Fracture of tooth enamel from incipient microstructural defects
Journal of the Mechanical Behavior of Biomedical Materials, 2010
We present definitive evidence for crack growth from internal defects called 'tufts' in human enamel. Transverse slices (normal to the tooth axis) sawn from extracted human teeth are embedded in a polycarbonate sandwich configuration and tested in simple flexural loading. The evolution of ensuing cracks across the enamel sections is viewed in situ by a video camera. The observations unequivocally identify tufts as sources of internal tooth fracture. In sufficiently thin slices the enamel becomes translucent, allowing for through-thickness observations of the crack topography. Crack segments that appear to be disjointed on a section surface link up into a contiguous primary crack below the surface, suggesting some crack resistance by 'bridging' behind the advancing crack tip. The role of these and other microstructural factors in determining the resilience of tooth structures is considered.
Stress analysis in single molar tooth
Materials Science and Engineering: C, 2013
The human tooth faces different stresses under environments of different loading conditions, these loading produces major factors in weakness of the tooth and bone structure. The need to save natural teeth has prompted the development of novel and complex techniques in endodontology, prosthodontics and periodontology. Despite a poor long-term prognosis and some prejudice to local bone, considerable efforts have been exerted for the realization of these techniques. Nowadays, the 3D finite element analysis (FEA) is one of the more recently used techniques for stress analysis in single human tooth under different loading cases. The von Mises stress distribution indicated that the greatest effort area of tooth lies at the base of crown up to the gingival line with varying intensities in the different loading cases. The highest stress in the cortical bone was predominantly found around the cervical region of the tooth and lowest in the cancellous bone and periodontal ligament (PDL). The PDL is a soft tissue, and it could function as an intermediate cushion element which absorbs the impact force and uniformly transfers the occlusal forces into the surrounding bone.
Analysis of stress generated in the enamel of an upper first premolar: a finite element study
STOMATOLOGY EDU JOURNAL
This study investigated the distribution and magnitude of stress generated in the enamel of an upper first premolar, after applying normal and excessive occlusal loads in a vertical and horizontal direction, using Finite Element Analysis (FEA). Methodology: A 3D virtual model of an upper first premolar was analyzed. The CT images of the tooth were converted into 3D data using the program MIMICS and Finite Element Analysis (FEA) was used for the stress study. To better understand the distribution of stress generated by occlusal loading, the situation of the enamel in various 3D virtual models was presented. 14 scenarios for the occlusal loading of the virtual models of the upper first premolar were obtained and the areas with the highest concentration of stress were emphasized. Results: In the model with the tooth intact, stress values were higher than the admissible ones in the simulation of the excessive vertical loading, normal horizontal loading and excessive horizontal loading. Stress was found in the buccal cusp area and in the cervical area, mainly on the buccal side of the tooth. In the models with horizontal occlusal tooth wear, stress values were higher than the admissible ones in the simulation of the excessive vertical loading. Stress was found in the cervical area. In the models with oblique occlusal tooth wear, stress values were higher than the admissible ones in the simulation of the normal and excessive horizontal loading. Stress was found mainly in cervical area, on the buccal side of the tooth. Conclusions: The most harmful loads were the heavy vertical ones and the horizontal ones, no matter the magnitude.
Enamel Microcracks Induced by Simulated Occlusal Wear in Mature, Immature, and Deciduous Teeth
BioMed Research International
Enamel wear, which is inevitable due to the process of mastication, is a process in which the microcracking of enamel occurs due to the surface contacting very small hard particles. When these particles slide on enamel, a combined process of microcutting and microcracking in the surface and subsurface of the enamel takes place. The aim of this study was to detect microscopic differences in the microcrack behavior by subjecting enamel specimens derived from different age groups (immature open-apex premolars, mature closed-apex premolars, and deciduous molars) to cycles of simulated impact and sliding wear testing under controlled conditions. Our findings indicated that the characteristics of the microcracks, including the length, depth, count, orientation, and relation to microstructures differed among the study groups. The differences between the surface and subsurface microcrack characteristics were most notable in the enamel of deciduous molars followed by immature premolars and m...
The dentin–enamel junction and the fracture of human teeth
Nature Materials, 2005
T he dentin-enamel junction (DEJ), which is the interfacial region between the dentin and outer enamel coating in teeth, is known for its unique biomechanical properties that provide a crack-arrest barrier for fl aws formed in the brittle enamel 1 . In this work, we re-examine how cracks propagate in the proximity of the DEJ, and specifi cally quantify, using interfacial fracture mechanics, the fracture toughness of the DEJ region. Careful observation of crack penetration through the interface and the new estimate of the DEJ toughness (~5 to 10 times higher than enamel but ~75% lower than dentin) shed new light on the mechanism of crack arrest. We conclude that the critical role of this region, in preventing cracks formed in enamel from traversing the interface and causing catastrophic tooth fractures, is not associated with the crack-arrest capabilities of the interface itself; rather, cracks tend to penetrate the (optical) DEJ and arrest when they enter the tougher mantle dentin adjacent to the interface due to the development of crack-tip shielding from uncracked-ligament bridging.
The Effects of Enamel Anisotropy on the Distribution of Stress in a Tooth
Journal of Dental Research, 1993
Enamel is thought to have highly anisotropic stiffness characteristics, because of its prismatic structure. It is probable that the enamel is stiffer in the prism direction compared with a direction perpendicular to it. The prisms are thought to run approximately perpendicular to the enamel-dentin junction. The curvilinear anisotropy that will result can readily be modeled by TOMECH, a finite element program developed at the University ofSheffield, since curvilinearity of mechanical properties is available as an automated feature of this program. The patterns of stress due to an external load were investigated in twodimensional abstract models, and in a model of a mandibular second premolar, for both anisotropic and isotropic enamel. Results were compared with the commercial code ANSYS and good agreement obtained. Enamel with anisotropic properties was found to have a profoundly different stress distribution under load when compared with models with isotropic enamel. For isotropic enamel, the load path is directed through the stiff enamel shell, while for anisotropic enamel, the load path is directed into the dentin, as the load path follows the stiffdirection ofthe enamel prisms. Thus, if enamel is indeed anisotropic, its function differs greatly from that suggested in previous hypotheses. Enamel with anisotropic material characteristics would provide a hard-wearing protective surfacecoating while simultaneously diverting the load away from this brittle, low-tensile-strength phase, thus reducing the potential for tooth fracture.