Abfraction Lesions Explained: What Finite Element Analysis Tells Us About Cervical Tooth Damage
Most clinicians have seen them: the characteristic wedge-shaped defects at the cervical margins of teeth β sharp-edged, non-carious, and often most pronounced on the mandibular first premolar. For decades the etiology of these lesions has been debated, with erosion, abrasion, and occlusal forces all implicated to varying degrees.
A 2014 study published in Acta Informatica Medica by JakupoviΔ, Cerjakovic, Topcic, AjanoviΔ and colleagues used finite element analysis (FEM) to model stress distribution within a mandibular first premolar under controlled loading conditions β providing some of the clearest biomechanical evidence to date for the occlusal stress theory of abfraction formation.
What Is Abfraction β and Why Does It Matter?
The term abfraction was introduced by Grippo in 1991 to describe non-carious cervical lesions (NCCLs) caused by occlusal biomechanical forces. Unlike erosion (chemical dissolution) or abrasion (mechanical wear from external contact), abfraction results from stress concentration at the cervical region of a tooth β an area where enamel is thinnest and where the geometry of the tooth creates a fulcrum-like stress concentration under off-axis loading.
The mechanism proposed is as follows: repeated tension and compression at the cervical region sever chemical bonds between hydroxyapatite crystals in both enamel and dentin. Once these bonds are broken, small molecules penetrate the tissue and prevent re-establishment of those bonds. Over time, progressive microstructural loss results in the characteristic wedge-shaped lesion that clinicians recognize clinically.
The mandibular first premolar has consistently shown the highest prevalence of NCCLs across multiple epidemiological studies β a finding that points toward the specific morphology and occlusal loading pattern of this tooth as a significant contributing factor.
The Research Approach β Finite Element Analysis
Finite element analysis is a computational engineering method that divides a complex structure into thousands of small elements and calculates how forces distribute through each element. It is widely used in structural engineering and has become increasingly valuable in dental research as a way to model stress in tooth tissues under conditions that cannot be directly measured clinically.
The study used a three-dimensional model of an intact mandibular first premolar derived from micro-CT scanning. The scanned images were processed into approximately 576 horizontal sections at 0.0361 mm thickness, from which a volumetric 3D CAD model was constructed. The final mesh consisted of 747,157 nodes and 439,113 elements β a resolution that allows detailed mapping of stress across all tissue types.
The model included separate tissue components: enamel, dentin, periodontal ligament modeled as a 0.3 mm membrane surrounding the root, and a segment of alveolar bone. The pulp space was modeled as empty, as its elastic modulus is negligibly small relative to adjacent structures. Material properties for each tissue were drawn from the established literature.
Two loading conditions were tested: axial load simulating central occlusion contact, and paraxial load simulating a laterotrusive movement at a 40Β° angle on the external surface of the buccal cusp. Both used a maximum force of 200 N, consistent with values reported in the literature for normal masticatory loads.
What the Results Showed
Stress in the Cervical Region
The most clinically significant finding was the dramatic difference in cervical stress between axial and paraxial loading. Under axial load, Von Mises stress in the cervical tooth region measured up to 12 MPa β a relatively modest value. Under paraxial load, stress in the same region exceeded 50 MPa β more than four times higher.
This finding directly supports the clinical observation that eccentric occlusal contacts, bruxism, and parafunctional loading are strongly associated with abfraction lesion formation. Central occlusion alone does not generate the cervical stress levels required to initiate tissue loss; it is the lateral and eccentric forces that drive the process.
The Sub-Superficial Enamel Finding
One of the more nuanced findings of the study relates to where within the enamel the highest stress concentrations occur. Analysis of stress distribution through a sagittal section of the tooth revealed that stress values in the cervical region are higher in the sub-superficial enamel layer than in the superficial layer.
This is significant because it suggests that abfraction lesions may initiate from within the enamel structure rather than at its outer surface. The sub-superficial enamel is also known to be structurally inferior to the surface enamel β it has a lower mineral content, higher protein percentage, and greater porosity. This combination of higher stress concentration and inferior structural properties explains why this zone is particularly vulnerable to bond breakage and tissue loss.
The finding also supports the undermining theory proposed by Rees and Hammadeh, which suggests that stress concentration at the dentine-enamel junction may cause progressive undermining of the overlying enamel β contributing to the characteristic cliff-like internal edges of abfraction lesions.
Stress Distribution Across Tissues
The study mapped stress through each tissue component separately, producing data that is useful for understanding the full biomechanical picture:
Enamel: Maximum stress was found in the contact region under both load types, reaching 205 MPa under axial load and 220 MPa under paraxial load. Enamel bears the dominant share of occlusal stress due to its high elastic modulus relative to dentin.
Dentin: Von Mises stress in dentin was significantly lower than in enamel β 67.72 MPa under axial load and 71.78 MPa under paraxial load. Stress concentrated in the crown and cervical regions, decreasing toward the apex. The relatively small difference between loading conditions in dentin reflects the buffering role of the enamel.
Periodontal Ligament: Maximum stress in the PDL was located at the upper edge of the ligament in the cervical area for both load types. Under central occlusion, calculated stress was approximately 5 MPa; under paraxial load this increased nearly threefold to approximately 13.5 MPa. The PDL's composition of discrete collagen fibers provides high-elasticity behavior that effectively absorbs much of the stress transmitted through the tooth β explaining why the absolute values remain relatively low despite the significant relative difference between loading conditions.
Alveolar Bone: The most striking difference between loading conditions was found in alveolar bone. Bone stress under paraxial load reached approximately 112 MPa β nearly ten times higher than the approximately 17 MPa recorded under axial load. The highest bone stress was located at the crestal edge of the alveolar socket. This finding has direct clinical relevance: it provides a biomechanical explanation for why excessive lateral occlusal forces are associated with crestal bone resorption, and why occlusal management is an important consideration in implant cases where bone preservation is critical.
Clinical Implications
Occlusal Analysis in Patients with NCCLs
The study strongly supports the role of eccentric occlusal contacts in abfraction formation. For patients presenting with wedge-shaped cervical lesions β particularly on mandibular premolars β a thorough occlusal analysis including assessment of lateral excursive contacts is essential. Eliminating or reducing premature contacts and lateral interferences is a logical conservative step before restorative treatment.
Bruxism and Parafunction
Paraxial forces in the study were simulated as static loads for computational simplicity. In clinical reality, bruxism and parafunction involve dynamic, repetitive loading cycles β a situation that would be expected to generate even greater cumulative stress in the cervical region over time. Patients with identified parafunctional habits who present with cervical lesions should be considered at elevated risk for ongoing abfraction, and occlusal splint therapy should be discussed before restoring these lesions.
Restoration of Abfraction Lesions
Understanding that abfraction lesions initiate sub-superficially and progress through stress concentration has implications for restoration planning. If the underlying occlusal etiology is not addressed, restored lesions are likely to fail or recur. The margins of cervical restorations placed without occlusal intervention are subject to the same stress concentrations that created the original lesion β which explains the relatively high failure rates of cervical restorations in the absence of occlusal management.
Implications for Implant Placement
The finding that paraxial loading generates alveolar bone stress nearly ten times higher than axial loading is directly relevant to implant dentistry. Implants β unlike natural teeth β lack the periodontal ligament's stress-absorbing capacity. The stress concentrations modeled in natural teeth under eccentric forces are expected to be even more pronounced at the bone-implant interface, where osseointegration creates a rigid connection without the viscoelastic buffering that the PDL provides. Occlusal design in implant cases should therefore prioritize axial loading and minimize lateral excursive forces on implant-supported restorations.
Limitations and Context
The authors appropriately acknowledge that the study modeled force as a static condition rather than the dynamic, repetitive loads that characterize real masticatory and parafunctional function. All tissues were modeled as isotropic and homogeneous, which is a simplification of the complex, anisotropic nature of biological tissues. These limitations are inherent to finite element modeling and do not invalidate the findings, but they mean that absolute stress values should be interpreted as approximations rather than precise measurements.
The study provides a clear single-moment snapshot of stress distribution β a basis for understanding cause-effect relationships in lesion formation, while acknowledging that many questions about the dynamic, cumulative nature of abfraction remain open.
Key Takeaways
The finite element analysis by JakupoviΔ, AjanoviΔ and colleagues provides clear computational evidence that:
Eccentric (paraxial) occlusal forces generate cervical stress levels more than four times higher than axial forces in the same tooth
The sub-superficial enamel in the cervical region is a specific zone of concentrated stress vulnerability, which explains the characteristic initiation point of abfraction lesions
Alveolar bone experiences nearly tenfold greater stress under paraxial loading β directly relevant to the management of both natural teeth and implant cases
The periodontal ligament's stress-absorbing capacity significantly limits bone stress transmission under normal conditions β a capacity that is absent around osseointegrated implants
For clinicians treating patients with non-carious cervical lesions, these findings reinforce the importance of occlusal analysis and management as an integral part of the restorative workflow β not an optional adjunct to it.
This article is based on: Jakupovic S, Cerjakovic E, Topcic A, Ajanovic M, Konjhodzic-Prcic A, Vukovic A. Analysis of the Abfraction Lesions Formation Mechanism by the Finite Element Method. Acta Informatica Medica. 2014;22(4):241-245. doi:10.5455/aim.2014.22.241-245
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