Analysis of the abfraction lesions formation mechanism by the finite element method

The Stresses and Deformations in the Abfraction Lesions of the Lower Premolars Studied by the Finite Element Analyses: Case Report and Review of Literature

BACKGROUND

The purpose of the study was to investigate the behavior of hard dental structures of the teeth with abfraction lesions when experimental occlusal loads were applied.

METHODS

A 65-year-old patient came to the dentist because she had painful sensitivity in the temporomandibular joints and the lower right premolars. The patient was examined, and cone-beam computed tomography (CBCT) of the orofacial area was indicated. The data provided from the CBCT were processed with Mimics Innovation Suite 17 software to create the desired anatomical area in 3D format. Then, the structural calculation module was used in order to perform a finite element analysis of the lower right premolar teeth. A focused review of articles published between 2014 and 2023 from specialty literature regarding the FEA of premolars with abfraction lesions was also conducted.

RESULTS

The parcel area and the cervical third of the analyzed premolars proved to be the most vulnerable areas under the inclined direction of occlusal loads. The inclined application of experimental loads induced 3-4 times higher maximum shears, stresses, and deformations than the axial application of the same forces.

CONCLUSIONS

FEA can be used to identify structural deficiencies in teeth with abfractions, a fact that is particularly important during dental treatments to correct occlusal imbalances.

Introspection of the Etiopathological Mechanisms Underlying Noncarious Cervical Lesions: Analysis of the Different Theories and Their Impact on the Mineralized Structures of the Tooth

The noncarious cervical lesions (NCCLs) recognize an etiological framework of onset very different from the carious processes with etiology whose bacteria aggregated in a biofilm play a predominant role, leading in this way to the loss of the mineralized structure of the tooth. The pathological picture of the NCCLs, which manifests itself with a clinical picture of dental wear, differs from caries because it mainly recognizes a series of pathological processes, such as erosion, through the action of generally acidic chemical agents and abrasion, which is basically expressed through repeated mechanical trauma characteristic of tooth brushing. However, in the literature, there is no unanimous agreement in identifying only these two mechanisms, but there are some who propose a more marked role of anomalous occlusal loads, which would be unloaded on some teeth which, in addition to both erosive and abrasive mechanisms, would give rise to abfraction. Therefore, the aim of this review was to collect literature etio-pathological information and discuss the mechanisms underlying NCCLs.

Noncarious cervical lesions in the aging population analyzed through digital scanning: occlusal risk factors, dimensions, and morphology

OBJECTIVES

To evaluate noncarious cervical lesions (NCCL) in older adults by analyzing each lesion's morphology, dimension, and occlusal risk factors using intraoral scanning and clinical evaluation.

MATERIALS AND METHODS

Individuals over 60 treated at the School of Dentistry in Minas Gerais, Brazil, were invited to participate in this cross-sectional study. We clinically evaluated 1245 teeth for the presence of NCCL and dentin hypersensitivity (DH) in 53 individuals. Three-dimensional models were obtained using Omnicam, and occlusal risk factors were evaluated through the presence of wear facets, intense occlusal contacts, and interferences. The 3Shape 3DViewer software was used to classify NCCL morphology and to measure their height. NCCL depth, width, and area measurements were determined using ImageJ. Descriptive analyses were performed. The Kolmogorov-Smirnov test showed that quantitative data exhibited non-normal distribution. For bivariate analyses of quantitative data, the Mann-Whitney test was employed. The results were reported with mean, standard deviation, median, minimum, and maximum. For bivariate analyses of categorical data, the Pearson chi-square test was used. The results were reported with frequencies (counts) and percentages. A regression model evaluating the association between occlusal risk factors and the absence/presence of NCCL was built.

RESULTS

Most participants were female (58.5%), with a mean age of 66. The frequency of NCCL was 28.27%, corresponding to 352 teeth. Of these, 68.18% exhibited saucer morphology and 31.82% wedge-shaped morphology. The frequency of DH was 13.92% in teeth with NCCL. Saucer NCCL exhibited significantly greater height (p = 0.02), while wedge-shaped lesions showed greater depth (p < 0.001). Also, teeth with NCCL had a higher proportion of wear facets (66.8%; p < 0.001), intense occlusal contacts (39.8%; p = 0.008), and occlusal interferences (21.9%; p = 0.05). The regression model showed that teeth with wear facets were 1.50 times more likely to exhibit NCCL than teeth without wear facets (p < 0.001). Teeth with intense occlusal contact were 1.22 times more likely to exhibit NCCL than teeth without intense occlusal contact (p = 0.031).

CONCLUSIONS

NCCL is a common dental condition in the older adults evaluated in this study. Wedge-shaped NCCL exhibited greater depth, while saucer NCCL had more expressive height. Occlusal risk factors may represent a crucial mechanism for the occurrence of NCCL in this population.

CLINICAL RELEVANCE

Understanding the mechanisms involved in developing NCCL is helpful in diagnostic and preventive practices. The study showed the importance of dental occlusion and characteristics of different NCCL morphologies that help the clinician in decision-making.

Stereomicroscopic Aspects of Non-Carious Cervical Lesions

Non-carious cervical lesions (NCCLs) represent a form of tooth wear, characterized by the irreversible loss of dental hard tissues at the enamel-cement junction, without the involvement of caries and dental trauma. The aim of this study was to highlight the morphological elements of NCCLs via their stereomicroscopic examination and to confirm the role of this examination in the diagnosis of early lesions. In addition, the association between the morphological aspects identified during the stereomicroscopic examination of NCCLs and their etiological factors was determined. For this study, extracted teeth with NCCLs were examined with a stereomicroscope. The morphological aspects of NCCLs were evaluated at magnifications up to 75×. In wedge-shaped NCCLs, the stereomicroscopic examination allowed the identification and measurement of scratches, furrows and cracks. In saucer-shaped NCCLs, the stereomicroscopic examination highlighted the smooth appearance of the walls. The presented study highlighted the role of stereomicroscopic examination in the assessment of NCCL morphology and in their early diagnosis. The study confirmed, in particular, the role of occlusal overloads and tooth brushing in determining the morphology of NCCLs.

Noncarious cervical lesions: Morphology and progression, prevalence, etiology, pathophysiology, and clinical guidelines for restoration

PURPOSE

To synthesize the literature regarding noncarious cervical lesions (NCCLs) and propose clinical guidelines when lesion restoration is indicated.

MATERIAL AND METHODS

A PubMed search was performed related to NCCL morphology, progression, prevalence, etiology, pathophysiology, and restoration.

RESULTS

NCCLs form as either rounded (saucerlike) depressions with smooth, featureless surfaces that progress mainly in height or as V-shaped indentations that increase in both height and depth. Prevalence ranges from less than 10% to over 90% and increases with age. Common locations are the facial surfaces of maxillary premolars. They have a multifactorial etiology due to personal habits such as excessive horizontal toothbrushing and consumption of acidic foods and drinks. Occlusal factors have been identified as contributing to the prevalence of NCCLs in some studies, whereas other studies indicate there is no relationship. The concept of abfraction has been proposed whereby mechanical stress from occlusal loading plays a role in the development and progression of NCCLs with publications supporting the concept and others indicating it lacks the required clinical documentation. Regardless of the development mechanism, demineralization occurs and they are one of the most common demineralization diseases in the body. Treatment should be managed conservatively through preventive intervention with restorative treatment delayed until it becomes necessary due to factors such as lesion progression, impact on patient's quality of life, sensitivity, poor esthetics, and food collection may necessitate restoration. Composite resins are commonly used to restore NCCLs although other materials such as glass ionomer and resin-modified glass ionomer are also used. Sclerotic dentin does not etch like normal dentin and therefore it has been recommended to texture the dentin surface with a fine rotary diamond instrument to improve restoration retention. Some clinicians use mechanical retention to increase retention. Beveling of enamel is used to increase the bonding area and retention as well as enhance the esthetic result by gradually creating a color change between the restoration and tooth. Both multistep and single-step adhesives have been used. Dentin etching should be increased to 30 seconds due to the sclerotic dentin with the adhesive agent applied using a light scrubbing motion for 20 seconds but without excessive force that induces substantial bending of a disposable applicator. Both flowable and sculptable composite resins have been successfully used with some clinicians applying and polymerizing a layer of flowable composite resin and then adding an external layer of sculptable composite resin to provide enhanced resistance to wear. When caries is present, silver diamine fluoride has been used to arrest the caries rather than restore the lesion.

CONCLUSIONS

Noncarious cervical lesions (NCCLs) form as smooth saucerlike depressions or as V-shaped notches. Prevalence values as high as 90% and as low as 10% have been reported due to habits such as excessive toothbrushing and an acidic diet. Occlusal factors have been proposed as contributing to their presence but it remains controversial. Publications have both supported and challenged the concept of abfraction. They are one of the most common demineralization diseases in the body. Conservative treatment through prevention is recommended with restorative treatment delayed as long as possible. When treatment is needed, composite resins are commonly used with proposed restorative guidelines including texturing the sclerotic dentin, beveling the enamel, potential use of mechanical retention, 30 seconds of acid etching, and use of either multistep or single-step adhesives in conjunction with a light scrubbing motion for 20 seconds without excessive force placed on disposable applicators.

Comparative Evaluation of Postoperative Sensitivity Using Three Different Tooth-Colored Restorative Materials in Non-carious Cervical Lesions: A Split-Mouth Design In Vivo Study

Introduction

Three different tooth-colored restorative materials were evaluated and compared for postoperative sensitivity using a split-mouth design. This is a double-blinded clinical trial assessed for a one-month follow-up period in patients with non-carious cervical lesions (NCCLs).

Materials and Methods

A total of 60 NCCLs in 20 participants were considered in this split-mouth design study and randomly divided into three different groups: Flowable composite (n = 20), resin-modified glass ionomer cement (RMGIC) (n = 20), and Zirconomer® (n = 20). The restorations were evaluated for postoperative sensitivity at baseline (BL-day 0), three, seven, and 21 days using the Schiff cold air sensitivity scale. Data were analyzed using IBM SPSS Statistics for Windows, Version 23.0 (Released 2015; IBM Corp., Armonk, New York, United States) using a post hoc test for postoperative sensitivity and one-way Anova to analyze all the groups together at the time interval of three, seven, and 21 days.

Results

In Group 1 (flowable composites) and Group 3 (Zirconomer), a statistically significant difference in terms of reduced postoperative sensitivity was seen after three and seven days. However, a significant reduction in postoperative sensitivity was seen after three, seven, and 21 days in Group 2 (RMGIC).

Conclusion

In this study, RMGIC showed reduced postoperative sensitivity after restoring NCCLs compared to Zirconomer and flowable composites. Compared with flowable composites and Zirconomer, RMGIC showed better clinical performance in terms of less postoperative sensitivity after restoring NCCLs.

Numerical Modeling of a New Type of Prosthetic Restoration for Non-Carious Cervical Lesions

The paper considers a new technology for the treatment of non-carious cervical lesions (NCCLs). The three parameterized numerical models of teeth are constructed: without defect, with a V-shaped defect, and after treatment. A new treatment for NCCL has been proposed. Tooth tissues near the NCCLs are subject to degradation. The main idea of the technology is to increase the cavity for the restoration of NCCLs with removal of the affected tissues. The new treatment method also allows the creation of a playground for attaching the gingival margin. The impact of three biomaterials as restorations is studied: CEREC Blocs; Herculite XRV; and Charisma. The models are deformed by a vertical load from the antagonist tooth from 100 to 1000 N. The tooth-inlay system is considered, taking into account the contact interaction. Qualitative patterns of tooth deformation before and after restoration were established for three variants of the inlay material.

The Influence of Different Occlusal Loading on Six Restorative Materials for Restoration of Abfraction Lesions-Finite Element Analysis

Objectives  The aim of the study was to analyze the occurrence of stress on teeth with abfraction lesions restored with six different restorative materials, and by introducing the tensile strength parameters to calculate the safety factor of the material under the load (ratio between the strength of the material and the maximum stress).

Materials and Methods  Three-dimensional models of the mandibular premolar are created from a microcomputed tomography images. An abfraction lesion is modeled on the tooth. The stress of the dental tissues and six restorative materials under functional and nonfunctional occlusal loading of 200 (N) are analyzed by finite element method.

Statistical Analysis  CTAn program 1.10 and ANSYS Workbench (version 14.0) were used for analysis. Results are presented in von Mises stress.

Results  Oblique loads caused ≈ four times higher stress in restorative materials than the axial ones. It is noticeable that high values of von Mises stress are measured at the bottom of the sharp lesion, even up to 240 MPa, that are significantly reduced after the restoration. The highest stresses at the restorative material are present at the lower (gingival) margin of the restoration. The highest stresses under both types of loads are measured in nanohybrid composite (Tetric EvoCeram, Ivoclar Vivadent). The lowest values of the stress are measured in the flowable composite (Tetric Flow, Ivoclar Vivadent), but at the same time, the highest value of the stress is measured in the surrounding dental tissues on the tooth restored with the flowable composite. The microhybrid composite (Herculite XR, Kerr), with the highest safety factor, is the material that best withstands the stresses it is exposed to. The obtained safety factor did not exceed the critical limit, except for the glass ionomer cement, with the safety factor lower than 1.

Conclusion  The type of tooth loading has the greatest influence on the intensity of stress. The value of the obtained stresses in the restorative material and dental tissues differ due to the different mechanical properties of the materials. Restoration of noncarious lesions significantly reduces extremely high stress values at their bottom.

Evaluation of the relationship between non-caries cervical lesions and the tooth and periodontal tissue: An ex-vivo study using micro-computed tomography

The purpose of this study was to analyze the relationship between the height and depth of buccal non-carious cervical lesions (NCCLs) and the relationship between the size of buccal NCCLs and clinical crown-root ratio of both buccal and lingual (palatal) sides using micro-computed tomography (micro-CT) images of the teeth and periodontal tissues from the cadavers. The micro-CT images of 56 teeth and their supporting tissues were obtained from 17 cadavers. From these images, the height and depth of NCCLs and the length of the buccal and lingual (palatal) clinical crowns were measured, and the conventional/modified clinical crown-root ratios were calculated. The height and depth ratio of NCCLs were analyzed statistically with the conventional/modified crown-root ratios by Pearson's correlation and multiple regression. According to the Pearson's correlation, the height and depth of buccal NCCLs were positively correlated with the modified buccal clinical crown-root ratio (p < 0.001 and p = 0.013, respectively). The regression model composed of variables of crown-root ratios explained the height of buccal NCCLs, and the prominent factor of the model was the modified buccal clinical crown-root ratio (p < 0.001). Moreover, the depth of buccal NCCLs was also explained by the regression model, and its prominent factor was the proportion of modified buccal and lingual (palatal) clinical crowns (p = 0.004). The buccal NCCLs were related to the crown-root ratios; particularly, the level of buccal gingival margin could be associated with the formation of buccal NCCLs.

Stress distribution in endodontically treated abfracted mandibular premolar restored with different cements and crowns: A three-dimensional finite element analysis

Context

Noncarious cervical lesions may penetrate the pulp and require root canal treatment followed by crown placement. Such teeth may be susceptible to fracture, especially at the cervical area.

Aims

To estimate which combination of restorative material and crown resulted in homogenous stress-strain distribution of endodontically treated abfracted mandibular premolar using three-dimensional finite element model (FEM).

Settings and Design

A three-dimensional model of mandibular single-rooted premolar along with alveolar bone was created in finite element analysis (FEA) software preprocessor ANSYS rel 14.5 FEM software (ANSYS Inc., Houston, USA, 1994). Cervical lesion was created in the model with specific dimensions, 3 mm mesiodistally and 2 mm gingivoocclusally with enamel occlusal margin and dentin gingival margin.

Materials and Methods

Tooth was simulated to be root canal treated and restored with different types of cements and crowns followed by placing a static load of 300 N at an angle of 135°. Analysis was run and stress distribution pattern was studied.

Results

Cervical region of an endodontically treated tooth is subjected to stresses, irrespective of restorative material used. Porcelain fused to metal (PFM) crowns showed least strain values with different postendodontic, restorative materials.

Conclusions

FEA is a predictable and reproducible model to predict stress-strain behavior. PFM crowns with different postendodontic restorative materials showed least strain values in the cervical area of abfracted, endodontically treated premolars.

Shear bond strengths of tooth coating materials including the experimental materials contained various amounts of multi-ion releasing fillers and their effects for preventing dentin demineralization

We examined shear bond strengths (SBSs) of various tooth-coating-materials including the experimental materials to dentin and demineralization resistance of a fractured adhesive surface after the SBS testing. Three resin-type tooth-coating-materials (BC, PRG Barrier Coat; HC, Hybrid Coat II; and SF, Shield force plus) and two glass-ionomer-type tooth-coating-materials (CV, Clinpro XT Varnish; and FJ, Fuji VII) were selected. The experimental PRG Barrier Coat containing 0, 17, and 33 wt% S-PRG filler (BC0, BC17, and BC33, respectively) were developed. Each tooth-coating-material was applied to flattened dentin surfaces of extracted human teeth for SBS testing. After storing in water for 32 days with 4000 thermal cycling, the specimens were subjected to the SBS test. Specimens after SBS testing were subjected to a pH cycling test, and then, demineralization depths were measured using a polarized-light microscope. ANOVA and Tukey's HSD test were used for statistical analysis. The SBS value of FJ and CV was significantly lower than those of other materials except for BC (p < 0.01). The lesion depth of FJ was significantly shallower than those of other materials (p < 0.01); that of CV was significantly shallower than those of BC, HC, SF, and the control; and those of BC0 and BC17 were significantly shallower than that of the control (p < 0.05). The resin-type tooth-coating-materials demonstrated significantly higher SBS for dentin than the glass-ionomer-type tooth-coating-materials; however, they were inferior to the glass ionomer-type tooth-coating-materials in regards to the acid resistance of the fractured adhesion surface.