Stresses at the cervical lesion of maxillary premolar--a finite element investigation

Restoration of Non-carious Cervical Lesions: A Brief Review for Clinicians

Non-carious cervical lesions (NCCLs) become common in individuals over the age of 40 and are progressive. Those that are wedge-shaped in cross-section likely develop hazardous stress concentrations along their sharp axial extent, which can be distributed to lower, safer levels over a larger area via adhesive restoration. Restoration is indicated once a lesion progresses to a minimum restorable axial depth of at least 1.5 mm at the deepest extent, which threatens the strength of the tooth, especially a single-rooted tooth. Restorations with a glass ionomer or resin composite employing an adhesive system that is total-etch or is a self-etching primer combined with selective enamel etching are equally effective. Consequently, the restorative material can be selected based on isolation or esthetic factors.

Investigating the etiology of non-carious cervical lesions: Novel µCT analysis

OBJECTIVES

The etiology of non-carious cervical lesions (NCCLs) is not fully understood, limiting treatment and prevention. Our aim was to evaluate the effect of mechanical loading and acid exposure on the cervical tooth region using a random spectrum loading model that simulates the nature of oral mastication.

METHODS

Thirty extracted human premolars were divided into three experimental groups: 1) unloaded teeth immersed in acid (erosion group: Er), 2) loaded teeth immersed in acid (erosion with spectrum loading group: Er-SL), and 3) loaded teeth immersed in distilled water (spectrum loading group: SL). Random spectrum loading with loads ranging from 100 to 500 N was performed. All teeth were scanned using micro-CT. A novel 3D analysis was developed to evaluate the circumferential cervical tissue loss and regions under tension and compression. For parametric and non-parametric comparisons, one-way ANOVA with Tukey post-hoc tests and Kruskal-Wallis with Bonferroni post-hoc tests were used.

RESULTS

A significant difference was observed in the circumferential volumetric loss, with the Er-SL exhibiting the greatest volume loss (p < 0.001). Moreover, in the loaded groups (Er-SL and SL), regions subjected to tension showed significantly greater loss (p < 0.001, p = 0.007) compared with regions subjected to compression.

CONCLUSIONS

The novel high-resolution micro-CT analysis provided new insights into the etiology of NCCLs. The results suggested that the cumulative effect of mechanical loading and acid exposure may play a major role in NCCL formation.

CLINICAL SIGNIFICANCE

This study investigates the etiology of NCCLs by examining the combined effects of occlusal loads and acid exposure on cervical tissue loss. Understanding the pathogenesis of NCCLs paves the way for the development of improved preventative measures and treatment strategies to prevent tooth structure degradation.

Conservative Treatment of Dental Non-Carious Cervical Lesions: A Scoping Review

This scoping review aims to evaluate methods of conservative reconstruction of dental enamel lesions resulting from abrasions and evaluate the effect of diode laser in reducing the symptoms of tooth sensitivity. The cementoenamel junction is more prone to substance loss because the enamel thickness is substantially decreased, resulting in a much weaker enamel-dentin bond.

METHODS

Dental abrasion was examined in the mechanical cause alone. Pubmed, Scopus, and Web of Science were used to discover publications that matched our topic from 1 January 2018 to 20 March 2023. A comparison of various non-carious cervical lesion (NCCL) restoration treatments was generated mostly by mechanical considerations.

RESULTS

A final number of 11 clinical trials and randomized controlled trials were included in the review for qualitative analysis. Composite resins performed well in clinical trials for the restoration of NCCLs.

CONCLUSIONS

Composite, in its different forms of filling and consistency, preceded by the use of adhesives, is an efficient and effective material for the treatment of NCCLs. Diode laser use prior to NCCL restoration of teeth does not diminish restoration retention rate, may lessen hypersensitivity, and may affect restoration success.

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.

Influence of different base materials and thicknesses on the fracture resistance of endocrown: A three-dimensional finite element analysis

INTRODUCTION

To analyze the stress distribution of the all-ceramic endocrown with different base materials and thicknesses using three-dimensional finite element analysis.

METHODS

A endodontically treated maxillary premolar was scanned by micro-CT, a three-dimensional finite element model of the endocrown with fluid resin as the base material was divided into control (0 mm), 1 mm, 2 mm, and 3 mm groups according to base thickness. Three kinds of conventional base materials were used and divided into glass ion group (A), fluid resin group (B), and nanocomposite resin group (C), and a three-dimensional finite element model of the endocrown with 1.0 mm thickness of base was established. A static loading with axial and 45° direction was applied to each model, the stress distribution of each part of the endocrown was analyzed under different base materials and thicknesses.

RESULTS

The different thickness of the base layer has an influence on the components of the restoration and the tooth. The stress in the control group was the largest. The stress was the lowest when the thickness of the base layer was 1 mm; The maximum of the equivalent stress, the first, second, and third principal stress in the endocrown, abutment, and alveolar bone, are basically the same with the different base materials. The stress on the base layer increases with the elastic modulus of base materials increases.

CONCLUSIONS

The base layer played a force buffering effect on the dental body restored with endocrowns, and the effect was the best at 1 mm; The selection of base material has little influence on the whole, but in order to protect the weak tissues of the cavity bottom, the base material with lower elastic modulus can be used.

Mechanical and Thermal Stress Analysis of Cervical Resin Composite Restorations Containing Different Ratios of Zinc Oxide Nanoparticles: A 3D Finite Element Study

Due to an increase in prevalence of cervical lesions, it is important to use appropriate restorative materials to reduce the incidence of secondary lesions. Owing to having antibacterial properties, cervical composite restorations containing different ratios of Zinc Oxide nanoparticles (ZnO NPs) have been analyzed using the Finite Element method to determine the optimal incorporation ratio from mechanical and thermal perspectives. A numerical simulation is conducted for a mandibular first premolar with a cervical lesion (1.5 × 2 × 3 mm³) restored with composites containing 0 to 5% wt. ZnO NPs. Subsequently, the samples are exposed to different thermo-mechanical boundary conditions, and stress distributions at different margins are examined. The accumulated stress in the restoration part increases for the 1% wt. sample, whereas the higher percentage of ZnO NPs leads to the reduction of stress values. In terms of different loading conditions, the least and most stress values in the restoration part are observed in central loading and lingually oblique force, respectively. The change in the surface temperature is inversely correlated with the ratio of ZnO NPs. In conclusion, the composite containing 5% wt. ZnO NPs showed the most proper thermo-mechanical behavior among all samples.

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.

Effect of cervical lesion centered access cavity restored with short glass fibre reinforced resin composites on fracture resistance in human mandibular premolars- an in vitro study

AIM

The aim of this study was to evaluate the fracture resistance of cervical lesion centered access cavity restored with short glass fibre reinforced resin materials in human mandibular premolars.

MATERIALS AND METHODS

Sixty freshly extracted human mandibular premolars were collected and assigned to positive control group (G1- Intact teeth) and other experimental groups (G2, G3. G4, G5, G6), Traditional Access Cavity(TAC) and Cervical Lesion Centered Access Cavity(CLCAC). Following endodontic therapy, samples were grouped accordingly, G2-CLCAC without restoration (Negative Control), G3-CLCAC restored with conventional nano-hybrid composite (Tetric-N-Ceram), G4-TAC restored with short glass fibre reinforced resin composite (Ever-X Posterior), G5-CLCAC restored with short glass fibre reinforced resin composite (Ever-X Posterior), G6- CLCAC restored with individually formed unidirectional fibre-reinforced post (Everstick post) and short glass fibre-reinforced resin composite (Ever-X Posterior). The samples were thermocycled (35 °C/28s, 15 °C/2s, 35 °C/28s, 45 °C/2s/10,000 cycles) and cyclically fatigued(2,50,000 cycles/15-30N/2 Hz) and then subsequently loaded to failure. The mean load to fracture (Newtons) were statistically analyzed using one-way ANOVA and Tukey's post HOC test and failure mode analysis was also done.

RESULTS

The mean fracture resistance of the CLCAC design restored with fibre reinforced materials was higher when compared to the TAC design but the difference was not statistically significant. The negative control group (CLCAC without restoration) showed significantly the least fracture resistance (P < 0.05) when compared to all the other groups except for group 3 (CLCAC restored with conventional composites).

CONCLUSIONS

Within the limitations of the study, it can be concluded that short glass fibre reinforced resin composites improved the fracture resistance of endodontically treated mandibular premolars irrespective of the type of access cavity designs. Favourable fractures were seen more in cervical lesion centered access cavity restored with short glass fibre reinforced composite materials. Nevertheless, the applicability of this design in multirooted teeth, canal cleanliness efficacy, and long term clinical performance are yet to be explored to complement this new access design.

Dental Restorative Materials for Elderly Populations

The incidence of dental caries, especially root caries, has risen in elderly populations in recent years. Specialized restorative materials are needed due to the specific site of root caries and the age-related changes in general and oral health in the elderly. Unfortunately, the restorative materials commonly used clinically cannot fully meet the requirements in this population. Specifically, the antibacterial, adhesive, remineralization, mechanical, and anti-aging properties of the materials need to be significantly improved for dental caries in the elderly. This review mainly discusses the strengths and weaknesses of currently available materials, including amalgam, glass ionomer cement, and light-cured composite resin, for root caries. It also reviews the studies on novel anti-caries materials divided into three groups, antimicrobial, remineralization, and self-healing materials, and explores their potential in the clinical use for caries in the elderly. Therefore, specific restorative materials for caries in the elderly, especially for root caries, need to be further developed and applied in clinical practice.

Validated Finite Element Models of Premolars: A Scoping Review

Finite element (FE) models are widely used to investigate the biomechanics of reconstructed premolars. However, parameter identification is a complex step because experimental validation cannot always be conducted. The aim of this study was to collect the experimentally validated FE models of premolars, extract their parameters, and discuss trends. A systematic review was performed following Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Records were identified in three electronic databases (MEDLINE [PubMed], Scopus, The Cochrane Library) by two independent reviewers. Twenty-seven parameters dealing with failure criteria, model construction, material laws, boundary conditions, and model validation were extracted from the included articles. From 1306 records, 214 were selected for eligibility and entirely read. Among them, 19 studies were included. A heterogeneity was observed for several parameters associated with failure criteria and model construction. Elasticity, linearity, and isotropy were more often chosen for dental and periodontal tissues with a Young’s modulus mostly set at 18–18.6 GPa for dentine. Loading was mainly simulated by an axial force, and FE models were mostly validated by in vitro tests evaluating tooth strains, but different conditions about experiment type, sample size, and tooth status (intact or restored) were reported. In conclusion, material laws identified herein could be applied to future premolar FE models. However, further investigations such as sensitivity analysis are required for several parameters to clarify their indication.

Application Solid Laser-Sintered or Machined Ti6Al4V Alloy in Manufacturing of Dental Implants and Dental Prosthetic Restorations According to Dentistry 4.0 Concept

This paper presents a comparison of the impact of milling technology in the computer numerically controlled (CNC) machining centre and selective laser sintering (SLS) and on the structure and properties of solid Ti6Al4V alloy. It has been shown that even small changes in technological conditions in the SLS manufacturing variant significantly affect changes from two to nearly two and a half times in tensile and bending strengths. Both the tensile and bending strength obtained in the most favourable manufacturing variant by the SLS method is over 25% higher than in the case of cast materials subsequently processed by milling. Plug-and-play SLS conditions provide about 60% of the possibilities. Structural, tribological and electrochemical tests were carried out. In vitro biological tests using osteoblasts confirm the good tendency for the proliferation of live cells on the substrate manufactured under the most favourable SLS conditions. The use of SLS additive technology for the manufacturing of dental implants and abutments made of Ti6Al4V alloy in combination with the digitisation of dental diagnostics and computer-aided design and manufacture of computer-aided design/manufacturing (CAD/CAM) following the idea of Dentistry 4.0 is the best choice of technology for manufacturing of prosthetic and implant devices used in dentistry.

Dentistry 4.0 Concept in the Design and Manufacturing of Prosthetic Dental Restorations

The paper is a comprehensive but compact review of the literature on the state of illnesses of the human stomatognathic system, related consequences in the form of dental deficiencies, and the resulting need for prosthetic treatment. Types of prosthetic restorations, including implants, as well as new classes of implantable devices called implant-scaffolds with a porous part integrated with a solid core, as well as biological engineering materials with the use of living cells, have been characterized. A review of works on current trends in the technical development of dental prosthetics aiding, called Dentistry 4.0, analogous to the concept of the highest stage of Industry 4.0 of the industrial revolution, has been presented. Authors’ own augmented holistic model of Industry 4.0 has been developed and presented. The studies on the significance of cone-beam computed tomography (CBCT) in planning prosthetic treatment, as well as in the design and manufacture of prosthetic restorations, have been described. The presented and fully digital approach is a radical turnaround in both clinical procedures and the technologies of implant preparation using computer-aided design and manufacturing methods (CAD/CAM) and additive manufacturing (AM) technologies, including selective laser sintering (SLS). The authors’ research illustrates the practical application of the Dentistry 4.0 approach for several types of prosthetic restorations. The development process of the modern approach is being observed all over the world. The use of the principles of the augmented holistic model of Industry 4.0 in advanced dental engineering indicates a change in the traditional relationship between a dentist and a dental engineer. The overall conclusion demonstrates that it is inevitable and extremely beneficial to implement the idea of Dentistry 4.0 following the assumptions of the authors’ own, holistic Industry 4.0 model.

Tooth surface loss: A review of literature

Objectives

Tooth surface loss (TSL) or tooth wear (TW) is an irreversible loss of hard tooth structure caused by factors other than those responsible for dental caries. TSL is observed clinically as attrition, abrasion, abfraction, and erosion. It may be associated with symptoms such as tooth hypersensitivity and function impairment, and may lead to change in the morphology of the affected tooth. However, it may also be asymptomatic, meaning the patient may not be aware of it. In this instance, the dentist is encouraged to make the patient aware of this issue.

The aim of this review is to provide an overview of the classification and management of TSL.

Material and methods

The PubMed (MEDLINE) search engine was used to gather the most recent information on TSL. The search was restricted to a five year period (1 September 2014–31 August 2019), and only English-language studies were included. A Boolean search of the PubMed dataset was implemented to combine a range of keywords: (Tooth surface loss OR tooth wear) AND (tooth attrition OR tooth Abrasion OR tooth erosion OR tooth abfraction OR non-carious cervical lesions) AND (humans). Studies were also obtained by manual searches and from Google Scholar.

Results

By this process, 560 articles and studies were obtained. More studies were also obtained by manual searches and from Google Scholar. The most relevant published studies were chosen and used in the current review. The selected articles are included in the reference list.

Conclusion

TSL is a clinical problem that dentists face on a daily basis. Therefore, a sound clinical approach by which TSL can be prevented and managed is essential. While this approach requires that dentists are knowledgeable about the issue, increasing public awareness of TSL is also vital.

Comparison of ultimate force revealed by compression tests on extracted first premolars and FEA with a true scale 3D multi-component tooth model based on a CBCT dataset

OBJECTIVE

The aim of this study was to develop a new method for creating a multi-component and true scale 3-dimensional (3D) model of a human tooth based on cone-beam computed tomography (CBCT) images.

MATERIALS AND METHODS

First maxillary premolar tooth model was reconstructed from a patient's CBCT images. The 2D serial sections were used to create the 3D model. This model was used for finite element analysis (FEA). Model validation was performed by comparing the ultimate compressive force (UF) obtained experimentally using a universal testing machine and from simulation. The simulations of three component-omitting models (silicone, cementum, and omitting both) were performed to analyze the maximum (max.) principal stress and stress distribution.

RESULTS

The simulation-based UF indicating tooth fracture was 637 N, while the average UF in the in vitro loading was 651 N. The discrepancy between the simulation-based UF and the experimental UF was 2.2%. From the simulation, the silicone-omitting models showed a significant change in max. principal stress, resulting in a UF error of 26%, whereas there was no notable change in the cementum-omitting model.

CONCLUSION

This study, for the first time, developed a true scale multi-component 3D model from CBCT for predicting stress distribution in a human tooth.

CLINICAL RELEVANCE

This study proposed a method to create 3D modeling from CBCT in a true scale and multi-component manner. The PDL-like component-omitting simulation led to a higher error value of UF, indicating the importance of multi-component tooth modeling in FEA. Tooth 3D modeling could help determine mechanical failure in dental treatments in a more precise manner.

Composite vs. ionomer vs. mixed restoration of wedge-shaped dental cervical lesions: Marginal quality relative to eccentric occlusal loading

Dental cervical restorations may be impacted by resultants of occlusal loads that may have already contributed to the development of the lesion and should rely on materials' favorable properties to bear the stresses. The marginal quality of cervical restorations made with materials of different moduli of elasticity in essence, isolated, or in combination, was evaluated relative to eccentric occlusal loading. Cervical wedge-shaped cavities, prepared in extracted premolars, were restored with a composite resin (CR), a restorative ionomer (GIC), or the composite in combination with a lining ionomer (Mixed restoration: M). Half of the teeth in each group were subjected to eccentric occlusal loading (eol; 150 N / 10⁶ cycles / 2.5 Hz; CReol / GICeol / Meol, n = 10), and the others were stored in 37 °C distilled water (Control: c; CRc / GICc / Mc, n = 10). A fluorescein-modified adhesive favored delimitation of formed gaps, which were evaluated by confocal laser scanning microscopy regarding their presence, location related to the cavity walls, and width and depth (µm), at a 5% significance level. From a comprehensive perspective, neither the loading nor the materials were significantly associated with the qualitative response variables or exerted any influence over the quantitative variables. More specifically, the use of the different materials was significantly associated with the frequency of gaps exclusively when loading was applied (Chi-square test, p = 0.029, CR > M > GIC). Though the marginal quality of cervical restorations may not be influenced by eccentric occlusal loading or the use of different materials, even in association in general, the unfavorable aspects of the use of the composite may be relevant, particularly in face of the existence of eccentric occlusal loads.

Abfraction lesions: etiology, diagnosis, and treatment options

Abfraction is a type of noncarious cervical lesion (NCCL) characterized by loss of tooth tissues with different clinical appearances. Evidence supports that abfraction lesions, as any NCCLs, have a multifactorial etiology. Particularly, the cervical wear of abfraction can occur as a result of normal and abnormal tooth function and may also be accompanied by pathological wear, such as abrasion and erosion. The interaction between chemical, biological, and behavioral factors is critical and helps to explain why some individuals exhibit more than one type of cervical wear mechanism than others. In an era of personalized dentistry, patient risk factors for NCCLs must be identified and addressed before any treatment is performed. Marked variations exist in dental practice concerning the diagnosis and management of these lesions. The lack of understanding about the prognosis of these lesions with or without intervention may be a major contributor to variations in dentists’ management decisions. This review focuses on the current knowledge and available treatment strategies for abfraction lesions. By recognizing that progressive changes in the cervical area of the tooth are part of a physiologically dynamic process that occurs with aging, premature and unnecessary intervention can be avoided. In cases of asymptomatic teeth, where tooth vitality and function are not compromised, abfraction lesions should be monitored for at least 6 months before any invasive procedure is planned. In cases of abfraction associated with gingival recession, a combined restorative-surgical approach may be performed. Restorative intervention and occlusal adjustment are not indicated as treatment options to prevent further tooth loss or progression of abfraction. The clinical decision to restore abfraction lesions may be based on the need to replace form and function or to relieve hypersensitivity of severely compromised teeth or for esthetic reasons.

Dental Materials: What Goes Where? Class V Restorations

A large number of Class V restorations are placed per annum to restore cervical lesions. This paper evaluates the pathogenesis of these lesions, with particular reference to the role of occlusal factors, and reviews the literature in order to provide advice on the material(s) which are most likely to produce optimal longevity of a Class V restoration. CPD/CLINICAL RELEVANCE: Resin-modified glass ionomer materials appear to provide optimal survival for a Class V restoration, but a (flowable) comDosite miaht Droduce a better aesthetic result.

Factors influencing the progression of noncarious cervical lesions: A 5-year prospective clinical evaluation

STATEMENT OF PROBLEM

The etiology (chemical, friction, abfraction) of noncarious cervical lesion (NCCL) progression is poorly understood.

PURPOSE

The purpose of this 5-year prospective clinical trial was to measure the relationship between NCCLs and various etiologic factors.

MATERIAL AND METHODS

After review board approval, 29 participants with NCCLs were enrolled. Polyvinyl siloxane impressions were made of each NCCL, and casts were poured at baseline, 1, 2, and 5 years. The casts were scanned with a noncontact profilometer, and 1-, 2-, and 5-year scans were superimposed over baseline scans to measure volumetric change in NCCLs. T-scan and Fujifilm Prescale films were used to record relative and absolute occlusal forces on teeth with NCCLs at the 5-year recall. Participant diet, medical condition, toothbrushing, and adverse oral habit questionnaires were given at the 5-year recall. Occlusal analysis was completed on mounted casts to determine the presence of wear facets and group function. Volumetric lesion progression from 1 to 5 years was correlated to absolute and relative occlusal force using mixed model analysis. The Kruskall-Wallis and Mann-Whitney analyses compared lesion progression with diet, medical condition, toothbrushing, adverse oral habits, wear facets, and group function.

RESULTS

The NCCL progression rate over 5 years was 1.50 ±0.92 mm(3)/yr. The rate of progression of NCCLs was related to mean occlusal stress (P=.011) and relative occlusal force (P=.032) in maximum intercuspation position. No difference was seen in NCCL progression between participants with any other factors.

CONCLUSION

Heavy occlusal forces play a significant role in the progression of NCCLs.

Stress distribution in a premolar 3D model with anisotropic and isotropic enamel

The aim of this study was to compare the areas of stress concentration in a three-dimensional (3D) premolar tooth model with anisotropic or isotropic enamel using the finite element method. A computed tomography was imported to an image processing program to create the tooth model which was exported to a 3D modeling program. The mechanical properties and loading conditions were prescribed in Abaqus. In order to evaluate stresses, axial and oblique loads were applied simulating realistic conditions. Compression stress was observed on the side of load application, and tensile stress was observed on the opposite side. Tensile stress was concentrated mainly in the cervical region and in the alveolar insertion bone. Although stress concentration analyses of the isotropic 3D models produced similar stress distribution results when compared to the anisotropic models, tensile stress values shown by anisotropic models were smaller than the isotropic models. Oblique loads resulted in higher values of tensile stresses, which concentrate mainly in the cervical area of the tooth and in the alveolar bone insertion. Anisotropic properties must be utilized in enamel stress evaluation in non-carious cervical lesions.

Fractographic features of glass-ceramic and zirconia-based dental restorations fractured during clinical function

Fractures during clinical function have been reported as the major concern associated with all-ceramic dental restorations. The aim of this study was to analyze the fracture features of glass-ceramic and zirconia-based restorations fractured during clinical use. Twenty-seven crowns and onlays were supplied by dentists and dental technicians with information about type of cement and time in function, if available. Fourteen lithium disilicate glass-ceramic restorations and 13 zirconia-based restorations were retrieved and analyzed. Fractographic features were examined using optical microscopy to determine crack initiation and crack propagation of the restorations. The material comprised fractured restorations from one canine, 10 incisors, four premolars, and 11 molars. One crown was not categorized because of difficulty in orientation of the fragments. The results revealed that all core and veneer fractures initiated in the cervical margin and usually from the approximal area close to the most coronally placed curvature of the margin. Three cases of occlusal chipping were found. The margin of dental all-ceramic single-tooth restorations was the area of fracture origin. The fracture features were similar for zirconia, glass-ceramic, and alumina single-tooth restorations. Design features seem to be of great importance for fracture initiation.

An Investigation Into the Relationship Between Noncarious Cervical Lesions and Premature Contacts

The aim of the present study was to investigate the relationship between noncarious cervical lesions (NCCL) and dental premature contacts (PC). Following examination of 1,974 teeth from 77 patients referred to the Department of Oral Medicine, Faculty of Dentistry, Mashad University of Medical Science, Iran, a total of 167 teeth were identified to have the criteria set for noncarious cervical lesions (regarded as NCCL group). Also, 167 teeth exhibiting no such lesions were selected randomly from the same population (regarded as control group). The results indicated that within the NCCL group, the frequency of noncarious cervical lesions differed significantly among the various teeth; the first premolar teeth showed the greatest number of cervical lesions, followed by the canine teeth, and the second molar teeth had the least number of lesions. A similar trend was detected in the total number of premature contacts among the seven types of teeth. The results revealed a highly significant and positive correlation between the incidence of NCCL and the PC. The NCCL group and the control group differed significantly in the number of premature contacts in centric relation (CR) and working side, but not in balancing and protrusion.

Clinical evaluation of the association between noncarious cervical lesions and occlusal forces

STATEMENT OF PROBLEM

Noncarious cervical lesions (NCCLs) are a frequent challenge in clinical dental practice, given the variety of opinions regarding their etiology, diagnosis, and treatment.

PURPOSE

The purpose of this study was to assess the potential relationship between occlusal forces and the occurrence of NCCLs.

MATERIAL AND METHODS

The participant population consisted of 111 volunteers (30 male and 81 female, mean age 23.6 years). General personal information was recorded, after which participants were examined for the presence and location of NCCLs, gingival recession, fracture lines, dental and restoration fractures, presence and location of tooth wear, type of occlusal guidance scheme for lateral mandibular movements, and existence of occlusal interference or premature contacts. The participants were divided according to the presence or absence of NCCLs, and data were statistically analyzed with the Independent t test, the Chi-square test, and the Fisher exact test (α=.05).

RESULTS

A significant association was found between the presence of NCCLs and age (P=.008), gingival recession (P<.001), occlusal trauma (P<.001), presence (P<.001) and location of tooth wear, and group function as occlusal guidance scheme in lateral excursive movements (P<.001).

CONCLUSIONS

A strong relationship between the presence of NCCLs and occlusal overload was found.

Stress analysis of occlusal forces in canine teeth and their role in the development of non-carious cervical lesions: abfraction

Non-carious cervical tooth lesions for many decades were attributed to the effects of abrasion and erosion mainly through toothbrush trauma, abrasive toothpaste, and erosive acids. However, though the above may be involved, more recently a biomechanical theory for the formation of these lesions has arisen, and the term abfraction was coined. The aim of this study was to investigate the biomechanics of abfraction lesions in upper canine teeth under axial and lateral loading conditions using a three-dimensional finite element analysis. An extracted human upper canine tooth was scanned by μCT machine (Skyscan, Belgium). These μCT scans were segmented, reconstructed, and meshed using ScanIP (Simpleware, Exeter, UK) to create a three-dimensional finite element model. A 100 N load was applied axially at the incisal edge and laterally at 45° midpalatally to the long axis of the canine tooth. Separately, 200 N axial and non-axial loads were applied simultaneously to the tooth. It was found that stresses were concentrated at the CEJ in all scenarios. Lateral loading produced maximum stresses greater than axial loading, and pulp tissues, however, experienced minimum levels of stresses. This study has contributed towards the understanding of the aetiology of non-carious cervical lesions which is a key in their clinical management.

Coupling image processing and stress analysis for damage identification in a human premolar tooth

Non-carious cervical lesions are characterized by the loss of dental hard tissue at the cement-enamel junction (CEJ). Exceeding stresses are therefore generated in the cervical region of the tooth that cause disruption of the bonds between the hydroxyapatite crystals, leading to crack formation and eventual loss of enamel and the underlying dentine. Damage identification was performed by image analysis techniques and allowed to quantitatively assess changes in teeth. A computerized two-step procedure was generated and applied to the first left maxillary human premolar. In the first step, dental images were digitally processed by a segmentation method in order to identify the damage. The considered morphological properties were the enamel thickness and total area, the number of fragments in which the enamel is chipped. The information retrieved by the data processing of the section images allowed to orient the stress investigation toward selected portions of the tooth. In the second step, a three-dimensional finite element model based on CT images of both the tooth and the periodontal ligament was employed to compare the changes occurring in the stress distributions in normal occlusion and malocclusion. The stress states were analyzed exclusively in the critical zones designated in the first step. The risk of failure at the CEJ and of crack initiation at the dentin-enamel junction through the quantification of first and third principal stresses, von Mises stress, and normal and tangential stresses, were also estimated.

Characteristics of non-carious cervical lesions--an ex vivo study using micro computed tomography

The aetiology of non-carious cervical lesions (NCCLs) is not well understood and still controversial. The aim of this ex-vivo study was to examine the morphological characteristics of NCCLs for clinical evidence of enamel loss above the cemento-enamel junction (CEJ) as suggested by the abfraction theory. Fifty extracted human teeth with various types of NCCLs were collected and scanned by micro computed tomography. The reconstructed three-dimensional models were evaluated from multiple aspects, including longitudinal cross-section series. The location of internal line angle and proximal exits of the lesions were evaluated in relation to the level of CEJ. The coronal margins of the lesions were inspected for evidence of enamel loss above the CEJ using the bucco-lingual longitudinal sectional images. Coronal margins of the lesions were located along and/or under the CEJ for all of the 50 samples. In most of the lesions, regardless of lesion type, the proximal exits and internal line angles were located below the CEJ. This study did not detect clinical evidence of enamel loss above the occlusal margin of NCCLs as would have been expected according to the general abfraction mechanism.

Development of 3D CAD/FEM Analysis System for Natural Teeth and Jaw Bone Constructed from X-Ray CT Images

A three-dimensional finite element model of the lower first premolar, with the three layers of enamel, dentin, and pulp, and the mandible, with the two layers of cortical and cancellous bones, was directly constructed from noninvasively acquired CT images. This model was used to develop a system to analyze the stresses on the teeth and supporting bone structure during occlusion based on the finite element method and to examine the possibility of mechanical simulation.

The effect of occlusal restoration and loading on the development of abfraction lesions: A finite element study

Background:

Abfraction, a type of non-carious cervical tooth loss, is a poorly understood condition. One factor thought to contribute to the development of these lesions is the effect of occlusal loading and the presence of occlusal restoration.

Aim and Objectives:

The aim of this paper is to study the stress profile in the cervical region of mandibular first premolar with variation of occlusal loads, and to compare the stress profile between sound and occlusally restored tooth under variation of occlusal load, using two-dimensional plane strain finite element model.

Materials and Methods:

A mandibular first premolar was sectioned and modeled in the finite element software, along with its peridontium. Varying occlusal loads were applied along the cuspal inclines, with and without an occlusal restoration. The software used was NISA II EMRC.

Result:

It was found that higher occlusal loads caused more cuspal flexure and that the maximum shear stress was much higher and closer to the cervical area. It was also observed that there was a slight increase in shear stress when occlusal restoration was present.

Conclusion:

It was suggested that high occlusal loading and the presence of an occlusal amalgam restoration increased the stress concentration at the cervical area, which may lead to the breakdown of enamel at the cervical region.

Three-dimensional stress distribution in the human periodontal ligament in masticatory, parafunctional, and trauma loads: finite element analysis

BACKGROUND

The presence of the periodontal ligament (PDL) makes it possible to absorb and distribute loads produced during masticatory function and other tooth contacts into the alveolar process via the alveolar bone proper. However, several factors affect the integrity of periodontal structures causing the destruction of the connective matrix and cells, the loss of fibrous attachment, and the resorption of alveolar bone.

METHODS

The purpose of this study was to evaluate the stress distribution by finite element analysis in a PDL in three-dimensional models of the upper central incisor under three different load conditions: 100 N occlusal loading at 45 degrees (model 1: masticatory load); 500 N at the incisal edge at 45 degrees (model 2: parafunctional habit); and 800 N at the buccal surface at 90 degrees (model 3: trauma case). The models were built from computed tomography scans.

RESULTS

The stress distribution was quite different among the models. The most significant values (harmful) of tensile and compressive stresses were observed in models 2 and 3, with similarly distinct patterns of stress distributions along the PDL. Tensile stresses were observed along the internal and external aspects of the PDL, mostly at the cervical and middle thirds.

CONCLUSIONS

The stress generation in these models may affect the integrity of periodontal structures. A better understanding of the biomechanical behavior of the PDL under physiologic and traumatic loading conditions might enhance the understanding of the biologic reaction of the PDL in health and disease.

The cervical wedge-shaped lesion in teeth: a light and electron microscopic study

BACKGROUND

The cervical non-carious wedged-shaped lesion is controversial in that its aetiology may involve attrition, erosion, abrasion and stress-corrosion (abfraction). This study examined the histopathology of anterior teeth with cervical wedge-shaped lesions by light and electron microscopy to elucidate their pathogenesis.

METHODS

Ten undecalcified human teeth with cervical lesions were available for investigation. Patency of the dentine tubules was tested using red dye penetration from the pulp chamber. The morphology of normal and sclerotic dentine adjacent to the cervical wedge-shaped lesions was investigated by scanning electron microscopy. The numbers and diameters of dentinal tubules were measured at different levels beneath the surfaces of the lesions.

RESULTS

The gross and microscopic features of the worn teeth were described. Red dye penetration tests showed white tracts of sclerotic tubules contrasted with red tracts of patent tubules. Numbers of tubules per square area and diameters of patent and sclerotic tubules varied at different levels within the dentine due to deposits of intratubular dentine.

CONCLUSIONS

The cervical wedge is shaped by interactions between acid wear, abrasion and dentinal sclerosis. No histopathological evidence of abfraction was found. Clinical diagnosis, conservation and restoration of non-carious cervical lesions need to take into account the extent of sclerotic dentine beneath wedge-shaped lesions.

A qualitative assessment of non-carious cervical lesions in extracted human teeth

BACKGROUND

Opinions vary about the causes of non-carious cervical lesions (NCCLs). They have been attributed to toothbrush abrasion, acid corrosion (commonly termed dental erosion), and abfraction. The purpose of this study was to examine the microwear details of NCCLs in a collection of extracted human teeth using scanning election microscopy (SEM).

METHODS

Negative replicas of large NCCLs in 24 extracted human teeth were obtained in polyvinylsiloxane impression material (Light Body Imprint II, 3M ESPE) and viewed under SEM.

RESULTS

All NCCLs extended from the cemento-enamel junction to the root surface and they displayed a variety of wedge-shaped appearances. There was evidence of both abrasion and corrosion in 18 of the 24 teeth (75.0 per cent), abrasion only in one tooth (4.2 per cent) and corrosion only in five teeth (20.8 per cent). Horizontal furrows with smooth edges and minor scratch marks, characteristic of abrasion and corrosion, were noted in 13 teeth (54.2 per cent).

CONCLUSIONS

Based on microscopic assessment of a sample of extracted teeth, it appears that abrasion and corrosion are common associated aetiological factors in the formation of NCCLs.

Incidence of noncarious cervical lesions and their relation to the presence of wear facets

PROBLEM

Noncarious cervical lesions are characterized by loss of tooth structure in the cervical area, compromising its integrity and resulting in esthetic problems for the patient.

PURPOSE

The purpose of this study was to assess noncarious cervical lesions in young patients in an attempt to establish a possible relationship to the presence of wear facets.

MATERIALS AND METHODS

First-year dental students of Bauru Dental School were studied to verify the prevalence of noncarious cervical lesions and their relationship to the presence of wear facets. After 3 years, the students were examined again to verify the incidence of new lesions, trying to establish a correlation to the previous existence of wear facets.

RESULTS

Of the 1,131 teeth analyzed, 129 had noncarious cervical lesions. Twenty-nine of the 40 students had at least one tooth with one lesion. After 3 years, the incidence of new lesions was 57. Mandibular first molars (22.3%), mandibular first premolars (13.2%), mandibular second premolars (13.2%), and maxillary first molars (12.4%) showed the highest prevalence of lesions. On final analysis, 86.8% of all teeth presenting lesions showed wear facets. The identification of new lesions associated with the presence of wear facets identified during the first exam 3 years earlier was statistically significant (p < 0.01).

CONCLUSIONS

The patterns of wear facets found in the study population examined were associated with an increased occurrence of noncarious cervical lesions.

CLINICAL SIGNIFICANCE

Occlusal factors, especially the presence of wear facets, should be considered in the management of noncarious cervical lesions.