The association between occlusal factors and noncarious cervical lesions: A systematic review

Risk factors for noncarious cervical lesions: A case-control study

OBJECTIVES

Noncarious cervical lesions (NCCLs) are multifactorial and can be caused by the anatomical structure of the teeth, erosion, abrasion and abnormal occlusion. The aim of this case-control study was to explore the risk factors for NCCLs.

METHODS

Cone-beam computed tomography was used to determine whether a wedge-shaped defect existed at the cementoenamel junction. We compared 63 participants with NCCLs with 63 controls without NCCLs, matched for sex, age (±1 year) and toothbrushing-related factors (e.g., type of bristle and brushing patterns, frequency and strength). All participants were asked to complete a questionnaire about self-administered daily diet habits and health condition. Univariate and multivariate logistic regression analyses were conducted to determine the risk factors for NCCLs.

RESULTS

Significant variables in the univariate analysis (i.e., p < .2) included frequency of carbonated beverage consumption, sella-nasion-point B angle (SNB) and Frankfort-mandibular plane angle (FMA). Multivariate logistic regression demonstrated that the consumption frequency of carbonated beverages (odds ratio [OR] = 3.147; 95% confidence interval [CI], 1.039-9.532), FMA (OR = 1.100; 95% CI, 1.004-1.204) and SNB (OR = 0.896; 95% CI, 0.813-0.988) was independent influencing factors. The area under the receiver operating characteristic curve (AUC) value of regression Model 1 (established with the frequency of carbonated beverage consumption, FMA, SNB and sleep bruxism) was 0.700 (95% CI, 0.607-0.792; p < .001), and that of regression Model 2 (established using the frequency of carbonated beverage consumption, FMA and SNB) was 0.704 (95% CI, 0.612-0.796; p < .001).

CONCLUSIONS

The consumption frequency of carbonated beverages and FMA was risk factors for NCCLs; the higher the frequency of carbonated beverage consumption and FMA, the higher was the probability of NCCLs. SNB was a protective factor for NCCL occurrence; the larger the SNB, the lower was the probability of NCCL occurrence. These findings have further clarified the aetiology of NCCLs and provided clinicians with valuable insights into strategies for preventing the loss of dental tissue.

Tooth Wear in Older Adults: A Review of Clinical Studies

INTRODUCTION

Tooth wear is a prevalent dental condition among older adults, leading to pain and adversely affecting aesthetics, functionality, and their overall quality of life. This review aims to update the information on tooth wear in older adults from the past five years and to provide guidance on the clinical management of tooth wear in older adults.

METHODS

A literature search was conducted in three electronic databases, Scopus, Pubmed, and Embase, for English publications from January 2019 to December 2023 on clinical studies with participants aged 65 or above on tooth wear. A total of 307 articles were retrieved and 14 articles were finally included as references for this study.

RESULTS

This review highlights the common causes of tooth wear and various risk factors, such as medical conditions, hyposalivation, dietary habits, oral hygiene practices, parafunctional habits, and occlusal factors, associated with tooth wear. It is crucial for oral health care professionals to diagnose and manage tooth wear at an early stage through a risk assessment and a clinical examination to avoid complex restorative procedures. Tooth wear management should prioritize prevention, aiming to control etiological and risk factors while employing non-restorative treatments. Restorative intervention, if indicated, should be simple, minimally invasive, and cost-effective. Tooth wear progression should be monitored regularly to determine if a further intervention is needed.

CONCLUSION

Since the clinical studies on tooth wear in older adults over the past five years are limited and mainly cross-sectional, more interventional clinical studies are warranted to provide more clinical guidance on tooth wear management in older adults.

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.

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.

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.

The early wear susceptibility of cementum, enamel and dentine in vitro

OBJECTIVES

To assess the differential early wear susceptibility of cementum, enamel and dentine at a micron level.

METHODS

Whole human molar buccal surfaces incorporating natural enamel and cementum (n = 20) confirmed by imaging (digital microscopy: Keyence, VHX-7000 Milton Keynes, UK), were mounted, scanned (profilometry: XYRIS 4000, Taicaan, Southampton, UK), and allocated to receive erosion (citric acid, pH 2.7, 30 min (n = 10)) or erosion/abrasion challenges (3 cycles of (citric acid, pH 2.7, 10 min, 60 300 g linear abrasion strokes), n=10). Samples were polished and the experiment repeated on polished enamel, and polished coronal and radicular dentine within the same tooth. Profilometric wear data were obtained using superimposition: GeoMagic (3Dsystems, Darmstadt, Germany) and subtraction: MountainsMap (DigitalSurf, Besancon, France). Data were normal. A general linear model was used to assess differences between groups and substrates.

RESULTS

The mean step height (SD) for natural enamel was 8.82 μm (2.53) for erosion and 11.48 μm (2.95) for erosion/abrasion. For natural cementum, the mean step height was 6.00 μm (2.29) for erosion and 4.67 μm (1.58) for erosion/abrasion. Dentine step heights ranged from 7.20 μm (1.53) for erosion and 9.79 μm (1.01) for erosion/abrasion with no statistical differences in dentine wear. Natural cementum surfaces had the lowest wear (p<0.001). Dentine had significantly less wear than natural enamel (p<0.02).

CONCLUSIONS

Cementum surfaces demonstrated the most wear resistance, followed by dentine under erosion dominant conditions in this in vitro study. Further in-vivo investigations are needed to confirm the intraoral stability of cementum.

CLINICAL SIGNIFICANCE

Cementum may be the least susceptible of dental substrates to wear and dentine does not wear at a faster rate than enamel under erosive conditions. This adds to our knowledge on the development of non-carious cervical lesions and questions whether wear rates will accelerate once dentine is exposed.

Non-carious cervical lesions (NCCLs) and associated factors: A multilevel analysis in a cohort study in southern Brazil

AIM

To investigate the prevalence of non-carious cervical lesions (NCCLs) and their association with individual and tooth-related factors in adults from the 1982 Pelotas Birth Cohort.

MATERIALS AND METHODS

Participants were interviewed and clinically examined at the age of 31. NCCL was defined as loss of dental tissue without bacterial involvement in the cervical region. Independent variables were the socioeconomic, demographic, behavioural, and clinical characteristics. Associations were tested using a multilevel Poisson regression model.

RESULTS

Five-hundred and thirty-nine participants were clinically examined, with a 26% prevalence of NCCLs, which were more prevalent in the maxilla (56.5%) and in premolars (72.9%). In the multilevel analysis, women presented lower prevalence than men [prevalence ratio (PR) 0.59 (0.48-0.73)]; those who reported smoking at both 22 and 30 years of age had more NCCLs than those who never smoked [PR 1.65 (1.31-2.07)]; and high-frequency brushers presented higher prevalence than low-frequency brushers [PR 1.26 (1.03-1.55)]. Gingival recession increased 10 times the prevalence of NCCLs [PR 10.03 (8.15-12.35)], while the presence of periodontal pockets (≥4 mm) reduced the prevalence of NCCLs [PR 0.43 (0.28-0.66)].

CONCLUSIONS

NCCLs were more prevalent in males, smokers, and those with higher frequency of toothbrushing. While the presence of periodontal pockets was associated with a lower prevalence of NCCLs, gingival recession was a strong clinical indicator for the presence of NCCLs.

Comparison of in vitro erosion protocols in bovine teeth to simulate natural erosion lesion: analysis of mechanical properties and surface gloss

OBJECTIVE

The aim of this study was to compare two in vitro erosion protocols, in which one simulates in vivo conditions experienced by patients with gastroesophageal disorders or bulimia (HCl-pepsin protocol), and the other simulates the diet of an individual who consumes a high volume of erosive beverages (citric acid protocol). In addition, the mechanical properties and surface gloss of eroded human dentin were compared with those of sound human dentin.

MATERIALS AND METHODS

Blocks of cervical dentin were used: sound human dentin (n=10), human dentin with erosive lesions (n=10), and bovine dentin (n=30). Twenty bovine blocks were subjected to either of two erosion protocols (n=10/protocol). In the first protocol, samples were demineralized using HCl-pepsin solution, then treated with trypsin solution. In the second protocol, samples were demineralized with 2% citric acid. Toothbrushing was performed in both protocols using a toothbrushing machine (15 s with a 150 g load). Ten bovine dentin blocks were not subjected to any erosive treatment. All samples of bovine and human dentin were analyzed to obtain Martens hardness values (MH), elastic modulus (Eit*) and surface gloss. One-way ANOVA and Tukey's test were performed to analyze the data (α=0.05).

RESULTS

Sound human and eroded human dentin groups showed similar MH and Eit* values (p>0.05); however, sound human dentin showed a higher surface gloss value when compared to eroded human dentin (p<0.05). Sound bovine dentin and HCl-pepsin-treated bovine dentin treatments resulted in similar values for both MH and Eit* (p>0.05), but HCl-pepsin-treated bovine dentin and citric acid-treated bovine dentin resulted in lower surface gloss than sound bovine dentin (p<0.05).

CONCLUSIONS

The HCl-pepsin protocol modified bovine dentin properties that could be similar to those that occur on human dentin surfaces with erosive lesions.

The Role of Occlusal Factors in the Presence of Noncarious Cervical Lesions in Young People: A Case-Control Study

Objective:

The aim of this retrospective case-control study was to evaluate the influence of different occlusal characteristics and self-referred bruxism in the presence of noncarious cervical lesions (NCCLs).

Methods and Materials:

The participants were 280 students (140 cases and 140 controls), with an average age of 24.5 years, from six schools of dentistry in Spain. Clinical examination was carried out to record the NCCLs and the static and dynamic occlusal characteristics. The side of mastication and bruxism was collected by questionnaire. Data variables were analyzed by means of univariate and multivariate logistic regression. Odds ratios and the respective 95% confidence intervals were calculated (p&lt;0.05).

Results:

The presence of NCCLs was significantly more likely in subjects with protrusive interferences (odds ratio [OR]=1.82); with lateral interferences, especially on the nonworking side (OR= 1.77); or who were self-reported bruxists (OR=1.72). In the multivariate analysis, protrusive interferences, bruxism, age, and the presence of attrition were risk factors for the development of NCCLs. These factors resulted in a model with an area under the receiver-operating characteristic curve of 0.667 and a positive predictive value of 61.43%.

Conclusions:

There was no significant relationship between most occlusal factors and the presence of NCCLs. Only bruxism, protrusive interferences, age, and occlusal wear were risk factors. The predictive model was not sufficiently explanatory. Occlusal factors alone do not appear to be sufficient to explain the presence of NCCLs.

Non-carious cervical lesions and risk factors: A case-control study

OBJECTIVES

To evaluate whether the presence of non-carious cervical lesions (NCCLs) was related to the considered risk factors and to show the corresponding odds ratio in a predictive model.

METHODS

The sample was 280 dentistry students. In an initial clinical examination, 140 cases were selected that presented one or more teeth with non-carious cervical wear. For each case, a similar sex and age control without any tooth with non-carious cervical lesions was selected. An occlusal examination and periodontal probing were performed in all cases and controls by skilled dentists. All the subjects answered a questionnaire referring to factors of brushing, bruxism, preferred chewing side, consumption of extrinsic acids and the presence of intrinsic acids. Data were analysed by means of univariate and multivariate logistic regression.

RESULTS

Of all the study variables, only the protrusion interferences, interferences on the non-working side, the brushing force, CPITN value and the consumption of salads increase the risk of NCCLs in the univariate regression. The best predictive model was formed by the combination of CPITN variables >1, the consumption of acidic salads, self-reported bruxism, brushing force and attrition. However, it only correctly classifies 68.75% of subjects.

CONCLUSIONS

This study supports the multifactorial aetiology of NCCLs, the combination of several factors being necessary to explain their presence. The risk factors that make up the predictive model are not sufficient to explain the appearance of NCCLs. Dentists should take into account all these risk factors in prevention, diagnosis and treatment.

Tooth wear and gingival recession in 210 orthodontically treated patients: a retrospective cohort study

Aim

To assess the association between tooth wear (TW) and gingival recession (GR).

Materials and Methods

Two hundred and ten orthodontically treated participants (100 males) were evaluated. GR and TW were rated independently by four raters on plaster models at four time points: before treatment (T1), mean age 13.8 years (SD = 3.7); after treatment (T2), mean age 16.7 years (SD = 3.9); 3 years after treatment (T3), mean age 19.7 years (SD = 4.2); and 7 years after treatment (T4), mean age 23.9 years (SD = 4.8). Univariable and mulitvariable random effects logistic regression analyses were performed with scores for GR as dependent variables and with TW, age, gender, dental segments (maxillary and mandibular anterior and posterior segments), time points, and Angle classification as independent variables. Method reliability was assessed with kappa statistics.

Results

Mandibular incisors, mandibular and maxillary first premolars and maxillary first molars were most vulnerable to GR. The prevalence of GR increased during the observation period. At T1 20.5% participants had one or more recession sites, at T4 85.7 % of the participants had at least one GR. There was evidence of association between moderate/severe TW and GR-for a tooth with moderate/severe wear, the odds of recession were 23% higher compared to a tooth with no/mild wear (odds ratio 1.23; 95% CI: 1.08-1.40; P = 0.002). Age, dental segment, and time were also significant recession predictors, whereas gender was not.

Conclusions

There is evidence that moderate/severe TW is associated with the presence of gingival recession. Clinical significance of this can be limited.

Enamel bevelling and retention of composite restorations in non-carious cervical lesions

Data sourcesMedline, Web of Science, Latin American and Caribbean Health Sciences Literature database (LILACS), Brazilian Library in Dentistry (BBO), the Cochrane Library, abstracts of the annual conference of the International Association for Dental Research (IADR), System for Information on Grey literature in Europe (SIGLE), ProQuest Dissertations and Theses Fulltext database as well as the Periódicos Capes Theses, Current Controlled Trials, International Clinical trials registry platform, the ClinicalTrials.gov, Rebec and the EU Clinical Trials Register.Study selectionRandomised clinical trials (RCTs) that compared the retention rates of restorations in NCCLs placed with or without bevel with at least one year follow-up were considered.Data extraction and synthesisData were abstracted using standardised forms and study quality was assessed using the Cochrane risk of bias tool. Marginal discolouration scores were dichotomised into yes and no, and risk differences for retention rate and marginal discolouration were calculated for each study for analysis.ResultsFour studies were included. Two studies were considered to be at high risk of bias and not included in the meta-analysis. The overall risk difference was 0.0 (95%CI; 0.04 to 0.04) for the retention rate and 0.05 ((95%CI; 0.02 to 0.13) for the marginal discolouration, suggesting that enamel beveling does not influence retention rate or marginal discolouration.ConclusionsOne may conclude that there is no difference between bevelled and non-bevelled technique over the short-term follow-up of 12-18 months of clinical service, although this conclusion was based on only two low risk of bias RCTs. Additionally, there is not enough evidence to support this conclusion over longer-term follow-ups. There is a need for better standardisation and the reporting of RCTs investigating this technique variation after longer-term follow-up periods.

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.

Thermal cycling effects on adhesion of resin-bovine enamel junction among different composite resins

Thermal cycling is used to mimic the changes in oral cavity temperature experienced by composite resins when used clinically. The purpose of this study is to assess the thermal cycling effects of in-house produced composite resin on bonding strength. The dicalcium phosphate anhydrous filler surfaces are modified using nanocrystals and silanization (w/NP/Si). The resin is compared with commercially available composite resins Filtek Z250, Z350, and glass ionomer restorative material GIC Fuji-II LC (control). Different composite resins were filled into the dental enamel of bovine teeth. The bond force and resin-enamel junction graphical structures of the samples were determined after thermal cycling between 5 and 55°C in deionized water for 600 cycles. After thermal cycling, the w/NP/Si 30wt%, 50wt% and Filtek Z250, Z350 groups showed higher shear forces than glass ionomer GIC, and w/NP/Si 50wt% had the highest shear force. Through SEM observations, more of the fillings with w/NP/Si 30wt% and w/NP/Si 50wt% groups flowed into the enamel tubule, forming closed tubules with the composite resins. The push-out force is proportional to the resin flow depth and uniformity. The push-out tubule pore and resin shear pattern is the most uniform and consistent in the w/NP/Si 50wt% group. Accordingly, this developed composite resin maintains great mechanical properties after thermal cycling. Thus, it has the potential to be used in a clinical setting when restoring non-carious cervical lesions.

Hydrodynamic Flow through Loading and in vitro Secondary Caries Development

This in vitro study investigated the effect of hydrodynamic flow through mechanical loading on development of secondary caries lesions. Forty-eight bovine tooth specimens (enamel and dentin; sizes 3.2 x 3.2 x 2.0 mm) were restored with resin-composite on polystyrene bars; 18 samples were bonded, and 30 were not bonded. Specimens were suspended in a lactic acid solution (pH = 5; 14 days) in a modified brushing machine, and artificial caries lesions were formed. During caries development, specimens were mechanically loaded at the surface of the polystyrene bar, bent so that the tooth- composite interfaces were subjected to opening forces (16x/min). Loads applied were either none (Control Bonded, CB, n = 6; and Control Non-bonded, CNB, n = 6), 200 gr (NB200, n = 12), or 350 gr (NB350 and B350, both n = 12). Before and after caries development, specimens were imaged with transverse wavelength-independent microradiography (T-WIM), and lesion depth (LD) and mineral loss (ML) were calculated at 4 different locations. An independent t test was used to compare the LD and ML at the 4 different locations. A statistically significant effect of the level of loading (comparing groups NB200 and NB350) and of bonding (comparing groups NB350 and B350) could be observed, with a higher load and absence of bonding leading to more advanced lesions.