Long-term evaluation of extensive restorations in permanent teeth

Dental Composite Performance Prediction Using Artificial Intelligence

There is a need to increase the performance and longevity of dental composites and accelerate the translation of novel composites to the market. This study explores the use of artificial intelligence (AI), specifically machine learning (ML) models, to predict the performance outcomes (POs) of dental composites from their composite attributes. A comprehensive dataset was carefully curated and refined from 200+ publications. Nine ML models were trained to predict discrete POs, and their performance was evaluated. Five models were used for regression analysis of continuous POs. Different ML models performed better on different POs. The k-nearest neighbors (KNN) model excelled in predicting flexural modulus (FlexMod), Decision Tree model in flexural strength (FlexStr) and volumetric shrinkage (ShrinkV), and Logistic Regression and Support Vector Machine models in shrinkage stress (ShrinkStr). Receiver-operating characteristic area under the curve analysis confirmed these results but found that Random Forest was more effective for FlexStr and ShrinkV, suggesting the possibility of Decision Tree overfitting the data. Regression analysis revealed that the voting regressor was superior for FlexMod and ShrinkV predictions, while Decision Tree Regression was optimal for FlexStr and ShrinkStr. Feature importance analysis indicated triethylene glycol dimethacrylate is a key contributor to FlexMod and ShrinkV, bisphenol A glycidyl dimethacrylate and urethane dimethacrylate to FlexStr, and depth of cure, degree of monomer-to-polymer conversion, and filler loading to ShrinkStr. There is a need to conduct a full analysis using multiple ML models because different models predict different POs better and for a large, comprehensive dataset to train robust AI models to facilitate the prediction and optimization of composite properties and support the development of new dental materials.

Experimental study of polishing systems on surface roughness and color stability of novel bulk-fill composite resins

OBJECTIVE

This in vitro study aimed to investigate the effect of five polishing systems on the surface roughness (SR) and color change (CC) of novel bulk-fill composite resins.

METHODS

Fifty composite resin samples were prepared for each of the five groups: Stark Bulk Fill, SDR Plus, SonicFill 3, Charisma Bulk Flow One, and Filtek Z250. Each group of composite resins was further subdivided into five subgroups based on the polishing method applied: OptraGloss (OG), OptraGloss combined with Diapolisher paste (OGD), OptiDisc (OD), OptiDisc combined with Diapolisher paste (ODD), and Occlubrush (OCC) (n = 10). Surface roughness was measured using a profilometer following the polishing procedures, while surface morphology was assessed through atomic force microscopy and scanning electron microscopy. Subsequently, the samples were divided into two further subgroups for aging in distilled water and coffee (n = 5). The initial color parameters and those measured after 7 days were recorded to evaluate color change. Statistical analysis was performed using two-way ANOVA, followed by Tukey's post-hoc tests (α = 0.05).

RESULTS

SR significantly varied based on the composite resin and polishing system (p < 0.001). OCC polishing yielded the smoothest surface for STARK and SDR composites, while Charisma exhibited the lowest roughness in the ODD group (p < 0.05). OGD group consistently produced lower SR across multiple composites compared to the OG group (p < 0.001). Significant color changes (ΔE00) were found, with SonicFill and Filtek showing the greatest color stability when polished with OGD and OCC. For all polishing systems, except ODD, the SDR composite showed the greatest CC in coffee storage (p < 0.003).

CONCLUSION

This study demonstrated that both the polishing technique and composite resin type significantly influenced SR. SR was notably affected by the interaction between the polishing method and resin type, with the OCC system consistently producing the lowest SR values. Additionally, Charisma exhibited surface properties similar to Filtek. Variations in color change were also observed based on both the polishing method and resin type, highlighting the critical role these factors play in determining the color stability of restorative materials.

Economic Evaluation of Community Water Fluoridation in an Upper-Middle-Income Country

The aim was to estimate the cost-effectiveness and cost-benefit of CWF for schoolchildren according to different population sizes served in Brazil. The economic evaluation was conducted from a societal perspective. Total costs were estimated using four variables across different population sizes: capital cost of initial installation, chemical product costs, system operational costs, and monitoring costs. The effect of CWF was analyzed in the context of the widespread use of fluoridated toothpaste, based on studies with Brazilian population groups. The total cost of dental treatment was estimated, including both direct and indirect costs, with a discount rate of 3.5%. A one-way sensitivity analysis was conducted to test the robustness of the results based on measured parameter values. The costs averted due to CWF were US$174.40 and US$85.67 for children aged 5-8 and 3-12 years, respectively, and US$46.66 for those aged 7-12 years, according to the average effectiveness of CWF for each age group. The cost-effectiveness and cost-benefit ratio results were favorable in all scenarios where the population served was 6,000 or more inhabitants. Scenarios unfavorable to CWF were observed only in populations of up to 2,000 inhabitants. The economic evaluation of CWF in an upper-middle-income country proved to be a cost-effective oral health intervention and more economically advantageous, especially in larger areas for both deciduous and permanent dentition.

Dental Composite Performance Prediction Using Artificial Intelligence

Objective

There is a need to increase the performance and longevity of dental composites and accelerate the translation of novel composites to the market. This study explores artificial intelligence (AI), specifically machine learning (ML), to predict the performance outcomes (POs) of dental composites from their composite attributes (CAs).

Methods

An extensive dataset from over 200 publications was built and refined to 233 samples with 17 CAs and 7 POs. Nine ML models were evaluated for PO prediction performance using classified data, and Five ML models were evaluated for PO regression analysis.

Results

The KNN model excelled in predicting flexural modulus (FlexMod), Decision Tree model in flexural strength (FlexStr) and volumetric shrinkage (ShrinkV), and Logistic Regression and SVM models in shrinkage stress (ShrinkStr). Receiver operating characteristic area under the curve (ROC AUC) analysis confirmed these results but found that Random Forest was more effective for FlexStr and ShrinkV, suggesting the possibility of Decision Tree overfitting the data. Regression analysis revealed that the Voting Regressor was superior for FlexMod and ShrinkV predictions, while Decision Tree Regression was optimal for FlexStr and ShrinkStr. Feature importance analysis indicated TEGDMA is a key contributor to FlexMod and ShrinkV, BisGMA and UDMA to FlexStr, and depth of cure, degree of monomer-to-polymer conversion, and filler loading to ShrinkStr.

Significance

There is a need to conduct a full analysis using multiple ML models because different models predict different POs better, and for a large, comprehensive dataset to train robust AI models to facilitate the prediction and optimization of composite properties and support the development of new dental materials.

The formation of cariogenic plaque to contemporary adhesive restorative materials: an in vitro study

The research exploiting the ability of dental materials to induce or prevent secondary caries (SC) development still seems inconclusive. Controlling bacterial adhesion by releasing bacteriostatic ions and improving the surface structure has been suggested to reduce the occurrence of SC. This paper analyses the impact of five distinctively composed dental materials on cariogenic biofilm formation. Forty-five specimens of three composites (CeramX Spectra ST, Admira Fusion, Beautifil II) and two glass-ionomers (Fuji II LC, Caredyne Restore), respectively, were incubated in bacterial suspension composed of Streptococcus mutans, Lactobacillus acidophilus, Streptococcus mitis, Streptococcus sanguinis, and Streptococcus salivarius at pH 7.0 and 5.5. Coverslips were used as a control. Adhered bacteria were collected after 2, 4, 6, 12, 24, and 48 h and analyzed using quantitative polymerase chain reaction (qPCR). Fluoride leakage was measured at each collection. The specimens' surface topography was assessed using interferometry. In the present study, surface roughness seemed to have a partial role in bacterial adhesion and biofilm formation, together with chemical composition of the materials tested. Despite differences in fluoride leakage, biofilm accumulation was similar across materials, but the number of adhered bacteria differed significantly. A release of other ions may also affect adhesion. These variations suggest that certain materials may be more prone to initiating secondary caries.

Multifactorial Contributors to the Longevity of Dental Restorations: An Integrated Review of Related Factors

PURPOSE

This integrated review aims to identify and analyze the multifactorial contributors to the longevity of direct restorations, focusing on tooth-, patient-, and dentist-related factors.

MATERIALS AND METHODS

A search of the literature was performed using an electronic database, PubMed/Medline, Web of Science, and Scopus, on papers published between 1980 and 2024. The titles and abstracts of papers that evaluated aspects categorized into tooth-related, patient-related, and dentist-related factors influencing restoration failure were selected and screened. Full-text assessments were conducted, and the extracted data were compiled, summarized, and synthesized. The reference lists of the collected papers were also screened, and relevant citations were included in this review. Data were gathered from clinical and laboratorial studies, systematic reviews, and meta-analyses to provide a comprehensive understanding of restoration longevity.

RESULTS

Among the tooth-related factors, multiple-surface restorations, deep margins, tooth location, and tooth vitality significantly impact restoration survival. Patient-related factors such as medical conditions, risk predictors of caries, age, sex, parafunctional habits, smoking, periodontal health, number of restorations, and socioeconomic status all play crucial roles. Regarding dentist-related factors, the decision-making process, age, experience, and dentist manual dexterity are vital aspects. Furthermore, the technique used, including isolation methods for moisture control, as well as the type of dental practice (large group vs. small practice), notably influenced the restoration survival.

CONCLUSIONS

The longevity of dental restorations is influenced by a complex interplay of tooth-related, patient-related, and dentist-related factors. Strategies to improve restoration outcomes should consider all these multifactorial contributors. Continuing professional education, diligent patient guidance on the factors that influence restoration survival, careful material selection and restorative technique, and tailored individual treatment are crucial factors to reduce failure rates and improve the lifespan of restorations.

Survival Rates of Amalgam and Composite Resin Restorations from Big Data Real-Life Databases in the Era of Restricted Dental Mercury Use

Tooth decay, also known as caries, is a significant medical problem that harms teeth. Treatment is based on the removal of the carious material and then filling the cavity left in the tooth, most commonly with amalgam or composite resin. The consequences of filling failure include repeating the filling or performing another treatment such as a root canal or extraction. Dental amalgam contains mercury, and there is a global effort to reduce its use. However, no consensus has been reached regarding whether amalgam or composite resin materials are more durable, and which is the best restorative material, when using randomized clinical trials. To determine which material is superior, we performed a retrospective cohort study using a large database where the members of 58 dental clinics with 440 dental units were treated. The number of failures of the amalgam compared to composite resin restorations between 2014 and 2021 were compared. Our data included information from over 650,000 patients. Between 2014-2021, 260,905 patients were treated. In total, 19,692 out of the first 113,281 amalgam restorations failed (17.49%), whereas significantly fewer composite restorations failed (11.98%) with 65,943 out of 555,671. This study indicates that composite is superior to amalgam and therefore it is reasonable to cease using mercury-containing amalgam.

Marginal adaptation of bulk-fill resin composites with different viscosities in class II restorations: a micro-CT evaluation

BACKGROUND

The purpose of this study is to evaluate the marginal adaptation of bulk-fill resin composites with different viscosities (paste-like and flowable) in Class II restorations using micro-CT imaging.

METHODS

Forty extracted human molars were used. Mesial and distal Class II box cavities (approximately 3 mm x 3 mm x 4 mm) were prepared for each tooth, with cavity floors located 1 mm below the enamel-cementum junction. Following adhesive application, teeth were restored using eight different groups: Group XB: X-tra Base Bulk-fill Flowable (VOCO), Group XF: X-tra Fill Bulk-fill (VOCO), Group FB: Filtek Bulk-fill Posterior (3 M ESPE), Group FF: Filtek Bulk-fill Flowable (3 M ESPE), Group BB: Beautifil-Bulk (SHOFU), Group BF: Beautifil-Bulk Flowable (SHOFU), and Group CO: "as a control group", Clearfil Majesty Posterior (KURARAY) and Group CF: "as a control group", Clearfil Majesty Flow + Clearfil Majesty Posterior (KURARAY). The restored teeth underwent an aging protocol involving 1000 cycles in a water bath fluctuating between 5 ± 1.0 °C and 55 ± 1.0 °C. Post-aging, teeth were immersed in 50% silver nitrate solution for 24 h and then in a film developer solution for 8 h. Microleakage analysis was performed using micro-CT, evaluated with 3D Slicer software. A two-way ANOVA was employed for statistical analysis.

RESULTS

Two-way ANOVA results indicated significant effects of both viscosity (p < 0.0001) and composite type (p < 0.0001) on marginal adaptation. Viscosity analysis (comparing flowable and paste-like) revealed no significant differences in the FB-FF, XB-XF and BB-BF groups but significant differences in the and CO-CF group, with flowable type exhibiting less microleakage than paste-like type.

CONCLUSIONS

The study suggests that while the viscosity of bulk-fill composites did not significantly affect marginal adaptation, the brand of bulk-fill composite did influence it.

Evaluation of photopolymer resins for dental prosthetics fabricated via the stereolithography process at different polymerization temperatures-Part I: Conversion rate and mechanical properties

STATEMENT OF PROBLEM

Improvement in the mechanical properties of 3-dimensional (3D) printed dental prostheses is necessary to prevent wear caused by an antagonist or fracture. However, how different printing temperatures affect their mechanical properties is unclear.

PURPOSE

The purpose of this in vitro study was to evaluate the mechanical properties of 3D printed parts fabricated at different printing temperatures.

MATERIAL AND METHODS

Photopolymer specimens were fabricated at 3 different temperatures (room temperature, 50 °C, and 70 °C) using a stereolithography 3D printer. After rinsing to remove the residual monomer, the specimens were divided into 2 groups: with or without postprocessing. The viscosity of the photopolymerization resin was measured while the temperature was increased. Furthermore, the double-bond conversion (DBC) of the printed part was evaluated (n=3). Mechanical properties were investigated via dynamic mechanical analysis (n=1) and tensile testing (n=5). Statistical comparisons were performed via 1-way analysis of variance, followed by the Tukey honestly significant difference test (α=.05).

RESULTS

The DBC rates of the green condition group increased from 66.67% to 86.33% with increasing temperature. In addition, these specimens exhibited improved mechanical properties and reduced residual monomer levels.

CONCLUSIONS

Specimens fabricated at a temperature of 70 °C exhibited mechanical properties suitable for clinical application.

Fatigue behaviour of a self-healing dental composite

OBJECTIVE

Novel self-healing resin-based composites containing microcapsules have been developed to improve the mechanical performance of dental restorations. However, the long-term fatigue behaviour of these self-healing composites has still been hardly investigated. Therefore, this manuscript studied the fatigue behaviour of self-healing composites containing microcapsules by subjecting the specimens to traditional staircase tests and ageing in a custom-designed chewing simulator (Rub&Roll) to simulate oral ageing physiologically relevant conditions.

METHODS

To prepare self-healing composite, poly(urea-formaldehyde) microcapsules containing acrylic self-healing liquids were synthesized. Subsequently, these microcapsules (10 wt%) and initiator (benzoyl peroxide, BPO, 2 wt%) were incorporated into a commercial flowable resin-based composite. Microcapsule-free resin-based composites with and without BPO were also prepared as control specimens. A three-point flexural test was used to measure the initial flexural strength (Sinitial). Subsequently, half of the specimens were used for fatigue testing using a common staircase approach to measure the fatigue strengths (FS). In addition, the other specimens were aged in the Rub&Roll machine for four weeks where after the final flexural strength (Sfinal) was measured.

RESULTS

Compared to Sinitial, FS of all tested specimens significantly decreased as measured through staircase testing. After 4 weeks of ageing in the Rub&Roll machine, Sfinal was significantly reduced compared to Sinitial for microcapsule-free resin-based composites, but not for the self-healing composites (p = 0.3658). However, the self-healing composites are still in the experimental phase characterized by a low mechanical strength, which still impedes further clinical translation.

SIGNIFICANCE

Self-healing composites containing microcapsules exhibit improved fatigue resistance compared to microcapsule-free non-self-healing composites.

Clinical efficacy of bioactive restorative materials in controlling secondary caries: a systematic review and network meta-analysis

BACKGROUND

This systematic review and network meta-analysis aimed to compare the clinical efficacy of bioactive and conventional restorative materials in controlling secondary caries (SC) and to provide a classification of these materials according to their effectiveness.

METHODS

A search was performed in Pubmed, Web of Science, Embase, BBO, Lilacs, Cochrane Library, Scopus, IBECS and gray literature. Clinical trials were included, with no language or publication date limitations. Paired and network meta-analyses were performed with random-effects models, comparing treatments of interest and classifying them according to effectiveness in the permanent and deciduous dentition and at 1-year or 2/more years of follow-up. The risk of bias and certainty of evidence were evaluated.

RESULTS

Sixty-two studies were included in the qualitative syntheses and 39 in the quantitative ones. In permanent teeth, resin composite (RC) (RR = 2.00; 95%CI = 1.10, 3.64) and amalgam (AAG) (RR = 1.79; 95%CI = 1.04, 3.09) showed a higher risk of SC than Glass Ionomer Cement (GIC). In the deciduous teeth, however, a higher risk of SC was observed with RC than with AAG (RR = 2.46; 95%CI = 1.42, 4.27) and in GIC when compared to Resin-Modified Glass Ionomer Cement (RMGIC = 1.79; 95%CI = 1.04, 3.09). Most randomized clinical trials studies showed low or moderate risk of bias.

CONCLUSION

There is a difference between bioactive restorative materials for SC control, with GIC being more effective in the permanent teeth and the RMGIC in the deciduous teeth. Bioactive restorative materials can be adjuvants in the control of SC in patients at high risk for caries.

Five-Year Clinical Performance of Complex Class II Resin Composite and Amalgam Restorations-A Retrospective Study

The aim of this retrospective study was to investigate the clinical performance of posterior complex resin composite (RC) and amalgam (AM) restorations after a five-year period. One hundred and nineteen complex Class II restorations placed by dental students were evaluated using the USPHS criteria. Data were analyzed using Chi-square, Mann-Whitney, and Wilcoxon tests at a 0.05 level of significance. After five years, the percentages of clinically satisfactory complex Class II RC and AM restorations were 78% and 76.8%, respectively. The main reasons for the failure of AM restorations included secondary caries (Bravo-10.1%), defective marginal adaptation (Charlie-8.7%), and fracture of the tooth (Bravo-7.2%). RC restorations presented failures related to the fracture of the restoration (Bravo-16%) and defective marginal adaptation (Charlie-8.2%). There was a significantly higher incidence of secondary caries for AM restorations (AM-10.1%; RC-0%; p = 0.0415) and a higher number of fractures for RC restorations (AM-4.3%; RC-16%; p = 0.05). Regarding anatomy, AM restorations presented a significantly higher number of Alfa scores (49.3%) compared to RC restorations (22.4%) (p = 0.0005). The results of the current study indicate that complex class II RC and AM restorations show a similar five year clinical performance.

Post-Fatigue Fracture Resistance of Lithium Disilicate and Polymer-Infiltrated Ceramic Network Indirect Restorations over Endodontically-Treated Molars with Different Preparation Designs: An In-Vitro Study

The aim of the present study was to evaluate the fatigue to cyclic and static resistance of indirect restorations with different preparation designs made either of lithium disilicate (LS) or polymer-infiltrated ceramic network (PICN). Eighty-four (n = 84) molars were chosen, endodontically treated, and prepared with standardized MOD cavities. The molars were randomly divided into 6 study groups (n = 14) taking into account the "preparation design'' (occlusal veneer with 1.2 mm occlusal thickness; overlay with 1.6 mm occlusal thickness; adhesive crown with 2 mm occlusal thickness) and the "CAD/CAM material'' (E-max CAD, Ivoclar vivadent; Vita Enamic, Vita). A fatigue test was conducted with a chewing simulator set at 50 N for 1,500,000 cycles. Fracture resistance was assessed using a universal testing machine with a 6 mm diameter steel sphere applied to the specimens at a constant speed of 1 mm/min. A SEM analysis before the fracture test was performed to visually analyze the tooth-restoration margins. A statistical analysis was performed with a two-way ANOVA and a post-hoc pairwise comparison was performed using the Tukey test. The two-way ANOVA test showed that both the preparation design factor (p = 0.0429) and the CAD/CAM material factor (p = 0.0002) had a significant influence on the fracture resistance of the adhesive indirect restorations. The interaction between the two variables did not show any significance (p = 0.8218). The occlusal veneer had a lower fracture resistance than the adhesive crown (p = 0.042) but not lower than the overlay preparation (p = 0.095). LS was more resistant than PICN (p = 0.002). In conclusion, in the case of endodontically treated teeth, overlay preparation seems to be a valid alternative to the traditional full crown preparation, while occlusal veneers should be avoided in restoring non-vital molars with a high loss of residual tooth structure. LS material is more resistant compared to PICN.

Quality of Cure in Depth of Commercially Available Bulk-fill Composites: A Layer-by-layer Mechanical and Biological Evaluation

Despite their popularity, the use of bulk-fill composites remains controversial, both in terms of their properties and their in-depth development. The objectives of the present work were (1) to provide a more comprehensive evaluation of the quality of cure in depth of commercially available bulk-fill composites by combining various key mechanical and biological characterization methods, (2) to evaluate the inter-material differences when optimally cured, and (3) to evaluate the efficiency of an antioxidant-N-acetyl-cysteine (NAC)-to restrain the adverse effects of the leached components on cell viability. Nine bulk-fill composites (including flowable and high-viscosity materials) were investigated and compared to two conventional resin-based composites, one flowable and one high-viscosity restorative material. The materials were injected or packed into Teflon molds of various configurations, up to 6 mm material thickness. They were then light-cured from the top for 20 seconds with Bluephase G2 (Ivoclar Vivadent, irradiance = 1050 mW/cm2). The following physicomechanical properties were measured for the upper (0-2 mm), intermediate (2-4 mm), and lower (4-6 mm) layers: degree of conversion using Raman Spectrometry (DC, in %), microhardness using a Vickers micro-indenter before (VHN dry) and after 24 hours of storage in ethanol (VHN EtOH), and flexural strength (in MPa) and flexural modulus (in GPa) using a three-point bend test. Each composite layer and an uncured layer were also stored for one week in a standard cell growth medium to generate conditioned media. Human dental pulp cells were then cultured for 24 hours with the latter and cell viability was measured using an MTS assay. A similar experiment was repeated with conditioned media produced in contact with uncured composites, with and without the addition of 4 mM NAC. The data were subjected to a Shapiro-Wilk test, then one-way ANOVA or Kruskal-Wallis test, followed either by Tukey's test (inter-material comparison) or by Dunnett's or Dunn's test (comparison between layers relative to the upper one). The level of statistical significance was set at 0.05. Some materials (EverX, X-traF, VenusBF, X-traB) did not show any significant differences (p>0.05) for any of the properties considered between the intermediate layers compared to the upper one (considered as reference). Others displayed significant differences, at least for some properties, highlighting the value of combining various key mechanical and biological characterization methods when investigating the quality of cure in depth. Significant inter-material differences (p<0.05) were observed when comparing the properties of their upper layer, considered as "optimally" polymerized. Hence, one needs to consider the absolute property values, not only their relative evolution concerning layer thickness. Finally, the use of NAC appeared as beneficial to reduce the risk of harmful effects to dental pulp cells, especially in case of excessive thickness use, and may therefore be of potential interest as an additive to composites in the future.

Effect of erosive media on microhardness and fracture toughness of CAD-CAM dental materials

Background

Erosive acids might create surface flaws and deteriorate the mechanical properties of CAD-CAM materials. This invitro study aimed to investigate the effect of simulated gastric HCl and extrinsic erosive acids on surface microhardness and fracture toughness of CAD-CAM materials.

Methods

400 bar-shaped specimens (17×4×2 mm³) were prepared from 4 different CAD-CAM dental materials (n = 100/group); monolithic zirconia (Ceramill Zolid HT+, Amanngirbach, Austria), lithium disilicate ceramic (IPS e.max CAD, Ivoclar Vivadent, Liechtenstein), nanohybrid resin composite (Grandio Blocs, VOCO) and polymer-infiltrated glass network (Vita Enamic, VITA Zahnfabrik). Specimens from each material type were further subdivided into 5 groups (n = 20) according to the erosive media applied (simulated gastric HCl, white wine, Coca-Cola®, orange juice, and artificial saliva that served as a control). Specimens were immersed for 24 h in an incubator at 37 ℃, then ultrasonically cleaned in distilled water and air-dried. Half of the specimens were tested for Vickers microhardness (VHN) at parameters of 500 gf for 10 s, while the rest of the specimens underwent 3-point flexure till fracture. Fractured surfaces were examined under a scanning electron microscope (SEM) for fracture toughness (K_IC) calculation using the quantitative fractographic analysis method. Data collected were statistically analyzed using two-way analysis of variance (α = 0.05) after verification of data normality and homogeneity of variances.

Results

Erosive media created surface flaws that lowered the surface microhardness of the material and initiated the fracture pattern under different loads according to material type. The material type was a more predominant factor than erosive media that affected either the microhardness or the fracture toughness of CAD-CAM dental materials. The highest VHN and K_IC values were found among Ceramill Zolid HT+ groups followed by IPS e.max CAD and Grandio Blocs regardless of the erosive media employed. Erosive media significantly reduced the VHN and K_IC in Vita Enamic specimens compared to the rest of the material types.

Conclusion

All CAD-CAM materials used, except Vita Enamic, showed high resistance against the erosive acids indicating higher longevity of the material in patients frequently exposed to either extrinsic or intrinsic acid.

Clinical outcome of bonded partial indirect posterior restorations on vital and non-vital teeth: a systematic review and meta-analysis

OBJECTIVES

The survival rate of indirect partial adhesive restorations on vital versus endodontically treated teeth is still controversial. The hypothesis is that there may be a difference in the survival rate of partial adhesive restorations performed on non-vital teeth compared to vital teeth.

MATERIALS AND METHODS

This systematic review was conducted following the PRISMA guidelines. The considered clinical studies investigated the outcomes of adhesive inlays, onlays, and overlays conducted over the past 40 years, focusing on Kaplan-Meier survival curves to calculate the hazard ratio (primary objective) and the survival rate (secondary objective) between vital and non-vital teeth. The risk of bias was assessed using the Newcastle-Ottawa Scale. Studies included in the review were identified through bibliographic research on electronic databases ("PubMed," "Scopus," "Cochrane Central Register of Controlled Trial," and "Embase"). The K agreement between the two screening reviewers was evaluated.

RESULTS

A total of 55,793 records were identified on PubMed, Scopus, and other bibliographic sources, and after the application of the eligibility and inclusion criteria, eight articles were included for qualitative analysis and six for quantitative analysis. The meta-analysis of the primary and secondary outcomes demonstrated that hazard ratios (HR = 8.41, 95% CI: [4.50, 15.72]) and survival rates (OR = 3.24, 95% CI: [1.76, 5.82]) seemed more favorable for indirect partial adhesive restorations on vital teeth than for those on endodontically treated teeth.

CONCLUSIONS

Within the limits of this study, these findings suggest that the risk of failure of indirect partial adhesive restorations on endodontically treated teeth is higher than on vital teeth.

CLINICAL RELEVANCE

The use of partial adhesive restorations on vital and endodontically treated teeth showed different long-term clinical outcomes.

Risk Factors Associated with Cusp Fractures in Posterior Permanent Teeth—A Cross-Sectional Study

Objectives: This cross-sectional study aimed to evaluate the frequency and risk factors associated with cusp fractures in posterior permanent teeth. Methods: Patients presented cusp fractures on posterior permanent teeth, clinically assessed in up to 7 days after the event, and requesting dental treatment at two public services were included in this cross-sectional study. Fractured teeth already treated, with antagonist absence, or with prosthesis (total or removable) were excluded. Demographic and clinical data were collected to draw the patient profiles and establish how teeth were affected individually. Statistical analysis was performed by the Fisher exact test, and uni- and multivariate logistic regression (α = 0.05). Results: One hundred and seventy-seven (177) patients from 16 to 66 years old (±41.56), from 1998 to 2016, were included in this study. Non-functional and lingual cusps presented a higher fracture than functional and buccal cusps, respectively. Fractures were more common in teeth with isthmus wider than 1/3 of the intercuspid distance and/or more than three restored surfaces. Teeth with endodontic treatment presented a higher subgingival fracture. On lingual cusps, fracture type and location were significantly associated, being that total fractures were 3.2 times more likely to occur than partial fractures, and subgingival were 3.62 times more likely to occur than supragingival fractures. Conclusion: Indications of classic protection on functional cusps (LUBL) was refuted since, generally, nonfunctional cusps fractured more than the functional cusps. However, upper pre-molars showed more fractures in functional cusps and lower molars presented more fractures on the nonfunctional cusps. In general, lingual cusps were the most fractured and were associated with a higher prevalence of severe fractures (total fractures at the subgingival level). Fractures were more common in teeth where the restoration had an isthmus wider than 1/3 of the intercuspid distance and/or involved more than three restored surfaces. Most of the patients did not show previous symptoms and signs. Overall, teeth with endodontic treatment presented a higher subgingival fracture.

Direct composite resin fillings versus amalgam fillings for permanent posterior teeth

BACKGROUND

Traditionally, amalgam has been used for filling cavities in posterior teeth, and it continues to be the restorative material of choice in some low- and middle-income countries due to its effectiveness and relatively low cost. However, there are concerns over the use of amalgam restorations (fillings) with regard to mercury release in the body and the environmental impact of mercury disposal. Dental composite resin materials are an aesthetic alternative to amalgam, and their mechanical properties have developed sufficiently to make them suitable for restoring posterior teeth. Nevertheless, composite resin materials may have potential for toxicity to human health and the environment. The United Nations Environment Programme has established the Minamata Convention on Mercury, which is an international treaty that aims "to protect the [sic] human health and the environment from anthropogenic emissions and releases of mercury and mercury compounds". It entered into force in August 2017, and as of February 2021 had been ratified by 127 governments. Ratification involves committing to the adoption of at least two of nine proposed measures to phase down the use of mercury, including amalgam in dentistry. In light of this, we have updated a review originally published in 2014, expanding the scope of the review by undertaking an additional search for harms outcomes. Our review synthesises the results of studies that evaluate the long-term effectiveness and safety of amalgam versus composite resin restorations, and evaluates the level of certainty we can have in that evidence.

OBJECTIVES

To examine the effects (i.e. efficacy and safety) of direct composite resin fillings versus amalgam fillings.

SEARCH METHODS

An information specialist searched five bibliographic databases up to 16 February 2021 and used additional search methods to identify published, unpublished and ongoing studies SELECTION CRITERIA: To assess efficacy, we included randomised controlled trials (RCTs) comparing dental composite resin with amalgam restorations in permanent posterior teeth that assessed restoration failure or survival at follow-up of at least three years. To assess safety, we sought non-randomised studies in addition to RCTs that directly compared composite resin and amalgam restorative materials and measured toxicity, sensitivity, allergy, or injury.

DATA COLLECTION AND ANALYSIS

We used standard methodological procedures expected by Cochrane.

MAIN RESULTS

We included a total of eight studies in this updated review, all of which were RCTs. Two studies used a parallel-group design, and six used a split-mouth design. We judged all of the included studies to be at high risk of bias due to lack of blinding and issues related to unit of analysis. We identified one new trial since the previous version of this review (2014), as well as eight additional papers that assessed safety, all of which related to the two parallel-group studies that were already included in the review. For our primary meta-analyses, we combined data from the two parallel-group trials, which involved 1645 composite restorations and 1365 amalgam restorations in 921 children. We found low-certainty evidence that composite resin restorations had almost double the risk of failure compared to amalgam restorations (risk ratio (RR) 1.89, 95% confidence interval (CI) 1.52 to 2.35; P < 0.001), and were at much higher risk of secondary caries (RR 2.14, 95% CI 1.67 to 2.74; P < 0.001). We found low-certainty evidence that composite resin restorations were not more likely to result in restoration fracture (RR 0.87, 95% CI 0.46 to 1.64; P = 0.66). Six trials used a split-mouth design. We considered these studies separately, as their reliability was compromised due to poor reporting, unit of analysis errors, and variability in methods and findings. Subgroup analysis showed that the findings were consistent with the results of the parallel-group studies. Three trials investigated possible harms of dental restorations. Higher urinary mercury levels were reported amongst children with amalgam restorations in two trials, but the levels were lower than what is known to be toxic. Some differences between amalgam and composite resin groups were observed on certain measures of renal, neuropsychological, and psychosocial function, physical development, and postoperative sensitivity; however, no consistent or clinically important harms were found. We considered that the vast number of comparisons made false-positive results likely. There was no evidence of differences between the amalgam and composite resin groups in neurological symptoms, immune function, and urinary porphyrin excretion. The evidence is of very low certainty, with most harms outcomes reported in only one trial.

AUTHORS' CONCLUSIONS

Low-certainty evidence suggests that composite resin restorations may have almost double the failure rate of amalgam restorations. The risk of restoration fracture does not seem to be higher with composite resin restorations, but there is a much higher risk of developing secondary caries. Very low-certainty evidence suggests that there may be no clinically important differences in the safety profile of amalgam compared with composite resin dental restorations. This review supports the utility of amalgam restorations, and the results may be particularly useful in parts of the world where amalgam is still the material of choice to restore posterior teeth with proximal caries. Of note, however, is that composite resin materials have undergone important improvements in the years since the trials informing the primary analyses for this review were conducted. The global phase-down of dental amalgam via the Minamata Convention on Mercury is an important consideration when deciding between amalgam and composite resin dental materials. The choice of which dental material to use will depend on shared decision-making between dental providers and patients in the clinic setting, and local directives and protocols.

Hands-on training based on quantifying radiant exposure improves how dental students cure composites: Skill retention at 2-year follow-up

INTRODUCTION

The durability and longevity of composite restoration are much dependent on the accurate delivery of the energy required to polymerise the material. This study aimed to investigate the extent to which undergraduate dental students acquire and retain light-curing skills following hands-on training.

MATERIALS AND METHODS

Hands-on training comprises faculty tutoring for critical aspects of the light-curing procedure, such as distance and angulation of the light-curing tip. Assessments of the students' ability to deliver a specified radiant exposure to class III and I simulated RBCs using a dental simulator (MARC-PS^® ) at three different time points after the training. Data were analysed using repeated measure ANOVA.

RESULTS

Immediately after the training, students' performance on curing was improved (p < .05). Overall, the radiant exposure increased after training, but the students lost some of the benefits with time. For curing in the anterior section (anterior sensor-class III), the mean radiant exposure values increased by approximately 20% after the training. After 2 years, the values were 15% greater than baseline values. For curing in the posterior section (posterior sensor-class I), the mean radiant exposure values increased by approximately 150% after the training. A significant decrease (p < .05) was observed; however, the radiant exposure values were still 82% greater than the baseline after 2 years.

CONCLUSION

A hands-on training dedicated to light-curing procedures facilitated acquisition and retention up to a 2-year follow-up of skill on how light cure composite inside the mouth. The training was more relevant for curing in posterior areas, where orientation can significantly impact light-curing. A hands-on training where the radiant exposure can be measure gave objective measurement metrics to guide the curing performance. This approach is an effective means of teaching practical skills to dental students.

The Potential of a Bioactive, Pre-reacted, Glass-Ionomer Filler Resin Composite to Inhibit the Demineralization of Enamel in Vitro

CLINICAL RELEVANCE

A prereacted, glass-ionomer filler fluoride-containing resin composite had lower remineralization potential than glass-ionomer cements but was able to inhibit enamel demineralization; thus, it may be an option for restoring dental surfaces for patients at high risk of caries.

SUMMARY

Evidence is lacking on the use of surface prereacted glass-ionomer filler resin composites to inhibit demineralization and that simulate real clinical conditions. The present laboratory study evaluated the potential of such composites to prevent demineralization and quantified fluoride (F) and other ions released from restorative materials after a dynamic pH-cycling regimen applied to the tooth material interface in vitro. The pH-cycling regimen was assessed by measuring surface hardness (SH) along with energy dispersive X-ray spectroscopy (EDX).

METHODS AND MATERIALS

Ninety blocks of bovine enamel were subjected to composition analysis with EDX, and were further categorized based on SH. The blocks were randomly divided into 6 treatment groups (n=15 each): F IX (Fuji IX Extra; GC Corporation); IZ (Ion Z, FGM); F II (Fuji II LC, GC Corporation); B II (Beautifil II, Shofu); F250 (Filtek Z250 XT, 3M ESPE); and NT (control, no treatment). The blocks were subjected to a dynamic pH-cycling regimen at 37°C for 7 days concurrently with daily alternations of immersion in demineralizing/remineralizing solutions. EDX was conducted and a final SH was determined at standard distances from the restorative materials (150, 300, and 400 μm).

RESULTS

The EDX findings revealed a significant increase in F concentration and a decrease in Ca2+ in the enamel blocks of group B II after the pH-cycling regimen (p<0.05). SH values for groups F IX, IZ, and F II were greater than those for groups B II, F250, and NT at all distances from the materials.

CONCLUSIONS

The results suggest that each of 3 restorative materials, F IX, IZ, and F II, partially inhibited enamel demineralization under a dynamic pH-cycling regimen.

Influence of Post-Core and Crown Type on the Fracture Resistance of Incisors Submitted to Quasistatic Loading

The aim of this paper was to evaluate the fracture resistance and failure type of maxillary incisor teeth, rebuilt with various types of post-core restorations and full crowns made of either direct conventional particulate filler composite (PFC, G-aenial Anterior, GC, Tokyo, Japan) or indirect CAD/CAM restorations (composite Cerasmart 270 and glass ceramic LiSi Block from GC). One hundred (n = 10/group) central incisors were cut and divided into 10 experimental groups restored with different approaches. In approach A, teeth were restored with a core build-up composite (Gradia Core, GC) for a core and full crown of PFC. Approach B had teeth restored using composite core and prefabricated fiber posts, and a complete crown of either PFC or CAD/CAM. Approach C contained teeth restored with a core of short fiber-reinforced composite (everX Flow, GC) and prefabricated fiber posts, and a complete crown of either PFC or CAD/CAM. In approach D, the teeth had a core of short fiber-reinforced composite only, and a complete crown of either PFC or CAD/CAM restorations. The root canals were prepared, and when posts were used, they were luted with either a dual-cure resin cement (LinkForce, GC) or everX Flow. As the control, sound teeth (n = 10) were used. Restorations were quasi-statically loaded until fracture. Failure type was visually investigated. The interface between the fiber post and luting cement was investigated using SEM, before and after completion of the loading test. The data were analyzed by analysis of variance (p = 0.05) followed by Tukey's test. None of the restorative approaches restored the fracture load strength of intact teeth (p < 0.05). Restorations with additional fiber posts (Approaches B and C) had higher load-bearing capacity (p < 0.05) than restorations without fiber posts (Approaches A and D). Restorations that had short fiber-reinforced composite cores with or without fiber posts presented more repairable failures. Using short fiber-reinforced composite as post-luting and core build-up material with conventional fiber posts proved to be a promising method to strengthen severely damaged incisors.

Long-term treatment costs and cost-effectiveness of restoration repair versus replacement

OBJECTIVES

When managing partially defective restorations, dentists can choose between repair and replacement. We aimed to assess the long-term treatment costs of repairs and replacements.

METHODS

Partially defective anterior and posterior composite restorations in permanent teeth had been repaired or replaced in a German university hospital and were retrospectively followed until censoring or one of the following events: (1) Extraction, (2) Major complications including placement of indirect restorations, endodontic treatments and extractions, or (3) Any complications including major complications and further direct restorations. Costs were estimated from a German mixed public-private-payer perspective. Cost-effectiveness differences were described using median-based incremental-cost-effectiveness ratios (ICER_MEDIAN). Statistical analysis was performed using generalized linear mixed modeling (GLM), Chi²-test, and Wilcoxon rank-sum test (p < 0.05).

RESULTS

A total of 616 repairs in 468 patients (follow-up: 4.9 ± 4.1 years) and 264 replacements in 218 patients (follow-up: 4.8 ± 4.3) were included. While replacements were associated with higher initial treatment costs, median annualized treatment costs did not significantly differ between repair (47.58 Euro [IQR: 24.41-107.04]) and replacement (50.64 Euro [IQR: 26.30-118.78]; p > 0.05), but were higher for molars (75.53 Euro [IQR: 24.41-92.18]) than incisors (45.03 Euro [IQR: 28.19-168.50]; p = 0.011). The difference in the % of extractions, major and any complications were minimal between both groups. The mean ICER_MEDIAN of replacement vs. repair was -146.8 Euro/% when extractions were considered as outcomes. Regarding major and any complications, mean ICER_MEDIAN amounted to 67.6 Euro/% and 23.9 Euro/%, respectively.

SIGNIFICANCE

Repairs and replacements of partially defective restorations showed similar long-term costs and cost-effectiveness.

The Effects of Food-Simulating Liquids on Surface Roughness, Surface Hardness, and Solubility of Bulk-Fill Composites

Aim:

To investigate the surface roughness, surface hardness, and solubility of bulk-fill composites after exposure to food-simulating liquids (FSLs).

Materials and Methods:

A total of 200 disc-shaped samples (8 mm diameter × 4 mm depth) were prepared using four bulk-fill composites (SonicFillTM, Tetric® EvoCeram Bulk Fill, Beautifil-Bulk Restorative, FiltekTM Bulk Fill Posterior Restorative) and a microhybrid composite (FiltekTM Z250) ( n = 40). Following the measurement of initial weights of the samples ( m1), the surface roughness measurements were gauged using a contact-profilometer. The samples were stored in four different FSLs for 7 days, and then the second surface roughness values were recorded. The samples were stored in a desiccator to reach the constant mass and the values were recorded as m2, then the solubility levels were calculated. The Vickers microhardness values of the samples were determined. A total of 20 specimens were evaluated in terms of surface morphology with a scanning electron microscope (SEM). Data were statistically analyzed with the two-way ANOVA and Bonferroni tests ( P < .05).

Results:

Beautifil-Bulk Restorative was affected at most in terms of surface roughness after storage in FSLs and citric acid caused the highest values in this group ( P < .005). Beautifil-Bulk Restorative and Filtek Z250 showed the highest surface hardness values, while the Tetric EvoCeram group had the lowest. The highest solubility values were found in Beautifil-Bulk Restorative, and citric acid and ethanol yielded the highest solubility values for all of the composites.

Conclusion:

Beautifil-Bulk Restorative is the most affected group in all parameters evaluated and also affected overly by citric acid among the FSLs in consequence of its prereacted glass ionomer fillers.

Antioxidants and Collagen-Crosslinking: Benefit on Bond Strength and Clinical Applicability

Antioxidants are known for their potential of strengthening the collagen network when applied to dentin. They establish new intra-/intermolecular bonds in the collagen, rendering it less perceptive to enzymatic hydrolysis. The study evaluated the benefit on shear bond strength (SBS) of a resin–composite to dentin when antioxidants with different biomolecular mechanisms or a known inhibitor of enzymatic activity are introduced to the bonding process in a clinically inspired protocol. Specimens (900) were prepared consistent with the requirements for a macro SBS-test. Four agents (Epigallocatechingallate (EGCG), Chlorhexidindigluconate (CHX), Proanthocyanidin (PA), and Hesperidin (HPN)) were applied on dentin, either incorporated in the primer of a two-step self-etch adhesive or as an aqueous solution before applying the adhesive. Bonding protocol executed according to the manufacturer’s information served as control. Groups (n = 20) were tested after one week, one month, three months, six months, or one year immersion times (37 °C, distilled water). After six-month immersion, superior SBS were identified in PA compared to all other agents (p < 0.01) and a higher reliability in both primer and solution application when compared to control. After one year, both PA incorporated test groups demonstrated the most reliable outcome. SBS can benefit from the application of antioxidants. The use of PA in clinics might help extending the lifespan of resin-based restorations.

Effect of amylase activity on mechanical properties of dental composite resin

The purpose of this study was to investigate the effect of amylase activity on the mechanical properties of three dental composite resin (Filtek Z350; Filtek Z250 and Polofil Supra). The specimens were immersed in amylase solution at four different activities (25, 50, 100 and 200 KIU/L) with an artificial saliva solution (AS) as a control. The flexural strength (FS) and elastic modulus (EM) were determined in a three-point bending test after immersion for periods up to 12 months. In addition, surface roughness and surface morphology also determined. The FS of Filtek Z350 reaching the lowest level of 67.86 MPa after AS immersion for one year. There was a general trend for FS to decrease following immersion in AS for all the tested materials. However, the amylase groups did not undergo a significant decrease in FS and EM, and there was a slight increase in FS and EM for Polofil Supra.

Does a new formula have an input in the clinical success of posterior composite restorations? A chat study

OBJECTIVE

To compare the clinical behavior of a universal light-curing, ultra-fine particle hybrid composite and successor of this material in class I and II cavities after 60 months.

MATERIALS AND METHODS

Forty patients (21 females, 19 males) with ages ranging between 18 and 38 years (23.15 ± 5.15) received 80 (13 Cl I and 67 Cl II) resin composite restorations (Charisma/Charisma Classic, Kulzer GmbH) in combination with an etch and rinse adhesive system (Gluma 2Bond) under rubber dam isolation. Two experienced operators performed all the restorations. Restorations were evaluated by the other two examiners according to the FDI criteria at baseline and at 6, 12, 18, 24, 36, 48 and 60 months. Surface characteristics of one restoration selected randomly were examined under a scanning electron microscope (SEM) at each recall. Data were analyzed statistically (p < 0.05).

RESULTS

After 60 months, recall rate was 90%. None of the restorations failed. Three restorations from Charisma and 4 from the Charisma Classic group showed minor surface staining. Twelve Charisma and 14 Charisma Classic restorations were scored as 2 for margin staining. Four restorations from both groups showed minor shade deviations but no significant difference was observed between the two restorative materials for any criteria evaluated after 60 months (p > 0.05). SEM evaluations were in accordance with the clinical findings.

CONCLUSIONS

Both materials exhibited clinically similar and successful performance over the 60-month observation period.

CLINICAL RELEVANCE

A new formulation of resin composite may not always perform better clinical performances.

TRIAL REGISTRATION

ClinicalTrials.gov : NCT02888873.

Depth-dependence of Degree of Conversion and Microhardness for Dual-cure and Light-cure Composites

CLINICAL RELEVANCE

New dual-cure bulk-fill composites show promise for uniform degree of conversion and microhardness throughout the entire depth of direct restorations.

SUMMARY

Quantitative fractography as a novel approach to measure fracture toughness of direct resin composites

Dental resin composites generally fail from small cracks. Large crack techniques are not representative of in vivo failures. Quantitative fractography relies on the observation of small "natural flaws". This study investigates the effect of flaws that occur from fabrication and handling on the measurement of fracture toughness for four different direct resin composites. Microtensile dog-bone shaped specimens for each of four composites were fractured to measure the strength. In addition, we measured crack sizes of the fracture initiating cracks and determined the fracture toughness from these measurements using quantitative fractographic analysis on selected specimens. The characteristic strengths (28-51 MPa) and Weibull moduli (4.9-7.8) were also determined and related to the toughness values (0.5-0.9 MPa m^1/2) obtained. The elastic moduli (5-10 GPa) were measured using an indentation technique that has not been used before for direct resin composites. The indentation technique offers an alternative method for small specimens. Quantitative fractographic analysis offers a useful technique to assess fracture toughness of resin composites from cracks of the same size as observed in practice. The toughness of the direct resin composites results from a balance between the size, number and shape of filler particles and the viscosity of the resin matrix.

Bilayered composite restoration: the effect of layer thickness on fracture behavior

Purpose: By combining the increased toughness of a resin composite reinforced with discontinuous fibers and the surface wear resistance of a particulate filler composite (PFC), a bilayered composite technique was recently introduced. This study aimed to evaluate the effect of the thickness of the overlaying PFC placed over a fiber-reinforced composite (FRC) core, on the fracture-behavior of direct crown restorations. Methods: Six groups of posterior crown restorations (n = 8/group) were fabricated having a discontinuous FRC-core (everX Flow) and a layer of surface PFC (Essentia U) with various thicknesses (0.5, 1.0, 1.5, 2.0 mm), with the remaining thickness of the bilayered being 6 mm. Control groups were only made of PFC or FRC materials. Restorations were statically loaded until fracture. Failure-modes were visually examined. Data were analyzed using ANOVA (p = .05) and regression analysis. Results: The regression analysis showed that by decreasing the thickness of PFC layer, the load bearing capacity of restorations increased linearly (R²=0.7909). ANOVA revealed that crown restorations made only from everX Flow composite had significantly higher load-bearing capacities (3990 ± 331 N) (p < .05) among all the groups tested. With regard to the failure-mode analysis, crowns that had a FRC core material of everX Flow revealed delamination of the PFC surface composite from the core. Crowns which were made only of PFC i.e. with no fiber reinforcement, showed a crushing-like fracture pattern. Conclusions: Restorations combining a thick FRC-core and a thin surface layer of PFC (0.5-1 mm), displayed promising performance related to fracture-behavior and load-bearing capacity.

Limited reciprocity in curing efficiency of bulk-fill resin-composites

OBJECTIVE

The aim of the study was to identify experimental limits of the general reciprocity hypothesis that the same photo-cure outcomes will result from applying essentially constant energy densities, despite reciprocal variations in the irradiance and irradiation time-period, for a representative set of bulk fill (BF) and non-BF resin composites.

METHODS

Six BF and two non-BF resin-composites were selected. The unset pastes were inserted into white acetal molds (5mm id) with (n=6) depths (1, 2, 3, 4, 5 and 6mm). Three light curing units (LCUs) of increasing radiant emittance capability: 1200, 2000 and 3200mW/cm² were used. Composite specimen groups (n=3, per depth, per LCU) were irradiated on the upper surface only. For each specific composite, the irradiation times for each LCU were reduced reciprocally, as the LCU irradiance increased, to deliver a constant energy density (J/cm²) to that composite. However, the required energy density for a given composite differed in accordance with each composite manufacturer recommendations. After storing for 24h at 37°C, light transmission measurements were made through each specimen and re-expressed as Apparent Absorbance (A'). Vickers hardness (H_V) measurements (n=10) were made on both top and bottom surfaces, for each specimen, and H_Vversus "depth" profile plots created. From the top-surface data, a Depth-of-Cure parameter could be derived. Data were statistically evaluated for differences between top and bottom H_V values and for other predefined variables of interest.

RESULTS

Irradiation with the LCU of 1200mW/cm² generally gave the highest H_V/depth for most materials tested compared to the other curing lights with higher power output, regardless of top and bottom measurements (p<0.001). However, this difference was material-dependent. With one BF composite, 1200 and 2000mW/cm² irradiance did not show a significant difference between top and bottom H_V. Composites with higher translucency showed reduced differences in top/bottom H_V than more opaque composites.

SIGNIFICANCE

Reciprocity was found to be limited with most materials examined, such that irradiance periods of 10s, gave generally better H_V outcomes than by using LCUs of superior radiant emittance while reciprocally reducing irradiance time to maintain constant dose of energy density.

Development and calibration of biochemical models for testing dental restorations

Currently, resin composites are the most popular materials for dental restoration in clinical practice. Although the properties of such materials have been improved significantly, together with better clinical techniques used for their placement, early restoration failure still occurs too frequently. As clinical studies take years to complete, and new resin composites are being produced at ever increasing pace, laboratory assessment using accelerated but representative tests is necessary. The main types of failure in resin-composite restoration are tooth/restoration fracture and secondary caries, which are caused by a combination of mechanical and biochemical challenges. In this study, a biofilm model (S. mutans) and a chemical model (lactic-acid buffer) for producing artificial caries in bovine dentin are developed and calibrated against in situ data. Using a power law relationship between the demineralization depth and challenge duration, scale factors that convert the in vitro durations to the equivalent clinical durations are determined for different pH values for each model. The scale factors will allow the synchronization of biochemical and mechanical challenges in terms of their rates of action to potentially test resin-composite restoration in an accelerated but clinically representative manner. STATEMENT OF SIGNIFICANCE: Although the properties of resin composites for dental restoration have been improved significantly, early restoration failure still occurs too frequently. As clinical studies take years to complete, accelerated laboratory testing is necessary. Resin-composite restoration fail mainly through fracture and secondary caries, caused by a combination of mechanical and biochemical challenges. In this study, a biofilm and a chemical model for producing artificial caries in bovine dentin are calibrated against in situ data. Using a power law relationship between demineralization depth and challenge duration, scale factors are determined for different pH for each model. The scale factors will allow the synchronization of biochemical and mechanical challenges in testing resin-composite restoration in an accelerated but clinically representative manner.

Influence of the coronal restoration on the outcome of endodontically treated teeth

Objective: The tooth weakens due to removal of hard tissue during an endodontic procedure. Many dentists find it difficult to choose between different coronal restorations after root canal treatment (RCT). Studies show that the coronal restoration may affect the endodontic prognosis. This student-based study had three aims. (1) Examine the choice of coronal restoration of endodontically treated teeth at a Scandinavian dental school, (2) examine the survival of these restorations and (3) evaluate the influence of the coronal restoration on the outcome of the RCT. Material and methods: Radiographic and clinical examination was performed on 127 posterior teeth. The quality of the root canal treatment and the periapical status (PAI-index) were evaluated. Results: 43.8% of the teeth were restored with an indirect coronal restoration and 47.2% with a direct coronal restoration. The period from finished root canal treatment until placement of a permanent coronal restoration was significantly longer for an indirect restoration than a direct restoration. The teeth treated with a PAI score of 1 and 2 following pulpectomy, necrotic pulp treatment and endodontic retreatment was 93.8%, 82.6% and 69.4%, respectively.Conclusion: There was no significant association between choice of coronal restoration and PAI-score.

The quest for stable biomimetic repair of teeth: Technology of resin-bonded composites

The rationale leading to the present generation of resin composites is surveyed. There are many sub-classes such as flowable materials with specialized clinical indications. But a simplistic categorization of resin-composite materials is inappropriate. It is better to appreciate the factors that have driven recent developments. These include the search for low shrinkage composites and for greater depth of cure. Other necessary features are good handling behavior and sufficient strength for load-bearing situations. The esthetic challenge is for materials with superior and life-like optical properties and it is important to identify products that are good in every critical property. Nanotechnology has led to certain improvements, but the possibilities and limitations of nanoparticles must be appreciated. In all these developments, the structure and properties of the host tissues are a challenge and inspiration. Thus materials that can emulate the features of enamel and dentin are the goal of biomimetic design.

Stainless steel crowns as a restoration for permanent posterior teeth in people with special needs: A retrospective study

BACKGROUND

Limited information exists regarding the use of stainless steel crowns (SSCs) in permanent teeth. The objective of this retrospective cohort study was to present the long-term clinical outcomes of the SSC compared with those of amalgam and composite resin restorations and the SSC radiographic outcomes in a special-needs population.

METHODS

This study included 271 patients with at least 1 SSC restoration from the Mount Sinai Hospital Dentistry Clinic for Persons with Special Needs in Toronto, Ontario, Canada. A total of 2,621 posterior permanent tooth restorations were documented: 766 SSCs, 1,651 amalgam restorations, and 204 composite resin restorations. Clinical analysis included patient demographics, treatment parameters, and outcome assessments for each restoration recorded. Radiographic analysis of SSC restorations included 127 bite-wing radiographs and 118 periapical radiographs, measurement of interproximal bone loss, and assessment of periapical status using the Periapical Index Scale.

RESULTS

The 10-year survival rates for new SSC and amalgam restorations were 79.2% and 63.5%, respectively. The 91 SSC failures included 2 recementations, 33 replacements, and 56 extractions. Primary diagnoses at the time of failure included chronic periodontal disease (25) and loose or lost SSCs (24). Of the 528 failed conventional restorations that were replaced, 60% were replaced with SSCs. The mean alveolar bone loss from mesial and distal sites was 1.36 millimeters and 1.40 mm, respectively. Therefore, 93% of the sites recorded were less than 2 mm and classified as healthy. All pre-SCC and post-SSC periapical radiographs had healthy Periapical Index Scale scores (1 or 2) recorded over an average duration of 8.4 years (1-29.1 years).

CONCLUSIONS

SSCs are a durable treatment option for the restoration of the posterior permanent dentition.

PRACTICAL IMPLICATIONS

Posterior permanent teeth restored with stainless steel crowns can be expected to last for 10 years and represent a viable treatment choice for severely carious or fractured posterior permanent teeth.

Composite removal by means of erbium, chromium:yttrium-scandium-gallium-garnet laser compared with rotary instruments

BACKGROUND

Complete removal of existing composite restorations without unnecessary removal of tooth structure is challenging. The authors compared the amount of tooth structure removed and composite remaining in Class III preparations when using an erbium laser or a rotary instrument.

METHODS

Mesiolingual and distolingual preparations were prepared in 14 extracted anterior teeth, restored with shade-matched composite, finished, and polished. One restoration was removed with an erbium, chromium:yttrium-scandium-gallium-garnet laser and the other with a rotary instrument (handpiece and carbide burs). Gypsum models made from vinyl polysiloxane impressions of the preparation and removal stages were scanned. The 2 scans were precisely aligned to calculate the amount of tooth structure removed and residual composite, which were statistically compared (t test) between the bur and laser groups.

RESULTS

Rotary instruments removed significantly more tooth structure than the laser in terms of mean depth (P = .0017) but not maximum depth (P = .0762). Although mean depth of tooth loss was smaller in the laser group, the area of tooth loss was significantly larger (P = .0004) because the rotary instrumentation left significantly more composite than the laser in terms of volume (P = .0104), mean depth (P = .0375), maximum depth (P = .0318), and area (P = .0056).

CONCLUSIONS AND PRACTICAL IMPLICATIONS

The erbium, chromium:yttrium-scandium-gallium-garnet laser was more selective in removing existing composite restorations than a rotary instrument because it removed less tooth structure and left behind less composite. Unintentional loss of tooth structure and unnoticeable residual composite are inevitable when removing existing composites. Erbium lasers are alternative means of composite removal that may be more selective than a rotary instrument.

Direct bilayered biomimetic composite restoration: The effect of a cusp-supporting short fiber-reinforced base design on the chewing fracture resistance and failure mode of molars with or without endodontic treatment

The aim of this study was to assess the chewing fracture resistance of compromised molars restored with direct composite resin (CR) restorations, with and without a short-fiber reinforcing (short-FRC) base. Wide extension of MOD cavities with removed palatal cusps preparations were simulated on 48 extracted maxillary molars. Five groups (n = 12) were designed: 1. control (intact teeth), 2. non-endodontically treated and 3. endodontically treated teeth with direct CR restorations (GC-Posterior), and 4. non-endodontically treated and 5. endodontically treated teeth with direct biomimetic bilayered restorations. Groups 4 and 5 included an anatomically shaped short-FRC base (everX Posterior), covered with a 2 mm CR layer (GC-Posterior). Restorations were subjected to chewing in water (1.5 Hz), with load of 85 N. Specimens were loaded until fracture or to a maximum of 120 000 cycles. Restorations that survived the chewing cycle were submitted to static load test (post-chewing test). The data were statistically analyzed using two-way ANOVA (p = 0.05) and fracture types with the chi-square test (p = 0.05). Fractures were classified into reparable, possibly reparable or non-reparable. All specimens survived the chewing cycle. The chewing fracture resistance of the direct biomimetic restorations prepared on non-endodontically treated teeth (2889 N) was statistically significantly higher than the direct CR counterparts (1966 N) (p = 0.00015), which was not the case for the groups with endodontically treated teeth (p = 0.257). Inclusion of a short-FRC base also influenced the fracture type resulting in most reparable fractures (67-75% versus 25% for biomimetic and CR groups respectively) (p = 0.054). Anatomically shaped i.e. a cusp-supporting design made of short-FRC base (everX Posterior) improved the chewing fracture resistance and fracture manner of compromised molars regardless of whether they were endodontically treated or not.

Resin based restorative dental materials: characteristics and future perspectives

This review article compiles the characteristics of resin based dental composites and an effort is made to point out their future perspectives. Recent research studies along with few earlier articles were studied to compile the synthesis schemes of commonly used monomers, their characteristics in terms of their physical, mechanical and polymerization process with selectivity towards the input parameters of polymerization process. This review covers surface modification processes of various filler particles using silanes, wear behaviour, antimicrobial behaviour along with its testing procedures to develop the fundamental knowledge of various characteristics of resin based composites. In the end of this review, possible areas of further interests are pointed out on the basis of literature review on resin based dental materials.

Polymerization shrinkage of resin-based composites for dental restorations: A digital volume correlation study

OBJECTIVE

Resin-based composites are widely used in dental restorations; however, their volumetric shrinkage during polymerization leads to several issues that reduce the restoration survival rates. For overcoming this problem, a deep study of shrinkage phenomena is necessary.

METHODS

In this study, micro-tomography (μ-CT) is combined with digital volume correlation (DVC) to investigate the effect of several factors on the polymerization strain of dental composites in model cavities: the presence/absence of an adhesive, the use of transparent/blackened cavities, and irradiation times between 1 and 40s.

RESULTS

The results indicate that the presence of an adhesive at the interface between the cavity and composite does not reduce the total strain but instead limits it to a preferential direction. In addition, regardless of the conditions, the main strain is generated along the axis parallel to the polymerization irradiation (the vertical axis). Finally, the total strain appears to occur in the first 5s of irradiation, with no further evolution observed for longer irradiation times.

SIGNIFICANCE

This work provides new insight into resin-based composite shrinkage and demonstrates the benefit of coupling DVC and μ-CT to better understand the degradation mechanisms of these materials.

Fracture behavior of Bi-structure fiber-reinforced composite restorations

OBJECTIVE

The aim of this study was to evaluate the fracture-behavior of direct composite restorations made with two different composite-core materials. In addition, fracture toughness (FT), flexural strength (FS) and flexural modulus (FM) of tested composites were evaluated.

METHODS

Twenty groups of posterior crown restorations were fabricated (n = 6/group). The groups were made of a 4-5 mm layer of composite-core materials (everX Flow and SDR Flow⁺) and covered by a 2 mm layer of conventional composite (G-aenial Anterior & Posterior, G-aenial Universal Injectable, Essentia, CeramX, Filtek Z500). Control groups were only made of conventional composites or composite-core materials. Crowns were statically loaded until fracture. Failure-modes were then visually examined. FT, FS and FM were determined for each tested composite (n = 6).

RESULTS

ANOVA revealed that crown restorations made only from everX Flow composite had significantly higher load-bearing capacities (3866 ± 263 N) (p < 0.05) among all the groups tested. No statistically significant differences were found in the load-bearing capacities between crowns made with different composite-core materials (p > 0.05). everX Flow exhibited the highest FT (2.8 MPa m^1/2) and Z500 presented the highest FS values (197 MPa) (p < 0.05) among tested composites. With regard to the failure-mode analysis, crowns that had a fiber-reinforced core material of everX Flow revealed delaminating of surface conventional composite from the substructure layer. While in crowns that had a core material of SDR Flow⁺ or having only conventional composites with no fiber reinforcement, showed a crushing fracture pattern.

CONCLUSION

Restorations combining a fiber-reinforced composite core and a surface layer of conventional composite, displayed promising performance related to fracture-behavior.

Hardness and fracture toughness of resin-composite materials with and without fibers

OBJECTIVE

To investigate the surface micro-hardness (VHN) and fracture toughness (K_IC) of resin-composites, with and without incorporated short fibers, after solvent storage.

METHODS

Three resin-composites incorporating fibers, additional to particle reinforcement, were examined: everX™, NovoPro Fill™ and NovoPro Flow™. Four composites were used as controls, with only particle reinforcement: Filtek bulk Fill™, Filtek bulk one™, Filtek XTE™, and Filtek Flow XTE™. For hardness measurement, materials were cured in 2mm thick molds for 20s by a LED source of average irradiance 1.2W/cm². Specimens (n=6/group) were stored dry for 1h and then in either water or 75% ethanol/water for 1h, 1 day and 30 days at 37±1°C. Vickers hardness was measured under a load of 300g for 15s. For fracture toughness (K_IC) measurements, single-edge-notched specimens (n=6/group) were prepared: (32×6×3mm) for 3-point bending and stored for 1 and 7 days in water at 37°C. Fractured surfaces of fiber-reinforced composite were examined by scanning electron microscopy (SEM). VHN data were analyzed using three-way ANOVA, one-way ANOVA and the Tukey post hoc test (p≤0.05). K_IC data were analyzed by two-way ANOVA and one-way ANOVA and the Tukey post hoc test (p≤0.05). An independent t-test was used to detect differences (α=0.05) in K_IC between stored groups for each material.

RESULTS

VHN decreased for all composites with storage time in both solvents, but more appreciably in 75% ethanol/water (an average of 20%). K_IC ranged from 2.14 (everX Posterior) to 0.96 NovoPro Flow) MPa.m^0.5. The longer storage period (7 days) had no significant effect on this property relative to 1 day storage.

SIGNIFICANCE

Reinforcement with short fibers, and possibly matrix compositional differences, significantly enhanced the fracture toughness of EVX. However, for nano-fiber containing composites, there were no evident beneficial effects upon either their fracture toughness or hardness compared to a range of control composites. Water storage for 7 days of all these resin-composites produced no significant change in their K_IC values, relative to 1 day storage.

Toward dental caries: Exploring nanoparticle-based platforms and calcium phosphate compounds for dental restorative materials

Millions of people worldwide suffer from a toothache due to tooth cavity, and often permanent tooth loss. Dental caries, also known as tooth decay, is a biofilm-dependent infectious disease that damages teeth by minerals loss and presents a high incidence of clinical restorative polymeric fillings (tooth colored fillings). Until now, restorative polymeric fillings present no bioactivity. The complexity of oral biofilms contributes to the difficulty in developing effective novel dental materials. Nanotechnology has been explored in the development of bioactive dental materials to reduce or modulate the activities of caries-related bacteria. Nano-structured platforms based on calcium phosphate and metallic particles have advanced to impart an anti-caries potential to restorative materials. The bioactivity of these platforms induces prevention of mineral loss of the hard tooth structure and antibacterial activities against caries-related pathogens. It has been suggested that this bioactivity could minimize the incidence of caries around restorations (CARS) and increase the longevity of such filling materials. The last few years witnessed growing numbers of studies on the preparation evaluations of these novel materials. Herein, the caries disease process and the role of pathogenic caries-related biofilm, the increasing incidence of CARS, and the recent efforts employed for incorporation of bioactive nanoparticles in restorative polymer materials as useful strategies for prevention and management of caries-related-bacteria are discussed. We highlight the status of the most advanced and widely explored interaction of nanoparticle-based platforms and calcium phosphate compounds with an eye toward translating the potential of these approaches to the dental clinical reality.

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Current progress and future applications of functional nanoparticles and remineralizing compounds incorporated in dental direct restorative materials.

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Overview of the antibacterial and remineralizing mechanisms presenting direct and indirect implications on the tooth mineral loss.

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These investigations, although in the initial phase of evidence are necessary and their results are encouraging and open the doors to future clinical studies that will allow the therapeutic value of nanotechnology-based restorative materials to be established.

Cuspal Flexure and Stress in Restored Teeth Caused by Amalgam Expansion

Objective:

Cracks in amalgam-filled teeth may be related to amalgam expansion. This study measured cuspal flexure and used finite element analysis to assess associated stress levels in amalgam-filled teeth.

Methods and Materials:

External surfaces of 18 extracted molars were scanned in three dimensions. Nine molars were restored with mesio-occluso-distal amalgam fillings; the other teeth were left intact as controls. All teeth were stored in saline and scanned after two, four, and eight weeks. Cuspal flexure and restoration expansion were determined by calculating the difference between scanned surfaces. Stresses in a flexed tooth were calculated using finite element analysis.

Results:

Cusps of amalgam-filled teeth flexed outward approximately 3 μm, and restoration surfaces expanded 4 to 8 μm during storage. Cuspal flexure was significantly higher in the amalgam group (multivariate tests, p&lt;0.05), but storage time had no significant effect (repeated measures, p&gt;0.05). Expansion caused stress concentrations at the cavity line angles. These stress concentrations increased stresses due to mastication 44% to 178%.

Conclusions:

Amalgam expansion pushed cavity walls outward, which created stress concentrations at the cavity line angles. Expansion stresses can raise stresses in amalgam-filled teeth and contribute to incidentally observed cracks.