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BACKGROUND: Glass ionomer cements are commonly utilized in dental restorations due to their biocompatibility, strong chemical bond with dental tissues, and ability to resist tooth decay. However, their effectiveness can be compromised by the presence of persistent cavity-causing microorganisms. Therefore, it is essential to consider incorporating antibacterial agents into these restorative materials. Swertia chirayita (S. chirayita) and Terminalia arjuna (T. arjuna) are well-known for their rich composition of phytochemicals that can potentially inhibit the growth of bacteria. Hence, the current research is focused on modifying glass ionomer cement with Chirayita and T. arjuna extracts to enhance its antibacterial properties. AIM: This research aims to determine the antimicrobial efficacy and compressive strength of glass ionomer cement modified with Chirayita and T. arjuna extracts. METHODOLOGY: Plant extracts were prepared from both Chirayita and T. arjuna. The powder and liquid components of conventional glass ionomer cement (GIC) were mixed, followed by adding these extracts at three different concentrations. To assess antimicrobial properties, typical strains of Streptococcus mutans and Lactobacillus were employed to test both the modified GIC and unmodified GIC (used as a control). For Chirayita and T. arjuna-modified GIC, minimum inhibitory concentration (MIC) assays were conducted at three different concentrations. MIC was assessed at various time intervals ranging from 1 to 4 hours for modified and unmodified groups. Moreover, compressive strength was measured using cylindrical molds. The highest force exerted at the point of specimen fracture was recorded to calculate the compressive strength values in megapascal (MPa). RESULTS: The antimicrobial efficiency of Chirata and T. arjuna-modified GIC was evaluated using a MIC assay, indicating a statistically significant enhancement in antimicrobial potency against S. mutans and Lactobacillus within the modified groups in contrast to the control group (p<0.05). However, there were no notable changes in compressive strength when comparing the control group to the modified groups (p>0.05). CONCLUSION: The antimicrobial effectiveness against S. mutans was observed to be greater in both T. arjuna and Chirayita-modified GIC. In the case of Lactobacillus, Chirayita-modified GIC exhibited more pronounced antimicrobial properties compared to T. arjuna. Importantly, both extracts did not alter the compressive strength of Conventional (unmodified) GIC. Hence, Chirayita-modified GIC appears to be a promising restorative material for combatting recurrent caries. Additional investigation is required to assess the material's stability over an extended period.

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OBJECTIVES: To review the literature on recurrent caries models used to evaluate restorative materials, compare reported methodology and parameters, and devise specific recommendations to be considered in future investigations. DATA: The following were extracted: study design, sample characteristics, source of teeth, name of restorations compared including controls, recurrent caries model type, type of demineralizing and remineralizing solutions, type of biofilm used, methods to detect recurrent caries. SOURCES: Literature searches were performed in OVID Medline, EMBASE, SCOPUS, and Cochrane Library. STUDY SELECTION: For a study to be included, it had to examine dental materials for tooth restoration purposes only with a valid control group and evaluate restorative dental materials regardless of the form of the teeth caries model used or nature of the tooth structure used. A total of 91 studies were included. Most of the studies presented were in vitro. Human teeth were the main source of specimens utilized. Around 88% of the studies used specimens without an artificial gap, and 44% used a chemical model. S. mutans was the main bacterial species used in microbial caries models. CONCLUSION: The findings of this review provided an insight into the performance of available dental materials assessed using different recurrent caries models, yet this review cannot be used as a guideline for material selection. Selecting the appropriate restorative material relies on several patient-related factors such as microbiota, occlusion, and diet that are not comprehensively taken into consideration in recurrent caries models and thus hinder reliable comparison. CLINICAL SIGNIFICANCE: Due to the heterogenicity of variables among studies on the performance of dental restorative materials, this scoping review aimed to provide insights for dental researchers concerning the available recurrent caries models, testing methods used, and aspects of comparison between these materials including their characteristics and limitations.

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OBJECTIVES: This prospective practice-based trial assessed the longevity of composite restorations made with an adhesive containing an antibacterial monomer compared to a conventional adhesive. METHODS: 9 general practices in the Netherlands were provided with two composite resin adhesives, each for a period of 9 months. Adhesive P contained the quaternary ammonium salt MDPB, and Adhesive S was a control. Patient's age and caries risk, as well as tooth type/number, reason for restoration placement, used restorative material and adhesive, and restored surfaces were recorded. All interventions carried out on these teeth in the 6 years after restoration were extracted from the electronic patient records, along with their date, type, reason, and surfaces. Two dependent variables were defined: general failure, and failure due to secondary caries. All data handling and multiple Cox regression analysis were carried out in R 4.0.5. RESULTS: 11 dentists from 7 practices made 10,151 restorations over a period of two years in 5102 patients. 4591 restorations were made with adhesive P, whereas 5560 were made with adhesive S. The observation period was up to 6.29 years, median observation time was 3.74 years. Cox regression showed no significant difference between the two adhesive materials when corrected for age, tooth type and caries risk, for general failure nor failure due to caries. SIGNIFICANCE: No difference in restoration survival could be shown between composite restorations made using an adhesive containing MDPB and control. Restorations made with the adhesive containing MDPB also did not fail more or less frequently due to secondary caries. This trial is registered on clinicaltrials.gov with identifier NCT05118100.

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Introduction: Lithium disilicate glass-ceramic (LDC) restorations exhibit microorganism infiltration, recurrent caries, pulpal lesions, periodontal inflammation, and cement exposure to the oral environment over time. All these factors lead to restoration failure. This systematic review aimed to investigate the clinical outcomes of LDC full-coverage crowns (FCC) in permanent teeth compared with those of other full-coverage restoration materials. Materials & Methods: Search strategies were developed for four databases: Web of Science, OVID, PubMed, and Scopus. Data extraction and quality appraisals were performed by two independent reviewers. Data on the presence of caries, post-operative sensitivity, and periodontal changes were extracted from the included clinical studies. In addition to the outcome measures, data on the sample size, study groups, method of restoration fabrication, type of impression, and type of abutment were recorded. Results: We retrieved 3989 records for the title and abstract screening. Of these, 19 clinical studies met the inclusion criteria. The overall quality of the included studies indicates a low risk of bias. Most studies reported no pulpal involvement, recurrent caries, or post-operative sensitivity and presented a favorable periodontal response after the cementation of LDC-FCC during different follow-up periods. Conclusion: Based on the endodontic and periodontic clinical responses of natural tooth abutments and their supporting periodontium, LDC-FCC can be considered a clinically successful restorative option.

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OBJECTIVE: The aim of this study was to compare and evaluate diagnostic accuracy of two different CBCT scan modes and digital bitewing radiography for detection of recurrent caries under five different restorative materials, and determine the relationship between the types of restorative materials. MATERIALS AND METHODS: In this in vitro study, 200 caries-free upper and lower premolars and molars were selected. A standard deep Class II cavities was created in the middle of the mesial surface of all teeth. In 100 teeth of the experimental and control groups, secondary caries was artificially demineralized. All teeth were filled with five types of restorative material including two types of conventional composite resins, flow composite resin, glass ionomer and amalgam. The teeth were imaged with high resolution (HIRes) and standard CBCT scan modes and digital bitewing. The AUC, sensitivity, specificity and areas under the ROC curve were calculated and verified through SPSS. RESULTS: CBCT technique was the best option in diagnosing recurrent caries. The diagnostic accuracy and specificity of HIRes CBCT scan mode was significantly higher than standard mode (P = 0.031) and bitewing (P = 0.029) for detection of recurrent caries, especially under composite group. There were no significant differences in accuracy value of bitewing and standard CBCT scan mode. CONCLUSION: CBCT showed higher accuracy and specificity on the detection of recurrent caries which was more accurate than bitewing radiography. The HIRes CBCT scan mode achieved the highest accuracy and performed the best in recurrent caries detection.

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Background: The aim of the present study is to evaluate the most common reasons for replacing posterior amalgam and resin composite restorations in patients attending the university dental restorative clinics. Methods: A total of 318 restorations which needed to be replaced were clinically and radiographically evaluated in a period of nine months. The frequencies of reasons for replacing posterior amalgam and resin composite restorations were calculated; secondary caries, restoration/tooth fracture, marginal discoloration/ditching, proximal overhang/open margin, loss of anatomy, pain/sensitivity, and esthetics. Results: The sample population comprised of 191 females and 106 males. The majority of the sample population fell in the age group of 40-50 years (n = 110). 318 restorations (n = 318) were examined in this study. 82% of examined teeth were restored with amalgam (n = 261), while posterior composite restorations comprised 18% of the examined teeth (n = 57). Among all restorations demanded to be replaced by the patients (n = 318), aesthetic need was the most common reason (n = 98), followed by Ditching or discoloration (n = 64), secondary caries (n = 57), and fracture (n = 44). Loss of anatomy was the least common cause to replace both amalgam and resin composite restorations (n = 5). The different reasons of failure were all significant between amalgam and resin composite restorations as shown in (Fig. 1) (p < 0.005). The most common reason for amalgam replacement was aesthetic. The most common reason for composite replacement was secondary caries and marginal ditching. Conclusion: Both amalgam and composite had different reasons for replacement. Amalgam had lesser risk of developing secondary caries and higher longevity than composite.

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This review addresses the rationale of recurrent and/or residual caries associated with resin composite restorations alongside current strategies and evidence-based recommendations to arrest residual caries and restrain recurrent caries. The PubMed and MEDLINE databases were searched for composite-associated recurrent/residual caries focusing on predisposing factors related to materials and operator's skills; patient-related factors were out of scope. Recurrent caries and fractures are the main reasons for the failure of resin composites. Recurrent and residual caries are evaluated differently with no exact distinguishment, especially for wall lesions. Recurrent caries correlates to patient factors, the operator's skills of cavity preparation, and material selection and insertion. Material-related factors are significant. Strong evidence validates the minimally invasive management of deep caries, with concerns regarding residual infected dentin. Promising technologies promote resin composites with antibacterial and remineralizing potentials. Insertion techniques influence adaptation, marginal seal, and proximal contact tightness. A reliable diagnostic method for recurrent or residual caries is urgently required. Ongoing endeavors cannot eliminate recurrent caries or precisely validate residual caries. The operator's responsibility to precisely diagnose original caries and remaining tooth structure, consider oral environmental conditions, accurately prepare cavities, and select and apply restorative materials are integral aspects. Recurrent caries around composites requires a triad of attention where the operator's skills are cornerstones.

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The aim of this study was to determine the effect of simulated occlusal loading on wall lesion development in cervical gaps of class II composite restorations in vitro. Sixty-four extracted human molars received standardized (4.0 × 4.2 × 3.0 mm) box preparations. The teeth were randomly assigned to one of two restoration groups: restoration with a normal or a low E-modulus composite material (CLEARFIL AP-X: E-modulus 16.8 GPa or CLEARFIL MAJESTY ES Flow: E-modulus 6.6 GPa). A metal matrix was placed at the bottom of the box for each restoration, creating a cervical gap of about 100 µm wide. Samples were exposed to simulated caries lesion development in a lactic acid solution (pH 4.8) for 8 weeks in a Rub&Roll device. Half of the samples were subjected to 90 N cyclic loading. After demineralization, the teeth were sectioned. Wall lesion development was measured using microradiography (transversal wavelength-independent microradiography) in two different locations (location 1: 1,000 µm and location 2: 1,600 µm from the gap entrance) and recorded in lesion depth (LD) (µm) and mineral loss (µm × vol%). Linear regression modeling was used to estimate the effect of loading and material on wall lesion development. Mean wall LD in location 1 across all groups was 150.83 µm with a standard deviation (SD) of 61.83 µm. In location 2, mean overall wall LD was 102.98 µm with an SD of 64.92 µm. Linear regression showed no significant effect of either loading or material on wall lesion development. Occlusal loading had no significant effect on secondary caries lesion development in composite class II restoration in this in vitro study.

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The risk of secondary bacterial infections resulting from dental procedures has driven the design of antimicrobial and antifouling dental materials to curb pathogenic microbial growth, biofilm formation and subsequent oral and dental diseases. Studies have investigated approaches based primarily on contact-killing or release-killing materials. These materials are designed for addition into dental resins, adhesives and fillings or as immobilized coatings on tooth surfaces, titanium implants and dental prosthetics. This review discusses the recent developments in the different classes of biomaterials for antimicrobial and antifouling dental applications: polymeric drug-releasing materials, polymeric and metallic nanoparticles, polymeric biocides and antimicrobial peptides. With modifications to improve cytotoxicity and mechanical properties, contact-killing and anti-adhesion materials show potential for incorporation into dental materials for long-term clinical use as opposed to short-lived antimicrobial release-based coatings. However, extended durations of biocompatibility testing, and adjustment of essential biomaterial features to enhance material longevity in the oral cavity require further investigations to confirm suitability and safety of these materials in the clinical setting. The continuous exposure of dental restorative and regenerative materials to pathogenic microbes necessitates the implementation of antimicrobial and antifouling materials to either replace antibiotics or improve its rational use, especially in the day and age of the ever-increasing problem of antimicrobial resistance.

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OBJECTIVE: Recurrent caries is a primary reason for restoration failure caused by biofilm acids. The objectives of this study were to: (1) develop a novel multifunctional composite with antibacterial function and calcium (Ca) and phosphate (P) ion release, and (2) investigate the effects on enamel demineralization and hardness at the margins under biofilms. METHODS: Dimethylaminohexadecyl methacrylate (DMAHDM) and nanoparticles of amorphous calcium phosphate (NACP) were incorporated into composite. Four groups were tested: (1) Commercial control (Heliomolar), (2) Experimental control (0% DMAHDM + 0% NACP), (3) antibacterial group (3% DMAHDM + 0% NACP), (D) antibacterial and remineralizing group (3% DMAHDM + 30% NACP). Mechanical properties and Ca and P ion release were measured. Colony-forming units (CFU), lactic acid and polysaccharide of Streptococcus mutans (S. mutans) biofilms were evaluated. Demineralization of bovine enamel with restorations was induced via S. mutans, and enamel hardness was measured. Data were analyzed via one-way and two-way analyses of variance and Tukey's multiple comparison tests. RESULTS: Adding DMAHDM and NACP into composite did not compromise the mechanical properties (P > 0.05). Ca and P ion release of 3% DMAHDM + 30% NACP was increased at cariogenic low pH. Biofilm lactic acid and polysaccharides were greatly decreased via DMAHDM, and CFU was reduced by 4 logs (P < 0.05). Under biofilm acids, enamel hardness at the margins was decreased to about 0.5 GPa for control; it was about 1 GPa for antibacterial group, and 1.3 GPa for antibacterial and remineralizing group (P < 0.05). CONCLUSIONS: The novel 3% DMAHDM + 30% NACP composite had strong antibacterial effects. It substantially reduced enamel demineralization adjacent to restorations under biofilm acid attacks, yielding enamel hardness that was 2-fold greater than that of control composites. The novel multifunctional composite is promising to inhibit recurrent caries.

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OBJECTIVES: Secondary caries can be accelerated by hydrodynamic flow in a gap between the tooth and restorative material. This study investigated whether occlusal loading can lead to increased hydrodynamic flow by deforming a gap between tooth and restorative material. METHODS: 3D finite element analysis was employed to model a molar containing a restoration with an interfacial gap. The model was loaded using direct cusp-to-restoration contact and using a rubber tube model simulating a food bolus. The object exerting pressure was moved across the molar from buccal to lingual side. The applied forces were 50, 100, 200 and 400N. The elastic modulus of the restoration material was varied between 5, 10, 15.9 and 25GPa to resemble different kinds of composite. The primary outcome parameter was the volume of the gap under occlusal pressure. RESULTS: Occlusal loading resulted in deformation of the gap area. Maximum deformation was seen when loading was applied in the middle of the restoration. Higher forces and lower restoration stiffness led to more deformation of the gap. Maximum deformation with a force of 100N and composite modulus of 15.9GPa was -0.0083mm3 (1.12%). SIGNIFICANCE: Deformation of the gap between tooth and restorative material could lead to increased hydrodynamic flow and faster secondary caries lesion formation. The measured deformation is small. Further research needs to show whether gap compression through occlusal loading affects secondary caries formation to a clinically relevant degree.

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OBJECTIVE: Composite restorations are increasingly popular, but recurrent caries is a main reason for composite restoration failures. The objectives of this study were to investigate a dual strategy of combining rnc gene-deletion for Streptococcus mutans (S. mutans) with antibacterial dimethylaminohexadecyl methacrylate (DMAHDM) composite, and determine the effects of rnc gene-deletion alone, DMAHDM composite alone, and rnc-deletion plus DMAHDM composite, on biofilm growth and lactic acid production. METHODS: Parent S. mutans (UA159, ATCC 700610) and rnc-deleted S. mutans were used. DMAHDM was incorporated into a composite at mass fractions of 0%, 1.5%, and 3%. Gene expressions for biofilm formation and drug resistance were analyzed using quantitative real-time polymerase chain reaction (qRT-PCR). Biofilms were grown on composite surfaces for 2 days. Live/dead, biomass, polysaccharide, metabolic activity (MTT), colony-forming units (CFU) and lactic acid production of biofilms were evaluated. RESULTS: Compared to the parent S. mutans, the rnc-deletion technique yielded significantly less biofilm biomass, polysaccharides, metabolic activity, CFU, and lactic acid for biofilms grown on control composite (p <  0.05). With no gene modification, the biofilm CFU was decreased by 5-6 logs at 3% DMAHDM, when compared to control composite group. The dual strategy of combining rnc-deletion with 3% DMAHDM composite achieved the strongest biofilm-inhibition, with the greatest reduction in CFU by 8 logs. The combination of rnc-deletion with 3% DMAHDM composite decreased the biofilm lactic acid production by 95% (p <  0.05). CONCLUSIONS: The dual strategy of rnc-deletion plus DMAHDM composite produced synergistic effects and achieved the strongest biofilm-inhibition. This method has great potential to inhibit dental caries and is promising to reduce secondary caries and protect tooth structures.

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The early noninvasive detection of crown microleakage is very important for tooth maintenance and preservation. A crown margin in a subgingival position combined with the obscuring effect of a ceramic crown make it difficult to diagnose microleakage using traditional methods such as visual-tactile examinations and radiography. The aim of this study was to determine the effectiveness of quantitative light-induced fluorescence (QLF) technology for diagnosing microleakage in an all-ceramic crown noninvasively. In this study the red fluorescence glow was detected through a crown wall using the Qraycam QLF device (AIOBIO, Seoul, Republic of Korea). No abnormalities were detected by a visual examination, whereas the Qraycam device revealed both strong red fluorescence and fluorescence loss in suspicious lesions, which were confirmed after crown removal. It was possible to determine that the carious lesions inside the crown were related to bacteria-induced microleakage. After performing caries removal and crown reattachment, the red fluorescence glow was no longer detected. QLF examinations made it easy to identify the presence of microleakage in an all-ceramic crown noninvasively based on red fluorescence. These findings indicate that QLF technology can be effectively applied to provide objective evidence for detecting microleakage and diagnosing carious lesions inside an all-ceramic crown noninvasively.

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OBJECTIVES: The objectives of this cross-sectional survey were to determine the prevalence of secondary caries (SC) in general population, to identify patient- and material-related factors which may affect the prevalence, and to describe some clinical characteristics of SC lesions. MATERIALS AND METHODS: A total of 4036 restorations in 450 patients, who visited the university dental clinic for a regular (half) yearly checkup, were examined clinically (and radiographically) for the presence of SC. Clinical characteristics of the detected SC lesions (size, activity, and location) and the planned treatment were recorded. In addition, patients' caries-risk status was assessed according to the modified "cariogram" model. RESULTS: In total, 146 restorations were diagnosed with SC, which gives an overall prevalence of 3.6%. Restorative material, restoration class, patient's caries risk, and smoking habits were shown to be important factors, as SC prevalence was significantly higher with composites, class II restorations, high-caries-risk patients, and smokers. Restorations' gingival margins were most frequently affected by SC. The largest number of restorations with SC (72%) was scheduled for the replacement. CONCLUSIONS: Prevalence of SC was higher with composite than with amalgam restorations, irrespective of the patient's caries-risk status. Gingival margins of class II, including MOD restorations, seem to be the place of less resistance to SC development. Management of SC seems to place a considerable burden on the health care workforce and expenditure. CLINICAL RELEVANCE: Secondary caries (SC) is considered to be the main cause of dental restoration failure and one of the biggest clinical challenges related to dental composites. Nevertheless, its prevalence in daily practice is still not clear, which impedes an accurate estimation of its impact on health care costs.

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Introduction: This study aimed to assess the effects of CO2 and erbium-doped yttrium aluminum garnet (Er:YAG) lasers with and without fluoride varnish on demineralization around composite restorations. Methods: This in vitro experimental study evaluated 96 extracted human premolars. After preparation and restoration of class V cavities in the buccal surface of the teeth with composite resin, they were randomly divided into 8 groups of control, CO2 laser (L1), CO2 laser-NaF (L1F), NaF-CO2 laser (FL1), Er:YAG laser (L2), Er:YAG laser-NaF (L2F), NaF-Er:YAG laser (FL2) and NaF (F). The entire surface of the teeth, except for the restored cavity in the buccal surface and 1 mm around the margin, was coated with two layers of nail varnish. The teeth then underwent pH cycling for 10 days (3 hours in demineralizing solution and 21 hours in remineralizing solution) to artificially induce demineralization. The amount of calcium and phosphorous released into the cariogenic solution was quantified using atomic absorption spectroscopy and spectrophotometry. The Vickers hardness tester was used to measure the hardness of the tooth structure adjacent to composite restoration. Data were analyzed using one-way ANOVA and Tukey's test. Results: The four groups of L1F, FL1, FL2 and L2F showed minimum loss of calcium and phosphorous ions, and the mean hardness of FL1 and FL2 groups was higher than that of other groups. Conclusion: The CO2 and Er:YAG lasers alone have no significant effect on the resistance of tooth structure to cariogenic solution. However, they can exert a synergistic effect when used along with NaF varnish. Fluoride varnish applied prior to laser irradiation confers further resistance to the tooth structure and positively affects its hardness.

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AIM: This retrospective study investigated the prevalence of defective restorations in a public dental service and factors associated with re-intervention in primary teeth. DESIGN: The sample consisted of all clinical records (census) of children presenting restorations in primary teeth, who had undergone dental treatment in a public set during 1-year period. For analysis, only restorations presenting defects related to esthetic, functional, or biological reasons at first clinical examination were included. The outcome 'Success' was set when the restoration received no treatment (monitored), refurbishing, sealing of margins, or was repaired. Otherwise, 'Failure' was set whenever the restoration was either replaced or if another treatment affecting the restoration was necessary (endodontic treatment or tooth extraction). Poisson regression model was used to assess the prevalence of patient- and tooth-related factors that may influence the re-intervention decision (repair or replacement). RESULTS: From a total of 302 restorations placed in 114 children, 37.7% presented some type of defect. Restorations with recurrent caries were more frequently present in caries-active patients (P = 0.03) and were frequently replaced (95% CI, 1.05-3.22, RR = 1.84, P = 0.03). CONCLUSION: Presence of recurrent caries influences the re-intervention decision, leading to restoration replacement in most cases.

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Dental caries, i.e., tooth decay mediated by bacterial activity, is the most widespread chronic disease worldwide. Carious lesions are commonly treated using dental resin composite restorations. However, resin composite restorations are prone to recurrent caries, i.e., reinfection of the surrounding dental hard tissues. Recurrent caries is mainly a consequence of waterborne and/or biofilm-mediated degradation of the tooth-restoration interface through hydrolytic, acidic and/or enzymatic challenges. Here we use amphipathic antimicrobial peptides to directly coat dentin to provide resin composite restorations with a 2-tier protective system, simultaneously exploiting the physicochemical and biological properties of these peptides. Our peptide coatings modulate dentin's hydrophobicity, impermeabilize it, and are active against multispecies biofilms derived from caries-active individuals. Therefore, the coatings hinder water penetration along the otherwise vulnerable dentin/restoration interface, even after in vitro aging, and increase its resistance against degradation by water, acids, and saliva. Moreover, they do not weaken the resin composite restorations mechanically. The peptide-coated highly-hydrophobic dentin is expected to notably improve the service life of resin composite restorations and to enable the development of entirely hydrophobic restorative systems. The peptide coatings were also antimicrobial and thus, they provide a second tier of protection preventing re-infection of tissues in contact with restorations. STATEMENT OF SIGNIFICANCE: We present a technology using designer peptides to treat the most prevalent chronic disease worldwide; dental caries. Specifically, we used antimicrobial amphipathic peptides to coat dentin with the goal of increasing the service life of the restorative materials used to treat dental caries, which is nowadays 5 years on average. Water and waterborne agents (enzymes, acids) degrade restorative materials and enable re-infection at the dentin/restoration interface. Our peptide coatings will hinder degradation of the restoration as they produced highly hydrophobic and antimicrobial dentin/material interfaces. We anticipate a high technological and economic impact of our technology as it can notably reduce the lifelong dental bill of patients worldwide. Our findings can enable the development of restorations with all-hydrophobic and so, more protective components.

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OBJECTIVES: This study investigated the influence of very small gaps in secondary caries (SC) development and additionally linked the threshold gap size with the caries activity level from volunteers. METHODS: For 21 days, 15 volunteers wore a modified occlusal splint loaded with dentin-composite samples restored with different interfaces: bonded (B = samples restored with complete adhesive procedure), no-bonded (NB = restored with composite resin without adhesive procedure), and 30, 60 and 90 µm (no adhesive procedure and with intentional gap). The splint was dipped in a 20% sucrose solution (10 min) 8 x per day. Samples were imaged with transversal wavelength independent microradiography (T-WIM) and lesion depth and mineral loss were calculated. Average wall lesion depth from each volunteer was determined and according to the values the volunteers were grouped as high, mid and low caries activity levels. RESULTS: No wall lesion formation was observed in B and NB groups. In general, intentional gaps led to SC lesion depth progression independent of caries activity level of volunteers. No substantial wall lesions were found for two volunteers. A trend for deeper lesion in larger gaps was observed for the high activity group. CONCLUSION: Very small gaps around or wider than 30 µm develop SC independent of the caries activity level of the patient and SC wall lesion progression seemed to be related to individual factors even in this standardized in situ model. SIGNIFICANCE: Independently of caries activity level of the patient, the threshold gap size for secondary caries wall lesion seems to be 30 µm at most.

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An esterase from S. mutans UA159, SMU_118c, was shown to hydrolyze methacrylate resin-based dental monomers. OBJECTIVE: To investigate the association of SMU_118c to the whole cellular hydrolytic activity of S. mutans toward polymerized resin composites, and to examine how the bacterium adapts its hydrolytic activity in response to environmental stresses triggered by the presence of a resin composites and adhesives biodegradation by-product (BBP). MATERIALS AND METHODS: Biofilms of S. mutans UA159 parent wild strain, SMU_118c knockout strain (ΔSMU_118c), and SMU_118c complemented strain (ΔSMU_118cC) were incubated with photo-polymerized resin composite. High performance liquid chromatography was used to quantify the amount of a universal 2,2-Bis[4-(2-hydroxy-3-methacryloxypropoxy)phenyl]propane (bisGMA)-derived BBP, bishydroxy-propoxy-phenyl-propane (bisHPPP) in the media. Fluorescence in situ hybridization (FISH) and quantitative proteomic analysis were used to measure SMU_118c gene expression and production of SMU_118c protein, respectively, from biofilms of S. mutans UA159 wild strain that were cultured with bisHPPP. RESULTS: The levels of bisHPPP released from composite were similar for ΔSMU_118c and media control, and these were significantly lower compared to the parent wild-strain UA159 and complemented strain (ΔSMU_118cC) (p < 0.05). Gene expression of SMU_118c and productions of SMU_118c protein were higher for bisHPPP incubated biofilms (p < 0.05). SIGNIFICANCE: This study suggests that SMU_118c is a dominant esterase in S. mutans and capable of catalyzing the hydrolysis of the resinous matrix of polymerized composites and adhesives. In turn, the bacterial response to BBP was to increase the expression of the esterase gene and enhance esterase production, potentially accelerating the biodegradation of the restoration, adhesive and restoration-tooth interface, ultimately contributing to premature restoration failure. STATEMENT OF SIGNIFICANCE: We recently reported (Huang et al., 2018) on the isolation and initial characterization of a specific esterase (SMU_118c) from S. mutans that show degradative activity toward the hydrolysis of dental monomers. The current study further characterize this enzyme and shows that SMU_118c is a dominant degradative esterase activity in the cariogenic bacterium S. mutans and is capable of catalyzing the hydrolysis of the resinous matrix of polymerized composites and adhesives. In turn, the bacterial response to biodegradation by-products from composites and adhesives was to increase the expression of the esterase gene and enhance esterase production, accelerating the biodegradation of the restoration, adhesive and the restoration-tooth interface, potentially contributing to the pathogenesis of recurrent caries around resin composite restorations.

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This paper discusses aspects of quality and safety improvement of the most commonly used dental restorative materials, the resin-based composites. From a patient's perspective, long-lasting resin-based restorations without complications are important. Recurrent caries and fracture are the most common causes for restoration failures. Proper handling and curing of the composites improve the mechanical properties of the restorations and increase safety by reducing exposure to residual methacrylate monomers. A number of compounds have been introduced in restorative materials to reduce the risk of recurrent caries, even though a real breakthrough has not yet been achieved. It is concluded that simple measures may improve the quality and safety of resin-based composite restorations.

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