Cellulose Nanocrystals Show Anti-Adherent and Anti-Biofilm Properties against Oral Microorganisms.

Cellulose nanocrystals (CNCs) are cellulose-derived nanomaterials that can be easily obtained, e.g., from vegetable waste produced by circular economies. They show promising antimicrobial activity and an absence of side effects and toxicity. This study investigated the ability of CNCs to reduce microbial adherence and biofilm formation using in vitro microbiological models reproducing the oral environment. Microbial adherence by microbial strains of oral interest, Streptococcus mutans and Candida albicans, was evaluated on the surfaces of salivary pellicle-coated enamel disks in the presence of different aqueous solutions of CNCs. The anti-biofilm activity of the same CNC solutions was tested against S. mutans and an oral microcosm model based on mixed plaque inoculum using a continuous-flow bioreactor. Results showed the excellent anti-adherent activity of the CNCs against the tested strains from the lowest concentration tested (0.032 wt. %, p < 0.001). Such activity was significantly higher against S. mutans than against C. albicans (p < 0.01), suggesting a selective anti-adherent activity against pathogenic strains. At the same time, there was a minimal, albeit significant, anti-biofilm activity (0.5 and 4 wt. % CNC solution for S. mutans and oral microcosm, respectively, p = 0.01). This makes CNCs particularly interesting as anticaries agents, encouraging their use in the oral field.

Natural, biphasic calcium phosphate from fish bones for enamel remineralization and dentin tubules occlusion.

OBJECTIVES: A calcium phosphate extracted from fish bones (CaP-N) was evaluated for enamel remineralization and dentinal tubules occlusion. METHODS: CaP-N was characterized by assessing morphology by SEM, crystallinity by PXRD, and composition by ICP-OES. CaP-N morphology, crystallinity, ion release, and pH changes over time in neutral and acidic solutions were studied. CaP-N was then tested to assess remineralization and dentinal tubules occlusion on demineralized human enamel and dentin specimens (n = 6). Synthetic calcium phosphate in form of stoichiometric hydroxyapatite nanoparticles (CaP-S) and tap water were positive and negative controls, respectively. After treatment (brush every 12 h for 5d and storage in Dulbecco's modified PBS), specimens' morphology and surface composition were assessed (by SEM-EDS), while the viscoelastic behavior was evaluated with microindentation and DMA. RESULTS: CaP-N consisted of rounded microparticles (200 nm - 1 µm) composed of 33 wt% hydroxyapatite and 67 wt% ß-tricalcium phosphate. In acidic solution, CaP-N released calcium and phosphate ions thanks to the preferential ß-tricalcium phosphate phase dissolution. Enamel remineralization was induced by CaP-N comparably to CaP-S, while CaP-N exhibited a superior dentinal tubule occlusion than CaP-S, forming mineral plugs and depositing new nanoparticles onto demineralized collagen. This behavior was attributed to its bigger particle size and increased solubility. DMA depth profiling and SEM showed an excellent interaction between the newly formed mineralized structures and the pristine tissue, particularly at the exposed collagen fibrils. SIGNIFICANCE: CaP-N demonstrated very good remineralizing and occlusive activity in vitro, comparable to CaP-S, thus could be a promising circular economy alternative therapeutic agent for dentistry.

Effect of open windows on airborne contamination and its topographical distribution in the dental operatory.

Aerosols produced by dental handpieces represent a permanent risk of disease transmission in the dental environment. The current study evaluated the effects of natural ventilation (open windows) on Streptococcus mutans airborne contamination by dental handpieces in simulated clinical conditions. A dental phantom was placed on a dental chair at a standard university dental clinic operatory. An S. mutans suspension was infused into the phantom's mouth while an operator performed standardized dental procedures using low (contra-angle) and high speed (turbine) dental handpieces or an ultrasonic scaler, with windows open or closed. Selective medium Petri dishes were placed in 18 sites of the operatory environment to evaluate contamination topographically. Sites were clustered as: wall, floor, ceiling, dental chair, and cabinet. Contamination was expressed as log10 CFU/cm2 . A linear mixed model analysis was used, nesting the sites within each ventilation and handpiece combination. Open windows significantly reduced contamination. The high-speed handpiece provided the highest contamination, followed by the ultrasonic scaler and the low-speed handpiece. Contamination values were much smaller at the ceiling, and much larger at the chair. Opening windows produced more homogeneous contamination of the operatory compared to closed windows. Natural ventilation during dental procedures decreases contamination and affects its topographical distribution.

Microbiological models for accelerated development of secondary caries in vitro.

OBJECTIVES: The current study aimed to compare the efficacy of two in vitro microbiological models based on open and closed systems designed to obtain secondary caries in an accelerated and reproducible way. METHODS: A conventional resin-based composite (RBC - Majesty ES-2; Kuraray, Japan) and a resin-modified glass-ionomer cement (RMGIC - Ionolux; VOCO, Germany) were used to restore standardized class II cavities (n = 4/tooth, cervical margin in dentin) in 16 human molars. The ability to produce secondary caries with Streptococcus mutans biofilms was tested using either an open-cycle or closed-cycle bioreactor (n = 8 specimens/model). Specimens were scanned before and after the biofilm exposure using micro-CT (Skyscan 1176, 9 µm resolution, 80 kV, 300 mA). Image reconstruction was performed, and demineralization depths (µm) were evaluated at the restoration margins and a distance of 1.0 mm. RESULTS: Dentin demineralization could be observed in all specimens, and enamel demineralization in 50% of the specimens. The open system bioreactor produced lesions with significantly higher overall demineralization depths (p < .001). However, demineralization depths at a 1.0 mm distance from the restoration margins showed no difference between open and closed systems or materials. In the open system, significantly lower demineralization depths were observed in proximity to RMGIC than RBC (p < .001), which was not significantly different in the closed system (p = .382). CONCLUSIONS: Both systems produced in vitro secondary caries in an accelerated way. However, the open-cycle bioreactor system confirmed the caries-protective activity exerted by the RMGIC material in contrast to the RBC, better simulating materials' clinical behavior. CLINICAL SIGNIFICANCE: The possibility of obtaining accelerated and reproducible secondary caries development in vitro is fundamental in testing the behavior of conventional and yet-to-come restorative dental materials. Such systems can provide faster outcomes regarding the performance of dental restorative materials compared to clinical studies, notwithstanding the importance of the latter.

Microstructure and Mechanical Behavior of Modern Universal-Chromatic and Bulk-Fill Resin-Based Composites Developed to Simplify Dental Restorative Procedures.

One of the recent trends in the development of resin-based composites (RBCs) focuses on universal coloring to avoid time-consuming color matching and RBC layering for a clinically appropriate esthetic impact. We evaluated an experimental material for posterior restorations combining universal coloring with the possibility of bulk-fill placement. Clinically established materials were analyzed as a reference, including a bulk-fill and a universal chromatic RBC. Microstructural features were described using scanning electron microscopy and related to macroscopic and microscopic mechanical behavior. Standards to be met before market launch were supplemented by fractography, Weibull analysis, and aging behavior assessment. Quasi-static and viscoelastic behavior were evaluated on a microscopic scale, incorporating a large number of parameters and increasingly aggressive immersion media. All materials complied with the standard requirements even after aging. The latter had little impact on the measured parameters, except for strength. Strength, modulus of elasticity, and hardness parameters on the one hand and damping behavior on the other were mutually exclusive. Despite considerable differences in the microstructure and type of filler, an increased filler amount remained critical for better mechanical properties. The lower proportion of inorganic fillers was directly transferred to the elastic modulus values, which, in turn, restricts the experimental material in its clinical applications to smaller occlusal fillings.

Physical-chemical and microbiological performances of graphene-doped PMMA for CAD/CAM applications before and after accelerated aging protocols.

OBJECTIVES: Innovative, nanotechnologies-featuring dental materials for CAD/CAM applications are becoming available. However, the interaction with the oral environment poses critical challenges to their longevity. The present study evaluated specific physical-chemical properties and antimicrobial potential of a CAD/CAM graphene-doped resin before and after accelerated aging protocols. METHODS: Graphene nanofibers (GNF)-doped (<50 ppm) PMMA (GPMMA) and control PMMA CAD/CAM discs were used. Specimens underwent aging procedures of their bulk (thermo- and load-cycling) and surface (24 h-immersion in absolute ethanol), then they were tested for flexural strength, ultimate tensile strength, sorption/solubility, and methyl-methacrylate elution. Surface characterization included x-ray diffraction, Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, surface roughness, microhardness, and scanning electron microscopy (SEM). Adherence of Streptococcus mutans and Candida albicans, and biofilm formation (continuous-flow bioreactor) by the same strains and an artificial oral microcosm were investigated. RESULTS: GNF-doping improved the physical-chemical bulk properties of the PMMA resin. Surface aging reduced microhardness and increased the roughness of both test and control materials. Surfaces displayed signs of swelling and degradation at SEM. Microbiological data of non-aged surfaces showed that GNF-doping significantly reduced biofilm formation by all tested strains despite having no impact on microbial adherence. After aging, microbial adherence was higher on GPMMA surfaces, while biofilm formation was not promoted. SIGNIFICANCE: GNF-doping improved the material's performance and influenced its antimicrobial potential. This strategy seems a valuable option to overcome the effects of surface degradation induced by aging on the antimicrobial potential of PMMA resin.

Prognostic Factors and Primary Healing on Root Perforation Repaired with MTA: A 14-year Longitudinal Study.

INTRODUCTION: Few data are available on the long-term efficacy of mineral trioxide aggregate (MTA) in treating root canal perforations. This prospective cohort study builds on a previously reported trial to determine the outcome for teeth with root perforations treated with orthograde MTA after longer follow-up and identify potential prognostic factors. METHODS: A prospective cohort study was performed, enrolling (1999-2009) patients with a single dental perforation treated with MTA. Preoperative, intraoperative, and postoperative information was evaluated, and the outcomes were dichotomized as healed or nonhealing. Patients were followed up yearly until 2018 for a maximum of 17 years after treatment, with controls carried out until 14 years. Clinical and radiographic outcomes were evaluated using standardized follow-up protocols. RESULTS: Of the 124 entrolled patients (median age = 36.5 years, 53.2% male), 115 were healed at the first (n = 110, 89%) or second (n = 5, 4%) annual posttreatment checkup, while 9 subjects (7%, 4 females, 18-65 years old) did not heal. Characteristics significantly associated with nonhealing were gender, positive probing, size, and perforation site. Perforations recurred in 48 teeth during the follow-up with the estimated probability of reversal at 5, 10, and 14 years of 6% (95% confidence interval [CI], 2%-10%), 30% (95% CI, 20%-38%), and 62% (95% CI, 46%-73%), respectively. Positive probing had a higher reversal risk (hazard ratio = 3.3, P ≤ .001), and perforations >3 mm were more likely to have a reversal (hazard ratio = 4.1, P < .001). CONCLUSIONS: The risk of reversal for healed MTA-treated root canal perforations, initially relatively low, vastly increases over time.

Airborne contamination of the dental operatory during activities performed with open or closed windows.

PURPOSE: To quantify the biological contamination of a dental operatory environment using a biological tracer. METHODS: A Streptococcus mutans suspension was infused into the mouth of a phantom, and an operator performed standardized dental procedures using an air turbine, a contra-angle handpiece, or an ultrasonic scaler either with windows open or closed. The presence of the tracer was measured by placing Petri dishes with a selective medium at 18 sites on the dental unit and 38 sites in the surrounding operatory environment. RESULTS: The contamination was drastically reduced when windows were opened, no matter which handpiece was used. Air turbine spread significantly higher contamination compared to contra-angle and scaler. All tested instruments spread the tracer over the entire dental unit and the surrounding environment, including the walls and ceiling; however, higher contamination levels were detected on the dental unit compared to the operatory surfaces. Opening windows during dental operative procedures greatly reduced contamination levels for all handpieces and can be recommended for reducing airborne contamination levels. CLINICAL SIGNIFICANCE: The significant levels of airborne contamination produced when operating dental handpieces can be significantly reduced by natural ventilation, i.e., simply opening the windows.

Characterization of universal chromatic resin-based composites in terms of cell toxicity and viscoelastic behavior.

OBJECTIVES: A current trend to simplify dental restorative procedures is toward using universal chromatic light-cured resin-based composites (RBCs) designed to adapt esthetically to various clinical situations. This study offers a comparative characterization of the mechanical and cytotoxic behavior of such materials that use different techniques to adjust their optical properties (e.g., structural color instead of pigment addition), have different filler systems but are based on a comparable organic matrix. METHODS: The structural appearance of the filler systems was assessed by scanning electron microscopy. Various quasi-static and viscoelastic parameters were evaluated at clinically relevant frequencies (0.5-5 Hz) using an instrumented indentation test with a Dynamic Mechanical Analysis (DMA) module. Cytotoxicity on human gingival fibroblasts (HGF-1), when exposed to eluates from tested RBCs specimens (up to one month), was assessed using a WST-1 colorimetric proliferation assay. Multifactor analysis of variance was applied to compare the parameters of interest (Martens, Vickers, and indentation hardness; elastic and total indentation work; creep, indentation depth; storage, loss, and indentation moduli; loss factor; cell viability) between analyzed RBCs, loading frequencies, and eluate age. RESULTS: Structural particularities of the filler systems are directly reflected in the mechanical behavior of the analyzed materials. Changes in the filler system, necessary to achieve structural color, generally resulted in lower mechanical properties but a better ability to absorb shock. In contrast, the cytotoxicity was comparable. SIGNIFICANCE: Based on the performed characterization, universal chromatic RBCs fits in the conventional RBCs class to expect comparable clinical behavior.

Influence of Curing Time on the Microbiological Behavior of Bulk-Fill Nanohybrid Resin Composites.

This in vitro study aimed to evaluate the influence of curing time on surface characteristics and microbiological behavior of three bulk-fill resin-based composites (RBCs). Materials were light-cured for either 10 s or 80 s, then finished using a standard clinical procedure. They were characterized by surface morphology (SEM), surface elemental composition (EDS), surface roughness (SR), and surface free energy (SFE). Microbiological behavior was assessed as S. mutans adherence (2 h) and biofilm formation (24 h) using a continuous-flow bioreactor. Statistical analysis included a two-way ANOVA and Tukey's test (p < 0.05). Materials differed substantially as filler shape, dimension, elemental composition and resin matrix composition. Significant differences between materials were found for SR, SFE, and microbiological behavior. Such differences were less pronounced or disappeared after prolonged photocuring. The latter yielded significantly lower adherence and biofilm formation on all tested materials, similar to conventional RBCs. Improved photoinitiators and UDMA-based resin matrix composition may explain these results. No correlation between surface characteristics and microbiological behavior can explain the similar microbiological behavior of bulk-fill materials after prolonged photocuring. This different performance of bulk-fill materials compared with conventional RBCs, where surface characteristics, especially surface chemistry, influence microbiological behavior, may have important implications for secondary caries occurrence and restoration longevity.

Activity of Experimental Mouthwashes and Gels Containing DNA-RNA and Bioactive Molecules against the Oxidative Stress of Oral Soft Tissues: The Importance of Formulations. A Bioreactor-Based Reconstituted Human Oral Epithelium Model.

BACKGROUND: DNA-RNA compounds have shown promising protection against cell oxidative stress. This study aimed to assess the cytotoxicity, protective, or preventive effect of different experimental formulations on oral epithelia's oxidative stress in vitro. METHODS: Reconstituted human oral epithelia (RHOE) were grown air-lifted in a continuous-flow bioreactor. Mouthwashes and gels containing DNA-RNA compounds and other bioactive molecules were tested on a model of oxidative stress generated by hydrogen peroxide treatment. Epithelia viability was evaluated using a biochemical MTT-based assay and confocal microscopy; structural and ultrastructural morphology was evaluated by light microscopy and TEM. RESULTS: DNA-RNA showed non-cytotoxic activity and effectively protected against oxidative stress, but did not help in its prevention. Gel formulations did not express adequate activity compared to the mouthwashes. Excipients played a fundamental role in enhancing or even decreasing the bioactive molecules' effect. CONCLUSION: A mouthwash formulation with hydrolyzed DNA-RNA effectively protected against oxidative stress without additional enhancement by other bioactive molecules. Active compounds, such as hyaluronic acid, ß-Glucan, allantoin, bisabolol, ruscogenin, and essential oils, showed a protective effect against oxidative stress, which was not synergistic with the one of DNA-RNA. Incorporation of surfactant agents showed a reduced, yet significant, cytotoxic effect.

Microtensile Bond Strength of Fiber-Reinforced and Particulate Filler Composite to Coronal and Pulp Chamber Floor Dentin.

This ex vivo study aimed to compare the microtensile bond strength of fiber-reinforced and particulate filler composite to coronal and pulp chamber floor dentin using a self-etching adhesive system. Coronal dentin of 40 human molar teeth was exposed by cutting occlusal enamel with a low-speed saw. Teeth were then randomly divided into two groups (n = 20). The first group was left as is, while in the second group, pulp chamber floor dentin was exposed by trepanation. After placement of a self-etching adhesive system (G-aenial Bond, GC, Tokyo, Japan), groups were further divided into two sub-groups (n = 10) according to the type of composite: fiber-reinforced composite (EP, everX Posterior, GC, Tokyo, Japan) and particulate filler composite (GP, G-aenial Posterior, GC, Tokyo, Japan). Then, composite blocks were built up. Sticks (1.0 × 1.0 mm2) were obtained from each specimen by sectioning, then microtensile bond strength (µTBS) test was performed. Statistical analysis included one-way ANOVA test and Student's t-test (p < 0.05). µTBS values were 22.91 ± 14.66 and 24.44 ± 13.72 MPa on coronal dentin, 14.00 ± 5.83 and 12.10 ± 8.89 MPa on pulp chamber floor dentin for EP and GP, respectively. Coronal dentin yielded significantly higher µTBS than pulp chamber floor dentin (p < 0.05), independently from the tested composites.

Effects of Na-DNA mouthwash solutions on oral soft tissues. A bioreactor-based reconstituted human oral epithelium model.

PURPOSE: To investigate whether the addition of sodium-DNA (Na-DNA) to chlorhexidine (CHX)-containing mouthwash influenced morphology and viability of a reconstituted human oral epithelium (ROE), and protects ROE against oxidative stress. METHODS: Multi-layered 0.5 cm² ROE specimens were positioned inside a continuous flow bioreactor and grown air-lifted for 24 hours. They were treated with phosphate-buffered saline (PBS) (n= 16) or 1 vol% H2O2 for 1 minute (n= 16). Then, they were treated for 5 (n= 8) or 30 minutes (n= 8) with the experimental mouthwash solutions containing: 0.2 wt% CHX, 0.2 wt% CHX + 0.2 wt% Na-DNA, 0.2 wt% Na-DNA, PBS. After 60 minutes washout specimens were subjected to tetrazolium-based viability assay (MTT) confocal laser-scanning microscopy (CLSM), and histological evaluation using optical microscopy and transmission electron microscopy (TEM). RESULTS: ROE treated with Na-DNA for 30 minutes revealed significantly higher viability than PBS, and CHX + Na-DNA showed higher viability after 30-minute treatment than after 5 minutes, suggesting a significant protective activity of Na-DNA. Moreover, the protective effect of Na-DNA on cell viability was higher after the induction of oxidative stress. After treatment with CHX, CLSM revealed cell stress, leading to cell death in the outer layer. On the contrary, specimens treated with Na-DNA showed a much lower number of dead cells compared to PBS, both in the absence or presence of oxidative stress. Histological examination showed that the protective action of Na-DNA formulations reached more in-depth into the epithelium exposed to oxidative stress, due to intercellular spaces opening in the outer epithelium layers, giving way to Na-DNA to the inner parts of the epithelium. It can be concluded that Na-DNA had a topical protective activity when applied for 30 minutes unless the epithelium barrier is damaged, allowing it to act more in-depth. CLINICAL SIGNIFICANCE: Na-DNA showed a clear and protective action against cellular degeneration due to oxidative stress and, partly, to the exposure to CHX. Its addition to chlorhexidine mouthwash or gels could be clinically helpful in contrasting the detrimental activity of CHX on oral tissues, and in the preservation of cell viability, control of inflammation and wound healing.

Distribution of adhesive layer in class II composite resin restorations before/after interproximal matrix application.

OBJECTIVES: This study aimed to morphologically investigate the distribution of the adhesive layer when placed prior, or subsequent, to matrix positioning in direct-bonded Class II RBC restorations. Additional aim was to evaluate possible differences when using two-steps (CSE, Clearfil SE Bond2) or one-step adhesive system (CU, Clearfil Universal Bond Quick). METHODS: Standardized mesio-occlusal and disto-occlusal cavities were prepared on 20 human molars. Teeth were randomly allocated to two protocols according to the positioning of contoured sectional metal matrices before (M->A, n = 10), or after adhesive application (A->M, n = 10). Both adhesive systems were additioned with crystal violet dye (CV, 10 vol%). Specimen sections were evaluated using optical and scanning electron microscopy (SEM). Dynamic viscosity, pH, microshear bond strength test (µ-SBS) on enamel and dentin, and three-point bend test (3PB) of polymerized adhesive rods, were performed on both pristine and CV-additioned adhesives. RESULTS: M->A produced a layer of adhesive both on tooth-restoration interface and on external restoration surfaces in contact with the matrix. A->M produced a thin layer of adhesive on external tooth surfaces, well beyond cavity and RBC restoration margins. In all restorations, excess RBC material with uneven margins was observed protruding over the cervical margin. CV addition slightly increased pH and decreased viscosity. µ-SBS: CU + CV showed a 10-fold reduction in adhesion forces on dentine. 3PB: CSE yielded higher flexural strength values than CU. CV addition reduced flexural strength of CSE. CONCLUSIONS: Both M > A and A > M generated adhesive placement disadvantages with adhesive materials being expressed in difficult to reach locations that may jeopardize complete adhesive polymerization. CLINICAL SIGNIFICANCE: All cervical margins of RBC restorations should be carefully finished to improve longevity, no matter the clinical protocol adopted. CV addition labelled the tested adhesives without compromising their performances considerably.

Topographic aspects of airborne contamination caused by the use of dental handpieces in the operative environment.

BACKGROUND: The use of dental handpieces produces aerosols containing microbial agents, bacteria, and viruses representing a high-risk situation for airborne cross infections. The aim of this study was to map and quantify the biological contamination of a dental operatory environment using a biological tracer. METHODS: Streptococcus mutans suspension was infused into the mouth of a manikin, and an operator performed standardized dental procedures using an air turbine, a contra-angle handpiece, or an ultrasonic scaler. The presence of the tracer was measured at 90 sites on the dental unit and the surrounding surfaces of the operatory environment. RESULTS: All tested instruments spread the tracer over the entire dental unit and the surrounding environment, including the walls and ceiling. The pattern and degree of contamination were related to the distance from the infection source. The maximum distance of tracer detection was 360 centimeters for air turbine, 300 cm for contra-angle handpiece, and 240 cm for ultrasonic scaler. No surface of the operative environment was free from the tracer after the use of the air turbine. CONCLUSIONS: Attention should be paid to minimize or avoid the use of rotary and ultrasonic instruments when concerns for the airborne spreading of pandemic disease agents are present. PRACTICAL IMPLICATIONS: This study supports the recommendations of dental associations to avoid treatments generating aerosols, especially during pandemic periods. Guidelines for the management of dental procedures involving aerosols, as well as methods for the modification of aerosols aimed to inactivate the infective agent, are urgently needed.

Characterization of a Toothpaste Containing Bioactive Hydroxyapatites and In Vitro Evaluation of Its Efficacy to Remineralize Enamel and to Occlude Dentinal Tubules.

Demineralization of dental hard tissues is a well-known health issue and the primary mechanism responsible for caries and dentinal hypersensitivity. Remineralizing toothpastes are nowadays available to improve conventional oral care formulations regarding the prevention and repair of demineralization. In this paper, we analyzed the chemical-physical features of a commercial toothpaste (Biosmalto Caries Abrasion and Erosion, Curasept S.p.A., Saronno, Italy), with particular attention paid to the water-insoluble fraction which contains the remineralizing bioactive ingredients. Moreover, the efficacy of the toothpaste to induce enamel remineralization and to occlude dentinal tubules has been qualitatively and semiquantitatively tested in vitro on human dental tissues using scanning electron microscopy and X-ray microanalysis. Our results demonstrated that the water-insoluble fraction contained silica as well as chitosan and poorly crystalline biomimetic hydroxyapatite doped with carbonate, magnesium, strontium, and fluoride ions. The formulation showed excellent ability to restore demineralized enamel into its native structure by epitaxial deposition of a new crystalline phase in continuity with the native one. It was also able to occlude the dentinal tubules exposed completely by acid-etching. Overall, this study demonstrated that the tested toothpaste contained a biomimetic ionic-substituted hydroxyapatite-based active principle and that, within the in vitro conditions analyzed in this study, it was effective in dental hard tissue remineralization.

Substituted Nano-Hydroxyapatite Toothpastes Reduce Biofilm Formation on Enamel and Resin-Based Composite Surfaces.

Background: Toothpastes containing nano-hydroxyapatite (n-HAp) substituted with metal ions provide calcium and phosphate ions to dental hard tissues, reducing demineralization, and promoting remineralization. Few data are available about the effect of these bioactive compounds on oral microbiota. Methods: This in vitro study evaluated the influence of two commercially-available substituted n-HAp-based toothpastes (α: Zn-carbonate substituted n-HAp; ß: F, Mg, Sr-carbonate substituted n-HAp) on early colonization (EC, 12 h) and biofilm formation (BF, 24 h) by oral microbiota. Controls were brushed with distilled water. Artificial oral microcosm and Streptococcus mutans biofilms were developed using human enamel and a resin-based composite (RBC) as adherence surfaces. Two test setups, a shaking multiwell plate and a modified drip-flow reactor (MDFR), were used to simulate clinical conditions during the night (low salivary flow and clearance) and daytime, respectively. Energy-dispersive X-ray spectrometry (EDS) was used to evaluate specimens' surfaces after toothpaste treatment. Fluoride release from ß toothpaste was evaluated. Viable adherent biomass was quantified by MTT assay, and biofilms' morphology was highlighted using confocal microscopy. Results: EDS showed the presence of remnants from the tested toothpastes on both adherence surfaces. ß toothpaste showed significantly lower EC and BF compared to control using the artificial oral microcosm model, while α toothpaste showed lower EC and BF compared to control, but higher EC and BF compared to ß toothpaste. The effect shown by ß toothpaste was, to a minimal extent, due to fluoride release. Interestingly, this result was seen on both adherence surfaces, meaning that the tested toothpastes significantly influenced EC and BF even on RBC surfaces. Furthermore, the effect of toothpaste treatments was higher after 12 h than 24 h, suggesting that toothbrushing twice a day is more effective than brushing once. Conclusions: The efficacy of these treatments in reducing microbial colonization of RBC surfaces may represent a promising possibility in the prevention of secondary caries.

Resin composite blocks for dental CAD/CAM applications reduce biofilm formation in vitro.

OBJECTIVES: Modern dentistry is increasingly focusing on digital procedures, including CAD/CAM technologies. New materials have to resist in a demanding environment that includes secondary caries occurrence. The current study hypothesized that the microbiological behavior of different RBCs for CAD/CAM applications is better than that of their counterparts for direct restorations due to differences in the surface characteristics. METHODS: Both direct and CAD/CAM RBCs were tested. Specimens were obtained from each group, polished, cleaned, stored in artificial saliva (1w), then sterilized under UV (24h). Specimens' surface was assessed using profilometry, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction; resin/filler content was assessed using thermogravimetry. After pre-incubation with sterile human saliva (24h), the microbiological behavior of the materials was assessed using four models: Streptococcus mutans adherence (2h), S. mutans biofilm formation in an orbital shaking bioreactor (24h), S. mutans biofilm formation in a continuous-flow bioreactor simulating shear forces (24h), and mixed-plaque formation in the bioreactor (24h). The viable biomass adhering to the specimens' surfaces was measured using a tetrazolium dye-based test. Statistical analysis included verification of normality of distribution and homoscedasticity, then Oneway ANOVA and Tukey's test (α=5%). RESULTS: When using the bioreactor setup, CAD/CAM RBCs generally yielded lower S. mutans and mixed-plaque biofilm formation compared to direct RBCs. This difference was not evidenced in the first two microbiological models. Differences in manufacturing and curing processes rather than in materials' surface roughness and composition could explain these results. SIGNIFICANCE: CAD/CAM RBCs are promising materials from a microbiological point of view, featuring reduced biofilm formation on their surfaces when shear conditions similar to in vivo ones are present.

Bond Strength of Individually Formed and Prefabricated Fiber-reinforced Composite Posts.

PURPOSE: To investigate the micro push-out bond strength of individually formed (everStick Post) and prefabricated (GC Fiber Post) fiber-reinforced composite (FRC) posts cemented with three different types of self-adhesive composite cements. MATERIALS AND METHODS: Forty-two single-rooted human teeth were decoronated, endodontically treated, and had post spaces prepared for everStick Post (n = 21) or GC Fiber Post (n = 21). The teeth were randomly divided into three subgroups (n = 7), and posts were cemented either with G-CEM LinkAce (GC), SpeedCEM (Ivoclar Vivadent) or RelyX U200 (3M Oral Care). Specimens were then perpendicularly sectioned and divided at the cementoenamel junction into two root levels: coronal or apical. A micro push-out test was performed using an 0.8-mm-wide stainless steel plunger. Bond strength was calculated in MPa by dividing the fracture load (N) by the bonded surface area (mm2). Log-transformed data was statistically analyzed using factorial ANOVA and Tukey's post-hoc test (α < 0.05). Fracture modes were determined employing a stereomicroscope, and differences were evaluated using a likelihood ratio test and Pearson's chi-squared test. Specimens were also observed using SEM. RESULTS: Bond strengths were significantly affected by both post type and root level (p < 0.05), but not by self-adhesive cement (p > 0.05). Fracture types showed a significantly higher prevalence of adhesive fractures at the apical level, with all fractures starting at the cement-dentin interface. CONCLUSION: Individually formed FRC posts demonstrated greater bond strength than their prefabricated FRC counterparts. The apical level of the luted posts yielded lower bond strengths than the coronal level. Failures were predominantly adhesive at the cement-dentin interface.