Nanoparticles in dentistry

OBJECTIVE: Nanoparticles having a size from 1 to 100nm are present in nature and are successfully used in many products of daily life. Nanoparticles are also embedded per se or as byproducts from milling processes of larger filler particles in many dental materials. METHODS AND RESULTS: Recently, possible adverse effects of nanoparticles have gained increased interest with the lungs being a main target organ. Exposure to nanoparticles in dentistry may occur in the dental laboratory, by processing gypsum type products or by grinding and polishing materials. In the dental practice virtually no exposure to nanoparticles occurs when handling unset materials. However, nanoparticles are produced by intraoral adjustment of set restorative materials through grinding/polishing regardless whether they contain nanoparticles or not. Nanoparticles may also be produced through wear of restorations or released from dental implants and they enter the environment when removing restorations. The risk for dental technicians is taken care of by legal regulations. Based on model worst case mass-based calculations, the exposure of dental practice personnel and patients to nanoparticles through intraoral grinding/polishing and wear is low to negligible. Accordingly, the additional risk due to nanoparticles exposure from present materials is considered to be low. However, more research is needed, especially on vulnerable groups (asthma or COPD). An assessment of risks for the environment is not possible due to the lack of data. SIGNIFICANCE: Measures to reduce exposure to nanoparticles include intraorally grinding/polishing using water coolants, proper sculpturing to reduce the need for grinding and sufficient ventilation of treatment areas.status: publishe

Scientific update on nanoparticles in dentistry

Nanoparticles having a size from 1 to 100 nm are present in nature and are successfully used in many products of daily life. In dental materials, nanoparticles are typically embedded but they may also exist as by-products from milling processes. Possible adverse effects of nanoparticles have gained increased interest, with the lungs being the main target organ. Exposure to nanoparticles in the dental laboratory is addressed by legal regulations. In dental practice, nanoparticles are mainly produced by intra-oral grinding/polishing and removal of materials, by wear of restorations or release from dental implants. Based on worst-case mass-based calculations, the additional risk as a result of exposure to nanoparticles is considered to be low. However, more research is needed, especially on vulnerable groups (patients with asthma or chronic obstructive pulmonary disease). An assessment of risks for the environment is not possible because of lack of data. Exposure-reduction measures mainly include avoidance of abrasive processes (for example, by proper sculpturing), cooling by the use of water spray and sufficient ventilation of treatment areas.status: publishe

Scientific update on nanoparticles in dentistry.

Nanoparticles having a size from 1 to 100 nm are present in nature and are successfully used in many products of daily life. In dental materials, nanoparticles are typically embedded but they may also exist as by-products from milling processes. Possible adverse effects of nanoparticles have gained increased interest, with the lungs being the main target organ. Exposure to nanoparticles in the dental laboratory is addressed by legal regulations. In dental practice, nanoparticles are mainly produced by intra-oral grinding/polishing and removal of materials, by wear of restorations or release from dental implants. Based on worst-case mass-based calculations, the additional risk as a result of exposure to nanoparticles is considered to be low. However, more research is needed, especially on vulnerable groups (patients with asthma or chronic obstructive pulmonary disease). An assessment of risks for the environment is not possible because of lack of data. Exposure-reduction measures mainly include avoidance of abrasive processes (for example, by proper sculpturing), cooling by the use of water spray and sufficient ventilation of treatment areas

Is secondary caries with composites a material-based problem?

OBJECTIVE: Secondary caries (SC) is one of the most important reasons for the failure of composite restorations, and thus has wide-reaching implications for the longevity of affected teeth and the health expenditure. Yet, it is currently not known whether secondary caries with composites is a material-based problem. The objective was to review literature with regard to SC around composite restorations to obtain better insights in the mechanisms behind SC with composites. METHODS: Using Pubmed and Medline, international literature was searched for all articles about the clinical diagnosis, incidence and prevalence, histopathology and factors involved in the onset and development of SC around composite restorations. Additional studies were included after checking the reference lists of included papers. RESULTS: SC with composites is to some extent associated to the restorative material, as significantly more caries occurred with composites than with amalgam. On the other hand, the class of the composite restoration (class V versus others and class I versus class II) was also determining for the development of SC, suggesting also other influencing factors than the material itself. The mechanisms behind the development of SC are much less clear and are most probably multifactorial. Even though the role of gaps an microleakage is questioned by some researchers, there are also indications that interfacial failure may play a role. Interfacial gaps larger than 60 μm seem to predispose interfacial demineralization, and may thus lead to caries. The question is therefore whether such interfacial gaps occur clinically? Initially, a gap may originate through polymerization shrinkage and through failure to obtain a good bond. Higher incidences of SC are observed in practice-based than in university-based studies, which may be attributed to different caries risk profiles of the included patients, or to the technique-sensitive placement procedure of composites. More research is necessary to investigate whether large gaps may arise through degradation processes. Apart from these factors, composites also seem to favor the growth of cariogenic bacteria on their surface, which has been associated with specific surface properties, release of components and lack of antibacterial properties. SIGNIFICANCE: Current literature suggests that the restorative material might influence the development of secondary caries in different ways. However, it should be emphasized that patient-related factors remain the most important determinant of secondary caries

Bonding Efficacy of a New Self-Adhesive Restorative onto Flat Dentin vs Class-I Cavity-bottom Dentin

PURPOSE: This study investigated the bonding efficacy of a new so-called self-adhesive composite hybrid onto flat (FLAT) and high C-factor class-I cavity-bottom (CAVITY) dentin. MATERIALS AND METHODS: The immediate and aged (50,000 thermocycles) microtensile bond strength (μTBS) to FLAT and CAVITY dentin of the experimental self-adhesive bulk-fill restorative (K-0180 ASAR pilot [ASAR-pilot], Dentsply Sirona) was compared to that of two universal adhesives applied in self-etch mode and combined with a bulk-fill composite (Prime&Bond Elect/QuiXfil [P&Be/QuiXF], Prime&Bond Active/QuiXfil [P&Ba/QuiXF], both Dentsply Sirona), two pre-conditioned materials (Activa Bioactive-Restorative [Activa], Pulpdent; Fuji II LC Improved [Fuji2LC], GC); and one bulk-fill glass-hybrid restorative (Equia Forte Fil [EquiaF], GC). Statistically significant differences were recorded using Welch's ANOVA with Games-Howell contrast (p < 0.05). RESULTS: No significant difference in immediate μTBS was recorded when the restorative materials were applied onto FLAT dentin, except for Activa_FLAT and EquiaF_FLAT. When bonded to CAVITY dentin, the significantly highest μTBS was recorded for Fuji2LC_CAVITY (layer filled), and was not significantly different only from P&Ba/QuiXF_CAVITY. Upon aging, the highest μTBS to flat dentin was achieved by ASAR-pilot_FLAT, which was not significantly different from P&Be/QuiXF_FLAT and Fuji2LC_FLAT. No significant difference between immediate and aged μTBS was recorded for ASAR-pilot when bonded onto FLAT or CAVITY dentin; the latter, however, was associated with low bond strength. CONCLUSION: Favorable bonding performance was found for the new self-adhesive bulk-fill composite hybrid ASAR-pilot when bonded to flat dentin. However, much lower bond strength was recorded when ASAR-pilot was bonded to high C-factor cavity-bottom dentin.status: publishe

Cytotoxic and genotoxic potential of respirable fraction of composite dust on human bronchial cells

OBJECTIVE: To determine the cytotoxic and genotoxic potential of the respirable fraction of composite dust (<4 μm) on human bronchial epithelial cells. METHODS: Composite sticks of three commercial dental composites (Filtek Supreme XTE, Grandio, Transbond XT) were ground in an enclosed plexiglass chamber with a rough dental bur (grain-size 100 μm) and the generated airborne respirable dust was collected in a personal cyclone on a teflon filter (pore size 5 μm). Immediately after particle collection, the dust was quantified gravimetrically and the particles were suspended in cell culturing medium. Next, human bronchial epithelial cells (16HBE14o-) were exposed to the suspensions (3 μg/ml-400 μg/ml). After 24 h, cell viability (WST-1 assay) and membrane integrity (LDH assay) were evaluated. Furthermore, the genotoxic effect of a sub-cytotoxic concentration (50 μg/ml) of composite dust was evaluated by the comet assay after 3 h exposure and cell cycle disturbances were analyzed by flow cytometry. Cellular uptake of particles was evaluated by transmission electronic microscope (TEM). RESULTS: For all three tested composite materials, a decrease in metabolic activity of 10-35% was observed when the cells were exposed to the highest concentrations (100 μg/ml-400 μg/ml). Toxicity was partially linked to membrane disruption especially after 72 h exposure. All tested composites provoked a mild genotoxic effect after short-term exposure compared to the control groups. TEM revealed that respirable particles of all tested composites were taken up by the cells. SIGNIFICANCE: The respirable fraction of composite dust only showed cytotoxic effects at the highest concentrations, whereas mild genotoxicity was observed after exposure to a sub-cytotoxic concentration.status: publishe

No evidence for the growth-stimulating effect of monomers on cariogenic Streptococci

BACKGROUND: In spite of contradicting results, the high susceptibility of composites for secondary caries is still often associated with the bacterial growth-stimulating effect of released methacrylate monomers. However, most studies that showed this effect were performed with techniques having inherent limitations (spectrophotometry). OBJECTIVES: Therefore, our objective was to determine the effect of four methacrylate monomers (2-Hydroxyethyl methacrylate (HEMA), triethylene glycol dimethacrylate (TEGDMA), ethylene glycol dimethacrylate (EGDMA), diethylene glycol dimethacrylate (DEGDMA)) on the growth of two caries-associated bacteria, Streptococcus mutans and sobrinus, and one non-cariogenic species, Streptococcus sanguinis, using TaqMan quantitative polymerase chain reaction (qPCR) to quantify bacterial DNA. MATERIALS AND METHODS: Cultures were exposed to monomer solutions selected after spectrophotometric growth measurements. At baseline and predetermined time intervals, bacterial DNA was extracted and quantified with TaqMan qPCR. Biofilms grown in the presence of monomers were analyzed with scanning electron microscopy (SEM). RESULTS: Spectrophotometry indeed showed increased growth rates of all three strains with 5 mM TEGDMA, EGDMA, and DEGDMA and increased total biomass of S. sanguinis with 5 mM TEGDMA. However, qPCR failed to show any growth-stimulating effect of these monomers on S. mutans and S. sobrinus. In contrast, some monomers exhibited a growth-inhibiting effect on S. sanguinis. SEM revealed extracellular matter in S. sobrinus and S. sanguinis biofilms, which might be attributed to polymer formation. CONCLUSIONS: Techniques which quantify bacterial DNA are more appropriate to evaluate bacterial growth in the presence of monomers than spectrophotometry. CLINICAL RELEVANCE: Even though methacrylate monomers did not affect the growth of cariogenic species, growth inhibition of S. sanguinis, a non-cariogenic antagonistic species, may lead to ecological shifts towards higher cariogenicity

In-vitro transdentinal diffusion of monomers from adhesives

OBJECTIVES: Biocompatibility of adhesives is important since adhesives may be applied on dentin near the pulp. Accurate knowledge of the quantity of monomers reaching the pulp is important to determine potential side effects. The aim of this study was to assess the transdentinal diffusion of residual monomers from dental adhesive systems using an in-vitro pulp chamber model. METHODS: Dentin disks with a thickness of 300 μm were produced from human third molars. These disks were fixed between two open glass tubes, representing an in-vitro pulp chamber. The etch-and-rinse adhesive OptiBond FL and the self-etch adhesive Clearfil SE Bond were applied to the dentin side of the disks, while on in the pulpal side, the glass tube was filled with 600 μl water. The transdentinal diffusion of different monomers was quantified using ultra-performance liquid chromatography-tandem mass spectrometry. RESULTS: The monomers HEMA, CQ, BisGMA, GPDM, 10-MDP and UDMA eluted from the dental materials and were able to diffuse through the dentin disks to a certain extent. Compounds with a lower molecular weight (uncured group: HEMA 7850 nmol and CQ 78.2 nmol) were more likely to elute and diffuse compared to monomers with a higher molecular weight (uncured group: BisGMA 0.42 nmol). When the adhesives were left uncured, diffusion was up to 10 times higher compared to the cured conditions. CONCLUSIONS: This in-vitro research resulted in the quantification of various monomers able to diffuse through dentin and therefore contributes to a more detailed understanding about the potential exposure of the dental pulp to monomers from dental adhesives. CLINICAL SIGNIFICANCE: Biocompatibility of adhesives is important since adhesives may be applied on dentin near the pulp, where tubular density and diameter are greatest.status: publishe

Degree of conversion and monomer elution of CQ/amine and TPO adhesives

Objective. To evaluate the effect of photo-initiator on the degree of conversion (DC) and elution of Bis-GMA and HEMA for 8 one-step adhesive formulations. Methods. We used Scotchbond Universal ('SBU-CQ/amine 4.0', 3M ESPE), containing about 2 wt% camphorquinone (CQ) and 2 wt% ethyl-4-dimethylamino benzoate( EDMAB), an experimental 'SBU-TPO 2.1' version, containing 2.1 wt% diphenyl(2,4,6-trimethylbenzoyl) phosphine oxide (TPO), and 6 experimental LUB adhesives (Kuraray Noritake), namely 'LUB-CQ/amine 0.7', 'LUB-CQ/amine 1.4', 'LUB-CQ/amine 4.0', 'LUBTPO 0.35', 'LUB-TPO 0.7' and 'LUB-TPO 2.0', respectively containing 0.35 wt% CQ and 0.35 wt% EDMAB, 0.7 wt% CQ and 0.7 wt% EDMAB, 2.0 wt% CQ and 2.0 wt% EDMAB, 0.35 wt% TPO, 0.7 wt% TPO, and 2.0 wt% TPO. DC was measured using micro-Raman spectroscopy. Additional specimens were immersed in ethanol for 24 h to determine the elution of Bis-GMA and HEMA using HPLC. Results. DC of the respective SBU and LUB adhesives was alike at high photo-initiator concentration. At low concentration, TPO was significantly more efficient than CQ/amine (LUB adhesives only). A statistically significant positive photo-initiator concentration effect on DC was noted for both CQ/amine and TPO (LUB adhesives only). A statistically significant inversephoto-initiator concentration effect on HEMA elution was noted for both the CQ/amine and TPO-containing LUB adhesives. A significantly strong correlation was found between DC and Bis-GMA elution (R-2 = 0.744, p = 0.026), and between DC and HEMA elution (R-2 = 0.913, p = 0.002) for the LUB adhesives. Significance. The photo-initiator kind and concentration affect DC and the Bis-GMA/HEMAelution. TPO can be used as an alternative photo-initiator for CQ/amine

Structural/Chemical Characterization and Bond Strength of a New Self-Adhesive Bulk-fill Restorative

PURPOSE: The material structure and chemical elemental composition of a new self-adhesive composite hybrid were investigated. The bonding performance when applied on flat (FLAT) vs high C-factor class-I cavity-bottom (CAVITY) dentin and in light-cure (LC) vs self-cure (SC) mode was determined. MATERIALS AND METHODS: The self-adhesive bulk-fill composite Surefil One (Su-O; Dentsply Sirona) was compared with the resin-modified glass-ionomer Fuji II LC Improved (Fuji2LC; GC) and the ion-releasing alkasite material Cention N (CentionN; Ivoclar Vivadent). The material structure was examined with SEM and TEM, while the chemical elemental composition was analyzed using EDS. The immediate and aged microtensile bond strength (μTBS) of Su-O_LC/SC was compared to that of Fuji2LC applied without any pre-treatment, and to that of CentionN applied following bonding with Adhese Universal (AU) (Ivoclar Vivadent) in self-etch mode (AU/CentionN). All restorative materials were bonded onto FLAT and CAVITY dentin. Statistical analysis was performed with the Kruskal-Wallis nonparametric test. RESULTS: EDS analysis revealed that Su-O was richer in C and P than the reference restorative materials. Applied to FLAT dentin, the significantly highest immediate and aged μTBS were recorded for AU/CentionN, which were not significantly different only from Su-O_LC. Applied to CAVITY dentin, the significantly highest immediate μTBS was recorded for AU/CentionN, which did not differ significantly only from Su-O_SC. Su-O_LC bonded to CAVITY dentin suffered from a high incidence of pre-test failures. CONCLUSION: While Su-O_LC bonded effectively and durably to FLAT dentin, Su-O_SC bonded more favorably than Su-O_LC in class-I cavities, which was probably related to shrinkage stress variously challenging the respective bond.status: publishe