Carine Tais Welter Meereis

BAPO as an alternative photoinitiator for the radical polymerization of dental resins

OBJECTIVES This study evaluated the performance of phenylbis (2,4,6-trimethylbenzoyl)-phosphine oxide (BAPO) as an alternative photoinitiator in the polymerization kinetics (PK), flexural strength (σ) and elastic modulus (E) of a model dental resin. METHODS A monomer mixture based on Bis-GMA and TEGDMA was used as model dental resin. Initially a screening was performed to evaluate BAPO concentrations (0.125, 0.25, 0.50, 1, 2, and 4 mol%). Photoinitiator systems were formed with the combination of camphorquinone (CQ), ethyl-dimethylamino benzoate (EDAB), diphenyliodonium hexafluorophosphate (DPIHFP), and BAPO. Groups with unitary photoinitiator systems (BAPO and CQ), binary (BAPO+EDAB, BAPO+DPIHFP and CQ+EDAB), ternary (BAPO+CQ+EDAB, BAPO+CQ+DPIHFP, BAPO+EDAB+DPIHFP and CQ+EDAB+DPIHFP) and quaternary (BAPO+CQ+EDAB+DPIHFP) were formulated for evaluation. Real-time Fourier transform infrared spectroscopy was used to investigate the PK and test mini-bending to evaluate σ and E. RESULTS When only CQ was used, a slow polymerization reaction was observed and a lower monomer conversion. When only BAPO was used as photoinitiator an increase in the polymerization rate was observed and conversion was higher than CQ+EDAB. The ternary system (BAPO+EDAB+DPIHFP) showed the highest polymerization and conversion rate, in short photo-activation time. SIGNIFICANCE BAPO it is a potential photoinitiator for the photopolymerization of dental materials.

Stability of initiation systems in acidic photopolymerizable dental material

OBJECTIVES This study simulated the shelf life to evaluate the stability of initiation systems on acidic photopolymerizable dental material, through an experimental self-adhering flowable composite resin (SACR). METHODS An SACR model was formulated with monomers Bis-GMA, TEGDMA, acidic monomer (GDMA-P), and inorganic fillers. Initiation system combinations of camphorquinone (CQ), tertiary amine (EDAB), diphenyl phosphine oxide (TPO), phenylbis phosphine oxide (BAPO), and the diphenyliodonium hexafluorophosphate (DPIHFP) were tested. Five SACRs were evaluated, varying the initiation system: SACRCQ, SACRCQ+EDAB, SACRCQ+EDAB+DPIHFP, SACRBAPO and SACRTPO. The SARC were stored at 23°C and, according to shelf life, were evaluated for degree of conversion (DC), polymerization rate (Rp) and microtensile bond strength (μTBS). The DC was evaluated after 0, 1, 2, 4, 8, 12, 24 and 48 storage weeks of SACRs. Bonding to dentin was performed after 0, 4, 8, 12 and 24 storage weeks of SACRs and tested immediately (24h) and after 6 and 12 months by μTBS. Halogen light curing unit (3M ESPE) was used for photoactivation procedures. RESULTS SACRCQ+EDAB+DPIHFP showed higher Rp. The DC of SACRCQ+EDAB, SACRCQ+EDAB+DPIHFP, and SACRBAPO were similar (40%) and higher than SACRTPO and SACRCQ (20 and 10%, respectively), staying stable up to 48 weeks. The SACRCQ, SACRCQ+EDAB, and SACRTPO had pre-testing failure on μTBS. The shelf life of SACRs did not affect the μTBS of the groups that obtained adhesion. Furthermore, the immediate μTBS (MPa) SACRCQ+EDAB+DPIHFP (8.4) was similar to SACRBAPO (10.5); however, after 12 months, only SACRCQ+EDAB+DPIHFP maintained the μTBS. SIGNIFICANCE The choice of a suitable initiation system is crucial to the performance and stability of acidic photopolymerizable dental material.

Polymerization shrinkage stress of resin-based dental materials: A systematic review and meta-analyses of technique protocol and photo-activation strategies

PURPOSE A systematic review was conducted to determine whether there were any alternative technique or additional step strategies available to reduce and control polymerization shrinkage stress development in dental resin-based restorative materials. DATA SOURCES This report followed the PRISMA Statement. A total of 36 studies were included in this review. Two reviewers performed a literature search up to December 2016, without restriction of the year of publication, in seven databases: PubMed, Web of Science, Scopus, SciELO, LILACS, IBECS, and BBO. STUDY SELECTION Only in vitro studies that evaluated polymerization shrinkage stress by direct testing were included. Pilot studies, reviews and in vitro studies that evaluated polymerization shrinkage stress by indirect methods (e.g., microleakage or cuspal deflection measurements), finite elemental analysis or mathematical models were excluded. Of the 6.113 eligible articles, 36 studies were included in the qualitative analysis, and the meta-analysis was performed with 25 studies. A global comparison was performed with random-effects models (α = 0.05). The strategies were subdivided as follows: the use of an alternative technique protocol of placing the material inside the tooth cavity; the modification of the irradiation intensity or total energy delivered to the material; the use of an alternative light-curing source; or the use of an alternative photo-activation mode. All alternative strategies showed statistically significant differences when compared with their respective controls (p < 0.05). CONCLUSION The use of alternative light-curing sources contributed more to minimizing stress development than placing the material by means of an alternative technique protocol or by modifying the irradiant intensity or total energy delivered to the material during photo-activation. Moreover, the use of an alternative photo-activation mode (intermittent light, exponential, soft-start or pulse delay modes) was shown to be an effective strategy for reducing and controlling stress development in resin-based dental materials.

Efficacy of antimicrobial agents incorporated in orthodontic bonding systems: a systematic review and meta-analysis

Aims The purpose of this study was to evaluate the efficacy of orthodontic bonding systems containing different antimicrobial agents, as well as the influence of antimicrobial agent incorporation in the bonding properties of these materials. Methods Eight databases were searched: PubMed (Medline), Web of Science, Scopus, Lilacs, Ibecs, BBO, Scielo and Google Scholar. Any study that evaluated antimicrobial activity in experimental or commercial orthodontic bonding systems was included. Data extraction Data were tabulated independently and in duplicated by two authors on pre-designed data collection form. Data synthesis The global analysis was carried out using a random-effects model, and pooled-effect estimates were obtained by comparing the standardised mean difference of each antimicrobial orthodontic adhesive with the respective control group. A p-value < .05 was considered as statistically significant. Results Thirty-two studies were included in the qualitative analysis; of these, 22 studies were included in the meta-analysis. Antimicrobial agents such as silver nanoparticles, benzalkonium chloride, chlorhexidine, triclosan, cetylpyridinium chloride, Galla chinensis extract, acid ursolic, dimethylaminododecyl methacrylate, dimethylaminohexadecyl methacrylate, 2-methacryloyloxyethyl phosphorylcholine, 1,3,5-triacryloylhexahydro-1,3,5-triazine, zinc oxide and titanium oxide have been incorporated into orthodontic bonding systems. The antimicrobial agent incorporation in orthodontic bonding systems showed higher antimicrobial activity than the control group in agar diffusion (overall standardised mean difference: 3.71; 95% CI 2.98 to 4.43) and optical density tests (0.41; 95% CI −0.05 to 0.86) (p < .05). However, for biofilm, the materials did not present antimicrobial activity (6.78; 95% CI 4.78 to 8.77). Regarding bond strength, the global analysis showed antimicrobial orthodontic bonding systems were statistically similar to the control. Conclusions Although there is evidence of antibacterial activity from in vitro studies, clinical and long-term studies are still necessary to confirm the effectiveness of antibacterial orthodontic bonding systems in preventing caries disease.

Addition of ammonium-based methacrylates to an experimental dental adhesive for bonding metal brackets: Carious lesion development and bond strength after cariogenic challenge

Introduction: In this study, we evaluated the caries inhibition and shear bond strength achieved with the addition of the antibacterial monomer [2‐(Methacryloyloxy)ethyl] trimethylammonium chloride (MADQUAT) to an adhesive used to bond orthodontic brackets. Methods: Experimental adhesives were formulated with addition of 0% (control), 5%, or 10% MADQUAT followed by measurement of the degree of conversion. These adhesives were used to lute brackets to the enamel of premolars (n = 30). Biofilm from a microcosm model was cultivated in half of the specimens under cariogenic challenge for 5 days. The brackets were subjected to a shear bond strength test followed by measurement of the internal hardness of the enamel around the brackets to calculate the integrated mineral loss. Results: The addition of MADQUAT slightly increased the degree of conversion. Adhesive containing 10% MADQUAT significantly reduced the integrated mineral loss around the bracket but also resulted in the lowest values of bond strength. No effects on bond strength and integrated mineral loss were observed with the addition of 5% MADQUAT to the adhesive. The cariogenic challenge did not affect the bond strength and the failure mode. Conclusions: MADQUAT was effective to reduce the integrated mineral loss only when added to the adhesive at a concentration of 10% despite the reduction of bond strength. HighlightsBrackets were fixed using adhesives with 0%, 5%, or 10% antibacterial monomer.Bond strength and mineral loss were analyzed after cariogenic challenge.Adding 10% antibacterial monomer to the adhesive reduced the mineral loss.Lowest bond strength was observed for adhesive with the 10% antibacterial monomer.

Radiopaque dental adhesive with addition of niobium pentoxide nanoparticles

Radiopacity is an important property of dental adhesives, because it allows the adhesive resin to be in contrast with the tooth structure and other restorative materials. This study aimed to develop a radiopaque experimental adhesive resin through the addition of niobium pentoxide (Nb2O5) particles. The effects of adding different concentrations of Nb2O5 nanoparticles synthesized by microwave-assisted hydrothermal synthesis (MHS) were compared to the commercial Nb2O5 microparticles. The experimental adhesive resin was formulated by mixing bisphenol A glycidyl methacrylate (Bis-GMA), 2-hydroxyethyl methacrylate (HEMA), camphorquinone (CQ) and ethyl 4-(dimethylamino)benzoate (EDAB). Experimental adhesive resins were evaluated by the radiopacity, degree of conversion, Knoop microhardness, translucency parameter, depth of cure, viscosity, and sedimentation rate. Synthesized Nb2O5 showed hexagonal structure and nanoneedles aggregates in form of nanoflowers. The incorporation of Nb2O5 nanoparticles into the dental adhesive resin showed high dispersion stability and improved the radiopaque properties.

Long-term bonding efficacy of adhesives containing benzodioxioles as alternative co-initiators

This study evaluated the three-year lifespan of the bond to dentin of experimental self-etch adhesives containing benzodioxole derivatives - 1,3-benzodioxole (BDO) and piperonyl alcohol (PA) - as co-initiator alternative to amines. Adhesive resins were formulated using Bis-GMA, TEGDMA, HEMA, camphorquinone and different co-initiators: BDO, PA or ethyl 4-dimethylamino benzoate (EDAB - amine). An experimental self-etch primer was used to complete the two-step, self-etch adhesive system. Clearfil SE Bond (CSE) was used as commercial reference. Bond strength to human dentin was assessed by microtensile bond strength (µTBS) test, and failure mode was classified. Morphology of the dentin bonding interface was assessed via scanning electron microscopy (SEM). Irrespective of the dental adhesives evaluated, µTBS was higher after 24 hours compared with that after 1.5 and 3 years (p ≤ 0.001). However, adhesives with BDO and PA as co-initiators showed significantly higher bond strength than the bonding resin with EDAB (p ≤ 0.002), independent of the time evaluated. The commercial adhesive CSE showed similar bond strength compared with the other groups (p ≥ 0.05). Mixed failures were mainly observed after 24 hours, while adhesive failures were more frequently observed after 1.5 and 3 years. No notable differences in homogeneity and continuity along the bonded interfaces were detected among the materials in the SEM analysis. In conclusion, benzodioxole derivatives are feasible alternative co-initiators to tertiary amine in camphorquinone-based self-etching dental adhesive formulations.

Evaluation of long-term bond strength and selected properties of self-adhesive resin cements

This study evaluated the shear bond strength (SBS) of self-adhesive resin cements (SARCs) to dentin and their physical-chemical properties. Five commercial SARCs were evaluated [SmartCem®2 - DENTSPLY (SC2); BisCem® - Bisco (BC); SeT PP® - SDI (SeT); Relyx U100® - 3M ESPE (U100) and YCEM® SA - Yller (YCEM)]. The SARCs were evaluated for SBS to dentin (n = 10) after 24 h, 6 months, and 12 months. The dentin demineralization caused by acidic monomers was observed by SEM, and pH-neutralization of eluate was observed for 24 h. Degree of conversion (DC), rate of polymerization (Rp), flexural strength (FS), and elastic modulus (E) were evaluated. Immediate SBS of SC2, SET, U100, and YCEM were statistically higher than that of BC (p < 0.001). After 12 months, all SARCs showed reduced SBS values and U100 showed values similar to those of SET and YCEM, and higher than those of BC and SC2 (p = 0.001). Demineralization pattern of SARCs was similar. At 24h, all SARCs showed no differences in the pH-value, except BC and U100 (p < 0.001). YCEM showed the highest Rp. U100, YCEM, and SC2 showed statistically higher FS (p<0.001) and E (p < 0.001) when compared with SET and BC. U100 and YCEM showed the best long-term bonding irrespective of the storage period. A significant reduction in SBS was found for all groups after 12 months. SBS was not shown to be correlated with physical-chemical properties, and appeared to be material-dependent. The polymerization profile suggested that an increased time of light activation, longer than that recommended by manufacturers, would be necessary to optimize DC of SARCs.

Characterization of Bis-Acryl Composite Resins for Provisional Restorations

This study investigated the in vitro performance of the commercial bis-acryl composite resins Systemp C&B II (SYS, Ivoclar Vivadent), Protemp 4 (PT4, 3M ESPE), Structur 2C (ST2, Voco) and ProviPlast (PVP, Biodinamica). Characterization involved optical (color stability, translucency parameter, fluorescence), surface (roughness, morphology and elemental composition), physical-chemical (viscosity, polymerization kinetics) and mechanical analyses (Poisson ratio, biaxial flexural strength, flexural modulus). Most tests were carried out after 24 h, but optical and mechanical analyses were carried out after storage in water at 37 °C for 1, 15, and 30 days. Data were statistically analyzed (a=0.05). Most results were material dependent. SYS and PT4 showed stability in color and translucency over time. All materials had similar or higher fluorescence than human enamel. SC2 and PVP showed rougher surfaces than the other bis-acryl composites. Smaller filler particles were observed on the surface of PT4 and PVP compared with the coarser particles from ST2 and SYS. Viscosity readings indicated a thixotropic behavior for all tested materials. SYS had the lowest and PT4 the highest degree of C=C conversion after 10 min. In the polymerization kinetics, PT4 had the highest maximum polymerization rate and reached earlier the transition between polymerization autoacceleration and autodeceleration. PT4 and SYS had significantly higher flexural strength and modulus than ST2 and PVP for most storage times. Results for Poisson ratio varied between materials. Longer storage periods were generally associated with higher frequency of catastrophic failures in the flexural tests. In conclusion, the performance of bis-acryl composite resins varied largely among materials.