Effect of charge density of bonding agent containing a new quaternary ammonium methacrylate on antibacterial and bonding properties

Objective

Quaternary amine charge density is important because when the negatively charged bacteria contact the positive quaternary amine charge, the electric balance is disturbed and the bacterium could be disrupted. There has been no report on the effects of charge density on the antibacterial efficacy of dental bonding agents. The objective of this study was to synthesize a new quaternary ammonium methacrylate, and investigate the effects of charge density of bonding agent on bacteria early-attachment, biofilm colony-forming units (CFU) and dentin bond strength.

Methods

Dimethylaminododecyl methacrylate (DMAHDM) with an alkyl chain length of 16 was synthesized and mixed into Scotchbond Multi-Purpose adhesive and primer (SBMP) at mass fractions of 0%, 2.5%, 5%, 7.5%, and 10%. A microtensile dentin bond test was performed. The density of quaternary ammonium groups was measured using a fluorescein dye method. Streptococcus mutans (S. mutans) early-attachment was examined at 4 h, and biofilm colony-forming units (CFU) were measured at 2 days.

Results

All groups had similar microtensile bonding strengths (mean ± sd; n = 40) of about 60 MPa (p > 0.1). Quaternary amine charge density of bonding agents monotonically increased with increasing DMAHDM mass fraction. Bacteria early-attachment coverage greatly decreased with increasing DMAHDM content in the resin. Biofilm CFU at 10% DMAHDM was reduced by more than 4 log, compared to SBMP control. Charge density of bonding agent was inversely proportional to bacteria early-attachment coverage and biofilm CFU.

Significance

Increasing the quaternary amine charge density of dentin bonding agent resin was shown to greatly reduce S. mutans attachment and decrease biofilm CFU by four orders of magnitude, without compromising the dentin bond strength. The new DMAHDM is promising for use in bonding agents and other antibacterial restorative materials to inhibit caries.     

Effect of water-ageing on dentine bond strength and anti-biofilm activity of bonding agent containing new monomer dimethylaminododecyl methacrylate

Objectives

The objectives of this study were to develop bonding agent containing a new antibacterial monomer dimethylaminododecyl methacrylate (DMADDM) as well as nanoparticles of silver (NAg) and nanoparticles of amorphous calcium phosphate (NACP), and to investigate the effects of water-ageing for 6 months on dentine bond strength and anti-biofilm properties for the first time.

Methods

Four bonding agents were tested: Scotchbond Multi-Purpose (SBMP) Primer and Adhesive control; SBMP + 5% DMADDM; SBMP + 5% DMADDM + 0.1% NAg; and SBMP + 5% DMADDM + 0.1% NAg with 20% NACP in adhesive. Specimens were water-aged for 1 d and 6 months at 37 °C. Then the dentine shear bond strengths were measured. A dental plaque microcosm biofilm model was used to inoculate bacteria on water-aged specimens and to measure metabolic activity, colony-forming units (CFUs), and lactic acid production.

Results

Dentine bond strength showed a 35% loss in 6 months of water-ageing for SBMP control (mean ± sd; n = 10); in contrast, the new antibacterial bonding agents showed no strength loss. The DMADDM–NAg–NACP containing bonding agent imparted a strong antibacterial effect by greatly reducing biofilm viability, metabolic activity and acid production. The biofilm CFU was reduced by more than two orders of magnitude, compared to SBMP control. Furthermore, the DMADDM–NAg–NACP bonding agent exhibited a long-term antibacterial performance, with no significant difference between 1 d and 6 months (p > 0.1).

Conclusions

Incorporating DMADDM–NAg–NACP in bonding agent yielded potent and long-lasting antibacterial properties, and much stronger bond strength after 6 months of water-ageing than a commercial control. The new antibacterial bonding agent is promising to inhibit biofilms and caries at the margins. The method of DMADDM–NAg–NACP incorporation may have a wide applicability to other adhesives, cements and composites.     

Novel protein-repellent dental adhesive containing 2-methacryloyloxyethyl phosphorylcholine

Objectives

Biofilms at tooth-restoration margins can produce acids and cause secondary caries. A protein-repellent adhesive resin can potentially inhibit bacteria attachment and biofilm growth. However, there has been no report on protein-repellent dental resins. The objectives of this study were to develop a protein-repellent bonding agent incorporating 2-methacryloyloxyethyl phosphorylcholine (MPC), and to investigate its resistance to protein adsorption and biofilm growth for the first time.

Methods

MPC was incorporated into Scotchbond Multi-Purpose (SBMP) at 0%, 3.75%, 7.5%, 11.25%, and 15% by mass. Extracted human teeth were used to measure dentine shear bond strengths. Protein adsorption onto resins was determined by a micro bicinchoninic acid (BCA) method. A dental plaque microcosm biofilm model with human saliva as inoculum was used to measure biofilm metabolic activity and colony-forming unit (CFU) counts.

Results

Adding 7.5% MPC into primer and adhesive did not decrease the dentine bond strength, compared to control (p > 0.1). Incorporation of 7.5% of MPC achieved the lowest protein adsorption, which was 20-fold less than that of control. Incorporation of 7.5% of MPC greatly reduced bacterial adhesion, yielding biofilm total microorganism, total streptococci, and mutans streptococci CFU that were an order of magnitude less than control.

Conclusions

A protein-repellent dental adhesive resin was developed for the first time. Incorporation of MPC into primer and adhesive at 7.5% by mass greatly reduced the protein adsorption and bacterial adhesion, without compromising the dentine bond strength.

Clinical significance

The novel protein-repellent primer and adhesive are promising to inhibit biofilm formation and acid production, to protect the tooth-restoration margins and prevent secondary caries.     

Nanotube-modified dentin adhesive—Physicochemical and dentin bonding characterizations

Objective

The aim of this study was to investigate the effect of aluminosilicate clay nanotubes (Halloysite, HNT) incorporated into the adhesive resin of a commercially available three-step etch and rinse bonding system (Adper Scotchbond Multi-Purpose/SBMP) on dentin bond strength, as well as the effect on several key physicochemical properties of the modified adhesive.

Methods

Experimental adhesives were prepared by adding five distinct HNT amounts (5–30 wt.%) into the adhesive resin (w/v) of the SBMP dentin bonding system. Bond strength to human dentin, microhardness, and degree of conversion (DC) of the modified adhesives were assessed.

Results

From the shear bond strength data, it was determined that HNT incorporation at a concentration of 30 wt.% resulted in the highest bond strength to dentin that was statistically significant (p = 0.025) when compared to the control. Even though a significant increase in microhardness (p < 0.001) was seen for the 30 wt.% HNT-incorporated group, a significantly lower DC (p < 0.001) was recorded when compared to the control.

Significance

It was concluded that HNT can be incorporated up to 20 wt.% without jeopardizing important physicochemical properties of the adhesive. The modification of the SBMP dentin bonding agent with 20 wt.% HNT appears to hold great potential toward contributing to a durable dentin bond; not only from the possibility of strengthening the bond interface, but also due to HNT intrinsic capability of encapsulating therapeutic agents such as matrix metalloproteinase (MMP) inhibitors.     

Novel antibacterial orthodontic cement containing quaternary ammonium monomer dimethylaminododecyl methacrylate

Objectives

Demineralized lesions in tooth enamel around orthodontic brackets are caused by acids from cariogenic biofilm. This study aimed to develop a novel antibacterial orthodontic cement by incorporating a quaternary ammonium monomer dimethylaminododecyl methacrylate (DMADDM) into a commercial orthodontic cement, and to investigate the effects on microcosm biofilm response and enamel bond strength.

Methods

DMADDM, a recently-synthetized antibacterial monomer, was incorporated into orthodontic cement at 0%, 1.5%, 3% and 5% mass fractions. Bond strength of brackets to enamel was measured. A microcosm biofilm model was used to measure metabolic activity, lactic acid production, and colony-forming units (CFU) on orthodontic cements.

Results

Shear bond strength was not reduced at 3% DAMDDM (p > 0.1), but was slightly reduced at 5% DMADDM, compared to 0% DMADDM. Biofilm viability was substantially inhibited when in contact with orthodontic cement containing 3% DMADDM. Biofilm metabolic activity, lactic acid production, and CFU were much lower on orthodontic cement containing DMADDM than control cement (p < 0.05).

Conclusions

Therefore, the novel antibacterial orthodontic cement containing 3% DMADDM inhibited oral biofilms without compromising the enamel bond strength, and is promising to reduce or eliminate demineralization in enamel around orthodontic brackets.     

Effects of the application sequence of calcium-containing desensitising pastes during etch-and-rinse adhesive restoration

Objectives

To evaluate the effects of different application sequence of calcium-containing desensitising pastes on bonding effectiveness and tubule occlusion during etch-and-rinse (E&R) adhesive restoration.

Methods

Seventy molars were sectioned parallel to the occlusal plane, polished and randomly divided into seven groups (n = 10). Group 1 was etched with 35% phosphoric acid for 15 s. Groups 2–4 were treated with different calcium-containing desensitisers, including an arginine-calcium carbonate (Arg-CaCO₃)-containing paste, a casein phosphopeptide-amorphous calcium phosphate (CPP-ACP)-containing paste and a calcium-sodium phosphosilicate (Novamin)-containing paste, respectively. Afterward, these groups were etched with 35% phosphoric acid for 15 s. Groups 5–7 were initially etched and then treated with Arg-CaCO₃-, CPP-ACP- and Novamin-containing desensitisers, respectively. In each group, samples were equally distributed into two subgroups (n = 5) to bond with either a two-step E&R adhesive Adper SingleBond 2 (SB) or a three-step E&R adhesive Adper ScotchBond Multi-Purpose (SBMP). The microtensile bond strengths (MTBS) were tested and fracture modes were analyzed by stereomicroscopy and field-emission scanning electron microscopy (FESEM). Eight additional dentine disks were prepared to evaluate tubule occlusion prior to bonding using FESEM.

Results

The application sequence of calcium-containing desensitising pastes did not significantly affect MTBS irrespective of two-step SB (P > 0.05) or three-step SBMP E&R adhesives (P > 0.05). Effective dentinal tubule occlusion was observed in the mode of etching-desensitising.

Conclusions

Applying calcium-containing desensitisers (particularly Arg-CaCO₃- and Novamin-based) after etching during E&R adhesive restoration could achieve effective tubule occlusion without affecting the bonding strength.     

Association between the cariogenicity of a dental microcosm biofilm and its red fluorescence detected by Quantitative Light-induced Fluorescence-Digital (QLF-D)

Objective

This study evaluated whether Quantitative Light-induced Fluorescence-Digital (QLF-D) can detect the levels of cariogenicity of dental microcosm biofilms by assessing the red fluorescence intensity.

Methods

Dental microcosm biofilms were initiated from human saliva on bovine enamel discs. Biofilms with various levels of cariogenicity were then grown in artificial saliva supplemented with sucrose at different concentrations (0.05%, 0.1%, 0.2%, and 0.5%) in 24-well microplates. After 10 days, fluorescence images of the biofilms were captured by the QLF-D to analyse the red fluorescence intensity, which was quantified as the red/green ratio (R/G value). The supernatant pH was also measured, as well as the total and aciduric bacteria counts of the collected biofilms. Mineral loss in enamel was also evaluated by calculating the percentage of surface microhardness changes (%SHC).

Results

The R/G values of the biofilms differed significantly with the sucrose concentration (p < 0.0001), increasing consistently as the sucrose concentration increased from 0.05% (=0.91) to 0.5% (=2.56). Strong correlation was identified between the R/G value and the number of aciduric bacteria (r = 0.83, p < 0.0001), supernatant pH (r = −0.95, p < 0.0001), and %SHC (r = 0.90, p < 0.0001).

Conclusions

The red fluorescence as observed by the QLF-D was correlated with the cariogenic properties of dental microcosm biofilms in vitro, which indicates that this device can be used to detect the levels of cariogenicity of a dental biofilm.

Clinical significance

The QLF-D is able to assess the cariogenic levels of dental plaque based on the intensity of red fluorescence.     

The inhibitory effect of a polymerisable cationic monomer on functional matrix metalloproteinases

Objectives

This study examined the use of methacryloxylethyl cetyl dimethyl ammonium chloride (DMAE-CB) as a potential matrix metalloproteinases (MMPs) inhibitor on both soluble recombinant and dentine matrix-bound endogenous MMPs, meanwhile attempted to determine the effective anti-MMP group of quaternary ammonium methacrylates (QAMs).

Methods

The possible inhibitory effects of five DMAE-CB mass concentrations (0.1%, 0.5%, 1%, 3%, 5%) on soluble rhMMP-9 were measured using a colorimetic assay kit. Methyl methacrylate (MMA) and [2-(methacryloyloxy)ethyl] trimethylammonium chloride (METMAC) were also screened against rhMMP-9 to compare the inhibitory effect with DMAE-CB. Matrix-bound endogenous MMP-activity was evaluated in completely demineralized dentine beams. Thirty beams were randomly divided into three groups (N = 10) and respectively placed into 500 μL of calcium- and zinc-containing media (CM; control), 0.2% chlorhexidine or 3% DMAE-CB in CM aged for 30 days. The changes in modulus of elasticity, loss of dry mass and solubilization of collagen peptides were measured via three-point bending, precision weighing and hydroxyproline assay, respectively.

Results

0.5–5% mass concentrations of DMAE-CB were highly effective (P < 0.05) in inhibiting rhMMP-9 varied between 76.56 ± 6.44% and 97.06 ± 3.24%, the inhibitory effect of MMA was much lower than that of METMAC and DMAE-CB at the same concentration (P < 0.05). Dentine beams incubated in 3% DMAE-CB showed only a 26.34% decrease in the modulus of elasticity (75.74% decrease in control), a 1.72 ± 1.56% loss of dry mass (29.70 ± 9.12% loss in control), and significantly less solubilized hydroxyproline when compared with the control (P < 0.05).

Conclusions

DMAE-CB is effective in inhibiting both soluble recombinant MMPs and matrix-bound dentine MMPs. Quaternary ammonium group is the effective anti-MMP group of QAMs.

Clinical significance

The incorporation of DMAE-CB into dental adhesives has the potential to enhance the durability of dentine bonding and thus increases the longevity of restorations.     

Effect of salivary pellicle on antibacterial activity of novel antibacterial dental adhesives using a dental plaque microcosm biofilm model

Objectives

Antibacterial primer and adhesive are promising to inhibit biofilms and caries. Since restorations in vivo are exposed to saliva, one concern is the attenuation of antibacterial activity due to salivary pellicles. The objective of this study was to investigate the effects of salivary pellicles on bonding agents containing a new monomer dimethylaminododecyl methacrylate (DMADDM) or nanoparticles of silver (NAg) against biofilms for the first time.

Methods

DMADDM and NAg were synthesized and incorporated into Scotchbond Multi-Purpose adhesive and primer. Specimens were either coated or not coated with salivary pellicles. A microcosm biofilm model was used with mixed saliva from ten donors. Two types of culture medium were used: an artificial saliva medium (McBain), and Brain Heart Infusion (BHI) medium without salivary proteins. Metabolic activity, colony-forming units (CFU), and lactic acid production of plaque microcosm biofilms were measured (n = 6).

Results

Bonding agents containing DMADDM and NAg greatly inhibited biofilm activities, even with salivary pellicles. When using BHI, the pre-coating of salivary pellicles on resin surfaces significantly decreased the antibacterial effect (p < 0.05). When using artificial saliva medium, pre-coating of salivary pellicles on resin did not decrease the antibacterial effect. These results suggest that artificial saliva yielded medium-derived pellicles on resin surfaces, which provided attenuating effects on biofilms similar to salivary pellicles. Compared with the commercial control, the DMADDM-containing bonding agent reduced biofilm CFU by about two orders of magnitude.

Significance

Novel DMADDM- and NAg-containing bonding agents substantially reduced biofilm growth even with salivary pellicle coating on surfaces, indicating a promising usage in saliva-rich environment. DMADDM and NAg may be useful in a wide range of primers, adhesives and other restoratives to achieve antibacterial and anti-caries capabilities.     

Nanofiller loading level: Influence on selected properties of an adhesive resin

Objectives

To evaluate the effect of the filler content in the cohesive strength (σ), Weibull modulus (m) and degree of conversion (DC) of an experimental adhesive system.

Methods

A HEMA/Bis-GMA/TEGDMA-based adhesive was formulated and filled with silica nanofillers in the following weight percentages (wt%): R0 = 0%; R1 = 1%; R3 = 3%; R5 = 5% and R10 = 10%. The adhesive of Adper Scotchbond Multi-Purpose (SBMP) system was used as a commercial reference. Twenty dumbbell-shaped specimens with cross-sectional area of 0.5 mm² were made per group and tensile tested with a crosshead speed of 0.5 mm/min until fracture. The cohesive strength was calculated in MPa. DC was obtained through FTIR after light curing for 25 s. Data were submitted to one-way ANOVA and Tukey's test (α = 0.05) and to Weibull analysis.

Results

Mean σ results were: R0 = 65.4 ± 8.4; R1 = 73.2 ± 8.8; R3 = 72.0 ± 8.4; R5 = 73.1 ± 9.7; R10 = 85.5 ± 13.1 and SBMP = 79.0 ± 11.0 MPa. R10 presented the highest σ, while R0 showed the lowest. R5 and SBMP did not differ significantly (p < 0.05). Weibull analysis revealed no significant difference in structural reliability between groups. The experimental adhesives presented similar results of DC, which, in turn, were significantly higher than the SBMP.

Conclusions

The addition of 10% filler in weight improves the cohesive strength of the adhesive, not interfering in the structural reliability or the degree of conversion.     

Monitoring the maturation process of a dental microcosm biofilm using the Quantitative Light-induced Fluorescence-Digital (QLF-D)

Objective

The aim of this study was to investigate whether Quantitative Light-induced Fluorescence-Digital (QLF-D) could monitor the degree of maturation of dental microcosm biofilms by observing the red fluorescence emitted from the biofilms.

Methods

Dental microcosm the biofilms were grown on bovine enamel discs. They were initiated from human saliva, and then grown in 0.5% sucrose growth media for 10 days. On days 1, 2, 3, 7, and 10 after the inoculation, fluorescence images of the biofilms were captured using the QLF-D and the red fluorescence intensity was quantified by calculating the red/green ratio (R/G value). Total and aciduric bacteria within the biofilms were counted, and the degree of demineralization was evaluated by measuring the percentage of surface microhardness change (ΔVHN) and lesion depth in the enamel.

Results

The R/G values of the biofilms assessed by the QLF-D increased significantly over time up to 7 days after inoculation (p < 0.0001). The R/G values showed significant positive correlations with the total bacterial CFUs (r = 0.74, p = 0.001), aciduric bacterial CFUs (r = 0.85, p = 0.001), ΔVHN (r = 0.65, p = 0.001), and lesion depth in the enamel (r = 0.82, p = 0.001) according to the maturation time.

Conclusions

The red fluorescence detected by the QLF-D increased according to biofilm maturation and was significantly associated with the cariogenicity of the biofilm. Therefore, this device could be used to monitor the degree of biofilm maturation by observing the red fluorescence emitted from cariogenic biofilms.

Clinical significance

The QLF-D enables the detection of a mature dental plaque and monitoring of its cariogenic status by observing the plaque fluorescence non-destructively, in real time.     

Novel magnetic nanoparticle-containing adhesive with greater dentin bond strength and antibacterial and remineralizing capabilities

Objectives

A nanoparticle-doped adhesive that can be controlled with magnetic forces was recently developed to deliver drugs to the pulp and improve adhesive penetration into dentin. However, it did not have bactericidal and remineralization abilities. The objectives of this study were to: (1) develop a magnetic nanoparticle-containing adhesive with dimethylaminohexadecyl methacrylate (DMAHDM), amorphous calcium phosphate nanoparticles (NACP) and magnetic nanoparticles (MNP); and (2) investigate the effects on dentin bond strength, calcium (Ca) and phosphate (P) ion release and anti-biofilm properties.

Dental composite materials containing carolacton inhibit biofilm growth of Streptococcus mutans

Objective

Caries adjacent to restorations is one of the main causes for restoration replacement. Antimicrobial substances incorporated into dental materials would potentially be able to reduce secondary caries initiation and progression. This study investigated biofilm growth of Streptococcus mutans UA159 on the surface of composite materials containing the biomolecule carolacton compared to materials containing chlorhexidine (CHX) and triclosan.

Methods

Biofilm inhibition was investigated by counting colony forming units (CFU), viability staining (Life/Dead), and real-time quantitative PCR.

Results

First, the antimicrobial substances were added to the cultivation medium at 2.5 μg/ml (0.0002%) and 0.25 μg/ml (0.00002%). CHX eliminated bacterial growth and biofilm formation completely. Triclosan was effective at 2.5 μg/ml, but at 0.25 μg/ml biofilm mass and viability were unchanged, yet the number of CFU increased due to disruption of cell chains and biofilm aggregates. Carolacton had a limited effect on biofilm growth and mass, but reduced viability significantly. When incorporated into composite materials carolacton (25 μg/ml resp. 0.002%, w/w) had no adverse effect on physical/mechanical properties and retained its biofilm inhibiting effect. Life/Dead staining revealed a reduction of biofilm viability of up to 64%. CFUs were reduced by 98% and qPCR demonstrated a mean inhibition of 87%. In contrast, materials containing CHX or triclosan showed an insignificant effect on biofilm formation, even at a 100fold increased concentration (0.2%). The anti-biofilm activity of composite material containing carolacton was stable over a period of 42 days.

Significance

Carolacton incorporated into dental filling material has a strong biofilm-inhibiting effect on S. mutans and is therefore potentially able to prevent secondary caries formation.     

Adjunctive application of chlorhexidine and ethanol-wet bonding on durability of bonds to sound and caries-affected dentine

Objectives

To examine the effect of adjunctive application of chlorhexidine (CHX) and ethanol-wet bonding (EWB) on bond durability and nanoleakage of hydrophobic adhesive to sound (SD) and caries-affected dentine (CAD).

Methods

Dentine surfaces of molars were etched after caries removal and randomly allocated to four groups (n = 12). In Groups 1 and 2, dentine surfaces were saturated with either 2 ml of 100% ethanol or 2 ml of ethanol with 2% CHX for 60 s. In Groups 3 and 4, dentine surfaces were saturated with either 15 μL of distilled water or 15 μL of distilled water with 2% CHX for 60 s. Two coats of primer, followed by neat resin were applied and light-cured for 40 s. Resin composite build-ups were placed and bonded specimens were sectioned for bond strength testing after 24 h and 12 months’ storage in artificial saliva. Bond strength data were analyzed using 3-way ANOVA and SNK tests. Interfacial nanoleakage was evaluated after 24 h and 12 months using a field-emission scanning electron microscopy and data were analyzed using Kruskal–Wallis test.

Results

Significant differences were observed for the three factors: “substrate” (p < 0.001), “rewetting agents” (p < 0.001) and “time” (p < 0.001) on bond strength. Incorporation of 2% CHX to EWB preserved bond strength to SD and CAD and reduced interfacial nanoleakage after 12 months. Incorporation of 2% CHX to WWB also preserved bond strength to SD after ageing.

Conclusions

Incorporation of chlorhexidine to ethanol-wet bonding has an interaction effect on preservation of bond durability to sound and caries-affected dentine.

Clinical significance

Incorporation of chlorhexidine to ethanol-wet bonding with hydrophobic adhesive enhances the success rate of aesthetic bonded restorations.     

The physical characteristics of resin composite–calcium silicate interface as part of a layered/laminate adhesive restoration

Objectives

To compare in-vitro micro-shear bond strengths (μSBS) of resin composite to calcium silicate cement (Biodentine™) vs. glass ionomer cement vs. resin modified glass ionomer cement (RM-GIC) using an adhesive in self-etch (SE)/total etch (TE) mode after aging three substrates and bond and characterizing their failure modes.

Methods

Resin composite was SE/TE bonded to 920 standardized disks of Biodentine™, GIC & RM-GIC. Dividing samples into two groups, the first underwent early (t = 0 min, 5 min, 20 min, 24 h) or delayed (t = 2 wk, 1 month, 3 months, 6 months) substrate aging before bonding and μSBS (t = 24 h) testing. In the second, adhesive was applied after either early (t = 5 min) or delayed (t = 2 wk) substrate aging and then tested after bond aging (t = 2 wk, 1 month, 3 months, 6 months). The failure modes were identified using stereomicroscope. SEM images of selected samples were analyzed.

Results

No significant differences were observed between (SE)/(TE) bonding modes (P = 0.42). With substrate aging, a significant reduction in μSBS occurred between early and delayed time intervals for Biodentine™ (P = 0.001), but none for the GIC/RM-GIC (P = 0.465, P = 0.512 respectively). With bond aging, there was no significant difference between time intervals for all groups, except at 6 months for the GIC (P < 0.05). Modes of failure were primarily cohesive within all the substrates (68.82%) followed by adhesive failure at the resin–substrate interface (21.71%).

Significance

Biodentine™ is a weak restorative material in its early setting phase. Placing the overlying resin composite as part of the laminate/layered definitive restoration is best delayed for >2 wk to allow sufficient intrinsic maturation to withstand contraction forces from the resin composite. A total-etch or self-etch adhesive may be used.     

A tentative model for d-glucose turnover in human saliva

Objective

The aim of the present study is to propose a tentative model for d-glucose turnover in human saliva. The whole saliva and the saliva from parotid and submandibular/sublingual glands were collected by use of the Salivette™.

Results

The saliva glucose concentration was measured by the hexokinase method, saliva bacteria glycolysis by use of d-[5-³H] glucose, and the saliva ATP content by the luciferase method. The concentration of glucose amounted to 43.9 ± 6.3 (n = 29), 197.5 ± 17.3 (n = 29), 104.0 ± 12.4 (n = 27) μM in whole saliva, parotid saliva and submandibular/sublingual saliva, respectively. The rate of d-glucose utilization by oral bacteria at a physiological concentration of d-glucose in saliva (50 μM) was estimated at 0.047 ± 0.003 (n = 11) nmol/min per 10⁶ bacteria. Unstimulated salivary d-glucose turnover rate, as calculated from the amount of glucose secreted in saliva which comes from parotid and submandibular and sublingual glands represented 214.6 ± 19.1%/min. In order for salivary d-glucose production to match bacterial utilization of the hexose, the total number of oral bacteria was estimated at about 2.0 × 10⁹ bacteria, in fair agreement with previously published data.

Conclusion

This study thus provides support for a tentative model for d-glucose turnover in human saliva.     

Bonding ability of 4-META self-etching primer used with 4-META/MMA-TBB resin to enamel and dentine: Primary vs permanent teeth

Objectives

The present study compared the efficacies of the self-etching Teeth Primer (TP: 4-META), and the etchants Red Activator (RA; 65% phosphoric acid) and Green Activator (GA; 10% citric acid with 3% ferric chloride), for bonding to enamel and dentine of human primary and permanent teeth, when used with 4-META/MMA-TBB resin (Bondfill SB).

Methods

Forty-eight non-carious primary canines and third molars were used. Eight groups were prepared: Group 1 (primary enamel with RA), Group 2 (permanent enamel with RA), Group 3 (primary enamel with TP), Group 4 (permanent enamel with TP), Group 5 (primary dentine with GA), Group 6 (permanent dentine with GA), Group 7 (primary dentine with TP) and Group 8 (permanent dentine with TP). Micro-tensile bond strengths (MTBS) were measured and analyzed statistically using ANOVAs and Tukey HSD tests at α = 0.05. Efficacy of etching/priming and the morphology of bonded interfaces were observed with SEM.

Results

Etching/priming efficacy of TP on enamel was low. The MTBS of Group 2 was significantly higher than the other groups (Groups 1, 3 and 4). For dentine, significant differences in MTBS were observed, in the order of Groups 6 > 8 > 7 = 5 (p < 0.05). The MTBSs of permanent dentine were significantly higher than primary dentine. For primary teeth, there was no significant difference in the MTBSs between enamel and dentine, irrespective of primer or etchant (p > 0.05).

Conclusion

TP primer/Bondfill SB may be used as an alternative to other adhesive/resin composite systems for bonding to enamel and dentine of primary teeth.     

Can 1% chlorhexidine diacetate and ethanol stabilize resin-dentin bonds?

Objectives

To examine the effects of the combined use of chlorhexidine and ethanol on the durability of resin-dentin bonds.

Methods

Forty-eight flat dentin surfaces were etched (32% phosphoric acid), rinsed (15 s) and kept wet until bonding procedures. Dentin surfaces were blot-dried with absorbent paper and re-wetted with water (water, control), 1% chlorhexidine diacetate in water (CHD/water), 100% ethanol (ethanol), or 1% chlorhexidine diacetate in ethanol (CHD/ethanol) solutions for 30 s. They were then bonded with All Bond 3 (AB3, Bisco) or Excite (EX, Ivoclar-Vivadent) using a smooth, continuous rubbing application (10 s), followed by 15 s gentle air stream to evaporate solvents. The adhesives were light-cured (20 s) and resin composite build-ups constructed for the microtensile method. Bonded beams were obtained and tested after 24-h, 6-months and 15-months of water storage at 37 °C. Storage water was changed every month. Effects of treatment and testing periods were analyzed (ANOVA, Holm–Sidak, p < 0.05) for each adhesive.

Results

There were no interactions between factors for both etch-and-rinse adhesives. AB3 was significantly affected only by storage (p = 0.003). Excite was significantly affected only by treatments (p = 0.048). AB3 treated either with ethanol or CHD/ethanol resulted in reduced bond strengths after 15 months. The use of CHD/ethanol resulted in higher bond strengths values for Excite.

Conclusions

Combined use of ethanol/1% chlorhexidine diacetate did not stabilize bond strengths after 15 months.     

Influence of glutaraldehyde priming on bond strength of an experimental adhesive system applied to wet and dry dentine

Objectives

This study tested the following null hypotheses: (1) there is no difference in resin–dentine bond strength when an experimental glutaraldehyde primer solution is added prior to bonding procedures and (2) there is no difference in resin–dentine bond strength when experimental glutaraldehyde/adhesive system is applied under dry or wet demineralized dentine conditions.

Methods

Extracted human maxillary third molars were selected. Flat, mid-coronal dentine was exposed for bonding and four groups were formed. Two groups were designated for the dry and two for the wet dentine technique: DRY: (1) Group GD: acid etching + glutaraldehyde primer (primer A) + HEMA/ethanol primer (primer B)-under dried dentine + unfilled resin; (2) Group D: the same as GD, except for primer A application; WET: (3) Group GW: the same as GD, but primer B was applied under wet dentine condition; (4) Group W: the same as GW, except for primer A application. The bonding resin was light-cured and a resin core was built up on the adhesive layer. Teeth were then prepared for microtensile bond testing to evaluate bond strength. The data obtained were submitted to ANOVA and Tukey's test (α = 0.05).

Results

Glutaraldehyde primer application significantly improved resin–dentine bond strength. No significant difference was observed when the same experimental adhesive system was applied under either dry or wet dentine conditions. These results allow the first null hypothesis to be rejected and the second to be accepted.

Conclusion

Glutaraldehyde may affect demineralized dentine properties leading to improved resin bonding to wet and dry substrates.