pH changes of self-etching primers mixed with powdered dentine

Properties of SiCN Films Relevant to Dental Implant Applications

The application of surface coatings is a popular technique to improve the performance of materials used for medical and dental implants. Ternary silicon carbon nitride (SiCN), obtained by introducing nitrogen into SiC, has attracted significant interest due to its potential advantages. This study investigated the properties of SiCN films deposited via PECVD for dental implant coatings. Chemical composition, optical, and tribological properties were analyzed by adjusting the gas flow rates of NH3, CH4, and SiH4. The results indicated that an increase in the NH3 flow rate led to higher deposition rates, scaling from 5.7 nm/min at an NH3 flow rate of 2 sccm to 7 nm/min at an NH3 flow rate of 8 sccm. Concurrently, the formation of N-Si bonds was observed. The films with a higher nitrogen content exhibited lower refractive indices, diminishing from 2.5 to 2.3 as the NH3 flow rate increased from 2 sccm to 8 sccm. The contact angle of SiCN films had minimal differences, while the corrosion rate was dependent on the pH of the environment. These findings contribute to a better understanding of the properties and potential applications of SiCN films for use in dental implants.

A self-etch bonding system with potential to eliminate selective etching and resist proteolytic degradation

OBJECTIVES

Bonded restorations using self-etch (SE) systems exhibit a limited lifespan due to their susceptibility to hydrolytic, enzymatic or fatigue degradation and poor performance on enamel. This study was conducted to develop and assess the performance of a two-step SE system using a functional monomer bis[2-(methacryloyloxy)ethyl]phosphate (BMEP) and demonstrate a strategy to enhance stability of bonded resin composite restorations to both enamel and dentine.

METHODS

A two-step SE system was formulated with a primer containing BMEP, with an adhesive with or without BMEP, and compared to a commercial 10-MDP-containing system, Clearfil^TM SE Bond 2 (CFSE). The systems were evaluated on enamel for surface roughness and microshear bond strength (µSBS) and on dentine for microtensile bond strength (µTBS), nanoleakage, MMP inhibition and cyclic flexural fatigue.

RESULTS

Whilst all bonding systems resulted in statistically similar µSBS, BMEP-based primers yielded greater enamel surface roughness than the CFSE primer. The BMEP-free adhesives resulted in statistically similar or higher µTBS and lower nanoleakage compared to CFSE. In situ zymography revealed minimal to no MMP activity within the hybrid layer of BMEP-based systems. The BMEP-free adhesive exhibited flexural strength and fatigue resistance statistically similar to CFSE.

CONCLUSIONS

Incorporation of BMEP in the primer led to satisfactory bond strengths with both enamel and dentine, potentially eliminating the need for selective enamel etching. Combined with an adhesive formulation that is solvent-free and hydrophobic, and confining the acidic functional monomer in the primer resulted in minimal interfacial leakage, and resistance to proteolytic degradation and the cyclic nature of chewing.

CLINICAL SIGNIFICANCE

The SE bonding system containing BMEP combines the potent etching of phosphoric acid with the therapeutic function of the phosphate-based monomer in creating a homogenous hybrid layer with protection against endogenous proteolytic enzymes. This strategy may overcome current challenges that arise during selective enamel etching.

Thirty-six-month follow-up of cervical composite restorations placed with an MDP-free universal adhesive system using different adhesive protocols: a randomized clinical trial

OBJECTIVES

To evaluate the influence of different application strategies on the clinical behavior of an MDP-free universal adhesive placed in non-carious cervical lesions (NCCLs) over the course of 36 months.

MATERIALS AND METHODS

Thirty-one patients participated in this study (N = 31). One hundred twenty-four restorations were assigned to four groups: We used the self-etch strategy on groups with (SE-et) and without (SET) selective enamel etching, and the etch-and-rinse strategy on groups with dry (ER-D) and moist (ER-M) dentin. After applying the MDP-free universal adhesive (Xeno Select universal adhesive, Dentsply Sirona), cavities were filled using EvoluX composite resin (Dentsply Sirona). The restorations were evaluated at baseline and after 36 months according to World Dental Federation (FDI) and US Public Health Service (USPHS) criteria. Friedman's repeated-measures analysis of variance rank (α = 0.05) was used for statistical analysis.

RESULTS

We evaluated the 31 patients after 36 months. Forty-two restorations were lost (ER-D = 5, ER-M = 7, SE-et = 14, SET = 16). The 36-month retention/fracture rates (95% confidence interval) were 83.9% for ER-D, 77.4% for ER-M, 54.9% for SE-et, and 48.4% for SET. ER strategy showed better retention rate than SE strategy (p < 0.05). Thirty-four restorations (ER-D = 6, ER-M = 10, SE-et = 10, SET = 8) showed marginal staining per FDI criteria and 15 restorations (ER-D = 1, ER-M = 2, SE-et = 6, SET = 6) showed marginal staining per USPHS criteria. No restorations showed postoperative sensitivity or recurrence of caries.

CONCLUSION

The retention rate of Xeno Select universal adhesive was poor, mainly in the self-etch strategy.

TRIAL REGISTRATION

REBEC clinical registry under protocol RBR-4wh4sh.

CLINICAL RELEVANCE

MDP-free universal adhesive behavior depends on the bonding strategy used.

Effects of Solvents and pH Values on the Chemical Affinity of 10-Methacryloyloxydecyl Dihydrogen Phosphate toward Hydroxyapatite

This study aimed to investigate the effects of solvents and pH values on the chemical interaction between 10-methacryloyloxydecyl dihydrogen phosphate (MDP) and hydroxyapatite (HAp). The chemical affinity of MDP toward HAp dissolved in different solvents (E-MDP: 10 wt % MDP and 90 wt % ethanol; E-W-MDP₁: 10 wt % MDP, 75 wt % ethanol, and 15 wt % water; A-W-MDP: 10 wt % MDP, 75 wt % acetone, and 15 wt % water; and E-W-MDP₂: 10 wt % MDP, 45 wt % ethanol, and 45 wt % water) was investigated. The pH of E-W-MDP₂ was increased from 2.04 to 5 (E-W-MDP_2/5) and to 7 (E-W-MDP_2/7). The reaction products were characterized by Fourier transform infrared spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), and nuclear magnetic resonance (NMR). XRD and NMR results revealed that no MDP-calcium salt formed in E-MDP. XRD, TGA, and XPS results indicated that MDP interacted with HAp, producing the MDP-calcium salt in all groups except E-MDP. NMR results revealed that the dicalcium salt of the MDP dimer (DCS-MD) and the MDP tripolymer (DCS-MT) and the monocalcium salt of the MDP monomer and the MDP dimer were formed in E-W-MDP₁. DCS-MD and DCS-MT were also formed in E-W-MDP₂ and A-W-MDP. In E-W-MDP_2/5 and E-W-MDP_2/7, DCS-MD was obtained. Both the solvents and pH values affect the chemical interactions between MDP and HAp and the types of reaction products formed. MDP and HAp do not form any MDP-calcium salt in pure ethanol; the structural stability of MDP-calcium salts is dependent on the solvent water content and the pH value. The ethanol/water mixture is recommended as the main solvent in an MDP-containing primer, and the ideal pH value is 2-7; if these conditions are satisfied, sufficient amounts of MDP-calcium salts with stable structures are expected to be formed, thus improving the longevity of dentin/enamel bonding.

Heating stability, physical and chemical analysis of calcium silicate-based endodontic sealers

AIM

To evaluate possible modifications in root canal sealers subjected to a variety of heating conditions using vibrational spectroscopy and analysis of physical and chemical properties.

METHODOLOGY

EndoSequence BC Sealer HiFlow, Bio-C Sealer, BioRoot RCS and AH Plus were analysed chemically using Raman spectroscopy (25-220 °C) and Fourier-transform infrared spectroscopy (FT-IR) (37-100 °C ). For FT-IR, the materials were tested individually and mixed with root dentine powder. Scanning electron microscopy (SEM) and coupled energy dispersive spectroscopy (EDS) were used to evaluate surface and chemical elements. ISO 6876-2012 and ASTM-C266-07 specifications were followed to evaluate flow, setting time (moist and dry), solubility and radiopacity. Also, pH analysis at 37 and 100 °C was performed. Shapiro-Wilk and Mixed ANOVA (within and between the effects of the subjects), Levene, and a post hoc analyses with Bonferroni correction were performed (P < 0.05).

RESULTS

Vibrational spectroscopy revealed peaks of tricalcium silicate, dicalcium silicate and zirconium dioxide. Chemical changes in the Raman spectra during heating were discrete, as the inorganic content predominated the signalling for all root canal sealers. FT-IR analysis exhibited spectral changes in water absorption for EndoSequence BC Sealer HiFlow and Bio-C Sealer, probably related to dehydration. For BioRoot RCS and AH Plus, no significant chemical changes were observed. Bio-C Sealer exhibited a band of polyethylene glycol only after heating to 100 °C, probably related to its thermal decomposition. SEM/EDS analysis corroborated the composition results observed in vibrational spectroscopy for all materials. Heating to 100 °C significantly changed the flowability of all calcium silicate-based sealers with a wide variation in setting times at both temperatures, along with solubility levels above ISO standards. For all tested sealers, radiopacity fulfilled the requirements, and pH exhibited alkaline values.

CONCLUSIONS

The tested calcium silicate-based sealers were affected by heating. Calcium silicate-based root canal sealers had high solubility which is a concern for their clinical use. AH Plus was the only root canal sealer that was stable after heating.

The ability of a nanobioglass-doped self-etching adhesive to re-mineralize and bond to artificially demineralized dentin

OBJECTIVE

To a self-etch adhesive doped with nano-bioglass and evaluate its ability to bond and re-mineralize artificially demineralized dentin.

METHODS

Experimental Si, Ca, Na and PO₄ based nanobioglass particles were synthesized, doped into experimental self-etch adhesives, and divided into 3 groups: Clearfi SE2 (CSE2), experimental (EXC), and experimental doped with 10% of nanobioglass (ExNB). The adhesives were applied onto the caries-affected dentin (chemically simulated), and evaluated after 24 h and 28 days of immersion in simulated body fluid. The remineralization process was assessed using optical coherence tomography, nanoindentation, in situ zymography, transmission electron microscopy, confocal laser scanning microscopy, μ-tensile bond strength, and pH buffer.

RESULTS

The addition of nanobioglass particles into the experimental self-etch adhesives altered the μTBS in the short-term jeopardizing dentin bonding properties, when compared to the non-doped self-etch adhesive. The remineralization recovered the nanohardness, and volume lost by caries lesion (p = 0.02). Moreover, reduced the enzymatic activity (p = 1.24^E-4) and formed new crystals within of the hybrid layer.

CONCLUSION

The use of nanobioglass was efficient to recover the properties of a caries affected dentin. Furthermore, the adhesive properties were not hampered and the probabilistic reliability increased.

Cytotoxicity of contemporary resin-based dental materials in contact with dentin

In this study, the cytotoxicity of different combinations of contemporary resin-based restoratives (adhesives, composites, luting agents) against human keratinocytes (HaCaT) was evaluated under two conditions, whether materials were applied to dentin or not. Adhesives (3-step etch-and-rinse/3ER: OptiBond FL; 2-step self-etch/2SE Clearfil SE Bond; Single Bond Universal/UNI), composites (conventional composite resin/CCR: Filtek Z350XT; flowable/FCR: Filtek Z350XT Flow; self-adhesive composite resin/SACR: Dyad Flow), and luting agents (conventional luting agent/CLA: Variolink-II; self-adhesive luting agent/SLA: RelyXU200) were combined according to their clinical use. Eluates from polymerized specimens applied to dentin were placed in contact with cells grown for 1 and 7 d. The controls were defined by cells without material contact. Cell viability was determined using MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide)] assay. C=C conversion was investigated using Fourier-transform infrared spectroscopy. After 1 d of incubation, when dentin was not present, 2SE yielded the highest cell viability, whereas 3ER, UNI, and SACR showed higher cell viability in the presence of dentin. After 7 d, when dentin was absent, 2SE and CLA achieved significantly higher cell viability. The presence of dentin resulted in a drastically higher cell viability for all materials, except 2SE and CLA. UNI had the lowest C=C conversion. The presence of dentin was a significant factor, which resulted in higher cell viability than what was seen for the material specimens per se. All materials resulted in a lower viability of HaCaT than what was seen under the no-material control conditions, with effects mainly limited to the first 24 h.

Atomic level observation and structural analysis of phosphoric-acid ester interaction at dentin

The functional monomer 10-methacryloyloxydecyl dihydrogen phosphate (10-MDP), used in many dental adhesives, self-assembles in nano-layers at adhesive-tooth interfaces. Recently, several states of the POH groups of 10-MDP_Ca salts were suggested, while their actual status has not been elucidated yet. We mechanistically investigated 10-MDP_Ca-salt nano-layering at adhesive-dentin interfaces, correlatively using scanning transmission electron microscopy with energy-dispersive X-ray spectrometry (STEM-EDS), X-ray diffraction (XRD) and solid state nuclear magnetic resonance (NMR). STEM-EDS confirmed the presence of Ca and P in each nano-layer. Both XRD and NMR revealed that the two terminal POH groups of 10-MDP reacted with Ca. This twofold POH interaction of 10-MDP with Ca was stable in water and is therefore expected to contribute to durable nano-layering of 10-MDP_Ca salts in the hybrid and adhesive layer. STATEMENT OF SIGNIFICANCE: The functional monomer 10-methacryloyloxydecyl dihydrogen phosphate (10-MDP), commonly used in dental adhesives with favorable long-term clinical outcome, has been documented to self-assemble into nano-layers at adhesive-tooth interfaces. Characterizing ultra-morphologically (STEM) and chemically (STEM-EDS, XRD, NMR) the mechanisms of interaction of 10-MDP with bulk dentin in a similar manner as what occurs clinically, it was found that the water stable 10-MDP_Ca salts consist of CaRPO₄, meaning that the two OH groups of the phosphate group of 10-MDP ionically reacted with Ca. This stable structure is expected to contribute to durable nano-layering of 10-MDP_Ca salts in the hybrid and adhesive layer and hence to clinical longevity of the adhesively bonded tooth restoration.

Etching Efficacy of Self-Etching Functional Monomers

Besides chemically interacting with hard tooth tissue, acidic functional monomers of self-etch adhesives should etch the prepared tooth surface to dissolve the smear layer and to provide surface micro-retention. Although the etching efficacy of functional monomers is commonly determined in terms of pH, the pH of adhesives cannot accurately be measured. Better is to measure the hydroxyapatite (HAp)-dissolving capacity, also considering that functional monomers may form monomer-Ca salts. Here, the etching efficacy of 6 functional monomers (GPDM, phenyl-P, MTEGP, 4-META, 6-MHP and 10-MDP) was investigated. Solutions containing 15 wt% monomer, 45 wt% ethanol, and 40 wt% water were prepared. Initially, we observed enamel surfaces exposed to monomer solution by scanning electron microscopy (SEM). X-ray diffraction (XRD) was employed to detect monomer-Ca salt formation. Phenyl-P exhibited a strong etching effect, while 10-MDP-treated enamel showed substance deposition, which was identified by XRD as 10-MDP-Ca salt. To confirm these SEM/XRD findings, we determined the etching efficacy of functional monomers by measuring both the concentration of Ca released from HAp using inductively coupled plasma-atomic emission spectroscopy (ICP-AES) and the amount of monomer-Ca salt formation using ³¹P magic-angle spinning (MAS) nuclear magnetic resonance (NMR). ICP-AES revealed that the highest Ca concentration was produced by phenyl-P and the lowest Ca concentration, almost equally, by 4-META and 10-MDP. Only 10-MDP formed 10-MDP-Ca salts, indicating that 10-MDP released more Ca from HAp than was measured by ICP-AES. Part of the released Ca was consumed to form 10-MDP-Ca salts. It is concluded that the repeatedly reported higher bonding effectiveness of 10-MDP-based adhesives must not only be attributed to the more intense chemical bonding of 10-MDP but also to its higher etching potential, a combination the other functional monomers investigated lack.

Six-month Follow-up of Cervical Composite Restorations Placed With a New Universal Adhesive System: A Randomized Clinical Trial

Purpose: The objective of this double-blind, randomized clinical trial was to evaluate the six-month clinical performance of a new universal adhesive (Xeno Select, Dentsply) in noncarious cervical lesions (NCCLs) using two evaluation criteria: World Dental Federation (FDI) and the US Public Health Service (USPHS).

Methods and Materials: A total of 124 restorations were randomly placed in 31 patients according to the following groups: ER-D = etch-and-rinse/dry dentin; ER-M = etch-and-rinse/moist dentin; SE-et = selective enamel etching; and SET = self-etch. The composite resin EVOLUX (Dentsply) was placed incrementally. The restorations were evaluated after one week (baseline) and at six months using the FDI and USPHS criteria. Statistical analyses were performed using appropriate tests (α=0.05).

Results: Fifteen restorations were lost or fractured at six months (one for ER-D, three for ER-M, five for SE-et, and six for SET) (p&gt;0.05 at six-month recall). When ER (ER-D and ER-M) was compared with SE (SE-et and SET) there was a significant difference in the retention rate after six months (p=0.001). Marginal staining and postoperative sensitivity to air were only observed in three (one for ER-M and two for SET) and two restorations (two for ER-D) in both evaluation criteria (p&gt;0.05), respectively. Forty-seven restorations were considered to have minor discrepancies in marginal adaptation at the six-month recall using the FDI criteria (13 for ER-D, 10 for ER-M, 11 for SE-et, and 13 for SET; p&gt;0.05 between groups). However, for all groups, a significant difference was detected when baseline and six-month data were compared (p&lt;0.05).

Conclusions: The six-month clinical behavior of Xeno Select Universal Adhesive depends on the bonding strategy used. The universal adhesive did not fulfill the American Dental Association criteria for full approval when used in the self-etch mode.

The effect of washing water temperature on resin-dentin micro-shear bond strength

BACKGROUND

The purpose of this study was to evaluate the effect of washing water temperature on the micro-shear bond strength (μSBS) of composite resin to dentin using a two-step etch-and-rinse system and a two-step self-etching system.

MATERIALS AND METHODS

In this in vitro study, the intact dentins of buccal and lingual surfaces of healthy third molars were exposed. Dentin surfaces were rinsed with different temperatures of distilled water (20 s) before applying Single Bond (SB) or Clearfil SE Bond(SE). After applying the adhesive, composite cylinders (0.8 mm diameter and 1 mm length) were bonded to the teeth surfaces. After storing the specimens in 37°C distilled water for 48 h and thermocycling, μSBS test was done. Data were analyzed using analysis of variance, post hoc Tukey tests, paired samples t-test, and Fisher exact test (α = 0.05).

RESULTS

Temperature and interaction of temperature and type of bonding agent affected the bond strength. The bond strength of SB groups was significantly higher at 50°C washing than 5°C (P = 0.003) and 22°C (P = 0.019), but no significant difference was observed between SE groups. The bond strength of SE was significantly higher at 22°C than that of SB (P = 0.031), whereas the bond strength of SB was significantly higher at 50°C than that of SE (P = 0.007).

CONCLUSION

The use of high-temperature washing water is an appropriate method to enhance bond strength in etch-and-rinse systems.

Interference of functional monomers with polymerization efficiency of adhesives

The degree of conversion (DC) of camphorquinone/amine-based adhesives is affected by acidic functional monomers as a result of inactivation of the amine co-initiator through an acid-base reaction. During bonding, functional monomers of self-etch adhesives chemically interact with hydroxyapatite (HAp). Here, we tested in how far the latter interaction of functional monomers with HAp counteracts the expected reduction in DC of camphorquinone/amine-based adhesives. The DC of three experimental adhesive formulations, containing either of the two functional monomers [10-methacryloyloxydecyl dihydrogen phosphate (10-MDP) or 4-methacryloxyethyl trimellitic acid anhydride (4-META)] or no functional monomer (no-FM; control), was measured with and without HAp powder added to the adhesive formulations. Both the variables 'functional monomer' and 'HAp' were found to be significant, with the functional monomer reducing the DC and HAp counteracting this effect. It is concluded that the functional monomers 10-MDP and 4-META interfere with the polymerization efficiency of adhesives. This interference is less prominent in the presence of HAp, which would clinically correspond to when these two functional monomers of the adhesive simultaneously interact with HAp in tooth tissue.

Evaluation of Bond Strength of Self-Etching Adhesives Having Different pH on Primary and Permanent Teeth Dentin

Purpose

The purpose of this in vitro study was to evaluate the dentin shear bond strength of 4 self-etching adhesives having a different pH on primary and permanent teeth dentin.

Methods

The occlusal enamel was removed from 60 freshly extracted third molar and 60 primary second molar human teeth, which were randomly separated into 4 groups (n = 15). Four adhesive systems were applied: G-Bond (GC Corporation, Tokyo, Japan, pH: 1.5), Futura Bond M (Voco, Cuxhaver, Germany, pH: 1.4), Adper Prompt L-Pop (3M/ESPE, St Paul, MN, USA, pH: 0.8), and Clearfil S3 Bond (Kuraray Medical, Tokyo, Japan, pH: 2.7) according to the manufacturer's instructions. After the application of dentin bonding agents, a composite resin material (Z250 Restorative A2, 3M ESPE, St. Paul, MN, USA) for permanent teeth and a compomer resin material (Dyract Extra A2, Dentsply, Konstanz, Germany) for primary teeth was applied onto the prepared dentin surfaces. The data were obtained by using a universal test machine at a crosshead speed of 1 mm/min.

Results

The mean values were compared using Tukey's multiple comparison test. Although there was no difference between adhesives on the permanent teeth, Clearfil S3 adhesive showed higher bond (18.07 ± 0.58 MPa) ( P>0.05). Lower bond strength values were obtained from primary teeth and especially G-Bond adhesive (9.36 ± 0.48 MPa) ( P<0.05).

Conclusions

Self-etching adhesives with different pH and solvent types can be used successfully for permanent teeth dentin but adhesives with low pH did not provide greater shear bond strength values.

Influence of powdered dentin on the shear bond strength of dentin bonding systems

This study evaluated the effect of different amounts of dentin powder (DP) mixed in Clearfil SE Bond (CSB) or Single Bond (SB) on adhesion to dentin. Human third molars (n=96) were sectioned to expose the mid-coronal dentin and divided into eight experimental groups (n=12 per group), namely, Group 1: CSB, Group 2: CSB+1.5 mg DP, Group 3: CSB+3 mg DP, Group 4: CSB+4.5 mg DP, Group 5: SB, Group 6: SB+1.5 mg DP, Group 7: SB+3 mg DP, and Group 8: SB+4.5 mg DP. Filtek Z250 composite was bonded onto dentin, and all specimens were subjected to shear bond strength test at a crosshead speed of 1 mm/min. Highest bond strength was obtained in Groups 1, 2, and 3 (15.1, 13.5, and 16.4 MPa respectively; p>0.05) and the lowest in Groups 6, 7, and 8 (5.5, 5.6, 4 MPa; p>0.05). DP addition, regardless of amount, adversely affected the bond strength of SB. Bond strength of CSB was not affected when 1.5 or 3 mg of DP was added.

Distinct photopolymerization efficacy on dentin of self-etch adhesives

The effect of application mode on polymerization effectiveness of self-etch adhesives with different pHs has rarely been studied. We applied 2 self-etch adhesives-Adper Prompt L-Pop (APLP, pH ~ 0.8) and Adper Easy-Bond (AEB, pH ~ 2.5)-to dentin with or without agitation (dynamic or static application), to investigate photopolymerization efficacy on dentin, and to understand the role of chemical interaction/reaction between adhesives and dentin. Micro-Raman spectra and imaging were acquired across the dentin/adhesive (D/A) interface. The degree of conversion (DC) of each adhesive as a function of position was calculated. SEM-EDS was used to obtain the elemental distribution along the interface. Photopolymerization efficacies of the two self-etch adhesives on dentin were apparently different. APLP exhibited decreasing DCs as the distance from the D/A interface became greater for both application modes, while the DCs for the dynamic mode were much higher than those for the static mode. As for AEB, the DCs remained almost constant across the adhesive layer and showed no significant difference between two modes. Raman spectral analysis disclosed that the chemical interaction between dentin and adhesives was responsible for the observations. We also verified this by tracking the distribution of the elements Ca and P in the adhesive layers.

Hydroxyapatite effect on photopolymerization of self-etching adhesives with different aggressiveness

OBJECTIVE

To understand the correlation of the acidic monomer/hydroxyapatite (HAp) reaction with the photopolymerization behaviour of self-etching adhesives with different aggressiveness.

METHODS

Two commercial self-etching adhesives the strong Adper Prompt L-Pop (APLP, pH ~ 0.8) and the mild Adper Easy Bond (AEB, pH ~ 2.5) were used. HAp powders were incorporated into both adhesives to acquire solutions with concentrations of 0, 1, 3, 5, 7 wt%. The attenuated total reflectance Fourier transform infrared (ATR/FT-IR) technique was employed to collect the in situ spectra during light-curing, from which the degree of conversion (DC) and polymerization rate (PR) were calculated. The pH of each tested solution was also measured.

RESULTS

Without HAp incorporation, the DC and PR of the strong APLP (7.8% and 0.12%/s, respectively) were much lower than those of the mild AEB (85.5% and 5.7%/s, respectively). The DC and PR of APLP displayed an apparent increasing trend with the HAp content. For example, the DC increased from 7.8% to 58.4% and the PR increased from 0.12 to 3.8%/s when the HAp content increased from 0 to 7 wt%. In contrast, the DC and PR of AEB were much less affected by the HAp content. The observations were correlated well with the spectral and pH changes, which indicated that APLP underwent a higher extent of chemical reaction with HAp than AEB.

CONCLUSIONS

The results disclosed the important role of the acidic monomer/HAp chemical reaction in improving the photopolymerization of the strong (low-pH) self-etching adhesives such as APLP. The phenomenon of polymerization improvement strongly depended on the adhesive aggressiveness.

Influence of oxygen inhibition on the surface free energy and enamel bond strength of self-etch adhesives

We compared the surface free energies and enamel bond strengths of single-step self-etch adhesives with and without an oxygen-inhibited layer. The adhesives were applied to the enamel surfaces of bovine incisors, light irradiated, and the oxygen-inhibited layer was either retained or removed with ethanol. The surface free energies and their components (γ(S)(LW), γ(S)(+), and γ(S)(-)) were determined by measuring the contact angles of three test liquids placed on the cured adhesives. The enamel bond strengths of specimens with and without the oxygen-inhibited layer were measured. For all surfaces, the value of the estimated surface tension component γ(S)(LW) was relatively constant. The value of the γ(S)(+) component increased slightly when the oxygen-inhibited layer was removed, whereas that of the γ(S)(-) component decreased significantly. The enamel bond strengths of the self-etch adhesives were significantly lower in the specimens without an oxygen-inhibited layer. The oxygen-inhibited layer therefore appeared to promote higher enamel bond strength.

The effect of hydroxyapatite presence on the degree of conversion and polymerization rate in a model self-etching adhesive

OBJECTIVE

The effect of hydroxyapatite (HAp) content on photopolymerization of a model self-etching adhesive was studied by using attenuated total reflectance Fourier transform infrared (ATR/FT-IR) spectroscopy.

MATERIALS AND METHODS

The model adhesive contained two monomers: bis[2-(methacryloyloxy)ethyl] phosphate (2MP) and 2-hydroxyethyl methacrylate (HEMA) using a 1:1 mass ratio, representing an acidic formulation. Camphorquinone and ethyl 4-dimethylaminobenzoate were added to enable visible light photopolymerization in a constant concentration of 0.022 mmol per gram monomer. HAp [Ca(10)(OH)(2)(PO(4))(6)] powder were added to the test solutions to obtain mass fraction of 0, 1, 2, 3, and 4 wt%. The degree of conversion (DC) and the polymerization rate (PR) with/without HAp were determined using ATR/FT-IR with a time-based spectrum analysis.

RESULTS

Monomer DC and PR were significantly enhanced by addition of HAp. Incorporation of 4 wt% of HAp increased DC from 20.8 (±0.3) % to 93.4 (±1.1) %, and PR from 0.42 (±0.01) %/s to 3.21 (±0.07) %/s. The pH of adhesive solutions was measured and correlated with DC and PR. The pH of test solutions was also controlled using a base (sodium hydroxide, NaOH) to similar values as when using HAp. Results indicated that both the DC and PR increased with increasing pH, regardless of additive, confirming the role of pH on polymerization. From the IR spectral comparison, changes in molecular structures of the self-etching adhesive after the addition of HAp were observed, which were correlated with the specific interaction between 2MP and HAp. The effect of viscosity was also proposed to be another possible reason for the improved polymerization.

SIGNIFICANCE

The photopolymerization of a self-etching adhesive was enhanced/accelerated in the presence of HAp. The results provide the critical information for understanding the interactions/bonding between self-etching adhesives and tooth substrates.

Influence of oxygen inhibition on the surface free-energy and dentin bond strength of self-etch adhesives

We compared the surface free-energies and dentin bond strengths of single-step self-etch adhesives with and without an oxygen-inhibited layer. The labial dentin surfaces of bovine mandibular incisors were wet ground with #600-grit silicon carbide paper. The adhesives were applied to the ground dentin, light-irradiated, and the oxygen-inhibited layer was either retained or removed with ethanol. The surface free-energies were determined by measuring the contact angles of three test liquids placed on the cured adhesives. The dentin bond strengths of specimens with and without the oxygen-inhibited layer were measured. For all surfaces, the value of the estimated surface tension component was relatively constant at 35.5-39.8 mJ m(-2) . The value of the , Lewis acid component increased slightly when the oxygen-inhibited layer was removed, whereas that of the , Lewis base component decreased significantly. The bond strengths of the self-etch adhesives were significantly lower in specimens without an oxygen-inhibited layer (13.2-13.6 MPa) than in those with an oxygen-inhibited layer (17.5-18.4 MPa). These results indicate that the presence of an oxygen-inhibited layer in single-step self-etch adhesives with advanced photoinitiators promotes higher dentin bond strength.

Effect of 3-year water storage on the performance of one-step self-etch adhesives applied actively on dentine

OBJECTIVES

To evaluate the effect of the application method on the immediate and 3-year resin-dentine bond strength (μTBS) and nanoleakage (NL) for 3 one-step self-etch adhesives (Adper Prompt L-Pop; Clearfil S(3) Bond and Xeno III).

METHODS

The occlusal enamel of 42 human molars were removed to expose a flat dentine surface. The adhesives were applied under inactive or active application. After light-curing (600mW/cm(2) for 10s), composite buildups were constructed incrementally and sectioned to obtain bonded sticks (0.8mm(2)) to be tested in tension immediately or after 3 years of water storage of water storage. For NL, 2 bonded sticks from each tooth at each time were coated with nail varnish, placed in silver nitrate and polished down with SiC paper. The μTBS data was submitted to a two-way repetead mesures ANOVA and Tukey's test for each adhesive (α=0.05).

RESULTS

The active application showed higher immediate and 3-year μTBS than the inactive application (p<0.05). An increase in the silver nitrate deposition was seen for all conditions after 3 years; however this was more pronounced for all materials under inactive application (p<0.05).

CONCLUSIONS

The active application improves the immediate bonding performance of the adhesive systems. Reductions of the bond strength were observed for all materials after 3 years, however reduced degradation rate was observed when the materials are applied actively in dentine.

An all-in-one adhesive does not etch beyond hybrid layers

Continuous etching of aggressive all-in-one adhesives occurs in wet dentin tubules after polymerization of the adhesives. This study challenged the hypothesis that unpolymerized acidic monomers from an aggressive all-in-one self-etching adhesive continue to etch beyond dentin hybrid layers. Dentin surfaces bonded with Adper Prompt L-Pop were sectioned into 0.3-mm-thick slabs. Some of the slabs were stored in water (pH 6.8) or glycine buffer (pH 11.1) for six weeks and then examined by CLSM, SEM, and TEM. The rest were immersed in a biomimetic remineralizing medium for up to 4 months. Morphologic analysis indicated no difference in demineralization thickness between the two 6-week storage groups. However, increased permeability and loss of integrity occurred along the base of the hybrid layers in the glycine buffer group, but not in the water storage group. These findings were also confirmed by the results of biomimetic remineralization along the bases of those hybrid layers.