Promotion of adhesive penetration and resin bond strength to dentin using non‐thermal atmospheric pressure plasma

Non‐thermal atmospheric pressure plasmas (NT‐APPs) have been shown to improve the bond strength of resin composites to demineralized dentin surfaces. Based on a wet‐bonding philosophy, it is believed that a rewetting procedure is necessary after treatment with NT‐APP because of its air‐drying effect. This study investigated the effect of ‘plasma‐drying’ on the bond strength of an etch‐and‐rinse adhesive to dentin by comparison with the wet‐bonding technique. Dentin surfaces of human third molars were acid‐etched and divided into four groups according to the adhesion procedure: wet bonding, plasma‐drying, plasma‐drying/rewetting, and dry bonding. In plasma treatment groups, the demineralized dentin surfaces were treated with a plasma plume generated using a pencil‐type low‐power plasma torch. After the adhesion procedures, resin composite/dentin‐bonded specimens were subjected to a microtensile bond‐strength test. The hybrid layer formation was characterized by micro‐Raman spectroscopy and scanning electron microscopy. The plasma‐drying group presented significantly higher bond strength than the wet‐bonding and dry‐bonding groups. Micro‐Raman spectral analysis indicated that plasma‐drying improved the penetration and polymerization efficacy of the adhesive. Plasma‐drying could be a promising method to control the moisture of demineralized dentin surfaces and improve the penetration of adhesive and the mechanical property of the adhesive/dentin interface.     

Effects of non‐thermal atmospheric pressure pulsed plasma on the adhesion and durability of resin composite to dentin

This study investigated the effect of low‐power, non‐thermal atmospheric pressure plasma (NT‐APP) treatments, in pulsed and conventional modes, on the adhesion of resin composite to dentin and on the durability of the bond between resin composite and dentin. A pencil‐type NT‐APP jet was applied in pulsed and conventional modes to acid‐etched dentin. The microtensile bond strength (MTBS) of resin composite to dentin was evaluated at 24 h and after thermocycling in one control group (no plasma) and in two experimental groups (pulsed plasma and conventional plasma groups) using the Scotchbond Multi‐Purpose Plus Adhesive System. Data were analyzed using two‐factor repeated‐measures anova and Weibull statistics. Fractured surfaces and the bonded interfaces were evaluated using a field‐emission scanning electron microscope. Although there were no significant differences between the plasma treatment groups, the plasma treatment improved the MTBS compared with the control group. After thermocycling, the MTBS did not decrease in the control or conventional plasma group but increased in the pulsed plasma group. Thermocycling increased the Weibull moduli of plasma‐treated groups. In conclusion, plasma treatment using NT‐APP improved the adhesion of resin composite to dentin. Using a pulsed energy source, the energy delivered to the dentin was effectively reduced without any reduction in bond strength or durability.     

Relationship between enamel bond fatigue durability and surface free‐energy characteristics with universal adhesives

The relationship between enamel bond fatigue durability and surface free‐energy characteristics with universal adhesives was investigated. The initial shear bond strengths and shear fatigue strengths of five universal adhesives to enamel were determined with and without phosphoric acid pre‐etching. The surface free‐energy characteristics of adhesive‐treated enamel with and without pre‐etching were also determined. The initial shear bond strength and shear fatigue strength of universal adhesive to pre‐etched enamel were higher than those to ground enamel. The initial shear bond strength and shear fatigue strength of universal adhesive to pre‐etched enamel were material dependent, unlike those to ground enamel. The surface free‐energy of the solid (γ_S) and the hydrogen‐bonding force () of universal adhesive‐treated enamel were different depending on the adhesive, regardless of the presence or absence of pre‐etching. The bond fatigue durability of universal adhesives was higher to pre‐etched enamel than to ground enamel. In addition, the bond fatigue durability to pre‐etched enamel was material dependent, unlike that to ground enamel. The surface free‐energy characteristics of universal adhesive‐treated enamel were influenced by the adhesive type, regardless of the presence or absence of pre‐etching. The surface free‐energy characteristics of universal adhesive‐treated enamel were related to the results of the bond fatigue durability.     

Glutaraldehyde collagen cross‐linking stabilizes resin–dentin interfaces and reduces bond degradation

This study evaluated the stability of resin–dentin interfaces treated with glutaraldehyde‐containing agents, and assessed collagen degradation in dentin matrices treated with Gluma. Microtensile bond strength (μTBS) was evaluated 24 h and 6 months after treatment with three desensitizers (Gluma Desensitizer, Gluma Desensitizer Power Gel, and MicroPrime G) and two etch‐and‐rinse adhesives (Comfort Bond & Desensitizer and iBond TE). Demineralized beams of human dentin were treated with water or Gluma, and the degradation of collagen in these beams was assessed by quantification of the dry mass loss and of the amount of hydroxyproline released from hydrolyzed specimens after 1 or 4 wk. All groups demonstrated significant reduction in μTBS after 6 months, except for Gluma Desensitizer and iBond TE groups, which showed decreases of 7.2% and 10.8%, respectively. The most prevalent failure mode was ‘mixed’. Significantly less hydroxyproline was released from Gluma‐treated beams than from control beams after 4 wk. Beams treated with Gluma yielded significantly less dry mass loss than did beams in the control group. Collagen cross‐linking with glutaraldehyde‐containing agents may assist in the stabilization of resin–dentin bonds by reducing the amount of collagen solubilized from dental matrices in the hybrid layer. In turn, this may contribute to the preservation of adhesive interfaces.     

Effect of final irrigation protocols on push‐out bond strength of an epoxy resin root canal sealer to dentin

The purpose of the present study was to evaluate the effect of different final irrigation protocols on push‐out bond strength of an epoxy resin root canal sealer to dentin. Eighty single‐rooted anterior teeth were used. The root canals were partially prepared using a rotary system and the final diameter was standardised using a #5 Gates‐Glidden drill prior to the push‐out bond test. During chemomechanical preparation, 5.25% NaOCl or 2% CHX gel was used. For smear layer removal, 17% ethylenediaminetetraacetic acid (EDTA) or QMix 2 in 1 was applied for 3 min. As final irrigant, 1 mL of NaOCl, CHX solution or distilled water was used. On conclusion of preparation, canals were filled with gutta‐percha/AH Plus sealer. Bond strength was measured by the push‐out test. Data were statistically analysed by Kruskal–Wallis and Mann–Whitney U‐tests. The group NaOCl/EDTA/NaOCl showed significantly higher bond strength values than other groups. In all groups, there were mainly mixed failure patterns. It can be concluded that 5.25% NaOCl proved to be the best solution for the final irrigation when combined with EDTA. The final irrigation protocols affect the push‐out bond strength of AH Plus to dentin.     

Effect of non‐thermal atmospheric plasma on the dentin‐surface topography and composition and on the bond strength of a universal adhesive

This study investigated the effect of application of non‐thermal atmospheric plasma (NTAP) on the topography and composition of the dentin surface, as well as the microtensile bond strength (μTBS) of a universal adhesive to NTAP‐treated dentin. Exposed flat dentin surfaces from human third molars were either treated with NTAP for 10 and 30 s or untreated (control). The dentin‐surface topography and chemical composition were characterized by atomic force microscopy (n = 3) and Raman confocal spectroscopy (n = 5), respectively. The μTBS (n = 8) of Scotchbond Universal to dentin was determined after storage for 24 h and 1 yr, either by direct water exposure or under simulated pulpal pressure. In‐situ zymography was used to evaluate the influence of NTAP on the dentin‐enzymatic activity. Non‐thermal atmospheric plasma produced no remarkable topographical or chemical alterations at the dentin surface; only the amount of phosphate decreased following 10 s of treatment with NTAP. After 1 yr of direct water exposure, the μTBS of NTAP‐treated specimens did not differ statistically significantly from that of untreated controls, whereas simulated pulpal pressure‐aging resulted in a significantly higher μTBS for NTAP‐treated dentin. The dentin‐enzymatic activity appeared to be treatment‐dependent, but the untreated controls showed more intense fluorescence within the hybrid layer. Scotchbond Universal maintained its μTBS strength after 1 yr of direct water exposure and simulated pulpal pressure, although remarkable statistical differences between treatments were observed depending on the aging condition.     

Dentin surface treatment using a non‐thermal argon plasma brush for interfacial bonding improvement in composite restoration

Ritts AC, Li H, Yu Q, Xu C, Yao X, Hong L, Wang Y. Dentin surface treatment using a non‐thermal argon plasma brush for interfacial bonding improvement in composite restoration.
Eur J Oral Sci 2010; 118: 510–516. © 2010 Eur J Oral Sci The objective of this study was to investigate the treatment effects of non‐thermal atmospheric gas plasmas on dentin surfaces used for composite restoration. Extracted unerupted human third molars were prepared by removing the crowns and etching the exposed dentin surfaces with 35% phosphoric acid gel. The dentin surfaces were treated using a non‐thermal atmospheric argon plasma brush for various periods of time. The molecular changes of the dentin surfaces were analyzed using Fourier transform infrared spectrophotometry/attenuated total reflectance (FTIR/ATR), and an increase in the amount of carbonyl groups was detected on plasma‐treated dentin surfaces. Adper Single Bond Plus adhesive and Filtek Z250 dental composite were applied as directed. To evaluate the dentin/composite interfacial bonding, the teeth thus prepared were sectioned into micro‐bars and analyzed using tensile testing. Student–Newman–Keuls tests showed that the bonding strength of the composite restoration to peripheral dentin was significantly increased (by 64%) after 30 s of plasma treatment. However, the bonding strength to plasma‐treated inner dentin did not show any improvement. It was found that plasma treatment of the peripheral dentin surface for up to 100 s resulted in an increase in the interfacial bonding strength, while prolonged plasma treatment of dentin surfaces (e.g. 5 min) resulted in a decrease in the interfacial bonding strength.     

Changes in surface characteristics of titanium and zirconia after surface treatment with ultraviolet light or non‐thermal plasma

Positive effects of irradiation with ultraviolet (UV) light or treatment with non‐thermal plasma on titanium and zirconia surfaces have been described in various studies. The aim of this study was to assess and compare the changes in the physicochemical surface conditions of titanium and zirconia surfaces after a short treatment with UV light or with non‐thermal plasmas of argon or oxygen. Titanium and zirconia samples with moderately rough surfaces were treated for 12 min either in a UV‐light oven or in a non‐thermal plasma reactor that generates non‐thermal plasmas of oxygen or argon. Changes in surface conditions were assessed by confocal microscopy, dynamic contact angle measurement, and X‐ray photoelectron spectroscopy (XPS). No changes in roughness occurred. Ultraviolet irradiation and non‐thermal plasma significantly increased the wettability of the titanium and zirconia surfaces. X‐ray photoelectron spectroscopy showed an increase of oxygen and a significant decrease of carbon after treatment with either method. Thus, ultraviolet light and non‐thermal plasma were found to be able to improve the chemical surface conditions of titanium and zirconia following a short exposure time. However, further in vitro and in vivo studies are needed to determine the relevance of the results.     

Effects of moisture degree and rubbing action on the immediate resin–dentin bond strength

OBJECTIVES: To compare the effects of moisture and rubbing action on the microtensile bond strength (BS) of an ethanol/water-based (Single Bond [SB]) and an acetone-based system (One-Step [OS]) to dentin. METHODS: On 60 human molars, a flat superficial dentin surface was exposed by wet abrasion. Two coats of the adhesives were applied on either a dry (D) or rewetted surface (W), under no rubbing action (NRA), slight (SRA) or vigorous rubbing action (VRA). After light curing (600 mW/cm2/10 s), composite build-ups were constructed incrementally and specimens were stored in water (37 degrees C/24 h). They were longitudinally sectioned in the "x" and "y" directions to obtain bonded sticks (0.8 mm2) to be tested in tension at 0.5 mm/min. Resultant BS was expressed as an index that includes bond strength values of the different fracture patterns and the specimens that failed during preparation for testing. The data were analyzed by a three-way ANOVA and Tukey's multiple comparison tests (95%). RESULTS: The interactions moisture/agitation and adhesive/agitation were statistically significant (p < 0.05). In D groups, the highest BS was obtained under VRA (37.11 +/- 7.3). In W groups, the BS at SRA (41.82 +/- 8.4) and VRA (38.89 +/- 8.2) were similar. For SB system, the SRA (33.6 +/- 8.3) and VRA groups (41.26 +/- 5.9) yielded similar BS while for OS the VRA was essential to reach high BS (34.2 +/- 8.4). SIGNIFICANCE: High BS to dentin can be obtained, under dry conditions, when ethanol/water and acetone-based systems, are vigorously agitated in the surface. On wet dentin, slight agitation seems to be enough to provide high BS to dentin.     

Effect of different protocols of eugenol removal on the bond strength between the fibre post and root dentin

The aim of this study was to evaluate the bond strength between the fibre post and root dentin after different cleaning protocols to remove eugenol from dentin. The residues and elemental composition of dentin were analysed using SEM and EDS. Bovine incisor roots were obturated with eugenol‐based sealer. The post space was prepared, and the roots were divided into the following groups according to the cleaning protocol: unfilled (negative control), saline solution (positive control), 70% ethanol, acetone and 70% isopropyl alcohol. The fibre posts were cemented and push‐out test realised. Chemical analysis of the dentin was performed using SEM and EDS. The bond strength values were analysed by anova /Fisher's and were as follows: negative control (7.30 ± 2.77) = 70% ethanol (6.64 ± 2.91) = 70% isopropyl alcohol (5.01 ± 3.15) = acetone (4.42 ± 1.53) >positive control (1.29 ± 0.56). It was concluded that 70% ethanol may be a good cleaning protocol to remove eugenol from dentin.     

Influence of chlorhexidine digluconate concentration and application time on resin–dentin bond strength durability

Although it is known that chlorhexidine application may preserve resin–dentin bonds from degradation, the lowest optimal concentration and application time have yet to be established. This study evaluated the effects of different concentrations of chlorhexidine digluconate and different application times on the preservation of resin–dentin bonds formed using two etch-and-rinse adhesives. In experiment 1, after acid etching, the occlusal demineralized dentin was rewetted either with water or with 0.002, 0.02, 0.2, 2, or 4% chlorhexidine for 60 s. In experiment 2, the surfaces were rewetted with water, or with 0.002% or 2% chlorhexidine for 15 or 60 s. After this, both adhesives and composite resin were applied and light-cured. Bonded sticks (0.8 mm²) were tested under tension (0.5 mm min⁻¹) immediately or after 6 months of storage in water. Two bonded sticks from each tooth were immersed in silver nitrate and analyzed quantitatively using scanning electron microscopy. Reductions in microtensile bond strengths and higher silver nitrate uptake were observed for both adhesives when the rewetting procedure was performed with water. Stable bonds were maintained for up to 6 months under all chlorhexidine conditions tested, irrespective of the chlorhexidine concentration and application time. The use of 0.002% chlorhexidine for 15 s seems to be sufficient to preserve resin–dentin interfaces over a 6-month period.     

Effect of desensitizing agents on the microtensile bond strength of two‐step etch‐and‐rinse adhesives to dentin

Desensitizers can be used to control postoperative sensitivity in adhesive restorations. The aim of this study was to evaluate the effect of desensitizing agents on the bond strength of two‐step etch‐and‐rinse adhesive systems to dentin. Forty‐two human molars were sectioned to obtain 3‐mm‐thick dentin discs. The discs were divided into three groups (n = 14 in each) – no‐treatment control group (CT), and oxalic acid [BisBlock (BB)] and calcium phosphate [Desensibilize Nano‐P (NP)] desensitizers – before the application of two adhesive systems [Adper Single Bond Plus (SB) and One‐Step Plus (OSP)]. A nanoparticle composite resin was used to create a 3‐mm‐thick build‐up. The specimens were stored in distilled water for 24 h before a microtensile bond‐strength test was performed. The failure modes were determined using a stereomicroscope at 100 × magnification. Specimens were sectioned perpendicular to the interface for scanning electron microscopy analyses. The CT‐SB group exhibited the highest bond strength, differing significantly from BB‐SB and BB‐OSP groups. Mixed failures were prevalent for all groups. Scanning electron microscopy revealed a continuous hybrid layer and resin tags in all groups. Dentin bond strength of etch‐and‐rinse adhesive systems was reduced by an oxalic acid desensitizer but was not affected by a calcium phosphate‐containing desensitizer.     

Temporary zinc oxide–eugenol cement: eugenol quantity in dentin and bond strength of resin composite

Uptake of eugenol from eugenol‐containing temporary materials may reduce the adhesion of subsequent resin‐based restorations. This study investigated the effect of duration of exposure to zinc oxide–eugenol (ZOE) cement on the quantity of eugenol retained in dentin and on the microtensile bond strength (μTBS) of the resin composite. The ZOE cement (IRM Caps) was applied onto the dentin of human molars (21 per group) for 1, 7, or 28 d. One half of each molar was used to determine the quantity of eugenol (by spectrofluorimetry) and the other half was used for μTBS testing. The ZOE‐exposed dentin was treated with either OptiBond FL using phosphoric acid (H₃PO₄) or with Gluma Classic using ethylenediaminetetraacetic acid (EDTA) conditioning. One group without conditioning (for eugenol quantity) and two groups not exposed to ZOE (for eugenol quantity and μTBS testing) served as controls. The quantity of eugenol ranged between 0.33 and 2.9 nmol mg^?1 of dentin (median values). No effect of the duration of exposure to ZOE was found. Conditioning with H₃PO₄ or EDTA significantly reduced the quantity of eugenol in dentin. Nevertheless, for OptiBond FL, exposure to ZOE significantly decreased the μTBS, regardless of the duration of exposure. For Gluma Classic, the μTBS decreased after exposure to ZOE for 7 and 28 d. OptiBond FL yielded a significantly higher μTBS than did Gluma Classic. Thus, ZOE should be avoided in cavities later to be restored with resin‐based materials.     

Evaluation of plasma treatment effects on improving adhesive–dentin bonding by using the same tooth controls and varying cross‐sectional surface areas

The objective of this study was to evaluate and verify the effectiveness of plasma treatment for improving adhesive–dentin interfacial bonding by performing microtensile bond‐strength (μTBS) testing using the same‐tooth controls and varying cross‐sectional surface areas. Extracted unerupted human third molars were used after removal of the crowns to expose the dentin surface. One half of each dentin surface was treated with a non‐thermal argon plasma brush, whilst the other was shielded with glass slide and used as an untreated control. Adper Single Bond Plus adhesive and Filtek Z250 dental composite were then applied as directed. The teeth thus prepared were further cut into micro‐bar specimens, with cross‐sectional sizes of 1 × 1 mm², 1 × 2 mm², and 1 × 3 mm², for μTBS testing. The test results showed that plasma‐treated specimens gave substantially stronger adhesive–dentin bonding than their corresponding same‐tooth controls. Compared with their untreated controls, plasma treatment gave statistically significant higher bonding strength for specimens with a cross‐sectional area of 1 × 1 mm² and 1 × 2 mm², with mean increases of 30.8% and 45.1%, respectively. Interface examination using optical and electron microscopy verified that plasma treatment improved the quality of the adhesive–dentin interface by reducing defects/voids and increasing the resin tag length in dentin tubules.