Enzymatic degradation of adhesive–dentin interfaces produced by mild self‐etch adhesives

De Munck J, Mine A, Van den Steen PE, Van Landuyt KL, Poitevin A, Opdenakker G, Van Meerbeek B. Enzymatic degradation of adhesive–dentin interfaces produced by mild self‐etch adhesives.
Eur J Oral Sci 2010; 118: 494–501. © 2010 Eur J Oral Sci Endogenous matrix metalloproteinases (MMPs) released by adhesive procedures may degrade collagen in the hybrid layer and so compromise the bonding effectiveness of etch‐and‐rinse adhesives. In this study, endogenous enzymatic degradation was evaluated for several simplified self‐etch adhesives. In addition, primers were modified by adding two MMP inhibitors: chlorhexidine, a commonly used disinfectant, but also a non‐specific MMP inhibitor; and SB‐3CT, a specific inhibitor of MMP‐2 and MMP‐9. Gelatin zymography of fresh human dentin powder was used to identify the enzymes released by the adhesives. Micro‐tensile bond strength (μTBS) testing was used to assess the mechanical properties of resin–dentin interfaces over time. In none of the experimental groups treated with the mild self‐etch adhesives was MMP‐2 and/or MMP‐9 identified. Also, no difference in the μTBS was measured for the inhibitor‐modified and the control inhibitor‐free adhesives after 6 months of water storage. It is concluded that in contrast to etch‐and‐rinse adhesives, the involvement of endogenous MMP‐2 and MMP‐9 in the bond‐degradation process is minimal for mild self‐etch adhesives.     

Ten‐years degradation of resin–dentin bonds

Hashimoto M, Fujita S, Nagano F, Ohno H, Endo K. Ten‐years degradation of resin–dentin bonds. Eur J Oral Sci 2010; 118: 404–410. © 2010 The Authors. Journal compilation © 2010 Eur J Oral Sci The purpose of this study was to evaluate the durability of resin–dentin bonds in 10‐yr water‐storage testing. Resin–dentin bonded bulk specimens were prepared using six commercially available resin adhesives. The resin–dentin bonded specimens were stored in water for 24 h (control group) or for 10 yr (experimental groups). After each storage period, the specimens were sectioned to make specimen beams and then subjected to a microtensile bond test. After the bond test, fractured surfaces were examined by scanning electron microscopy (SEM). In addition, interfacial observation of silver nanoleakage was performed using the backscatter electron mode of SEM. The bond strengths of four of the six adhesive systems tested decreased significantly after 10 yr. However, no significant bond‐strength reduction was recorded for the other two systems. The interfacial observations showed water tree propagation in the bonding resin layer as a typical morphological change after aging for five of the six adhesives tested. Water tree propagation may be a symptom of degradation in the resin bonding layer of resin–dentin bonds.     

Chlorhexidine-modified nanotubes and their effects on the polymerization and bonding performance of a dental adhesive

ObjectivesThe purpose of this study was to synthesize chlorhexidine (CHX)-encapsulated aluminosilicate clay nanotubes (Halloysite®, HNTs) and to incorporate them into the primer/adhesive components of an etch-and-rinse adhesive system (SBMP; Scotchbond Multipurpose, 3M ESPE) and to test their effects on degree of conversion, viscosity, immediate and long-term bonding to dentin.MethodsCHX-modified HNTs were synthesized using 10% or 20% CHX solutions. The primer and the adhesive components of SBMP were incorporated with 15 wt.% of the CHX-encapsulated HNTs. Degree of conversion (DC) and viscosity analyses were performed to characterize the modified primers/adhesives. For bond strength testing, acid-etched dentin was treated with one of the following: SBMP (control); 0.2%CHX solution before SBMP; CHX-modified primers + SBMP adhesive; SBMP primer + CHX-modified adhesives; and SBMP primer + CHX-free HNT-modified adhesive. The microtensile bond strength test was performed after immediate (24 h) and long-term (6 months) of water storage. Data were analyzed using ANOVA and Tukey (α = 5%) and the Weibull analysis.ResultsDC was greater for the CHX-free HNT-modified adhesive, whereas the other experimental adhesives showed similar DC as compared with the control. Primers were less viscous than the adhesives, without significant differences within the respective materials. At 24 h, all groups showed similar bonding performance and structural reliability; whereas at the 6-month period, groups treated with the 0.2%CHX solution prior bonding or with the CHX-modified primers resulted in greater bond strength than the control and superior reliability.SignificanceThe modification of a primer or adhesive with CHX-encapsulated HNTs was an advantageous approach that did not impair the polymerization, viscosity and bonding performance of the materials, showing a promising long-term effect on resin-dentin bonds.     

Enamel microhardness and bond strengths of self‐etching primer adhesives

Adebayo OA, Burrow MF, Tyas MJ, Adams GG, Collins ML. Enamel microhardness and bond strengths of self‐etching primer adhesives. Eur J Oral Sci 2010; 118: 191–196. © 2010 The Authors. Journal compilation © 2010 Eur J Oral Sci The aim of this study was to determine the relationship between enamel surface microhardness and microshear bond strength (μSBS). Buccal and lingual mid‐coronal enamel sections were prepared from 22 permanent human molars and divided into two groups, each comprising the buccal and lingual enamel from 11 teeth, to analyze two self‐etching primer adhesives (Clearfil SE Bond and Tokuyama Bond Force). One‐half of each enamel surface was tested using the Vickers hardness test with 10 indentations at 1 N and a 15‐s dwell time. A hybrid resin composite was bonded to the other half of the enamel surface with the adhesive system assigned to the group. After 24 h of water storage of specimens at 37º°C, the μSBS test was carried out on a universal testing machine at a crosshead speed of 1 mm min^?1 until bond failure occurred. The mean μSBS was regressed on the mean Vickers hardness number (VHN) using a weighted regression analysis in order to explore the relationship between enamel hardness and μSBS. The weights used were the inverse of the variance of the μSBS means. Neither separate correlation analyses for each adhesive nor combined regression analyses showed a significant correlation between the VHN and the μSBS. These results suggest that the μSBS of the self‐etch adhesive systems are not influenced by enamel surface microhardness.     

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.     

Surface free‐energy measurements as indicators of the bonding characteristics of single‐step self‐etching adhesives

Inoue N, Tsujimoto A, Takimoto M, Ootsuka E, Endo H, Takamizawa T, Miyazaki M. Surface free‐energy measurements as indicators of the bonding characteristics of single‐step self‐etching adhesives.
Eur J Oral Sci 2010; 118: 525–530. © 2010 Eur J Oral Sci This study examined the surface free‐energy of dentin treated with the single‐step self‐etching adhesives Bond Force, Clearfil tri‐S Bond, and G‐Bond Plus. The labial dentin surfaces of bovine mandibular incisors were wet ground with #180‐, #600‐, and #2,000‐grit silicon carbide paper. The adhesives were applied to the ground dentin, and then rinsed with acetone and distilled water. The surface free‐energies were determined by measuring the contact angles of three test liquids placed on the adhesive‐treated dentin. The surface free‐energies of the samples treated with the G‐Bond Plus and Clearfil tri‐S Bond adhesives increased as the surface roughness decreased. No significant differences in the surface free‐energy were found for the samples treated with the Bond Force adhesive, regardless of the surface roughness. These results indicated that dentin surfaces treated with adhesives did not promote a higher surface‐energy state, and that differences in the components of surface energy were apparent for the adhesives tested.     

Role of preliminary etching for one‐step self‐etch adhesives

Taschner M, Nato F, Mazzoni A, Frankenberger R, Krämer N, Di Lenarda R, Petschelt A, Breschi L. Role of preliminary etching for one‐step self‐etch adhesives.
Eur J Oral Sci 2010; 118: 517–524. © 2010 Eur J Oral Sci The aim of this study was to analyse the effect of preliminary phosphoric acid etching of enamel and dentine before the application of two, one‐step self‐etch adhesive systems. The systems were applied onto acid‐etched or smear‐layer‐covered enamel and dentine. The treatment groups were as follows: group 1, Adper Easy Bond (3M ESPE) on etched substrate; group 2, Adper Easy Bond (control); group 3, iBond Self‐Etch (Heraeus Kulzer) on etched substrate; and group 4, iBond Self‐Etch (control). Enamel and dentine bond strengths were calculated using microshear and microtensile bond‐strength tests. Additional specimens were prepared to evaluate nanoleakage at the dentine–adhesive interface and were investigated using light microscopy or transmission electron microscopy. Both adhesives demonstrated higher microshear bond strengths when enamel was pre‐acid‐etched with phosphoric acid (Adper Easy Bond 28.7 ± 4.8 MPa; iBond Self‐Etch 19.7 ± 3.6 MPa) compared with controls (Adper Easy Bond 19.2 ± 3.3 MPa; iBond Self‐Etch 17.5 ± 2.7 MPa) and increased microtensile bond strength when applied on acid‐etched (Adper Easy Bond 35.8 ± 5.7 MPa; iBond Self‐Etch 24.3 ± 7.9 MPa) vs. smear‐layer‐covered dentine (Adper Easy Bond 26.9 ± 6.2 MPa; iBond Self‐Etch 17.6 ± 4.3 MPa). Adper Easy Bond showed lower nanoleakage than iBond Self‐Etch, irrespective of preliminary etching. The results of this study support the use of phosphoric acid etching before the application of one‐step self‐etch adhesive systems.     

Influence of ageing on self‐etch adhesives: one‐step vs. two‐step systems

The aim of this study was to evaluate microtensile bond strength (μTBS) to dentine, interfacial nanoleakage expression, and stability after ageing, of two‐step vs. one‐step self‐etch adhesives. Human molars were cut to expose middle/deep dentine, assigned to groups (n = 15), and treated with the following bonding systems: (i) Optibond XTR (a two‐step self‐etch adhesive; Kerr), (ii) Clearfil SE Bond (a two‐step self‐etch adhesive; Kuraray), (iii) Adper Easy Bond (a one‐step self‐etch adhesive; 3M ESPE), and (iv) Bond Force (a one‐step self‐etch adhesive; Tokuyama). Specimens were processed for μTBS testing after 24 h, 6 months, or 1 yr of storage in artificial saliva at 37°C. Nanoleakage expression was examined in similarly processed additional specimens. At baseline the μTBS results ranked in the following order: Adper Easy Bond = Optibond XTR ≥Clearfil SE = Bond Force, and interfacial nanoleakage analysis showed Clearfil SE Bond = Adper Easy Bond = Optibond XTR> Bond Force. After 1 yr of storage, Optibond XTR, Clearfil SE Bond, and Adper Easy Bond showed higher μTBS and lower interfacial nanoleakage expression compared with Bond Force. In conclusion, immediate bond strength, nanoleakage expression, and stability over time were not related to the number of steps of the bonding systems, but to their chemical formulations.     

Effects of increased exposure times of simplified etch‐and‐rinse adhesives on the degradation of resin–dentin bonds and quality of the polymer network

Reis A, Ferreira SQ, Costa TRF, Klein‐Júnior CA, Meier MM, Loguercio AD. Effects of increased exposure times of simplified etch‐and‐rinse adhesives on the degradation of resin–dentin bonds and quality of the polymer network.
Eur J Oral Sci 2010; 118: 502–509. © 2010 Eur J Oral Sci One of the reasons for resin–dentin degradation is poor polymerization of the adhesive layer. This study evaluated the effect of prolonged polymerization times on the immediate and 6‐month resin–dentin bond strengths, silver nitrate uptake, and polymer quality of etch‐and‐rinse adhesives. Thirty extracted teeth were obtained, and a flat dentin surface was exposed on each tooth. Adhesives (Adper Single Bond 2 and One Step Plus) were applied to the dentin surface of these teeth and light‐cured for 10, 20, or 40 s at 600 mW cm^?2. Bonded sticks (0.6 mm²) were tested in tension (0.5 mm min^?1) and analyzed, after immersion in 50% silver nitrate, using scanning electron microscopy. The polymer quality of adhesive films was evaluated using thermogravimetric analysis. Statistically higher bond strengths were observed for both adhesives when light‐cured for 40 s. Degradation of dentin bonds occurred under all experimental conditions but it was less pronounced for adhesives light‐cured for 40 s. Longer exposure times reduced silver nitrate uptake for Adper Single Bond 2. Solvent retention and the amount of residual monomer were statistically lower when both adhesives were light‐cured for 40 s. Although longer exposure times than those recommended cannot prevent degradation of the dentin bonds, they can increase bond strength, probably because of the removal of an increased amount of solvent and the presence of a lower amount of residual monomer.     

Influence of contamination on resin bond strength to nano‐structured alumina‐coated zirconia ceramic

Zhang S, Kocjan A, Lehmann F, Kosma? T, Kern M. Influence of contamination on resin bond strength to nano‐structured alumina‐coated zirconia ceramic. Eur J Oral Sci 2010; 118: 396–403. © 2010 The Authors. Journal compilation © 2010 Eur J Oral Sci The purpose of this study was to evaluate the influence of contamination and subsequent cleaning on the bond strength and durability of an adhesive resin to nano‐structured alumina‐coated zirconia ceramic. Zirconia ceramic disks were coated with nano‐structured alumina, utilizing the hydrolysis of aluminum nitride powder. After immersion in saliva or the use of a silicone disclosing agent, specimens were cleaned with phosphoric acid etching or with tap water rinsing only. Uncontaminated specimens served as controls. Plexiglas tubes filled with composite resin were bonded with a phosphate monomer [10‐methacryloxydecyl‐dihydrogenphosphate (MDP)]‐containing resin (Panavia 21). Subgroups of eight specimens each were stored in distilled water at 37°C, either for 3 d without thermal cycling (TC) or for 150 d with 37,500 thermal cycles from 5 to 55°C. The tensile bond strength (TBS) was determined using a universal testing machine at a crosshead speed of 2 mm min^?1. The topography of the debonded surface was scrutinized for fractographic features, utilizing both optical and scanning electron microscopy. The TBS to uncontaminated nano‐structured alumina‐coated zirconia ceramic was durable, while contamination significantly reduced the TBS. Phosphoric acid cleaning was effective in removal of saliva contamination from the coated bonding surface but was not effective in removal of the silicone disclosing agent. Nano‐structured alumina coating improves resin bonding to zirconia ceramic and eliminates the need for air‐abrasion before bonding.     

Measurements of volatile compound contents in resins using a moisture analyzer

Hashimoto M, Nagano F, Endo K, Ohno H. Measurements of volatile compound contents in resins using a moisture analyzer. Eur J Oral Sci 2010; 118: 94–99. © 2010 The Authors. Journal compilation © 2010 Eur J Oral Sci
The contents of volatile adhesive compounds, such as water, solvents, and residual unpolymerized monomers, affect the integrity and durability of adhesive bonding. However, there is no method available that can be used to rapidly assess the residual solvent or water contents of adhesive resins. This study examined the effectiveness of a digital moisture analyzer to measure the volatile compound contents of resins. Five self-etching adhesives and seven experimental light-cured resins prepared with different contents (0, 10, and 20% by weight) of water or solvents (acetone and ethanol) were examined in this study. The resins were prepared using different methods (with and without air blast or light-curing) to simulate the clinical conditions of adhesive application. Resin weight changes (% of weight loss) were determined as the residual volatile compound contents, using the moisture analyzer. After the measurements, the resin films were examined using a scanning electron microscope. The weight changes of the resins were found to depend on the amount of water or solvents evaporating from the resin. Water and solvents were evaporated by air blast or light-curing, but some of the water and solvents remained in the cured resin. The moisture analyzer is easy to operate and is a useful instrument for using to measure the residual volatile compound contents of adhesive resin.     

The effect of repeated fluoride recharge and storage media on bond durability of fluoride rechargeable Giomer bonding agent

Background:  For a restorative material or adhesive to exhibit caries inhibitive potential through fluoride release, it must be capable of fluoride recharge. The aim of this study was to evaluate the effect of repeated fluoride recharge and different storage media on dentine bond strength durability. Methods:  Two self‐etch adhesive systems (two‐step) were evaluated: fluoride‐rechargeable Giomer FL‐Bond II and non‐fluoride‐containing UniFil Bond. For each adhesive 32 human dentine specimens were prepared for shear bond strength testing. The specimens were randomly allocated to one of four storage groups: Group 1 – 24‐hour water ageing; Group 2 – four‐month water ageing; Group 3 – four‐month water ageing with weekly fluoride recharge (5000 ppm for 10 minutes); and Group 4 – four‐month acid ageing with weekly fluoride recharge. Results:  Weekly fluoride recharge over four months ageing did not significantly (p > 0.05) reduce the dentine shear bond strength of FL‐Bond II or UniFil Bond. Storage media did not significantly (p > 0.05) affect bond durability. Conclusions:  The adhesion between fluoride rechargeable FL‐Bond II and dentine maintained durability despite regular fluoride recharge over the four months ageing. Clinicians prescribing the fluoride recharge regime used in the present study to reduce recurrent caries incidence associated with Giomer FL‐Bond II restorations can do so without compromising dentine bond strengths.     

Effects of chlorhexidine on bonding durability of different adhesive systems using a novel thermocycling method

Background

The purpose of this study was to evaluate the influence of chlorhexidine on the bonding durability of etch‐and‐rinse and self‐etch adhesive systems using the polymerase chain reaction (PCR) thermocycling method.

Methods

Twenty freshly extracted intact human third molars were ground and bonded with either an etch‐and‐rinse adhesive (Single‐Bond) or a self‐etch adhesive (G‐Bond). Specimens were either left untouched or placed in PCR tubes filled with three thermocycling mediums: water, chlorhexidine or silicone oil. Thermocycling (5000 cycles) was done using the PCR programme at temperatures of 5 °C and 55 °C. The microtensile bond strength (μTBS) was evaluated and interfacial nanoleakage was assessed by scanning electron microscopy before and after thermocycling.

Results

Significant differences were detected among groups kept in different media after thermocycling. For Single‐Bond, both the chlorhexidine and silicone oil groups could preserve the μTBS (p < 0.001). For G‐Bond, μTBS of the chlorhexidine and water groups were significantly decreased (p < 0.05). No obvious increase in silver deposition was observed in specimens incubated in water after thermocycling, less silver penetration was found in specimens incubated in chlorhexidine.

Conclusions

In this experimental model, chlorhexidine was found to preserve bonding durability in Single‐Bond but have no significant effects on G‐Bond.     

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.     

Does inhibition of proteolytic activity improve adhesive luting?

Endogenous enzymes may be involved in the biodegradation of adhesive restoration–tooth interfaces. Inhibitors of matrix metalloproteinases (MMPs) have been suggested to retard the bond‐degradation process. Limited data are available on whether composite cements may also benefit from MMP inhibitors. Therefore, the aim of this study was to determine the effect of two MMP inhibitors – chlorhexidine digluconate (CHX) and galardin – on the microtensile bond strength (μTBS) of two self‐adhesive composite cements to dentin. Ceramic specimens were cemented to bur‐cut dentin surfaces using the self‐adhesive composite cements RelyX Unicem 2 (3M ESPE) or Clearfil SA (Kuraray), or the etch‐and‐rinse composite cement Nexus 3 (Kerr) that served as the control. The surfaces were left untreated or were pretreated with MMP inhibitors (2% CHX or 0.2 mM galardin). The μTBS was determined ‘immediately’ and upon ageing (water storage for 6 months). Statistical analysis revealed a significant effect of the factors ‘composite cement’ and ‘storage’, as well as all interactions, but no effect of the MMP inhibitors. After 6 months of ageing, the μTBS decreased for all cements, except for the multistep etch‐and‐rinse luting composite when it was applied without MMP inhibitors. The MMP inhibitors could not prevent the decrease in μTBS upon ageing and therefore do not improve the luting durability of the composite cements tested.     

Crystal growth by restorative filling materials

Endo K, Hashimoto M, Haraguchi K, Ohno H. Crystal growth by restorative filling materials.
Eur J Oral Sci 2010; 118: 489–493. © 2010 Eur J Oral Sci This study examined the activity and ability of materials to mineralize teeth in gaps, simulating microleakage between the materials and teeth. Three restorative materials (two glass ionomer cements and a compomer) were used in this study. Cured disks of restoratives were placed over flat human tooth surfaces (enamel and dentin), separated by a standardized 20‐μm interfacial space, and stored in water for 24 h or 1 yr. After the water‐storage period, the materials were detached from the teeth and the opposing surfaces were examined by scanning electron microscopy (SEM) and electron probe micro analysis (EPMA).Hemispherical‐shaped precipitations, composed of minute semicircle plate‐like crystals, were observed by SEM on the enamel surface after 1 yr of water storage for glass ionomer cement. The amount of crystal growth with the chemical‐cured type of glass ionomer cement was greater than with the dual‐cured type of glass ionomer cement. However, there was no crystal formation in the compomer. Moreover, no structural changes were observed on dentin surfaces for any material in water after 1 yr. The elements detected in the crystals by EPMA were calcium (Ca), phosphorus (P), and aluminum (Al). The two glass ionomer cements tested have the ability to induce crystals whose composition might be derived from cured glass ionomers.     

Elution of substances from a silorane-based dental composite

Kopperud HM, Schmidt M, Kleven IS. Elution of substances from a silorane-based dental composite. Eur J Oral Sci 2010; 118: 100–102. © 2010 The Authors. Journal compilation © 2010 Eur J Oral Sci
Previous studies have shown that residual monomers, initiators, and additives are eluted from methacrylate-based dental composite materials. Recently, a composite material (Filtek Silorane), based on a new resin chemistry, was introduced. The purpose of this study was to investigate substances eluted from Filtek Silorane in water and ethanol. Polymerized specimen discs of the material were immersed in either distilled water or 75 vol% ethanol at 37°C, and the solutions were analyzed using liquid chromatography-mass spectrometry after 1, 4, 24, and 72 h eluting time. No substances were found to leach from Filtek Silorane in water, whereas silorane monomers and an initiator component were eluted from the material into the ethanol solution.     

Effect of a functional monomer (MDP) on the enamel bond durability of single‐step self‐etch adhesives

The present study aimed to determine the effect of the functional monomer, 10‐methacryloxydecyl dihydrogen phosphate (MDP), on the enamel bond durability of single‐step self‐etch adhesives through integrating fatigue testing and long‐term water storage. An MDP‐containing self‐etch adhesive, Clearfil Bond SE ONE (SE), and an experimental adhesive, MDP‐free (MF), which comprised the same ingredients as SE apart from MDP, were used. Shear bond strength (SBS) and shear fatigue strength (SFS) were measured with or without phosphoric acid pre‐etching. The specimens were stored in distilled water for 24 h, 6 months, or 1 yr. Although similar SBS and SFS values were obtained for SE with pre‐etching and for MF after 24 h of storage in distilled water, SE with pre‐etching showed higher SBS and SFS values than MF after storage in water for 6 months or 1 yr. Regardless of the pre‐etching procedure, SE showed higher SBS and SFS values after 6 months of storage in distilled water than after 24 h or 1 yr. To conclude, MDP might play an important role in enhancing not only bond strength but also bond durability with respect to repeated subcritical loading after long‐term water storage.     

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.     

Ultrasonic measurement of the effects of light irradiation and presence of water on the polymerization of self‐adhesive resin cement

Self‐adhesive resin cements are useful in restorations because they reduce the number of clinical steps involved in the restoration process. This study evaluated, using ultrasonic measurements, the influence of light irradiation and the presence of water on the polymerization behavior and elastic modulus of a self‐adhesive resin cement. A self‐adhesive resin cement (RelyX Unicem 2 Automix) or a resin cement (RelyX ARC) was inserted into a transparent mold on a sample stage, and the presence of water and effect of light‐irradiation were evaluated. The transit time of a sonic wave through the cement disk was divided by the specimen thickness to obtain the sonic velocity, and longitudinal and shear waves were used to determine the elastic modulus. When the resin cements were light‐irradiated, the sonic velocity rapidly increased and plateaued at 2,500–2,700 m s^?1. When the cements were not irradiated, the rates of increase in the sonic velocity were reduced. When water was applied to the sample stage, the sonic velocity was reduced. The elastic modulus values of the specimens ranged from 9.9 to 15.9 GPa after 24 h. The polymerization behavior of self‐adhesive resin cements is affected by the polymerization mode and the presence of water.