Effect of modulated photo‐activation on polymerization shrinkage behavior of dental restorative resin composites

This study investigated the influence of modulated photo‐activation on axial polymerization shrinkage, shrinkage force, and hardening of light‐ and dual‐curing resin‐based composites. Three light‐curing resin composites (SDR bulk‐fill, Esthet X flow, and Esthet X HD) and one dual‐curing material (Rebilda DC) were subjected to different irradiation protocols with identical energy density (27 J cm^?2): high‐intensity continuous light (HIC), low‐intensity continuous light (LIC), soft‐start (SS), and pulse‐delay curing (PD). Axial shrinkage and shrinkage force of 1.5‐mm‐thick specimens were recorded in real time for 15 min using custom‐made devices. Knoop hardness was determined at the end of the observation period. Statistical analysis revealed no significant differences among the curing protocols for both Knoop hardness and axial shrinkage, irrespective of the composite material. Pulse‐delay curing generated the significantly lowest shrinkage forces within the three light‐curing materials SDR bulk‐fill, Esthet X flow, and Esthet X HD. High‐intensity continuous light created the significantly highest shrinkage forces within Esthet X HD and Rebilda DC, and caused significantly higher forces than LIC within Esthet X flow. In conclusion, both the composite material and the applied curing protocol control shrinkage force formation. Pulse‐delay curing decreases shrinkage forces compared with high‐intensity continuous irradiation without affecting hardening and axial polymerization shrinkage.     

Influence of power density and primer application on polymerization of dual‐cured resin cements monitored by ultrasonic measurement

Takubo C, Yasuda G, Murayama R, Ogura Y, Tonegawa M, Kurokawa H, Miyazaki M. Influence of power density and primer application on polymerization of dual‐cured resin cements monitored by ultrasonic measurement. Eur J Oral Sci 2010; 118: 417–422. © 2010 The Authors. Journal compilation © 2010 Eur J Oral Sci We used ultrasonic measurements to monitor the influence of power density and primer application on the polymerization reaction of dual‐cured resin cements. The ultrasonic equipment comprised a pulser–receiver, transducers, and an oscilloscope. Resin cements were mixed and inserted into a transparent mould, and specimens were placed on the sample stage, onto which the primer, if used, was also applied. Power densities of 0 (no irradiation), 200, or 600 mW cm^?2 were used for curing. The transit time through the cement disk was divided by the specimen thickness to obtain the longitudinal sound velocity. When resin cements were light‐irradiated, each curve displayed an initial plateau of ～1,500 m s^?1, which rapidly increased to a second plateau of 2,300–2,900 m s^?1. The rate of sound velocity increase was retarded when the cements were light‐irradiated at lower power densities, and increased when the primer was applied. The polymerization behaviour of dual‐cured resin cements was therefore shown to be affected by the power density of the curing unit and the application of self‐etching primer.     

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.     

effects of sequential versus continuous irradiation of a light-cured resin composite on shrinkage, viscosity, adhesion, and degree of polymerization

Objective : This in vitro study compar ed different properties of a resin composite using a two‐step light‐curing method and a conventional continuous curing approach. Materials and Methods : Five different tests were performed on specimens of resin composite. Fifty‐five specimens of 3.5‐mm thickness were divided among 11 different test groups that varied in light‐curing protocols. Top and bottom surface hardness were measured after curing. Adhesion of composite to pretreated metal surfaces was tested using 36 specimens irradiated with four different curing methods. Linear and volumetric shrinkage of adhesion specimens were measured using a linometer. Measurements of viscosity were performed on 10 specimens during polymerization. Finally, the dynamics of polymerization during two‐step versus continuous light‐curing were evaluated by measuring the residual monomer concentration in each specimen after different irradiation. Results : Surface hardness depended on the total dose of light delivered, but not on how the light was delivered. Concerning adhesion, the results indicated that marginal adhesion was weakened by fast polymerization and was improved with a low‐intensity pre‐polymerization period. The results of the shrinkage test indicated less shrinkage a t the beginning of the process with the lower intensity light. However, at completion of polymerization, the total shrinkage did not differ significantly between groups. Also, during the curing process, the same viscosity changes occurred in the resin composite regardless of the irradiation method used. Finally, by the 40‐second completion point, specimens made with either two‐step or continuous light‐curing had reached a similar 90% degree of polymerization. Conclusions : With an adequate total irradiation dose, the properties of resin composite cured with a two‐step approach were as good as or better than those obtained using a conventional continuous curing method. Moreover, marginal adaptation was improved by two‐step polymerization, which could be explained by the ability of the material to flow during the early stages of the curing process.     

A new method to measure the polymerization shrinkage kinetics of light cured composites

This study was undertaken to develop a new measurement method to determine the initial dynamic volumetric shrinkage of composite resins during polymerization, and to investigate the effect of curing light intensity on the polymerization shrinkage kinetics. The instrument was basically an electromagnetic balance that was constructed with a force transducer using a position sensitive photo detector (PSPD) and a negative feedback servo amplifier. The volumetric change of composites during polymerization was detected continuously as a buoyancy change in distilled water by means of the Archimedes' principle. Using this new instrument, the dynamic patterns of the polymerization shrinkage of seven commercial composite resins were measured. The polymerization shrinkage of the composites was 1.92 approximately 4.05 volume %. The shrinkage of a packable composite was the lowest, and that of a flowable composite was the highest. The maximum rate of polymerization shrinkage increased with increasing light intensity but the peak shrinkage rate time decreased with increasing light intensity. A strong positive relationship was observed between the square root of the light intensity and the maximum shrinkage rate. The shrinkage rate per unit time, dVol%/dt, showed that the instrument can be a valuable research method for investigating the polymerization reaction kinetics. This new shrinkage-measuring instrument has some advantages that it was insensitive to temperature changes and could measure the dynamic volumetric shrinkage in real time without complicated processes. Therefore, it can be used to characterize the shrinkage kinetics in a wide range of commercial and experimental visible-light-cure materials in relation to their composition and chemistry.     

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.     

Characterization of a novel light‐cured star‐shape poly(acrylic acid)‐composed glass‐ionomer cement: fluoride release,water sorption,shrinkage, and hygroscopic expansion

This study evaluated the fluoride release, water sorption, curing shrinkage, and hygroscopic expansion of a novel experimental light‐cured glass‐ionomer cement. The effects of glycidyl methacrylate (GM) grafting, polymer : water (P : W) and powder : liquid (P : L) ratios were investigated. Commercial Fuji II and Fuji II LC cements were used as controls for comparison. All the specimens were conditioned in deionized water at 37°C before testing. The results demonstrated that the experimental cement showed lower burst and slower bulk fluoride release than Fuji II and Fuji II LC. The experimental cement absorbed more water than Fuji II and Fuji II LC as a result of its hydroxyl and carboxyl functional group content. The lower water‐diffusion rate and reduced hygroscopic expansion of the experimental cement suggest that it had a highly crosslinked network. Both Fuji II and Fuji II LC exhibited much higher shrinkage values (2.8% and 4.7%) than the experimental cement (0.8%). It appears that this novel cement will be a clinically attractive dental restorative because not only has it shown superior mechanical strength, it has also demonstrated satisfactory physical properties.     

Spatio-temporal analysis of shrinkage vectors during photo-polymerization of composite

Objectives

The purpose of this study was to validate a new method to investigate the polymerization shrinkage vectors of composite during light curing and to evaluate the overall utility and significance of the technique.

Methods

An optical instrument was developed to measure the location and direction of the polymerization shrinkage strain vectors of dental composite during light curing using a particle tracking method with computer vision. The measurement system consisted of a CCD color camera, a lens and a filter, and software for multi-particle tracking. A universal hybrid composite (Z250, 3M ESPE, St. Paul MN, USA) was molded into thin disk-shaped specimens (un-bonded and bonded) or filled into a cavity within a tooth slab (bonded). The composite surface was coated with fluorescent particles prior to light curing. The images of the fluorescent particles were stored at 2 frames/s for 10 min, and the movements of the particles on the composite surface were tracked with computer vision during curing. The polymerization shrinkage strain vectors as a function of time and location were analyzed. The volume shrinkage of the composite was also measured for comparison.

Results

The linear and volume shrinkage of the composite at 10 min were 0.75 (0.12)% and 2.26 (0.18)%, respectively. The polymerization shrinkage vectors were directed toward the center of the specimen and were isotropic in all directions when the composite was allowed to shrinkage freely without bonding. In contrast, the shrinkage vectors were directed toward the bonding surface and were anisotropic when the composite was bonded to a fixed wall. The regional displacement vectors of composite in a tooth cavity were dependent on the location, depth and time.

Significance

The new instrument was able to measure the regional linear shrinkage strain vectors over an entire surface of a composite specimen as a function of time and location. Therefore, this instrument can be used to characterize the shrinkage behaviors for a wide range of commercial and experimental visible-light-cure materials in relation to the composition, boundary condition and cavity geometry.     

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.     

The effect of curing with plasma light on the shrinkage of dental restorative materials

Commercially available light activated dental composites were used in this study to compare the shrinkage following curing with plasma light (Apollo95E, DMDS) and a convention halogen dental curing light (Prismetics Lite II, Dentsply). Polymerization shrinkage was determined by measuring the strain in one dimension by means of a contacting transducer. The percentage linear shrinkage were: Spectrum H = 1.84 + 0.31, P = 1.49 + 0.35*; Ana aesthetic H = 2.04 + 0.38, P = 1.85 + 0.27; Esthet.x H = 1.66 + 0.28, P = 1.69 + 0.25; Dyract AP H = 2.39 + 0.33, P = 2.18 + 0.35*; Apollo Restore H = 1.88 + 0.36, P = 1.42 + 0.33*; Surefil H = 0.88 + 0.28, P = 0.99 + 0.30 where * = significantly different, t-test at P < 0.05. The results suggested that there was less shrinkage when curing some, but not all, materials using the plasma light, although this could be attributed to a reduced level of polymerization.     

Curing depths of a universal hybrid and a flowable resin composite cured with quartz tungsten halogen and light‐emitting diode units

This in vitro study evaluated curing depths of a universal hybrid resin composite with two viscosities (Tetric Ceram and Tetric Flow) after curing with 6 different quartz tungsten halogen and light‐emitting diode curing units. Irradiance (light intensity) of the curing units varied between 200 and 700?mW/cm ² . The curing units were used for standard, soft‐start, or pulse curing. Curing times were 20 and 40?s for standard curing, 3?+?10?s and 3?+?30?s for pulse curing, and 40?s for soft‐start. Resin composite specimens, 5 in each group, with a diameter of 4?mm and a height of 6?mm, were made in brass molds and cured from one side at a distance of 6?mm. After 2 weeks, the specimens were ground longitudinally half through the specimen. Curing depth was then determined by measurement of Wallace hardness for each half millimeter starting at 0.5?mm from the top surface. For all curing units and for both resin composites an increased curing time led to statistically significantly higher depth of cure (P?P?r?=?0.89, P?r?=?0.91, P?相似文献   

Soft-start polymerization: influence on effectiveness of cure and post-gel shrinkage

This study investigated the influence of soft-start polymerization on the effectiveness of cure and post-gel shrinkage of a visible light cured resin composite (Z100). Three cure modes (LH-high intensity; LA-soft-start polymerization involving step-wise modulation of light intensity and LL-low intensity) of a commercial light-cure unit (Kavo PolyLUX II) were examined and compared to another light-cure unit (Spectrum). The effectiveness of cure with the different cure modes was assessed by computing the hardness gradient between top and bottom surfaces of 2 mm composites specimens after different light exposure times. A strain-monitoring device was used to measure the linear polymerization shrinkage associated with the different cure modes and exposure times over 180 minutes. A sample size of five was used for both experiments. Data was analyzed using one-way ANOVA and Scheffe's post-hoc test at significance level 0.05. Results showed that effectiveness of cure generally increased with increase cure time. Although modulation of light energy intensity (LA 40/80 seconds) resulted in lower polymerization shrinkage compared to LH 40 seconds, no significant difference was observed between these three cure regimes. Curing with the Spectrum curing light resulted in the lowest polymerization shrinkage.     

Influence of Zirconia Base and Shade Difference on Polymerization Efficiency of Dual‐Cure Resin Cement

Purpose : The aim of this study was to investigate the polymerization efficiency of dual‐cured resin cement beneath different shades of zirconia‐based feldsphathic ceramic restorations. Materials and Methods : Five translucent zirconia (Zirkonzahn) discs (4.0‐mm diameter, 1.2‐mm height) were prepared. Feldsphathic ceramic (1.2 mm) (Noritake Cerabien Zr) in 5 shades (1M2, 2M2, 3M2, 4M2, 5M2) was applied on the zirconia discs. Twelve dual‐cure resin cement specimens were prepared for each shade, using Panavia F 2.0 (Kuraray) in Teflon molds (4.0‐mm diameter, 6.0‐mm height), following the manufacturer's instructions. Light activation was performed through the zirconia‐based ceramic discs for 20 seconds, using a quartz tungsten halogen curing device (Hilux 200) with irradiance of 600 mW/cm². Immediately following light curing, specimens were stored for 24 hours in dry, light‐proof containers. Vickers hardness measurements were conducted using a microhardness tester with a 50‐g load applied for 15 seconds. The indentations were made in the cross sectional area at four depths, and the mean values were recorded as Vickers hardness number (VHN). Results were statistically analyzed with one‐way ANOVA and Tukey HSD test (p < 0.05). Results: A statistically significant decrease in VHN of the resin cement was noted with increasing depth and darkness of the shade (p < 0.05). Conclusion : Curing efficiency of dual‐cure resin cement is mainly influenced by the lightness of the shades selected.     

Hardness,Flexural Strength,and Flexural Modulus Comparisons of Three Differently Cured Denture Base Systems

Purpose: This study compared the surface hardness, flexural strength, and flexural modulus of a light‐ and heat‐cured urethane dimethacrylate (UDMA) to two conventional polymethyl methacrylate (PMMA) denture base resins. The effect of less‐than‐optimal processing condition on the hardness of internal and external surfaces of UDMA specimens was also investigated. Materials and Methods: The materials tested were Eclipse (light‐ and heat‐cured UDMA), Meliodent (heat‐cured PMMA), and Probase Cold (auto‐cured PMMA). Eclipse specimens were prepared by adapting the material onto the master cast and light curing in the processing unit for 10 minutes. Meliodent and Probase Cold specimens were prepared according to the manufacturers' instructions. Twenty rectangular specimens measuring 65 × 10 × 2.5 mm³ were prepared for each material. They were stored in water at 37°C for 30 days before testing. The surface hardness was measured using Vickers Hardness (VHN) test, and flexural strength and flexural modulus were measured using a 3‐point bending test. Twenty‐five additional Eclipse specimens were similarly prepared and were processed at various times of less than 20 minutes of curing. Vickers Hardness was determined on both the external and internal surfaces of specimens. Data were analyzed using a one‐way ANOVA for comparisons of hardness, flexural strength, and flexural modulus between the three denture base materials and for hardness values of both the internal and external surface of Eclipse specimens with curing times. Post hoc analyses (Scheffé test) determined the difference between the groups. Student t‐test was used for comparison of hardness between the external and internal surfaces of Eclipse specimens. Results: The hardness (VHN) values were 19.4 ± 0.7, 17.0 ± 0.4, and 16.0 ± 0.4; the flexural strengths (MPa) were 103 ± 4, 78 ± 3, and 63 ± 4; and the flexural moduli (MPa) were 2498 ± 143, 1969 ± 55, and 1832 ± 89 for Eclipse, Meliodent, and Probase Cold materials, respectively. A comparison among the three polymers showed there were significant differences in surface hardness, flexural strength, and flexural modulus (p < 0.05). No significant difference in surface hardness (VHN) between the internal (19.1 ± 0.6 to 19.4 ± 0.7) and external surfaces (18.9 ± 0.4 to 19.2 ± 0.6) of irradiated Eclipse specimens was observed at 10‐, 12‐, and 14‐minute polymerization times. Conclusion: The surface hardness, flexural strength, and flexural modulus of light‐ and heat‐cured UDMA (Eclipse) were significantly higher than the values obtained for heat‐only cured (Meliodent) and auto‐cured (Probase Cold) PMMA denture base systems.     

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.     

Sodium bicarbonate solution as an anti‐erosive agent against simulated endogenous erosion

Messias DCF, Turssi CP, Hara AT, Serra MC. Sodium bicarbonate solution as an anti‐erosive agent against simulated endogenous erosion. Eur J Oral Sci 2010; 118: 385–388. © 2010 The Authors. Journal compilation © 2010 Eur J Oral Sci This study investigated whether sodium bicarbonate solution, applied on enamel previously exposed to a simulated intrinsic acid, can control dental erosion. Volunteers wore palatal devices containing enamel slabs, which were exposed twice daily extra‐orally to hydrochloric acid (0.01 M, pH 2) for 2 min. Immediately afterwards, the palatal devices were re‐inserted in the mouth and volunteers rinsed their oral cavity with a sodium bicarbonate solution or deionized water for 60 s. After the washout period, the palatal devices were refilled with a new set of specimens and participants were crossed over to receive the alternate rinse solution. The surface loss and surface microhardness (SMH) of specimens were assessed. The surface loss of eroded enamel rinsed with a sodium bicarbonate solution was significantly lower than the surface loss of eroded enamel rinsed with deionized water. There were no differences between treatments with sodium bicarbonate and deionized water for SMH measurements. Regardless of the solution used as an oral rinse, eroded enamel showed lower SMH than uneroded specimens. Rinsing with a sodium bicarbonate solution after simulated endogenous erosive challenge controlled enamel surface loss but did not alter the microhardness.     

The effect of ageing on the elastic modulus and degree of conversion of two multistep adhesive systems

Marchesi G, Navarra CO, Cadenaro M, Carrilho MR, Codan B, Sergo V, Di Lenarda R, Breschi L. The effect of ageing on the elastic modulus and degree of conversion of two multistep adhesive systems. Eur J Oral Sci 2010; 118: 304–310. © 2010 The Authors. Journal compilation © 2010 Eur J Oral Sci During the curing reaction, the monomers of dentine bonding systems should cross‐link sufficiently to strengthen an adhesive so that it is clinically reliable. This study evaluated how different storage conditions (air vs. water storage) affect the elastic modulus (E‐modulus) and degree of conversion (DC) of a three‐step etch‐and‐rinse adhesive and a two‐step self‐etch adhesive. The biaxial flexural test and Raman microscopy were performed on resin disks made from the bonding agents Adper Scotchbond Multi‐Purpose (SBMP; 3M ESPE) and Clearfil Protect Bond (CPB; Kuraray). The measurements were repeated after storage in either air or water for 15 and 30 min and for 1, 24, and 72 h. At time 0, the E‐modulus was not affected by the adhesive system, whilst the degree of cure of CPB was higher than that of SBMP. Air storage increased the E‐modulus at each ageing interval. Storage in water increased the E‐modulus until it reached a maximum at 24 h, after which it decreased significantly at 72 h. No linear correlation between the percentage DC and E‐modulus of the two adhesives was found when stored in water. The results of this study indicate that the mechanical properties and polymerization kinetics of SBMP and CPB are affected by storage time and medium.     

Real‐time curing characteristics of experimental resin composites containing amorphous calcium phosphate

The real‐time polymerization of light‐curable experimental resin composites filled with amorphous calcium phosphate (ACP) was monitored. Experimental composites were based on a 2,2‐bis[4‐(2‐ethoxy‐3‐methacryloyloxy propoxy)phenyl]propane (Bis‐EMA)/triethyleneglycol dimethacrylate (TEGDMA)/2‐hydroxyethyl methacrylate (HEMA) resin photoactivated by a camphorquinone/tertiary amine system. Four ACP composites were prepared, containing 40 wt% ACP and 0/10 wt% reinforcing fillers (barium glass and silica). Additionally, two control composites were prepared which contained only reinforcing fillers (40–50 wt%). The degree of conversion (DC) was monitored in real time using a Fourier‐transform infrared (FTIR) spectrometer with an attenuated total reflectance accessory. During the light curing (1,219 mW cm^?2) for either 20 or 40 s, infrared spectra were collected from the bottom of 2‐mm‐thick composite specimens at the rate of two spectra per second over 5 min. When cured for 40 s, the ACP composites attained a high DC (89.1%–92.4%), while the DC of control composites was significantly lower (53.5%–68.4%). All materials showed a lower DC for the shorter curing time (20 s) and various extents of 5‐min postcure polymerization: 12.9%–21.5% for the ACP composites and 2.7%–5.2% for the control composites. The control composites reached the maximum reaction rate much earlier (4.1–4.3 s) and at lower DC (9.9%–10.4%) than did the ACP composites (17.4–22.0 s and 43.5%–49.3%, respectively).     

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.     

Chemical versus dual curing of resin inlay cements

Dual-cure inlay resin cements polymerize both chemically and through light activation; however, clinically some aspects of the cement are not readily accessible to the light source. This study investigated the degree of cement hardening achieved through chemical curing only versus dual curing and the effect of inlay thickness on cement hardness. Disks 6 x 2.5 mm were prepared from seven commercially available cements. Eight specimens were prepared from each material; half of the specimens were cured chemically only, and the remainder were dual-cured. Knoop hardness measurements were then recorded at 1-hour, 1-day, and 1-week intervals. In addition, 24 specimens of the same dimensions were prepared from each cement. Twelve specimens were dual-cured through resin composite spacers of varying thicknesses (1 to 6 mm), and the others were cured through similar ceramic spacers, and hardness measurements were recorded. Multivariate analysis of variance revealed significant differences in hardness of chemically cured versus dual-cured specimens at the 5% level of significance for all examined cements. Significant differences were also found in the hardness of specimens dual cured through ceramic or resin composite spacers 2 to 3 mm in thickness or more versus those that were dual cured without spacer regardless of the spacer material. It is concluded that chemical curing alone was not sufficient to achieve maximum hardening of the examined cements. Cement hardness was significantly reduced when inlay thickness was 2 to 3 mm or more.