Self-curing Mode Research Articles

Panavia F: the role of the primer

This study evaluated the rate of polymerization (R(p)) and degree of conversion (DC) of Panavia F when self- or dual-activated, and the influence of either using or not using a primer containing co-initiators (ED Primer) mixed with the material. The conversion reaction was monitored using real-time infrared spectroscopy with an attenuated total reflectance device. The cement was mixed, put onto the device and irradiated for 20 s (dual-cured). A self-cured group was also prepared. Similarly, dual- and self-cured groups were evaluated after mixing ED Primer with the cement. The DC was monitored for 1 h and the R(p) was calculated. For the dual-cured mode, the most significant effect of ED Primer was to reduce the R(p)(max). For the self-cured mode, the primer was shown to be essential for polymerization of Panavia F: without ED Primer, the reaction started only after approximately 500 s, with a final DC of 50%, whereas a continuous increase in conversion was observed for the group mixed with ED Primer, with a final DC of 74%. The ED primer is essential for proper polymerization of Panavia F; the cement becomes independent of the light when the primer is used.

Contemporary Methacrylate Resin–based Root Canal Sealers Exhibit Different Degrees of Ex Vivo Cytotoxicity When Cured in Their Self-cured Mode

The cytotoxicity of four methacrylate resin–based sealers was investigated by the 3-(4,5-dimethyl-thiazoyl)-2,5-diphenyl-tetrazolium bromide assay, which measures cell viability by assessing its succinate dehydrogenase activity. The sealers were polymerized in the self-cured mode to simulate the setting condition upon their extrusion into periradicular tissues. Disks were prepared from EndoREZ (Ultradent, South Jordan, UT), RealSeal (SybronEndo, Orange, CA), MetaSEAL (Parkell, Farmington, NY), and RealSeal SE (SybronEndo) together with positive and negative controls. After setting, they were placed in direct contact with rat osteosarcoma (ROS 17/2.8) cells and for 5 succeeding weeks after immersing in simulated body fluid (SBF). All sealers exhibited severe toxicity initially (week 0). EndoREZ and RealSeal remained severely toxic after five cycles of SBF immersion. Toxicity of the two self-etching resin-based sealers MetaSEAL and RealSeal SE decreased gradually over time. Transmission electron microscopy of cells exposed to RealSeal SE showed variable degrees of cell injury that reflect its toxicity status. Cells with intact mitochondria were identifiable after the sealer became noncytotoxic at week 5.

Effect of curing mode on the polymerization characteristics of dual-cured resin cement systems

Objectives To evaluate the effects of different curing conditions on the degree of conversion (DC) of dual-cured cementing systems [combination of bonding agent (BA) and resin cement (RC)] using infrared spectroscopy. Methods Four fourth generation products [Scotchbond Multipurpose Plus/RelyX (3M ESPE), Optibond/Nexus 2 (Kerr), All Bond2/Duolink (Bisco), and Bond-It!/Lute-It! (Pentron)], and three fifth generation materials [Bond1/Lute-It! (Pentron), Prime&Bond NT Dual-Cure/Calibra (Dentsply), and Optibond Solo Dual Cure/Nexus 2 (Kerr)] were applied to the surface of a horizontal attenuated-total-reflectance unit, and were polymerized using one of four conditions: self-cure (SC), direct light exposure through glass slide (DLE, XL3000/3M ESPE) or through pre-cured resin discs (shades A2;A4/2 mm thick/Z250/3M ESPE). Infrared spectra of the uncured cementing systems were recorded immediately after application to the ATR, after the system was light-cured or left to self-cure, and spectra were obtained 5 and 10 min later. DC was calculated using standard techniques of observing changes in aliphatic-to-aromatic peak ratios pre- and post-curing. Data ( n = 5) were analyzed by two-way repeated measures ANOVA and Tukey's test ( p = 0.05). Results Changes in aliphatic-to-aromatic peak ratios before and after placing RC onto the BA demonstrated that a combined layer was created. All groups exhibited higher DC after 10 min than after 5 min, except the DLE group of Bond-it!/Lute-it!. No significant differences in DC were observed among light-activated groups regardless of the resin disc shade in three of the four fourth generation cementing systems. The SC groups exhibited lower DC than the DLE groups for both fourth and fifth generation products either after 5 or 10 min. Conclusion The chemistry of the bonding interface changed when RCs were applied to uncured BAs. The presence of an indirect restoration can decrease the DC of some cementing systems and the self-curing mode leads to lower DC than the light-activating one.

Adhesion of a quartz fibre post to a composite resin core: influence of bonding agents and their curing mode

Fibre-reinforced composite posts are currently used to restore endodontically-treated teeth. Push-out tests were carried out to evaluate the performance of several bonding agents on the retention of an endodontic quartz fibre post to a composite resin core. Five bonding agents were investigated in both self-cure and light-cure modes. Ten experimental groups of 10 posts each were constituted as a function of curing mode and bonding agent. Specimens were mounted in a dedicated Teflon mould. This experimental set-up allowed the determination of true shear strength. One-way ANOVA and Student–Newman–Keuls tests were used for statistical analysis. The bonding strengths ranged from 23.4 MPa to 35.3 MPa. The best results were obtained with a light-cure self-etch bonding agent; in all cases photo-polymerisation led to statistically higher bonding strengths compared to chemical auto-polymerisation. Shear bond strength at the post–adhesive interface was also found to be significantly dependant on the nature of the bonding agent. AdheSe self-etch bonding agent was more effective than etch-and-rinse single-component bonding agents.

The effect of bonding resin on bond strength of dual-cure resin cements

The objective of this study is to evaluate the effect of an additional application of bonding resin on the bond strength of resin luting cements in both the light-cure (LC) and self-cure (SC) modes by means of the μ TBS tests. Three combinations of One-Step Plus with Choice, Single Bond with Rely X ARC, and One-Up Bond F with Bistite II were used. D/E resin and Pre-Bond resin were used for the additional application. Twelve experimental groups were made. Three mandibular 3 rd molars were used in each group. Indirect composite blocks were cemented on the tooth surface. 1 × 1 ㎟ dentin-composite beam for μ TBS testing were made and tested. When total-etching dentin adhesives were used, an additional application of the bonding resin increased the bond strength ( P 0.05). In conclusion, the results suggest that an additional application of the bonding resin increases bond strength and enhances quality of bonding when using total-etching dentin adhesives. [J Kor

Influence of thickness on the degree of cure of composite resin core material

The purpose of this study was to investigate the influence of thickness on the degree of cure of dual-cured composite core. 2, 4, 6, 8 mm thickness Luxacore Dual and Luxacore Self (DMG Inc, Hamburg, Germany) core composites were cured by bulk or incremental filling with halogen curing unit or self-cure mode The specimens were stored at for 24 hours and the Knoop's hardness of top and bottom surfaces were measured. The statistical analysis was performed using ANOVA and Tukey's test at p = 0.05 significance level. In self cure mode, polymerization is not affected by the thickness. In Luxacore dual, polymerization of the bottom surface was effective in 2, 4 and 6 (incremental) mm specimens. However the 6 (bulk) and 8 (bulk, incremental) mm filling groups showed lower bottom/top hardness ratio (p

Micro-tensile bond strength of three luting resins to human regional dentin

To evaluate the micro-tensile bonding strength (muTBS) of three luting resins to human regional dentin. Dentin disks from non-carious third molars were prepared from different regions (s, superficial dentin; d, deep dentin; c, cervical dentin), and divided into groups based on anatomical locations and luting resins (Super-Bond C&B: SB; Panavia F 2.0: PF; RelyX Unicem: RU): SB-s, SB-d, SB-c; PF-s, PF-d, PF-c; RU-s, RU-d, RU-c. Luting resins were used according to the manufacturers' instructions, to bond 1-mm-diameter PMMA or composite rods to the exposed dentin specimens under a load of 7.5 N, in the self-curing mode. After storage for 1 or 3 days, muTBS was tested at a cross-head speed of 1mm/min. Data were analyzed with ANOVA and Fisher's PLSD test. The bonding interface and fractography analyses were performed with SEM and TEM. ANOVA results showed that muTBS to superficial dentin was significantly higher than to deep or cervical dentin for all three luting resins. SB-s and PF-s, with the highest muTBS, failed primarily cohesively in luting resin. muTBS of SB-d and SB-c were significantly higher than those of PF and RU. RU, with the lowest regional muTBS, failed mostly within demineralized dentin. SEM and TEM showed that adhesive failures in SB and PF occurred at the top of the hybrid layer (HL), but no obvious HL was observed in RU. Luting resins with different chemical formulations and applications yield significantly different bond strengths to different regions in human dentin.

Polymerization contraction stress in dual-cure cements and its effect on interfacial integrity of bonded inlays

Objectives. To compare the polymerization contraction stress of resin cements in dual-cure and self-cure modes, and verify its effect on microleakage and gap formation in class I cavities restored with porcelain inlays. Methods. Dual-cure cements (Calibra, Choice and RelyX ARC) were monitored for contraction stress during 30 min in the tensilometer, in the presence or absence of photo-activation. Microleakage was evaluated in porcelain inlays bonded to cavities prepared in bovine incisors, combining the same adhesive (One-Step) with each of the cements in both activation modes. Epoxy replicas of the sectioned specimens were analyzed in the SEM to determine the percentage of discontinuous margins. Results. The stress developed in dual-cure mode was higher than in self-cure mode for all cements. In self-cure mode, no significant difference in stress was found among materials. Choice and RelyX ARC showed higher microleakage in dual-cure mode than in self-cure mode. Calibra did not show a significant difference in microleakage between activation modes. Contraction gap results showed wide variations, and no significant differences were detected among the groups. Gaps occurred more often in dentin, with an overall average of 22±17.5%. Conclusions. The higher stress generated in dual-cure cements subjected to photo-activation may lead to higher marginal leakage. In the confinement condition represented by the class I inlay, even the lower contraction stress of the cements in self-cure mode had enough magnitude to disrupt the bonding to dentin.

Mechanical properties of resin cements with different activation modes.

Dual-cured cements have been studied in terms of the hardness or degree of conversion achieved with different curing modes. However, little emphasis is given to the influence of the curing method on other mechanical properties. This study investigated the flexural strength, flexural modulus and hardness of four proprietary resin cements. Materials tested were: Enforce and Variolink II (light-, self- and dual-cured), RelyX ARC (self- and dual-cured) and C & B (self-cured). Specimens were fractured using a three-point bending test. Pre-failure loads corresponding to specific displacements of the cross-head were used for flexural modulus calculation. Knoop hardness (KHN) was measured on fragments obtained after the flexural test. Tests were performed after 24 h storage at 37 degrees C. RelyX ARC dual-cured showed higher flexural strength than the other groups. RelyX ARC and Variolink II depended upon photo-activation to achieve higher hardness values. Enforce showed similar hardness for dual- and self-curing modes. No correlation was found between flexural strength and hardness, indicating that other factors besides the degree of cure (e.g. filler content and monomer type) affect the flexural strength of composites. No statistical difference was detected in the flexural modulus among the different groups.