The Effect of the Initiator/Activator/Accelerator Ratio on the Degree of Conversion, Film Thickness, Flow, and Cytotoxicity of Dual-Cured Self-Adhesive Resin Cements.

Although self-adhesive resin cements are convenient and less technique-sensitive materials for dental clinicians, they exhibit a lower degree of conversion due to acidic components in their composition. Supplementation of the initiator, accelerator, and activator in self-adhesive resin cements has been suggested to compensate for the lower degree of conversion. This study aimed to evaluate the effects of different combinations of self-curing initiators, self-curing activators, and accelerators on the degree of conversion (DC) of self-adhesive resin cements. A dual-cured self-adhesive resin was prepared using six combinations of initiators, activators, and accelerators. The change in the DC over time was evaluated with and without light curing. The film thickness, flow properties, and cytotoxicity of each formulation were assessed. The results showed that all supplemental components had an effect on increasing the DC, but a greater increase in the DC was observed in the following order: activator, accelerator, and initiator. The cytotoxicity of the resin cements was related to the DC values, as resin cements with lower DC values exhibited higher cytotoxicity. The film thickness met the ISO standards for all groups. The results suggest that utilizing an activator is the most effective approach to enhance the DC in self-adhesive resin cement and that cytotoxicity tended to increase with lower DC values, whereas film thickness and flow properties demonstrated no correlation with DC values.

Assessment of Degree of Conversion and Volumetric Shrinkage of Novel Self-Adhesive Cement.

The degree of monomer conversion and polymerization shrinkage are two of the main reasons for potential adhesion failure between the tooth structure and the restoration substrate. To evaluate the degree of conversion and polymerization shrinkage of a newly developed self-adhesive resin cement, the degree of conversion (DC) was measured using FTIR under different activation modes, temperatures, and times. Volumetric shrinkage was tested using the AcuVol video imaging method. The experimental cement showed a higher DC than other cements under self-curing. The DC of the experimental cement was higher than that of other cements, except SpeedCem Plus under light curing. The experimental cement had a higher DC than other cements, except SpeedCem Plus in some conditions under dual curing. All self-adhesive cements had a higher DC at 37 °C than at 23 °C under self-curing, and there was no statistical difference between 23 °C and 37 °C under light curing. All self-adhesive cements showed a significantly higher DC at 10 min than at 5 min under self-curing. There was no statistical difference between 5 min and 10 min for most cements under dual curing. All self-adhesive cements statistically had the same volumetric shrinkage under light curing and self-curing. The newly developed self-adhesive resin cement exhibited a higher degree of conversion and similar volumetric shrinkage compared to these commercial self-adhesive resin cements.

Influence of the Fiber Post Length on the Fracture Strength of Endodontically Treated Teeth.

Background and Objectives: Although fiber posts are widely used in the restoration of endodontically treated teeth (ETT), their ideal cementation depth into the root canal is still debated in literature. The aim of the present study was to evaluate whether the different intra-radicular insertion lengths of the fiber posts influence the fracture strength of ETT. Materials and Methods: A total of 10 permanent human lower incisors with straight roots of similar length and volume extracted for periodontal reason were sectioned 2 mm above the cement-enamel junction (CEJ) to a total length of 18 mm and endodontically treated in the same manner, then randomly divided into two groups of five each (Groups 1 and 2, n = 5). Two sound incisors, with no endodontic treatment, were used as the control group (Group 3, n = 2). After one week of storage in a humid environment, spaces for fiber post no. 1 (Reforpost, Angelus, Londrina, PR, Brazil) were prepared in the first two groups at a depth of 5 mm (Group 1) and 7 mm (Group 2), and the fiber posts were adhesively cemented using self-adhesive resin cement (Maxcem Elite, Kerr GmbH, Herzogenrath, Germany). After 7 days, the samples were vertically positioned and fixed in a self-curing transparent acrylic resin, up to 2 mm below the CEJ level, and mechanically tested in compression after another week of storage using a displacement-controlled testing machine up to each sample's fracture. The force-displacement curves were recorded for each sample, the means were calculated for each group and a statistical comparative analysis between groups was conducted. Results: Although no statistically significant differences between groups were observed, the highest mean fracture force (N) was recorded in Group 2 (1099.41 ± 481.89) in comparison to Group 1 (985.09 ± 330.28), even when compared to the sound, non-treated teeth (1045.69 ± 146.19). Conclusions: Within the limitations of this in vitro study, teeth where fiber posts were placed deeper into the root canal (7 mm) recorded slightly higher fracture forces in comparison with shorter lengths (5 mm). However, similar biomechanical performances obtained in the mechanical tests showed no statistical differences between the 7 mm and the 5 mm inserted posts.

Effectiveness of dentin pre-treatment on bond strength of two self-adhesive resin cements compared to an etch-and-rinse system: an in vitro study.

STATEMENT OF PROBLEM: It has been shown that selective etching improves the bond strength of some self-adhesive resin cements to enamel. The same has yet to be determined with dentin pre-treatment. PURPOSE: To evaluate the tensile bond strength of two self-adhesive resin cements after two dentin surface pre-treatments, and also to analyze the cement/dentin interface. MATERIAL AND METHODS: One hundred and twelve human third molars were extracted. The teeth were distributed into seven groups (n = 16). Maxcem Elite Chroma (MAX) (Kerr, Scafati, Italy) and Relyx U200 (RLX) (3M ESPE, Neuss, Germany) were used without pre-treatment or with two dentin pre-treatments (polyacrylic acid or phosphoric acid). A conventional etch-and-rinse (EAR) luting cement, NX3 Nexus (NX3) (Kerr, Scafati, Italy), was used as an external control group. Before testing, all specimens were stored in distilled water for 24 hours. Three specimens from each group were prepared for scanning electron microscopy observation (SEM). A tensile bond strength test (TBS) was performed for the remaining samples. The data were statistically analyzed using the Kruskal-Wallis test and Pairwise comparisons using the Wilcoxon rank sum test. RESULTS: MAX without pre-treatment and with phosphoric acid etching attained statistically similar bond strengths to NX3 (P > 0.05). There was a statistical difference (P = 0.00488) between RLX without pre-treatment (5.62 MPa) and NX3 (10.88 MPa). Phosphoric acid pre-treatment increases the bond strength values of RLX to a strength that is comparable to NX3 (P > 0.05). The lowest tensile bond strength (TBS) was attained after the application of polyacrylic acid with MAX (1.98 MPa). No statistical differences were found between the RLX bond strength values after polyacrylic acid treatment and RLX without pre-treatment or NX3 (P > 0.05). SEM observations disclosed an enhanced potential of the self-adhesive cements to infiltrate into dentin tubules and form resin tags when applied after phosphoric acid pre-treatment. The failure mode was dominantly adhesive. CONCLUSIONS: On dentin, the self-adhesive resin cement MAX might be an effective alternative to conventional resin cement. Etching the dentin with phosphoric acid does not have a negative effect on the bond strength of MAX to dentin. On the other hand, phosphoric acid improved the bond strength of RLX when compared to EAR cement.

Randomized clinical split-mouth study on the performance of CAD/CAM-partial ceramic crowns luted with a self-adhesive resin cement or a universal adhesive and a conventional resin cement after 39 months.

Objectives To determine the clinical performance of partial ceramic crowns (PCCs) luted with a conventional resin cement combined with a universal adhesive without or with selective enamel etching or luted with a self-adhesive resin cement. Methods In a split-mouth design, each three CAD/CAM-PCCs (Vita Mark II, Cerec) were placed in 50 patients. Two PCCs were luted with a conventional resin cement (RelyX Ultimate) combined with a universal adhesive (Scotchbond Universal) without (SB-E) or with (SB+E) selective enamel etching. The third PCC was luted with a self-adhesive resin cement (RelyX Unicem 2; RXU). Chi-square tests (α≤0.05) were applied. Based on clinical failures (complete debonding or need for replacement of the restorations), Kaplan-Meier survival analysis was performed. Results 31 patients were evaluated clinically using FDI criteria at 39 months. Clinically acceptable results were detected over time, except for "fracture of material and retention" (inacceptable fractures and debondings). Within materials, statistically significant differences (p ≤ 0.003) between baseline and 39 months were found for "marginal adaptation" and "marginal staining". At 39-month, SB+E and SB-E showed significantly better results compared to RXU in "marginal adaptation"(p ≤ 0.021) and "marginal staining"(p ≤ 0.013). Kaplan-Meier analysis showed higher survival rates after 39 months for SB+E (96%) and SB-E (88%) compared to RXU (69%) with statistically significant differences between RXU vs. SB-E (p = 0.022) and RXU vs. SB+E (p ≤ 0.001). Conclusions After 39-months, PCCs luted with the self-adhesive resin cement exhibited a statistically significant inferior survival rate compared to restorations luted with the conventional resin cement combined with a universal adhesive without or with selective enamel etching. Clinical significance Currently, self-adhesive resin cements cannot be recommended for luting partial ceramic crowns. However, the standard adhesive luting procedure comprising a universal adhesive and luting composite yielded good clinical results for more than 3 years irrespectively of application of a selective enamel etching step.

Changes of residual stresses on the surface of leucite-reinforced ceramic restoration luted with resin composite cements during aging in water.

The objective of this study was to compare the changes in the residual stresses present on the surface of leucite-reinforced dental ceramic restorations luted with a self-adhesive and a conventional resin composite cement during aging in water. Ring specimens made of a leucite-reinforced ceramics were luted to ceramic cylinders using a self-adhesive (Panavia SA Luting Plus) or a conventional resin composite cement (Panavia V5) in dual-cure or self-cure mode. Residual stresses on the ring surface were measured using indentation fracture method at 1 h, 1, 3, 7, 14 and 28 days of the 37 °C water immersion. Water sorption, water solubility and elastic modulus of the cements were also measured. Compressive stress was generated on the surface of the ceramic rings by the polymerization of the resin composite cements, and the stresses appeared to decrease over time by water sorption of the cements. The dual-cured conventional resin composite cement remained compressive stresses on the ceramic surface, while only the self-cured self-adhesive cement, which demonstrated the greatest water sorption, generated tensile stresses during the four weeks of aging in water. The elastic moduli of cements did not significantly change through the immersion, suggesting that the stresses were less affected by the modulus. To prevent the generation of tensile stresses on the leucite-reinforced ceramic restoration, self-adhesive cements exhibiting small water sorption should be clinically selected.

Micromorphology of the Adhesive Interface of Self-Adhesive Resin Cements to Enamel and Dentin.

Interfaces between dentin, enamel and luting agents were characterized using low vacuum Scanning Electron Microscopy (SEM). After smear layer creation, one of three luting agents (RelyX Unicem 2, Clearfil SA Cement and Panavia F 2.0/ED Primer II) was applied on 60 enamel-dentin specimens and dual-cured or self-cured. Specimens were polished (Experiment 1) and subsequently demineralized and deproteinized (Experiment 2). Adhesive interfaces were analyzed (low vacuum SEM, ×3000). Presence of an interdiffusion zone, tag-like structures (dentin) and marginal gaps (enamel) were assessed. Non-parametrical tests (χ2-test, α = 0.05) were performed. The first null-hypothesis was that the adhesive interface micromorphology between enamel and dentin and self-adhesive resin cements (SARCs) is similar with conventional resin cement used with a self-etch adhesive (CRC+SE). The second null-hypothesis was that the micromorphology is not influenced by curing modes. Interdiffusion zones and tag-like structures (dentin) were observed more frequently for CRC+SE compared to SARCs. For each luting agent, there was a non-significant (p > 0.05) tendency for interdiffusion zone and tag-like structures detectable in more specimens after self-curing compared to dual-curing. Marginal gaps (enamel) were found only for SARCs. The first null-hypothesis was not rejected fully: Tag-like structures and interdiffusion zones in dentin were found for CRC+SE and SARCs. The second null-hypothesis was not rejected.

Influence of resin cements and root canal disinfection techniques on the adhesive bond strength of fibre reinforced composite post to radicular dentin.

AIM: To determine the push out bond strength (PBS) of fibre reinforced composite post (FRCP) bonded to radicular dentin using different cement types total etch resin cement (TERC) and Self-adhesive resin cement (SARC) conditioned with (PDT, 5.25 % NaOCl with EDTA and 1% NaOCl) MATERIALS AND METHODS: Sixty freshly extracted (orthodontic purpose) human single rooted mandibular premolars were collected. Teeth were disinfected and coronal part of all samples were removed. Cleaning shaping and finishing of canal space was performed and filled with gutta percha via lateral condensation. Post space was prepared and disinfected with three irrigating solutions. Samples in group 1 and 2 disinfected 5.25 % NaOCl with EDTA, group 3 and 4 steriled with 1% NaOCl and group 5 and 6 disinfected with Methylene Blue photodynamic therapy (PDT). Based on the resin cement, FRCP was luted with TERC in group 2, 4 and 5; and with SARC in group 1,3 and 6 respectively. All specimens were subjected to aging and push-out bond strength (PBS) on universal testing machine after sectioning of each sample in three segments (coronal, middle and apical). Following push out bond strength (PBS), debonded surface were observed under stereomicroscope at 40x magnification. PBS were equated by means of analysis of variance (ANOVA) and Tukey's post hoc test maintaining level of significance (p < 0.05) RESULTS: Group 1 (SARC) and 2 (TERC) disinfected with 5.25 % NaOCl with 17 % EDTA, TERC (group 2) showed higher extrusion bond strength at all three levels coronal (9.25 ±â€¯0.21 MPa) middle (8.81 ±â€¯0.94 MPa) and apical (8.21 ±â€¯0.93 MPa). Whereas, canal space sterilized with 1% NaOCl [group 3 (SARC) and group 4 (TERC)], posts cemented with TERC exhibited the higher PBS at all three levels of root canal (10.22 ±â€¯0.36 MPa), (9.68 ±â€¯0.51 MPa), (6.33 ±â€¯0.08 MPa). Similarly, among PDT disinfected fiber post [group 5 (TERC) and group 6 (SARC)], TERC exhibited the greater PBS values at coronal, middle and apical levels (6.25 ±â€¯0.39 MPa) (5.17 ±â€¯0.22 MPa) (4.32 ±â€¯0.69 MPa) compared to SARC specimens CONCLUSION: Irrespective of canal irrigant, fiber post bonded with TERC showed higher PBS at coronal and middle third. Fiber post bonded with SARC when irrigated with 5.25 % NaOCl with EDTA, 1% NaOCl displayed higher PBS at apical third. Canal disinfected using PDT showed lower PBS for FRCP compared to 5.25 % NaOCl with EDTA and 1% NaOCl.

The Retentive Strength of Zirconium Oxide Crowns Cemented by Self-Adhesive Resin Cements before and after 6 Months of Aging.

The aim of this study was to evaluate the retentive strength of zirconium oxide (yttria-stabilized tetragonal zirconia polycrystals (Y-TZP)) crown-copings treated by combined mechanical and chemical treatments and cemented by four types of self-adhesive resin cements (SARCs) to human prepared teeth, before and after six months of aging in water and thermocycling. A total of 120 molar teeth were mounted, prepared using a standardized protocol and digitally scanned, and Y-TZP copings were produced. Teeth were randomly assigned to four SARC groups. Prior to cementation, the intaglio surfaces of all crowns were sandblasted and then coated with Z-Prime™ Plus (Bisco Dental, Schaumburg, IL, USA). Post cementation, each cement group was subdivided into aged and non-aged groups. After aging, the cemented assemblies were tested for retentive strength using a universal testing machine. Failure analysis was conducted by inspecting all matched debonded surfaces of the teeth and crowns at 3× magnification. Aging treatment did not affect the retentive strength of the Y-TZP crown-copings (p = 0.918). The interaction between cement and aging was statistically significant (p = 0.024). No significant differences in the retentive strengths between the different SARCs were observed pre-aging (p = 0.776), whereas post-aging, Panavia SA (PAN; Kuraray Dental Co Ltd., Osaka, Japan) showed significantly higher strength than RelyX U-200 (RU200; 3M ESPE, Seefeld, Germany). The predominant failure mode was adhesive between the cement and dentin, followed by mixed mode failure.

Fracture Resistance of Endodontically Treated Teeth Restored with Fiber Posts Luted with Composite Core Materials.

AIM: This study aimed to investigate the influence of using dual-cure composite core materials for fiber post luting on the fracture resistance of endodontically treated maxillary central incisors. MATERIALS AND METHODS: Fifty sound and recently extracted maxillary central incisors were endodontically treated and distributed into five groups. In the control group, access cavities were restored with the composite resin. Experimental groups had the coronal structure trimmed 2 mm above the cementoenamel junction. Teeth were restored with fiber posts and different combinations of luting and core materials: RelyX Unicem for post luting and MultiCore for core buildup; MultiCore for post luting and core buildup; RelyX Unicem for post luting and LuxaCore for core buildup; or LuxaCore for post luting and core buildup. All teeth were restored with zirconium crowns and subjected to thermocycling (6000 cycles 5/55°C). Loading of the teeth was applied at 135° to the palatal surface, using a universal testing machine at a cross-speed of 0.5 mm/minute until failure. The mode of failure was analyzed under a digital microscope. RESULTS: The fracture resistance of the control group was significantly higher than the experimental groups (p < 0.05). There was no significant difference between the experimental groups (p > 0.05). All teeth demonstrated nonrestorable failures. CONCLUSION: With the presence of the ferrule effect and crown restoration, the selected materials for post luting and core buildup have no significant influence on the fracture resistance of the endodontically treated teeth. CLINICAL SIGNIFICANCE: The use of the same dual-cure composite core materials for fiber post luting and core buildup would simplify the clinical procedure without enhancement of the fracture resistance of the endodontically treated tooth.

Cytotoxic effects of different self-adhesive resin cements: Cell viability and induction of apoptosis.

PURPOSE: The effects of four different self-adhesive resin cement materials on cell viability and apoptosis after direct and indirect exposure were evaluated using different cell culture techniques. MATERIALS AND METHODS: Self-adhesive cements were applied to NIH/3T3 mouse fibroblasts by the extract test method, cell culture inserts, and dentin barrier test method. After exposure periods of 24 h and 72 h, the cytotoxicity of these self-adhesive materials was evaluated using the MTT assay (viability) and the Annexin-V-FITC/PI staining (apoptosis). RESULTS: The lowest cell viability was found in cells exposed to BeautiCem SA for 24 h in the extract test method. Cell viability was reduced to 70.6% compared to negative controls. After the 72 h exposure period, viability rate of cell cultures exposed to BeautiCem SA decreased more than 2- fold (29.5%) while cells exposed to RelyX U200 showed the highest viability rate of 71.4%. In the dentin barrier test method, BeautiCem SA induced the highest number of cells in apoptosis after a 24 h exposure (4.1%). Panavia SA Cement Plus was the material that caused the lowest number of cells in apoptosis (1.5%). CONCLUSION: The used self-adhesive cements have showed different cytotoxic effects based on the evaluation method. As exposure time increased, the materials showed more cytotoxic and apoptotic effects. BeautiCem SA caused significantly more severe cytotoxic and apoptotic effects than other cements tested. Moreover, cements other than BeautiCem SA have caused necrotic cell death rather than apoptotic cell death.

Effect of Sonic Application of Self-Adhesive Resin Cements on Push-Out Bond Strength of Glass Fiber Posts to Root Dentin.

The aim of this study was to evaluate the influence of a sonic application of self-adhesive resin cements on the bond strength of glass fiber posts to root dentin. Eighty bovine incisors were randomly divided into eight groups (n = 10). Four self-adhesive resin cements were used-RelyX U200 (3M/ESPE), Bifix SE (Voco), seT PP (SDI), and Panavia SA (Kuraray). The cements were inserted into the root canal in two different modes-Centrix syringe (control) or with a sonic device (Sonic Smart). The roots were sectioned and taken to a universal test machine (Instron 3342) to perform the push-out test. The fracture pattern was evaluated by stereomicroscope and scanning electron microscope. The bond strength data were analyzed by two-way ANOVA and Tukey tests (α = 0.05). The interaction between the main factors was significant (p = 0.002). The sonic application increased the bond strength in comparison with the conventional application for the RelyX U200 (p < 0.001) and Bifix SE (p < 0.017) cements. However, for the seT PP and Panavia SA cements, the bond strength values did not differ significantly (p > 0.05). The fracture pattern showed adhesive at the interface between the luting cement and the dentin. Using a sonic device in the application of self-adhesive resin cement helpedpromote an increase in the bond strength for RelyX U200 and Bifix SE.

Phosphoric and carboxylic methacrylate esters as bonding agents in self-adhesive resin cements.

The aim of the present study was to investigate the effect of pH and phosphoric ester structure (phosphonate or phosphate) on the bond strength of different dental restorative materials. The following three self-adhesive resin cements were used in the present study: RelyX™ Unicem, Maxcem and Multilink Sprint The pH of each cement was measured using a pH meter. The cements were used to attach a variety of restorative materials to human dentin and the bond strength was measured by assessing shear strength using a universal testing machine. The pH values of RelyX Unicem, Maxcem and Multilink Sprint were 3.78, 1.78 and 3.42, respectively. Maxcem, a phosphate-based self-adhesive cement, was demonstrated to form the weakest bonds. No significant difference in bond strength was observed between RelyX Unicem and Multilink Sprint, which are phosphonate-based cements. The results of the present study suggest that the chemical structure of the functional monomer influences the performance of an adhesive material. Furthermore, the pH of acidic functional monomers containing phosphonate or phosphate groups has an effect on the strength of bonds formed between dentin and restorative materials.

Hygroscopic expansion of self-adhesive resin cements and the integrity of all-ceramic crowns.

OBJECTIVE: Low pH neutralization and subsequent remnant hydrophilicity can lead to hygroscopic expansion of self-adhesive resin cements (SARCs) after water storage. The aim of this in vitro study was to investigate the effects of hygroscopic expansion of SARCs, used as luting and partial core build-up material, on integrity and cement gap thickness increase of all-ceramic CAD/CAM crowns. METHODS: Human third molars (n=48) were prepared and anatomical all-ceramic CAD/CAM crowns were manufactured (VITABLOCS Mark II, VITA Zahnfabrik). Crowns internal surfaces were HF etched and silanized. The prepared teeth with their respective crowns were divided into 6 groups (n=8). In groups 1, 3 and 5 the coronal dentin was removed to simulate a partial core build-up. Groups 1 and 2 were luted with iCEM (Heraeus Kulzer), 3 and 4 with RelyX Unicem 2 Automix (3M), 5 and 6 with Variolink Esthetic DC (Ivoclar Vivadent). All specimens were dual cured and stored in distilled water at 37°C. Crown integrity was controlled at baseline and in regular intervals until 180 days. Cement gap thickness was measured using an optical 3D scanner (ATOS Triple scan, GOM) at baseline and after 180 days. Crown integrity was statistically analysed using Kaplan-Meier survival analysis and cement gap thickness increase using two-way ANOVA (α=0.05). RESULTS: After 180 days storage, crack formation was observed in all specimens of group 1 (mean survival time of 85.5 days), in one specimen of group 2 and in two specimens of group 4. Two-way ANOVA analysis revealed a statistically significant interaction between material type and build-up on cement gap size increase for iCEM. SIGNIFICANCE: Within the limits of this study, the application of SARCs with low pH neutralization as partial build-up material under CAD/CAM crowns is not recommended for clinical use.

Effect of light irradiation and primer application on polymerization of selfadhesive resin cements monitored by ultrasonic velocity.

In this study, we investigated the effect of light irradiation and primer/adhesive application on the polymerization reaction and elastic modulus (E) of self-adhesive resin cement (SAC) through ultrasonic velocity (V) measurements. The V values of longitudinal and shear waves were determined based on the transit time through the specimens and specimen thicknesses, and were used to calculate the E values. Analysis of variance and Tukey tests revealed that V increased rapidly, reaching a plateau at 2,700-2,900 m/s, when the SACs were light-irradiated. However, the increasing rate of V was retarded for the non-irradiated SACs. In addition, when the primer/adhesive was applied, higher E values were obtained after 24 h. Finally, the polymerization behavior of the SACs was affected by light irradiation and primer application, and the use of prime/adhesive might improve mechanical properties. In clinical situations, use of primer/adhesive is recommended for getting proper adhesion.

Differential cytotoxic effects on odontoblastic cells induced by self-adhesive resin cements as a function of the activation protocol.

OBJECTIVES: To evaluate the cytotoxic effects of exposing odontoblast cells to a variety of commercial self-adhesive cements polymerized using different activation modes. METHODS: Five cements: MaxCem Elite (MAX), Bifix SE (BSE), G-Cem LinkAce (GCE), Clearfil SA Luting (CAS), and RelyX U200 (U200) were mixed, dispensed into molds, and distributed in groups, according to polymerization protocols: immediate photoactivation; delayed photoactivation (10min self-curing plus light-activation); and chemical activation (no light exposure). Immortalized rat odontoblast cells (MDPC-23) were cultured. Cell viability was assessed by Trypan Blue staining and total cell death was assessed by annexin V-APC/7-AAD double staining and flow cytometry. Volatilized compounds from polymerized specimens of cements were evaluated by gas chromatography/mass spectrometry (GC-MS). Data was analyzed with 2-way ANOVA/Tukey tests (α=0.05). RESULTS: Exposure to all of the cements tested significantly reduced the cell viability, irrespective of the activation protocol (p<0.05). The least harmful cements were CSA and U200. Total death of cells significantly increased when exposed to BSE, GCE, and MAX, especially when chemically activated (p<0.05). Characteristic apoptotic cells increased after exposure to cements, mainly for MAX, regardless of the activation mode. Chemical activation of MAX also induced necrosis. Moreover, GCE and MAX exhibited higher percentages of late apoptotic/dead cells. Chromatograms revealed 28 compounds released from the cements tested, some of them with known carcinogenic effects. Selection of self-adhesive cements and polymerization protocols affect the cytotoxicity and cell viability of odontoblastic cells. CLINICAL SIGNIFICANCE: Despite the simplified cementation protocol, care is needed when cementing indirect restorations with self-adhesive cements, especially on recently exposed dentin. This category of material may cause differential cytotoxic effects and should be considered when selecting a cement. This is particularly true in clinical cases of light attenuation, where the polymerization depends on chemical activation, inducing higher cytotoxic damages when using some of the cements tested.

Dental Cements for Luting and Bonding Restorations: Self-Adhesive Resin Cements.

Self-adhesive resin cements combine easy application of conventional luting materials with improved mechanical properties and bonding capability of resin cements. The presence of functional acidic monomers, dual cure setting mechanism, and fillers capable of neutralizing the initial low pH of the cement are essential elements of the material and should be understood when selecting the ideal luting material for each clinical situation. This article addresses the most relevant aspects of self-adhesive resin cements and their potential impact on clinical performance. Although few clinical studies are available to establish solid clinical evidence, the information presented provides clinical guidance in the dynamic environment of material development.

Self-adhesive resin cements: pH-neutralization, hydrophilicity, and hygroscopic expansion stress.

OBJECTIVES: The objective of the study was to investigate the relationship between pH-neutralization, hydrophilicity, and free hygroscopic expansion stress of self-adhesive resin cements (SARCs) after storage in artificial saliva. MATERIALS AND METHODS: The SARCs RelyX Unicem Automix 2 (RX2, 3 M ESPE), iCEM (iCEM, Heraeus) and Maxcem Elite (MCE, Kerr) were under investigation in this study. Cylinders (height × diameter, 6 × 4mm) were prepared from each material and stored in artificial saliva (7d at 37 °C). Cylinder height was measured at baseline and after 7 days. After storage, the compression modulus was measured to calculate the free hygroscopic expansion stress. For pH-neutralization and hydrophilicity assessment, disks (height × diameter, 1 × 1.5 mm) were prepared, covered with electrolyte, and monitored over 24 h at 37 °C. Hydrophilicity was assessed using the static sessile drop technique at baseline and at different time intervals up to 24 h. Data were analyzed using one-way ANOVA and post hoc Student-Newman-Keuls test (S-N-K, α = 0.05). RESULTS: After 24 h, RX2 (pH24h 4.68) had a significantly higher (p < 0.05) pH-value than MCE (pH24h 4.2) and iCEM (pH24h 3.23). iCEM showed the significantly highest hydrophilicity (p < 0.05) after 24 h (θ24h 85.02°), while MCE resulted lower (θ24h 113.01°) in comparison with RX2 (θ24h 108.11°). The resulting hygroscopic expansion stress of iCEM (29.15 MPa) was significantly higher (p < 0.05) compared to RX2 (14.5 MPa) and MCE (21.02 MPa). CONCLUSIONS: The material with lowest pH-neutralization capacity displayed higher hydrophilicity after 24 h and higher hygroscopic expansion stress after 7 days compared to those with high pH-neutralization. CLINICAL SIGNIFICANCE: Remnant hydrophilicity due to low pH-neutralization of SARCs could lead to cement interface stress build-up and long-term failure of silicate ceramic restorations.

Push-out Bond Strength of Glass Fiber Posts Cemented in Weakened Roots with Different Luting Agents.

AIM: To evaluate the push-out bond strength (BS) of direct anatomic posts (DAPs) and conventional fiber posts (CFPs) cemented with different luting agents in different thirds of flared root canals. MATERIALS AND METHODS: A total of 60 human single-rooted canine teeth were transversally sectioned 16 mm from the radicular apex. After endodontic treatment, canals were flared with diamond burs. Samples were divided into six groups according to post type and luting agent: DAP and RelyX U100 (RXU); DAP and RelyX ARC (RXA); DAP and RelyX Luting 2 (RXL); CFP and RXU; CFP and RXA; CFP and RXL. Roots were sectioned transversely into six 1-mm-thick slices. The push-out test was performed and failure modes were observed. RESULTS: The DAP groups (7.23 ± 2.05) showed highest BS values (p < 0.05) when compared with CFP (5.93 ± 1.76). RelyX U100 (8.17 ± 1.70) showed higher BS values (p < 0.05) than RXA (6.46 ± 1.38), and RXL (5.10 ± 1.65) showed the lowest values. Bond strength on the apical third was statistically lower (p < 0.05) than that on the other thirds of the root canals. There was a predominance of adhesive failure for all groups. CONCLUSION: The DAPs improved retention in flared root canals, and RXU was the most effective luting agent. The apical third showed the lowest BS values. CLINICAL SIGNIFICANCE: The relining procedure of fiber posts with composite and the proper selection of luting resin cement are important for increasing bonding effectiveness in flared root canals.

Effect of dentin pretreatment and curing mode on the microtensile bond strength of self-adhesive resin cements.

PURPOSE: The aim was to evaluate the effect of curing mode and different dentin surface pretreatment on microtensile bond strength (µTBS) of self-adhesive resin cements. MATERIALS AND METHODS: Thirty-six extracted human permanent molars were sectioned horizontally exposing flat dentin surface. The teeth were divided into 12 groups (3 teeth/group) according to the dentin surface pretreatment methods (control, 18% EDTA, 10% Polyacrylic acid) and curing mode (self-curing vs. light-curing) of cement. After pretreatment, composite resin blocks were cemented with the following: (a) G-CEM LinkAce; (b) RelyX U200, followed by either self-curing or light-curing. After storage, the teeth were sectioned and µTBS test was performed using a microtensile testing machine. The data was statistically analyzed using one-way ANOVA, Student T-test and Scheffe's post-hoc test at P<.05 level. RESULTS: For G-CEM LinkAce cement groups, polyacrylic acid pretreatment showed the highest µTBS in the self-cured group. In the light-cured group, no significant improvements were observed according to the dentin surface pretreatment. There were no significant differences between curing modes. Both dentin surface pretreatment methods helped to increase the µTBS of RelyX U200 resin cement significantly and degree of pretreatment effect was similar. No significant differences were found regarding curing modes except control groups. In the comparisons of two self-adhesive resin cements, all groups within the same pretreatment and curing mode were significantly different excluding self-cured control groups. CONCLUSION: Selecting RelyX U200 used in this study and application of dentin surface pretreatment with EDTA and polyacrylic acid might be recommended to enhance the bond strength of cement to dentin.