William Cunha Brandt

Light- and time-dependent polymerization of dual-cured resin luting agent beneath ceramic

Objective. In this study we investigated the degree of conversion (DC) of a dual-cured resin luting agent beneath a ceramic of different thickness. Material and Methods. The luting material (RelyX) was photo-activated for 40s through ceramic disks (Empress Esthetic, 0.7, 1.4, or 2mm thick). Dual (DUC) and chemically cured (CC) control groups were obtained. A delayed exposure (DE) procedure was tested in which the material was light-activated after 5 min without using ceramic. DC (%) was measured using infrared spectroscopy at 40 s, 1, 2, 4, 6, 8, and 10min. Light irradiance and spectrum transmitted through ceramic were measured using a power meter and a spectrometer. Results. A decrease in irradiance was detected with increasing ceramic thickness, but no alteration in the emission profile was observed. At 10min, all groups showed DC higher than at 40s. No significant differences were detected for DUC compared with the groups indirectly activated through the ceramic disks. Generally, CC showed the lowest DC values. No significant effect in DC was detected for DE after 10min. A significant increase in DC was generally detected only up to 4min. Conclusions. The luting agent was dependent on light exposure and time to obtain improved DC. Neither the indirect activation nor the DE procedure significantly influenced the final DC.

Mechanical and physical properties of silorane and methacrylate-based composites

OBJECTIVES This study measured the degree of conversion (DC), sorption, solubility and microhardness of methacrylate (Filtek Z250 and Filtek Z350XT) and silorane-based composites (Filtek P90). METHODS DC was measured using near infrared spectroscopy immediately and 24h after the photoactivation. Sorption and solubility measurements were performed after 24h, 4 weeks and 12 weeks of storage in water. Knoop microhardness was measured after 24h and after thermal cycling. The data were statistically analyzed using ANOVA followed by Tukeys, Tamhane or paired t-tests (α=0.05). RESULTS The DC for P90 (37.22±1.46) was significantly lower than the Z250 (71.44±1.66) and Z350 (71.76±2.84). Water sorption was highest in the Z250 and lowest in the P90. All the tested composites exhibited similar values after 24h of immersion, and no significant differences were observed. No significant differences were observed between the solubilities of the P90 composite (12 weeks) and the Z250 or Z350 composites (4 weeks). KHN values were less elevated for the P90 composite and similar for the Z250 and Z350 composites. An effect of thermal cycling on KHN values was observed for all the composites (p<0.001). CONCLUSIONS Silorane produced the lowest DC and KHN values and exhibited lower water sorption and solubility compared to methacrylate-based composites. These differences suggest that silorane composites exhibit better hydrolytic stability after 3 months of water immersion compared to conventional methacrylate-based composites. CLINICAL SIGNIFICANCE Silorane had higher hydrolytic stability after 3 months of water immersion than the methacrylate-based resins, despite the lower values of DC and KHN recorded.

In vitro toothbrushing abrasion of dental resin composites: packable, microhybrid, nanohybrid and microfilled materials

This study evaluated weight loss and surface roughening after toothbrushing of different resin composites: one packable (Solitaire 2, Heraeus Kulzer), one microhybrid (Charisma, Heraeus Kulzer), one nanohybrid (Simile, Pentron) and one microfilled (Durafill VS, Heraeus Kulzer). Cylindrical specimens (n = 20) were prepared. Half of the samples were submitted to 60,000 strokes, at 4 Hz, with a dentifrice-water slurry. Control samples (n = 10) remained stored at 37 degrees C. Pre- and post-abrasion parameters for weight (mg) and surface roughness (Ra, microm) were determined on an analytical balance and a surface profilometer. Data were separately submitted to Repeated Measures ANOVA and Tukeys test (a = 0.05). Percentages of weight loss were analyzed by ANOVA and Tukeys test (a = 0.05). The relationship between both evaluations was assessed by Pearsons test (a = 0.05). The means (%) for weight loss (standard deviation) were 0.65(0.2), 0.93(0.2), 1.25(0.6) and 1.25(0.4) for Simile, Durafill, Charisma and Solitaire, respectively. Baseline roughness means ranged from 0.065(0.01), 0.071(0.01), 0.066(0.02) and 0.074(0.01) for Simile, Durafill, Charisma and Solitaire, respectively, to 0.105(0.04), 0.117(0.03), 0.161(0.03) and 0.214(0.07) after testing. The composites with larger fillers presented higher weight loss and roughening than the finer materials (p < 0.05). For both evaluations, control specimens showed no significant alteration. No significant relationship between loss of weight and roughness alteration was detected (r = 0.322, p = 0.429).

Can phenyl-propanedione influence Knoop hardness, rate of polymerization and bond strength of resin composite restorations?

OBJECTIVES The aim of this study was to evaluate the degree of conversion (DC), rate of polymerization (R(p)(max)), Knoop hardness (KHN) and bond strength between tooth/restoration of composite resins containing different photo-initiators photo-activated by different light-curing units (LCUs). MATERIALS AND METHODS A mixture of BisGMA, UDMA, BisEMA and TEGDMA was prepared along with the following photo-initiators: camphorquinone (CQ), phenyl-propanedione (PPD) or the association (CQ/PPD) and 65 wt% of silanated filler particles. The LCUs included a halogen lamp XL 2500 and two LEDs: UltraBlueIS and UltraLume5. The conversion profiles during photo-polymerization were investigated using middle-infrared spectroscopy (mid-IR). Bond strength was evaluated using push-out test in ninety teeth with prepared cavities. Before the push-out test, Knoop hardness (KH) was verified in the top and at the base of the restorations. RESULTS PPD obtained lower R(p)(max) values, regardless of the LCU used. It also provided a greater bond strength than CQ when the LEDs LCUs were used. The degree of conversion after 40s of irradiation was the same for all composite resins, except PPD photo-activated for XL 2500, which showed lower DC values than CQ and CQ/PPD. In the top and at the base of the restorations, PPD showed the lowest KH values when photo-activated with XL 2500. XL 2500 produced higher KH values than UltraBlueIS when used with CQ or CQ/PPD photo-initiators. CONCLUSION Because it increased the bond strength without compromising the properties of composite resins when photo-activated by an LED, PPD can be used as an alternative photo-initiator.

Stability of external and internal implant connections after a fatigue test

Objective: The objective of this study was to compare the torque and detorque values of screw intermediates of external hexagon, internal hexagon, and Morse taper implants in single restorations before and after mechanical cycling. Materials and Methods: The study sample was divided into three groups (n = 10) as follows: group EH - external hexagon implant, group IH - internal hexagon implant, and group MT - Morse taper implant. Universal abutments were screwed on the implants, and metal crowns were cemented onto the abutment. The samples were submitted to a mechanical testing of 1 million cycles, with a frequency of 8 cycles per second under a 400 N load. The application and registration of the screw torque (T0) and detorque (T1) values of the intermediate were performed before and after the test. The results were statistically evaluated by analysis of variance (ANOVA) and Tukey′s test (α = 0.05). Results: There was no difference between the values of T0 and T1 in the intra-group samples. However, the inter-group difference in T0 between the EH (12.8 N cm) and MT (18.6 N cm) groups and in T1 between the EH (10.4 N cm) and IH (13.8 N cm), EH and MT (19.4 N cm), and MT and IH (P = 0.001) groups were significant. The MT group showed a lower variation of T0 and T1. Conclusion: The internal implants, particularly MT, showed better stability in these cases when used for single restorations.

Experimental and FE displacement and polymerization stress of bonded restorations as a function of the C-Factor, volume and substrate stiffness

OBJECTIVES To determine the free surface displacement of resin-composite restorations as a function of the C-Factor, volume and substrate stiffness, and to compare the results with interfacial stress values evaluated by finite element analysis (FEA). METHODS Surface displacement was determined by an extensometer using restorations with 4 or 6mm diameter and 1 or 2mm depth, prepared in either bovine teeth or glass. The maximum displacement of the free surface was monitored for 5 min from the start of photoactivation, at an acquisition rate of 1s(-1). Axisymmetric cavity models were performed by FEA. Structural stiffness and maximum stresses were investigated. RESULTS For glass, displacement showed a stronger correlation with volume (r=0.771) than with C-Factor (r=0.395, p<0.001 for both). For teeth, a stronger correlation was found with C-Factor (r=0.709; p<0.001) than with volume (r=0.546, p<0.001). For similar dimensions, stress and displacement were defined by stiffness. Simultaneous increases in volume and C-Factor led to increases in stress and surface displacement. Maximum stresses were located at the cavosurface angle, internal angle (glass) and at the dentine-enamel junction (teeth). The displacement of the restorations free surface was related to interfacial stress development. CONCLUSIONS Structural stiffness seems to affect the shrinkage stress at the tooth/resin-composite interface in bonded restorations. Deep restorations are always problematic because they showed high shear stress, regardless of their width. FEA is the only tool capable of detecting shear stress due to polymerization as there is still no reliable experimental alternative.

Influence of the curing mode on the degree of conversion of a dual-cured self-adhesive resin luting cement beneath ceramic

Abstract Objective. To evaluate the effect of the delayed photoactivation and ceramic barrier on the degree of conversion (DC) of self-adhesive resin cement. Materials and methods. Circular specimens (5 mm in diameter × 1 mm in thickness) of the RelyX U-100 resin cement were made using the following curing protocols (n = 10): (G1) 40 s beneath a IPS Empress II ceramic; (G2) 40 s of direct photocuring; (G3) 80 s beneath the ceramic; (G4) 80 s of direct photocuring; (G5) self-curing; (G6) 5 min in the absence of light (self-curing) followed by transceramic photocuring for 40 s; (G7) 5 min in the absence of light (self-curing) followed by transceramic photocuring for 80 s. All the specimens were photoactivated by LED (800 mW/cm2). After 24 h of dry storage, the DC was measured by FTIR, on the top surface of the specimens. Data were submitted to one-way ANOVA and Tukey test (p ≤ 0.05). Results. Direct photocuring with no ceramic interposition, regardless of the curing time (40 s and 80 s) promoted the highest conversion mean (56.79 ± 1.19 and 59.98 ± 2.93, respectively) and the 5 min delay time for the transceramic photocuring presented a similar mean compared to the immediate transceramic photocuring. The DC was influenced by the ceramic barrier, decreasing the conversion values (49.72 ± 1.91 for 40 s and 52.36 ± 2.50 for 80 s), with no statistical difference from the groups with the previous 5 min of photoactivation delay. The self-cure only showed the worst DC values. Conclusion. Direct photocuring provided a higher degree of conversion for the self-adhesive resin cement. The delayed light activation did not influence the degree of conversion for the resin cement tested.

Photoelastic Analysis of the Distribution of Stress in Different Systems of Overdentures on Osseous-Integrated Implants

ObjectiveThe aim of this study was to evaluate the distribution of generated stress around implants and adjacent bone tissue using different implant-retained overdenture designs through photoelastic analysis. MethodsOver an edentulous human mandible, achieved from a human model, 2 or 4 microunit analog abutments were embedded (Master; Conexao Systems Prosthodontics, São Paulo, Brazil), settled in the interforaminal region. Three models of photoelastic resin (Araltec Chemicals Ltda, Hunstman, Guarulhos, São Paulo, Brazil), with 2 or 4 incorporated implants and microunit abutments, were obtained from molds using silicone for duplication. Inclusion, finishing, and polishing procedures were applied on the frameworks. This study was based on 3 different mechanisms of implant-retained mandibular overdentures: O’ring (GI), bar-clip (GII) (both with 2 implants), and their association (GIII) (with 4 implants). After the adaptation of each overdenture system on the photoelastic models, 100-N alternate occlusal loads were applied on back-side and front-side regions. The photoelastic analysis was made with the aid of a plain polariscope linked to a digital camera, Sony Cybershot &agr;100, which allowed visualization of the fringes and registration of images on digital photographs. ResultsThe results demonstrated higher tension concentrated over the GIII, with a flat distribution of stress to the posterior ridge and overload on the posterior implants. GI showed the smaller stress level, and GII, intermediate level; there was distribution of stress to the posterior ridge in these 2 groups. ConclusionThe use of bar attachment proved to be a better alternative, because it showed a moderate level of tension with a more uniform stress distribution and possessed higher retention than did the ball system.

Photoelastic evaluation of the effect of composite formulation on polymerization shrinkage stress

We compared polymerization stress in two commercial composites and three experimental composites made using camphorquinone (CQ) and/or phenylpropanedione (PPD) as photoinitiators. The internal surfaces of photoelastic resin discs with cylindrical cavities were roughened and treated with adhesive. Composites were divided into five groups: two commercial composites (Filtek Silorane and Filtek Z250) and three experimental composites with CQ/amine, CQ/PPD/amine, and PPD/amine. Composites were photopolymerized inside cavities, and subjected to photoelastic analysis immediately and at 24 hours and 7 days later using a plane polariscope. Stress created by Silorane (3.08 ± 0.09 MPa) was similar to that of Z250 (3.19 ± 0.13 MPa) immediately after photopolymerization (p > 0.05). After 24 hours and 7 days, Z250 (3.53 ± 0.15 and 3.69 ± 0.10 MPa, respectively) showed higher stress than Silorane (3.19 ± 0.10 and 3.16 ± 0.10 MPa, respectively). Qualitative analysis immediately after photopolymerization showed composite/CQ promoted higher stress than PPD, but stress levels at other evaluated times were statistically similar, varying between 3.45 ± 0.11 MPa and 3.92 ± 0.13 MPa. At 24 hours and 7 days, Silorane created the lowest stress. All photoinitiators created comparable tensions during polymerization.

Influence of Photoinitiator and Light-Curing Source on Bond Strength of Experimental Resin Cements to Dentin

This study evaluated the bond strength (BS) of experimental resin cements formulated with different photoinitiators when activated by two kinds of light-curing units (LCUs) through a ceramic material. Seven resin blends with different camphorquinone (CQ) and/or phenylpropanedione (PPD) concentrations (weight) were prepared: C5: 0.5% CQ; C8: 0.8% CQ; P5: 0.5% PPD; P8: 0.8% PPD; C1P4: 0.1% CQ and 0.4% PPD; C4P1: 0.4% CQ and 0.1% PPD; C4P4: 0.4% CQ and 0.4% PPD. Two LCUs were used: one quartz-tungsten-halogen (QTH - 850 mW/cm²) and one light-emitting diode (LED - 1300 mW/cm²). The microtensile bond strength of each blend was assessed. Data were submitted to two-way ANOVA and Tukeys test (α=0.05). The BS values did not exhibit significant differences for LCUs, regardless of the photoinitiator type. Three cements showed significant differences: P5 and C5 had higher BS with QTH, and C4P1 with LED. For QTH, P5 showed the highest and C1P4 the lowest BS. For the LED, C4P1 showed the highest BS of all the cements. The results indicated that PPD was a viable alternative in the formulation of photocured resin cements, reducing or eliminating CQ that is yellowish without impairing the bond strength. Furthermore, both LED and QTH were effective in curing resin cements that contain PPD or CQ.