Larissa Maria Cavalcante

Shrinkage Stresses Generated during Resin-Composite Applications: A Review

Many developments have been made in the field of resin composites for dental applications. However, the manifestation of shrinkage due to the polymerization process continues to be a major problem. The materials shrinkage, associated with dynamic development of elastic modulus, creates stresses within the material and its interface with the tooth structure. As a consequence, marginal failure and subsequent secondary caries, marginal staining, restoration displacement, tooth fracture, and/or post-operative sensitivity are clinical drawbacks of resin-composite applications. The aim of the current paper is to present an overview about the shrinkage stresses created during resin-composite applications, consequences, and advances. The paper is based on results of many researches that are available in the literature.

Curing efficiency of dental resin composites formulated with camphorquinone or trimethylbenzoyl-diphenyl-phosphine oxide

OBJECTIVES Since photoinitiator systems for dental resins based on camphorquinone (CQ) present color disadvantages, trimethylbenzoyl-diphenyl-phosphine oxide (TPO) has been proposed as an alternative. However, there are remaining considerations about its curing efficiency. The aims of the present investigation were: to characterize the relationship between the photoinitiator absorption spectra and the light spectrum emitted from a QTH light (absorbed power density, PD(abs)); to evaluate the kinetics of polymerization, and the depth of cure for filled dimethacrylate resins formulated with different photoinitiator systems. METHODS CQ+EDMAB (control); TPO and TPO+EDMAB were used in 50:50 Bis-GMA/TEGDMA resins. Photoinitiator absorption and QTH-light emission were evaluated using a spectrophotometer and kinetics of polymerization with differential scanning calorimetry (DSC) (n=3). Depth of cure was analyzed by the scraping method (n=5), as recommended by ISO4049. One-way ANOVA/Tukeys (p<0.05) was used to analyze the results. RESULTS CQ presented higher PD(abs) than TPO (364 and 223 mW/cm(3), respectively). The DSC revealed that TPO and TPO+EDMAB produced a faster reaction than CQ+EDMAB. Composite formulated with CQ+EDMAB produced higher depth of cure (6.3±0.4 mm) than those with TPO (4.3±0.1) or TPO+EDMAB (4.2±0.3). SIGNIFICANCE Although CQ presented higher PD(abs) than TPO, formulations containing TPO exhibited higher reactivity than that with CQ. On the other hand, materials formulated with TPO demonstrated lower depth of cure than that with CQ. Therefore, its use as an alternative photoinitiator requires further investigation, with higher concentrations.

Effect of co-initiator ratio on the polymer properties of experimental resin composites formulated with camphorquinone and phenyl-propanedione

OBJECTIVES To evaluate the effect of amine ratio (ethyl 4-dimethylaminobenzoate, EDMAB) on the maximum rate of polymerization (R(p)(max)), degree of conversion (DC), Knoop hardness (KH), water sorption (Wsp), water solubility (Wsl) and color changes (DeltaE) over time of resin composites formulated with the photoinitiators camphorquinone (CQ), phenylpropanedione (PPD) and CQ-PPD in combination. MATERIALS AND METHODS Experimental resin composites were made with photoinitiator:amine ratios of 2:1, 1:1, 1:1.5 and 1:2 by weight. R(p)(max) was evaluated with differential scanning calorimetry (DSC), DC with DSC and Fourier transformed infrared (FTIR) spectroscopy, KH with Knoop indentation, Wsp and Wsl adapted from ISO 4049; and color with a chromameter. The results were analyzed with two-way ANOVA/Tukeys multiple comparison test (p<0.05). RESULTS The higher the amine ratio in the composite, the higher was DC, R(p)(max), and KH, and the lower was Wsl, regardless of the photoinitiator type. The use of PPD alone resulted in poorer properties than CQ and CQ-PPD. Many factors seem to affect the color changes and the b-axis data revealed that the higher the amine ratio, the higher was the +b value (yellowing) for CQ and CQ-PPD formulations. CONCLUSIONS Higher amine ratios led to improved polymer properties, but also produced more yellowing in resin composites with CQ and CQ-PPD. The use of PPD alone was not advantageous for producing good final properties when compared to CQ and CQ-PPD.

Color stability, conversion, water sorption and solubility of dental composites formulated with different photoinitiator systems

OBJECTIVES The aim of this study was to formulate materials with high color stability and reduced degradation by using photoinitiator systems derived from phosphine oxides alternative to the traditional camphorquinone (CQ)/amine system. METHODS Materials were formulated with the monomers BisGMA and TEGDMA as organic matrix. The photoinitiators tested were CQ+amine (EDMAB), phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (BAPO), BAPO+EDMAB, diphenyl(2,4,6-trimethylbenzoyl)-phosphine oxide (TPO) and TPO+EDMAB. A 60% mass of silanated glass filler particles was added. Degree of CC conversion was evaluated by Fourier-transformed infrared spectroscopy 10min after photopolymerization. The color properties were evaluated by a digital spectrophotometer, applying the CIELab parameters, either before photoactivation, immediately after photoactivation, 24h after dry storage, and one month after water immersion. Water sorption and solubility were assessed by mass gain or loss after storage in water for 30 days. Data were analyzed using ANOVA and Tukeys test (5%). RESULTS Degree of conversion did not differ statistically among all the tested formulations. Regarding color, only groups with TPO presented satisfactory color stability after one month of water storage (ΔE<3.3). Water sorption and water stability did not differ among the groups. CONCLUSIONS Degree of conversion, water sorption and water solubility did not differ among all the tested groups. The TPO-based groups were the only materials with satisfactory color stability after one month of water storage. CLINICAL SIGNIFICANCE The use of a photoinitiator system containing TPO might improve the color stability of resin composites compared with the traditional CQ/amine system while attaining similar physico-chemical properties for the composite.

Influence of photoinitiator system and nanofiller size on the optical properties and cure efficiency of model composites

OBJECTIVE To establish the relationship between photoinitiator system and nanofiller size on the optical properties and cure efficiency of model composites. METHODS Model composites based on BisGMA/TEGDMA (60:40mol%) were loaded with 40wt% of 7nm or 16nm-sized filler particles. One of the following photoinitiator systems was added: camphorquinone (CQ) associated with an amine (EDMAB), monoacylphosphine oxide (TPO), or bysacylphosphine oxide (BAPO). The optical properties of disk-shaped specimens were measured 24h after curing and repeated after storage in water for 90 days and coffee for 15 days. A large spectrum LED unit (Bluephase G2, Ivoclar Vivadent) was used for photoactivation. CIE L*a*b* parameters, color difference (ΔE), and translucency parameter (TP) were calculated. Knoop hardness readings were taken at top and bottom composite surfaces. Cure efficiency was determined by bottom/top hardness ratio. Data were statistically analyzed at α=0.05 significance level. RESULTS Composites formulated with 16nm particles had higher CIE L* than those with 7nm particles in all storage conditions. BAPO-based composites generally had lower CIE a* than the other composites. The group TPO+16nm before storage and all groups with 16nm-sized particles after storage had lower CIE b* (i.e. lower degree of yellowing) than the other groups. TPO-based materials had higher color stability. The cure efficiency was not significantly affected by photoinitiator system or particle size. CQ+7nm had the lowest and BAPO+16nm the highest hardness values. SIGNIFICANCE Combination of photoinitiator system and filler particle size might affect the optical properties of composites, with low influence on cure efficiency.

The influence of nanoscale inorganic content over optical and surface properties of model composites

OBJECTIVES To investigate the influence of nanoscale inorganic content over optical and surface properties of model composites before and after ageing. METHODS Three model composites were formulated with silica fillers in nanoscale of 7 nm (G1), 12 nm (G2) and 16 nm (G3), at 45.5% by weight in a matrix of BisGMA/TEGDMA 1:1. Color coordinates (CIE L*a*b* parameters), color difference (ΔE*), translucency parameter (TP), surface gloss (SG) and surface roughness (SR) were measured before and after ageing procedures of immersion in water and toothbrush abrasion. Surface hardness (SH) were evaluated before and after immersion in absolute ethanol. Results were submitted to two-way ANOVA followed by Tukeys post hoc test performed at a pre-set alpha of 0.05. RESULTS Regarding CIE L*a*b* parameters, a darkening, a redness and a blueness effect, were respectively detected after water storage for all groups. Smaller filler sizes (G1) had the highest CIE b* values, whereas medium (G2) (p<0.05) had higher values than larger fillers (G3) (p<0.05) either before or after water immersion. Toothbrush abrasion did not produce any significant effect on CIE a* and CIE b* values, however increased CIE L*, decreased TP in addition to produce rougher and matte surfaces in all groups. Filler size did not influence ΔE* (p>0.05), although a tendency towards lower values in smaller filler materials was observed. Ageing after immersion in absolute ethanol decreased SH for all model composites. CONCLUSIONS Filler sizes and ageing procedures influenced the optical and surface properties of the nanostructured composites evaluated in this study. CLINICAL SIGNIFICANCE Filler size influenced optical and surface properties of resin composites. Materials containing smaller filler size offered improved optical stability and surface properties that can lead to longer maintenance of the restorations appearance in the oral environment.

Comparative evaluation of dental resin composites based on micron- and submicron-sized monomodal glass filler particles

OBJECTIVES A model resin composite containing a novel monomodal inorganic filler system based on submicron-sized Ba-Si-Al glass particles (NanoFine NF180; Schott) was formulated and compared with an experimental composite containing micron-sized particles (UltraFine UF1.0; Schott). METHODS The filler particles were characterized using X-ray microanalysis and granulometry, while the composites were characterized in terms of filler-resin morphology, radiopacity, degree of CC conversion, hardness, flexural strength/modulus, work-of-fracture, surface roughness and gloss (before and after simulated toothbrushing abrasion), and bulk compressive creep. The composites were formulated from the same photoactivated dimethacrylate co-monomer, incorporating mass fractions of 75% micron- and 78% submicron-sized particles. Quantitative data were analyzed at a significance level of p<0.05. RESULTS Both filler systems exhibited a narrow grain size range (175±30 and 1000±200 nm), with differences restricted to the size and specific area of the particles. The composites were similar in radiopacity, flexural strength, work-of-fracture, and creep. The submicron composite was harder but had lower flexural modulus and CC conversion. No significant differences in roughness were observed before brushing, although the submicron composite had higher gloss. Brushing increased roughness and decreased gloss on both materials, but the submicron composite retained higher gloss after brushing. SIGNIFICANCE The monomodal submicron glass filler system demonstrated potential for use in restorative dental composites, particularly due to improved esthetic properties.

Degree of Conversion, Depth of Cure, and Color Stability of Experimental Dental Composite Formulated with Camphorquinone and Phenanthrenequinone Photoinitiators

PURPOSE This study evaluated the applicability of 9,10-phenanthrenequinone (PQ) in experimental dental composites. MATERIALS Camphorquinone (CQ), PQ, ethyl 4-N,N-dimethylaminobenzoate (EDMAB) and diphenyliodonium salt (DPI) were employed. A mixture of 2,2-bis(4-[2-hydroxy-3-methacryloxypropoxy]phenyl)-propane/triethylene glycol dimethacrylate (60:40%) and silanated glass filler at 60% were used. A two-peak-based light-emitting diode (LED) was used. METHODS The photoinitiator absorption and the light emission spectra were determined by a Ultraviolet-visible spectroscopy and a spectroradiometer, respectively. Relative photon absorption (RPabs) was calculated. Fourier-transformed infrared spectroscopy analysis was used to determine the degree of conversion (DC). The optical properties were determined with a spectrophotometer. Depth of cure was assessed from adapted International Organization for Standardization (ISO) 4049. Results were analyzed with descriptive analysis, analysis of variance, and Tukeys test (α = 5%). RESULTS PQ showed higher RPabs than CQ. Regarding the DC, CQ + EDMAB (control), CQ + EDMAB + DPI, PQ + DPI, and PQ + EDMAB + DPI produced statistically similar results. Groups formulated with CQ presented higher depth of cure. Only the group formulated with CQ + EDMAB presented satisfactory color stability (ΔE < 3.3). CONCLUSION PQ presented higher RPabs than CQ and it was able to produce DC similar to CQ + EDMAB, when used with DPI. However, groups formulated with PQ produced lower depth of cure, greater yellowing, and less color stability than the traditional combination CQ and amine. CLINICAL SIGNIFICANCE Although research with novel photoinitiator systems should be encouraged, the traditional camphorquinone and amine pair remains as a reliable combination for the formulation of dental composites.

Repair bond strength in aged methacrylate- and silorane-based composites.

PURPOSE To evaluate the tensile bond strength at repaired interfaces of aged dental composites, either dimethacrylate- or silorane-based, when subjected to different surface treatments. MATERIALS AND METHODS The composites used were Filtek P60 (methacrylate-based, 3M ESPE) and Filtek P90 (silorane-based, 3M ESPE), of which 50 slabs were stored for 6 months at 37°C. The surface of adhesion was abraded with a 600-grit silicone paper and the slabs repaired with the respective composite, according to the following surface treatment protocols: G1: no treatment; G2: adhesive application; G3: silane + adhesive; G4: sandblasting (Al2O3) + adhesive; G5: sandblasting (Al2O3) + silane + adhesive. After 24-h storage in distilled water at 37°C, tensile bond strength (TBS) was determined in a universal testing machine (Instron 4411) at a crosshead speed of 0.5 mm/min. The original data were submitted to two-way ANOVA and Tukeys test (α = 5%). RESULTS The methacrylate-based composite presented a statistically significantly higher repair potential than did the silorane-based resin (p = 0.0002). Of the surface treatments for the silorane-based composite, aluminum-oxide air abrasion and adhesive (18.5 ± 3.3MPa) provided higher bond strength than only adhesive application or the control group without surface treatment. For Filtek P60, the control without treatment presented lower repair strength than all other groups with surface treatments, which were statistically similar to each other. The interaction between the factors resin composite and surface treatment was significant (p = 0.002). CONCLUSION For aged silorane-based materials, repairs were considered successful after sandblasting (Al2O3) and adhesive application. For methacrylate resin, repair was successful with all surface treatments tested.

Surface integrity of solvent-challenged ormocer-matrix composite

OBJECTIVE To investigate the surface integrity of solvent-challenged ormocer-matrix composites, photoactivated by different light exposure modes, through surface-hardness measurements at different periods of time; and to compare such behavior with dimethacrylate-based materials. METHODS One hundred percent ormocer-based matrix (experimental ormocer (ORM)), a commercial mixed dimethacrylate-ormocer-based matrix (Admira (ADR)) and two commercial dimethacrylate-based matrix composites (experimental controls, (Grandio (GRD) and Premise (PRE)) were evaluated. Disk specimens (4 mm × 2 mm) were prepared from each material and light-activated using either a standard (S) or soft-start (SS) light exposure protocol with an LED-curing unit. Top, irradiated surface Knoop hardness (KHN) was measured within the following experimental groups (n=5): Group 1: immediately after exposure; Group 2: after dry and dark storage, Group 3: after storage in distilled water, and Group 4: immersion in absolute ethanol. Hardness of Groups 2-4 were measured after 7 days storage. Immediate hardness values were submitted to Students t-tests separately for each material. Hardness values after treatments were submitted to two-way ANOVA and Tukeys post hoc test to compare values among different storage media and light exposure mode protocols. Comparisons among materials were described using percentage of hardness change. Statistical testing was performed at a pre-set alpha of 0.05. RESULTS Immediate hardness values were not affected by the light exposure mode, regardless of the material. In general, exposure mode did not significantly affect hardness after 7 days storage, regardless of storage media or material. After 7 days dry storage, hardness values increased for all materials relative to immediate testing, and decreased after water and ethanol storage, with ethanol showing the greatest effect. The experimental ormocer-based material had the lowest percentage hardness change and thus proved more resistant to solvent degradation than the other materials, regardless of the light exposure method. SIGNIFICANCE Irradiated surface hardness values and surface integrity were unaffected by light exposure mode, regardless of the material tested. The experimental ormocer-based material presented the least change in hardness as a result of solvent challenge than any of the commercial products: ormocer or conventional resin-based, and thus showed better surface integrity.