Paulo Henrique Perlatti D'Alpino

Mechanical properties of dental restorative materials: relative contribution of laboratory tests

A wide variety of dental products that are launched on the market becomes the correct selection of these materials a difficult task. Although the mechanical properties do not necessarily represent their actual clinical performance, they are used to guide the effects of changes in their composition or processing on these properties. Also, these tests might help somehow the clinician to choose once comparisons between former formulations and new ones, as well as, with the leading brand, are highlighted by manufactures. This paper presents a review of the most important laboratory tests. In this manner, the knowledge of these tests will provide a critical opinion related to the properties of different dental materials.

Bond strength and interfacial micromorphology of etch-and-rinse and self-adhesive resin cements to dentin.

PURPOSE To evaluate the microtensile bond strength and interfacial micromorphology of indirect composite restorations to dentin using three commercial resin cements after 24 hours and 30 days of water storage. MATERIALS AND METHODS The medium dentin of third human molars was exposed (N = 30, n = 10 per group). Three commercial resin cements were used to cement indirect resin composite restorations to dentin: the auto-cured C&B Cement/All Bond 2, the dual-cured RelyX ARC/Adper Single Bond 2, and the self-adhesive dual-cured RelyX Unicem. Teeth were sectioned after water storage at 37°C (24 hours and 30 days) to obtain beams with a bonded area of 0.8 mm(2) . The specimens were tested in a universal testing machine at a 0.5 mm/min crosshead speed. Scanning electron microscopic fractographic and interfacial micromorphology analyses were performed. Data were analyzed using two-way ANOVA and Tukeys test (α= 0.05). RESULTS Mean bond strength (MPa) after 24 hours: C&B Cement 19.5 ± 3.8, RelyX ARC 40.8 ± 9.4, RelyX Unicem 31.3 ± 7.4; after 30 days: C&B Cement 24.5 ± 5.1, RelyX ARC 44.2 ± 8.5, RelyX Unicem 28.3 ± 7.1. The mean bond strengths of both dual-cure cements were significantly higher than that obtained with C&B Cement after 24 hours. A significant increase in the bond strength of C&B Cement was verified after 30 days, reaching values statistically equivalent to those produced by RelyX Unicem and RelyX ARC. The self-adhesive cement preserved the same level of bond strength after 30 days. Fractographic analysis revealed a prevalence of cohesive fractures in the hybrid layer for C&B Cement, mixed (cohesive in the cement, hybrid layer, and adhesive) for RelyX ARC, and cohesive in the cement for RelyX Unicem. No distinguishable hybrid layer or resin tags were observed in the interaction of RelyX Unicem with dentin. CONCLUSIONS The particular interaction of each cement with dentin results in specific bond strength and failure patterns that varied among groups in both evaluation times. Even though the self-adhesive cement tested exhibited no authentic hybrid layer, it was able to promote reliable adhesion with the underlying dentin.

Fracture resistance of teeth restored with different resin-based restorative systems

The aim of the present study was to evaluate the fracture resistance of teeth restored with resin composite. Forty-eight maxillary premolar teeth were chosen and randomly divided to six groups: G1 (control): sound teeth; G2: MOD preparation, unrestored; G3: MOD + Adper Single Bond 2/P60; G4: MOD + Adper Easy One/P60; G5: MOD + P90 restorative system; G6: MOD + Adper Easy One/P90 Bond/P90. Specimens were subjected to compressive axial loading (0.5 mm/min). Flexural strength and the modulus of elasticity were also tested (n = 7). The only statistical equivalence with sound teeth was noted for G3 (p < 0.05). Flexural strength and the modulus of elasticity varied among the composites tested (n = 10). The reestablishment of the resistance to fracture in premolars subjected to Class II MOD preparations is restorative-system-dependent. The silorane restorative system is not able to recover the resistance to fracture.

Influence of pH of different adhesive systems on the polymerization of a chemically cured composite resin

The purpose of this study was to investigate the effect of pH of different adhesive systems on the polymerization of a chemically cured composite resin (Adaptic--AD), by means of tensile bond strength testing. The adhesive systems tested were: ARM, Prime & Bond 2.1 (PB), Scotchbond Multi Purpose (SMP) and Single Bond (SB). Bond strength at the resin/adhesive system/resin interface was assessed. Five groups (n=5) were formed, according to following configuration: G1: AD/ARM/AD; G2: AD/PB/AD; G3: AD/SMP/AD; G4: AD/SB/AD; G5: AD/AD (no adhesive). A two-mold stainless steel matrix with a cone-shaped opening (1-mm-thick; 4 mm in diameter) was used to obtain resin discs. AD resin was inserted into the first mold, left-self curing and an adhesive layer was applied onto resin surface and light-cured. The second mold was assembled over the first and was filled with the resin. After 10 min, this setting was loaded in tension in a universal testing machine running at a crosshead speed of 0.5 mm/min. Data were submitted to one-way ANOVA and Tukeys test (p<0.05). Bond strength means (kgf) were: G1: 15.23 +/- 4.1; G2: 0.00 +/- 0.0; G3: 16.96 +/- 2.4; G4: 10.08 +/- 2.7; G5: 15.44 +/- 0.9. There were statistically significant differences (p<0.05) between G2-G1; G2-G3; G2-G4; G4-G1; G4-G3. The systems with the lowest pHs (PB and SB) yielded the lowest bond strength. The findings of this in vitro study demostrates that the pH of adhesive systems influences the polymerization and bond strength of chemically cured resin materials. The low pH simplified adhesive systems showed distinct degrees of incompatibility with the chemically cured resin, when compared to the conventional adhesive systems.

The effect of polymerization mode on monomer conversion, free radical entrapment, and interaction with hydroxyapatite of commercial self-adhesive cements

OBJECTIVES This study evaluated the degree of conversion, the free radical entrapment, and the chemical interaction of self-adhesive resin cements mixed with pure hydroxyapatite, as a function of the polymerization activation mode among a variety of commercial self-adhesive cements. MATERIALS AND METHODS Four cements (Embrace WetBond, MaxCem Elite, Bifix SE, and RelyX U200) were mixed, combined with hydroxyapatite, dispensed into molds, and distributed into three groups, according to polymerization protocols: IP (photoactivation for 40s); DP (delayed photoactivation, 10 min self-curing plus 40s light-activated); and CA (chemical activation, no light exposure). Infrared (IR) spectra were obtained and monomer conversion (%) was calculated by comparing the aliphatic-to-aromatic IR absorption peak ratio before and after polymerization (n=10). The free radical entrapment values of the resin cements were characterized using Electron Paramagnetic Resonance (EPR) and the concentration of spins (number of spins/mass) calculated (n=3). Values were compared using two-way ANOVA and Tukeys post-hoc test (α=5%). X-ray diffraction (XRD) characterized the crystallinity of hydroxyapatite as a function of the chemical interactions with the resin cements. RESULTS The tested parameters varied as a function of resin cement and polymerization protocol. Embrace WetBond and RelyX U200 demonstrated dependence on photoactivation (immediate or delayed), whereas MaxCem Elite exhibited dependence on the chemical activation mode. Bifix SE presented the best balance based on the parameters analyzed, irrespective of the activation protocol. CONCLUSIONS Choice of polymerization protocol affects the degree of conversion, free radical entrapment, and the chemical interaction between hydroxyapatite and self-adhesive resin cement mixtures.

Hydrolytic degradation of silorane- and methacrylate-based composite restorations: Evaluation of push-out strength and marginal adaptation

Abstract Objectives. This study compared the hydrolytic degradation of composite restorations based on methacrylate and silorane systems regarding bond strength and marginal adaptation. Materials and methods. Sixty bovine incisors were ground flat to obtain a 2-mm thick slice in which conical preparations were made. The specimens were randomly distributed into four groups (n = 15) according to the restorative system (silorane–Filtek LS/P90 adhesive; methacrylate–Filtek P60/Adper Easy Bond) and the degradation protocol (control: immediate evaluation; hydrolytic degradation: 6 months storage in water at 37°C). Marginal adaptation was evaluated using a dye staining technique. Digital images of the stained gaps were obtained to calculate the marginal gap (%), the ratio between the stained margins and the total length of the margin. Push-out bond strength test was conducted (0.5 mm/min). Marginal adaptation data was submitted to Kruskal-Wallis test and the bond strength data to two-way ANOVA/Tukeys test (α = 0.05). Results. The marginal adaptation was neither affected by the restorative system nor by the degradation protocol, although the number of perfect sealed reduced after 6 months. No significance was observed among the groups. No significance was noted between the silorane- and the methacrylate-based restorations for immediate bond strength. After the hydrolytic degradation, the silorane system showed higher bond strength then the methacrylate restorations. Conclusion. The silorane and methacrylate restorative systems produce restorations with similar immediate interfacial quality and 6 months of water storage does not cause significant bonding degradation for both systems. The silorane restorations show an increase in the bond strength after 6 months.

Hardness of a bleaching-shade resin composite polymerized with different light-curing sources

The microhardness of a bleaching-shade resin composite polymerized with different light-curing units was evaluated. Composite samples (3M ESPE Filtek Supreme) were applied to brass rings (2 mm in thickness, 5 mm in diameter). Three commercial LED lights were used to polymerize the specimens and the results were compared to those of a conventional halogen light. The light sources used in the present study were: Demetron Optilux 401 (QTH), 3M ESPE Elipar FreeLight (LED 1); Kerr L.E. Demetron I (LED 2), and ColtoluxLED lights (LED 3). The microhardness of the top and bottom surfaces was assessed with a digital Vickers hardness-measuring instrument, under load. At the bottom surface, no significant difference among the light sources was observed (two-way ANOVA). At the top surface, the QTH light source presented significantly higher hardness values compared to the values observed when LED 1 and LED 3 were used. There were no significant differences between the QTH and LED 2 light sources. Significantly higher hardness values were also found at the top surface when compared to the values observed at the bottom surface. The power density of the polymerization light sources seemed to be responsible for the observed resin composite hardness, not their irradiance.

Effect of light curing unit on resin-modified glass-ionomer cements: a microhardness assessment.

OBJECTIVE To evaluate the microhardness of resin-modified glass-ionomer cements (RMGICs) photoactivated with a blue light-emitting diode (LED) curing light. MATERIAL AND METHODS Thirty specimens were distributed in 3 groups: Fuji II LC Improved/GC (RM1), Vitremer/3M ESPE (RM2) and Filtek Z250/3M ESPE (RM3). Two commercial light-curing units were used to polymerize the materials: LED/Ultrablue IS and a halogen light/XL3000 (QTH). After 24 h, Knoop microhardness test was performed. Data were submitted to three-way ANOVA and Tukeys test at a pre-set alpha of 0.05. RESULTS At the top surface, no statistically significant difference (p>0.05) in the microhardness was seen when the LED and QTH lights were used for all materials. At the bottom surface, microhardness mean value of RM2 was significantly higher when the QTH light was used (p<0.05). For RM1, statistically significant higher values (p<0.05) were seen when the LED light was used. No statistically significant difference (p>0.05) was seen at the bottom surface for RM3, irrespective of the light used. Top-to-bottom surface comparison showed no statistically significant difference (p>0.05) for both RMGICs, regardless of the light used. For RM3, microhardness mean value at the top was significantly higher (p<0.05) than bottom microhardness when both curing units were used. CONCLUSION The microhardness values seen when a LED light was used varied depending on the restorative material tested.

Prevalence of enamel defects in permanent teeth of patients with complete cleft lip and palate

Objective To evaluate the prevalence, types, location, and characteristics of enamel defects in anterior permanent teeth of patients with complete unilateral and bilateral cleft lip and palate, as well as the relation with the cleft. Setting Hospital for Rehabilitation of Craniofacial Anomalies, Bauru, São Paulo, Brazil. Participants Eighty patients of both genders, 12 years and older, with unilateral or bilateral cleft lip and palate. Methods A single examiner carried out clinical examination under artificial light with a dental probe and mirror after drying teeth according to the modified DDE index. Results Seventy-four of 80 patients presented with at least one tooth affected by enamel defects: 165 of 325 evaluated teeth (50.8%) presented enamel defects, with hypoplasia being the most prevalent (50.7%), followed by diffuse opacity (23.1%) and demarcated opacity (18.4%). The most affected tooth was 21 (36.5%), followed by 11 (34%), located at the middle (40%) and incisal (33%) thirds. Most defects occur at the buccal surface (47.7%), followed by the distal (22.7%), the mesial (19%), and the palatal (10.6%) surfaces. A significant relationship was found between the cleft side and enamel defects. Conclusion Upper anterior teeth of patients with complete cleft lip and palate present a high prevalence of enamel defects; the highest percentage on the cleft side suggests that the cleft does influence the occurrence of enamel defects in permanent teeth.

Evaluation of internal adaptation of Class V resin composite restorations using three techniques of polymerization.

Objective: The purpose of this in vitro study was to evaluate the internal adaptation of Class V composite restorations to the cavity walls using three different techniques of polymerization. Methods: Standard cavities were prepared on the buccal and lingual surfaces of 24 extracted human third molars with margins located above and below the cementoenamel junction. Restorations were placed in one increment using two restorative systems: 3M Filtek A110/ Single Bond (M) and 3M Filtek Z250/ Single Bond (H) in the same tooth, randomly in the buccal and lingual surfaces. Resin composites were polymerized using three techniques: Group 1 – Conventional (60 s - 600 mW/cm2); Group 2 – Soft-start (20 s – 200 mW/cm2, 40 s - 600 mW/cm2); Group 3 – Pulse Activation (3 s - 200 mW/cm2, 3-min hiatus, 57 s - 600 mW/cm2). Buccolingual sections were polished, impressions taken and replicated. Specimens were assessed under scanning electron microscopy up to X1000 magnification. Scores were given for presence or absence of gaps (0 – no gap; 1 – gap in one wall; 2 – gap in two walls; 3 – gap in three walls). Results: The mean scores of the groups were (±SD) were: G1M–3.0 (± 0.0); G2M–2.43 (± 0.8); G3M– 1.71 (± 0.9); G1H– 2.14 (± 1.2); G2H- 2.00 (± 0.8); G3H- 1.67 (± 1.1). Data were analyzed using Kruskal-Wallis and Dunnet’s tests. No statistically significant difference (p>0.05) was found among groups. Gaps were observed in all groups. Conclusions: The photocuring technique and the type of resin composite had no influence on the internal adaptation of the material to the cavity walls. A positive effect was observed when the slow polymerization techniques were used.