Towards a better understanding of the adhesion mechanism of resin-modified glass-ionomers by bonding to differently prepared dentin.

OBJECTIVES: The purpose of this study was to evaluate the bonding effectiveness of a resin-modified glass-ionomer (RMGI) to differently prepared dentin and how this restorative material interacts with these distinct substrates. Also the potential adhesion-promoting role of a polyalkenoic-acid conditioner was assessed. METHODS: Forty-eight dentin surfaces were prepared from sound human molars and randomly distributed among 6 experimental groups. Fuji II LC (GC) was applied on bur-cut (100 µm diamond), fractured and Er:YAG laser-irradiated (200mJ, 10Hz, 31.4J/cm(2)) dentin with or without the beforehand application of the aqueous polyalkenoic-acid conditioner, Cavity Conditioner (GC). After 7 days of storage in water at 37 °C, specimens were prepared for microtensile bond strength testing (µTBS), as well as for TEM characterization of the resultant RMGI-dentin interface. Statistical analysis of the µTBS results was performed using ANOVA and Tukey's test (p<0.05). RESULTS: The use of conditioner resulted in a significantly higher bond strength only when dentin was prepared by diamond bur (p<0.05). Laser irradiation induced micro-cracks on the dentin surface and led to the lowest bond strength, irrespective of the use of conditioner (p<0.05). Fuji II LC was able to partially demineralise (up to 2.0µm) and infiltrate bur-cut and fractured dentin, but no evident interaction was observed at the interface between the RMGI and laser-irradiated dentin. CONCLUSIONS: Laser-induced surface modifications impaired the interaction of the RMGI with dentin, thereby negatively influencing its bonding effectiveness. The use of a polyalkenoic-acid conditioner remains crucial for the RMGI to bond effectively to bur-cut dentin.

Microleakage of glass ionomer formulations after erbium:yttrium-aluminium-garnet laser preparation.

The aim of this study was to investigate the microleakage in class V cavities restored with four conventionally setting glass ionomers (CGIs) and one resin-modified glass ionomer (RMGI) following erbium:yttrium-aluminium-garnet (Er:YAG) laser or conventional preparation. Four hundred class V cavities were assigned to four groups: A and B were prepared by an Er:YAG laser; C and D were conventionally prepared. In groups B and D, the surface was additionally conditioned with Ketac conditioner. Each group was divided into five subgroups according to the glass ionomer cement (GIC) used: groups 1 (Ketac Fil), 2 (Ketac Molar), 3 (Ionofil Molar), 4 (Ionofil Molar Quick) and 5 (Photac Fil Quick). After thermocycling, a 2% methylene blue solution was used as dye. Scanning electron microscope (SEM) photographs were taken to show the conditioner's effect. Complete marginal sealing could not be reached. PhotacFil showed less microleakage than the conventionally setting glass ionomer cements (CGICs) investigated. Conditioning laser-prepared cavities did not negatively influence microleakage results except for Ionofil Molar Quick.

Transmission electron microscopic examination of the interface between a resin-modified glass-ionomer and Er:YAG laser-irradiated dentin.

OBJECTIVE: The aim of this study was to analyze the ultrastructural characteristics of the interface between a resin-modified glass ionomer (RMGI) and Er:YAG laser-irradiated dentin. BACKGROUND DATA: The Er:YAG laser has been considered as a possible alternative for cavity preparation, but the interaction between glass ionomers and Er:YAG-lased dentin still needs further investigation. MATERIALS AND METHODS: Five dentin surfaces were prepared by diamond bur (120,000 rpm) as controls or for Er:YAG laser irradiation (31.45 J/cm(2), 200 mJ, 10 Hz, 100 micros). The RMGI Fuji II LC (GC) was then applied to their surfaces, which were previously conditioned with a 20% polyalkenoic acid conditioner. The samples were sealed with an unfilled resin, stored in distilled water for 1 wk at 37 degrees C, and then processed for transmission electron microscopic (TEM) examination. RESULTS: When applied to bur-cut dentin (controls), Fuji II LC was able to partially demineralize the dentin surface, resulting in the formation of a hybrid layer, on top of which a sub-micron gel-phase was observed. In the laser-irradiated samples, the RMGI was in close contact with the irregular dentin substrate, but no hybrid layer or gel-phase formation could be detected, nor were there signs of dentin demineralization or collagen melting. Horizontal cracks were clearly seen in the sub-surface layer of dentin. CONCLUSION: Although presenting horizontal micro-cracks in its sub-surface, the irregular laser-irradiated dentin showed close contact with the RMGI. However, no hybrid layer or gel-phase could be detected, and there were no signs of dentin demineralization and collagen melting.

Microleakage of four different restorative glass ionomer formulations in class V cavities: Er:YAG laser versus conventional preparation.

OBJECTIVE: To investigate microleakage in class V cavities following restoration with conventional glass-ionomer cements (CGICs) or resin-modified glass-ionomer cements (RMGICs), following Er:YAG laser or conventional preparation. BACKGROUND DATA: The sealing ability of GICs in Er:YAG-lased cavities has not been studied extensively. METHODS: Three hundred and twenty class V cavities were assigned to four groups: those in groups A and B were prepared using an Er:YAG laser, and those in groups C and D were conventionally prepared. In groups B and D the surface was additionally conditioned with cavity conditioner. Each group was subdivided according to the GIC used: groups 1 (Fuji II), 2 (Fuji IX), 3 (Fuji II LC) and 4 (Fuji VIII). After thermocycling, the specimens were immersed in a 2% methylene blue solution, sectioned oro-facially, and analyzed for leakage. The effect of the conditioner was analyzed using a scanning electron microscope (SEM). RESULTS: Significant differences between occlusal and gingival margins were found in all groups (p < 0.05) except B4, D3, and D4. Comparison of preparation methods (groups A-D) revealed significant differences at the occlusal margin in groups 1 and 3, but in all groups at the gingival margin (p < 0.05). Laser preparation without conditioning allowed more leakage (p < 0.05). Comparison of filling materials (groups 1-4) revealed significant differences in groups B and C at the occlusal margin, and in all groups at the gingival margin (p < 0.05). In these groups, laser-prepared cavities (with or without conditioning) restored with Fuji II LC and Fuji VIII showed the least leakage at both margins. CONCLUSION: RMGICs allowed less microleakage than CGICs. Complete marginal sealing was not achieved and conditioning is recommended.