The Setting Chemistry of Glass Ionomer Cement

The setting chemistry of glass ionomer cement was imestigated by using mechanical determination of compressive strength at predetermined intervals,and measurement of structure changes of correspondling fracture sample by means of IR spectra and differential scanning calorimetry（DSC）.Zinc polycarboxylate cement was used as a comparison sample.The compressive strength of glass ionomer cement（GIC） increases with aging.IR spectra and DSC of corresponding fracture sample show the structure changes of the matrix and interface layer comprising of silica gel during the predetermined intervals studied.however,no significant changes occur in the zinc polycarxyolate cement.Hence the structure changes of the matrix and/or interface layer are responsible for compressive strength increasing with aging.The structure changes include the crosslink density,the ratio of complex form to ionic form,the content ratio of Al-PAA to Ca-PAA,the forming and maturing process of the interface layer comprising of silica gel.

Anti-biofilm Effect of Glass Ionomer Cements Incorporated with Chlorhexidine and Bioactive Glass

The effect of glass ionomer cement and resin-modified glass ionomer cement incorporated with chlorhexidine and bioactive glass on antimicrobial activity and physicochemical properties were investigated. The experimental results showed that groups incorporated with 1% chlorhexidine exhibited a significant reduction of optical density values of the bacterial suspension and increased the degradation of Streptococcus mutans biofilm. However, groups incorporated with 10% bioactive glass did not affect the optical density values and the biofilm formation. The mechanical properties of the materials and the polymerization were not influenced by the addition of chlorhexidine. Nevertheless, the compressive strength was lower when the materials were incorporated with bioactive glass. It can be concluded that glass ionomer cements incorporated with chlorhexidine can maintain its mechanical properties as well as reduce early S mutans biofilm formation. Controlled release/sustained release technology may be required to optimize the antibacterial activity of glass ionomer cements incorporated with bioactive glass.

Short-term Mechanical Properties of Glass Ionomer Cement

The setting reaction of glass ionomer cement was studied by analyzing and comparing the short-tem mechanical properties of set cement stored in silicone oil, air and distilled water respectively at different temperatures. For the set cement stored at 37 ℃, the strength of the sample in the air reached the maximum value after 24 h, then decreased to about 210 MPa and kept steady. The strength of the sample in water increased continuously and slowly, however, the increasing rate of sample stored in silicone oil was higher than that in the water. At 20 ℃, the increasing rate of compressive strength for sample in air was higher than those in silicone oil and water. The diffusion speed and maintenance of water has significant effects on the mechanical properties of glass ionomer cements.

MICROLEAKAGE OF CLASS V RESIN-MODIFIED GLASS IONOMER CEMENT AND COMPOMER RESTORATIONS IN VITRO

Objective To assess the microleakage of Class V restorations made with two resin-modified glass ionomer cements （RMGICs） and two polyacid-modified composite resins （PMCRs）. Methods Restorations of the four materials （ GC Fuji Ⅱ LC, Vitremer^TM, Dyract AP and F2000^TM ） were placed in facial Class V cavity preparations in forty noncarious human molar teeth. Teeth were randomly assigned to 4 experimental groups of 10 teeth each. After thermal cycling（ ×20, 5 -55℃ ） , the interface between dentin and restorations was spattercoated with gold and observed under scanning electron microscopy （SEM）. Then the square and average width of margin gaps of central 1/3 interface were recorded with image analysis software. Results The data indicated no significant differences between all the restorative materials for both occlusal and gingival margins. Further analysis revealed there were statistically significant differences between occlusal margins and gingival margins for VitremerTM and Dyract AP, respectively. Conclusion None of the tested materials guaranteed margins free of microleakage. Resin-modified glass ionomer cements showed similar margin gaps to the polyacid-modified composite resins tested.

Setting kinetics and mechanical properties of flax fibre reinforced glass ionomer restorative materials

Regardless of the excellent properties of glass ionomer cements,their poor mechanical properties limit their applications to non-load bearing areas.This study aimed to investigate the effect of incorporated short,chopped and randomly distributed flax fibers（0,0.5,1,2.5,5 and 25 wt%） on setting reaction kinetics,and mechanical and morphological properties of glass ionomer cements.Addition of flax fibers did not significantly affect the setting reaction extent.According to their content,flax fibers increased the compressive（from 148 to 250 MPa） and flexure strength（from 20 to 42 MPa）.They also changed the brittle behavior of glass ionomer cements to a plastic one.They significantly reduced the compressive（from 3 to 1.3 GPa） and flexure modulus（from 19 to 14 GPa）.Accordingly,flax fiber-modified glass ionomer cements could be potentially used in high-stress bearing areas.

The Effect of ZnO on the Physicochemical and Mechanical Properties of Aluminosilicate Dental Cements

In this study,the effect of the addition of various amounts of ZnO(0,1,2,and 3 wt.%)to aluminosilicate bioactive glass(BGs)network(SiO_(2)-Al_(2)O_(3)-P_(2)O_(5)-CaF_(2)-CaO-K_(2)O-Na_(2)O)on the mechanical properties of the fabricated glass ionomer cement(GIC)samples was studied.The GIC samples were fabricated by mixing the synthesized aluminosilicate BGs with Riva-self cure liquid.The synthesized aluminosilicate glass was characterized using differential thermal analysis(DTA),X-Ray diffraction(XRD),Fourier-transform infrared spectroscopy(FTIR),and scanning electron microscopy(SEM).Besides,the mechanical properties of GICs were evaluated using Vickers microhardness and Diametral tensile strength(DTS)test.According to DTA analysis,the glass transition temperature(Tg)of aluminosilicate BGs was decreased from 575 to 525°C.According to the results,the aluminosilicate BGs with an amorphous state(~90%)and the grain size of 36μm were synthesized.Doping of the ZnO to glass network up to 3 wt.%could increase the amorphous phase up to 95%and decrease the grain size of the particles up to 28μm.The microhardness and DTS of the GIC samples containing the aluminosilicate BGs were about 677 Hv and 8.5 MPa,respectively.Doping of ZnO to the glass network increased the mentioned values up to 816 Hv and 12.1 MPa,respectively.

Improvement of enamel bond strengths for conventional and resin-modified glass ionomers: acid-etching vs. conditioning

Objective:This study deals with the effect of phosphoric acid etching and conditioning on enamel micro-tensile bond strengths(μTBSs)of conventional and resin-modified glass ionomer cements(GICs/RMGICs).Methods:Forty-eight bovine incisors were prepared into rectangular blocks.Highly-polished labial enamel surfaces were either acid-etched,conditioned with liquids of cements,or not further treated(control).Subsequently,two matching pre-treated enamel surfaces were cemented together with one of four cements[two GICs:Fuji I(GC),Ketac Cem Easymix(3M ESPE);two RMGICs:Fuji Plus(GC),RelyX Luting(3M ESPE)]in preparation forμTBS tests.Pre-treated enamel surfaces and cement-enamel interfaces were analyzed by scanning electron microscopy(SEM).Results:Phosphoric acid etching significantly increased the enamelμTBS of GICs/RMGICs.Conditioning with the liquids of the cements produced significantly weaker or equivalent enamelμTBS compared to the control.Regardless of etching,RMGICs yielded stronger enamelμTBS than GICs.A visible hybrid layer was found at certain enamelcement interfaces of the etched enamels.Conclusions:Phosphoric acid etching significantly increased the enamelμTBSs of GICs/RMGICs.Phosphoric acid etching should be recommended to etch the enamel margins before the cementation of the prostheses such as inlays and onlays,using GICs/RMGICs to improve the bond strengths.RMGICs provided stronger enamel bond strength than GICs and conditioning did not increase enamel bond strength.

Twelve-month evaluation of the atraumatic restorative treatment approach for class Ⅲ restorations:An interventional study

BACKGROUND Atraumatic restorative treatment(ART)may be appropriate for populations without accessibility and affordability.More data are required regarding the success rate of ART in anterior teeth.AIM To evaluate the clinical performance of restoring class III cavities in anterior teeth of permanent dentition using the ART approach.METHODS A longitudinal interventional field study was carried out at two rural primary health centers,Tumkur district,India.A total of 54 teeth in 39 patients were evaluated for the survival rate of class III restorations in permanent anterior teeth using the ART approach in children and adult populations.Evaluation of ART restoration was carried out using Frencken J criteria,the mean procedure time,patient acceptance and reported pain severity during the ART approach were evaluated using a visual analog scale.Calculation of the cost of ART was also performed.RESULTS The mean time taken to perform the ART procedure was 14.79±5.8 min with the majority of patients reporting only mild pain.At 6 mo follow-up,72.2%remained in a good state,but this reduced to 27%at 12 mo.The cumulative survival rate of the restorations was 94.4%at 6 mo and 80.9%at 12 mo follow-up.Estimation of the direct cost for a single class III restoration was 186.50 INR(2.64 USD).CONCLUSION ART may be a good comprehensive option for basic oral health care for underserved or inaccessible populations,and preventive care for patients.

A Novel Open C-shaped Molar Band for Orthodontic Applications： Mechanical Characterizations and Clinical Trials

To evaluate the retention properties of the novel ‘C＇-shaped molar bands at a laboratory level. Resin-modified glass ionomer cement（RMGIC） was used as a luting agent for the novel C-shaped molar band. The mechanical properties of the band were examined and the retention performance was characterized in the mesial, distal and vertical directions. A clinical trial was conducted using a spilt-mouth design on 50 patients. The novel C-shaped molar bands fit most molars without a repeated try-in process.The use of both nanoHA coating and RMGIC enhanced the tensile（8.00 ± 1.8 MPa） and shear strengths（27.17 ± 8.6 MPa） of the molar bands, leading to high retention in vertical, mesial and distal directions（ p 〈 0.001）. In clinical trials, the C-shaped molar bands had a failure rate（15%） comparable to that of traditional bands, and 93% of the failed bands demonstrated an adhesive remnant index score of 0, corroborating the observation that no luting agent residue remained on the tooth surface in most cases. The novel C-shaped molar bands appear to be a promising appliance that requires further clinical investigations, and may be used effectively in orthodontics.