| Objectives:By comparing and studying the changes of marginal tightness of 2 bonding systems under the effect of different light intensities and light durations,we want to discover the interaction between light intensity and duration,and provide experimental basis for choosing different bonding systems,as well as suitable light intensity and duration in clinical practice.Methods:There were 153 isolated human permanent molars were collected and their roots were cut off.Their crowns were split from mesial side to distal side.Cylindrical single-sided cavities with depth of 2mm and diameter of 3mm were prepared on the buccal and lingual pieces.Totally 306 samples were prepared.According to different conditions of adhesives(full-etching adhesive AdperTMSingle Bond 2 and self-etching adhesive AdperTM Easy One),light intensities(700mW/cm2,1400mW/cm2,and 2100mW/cm2)and durations(It was 1 time,3 times,5 times of the initial light duration corresponding to the light intensity,a total of three groups),we set 18 groups each of which contained 17 random samples.Each experimental group was named with the first letter and four digits:the first letter S represented AdperTM Single Bond 2 adhesive,E represented AdperTM Easy One adhesive;the middle two digits represented light intensity of adhesive;the last two digits represented actual light duration of adhesive.For example,the S0710 group meant using AdperTM Single Bond 2 adhesive,700mW/cm2 light intensity,and irradiating 10s for adhesive.The remaining experimental groups were S0730 group,S0750 group,S1405 group,S1415 group,S1425 group,S2103 group,S2109 group,S2115 group,E0710 group,E0730 group,E0750 group,E1405 group,E1415 group,E1425 group,E2103 group,E2109 group,E2115 group.FiltekTMZ350XT A2 Body shade composite resin was used for samples filling.The filled samples were stored in distilled water at 37℃ for 24 hours,and then,according to ISO standard TS 11405:2015(E),thermocycling was used to simulate the aging of the material.In each group,one sample was randomly selected for SEM observation,and the others were dyed in 1%methylene blue solution for 24 hours.Stereomicroscope was used to observe the microleakage.Kruskal-Wallis test,Mann-Whitney test and Wilcoxon signed rank test were used for statistical analysis of microleakage.Results:Stereomicroscope results:①There was no statistically significant difference(P>0.05)in the comparison of overall,crown side and root side microleakage when using full-etching bonding system,and the 700mW/cm2,1400 mW/cm2,2100mW/cm2 light intensities and different light durations were used for adhesive light curing.There was statistically difference(P=0.044)in the comparison of root side microleakage when using self-etching bonding system,and the 2100 mW/cm2 light intensity and different light durations were used for adhesive light curing.A further pairwise comparison of root side microleakage among the three groups of E2103,E2109,and E2115 showed that there was no statistically significant difference(P>0.05)in the pairwise comparison.In the other groups,there was no statistically significant difference(P>0.05)in the comparison of overall,crown side and root side microleakage.②There was no statistically significant difference(P>0.05)in the comparison of overall,crown side and root side microleakage when using full-etching bonding system and using 700mW/cm2,1400mW/cm2,2100 mW/cm2 light intensities,and when corresponding light duration to each light intensity was the same multiple of the initial light duration(ltime,3times,and 5 times,the specific light duration was related to the light intensity).When light duration of self-etching bonding system was 1 time the initial light duration:the E0710 group with 700mW/cm2 light intensity,the E1405 group with 1400mW/cm2 light intensity,the E2103 group with 2100mW/cm2 light intensity,there was statistically significant difference in the comparison of overall(P=0.026),root side microleakage(P=0.042)between E0710 group and E1405 group and there was statistically significant difference(P=0.009)in the comparison of root side microleakage between E1405 group and E2103 group.However,there was no statistically significant difference(P>0.05)in the comparison of overall,crown side and root side microleakage between E0710 group and E2103 group.When light duration of self-etching bonding system was 3 times the initial light duration:there was statistically significant difference(P=0.014)in the comparison of crown side microleakage between the E0730 group with 700mW/cm2 light intensity and the E1415 group with 1400mW/cm2 light intensity.In the other groups,there was no statistically significant difference(P>0.05)in the comparison of overall,crown side and root side microleakage.When light duration of self-etching bonding system was 5 times the initial light duration:there was no statistically significant difference(P>0.05)in the comparison of overall,crown side and root side microleakage.③When using same light intensity and light duration,there was significant difference in the comparison of overall(P=0.039),crown side microleakage(P=0.035)between S1405 group which using full-etching bonding system,1400mW/cm2 light intensity,irradiating 5s and E1405 group which using self-etching bonding system,1400mW/cm2 light intensity,irradiating 5s.But in the other groups,there was no statistically significant difference(P>0.05)in the comparison of overall,crown side and root side microleakage.④With same light intensity and light duration,in group S1415(P=0.025)using full-etching bonding system,1400mW/cm2 light intensity,irraditing 15s,and group E1415(P=0.046),using self-etching bonding system,1400mW/cm2 light intensity,irradiating 15s,there was statistically significant difference of crown side and root side microleakage among the samples of these 2 groups.There was no statistically significant difference(P>0.05)of crown side and root side microleakage among the samples of the other 16 groups.SEM results:S0710,S1405,S2103,S2115,E0710,E1405,E2115 groups(7 groups in total),the composite resin adhered tightly to the tooth tissue,and no obvious cracks were seen at the crown side bonding interfaces and root side bonding interfaces.In the other 11 groups,there were different cracks at the crown side bonding interfaces or root side bonding interfaces.Conclusions:①Under the same light intensity and light duration,there is no significant difference of marginal tightness between full-etching bonding system and self-etching bonding system,but the marginal tightness of full-etching bonding in crown side is slightly better than self-etching bonding.For same bonding system,there is no significant difference of marginal tightness between crown side and root side of the filling body.Clinically,we can choose suitable bonding system according to the condition of the pulp,the difficulty of operation,the degree of patient cooperation and so on.And we need to apply every step carefully and meticulously.②Using full-etching bonding system,when corresponding light duration to each light intensity is the same multiple of the initial light duration,there is no significant difference of marginal tightness between the groups using high intensity,short-time irradiation and the groups using low intensity,long-time irradiation.Clinically,we can reduce operating time by using high intensity curing lamps.③Light intensity and lightduration follow the law of exposure reciprocity in a certain range of light intensity.Clinically,we can choose suitable light intensity and light duration by the formula of law of exposure reciprocity(total light energy=light intensity × light duration).But,the maximum of light intensity applicable to this law still needs further study. |
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