The researches of topography and the shear strength of adhesive bonded to laser-pretreated or etched human enamel

• Main Authors: Shang-Wuu Tsai, 蔡尚武
• Other Authors: Prof.Shun-Te Huang,Ph.D.
• Format: Others
• Language: zh-TW
• Published: 1999
• Online Access: http://ndltd.ncl.edu.tw/handle/43355305684320082273

碩士 === 高雄醫學院 === 牙醫學研究所 === 87 === The researches of topography and the shear strength of adhesive bonded to laser-pretreated or etched human enamel Pediatric Dentistry , Graduate Institute Of Dental Science ,Kaohsiung Medical College Number:8652013 By Shang-Wuu Tsai Advisor:Prof. Shun-Te Huang Abstract The CO2 laser has a similar effect on enamel and dentin to that of the traditional acid-etching technique. It is apt to be absorbed by the enamel and water .The clinical manipulation of laser-etching is simpler and more convenient than that of traditional acid-etching ,does not have the limitations caused by moisture ,and laser-etched area can be more easily controlled. Unlike Nd:YAG laser ,the substrate surface does not need to be coated with black ink for CO2 laser-etching procedure . CO2 lasered enamel is more resistant to acid attack .Because of these advantages , we wanted to know wheather a laser beam could be an alternative to the acid-etching technique. The purpose of this study was to compare laser-treated specimens with a- cid-etched specmens and different dental adhesive materials to determine the effects of varying wattage and energy levels of the CO2 laser on shear bond st- rength. We also observed the fracture surface of laser-etched specimens after bracket debonding by a shear bond strength test. 88 healthy human premolars extracted for orthodontic therapy were used in this study ,and were divided into: Control group(8 premolars) , laser group(3 2 premolars) dental adhesive materials group(24 premolars) and acid-etched group(32 premolars) . At first 88 premolars, roots were cut and sectioned lon- gitudinaly from the middle occlusal surface to a point 1 to 2 mm apical to the cementoenamel junction (CEJ) . The specimens were embedded and set .Then the 320#,600#,800#,1200# grit were used to polish the enamel surface ( 5×5mm2) respectively . The control group was not treated .The acid-etched group was treated with 35%phosphoric acid for 15sec or 60sec (Ultradent) , 10 %maleic acid for 15sec (3M), 10 %polyacrylic acid for 15sec (GC) ,respectively.A CO2 laser (spot size 1.3mm) was used to treat the 4 laser subgroups. Varying wattage (5 W,10 W,15 W,20 W) was used on the human enamel. The composite resin (Z-100) was bonded to the above samples.The dental adhesive materials group was etched with 35%phosphoric acid(ultradent) for 15sec except for the light-curing glass-ionomer subgroup,which was etched with 10%polya-crylic acid. Then the light-curing resin[Z-100(3M)],self-curing resin Ormco) and light-curing glass-ionomer(GC Ortho LC) were bonded to the above samples respectively. All the specimens were stored in distilled water at 37℃ for 1 day. Shear strength required to debond the bracket was measured by Instron at a crosshead speed of 1mm/min and the fracture surface was observed by scaning electron microscope. The results were as follows: 1.The mean shear bond strength: (1)etching group:35%Phosphoric acid(60sec)[17.2±2.75MPa]>10%Maleic acid(15sec)[13.87±2.12MPa]>35%Phosphoric acid(15sec)[9.13±1.54MPa]>10%Polyacrylic acid(15sec)[2±0.57MPa] .(2)Laser group:15W[10.83±1.72MPa] >10W[7.31±2.06MPa]>20W[6.73±1.18MPa]>5W[3.12±0.95MPa] .(3)dental adhesive material group:light-curing glass-ionomer(GC Orth LC)[10.19±2.1MPa]>self-curing composite resin(Ormco)[10±2.27MPa]>light-curing composite resin(Z-100,3M)[9.13±1.54 MPa] . (4)control group:1.1±0.51MPa . 2.SEM was used to observe fracture surface after debonding of bracket . 15 W obtained the largest shear bond strength of 10.83±1.72MPa in CO2 laser group . And small fracture fragements of lasered enamel were occasionaly found in 10 W samples. The mean shear bond strength was measured 7.31±2.06MPa in 10 W samples. Enamel surface deepened by laser treatment can be clearly seen by naked eye in 15 W and 20 W subgroups. The mean shear bond strength of 20 W was reduced to 6.73±1.18 MPa ,with more fracture surface and severe sound and light manipulation.Therefore,20 W of continuous wave type is not satisfactory for use.10 W、15 W should be acceptable to lasered dental hard tissue ,but 15 W need be modified . The results of this study among groups are statistically significant except for the relationships between various adhesive materials ( dental adhesive materials group)and between 10 W and 20 W of CO2 laser group. From the viewpoint of orthodontic therapy, the mean shear bond provides nearly enough strength for use in orthodontic treatment . In conclusion , We suggest that when we use composite resin (Z-100) and Scotchbond Multipurpose for restorations and bonding of enamel ,10 W or 15 W of CO2 laser is effective for the laser-etching tecnique.