Transbond xt light cure adhesive paste

The brackets were bonded to each tooth following the current clinical procedure. The entire facial surface of the tooth was etched with 37% phosphoric acid for 30 s and then rinsed and dried using the dental air-water syringe. For the control group, Transbond® XT light-cure adhesive paste (3M Unitek, St Paul, MN) was placed on the bottom of an orthodontic bracket (lower incisor brackets), and the bracket bonded to the center of the etched tooth surface, and cured with LED light (Ultradent Products, Inc, USA) for 20 s. For the LLP, DS-P, DS-S, RPS and UOS, following etching and drying, each material was painted on the entire etched surface of their respective tooth samples. Then the bracket was bonded and cured as described for the control group. For the DS-PS group, following etching and drying, DS primer was coated on the entire facial surface of each tooth, and the bracket was bonded and cured as described for the control group. Following bracket bonding, DS enamel surface sealant was coated on remaining facial surface of the tooth around the bracket, and light cured with LED light for 20 s.

The teeth were randomly divided into two groups of 30 for laser-etching (group A) and acid-etching (group B). In group A, the teeth were etched with 37% phosphoric acid gel (Gel ETCH, 3M Unitek, Monrovia, CA, USA) for 15 seconds, were rinsed for 15 seconds, and were air dried for 15 seconds. In group B, the teeth were irradiated with Er,Cr:YSGG laser (Waterlase iPlus, Biolase Inc., Irvine, CA, USA) for 60 microseconds by a gold handpiece with MZ8 tip (0.8 mm in diameter) operated at the 2780nm wavelength, 50Hz frequency and 4.5W output power with 80% water and 60% air.
After surface preparation in both groups, a thin layer of primer (Transbond XT, 3M Unitek, Monrovia, CA, USA) was applied on the enamel in both groups and was cured for 20 seconds using a light-curing unit (PenCure LED light, Morita, Kyoto, Japan). After applying the adhesive resin (Transbond XT light cure adhesive paste; 3M Unitek, Monrovia, CA, USA) on the bracket base (standard edgewise brackets with a 0.018-inch slot; DynaLock, 3M Unitek, Monrovia, CA, USA), the bracket was placed at the center of the buccal surface of each tooth [10 (link), 17 (link)]. An explorer was used to place the bracket on the enamel surface by a uniform force and also to remove the excess adhesive. Light-curing was done for 20 seconds. The teeth were stored in distilled water for 48 hours to prevent dehydration prior to debonding.

All methods were carried out in accordance with relevant guidelines and regulations. The study was initiated after securing Internal Review Board (IRB). The samples in this study were prepared with human mandibular premolars, stainless steel lower premolar brackets (Victory Series, 3 M Unitek) and a bis‐acryl composite resin provisional material, Protemp 4 Garant (3 M ESPE). An adhesive resin (Transbond XT Light Cure Adhesive Paste; 3 M Unitek) was used to bond orthodontic brackets to tested substrates. Given that this is the first time that metal primer is used for bracket bonding there are no previous studies for a proper sample size calculation. Therefore, the number of 10 specimens per group was adopted which is a common number for decades of published papers dealing with the shear bond strength of orthodontic brackets.

For Group 1 (etch-and-rinse), acid-etching was applied with 37% phosphoric acid for 30 s and then rinsed with water for 30 s and air dried for 10 s. After seeing the chalky white surface, Transbond™ XT Light Cure Adhesive Primer (3M/Unitek, Monrovia, CA, USA) was applied as a thin layer on the tooth surface.
For Group 2 (self-etching-primer), routine care control was completed so that the buccal surfaces of the teeth were clean. Transbond™ Plus Self Etching Primer (3M/Unitek, Monrovia, CA, USA) was applied to the tooth surface for five seconds. Consequently, air was feebly applied to the surface with an air-water syringe. Then, APC brackets were removed from their protective boxes and placed in their correct position on the tooth surface. Transbond™ XT Light Cure Adhesive Paste (3M/Unitek, Monrovia, CA, USA) was placed on the base of the remaining brackets. All brackets were placed in the precise position on the tooth surface and the flashes were removed. All brackets were cured from mesial and distal for 20 s using 3M Espe Elipar S10 (3M ESPE Dental Products) which has the intensity of 430–480 nm at about 1200 mW/cm², respectively.

The specimens were etched with 37% phosphoric acid for 30 s, washed for 20 s, and dried with oil‐free compressed air for 20 s, after which a thin uniform coat of primer (Transbond XT Primer; 3 M Unitek) was applied. The adhesive resin (Transbond XT Light Cure Adhesive Paste; 3 M Unitek) was placed onto the bracket base, and the bracket was positioned on the specimen surface. Excess adhesive resin was removed with an explorer. Adhesive resin was polymerized using curing light (Ortholux LED; 3 M Unitek) at approximately 1000 Mw/cm² for a total of 10 s from two directions (mesial and distal).

The adhesive agents used in the study for Group 1, Group 2, and Group 3 are listed below:
Group 1:
Transbond™ XT Primer (3M Unitek, Monrovia, CA, USA);
Transbond™ XT Light Cure Adhesive Paste (3M Unitek, Monrovia, CA, USA).
Group 2:
BracePaste^® MTP Primer (American Orthodontics, Sheboygan, WI, USA);
BracePaste^® Adhesive (American Orthodontics, Sheboygan, WI, USA).
Group 3:
Ortho Solo™ Primer (Ormco, Orange, CA, USA);
Grengloo™ Adhesive (Ormco, Glendora, CA, USA).
The compositions and weight percentages of the adhesive agents used in Group 1, Group 2, and Group 3 are given in Table 1.