## 4 Discussion
The results of this study show that patients with hyperdivergent skeletal patterns are more prone to bracket bonding failure due to the influence of muscle force and occlusal force cyclic loading when compared with normodivergent and hypodivergent patients. To discuss the factors influencing the IDBS failure rate, orthodontic adhesives must be considered. A Transbond XT (3M Unitek, Monrovia, CA, USA) was used in this study. This is a high inorganic filler-contented direct bonding light-curing resin, considered the \"gold standard\" of orthodontic DB adhesives [36]. IDB orthodontic adhesives have the characteristics of low viscosity, nanometric filler particles, and modified properties. IDBS adhesives can maintain their shape after placement until light-curing without draining around the bracket during the bonding procedure [37]. Although the use of IDBS adhesives was an option, an in vivo study of failure rates of different resins found that the use of Transbond XT for the IDB was acceptable in clinical application [38]. Therefore, the use of Transbond XT in this study is reasonable and would not affect the research results. Finally, the failure rate of the IDBS has been demonstrated to be higher than that of the DB technique during long-term follow-up (12-15 months) in previous studies [36]. The results of this study show that age, sex, treatment stage, vertical skeletal divergence, and tooth position are risk factors for bracket bonding failure. Orthodontists should carefully control these risk factors as much as possible to reduce the bracket bonding failure rate in the clinic. Based on the results of this study, the following suggestions are provided for clinical guidance:  
1. Considering that mandibular teeth, especially mandibular anterior teeth, had a higher bonding failure rate, it is recommended to control the thickness of the resin adhesive as much as possible during the IDB process. For mandibular anterior teeth, the unexpected movement of the surrounding soft tissue must be limited, and contamination of the bonding interface caused by excessive salivation must be controlled. A small archive was chosen for overcrowded cases to avoid bonding failure due to excessive orthodontic force. Additionally, care should be taken to check and remove premature contact spots. Resin bite blocks can be added when necessary to open the bite;
2. Considering that the anterior teeth had a higher position error rate, the application of stable and steady occlusal pressure along the long axis of the tooth on the transfer jigs in the IDBS is suggested;
3. The effects of sex, age, and vertical skeletal pattern warranted careful follow-up of male patients under 20 years of age with hyperdivergent skeletal patterns, provided they followed the treatment instructions. Moreover, patients should be advised to change their dietary habits. This study has some limitations. Bracket bonding was not performed by the same operator. Although the technical sensitivity of different operators may have affected the results, the operators in this study were professional orthodontists who had received the same years of training from a standardized resident training institution to minimize operator error as much as possible. We, therefore, divided the reasons for bracket responding into two factors. A more precise and specific investigation of the samples bonded by a single operator should be conducted in a future study.