## 1 Introduction  
Dentofacial deformities are disharmonies between the facial, dental and bone structures that could impact a patient's quality of life (QoL), functionally and esthetically [1]. Orthognathic surgery combined with orthodontic treatment improves facial profile and occlusal function [2]. Orthognathic surgery also has significant psychosocial benefits for patients, in terms of self-confidence, relationships and social interaction [3]. Improvement of function, esthetic, and psychological status after orthognathic surgery increases the patient's QoL [4; 5; 6]. The \"orthodontic first\" approach (OFA) consists of a presurgical orthodontic treatment to decompensate teeth, causing worsened occlusion before surgery [7]: the study found that this approach is time-consuming and, during the presurgical orthodontic phase, deteriorates the facial profile [8; 9]. The study also discovered that the presurgical orthodontic phase significantly worsened oral health-related quality of life (OHRQL) in the facial esthetics and oral function domains [9]. The \"surgery first\" approach (SFA) is an alternative option for orthognathic surgery, in some cases, that eliminates the drawbacks of the presurgical orthodontic phase, and utilizes the potency of the regional accelerated phenomenon (RAP), to facilitate postsurgical orthodontic tooth movement [10; 11].  
The treatment outcomes of orthognathic surgery can be evaluated physically by clinical and radiographic findings. Many studies have monitored the outcomes of the SFA, in terms of stability or relapse: the SFA had stability and relapse rates similar to the OFA [12; 13; 14; 15]. In addition to stability, patient satisfaction and quality of life are important factors that medical teams should carefully address. Orthognathic surgery is reported to have significantly improved patient QoL [1; 4; 6; 16; 17].  
Many tools have been used to assess QoL. WHOQoL or SF-36 is a generic health questionnaire. The Oral Health Impact Profile (OHIP) and Oral Impacts on Daily Performances (OIDP) have been commonly used, in regard to focusing on the oral health of patients. In addition, there is a set of questions, which pertains specifically to this patient group's condition, called the Orthognathic Quality of Life Questionnaire (QQLQ). The QQLQ was developed by [PERSON] et al. in 2000, and consists of 22 items from four domains: facial esthetics (E), oral function (F), awareness of facial deformities (A) and social aspects of deformity (S). The patients rate accordingly, for each question, the degree of severity influencing their routine life [18]. The total score is rated from 0 to 88 points: the higher scores represent a greater influence on the patient's quality of life, while the lower scores represent a lower influence on the patient's quality of life. The studies showed that QQLQ is a suitable tool for assessing QoL, in particular for orthognathic surgery patients, when compared to generic health or oral health questionnaires [19; 20]. The original English version has been translated and used in various countries, such as Brazil, Japan, South Korea, the United Kingdom and Italy. The results of QQLQs show that the questionnaire is used for the validity and reliability of its QoL assessment [2; 9; 21; 22; 23]. In Thailand, no standard tool for QoL assessment had been used until the QQLQ was translated and validated into the Thai version, in 2021. The Thai version of the QQLQ was used in this study, to investigate patients' QoL after orthognathic surgery, and to compare the differences in QoL changes between the OFA and the SFA.