This study aimed to compare experiences between adult patients receiving clear aligners and fixed appliances during the initial stage of orthodontic treatments.

Patients receiving either clear aligner treatments were enrolled in this study. During the same time period, patients receiving fixed orthodontic treatments well-matched with clear-aligner patients by similar ages (difference < 3 years), same gender and similar levels of severity of malocclusion [similar Index of Complexity Outcome and Need (ICON) level] were enrolled.The two groups were well-matched with ages, gender and levels of malocclusion severity. Pain perception, anxiety and quality of life were assessed through visual analogue scale (VAS), state-trait anxiety inventory (STAI) and oral health impact profile-14 (OHIP-14), respectively.

Inclusion Criteria:

• Must be 18 years of age or older;
• Must be in good general health;
• Upper and lower arches were both involved in two groups;
• The fixed appliances group must be treated with wires and brackets only with the initial arch wire of 0.012 NiTi ;
• Must be willing to sign and give written informed consent in accordance with institutional and federal guidelines.

Exclusion Criteria:

• Once been undergoing with orthodontic treatment;
• Experienced tooth ache recently;
• Been diagnosed with contagious and/or systematical diseases;
• Have taken any kind of painkillers three days before the initial treatment;
• When Trait Anxiety Inventory (T-AI) shows a score believed to define a psychological state of over anxiety (male over 53 points and female over 55 points).

Patients receiving either clear aligner or conventional fixed appliance treatments from December 2013 to December 2015 in West China Hospital of Stomatology were enrolled in this study.