## 2 Materials and Methods
### Experimental Procedure  
The teeth were randomly (Epidat 4.1, Galicia, Spain) embedded into two experimental models of epoxy resin (Ref. 20-8130-128, EposiCure(r), Buehler, IL, USA) with 10 teeth each (central incisors, lateral incisors, canines, first and second premolars) following the manufacturer's recommendations, and the experimental models were randomly distributed to the following study groups. Group A: Buccal multibracket appliance therapy (MBT, 0.022,Pacific Orthodontics, Guadalajara, Spain) (Buccal) (\(n\) = 10); Group B: Lingual multibracket appliance therapy (Ref. 740-0430, Alias, Ormco, Glendora, CA, USA) (Lingual) (\(n\) = 10). The teeth were stored under humid conditions until the beginning of the study. Two experimental models were necessary in order to use an intact surface (buccal or palatal) to align the digital files. Afterwards, the experimental model was scanned with an intraoral scan (True Definition, 3M ESPE(tm), Saint Paul, MN, USA) to obtain a standard tessellation language (STL) digital file (STL1), with a resolution of 54.68 pts/mm\({}^{2}\)[12]. Then, buccal and lingual multibracket appliance therapies were bonded to the buccal and palatal enamel surface by a single operator using a three-step adhesive technique. An acid etching agent (Ortho Solo(tm), Ormco Corporation, CA, USA) was applied to the buccal and palatal enamel surface for 20 s; afterwards, the acid etching (Ortho Solo(tm), Ormco Corporation, CA, USA) was removed under profuse washing and dried. Furthermore, a photopolymerized resin adhesive primer (Unitek Transbond(tm) XT, 3M ESPE(tm), Saint Paul, MN, USA) was gently applied using a microbrush (Plus slim; Microbrush International; Grafton; NSW, USA) on the previously etched buccal and palatal enamel surface and was photopolymerized (BluePhase G2(tm), Ivoclar Vivadent, Schaan, Principado de Liechtenstein) for 20 s. The fixed buccal (MBT, 0.022, Pacific Orthodontics, Guadalajara, Spain) and lingual (Ref. 740-0430, Alias, Ormco, Glendora, CA, USA) multibracket appliances were directly cemented from tooth 15 to 25 in the center of the buccal and palatal surface of the clinical crown with a photopolymerized composite resin cement (Transbond(tm) XT, 3M ESPE(tm), Saint Paul, MN, USA), which was photopolymerized (BluePhase G2(tm), Ivoclar Vivadent, Schaan, Principado de Liechtenstein) for 20 s. After that, the experimental models were subjected to digital impression through an intraoral scan (True Definition, 3M ESPE(tm), Saint Paul, MN, USA). Afterwards, the fixed buccal and lingual multibracket appliances were debonded using bracket remover Weingart pliers ([PERSON], Solingen, Germany). Then, digital impressions (True Definition, 3M ESPE(tm), Saint Paul, MN, USA) were performed obtaining the STL2. Afterwards, the remaining cement of the fixed buccal and lingual multibracket appliances was removed from the buccal and palatal surfaces of the teeth using an adhesive remover bur (H379 AGK, KOMET Dental, [PERSON], Germany) mounted on a micromotor handpiece (INTRA MULTflex L181M, KaVo, Biberach an der Riss, Germany) at 20,000 rpm with profuse irrigation until no cement remnants were visible to the clinician's eye. Finally, digital impressions (True Definition, 3M ESPE(tm), Saint Paul, MN, USA) of the experimental models were performed (STL3). The experimental procedures performed for both experimental models were performed by a unique operator.