This article describes a new technique to transfer the 3D bracket positioning by an effective indirect bonding procedure. Advantages and disadvantages of the CAD/CAM technology for the indirect bonding technique are discussed to help clinician use the indirect digital system routinely.
Recently, a modified indirect bonding technique for a standardized and effective indirect bonding procedure has been described  to help orthodontists in bracket positioning accuracy and to exploit full potential of pre-adjusted appliance , saving time at chair and giving comfort to the patients .
This technique consisted in making bracket-positioning guide on the cast manually by using McLaughlin method , with the aim to align, leveling teeth and marginal ridges . It also allowed to control the procedural variables (e.g. tray stability, flushes, curing time, etc.), standardizing indirect bonding technique for the routine and effective use of indirect bonding procedure.
Despite the described advantages of this technique, the accuracy in bracket positioning was influenced by manual skills of clinicians in tracing the bracket-positioning guide on the cast, and by the ability of the trained technician in positioning the brackets on the cast precisely.
The advent of digital orthodontics, in particular digital impression, simplified the process to have a digital model by dedicated CAD software, allowing analysis, measurements, virtual setup, and digital bracket positioning. Since the first paper on prototyped transfer tray published in 2006 , several digital systems allowed to transfer virtual bracket position by using a prototyped gig/tray, in which the real brackets were inserted, then transferred on the teeth by using light-curing bonding with some limitation in the clinical stage (eg. Flushes, light curing process).
On the contrary, as reported in 2012 , the use of customized bracket base, by pre-dosed light-cured adhesive, showed two main clinical advantages: (1) The customised bracket base respected the surface anatomy reducing the errors related to adhesive excess and flushes; (2) Self-curing indirect bonding used in the clinical stage took just 4 minutes and needed no attention from the operator, whereas the indirect light-curing and bonding took 30 seconds for each bracket from first molar to last molar, requiring also active attention all the time.
As reported in the previous paper , one advantage of that technique was the possibility to be integrated with CAD/CAM procedure; since, to our knowledge, there are no papers showing CAD-CAM system able to transfer the virtual bracket position with a pre-dosed customized bracket base. The aim of this paper is to describe a new method to transfer the digital bracket positioning by an effective indirect bonding technique.
The method in ten steps
- Scan both arches by an intraoral scanner (Trios, 3Shape, Copenhagen, Denmark) and occlusal registration.
- Prepare digital model by a CAD software (Ortho Analyzer, 3Shape, Copenhagen, Denmark).
- Separate the teeth in order to perform virtual setup.
- Using a virtual library, select the bracket system together with the type of arch form in order to align and level both arches. Fix the brackets adjusting the ideal position of each tooth using 3D setup (Figure 1). Then the achievement of six key of normal occlusion5 can be checked (Figures 2-4).
- Prototype the model of malocclusion with and without positioned brackets by 3D printing machine (form 2, Formlab, Somerville, Massachusetts, USA).
- Vacuum-form a 0.3mm bracket-template (Erkodent Erich Kopp GmbH, Pfalzarafenweiler, Germany) on the 3D model with bracket printed on, then cut and mark single gauges for each tooth.
- Put separating agent on the model (Unifol, Perident Dental Products, Florence, Italy) and adhesive on the bracket base.
- Positioning brackets on the model, remove all flushes. Desired position is obtained by using the gauges described above.
- Light-cure the adhesive of all brackets by using light-cure machine (Fotolab UV, Tissi Dental, Milan, Italy). When all the braces were positioned, the adhesive were light-cured. From this point the process continues as described in the previous paper, briefly summarized as follows: use of soft silicone (Emiluma, Opal Orthodontics, South Jordan, Utah) covering the braces in order to have a soft tray; vacuum form and properly cut a 0.3mm tray to contain the soft tray; Soak the model in water for 30 minutes and gently debond the brackets from model; clean residual separating agent with 50-μm size sand in a dedicated machine (Uno, Tissi Dental, Milan, Italy) at 1 bar pressure, then wash the transfer tray with toothbrush and soap, rinse, and dry fully.
- The transfer tray with pre-dosed bracket base positioned by CAD setup is ready together with its bracket template (Figure 5). The clinical stage procedure may start as reported in the previous paper1: Polish the tooth surfaces; Isolate the dentition to obtain a dry field (Nola Dry Field System; Great Lakes Orthodontics, Tonawanda, NY); Prepare the tooth surfaces by etching with 37% phosphoric acid gel for 30 seconds, rinse and dry fully; Apply a thin layer of primer (Transbond MIP; 3M Dental Products) on the teeth and apply self-curing components A and B (Sondhi Rapid Set; 3M Dental Products) on teeth and bracket bases respectively; Firmly seat the transfer tray with both hands, maintaining 2 vectors for 60 seconds: one stabilizes the tray on the arch, and the other keeps brackets and tooth surfaces matched. After first minute, leave the tray on for 3 minutes more, to complete the self-curing process. Remove the tray with a scaler, silicone layer and any residual primer with utility tool; the arch wire can be engaged.
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