## 4 Discussion
### Interpretation and Generalizability  
When approaching the treatment plan for a maxillary impacted canine, one of the most relevant factors to be evaluated is anchorage. [PERSON] et al. (2016); [PERSON] et al. (2016); [PERSON] et al. (2016) showed that poor anchorage can be one of the most frequent reasons for impacted canine treatment failure. Poor anchorage indicates a failure in the control of reactive force during orthodontic treatment, causing unwanted tooth movement as well as making the treatment more difficult. During canine traction, it is also possible to face another side effect: root resorption of adjacent teeth due to the compressive intrusive forces generated or, alternatively, due to incorrect force vector planning ([PERSON] et al., 2016; [PERSON] et al., 2016). Another possible risk during canine traction is orthodontically induced external root resorption (OIRR), as shown by [PERSON] et al. (2016). For all of these reasons, the canine-first approach with miniscrews as anchorage was proposed ([PERSON] et al., 2016; [PERSON] et al., 2016; [PERSON] et al., 2016; [PERSON] et al., 2016; [PERSON] et al., 2016). The rationale behind this treatment is to avoid any side effects on teeth adjacent to the impacted canine, including root resorption and undesirable tooth movement. [PERSON] also reported the \"reducing time in orthodontic appliances\" as an important factor; in fact, this kind of therapeutic choice could limit the overall treatment time wearing the brackets. Therefore, this approach could be a valid option for the treatment and management of palatally impacted canines, as it allows the first step of the treatment with minimal effort both for the patients and the clinician, and it avoids any possible side effects by using the proper force vectors. In the present study, all of the impacted canines were successfully treated, and no lesions on adjacent teeth were detectable at T2. Direct anchorage approaches have previously been proposed and represent a valuable method, even though they can present some difficulties in the clinical management--especially for less experienced orthodontists. Figure 5: (**a**) Median and interquartile range of monthly apex speed in each group; (**b**) median and interquartile range of monthly cusp speed in each group. mTPA, on the other hand, with a completely digital approach and the use of surgical guides and planning, can result in a useful and efficient alternative. A previously published study [24] reported a lateral incisor root length reduction of 1.87 mm compared to the untreated side, while in the present study the median reduction was \(-\)0.04 (IR [\(-\)0.53, 0.10]) mm and 0.01 mm (IR [\(-\)0.55, 0.16]) for lateral incisors and first premolars of the treated side, respectively (Table 2). Both direct and mTPA anchorage resulted in similar values in terms of movement speed for both cusp and root measurements, although a slightly faster movement was detected for the direct anchorage group patients. The direct approach required less preparation, and the miniscrews could be placed on the same day as the exposure intervention and the start of traction. The mTPA requires lab phases and incurs greater costs; on the other hand, the bands can be successively used as part of the multibracket therapy. The mTPA was digitally planned as along with the surgical guide, enabling a one-visit protocol; alternatively, the traditional two-phase approach could be used. All of the TPAs were produced using the SLM technique, resulting in a more rigid structure in comparison to traditional TPAs. The single-miniscrew approach is noteworthy and simple to manage, but it should be noted that some authors prefer the use of two miniscrews to reduce any stability issues due to the activation of the traction [10]. Clinically, both approaches led to the exposure of the impacted canine and successive completion of the orthodontic treatment.