## 4 Discussion  
Over the years, the use of clear aligners systems for orthodontic treatment has become increasingly frequent because of the indisputable advantages they offered, such as aesthetic, ease of use, comfort for the patient, ease in oral hygiene maintenance, and possibility to manage a variety of different malocclusions [4; 11; 12]. The rationale that guided the authors to conduct the research this paper is based on was that composite attachments bonded on teeth's surface constitute a fundamental component in clear aligner's therapy. The attachments are virtually planned and then precisely transferred on the teeth's surface using a template provided to the clinician by the clear aligners' manufacturer company. Given this premise, an equally essential point is that the attachments have to be performed as perfectly as possible on the day of their bonding. The bonding procedure in itself is relatively quick, as the attachments are pre-formed due to the presence of special attachment wells on the template that the clinician only has to fill with the composite resin; moreover, thanks to the template, all the attachments of the dental arch can be positioned simultaneously. However, if during the template removal an attachments' debonding occurs, the clinician should have to repeat the bonding procedure, greatly amplifying the required operative time. With the same attachments bonding procedure, this study revealed that a lower frequency of attachment debonding occurred in the cases where the Spark(tm) system was used, with a percentage of patients who did not show any bonding failure considerably higher in the Spark(tm) group than in the Invisalign group. This evidence can be considered statistically significant (\(p<0.001\)). The sample size calculation performed during the study design phase allowed to include in this randomized clinical trial a number of patients adequate to exclude variables such as the attachments shape prescribed for different cases, the strength characteristics of the composite used and all the possible variables that could influence the bonding process. Therefore, the results can be considered indicative of the fact that the Spark(tm) template can be defined as more effective in attachments' transferring to the tooth surface than the Invisalign(tm) one. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Number of Debonded Attachments** & **Spark Group** & **Invisalign Group** \\ \hline \hline
**None** & & \\ \hline Number of patients & 35 & 11 \\ \hline Percentage of patients in the group & 87.5\% & 27.5\% \\ \hline
**One debonded attachment** & & \\ \hline Number of patients & 2 & 12 \\ \hline Percentage of patients in the group & 5\% & 30\% \\ \hline
**Two debonded attachments** & & \\ \hline Number of patients & 3 & 13 \\ \hline Percentage of patients in the group & 7.5\% & 32.5\% \\ \hline
**Three debonded attachments** & & \\ \hline Number of patients & 0 & 4 \\ \hline Percentage of patients in the group & 0\% & 10\% \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Frequency distribution of attachment bonding failure in the two groups. The hypothesis of the present study can be extended to try to explain the results that have emerged in that the Spark(tm) template appears to be less rigid than that of Invisalign(r), and that, therefore, this might allow a less traumatic template removal from the dental arch and from the just-bonded attachments. However, this one derives from a tactile perception of the clinicians, as the clear aligners' manufacturer companies do not provide specific information regarding the production materials of the templates. Furthermore, an analysis of the recent literature did not uncover studies specifically analyzing the characteristics of the template or its efficacy in the attachments bonding procedure, both for Spark(tm) and Invisalign(r) and for other clear aligners' manufacturer companies. For this reason, the authors do not have the possibility of comparing the results of their study with another similar study.