# Microbiological Changes during Orthodontic Aligner Therapy: A Prospective Clinical Trial
## 4 Discussion  
Fixed orthodontic therapy has been related to a worsening of periodontal status and microbiological equilibrium several times; therefore, clinicians should be aware of the risk represented by the orthodontic treatment on these parameters [17]. Several studies in the literature have emphasised the impact of fixed orthodontic appliances on the arising of gingival inflammation, despite the fact that this event is generally regarded as a reversible condition with resolution after a few months from their removal, especially in patients \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Group** & **Mean** & **SD** & **Min** & **Median** & **Max** & \
\begin{tabular}{c} **Intergroup** \\ **Differences \({}^{\star}\)** \\ \end{tabular} &
\begin{tabular}{c} **Intragroup** \\ **Differences \({}^{\star}\)** \\ \end{tabular} \\ \hline Control T\({}_{0}\) & 86,800 & 54,597 & 19,000 & 100,000 & 166,000 & \(p<0.05\) & \\ Control T\({}_{1}\) & 338,960 & 414,281 & 67,800 & 100,000 & 1,130,000 & \(p<0.05\) & T\({}_{0}\)-T\({}_{0}\); \(p>0.05\) \\ \hline Trial T\({}_{0}\) & 128,010 & 219,412 & 1480 & 4270 & 546,000 & \(p<0.05\) & T\({}_{1}\)-T\({}_{1}\); \(p>0.05\) \\ Trial T\({}_{1}\) & 320,960 & 334,473 & 78,400 & 260,000 & 1,260,000 & \(p<0.05\) & \\ \hline \hline \end{tabular} Legend: \({}^{\star}\): \(p>0.05\) means that there is no significant difference; \(p<0.05\) means that there is a significant difference.  
\end{table} 
Table 6: Descriptive statistics of the total bacterial count expressed as copies/microlitre. Figure 4: Total bacterial count expressed as copies/microlitre (this figure shows the data reported in Table 6). with a good oral hygiene [5, 18]. However, specific fixed orthodontic appliances, such as bands, are more likely to cause an impairment of both soft and hard tooth-supporting tissues [19]. In general, the appearance in the mouth of new retentive surfaces represented by the orthodontic appliances causes an increased accumulation of dental plaque with an inflammatory response [5]. At a later stage, quantitative and qualitative alterations of subgingival biofilm occur with a selection of periodonontopathic microorganisms and an increase in inflammatory mediators [4, 20]. Specific periodontal therapies have been proposed to prevent periodontitis and reduce the risk of gingivitis and discomfort in patients with orthodontic appliances. [PERSON] et al. [21] found that the non-surgical periodontal treatment combined with professional and domociliary ozonised water could be effective in improving the clinical periodontal parameters in orthodontic patients because of the anti-inflammatory and anti-plaque effect, compared to the traditional non-surgical periodontal treatments combined with the home-care use of chlorhexidine therapy. Clear aligners have been proposed in dentistry thanks to the higher aesthetic value and acceptability by patients, if compared to fixed appliances. Despite their wide diffusion, there is still a lack of solid scientific evidence as regards their impact on the periodontal status and microbial community, considering that controversial results have been reported. For instance, a study conducted by [PERSON] and [PERSON] [22] assessed the differences of periodontal indexes on patients treated with clear aligners and fixed lingual attachments, with a higher worsening of periodontal conditions in patients of the latter group, which is linked to the difficulties in cleaning lingual tooth surfaces when fitted with a fixed appliance. However, PPD was the only index with very similar values in both treatment groups. Conversely, several studies have stated a significantly higher PPD increase in patients with fixed appliances if compared to those under CAT [11, 12]. Whereas a limited, but not irrelevant, increase in PPD was found in this last group of patients, the study conducted by [PERSON] et al. [10], considering a 3-month evaluation, reported no significant variation from the beginning to the end of the follow up.