Edge level of aligners and periodontal health: a clinical perspective study in young patients

ABSTRACT Introduction: Although the superiority of clear aligners over multi-bracket appliances in keeping gingiva healthy has been suggested, the possible benefits of one aligner design over another have not yet been investigated, especially with regard to the vestibular edge. Objective: The aim of this study was to measure several periodontal indexes in adolescents undergoing orthodontic treatment with aligners, comparing two different types of rim. Methods: The study involved 43 patients aged between 14 and 18 years. The periodontal health was assessed using plaque index (PI), gingival index (GI), and gingival bleeding index (GBI), at the start of the treatment with aligners (T0), with a vestibular rim (VR) reaching up to 3 mm beyond the gingival margin. Three months later (T1), aligners were set to obtain a juxtagingival rim (JR) on the second quadrant and VR on the first quadrant. The periodontal indexes were measured again, both at T1 and then three months later (T2). Results: Intra-quadrant comparisons revealed a statistically significant worsening of the periodontal indexes only for the second quadrant (p<0.05), at T1 (GI), and especially at T2 (PI, GI, GBI), while no statistically significant changes were found for the first quadrant. Conclusions: More severe mechanical irritation, especially during insertion and removal of the aligner, can explain the worsening inflammatory indexes with the JR. In addition, the pressure exerted by the JR on the gingival sulcus seemed to facilitate plaque deposition, whereas the VR had a protective effect, reducing the risk of mechanical trauma.


INTRODUCTION
Orthodontic treatment with aligners has attracted increasing interest in recent years and their use has become more widespread, coinciding with ongoing improvements in biomechanics and scientific evidence. 1,2 In addition to their excellent aesthetic qualities and greater acceptance by patients, interest in this approach is also motivated by the opportunity to preserve periodontal health better than with the multi-bracket appliances, because aligners make dental hygiene easier to manage at home and at the dental office. 3 Several studies 4,5 compared the periodontal indexes, the total mass of the biofilm and the bacterial population, demonstrating the superiority of transparent aligners over fixed appliances in maintaining periodontal health. In a meta-analysis 6   The potential toxicity for the gingiva and periodontal tissues of the plastics commonly used to produce aligners has recently been investigated. 8 Despite the unavoidable dispersion of cytotoxic monomers in the juxtagingival environment, the results of the study showed that the effects were clinically irrelevant, given the negligible quantity of toxic molecules released.
No studies to date have considered the periodontal effects of aligners in adolescent patients, or how the two main types of rim used on aligners affect the patient's periodontal health. The rim may be designed either to extend beyond the free gingiva line and reach into the vault on a level with the adherent gingiva, or to follow a juxtagingival course along each gingival outline.
Thus, the aim of the present study was to identify any differences in periodontal indexes in relation to the type of rim on aligners used in a sample of adolescent patients. 9,10 The null hypothesis was that the vestibular rim would not affect the adolescent patients' periodontal health.

SAMPLE SELECTION
This prospective observational study enrolled 48 patients.     (Tables 3 and 4).         » At T2, after further three months, the periodontal indexes were measured again and compared with the previous findings.      considering the results of all three Periodontal Indexes (PI, GI, and GBI). To take type I error rate inflation relating to multiplicity problems into account, adjustments for multiplicity were made using the Benjamini Hochberg procedure. 13 The 95% CI was calculated for each value estimated. All computations were done using R software v. 3.3.2, 14 with the mmm, gee, multcomp and RMS packages.

RESULTS
The results are summarized in Tables 5, 6 Table 5: Intra-quadrant comparison (first quadrant). PI = plaque index, GI = gingival index, and GBI = gingival bleeding index. *= statistically significant.    The comparison for the second quadrant between T0 and T2 generated the most significant data, with all periodontal indexes worsening to a statistically significant degree. There was also evidence of a statistically significant worsening of GI and GBI In contrast, the higher edge of the VR, positioned farther from the gingival sulcus, would provide better protection, causing less inflammation and a lower accumulation of plaque.
Thus, the null hypothesis was rejected.