During the first sitting (T0), after checking the inclusion criteria to enter the re-search protocol, a professional oral hygiene session is carried out through the use of ultrasonic inserts, hand instruments, and glycine powder.

One month after the first session (T1), FMPS and FMBS are detected. Probiotic administration is discontinued in patients belonging to the test group.

At 2 months from baseline (T2), plaque and bleeding indices are recalculated and, for test group patients only, probiotic supply is delivered for 1 month.

Then, after 1 month (T3), plaque and bleeding indices are measured and probiotic supply is discontinued.

During the first sitting (T0), after checking the inclusion criteria to enter the re-search protocol, a professional oral hygiene session is carried out through the use of ultrasonic inserts, hand instruments, and glycine powder. All patient is instructed to perform home oral hygiene procedures using a medium-bristle manual toothbrush and fluoride toothpaste (1450 ppm F) with no added anti-plaque or anti-calculus property. Patients are advised against the use of any mouthwash.

The probiotic used in the study is Bifidobacterium Lactis HN019, distributed com-mercially in Italy by Curasept (Curasept Prevent®, Curasept S.p.A., Saronno, VA, Italy), with added Kluyveromyces Marxianus Fragilis B0399, colostrum and biotin. The probiotic was taken by patients following the manufacturer's directions via 2 chewable tablets daily, morning and evening, after normal daily oral hygiene, achieving daily average values of B. Lactis HN019 of 2*107 CFU and Kluyveromyces marxianus fragilis B0399 of 2*109 CFU.

FMBS is a dichotomous index indicating the presence of gingival bleeding on 6 surfaces, the same as FMPS, after light probing. The ratio of surfaces with bleeding to the total of the assessed surfaces is presented as a percentage.

FMPS is a dichotomous index indicating the presence of bacterial biofilm on 6 tooth surfaces: mesio-vestibular, vestibular, disto-vestibular, disto-palatal/lingual, pala-tal/lingual, and mesio-palatal/lingual. The ratio of surfaces with plaque to the total of the assessed surfaces is presented as a percentage.