We designed our project as a split-mouth study, therefore each patient received both SH2018-10 and SH1514-08 miniscrews, randomly assigned to either left or right side. To do so, our nurse divided both miniscrew types into two halves and assigned symbols appropriate for blinding the intervention. Thus, two combinations of miniscrew sets aroused: 1. SH1514-08R and SH2018-10L or 2. SH1514-08L and SH2018-10R, which were placed separately in opaque packages marked consecutively from "1" to "100" and stored on the tray with dividers. One hundred cards, labeled accordingly, were placed in an envelope, from which the nurse blindly pulled the card just before the miniscrew insertion, this way assigning the set number to every patient. Thus both: the placement side and the screw size were random for clinician.

We designed our project as a split-mouth study, therefore each patient received both SH2018-10 and SH1514-08 miniscrews, randomly assigned to either left or right side. To do so, our nurse divided both miniscrew types into two halves and assigned symbols appropriate for blinding the intervention. Thus, two combinations of miniscrew sets aroused: 1. SH1514-08R and SH2018-10L or 2. SH1514-08L and SH2018-10R, which were placed separately in opaque packages marked consecutively from "1" to "100" and stored on the tray with dividers. One hundred cards, labeled accordingly, were placed in an envelope, from which the nurse blindly pulled the card just before the miniscrew insertion, this way assigning the set number to every patient. Thus both: the placement side and the screw size were random for clinician.

Each patient received miniscrews in both sizes. The same orthodontist (M.S.) performed all the insertion procedures. Miniscrews were always placed in the mandibular buccal shelf, laterally to the first and second molar interproximal area, with angulation 30 degree to the bone surface, meaning that miniscrew angulation should be approximately the same as the axial inclination of the adjacent molar. Miniscrews were loaded with orthodontic force 2 weeks after the surgery. The investigated factors were:

• long-term success rate of the miniscrews in the buccal shelf of the mandible (miniscrews were considered long-term stable if they served as an anchorage until completion of mandibular distalization, at least 9 months);
• peri-implantitis development (enlargement of the gingiva and/or redness and/or tendency to bleed);
• the patient's report of pain lasting longer than 48 hours after miniscrew insertion.

The mobility of the miniscrews was checked clinically with cotton tweezers at each visit. Miniscrews that could not sustain orthodontic force and required replacement because of mobility were considered failures.

Hypertrophy of the gingiva and/or redness and/or tendency to bleed was noted as the inflammation presence.

Two weeks after the miniscrew implantation patients were surveyed upon pain incidence lasting longer than 48 hours.