Success Rate of the Miniscrews in the Mandibular Buccal Shelf

Evidence-based Selection of Orthodontic Miniscrews, Increasing Their Success Rate in the Mandibular Buccal Shelf: A Randomized, Prospective Clinical Trial

Stability of the orthodontic miniscrews placed in the mandible is still considered to bare higher risk of failure compared to other intraoral locations. The aim of our study was to determine the influence of the miniscrew size on their long-term stability, occurrence of oral mucosa inflammation and pain lasting over 48 hours after implantation.

200 Absoanchor® miniscrews (Dentos, South Korea) in two sizes: SH2018-10 (length 10 mm, ø 18-20 mm) and SH1514-08 (length 8 mm, ø 14-15 mm) were inserted in the mandibular buccal shelf of 100 Caucasians aged 20-50 years, diagnosed with Class III malocclusion that required en-masse distalization of the mandibular dentition. We designed our project as a split-mouth study, therefore each patient received both SH2018-10 and SH1514-08 miniscrews. The same orthodontist (M.S.) inserted the screws near the muco-gingival junction, following one surgical protocol. Miniscrews were loaded with orthodontic force (NiTi coil springs) of approximately 200 g, two weeks after the surgery. On the same visit patients were surveyed upon pain incidence lasting longer than 48 hours. Then TISAD stability and soft tissue condition were closely examined at each appointment. Miniscrews were considered long-term stable if they served as an anchorage until completion of distalization of the mandibular teeth.

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.

The first evaluation was performed 2 weeks after miniscrew insertion and then every 4-6 weeks (at follow-up visits) throughout the duration of distalization (up to 2 years).

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

The first evaluation was performed 2 weeks after miniscrew insertion and then every 4-6 weeks (at follow-up visits) throughout the duration of distalization (up to 2 years).

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

Inclusion Criteria: generally healthy Caucasians mild Class III maloclussion that required an absolute anchorage for en-masse distalization in the mandible hypodivergent or normal angle between the maxillary and mandibular planes excellent oral hygiene Exclusion Criteria: Hyperdivergent angle between the maxillary and mandibular planes unfavorable anatomical conditions - e.g. presence of a strong frenulum potentially irritating the miniscrew head during chewing and/or facial movement

Sarul M, Lis J, Park HS, Rumin K. Evidence-based selection of orthodontic miniscrews, increasing their success rate in the mandibular buccal shelf. A randomized, prospective clinical trial. BMC Oral Health. 2022 Sep 20;22(1):414. doi: 10.1186/s12903-022-02460-3.