Anchorage is Alaska’s largest city located in the south-central part of the state on the Cook Inlet, while Orthodontic anchorage is the resistance to unwanted tooth movement.
Orthodontic anchorage can be classified into different types as shown in the attached picture. Currently, temporary anchorage devices (TADs) is one of the most popular orthodontic anchorage method.
Materials used to construct TADs ar either cobalt-chromium base alloy (uncommon), stainless steel, titanium or titanium alloy (usually with aluminium and vanadium).
The failure rate of mechanically retained inter-radicular TADs is the highest among all TADs types and could reach 13.5 per cent (95% CI 11.5–15.9) (Alharbi and Almuzian 2018).
The parameters that could affect the success of the mechanically retained TADs are:
· Age (questionable)
· Oral hygiene (Hisham and Almuzian 2018)
· Smoking (Hisham and Almuzian 2018)
· Maxillo-mandibular planes angle but questionable (Miyawaki et al., 2003)
· Diameter if less than 1.4 mm (Alharbi and Almuzian, 2018)
· Length if less than 5mm (Alharbi and Almuzian, 2018)
· Miniscrew head and shape but questionable (Alharbi and Almuzian 2018).
· Implant site and attached gingivae (Hisham and Almuzian 2018)
· Insertion angle and loading protocol (Migliorati 2016)
· Sterilization/ asepsis and experience
· Proximity to the roots (Hisham and Almuzian 2018)
· Torque if greater than 15N in mandible and 30N in the maxilla (Motoyoshi 2014)
· The amount of primary stability
Complications that might be associated with TADs, in particular, the inter-radicular types are (Kravitz 2007, Hisham and Almuzian 2018)
· Root, nerve and vessels trauma
· Nasal or maxillary sinus
· Slippage and migration
· Patient discomfort
· Interference with teeth movement
To avoid interference with teeth movement and to improve primary stability, extra-radicular TADs and plates were introduced. These include:
· Mid- and paramedian palatal screws
· Infra-zygomatic screws (IZC)
· Maxillary tuberosity screws
· Retromolar screws
· Infra-nasal plates and screws
· Mental bone plate and screws
· Zygomatic plates
· Buccal shelf screws (BSS)
Primary stability of BSSs depends on many factors including but not limited to bone height and thickness (minimum cut-off value of 5 mm of the buccal extension of the mandibular buccal shelf, Nucera 2017) which in turn depend on other factors such as anatomical sites, gender, side and vertical and sagittal skeletal patterns.
Orthodontic and Craniofacial Research Journal in their December 2020 issue published a retrospective study that answered some of these questions. The paper titled “Assessment of the mandibular buccal shelf for orthodontic anchorage: influence of side, gender and skeletal patterns”.
A team from Brazil led by Dr Costa undertook this CBCT-based study which included data from 94 orthognathic patients.
In summary, the author found that the region near the second molar was the only one that showed an average thickness greater than 5mm. No statistically significant differences between the right and left sides, nor males and females, however, hypodivergent and Class III subjects had greater bone thickness in the buccal shelf region.
What do you think?
Link to the paper:
PS: I have no financial interest