Module 1 — Selecting the Screw
The slide deck for this module is in the members’ board.
Learning objectives
By the end of this module you should be able to:
- Choose a head and slot design that serves your mechanics, not just retention
- Pick length and diameter from the anatomy, including the CBCT divide-by-two rule
- Argue the honest trade-off between stainless steel and titanium
Head and slot — the mechanics live here
- Never buy head-less designs. The head is your attachment point; fixation heads belong to surgical plating, not orthodontics.
- Rectangular slot over round — always. A round slot takes only round wire and your mechanics lose control; a rectangular slot accepts rectangular wire, which opens uprighting, cantilever bending, and controlled force vectors.
- Extra slots and eyelets give elastics and coil springs more than one anchorage option.
- Bracket heads trap plaque — avoid in patients with poor oral hygiene.
- Unbox every screw with your eyes open: a bent tip is a factory defect — reject it before it meets a patient.
- Buy specifications, not brand names — but only from credible, reputable manufacturers. When your anchorage is extra-radicular and you cannot palpate roots, the brand’s quality is what you are trusting.
Length — anatomy decides
| Length | Where |
|---|---|
| 8 mm | The everyday workhorse — inter-radicular posterior AND anterior intrusion |
| 6 mm | Thin, risky sites (lower incisor region — only with long roots and a confirmed safe zone) |
| 10–12 mm, long neck | Extra-radicular: zygomatic arch, buccal shelf, ramus — thick soft tissue is why the neck is long |
Soft tissue consumes roughly 1 mm of every screw before bone begins. Thread engages cortical + medullary bone; more thread engagement, more stability.
Diameter — the divide-by-two rule
Measure the inter-radicular width on CBCT and divide by two — that is your maximum screw diameter. (3.5 mm of space → a 1.6–1.8 mm screw.)
- 1.1–1.2 mm: high fracture and failure rates in the literature — do not use.
- 1.4 / 1.6 / 1.8 mm — the working range for inter-radicular placement.
- Above 1.6 mm confers no stability advantage and raises root-contact risk between roots.
- 2.0 mm belongs extra-radicular (zygomatic, retromolar) where there are no roots to hit.
Material — the honest answer
Neither is globally superior. Stainless steel is cost-effective and physically tougher — the choice for small diameters where fracture resistance matters. Titanium is more biocompatible, holds exceptionally well in biologic environments, and shows less soft-tissue overgrowth.