PRACTICAL GUIDE FOR MINISCREW INSERTION – Part I
Orthodontic miniscrew represented a boon for our profession, allowing for daring biomechanics, or just simplifying things, that would have been much more complicated without skeletal anchorage.
Despite their usefulness, many orthodontists are scared from miniscrew and commit their placement to the surgeon: while this could be considered correct, in my opinion (and not only mine) they should be placed by the orthodontist. In fact, they are part of the appliance, and their positioning should be biomechanically-driven, so learning to do it by yourself
could be a dramatic improvement.
This brief guide has the aim to cover the most important factors to consider for miniscrew positioning, and to show a simple and repeatable procedure. The first part of this guide will focus on the components and characteristics of the miniscrew.
First, choosing the miniscrew:
There are many types of miniscrew on the market, which one to choose? Every aspect of the screw design has his own pros and cons. First, we have two main types of miniscrew: self-tapping, which have a non-cutting tip and require the preparation of a pilot hole with a drill, and self-drilling, which have a cutting tip that dig into the bone while the screw is being inserted. Both types can be screwed manually or with a contra-angle, while the self-tapping ones need the additional step of mechanical drilling of the insertion site. Both can be used succesfully,1 the main difference lies in the number of steps to perform.
The head of the screw can be a button, a bracket, or even a “self-ligating” slot: this depends on how we plan to use the miniscrew, a button is more than enough for a powerchain or a closed coil, while a bracket head is needed if we want to insert a cantilever in it. The neck can be straight or flaring, and of different lenghts: this depends on the thickness of the soft tissues, that can be easily measured using an endodontic file or its rubber stop placed on an explorer.
The body can be cylindrical or tapered, usually the latter is preferred because while proceeding through the bone has always a perfect fitting into its socket,2 while a cylindrical body will become loose if your hand is shaking a little bit while screwing it. Then, we need to choose the diameter and the lenght of the miniscrew: narrower screw need less space, but are more fragile than the thicker ones. Regarding miniscrew’s lenght, the literature demonstrates that 6 mm are sufficient for primary stability of the screw,3 but sometimes you will need a longer one, especially in presence of a thin cortical bone.
- Gupta N, Kotrashetti SM, Naik V. A comparitive clinical study between self tapping and drill free screws as a source of rigid orthodontic anchorage. J. Maxillofac. Oral Surg. 2012;11(1):29–33.
- Desai S, Upadhyay M, Nanda R. Dynamic smile analysis: changes with age. Am. J. Orthod. Dentofacial Orthop. 2009;136(3):310.e1-10; discussion 310-1.
- Suzuki M, Deguchi T, Watanabe H, et al. Evaluation of optimal length and insertion torque for miniscrews. Am. J. Orthod. Dentofacial Orthop. 2013;144(2):251–9.