Mini-screws is just a tool among others!

With Dr. Kokich at the EOS 2012

Driven from the recent editorial article of Dr. Kokich at the AJODO, I would like to emphasize what this article was all about.


TADs have been around for some time now in the orthodontic field, and have changed the approach we follow at a number of cases.

• This is all wonderful but we should also remember that mini-screws are just a tool among others. 
• What is really important is correct diagnosis, individualized treatment planning and well designed biomechanics applied to the right patient.

PURE intrusion of anterior and/or posterior teeth for example, is a tooth movement that can be achieved ONLY when the reacting force is not applied to the dentition. A clean way of doing that is bone anchorage. 

• However we don't want to intrude the anterior too much especially when treating adolescence, where a gummy smile of 4mm IS very normal for their age!
• Let alone the issue of muscle adaptation when intruding posterior teeth and altering the vertical height of open bite patients...

It feels good to read what I was taught in Aarhus, been repeated by someone like Dr. Kokich and at the AJODO, because unfortunately when you say these things to a group of fellow orthodontists, people tend to look at you a bit strange. Marketing you see...

Thank you ;)

p.s. Here you can find the pdf of the AJODO Editorial

D.G.

Root resorption and orthodontics

A Swedish prospective clinical trial (Gothenburg), of 152 orthodontic patients, is published at the current issue of The Angle Orthodontist. The study is performed on CBCT data collected at baseline, 6-months in treatment, and treatment finish.

CBCT allows for differentiation of the exact root surface that has been resorbed, such as lingual/palatal, buccal, or mesio-distal. This cannot be differentiated by conventional 2D radiographs.

A case of severe root resorption

JCO, Miniscrew Loosening, Prof B.Melsen

Prof. B. Melsen talks in simple words  about miniscrews and the reasons behind failure.
First of all the failure of miniscrews can be seen immediately (in the first couple of weeks) or later.


A summary of some of the points given in this article:


Early Failure:

• Insufficient primary stability (wrong site selection, due to insufficient bone quality, or quantity)
• Iatrogenic failures (jiggling during the insertion, over-screwing)
• Magnitude and direction of the force loading (high magnitude of force, it is advised to start with around 50cN and increase the force gradually, also unscrewing moments should be avoided)

Later Failure:

• Change of the local environment (inflammation due to root proximity, or change of the local bone turn over, e.g. in relation to resorption of the root of a deciduous tooth)
• Systemic factors (such as smoking, alcoholism, and medication that influences bone turnover have been proven risk factors for implant failure in general)

In any case when a miniscrew fails, the new insertion site has to further away from the old one, at least twice the diameter of the screw. In addition choosing to change the site and use the screw with an indirect loading instead of direct could be advised if a screw fails more than once at the same patient.

This is the link of Prof B. Melsen's article at the current issue of the JCO.


References:
Clinical Guide
Clinical Applications

D.G.

Force extension relaxation of medium force orthodontic latex elastics, AngO June 2011, early access

The Angle Orthodontist of June 2011, has a very interesting article concerning the forces of latex elastics, over time.
The elastics is one of the few tools so widely used and so little studied in orthodontics.

The graph on the left shows for three commercial latex elastics, that for the first 3 hours there is a decrease of force.
This force increases for the next 3-6 hours and decreases again up to 12 hours of stretching.

In-Vitro studies of resistance to sliding and its clinical relevance.

The issue of Seminars in Orthodontics of December 2010 is dedicated to evaluation of different in-vitro study models and its clinical relevance. This is of major importance to the clinician who likes to question and not only digest what he is confronted with in the literature.

What is the reason for spending our precious and limited time reading articles, if the results are of little to no use to what actually happens clinically. As such a small presentation is attempted of resistance to sliding in-vitro models.

Starting with tooth movement while sliding on a main wire:

1. The tooth initially starts moving tipping back towards the force applied to it. This happens until a critical angle is achieved and the bracket slot edges come in contact with the main wire.
2. Binding happens and the tooth movement is reduced drastically.
3. Notching hinders the tooth movement completely and uprighting of the root will have to take place for the circle to commence again.

Accelerated Tooth Movement, short review and future application.

This is how the normal bone remodeling is illustrated with this flash taken from the website of Susan Ott, MD, Osteoporosis and bone physiology. The green is the mineralized bone and the newly formed osteoid is illustrated with red lines. Remodeling is the process that without altering the shape of the bone  is keeping a homeostasis, according to the local needs and mechanical loads.