Use of intermaxillary elastics
What do the measurements on the packet mean
Let’s start with the size: ‘5/16” or 7.9mm’ indicates the diameter of the inner lumen size of the elastic without it being stretched. The sizes of intra-oral elastics are standardised to 1/8″ / 3.2mm, 3/16″ 4.8mm, 1/4″ 6.4mm, 5/16″ 8.0mm, 3/8″ 9.5mm
Next is the force: This is the measure of force delivered at both points of attachment. The measurement is given on ounces or grams. 4.5oz / 126g indicate the force delivered if the elastic is stretched 3 x its size
What forces do I need?
This depends on the clinical situation:
- En-mass movement (non extraction) -– class 2 / 3 elastics = 5-6 ounces 142-170g
- En-mass movement (extraction) – class 2 / 3 elastics = 4-5 ounces / 113-142g
- Anterior elastics – box elastic for anterior openbite = 1-2 ounces / 28-57g
- Posterior box elastics = 6 ounces / 170g
The difference in force levels required for non-extraction Vs extraction cases has been attributed to the greater number of teeth / units in non-extraction cases, requiring greater force levels for en mass movement.
Does the thickness make a difference?
Yes, some elastics are thinner and some are thicker,
When stretched 3 x the lumen delivers either a light (2.5oz), medium (3.5oz) or heavy force (4.5oz): see the diagram
How do I know if it is the right force?
- Use of a correx gauge is recommended Kleber Meireles
- Measuring the distance elastics are planned to be used intraorally, and using the table below selecting the appropriate size elastic.
This is especially important during space closure as the distances change throughout the process.
What does the research say?
A recent study found that 1/4” / 6.4mm elastics covered a wider range of force levels compared to 3/16 / 4.8mm elastics.
Conclusion: 1/4” / 6.4mm and /16 / 4.8mm fulfil most clinical situations, except for box elastics
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