Silicones in podiatry: differential hardness
In podiatrics the hardness of a silicone is expressed in Shores, the higher the Shore the harder the silicone obtained by polymerisation.
The use of silicones with high Shore ratings (e.g. 35 Shore) demands greater skill and precision from the Specialist Podiatrist when creating the orthosis because the silicone hardening process (polymerisation) takes place much more quickly.
The harder the orthosis, the more hardwearing it will be and the lower the risk of it releasing oils, and therefore shrinking, making it uncomfortable for the patient and forcing him or her to request a new orthosis after just a short while.
Depending on the case being treated with an interdigital orthosis, the Specialist Podiatrist will select the silicone with the most suitable Shore hardness.
The latest generation of poly-addition silicones make it possible to create differential and/or intermediate hardness orthoses by combining silicones with different Shore ratings.
LOW SHORE SILICONES
Silicones with a low Shore hardness (usually under 16 Shore) and which are therefore soft are used mainly in cases that need treatment with protective orthoses. In these cases the Specialist Podiatrist does not need to be highly skilled because even if the orthosis is not a perfect fit, it will not be uncomfortable for the patient wearing it. However, soft orthoses have various disadvantages:
- They release oil while the patient is wearing them
- They shrink
- They do not last long (usually about 3 months)
- They cannot be moulded using a grinder as the grinding tool slips on the material
22 SHORE SILICONE
A 22 Shore silicone possesses the ideal hardness because it is versatile and can be used in all cases that require an orthosis; it is especially suitable for protective orthoses.
An orthosis made with 22 Shore silicone is soft but, it does not release oil, will not shrink, is hardwearing (if maintained properly, it can last over a year), and can be moulded with a grinder. A specialist podiatrist even with the minimum of skills can therefore create extremely well-made orthoses.
The latest generation of poly-addition silicones allow the Specialist Podiatrist to repair orthoses. Usually a patient who has been wearing an orthosis suitable for their needs for a long time, tends not to want to throw it away, even if it is well worn, for fear that the new orthosis will not be as comfortable as the old one.
In the specific case of the orthosis having become thin (worn) due to rubbing against the shoe, the correct volume can be restored at that point by adding silicone in the following way:
- Put the orthosis on the grinder to make the surface rough and to clean it.
- Mix a little base and hardener (always with the utmost precision in the ratio 1:1) to obtain fresh silicone;
- Place the silicone obtained by mixing on the worn point of the orthosis, moulding it into the correct shape.
- When the silicone has hardened it will be a single block.
The grinder cannot be used on softer silicones because the grinding tool slips on the material.
35 SHORE SILICONE
Podikon 35 shore is normally used for making corrective orthoses or for making orthoses that are subject to considerable stress such as for example those used by sportspeople.
An orthosis of this hardness can easily be shaped with the grinder managing to reproduce thicknesses of just a few millimetres. In these cases the Specialist Podiatrist must be extremely precise and if the orthosis has creases or excess material in any points it should be sanded to provide the patient with the maximum comfort.
8 SHORE PRE-CATALYSED STRIP
The 8 shore pre-catalysed silicone strip is normally used in association with 22 or 35 Shore silicones in order to obtain an orthosis of differentiated hardness in the areas where relief is required, but at the same time to prevent a gap in the medical device as in the case of the correction of Hallux Valgus (WATCH THE VIDEO).
