NOT ALL MODEL TRAYS ARE THE SAME. BY JOHN MCCARTHY, JPM CERAMICS Leave a comment
Having qualified as a technician in a small prosthetics only lab, I decided to move on to a much larger lab who had a Crown & Bridge dept which I was keen to learn.
In order to get the job in their C&B department without experience I had to start from the basics, “the model room”.
This was run by Neil Man an ex military policeman, who didn’t suffer fools or shirkers. From day one I realised this was a clockwork operation where a hundred models a day was not unusual. The method back then was a stone arch, poured, hand pinned, then based with a second stone mix, trimmed up, sectioned, and dies trimmed.
After a few weeks of this my mind began to wonder if there wasn’t a more productive system we could use, but questioning a well oiled machine of many years was not an option.
So after going through the model room, metal department and then ceramics I decided to leave to set up my own lab.
It was at this point as a one man lab I thought there’s got to be a more accurate and quicker model method than the one I was using, as it was a major chunk of the day being taken up.
So I began exploring other options and must say my first experiences of what was on the market was not good, along with many others I was not impressed with the tray systems I tried especially the market leader, and to this day some people believe tray systems are all bad.
It was at this point I decided that there was a need for a better model tray system designed by a technician for technicians and set about working towards this goal.
My first strategy was to get samples of all the systems on the market at that time and trial them all in my own lab recording my likes and dislikes of each one, the dreadfully sloppy one that when you turn it upside down all the parts fall out, the one with the extra lugs to push in, the one with the removable central spine, the one with the many points inside it’s base etc I tried them all.
Having trialled them all I categorised the various formats to have them studied independently by our local University engineering department. The end result of the independent analysis was pretty enlightening. The most surprising analysis found was that by adding “lugs” which push in and out to secure the sections was actually causing more inaccuracies than a design without . In the same way the more points projecting from the base of some designs to give more location for sections to be relocated, was actually giving more opportunities for debris to be caught in those concavities leading to inaccuracies on relocation.
So the conclusion from the university study was actually that the simplest design was the most accurate for the use intended, which is to section and relocate those sections without increasing inaccuracies. With this now identified the objective now became how can the simple model tray be improved upon to maximise its accuracy, speed and ease of use.
The needed improvements were identified as:
(1) Improve the fit of the stone sections to the tray
The popular tray system at the time was using a mould which was 20 yrs old, and had produced millions of trays therefore it had become sloppy, also identified was the wall depths were deemed to be to shallow and the incorrect angle. Our tray has been designed to address these issues. The walls are taller, the angle changed and it’s a brand new tooling
(2) when producing a multi “tool” (that’s a mould to us )
With the best will in the world a very skilled engineer can not produce a 8/10/12 part tool that each part is absolutely identical, therefore if your stone sections become separated from your tray, they can not necessarily be put back into another tray with 100% accuracy.
This issue has also been addressed by making a four part tool with each part having a unique number imprinted on it, this is then reproduced inside each tray produced, so the stone sections from tray number 4 fit precisely back into another tray number 4 tray.
(3) There was not an ergonomic tray which was comfortable to the user.
We addressed this by taking away the sharp angles of the former trays, adding ergonomic internal and external corners, and taking into allowance the tongue shape which had previously been ignored.
Finally for the first time with any model tray system we added an articulating ball & socket system to allow a plastic articulator to be used. This is particularly useful for those pesky part impressions which we all get sent more often than we’d like.
Both the full arch tray and the quadrant tray work well without the use of a separator, and combined with a good quality crown and bridge stone, I have a video showing the working time of 2mins 28seconds to make a sectioned model from start to finish (not including setting time)
As a working lab ourselves we have used these trays for over 5yrs now and have had no issues using them for our digital work both sectioned or not. The sections relocate with great accuracy allowing us to do implant or large bridge cases regularly.
If you would like to try our trays please email: John@jpmceramics.co.uk for free samples. Lab to lab prices are vat free. Tel: 0116 2368127.
