The weeks leading up to the start of a new semester are busy ones filled with ordering supplies, scheduling teaching assistants, and cleaning the lab. After scheduling custodial services for the big jobs and performing the little jobs, I never seem to have time to clean the models (most of which are 30+ years old!). A couple of models were so covered in grime, grease, adhesives from practicals past, ink, etc., that it was easier to put them back on the shelf and ‘deal with it later.’ In January 2018, however, I found myself with a bit of time and was finally going to clean one of our dental models that I couldn’t, in good conscience, discard without at least trying to clean it. My original plan was to use dish soap and an old toothbrush to clean it. I gave up after 30 minutes as I wasn’t making a dent in the grime. I considered other options, but the model was too big for our ultrasonic cleaner and I didn’t want to put it through a cycle in a dishwasher for fear that the force of water jets and heat would warp the model or remove paint.
As I considered my next step, I recalled my recent dental work — two root canals, a bone graft, failed implants, and a temporary bridge. In an example of chance favoring the prepared mind, I thought: ‘I’m holding a model of teeth. It is made of plastic, a little metal, and a bit of paint — just like the bridge I soak every night. Would denture cleaning tablets work? It’s unlikely that I would damage the model by soaking it overnight and worth a try.’
After a 30-second rinse and brushing the morning after the soak, the model was like new. The difference was so striking I felt I had performed a magic trick. I immediately set out to clean another model to convince myself that this was repeatable. I use a basic methodology of 1 denture-cleaning tablet per 250ml of water (approximate) and an overnight soak. Models are rinsed the next day and gently scrubbed with a soft sponge. Paint that is not heat-set can be rubbed off if you scrub too vigorously. An old toothbrush can be helpful for hard-to-reach places.
Why does it work?
Denture cleaning tablets are primarily composed of sodium bicarbonate (i.e., baking soda — a mild alkali which functions as a degreaser), an oxidizer, and a scent (typically mint). I have been testing the use of baking soda and hydrogen peroxide as soaking and cleaning agents with similar results and have been considering OxiCleanTM (composed of sodium percarbonate (i.e., sodium carbonate and hydrogen peroxide), soda ash, and detergents) as a cleanser. Costs for denture cleaning tablets, baking soda and hydrogen peroxide, and OxiCleanTM are minimal and can ‘pay for themselves’ by extending the working life of your models. Limitations are the size of soaking containers and rinsing facilities.
- Perform a small-model test case before working with larger models or several models at once.
- I do not recommend using this technique on models made of plaster.
- Examine models for any puncture holes (for screws, hooks, etc.) and position models during soaking to avoid waterlogging.
Carol Britson is an Instructional Associate in the Department of Biology at the University of Mississippi where she teaches Vertebrate Histology, Human Anatomy, and Introductory Physiology for science majors and Human Anatomy and Physiology I & II for allied health students. In 2018 she received the University of Mississippi Excellence in Teaching award from the PLATO (Personalized Learning & Adaptive Teaching Opportunities) Program supported by the Association of Public and Land-Grant Universities and the Bill and Melinda Gates Foundation.