Quality Waterjet Newsletter 10/16/2007

Dental Waterjets Parameters


Dental drill is currently the most popular tool for removing tooth decay. Even though the drill is fast and inexpensive, it may cause pain and dentin micro fracture. The drill tip is often too large and removes unnecessarily healthy enamel as a result. An alternative way since 1995 is the use of laser. But the equipment cost of laser is relatively high and it also takes longer time than the drill. Another alternative method is air abrasion (sand-blasting). But it is also relatively slow and has an issue with dust control. Grygla & Todd* anticipated that a low pressure abrasive water jet should have the potential to overcome the weaknesses of these methods.


Some previous studies have demonstrated the potential of using low pressure suspension waterjet for cutting teeth. A batch type setup (like the one shown in the figure) was proposed for the dental application. The waterjet will be powered by compressed air or a nitrogen tank since it is commonly found in dental offices. However, the abrasive particles in the suspension tend to settle and clog the test apparatus. Therefore this research were conducted to study three possible methods of mixing and suspending abrasive particles homogeneously in a low pressure waterjet intended for a dental system.


The first method is a xanthan polymer suspension. After the xanthan suspension was prepared and tested at several different concentrations levels, it was determined that a xanthan concentration of 0.50% provides sufficient viscosity to suspend the aluminum oxide particles. However, the xanthan suspension would leave a layer of obscure slurry, which could block the dentist's vision of the tooth. The second method is a magnetic stirring apparatus. A ferrous rod was placed inside of a 50 ml container that contains a mixture of water and 11.0% abrasive material by weight. The container was then placed on a magnetic stirring table that has a rotating magnetic bar. The rod inside the container responded to the rotating action of the magnetic bar and was able to successfully mix the water and abrasive to create the desired homogeneous slurry. The third method is by ultrasonic cavitation. A sonic dismembrator, model 550 by Fisher Scientific was used to produce the ultrasonic cavitation. The sonicating horn was lowered into a 50 ml container filled with the abrasive material. By testing at several different intensity levels (0-5), complete mixing was achieved at a setting of three. It was also noted that ultrasonic cavitation produced an extreme amount of heat, causing temperature rise at 1.2°C/min. These test results serve as stepping stones for future research.


*Grygla, M.S. & Todd, R.H. (2007) An investigation of methods to homogeneously entrain and suspend abrasive particles in a low pressure dental water jet, in Proceedings of the 2007 American WJTA Conference and Expo, August 19-21, Houston, Texas, Paper 4-D.


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