In the 2000s, in contrast to the smooth and ergonomic body shape of air turbines, red band handpieces were made with a square and rugged design without considerations for ergonomics or easy access. It was a common understanding in the industry that this design aspect could not be avoided due to the gear system constraints. However, as a latecomer in the red band market, Morita needed to develop a feature that could make our product stand out and be truly competitive. This is why we decided to rigorously pursue the development of a red band handpiece with a body shape closer to that of air turbines. Inside its body, the red band handpiece increases the input rotation five times from 40,000 rpm to 200,000 rpm. This rotation is nearly 100 times faster than that of an automobile engine, which rotates at several thousands of rpm, indicating how durable the gear system incorporated in the product needs to be.
Could you describe in more detail why the red band handpiece in those days had such a rugged shape?
Tanaka : In those days, a red band handpiece was built with two gears. The five times speed increase was achieved by about 3.7 in the body angle part, and about 1.3 inside the head. In designs based on this conventional concept, it could not be avoided to design a product with a protruding lower angle part, which interfered with front teeth during access to the molar. This was a substantial disadvantage of the red band handpiece, which could not have an ideal body shape due to more complex internal mechanisms compared to turbines.
That was the reason all other competitors' models had similarly rugged shapes?
Tanaka : Yes. As I mentioned earlier, Morita was rather late to the market of red band handpieces. Therefore, our product needed to have a distinctive feature to be accepted in the market. This is why we started development focusing on a turbine-like smooth body shape and durable gear system.
How did the actual development proceed?
Tanaka : Usually, the design of a gear system starts with the gear part, and the body was shaped to suit the gear structure. However, this procedure only led to shapes similar to those of conventional products. Therefore, we decided to determine an ideal body shape first, and subsequently figure out how to contain the gear system inside it. With this reverse concept in mind, it was a considerable process of trial and error.The double internal bevel gear system was developed through this process. We succeeded in laying out a gear system inside the body designed as above by increasing from two to three gear sets and slightly inclining the central axes.
This substantially improved ergonomics and access to the molars, making great advancements in practitioner and patient comfort. We are confident that this is the most ideal shape achievable at present, because further reduction in the gear size would compromise durability due to technological obstacles.
Could you describe the double internal bevel gear system in more detail?
Tanaka : To contain the gear system inside the predetermined body shape, it was essential to increase from the conventional two to three gear sets, as I mentioned earlier. By dividing gears into two stages, we could lay out the gears in steps, thereby achieving reduction in the protruding lower part, which had been the conventional problem. However, it was impossible to contain the gear system in the body shape if the first axis and second axis were laid out in parallel, because of difficulty in reducing the size of the upper angle part. We examined many gear layouts, and finally developed a double internal bevel gear system, which had an inclined second axis and used an internal gear mechanism advantageous for speed increase for the first and second gear stages.
What is the internal gear mechanism?
Tanaka : The external gear mechanism is a common gear structure, where gears mesh externally with each other. In contrast, internal gear mechanisms have a structure where a gear meshes against another gear that has teeth inside it. This structure achieves larger teeth in a smaller space, with increased gear strength and durability. On the other hand, it causes difficulties in processing. In particular, precise processing is considered extremely difficult for internal gears with inclined axes. The outer circumference of usual gears can be processed using a cutter. On the other hand, this usual processing is difficult for a gear with internal teeth, which needs be cut out using a pencil-like tool called a “ball end mill.” It had been unthinkable in common understanding to use this method for two gear sets, because it took so much time and labor.
The double internal bevel gear system was a challenge to this preconception.
The Torqtech red band handpiece uses double internal gear sets. By using internal gears with inclined axes, despite the extreme difficulties in processing, the product achieves increased gear strength, durability, and access, thereby prioritizing precise treatment that benefits both dentists and patients.
However, because the double internal bevel gear system was extremely specialized, there had been no means for measuring whether the processed shape conformed to the design. Therefore, we needed to develop a dedicated shape measuring device in collaboration with a device manufacturer. In those days, there were opinions in the company that doubted the commercialization of a high-quality red band handpiece. An unprecedented investment also became necessary to develop a measuring device in addition to the design of the Torqtech unit. (The double internal bevel gear system has been evaluated for its innovativeness and awarded Patent No. 5645447.)
Does the Torqtech Red Band Handpiece have any other features you want to emphasize?
Tanaka : Just like turbines, Torqtechs need lubrication, but are not continuously immersed in oil, unlike automobile gears. Therefore, we needed to design the gears to withstand friction with only a thin layer of oil. This really highlights the importance of the precision and durability of gear teeth. Torqtech red band handpiece use an involute tooth profile based on involute curves for all its gears. An involute curve is a curve formed when a string is wrapped around a circle and then unwrapped. A gear processed in this shape minimizes slipping, rotates smoothly and efficiently, and reduces friction. Nevertheless, the gear would rapidly wear out if made of a common material. We use a special material that is extremely hard and withstands friction.