Using Lean Six Sigma to design the perfect dental retainer!

Lean Six Sigma can be applied in an infinite variety of scenarios. Can you guess what happened when I applied the methodology to design a dental retainer?

I’m an Innovation Engineer and during my studies, challenges were present in almost every single course of my study plan. In this specific class, the goal was to deepen in a research involving topics concerned to our personal specialization. I knew that design, innovation, quality and processes needed to be part of this experience, and with my professor’s help, the subject was decided: The Manufacture of a Dental Retainer Made by the Thermoforming Process Avoiding the Acquisition of Traces on its Surface. Needless to say, I was excited thinking about the idea of being an engineering student thermoforming dental retainers.

Although the thermoforming process has been a solution for the dental industry when intending to manufacture retainers, the acquisition of traces on its surface is still a quality issue. The lack of quality of surface finish can be caused by the 3D printed mold that is part of the thermoforming procedure as shown in Figure 1.

Figure 1. Traces in a Dental Retainer

Even though there are some additional substances that might help to improve its finish, there should be no need to come up with this extra step. In fact, this was part of my goal since I wanted to include the Lean Six Sigma (LSS) methodology, which consists of five steps that aim to guarantee the quality of any process by removing waste and reducing variation.

Not even the pandemic could stop me from planning a complete Design of Experiments (DOE), to determine the significance level of three principal variables involved in the process: materials (PET and PETG), two operators (A and B), and three timings (20, 40, and 60 seconds). A score was given to each sample in order to use a three factorial ANOVA to determine the presence of any significant interaction in the production of 36 dental retainers. This number corresponded to an evaluation of six essential quality requirements as shown in Figure 2.

Figure 2. Surface Quality Assessment

Following the DMAIC methodology stages (define, measure, analyze, improve, and control), the outcomes turned out to be compelling. The results show that the optimal combination was reached when having the Operator B working with the PETG and waiting 60s for the material to heat. With this being said, the most transcendent learnings of the experiment were the following:

To be honest, this was the first time designing a real DOE out of the examples our professor presented from the book. I was really proud to do it by myself and having the ability to visualize the potential of Lean Six Sigma to manufacture the perfect dental retainer.