Good vibrations coming soon to a dentist's chair near you.

If ever a company had a doubt as to whether or not its new product was making the world a better place, Philadelphia, PA-based Bresslergroup holds no such qualms. The product design firm recently spearheaded the development of the DentalVibe, a new device that will be used by dentists to make anesthetic injections more comfortable and painless for patients. The DentalVibe is the brainchild of Dr. Steven G. Goldberg, DDS, a man who started with a core concept and a crude mockup.  

Anyone who has been to a dentist has more than likely received an anesthetic injection, and it has likely been the most painful part of the entire process — one source notes that this simple procedure is single-handedly keeping 50 percent of a dentist's patient population at bay. When the masked man or woman leans over your torso to plunge that needle into your gums, you feel that needle stick followed by a discomforting pressure before your mouth goes numb.

Before the DentalVibe, Dr. Goldberg used a rudimentary technique to mask the pain. He would grab the patient's cheek and shake it with one hand while administering the shot with the other. The trick made Dr. Goldberg think of the many varieties of vibrating electric toothbrushes and flossers on the market. What if he used a similar device to vibrate the cheek and gum right at the dental site?

The new device has multiple purposes. The primary purpose is to vibrate at the injection site in order to mask the pain.

DentalVibe employs the gate control theory of pain management —meaning it creates a diversion for the brain. The DentalVibe rapidly vibrates the oral mucosa (gum tissue) surrounding the injection site while the injection is simultaneously administered. When processed by the patient's brain, the vibrations register while the pain doesn't.

The device also acts as a retractor used to pull the cheek away and give the dentist access to the site. Its third function is as a device to transmit light and illuminate the injection site. This helps avoid accidental needle sticks and enhance operator visibility.

What's Inside?

The DentalVibe is a rechargeable hand-piece that, according to Bresslergroup's Director of Engineering David Schiff, is essentially a motor-driven eccentric cam that drives a rocker. The rocker vibrates and delivers the vibration to the disposable tip.

The tip is a three-part assembly that is consists of two hard plastic parts with an overmolded soft rubber, which ties the two pieces together, but allows them to vibrate relative to each other. The sleeve component is what attaches the tip to the hand piece, and the forked tip component is the part that actually comes in contact with the injection site on the gum. 

The tip is a three-part assembly that consists of two hard plastic parts with an overmolded soft rubber, which ties the two pieces together, but allows them to vibrate relative to each other.

"Since the overmolded rubber tip is used in the mouth, one of the key functional points of the device is that the tip wouldn't be shared from one patient to another," says Schiff. "It was designed to be a one-use tip connected to the reusable hand piece. We designed a one-use interlock into the hand piece so that the action of removing the tip from the device breaks the interlock in the tip and it can't be reused."

When the tip is installed, it has an electrical interlock that closes a contact and allows the device to turn on. When the user gives the tip a quarter-turn to remove it, it is supposed to permanently deform the electrical interlock feature.

According to Schiff, finding the right configuration and selecting the best material were both challenges at the prototype stage since modeling production and rapid prototyping materials can only go so far. It took a couple of iterations to get the interlock to work.

The device delivers light to the site, which in itself was a technical challenge for the design firm. The rod that is connected to the rocker, which delivers the vibration to the tip, is actually a clear light pipe. It's a single part serving dual functions: one end of it is a cam follower that rides in the eccentric cam to deliver the vibration to the other end, but the main shaft of that rocker is a light pipe with an LED that shines through the tube and the lens at the end of the tip.

"The product was designed in SolidWorks, but the development of the light pipe was so technically challenging that we used ray tracing software specifically designed to model light transmission," recalls Schiff. "The software was really helpful in optimizing the shape of the light to receive the most output."

A rechargeable nickel-metal hydride battery acts as the power supply. Because the device needs to be wiped down before it is put into the base, the inductive charging base had to be sealed without any exposed contacts. As to why Schiff opted for nickel-metal hydride over lithium ion: it's readily available, has enough power, meets the life requirements and isn't nearly as costly.

Work Flow

The design firm started out with very rough sketches and quickly evaluated other vibrating products on the market in order to understand some of the basic functionality. Within a couple of weeks, Bresslergroup had built its first proof of principle model.

From there, most of the challenge remained in getting the right shape and form factor for the tip to be not only comfortable for the doctor to use, but also provide the right clearances when working with tissue in the mouth.

"We went through a number of iterations on the shape of the tip," Schiff adds. "Then there was a six-month detailed design engineering effort that resulted in the alpha prototype, which was one or two fabricated hand pieces made of rapid prototyped components, what we call a ‘looks like, works like' prototype."

Bresslergroup has a fused deposition modeling (FDM) rapid prototype machine in-house, and the primary parts for the prototype were stereolithography (SLA) parts. Some key components, such as high-stress parts like the cam, were CNC machined from polycarbonate or Delrin materials. To simulate the rubber, the firm used cast urethane parts to simulate the overmolded parts.

For the hand piece, Schiff wanted two overmolded grips to make it more stable in the hand and easier to grip and rotate. The company went with polycarbonate and Santoprene as the overmold material.

The alpha prototype had the look and feel of a production device, but it wasn't made with production materials or processes. It took another six-month process to take the alpha prototype and work with an Allentown, PA-based manufacturer to turn this pipedream into a manufactured product. 

Feature Creep

When dealing with an inventor who doesn't have a great deal of understanding about the technicalities in how things work, feature creep can force a good idea into a Duke Nukem-esque infinite development loop.

"[Dr. Goldberg] was great at coming up with ideas, but there were points where we had to say, ‘That's a great idea, but let's put that into the second-generation product," Schiff laments. "There comes a point when you go with what you have, assuming that you've met your benchmarks, and it's more important that the product work and get on the market. We'll have opportunities to improve later."

Testing

In order to characterize the vibration of a number of similar devices, the design firm used a laser interferometer to measure the frequency and amplitude of the vibration.

It was during this phase of testing that the team established the frequency targets that they wanted and the dentist used the proof-of-principle prototypes on volunteer patients. The doctor used multiple devices with different cam eccentricities so he could evaluate the different vibrations and report on the most effective.

"As we developed the prototype further, we were testing it on our own skin with a sharp probe that would give us the pain sensation. We could actually feel that when you touch the vibrating forks to your skin while that probe is being pressed, you don't feel the probe, it numbs you completely," says Schiff.

As part of the same test, the team discovered that if the vibration was left on for longer than a few seconds, the sharp pain would return.

"In retrospect, it is fairly well known in a lot of sensory areas that if you have a continuous sensation, your body or brain gets used to it, such as when you get used to an odor in the room," says Schiff. "After awhile, your body gets used to the vibration and you'll begin to feel the pain again. We've discovered that if we pulse the vibration, if we run the vibration for one second, turn it off for a fraction of a second and then turn it back on, it's enough to keep refreshing the signal for that gate control to happen."

When he found Bresslergroup, Dr. Goldberg was a dentist from Boca Raton with Philadelphia roots that sparked the relationship with the firm in his one-time hometown.

As Schiff recalls, "He essentially had the core idea of a handheld device that would vibrate and a very crude mockup that he made from an electric toothbrush – it wasn't a working prototype, but it demonstrated what the device might look or feel like. We helped him figure out what the device might look like; how it would be held; and how it could be used most effectively and worked out the mechanics."