Choose the right patients for flexible removable partial dentures

Flexible partial denture materials are an excellent option for many partially edentulous patients. However, what are the benefits of flexible materials in partial dentures and which partially edentulous patients are a best candidate for flexible? We asked two experts and here’s what they had to say.

When it comes to removable dentures, you want something that fits and functions and looks great for your patient. How you get those qualities, however, depends on the materials you choose. For many cases, particularly those requiring removable partial dentures (RPDs), flexible materials can give you all three.

Flexible RPD denture materials are not made of acrylic like traditional metal-cast RPDs. Instead, they use a thin thermoplastic, like nylon. The nylon-based materials were first introduced in the 1950s by Valplast and have been an option for partial dentures ever since, particularly for patients allergic to acrylics.

Flexible dentures are thinner than acrylics. Their physical properties make them durable.¹ Flexible denture materials provide many benefits as well. They are acknowledged as the most biocompatible material for removable dentures. Also, flexible materials do not contain BPA and resist absorbing odors or stains.²

While you can make a full or complete denture out of them, most often the flexible material is used for RPDs. Usually, a full denture is made from flexible material only when the patient is allergic to acrylics.

Clark Damon, DDS, a private practice dentist in the Amarillo and Dallas metro areas and an lecturer on implants for Nobel Biocare says patients either love flexible RPDs or hate them. The ones that love flexible partials feel that way because there's no metal.

“They think that it is more comfortable once it is well adjusted,” Dr. Damon says.

Related reading: What you need to know about the evolution of dentures

Justin Marks, CDT, and founder and CEO of Arfona says from the patient’s standpoint, flexible dentures are both cosmetic and comfortable. Cosmetic, because they do not display a metal clasp, and comfortable because they are lightweight, and there is neither a metallic taste nor a rigid, bulky appliance in the mouth. 

From a clinician’s perspective, Marks says flexible dentures are beneficial because studies show flexible materials are less destructive than a chrome-based appliance on the natural structures of the mouth. Marks thinks the most significant factor in resistance or reluctance to using flexible materials with an RPD is unfamiliarity with the material.

“It's acknowledged in most literature on removable prosthodontics an RPD even under the best of circumstances can carry destructive forces against the teeth and tissue in the mouth. So, it's widely acknowledged the incorporation of stress breakers into the denture, whether it be in the design or in the material itself, would be favorable to reduce the stress on the natural structures of the mouth,” Marks says.

Marks, whose grandfather invented Valplast’s flexible material in the 1950s, says flexible materials, like nylon, inherently have stress breaking function, making them friendlier and more forgiving to the teeth and tissues under normal use without requiring a complicated design. Traditional chrome-cobalt partial dentures need to be designed in a particular way to prevent those destructive forces.

“Now, I am going to get a world of criticism for saying that, but it is the absolute truth, and is backed by almost seventy years of science and user experience,” Marks says.

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Marks worked with Valplast for 12 years before founding Arfona three years ago, which specializes in 3D printing for dentures and removable partial dentures. He has been addressing the issue of destructive forces on the oral environment from the traditional materials used for RPDs for his entire 15-year dental career. 

“No literature dictates you have to use a rigid material in the first place. When you bypass all of that and find a material more harmonious with the oral environment, you eliminate some of the complications and challenges associated with partial dentures,” Marks says. 

However, flexible materials also have some drawbacks. Dr. Damon says one of the drawbacks to flexible partials is the prosthesis moves around more.  Also, he says the material is not as sturdy as a cast-metal partial. Despite these challenges with flexible RPDs, Dr. Damon says flexible dentures have their place.

“Often, we're able to generate better esthetics on certain cases, like the Kennedy Class III patients,” Dr. Damon says.

Marks has never shied away from using flexible materials for patients. However, he recognizes some cases are more challenging than others. For example, with a Kennedy Class II, Marks likes having a rigid major connector, a combination flexible and chrome-cobalt RPD to ensure a proper design.

“However, for any other situation, Kennedy Class I, III or IV, I would easily choose a flexible denture over any other chrome cobalt or rigid appliance,” Marks says.

Related reading: 5 things you need to know about implants

Dr. Damon does not have the same all-inclusive approach to case selection for flexible dentures. If a patient is already using a flexible partial, he will keep them in it, and likewise for cast-metal partials. When a patient is getting a partial for the first time, Dr. Damon emphasizes the importance of case selection.

“Let's say the patient is missing a few teeth, but there are natural teeth in between. That's a good case for a flexible partial,” Dr. Damon says.

Most of his younger patients tend to move toward implants. However, if implants are not an option, Dr. Damon would also recommend a flexible RPD for his more esthetically-demanding patients, which often skew to the younger side.

However, Dr. Damon says tried and true cast-metal partials are the way to go for Kennedy Class I and II scenarios where the posterior segments are not bound by teeth. These Kennedy classes are more common than the Kennedy Class III and IV that work well with flexible partials.

“Using flexible materials when there aren’t any teeth in the posterior doesn’t make sense,” Dr. Damon says. “It's like running on sand in a size 16 tennis shoe.”

Dr. Damon also does not like to use flexible partials when the patient presents with a bilateral distal extension partial. That scenario, he says, needs more support, so the cast metal version performs better than flexible RPDs. 

Marks disagrees. He says those cases are why flexible RPDs were invented.

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“In fact, the distal extension partials are where you will get the most functional benefit out of a flexible RPD because of the way it acts as a stress breaker,” Marks explains.

Flexible material looks like pink plastic but behaves differently than an acrylic material used for full dentures. As a result, Marks says the dentist needs to get the best tools and instruments for adjustments.

“Contact the manufacturer of the material to find out what the best tools are to use to adjust it. For example, I use Valplast, and they have a specific adjustment kit and a polish  used for their material,” Marks says.

Marks also recommends when placing all flexible dentures, seat them so they are entirely passive. The appliance shouldn't flex or compress the gums once it's seated in the mouth. For the best results here, Marks and his team recommend taking a static impression where the tissues are at rest.

“The best methods for doing that are either alginate impressions or intraoral scanning. The newer generation of dentists may use all scanning, which takes a picture of the tissues at rest, so it doesn't move the tissue or touch them at all,” Marks says.

Dr. Damon does not use digital impressions for dentures. He recommends a polyvinyl siloxane impression material that is going to capture the detail needed for a good fit. 

“Studies show polyvinyl siloxane impressions capture more detail than scanning, at least for dentures,” Dr. Damon says.

Marks agrees conventional impressions are still the most common method for capturing the data a technician needs for building a removable partial denture, but stresses the importance of using mucostatic materials. However, scanning technology is improving. For the past 18 months, Marks has been producing all his flexible RPDs digitally.

Marks says migrating to the digital workflow with flexible dentures has additional benefits. Patient acceptance is high once clinicians move to capturing impressions digitally. It also cuts down the time for the workflow.

“All of a sudden you can have final impressions and bite registration in a single appointment,” Marks says. “Often, the dentures could be delivered at the second appointment.”

More by the author: What you should know about bite registration

Marks compares that with the traditional five-appointment delivery timeline of a chrome-cobalt RPD workflow, beginning with two appointments for physical impressions. Then, an appointment for bite registration followed by a try-in appointment. The patient usually gets the final denture on the fifth appointment.

“You're looking at a minimum of five appointments compared to two or three for a flexible denture,” Marks says.

Dr. Damon recommends a try-in with flexible RPDs to check the tooth position and esthetics. While it isn’t possible to check the seal when the tooth or teeth are in wax, it is possible to see how the prosthesis looks.

“Clinicians and patients are going to check if they like the size, shape, and color of the requested denture teeth,” Dr. Damon says.

From a technician’s perspective, Marks says the design process is simplified with flexible materials. Flexible RPDs also require fewer appointments and less time and preparation before delivery. However, all of the requirements of a partial denture are the same and apply regardless of what materials are used.

“It is still important to have retention, support and stability. Those are requirements you can't ignore in any partial denture,” Marks explains. “It's just addressed differently in terms of how it's designed.”

References

1. Salcetti, Mary Anne. “The Pros and Cons of Thermoplastic Partial Dentures.” www.speareducation.com. 12 March 2019. Web. 3 May 2019. < https://www.speareducation.com/spear-review/2015/09/the-pros-and-cons-of-thermoplastic-partial-dentures>.

2. Ibid.