(re)Classification of Removable Partial Dentures
I'm working on a new article for publication and in the process thought it might be appropriate to share a condensed version for our blog. The subject is removable partial dentures (no surprise, given that the article is authored by yours truly) and some of the lack of clarity that often surrounds the various types of RPDs and the materials that are available to us.
By some estimates RPDs constructed entirely from polymers now represent more than 25% of the partials made and delivered each year in the United States. This is not a small number, as it equates to several million RPDs constructed annually from various polymers including polyamide (nylon), PEEK, acetal and polyolefin. As such, it is important to take a second look at the category as a whole and determine a new classification system for the various types of partial dentures.
There are several factors that go into material selection for a removable partial denture, including:
- Speed of fabrication
- Life expectancy of the appliance
- Physiological factors
- Biomechanical forces
- Holistic concerns
Based on these factors and the various combinations of them that comprise material selection, I am proposing the following five categories to accurately describe and differentiate the various types of RPDs:
- Conventional framework supported RPDs
- Interim RPDs
- Metal-free RPDs
- Aesthetic RPDs
- Flexible RPDs
CONVENTIONAL FRAMEWORK SUPPORTED RPDs
Traditional RPDs as we know them. Consist of a rigid framework with plastic teeth connected by plastic resin. Tooth supported or tooth and tissue supported depending on its Kennedy classification. Typically regarded as long-term appliances.
Fabricated for the purpose of restoring missing teeth temporarily before a more permanent restoration can be arranged. Typically made from PMMA either with or without wrought-wire clasps. Usually tissue supported. Can be made quickly and at low cost, and can be easily modified as changes occur in the mouth (relines, tooth additions, etc.)
Fabricated entirely of polymer with the primary concern bring that the appliance is metal-free. May be a tooth-supported framework or tissue supported design based on the material selection and preferences of the clinician. May be rigid or flexible depending on the material selection.
Prescribed when the primary concern is aesthetics. May be fabricated from polymers or metal alloys. Aesthetics are achieved with clasps that blend in with teeth or tissues (gingival colored, clear, tooth colored, etc.) or when clasps are concealed from anterior views (Equipoise, Saddle-Lock, etc). Typically fabricated as long-term appliances with varying degrees of repairability depending on material selection.
Fabricated from flexible polymers with a focus on aesthetics and long-term function. Designed to be tissue supported to leverage stressbreaking properties of the resin and promote the snowshoe principle of stress distribution. Differentiated from asesthetic and metal-free RPDs because stressbreaking function is a primary concern. Flexible polymers with tooth-supported frameworks (i.e. PEEK, acetal, etc.) are not included in this category because they do not promote stressbreakers and do not disengage forces from abutment teeth. Typically fabricated as long-term appliances with varying degrees of repairability depending on material selection.
The complete article elaborates more on these categories and the requirements for each. As we approach the centennial of the publishing date of Partial Denture Construction by Dr. Edward Kennedy, we need to take a step back and not only acknowledge the developments that have taken place over the past century but start to include them in our educational programs and the supporting literature. This is particularly important with the advent of digital design and fabrication techniques and the influx of new materials that have recently become availabe. More to come!