February 2012, Volume 8, Issue 2
Published by AEGIS Communications
Complete Denture Prosthodontics
Many of the clinical and laboratory materials and procedures used remain essentially unchanged from their historical inceptions.
By Joseph J. Massad, DDS | David R. Cagna, DMD, MS
Miraculous advancements in dentistry have been made since the inception of organized and intentional dental therapeutic intervention. Most recently, the advent and clinical refinement of dental implant therapy using root-form endosseous implants1 is an example of one such advancement that has revolutionized the profession’s approach to prosthetic replacement of missing teeth. Additional revolutionary advancements ride on the heels of the ever-progressive digital world, making once cumbersome procedures (eg, radiology, treatment planning, impression making, prosthetic design, and prosthesis fabrication) more readily available, and in some cases, more accurate and precise. In fact, advances in the modern dental world are occurring at such rapid rates that the challenge for practicing dentists is to keep up with the latest materials, devices, and procedures, as well as the evidence basis for their clinical implementation.
Despite the remarkable advances impacting so many facets of modern dentistry, pockets of routine treatment seem to have remained relatively stagnant over time. For many practitioners, the routine provision of complete denture therapy includes procedures that seem to have escaped the progresses of modern dentistry. When considering today’s conventional complete denture treatment, it is interesting to note that many of the clinical and laboratory materials and procedures used remain essentially unchanged from their historical inceptions. A glance at key aspects of dental history2-28 (Table 1) illustrates this point.
While today’s complete denture therapy incorporates several significant improvements, fundamental concepts and techniques remain remarkably similar to historical treatment approaches. Positive advancements have been made in the area of materials and a resurgence of useful therapeutic devices results in improved complete denture outcomes. In order to achieve the fabrication of successful, well-accepted conventional complete dentures, practitioners should thoughtfully combine historically proven concepts with modern materials and devices. This article provides a brief overview of several clinical concepts and new materials that have been used to enhance modern complete denture therapy.
The number of available edentulous impression procedures is a varied as practitioners interested in treating edentulous patients.29-35 Subtle variations in the material or design of impression trays, impression material handling, border molding, management of the denture-bearing foundation, perceived delivery of pressure during impression making, patient-induced functional activity during the procedure, etc, will undoubtedly influence the resulting edentulous impression. Though most of these clinical procedures have enjoyed at least reasonable success, the relatively recent appearance of materials and devices unique to complete denture therapy may prove beneficial. New materials and new anatomically designed stock impression tray systems may facilitating accurate, pressure-controlled, definitive impressions without the need to develop primary casts and custom impression trays.
Practitioners should appreciate the following basic principles of impression making for edentulous patients36:
- Impressions should extend to include the entire denture foundation within the health and functional tolerance of the supporting and limiting tissues.
- Impression borders should be in harmony with the anatomic and functional limits of the denture foundation and adjacent tissues. Therefore, impression borders should be identified using functional movements.
- Adequate space for impression material within the impression tray must be available.
- A guiding mechanism, or stop, should be available to accommodate the correct positioning of the impression tray relative to the edentulous ridge and associated tissues, particularly if multiple insertions of the impression tray are required.
- The impression tray and impression material should be made of dimensionally accurate and stable materials.
- Impression contours and dimensions should replicate intended contours and dimensions of the planned prosthesis.
A recently described method for edentulous impression making abides by these basic principles, uses readily available and anatomically designed stock impression trays (Figure 1 and Figure 2), incorporates familiar vinyl polysiloxane (VPS) impression materials, and is a relatively time-conservative procedure. This modern edentulous impression system has been previously been described in great detail.37
The unique anatomically designed stock edentulous impression trays used in this impression procedure permit several advantages. The trays come in an acceptable variety of sizes, can readily be subtractively adjusted using standard acrylic resin burs, and permit thermoplastic manipulations with shape-stable results. Additionally, the impression system incorporates a wide range of viscosity-specific VPS impression materials that are typically very familiar to most practitioners. Again, readers are encouraged to review previously published descriptive literature37 for procedural suggestions for making edentulous impressions.
A variety of VPS impression material viscosities are available. Thoughtful application of viscosity-specific materials during the impression procedure and in different areas of the tray permits predictable tissue placement and control. VPS offers several potential advantages for making edentulous impression, including:
- Availability of different viscosities. For example, Aquasil Ultra Smart Wetting® Impression Materials (DENTSPLY Caulk, www.caulk.com) is provided in five viscosities (ie, extra low, low, medium, medium-high, and high).
- Convenient delivery system (ie, automix cartridges).
- Predictable material adhesion between sequential layers of different material viscosities.
- Materials with various working times are available to satisfy operator preference. For example, use of a fast-set material permits the operator approximately 30 seconds to dispense the material into the impression tray, 1 minute to insert the tray into the patient’s mouth and perform tissue manipulations, and then 1 minute to final cure.
- The material is sufficiently elastic with clinically acceptable tear strength.
- Newer VPS materials have been chemically modified to improve wettability and hydrophilicity.38-41
- The material is generally biocompatible and does not possess an offensive taste or odor.
Steps used to make these modern edentulous impressions include: (1) develop stops in properly adjusted stock impression trays using a high-viscosity VPS; (2) complete border molding procedures using a high- or medium-viscosity VPS; (3) trim tray overextensions using an acrylic resin carbide bur; (4) reduce border molding and tray stops by 1 mm to 2 mm in all dimensions and according to the dictates of selective pressure impression making to provide adequate space for the final wash of the impression material; and (5) introduce medium-, low-, and extra-low–viscosity VPS materials into the tray and make the definitive impression (Figure 3, Figure 4, Figure 5, Figure 6). Again, readers are encouraged to visit previously published detailed descriptions of this procedure37 for predictable clinical implementation.
The Central Bearing Device
The most appropriate relationship of the edentulous maxilla to the edentulous mandible when fabricating conventional complete dentures may be debated. However, most agree that achieving anatomically and physiologically optimal vertical and horizontal jaw relationships is important to successful therapy. It is the opinion of the authors that most clinicians skilled in modern complete denture therapy rely on centric relation as a physiologically stable and repeatable mandibular treatment position.42 Unfortunately, the ability to reliably record this interarch relationship is in part determined by the clinician’s detailed understanding of the anatomy and physiology of temporomandibular joint function, effective handling of clinical materials and devices, patient cooperation, and his or her skill and experience.
Historically, a number of techniques have been suggested for registering interarch relationships during complete denture therapy. These clinical techniques can be broadly classified as direct interocclusal records, graphic recordings, and functional records.43 A graphic recording method dating to the turn of the 20th century,44,45 but recently updated, involves use of a central bearing device. This device can aid the practitioner in the clinical achievement and registration of both horizontal and vertical jaw relationships and is particularly useful when muscle deprogramming of habitual mandibular closure is indicated.46
Use of a central bearing device has been shown to be very precise.47 The concept has recently enjoyed a resurgence of interest due in part to newly developed instrumentation (Massad Jaw Recorder System, Global Dental Impression Trays, Inc., www.gdit.us). Advantages of this new central-bearing device include: ease of attachment to record bases using conventional light-activated laboratory resin and a unique pivoting central bearing pin for adjustment in all dimensions during the recording process.
This new central-bearing device comes complete with all of the elements necessary to assist in the registration of centric relation in various clinical situations, including dentulism, partial edentulism, full edentulism, small-arch diameter, and large-arch diameter (Figure 7, Figure 8, Figure 9, Figure 10). All components are disposable and setting the device up on record bases or paraocclusal bases is straightforward and time-conservative (Figure 11, Figure 12, Figure 13, Figure 14, Figure 15, Figure 16). The steps required to incorporate the new central bearing device into edentulous record bases are presented in great detail elsewhere (Figure 17, Figure 18, Figure 19, Figure 20).48
While today’s complete denture therapy relies heavily on procedures and materials steeped in historic significance, incorporation of modern materials and processes can facilitate predictable and successful outcomes. Clinicians who make complete denture therapy a substantial portion of their daily practice must keep an eye out for procedural modifications that aid in improved patient service. The procedures and materials detailed in the present article have been offered for consideration in modern complete denture therapy.
Dr. Massad is the founder and president of Global Dental Impression Trays, Inc.
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About the Authors
Joseph J. Massad, DDS
Tufts University School of Dental Medicine
Adjunct Associate Faculty
Department ofComprehensive Dentistry
University of Texas HSCSA School of Dentistry
San Antonio, Texas
David R. Cagna, DMD, MS
Associate Dean, Postgraduate Affairs
Professor, Department of Prosthodontics
Director, Advanced Prosthodontic Program
University of Tennessee Health Science Center
College of Dentistry