The Equipoise® Complete R.P.D. System

"For most Dentists and patients, Removable Partial Denture restorations are failures."1 This statement is as true today as it was then. Dental Schools in general have treated R.P.D.’s with little or no consideration for scientific evidence. Without uniform design principles, most dentists are ill prepared in properly diagnosing abutment teeth in R.P.D. design.

Removable Partial Dentures in Dentistry are now at the advent of a new age. Several factors indicate the need for an increase in RPDs:

1. People are living longer and saving more of their remaining teeth.
2. Baby Boomers, the largest segment of the population (Approximately 76 million), are now reaching the age of prosthetic needs.
3. Implants and crown and bridge, although preferred treatment plans, are not always indicated and are far more expensive for the patient.
4. Dentistry is more accessible for more people than ever before. Immigration has increased and many of these people have not had the benefit of proper dental care in others parts of the world.
5. Managed Care is on the rise. Most insurers are very particular about paying out for "fixed" restorations (i.e. Implants and Crown and Bridge), limiting treatment plans.

In order for a R.P.D. to function properly, certain physics and engineering principles must be applied to their design, and ultimately to the abutment teeth. These laws of physics known as class II level (Fig 1) and balance of force principles are necessary to direct forces vertically along the long axis of the tooth, while minimizing any horizontal torque forces. Balance of force principles must also be followed so that retention of R.P.D.’s is passive during mastication. Passive retention will virtually eliminate the "extraction forceps" design of conventional partial dentures (Fig 2). The Equipoise® Complete Removable Partial Denture System meets all the above necessary criteria to properly strengthen, protect and preserve the abutment teeth.

The Equipoise® Complete Removable Partial Denture System runs the full gamut of Removable Partial Design. Whether replacing one tooth or only one tooth remains, Equipoise® has a solution. (Figs 3 and 4). The Equipoise® System enables the dentist to choose from conventional, semi-precision, and precision Equipoise® designs. The precision (Counterpoise stabilizer) C-rest and L-spring (retentive device) enable the dentist to prepare as little as a single abutment crown for free-end saddle design (Fig 5).

The Interproximal guide Plane
The interproximal guide plane, when used in removable partial denture design, plays an important role in stabilizing the abutment tooth (Fig 6). The guide plane, along with a prepared rest, stabilizes the abutment tooth along the long axis during function. In order to achieve forces along the long axis of the tooth, both the rest and the interpromixal guide plane are placed on the abutment tooth opposite the edentulous area. The interproximal guide plate and prepared rest stabilize the tooth along the long axis during function. The Equipoise® Clasp, placed equal and opposite to the plate and rest, faces the edentulous area and moves away from the tooth in the same direction as the denture base. The Equipoise® intra-arch configuration maximizes the effect of the class II lever system insuring that retention is only frictional during the dislodging motion (Fig 7). This insures passive retention and proper stability along the long axis of the tooth.

Tooth Preparations:
Designing an Equipoise® Partial on existing dentition requires simple tooth preparations. A guide plane is placed on the same side of the tooth as the rest preparation, opposite the edentulous side (Fig 8). All posterior abutment teeth receive a spoon-shaped rest no more than 1 _ mm. in depth. Anterior teeth receive a choice of an incisal, inward bevel, or lock-in rest depending on tooth position and contour (Fig 9). A reduction of _ mm. is made on both the abutment tooth and the adjacent tooth when preparing an interproximal guide plane. A proper restoration, such as an amalgam, composite, or an Equipoise® designed crown may be placed to house the rest or guide plane if the preparation of enamel is felt to possibly lead to the deterioration or loss of a tooth. There are no special requirements in the preparation of any Equipoise® type crown. A 1.7-mm. Clearance between abutment tooth and the adjacent tooth is necessary for a single abutment precision C&L crown. When preparing a splint, 2.2-mm. Clearance is needed in the area designed for the placement of the interproximal C-rest.
The Equipoise® Dental Institute has available for the dentist two tools that aid and assist with these measurements. The Equipoise® Paralleler is used to check parallelism when creating more than one guide plane (Fig 10). The Equipoise® Analyzer (Fig 11) has multiple uses. One end of the analyzer has a 1-_ -mm. Measurement to aid the dentist with rest seat preparations. The other end of the Equipoise® Analyzer has a cylinder with three graduated measurements. The first cylinder measurement is 1-mm. In diameter and used to measure the interproximal guide plane. The second cylinder measurement is 1.6-mm in diameter and the third cylinder measurement is 2.2 mm. The last two measurements are used for the single abutment and splinted units respectively.

The Five Major Criteria for Removable Partial Design
Function: Primarily, a removable partial denture must exhibit proper function. If a R.P.D. does not function properly, it cannot be a success. The prosthesis will either be unstable, lack proper retention, or both. To eliminate these problems, teeth must be prepared in a way so that all forces are applied along the long axis of the tooth, and function is passive (Fig 12).

Comfort: Comfort along with function are the cornerstones to successful R.P.D.s. The patient will only use the appliance out of necessity, or not at all, if it is not tolerated in the mouth (Fig 13).

Aesthetics: The number one reason patients object to removable partial dentures is unsightly clasps (Fig14). Equipoise® C&L crowns can be used to create desired aesthetic results when indicated (Fig 15).

Cost: The price of the prosthesis must be comparable to that of similar appliances, so as not to be too costly for the patient or the dentist. A simple designed Equipoise® prosthesis with minimal amount of metal can be constructed to fit the pocketbooks of all patients.

Built in Permanence: A properly design prosthesis must have built in permanence to allow for the possible loss of teeth (Fig 16). Teeth double plated with rests on the same side of the tooth will perform during function as a periodontal splinting unit. The appliance must be able to be repaired simply and inexpensively if an abutment tooth is lost. A properly designed Equipoise® prosthesis will allow for the possible loss of teeth.

The Equipoise® System is based on four different design scenarios:

The Four Basic Designs:
Design #1. The single of double free end saddle removable prosthesis with either anterior or posterior free end saddles. (Fig 17)
Design #2. Free end saddle on one side, all tooth borne on the other. (Fig 18)
Design #3. One edentulous area or two edentulous areas all tooth borne. The free end tips with this design always face the edentulous area. (Fig 19)
Design #4. Three edentulous areas or more all tooth borne. The free end tips,where possible, always face the same direction with this design. (Fig 20)

Summary:
The Equipoise® System is the only complete partial denture system in dentistry today. Equipoise® eliminates the hodgepodge design of R.P.D.s with sound principles of physics and engineering behind it. Why should the design of a R.P.D. be left to creativity spawning bizarre clasp configurations for retention while building in unaesthetic deleterious forces? Removable partial dentures should be an important option offered to patients. Priorities of the Equipoise® design system are aesthetics, function and above all, preservation of the abutment teeth. Removable partial dentures should be the end itself, not a stepping-stone to a full denture.

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1 Krajicek, Dayton Dunber, "Why Partial Dentures Fail", The Dental Clinics of North American, Phil., PA. 16:no.1, Jan.1972