Ted Wong, DDS,” M. J. Calverley, DDS,b and William W. Nagy, DDS”
U.S. Army DENTAC, Fort Sam Houston, Tex. Removable partial denture frameworks must fit accurately to function ,properly and not cause injury to remaining teeth or soft tissue. This article presents a logical method and rationale for seating a removable partial denture framework and a review of several disclosing media used in the try-in procedure. (J PROSTHET DENT 1993;69:363-8.)
T he removable
partial denture is a viable and effective treatment modality with a proved history of success. The objectives of a successful removable partial denture are: to preserve the health of remaining oral structures,’ restore function, and restore esthetics.” A removable partial denture must fulfill the basic principles of bracing, retention, aesthetics, support, and stability to be successful. To fulfill these principles the removable partial denture must be designed properly, and the components of the removable partial denture framework must fit accurately and adapt intimately to structures in the mouth. The framework try-in procedure can be an exacting and sometimes frustrating process for the dentist. However, the precise adapt.ation and seating of a removable partial denture framework does not have to be a tedious and unsettling experience if proper procedures are executed in a rational and systematic manner. The development of improved disclosing media has also facilitated the ability to detect obstacles that interfere with complete seating of frameworks. The purpose of this article is to describe a rational and systematic method for fitting a removable partial denture framework and to review the various disclosing media used for detecting areas of interference.
TRY-IN STEPS 1. Inspect the framework off the master cast Inspect for bubbles and other defects on the intaglio surface. Use of magnifying loops or a microscope will aid in identifying
casting defects. Close attention should be
The views expressedherein are those of the authors and do not necessarilyreflect the views of the United States Army or the Department of Defense. Presentedat the fall meeting of the American Collegeof Prosthodontics, South Texas Chapter, San Antonio, Texas. aMajor, VS. Army; Chief, Removable Prosthodontics, Budge Dental Clinic. hColonel, U.S. Army; Assistant Director, Advanced Prosthodontic Residency Program; Chief, Removable Prosthodontics. Tolonel, U.S. Army; Program Director, Advanced Prosthodontic Residency Program; Chief, Fixed Prosthodontics. 10/l 144469
paid to rests, guide planes, clasp arms, and minor connectors. Defects on the tissue side of the framework will prevent complete seating of the framework and can cause trauma and discomfort to the patient. Sharp areas, which have a potent,ial for injuring soft tissue, should be checked, especially along the beaded areas of the major connector. Check for abraded areas on the master cast. Inexperienced laboratory technicians may inadvertently damage the cast while adjusting the framework to be placed. The result will be abraded areas on the cast that will correspond to areas of interference in the mouth. Areas that warrant close scrutiny include rest seats, guide planes, the lingual surfaces of mandibular bicuspids and molars, retentive areas, and the junction between minor connectors and clasp arms (Fig. 1). Check polished and nonpolishsd areas, The tissue side of the maxillary major connectors and areas where the lingual plate contacts the teeth should be smooth but not highly polished. Internal and external finish lines should be sharp, distinct, and undercut slightly to provide additional mechanical retention of the acrylic resin. Clasp arms, indirect retainers, minor connectors, and mandibular major connectors should be highly polished and free of irregularities such as waves, scratches, and pitting. The retentive mesh should be finished but not highly polished. A slightly rough surface will aid in the retention of the acrylic resin. Check for adequate thickness. Examine the thicknesses of major and minor connectors, rests, and clasp arms. Try to flex the major connector wilb finger pressure. No amount of fiexing should be detected
2. Check the framework
on the master
Verify the design of the framework with the laboratory prescription or diagnostic cast. Check the positions of the major connector, retentive clasp tips, acrylic finish lines, indirect retainers, and rests. Evaluat,e the amount of undercut
and soft tissue relied’.
Inspect the rests. Check to see whether t,he rests are fully seated. The margins of the rests should be flush with the margins of the rest seats. If they are not, the source of interference should be determined and corrected. The margins of the rests are frequently overextended and will interfere with tbe seating of the framework. Evaluate the
1. Abraded areas on cast (distolingual) will be good indicators of potential areas of interference.
Fig. 2. Overfinished distal rest and gap under clasp arm on premolar can be seen.
contours of the rests; overcontoured rests will interfere with occlusion, and undercontoured rests may be too thin and weak and subject to fracture (Fig. 2). Examine the relationship between the framework and the soft tissue areas. Inspect areas where the major connector is in contact with soft tissue, and make sure there is intimate contact to prevent food from getting beneath the framework. Make sure there is adequate gingival exposure around minor connectors and approach arms for I-bar-type clasp assemblies. There should be 5 mm between minor connectors and other vertical components. Horizontal portions of I-bars should be 3 mm from the gingival margin, and the vertical portion should be 5 mm from other vertical components.3 Check relief under bar clasps and acrylic resin retentive mesh, and make sure the tissue stop rests on the crest of the edentulous ridge. Check for proper adaptation and placement of clasps. Clasp arms, guide planes, and reciprocating arms should be in intimate contact with the tooth structure.
Fig. 3. Wrought wire clasp has been soldered too close to abutment tooth.
Gaps left between clasps and tooth structure will allow food to collect between the framework and the teeth, which may result in decalcification, caries, and gingival inflammation (Fig. 2). Clasp arms should have the proper shape, diameter, and taper. Wrought wire clasps should be long enough and the solder joint placed far enough away from the tip to allow adequate flexibility (Fig. 3). Another critical area to check is the lingual surface of mandibular incisors when a lingual plate is used. When properly designed and constructed, the lingual plate will be scallop shaped to close off the interproximal embrasures and cover the cingulum areas. Open spaces between the lingual plate and the teeth can result in food impaction and gingival inflammation, which may lead to bone loss in the area. A space may also encourage the patient’s tongue to play with the edge of the framework. Check the ease of framework removal. The retention of the framework on the cast may not, and probably will not, be the same in the mouth. In fact retention may be greater on the cast because of friction and the rough surface of the cast.
If the framework is acceptable, schedule the patient as soon as possible. Excess time between the final impression appointment and the framework try-in appointment can result in migration of teeth and prevent a framework from fitting in the mouth. This is important for patients who have had recent periodontal treatment or extractions of teeth next to removable partial denture abutments. If the framework does not fit the master cast well, then it usually will not fit in the mouth. In this event it would be best to make another impression and remake the framework.
4. Check the framework
in the mouth
If the framework fits the cast but does not fit in the mouth, it is likely the cast is not an accurate reproduction of the mouth. Causes for this situation could be a distorted
4. When framework is seated with firm pressure and removed, area of interference shows through disclosing wax (cingulum rest area).
impression, an improperly poured cast, an abraded cast, and/or shifting teeth. In the latter two instances, if the interferences are minor and can be located, one may be able to judiciously adjust the framework into place. Although most frameworks should fit with little adjustment, all will benefit from judicious finishing procedures. The fitting of the framework to the mouth should be done in two phases: (1) fitting the framework to the abutment teeth and soft tissue and (2) adjusting the framework to the opposing occlusion.
5. Fit the framework
to the abutment
The best aid in trying in the framework is the use of a disclosing medium. There are numerous acceptable disclosing media on the market: Occlude (Pascal, Bellevue, Wash.), Accufilm (Parkell, Farmingdale, N.Y.), disclosing wax (Kerr/Division of Sybron Corp., Romulus, Mich.), pressure-indicating paste (Mizzy Inc., Clifton Forge, Va.), Fit Checker (GC Dental Industrial Corp., Tokyo, Japan), and chloroform and rouge. To use disclosing media effectively, dry off the framework in the areas where the disclosing medium will be applied. Apply the disclosing medium, gently seat the framework, and remove. Areas that exhibit metal showing through should be adjusted. The old disclosing medium should be cleaned off, new medium applied, and the framework tried in again. One should avoid overreducing contacts on guide planes, rests, and retentive tips. Contacts between the framework and the teeth below the survey line should not be arbitrarily removed, because these contacts can help guide the framework into place and provide some degree of retention and stability. With sufficient practice the dentist should be able to distinguish between marks caused by interferences and those resulting from rub off as the framework is inserted and removed. The advantages of disclosing wax are it provides three-
Fig. 5. A, Polyvinyl siloxanes are very effective in identifying high spots (cingulum rest area). B, Set impression material is easy to remove and provides three-dimensional representation of framework adaptation,
dimensional representation of framework adaptatron and it shows the degree of interference (Fig. 4). The disadvantages of disclosing wax are it requires a flame source and is relatively difficult to remove. The advantages of polyvinyl siloxanes are they are easy to read, easy to remove from the framework, and provide a three-dimensional model (Fig. 5). The disadvantages are polyvinyl siloxanes are expensive, require mixing. and need time for the material to set. The advantages of Occlude disclosing medium are it marks areas of interference well and is easy to clean off. The disadvantages of Occlude medium are it is expensive, there is potential for applying too thick a layer of material, and it is difficult to work with in a wet environment (Fig. 6). The advantages of Accufilm disclosing film are it marks interferences well and is not as messy as some of the other media (Fig. 7). The disadvantages of Accufihn medium are it is relatively difficult to manipulate intraorally and there is the potential for false positive results. The advantages of air abrasion with 50 pm aluminum oxide are it identifies areas of interference well and it is a
marks caused by interferences should be distinguished from normal abrasion as framework is seated in place. Fig.
Fig. 7. Accufilm disclosing film generates marks similar to Occlude disclosing medium.
clean method of disclosing. The disadvantages of air abrasion with 50 pm aluminum oxide are it requires access to air-abrading equipment, and extended use of air abrasion may affect adaptation of the framework by abrading the intaglio surface of the framework. The advantages of chloroform and rouge are it is easy to apply and identifies interferences well. The disadvantages of chloroform and rouge are it is difficult to remove and it has carcinogenic potential. Seat the framework in place in incremental steps with minimal force. Use gentle pressure over the rests as the framework is seated along the path of insertion. If the framework is forced into place in one try, the patient could have severe discomfort, and the framework could be difficult to remove. Areas of binding must be relieved. The most common areas that will bind are the junction between rests and minor connectors, periphery of rests, guide planes, un366
Fig. 8. Lingual plates can be difficult to seat, especially interproximal extensions. This lingual plate demonstrates acceptable adaptation to teeth.
dercut areas, and clasp arms. Failure to relieve even the smallest amount of interference can cause slight but continuous pressure on abutment teeth, which may cause pain and discomfort. Repeat the adjustment steps until the framework is seated in place uniformly and completely. Check for rocking of the framework in both an teroposterior and buccolingual directions. Place fingers on the rests and rock the framework. The rests should stay in place and not lift out of the rest seats as pressure is applied to one side and then the other. Check for close adaptation of rests, clasps arms, and lingual plates. To accurately assess the fit of the framework, excess saliva and bubbles should be blown off the teeth. All metal structures designed to contact tooth structure should be adapted closely to the teeth, which will ensure a precise fit. A sharp explorer is the instrument of choice to determine whether margins are open or closed (Fig. 8). Check for physiologic relief on distal extension frameworks.* Place pressure on the retentive meshwork areas and observe the movement of the clasp arms and guide planes. Check for disengagement of the retentive tips and guide planes as the framework rotates around the rest seats. Identify areas that are binding with a disclosing medium. Evaluate proximal contact areas between abutments and adjacent teeth to ensure that the abutments are not being torqued during rotation of the framework. Care should be taken when the framework is adjusted along the occlusal edge of guide planes, rests, and major connectors. Do not inadvertently open the tooth/metal contact and create an area for food impaction. Make sure there is enough clearance between the proximal plate and gingiva to allow some movement of the framework without tissue impingement. Check retention. After the framework is properly seated, remove and replace the framework several times to evaluate retention. If there is too little or too much reten-
tion, the clasps can be carefully adjusted. The instruments of choice are orthodontic contouring pliers, which have smooth beaks, or three-pronged orthodontic pliers. Serrated pliers will scratch or nick the clasps and possibly weaken the metal. When making adjustments to the clasps, establish the preferred contour through a series of small bends rather than a few large bends. After adjustment the clasp should have the desired retention and still be intimately adapted to the tooth surface. Avoid overbending the clasps, which may change the characteristics of the metal through work hardening. An overretentive framework can be detected by a snap or click as the framework seats. The problem is usually a clasp arm that engages too deep an undercut. The clasp should be in passive contact with the tooth when the framework is completely seated. With overly retentive clasps, tipping forces will cause a destructive whiplash effect on the periodontal support tissues. The amount of retention can be reduced by adjusting the clasp to engage a smaller amount of undercut or by reducing the degree of adaptation to the tooth surface. According to McGivney and Castleberry, as long as the forces are limited and do not exceed the elasticity of the periodontal fibers, there should not be any damage to the teeth. Check soft tissue contact or relief. Make sure there is adequate space between the meshwork and the soft tissue to allow a sufficient amount of acrylic resin material under the retentive meshwork. The tissue stop must be in contact with the edentulous ridge. The retentive arm of a bar-type clasp should not impinge on soft tissue, and conversely there should not be an excessive amount of relief that. could result in a food trap. The same can be said for minor connectors that cross soft tissue. Lingual plates or bars should not impinge on soft tissue in the lingual vestibule area. Additional relief may be necessary if tori are present.
6. Adjusting the framework opposing occlusion
Identify natural tooth contacts in the centric oc clusion(C0) or maximum intercuspation positions (MIP). The framework should not prevent the natural dentition from contacting in the COBUP or during normal functional movements. Start by removing the framework, and identify CO/MIP and eccentric contacts between the natural dentition. These contacts will be the reference points for judging the amount of occlusal adjustment needed. Adjust the framework in the CO LMIP position. Place the framework in the mouth, and determine whether the natural dentition is able to reproduce the CO/MIP contacts. If not adjust the framework until the teeth reproduce the desired occlusal contacts (Fig. 9). Roughen up the surface by sandblasting with aluminum oxide or lightly grinding with a fine Carborundum stone, since highly polished framework metal does not mark well with
Fig. 9. A, Occlusal interference caused by framework has resulted in a gap. B, Interference has been eliminat,ed so that teeth are in contact again.
articulating paper. When using articulating paper, place strips simultaneously on both sides of the mouth, and have the patient close into the CO/MIP position. Two strips are necessary because patients will tend to bite to one side if only one strip of articulating paper is used. Adjust the framework without overthinning and weakening the metal components. Rests and clasp arms are usually at risk of being excessively adjusted and subsequently weakened. Ii correct tooth preparation and recontouring have been done in the preparation phase, there should be adequate occlusal clearance for these important elements of the framework. However, sometimes tooth migration can reduce the desired occlusal clearance. If there is a risk that the metal framework might be weakened, adjustment of the opposing natural teeth may be necessary. Avoid exposing dentin, and polish and fluoridate the teeth aft,er the adjustment. Adjust the framework during eccentric move ments. After CO/MIP contacts have been reest,ablished, adjust the framework during mandibular tIccentric movements, The patient should reproduce movements representative of normal masticatory function and not wide excursions into lateral and protrusive positions. Instruct the patient to use relatively moderate to healrv biting fhrce. 367
THE JOURNAL OF PROSTHETIC DENTISTRY
WONG, CALVERLEY, AND NAGY
Occlusal adjustment of two frameworks. If there are two frameworks, adjust the occlusion of each framework independently. Once each framework is in occlusal harmony with the opposing natural dentition, place both frameworks in the mouth and adjust the frameworks to occlude with each other. Any interferences detected should be between frameworks. If adjustment procedures are carried out correctly, the patient’s occlusion should be the same with and without the frameworks in the mouth. 7. Materials The framework can be adjusted with various burs, coarse Carborundum stones, or both. All adjusted areas should be repolished with rubber points and wheels. When relieving and polishing, avoid staying in one spot for extended periods of time to prevent the generation of localized areas of high temperature. Morris and Brudvik6 showed that creation of excessive localized temperatures can run the risk of changing the temper of the framework metal. For final polishing use a rag wheel and polishing compound. SUMMARY
Use of a logical and orderly process will ensure a precise fit and minimize frustration during the try-in phase. The framework should first be evaluated off the cast, examining both the intaglio and cameo surfaces for casting defects and finishing errors. The framework should then be inspected on the master cast and the design checked and fitted. Finally, the framework should be adjusted to completely seat in the mouth and harmonize with the occlusion. This article has described a step-by-step method for fitting a removable partial denture framework to the mouth. A review of several disclosing media has also been presented. REFERENCES 1. DeVan MM. The nature of the partial denture foundation: suggestions for its preservation. J PROSTHET DENT 1952;2:210-8. 2. Zarb GA, Bergman B, Clayton JA, MacKay HF. Prosthodontic treatment for partially edentulous patients. St. Louis: CV Mosby, 1978. 3. Krol AJ, Jacobson TE, Finzen FC. Removable partial design, outline syllabus. San Rafael, CA: Indent, 1990. 4. Kratochvil FJ. Influence of oeclusal rest position and clasp on movement of abutment teeth. J PROSTHET DENT 1963;13:114-24. 5. McGivney GP, Castleberry DJ. McCracken’s removable partial prosthodontics. 8th ed. St. Louis: CV Mosby, 1989. 6. Morris HF, Brudvik JS. Influence of polishing on cast clasp properties. J PROSTHET DENT 1986;55:75-7.
The ultimate success of a properly designed removable partial denture depends on how well it fits and adapts to structures in the mouth. One of the most important steps to ensure an accurate fit is the seating of the framework.
Reprint requests to: DR. M. TED WONG 518 WHEAT~N FORT SAM HOUSTON, TX 78234
of JOURNAL back issues, 1987-1992
Back issues of THE JOURNAL OF PROSTHETIC DENTISTRY are available for purchase from the publisher, Mosby, at a cost of $7.50 per issue. (Foreign postage is not included.) The following quantity discounts are available: 25 % off on quantities of 12 to 23, and one third off on quantities of 24 or more. Please write to Mosby, Subscription Services, 11830 Westline Industrial Drive, St. Louis, MO 63146-3318, or call (800)325-4177, ext. 4351, or (314)453-4351 for information on availability of particular issues for that period from 1987 to 1992. If unavailable from the publisher, photocopies of complete issues are available from University Microforms International, 300 N. Zeeb Rd., Ann Arbor, MI 48106, (313)7614700.
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