Review of the SwinglockRemovable Partial Denture

Toby R. Talbot, BDS, MSD, FDSRCSDepartment of Restorative DentistryEastman Dental HospitalCray's Inn RoadLondon WCl 8LD, England

Tbe autbor's experience with the swinglock removable partialdenture concept is described. This infrequently utilizedtechnique allows the use of undercuts that areunapproachable with other partial denture designs.Indications include missing or weakened key abutment teeth,tooth mobility, aesthetics, economic considerations, and thepresence of certain ablative defects following oncologicsurgery. The clinician must consider lip position, facial sulcusdepth, position of frena, and the periodontal healtb ofpotential abutment teeth when considering a swinglockremovable partial denture. Specific instructions for blockout,relief, and position of hinge and clasp assemblies should bepart of the written laboratory instructions. Int J Prosthodont1991,-4:80-88.

T be swinglock removable partial denture was firstdescribed and documented by Simmons' in

1963. The technique addressed particular partiallyedentate situations in wbicb conventional partialdenture designs were inadequate. The concept wasrecommended for maximizing stability and reten-tion by gaining access to many more tootb surfaceswith tbe unique clasping mechanism offered byincorporation of the lock, hinge, and gate assembly,allowing all remaining teeth to become primaryabutments.

Indications^

Tbe indications for a swinglock removable partialdenture include:1. Situations in which a key abutment tooth (eg,

a canine) is lost and the adjacent tooth (eg, Ihelateral incisor) becomes the terminal abutment(Fig 1 ). Such a tooth offers poor support for theprosthesis, and the placement of rests and

A portion of this materiai was used as a table clinic presentationbefore the American Dental Society of London, London, April1989, and a portion was used in a presentation to the Con-sultants in Restorative Dentistry Group, London, October1989.

clasps is often compromised. The inability touse a rest can easily lead to soft-tissue traumafrom displacement of tbe prostbesis, especiallya distal extension base. Clasps may compro-mise aestbetics and/or produce potentiallydamaging forces to tbe periodontium from tbeincreased forces. Tbe use of less rigid claspingdesigns/materials sucb as wrought wire oftendo not provide adequate retention.Circumstances in which tooth mobility is caus-ing functionai embarrassment to the patient. Along-term questionable prognosis during orafter periodontal therapy may be treated usinga swinglock prostbesis for tootb replacementand/or splinting (Figs 2a to 2c). Tbe removablesplint allows optimum access for interdentalcleaning by the patient. Continued periodontaltberapy is unhindered, the assessment of indi-vidual teeth is facilitated, and progressivemobility of a single tootb can be recognised.The loss of a tooth does not compromise theprosthesis, as the design allows the addition ofteetb.Therapy for oncology patients who haveundergone ablation surgery and have fewremaining teeth (Figs 3a and 3b). Loss of palataltissue in the bemimaxillectomy patient and thedistortion of residual tissues in tbe mandibu-

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Swinglock Re able Partial Denture

Fig 1 Loss of a canine leaves a vulnerable lateral incisor asterminal abutment.

Fig 2a This patient had difficulty in mastication as the resultof tooth mobility following periodontal therapy.

Fig 2b (Left) Swinglock partial denture gains maximum sup-port with the major connector.

Fig 2c ¡Above) Gate with an acrylic resin veneer allowedsplinting of the remaining teeth (functional for 9 years).

Fia 3a Hemimaxillectomy patient offers compromised sup-port and stability for a conventional prosthesis.

Fig 3b Swinglock partial denture maximizes the tissueavailable for support and stability.

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Swinglock Removable Partial Denl un

lectomy patient necessitate maximizing reten-tion and stability. The swinglock prosthesisdesign may avoid the need for the placementof implants.

4. Treatment following the loss of strategic abut-ment support wher\ the patient has great func-tional demands (Figs 4a and 4b).

5. Economic considera fions. The swinglock par-tial denture provides the ability to splint teethwithout fabricating castings with fixed connec-tors. This offers considerable financial savings,even though the cost of fabricating the swing-lock framework is greater than that of a con-vent ional removable part ia l dentureframework.

Treatment Planning^

When the swinglock removable partial denture isconsidered, the position of the lips during smilingis recorded and transferred to the primary diagnosticcasts, A facial sulcus depth of 6 to 8 mm is rec-ommended for placement of the retentive gate ele-ment. A high frenal attachment and/or shallowsulcus requires surgical correction prior to makinga working impression (Figs 5a and 5b). Periodontal

health is a prerequisite to therapy unless the pros-thesis is considered an interim measure for theinformed patient or is used as a provisional/defin-itive prosthesis as periodontal therapy is provided.The diagnostic cast is surveyed to plan further toothpreparation, including guide planes and rest seats,and to establish clasp placement. The major depar-ture from the conventional prosthesis is the accessto the maximum available undercuts provided bythe opening of the gate of the swinglock prosthesis.

The desired tooth modifications may be achievedby reshaping the teeth or, when castings are indi-cated, by incorporating the desired contours intothe restoration(s). Following mouth preparation, aworking impression is made.

Irreversible hydrocolloid in a selected rimlockstock tray has often proved adequate. Mobile teethindicate the use of reversible hydrocolloid to avoidany tooth displacement.

Conventional laboratory procedures are followed.The cast is poured with a compatible vacuum-mixed dental stone. A wax occlusal rim with anacrylic resin base can be fabricated on the workingcast, a facebow transfer and occlusal registrationrecord are obtained, and the casts are mounted ona semiadjustable articulator. The tooth mold and

Fig 4a Uniiateral loss of teetli with eöentuious areasopposed by teeth in a patient with great functional demands.

Fig 4b Maxiilary swinglock partial denture aiiowed for thenecessary stability for this functionally demanding patient.

Fig 5a (Left) Shallow sulcusnecessitated a sulcus deep-ening procedure.

Fig 5b (Right) One weekafter placement of free gin-gival graft. The palate was thedonor site.

The International lournal of Prosthodontii Volume 4, Numbe

shade are selected, and the trial arrangement is clin-icaily evaluated (Figs 6a and 6b). A repeat of theinterarch registration record will reveal any inac-ctiracies in the previous record(s), and the casts areremounted if necessary,

A siiicone putty index of the tooth and flange

Swinglock Removable Partial Dcniure

positions can be made on the cast (Fig 7a). Thisindex will ensure that the framework will not extendbeyond these contours and not compromise toothposition or result in traumatic ulcération of the oralmucosa as a result of the placement of the hingeand lock (Fig 7b), The positions of the hinge and

Fig 6a Teeth are arranged for clinical evaluation. Fig Bb Position of teeth and border extensions are estab-lished.

Fig 7a Siiicone indices record tooth and border position.

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Swin Block Removable Partial Denture Ta i hot

Fig 8a Laboratory work authorization for framework designon the diagnostic cast.

Fig 8b Drawing ot desired design on the cast demonstratesthe position of gate and retentive elements.

Fig 8c Work authorization fcr framework design.

lock are established according to the patient's pref-erence to use a finger/thumb of the left or righthand.

Framework Fabrication"

The laboratory work authorization must includethree elements for fabricating the framework: 11) thedesign drawn on the primary diagnostic cast withreference survey lines recorded (Figs 8a and 8b); (2)drawing of the design of the swinglock framework(Fig 8c); and (3) a written authorization, specifyingthe following instructions:a. Place 28-gauge wax relief under the tissue por-

tion of lingual plate (mandibular prosthesis).b. Place 0,01-mm tinfoil relief under tissue por-

tion to be covered by labial/buccal gate,c. Place 28-gauge wax relief under the retention

mesh site for edentulous ridge(s),d. Block out undercuts related to rigid compo-

nents of major and minor connectors andreciprocal elements,

e. DO NOT block out undercuts to be engagedby retentive clasps,

f. Place hinge and lock, as indicated, one toothaway from terminal abutment teeth withinestablished contours dictated by the siliconeindex,

g. Ensure that the inferior border of the facial gatearm does not extend below the drawing on thecast,

h. Place retentive elements as drawn on the cast.i, DO NOT place stress distributors (hinges) in

wax-up,j . Please return wax-up on refractory cast and

hlocked-out master cast for evaluation beforeproceeding with casting.

It has been the experience of the author thatunless all the above information is included, prob-lems easily arise, especially when working with a

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Swinglock Re able Partial Denture

commercial laboratory. Quality control basimproved considerably wben the waxed refractorycast has been seen. This is strongly recommendedfor all partial denture frameworks (Figs 9a to 9c).

Preformed wax patterns of the hinge and lockassemblies are commercially available (Chaperlinand Jacobs Ltd, Sutton, Surrey, England}. The precast

elements are then coated witb a grapbite suspen-sion before incorporation into tbe framework wax-up. Four 3-mm sprues are attacbed to the wax-up—two directed to the thickest portions of the majorconnector and two to each end of the gate to ensurea complete porosity-free casting (Fig 10).

The wax-up is invested and, after the investment

Fig 9a Working cast withblockout wax overextendedas a result ot the tectirician'slack of understanding of tfie(unction of a swinglockdesign removable partial den-ture.

Fig 9b Predictable result witti retentive elements onlyengaging conventional undercuts of 0.015 incties. Appraisalof the blocked-out master cast wouia have avoided this costiyerror.

Fig 9c Remake ot tramework witti the correct placement ofretentive elements.

Fig 10 Completed wax-up.

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Swinglock Removable Paitial Dentun

is set, the casting ring is placed in a cold oven. Thetemperature is slowly raised to 950°C in 2.5 hoursand the casting ring is heat soaked for 30 minutes.

The casting is made using a base metal alloy ofthe clinician's choice, following the manufacturer'sinstructions. The author prefers to use a cobalt-chro-mium-molybdenum alloy (Wisi!, Krupp Medizin-technik GmbH, Essen, Germany) in an atmospherichigh-frequency melting and centrifugal casting unit(Galloni Gasteliini, Milano, Italy] for consistentresults (Fig 11).

It is necessary to remove the casting ring from theoven 80 to 90 seconds prior to melting the alloy toallow a drop in temperature before completion ofthe casting process. Failure to follow these instruc-tions will result in welding of the molten alloy tothe precast components of the hinge and lockassemblies in spite of the use of graphite, and thegate assembly will not be operable.

The author presumes that eariy removal of thecasting ring from the oven allows a greater tem-perature differential between the precast compo-nents and the molten metal, preventing fusion.When this is done, the use of graphite has beenfound to be unnecessary.

Framework Evaluation

The fit of the casting is checked on the cast withthe gate open and closed (Fig 12a). The casting istried in the patient's mouth, and necessary adjust-ments are carried out using a disclosing medium(Occlude, Pascal Co, Bellevue, Washington] anddiamond burs in a high-speed handpiece (Fig 12b).Altered cast impression trays are then attached tothe retention mesh element if there is a distal exten-sion base, and the altered cast impression is made(Figs 13a and 13b). The altered cast then allows forocclusal rims to be made for repeat of the interarchrelationship record. The teeth are arranged for aclinical try-in and confirmation of the registration.The prosthesis can finally be conventionally pro-cessed.

Prosthesis Placement

At the placement appointment, pressure reliefcream (Sybmn/Kerr, Romulus, Michigan) is appliedto the tissue surfaces of the acrylic resin bases toadjust any areas of excess pressure. The accuracyof the adaptation can be confirmed by the intimatecontact of the framework to the teeth. If there is adistal extension base, the author prefers to repeatthe recording of the retruded mandibular positionand remount the prosthesis for refinement of theocclusal contacts. Shimstock (12-iim plastic foil,Artus Corp, Englewood, New |ersey] is used to eval-uate and aid in establishing good holding contactsbetween opposing natural teeth and light holdingcontacts of the denture teeth on the distal extensionsegment. Final confirmation of these contacts ismade in the mouth.

The patient is given verbal and written instruc-tions in caring for the prosthesis. The placement andremoval of the prosthesis is demonstrated. Cleaninginstructions must include the names of effectivecleaning agents that will not cause tarnishing of theframework. The gate must be in the closed positionwhen the prosthesis is cleaned to avoid distortionof the framework. If the patient has poor manualdexterity, eg, arthritic hands, a customised rectan-

Fig 11 Satisfactory casting.

Fig 1 2 B (Left) Castingrelated to master cast withgate open.

Fig 12b (Right) Clinical trialof casting revealing seating ofincisai rests and correctplacement of retentive ele-ments.

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clí Removable Partial Dentuie

guiar orthodontic wire loop with an acrylic resinhandle may be provided (Fig 14a), Alternatively, a2-mm screwdriver (electrical screwdriver, CekaWorks Ltd, Pwllheli, Gwynedd, Wales, United King-dom) may be used (Fig 14b), Optimum plaque con-trol is reinforced, and a neutral pH fluoridemouthwash can be prescribed. Review appoint-ments are scheduled for any necessary adjustments.Once the patient is comfortable, routine recallmaintenance appointments are arranged.

A longitudinal clinical study of 53 patients froma pool of 78 patients treated over a 5-year periodhas been reported.^' No compromise to the perio-dontium was evident after using swinglock partialdentures for 13 to 75 months. The patient accept-ance was good, A high caries incidence and needfor reiines of the distal extension bases reinforcedthe need for proper recall. An equal number of car-ious lesions associated and not associated with theframework were reported. This suggests that thepresence of the prosthesis does not influence theincidence of carious lesions. Dietary counseling and

the daily use of fluoride mouthwash should reducethe incidence of new carious lesions. Tissueimpingement was only recorded with earlier designsthat did not incorporate rest seats. Therefore, restsare now always incorporated, no matter how fewteeth may remain.

Summary

A review of the use of the swinglock removablepartial denture, including clinical indications andtreatment planning, has been presented. The lab-oratory authorization requires detailed instrtictions.Framework evaluation and subsequent placementnecessitates adherence to basic prosthodontic prin-ciples. Longitudinal clinical studies confirm the effi-cacy of this treatment.

Conclusion

There is a small group of partially edentatepatients whose loss of teeth/tissue causes severe

ñg13a Altered cast impression of bilateral distal extension Fig 13b Altered cast impression of hemimaxillectomyareas. defect.

Fig 14a Wire loop used to open gate. Fifl 14b Small screwdriver used to open gate.

Swinglock Kemuvablo Partial Denture

compromise to the support and stability of conven-tionally designed removable partial dentures. Theswinglock prosthesis offers a solution for these func-tionally demanding clinical situations.

AcknowledgmentThe author thanks Mr C. Mslton, Chief Dental Instructor,

Department of Prosthetics, Eastman Dentai Hospital, London,England, for assistance and advice with the iahoratory pro-cedures.

References

1, Simmons ||: Swinglock stabilization and retention, A pre-liminary clinical report, Tex Dentj 1963;81:]0-12,

2, Bolender CL, Becker CM: Swinglock removable partial den-tures: Where and when. / Prosthet Dent 1981;45:4-1O.

3, Becker CM, Bolender CL: Designing swinglock partial den-tures, / Prosthet OenM981;46:126-l32,

4, Schwalm CA, LaSpina FV: Fabricating swinglock removablepartial denture frameworks, / Prosthet Denn9ei,45:216-220,

5, Schulte |K, Smith DE: Clinical evaluation of swinglock par-tial dentures, / Prosthet Deni 1980;44:595-603.

Literature Abstracts.

A Comparison of Glass-lonomer Cements Used toRepair Cast Restorations

Scanning electron microscopy was used to examine the integrity of margin interfaces between goldcastings and one traditional and two silver-containing glass-ionomer cements. These micrographswere aiso compared to those previousiy oDtained for margin interfaces between gold castings andcomposite resin, high-copper amalgam, and direct-filling gold. Although there were visible differencesin ttie surface micromorphology of the different cements, all of the glass-ionomer cement repairsappeared to remain well-adapted to the gold casting after thermocycling. The adaptation of all theglass-ionomer cements was superior to that demonstrated by amalgam and resin in a previousstudy. The adaptation of the direct gold was found to Oe equal to or better than that found for anyother material. The authors believe that direct gold is the material of choree for casting repairbecause of its adaptability, similar composition, polishability, and documented longevity. Theexceptions to using direct gold are related to concerns for esthetics and inconvenience ot makingappropriate preparations

Carlson TJ, Naguib EA, Cochran MA, Lund MR, Oper Deni 1990;15(5):16E-166. Relerences: 5. Reprints: Dr T.J,Carlson, Indiana Uiiii/ersity School of Dentistry, 1121 W Michigan Street, Indianapolis, Indiana 4620Z,-Richard fl.Seats, Jr, DDS, MEd. MS, tjniversity of Taxas Health Science Center at San Antonio, San Antonio. Texas

Effect of .12% Chiorhexidine Rinses on Incidence ofAlveolar Osteitis Following Extraction of ImpactedMandibular Third Molars

The occurrence of alveolar osteitis (AO) after extraction of impacted mandibuiar third molars isreported to be between 15% and 20%, Local disturbance in fibrinoiytic activity caused by orai microbesmay be a mechanism, since the incidence ot AO has been successfuliy reduced using oral andsystemic antibiotic therapy. The study included a randomiïed double-blind evaluation of 0,12%chiorhexidine mouth rinse and a placebo mouth rinse (not described). One hundred thirty-four patientswith bilateral impacted third molars were randomized to the two groups. A finding of AO was definedas pain in association with: {1| pain increasing over 3 to 5 days, (2) necrotic tissue in the extractionsite, and (3¡ exposed bone or ioss of clot within the extraction site. There were 12 findings of AO in144 extraction sites in the chiorhexidine group and 28 in 134 extraction sites in the placebo group(P = 0,0174), It is concluded that 0,12% chiorhexidine mouth rinse used twice a day for 7 daysfoliowing extraction of impacted third molars can signiticantiy reduce the incidence ot alveolar osteitis.

LarsBn PE, J Orat Maxiiiofaç Surg ^5^0AB(s\^pp\ 1):123-124, Heterences: 2, fleprints: Dr Larsen, The Ohio StateUniversity Coiiege of Dentistry, Department of Oral art) Maxillofacial Surgery, 305 W 12th Avenue, 2131 Postia Hall,Coiumbus, Ohio 43210,-HnondaF,JacoiJ, DDS, MS, M.D. Anderson Cancer Center, Houston, Texas

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