M. Burban AiKhatib, DOS, MSDFormer Clinical Feliow

Construction of an InterimObturator Using a

Microwave-PolymerizedDenture Base Resin

Robert £. MçKinstry, DMD, MDS, MAOirectOT

Regional Center ¡or Maxillofadai Prosttietic RehabilitationEye and £ar HospitaiUniversity ol PittsburghSchool of Dental MedicinePittsburgh, Pennsylvania

This article describes a technique for fabricating an interimobturator for maxillectomy patients using a microwave-polymerized denture base resin. The use of microwaveirradiation to polymerize this type of resin reduces the timerequired to fabricate interim obturators and results inprostheses comparable in physical properties and superior indimensional accuracy to prostheses made with conventionalheat-polymerized acrylic denture base resin. The techniqueis simple and time efficient, and it does not require anyspecial or elaborate laboratory equipment, itit I Prosthodont1991:4:524-528.

R esection of the hard palate establishes com-munication between the oral and nasal cavities

and often the maxillary sinus. This type of ablativesurgery is performed for eradication of tumors aris-ing from the palate or maxillary sinus.'

A maxillary obturator prosthesis can re-establishphysical separation of the oral and nasal cavities.^*'Obturators constructed for maxillectomy patientsare grouped according to their stage of use. Thesurgical obturator is fabricated prior to surgery, theinterim obturator prosthesis is constructed afterremoval of the surgical obturator and packing,while the definitive obturator prosthesis is pro-vided for the patient 6 to 12 months after surgery.^-'

Usually a new impression is made to fabricatean interim obturator after removal of the surgicalobturator." In tbe partially edentulous patient,support, retention, and stability of the interimprosthesis are provided with only minimai engage-ment of the defect,^ Complete extension of aninterim obturator is not advisable because of lim-ited mouth opening and potential interferencewith healing.̂ 'S Many clinicians agree that the ob-turators should be hollow and light in weight.^''The superior surface of the obturator can be leftopen or closed. A delay in adding teeth to the

Reprint requests: Or Robert f . McKinstry, SS47 Beverly Place,Pittsburgh, Pennsylvania 15206.

interim obturator has the advantage of preventingocclusal loading to the resected area and reducingirritation that could affect the healing of the sur-gical site."

Numerous methods of polymerization and pro-cessing are now available and have attracted theattention of several investigators.'-'^ Takamata andSetcos^ reviewed the various modifications ofdenture base resins and evaluated pourable res-ins, microwave-polymerized resins, and light-acti-vated resins. They found that the conventionaltechniques with h eat-activated resins are not onlymore time consuming, but also may providereduced accuracy. Takamata et al" compared theadaptation of dentures made from six differentdenture base materials processed on a mastercast. The greatest discrepancy in adaptation to tbemaster cast occurred with the heat-activated resin,while a specially processed pour resin and themicrowave-processed resin provided the bestadaptation. A light-polymerized resin, anotberheat-activated resin, and a different microwave-processed resin were intermediate in accuracy ofadaptation.

Early investigators^'" found that there were nodifferences between the physical properties ofdenture base resins processed in a microwaveoven and those processed using a conventionalhot water balb. However, these investigatorsfound that denture base resins processed by

The International Journai of Prosthodontics 5 2 4 Volume 4, Number ' ' " " •

.1 Kha lib/Me Kin i l rv e-Polymenzeil Interim Obturator

microwave irradiation exhibit porosity when theresin thickness exceeds 2.5 or 3 mm. Sanders eta l " noted that to minimize porosity in relativelythick specimens of acrylic resin processed in themicrowave oven, it is important to select anappropriate resin. AlKhatib et al'^ found no poros-ity when a special denture base resin materialdesigned for microwave processing was used,regardless of the thickness of the resin.

This article describes a technique for making ahollow interim obturator using a denture baseresin specially formulated for microwave pro-cessing.

Methods

1 . An impression is made of tbe maxillary defectusing a suitable stock tray and irreversiblehydrocoiioid impression material. If necessary,the tray should beextended witb wax to coverthe posterior part of the defect (Fig 1).

2. The impression is poured in dental stone usingthe appropriate boxing technique.

3. Wrought wire clasps are adapted aroundselected teeth for retention (partially eden-tulous nnaxillectomy patients). The cast,except for tbe superior aspect of the defect,should then be covered with approximately 3to 4 mm of pink baseplate wax.

4. After the waxing bas been completed, the castis placed into cold water for approximately 5minutes. Dental stone is then poured into theopen defect area. Before the stone has set andusing the patient's normal palatal ridge as aguide, a false palate and ridge should beshaped and contoured in the stone.'^ Approx-imately 2 mm of thickness is left for relief ofthe wax pattern of the reshaped palate andridge. The false palate and ridge are thenwaxed,

5. The cast is flasked in the conventional mannerusing a special microwave flask (GC fiber-rein-forced plastic flask, GC International, Scotts-da le, Ar iz) designed for use wi th themicrowave-polymerized denture base resin(Fig 2). Other types of microwavable dentureflasks can be used with this type of acrylicresin.'''

6. Wax elimination is accomplished in the usualmanner, and the wax is completely removedusing clean water and detergent (Fig 3). Thecast is then coated with tin foil substitute (Al-Cote, Dentsply, York, Pa).

7. Acron MC (GC International), a new denturebase acrylic resin specially formulated formicrowave processing, is mixed according to

Fig 1ator.

Maxillary defect atter removal of the surgical obtur-

Fig 2 Interim obturator waxed and invested in the fiber-rein-forced plastic ilask.

Fig 3 Flask after completed investment and wax eliminationof tfie waxed interim obturator.

4, Number 6, 1991 5 2 5 Tfie Inlemational Journal of Prosthodonlicî

Microwave-Polymerized Inte M K lu i ib/M cK ins try

Fig 4 Flask guard is used to align tfie sections of the flask. Fig 5 Trial closure with flask guard in place.

the manufacturer's instructions using the stan-dard powder/iiquid ratio of 43 mL of liquid to700 g of powder. Enough powder and liquidare measured, and the powder is sifted overthe liquid in the mixing jar. The mix is thenallowed to reach the dough stage in about 20minutes at room temperature, according tothe manufacturer's instructions. Mixing thepowder with liquid is not recommended.

8, The resin dough is removed in one piece fromthe mixing jar without producing air bubbles.It is then packed in the fiber-reinforced plasticflask.

9. The flask guard is installed by fitting its legsinto the bolt holes of the flask. The guard willalign the cover, upper half, and lower half ofthe flask to the correct position when the flaskand the guard are placed under the press (Fig4). Trial closures are then completed using theflask guard as a guide (Fig 5).

10. The excess resin is removed, followed by finalclosure of the flask. The nuts for the flask arefastened to the polycarbonate bolts while theflask is still under the press. The nuts are tight-ened, first mantially and then using thewrench supplied with the flask.

11. The flask is placed in the microwave oven andthe interim obturator is polymerized at 500 Wfor 3 minutes. It is not necessary to turn theflask while processing. If a microwave ovenwith a maximum output of 500 W is not avail-able, the following three-part formula can beused to calibrate the power setting of the ovento the appropriate wattage: (1) Q = C X mX t {Q = the heat in calories; C = specific

heat of the container (plastic, ie, polypropyl-ene or glass] that will hold approximately 1000mL of water in the microwave oven'^; m =mass of water; í = temperature rise of thewater, in °C, after irradiation in the microwaveoven]. {2) E= QX 4.184 ( f = energy; 4.184is conversion factor to convert calories tojoules, ie, 1 cal = 4.184 )). (3] Power (watts)= E/T {T = time, in seconds, used to raisethe temperature of the water in the bottle).This formula will provide the wattage valuefor each power setting on a microwave ovenregardless of the maximum output of theoven.

12. The flask Is removed from the oven andallowed to bench cool for 30 minutes fol-lowed by further cooling under cold, runningtap water for 20 minutes.

13. The interim obturator is deflasked by tappinglightly on the thick-walled portion of the backrim of the fiber-reinforced plastic flask usinga wooden mallet.

14. The obturator is finished in the usual manner(Figs 6 and 7).

15. The interim obturator Is placed and all nec-essary adjustments are made (Fig 8).

Discussion

The technique of processing an interim obturatorusing microwave irradiation and the appropriatedenture base resin allows the prosthodontist to fab-ricate an interim obturator in a single, one-daypatient visit. The use of conventional heal polym-erized denture base resin in the fabrication of an

journal of Prosthodontit 526

Khatib/McKinstry Microwave-Paly

Fig 6 Poiished surtace of the interim obturator. Fig 7 Tissue surface of the interim obturator.

interim obturator generally requires more than onepatient visit, particularly if a long polymerizationcycle is used. The microwave-polymerized denturebase resin is easy to finish and thereby eliminatesthe time required to complete an interim obturatortbat might be constructed using autopolymerizeddenture base resin. Additionally, this microwave-polymerized denture base resin bas been found byTakamata et al^ to possess superior dimensionalaccuracy wben compared to conventional heat-polymerized denture base resin. Tbe presentauthors bave not observed porosity with the useof this special microwave-polymerized denturebase resin, regardless of the tbickness of tbe acrylicresin.

In terms of time efficiency, the use of micro-wave-polymerized denture base resin is compa-rable to the use of light-activated denture baseresin for tbe fabrication of interim obturators. How-ever, tbe microwave-polymerized denture baseresin is easier to finisb than tbe ligbt-activated den-ture base resin.

Summary

Tbe technique described for fabricating interimobturators using a microwave-polymerized den-ture base resin allows tbe prosthodontist to com-plete an interim obturator in a single patient visit.Interim obturators fabricated using tbe microwave-polymerized denture base resin are easy to finish,and tbey have comparable physical properties andSuperior dimensional accuracy to obturators madewitb conventional heat-poiymerized denture base

resin. Tbe fabrication tecbnique is simple and timeefficient, and it does not require elaborate orexpensive laboratory equipment.

Fig 8 interim obturator is piaced in the patient's mouth.

References

1. lohnson JT, Aramany MA, Myers EN: Palatal neoplasms:Reconstruction considerations. Otolaryngot Clin NorthAm 1983:16:441-456.

2. Desjardins RP: Fariy rehabilitative management of themaxillectomy patients. / Prosthet Dent 1977:38:311-318.

3. Myers FN, lohnson |T, Aramany MA: Oral cavity recon-struction, in Bull TR, Myers EN (edi): Plastic Reconstruc-tion in the Head and Neck. Stoneham, Mass, ButterworthPubl Co, 1986, pp 1-30,

4. Chalian VA, Drane JB, Standish SM: Maxiilofacial Pros-thetics: MuitidisciplinaryApproach. Baltimore, Williams &Wilkins, 1971:133-157.

5. Laney WR: Maxiilofacial Prosthetics. Littleton, Mass, PSCPubl Co, 1979, pp 69-102.

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e-Polymerized Interim Obturalor AlKtiatib/McKinslry

6. Beumer I, Curtis TA, Firtell DN: Maxillofacial Rehabilita-tion: Prosthetic and Surgical Considerations, St Louis, CVMosby Co. 1979, pp 188-243.

7. Takamata T. Setcos iC: Resin denture bases: Review ofaccuracy and methods of polymerization, /nf / Prostho-dont 1969;2:555-562.

a. Takamata T, Setcos IC, Phillips RW, Boone ME: Adaptationof acrylic resin dentures as influenced by the methods ofpolymerization. I Ant Dent ABSOC I<3a9;119:271-276.

9. Reitz PV, Sanders IL, Levin B: The curing of denture acrylicresins by microwave energy: Physical properties. Quin-tessence Int 1985;8:S47-551.

10. AI Doori D, Huggett R, Brooks SC, Bates |F: Microwaveirradiation versus conventionai water bath curing: Effects

on mechanical properties of acrylic resins. Q " " " '^^"'rec/ino/1988;13:187-192.

11. Sanders |L, Levin B, Reitz PV: Porosity in denture aery icresins cured by microwave energy. Quín/eísence Int1986;18:453-456.

12. AlKhatib MB, Coodacre CI, Swartz M l , Munoz CA,Andres C): Comparison of microwave-polymerized den-ture base resins. Int i Prosfhodon/1990;3:249-255.

13. Oral K: Construction of the buccal flange obturator. /Prosthet Dent 1S79;41:193-197.

14. McKinstry RE, Zini I: How to make microwavable dentureflasks. ; Prosthet Dent 1990;63:104-l 10.

15. Bolz RE, TuveCL: Handbook of Tables for Applied Engi-neering Science, ed 2. C\eve\atid. CRC Press. 1973, p i 41.

Literature Abstracts,

incidence of Adverse Effects of Dental Materiais

The purpose of this study was to assess adverse reactions from dental materiais by recording sideeffects in ciinicai practice and by retrospective reports from a group of ciinicians. in the first survey,acute and long-standing adverse effects from dental materials used in the treatment of 13,325 patientsin 15,820 appointments during 10 consecutive days in practice were recorded by 137 dentists. Twenty-four suspected side effects were reported by the patients and 32 by the clinicians: 7 were ciassified as"probable" or 'possible" acute reactions and 15 as long-standing effects, 13 being "verified" and 2' probabie." In the second survey, 31 dentists representing a total of 387 years of practice recollected113 patients with side effects from dentai materials. The incidence rate reported indicates that thetotal number of subjective and objective side effects was at a levei of 1:700. Many materials wereassociated with these reactions. The authors point out that the presence of an ailergen or a toxiccomponent in a material is not verification of the reason for a reaction per se.

KallusT, Mjör lA. Scand J Dent Res 1991:99(3).236-24Q. References; 13. Reprints: Thomas Kailus, Specialist Cenirefor Dental Implants, Varmdöuägen 121, S-131 37, NacKa, S'ngagn.—Richard R. Seals. Jr, DDS. MEO, MS, TneUniversity ot Texas Healtn Science Center at San Antonio

The Prognosis With Postherpetic Neuraigia

The incidence of postherpetic neuralgia foilowing herpes zoster has been estimated at 9% to 34%, Inthis study, 156 patients with moderate to severe postherpetic neuraigia were followed for up to 11years. Nearly half of the patients were doing well, but more than 25% were receiving therapy for painat the time ot the study. When therapy was given, tfie best resulls were obtained by usingantidepressants, topical capsaicin, and analgesics of various types. Patn was uncontrolied in a smallgroup of the patients studied. Pain in patients wifh iong-duration postherpetic neuralgia appeared to bemore difficult to allay.

Walson CPN. et aL Pain 1991;46:195-199. References: 9. Reprints: Christopher Peter North Watson AssistantProfessor, Department of r̂ edioina, Irene Eleanor Smyths Pain Clinic, University of Toronto Toronto ' Ontario M-ir2C4, Canaöa.-Slep/ien Wagner. UP Attstract/Book Review Editor '

The International Journal of Prosthodontics 528 Volume a. Number 6. 1991