540 THE JOURNAL OF PROSTHETIC DENTISTRY VOLUME 80 NUMBER 5

Low fusing alloy has been used in a variety of den-tal applications for at least the last 36 years. Its first usewas documented by Lucia1 in 1961 for the purpose ofremounting crowns and fixed partial dentures. Sincethen, the use of low fusing alloy has been documentedin fixed prosthodontics,1-7 removable prosthodontics,8and implant prosthodontics.9 In maxillofacial prosthet-ics, low fusing alloy is used to fabricate oral radiationshield prostheses.9-16 Dental researchers who are famil-iar with the properties of low fusing alloy have also usedit creatively within their research methods.17-19

Many low fusing alloys are available commercially(Table I), vary in composition, and display differentdesired properties. As its name implies, low fusing alloymelts at a low temperature, within the range of 117°Fto 338°F.20 Low fusing alloy is easily cast into moldsand ready for use after a rapid solidification of less than5 minutes. The alloy may be easily recovered and recy-cled for reuse any number of times.

This article presents a literature review that examinesthe physical properties and metallurgical considerationsof low fusing alloy and its applications within prostho-

dontics and dental research. A safe, precise, and effi-cient method to use low fusing alloy is also presented.

PHYSICAL PROPERTIES ANDMETALLURGICAL CONSIDERATIONS

The chief elemental components of low fusingalloy are bismuth, lead, tin, and occasionally indium(Table I). Most low fusing alloys are composed of 3 ormore metals. Alloy systems that contain more than2 metals have not been developed to the extent of bina-ry diagrams because of the difficult preparation of thealloy systems.21 Published binary phase diagrams22 ofbismuth, lead, tin, and indium illustrate some eutecticalloys in their microstructures. A mixture is identified aseutectic when the compositional metals are miscible inthe liquid state but separate into 2 phases in the solidstate. The 2 phases often precipitate as fine layers ofone phase over the other.23 The partial eutecticmicrostructure in the composition of low fusing alloycan account for its physical properties.

Eutectic alloys are relatively brittle as the presence ofinsoluble phases inhibits slip in the alloy. At times, thestrength and hardness of these alloys may exceed theirprimary components, due to the composite structure ofthe alloy. In contrast, alloys composed of low fusingmetals with partial eutectic microstructure typicallyretain their expected high ductility.21In a study byToreskog et al.,24 a low fusing alloy (Cerrolow 136,Marmon Group, Inc., Belleforte, Pa.) was shown to berelatively soft. The alloy demonstrated a Knoop hard-ness of 9 but was too soft to be measured for Brinellhardness. However, these researchers reported a negli-gible relationship between Knoop hardness and abra-

Use of low fusing alloy in dentistry

Alvin G. Wee, BDS, MS,a Robert L. Schneider, DDS, MS,b and Steven A. Aquilino, DDS, MSc

College of Dentistry, University of Iowa, Iowa City, Iowa

Statement of problem. Low fusing alloy has been used in dentistry for remount procedures in bothfixed and removable prosthodontics, in implant prosthodontics for the fabrication of solid implant casts, inmaxillofacial prosthetics as oral radiation shields, and in dental research for its unique properties. Previously,the use of low fusing alloy was thought to offer a high degree of dimensional accuracy. However, multiplein vitro studies have shown that its presumed dimensional accuracy may be questionable. Purpose. This article reviews the physical properties, metallurgical considerations of low fusing alloy, itsapplications in dentistry, and a safe, simple method of using low fusing alloy. (J Prosthet Dent 1998;80:540-5.)

Supported in part by a Rotary International Foundation Multi-YearAmbassadorial Scholarship 1994-96.

The authors have no connection with or conduct research for anycompany that is associated with low fusing alloy.

aAssistant Professor, Sections of Restorative Dentistry, Prosthodon-tics and Endodontics, Department of Prosthodontics.

bClinical Director, Oral and Maxillofacial Implant Center, AssociateProfessor, Department of Prosthodontics.

cDirector, Graduate Prosthodontics, Professor, Department ofProsthodontics.

CLINICAL IMPLICATIONS

Although many uses of low fusing alloy have been described previously in the dental lit-erature, the clinician/researcher must be aware of the accuracy of the material andpotential health risks associated with its use.

sive resistance for low fusing alloy.24 This differs fromthe “apparent” positive correlation between hardnessand abrasion resistance associated with the majority ofthe other materials tested in their study.24

The presence of partial eutectic microstructures in alow fusing alloy also contributes to its low meltingpoint. Solidification of eutectic alloys present similarcurves to their pure metals, with the exception thatsolidification temperature is lower than that of the puremetals. These eutectic alloys possess a melting point atthe eutectic composition, rather than a melting range.Any other possible combinations of the pure metals inthe alloy system will have a higher fusion temperaturethan the melting point of the eutectic mixture.23 Thus,

eutectic alloys have been used to lower the fusion tem-perature of alloys if desired.21 In a eutectic alloy, a flowor creep may occur even at room temperature if therecrystallization temperature of the matrix metal (lead)is low.21 As one of the chief elements of low fusingalloy, lead causes the alloy to slowly expand over time(Table II).

It is unusual for products with different trade namesto demonstrate similar composition and melting tem-peratures (Table I). Alloys that demonstrate such simi-larities most likely are provided by the same supplierbut marketed under different trade names. The oftenreferred to “Melotte’s metal” in the dental literature isactually Belmont alloy 2491 (Belmont Metals Inc.),

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Table I. List of low fusing alloys used in the dental literature

Melting Composition*

Alloy Manufacturer’s name temperature Bi Pb Sn In Ag Cd

Fusible metal Williams Dixon, Inc., Carstadt, N.J. NA NAPlumbers solder NA NA 0 50 50 0 0Metallomat alloy Ivoclar, Schwann, Liechtenstein NA 53 0 45 0 2B2OE2 alloy Alpha Metals Inc., Jersey City, N.J. NA 52 32 16 0 0Melotte’s metalBelmont alloy 2491 Belmont Metals Inc., Brooklyn, N.Y. 136°F 49 18 12 21 0Indalloy 136 Indium Corp., Utica, N.Y. 136°F 49 18 12 21 0Cerrolow 136 Marmon Group Inc., Belleforte, Pa. 136°F Likely to be similar to Belmont alloy 2491

and Indalloy 136Lipowitz’s metalBelmont alloy 2503 Belmont Metals Inc. 158°F 50 26.7 13.3 0 0 10Ostalloy 158 Arconium Corp. of America, Providence, R.I. 158°F 50 26.7 13.3 0 0 10Cerrobend Cerro Metal Products, Belleforte, Pa. 158°F 50 26.7 13.3 0 0 10

*Reported as percentage.NA: Not available.

Table II. Percentage expansion of low fusing alloy

Study Alloy Reported expansion* (time) Actual expansion* (time)

Toreskog et al.24 Cerrlow 136 NA Occlusal = +0.42(Marmon Group Inc.) Cervical = +0.24 (24 h)

Yoon et al.26 Indalloy 136 0 (1 h) 0.00 (0 h)(Indium Corp.) –0.05 (0.5 h)

0.12 (336 h)Plumber’s solder (NA) NA 0.00 (0 h)

–0.40 (0.5 h)–0.43 (336 h)

Metallomat alloy +0.10 0.00 (0 h)(Ivoclar) 0.01 (0.5 h)

0.08 (336 h)B2OE2 alloy NA 0.00 (0 h)(Alpha Metals Inc.) 0.28 (0.5 h)

0.024 (336 h)Wee et al.27 Belmont alloy 2491 0.0 (initially) 0 - High SD

(Belmont Metals Inc.) –0.02 (5 h) (at least 24 h)

*Reported as percentage.NA: Not available.

which has been clarified by Pameijer.5 Examination ofthe composition and melting temperatures of Indalloy136 (Indium Corp., Utica, N.Y.), Cerrolow 136(Marmon Group Inc.) and Belmont Alloy 2491 (Bel-mont Metals Inc.) suggests that these alloys are similar(Table I). Lipowitz’s metal is also marketed under dif-ferent trade names, including Ostalloy 158 (ArconiumCorp. of America), Belmont Alloy 2503 (BelmontMetals Inc.), and Cerrobend (Cerro Metal Products).7

Some manufacturers claim that low fusing alloy haslittle or no dimensional change when passing from theliquid to the solid state.20 However, the properties anduse of low fusing alloy and its dimensional accuracy arequestioned.24-27 It is not surprising, given the compo-sitional variation of these alloys, that low fusing alloysproduced by different manufacturers have a wide rangeof dimensional accuracy.

Low fusing alloy, as examined by Toreskog et al.,24

was found to be completely compatible with all theimpression materials studied at that time, includingpolysulfide (Permlastic, Kerr Mfg. Co., Detroit,Mich.). However, it was found that dies produced bythe alloy frequently exhibited rounded corners and pitsor nodules as a result of the collapse of voids in theimpression.

CLINICAL APPLICATIONS INPROSTHODONTICSRemount procedures in fixed and removableprosthodontics

Although remounting fixed and removable prosthe-ses involves a number of additional procedures, theremounting technique permits the clinician to refinethe occlusion in a more controlled environment thancan be experienced intraorally. The decision to carryout a clinical remount is made by assessing the difficul-ties associated with refining the occlusion intraorally, as

compared with the process of remounting on the artic-ulator.

The use of low fusing alloy to fabricate remountcasts for multiple fixed units has been recommended(Fig. 1).1-6 After fitting the castings intraorally forproximal contacts, marginal fit, and contours, it hasbeen recommended that the fixed restorations be stabi-lized with a mixture of temporary cement and petrole-um jelly,6 or a multiform impression paste (LactonaCorp., Philadelphia, Pa.).4 After an interocclusal recordand face-bow transfer are made, an impression is madeover the seated castings. Several techniques have beendescribed to ensure the “absolute” accuracy of theremount impression.4-6

Before pouring the remount impression, internalsurfaces of the castings are painted with a separatingmedium (petroleum jelly,4 Rubbersep, or Mucolube5).All exposed external portions of the castings are cov-ered with either melted baseplate wax, reversible, orirreversible hydrocolloid material. A low fusing alloy ismelted and poured into the impression containing thecastings to cover and include the occlusal one third ofthe dental alveolar ridges. Walker4 used a low fusingalloy from Dentalloy Inc. (Stanton, Calif.), whereasPameijer5 recommended using a low fusing alloy called“Melotte’s metal/Belmont alloy 2491” (Belmont Met-als Inc.). Retentive components, such as pins or paperclips, are heated and placed into the cooled alloy, andthe remainder of the cast is poured in die stone. Thelow fusing alloy allows easy and repeated removal of thecastings from the remount cast.5,6 If gypsum is used,abrasion and possible fracture of the die5 can occur.

Low fusing alloy has also been used to fabricate aremount cast for removable partial dentures (RPDs)(Fig. 2). Reitz8 recommended making an interocclusalrecord and a face-bow transfer before making an intra-oral irreversible hydrocolloid impression of the seated

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Fig. 1. Low fusing alloy used in remount cast for multipleposterior single crowns in mandibular arch.

Fig. 2. Low fusing alloy used in remount cast for mandibularRPD.

RPD. A low fusing alloy (Melotte’s metal/Belmontalloy 2491) was then poured into the natural teeth por-tion of the impression. A retentive component washeated and embedded into the low fusing alloy withinthe impression, and the rest of the cast was poured withplaster. This method allows the removal of the RPDafter the remount cast is made, so that any type of inte-rocclusal record can be taken. Teeth chipping or wearare less likely to occur during the process of equilibrat-ing the prosthesis.

Implant solid cast fabrication

Recently, low fusing alloy has also been recommend-ed as a material for the fabrication of solid implant casts.Schneider and Wee9 described the use of a low fusingalloy in the fabrication of a solid multi-implant cast. Thelow fusing alloy (Belmont 2491) has a melting pointof 136°F and a linear expansion after solidification of0.05%.20 The melted alloy was poured into the implantimpression around abutment replicas. Once the alloysolidified, retentive components were placed in the alloyand the rest of the impression was poured in either ADAtype IV or V dental stone (Fig. 3).

Applications in dental research

Dental researchers knowledgeable of the properties oflow fusing alloy have used the alloy successfully in theirresearch methods. Particularly useful properties includethe castability of the alloy at low temperatures17 and thenonbrittle nature of the alloy.18,19 Low fusing alloy hasbeen used to measure the accuracy of die materials andimpressions. Stackhouse et al.17 used low fusing alloy(Indalloy 136, Indium Corp.) to create a counter die toevaluate the accuracy of various die/impression materialcombinations. Wang et al.18 developed an accurate andreproducible intraoral method of measuring the distancebetween 2 teeth by using casts fabricated from lowfusing alloy (Cerrolow-136). Zwetchkenbaum et al.19

used low fusing alloy in a study comparing the sizes ofthe marginal gaps of nonrelined, relined corrected, andpaint-on corrected acrylic resin provisional crowns afterthermocycling and occlusal loading.

Accuracy of low fusing alloy

A common presumption when low fusing alloy isused for fixed and removable prosthesis remount pro-cedures, for solid implant cast fabrication, or in dentalresearch has been its accuracy. The recommended useof this alloy had been based on empirical evidence forparticular techniques, as described by various clini-cians.1,3-5,9 Measurements of accuracy of low fusingalloy were not documented to accompany these tech-nique investigations.

Low fusing alloy properties have been investigat-ed,25 and its accuracy has been investigated for use astransfer casts after indexing,25 as counter dies for mea-

suring impression and die material accuracy,17 and assolid implant casts27 (Table II).

Toreskog et al.24 evaluated the use of low fusingalloy (Cerrolow-136) as a die material. The alloy with amelting point of 136°F was heated to 145°F in a con-stant temperature oven. The die was then poured, andthe alloy was allowed to solidify under 30 pounds ofpressure. The authors found that the alloy expanded to0.42% at the occlusal region and 0.24% at the cervicalregion of the die. Harper and Nicholls25 evaluated dis-tortion in indexing methods and investing media forsoldering and remount procedures. They tested anADA type IV dental stone (Vel-mix, Kerr Mfg. Co.,Emeryville, Calif.), an autopolymerizing acrylic resin,and a low fusing alloy (Fusible Metal, Williams Dixon,Inc., Carstadt, N.J.) as a transfer cast after indexingwith either polyether or zinc oxide eugenol (ZOE)impression paste. A 3-dimensional analysis of distortionwas conducted. For the remount procedure, low fusingalloy exhibited significantly more 3-dimensional distor-tion than the ADA type IV dental stone.

Yoon et al.26 investigated the linear dimensionalchanges of 3 low fusing alloys, using the master die ofADA Specification No. 19.28 The samples were benchcooled at room temperature for a half hour, separated,then measured with a toolmaker’s microscope that had amicrometer divided to 2.5 µm. Subsequent measure-ments were made at 1 hour, 1.5 hours, and 2-weekintervals after casting. The authors reported a highdegree of a dimensional change with the B20E2 alloy(Alpha Metals Inc.) (+0.3%) and the plumbers solder(–0.4%). The Indalloy 136 alloy shrank 0.05% ± 0.02%,then slightly expanded to 0.12% after 2 weeks. Theyconcluded that this alloy presented desirable features,including a low fusing temperature, small dimensionalchange, minimal surface bubbles, relatively satisfactory

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Fig. 3. Low fusing alloy used in solid implant master cast.

surface detail, and availability. The dimensional changeof the tested low fusing alloys did not coincide with themanufacturers’ stated dimensional accuracy of the alloys.

Such results are not uncommon when consideringdifferences in method and measurement conditions.Wee et al.27 evaluated the accuracy of low fusing alloysolid implant casts compared with gypsum casts pouredin a polyether impression. The materials evaluatedincluded a low fusing alloy (Belmont alloy 2491), Vel-mix, Die Keen (Miles Dental Products, South Bend,Ind.), and Resin Rock resin impregnated gypsum hybridalloy (Whip Mix Corp, Louisville, Ky.). A digital veneercaliper was used to evaluate the linear horizontal dimen-sional change of the most distal abutments of the mastercast and experimental casts were made from the varioustested materials. Although the low fusing alloy wasfound to produce the least horizontal linear dimension-al change, it also exhibited the greatest standard devia-tion. The mesiodistal strain was also evaluated when amaster framework was secured to the various experi-mental casts by prosthetic retaining screws torqued to10 Ncm. A 1-way analysis of variance (ANOVA) (α=.05)revealed a statistically significant difference from themean (absolute) strain values among the materialsgroups (P=.0261, power=0.99) Duncan’s multiplerange test (α=.05) indicated that low fusing alloy did notdiffer significantly from the other materials. Casts madefrom Resin Rock material produced the least amount ofmean microstrain on the framework. Overall, studiesthat have evaluated the dimensional accuracy of low fus-ing alloy have shown them not to be accurate, as com-pared with standard gypsum materials.

CLINICAL APPLICATIONS INMAXILLOFACIAL PROSTHETICS

Low fusing alloy has been documented by many foruse as oral radiation shield prostheses.7,11-13,29,30 Radi-

ation protection prostheses can be constructed as a1-piece7,10,11,13,29 or a 2-piece16 oral radiation shield.Noncancerous oral structures in the field of the exter-nal radiation beam are protected from unnecessarysequelae of therapeutic radiation31 through the use ofthe shield. A radiation protection prosthesis can shielda portion of the radiation from the tongue,11 alveolarridge, and/or the oral tissues opposite the radiationsource.16

Low fusing alloy has also been used to obturate thepalatal vault to decrease radiation exposure to nonin-volved, previously irradiated tissues during brachyther-apy of the palate.14 Shielding adjacent tissues of thenose from radiation to treat carcinoma of the nasalcavity and/or nasal vestibule has also been described.29

Although lead is the ideal material for maximumshielding of radiation,12 its melting temperature ofmore than 600°F melts or distorts the methylmethacrylate that would be used as its carrier. The pop-ular shielding material of choice to fabricate an oralshield prosthesis is a low fusing alloy called Lipowitzmetal. Various thicknesses of Lipowitz’s metal (Ostal-loy 158, Belmont Alloy 2503, and Cerrobend) havebeen shown to prevent a percentage of the therapeuticradiation passing through the shield to noncanceroustissue.7,11,32 Lipowitz low fusing alloy, with a lead con-tent of 26.7% and a melting temperature of 158°F, canbe poured into a shell of methyl methacrylate withoutaffecting that material.

SAFETY RECOMMENDATIONS

Health hazard information for low fusing alloy cau-tions that dust vapors and/or fumes from the low fus-ing alloy may be irritating to the respiratory system anddigestive system when ingested, resulting in acuteand/or potentially chronic body reactions with overex-posure.20 Because exposure may also cause irritation to

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Fig. 4. Melted low fusing alloy in hot water bath with plas-tic syringe.

Fig. 5. Plastic syringe used as dispenser for melted low fus-ing alloy.

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the eyes and skin, a face shield and/or vented gogglesshould be worn with gloves before handling the lowfusing alloy. Protective clothing should also be wornand properly laundered after use.

The low fusing alloy from the manufacturer shouldbe sectioned in strips19 and melted in a water bath 20°Fabove the melting temperature of the alloy (Fig. 4).5,27

This will prevent overheating and emission of toxicvapors20 and minimize alloy shrinkage.5 A plasticsyringe19,24 or an “eye drop” dispenser5 can be usedto transfer the low fusing alloy from the water bath(Fig. 5). Use of a plastic calibrated syringe allows a pre-cise amount of alloy to be dispensed27; small incre-ments should be dispensed to minimize the shrinkageof the alloy.5

CONCLUSION

The popularity of low fusing alloy in the 1970s and1980s as a remount material has declined, due in partto the associated health hazards when the alloy is notproperly manipulated20 and its questionable accura-cy.17,24,25,27 However, the use of low fusing alloy inselected prosthodontic procedures and in dentalresearch is still applicable, with consideration of safe,and efficient methods of handling.

REFERENCES

1. Lucia VO. Modern gnathological concepts. 1st ed. St Louis: CV Mosby;1961.

2. Huffman RW, Regenos JW. Principles of occlusion. Volume VIII. London(OH): H & R Press; 1973.

3. Kornfeld M. Mouth rehabilitation—clinical and laboratory procedures.Volume II. St Louis: CV Mosby; 1974. p. 904-5, 988-90, 1027-9.

4. Walker PM. Remounting multiples casting prior to final cementation. JProsthet Dent 1981;46:145-8.

5. Pameijer JH. Remounting procedures. Periodontal and occlusal factors incrown and bridge procedures. Holland: Dental Center for PostgraduateCourse; 1985. p. 404-12.

6. Rhoads JE, Rudd KD, Morrow RM. Impression and cast. Dental laborato-ry procedures—fixed partial dentures. Volume II. Second edition. St Louis:CV Mosby; 1981. p. 45-8.

7. Bashiri H, Suen JY. Dental considerations. In: Myers EN, Suen JY, editors.Cancer of the head and neck. 3rd ed. Philadelphia: WB Saunders; 1996.p. 117-30.

8. Reitz PV. Technique for mounting removable partial dentures on an artic-ulator. J Prosthet Dent 1969;22:490-4.

9. Schneider RL, Wee AG. Fabricating low-fusing metal casts for more accu-rate implant prosthodontics. J Prosthodont 1996;5:301-3.

10. Aramany MA, Drane JB. Radiation protection prostheses for edentulouspatients. J Prosthet Dent 1972;27:292-6.

11. Fleming TJ, Rambach SC. A tongue shielding radiation stent. J ProsthetDent 1983;49:389-92.

12. Rahn AO, Boucher LJ. Maxillofacial prosthetics—principles and concepts.Philadelphia: WB Saunders; 1970. p. 49-82.

13. Poole TS, Flaxman NA. Use of protective prostheses during radiation ther-apy. J Am Dent Assoc 1986;112:485-8.

14. Randall ME, Salisbury PL 3d, Schmidtke M. Afterloaded radiation carrierfor carcinoma of the palate. A clinical report. J Prosthet Dent1988;60:655-9.

15. Beumer J III, Curtis TA, Morrish RB Jr. Radiation complications in edentu-lous patients. J Prosthet Dent 1976;36:193-203.

16. Coleman AJ. A technique for shielding electron beams used in radiother-apeutic management of head and neck cancer. J Prosthodont 1996;5:129-32.

17. Stackhouse JA Jr, Yoon W, Von Hagen S. Low-fusing counterdies for mea-suring accuracy of dies or impression materials. J Prosthet Dent 1994;71:209-14.

18. Wang JC, Charbeneau GT, Gregory WA, Dennison JB. Quantitative eval-uation of approximal contacts in Class 2 composite resin restorations: aclinical study. Oper Dent 1989;14:193-202.

19. Zwetchkenbaum S, Weiner S, Dastane A, Vaidyanathan TK. Effect of relin-ing on long-term marginal stability of provisional crowns. J Prosthet Dent1995;73:525-9.

20. Material safety data sheet: Low melting alloys. Brooklyn: Belmont Metals;1992.

21. Anusavice JK, editor. Phillip’s science of dental materials. 10th ed.Philadelphia: WB Saunders; 1996. p. 336-40.

22. Hansen M, Anderko K. Constitution of binary alloys. 2nd ed. New York:McGraw-Hill; 1958. p. 313-4,324-6,336-9,1106-9.

23. Craig RG. Restorative dental materials. 10th ed. St Louis: CV Mosby;1997. p. 111-7.

24. Toreskog S, Phillips RW, Schnell RL. Properties of die materials—a com-parative study. J Prosthet Dent 1966;16:119-31.

25. Harper RJ, Nicholls JI. Distortion in indexing methods and investingmedia for soldering and remount procedures. J Prosthet Dent 1979;42:172-9.

26. Yoon W, Wexler I, Stackhouse JA. Low fusing counterdies to testdie/impression accuracy. J Dent Res 1985;64:906 [abstract].

27. Wee AG, Schneider RL, Aquilino SA, Huff TL, Lindquist TJ, WilliamsonDL. Evaluation of the accuracy of solid implant cast. [Master’s thesis.]Iowa City: The University of Iowa; 1997.

28. Revised American Dental Association Specification No. 19 for non-aque-ous, elastomeric dental impression materials. American Dental Associa-tion. J Am Dent Assoc 1977;94:733-41.

29. Ghalichebaf M, Chalian VA, Shidnia H. A shielded radium source carriernasal stent for the treatment of primary carcinoma of the nasal cavity. JProsthet Dent 1984;51:383-6.

30. Beumer J, Curtis TA, Nishimura R. Radiation therapy of head and necktumors. In: Beumer J, Curtis TA, Marunick MT, editors. Maxillofacial reha-bilitation—prosthodontic and surgical considerations. St Louis: IshiyakuEuroAmerica; 1996. p. 43-111.

31. Arcuri MR, Schneider RL. The physiological effects of radiotherapy on oraltissue. J Prosthodont 1992;1:37-41.

32. Farahani M, Eichmiller FC, McLaughlin WL. New method for shieldingelectron beams used for head and neck cancer treatment. Med Phys1993;20:1237-41.

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