Residual methyl methacrylate monomer, water sorption, and water solubilityof hypoallergenic denture base materials

Peter Pfeiffer, DMD,a and Ernst-Ulrich Rosenbauer, DMDb

School of Oral Medicine, University of Cologne, Cologne, Germany

Statement of problem. Denture base materials have the potential to cause irritation and allergic reaction tothe oral mucosa. Water sorption and water solubility of denture base resins affect dimensional behavior anddenture stability. A correlation between residual monomer and water sorption exists.

Purpose. This in vitro study compared the amount of residual monomer, quantity of water sorption, andsolubility of 4 denture base materials purported to be hypoallergenic with those of a polymethyl methacrylate–based (PMMA) heat-polymerizing acrylic resin.

Material and methods. The denture base resins Sinomer (heat-polymerized, modified methacrylate), Polyan(thermoplastic, modified methacrylate), Promysan (thermoplastic, enterephthalate-based), and Microbase(microwave polymerized, polyurethane-based), which are purported to be hypoallergenic, and Paladon 65(heat-polymerized, methacrylate, control group) were examined. Specimens of each material were tested forresidual methyl methacrylate (MMA) monomer (% wt, n=3), amount of water sorption (mg/mm3, n=5) andwater solubility (mg/mm3, n=5), according to ISO 1567:2000. The residual MMA monomer concentrationswere determined by gas chromatography (GC). The data were analyzed with 1-way ANOVA and theBonferroni-Dunn multiple comparisons post hoc analysis for each test variable (a=.05).

Results. Significantly lower residual MMA monomer was shown for Sinomer and Polyan compared to thePMMA control group (0.90 6 0.20% wt, P\.05). Sinomer contained 0.31% 6 0.00% wt MMA monomer, andPolyan exhibited residual MMA monomer content of 0.44% 6 0.01% wt. Promysan and Microbase did notcontain detectable residual MMA. Water sorption of Promysan (16.21 6 0.96 mg/mm3) was significantly lowerthan Paladon 65 (23.04 6 3.13 mg/mm3, P\.0001), whereas water solubility of the hypoallergenic denturebase materials (0.34-0.84 6 0.05-0.09 mg/mm3) was not significantly lower than the PMMA material (0.40 6

0.06 mg/mm3, P[.05). Except for Sinomer, the tested denture base resins passed the requirements of ISO1567 regarding residual MMA monomer (\2.2% wt). Sinomer failed to comply with the requirements forresidual MMA monomer because the manufacturer claimed that the material did not contain any MMA. Thetested denture base materials fulfilled the requirements regarding water sorption (\32 mg/mm3) and solubility(\1.6 mg/mm3).

Conclusion. The tested hypoallergenic denture base materials exhibited significantly lower residual monomercontent than PMMA. Promysan and Microbase showed no detectable residual MMA. (J Prosthet Dent2004;92:72-8.)

CLINICAL IMPLICATIONS

For denture-wearing patients with potential allergy susceptibility, hypoallergenic denture basematerials represent an alternative to conventional polymethyl methacrylate (PMMA) tominimize the risk of adverse reactions induced by residual methyl methacrylate monomer.Water sorption and solubility of the hypoallergenic denture base materials were in the samerange as the PMMA material tested. The mechanical and clinical properties of thehypoallergenic materials, however, require further investigation.

Polymethyl methacrylate (PMMA) denture base hasdominated the market for more than 50 years.1-5 Dueto the general increase in patients with allergies,dentists are confronted with more patients with

aAssociate Professor, Department of Prosthetic Dentistry.bResearch Assistant, Department of Prosthetic Dentistry.

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allergic reactions to the classic PMMA denture basematerials.6-9

Kanerva et al9 compared 30 different acrylates, whichwere tested for a period of 10 years in 275 patients withpatch tests. Forty-eight patients (17.5%) exhibitedallergic reactions to at least 1 acrylate. The substancesthat caused the majority of allergic reactions were2-hydroxyethyl acrylate (2-HEA, 12.1%) and

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2-hydroxypropyl acrylate. The authors, however, in-dicated that it was not possible to identify which sub-stance featured the highest allergic potential. Vilaplanaet al7 evaluated tests with denture materials. Contactdermatitis to cobalt, nickel, beryllium, methyl methac-rylate (MMA), and other substances was detected.

Dental technicians processing the material are also athigh risk for allergies to denture base resin.10-15 Kanervaand Estlander10 reported that MMA is still the mostfrequent allergen in denture base materials for dentaltechnicians. After demonstrating allergic reactions toacrylates in 81 patients using patch tests, Ekstrand et al15

recommended stricter precautionary measures for allexposed persons when working with allergy-causingsubstances. In a 12-month study with Finnish dentaltechnician trainees, Murer et al 11 showed that there wasa significant increase in skin allergies that could beattributed to processing acrylates. The risk of developingskin allergies was 8 times higher for dental techniciansthan for the average population. After interviewing1132 dental technicians, Rustemeyer and Frosch14

examined and patch tested 55 dental technicians withsuspected occupational skin disease; 63.6% of the dentaltechnicians exhibited contact dermatitis, and 74% ofthese could be attributed to an allergy to MMA. Studiesof Kiec-Swierczynska13 showed that 9 out of 1619patients had an allergic reaction to acrylates (4 dentaltechnicians, 4 dentists, 1 textile printer). Ethylene glycoldimethacrylate, MMA, 2-hydroxyethyl methacrylate,and triethylene glycol methacrylate were the mostfrequent sensitizing substances. Comparing patchtests,16 dentists were allergic to several dentalsubstances, whereas dental technicians were almostexclusively allergic to MMA.13,17,18 Gloves provide onlylimited protection since the monomer released from thematerials can penetrate latex and vinyl gloves andpotentially cause contact dermatitis.19

To overcome the allergy problem, new denture basematerials, including MMA-free materials, have beenintroduced. The MMA has presumably been replacedby hypoallergenic resins, such as diurethanedimethacrylate, polyurethane, polyethylenterephthalat,and polybutylenterephthalat.4,5 Unfortunately, thesematerials are not completely risk free. Rustemeyer andFrosch10 reported on dental technicians with a clinicallyproven allergy to urethane dimethacrylate. The releasedresidual monomer is the primary cause of irritation tothe mucous membrane.20-24 To reduce the allergyrisk,20 manufacturers have attempted to lower residualmonomer content in denture base resin by alteringthe manufacturing process, using thermoplastic andmicrowave polymerization rather than heat polymeri-zation.21-23 Some authors25,26 reported that an increasein polymerization temperature and time was accompa-nied by a decrease in residual monomer content. Variousauthors27-29 have demonstrated that the residual mono-

JULY 2004

mer content could be lowered if the denture was storedin water after processing. Another significant factor forresidual monomer release is the surface condition of thedenture base resin. Specimens polished to high lusterdemonstrated significantly reduced monomer releasecompared to unpolished specimens.30

One of the properties of acrylates is water sorptionand release, which cause dimensional instability, therebysubjecting the material to internal stresses that mayresult in crack formation and, eventually, fracture ofthe denture.31-35 Takahashi et al34 found that watermolecules spread between the macromolecules of thematerial, forcing them apart. This behavior affectsdimensional behavior and denture stability; therefore,water sorption and solubility of these materials shouldbe as low as possible.33,36 Jagger36 reported a correlationbetween residual monomer and water sorption. Ifresidual monomer is present, less monomer conversionoccurs and may result in increased sorption andsolubility.36,37

This in vitro study evaluated the amount of residualmonomer content, water sorption, and water solubilityof denture base materials purported to be hypoaller-genic, compared to a conventional heat-polymerizedPMMA material. The research hypothesis was thatrecently introduced denture base materials have lowerresidual monomer content and reduced tendency forwater sorption and solubility than PMMA materials.

MATERIAL AND METHODS

The denture base resins Sinomer (heat-polymerized,modified methacrylate), Polyan (thermoplastic, modi-fied methacrylate), Promysan (thermoplastic, en-terephthalates), Microbase (microwave-polymerized,polyurethane), which are purported to be hypoaller-genic, and Paladon 65 (heat-polymerized, methacrylate,control group) were tested (Table I). The group of auto-polymerizing polymers, which release significantly moreresidual MMA monomer than heat-polymerized den-ture base materials, was excluded from this study.23 Thefollowing tests were performed according to ISO1567:2000 (E).38

Residual monomer

To determine the amount of residual MMA mono-mer, 3 specimen discs, 50 mm in diameter and 3-mmthick, were prepared from 3 separate mixes of the ma-terial according to manufacturers’ instructions. Thespecimens were stored in dark laboratory conditions(238 6 28C and 50% 6 10% relative humidity) for 24hours, then ground to a thickness of 2 mm with anautomatic grinding and polishing unit under watercooling (Phoenix Beta; Buehler Ltd, Lake Bluff, Ill),using water-resistant, metallographic grinding paper(1200 FEPA; Buehler Ltd) with a grain size of 15 mm.

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Table I. Denture base materials tested

Material Batch number Polymerization Composition Manufacturer

Microbase 2/1 D Microwave Highly cross-linked polyurethane Dentsply De Trey, Konstanz,

Germany

Polyan 980730 Thermoplastic Modified MMA Polyapress, Altkirchen, Germany

Promysan 99-05/R Thermoplastic Polyethylenterephthalate,

polybutylenterephthalate

Pedrazzini Dental Technologie,

Munchen, Germany

Sinomer IPMF 103 Heat Acrylic polymers of MMA,

urethane, and acrylate-based

oligomers

Alldent, Rugell, Liechtenstein

Paladon 65

(control group)

9044072 Heat PMMA Heraeus Kulzer, Hanau, Germany

All specimens were examined for porosity beforebeing dissolved in an acetone solution according to ISO1567.38 Acetone solution (acetone and 0.02 g hydro-quinone, total volume 1 L) was added to the specimensin a volumetric glass flask (Brand, Wertheim, Germany)until the total volume was 10 mL. Specimen-containingsolutions were agitated by magnetic stirring (Rotilabo;Carl Roth GmbH & Co KG, Karlsruhe, Germany) for72 hours at room temperature (218 6 28C). To assessreleased residual MMA monomer in the acetonesolution, the dissolved polymer must be precipitatedout of the solution. To precipitate the dissolved poly-mer, a volumetric pipette (Brand Ltd) was used totransfer a 2-mL aliquot of each specimen solution toa 10-mL volumetric glass flask (Brand Ltd). Onehundred mL of an internal standard solution (methanoland 350 mg n-pentanol, total volume 10 mL) was addedto each flask. A methanol solution (methanol and 0.02 ghydroquinone, total volume 1 L) was then added to thespecimen solution until the total volume was 10 mL.Separate volumetric pipettes were used to transfer 5 mLof each mix to glass centrifugation tubes. The solutionswere centrifuged (Biofuge pico; Heraeus Kulzer,Hanau, Germany) for 15 minutes. Separate volumetricpipettes were used to transfer a 3-mL aliquot of eachcentrifuged solution to separate glass tubes. Methanolsolution was added until the solution appeared clear.The volume of the methanol solution necessary tocomplete precipitation of polymer was recorded. Thesolutions were heated in the injection system(Headspace sampler HS40 XL; PerkinElmer, Wellesley,Mass) so that a balance between gaseous and liquidphases was obtained. The gas phases of the test solutionswere directed automatically to the gas chromatograph39

(detection limit: 0.002% wt; column: fused silicacapillary tube of length 30 m and internal diameter of0.25 mm, PerkinElmer), where specimens were exam-ined and the results calculated. Three test solutions ofeach specimen were examined. According to ISO1567,38 the maximum residual monomer content ofdenture base materials of Type 1, Type 3, Type 4, andType 5 (heat-polymerized polymers, thermoplastic

74

blank or powder, light-polymerized materials, andmicrowave polymerized materials, respectively) shouldnot exceed 2.2% wt. If results obtained for at least 7 ofthe specimen solutions comply with this requirement,the material passes. If 4 or fewer of the specimensolutions comply with the requirement, the materialfails. If 5 or 6 specimen solutions comply with ISO1567,38 new specimen discs and solutions must beprepared and the test repeated. If at least 8 of the secondseries of solutions comply with the requirements, thematerial passes. If the manufacturers specified a lowerresidual monomer content, the value determined couldexceed the specified value by a maximum of 0.2% wt.

Water sorption

Five disc-shaped specimens, 50 6 1 mm in diameterand 0.5 6 0.1-mm thick, of each material from 5different mixes were prepared according to manu-facturers’ instructions. The specimens were storedin a desiccator (Rotilabo Modell I; Carl Roth GmbH &Co KG) at 378 6 18C for 23 hours. The specimens werethen transferred to a second desiccator (Rotilabo ModellI) at 238 6 28C for 1 hour and weighed. This cycle ofdesiccation, 378C for 23 hours and 238C for 1 hourbefore weighing, was continued until a constant mass(m1) was reached. The silica gel (Riedel-de Haen,Seelze, Germany) in the desiccators was changed every60 minutes. The weight (m1) of the dried specimen wasdetermined using a scale with an accuracy of 0.2 mg(Satorius MC 1; Satorius AG, Gottingen, Germany),and the volume (mm3) of the specimen was calculated.The dried specimens were immersed in water at atemperature of 378 6 18C for 7 days, then dried witha clean towel and weighed again (m2). The difference inweights m2 and m1 divided by the volume of thespecimen determined the amount of water absorbed(mg/mm3). According to ISO 1567, the increase involumetric mass of the denture base material per unitvolume (water sorption) should not exceed 32 mg/mm3. The requirements are fulfilled if at least 4specimens exhibit water sorption of 32 mg/mm3. Ifat least 3 of the specimens do not comply with the

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Table II. Mean residual monomer content, water sorption, and solubility of denture base materials

Residual MMA monomer (% wt) Water sorption (mg/mm3) Water solubility (mg/mm3)

Test group Mean SD SSD Mean SD SSD Mean SD SSD

Microbase (Mi) 0.00 0.00 Po Si Pa 28.52 0.66 Po Pr Pa 0.34 0.07 Po Pr Si

Polyan (Po) 0.44 0.01 Mi Pr Pa 23.67 1.39 Mi Pr 0.50 0.05 Mi Pr Si

Promysan (Pr) 0.00 0.00 Po Si Pa 16.21 0.96 Mi Po Si Pa 0.76 0.09 Mi Po Pa

Sinomer (Si) 0.31 0.00 Mi Pr Pa 26.38 1.19 Pr 0.84 0.06 Mi Po Pa

Paladon 65 (Pa)

(control group)

0.90 0.20 Mi Po Pr Si 23.04 3.13 Mi Pr 0.40 0.06 Pr Si

SSD, Statistically significant difference (from group P#.0018).

requirement, the material fails. If 3 of the water sorptionspecimens comply with the requirements, 6 newspecimens should be prepared. If at least 5 specimensof the second series comply with the requirement, thematerial passes.

Solubility

Following the weighing for sorption, the specimenswere dried to a constant mass (m3) using the protocolpreviously described for the m1 determination. Thevalue m3 was subtracted from m1 and divided by thevolume of the specimen. The value obtained indicatedthe solubility of the specimens. According to ISO 1567,the soluble substances eluted during storage in watershould not exceed 1.6 mg/mm3. The requirements arefulfilled if at least 4 of the 5 specimens demonstratea solubility of 1.6 mg/mm3. If at least 2 specimens donot comply with the requirements, the material fails. If 3of the water solubility specimens comply with therequirements, 6 new specimens must be prepared. If atleast 5 specimens of the second series comply with therequirement, the material passes. Statistical analysis ofthe results was carried out with 1-way ANOVA and theBonferroni-Dunn multiple comparisons post hoc anal-ysis for each test variable (a=.05).

RESULTS

Table II summarizes the results of the determinedresidual MMA monomer content. ANOVA revealeda significant effect of brand of polymer on the residualmonomer (df=4, f=53.664, P\.0001). Significantlylower residual MMA monomer was obtained fromMicrobase, Polyan, Promysan, and Sinomer comparedto the conventional PMMA group (P\.05, Table II).Sinomer failed to comply with the requirements of theresidual MMA monomer of ISO 1567 becauseit contained 0.3160.02% wt MMA monomer,although the manufacturer claimed that the materialdid not contain any MMA. Yet Polyan passed with0.44% wt residual MMA monomer because the manu-facturer did not specify a lower residual monomercontent, and the value did not exceed 2.2% wt. Except

JULY 2004

for Sinomer, the tested denture base resins passed therequirements of ISO 1567 regarding residual MMAmonomer.

ANOVA revealed a significant effect of brand ofpolymer on the water sorption (df=4, f=37.424,P\.0001) and solubility (df=4, f=54.401, P\0.0001).The water sorption of Promysan was significantly lowercompared to Paladon 65 (P\.0001, Table II), whereaswater solubility of the hypoallergenic denture basematerials (Microbase, Polyan, Promysan, and Sinomer)was not significantly lower than that of PMMA basematerial (Table II). All specimens fulfilled the re-quirements of ISO 1567 regarding water sorption andsolubility.

DISCUSSION

Based on the results, the hypothesis that recentlyintroduced denture base materials are purported to havelower residual monomer content than PMMA materialsis accepted. Except for Promysan (water sorption), thehypothesis that hypoallergenic denture base materialshave reduced tendency for water sorption and solubilitythan PMMA materials is rejected for the tested denturebase resins. Polymethyl methacrylates dominate themarket of denture base resin materials. New productsmust not only equal the approved PMMA products butalso offer improved properties and advantages to becompetitive. It is important to determine the residualmonomer content and solubility of the tested materials,as these properties influence the allergy susceptibility ofthese materials.6-15

Gas chromatography, which was utilized in thepresent study, is a precise and simple method todetermine the residual MMA monomer content.6,39

The Microbase (microwave, polyurethane) andPromysan (thermoplastic, enterephthalates) materialsdid not contain detectable residual MMA. According tothe purported composition of these materials, the lack ofresidual MMA is due to the formulation of the products.In the present study, the residual monomer content ofPolyan (thermoplastic, modified methacrylate) was1.76% wt below the upper limit for Type 3 denture

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base materials as specified by the ISO standard (2.2%wt). Microbase, Polyan, and Promysan complied withthe requirements of ISO 156738 for all properties testedin the present study. The Sinomer denture base materialfulfilled the ISO standard requirements concerning thewater sorption and solubility, but not that of the residualmonomer content, because the manufacturer claimedthat the material did not contain MMA. The ISOstandard requires that the residual monomer contentnot exceed the value given by the manufacturer by morethan 0.2% wt. The obtained values, however, werebetween 0.3% wt and 0.31% wt. These values were atleast 1.9% wt below the upper limit for Type 1 denturebase materials specified in the standard (2.2% wt). Lassilaand Vallittu24 confirmed that Sinomer contained re-sidual MMA monomer. The material would havefulfilled the ISO requirements if the manufacturer hadindicated a residual monomer content of 0.3% wt.Paladon 65, representative of heat-polymerized PMMAmaterial, complied with the requirements of ISO1567.38 There were significant differences in theresidual MMA content of Paladon 65 and the othermaterials tested in the present study. The alternatematerials exhibited a significantly lower residual MMAcontent. Some authors24-28reported that compositionand processing of denture base resins influence therelease of residual monomer. Miettinen and Vallittu24

compared the residual monomer content released fromheat-polymerized and auto-polymerized denture basematerials and concluded that the auto-polymerizedmaterials released considerably more residual MMAthan heat-polymerized materials (1%-2% wt). Moreover,these authors showed that the residual monomercontent could be reduced when the polymerizationtime was extended. Dogan et al25 studied the effects ofvarying polymerization times and temperatures on theresidual monomer content of polymer/monomer-based denture base materials. The authors showed thatincreased temperatures and extended polymerizationtimes were accompanied by a decrease in the residualmonomer content. Tsuchiya et al26 demonstrated thatthe residual monomer content of denture base materialsis lowered to a quarter of the initial value if the denture isimmersed in water at 508C for 1 hour after polymeri-zation. Vallittu et al27 obtained similar results. If thespecimens were immersed in water at 378C for 24 hours,considerably more monomer was removed than duringimmersion in water at 228C. Accordingly, Vallittu et al27

recommended immersing a denture in water at 378C forone dayprior to insertion.ShimandWatts28 examinedtheresidual monomer content after additional immersioncycles of different durations at 1008C and demonstratedthat the residual monomer content could be reducedconsiderably. The experimental design of the presentstudy adhered to the ISO standards. Modifying ofthe parameters (polymerization times and temperatures,

76

water immersion) may have effects on the release ofresidual monomer of the tested denture base materials.These effects should be tested in further studies.

The surface condition of a denture also playsa significant role in the release of residual monomer.Vallittu29 examined whether a polishing process or alight-polymerized varnish affected the residual mono-mer content in a denture. The author demonstrated thatmonomer release reached the lowest level during 2-daysoaking of varnished specimens. High-luster polishedspecimens, however, revealed clearly lower monomerrelease than untreated specimens. A major advantage ofPolyan, Microbase, and Promysan compared to Paladon65 is that technicians will not come into contact withunpolymerized materials, as these materials are suppliedin ready-to-use cartridges.

Yutaka et al33 showed that the mechanical propertiesof denture base materials decreased if the solubilityincreased. Additionally, it was apparent that solubilitydecreased proportionally to the thickness of the speci-mens. Wong et al34 examined the dimensional behaviorof dentures during the sorption and the release of water.The authors showed that the dimensional change of thespecimens was proportional to the sorption and releaseof water. The dimensional change ranged from 0.42% to0.58% and the solubility values varied from 0.48% wt to0.50% wt. In the present study, water sorption rangedfrom 16 to 28 mg/mm3 for the denture base resinstested. Water solubility varied from 0.3 to 0.8mg/mm3.As reported by Wong et al,34 water sorptionand solubility of the tested denture base resins mayindividually affect dimensional changes of denture bases.

A study35has shown that water bath polymerizationresults in enhanced mechanical properties. If thetemperature cycles and polymerization time are changedwhen using PMMA materials, the material propertiescan be influenced positively. Extended polymerizationtime results in longer polymers so that reduced watersorption, solubility, and residual monomer contentwere obtained.35 Miettinen and Vallittu24 stated thatwater sorption and solubility of polymers depended onthe homogeneity of the material. The more homoge-neous a material, the less water it absorbs and the lesssoluble it is. Almost identical results of the differentdenture base materials were obtained in the present testsof water sorption and solubility. Only Promysanabsorbed significantly less water than the remainingmaterials. Szabo et al30 indicated that heat-polymerizeddenture base materials complied with the requirementsfor water solubility and water sorption of the standardISO 1567. However, the authors also showed that heat-polymerized denture base materials with surface coatingpolymers led to a significant reduction of the values. Thevalues of water solubility and water sorption obtainedfor heat-polymerizing materials were 5 times better thanthose of autopolymerizing acrylic resins.

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Currently, there are a range of alternatives to thePMMA-based heat-polymerizing denture base materialsavailable. This in vitro study demonstrated that some ofthese materials represent an alternative to the classicPMMA resins for patients who are allergic to MMAmonomer. In this study, significant differences inresidual MMA monomer, water sorption, and solubilitywere obtained between different brands of materialsused for denture bases. To overcome the limitations ofthe in vitro tests, denture base materials must beevaluated intraorally. Further investigation regardingother properties of these materials is necessary.

CONCLUSIONS

Within the limitations of this study, the followingconclusions were drawn:

1. Modified methacrylate-based denture base resins(Polyan, thermoplastic and Sinomer, heat-polymer-ized) exhibited a significantly lower residual monomercontent than the heat-polymerized PMMA material(Paladon 65) tested.

2. The enterephthalate-based (Promysan, thermo-plastic) and the polyurethane-based denture basematerial (Microbase, microwave-polymerized) did notcontain any detectable residual MMA monomer.

3. Water sorption of the hypoallergenic denture basematerials (Sinomer, Polyan, Promysan, and Microbase)was as high as or above the results obtained for thePMMA material.

4. Only the enterephthalate-based material (Promy-san, thermoplastic) exhibited significantly lower watersolubility than the PMMA material (Paladon 65).

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77

THE JOURNAL OF PROSTHETIC DENTISTRY PFEIFFER AND ROSENBAUER

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DR PETER PFEIFFER

DEPARTMENT OF PROSTHETIC DENTISTRY

SCHOOL OF ORAL MEDICINE

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1

Complications of deand associated riskMcDermott NE, ChuImplants 2003;18:84

Purpose. This study sought to identify the types, freqfollowing placement of dental implants. It was hypothare associated with an increased risk for complicatiooutcome.Materials and Methods. A retrospective cohort studBicon implants (Bicon, Boston, MA) between 199demographic, medical history, implant-specific, aComplications were grouped into inflammatory, proproportional hazards regression models were developeResults. The sample was composed of 677 patients. Th(10.2% inflammatory, 2.7% prosthetic, 1.0% operative)revealed that smoking, use of 1-stage implants, and recan increased risk for overall complications (P\or =.05(range 0 to 85.6 months).Discussion. A lower frequency of complications was foreports. Investigations examining the influence ofcomplications are recommended.Conclusion. Of the 3 factors associated with an incrstaging may be modified by the clinician to enhancePublishing.

Noteworthy Abstractsof theCurrent Literature

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0022-3913/$30.00

Copyright ª 2004 by The Editorial Council of The Journal of Prosthetic

Dentistry

doi:10.1016/j.prosdent.2004.04.003

ntal implants: identification, frequency,factorsang SK, Woo VV, Dodson TB. Int J Oral Maxillofac8-55.

uencies, and risk factors associated with complicationsesized that one or more factors could be identified thatns and may be modified by the clinician to enhance

y design was used that included patients who received2 and 2000. Predictor variables were grouped intonatomic, prosthetic, and reconstructive categories.sthetic, operative, and major or minor categories. Coxd to identify risk factors for complications.e overall frequency of implant complications was 13.9%

, of which 53% were minor. The multivariate Cox modelonstructive procedures were statistically associated with). The median duration of follow-up was 13.1 months

und compared to mean frequencies calculated from pastsmoking and reconstructive procedures on implant

eased risk for complications, tobacco use and implantoutcome.—Reprinted with permission of Quintessence

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