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Impact Absorption of FourProcessed Soft DentureLiners as Influenced byAccelerated Aging

FumistiiKawano,DDS PhD'AndrewKaran,ODS MS**Archadinn Nuryanti,DDS MS*Sanshiiro Inoue, DDS 'University of MiM ganAn nArbor Michigan; andUniversity ofTokushimaTokuihima,japan

The cu shio ning effect of soft denture l iners was evaluated hy using a freedrop test with an acceierometer. Materials fesfed included SuperSoff (CoeLaboratories, Chicago, iL), Kurepeet-Dough (Kreha Chemical, Tokyot,Mo iteno Soff (M olten, Hiros hima, Japan), and Mo l lopla5f -B [Mol loplastRegneri, Karlsruhe, Germanyl. All materials were found to reduce the impactforce when compared to acrylic denture base resin. A2.4-mm layer of softdenture mater ia l demonstrated good impact ab sorpt ion, and Mol loplast -Band Mo iteno had excel lent impact ab sorpt ion. Wh en the soft denture l inerwas kept in an acceierated aging chamber for 900 hours, the damping effectrecorded increased for aii materials tested. Aging o f all m aterials also affectedthe cushioning effect. Int i Prosthodont 1997:10:55-60.

e t h y l / e t h y l m e t h a c r y l a t e , s i i i c o n e , a n dpo lyphosphazene f luo roe las tomers havebeen used as soft denture liners to assist in a moreeven distribution of functional forces and improve-ment in denture retent ion by engaging under-cuts.^'^ Because the laboratory-processed materialsgenerally retain tbeir softness in vivo, tbey havebeen used as long-term denture liners for manage-ment of sore or atrophied mucosa, traumatic ulcr-ation, and for obturators after maxillofacial surgery.However, these materials cannol be used for ex-tended periods of time because of change of prop-erties, colonization by Candida aibicsns, and poortear strength.'-^

Aislant Professor, Department of Rem ovable Pros-thodontics, University ofTokushima Schoofo fDenlistry.Professor, Departmen t of Prosthodontics, University ofMichigan School ofDentistry . 'Research Student Departmento iRemovableProslhodontici,University ofTokushima Schoolo fOentistry.

eprint requests: Dr Funiiaki Kswano. Departmen t oemovable- Pmsthodontics University of Toi

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npatt Aluo rptioii nf Soli Denlurt Line

Ta ble 1 List of Mater ia ls and Man ufacturersMaterials Manufacturer TypeSuperSoft Coe Laboratories Plasticized PMMAChicago, ILKurepeet-Dough Kreha Chemical FiuoropolymerTokyo, JapanMolteno Soft Molten Polyorep hinHiroshima, JapanMolloplast-B Moliopiast Regneri Heat cure siiiconeKarlsruhe, Germany

Materials and MethodsFour soft denture liners were chosen on the basisof different chemical components (Table .Dentalstone molds were made in a denture flask by in-vesting wax patterns of the shape and size of thedesired specimen. Ten 1.2-mm-thick disks and 102.4-m m-th ick d isks, 20 mm in d iameter, weremade for each material. The soft denture linerswere mixed, packed, and processed according tothe manufacturers' instructions. Molteno Soff wasput into a handpress and held for 5 minutes afterthe material was preheated for minutes. Afterpolymerization, all specimens were removed fromthe flask, and any flash was trimmed with a sharpblade. Five samples were made for each materialfor each test condition for a total 80 specimens.Forty specimens were stored in distilled water it37C r C for 24 hours. Another forty specimenswere stored in a Weather-Ometer (Model 25 W R,Atlas Electric Devices, Chicago, IL) for 900 hours,as recommended by Yu et al.^-* The samples werecontinuously exposed to a visible ultraviolet light(2500 Watt xenon light source with borosilicate fil-ters) and sprayed with distilled water for 8 minutesin every 120-minute cycle. The humidity in thechamber was m aintained at 90 % , and the tempera-ture at 43C. The impact absorption of soft dentureliners was determined before and after weathering.Five 1.2-mm-thick and five 2.4-mm-thick, 20 mmin diameter, poly(methyl methacrylate) hard resin(PMMA] (Acron, GC, Tokyo) specimens also weremade as controls according to manufacturer's in-struction.

The test instrument consisted of a resin block, anaccelerometer mounted on the resin block, and anelectromagnet at the top of the resin support (Figsla and Ib). A titanium abutment 7 mm in diameterwas screwed into the middle of the accelerometerimpact cap. The position of these components washeld constant during the study. Fach specimen wasf ixed to the abu tment us ing a cyanoacry la teadhesive (Aron Alpha, Toa Chemical, Tokyo). An

electromagnet 150 mm above the specimen held a10-mm-diameter, 5.5-g steel ball , which, when re-leased, fell in the center of the specim en. The samesleel ball was used for all tests. The position of theresin block on which the specimen was mountedcould be adjusted so that the length of travel of theball was constant.A shielded cable connected the accelerometer toa personal com puter (PS 9000 Mod el 310 M, TEAC,Tokyo) with an A/D converter (DM-7100, IwatsuElectric, Tokyo) for recording the complete accel-eration response. The insfantaneous acceleration offirst wave acceleration response was measured anddefined in C (unit of acceleration). Smaller G unitscorrelate with greater impact absorption.The tests were carried out at 24 hours after pro-cessing and 900 hours after weathering. For PMMAspecimens the test was performed at 24 hours.Mean values for each material at each test condi-tion were compared using a three-way analysis ofvariance and ca lcula ting the Tukey interval^ '* atP< ,05 to compare all experimental groups.

ResultsTables 2 and 3 show the ranking, instantaneous ac-celeration, and standard deviation for the materialstested. At 24 hours after processing the peak forceranged from 6.5 to 365.9 G for the1.2-mmsoft den-ture liners and fro m . 3.1 to 327 G for the 2.4-mmsoft denture liners. After weathering, the force peakranged from 2.2 to 120.0 G for1.2-mmsoft dentureliners and from 1.1 to 95.1 G for 2.4-mm speci-mens. The rank order of the soft denture liners wasthe same at both 24 hours and 900 hours.

The m ean value of the acceleration for the den-ture base resin was 795.0 58,5 G for the 1.2-mmspecimen and 652.0 28.6 G for the 2.4-mm spec-imen. The ratio of the shock absorption for eachmaterial was calculated by following equation;Ratio of shock absorption (7u)=

Accelerat ion Accelerat ionof resin - of soft linerAccelerat ion of ream X 100

The results of this calculation are shown in Table4. This ratio indicates the material impact absorp-t ion. Molteno Soft and Molloplast-B demonstratedgood impact absorption, and SuperSoft showed theleast impact absorption. However, the impact forcetransmitted to the transducer through SuperSoftwas 40% that of denture base resin. After weather-ing, the impact absorption of the soft denture liners

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Elect rcmagne l

SpecimenAccelerometer

Stee l ba l l

,Tifanium autment

KiiW iijiQc l ,il Impact Abs orplifin ul Suft Denture Liners

Figs la and 1b Testing apparatus left)and the measuringsystem above).

Table2 Maximum Acceleration of the Sott DentureLiner at 24 Hours After Processing

MaterialsSuperScttKurepeet-DoughMolteno SottMolloplast-B

1 2-mmdenture liner365.9187.217.0

6. 5

(G )44.5)(18 .5 )

(1-9)(1-3)

2 . 4 - m mden tu re l ine r

(G )3 2 7 . 01 2 3 . 7

7. 83 .1

(35 -8 )(15 .4 )

(1 .0 )(0 .5 )

Connecling bars ^ no significant difference (P > .05}. Tukey intervals.between materials = 12.8; between thickness = 6.5.

Table 3 Maximum Acceleration of the Soft DentureLiner at Weathering for 900 Hours

via teria lsS u p e rS o t tK u r e p e e t - D o u g hMo l t e n o S o f tMo l l o p l a s t -B

I a mmden tu re l ine r

(G )19.87 9 . 910 .1

2 .2

(15.01(14 .5 )

(1 .4 )(0 .5 )

2 4 - m mden tu re l ine r

(G )95 1 (12 .3 )61-1 (3 .3)

5-6 (0.4)1-1 (0.7)cting bars = ro significant flitterence (P > 05) Tukey intervals:between materials = 12.9; between ttiJCkness = 6 5.

increased. SuperSoft and Kurepeet-Dough showedthe greatest change, although aging did not affectthe soft denture liner rankings.Three-way ANOVA showed that the materials,thickness, and aging all significantly affected accel-eration and calculated shock absorption (Table 5).However, signif icant interaction between materi-als, thickness, and aging was not observed. TheTukey Intervals were calculated to compare allgroups (see Tables 2 and 3).

Significant differences were observed betweenall materials except between Molteno Soft andMollop last-B. No s igni f icant d i f ference was ob-served between Molloplast-B at 24 hours and be-tween Molteno Soft and Molloplast-B after weath-ering as a function of thickness while SuperSoftand Kurepeet-Dough were signif icantly different.Thicker SuperSoft and Kurepeet-Dough specimensdemonstrated a good cushioning effect.

Table 4 Impact Absorption ot Soft Denture Liner as aFunction ot Thickness and Weattiering

Materials24 hours after processingSuperSoftKurepeet-DoughMolleno SottMolloplast-BAfter weathering for 900 hoursSuperSottKurepeet-DoughMolteno SottMolloplast-B

1 2 mmdenture liner(% )62.180 698.298.287.691.799.099.8

2.4-mmdenture liner(% )62.285.799 19 9 . 08 9 . 09 2 . 99 9 . 499 .9

Connecting bars = no significant difference {P> .05).

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Ahsr>rption of Soft Dcntiiro Liners

Table Result of Three-way ANOVA of Accelerat ionDegrees offreedom Sum otsquares Meansquare

M aten als (A)Thickness (B)g [CA X BAX CB X CAX X CError

3tt33136 4

663615.58399.1137460.75355.618432S.91356.21421.01S294.1

221205.28399.t137460.71785.261443.01356.2473.7239.0

925.735.1575.27.5257.15.72 0

.0001.0001.0001.0002.0001.0302.1255

DiscussionSoft denture liners are used fo reduce impact forceson denture-bearing mucosa,'""'- The data from thefree-drop acceleration test used in this study reflectthe impact-absorbing behavior of each material.'^A reduction in the value of the acceleration mea-sured implies an increased cushioning effect of thesoft denture liner.At 24 hours after processing, the force peak forKurepeet-Dough was approximately half of thatfor SuperSoft. The force peaks for Molteno Softand Mol loplasf-B were less than O.O. i that forSuperSoft. It is interesting to note that the impactforces transmitted to fhe transducer through softdenture liners were less than 40% of those of den-ture base resin. Molteno Soft and Molloplast-B ab-sorbed most of the impact force applied, and,therefore, had the greatest impact absorpt ion(Table 4).Figures 2 and present the results of the Tukeyinterval for the comparison of means at 24 hoursafter proce.ssing and at 900 hours after weathering.The maximum impact force of SuperSoft, Kurepeet-Dough, and Molloplast-B at 900 hours was aboutone third that at 24 hours after processing. Themaximum impact force of Molteno Soft at 900hours was about two thirds that at 24 hours after

processing. The impact absorption of all soft den-tu re l i ne rs inc reased a f te r wea the r ing , andSuperSoft showed the greatest change. The impactabsorption of SuperSoft and Kurepeet-Dough in-creased after weathering (25% and 10%, respec-tively}, regardless ofthe specimen thickness, whileMolteno Soft and Molloplast-B had less than a 1%increase. However, the aging (weathering) did notaffect the impact absorption ranking of the softdenture liners. In a previous study, the impact ab-sorption of the four soft denture liners was deter-mined at 80 days after storage in the 37C dis-tilled water,^^ In that study, the shock absorptionfor four processed soft denture liners also increased

after 180 days in water.'^ The results of this studysupport those of the previous study.Water spray and visible ultraviolet light have adirect effect on the properties of soft denture linersand cause them to swell. Although water sprayand high humidity may affect impact reaction bywater sorption, the visible ultraviolet l ight mayscarcely alter the elastometric morphology and af-fect the impact absorption. Compared to the previ-ous study, there was no difference in impact ab-so rp t ion a f te r the wa te r immers ion tes t o raccelerated aging. Water sorption and solubility ofsoft denture liners are important factors that mayalter the physical properties of soft denture lin-ers. '^"' ' ' The leaching of plasticizers may increasethe stiffness and hardness, which may explain whythe hardness of SuperSoft and Kurepeet-Dough in-creased markedly with t ime.^^ Since the impactforce for each material decreased at 900 hours. Itmay be reasonable to conjecture that soft dentureliners that have absorbed water may act as betterdamping materials.Other factors equally affect the ability of softdenture liners to absorb impact. Resiliency, creepcompliance, and dynamic modulus are also impor-tant factors. In addition, the design of the soft den-ture liners' basal surface cannot be ignored. Thesefactors are currently being studied.It is clear that soft denture liners reduce the im-pact force transmitted to the supporting structuresand act as damping materials. In particular, the sili-cones are known to demonstrate excellent impactabsorption. Since sofl denture liners may affect forcedistribution during function, it is essential to choosethe proper materials and consider soft denture-linerthickness. Although the water absorption and accel-erated aging increased the stiffness of the soft den-ture liners, the function of the soft denture liners asdamping materials was not influenced by either fac-tor. The results of this study support the use of softdenture liners to protect denture-bearing mucosafrom unnecessary impac t force.

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Kawano et al Inip.ict Atisorp tion of Soil Denture tin e

2 Aocelera fion of 1.2-mm-

P > .05); Tukey inlervai =

SuperSott Kurepeel-Dougfi Molteno Sofl fulolloplast

3 Acceleration o 2.4-mm-

{P> .05); Tuf^ey interval

SuperS ott Kurepeet-Dough fulolteno Soft /oiloplasf-B

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Impacl Alsoiption of Soit Denturelu

Conclusions1 . Molloplast-B and Moiteno Soft had greater im-

pact absorption than SuperSoit or Kurepeet-Dough.2. Thicker liners (2.4 mm) were more effectivethan thinner liners (1.2 mm) in decreasing im-pact forces.

3. In a comparison of the acceleralion measuredat 24 hours and at 900 hours, the accelerationof SuperSoft and Kurepeet-Dough decreasedsignificantly at 900 hours. However, there wasno significant decrease in acceleration ofMoiteno Soft and Molloplast-B.

4 . Accelerated aging favorably affected the impactabsorption of all the soft denture liners evalu-ated in tbis study.

References1. Crum RJ,toi5sei[eR I,KooneyRE |r. Clinical useofaresilienlmandibular denture.IAm Denf Assoc1971 ;B3:]093-1096.2. CraigRC. Restorative Dentai Maferiais, ed 8. Sf Louis: Mosby,1955:541-544.3. HirasawaT,H irabayashi S. Ein berblick berdie ver-schiedenen protbesen Unterutterungsmateiialien und ihreKlassifizierung aus maferialwisserschafflicher Schift (11).Quintessenz Zahniecb 1990; 6:59-73.4. Travagliri G, Gibbons P, Craig RG. Resilienl liners for den-tures.I Prosfhel Dent1960;10:664-672.

5. Cr jig RG, Gibbons P. Propertiesof resilierl rl.niuie liners.|Am D eri A sso d 961,63:382-390.6. Eicii ID, Craig RG, Peyfon FA. Propertiesot rMii--nt dentureliners in simulafed mouth condif ions.I Prosthef Denff962;12:104 3-1052.7. Bafes )F, Smitb DC. Evalualionof Indirect resilient linersfordentures: Laboratory and clinical fesis.I AmDenf Assoc1965;70:344-353.f . Doofz ER, Koran A, Craig RG. Comparisonofpiiysicai prop-ertiesof 11 sofl denfure liners.I Prosfbel Deni ]992;67;707-712.9. Kawano F, Tada N, Nagao K, Malsumoto N. Infiuerceofsoftfining malerialsonpressure dislribulion. J Proslhel Dem[991;6S:567-575.10. Parker HM. Impacl reductionmcomplete and partial den-lures: A pilot study.J Proslliet Dent1966;16:227-245.11. Plotnick IJ. Stress regulator for complete and partiai denlures.1Prosthel Dent 1967;l7:166-171.12. Kawano F, Koran A, Kon M, Matsumoto N. Shock-absorbingbebaviorof four processed soft denture iiners.JProstbet DentI994;72:599-6O5.13. Yu R, Koran A, Craig RG. Pbysical propertiesofmasillofacial

eiasfomers. I Dent Res l980 ;59t104 1-1047.14. Guenfher WC. AnalysisofVariance. Englewood Cliffs,N|:PrenliceHali,1964:31-63.t5 . Kazan i MN M, Watkinson AC. Soff i in ingmaterials: Their ab-sorption of and soiubiiity in artificial saliva.GrDenf|1988;165:91-94.16. Hirabayashi S, Nomoto R, Ohkubo K,Hirasawa T. Fluidityand waler absorptionofsoft lining materials for denfure bases|in Japanesel. TurumiShigaku 1990;I6:305-311.17. Kawano F, Dootz ER, Koran A, Craig RG. Sorption andsolu-bility of 12 sofl denture liners.| Proslbet Dent 1994;?2:393-398.

LiteratureAbitraa ealing of apical periodontitis in dogs after apicoectomy and retrofiilingwith various filling materialsTfiis sfudy evaluated tissue response to various retrofiiling materials usedinapicai su rgeiy.The puipsofmandibular premoiarsofseven beagie dogs were exposed fo induce apicalperiodonfitis. Affer a periodol Imontfi, ninefy retrograde fillings were performed. There were7 exprimentai groups: 1)super EBA; 2) glass ionomer formula1 ; 3) amalgam wiiti var-nisti; 4 }IRM:5 )giass-ionomer formuia 2; 6resin com posife; and 7)positive controi-re-section without refrofiil. The an imais were sacn ficed6months posfsurgery. The histologiesfudies were conducted in two categories: percentageofbone and numberofinflammaforycells/mm^ The resulfs demonsfrated thaf fhe percentageofbone around super EBA, IRM,and amalgam was greafer than the other groups. The numberofinflammatory cells aroun dthe super EBA was less fhan all groups. Ten percenf ol fhe roots were lost and excludedfrom the results becauseofthe developm entofperiodontal pockefs wifhin 2 weeks affersurgery.TropeM LoslC,Sohm iti H-J, Friedma ns. J Ora//Han/loac Sur^ 1996:54:486-494 References: 13HeprinfB:Dr Triplett, Departmerl ofOral SMaxillofacial SurgeryandPharmacology, Baylor College otDerfistrv.POBox 660677, Dallas, Texas.M LTtieerattiavaiSfithsvS). MS,DDS dvancedEducational Program in Prosthodontics. New York University CollegeofDentistry Ne w York New Yorh

IofPro&thodontrt 60 V Q l u m e l O , N j m b c r 1 . 1997