Force Versus Time Of heat processed liner

8/14/2019 Force Versus Time Of heat processed liner

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Force Versus Time Profi lesof Selected Heat-ProcessedDenture Liners

Raleigh A. Holt. DMD 'Christian C. Zylinski, ODSManville G. Dunca nson, r, ODS , PhD'University o OklahomaCollege of Den tistryP Box 26901OklahomaCity Oklahoma 73190

The potent ia l corre lat ion of the force versus time beh vior offour resi l ient l in ing mater ia ls and their acceptance hy pat ientswas invest igated. Two modif ied acry l ic resins and twosi l icone denture l in ing mater ia ls were tested. The response ofthe sof t l in ing mater ia ls to a programmed indentat ion testwas used to def ine a parameter for each denture l inerproduc t . A parameter def in ed as the R eb ou nd Inde x, us ingforce- t ime data obta ined f rom the indenta t ion measurements ,was s igni f icant ly d i f ferent for the modif ied acry l ic resinscompared to the s i l i cone mater ia ls . Improved pat ien tacceptance was cor re la ted wi th h igher va lues o f th is index.Intj Prosthodont ]99I;4:164-168.

everal authors have suggested requirem ents forresilient materials used as denture base liners.'''These requirements have included dimensionalstability in processing and oral use, permanentresilience, minimal absorption of oral fluids, andadequate bond strength to the denture base. Theliner materials should also be hygienic, odorless,tasteless, nonirritating, and nontoxic.One of the first materials used for a denture linerw i th ac ry l i c res in den tu res was p las t i c i zedpoly(vinyl]chloride.' Many varieties of plasticizedacrylic resins and silicones have also b een used asdenture l iners. Investigators have studied themechanical and physical properties of these mate-rials.' ^ There have been numerous clinical evalu-ations of soft-lined prostheses reported in theliterature.^ ''' Others have review ed th e physicalproperties, use, and manipulation of resilient linersfor dentures.'^ '*'

Past research has illustrated that it is difficult touse a single physical p roperty for the d eterm ina-tion of the clinical success of a denture liner.'However, many clinicians have assumed that thet ime-dependen t shape- recove ry behav io r o fheat-cured resilient liners is related to the liner's

'AssociateProtessor ofRemovable Prosthodoritics.

potential for ridge adaptability and clinical scess.' '* '^ Shape changes in denture liners accompanied by an instantaneous compon(res i liency) and a t ime -dep end ent com pon(recovery).^ Wilson and Tomlin' used indentatand shape-recovery tests to evaluate the reiency of soft l iner materials. They theorized ta denture l iner material must have the abil i tyreturn to its original shape as completely as psible after it has been compressed. Their evaation of several acrylic resin and silicone dentliner materials under simulated oral conditishowed that appreciable recovery occurred formaterials. They concluded that the materials msuitable for cl inical use were soft and completrecovered the i r shape a f te r compress ion. material tested possessed both of these charteristics. Eick et al^ evaluated resilient materfor recovery and any appreciable f low fol lowthe application of compression forces for varyperiods of time. Several resilient materials wcompressed for 24 hours, and their recovery wmeasured at1 minute and1 hour intervals. Macryl ic resin materials showed incomplete recery even after 1 hour. The si l icones sh ow ed greatest total recovery within 1 minute.

Even though many tests have been performto characterize the behavior of resilient materused for denture liners, no parameter to acc


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Vs Tim e Profiles ol He at-Cured Denlure Line

us ing se lec ted denture l iners to de termine aparameter for characterization of these materials.A programmed indentation test was used on thedenture liner material, in situ, and a specificparameter was obtained for comparison of thevarious liners tested.Materials and Methods

Table lists the denture liners used in this study.They were evaluated, insitu, on complete mandib-ular dentures wo rn by patients requ iring this m etho dof treatment. Each patient's mandibular denturebase area was divided at the midiine. The two sil-icones and the tw o acrylic resin soft lining materialswere paired, since they have similar chemical clas-sifications and laboratory processing procedures. Italso allowed for intrapatient evaluation of two dif-ferent products.Patients who could not satisfactorily wear a hardacrylic resin denture base were obtained from theUniversity of Oklahoma College of Dentistry Stu-dent Cl in ics. These pat ients were a l ternate lyassigned to the acrylic resin gr ou p or the silico negroup . These patients we re we aring dentures thathad been fabricated in the student clinics within a6-month interval prior to this investigation. The cri-teria for the patients' dissatisfaction were 11) theinability to wear their mandibular dentures for aperiod of 6 hours wit ho ut soreness, requiring adental visit for adjustment, and (2) inability to chewa soft-solid diet consisting of soups, cooked vege-tables, and ground meat.A previously described functional impressiontechnique with Lynal (LD Caulk Co, Milford, Del-aware) was used to make a final impression for thereline of the mandibular d entures, and a wa x-shim techn ique was used to place the resilientmaterials for processing onto the denture s.' The

Tab le 1 Heat-Processed Denture Liners StudyGroupProduct Name Type Manufacturer

Protech Acrylic Pro tecfi, Incresin Cen terreach, NYCoe Super-S oft Acrylic Coe Labo ratories, Incresin Chicago, ILProlastic Silicone Young Dental Produ ctsivlaryland Heights. MOfwiolloplast B Silicone Regeneri S CoGermany

w ax-s him technique was used to ensure a properthickness of the soft lining materials in each denturebase. A brief review of the procedure follows.After wax elimination procedures and recovery oftbe denture from the flask, tinfoil substitute isapplied to the master cast. The cast is allowed tocool, and a wax shim is placed on the master castin the areas where the denture lining material isdesired. Sheets of record base are placed approxi-mately 2 mm thick, and a periodontal probe is usedto measure this thickness. The denture base thick-ness is reduced to allow space for additional acrylicresin. This procedure permits filling of the denturebase area with hard acrylic resin, except in the areaof the wax shim. The new acrylic resin is benchprocessed for 4 to 6 hours. The flask is then ope nedand the wax shim removed. The denture lining

material is placed in the space left by removal ofthe wax shim, and the flask is closed under rec-ommended pressure and heat processed. Fivepatients received soft liners of the modified acrylicresin types (A and B) on each half of their dentures,and four patients received soft liners of siliconetypes (C and D) on each half of their dentures (Fig1). Identical home care instruction sheets weregiven to all patients and reviewed with them.

Fig 1 Five patients receivedsoft l iners of the modi f iedacrylic resin types (A and B}on eacfi half of tfieir de ntures,and four patients recervedsoft l iners of t f ie s i l iconetypes (C and D| on each half


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Force Vs Time Proliies of Hoat-Curcd Denture Une

A mechanical testing instrument (Model 1135,Instron Corp, Canton, Massachusetts) was used toperform the indentation tests on the soft-lined den-tures. An orientation plate was machined for place-ment on the platen of a 2,000-g load cell.The platewas constructed to fit a modified surveyor so thata plaster index co uld be fabricated for each dentu re.Each plaster index was designed to locate an area

of denture liner on the buccal flange of ihe dentw ith a 2,0-mm thickness. An indentor ,0 m mdiameter was used to indent this arej on each dture base at the time intervals of the tests (FigFach denture was tested before clinical placemand then retested at 7, 32, and 92 days followplacement. The indentation tests were conducon the dentures after temperature equilibration

Fig 2


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V i Time Profiles of Heat-Cureri Demure Lir

Table 2 Mean Values and Standard Deuiations tor Parameters Studied

ProductABCD

MaximumforceF .(kg)0 .47 0.120.42 0.120.91 0.180.98 0.20

MinimumforceF_ (kg)0.37 -^ 0.090.36 -^ 0.100.84 -^ 0.170.89 0.18

Timet,(sec)

115 29138 30136 1 23U l 18

Rebound indexF 11

56.82 + 1464.29 * 989.63 15

F , ^ maximum recorded iorce load afer loading @ 0 02 in/mm.F. = reco rded Iorce after (iie relaxation interval.I = loading time interval = 120seconds.t = unloading time interval.

37C for 5 minutes. T he dentures w ere placed ontheir individual indices on tbe orientation plate (Fig3). For test uniformity, tbe area selected for inden-tation was preloaded to 90 g to ensure comparableinitial indentor contact. With an Instron crossbeadspeed of 0.02 in /m in , the selected area of the soft-lined denture was continually loaded for a periodof 2 minutes. Tbe indentor was beld at this p ositionfor another m inute, and an observation of the force-relaxation phenomenon of the liner materials wasrecorded. After this relaxation interval, the unload-ing, at 0.02 in/min, was performed until the forcerecording was 0, Recording of the force versus timedata was accom plished w ith an X-Y recorder (M odel7005B, Hewlett Packard, Mountain View, Califor-nia), set at a chart sp eed of 10 seconds pe r inch (0.1in/sec). An example of a typical graph recordingduring a test cycle is shown in Fig 4.

measured and used in the statistical analysis arelisted and defined in Table 2.Means and standard deviations we re obtaine d forthe calculated Rebound Indices to compare theproducts. A one-way analysis of variance indicatedthat a statistically significant differe nce existedamong the four means (F = 21.49, df = 3, P > \^= .0001). A specific comparison test was then per-formed to rank the products and determine signif-icant differences wit h respect to the Rebound Index.The significance level for this analysis wasP< .05.A p lot of the value of the Rebound Index as afunction of time is shown in Fig 5. Considerablevariation in the value of the Rebound index can beseen at the different time intervals. At one obser-vation interval, namely 7 days, the value is greaterthan 1 00 . F ,7F ,^ is still less than 1 , but the ratioof t|/tî is greater than 1.0 because of the greater

ResultsThe Rebound Index (Rl) is defined by the follow-

ing equation:RI = - ^ X X 100

This equation stems from an examination of themeans of the experim ental data. Obse rvation of thedata for F^,, F , t i,and t, support the fact that fortheir means, F, < F and t, < t,. Since this istrue, the ratio of Fî/Fîs also less than 1 for F^,.not equal to 0. F^, > 0 and F ^ > 0; therefore,the ratio of F^,/F^ is between 0 and 1, since F^,n< F^^. Also, t| > 0 and t, > 0; therefore, the ratioof tî/ti 5 also b etw een 0 and 1, since t| < t,. Theproduct of the two rational numbers (F,n/F^J(tî/t|) will therefore be less than 1 and greater than 0.This prod uct times 10 0 is defined as the ReboundIndex and is asserted, and supported by the data,to distinguish amo ng the com positional types of the

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32 92

Time Wear (days)

Fig 5 Plot of the value of the Rebound Index as a tunctionof time. A. Protech; B, Coe Super Soft; C, Prolastic; D, Mol-


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Force Vs Time Proliiesof Heat-Cured Dentun

time required for loading in relationto the t imerequiredtorunloading. Isolated occurrencesofthisnatureareassumedto be relatedlo the intrinsicviscoelastic p roperties of the ma terial, wh ich are yetto be investigated. Ho weve r, Ihe preponderanceofthe data points toward theReboun d Index lyingwithin the interval0 to 1.No regular specimen dimensions exist that couldallow the useofviscoelastic equationsforthe com -pu ta t i on of t ime -d epen den t p rope r t i es .TheRebound Index calculation makes some assump-tions that couldbecalled into que stion.If the loadand un load curves are considered triangles, the loadcurve wo uld represent the work doneincompress-ingthe reline materialand the unload curvetheenergy released after the re laxat ion t im e.Theenergy relationships, or work d one, w ould be: W orkdone in compressing = 1/2F^J (tj. However,

since the load curveis not atriangle, the equa tionmust be modified to:1/2 F^^,] R,), wh ere R, mustbe less than1.0andis acorre ction factor, the ratioof the actual area beneaththe load curve to thetriangular area.Similarly,theunload curve expressionis:energyreleased in decompressing = 1/2 (F^J (tJ (R ),whe re R; is a similar co rrection factor for the unloadcurve. Taking the ratio of work done in comp ressionto energy released after minute relaxation resultsin the equationforthe Reb ound Index onlyifR,=

R;. How ever, the co rrection factors are probably notcalculable under the conditionsof this indentationtest.Sum mary and onclusions

The Rebound Index separatesthedenture linersinto twodistinct groups, w hich elicited differentclinical responses.Thesame criteria und er whic hpatients were selectedforthis study we re usedtoobserve the clinical experiences of the patientswear ing thevar ious den ture l in ing mater ia ls .Patients who used productsAandBcontinuedtoexperience soreness that req uired adjustments after6 hoursof use. These patients reported very littleimprovement in their ability to chew a soft-soliddiet. Patients with productsC and D reportednosoreness requiring adjustmentsof the liner materialduring the 92 days of this study. On the other hand,allof these patients had improved abilitytochewa soft-solid diet. Theden ture liners used in thisgroupof patients had higher Rebound Indices thanthoseofproducts A and B. After 92 days, all pa tientswere givenachoiceofden ture lining materialsfor

material.Allpatientsingroup C -D requested e ithCor D materials. After receiving product C orpal ients in g roup A-B show ed s imi lar c l in icimprovement as group C-D,Although one parameter does not necessarmake a denture lining material acceptableorunaceptable for clinical use, the Rebou nd Indexd

separate these heat-processed soft liners intotwdistinct groups. The higher R eboun d Indicesproducts C andD did correlate with improved cliical performance, eg,nonsymptomatic wear t imand increased chew ing ability. Althoug h the sampsizeof this study wassmall, th ere is evidencemerit further investigationofthe usefulnessof Rebound Index parameter.

References1. Wilson HJ, Tomlin HR: Soft lining materials: Some relevproperties and their determination. / Prosthet DI969;21:244-25O.2. Craig RC, Gibbons P: Properties of resilient denture line

/Am Dent Assot 1961;6:382-39O.3. Lammie GA, Storer R: Preliminary report on resilient delure plastics. / Prosthet Dent195 :SA ft-424.4. Srorei R: Resilient denture base materials. Fr DenI962;i13:195-2O3.5. Eick ID, Craig RG, Reyton FA: Properties of resilient deture liners in simulated mouth conditions. / Prosthet D1962;12:1O43-1O52.6. Schmidt WF, 5mith DE: A six-year retrospective study

Molloplast B-lined dentures. Part II: Liner serviceabilityProsthet Dent 1983;50:459-465.7. Matthews E: Soft resin lining for dentures. Br Den]945;7B:I4O-145,8. Robinson JE: Clinical experiments and experiences wisilicone rubber in dental prostheses. ; Prosthet D1963:13:669-675.9. Means CR, Rupp NW, Paffenbarger GC: Clinical evalution of two types of resilient liners on dentures. Mm D

Assoc l971;e2:1376-1380.10. Wrigbt PS: The success and failure of denture soft-linmaterials in clinical use, /Dent 1984;12:319-327.1 1 . Bascom PW: Resilient denture base materials. ;Prost

Dent ]9 6;16:646-649.12. Segall BW, Glassman A: Use of a medical-grade silicomucosal irritation. / ProsthetDenf 1982:47:85-87,13. Crum R), Loiselle R|, Rooney GE: Clinical use of a resililined mandibular denture, / Am Dent Ass1971;fi,1:1093-1096.14. Duncan |D, Clark L: The use of a soft denture liner chronic residual ridge soreness. ; Am Dent Ass1985:111 64-65.15. Laney WR: Processed resilient denture. Denf Clin No

Am1970;14:531-551.16. Gonzalez |B, Laney WR: Resilient materials for dentuprostheses. / Prosthet Dent 1 966,1 6:438-444.17. Makila E:Soft linings to relieve soreness beneath dentur/ Ora; Re/ia/V ]976;,:145-I5D.18. Holt RA, Stratton R), McBride C: Impression techniq


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Force Versus Time Of heat processed liner

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