A Study of the SurfaceHardness and

Dimensional Stability ofSeveral IntermaxillaryRegistration Materials

/ohn Chai, ,

Edwin Tan, BDS"

Northwestern University Dental SchoolChicago, Illinois

lok-Chao Pang. BDS, MS—

Taichung Veterans General HospitalTaichung, TaiujanRepublic of China

This study compared the surface hardness, the effect of time on surfacehardness, and the dimensional stability of various intermaxillary relationshipregistration materials. The Shore hardness values of one zinc oxide-eugenolmaterial, one polyether, and seven poly(vinyl siloxane! materials wereobtained at 30 minutes and 24 hours after the start of mixing. Thedimensional stability of one polyether and seven poly(vinyl siloxahe)materials was measured using a standard mold as described in AmericanDental Association (ADA! Specification No. 19. All materials exhibitedrelatively high surface hardness despite some statistical differences amongthem. Four materials possessed higher surface hardness at 24 hours than at30 minutes. Although the polyether showed significantly lower dimensionalstability than the other materials, all materials satisfied the minimumrequirement for Type I elastomeric impression material,int I Prosthodont 1994:7:538-542.

A n ideal occlusal registration material shouldprovide minimal resistance to mandibular clo-

sure during the registration of maxillomandibularrelationships to avoid distortion of the soft tissueand/or displacement of the mandible, and shouldallow a reasonable length of manipulation timewhen the viscosity of the polymerizing occlusalregistration material remains low. Once the materi-al is placed, it should polymerize to a degree ofrigidity that allows its removal from the mouthwithout distortion. The material should reproducedetails of the registration and be dimensionally sta-ble over time so that subsequent use of theocclusal registration is accurate. When theocclusal registration is used to relate the position ofthe dental casts on an articulator, it should be rigidenough to resist distortion that might result fromthe weight of the dental cast and the components

'Assistant Professor, Director of Advanced Educatian Pros-thodontics.

'*Craduate. Advanced Education Prosthodontia."'Attending Doctor, Department of Dentistry.

Reprint requests: Dr John Chai. Assistant Prafessar, Director ofAdvanced Education Prosthodontics, Northvfestern UniveriityDental School. 240 E. Huron Street. Chicago. Illinois 6061!.

of the articulator. This investigation focused on therigidity and the dimensional stability of maxillo-mandibular relationship registration materials.

Several materials and numerous methods havebeen used for interarch registration. Thermoplasticmaterials such as wax and modeling plasticimpression compound, when used alone, showedsignificant distortion as a result of the considerableamount of thermal shrinkage. The distortion alsoincreased with time. Accuracy of these materialsimproved when a zinc oxide-eugenol paste cor-rection was made. It was recommended that castsshould be related as soon as possible after the reg-istration.'-• Impression plaster was shown to bavegood dimensional stability over time." AlthoughLassila^ demonstrated that an acrylic resin distortedless than 0,3% for up to 72 hours. Miller et al 'found that dental casts related with an acrylic resinregistration were inaccurate, Polyether occlusalregistration material has enjoyed favorable criti-cism because of its excellent dimensional stabilityand accuracy in relating dental casts.'"' Its usewithout a carrier was shown to be more accuratethan with a carrier.' A disadvantage of using anelastomeric occlusal registration material is tbelack of sufficient rigidity when the dental casts arearticulated. Hence, an alteration in the relationship

The Inlernational tournai of Praslhodontii 538 Volume 7, Numbp

Hardness and Slabilily oí Inlermasillary RegisLralion Male

Table 1 Occlusal Registration Matenals Tested

Brand Material typeBatch

number Manufacturer

Bite registration paste

Pegisii PBBlu MousseStat BRRe'cordPresiden! Jet Bite

Regisil 2XMemosii CDRamitec

Zinc oxide-eugenoiType 1 tHardPoly (vinyl siloxane)Poiy(vinyl siloxane)Poly (vinyl siloxane)Poiy(vinyl siloxane)Poiy(vinyl siioxane)

Poiy(vinyl siioxane)Poiy(vinyl siioxane)Poiyether

1 1286/1 1309930611S43e31015092131563383

9211023806H/3794HT338

Ken, Romulus, Ml

LD Caulk, Miltord, DEParkeil, Farmington, NYKerr, Romulus, MlHatr/J. Boswonh, Skokie, ILColtene / Whaledent,

New York, NYLD Caulk, Milford, DECjtter/Miles, South Bend, INESPE / Premier, Norristown, PA

of the casts may result if the material is not usedproperly.' According to the manufacturer's sugges-tion, the rigidity of a polyether occlusal registrationmaterial (Ramitec, ESPE-Premier, Norristown, PA)improves with time, and its use to relate dentalcasts should be delayed until 30 minutes after thestart of mixing. It would be valuable to understandthe effect of time on the rigidity and dimensionalstability of interarch registration materials,

A Shore-A durometer (Shore Instrument &Manufacturing, Jamaica, NY) is an establishedmethod of testing the surface rigidity or hardness ofelastomeric polymeric materials,^ This instrumentregisters surface hardness by recording the resis-tance to indentation of the elastomeric materialtested. The Shore hardness units are quantified ona scale from 0 to 100, To the authors' knowledge,there are no published data on the hardness ofocclusal registration materials; however, typicalShore hardness units of facial prosthetic materialswere reported to range from 25 to 55,'"'

The popularity of poly(vinyi siloxane) occlusalmaterials has increased recently because of theease of use of automixing cartridges and theclaimed dimensional stability. However, to theauthors' knowledge, there has been no scientificreport of the dimensional stability of these materi-als. Tbe purpose of this study was to investigate (1)the Shore hardness of nine occlusal registrationmaterials and the effect of time on the hardnessvalues, and (2) the dimensional stability of eightelastomeric occlusal registration materials.

Materials and Methods

Nine materials for registering maxillomandibularrelationships were included in this study: one zincoxide-eugenol material, one polyether material,and seven poly(vinyi siloxane) materials (Table 1),All nine materials were tested for surface hardness.Only the polyether and the poly(vinyl siloxane)

materials were tested for dimensional stability,using the mold for elastomeric impression materialaccording to ADA Specification No.l9, All materi-als were conditioned at ambient room temperaturefor at least 24 hours prior to testing. Materials thatwere supplied in automixing cartridges were dis-pensed from those cartridges. Materials supplied intubes were dispensed in equal lengths of base andcatalyst. The material was mixed with a spatula toa streak-free consistency.

Surface Hardness

Mixed materials were loaded into a 6,5-mm-thick nylon mold having a 12.5-mm diameter cir-cular opening. The mold was then placed betweentwo glass slabs and secured with a C-clamp. Theeffect of the pressure from the C-clamp on thedimensions of the mold was considered negligible.All materials were allowed to polymerize for 20minutes, A total of 10 samples were tested for eachmaterial. The surface hardness of each sample wastested with a Shore-A durometer. Three measure-ments were made near the center of each samplewithout the indentations overlapping each other.This amounted to 30 measurements for each mate-rial. The initial measurements were made 30 min-utes after the start of mixing (group A). Another setof measurements was made 24 hours after the startof mixing but on the opposite surface of the sam-ples (group B), A two-way analysis of variance(ANOVA) was applied to detect significance differ-ences in the time and/or materials. If significancewas found, a one-way ANOVA and a Newman-Keuls post-hoc comparison (P = ,05) would beapplied to the materials for the 30-minute and 24-hour samples separately. Two-tailed pairedStudent's f test (P = ,01) was applied to individualmaterials to detect tbe significance of the effect oftime.

7, Number 6, 1994 539

Hardness snd Stabilitv of lute iiy Regislrstiori Materials

Dimensional Stability

Tbe mold for measuring dimensional stability ofnonaqueous elastomeric dental impression materi-als according to ADA Specification No, 19 wasused (Fig 1)," A detailed description is outlined inthe specification. Briefly, 10 discoid samples ofeach elastomeric occlusal registration materialwere formed with a mold. The material wasallowed to polymerize for 15 minutes in a thermo-stat-controlled water bath at a temperature of 32 ±2°C to simulate polymerization in an intraoralenvironment. Fach sample recorded three scribedlines of 25 mm from the mold. The length of thecenter line was measured under a traveling micro-scope at a magnification of 25 x at 25 minutes andat 24 hours after the start of mixing. One operator

made measurements of all readings, A pilot studywas performed to verify the repeatability of mea-surements by the operator of 20 repej'^ •' M'̂ 'isu^e-ments of the center line of the mold, ihe standarderror of the measurements was 0,432 |.im. Hence,the repeatability was deemed sufficient for the pur-pose of the study,

A one-way ANOVA and a Newman-Kuuls post-hoc (P = .05) comparison were applied to detectsignificance among the occlusal registration mate-rials.

Results

Surface Hardness

Fig 1 ADA Specification No. 19 mold for dimensionalstability.

The means and standard deviations of the mea-surements are depicted in Table 2 and Fig 2, Two-way ANOVA revealed significant differencesresulting from the variation in time and material (P< ,00000), Significant cross-product (time x materi-al) interaction was also found (P < ,00000). One-way ANOVA for the 30-minute and 24-hour sam-ples separately showed significant differencesamong the materials (P < .00000), For the 30-minute samples, Newman-Keuls post-hoc testsshowed no significant difference between jet Biteand Regisil 2X, or between Ramitec and Memosil(P> ,05), All other material combinations were sig-nificantly different from each other. For the 24-hour samples, Newman-Keuls post-hoc testsshowed no significant difference between Jet Biteand Ramitec, nor between Regisil 2X and Memosil

Table 2 Paired (Test to Compare Shore Hardness Between Groups of VariousOcclusal Registration Materials

Brand

Bite registration paste

Regisil PB

Biu iWousse

Stat BR

Re'Cord

President Jet Bife

Regisii 2X

Ramitec

Memosil

Group'

ABA

BABABABABABABAB

N

303030303030303030303030303030303030

Mean

94,5094,6790,0090.0087.5089.1782.6785,0079,0084,1775,1777,6775,0075,0073,3477,5072,5075.00

SD

1,5261,826002,5431,8953.40702,7541,8950,9132,537003.5562.5432,5430

Pvaiue

,703

—

_

,000'

,000'

—

,000'

—

'Group A tested at 30 minutes; Group B tested at 24 hours.'Significance at P= .05.

The Irlernationa uf Proitliodontici 540

HsrdnessündStahililyoílnle llary Regiîlration Mate

(P> .05) (Table 3|. All other material combinationswere significantly different from each other. Forindividual materials. Student's í test revealed thatthe surface hardness of the 24-hour samples of fourmaterials was significantly higher than that of the30-minute samples (P < .01) (Table 2). These fourmaterials were Blu Mousse, Re'Cord, ¡et Bite andRamitec. There was no significant difference in sur-face hardness between the 30-minute and 24-hoursamples of the other five materials.

Dimensional Stability

The means and standard deviations of the mea-surements are depicted in Table 4 and Fig 3. Thepercentage change in linear dimension varied fromabout 0.01 5% for Blu Mousse to 0.1 8% for Ramitec-One-way ANOVA sbowed significant differencesamong the materials (P < .00000). Newman-Keuls

post hoc test indicated no significant differencesamong Blu Mousse, Re'Cord, Regisil 2X, Stat BR,Regisil PB, and Jet Bite (P> .05). There were also nosignificant differences among Regisil PB, Jet Bite,and Memosil (P> .05).

Discussion

All samples displayed surface hardness above 70units. The range extended from a minimum of anaverage Shore hardness value of 72.50 units for apoly(vinyl siloxane), Memosil (group A), to 94.50units for the zinc oxide-«ugenol paste (group A).Four intermaxillary registration materials testedshowed significantly greater surface hardness at 24hours. This continued increase in surface hardnessmay be attributed to ongoing polymerization reac-tion after 30 minutes. Since the dimensional stabil-ity of these four materiais is not compromised at 24

Table 3 Comparison Among Samples Tested at 30Minutes and at 24 Hours

Occlusal registrationmaterial 30 min 24 h

Bite régi station pasteRegisil PBB!u MousseStatBRRe'CordJet BiteRegisil 2x ' 'Ramitec 'Mamosil ' '

One-way ANOVA and Newman-Keuls (est: P = .05. • and ' denotegroups with no signifcani ditference.

Table 4 One-Way ANOVA and Newman-Keuls Tests(P = .05) to Compare the Dimensional Stability ofVarious Occlusal Registration Materials

3 rand

3lu MousseRe'CordRegisii 2XStat BRRegisii PB'resident Jet BiteMemosilRamitec

N

1010101010101010

Vertical line connects groups with n

Mean

0.015150.016520.026930.027780.047640.054790.083650.18121

o significant ditte

SD

0.015870.022720.038920.036930,045550.020530.051010.06295

rence.

SlalBFi

ReCorO

Jet Bite

o 10 20 30 40 50 60 70 80 90 100Shore Hardness Units

Fig 2 Shore hardness values ot the intermaxiilary registra-tion materials at 30 minutes and 24 hours.

Regisil PB

Blu Mousse

Stat BR

Re'Cord

Jet Bite

Regisil 2X

Memosil CD

^ .

• '

• '0.00 ,05 10 .15 20 .25 .301

Percent linear dimensional change

Fig 3 Dimensiona! stability of the interma>;illary registrationmateriais.

••oli inie7. Mumbere, 1994 541 The Inlernational lournal of Prosthodontii

Hardness and Stability of Inte iry Registration Maleiials

hours, it may be speculated that relating dentalcasts with registrations made with one of these fourmaterials at 24 hours w i l l be more accuratebecause of the higher surface hardness. Additionalresearch to estabhsh the relationship between sur-face hardness and the accuracy of mounting isnecessary before a definite conclusion maybe made.

Zinc oxide-eugenoi paste has been used as anocciusal registration materiai for a long time. Theadvantages of zinc oxide-eugenol paste are itslow resistance to initial mandibular closure andgood dimensional stability.- This study also con-firmed the clinical impression of its surface hard-ness, which was higher than that of all the elas-tomeric materials tested. However, the brittlenessof zinc oxide-eugenol demands extreme care inits handling.

There was much variation among the elastomer-ic materials. However, the lowest recorded hard-ness, at 72.50 units, is still relatively high. It isunknown whether the observed statistical differ-ences in surface hardness will severely compro-mise clinical performance. The highly consistentsurface hardness of some materials was also unex-pected. Regisil PB and Regisil 2X showed hard-nesses of 90 and 75 units, respectively, for all mea-surements. This might have contributed to theobserved statistical differences among the materi-als. Since it has been shown that, generally, thickerelastomeric occlusal registration materials aremore compressible,'" a minimal thickness of thesematerials should be used to avoid distortion result-ing from compression.

The polyether occlusal registration materialexhibited significantly lower dimensional stabilitythan all other polyivinyl siloxane] materials tested.This could be explained by the difference in thepolymerization kinetics of polyether and polylvinylsiloxane). Cook" reported a more abrupt transitionbetween the gei (initial) and the final set stages ofpoly(vinyi sÜoxane) than of the polyether. Thiscould have accounted for the increased in dimen-sional change of the polyether after the first mea-surement. The protocol of this experiment was per-formed according to ADA specification No. "19 onimpression materials, which calls for the polymer-ization of the materials for 15 minutes in a waterbath to simulate the oral environment. The dimen-sional distortion of polyether material as a result ofwater sorption may have contributed to thedecreased dimensional stability." The clinical sig-nificance of the lower dimensional stability ofpolyether is not known. However, all materialstested satisfied the 0,5% criteria for dimensional

stability of Type I non-aqueous elastomeric impres-sion material as described in ADA SpecificationNo. 19.

Conclusions

Under the conditions of tbe present study, thefollowing conclusions can be made:

1. There were significant differences among thehardness and dimensional stability of theocclusal registration materials.

2. The dimensional stabi l i ty of a polyetherocclusal registration material was significantlylower than that of the poly(vinyl siloxane)materials tested.

3. The percentage dimensional change of allmaterials was acceptable according to the limitof 0.5% suggested by ADA Specification No.19 for nonaqueous elastomeric impressionmaterials.

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