- Email: [email protected]
A new method of measuring dimensional change
STERN,
identification of organisms transmitted to dental laboratories. Accepted for publication, J PROSTHET DENT 1990. 5. Skinner EW, Phillips RW. The science of dental materials, gypsum products: Technical considerations. Philadelphia: WB Saunders Co, 1982:77 and 87. 6. Peyton FA, Leibold JP, Ridgley GV. Surface hardness, compressive strength, and abrasion resistance of indirect die stones. J PROSTHET DENT
DENT
AND
TOOLSON
10. Drennon DG, Johnson GH, Powell GL. The accuracy and efficacy of disinfection by spray atomization on elastomeric impressions. J PROSTHET DENT 1989;62:468-75. 11. Powell GL, Whisenant JR, Saxon BA, Johnson
and immersion disinfectants Res 1990;69:348. Reprint
1952;2:381-9.
7. Boswell PG, Stevens ble-punch testing of 8. Schneider RL, Taylor of type IV die stone
JOHNSON,
requests
in simulated
GH. Efficacy of spray use tests [Abstract]. J Dent
to:
DR. MITCHELL A. STERN SCHOOL OF DENTISTRY, SM-52 UNIVERSITY OF WASHINGTON SEATTLE, WA 98195
L. A comparison between the diametral and doua dental gypsum. Aust Dent J 1979;24:238-43. TD. Compressive strength and surface hardness when mixed with water substitutes. J PROSTHET
1984;52:510-4.
9. Mahler
DB. Hardness
PROSTHET
DENT
and flow properties
of gypsum
materials.
J
1951;1:188-95.
A new method
of measuring
dimensional
E. L. DaBreo, D.D.S., M.S.D.,* and Paul Herman, Ohio State University, College of Dentistry, Columbus, Ohio
change
B.S.E.**
A new method of measuring linear dimensional change in denture base resins is presented and its precision in determining distances between two points was investigated. Chrome steel ball bearings 1.57 mm in diameter were invested in a stone mold and were used to record measurements by a reflection from the surface of the ball bearings. The accuracy of this method was determined by performing repeated measurements between two points in a stone mold. Random measurements were made to an accuracy of 0.002 mm. The dimensional change of lightcured, heat-cured, and self-cured denture base resins was also determined with this method, followed by an analysis of variance of the data. The findings support the accuracy and reproducibility of this new method in recording linear measurements. The dimensional changes of all threk resins were different from each other after the specimens were processed and stored in distilled water for 7 days at 37’ C. (J PROSTHET DENT 1991;66:718-22.)
S-
mce the advent of denture basepolymers, in vitro studiesof dimensionalaccuracy have been a critical component in assessing in vivo performance of thesematerials. Acceptable methodsof measuringdimensionalchangemay use calipers, gauges,comparators, micrometers, or radiographs. Dukeset al.,l Mainieri et al.,2and Garfunke13useda dial caliper to register changesin vertical dimension of occlusion of processeddentures with a precision of 0.002 inch and 0.01 mm. Morris et a1.4alsouseda dial caliper with a precision of 0.01 cm to measurethe palatal thickness of complete dentures before fracture. A caliper and outside micrometer were used by McCartney5 to measure the cross-archdistance of processeddentures to the nearest 0.001inch. Woelfel et al6 useda dial gaugeto measuredimensionalchangein dentures during processing.
‘Assistant ative
Professor,
Maxillofacial
Prosthetics,
Section
of Restor-
andProstheticDentistry. **Research Associate, Sectionof RestorativeandProstheticDentistry. 10/l/24232
718
An optical comparator was usedby Hugget et a1.7to determine the effect of different curing cycles on the dimensional accuracy of acrylic resin denture base materials. Firtell et al.* usedan optical micrometer with a tolerance of 0.005 inch to evaluate posterior border seal distortion related to processingtemperature. Radiographswereusedby Lechner and Lautenschlager9 to observeprocessingchangesin maxillary complete dentures. O’Toole et aLlo used a microscopeto determine the effects of the processingtechnique on dimensionalstability. With the processeddenture on the mastercast, palatal spacedistortion can be observedby measuringadaptation discrepancy at the posterior palatal sealarea. Changesin the vertical dimensionof occlusionare determined by the opening of the incisal pin after remounting the casts. Another method of measurementis to usea microscope or a traveling stage microscope.Goldfogel et al.” used a measuringmicroscopeto determine dimensionalchangeof acrylic resin tray materials, and Bessinget a1.12compared processedheat-cured denture basematerials. Woelfel et al.,13Woelfel and Paffenbarger,14and Paffenbarger et a1.15 used a machinist’s microscopeto determine dimensional changein complete dentures. Regardlessof which method MAY
1991
VOLUME
66
NUMBER
6
METHOD
OF MEASUREMENT
Fig. 1. A, Light
source in relation to microscope stage. B, Close-up of reflection from surface of ball bearing in relation to microscope lens. C, Light reflection on surface of ball bearing.
is used, reference points for accurate measurements are a prerequisite for accurate recordings. In many of these studies, marks placed or scribed on the surface of the denture base resin or teeth are used as refTHE
JOURNAL
OF PROSTHETIC
DENTISTRY
erence points to record linear measurements across the molar-to-molar and flange-to-flange distances before and after processing the wax model denture and after its storage in water. This study investigated the accuracy of a new 719
DABREO
Fig.
Table
HERMAN
2. Percent of mean dimensionalcontraction of three types of resin.
I. Repeated measurements*between two points
01A+0000.000 02A+OO00.002 03A+0000.007 01A+0000.001 02A+0000.000 03A+0000.004 01A+0000.002 02A+0000.001 03A+0000.003 01A+OO00.001 02A+0000.000 03A+0000.006 01A+0000.000 02A+0000.000 03A+0000.008 01A+0000.002 02A+OOOO.000 03A+OOO0.003 All measurements *Measurements
in millimeters. were made on e machinist
MATERIAL Part I
AND
01A+0000.001 02A+0000.000 03A+OOOO.005 01A+OOO0.000 02A+0000.001 03A+0000.008 01A+OOO0.000 02A+0000.000 03A+0000.009 01A+OO00.001 02A+0000.001 03A+0000.007 01A+OO00.000 02A+0000.000 03A+OOO0.006 01A+0000.000 02A+OOOO.O04 03A+0000.011
OlA+OO39.150 02A-0000.724 03A-0000.092 OlA+0039.150 02A-0000.724 03A-0000.091 OlA+OO39.151 02A-0000.724 03A-0000.092 OlA+OO39.150 02A-0000.724 03A-0000.092 OlA+0039.150 02A-0000.724 03A-0000.092 OlA+OO39.150 02A-0000.724 03A-ooO0.092 microscope
(Leitz
model
UMW,
method of measuringlinear dimensional changesin denture base resins using the reflective surface of spherical chrome steel ball bearings.
METHODS
Five rectangular acrylic resinspecimensmeasuring50 X 10 X 2.5 mm were used to prepare a mold in a maxillary denture flask made of artificial stone (Whip-Mix Corp., 720
AND
Opto-Metric
Tools
OlA+0039.151 021\+0039.724 03A+OO39.093 01At0039.150 02AtO039.723 03AtO039.092 OlAtOO39.152 02At0039.724 03AtOO39.089 01At0039.151 02A+OO39.722 03AtO039.087 01At0039.150 02AtO039.723 03AtO039.093 01At0039.151 02AtO039.723 03A+0039.086
Inc.).
Louisville, KY.). Two depressionswere madein eachspecimen with a No. 2 round bur. Each specimen had two chromesteelball bearings(Bearings,Inc. Columbus,Ohio), 1.57mm in diameter, luted to the surfaceat a fixed distance of approximately 40 mm. The acrylic resin specimenswere invested in artificial atonemixed under vacuum conditions following the manufacturer’s recommendedwater-to-powder ratio. After the stone was set, the acrylic resin specimens were removed, resulting in the ball bearings being MAY
lQ91
VOLUME
66
NUMBER
5
METHOD
OF MEASUREMENT
Table II. Linear (percent) dimensional change Mold dimension
Self-cured resin I II III IV V
(mm)
(mm)
After storaget (mm)
-0.58 -0.50
39.46 40.95
% Change
39.64
39.41 40.89
39.74 44.69
39.51
-0.59
39.58
44.44 39.05
-0.57 -0.57
44.50 39.10
-0.45 -0.38 -0.40 -0.43 -0.44
39.64 41.10 39.74
39.39
44.69 39.28
44.42 39.02
-0.64 -0.62 -0.73 -0.60 -0.66
39.45 40.89 39.51 44.45 39.07
-0.48 -0.50 -0.59 -0.53 -0.54
39.64 41.10 39.75 44.69
39.53 40.99 39.61 44.59
39.28
39.18
-0.27 -0.25 -0.32 -0.21 -0.23
39.56 41.03 39.65 44.61 39.20
-0.20 -0.17 -0.24 -0.18 -0.19
39.28
Light-cured I II III IV
% Change
41.10
Heat-cured resinj I II III IV V
After deflasking*
40.85
39.45
resin
V
*After polymerization. Seven days in 37” C distilled water. $Short cure cycle (l/2 hours at 73’ C and l/2 hour at 100’ 0.
transferred into the stone. The surfaces of the bearings were cleansedand buffed with dry 2 X 2 mm gaugepads and the mold wasplaced under the microscopein preparation for measuringthe distance between the ball bearings. Only the distance between the two ball bearings in specimen V was used in part I of this study. Part
II
The linear dimensional change of three denture base resins was determined after processingand storing the specimensin 37” C distilled water for 7 days using a short cure cycle (1 hour at 73” C and 1 hour at 100’ C). The materials studied were Repair Material, self-cured resin; Lucitone 199, heat-cured resin; and Triad, light-cured resin (all products of Dentsply International Inc., York, Pa.). Each material wasmixed (when appropriate), packed, and cured following the manufacturer’s recommendations.After deflasking, the ball bearings were embedded in each specimen.Measurementswere madebetweenball bearings for all five specimens. The specimens were labeled I through V. Experimental design. All measurementswere made on a machinist’s traveling stage microscope(Leitz model UMW, Opto-Metric Tools Inc., New York, N.Y.), which was upgraded with electronic digital micrometer heads (Digimatic Head 164 series,Mitutoyo Manufacturing Co. Inc., Tokyo, Japan) having a precisionof 0.001mm and an accuracy of kO.003 mm. An overhead light source was mounted on the ceiling above the microscopein a fixed position approximately 3 m from the microscopestage(Fig. 1, A). Two lines perpenTHE
JOURNAL
OF PROSTHETIC
DENTISTRY
dicular to eachother were drawn with a black marker on a sheetof paper. The paper wascut to the diameter of the rim of the light source and was glued in place with a silicone rubber medical adhesive (Dow Corning, Midland, Mich.) material. Measurementswere obtained by aligning the crosshairs in the microscopelenswith the reflection of the crossfrom the light sourceon the surface of the ball bearings(Fig. 1, B). After focusing, the cross from the light source was clearly reflected from the surface of the ball bearing (Fig. 1, C) into the lensof the microscope.The crosson the light sourcewasrotated until it matched up with the crosshairs in the microscopelens. Verification of the accuracy of the method was accomplishedby performing repeated measurements between the ball bearings embedded in the stone mold and the specimens.Note that reference positions are transferred with great accuracy from the stone moldswith ball bearingshalf embeddedto the specimens, often by the transfer of the ball bearingsthemselves,and that the crossreflections refer to identical (spherical center) points in both hemispherical locations. Five measurementswere made for each specimen. Measurements were made in the mold, after deflasking, and after storagein water. The averageof the five recordings was used as the final measurementfor each specimen. RESULTS Part I The results of repeated measurementsbetween two ball bearingsfrom specimenV are shown in Table I. The pre721
DnBREO
fixes IA, 2A, and 3A represent the X, Y, and Z axes COOTdinates of each measurement from the microscope.
Part
II
The results of the measurements on specimens I through V and the percent change are shown in Table II. Fig. 2 shows the percent of dimensional contraction of the three types of denture base resins.
DISCUSSION
CONCLUSIONS, SIGNIFICANCE
AND
The accuracy of a new method of measuring dimensional change in denture base resins was investigated in this study. In light of the continual need to assess the dimensional accuracy of denture base resins used clinically, this method provides an accurate alternative method for mea-
722
HERMAN
suring dimensional change. The use of the reflective surface of chrome steel ball bearings resulted in accurate and reproducible linear measurements between two points. Of the three denture base resins evaluated, the light-cured resins had the least dimensional change. We thank Drs. M.H. with the experimental
Reisbick design.
and W.M.
Johnston
for their
help
REFERENCES
The data in Table I were compiled from recordings made from the mold space of specimen V only. The recordings reveal an accuracy to within + 0.002 mm. The accuracy of the measurements may have been degraded when moving the turret from the pointer to the 32 power lens during measurements. The mold dimension and specimen measurements are calculated as the square root of the sum of squares of individual dimensions (X, Y, Z coordinates) expressed by the square root of a2+b2+v2, where a=xz-xl, b=ys-yi, and c=zz-zr. By placing the light source at a fixed distance and position with respect to the microscope stage, optical error from the surface reflection is minimized. Therefore the reflection from the surface of the ball is viewed in the same relative position to the microscope lens each time a measurement is made. The heat-cured resin exhibited the greatest dimensional change, which in part could be a result of the short curing cycle used. McCartney5 and Hugget et al7 concluded that a short curing cycle produced more processing shrinkage. The light-cured resin had the least amount of dimensional change, particulary after storage in water. Ogle et a1.16 compared light-cured resin with heat-cured and self-cured orthodontic resin and found that light-cured resin exhibited the least amount of dimensional change. Woelfel et al6 found that the amount of water absorbed by acrylic resins can result in almost complete recovery from the processing shrinkage.
SUMMARY, CLINICAL
AND
1. Dukes BS, Fields H, Olson JW, Scheetz JP. A laboratory study of changes in vertical dimension using a compression molding and a pour resin technique. J PROSTHET DENT 1985;53:667-9. 2. Mainieri ET, Boone ME, Potter RH. Tooth movement and dimensional change of denture base materials using two investment methods. J PROSTHET
DENT
1980;44:368-73.
3. Garfunkel E. Evaluation of dimensional changes in complete dentures processed by injection-pressing and the pack-and-press technique. J PROSTHET
DENT
1983;50:757-61.
4. Morris JC, Khan 2, van Fraunhofer JA. Palatal shape and the flexural strength of maxillary denture bases. J PROSTHET DENT 1985;53:670-3. 5. McCartney JW. Flange adaptation discrepancy, palatal base distortion, and induced malocclusion caused by processing acrylic resin maxillary complete dentures. J PROSTHET DENT 1984;52:545-53. GC, Sweeney WT. Dimensional changes oc6. Woelfel JB, Paffenbarger curring in dentures during processing. J Am Dent Assoc 1960;19:415-30. I. Hugget R, Brooks C, Bates JF. The effect of different curing cycles on the dimensional accuracy of acrylic resin denture base materials. Quintessence Dent Tech 1984;8:81-5. 8. Firtell DN, Green AJ, Elahi JM. Posterior peripheral seal distortion related to processing temperature. J PROSTHET DENT 1981;45:598-601. EP. Processing changes in maxillary com9. Lechner SK, Lautenschlager plete dentures. J PROSTHET DENT 1984;52:20-4. JA. Linear distortion of 10. G’Toole TJ, Furnish GM, van Fraunhofer acrylic resin. J PROSTHET DENT 1985;53:53-5. 11. Goldfogel M, Harvey WL, Winter D. Dimensional change of acrylic resin tray materials. J PROSTHET DENT 1985;54:284-6. 12. Bessing C, Nilsson B, Bergman M. SR 3/60 and sr-ivocap. A comparison between two heat-cured denture base resins with dissimilar processings. Swed Dent J 197%3:221-S. 13. Woelfel JB, Paffenbarger GC, Sweeney WT. Dimensional changes in complete dentures on drying, wetting, and heating in water. J Am Dent Assoc 1962;65:495-505. 14. Woelfel JB, Paffenbarger GC. Expanding and shrinking 7-year-old dentures: report of cases. J Am Dent Assoc 1970;81:1342-8. 15. Paffenbarger GC, Woelfel JB, Sweeney WT. Dimensional change in dentures. Dent Pratt 1962;13:64-9. 16. Ogle RE, Sorensen SE, Lewis EA. A new visible light-cured resin system applied to removable prosthcdontics. J PROSTHET DENT 1986;56:497-506.
Reprint
requests
to:
DR. ERNEST L. DABREO COLLEGE OF DENTISTRY THE OHIO STATE UNIVERSITY COLUMBUS. OH 43210-1241
MAY
1991
VOLUME
65
NUMBER
5
identification of organisms transmitted to dental laboratories. Accepted for publication, J PROSTHET DENT 1990. 5. Skinner EW, Phillips RW. The science of dental materials, gypsum products: Technical considerations. Philadelphia: WB Saunders Co, 1982:77 and 87. 6. Peyton FA, Leibold JP, Ridgley GV. Surface hardness, compressive strength, and abrasion resistance of indirect die stones. J PROSTHET DENT
DENT
AND
TOOLSON
10. Drennon DG, Johnson GH, Powell GL. The accuracy and efficacy of disinfection by spray atomization on elastomeric impressions. J PROSTHET DENT 1989;62:468-75. 11. Powell GL, Whisenant JR, Saxon BA, Johnson
and immersion disinfectants Res 1990;69:348. Reprint
1952;2:381-9.
7. Boswell PG, Stevens ble-punch testing of 8. Schneider RL, Taylor of type IV die stone
JOHNSON,
requests
in simulated
GH. Efficacy of spray use tests [Abstract]. J Dent
to:
DR. MITCHELL A. STERN SCHOOL OF DENTISTRY, SM-52 UNIVERSITY OF WASHINGTON SEATTLE, WA 98195
L. A comparison between the diametral and doua dental gypsum. Aust Dent J 1979;24:238-43. TD. Compressive strength and surface hardness when mixed with water substitutes. J PROSTHET
1984;52:510-4.
9. Mahler
DB. Hardness
PROSTHET
DENT
and flow properties
of gypsum
materials.
J
1951;1:188-95.
A new method
of measuring
dimensional
E. L. DaBreo, D.D.S., M.S.D.,* and Paul Herman, Ohio State University, College of Dentistry, Columbus, Ohio
change
B.S.E.**
A new method of measuring linear dimensional change in denture base resins is presented and its precision in determining distances between two points was investigated. Chrome steel ball bearings 1.57 mm in diameter were invested in a stone mold and were used to record measurements by a reflection from the surface of the ball bearings. The accuracy of this method was determined by performing repeated measurements between two points in a stone mold. Random measurements were made to an accuracy of 0.002 mm. The dimensional change of lightcured, heat-cured, and self-cured denture base resins was also determined with this method, followed by an analysis of variance of the data. The findings support the accuracy and reproducibility of this new method in recording linear measurements. The dimensional changes of all threk resins were different from each other after the specimens were processed and stored in distilled water for 7 days at 37’ C. (J PROSTHET DENT 1991;66:718-22.)
S-
mce the advent of denture basepolymers, in vitro studiesof dimensionalaccuracy have been a critical component in assessing in vivo performance of thesematerials. Acceptable methodsof measuringdimensionalchangemay use calipers, gauges,comparators, micrometers, or radiographs. Dukeset al.,l Mainieri et al.,2and Garfunke13useda dial caliper to register changesin vertical dimension of occlusion of processeddentures with a precision of 0.002 inch and 0.01 mm. Morris et a1.4alsouseda dial caliper with a precision of 0.01 cm to measurethe palatal thickness of complete dentures before fracture. A caliper and outside micrometer were used by McCartney5 to measure the cross-archdistance of processeddentures to the nearest 0.001inch. Woelfel et al6 useda dial gaugeto measuredimensionalchangein dentures during processing.
‘Assistant ative
Professor,
Maxillofacial
Prosthetics,
Section
of Restor-
andProstheticDentistry. **Research Associate, Sectionof RestorativeandProstheticDentistry. 10/l/24232
718
An optical comparator was usedby Hugget et a1.7to determine the effect of different curing cycles on the dimensional accuracy of acrylic resin denture base materials. Firtell et al.* usedan optical micrometer with a tolerance of 0.005 inch to evaluate posterior border seal distortion related to processingtemperature. Radiographswereusedby Lechner and Lautenschlager9 to observeprocessingchangesin maxillary complete dentures. O’Toole et aLlo used a microscopeto determine the effects of the processingtechnique on dimensionalstability. With the processeddenture on the mastercast, palatal spacedistortion can be observedby measuringadaptation discrepancy at the posterior palatal sealarea. Changesin the vertical dimensionof occlusionare determined by the opening of the incisal pin after remounting the casts. Another method of measurementis to usea microscope or a traveling stage microscope.Goldfogel et al.” used a measuringmicroscopeto determine dimensionalchangeof acrylic resin tray materials, and Bessinget a1.12compared processedheat-cured denture basematerials. Woelfel et al.,13Woelfel and Paffenbarger,14and Paffenbarger et a1.15 used a machinist’s microscopeto determine dimensional changein complete dentures. Regardlessof which method MAY
1991
VOLUME
66
NUMBER
6
METHOD
OF MEASUREMENT
Fig. 1. A, Light
source in relation to microscope stage. B, Close-up of reflection from surface of ball bearing in relation to microscope lens. C, Light reflection on surface of ball bearing.
is used, reference points for accurate measurements are a prerequisite for accurate recordings. In many of these studies, marks placed or scribed on the surface of the denture base resin or teeth are used as refTHE
JOURNAL
OF PROSTHETIC
DENTISTRY
erence points to record linear measurements across the molar-to-molar and flange-to-flange distances before and after processing the wax model denture and after its storage in water. This study investigated the accuracy of a new 719
DABREO
Fig.
Table
HERMAN
2. Percent of mean dimensionalcontraction of three types of resin.
I. Repeated measurements*between two points
01A+0000.000 02A+OO00.002 03A+0000.007 01A+0000.001 02A+0000.000 03A+0000.004 01A+0000.002 02A+0000.001 03A+0000.003 01A+OO00.001 02A+0000.000 03A+0000.006 01A+0000.000 02A+0000.000 03A+0000.008 01A+0000.002 02A+OOOO.000 03A+OOO0.003 All measurements *Measurements
in millimeters. were made on e machinist
MATERIAL Part I
AND
01A+0000.001 02A+0000.000 03A+OOOO.005 01A+OOO0.000 02A+0000.001 03A+0000.008 01A+OOO0.000 02A+0000.000 03A+0000.009 01A+OO00.001 02A+0000.001 03A+0000.007 01A+OO00.000 02A+0000.000 03A+OOO0.006 01A+0000.000 02A+OOOO.O04 03A+0000.011
OlA+OO39.150 02A-0000.724 03A-0000.092 OlA+0039.150 02A-0000.724 03A-0000.091 OlA+OO39.151 02A-0000.724 03A-0000.092 OlA+OO39.150 02A-0000.724 03A-0000.092 OlA+0039.150 02A-0000.724 03A-0000.092 OlA+OO39.150 02A-0000.724 03A-ooO0.092 microscope
(Leitz
model
UMW,
method of measuringlinear dimensional changesin denture base resins using the reflective surface of spherical chrome steel ball bearings.
METHODS
Five rectangular acrylic resinspecimensmeasuring50 X 10 X 2.5 mm were used to prepare a mold in a maxillary denture flask made of artificial stone (Whip-Mix Corp., 720
AND
Opto-Metric
Tools
OlA+0039.151 021\+0039.724 03A+OO39.093 01At0039.150 02AtO039.723 03AtO039.092 OlAtOO39.152 02At0039.724 03AtOO39.089 01At0039.151 02A+OO39.722 03AtO039.087 01At0039.150 02AtO039.723 03AtO039.093 01At0039.151 02AtO039.723 03A+0039.086
Inc.).
Louisville, KY.). Two depressionswere madein eachspecimen with a No. 2 round bur. Each specimen had two chromesteelball bearings(Bearings,Inc. Columbus,Ohio), 1.57mm in diameter, luted to the surfaceat a fixed distance of approximately 40 mm. The acrylic resin specimenswere invested in artificial atonemixed under vacuum conditions following the manufacturer’s recommendedwater-to-powder ratio. After the stone was set, the acrylic resin specimens were removed, resulting in the ball bearings being MAY
lQ91
VOLUME
66
NUMBER
5
METHOD
OF MEASUREMENT
Table II. Linear (percent) dimensional change Mold dimension
Self-cured resin I II III IV V
(mm)
(mm)
After storaget (mm)
-0.58 -0.50
39.46 40.95
% Change
39.64
39.41 40.89
39.74 44.69
39.51
-0.59
39.58
44.44 39.05
-0.57 -0.57
44.50 39.10
-0.45 -0.38 -0.40 -0.43 -0.44
39.64 41.10 39.74
39.39
44.69 39.28
44.42 39.02
-0.64 -0.62 -0.73 -0.60 -0.66
39.45 40.89 39.51 44.45 39.07
-0.48 -0.50 -0.59 -0.53 -0.54
39.64 41.10 39.75 44.69
39.53 40.99 39.61 44.59
39.28
39.18
-0.27 -0.25 -0.32 -0.21 -0.23
39.56 41.03 39.65 44.61 39.20
-0.20 -0.17 -0.24 -0.18 -0.19
39.28
Light-cured I II III IV
% Change
41.10
Heat-cured resinj I II III IV V
After deflasking*
40.85
39.45
resin
V
*After polymerization. Seven days in 37” C distilled water. $Short cure cycle (l/2 hours at 73’ C and l/2 hour at 100’ 0.
transferred into the stone. The surfaces of the bearings were cleansedand buffed with dry 2 X 2 mm gaugepads and the mold wasplaced under the microscopein preparation for measuringthe distance between the ball bearings. Only the distance between the two ball bearings in specimen V was used in part I of this study. Part
II
The linear dimensional change of three denture base resins was determined after processingand storing the specimensin 37” C distilled water for 7 days using a short cure cycle (1 hour at 73” C and 1 hour at 100’ C). The materials studied were Repair Material, self-cured resin; Lucitone 199, heat-cured resin; and Triad, light-cured resin (all products of Dentsply International Inc., York, Pa.). Each material wasmixed (when appropriate), packed, and cured following the manufacturer’s recommendations.After deflasking, the ball bearings were embedded in each specimen.Measurementswere madebetweenball bearings for all five specimens. The specimens were labeled I through V. Experimental design. All measurementswere made on a machinist’s traveling stage microscope(Leitz model UMW, Opto-Metric Tools Inc., New York, N.Y.), which was upgraded with electronic digital micrometer heads (Digimatic Head 164 series,Mitutoyo Manufacturing Co. Inc., Tokyo, Japan) having a precisionof 0.001mm and an accuracy of kO.003 mm. An overhead light source was mounted on the ceiling above the microscopein a fixed position approximately 3 m from the microscopestage(Fig. 1, A). Two lines perpenTHE
JOURNAL
OF PROSTHETIC
DENTISTRY
dicular to eachother were drawn with a black marker on a sheetof paper. The paper wascut to the diameter of the rim of the light source and was glued in place with a silicone rubber medical adhesive (Dow Corning, Midland, Mich.) material. Measurementswere obtained by aligning the crosshairs in the microscopelenswith the reflection of the crossfrom the light sourceon the surface of the ball bearings(Fig. 1, B). After focusing, the cross from the light source was clearly reflected from the surface of the ball bearing (Fig. 1, C) into the lensof the microscope.The crosson the light sourcewasrotated until it matched up with the crosshairs in the microscopelens. Verification of the accuracy of the method was accomplishedby performing repeated measurements between the ball bearings embedded in the stone mold and the specimens.Note that reference positions are transferred with great accuracy from the stone moldswith ball bearingshalf embeddedto the specimens, often by the transfer of the ball bearingsthemselves,and that the crossreflections refer to identical (spherical center) points in both hemispherical locations. Five measurementswere made for each specimen. Measurements were made in the mold, after deflasking, and after storagein water. The averageof the five recordings was used as the final measurementfor each specimen. RESULTS Part I The results of repeated measurementsbetween two ball bearingsfrom specimenV are shown in Table I. The pre721
DnBREO
fixes IA, 2A, and 3A represent the X, Y, and Z axes COOTdinates of each measurement from the microscope.
Part
II
The results of the measurements on specimens I through V and the percent change are shown in Table II. Fig. 2 shows the percent of dimensional contraction of the three types of denture base resins.
DISCUSSION
CONCLUSIONS, SIGNIFICANCE
AND
The accuracy of a new method of measuring dimensional change in denture base resins was investigated in this study. In light of the continual need to assess the dimensional accuracy of denture base resins used clinically, this method provides an accurate alternative method for mea-
722
HERMAN
suring dimensional change. The use of the reflective surface of chrome steel ball bearings resulted in accurate and reproducible linear measurements between two points. Of the three denture base resins evaluated, the light-cured resins had the least dimensional change. We thank Drs. M.H. with the experimental
Reisbick design.
and W.M.
Johnston
for their
help
REFERENCES
The data in Table I were compiled from recordings made from the mold space of specimen V only. The recordings reveal an accuracy to within + 0.002 mm. The accuracy of the measurements may have been degraded when moving the turret from the pointer to the 32 power lens during measurements. The mold dimension and specimen measurements are calculated as the square root of the sum of squares of individual dimensions (X, Y, Z coordinates) expressed by the square root of a2+b2+v2, where a=xz-xl, b=ys-yi, and c=zz-zr. By placing the light source at a fixed distance and position with respect to the microscope stage, optical error from the surface reflection is minimized. Therefore the reflection from the surface of the ball is viewed in the same relative position to the microscope lens each time a measurement is made. The heat-cured resin exhibited the greatest dimensional change, which in part could be a result of the short curing cycle used. McCartney5 and Hugget et al7 concluded that a short curing cycle produced more processing shrinkage. The light-cured resin had the least amount of dimensional change, particulary after storage in water. Ogle et a1.16 compared light-cured resin with heat-cured and self-cured orthodontic resin and found that light-cured resin exhibited the least amount of dimensional change. Woelfel et al6 found that the amount of water absorbed by acrylic resins can result in almost complete recovery from the processing shrinkage.
SUMMARY, CLINICAL
AND
1. Dukes BS, Fields H, Olson JW, Scheetz JP. A laboratory study of changes in vertical dimension using a compression molding and a pour resin technique. J PROSTHET DENT 1985;53:667-9. 2. Mainieri ET, Boone ME, Potter RH. Tooth movement and dimensional change of denture base materials using two investment methods. J PROSTHET
DENT
1980;44:368-73.
3. Garfunkel E. Evaluation of dimensional changes in complete dentures processed by injection-pressing and the pack-and-press technique. J PROSTHET
DENT
1983;50:757-61.
4. Morris JC, Khan 2, van Fraunhofer JA. Palatal shape and the flexural strength of maxillary denture bases. J PROSTHET DENT 1985;53:670-3. 5. McCartney JW. Flange adaptation discrepancy, palatal base distortion, and induced malocclusion caused by processing acrylic resin maxillary complete dentures. J PROSTHET DENT 1984;52:545-53. GC, Sweeney WT. Dimensional changes oc6. Woelfel JB, Paffenbarger curring in dentures during processing. J Am Dent Assoc 1960;19:415-30. I. Hugget R, Brooks C, Bates JF. The effect of different curing cycles on the dimensional accuracy of acrylic resin denture base materials. Quintessence Dent Tech 1984;8:81-5. 8. Firtell DN, Green AJ, Elahi JM. Posterior peripheral seal distortion related to processing temperature. J PROSTHET DENT 1981;45:598-601. EP. Processing changes in maxillary com9. Lechner SK, Lautenschlager plete dentures. J PROSTHET DENT 1984;52:20-4. JA. Linear distortion of 10. G’Toole TJ, Furnish GM, van Fraunhofer acrylic resin. J PROSTHET DENT 1985;53:53-5. 11. Goldfogel M, Harvey WL, Winter D. Dimensional change of acrylic resin tray materials. J PROSTHET DENT 1985;54:284-6. 12. Bessing C, Nilsson B, Bergman M. SR 3/60 and sr-ivocap. A comparison between two heat-cured denture base resins with dissimilar processings. Swed Dent J 197%3:221-S. 13. Woelfel JB, Paffenbarger GC, Sweeney WT. Dimensional changes in complete dentures on drying, wetting, and heating in water. J Am Dent Assoc 1962;65:495-505. 14. Woelfel JB, Paffenbarger GC. Expanding and shrinking 7-year-old dentures: report of cases. J Am Dent Assoc 1970;81:1342-8. 15. Paffenbarger GC, Woelfel JB, Sweeney WT. Dimensional change in dentures. Dent Pratt 1962;13:64-9. 16. Ogle RE, Sorensen SE, Lewis EA. A new visible light-cured resin system applied to removable prosthcdontics. J PROSTHET DENT 1986;56:497-506.
Reprint
requests
to:
DR. ERNEST L. DABREO COLLEGE OF DENTISTRY THE OHIO STATE UNIVERSITY COLUMBUS. OH 43210-1241
MAY
1991
VOLUME
65
NUMBER
5