This study investigated the effect of material chemistry and prolonged setting time on the permanent deformation of six light-body elastomeric impression materials after stretching. The materials tested were subjected to 80% stretching either after the manufacturer's recommended setting time or after 5 minutes of setting. Polyether materials showed significantly higher permanent deformation than vinyl polysiloxane materials. Extending the setting time reduced permanent deformation for materials with a polyether backbone but not for vinyl polysiloxanes. Increasing the setting time may improve elastic recovery of polyether impression materials.

1. Influence of prolonged set ting time on
permanent deformation of elastomeric
impression materials
Markus Balkenhol, Prof Dr med dent,a Sylvia Haunschild,b
Christina Erbe, Dr med dent,c and Bernd Wöstmann, Prof Dr
med dentd
Justus Liebig University, Giessen, Germany; University Medical
Centre, Mainz, Germany
Statement of problem. Upon removal, tear forces occur in various areas of an impression. As a result, thin sulcus
details may be permanently deformed, affecting the impression’s accuracy.
Purpose. The purpose of this study was to investigate the effect of the chemistry and prolonged setting time on the
permanent deformation of light-body impression materials after stretching.
Material and methods. A dumbbell-shaped mold (2 mm x 4 mm x 75 mm) was used to prepare specimens (n=20)
of 6 different impression materials (Affinis Light Body, Aquasil Ultra XLV, Express 2 Light Body Flow Quick, Flexitime
Correct Flow, P2 Polyether Light, and Impregum Garant L DuoSoft). After water storage (35°C), either for the manu-
facturer’s suggested setting time or for 5 minutes, specimens were stretched by 80% using a universal testing machine
at a crosshead speed of 200 mm/min. The permanent deformation (Δl (%)) was determined after 2 hours of storage
in ambient conditions. A 2-way ANOVA followed by a Games-Howell test was used to analyze the influence of mate-
rial and storage time (α=.05).
Results. Polyether materials showed a significantly higher permanent deformation (Δl>4% to 5%) than vinyl polysi-
loxane materials (P<.05). Extending the manufacturer’s suggested setting time resulted in clinically relevant improve-
ments in elastic recovery for products with a polyether backbone only.
Conclusions. Increasing the setting time might be necessary for impression materials with a polyether backbone to
improve elastic recovery. (J Prosthet Dent 2010;103:288-294)
Clinical Implications
For vinyl polysiloxane materials, an extension of the manufacturers’
recommended setting time does not provide a relevant improvement in
elastic recovery. In contrast, increasing the manufacturers’ recommend-
ed setting time may be advisable for polyether impression materials.
Impression making is an essential rect application, the impression tray with finish lines located more than 2
step during prosthodontic treatment and material combination, local con- mm subgingivally is a challenging pro-
procedures, as the quality of an im- ditions in the oral cavity (periodontal cedure.
pression significantly affects the accu- status, location of the finish line), For many years, impressions re-
rate fit of the definitive restoration.1-3 and, finally, the properties of the im- quiring a high level of precision have
The quality of an impression, in turn, pression material used.4-11 According been made with elastomeric impres-
is influenced by many factors; namely, to the authors’ clinical experience, sion materials, such as polyether or
the impression technique and its cor- making impressions of prepared teeth polysiloxanes, due to their excellent
a
Assistant Professor, Department of Prosthodontics, Justus Liebig University.
b
Research Assistant, Department of Prosthodontics, Justus Liebig University.
c
Assistant Professor, Department of Orthodontics, University Medical Centre.
d
Professor, Department of Prosthodontics, Justus Liebig University.
The Journal of Prosthetic Dentistry Balkenhol et al

2. May 2010 289
chemical and physical material prop-
erties.12-14 A fundamental property of
an elastomeric impression material,
which significantly influences an im-
pression’s accuracy, is its elastic recov-
ery from deformation.2,15-17 Permanent
deformation can be related to the vis-
coelastic properties inherent in elasto-
meric impression materials.2,13,18-20
According to the ISO standard
4823, permanent deformation of an
impression material is determined after
compression of a test specimen.21 The 1 Areas where light-body material is exposed to considerable tensile
strain (typical clinical situation). A, Interproximal spaces with under-
direction of load, therefore, reflects
cuts. B, Undercuts beneath finish lines. C, Subgingival undercuts result-
deformation that occurs horizontally
ing in thin sulcus/finish line cuff of light-body impression material.
in undercut areas toward the impres-
sion tray upon removal of the impres-
sion from the patient’s mouth.1,2,22-25 duce the risk of permanent deforma- manufacturers as vinyl polysiloxane
However, tensile strain, occurring tion and inaccuracies. (VPS) materials and, therefore, po-
in different areas of the set light-body While permanent deformation re- lymerize by a Pt-catalyzed hydrolyza-
material upon removal of the impres- sulting from tensile strain has been tion reaction of vinyl end groups.13,31
sion, may be even more critical with investigated in a number of prior Impregum is a conventional polyether
respect to permanent deformation.26 studies,15,17,28,30 this clinically impor- that polymerizes by ring-opening
Elastic recovery resulting from ten- tant issue has only been reported in polymerization of the end groups of
sile strain reportedly decreases with a single contemporary investigation an ethylene-imine terminated poly-
increasing strain and could not be that compared the influence of the ether compound.13 P2 is classified
predicted from results obtained from deformation’s magnitude (50% strain as a polyether by its manufacturer.
compression tests.27 Tensile load clini- vs. 100% strain).27 This study did not, However, as P2 polymerizes via an
cally occurs in undercut areas and in- however, cover the entire range of acid-catalyzed cross-linking reaction
terproximal spaces, particularly in the frequently used impression materials of silane end groups connected to
thin cuff of light-body impression ma- (vinyl polysiloxane, polyether, and hy- a polyether backbone,32,33 it should
terial injected into the gingival sulcus of brid polyether siloxane). In addition, rather be considered a hybrid poly-
the prepared tooth (Fig. 1).13,26,28 Upon the study did not test whether or not ether siloxane, similar to the product
removal of the impression, the thin sul- increasing the setting time might de- Senn (GC Corp, Tokyo, Japan).27 All
cus/finish line cuff is stretched and may crease the permanent deformation re- materials were delivered in automixing
easily tear.13,24,26,28 In clinical practice, sulting from tensile strain. Therefore, cartridges and used according to their
torn areas are easily detectable, but the purpose of the present study was respective manufacturers’ instructions
often require remaking the impression. to answer these important questions in ambient laboratory conditions (23
Inaccuracies resulting from permanent relevant to the clinical application of ±1°C; 50 ±10% relative humidity).
deformation, in contrast, can rarely be elastomeric impression materials. Before the mixing tips were at-
detected, resulting in distorted impres- The following twofold null hy- tached to the automixing cartridges,
sions and imperfectly fitting definitive pothesis was tested: the permanent the orifices of both chambers were
restorations.2,13 deformation of a light-body impres- inspected for plugging. The impres-
The chemistry of the material used, sion material would not be affected sion materials were directly dispensed
layer thickness, duration of deforma- by (1) its chemistry or (2) the setting from the mixing tip into the dumb-
tion, magnitude of strain, as well as time period at 35°C prior to stretch- bell-shaped mold (2 mm x 4 mm x
the degree of polymerization are fac- ing the specimens. 75 mm),27 which featured 2 semicir-
tors which reportedly influence an cular measuring marks on each side,
impression’s ability to recover from MATERIAL AND METHODS positioned 20 mm apart (Fig. 2). The
deformation upon removal from the mold was placed between 2 glass
mouth.13,15,20,22,24,28,29 Extending the in- Table I lists the materials used slides, covered with polyester foil (Ho-
traoral setting time may improve the in the study to prepare dumbbell- staphan RN 50; Pütz, Taunusstein,
elastic properties of the polymerized shaped specimens. The materials Af- Germany), and placed beneath a par-
impression material, due to a higher finis, Aquasil, Express 2, and Flexitime allel press (Leitz GmbH, Wetzlar, Ger-
degree of polymerization,13,28 and re- are characterized by their respective many) to obtain uniform specimens
Balkenhol et al

3. 290 Volume 103 Issue 5
Table I. Impression materials investigated
Manufacturer’s
Recommended Chemical
Product Manufacturer Lot Setting Time (min) Type
Affinis Fast Coltène/Whaledent AG, 94622 2:00 VPS
Light Body Altstätten, Switzerland
Aquasil Ultra Dentsply DeTrey GmbH, 60412 3:00 VPS
XLV Fast Set Konstanz, Germany
Express 2 Light 3M ESPE, 242260 2:30 VPS
Body Flow Quick Seefeld, Germany
Flexitime Heraeus Kulzer GmbH, 230525 2:30 VPS
Correct Flow Hanau, Germany
P2 Polyether Heraeus Kulzer GmbH 290143 3:15 hybrid polyether
Light siloxane*
Impregum Garant 3M ESPE B 293554 3:30 polyether
L Duo Soft C 293427
VPS: Vinyl polysiloxane
(*As P2 Polyether Light polymerizes via acid-catalyzed cross-linking reaction of silane end groups connected to polyether backbone,
it is described as hybrid polyether siloxane.32,33 Information provided by respective manufacturers)
2 Schematic drawing of specimen configuration (upper: top view; lower:
side view). Dimensions: l = distance between measuring marks (20 mm);
w = width (4 mm); h= height (2 mm); o = overall length (75 mm).
of the desired thickness. The speci- yielded an adequate power (0.80) to 1454; Zwick Roell AG, Ulm, Ger-
mens were placed in a water bath (Ju- detect statistically and clinically rel- many), stretched by 80% of their
labo Labortechnik GmbH, Seelbach, evant significant differences. original length at a crosshead speed
Germany) at 35°C, 25 seconds after After removal from the water of 200 mm/min, and released after
the start of mixing, and allowed to bath, the specimens were removed 2 seconds.
set for the manufacturers’ suggested from the mold and trimmed using a The specimens were placed on
intraoral setting time (Table I) and for scalpel (No. 11; Feather Safety Ra- PMMA beads (Palavit G Powder; Her-
5 minutes, respectively (n=10 per im- zor Co, Osaka, Japan). Subsequently aeus Kulzer GmbH, Hanau, Germany)
pression material and storage time). (1.5 minutes following removal from to allow unrestrained dimensional
A sample size of 10 was chosen, since the water bath), the specimens were changes in ambient laboratory con-
comprehensive preliminary tests had clamped in a tension-free manner in ditions for 2 hours (±10 minutes),
demonstrated that this sample size a universal testing machine (model and aligned with a transparent plastic
The Journal of Prosthetic Dentistry Balkenhol et al

4. May 2010 291
pane on the XY stage of a travelling used to test the influence of the im- deformation varied greatly between
microscope (M420; Leica Microsys- pression material and storage time, the different materials at the manufac-
tems, Wetzlar, Germany). The dis- respectively. Due to a lack of homo- turer’s recommended intraoral setting
tance between both measuring marks geneity of variances, a Games-Howell time (0.03% to 6.23%), as well as after
on each side was determined 3 times test was applied for statistical com- 5 minutes of storage (0.04% to 5.01%).
at ×40 magnification, and mean val- parison of the impression materials The polyether materials showed a sig-
ues were calculated. The following at each storage time. The influence nificantly greater permanent defor-
formula was used to determine the of storage time was tested for each mation (P<.05) compared to the VPS
permanent deformation (Dl (%)): material using a t test for unpaired materials tested. Aquasil Ultra XLV
sample groups. All statistical analyses showed a significantly greater perma-
l1 - l 0
l= x100 were carried out at a significance level nent deformation than all other VPS
l0 #%%! of .05 and performed using statistical materials (P<.05). A prolongation of
where: l1 equals the length of specimen software (SPSS 15.01; SPSS, Inc, Chi- storage time in water significantly re-
after stretching (mm), and l0 equals cago, Ill). duced the permanent deformation in
the original length of the specimen 4 of the 6 materials tested (P<.05).
(mm). RESULTS Both the impression material and
Data were subjected to a Levene storage time had a significant influ-
test to check for homogeneity of vari- Table II displays the mean values ence on the permanent deformation
ances and to a Kolmogorov-Smirnov and standard deviations of the per- (Table III). In addition, the impression
test for normal distribution. The manent deformation (Dl (%)) for all material and the storage time influ-
mean values and standard deviations materials and includes the results of enced the permanent deformation in
were calculated. A 2-way ANOVA was the statistical analysis. The permanent interaction (P<.001).
Table II. Mean values (standard deviations) of permanent deformation (Δl (%))
I (%)
Manufacturer’s
Recommended I (%)
Product Setting Time (min) 5 min P*
Affinis Light 0.03 (0.09) a – 0.04 (0.02) a .029
Body Fast Set
Aquasil Ultra 1.33 (0.16) b 1.14 (0.16) b .019
XLV Fast Set
Express 2 Light 0.10 (0.09) a 0.08 (0.02) c .510
Body Flow Quick
Flexitime Correct 0.28 (0.10) c 0.21 (0.12) c .147
Flow
Impregum Garant 5.91 (0.44) d 5.01 (0.34) d <.001
L Duo Soft
P2 Polyether Light 6.23 (0.70) d 4.30 (0.63) d <.001
Same lowercase superscript letters in columns denote material groups that do not differ significantly
(Games-Howell test, P >.05, n = 10) regarding permanent deformation within 1 setting time group.
*P values of the pairwise comparison using t test for independent sample groups
Balkenhol et al

5. 292 Volume 103 Issue 5
Table III. Results of the 2-way ANOVA to identify influence of material and storage time
on permanent deformation of materials tested
Type III Mean
Source Sum of Squares df Square F P
Corrected model 707a 11
Intercept 503 1
Material 679 5 136 1273 <.001
Storage 8.4 1 8.4 79 <.001
Material x storage 14.4 5 2.9 27 <.001
Error 11.5 108
Total 1216 120
Corrected total 713 119
aR squared =.984 (adjusted R squared =.982)
DISCUSSION influenced the results. However, as storage in water at 35°C, in addition
the coefficient of thermal expansion to the manufacturers’ suggested intra-
The primary purpose of this study is low for elastomeric impression ma- oral setting time, as recommended by
was to evaluate whether or not an im- terials (polyether, 322 ppm/°C; VPS Nayyar et al.6 Longer storage periods
pression material’s chemistry as well as light body, 208 ppm/°C), this param- prior to strain application were not
the setting time period at 35°C might eter is regarded as negligible.35 used as, in the authors’ experience,
affect its permanent deformation af- The magnitude of compression such time frames are regarded as clini-
ter stretching. The results support or elongation reportedly influences cally unacceptable for daily practice.
rejection of the first part of the null the extent of permanent deforma- The selected study design allowed
hypothesis. The second part of the null tion.20,22-24,27 The amount of elongation an accurate determination of Dl for
hypothesis, however, was not rejected, in the current experiment, compared to all materials apart from P2 Polyether
since the permanent deformation was the study by Mansfield and Wilson,15 Light. The high standard deviation
not significantly influenced by the set- provided that no rupture occurred of P2 may be related to an inhomo-
ting time for all materials tested. during testing. Other investigators geneous result from mixing, which
The mold used and the specimen have tested materials using greater seems to be a general problem with
preparation were identical to those in strains.17,27 As manufacturers gener- this product.22 The vinyl polysiloxane
the study by Lawson et al.27 However, ally recommend that impressions (VPS) materials showed low perma-
in contrast to that investigation, the be removed quickly, elongation was nent deformation (Dl<0.3%), with the
present study did not subtract shrink- performed rapidly.28 A longer duration exception of Aquasil Ultra XLV. In con-
age effects caused by polymerization of strain reportedly results in great- trast, Lawson et al27 observed a lower
contraction from the permanent de- er permanent deformation.23,28 To permanent deformation for Aquasil.
formation,13,29,34 as the final perma- provide the specimens sufficient time However, it is not clear whether the
nent deformation of an impression is for elastic recovery, measurements XLV version of the product was used.
a combined result of viscoelastic and were performed 2 hours after strain Klooster et al28 reported similarly low
shrinkage phenomena. Determining application.14,20,23,27 values measured 1 hour after strain
the sum of these effects seemed to be Dental impression materials may application for VPS impression ma-
more relevant to the clinical situation. not be completely polymerized after terials. Unlike in the present study,
This approach explains the negative the manufacturers’ suggested intra- however, Klooster and colleagues
permanent deformation obtained oral setting time and, in turn, may not stretched the specimens until rupture
for Affinis Light Body Fast Set. In ad- have fully developed elastic properties and determined the permanent defor-
dition, differences in the thermal ex- when removed from the mouth.5,13 mation after reassembling the ends
pansion coefficient obtained for the Therefore, in this study, the tensile at various points in time after tear
various materials tested may have strain was applied after 5 minutes of strength testing.
The Journal of Prosthetic Dentistry Balkenhol et al

6. May 2010 293
The significant differences ob- between oligomer chains has ad- REFERENCES
served between the VPS materials are vanced sufficiently at the manufactur-
1. Braden M, Inglis AT. Visco-elastic prop-
not expected to be clinically relevant er’s recommended intraoral setting erties of dental elastomeric impression
regarding the precise fit of definitive time, exhibiting highly elastic proper- materials. Biomaterials 1986;7:45-8.
restorations.26 The slightly larger per- ties at this stage. 2. Jörgensen KD. A new method of recording
the elastic recovery of dental impression ma-
manent deformation of Aquasil Ultra In contrast, the improvements terials. Scand J Dent Res 1976;84:175-82.
XLV is presumably induced by this ma- regarding elastic recovery were no- 3. McCabe JF, Walls AW. Applied dental mate-
terial’s different filler content and/or ticeably higher for the polyether rials. 9th ed. Oxford: Wiley-Blackwell; 2008.
p. 136-77.
lower cross-linking density compared materials. This indicates that the amount 4. Balkenhol M, Ferger P, Wöstmann B.
to the other VPS materials tested.18,22 of elastic recovery is closely related Dimensional accuracy of 2-stage putty-
wash impressions: influence of impres-
In the current tear test, the perma- to the impression materials’ chemical
sion trays and viscosity. Int J Prosthodont
nent deformation of the VPS materi- composition.18,27 In contrast to tensile 2007;20:573-5.
als was, except for Aquasil Ultra XLV, strain, permanent deformation deter- 5. Tan E, Chai J. Working times of elastomeric
impression materials according to dimen-
lower compared to the permanent mined after compression is reportedly sional stability and detail reproduction. Int
deformation resulting from compres- low (<1%) for polyether-based materials J Prosthodont 1995;8:541-7.
sion tests, according to the ISO stan- and did not differ in a clinically relevant 6. Nayyar A, Tomlins CD, Fairhurst CW,
Okabe T. Comparison of some properties
dard.8,27 magnitude from that of vinyl polysilox- of polyether and polysulfide materials. J
The polyether materials, however, anes.8 Therefore, results obtained for Prosthet Dent 1979;42:163-7.
showed a permanent deformation permanent deformation after compres- 7. Chai J, Takahashi Y, Lautenschlager EP.
Clinically relevant mechanical properties
greater than 4% to 5%, which is likely sion do not allow for a prediction of the of elastomeric impression materials. Int J
to be of clinical relevance.26 Sulcus permanent deformation resulting from Prosthodont 1998;11:219-23.
extensions 2 mm in length would be tensile strain.15,27 As the elastic recovery 8. Lu H, Nguyen B, Powers JM. Mechanical
properties of 3 hydrophilic addition silicone
permanently deformed up to 100 from tensile strain is a clinically impor- and polyether elastomeric impression mate-
µm or more. It should be addition- tant material parameter which cannot be rials. J Prosthet Dent 2004;92:151-4.
9. Wöstmann B, Blösser T, Gouentenoudis M,
ally considered that the duration of deduced from other test configurations,
Balkenhol M, Ferger P. Influence of margin
straining was relatively short in the this test should be included in the ISO design on the fit of high-precious alloy res-
present study and can exceed that standard (ISO 4823). torations in patients. J Dent 2005;33:611-8.
10.Endo T, Finger WJ. Dimensional accuracy
time period in clinical situations,16 Because this was an in vitro study, of a new polyether impression material.
which would result in even greater certain limitations exist regarding Quintessence Int 2006;37:47-51.
permanent deformation.15,22 Klooster the application of the results to the 11.Blatz MB, Sadan A, Burgess JO, Mercante
D, Hoist S. Selected characteristics of a new
et al28 recorded values of similar scale clinical situation. The specimens had polyvinyl siloxane impression material--a
for a medium-bodied polyether (4.3 a cross-section of 2 x 4 mm, which is randomized clinical trial. Quintessence Int
±1.1%), whereas Hondrum17 found much thicker than the thin sulcus areas 2005;36:97-104.
12.Chee WW, Donovan TE. Polyvinyl siloxane
similarly low values for polyether and that are observed clinically. Addition- impression materials: a review of prop-
VPS impression materials (<1%). ally, the amount of stretching might erties and techniques. J Prosthet Dent
It is hypothesized that the dif- vary clinically depending on sulcus 1992;68:728-32.
13.Anusavice KJ. Phillips‘ science of dental
ferent results for the polyether ma- depth and actual tear forces. However, materials. 11th ed. St. Louis: Elevier; 2003.
terials may be due to breakage of both parameters were kept constant in p. 205-54.
polymer chains and a weaker or less the current study for standardization 14.Goldberg AJ. Viscoelastic properties of sili-
cone, polysulfide, and polyether impression
elastic polymer network, respective- purposes and proper testing. Notwith- materials. J Dent Res 1974;53:1033-9.
ly.24 Other authors came to a similar standing these limitations, the authors 15.Mansfield MA, Wilson HJ. A new method
for determining the tension set of elas-
conclusion,22,27 as elastic recovery of assume that the results are clinically
tomeric impression materials. Br Dent J
polyether-based materials tended to relevant. As the current study focused 1973;135:101-5.
be lower compared to VPS materials on fast-setting vinyl polysiloxane mate- 16.Blomberg PA, Mahmood S, Smales RJ,
Makinson OF. Comparative elasticity tests
in shear tests.22 rials, future investigations should ana- for elastomeric (non putty) impression
Although prolonged polymeriza- lyze regular-set materials. materials. Aust Dent J 1992;37:346-52.
tion in water for 5 minutes significantly 17.Hondrum SO. Tear and energy properties
of three impression materials. Int J Prostho-
reduced the permanent deformation CONCLUSIONS dont 1994;7:517-21.
for the majority of the products tested, 18.McCabe JF, Wilson HJ. Polymers in den-
the improvement in elastic recovery was Increasing the manufacturers’ tistry. J Oral Rehabil 1974;1:335-51.
19.Craig RG. Review of dental impression
small for the VPS materials. Therefore, recommended intraoral setting time materials. Adv Dent Res 1988;2:51-64.
a general recommendation to increase does not provide relevant improve- 20.de Araujo PA, Jorgensen KD, Finger W.
intraoral setting time is probably un- ments in elastic recovery for vinyl poly- Viscoelastic properties of setting elasto-
meric impression materials. J Prosthet Dent
necessary for this group of materials.6,28 siloxane materials; however, it may for 1985;54:633-6.
Presumably, the cross-linking reaction polyether materials.
Balkenhol et al

7. 294 Volume 103 Issue 5
21.International Organization for Standard- 28.Klooster J, Logan GI, Tjan AH. Effects of 35.McCabe JF, Storer R. Elastomeric impres-
ization. ISO Specification No. 4823:2000. strain rate on the behavior of elastomeric sion materials. The measurement of some
Dentistry - elastomeric impression materi- impression. J Prosthet Dent 1991;66:292-8. properties relevant to clinical practice. Br
als. 3rd ed. Geneva: ISO; 2000. Available at: 29.Kim KM, Lee JS, Kim KN, Shin SW. Dimen- Dent J 1980;149:73-9.
http://www.iso.org/iso/store.htm sional changes of dental impression materi-
22.Endo T, Finger WJ. Evaluation of the elastic als by thermal changes. J Biomed Mater Res Corresponding author:
recovery of polyether impression materials. 2001;58:217-20. Dr Markus Balkenhol
Am J Dent 2005;18:355-60. 30.Kaloyannides TM. Elasticity of elastometer Justus Liebig University
23.Inoue K, Wilson HJ. Viscoelastic properties impression materials. II. Permanent defor- Department of Prosthodontics
of elastomeric impression materials. III. mation. J Dent Res 1973;52:719-24. Schlangenzahl 14, 35392
The elastic recovery after removal of strains 31.Rosenstiel SF, Land MF, Fujimoto J. Con- Giessen
applied at the setting time. J Oral Rehabil temporary fixed prosthodontics. 4 th ed. St. GERMANY
1978;5:323-7. Louis: Elsevier; 2006. p. 431-65. Fax: +49-641-9946 139
24.Jamani KD, Harrington E, Wilson HJ. The 32.Balkenhol M, Wöstmann B, Kanehira E-mail: markus.balkenhol@dentist.med.uni-
determination of elastic recovery of impres- M, Finger WJ. Shark fin test and impres- giessen.de
sion materials at the setting time. J Oral sion quality: a correlation analysis. J Dent
Rehabil 1989;16:89-100. 2007;35:409-15. Acknowledgments
25.Sotiriou M, Hobkirk JA. An in vivo investi- 33.Kanehira M, Finger WJ, Endo T. Volatil- The authors thank Michael Köhl, Dipl Ing, and
gation of seating and removal forces associ- ization of components from and water Dr Jürgen Riehl for their assistance with the
ated with recording impressions in dentate absorption of polyether impressions. J Dent statistical analysis. In addition, the authors
patients. J Prosthet Dent 1995;74:455-62. 2006;34:134-8. thank the respective manufacturers for the
26.Laufer BZ, Baharav H, Ganor Y, Cardash 34.Lampé I, Marton S, Hegedüs C. Effect donation of materials.
HS. The effect of marginal thickness on the of mixing technique on shrinkage rate of
distortion of different impression materials. one polyether and two polyvinyl siloxane Copyright © 2010 by the Editorial Council for
J Prosthet Dent 1996;76:466-71. impression materials. Int J Prosthodont The Journal of Prosthetic Dentistry.
27.Lawson NC, Burgess JO, Litaker MS. Tensile 2004;17:590.
elastic recovery of elastomeric impression
materials. J Prosthet Dent 2008;100:29-33.
Noteworthy Abstracts of the Current Literature
In vitro cytotoxicity evaluation of elemental ions released from different prosthodontic
materials
Elshahawy WM, Watanabe I, Kramer P.
Dent Mater 2009;25:1551-5. Epub 2009 Aug 13.
Objectives. This study investigated the cytotoxicity of elemental ions contained in four fixed prosthodontic materials
(gold, nickel-chromium, stainless-steel alloys and CAD-CAM ceramics).
Materials and methods. According to the determination of elements released from prosthodontic materials by using
inductively coupled plasma mass spectroscopy, similar amounts of elements Pd, Ag, Zn, Cu, Ni, Cr, Mo, Be, Fe, Al,
and K were prepared as salt solutions. Wells with a tenfold higher concentration of the tested elements were used as
positive controls, while a well without any tested element was used as a negative control. These salt solutions were
tested for cytotoxicity by culturing mouse L-929 fibroblasts in the salt solutions for a 7-day period of incubation.
Then, the percentage of viable cells for each element was measured using trypan blue exclusion assay. The data (n=5)
were statistically analyzed by ANOVA/Tukey test (p<0.05).
Results. The results showed a statistically significant difference for the cytotoxic effect of the tested elements salt
solutions. For the released element concentrations the lowest percentage of viable cells (mean ± SD) was evident with
Zn, Cu or Ni indicating that they are the highly toxic elements. Be and Ag were found to be intermediate in cytotoxic
effect. Fe, Cr, Mo, Al, Pd or K were found to be the least cytotoxic elements.
Significance. Zn and Cu released from gold alloys, and Ni released from nickel-chromium alloys, which are commonly
used as fixed prosthodontic restorations, show evidence of a high cytotoxic effect on fibroblast cell cultures.
Reprinted with permission of the Academy of Dental Materials.
The Journal of Prosthetic Dentistry Balkenhol et al