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Inhibition of polymerization of polyvinyl siloxanes by
medicaments used on gingival retraction cords
Luciano M. de Camargo, DDS, MEd,a Winston W. L. Chee, BDS,b and
Terry E. Donovan, DDSC University of Southern California, School of
Dentistry, Los Angeles, Calif.
Inhibition of polymerization of polyvinyl siloxane materials by
latex products is well documented. It is thought to be caused by
contamination of the chloroplatinic acid catalyst by sulfur
compounds. Many medicaments, such as aluminum sulfate and ferric
sulfate, used on gingival retraction cords have been accused of
causing inhibition of set of polyvinyl siloxane materials. Several
of these medicaments were tested with two polyvinyl siloxanes and
found not to cause any inhibition of set. (J PROSTHET DENT
i99>;70;114-7.)
P. olyvmyl siloxane impressions have become popu- lar in recent
years because of their accuracy, ease of manipulation, excellent
elastic recovery, and dimensional stabi1ity.l Inhibition of
polymerization of these materials by chemical agents in latex
rubber has been well docu- mented.2-4 This can occur when putty
materials are mixed with latex gloves, when the impression material
is in con- tact with a rubber dam, and even by indirect intraoral
con- tact of teeth and soft tissue structures with latex gloves be-
fore impression making. 5, 6 The mechanism of inhibition of
polymerization is thought to be contamination of the chlo-
roplatinic acid catalyst by sulfur compounds in the latex
products.7
Many different medicaments are used on gingival re- traction
cords to attempt to minimize hemorrhage from the gingival sulcus
during impression making.8 This is espe- cially critical in using
hydrophobic impression materials such as polyvinyl siloxanes.
Manufacturers claims to the contrary, these materials are not truly
hydrophilic and they require an absolutely dry sulcus if
impressions are to be predictably successful.g It has been
suggested that certain of these medicaments may inhibit the
polymerization of polyvinyl siloxanes in a manner similar to that
of latex rubber.lO Clinicians have reported such occurrences anec-
dotally in the clinical setting to one of the authors on nu- merous
occasions.
Concern with some of the medicaments, especially those
containing aluminum sulfate or ferric sulfate, seems valid. It is
also possible that the inhibition reported anecdotally
aGraduate student, Advanced Education in Prosthodontics.
bAssistant Professor, Director of Implant Dentistry. CAssociate
Professor, Chairman, Department of Biomaterials Sci-
ence. Copyright 9 1993 by The Editorial Council of THE JOURNAL
OF
PROSTHETIC DENTISTRY. 0022-3913/93/$1.00 + .lO. 10/l/47313
114
was caused by contact of the intraoral soft .and hard tissues
with latex gloves, and had nothing to do wit.h the medica- ment
used. This study was done to determine whether any of the commonly
used gingival retraction medicaments could inhibit the
polymerization of polyvinyl siloxane im- pression materials when
they are in direct contact with the setting material.
Inhibited polymerization of polyvinyl siioxanes is man- ifested
by the appearance of a rippled surface on the set impression
material (Fig. 1). The material on the surface of the impression in
the areas that were contaminated will be slippery to the touch.
This inhibition is limited and super- ficial, not unlike the
oxygen-inhibited layer encountered with resin composites. This
rippling is duplicated in the gypsum cast, and the cast may appear
wet. wrinkled, or poorly defined. Often, unpolymerized impression
material will be adherent to the prepared teeth or to the cast when
the impression is separated (Fig. 2). Regardless, the surface
detail of the cast will be compromised and unsuitable for use in
the fabrication of cast restorations.
METHODS AND MATERIAL
A number of commercially available gingival retraction
medicaments were purchased from dental supply houses. The active
agents in these materials included racemic epi- nephrine, aluminum
chloride, aluminum sulfate, alumi num potassium sulfate, and ferric
sulfate. The products tested, along with the active agents and
manufacturers, are listed in Table I.
In phase one of this investigation, l-inch length segments of
plain retraction cord (Ultrapack Cord, size 1, Ultradent Products,
Salt Lake City, Utah) were soaked in the various medicaments for 10
minutes and blotted dry on a sterile cotton towel. Additional
l-inch segments of cords impreg- nated with various medicaments by
manufacturers were also tested along with untreated cord, which was
used as the control. Three cords in each category were tested.
Low-
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Fig. 1. The rippled surface of the impression material opposing
the labial surfaces of the teeth is characteristic of inhibited
polymerization. Fig. 2. Often unpolymerized impression material
will remain adherent to the teeth if contamination has
occurred.
Fig. 3. This is representative of the surface of impression
material allowed to set against a gauze sponge impregnated with one
of the medicaments tested. No evidence of inhibi- tion of
polymerization is present.
Fig. 4. The surface of the impression material allowed to set
against a sample of latex demonstrates the rippling characteristic
of inhibited polymerization.
viscosity polyvinyl siloxane impression materials (Repro- sil,
L. D. Caulk Co., Milford, Del.; and Extrude, Kerr Den- tal Mfg.,
Romulus, Mich.) were mixed and injected by use of the automix
system over all of the cords. The impression material was allowed
to set for 10 minutes. The surface of the set impression material
was independently examined by the naked eye and under X10
magnification for the presence or absence of inhibited
polymerization.
The criteria used to determine whether polymerization was
inhibited were (1) the presence of an oily, slippery substance on
the surface of the impression material; (2) a rippled appearance on
the surface of the impression mate- rial; or (3) an obvious lack of
detail reproduction on the surface of the impression material.
In phase two of the study, squares of cotton sheets, 1 cm x 1
cm, were soaked in the medicaments (solutions 6 through 9 listed in
Table I) for 10 minutes and blotted dry on a cotton towel. Similar
squares of latex rubber cut from gloves known to inhibit
polymerization of the impression
materials tested (Alpine Latex Gloves, Redondo Beach, Calif.)
were used as controls. Three samples in each cate- gory were
tested. Impressions of the squares were made in a manner identical
to those made in phase one. The set im- pression materials were
evaluated for inhibited polymer- ization also in the same manner,
with the same criteria as in phase one.
RESULTS
In phase one of the investigation, none of the materials tested
appeared to have any inhibitory effect on the poly- merization of
either of the polyvinyl siloxane impression materials used.
However, the small surface area afforded by use of retraction cords
per se made it somewhat problem- atic to evaluate the samples,
especially when it came to an attempt to feel the nature of the
surface of the set impression. Phase two was initiated with a
larger surface generated so this evaluation would be more
meaningful.
None of the medicaments tested demonstrated any
AUGUST 1993 115
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Table I. Products tested DISCUSSION
Product Active agent Manufacturer
1. Iiltrapak non- None Ultradent impregrated Products cord Salt
Lake City,
Utah 2. Gingi-Pak Racemic Gingi-Pak
impregnated epinephrine Camarillo, Calif. cord 0.5 mg/inch
3. Hemodent Buffered Premier Dental gingival aluminum Products
retraction chloride Norristown, Pa. cord 0.8 mg/inch
4. Pascord 8 Aluminum Pascal Co. Inc. sulphate Bellevue, Wash.
0.48 mg/inch
5. Racord Two Racemic Pascal Co. Inc. 9 epinephrine
0.30 mg/inch plus zinc phenolsulfonate 0.70 mg/inch
6. Ultrapak Aluminum U.S.C. nonimpregnated sulphate Pharmacy
cord saturated Los Angeles,
solution Calif. 7. Ultrapak Aluminum U.S.C.
nonimpregnated potassium Pharmacy cord sulphate
saturated solution
8. Astringedent Ferric sulphate Ultradent Products
9. Hemodent Aluminum Premier Dental chloride Products
(buffered)
The concern that certain medicaments used with gmg:i- val
retraction procedures may interi+ :vil h p~,l:Vmeriz;~- tion of
polyvinyl siloxane is undersiantiabie. Ihi5 inhitii tory effect has
been clearly demonstrated iii lhe cuse of IX tex rubber products,
likely because oi :tnre;-rct,ed sulfur that remained from the
manufacturing procehs. However, OFi the basis of data from this
study, it does not appear t.hat :iri~ of the materials commonly
used in gingivai ret racl ion pro- cedures have an inhibitory
effect.
A likely explanation for the clinical situations in which
inhibited polymerization was reported is that the leetb and/or the
surrounding soft tissues were contammated i-r) latex gloves before
the impression making. This contarn- nation, which is difficult to
remove, was likely the cause ok the inhibited set. In this regard,
it is interesting to note that all of the reports of inhibition
have surfaced in recent years since improved infection control and
barrier techniques have become widespread. Before this. polyvinyl
siloxanes had been used successfully for many years in conjunction
with all of the medicaments tested. The evidence point;; to the
latex gloves and not the medicamrnts
SUMMARY AND CONCLUSIONS
In light of the finding that the polymerization of polyvi- nyl
siloxane impression materials can be inhibited by sul- fur in latex
rubber products, and because many gingival retraction medicaments
contain chemically act.ive agents, a study was conducted to
determine whether tiny of the commonly used gingival retract,ion
medicaments inhibited the set of these materials. The following
cclnclusions appear to be valid:
I. Latex rubber can inhibit the set oi polyvinyl siloxane
impression materials.
inhibitory effect on the setting of the two polyvinyl silox-
anes studied in phase two of the investigation. The surfaces of the
set impression materials appeared completely nor- mal (Fig. 3). The
impression materials setting against the control samples of latex
rubber displayed the classic rippling characteristic of inhibited
polymerization (Fig. 4).
2. The inhibition of set seen with latex rubber is limited to
the most superficial layer of the impression material.
3. None of the medicaments tested had an>- inhibitor) effect
whatsoever on polymerization.
4. The inhibited polymerization mentioned in anecdotal reports
is more likely caused by inadvertent contamination by latex rubber
gloves than by the gingival retraction me- dicaments.
Although the samples in phase two were easier to eval- uate than
those in phase one, the apparent lack of inhibi- tion of
polymerization by aluminum sulfate and aluminum chloride in both
groups would lend credence to the validity of the data in phase
one. The potential inhibitory effect of epinephrine was not tested
in phase two, but the likelihood that it would cause a problem is
extremely small in any case. Epinephrine-impregnated cord was only
included in phase one for the sake of completeness because it is a
com- monly used agent.
REFERENCES
1.
2.
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1)~: CAMARGO, CHEE, AND DONOVAN THE JOURNAL OF PROSTHETIC
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Reprint requests to: DR. TERRY E. DONOVAN SCHOOL OF DENTISTRY,
RM. 4376 UNIVERSITY PARK UNIVERSITY OF SOUTHERN CALIFORNIA Los
ANGELES, CA 90089.0641
AUGUST 1993 117