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-

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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

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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.

Craig RG. Kestorative dental materials. 8th pd. .St, Louis: Mosby. 1989;309-25. Reitz CD, Clark NP. The setting ofvinyl polysiloxanr and condensat.iw silicone putties when mixed with gloved hands. .I Am Dent Assw 1988;116:371-5.

3.

4.

Noonan dE, Goldfogel MH, Lambert RL. Inhibited Seth of the surfaw of addition silicones in contact with rubber dam. Oper Dent 1986;10:3B-8. Chee WWL, Donovan TE, Kahn RL. Indirect inhibition ofpolymerizn t ion of a polyvinyl siloxane impression material: a case report. Quint Tnt 1991;22:1:13--5.

Because no inhibitory effect on polymerization of the polyvinyl siloxane impression materials tested was appar- ent, no statistical analysis was done.

5. Kahn RL, Donovan TE, Chee WWL. A pilut study of polymerization inhibition of poly (vinyl siloxane) materials by latex gloves. Int .I Prosthodont 1989;2:128-30.

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dam with a poly (vinyl siloxane) impression material: a screening test. Int J Prosthodont 1989;2:342-6.

7. Cook WD, Thomas F. Rubber gloves and addition silicone materials. Aust Dent J 1986;31:140.

8. Donovan TE, Gandara BK, Nemetz H. Review and survey of medica- merits used with gingival retraction cords. J PROSTHET DENT 1985;53:525-31.

9. Donovan TE. A review of contemporary impression materials. Calif Inst Cont Ed 1988;24:9-20.

10. Phillips RW. Skinners science of dental materials, Philadelphia: WB Saunders, 1991;154.

Reprint requests to: DR. TERRY E. DONOVAN SCHOOL OF DENTISTRY, RM. 4376 UNIVERSITY PARK UNIVERSITY OF SOUTHERN CALIFORNIA Los ANGELES, CA 90089.0641

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