Prosthodontics

Impressions for complete dentures usingnew silicone impression materialsIwao Hayakawa, DDS, DDScVlkki Watanabe, DDS,

This articie describes a convenient technique tor mailing impressions ol complete dentures using twonewly developed silicone materials. One of these materials, a heavy-bodted silicone materiai, is used torsimultaneous molding of ali borders. The material is avaiiabie in automatic mixing systems, so it can beeasily and evenly applied on the tray borders. The material is designed to have a low elasticity atter settingso that excess material can be carved or deficient sites corrected with a small mix. The other newiy devel-oped material, a light-bodied silicone material, possesses better flow than the usuai light-bodied silicones.In addition, since viscosity Is controlled and adequate flow is maintained during seating in the mouth, mu-cosal detail is superior, (Quintessence Int 2003:34:177-180)

Key words: complete dentures, impression, one-step border molding technique, siiicone impressionmaterial

CLINICAL RELEVANCE: The impression technique forcomplete dentures using new silicone materials enablesclinicians fo make impressions with relative ease and sig-nificantly reduces the time required for making impres-sions, in particular, this convenient technique may be rec-ommended for beginners.

In denture fabrication, the impression tecbniques andmaterials used vary depending on the condition of

the oral cavity and the dentist's perspective on impres-sion making, A common procedure for impressionmaking of an edentulous jaw is to first make an indi-vidual tray on the study cast obtained from a prelimi-nary impression. The borders are tben molded with

^Pfotessor and Cf ia irmar, Department cf Complete Denture Prcs-thodontcs. Graduate Sctiool, Tokyo Medical a rd Dental tJniversit/, Tokyo,Japan.

'Research Associate, Department of Complete Denture Prosthodonttcs,Graduate Sctiool, Tokyo Medical and Dental University, Tokyo, Japan

Reprint requesis: Dr Iwao Hayakawa, Department cf Complete DenturePiosthodontics, Graduate School, Tokyo Medical and Dental University,1-5-4S,Yijshima, Bunkyo-ku,Tokyo, Japan tt3-8549.E-mail: i,hayakawa,ore@tmd.ac,ip

modeling compotmd, and ñnally an impression is com-pieted witb an impression material that flows easily.

An accurate impression is achieved using this tech-nique, but it is time consuming and often difficult forbeginners to master. In order to reduce tbe impressiontime, some dentists use a simple impression techniquesuch as alginate made with a stock tray. If such a sim-ple single-impression technique is used, the compieteddenture often will not be adequate during function,since border molding, wbicb records the mobilities ofthe muscles during function, cannot be performed.Molding the borders with an individual tray is an es-sential step in impression making.

Levin' has observed tbat many dental students onlyremember the long hours spent border molding withmodeling compound during their clinical training, andmost of them seem to be firmly determined not to touchanymore modeling compound after graduation.

This article introduces an impression technique usingtwo new silicone impression materials developed hy theauthors, a heavy-bodied silicone (Exahiflex tray type,GC) for simultaneous molding of all borders, and afree-flowing, light-bodied silicone (Exadenture, GC},which helps resolve the problems conventional tech-niques have possessed. The technique is easy to performand is recommended for beginners, as weli as clinicianswho are not confident in denture construction.

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BORDER MOLDING MATERIALS

The techniques that use sectional functional bordermolding with modeling compound require skill andexperience to achieve even molding along all the bor-ders. Materials that allow simultaneous tnoldings of allborders are designed to have the proper plastic consis-tency for molding and recording borders of the den-ture,^ The entire border can be molded with one inser-tion during the working time of the material, leadingto a great reduction in chairtime compared to tradi-tional modeling compound. Putty silicone andheavy-bodied polysulfide impression materials haveheen proposed for use in the clinical setting as materi-als for simuhaneous molding of all borders,^-^ Sinceheavy-bodied polysulfide rubber is viscous and adher-ent, it is difficult to evenly place this material on allthe borders. After setting, it becomes elastic, and thusis difficult to trim with a Imife, Borders molded usingmateriais that possess high elasticity may be displacedor deformed by the final impression "wash" material.Putty silicone materials are not sticky like polysulfides,but using these can be time consuming since theymust be rolled prior to being placed on the borders.They then become stiff after setting, so excess materialcan be carved and shaped with a knife before the final"wash" impression,

Tesfing for consistency and strain in compressionhas been completed for a new heavy-bodied siliconematerial (Exahiflex tray type, GC), The strain in com-pression represents the flexibility of the material.These measurements were carried out according toISO 4823, and results were very favorable for usingthis material in complete denture impressions.

These standardized tests demonstrate that this newsilicone material possesses a proper consistency,which allows it to remain in position on the bordersduring loading of the tray and to record the functionalmovements of the surrounding tissues appropriately.In addition, this material has been designed to possessa slightly lower consistency than a putty silicone mate-rial, enabling it to be available in automatic mixingsystems. An equal quantity of the impression materialcan thus be applied onto the entireties of the bordersthrough the mixing tip. The material can be easily ap-plied onto the borders without haste because the usualmixing procedure is not necessary. The material is de-signed to have a low elasticity after setting so that ex-cess material can be carved or deficient sites correctedwith a small mix. After completing the border mold-ing, a precise final wash impression can be tnade usinga light-bodied silicone material.

FINAL IMPRESSION MATERIAL

Zinc oxide-eugenol paste and elastomeric impressionmaterials, such as light-bodied polysulfide rubbers andlight-bodied silicones, are generally used for the finalimpression of a complete denture. Zinc oxide-eugenoland polysulfide rubber possess technical complicationsthat render them less than ideal, Silicone impressionmaterials are nonirritating, causing minimal discom-fort for the patient. Most light-bodied sihcone materi-als possess good fiow for use as a final impression ma-terial for dentures, but the viscosity rapidly increasesjust after seating the tray in the mouth, resulfing in thedifticulty of making the final impression.

Consistency and strain in compression for the newlight-bodied silicone (Exadenture, GC) were testedand found to be very favorable.

The new light-bodied silicone possesses better flowthan the traditional light-bodied silicone. In addition,as the rapid increase in viscosity is controlled and ade-quate fiow is maintained during seating in the mouth,the tray can be accurately seated in place and the de-tails of the mucosa can be recorded.

PROCEDURE

1, Try the individual tray in the mouth and reduce allperipheries so that they are 2 to 3 mm short of thetissue reflection. The distal end of the maxillary traymust contain both hamular notches and extend ap-proximately 2 mm beyond the vibrating line (Fig 1),The mandibuiar tray borders shouid be trimmed byreferring to the retromolar pad, external obliqueridge, and mylohyoid ridge,

2, Apply adhesive for the sificone material on the bor-ders of the tray (Fig 2),

3, Position the heavy-bodied silicone material on theborders, making certain to evenly apply it through amixing tip. The silicone material should be placedacross the posterior palatal seal area. The applica-fion of the material using the dispenser is so easythat sufficient working time is provided to completethe border molding (Fig 3), It may be difficult for thebeginners to insert the mandibular tray withoutscraping the silicone from the borders. To avoid this,the border molding procedure shouid be separatedinto two stages; hngual and buccal (Fig 4), In themandibular cases with a severeiy resorbed ridge, it isrecommended to apply the heavy-bodied siliconematerial onto the enfire inner surface of the tray,

4, The tray should be rotated into the mouth with thecheek retracted by the finger to avoid scraping thesilicone material from its borders. Instruct the pa-tient to perform movements such as pushing the

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Fig 1 "•: =•';,'•' :•" ne tray borae' 3"OJIÍ; bo checked by obser-•.a;.Q.n. Tne I ay sioulO be 2 mm snort of the tissue rellection.

Fig 2tray.

Place adhesive tor silioone material on the borders of the

Fig 3 Add the siiicone material onto the borders and across theposterior p ai ata I seal area.

Fig 4 Border molding the mandibular tray. This procedure maybe separated into lingual and buccal steps in order to insert thetray without scraping the siiicone from the borders

Figs 5a and 5b Remove the tray ar.d examine the borders. Excess material shouid be trimmed with a sharp knife. Any deficient sitesshouid be remolded by adding a small mix of silicons material.

tongue forward and laterally and pursing tbe lips.Simuitaneously, the hps and cheeks should beslightly massaged to assist border molding.

5. Remove the tray when the impression material hasset and examine the borders. Excess materialshould be trimmed with a sharp knife. Any deficientsites shouid be remolded by adding a small mix of

Quintessenoe International

siiicone material- Excess sihcone that flows ontothe inner surface of the tray should be removedwith a sharp l<niie to form a smooth surface be-tween tbe siiicone and the tray {Figs 5a and 5b).

6. Apply siiicone adhesive on tbe inner surface of thetray. Light-bodied siiicone materiai (Exadenture) ismixed and applied on the tray (Fig 6).

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Fig 6 Paint silicone adhesive on the inner surface ot the tray.Light-bodied silioone materiai is mixed and piaoed on tiie tray inpreparation for the (inai wash impressicn.

Figs 7a and 7b The ccnpieteö •iipressions The borders are smooth and rounded. The notches for the trena are deliniteiy recorded.

7, The tray should be seated properly in tbe moutband held gently in place. When seating the tray inplace, care must be taken not to use excessive pres-sure, otberwise this will result in tbe inner surfaceof tbe tray coming in direct contact witb tbe mu-cosa. The lips and cbeeks sbould be gentiy mas-saged so tbat any excess material can flow out-Remove tbe tray wben tbe impression material basset (Figs 7a and 7b),

CONCLUSION

A technique has been described that uses newly devel-oped silicone materials for complete denture impres-sions. The new heavy-bodied silicone is designed tohave a proper consistency so that it can he used for si-multaneous molding of all horders and dispensed byautomatic mixing systems, allowing easy and evenloading of the tray. The new final impression materiaipossesses better flow than the usual light-bodied sili-

cone- During seating of the tray in the mouth, viscosityis controlled and adequate flow is maintained so thatthe tray can be seated in place, and details of the mu-cosa are recorded-

REFERENCES

1, Levin B, IrTipressions for Complete Dentures, Chicago:Quintessence, 1984,

2, Zarb GA, Bolender CL, Carlsson GE, Boucher'sProsthodontic Treatment for Edentulous Patients, ed 11, StLouis: CV Mosby, 1997.

3, Appelbaum EM, Mehra RV, Clinical evaluation of polyvinyl-siloxane for complete denture impressions, J Prosthet Dent1984;52:537-539,

4, Hosoi T, Morito M, Mizuno Y, Sugiyama K, A reiiabiemethod for fabricating complete dentures, L Dent Magt998;92:168-175.

5, Clinical syliabus for compiete dentures (1991-1992],Portland: Department of Prosthodontics, Schooi ofDentistry. Oregon Health Sciences University, 1991,

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