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Shillingburg HT, Hobo S, Whitsett LD. Fundamentals of fixed prosthodontics. 2nd ed. Chicago: Quintessence Publishing Co, 1981;83. Kaufman EC, Coelho DH, Colin L. Factors influencing the retention of cemented gold castings. J PROSTHET DENT 1961; 11:487-502. Jorgenson KD. The relationship between retention and conver- gence angle in cemented veneer crowns. Acta Odontol Stand 1955;13:35-40. Rosenstiel E. The retention of inlays and crows as a function of geometrical form. Br Dent J 1957;103:388-94. Weed RM, Baez RJ. A method for determining adequate resistance form of complete cast crown preparations. J PROSTHET DENT 1984;52:330-4.

8. Lewis RM, Owen MM. A mathematical solution of a problem in full crown construction. J Am Dent Assoc 1959;59:943-7.

9. Shillingburg HT, Hobo S, Fisher DW. Preparations for cast gold restorations. Chicago: Quintessence Publishing Co, 1974; 21:2.

10. Owen CP. Retention and resistance in preparations for extracor- onal restorations. Part II: practical and clinical studies. J PROSTHET DENT 1986:56:148-53.

Reprint requests to: DR. MERLE H. PARKER U.S. ARMY DENTAL ACTIVITV FT. SILL, OK 73503

Accuracy of impression materials for complete-arch fixed partial dentures

Chang-Chi Lin, B.M.D., M.S.,* Gerald J. Ziebert, D.D.S., M.S.,** Sara Jean Donegan, D.D.S., MS.,*** and Virenda B. Dhuru, B.S., B.D.S., M.S.**** Marquette University, School of Dentistry, Milwaukee, Wis.

lJ imensional accuracy of impression materials is crucial for the production of working casts in fixed prosthodontics. The accurate replication of tooth prepa- rations and their arch position requires impression materials that exhibit limited distortion.

Research on dimensional stability of impression materials has commonly concentrated on the accuracy of individual dieslm5 and quadrant fixed partial denture (FPD) abutments. MO Studies reporting the accuracy of complete arch impressions have been sparse. Henry and Harnist” compared the accuracy of 14 different impres- sion materials by using a four-posted, silver-plated, full-arch model and concluded that polyethers were the most reliable. In .another study of full-arch impressions of two machined aluminum alloy dies, Lacy et al.‘* reported that the addition silicones were the most stable, followed by the polyethers. Stauffer et a1.13 studied the accuracy of six impression materials used in complete- arch FPD impressions with four intricate abutment preparations machined of stainless steel. A prosthesis

Submitted in expanded form by the first author as a thesis in partial fulfillment of the requirements for a Master of Science degree, Marquette University.

*

**Professor and Chairman, Fixed Prosthodontics. ***Adjunct Clinical Professor, Fixed Prosthodontics. ****Associate Professor, Operative Dentistry and Dental Materials.

288

Table I. Impression materials used in study

Type of material Manufacturer

Polyether Polyjel L.D. Caulk, Milford, Del. Impregum Premier, ESPE, West Germany

Vinyl polysiloxane Reprosil L.D. Caulk Mirror 3 Sybron/Kerr, Romulus, Mich.

Polysulfide Neo Plex Columbus Dental, St. Louis, MO. Permlastic Sybron I Kerr

Reversible hydrocolloid Surgident Columbus Dental Agarloid Van R, Los Angeles, Calif.

Irreversible hydrocolloid Jeltrate Plus L.D. Caulk Shurgel Columbus Dental

Irreversible-reversible hydrocolloid combination Dentloid and Denterials, St. Louis, MO.

Jeltrate Plus L.D. Caulk Dentloid and Denterials

J&rate L.D. Caulk

was made to fit the master cast and the adaptation was evaluated on casts obtained from the various impression materials. They concluded that polyethers and addition silicones produced the most accurate working casts.

MARCH 1988 VOLUME 59 NUMBER 3

ACCURACY OF IMPRESSION MATERIALS

Fig. 1. Occlusal view of master dentoform model. Fig. 2. Cast copings with connecting arms fitted on master dentoform model.

Table II. Mean marginal openings of assembled castir ags at each abutment (in microns)

Material type 2

Abutment No.

6 11 15

1 27+ 6 51k 6 472 8 21+ 5 2 136 + 10 225 +- 17 224 f 12 157 * 11

3 237 + 17 347 + 27 353 * 22 6 255 f 25 451 + 37 453 * 41 i~~E~~ 4 411 f 12 640 2 34 636 f 41 410 + 18 5 518 f 45 743 2 30

I 771 f 37 554 -t 55

Master 15 39 22 7

Types: 1, Polyether; 2, vinyl polysiloxane; 3, polysulfide; 4, reversible hydrocolloid; 5, irreversible hydrocc?lloid; 6, irreversible-reversible combination hydrocolloid. Vertical bars denote the means that were not significant at the 0.05 level.

This study used an experimental design similar to that of Stauffer et a1.13 to compare the accuracy of complete- arch impressions of six impression materials using complete crown preparations.

METHODS AND MATERIAL

The six impression materials used in this study were polyether, addition silicone, polysulfide rubber, revers- ible hydrocolloid, alginate (irreversible) hydrocolloid, and irreversible-reversible hydrocolloid combination. Two commercial brands of each material were included (Table I). Polyjel, Impregum, and Mirror 3 materials were examined in a single-mix technique and Reprosil, Noe-Plex, and Permlastic materials were examined in a double-mix technique. A thinner was introduced for the syringes of Polyjel and Impregum. Five satisfactory impressions were obtained for each of the 12 brands of materials for a total of 60 impressions.

A maxillary partially edentulous model (Columbia Dentoform Model No. 567M, Columbia Dentoform Corp., New York, N.Y.) was modified as the master model. The first premolars were removed and the sockets were filled with inlay pattern resins (Duralay, Reliance

THE JOURNAL OF PROSTHETIC DENTISTRY

Dental Mfg. Co., Worth, Ill.). The remaining canines and second molars were the four abutment teeth for the maxillary prosthesis. The root surfaces of the abutment teeth and their respective sockets were roughened and scored. The sockets were filled with Duralay resin and the teeth were immediately replaced and the screw tightened to secure each abutment to the base. After 48 hours, the abutment teeth were prepared for complete crowns with 1 mm shoulder margins by using a hand- piece mounted on a parallelometer. In addition, antiro- tational grooves 0.5 mm deep were placed on the buccal and lingual surfaces of each abutment tooth. The height of the molar tooth preparations was 7 mm and that of the canine preparations was 8 mm.

Four orientation marks were made on the palatal surface of the Dentoform model to standardize the measuring position of each stone cast in front of the traveling microscope. The occlusal view of the complete master model is seen in Fig. 1.

Wax patterns in the form of copings were made on each of the abutment preparations. Number 8 gauge round wax (Sybron/Kerr, Romulus, Mich.) was used for making connecting arms extending from each abut-

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LIN ET AL

Big. 3. Cast copings connected with Duralay resin.

Table III. Mean marginal openings of individual castings at each abutment (in microns)

Material Abutment No.

type 2 6 11 15

1 12 + 1 23 zt 1 16 f 1 0 2 25 + 1 32 + 2 28 c 2 0 3 46 k 5 56 f 6 52 f 5 0 6 25 + 2 53 k 3 48 + 5 0 4 45 zk 3 80 + 6 123 + 6 0 5 99 k 6 76 f. 4 102 + 4 0

Master 29 32 30 0

Types: 1, Polyether; 2, vinyl polysiloxane; 3, polysulfide; 4, reversible hydrocolloid; 5, irreversible hydrocolloid; 6, irreversible-reversible hydrocolloid.

ment halfway toward the adjacent crowns. Each coping had two connecting arms. The wax patterns were invested and cast in a ceramometal (Olympia, J.F. Jelenko Co., Armonk, N.Y.). Each casting was fitted and finished on the master dentoform model (Fig. 2).

Five impressions using the 12 materials were made of the Dentoform model. Custom acrylic resin trays were constructed with a 3 mm space for the polysulfide and silicone materials and a 4 mm space for the polyethers. Metal rim-lock water-cooled trays were used for the reversible hydrocolloid and perforated metal trays were used for the irreversible hydrocolloid and the irrevers- ible-reversible combination hydrocolloid impressions. A thermostatic mixing valve (Fotoguard, Powers Regula- tor Co., Skokie, Ill.) facilitated the delivery of water at 68” F to the water-cooled trays. The impressions were poured in die stone (Vel-Mix, Sybron/Kerr), separated after 1 hour, and trimmed after 24 hours. The casts were examined under X10 magnification to remove minor bubbles with a sharp instrument.

Fig. 4. Diagrammatic illustration of measuring posi- tions.

Table IV. Multiple-range test for means of individual marginal discrepancies

Abutment No. Material tvDe

2 6

11

Type key in Tables II and III. Underlined group denotes means that were not significantly different at 0.05 level.

The four cast copings with their connecting arms were seated on the Dentoform model. Inlay pattern resin (Duralay, Reliance Dental Mfg.) was used to connect the four castings into one piece (Fig. 3). The space between the connecting arms ranged from 237 to 425 pm. One joint at a time was connected and the resin was allowed to cure for 30 minutes before the next joint was connected. The entire connected assembly was then allowed to set for 48 hours before measurements were recorded.

The casting assembly was seated with light finger pressure on the master cast. Gingival margin discrepan- cy was measured in microns with a travelling microscope (Gaertener Scientific Corp., Chicago, Ill.). The mesiofa- cial, midfacial, and distofacial margins were selected for measurement (Fig. 4). The casting assembly was seated on each of the 60 stone casts and the marginal discrep- ancies were then measured. The casting was disassem- bled by means of burning off the Duralay resin. Each coping was placed on its respective die and the marginal measurements were repeated.

RESULTS

The mean marginal openings of each retainer for each impression material with the assembled casting are presented in Table II. The mean values were subjected to. the one-way analysis of variance. The Student-

290 MARCH 1988 VOLUME 59 NUMBER 3

ACCURACY OF IMPRESSION MATERIALS

Neuman-Keul test was performed to analyze the data for differences among the means. The marginal fit of the individual castings when the assembly was disconnected is illustrated in Table III. A multi-range test was done for the means of the individual marginal discrepancies listed in Table IV.

abutment teeth. The master prosthesis was seated on the stone casts produced from the impressions. The marginal adaptation on the four abutments was then evaluated with a travelling microscope. The individual marginal adaptation of the four castings on the abutments was also examined after sectioning the four joints.

DISCUSSION

When used with complete-arch impressions, the polyether materials were significantly more accurate, a result that agrees with Stauffer et a1.13 The addition silicones were the second most accurate. The combina- tion hydrocolloids and the polysulfides were the next most accurate whereas the reversible hydrocolloids and the irreversible hydrocolloids were the least accurate. The details of the dies obtained from the irreversible hydrocolloid impressions were indefinite. A surprising result was that the irreversible-reversible hydrocolloid combinations were as accurate as the polysulfides and significantly more accurate than the reversible hydrocol- loids.

The following conclusions were drawn. 1. The polyethers produced the most accurate com-

plete-arch replicas. The second most accurate were the vinyl polysiloxanes, followed by the polysulfides and the irreversible-reversible hydrocolloids. The least accurate were the reversible hydrocolloids and the irreversible hydrocolloids.

2. The polyether impression materials exhibited the most consistent accuracy for a master cast to fabricate a complete-arch FPD.

REFERENCES

When the materials were compared by the fit of the disconnected castings, a similar ranking was found. The casting for thle upper molar exhibited no marginal discrepancy when seated on any of the dies. The probable reason was that the casting was slightly over- sized. The marginal openings were less apparent with the individual castings compared with the assembled arch impression. The marginal fit of the individual castings on the stone die made from the polyether impressions was slightly better than the fit on the Dentoform model. This may have resulted from slight wear of the dies by the friction created with repeated adaptation of t.he casting.

Brindsden GI, Sorensen S, McClenahan J. Dimensional accura- cy of five impression materials using a copper-shell technique. J Dent Res 1964;43(Supp1):911. Hembree JH Jr. Comparative accuracy of elastomer impression materials. J Tenn Dent Assoc 1974;54:164-7. Eames WB, Wallace SW, Suway NB, Rogers LB. Accuracy and dimensional stability of elastomeric impression materials. J PROSTHET DENT 1979;42:159-62. Ciesco JN, Malone WFP, Sandrik JL, Mazur B. Comparison of elastomeric impression materials used in fixed prosthodontics. J PROSTHET DENT 1981;45:89-94.

Measurements of the marginal fit of the castings were recorded only from the facial surface because an unob- structed view from the lingual surface was impossible with the travelling microscope. The three measurements from the facial. surface were representative of the fit of all of the surfaces.

Measurements of the distances between the ends of the connecting bars after separation were recorded antero- posteriorly, occlusogingivally, and faciolingually to determine the trends of distortion. The values exhibited considerable variation without identifiable patterns.

SUMMARY AND CONCLUSIONS

The accuracy of 12 impression materials of six different types were studied by using complete-arch FPD impressions. Sixty impressions were made of a Columbia dentoform maxillary model with complete cast crown abutment preparations on the canines and the second molars. A one-piece casting was constructed by connecting the four individual castings made for the four

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Mincham W, Thurgate SM, Lewis AJ. Measurement of dimen- sional stability of elastomeric impression materials by holograph- ic interferometry. Austl Dent J 1981;26:395-9. Bassett RW, Vander Heide JD, Smith DD. Clinically oriented tests comparing accuracy of elastic impression materials. J South Calif Dent Assoc 1969;37:47-57. Sawyer HF, Birtles JT, Neiman R, Podshadley AG. Accuracy of casts produced from seven rubber impression materials. J Am Dent Assoc 1973;87:126-30. Sawyer HF, Dilts WE, Aubrey ME, Neiman R. Accuracy of casts produced from the three classes of elastomer impression materials. J Am Dent Assoc 1974;89:644-8. Vermilyea SG, Powers JM, Craig RG. Polyether, polysulfide and silicone rubber impressions materials. Part 2: accuracy of silver-plated dies. J Mich Dent Assoc 1975;57:405-10. Stackhouse JA. A comparison of elastic impression materials. J PROSTHET DENT 1975;34:305-13. Henry PJ, Harnist DJR. Dimensional stability and accuracy of rubber impression materials. Aust Dent J 1974;19: 162-6. Lacy AM, Fukui H, Bellman T, Jendresen MD. Time- dependent accuracy of elastomer impression materials. Part II: polyethers, polysulfides, and polyvinylsiloxanes. J PROSTHET DENT 1981;45:329-33. Stauffer J, Meyer J, Nally J. Accuracy of six elastic impression materials used for complete-arch fixed partial dentures. J PROSTHET DENT 1976;35:407-15.

Reprint requests to: DR. GERALD J. ZIEBERT Marquette University School of Dentistry Milwaukee. WI 53233

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