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Comparison of changes in vertical dimension between compression and injection molded complete dentures
SECTION
EDITOR
Comparison compression
of changes in vertical and injection molded
dimension between complete dentures
Robert A. Strohaver, D.D.S., M.Sc.* Medical University of South Carolina, College of Dental Medicine, Charleston, S.C. Complete dentures were made for 30 patients. Fifteen sets were processed by conventional compression molding and 15 sets were processed by using the SR-Ivocap injection system. Changes in vertical dimension between the waxed and processed dentures were measured at the incisal guide pin by using a dial indicator. The difference between the two methods was highly significant on the basis of t-test statistics. Whereas the processing changes noted with the conventional pack-and-press method were similar to previous studies, the injection method produced little or no pin opening. The superiority of the injection method before decasting was indisputable, and the results suggest that the laboratory remount procedure may be unnecessary when this system is used. (J PROSTEET DENT 1989;62:716-8.)
C
ompression molded methylmethacrylate has been the standard denture base material for more than 40 years. Undesirable dimensional changes that occur during processing by this method have been thoroughly documented.1-4 More recently, an injection pressing Presented in part before the Carl 0. Boucher Prosthodontic ference, Columbus, Ohio. *Associate Professor, Department of Prosthodontics. 10/l/15328
Con-
method, the SR-Ivocap system (Ivoclar USA Inc., San Marcos, Calif.), has come to North America from Europe. This method for processing poly(methylmethacrylate) is said to totally compensate for the shrinkage occurring during polyme;ization.5 Early reports on the SR-Ivocap system are generally favorable regarding dimensional characteristics and opening of the vertical dimension of occlusion.6-g However, one study concluded that the amount of pin opening with the injection method was nearly two times greater than’with
Fig . 1 . Waxed trial denture on articulator with dial indicator attached to incisal gu lide pin and set I at zero.
716
DECEMBER
1989
VOLUME
62
NUMBER
6
INJECTION
VERSUS
COMPRESSION
MOLDING
Fig. 2. Processed dentures reattached to original articulator mountings and pin setting. Change in vertical dimension is indicated on dial group.
Table
I.
Summary of changes in the laboratory remount
procedure Trials
Removal and replacement of mounting rings Separation of casts and replacement on mountings
30
30
Range (inch) -0.002
0.002
to .002
to ,018
Mean (inch) 0.0003
0.008
Mean (mm)
0.01
AND
MATERIAL
Maxillary and mandibular complete dentures were made for 30 patients. Fifteen sets of complete dentures were processed in Microlon-LW denture resin (Hygienic Corp., Akron, Ohio) by using the conventional pack-and-press method’as described by Woelfel.” The remaining 15 sets of dentures were processed with the SR-Ivocap injection system by carefully following the manufacturer’s instructions. All of the laboratory phases of the denture processing were accomplished by the same dental technician and under the same conditions.
THE
;IOURNAL
OF PROSTHETIC
DENTISTRY
Method
Compression Injection
sets of dentures 15
15
SD (inch)
Mean (inch)
Mean
0.010 0.003
0.026
0.66 0.02
0.001
(mm)
0.20
the compression method.lO This study helps to clarify conflicting reports by comparing changes in the vertical dimension of complete dentures processed by the compression and injection methods.
METHODS
II. Summary of changes in vertical dimension after processing
Table
All of the dentures were made on dental stone casts. The base of each cast was indexed with V-shaped notches before it was mounted on the articulator. Each denture could then be remounted in the same position on the articulator after processing. This laboratory remount procedure is often used clinically to measure processing error as manifested by the separation of the incisal guide pin from the incisal guide table. Changes in the vertical dimension of occlusion during this study were measured with a dial indicator (Mitutoyo Manufacturing Co., Ltd., Tokyo, Japan) attached to the incisal guide pin of an articulator (Hanau Wide Vue, Teledyne Hanau, Buffalo, NY). The measuring device registered changes to within 0.001 inch (Fig. 1). Plastic artificial teeth (Bioblend and IPN Monoline, Dentsply, York, Pa.) were used in this study because it has been demonstrated that greater changes in vertical dimension occur when porcelain teeth are used.r2 As each waxed setup was completed, the incisal pin was examined to ensure that it was in contact with the in&al guide table at the selected vertical dimension of occlusion and the measuring
device was then attached to the incisal pin. With the artic-
717
ulator positioned in a constant, predetermined location on a glass tabletop, the dial indicator was set at zero. This method of measurement is similar to that used by Dukes et all2 but involves no modification of the incisal guide table. Measurements were made by the author and each measurement was made five times to establish a mean value. To separate each cast with its waxed denture from its mounting, a knife blade was placed at the junction of the cast and mounting gypsum and tapped sharply with a hammer. After separation, the rings and casts were returned to the articulator, The casts were secured to their mountings with sticky wax. Again the pin was examined and contact with the table was ensured. After the changes were recorded, the dial indicator was reset at zero so that errors in the remount procedure would not be considered processing errors. Changes in pin opening caused by the laboratory remount procedure are summarized in Table I. The dentures were processed and deflasked. All investment material was removed from the teeth and casts. The casts were returned to their indexed mountings and secured with sticky wax. The difference in vertical dimension after processing was registered on the dial indicator and recorded (Fig. 2).
RESULTS
AND
CONCLUSIONS
Changes in the vertical dimension of occlusion after processing, as measured at the incisal guide pin, are summarized in Table II. Thirty mean measurements were obtained, representing 15 sets each of complete dentures processed by the compression method and the injection molding method. The mean increase in vertical dimension for the conventional pack and press method was 0.025 inch with a standard deviation of 0.010 inch. This increase compares favorably with the findings of similar studies.41iof l1 The mean increase in vertical dimension for the injection method was 0.001 inch with a standard deviation of 0.003 inch. These results conflict sharply with the results of Garfunkel.rO A t-test was used to compare the means of the two groups. The computed t value was 9.277 and the level of significance was p < 0.00001. Hence it can be concluded that the difference between the two methods was highly significant. Although some slight changes in vertical dimension were recorded with the SR-Ivocap system, it should be noted that the mean of these changes is considerably less than the sum of the errors in the remount procedure.
CLINICAL
SIGNIFICANCE
in little or no processing error.6-g Because the changes in the vertical dimension of occlusion are clinically insignificant before decasting, the laboratory remount and occlusal correction procedures may be eliminated. In addition, this study provides an indication of the magnitude of potential errors involved when the laboratory remount procedure is used. In the past, these remounting errors have seldom been distinguished from processing errors.
SUMMARY An investigation was conducted to compare changes in vertical dimension between complete dentures processed by conventional compression molding and those processed by injection pressing. The injection method produced negligible change in vertical dimension as measured at the incisal pin, whereas the pack-and-press method produced pin openings many times greater. On the basis of t-test statistics, the difference between the two methods was highly significant. I thank Mike Veronee, CDT, Staff Photographer Tom Rast, and Dr. Hershel1 Hunt of the Department of Biometry for their technical assistance with this project.
REFERENCES Mahler DB. Inarticulation of complete dentures processed by the compression molding technique. J PROSTHET DENT 1951;1:551-9. Woelfel JB, Ptienbarger GC, Sweeney WT. Dimensional changes occurring in dentures during processing. J Am Dent Assoc 1960;61:413-30. Anthony DH, Peyton FA. Dimensional accuracy of various denture base materials. J PNSTHET DENT 1962;12:67-81. 4. Wesley RC, Henderson D, Frazier QZ, et al. Processing changes in complete dentures: posterior tooth contacts and pin opening. J PROSTHET DENT 1973;29:46-53.
The Ivocap Denture System (brochure). San Marcos, Calif: Ivoclar (U.S.A.) Inc, 1985. Trage R. Experience gained with the SR-Ivocap system. Quintessenz 1975;26:65-71. Schmidt KH. SR-Ivocap system and denture structure. Quintessence Int 1976;7:7-14. Arnold TG, Schulte JK, Anderson GC. Dimensional stability of injection and conventional processing of denture acrylic [Abstract]. J Dent Res 1987;66:150. 9. Sykora 0, Sutow EJ. Practical assessment of a continuous-injection denture processing technique (SR-Ivocap). Quintessence Dent Technol 1988;12(Yearbook):147-54. 10. Garfunkel E. Evaluation of dimensional changes in complete dentures processed hy injection-pressing and the pack-and-press technique. J PR~STHET DENT 1933;50:757-61. 11. Woelfel JB. Processing complete
dentures. Dent Clin North Am 1977;21:329-38. 12. Dukes BS, Fields H, Olson JW. A laboratory study of changes in vertical dimension using acrylic resin and porcelain teeth. J Am Dent Aseoc 1983;106:842-3. Reprint
requests
to:
DR. ROBERT A. STROHAVER MEDICAL UMVERHTY OF SOUTH CAROLINA COLLEGE OF DENTAL MEDICINE CHARLESTON, SC 29425
This study supports previous observations that complete dentures processed with the SR-Ivocap system can result
718
DECEMBER
1989
VOLUME
62
NUMBER
6
EDITOR
Comparison compression
of changes in vertical and injection molded
dimension between complete dentures
Robert A. Strohaver, D.D.S., M.Sc.* Medical University of South Carolina, College of Dental Medicine, Charleston, S.C. Complete dentures were made for 30 patients. Fifteen sets were processed by conventional compression molding and 15 sets were processed by using the SR-Ivocap injection system. Changes in vertical dimension between the waxed and processed dentures were measured at the incisal guide pin by using a dial indicator. The difference between the two methods was highly significant on the basis of t-test statistics. Whereas the processing changes noted with the conventional pack-and-press method were similar to previous studies, the injection method produced little or no pin opening. The superiority of the injection method before decasting was indisputable, and the results suggest that the laboratory remount procedure may be unnecessary when this system is used. (J PROSTEET DENT 1989;62:716-8.)
C
ompression molded methylmethacrylate has been the standard denture base material for more than 40 years. Undesirable dimensional changes that occur during processing by this method have been thoroughly documented.1-4 More recently, an injection pressing Presented in part before the Carl 0. Boucher Prosthodontic ference, Columbus, Ohio. *Associate Professor, Department of Prosthodontics. 10/l/15328
Con-
method, the SR-Ivocap system (Ivoclar USA Inc., San Marcos, Calif.), has come to North America from Europe. This method for processing poly(methylmethacrylate) is said to totally compensate for the shrinkage occurring during polyme;ization.5 Early reports on the SR-Ivocap system are generally favorable regarding dimensional characteristics and opening of the vertical dimension of occlusion.6-g However, one study concluded that the amount of pin opening with the injection method was nearly two times greater than’with
Fig . 1 . Waxed trial denture on articulator with dial indicator attached to incisal gu lide pin and set I at zero.
716
DECEMBER
1989
VOLUME
62
NUMBER
6
INJECTION
VERSUS
COMPRESSION
MOLDING
Fig. 2. Processed dentures reattached to original articulator mountings and pin setting. Change in vertical dimension is indicated on dial group.
Table
I.
Summary of changes in the laboratory remount
procedure Trials
Removal and replacement of mounting rings Separation of casts and replacement on mountings
30
30
Range (inch) -0.002
0.002
to .002
to ,018
Mean (inch) 0.0003
0.008
Mean (mm)
0.01
AND
MATERIAL
Maxillary and mandibular complete dentures were made for 30 patients. Fifteen sets of complete dentures were processed in Microlon-LW denture resin (Hygienic Corp., Akron, Ohio) by using the conventional pack-and-press method’as described by Woelfel.” The remaining 15 sets of dentures were processed with the SR-Ivocap injection system by carefully following the manufacturer’s instructions. All of the laboratory phases of the denture processing were accomplished by the same dental technician and under the same conditions.
THE
;IOURNAL
OF PROSTHETIC
DENTISTRY
Method
Compression Injection
sets of dentures 15
15
SD (inch)
Mean (inch)
Mean
0.010 0.003
0.026
0.66 0.02
0.001
(mm)
0.20
the compression method.lO This study helps to clarify conflicting reports by comparing changes in the vertical dimension of complete dentures processed by the compression and injection methods.
METHODS
II. Summary of changes in vertical dimension after processing
Table
All of the dentures were made on dental stone casts. The base of each cast was indexed with V-shaped notches before it was mounted on the articulator. Each denture could then be remounted in the same position on the articulator after processing. This laboratory remount procedure is often used clinically to measure processing error as manifested by the separation of the incisal guide pin from the incisal guide table. Changes in the vertical dimension of occlusion during this study were measured with a dial indicator (Mitutoyo Manufacturing Co., Ltd., Tokyo, Japan) attached to the incisal guide pin of an articulator (Hanau Wide Vue, Teledyne Hanau, Buffalo, NY). The measuring device registered changes to within 0.001 inch (Fig. 1). Plastic artificial teeth (Bioblend and IPN Monoline, Dentsply, York, Pa.) were used in this study because it has been demonstrated that greater changes in vertical dimension occur when porcelain teeth are used.r2 As each waxed setup was completed, the incisal pin was examined to ensure that it was in contact with the in&al guide table at the selected vertical dimension of occlusion and the measuring
device was then attached to the incisal pin. With the artic-
717
ulator positioned in a constant, predetermined location on a glass tabletop, the dial indicator was set at zero. This method of measurement is similar to that used by Dukes et all2 but involves no modification of the incisal guide table. Measurements were made by the author and each measurement was made five times to establish a mean value. To separate each cast with its waxed denture from its mounting, a knife blade was placed at the junction of the cast and mounting gypsum and tapped sharply with a hammer. After separation, the rings and casts were returned to the articulator, The casts were secured to their mountings with sticky wax. Again the pin was examined and contact with the table was ensured. After the changes were recorded, the dial indicator was reset at zero so that errors in the remount procedure would not be considered processing errors. Changes in pin opening caused by the laboratory remount procedure are summarized in Table I. The dentures were processed and deflasked. All investment material was removed from the teeth and casts. The casts were returned to their indexed mountings and secured with sticky wax. The difference in vertical dimension after processing was registered on the dial indicator and recorded (Fig. 2).
RESULTS
AND
CONCLUSIONS
Changes in the vertical dimension of occlusion after processing, as measured at the incisal guide pin, are summarized in Table II. Thirty mean measurements were obtained, representing 15 sets each of complete dentures processed by the compression method and the injection molding method. The mean increase in vertical dimension for the conventional pack and press method was 0.025 inch with a standard deviation of 0.010 inch. This increase compares favorably with the findings of similar studies.41iof l1 The mean increase in vertical dimension for the injection method was 0.001 inch with a standard deviation of 0.003 inch. These results conflict sharply with the results of Garfunkel.rO A t-test was used to compare the means of the two groups. The computed t value was 9.277 and the level of significance was p < 0.00001. Hence it can be concluded that the difference between the two methods was highly significant. Although some slight changes in vertical dimension were recorded with the SR-Ivocap system, it should be noted that the mean of these changes is considerably less than the sum of the errors in the remount procedure.
CLINICAL
SIGNIFICANCE
in little or no processing error.6-g Because the changes in the vertical dimension of occlusion are clinically insignificant before decasting, the laboratory remount and occlusal correction procedures may be eliminated. In addition, this study provides an indication of the magnitude of potential errors involved when the laboratory remount procedure is used. In the past, these remounting errors have seldom been distinguished from processing errors.
SUMMARY An investigation was conducted to compare changes in vertical dimension between complete dentures processed by conventional compression molding and those processed by injection pressing. The injection method produced negligible change in vertical dimension as measured at the incisal pin, whereas the pack-and-press method produced pin openings many times greater. On the basis of t-test statistics, the difference between the two methods was highly significant. I thank Mike Veronee, CDT, Staff Photographer Tom Rast, and Dr. Hershel1 Hunt of the Department of Biometry for their technical assistance with this project.
REFERENCES Mahler DB. Inarticulation of complete dentures processed by the compression molding technique. J PROSTHET DENT 1951;1:551-9. Woelfel JB, Ptienbarger GC, Sweeney WT. Dimensional changes occurring in dentures during processing. J Am Dent Assoc 1960;61:413-30. Anthony DH, Peyton FA. Dimensional accuracy of various denture base materials. J PNSTHET DENT 1962;12:67-81. 4. Wesley RC, Henderson D, Frazier QZ, et al. Processing changes in complete dentures: posterior tooth contacts and pin opening. J PROSTHET DENT 1973;29:46-53.
The Ivocap Denture System (brochure). San Marcos, Calif: Ivoclar (U.S.A.) Inc, 1985. Trage R. Experience gained with the SR-Ivocap system. Quintessenz 1975;26:65-71. Schmidt KH. SR-Ivocap system and denture structure. Quintessence Int 1976;7:7-14. Arnold TG, Schulte JK, Anderson GC. Dimensional stability of injection and conventional processing of denture acrylic [Abstract]. J Dent Res 1987;66:150. 9. Sykora 0, Sutow EJ. Practical assessment of a continuous-injection denture processing technique (SR-Ivocap). Quintessence Dent Technol 1988;12(Yearbook):147-54. 10. Garfunkel E. Evaluation of dimensional changes in complete dentures processed hy injection-pressing and the pack-and-press technique. J PR~STHET DENT 1933;50:757-61. 11. Woelfel JB. Processing complete
dentures. Dent Clin North Am 1977;21:329-38. 12. Dukes BS, Fields H, Olson JW. A laboratory study of changes in vertical dimension using acrylic resin and porcelain teeth. J Am Dent Aseoc 1983;106:842-3. Reprint
requests
to:
DR. ROBERT A. STROHAVER MEDICAL UMVERHTY OF SOUTH CAROLINA COLLEGE OF DENTAL MEDICINE CHARLESTON, SC 29425
This study supports previous observations that complete dentures processed with the SR-Ivocap system can result
718
DECEMBER
1989
VOLUME
62
NUMBER
6