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Trouble-shooting the pour resins
Dental technology _
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DANIEL H. GEHL and S. HOWARD PAYNE, Associate Editors
Trouble-shooting the pour resins Sherman Axinn, D.D.S.,* Edgar N. Kopp, D.D.S.,** and Jay G. Hanson, D.D.S;*** United States Army Regional, Dental,Activity, Fort McPherson, Ga., and School o] Dentistry, State University o[ Iowa, Iowa City, Iowa
T h e pour resins have been utilized for the processing of denture bases since 1963. Some fabrication problems have been experienced, as with any new technique. None of these problems was of a magnitude to cause the abandonment of the material when the advantages were considered. The results obtained with materials currently available compare favorably with the results obtained by use of conventional packing techniques. Many pour resins are available today. All-of them, as polymers of methyl methacrylate, work i n basically th~ same manner,, and acceptable results can be achieved with most. An evaluation of pour resins which are commercially available has been undertaken, t When this study and data collection are Completed, the results Will be published. Acceptable results have been achieved for each of tl~e resins tested. Three of the procedures critical to the successful use of the pour resins are presented here.
TECHNIQUE
Preparation of the master cast. Treat the master cast in precisely the same manner as for a heat-processed denture. During processing, the master cast is enclosed in a matrix of hydrocolloid. T h e cast is su]~ported entirely by the land portion during the pouring and processing procedure; therefore, adequate land and base are mandatory for positioning the cast accurately. The land is particularly important for the maxillary cast due to the absence of the lingual tongue land portion, which is present on the mandibular cast. Tiffs land portion of the cast must be kept sufficiently prominent to fulfill its purpose; 5 ram. are adequate. *Chief, Removable Prosthetic Department, United States Army Regional Dental Activity. **Commander, United States Army Regional Dental Activity. ***Associate Professor, Removable Prosthodontics, School of Dentistry, State University oI Iowa. tShepard, W. L. : Personal communication, 1974. 689
690
Axinn, Kopp, and Hanson
J. V,o~th,t. D~,,t. June, 1975
Setup and wax-up. One of the advantages of the pour-resin technique is the minimal finishing that is necessary upon the recovery of the denture from its investing medium. In order to fully realize this advantage, the prosthesis in wax must look exactly the same as the completed denture, including the carving, festooning, and even the stippling. A disadvantage of this technique is the possible movement of teeth during processing. This movement can be minimized and prevented in most instances by removing every remnant of wax from the clinical crowns of the denture teeth before investing in hydrocolloid. The land of the cast must be conlpletely cleansed of residual wax. An attempt to process overwaxed dentures with the intention of taking care of the excess bulk during finishing procedures is a mistake. This nullifies one of the advantages of the technique. The beautiful, smooth, almost polished surface of the denture must be reduced and then resmoothed. Most important, the dimensional change that must be expected with all resins is a factor of bulk. By reducing the form and contour of the wax denture to that of the completed denture, the amount of dimensional change is minimized. (An enlarged lingual flange area is not needed to permit flask opening and closing.) Care should be taken to seal the wax denture to its east to prevent intrusion of hydrocolloid between the wax and master cast. Processing. Soak the wax denture on its master cast in a warm (100 ° to 110 ° F.) water bath to remove all air from the cast. If this step is missed, the air Will come to t h e surface when the denture is invested in the hydrocolloid. This air ultimately makes bubbles in the resin on the tissue surface of the prosthesis. The processing investment material is hydrocolloid, and Bake-lite flasks with metal bases are preferred. The use of this type of flask in conjunction with a cool water (55 ° F.) bath, which does not cover any more than the lower half of the flask, insures that the cooling shrinkage of the hydrocolloid will start at the base and be con trolled. Several sprueing techniques are acceptable. In mzder not to overcomplicate a simple technique, there are a few precautions. Sprue holes of 3~ inch diameter are adequate. Too many sprues will complicate denture finishing. Also, the sprues contribute to undesirable dimensional changes. The main sprue should permit the liquid resin to be poured so that it can reach the lowest portion in the flask first and then fill to the highest portion. The vent hole is located at the highest point. Resin should never be poured into the vent hole, because this may trap air and create large voids. When mixing the monomer and polymer, follow the manufacturer's directions. Proportions are critical; 0.5 c.c. of excess monomer will cause a drastic dimensional change which will render the restoration useless. This is the most critical part of the technique. There are newer pour resins which require reduced amounts of monomer for successful blending. This may further improve the dimensional stability and quality of the resin. The denture teeth and master cast must be scrupulously cleaned prior to being re-placed in the mold. Occasionally, teeth will have been reduced so much that insufficient clinical crown remains to hold the teeth firmly in place in the hydrocolloid. This will most frequently involve second molars and mandibular anterior teeth.
volume, ~.~ Number 6
Trouble-shooting the pour resins
691
When this occurs, place a small amount of petrolatum on the occlusal (or incisal) surface of the denture tooth, and place it back into the mold. The petrolatum will increase adhesion between the tooth and mold surface. Many misconceptions are prevalent about the manner in which the separating medium functions. These misconceptions lead to misuse of the material. Most of these products, regardless of brand, consist of alginic acid and fillers. When the alginic acid is applied to a stone cast, the result is a surface layer of calcium alginate which will not adhere to anything. The placement of a large amount of separating medium on the cast prior to pouring the fluid resin results in surface accumulation which the resin is not capable of displacing. The tissue surface of the denture will show voids a n d / o r a worm-eaten appearance. This can be prevented by keeping the separating medium at its original fluid consistency, applying the separating medium sparingly onto warm casts, and then placing the casts on their heels to drain while they cool. To repeat, thick coats of separating medium are not desirable with any denture technique. Another frequent error in the use of separating medium is to place the brush back into the container after contact with the stone cast. This will contaminate the entire amount of separating medium with stone particles, rendering the medium useless. This can be avoided by pouring enough sephrating medium for several hours use into a small container. Keep the brush in this container and discard any separating medium remaining at the end of the day. Pour no more than two dentures at one time. This allows the dental laboratory technician to properly mix and carefully pour the resin and to have the mold completely filled prior to the initial set of the resin. The amount of time saved on repairs and the quality of the processed prosthesis justify the restriction of pouring only two dentures at a time. SUMMARY
Information is provided to update the clinician on tile pour-resin technique. Procedures have been emphasized which may cause quality control problems. The greatest disadvantage of the pour resin is its "technique sensitivity," and care nmst be taken. Technique "shortcuts" will have a deleterious effect oll the accuracy and quality of the denture base. As in all phases of dental science, attention to detail must be observed. DRS. AXINN AND Kopp UNITED STATES ARIM'~"REOIONAL DENTAL ACTXVITY
FoRT McPHERsox, GA. 30330 DR. HANSON STATE UNIVERSITY Ol: IO~VA SCttOOI, OF DENTISTRY"
Iowa C~Tv, Iowa 5224{)
_
'
-
.
.
.
.
.
.
.
.
.
,,
.
i
el
_
DANIEL H. GEHL and S. HOWARD PAYNE, Associate Editors
Trouble-shooting the pour resins Sherman Axinn, D.D.S.,* Edgar N. Kopp, D.D.S.,** and Jay G. Hanson, D.D.S;*** United States Army Regional, Dental,Activity, Fort McPherson, Ga., and School o] Dentistry, State University o[ Iowa, Iowa City, Iowa
T h e pour resins have been utilized for the processing of denture bases since 1963. Some fabrication problems have been experienced, as with any new technique. None of these problems was of a magnitude to cause the abandonment of the material when the advantages were considered. The results obtained with materials currently available compare favorably with the results obtained by use of conventional packing techniques. Many pour resins are available today. All-of them, as polymers of methyl methacrylate, work i n basically th~ same manner,, and acceptable results can be achieved with most. An evaluation of pour resins which are commercially available has been undertaken, t When this study and data collection are Completed, the results Will be published. Acceptable results have been achieved for each of tl~e resins tested. Three of the procedures critical to the successful use of the pour resins are presented here.
TECHNIQUE
Preparation of the master cast. Treat the master cast in precisely the same manner as for a heat-processed denture. During processing, the master cast is enclosed in a matrix of hydrocolloid. T h e cast is su]~ported entirely by the land portion during the pouring and processing procedure; therefore, adequate land and base are mandatory for positioning the cast accurately. The land is particularly important for the maxillary cast due to the absence of the lingual tongue land portion, which is present on the mandibular cast. Tiffs land portion of the cast must be kept sufficiently prominent to fulfill its purpose; 5 ram. are adequate. *Chief, Removable Prosthetic Department, United States Army Regional Dental Activity. **Commander, United States Army Regional Dental Activity. ***Associate Professor, Removable Prosthodontics, School of Dentistry, State University oI Iowa. tShepard, W. L. : Personal communication, 1974. 689
690
Axinn, Kopp, and Hanson
J. V,o~th,t. D~,,t. June, 1975
Setup and wax-up. One of the advantages of the pour-resin technique is the minimal finishing that is necessary upon the recovery of the denture from its investing medium. In order to fully realize this advantage, the prosthesis in wax must look exactly the same as the completed denture, including the carving, festooning, and even the stippling. A disadvantage of this technique is the possible movement of teeth during processing. This movement can be minimized and prevented in most instances by removing every remnant of wax from the clinical crowns of the denture teeth before investing in hydrocolloid. The land of the cast must be conlpletely cleansed of residual wax. An attempt to process overwaxed dentures with the intention of taking care of the excess bulk during finishing procedures is a mistake. This nullifies one of the advantages of the technique. The beautiful, smooth, almost polished surface of the denture must be reduced and then resmoothed. Most important, the dimensional change that must be expected with all resins is a factor of bulk. By reducing the form and contour of the wax denture to that of the completed denture, the amount of dimensional change is minimized. (An enlarged lingual flange area is not needed to permit flask opening and closing.) Care should be taken to seal the wax denture to its east to prevent intrusion of hydrocolloid between the wax and master cast. Processing. Soak the wax denture on its master cast in a warm (100 ° to 110 ° F.) water bath to remove all air from the cast. If this step is missed, the air Will come to t h e surface when the denture is invested in the hydrocolloid. This air ultimately makes bubbles in the resin on the tissue surface of the prosthesis. The processing investment material is hydrocolloid, and Bake-lite flasks with metal bases are preferred. The use of this type of flask in conjunction with a cool water (55 ° F.) bath, which does not cover any more than the lower half of the flask, insures that the cooling shrinkage of the hydrocolloid will start at the base and be con trolled. Several sprueing techniques are acceptable. In mzder not to overcomplicate a simple technique, there are a few precautions. Sprue holes of 3~ inch diameter are adequate. Too many sprues will complicate denture finishing. Also, the sprues contribute to undesirable dimensional changes. The main sprue should permit the liquid resin to be poured so that it can reach the lowest portion in the flask first and then fill to the highest portion. The vent hole is located at the highest point. Resin should never be poured into the vent hole, because this may trap air and create large voids. When mixing the monomer and polymer, follow the manufacturer's directions. Proportions are critical; 0.5 c.c. of excess monomer will cause a drastic dimensional change which will render the restoration useless. This is the most critical part of the technique. There are newer pour resins which require reduced amounts of monomer for successful blending. This may further improve the dimensional stability and quality of the resin. The denture teeth and master cast must be scrupulously cleaned prior to being re-placed in the mold. Occasionally, teeth will have been reduced so much that insufficient clinical crown remains to hold the teeth firmly in place in the hydrocolloid. This will most frequently involve second molars and mandibular anterior teeth.
volume, ~.~ Number 6
Trouble-shooting the pour resins
691
When this occurs, place a small amount of petrolatum on the occlusal (or incisal) surface of the denture tooth, and place it back into the mold. The petrolatum will increase adhesion between the tooth and mold surface. Many misconceptions are prevalent about the manner in which the separating medium functions. These misconceptions lead to misuse of the material. Most of these products, regardless of brand, consist of alginic acid and fillers. When the alginic acid is applied to a stone cast, the result is a surface layer of calcium alginate which will not adhere to anything. The placement of a large amount of separating medium on the cast prior to pouring the fluid resin results in surface accumulation which the resin is not capable of displacing. The tissue surface of the denture will show voids a n d / o r a worm-eaten appearance. This can be prevented by keeping the separating medium at its original fluid consistency, applying the separating medium sparingly onto warm casts, and then placing the casts on their heels to drain while they cool. To repeat, thick coats of separating medium are not desirable with any denture technique. Another frequent error in the use of separating medium is to place the brush back into the container after contact with the stone cast. This will contaminate the entire amount of separating medium with stone particles, rendering the medium useless. This can be avoided by pouring enough sephrating medium for several hours use into a small container. Keep the brush in this container and discard any separating medium remaining at the end of the day. Pour no more than two dentures at one time. This allows the dental laboratory technician to properly mix and carefully pour the resin and to have the mold completely filled prior to the initial set of the resin. The amount of time saved on repairs and the quality of the processed prosthesis justify the restriction of pouring only two dentures at a time. SUMMARY
Information is provided to update the clinician on tile pour-resin technique. Procedures have been emphasized which may cause quality control problems. The greatest disadvantage of the pour resin is its "technique sensitivity," and care nmst be taken. Technique "shortcuts" will have a deleterious effect oll the accuracy and quality of the denture base. As in all phases of dental science, attention to detail must be observed. DRS. AXINN AND Kopp UNITED STATES ARIM'~"REOIONAL DENTAL ACTXVITY
FoRT McPHERsox, GA. 30330 DR. HANSON STATE UNIVERSITY Ol: IO~VA SCttOOI, OF DENTISTRY"
Iowa C~Tv, Iowa 5224{)