Journal of Oral Rehabilitation, 1990, Volume 17, pages 425-434
Retention of denture adhesives — an in vitro study C.
L.
C H E W Faculty of Dentistry, National University of Singapore, Singapore
Summary
Denture adhesives are being used by patients to aid the retention and stability of their dentures. A number of laboratory and clinical investigations have been conducted to study the effects of such adhesives. This study describes a simple in vitro method for measurement of their retentive effect and its relation to loss of adhesive. The results show that there is a reduction in the effectiveness of adhesives, and that there is also an increase in adhesive loss, with time. There appears to be a correlation between these two properties. Introduction
Denture adhesives are probably the most widely used and least harmful of the overthe-counter denture additives. They were introduced in the early part of the century, and many different types have subsequently been made available. Patients use these materials to improve the retention and stability of their dentures. Studies on the effectiveness of denture adhesives have been conducted by Boone (1962), Kapur (1967), Ow and Beam (1983) and Chew et al. (1985). Their results indicated that adhesives do improve the retention of dentures. Swartz, Norman and Phillips (1967) have measured the loss of denture adhesives under dentures with the aid of radioactive materials. : The purpose of this study was to investigate the retentive effect of denture adhesives, and to determine whether this property is related to loss of the adhesives. Materials and methods
The denture adhesives selected for this study were Fixodent®* and Super Polygrip®!, both of which were in the form of a paste, and also Secure,*, which was in the form of a powder. . . . . . The skin of the rat was selected as a substitute for the oral mucosa. The rat was killed, skinned, and the subcutaneous fat removed. It was then shaved clean of all hair. Rat skin was selected because its surface, which is similar to palatal mucosa, is keratinized and can be kept moist due to its ability to retain moisture. The skin was mounted on the flat surface of a cylindrical block of wood of diameter 35 mm and length 50 mm, and held taut with a ring clamp (Fig. 1). The end surfaces of the wooden block were trimmed flat and parallel to each other, in order to allow vertical * Richardson-Vicks, Wilton, Connecticut, U.S.A. t Block Drug Co. Inc., Jersey City, New Jersey, U.S.A. Correspondence: Dr C.L. Chew, Department of Prosthetic Dentistry, Faculty of Dentistry, National University of Singapore, National University Hospital, Lower Kent Ridge Road, Singapore 0511.
425
426
C. L. Chew
Fig. 1. Rat skin mounted on flat surface of a cylindrical wood block, held taut with a ring clamp.
positioning of the block, with the aid of a spirit level, for the adhesion test. The skin on the block was stored in tap water until needed. A circular, heat-cured, clear acrylic disc of diameter 32 mm and thickness 2 mm was used to represent the denture. A wire loop was attached to one surface of the disc. Four circular marks, of approximately the same size as the window of the miniature Geiger-Muller tube, were made on this surface to enable radioactive counts to be monitored over the same area in each set of measurements (Fig. 2). The other surface was ground flat to ensure even contact of the resin disc with the skin. Adhesive loss was measured using the method described by Swartz et al. (1967). Each adhesive was tagged with the radioisotope "^^P, by dripping a solution of K3P^^O4 on to zinc oxide powder (0-3 |im particle size) in an amount sufficient to yield a concentration of 4 [iCi of ^^P in 0-2 g of zinc oxide. After the powder had been dried under a heat lamp, it was mixed to ensure uniform distribution of the isotope throughout the powder. Enough powder to provide 0-2 g of zinc oxide (4 [xCi of -^^P) per dose was then incorporated into the respective adhesives. Each dose of adhesive was considered to represent the average amount of adhesive required for each clinical application. The zinc oxide and adhesive were mixed with a spatula on a glass slab until the zinc oxide was uniformly dispersed throughout the adhesive. The dose for each material was established by determining the average quantity of adhesive required per application. These values were obtained by trial and error. The maxillary denture was weighed and the adhesive applied to its tissue surface using the procedure specified by the respective manufacturers. The combined mass of the denture and the adhesive was determined, and the denture was then seated firmly in
Retention of denture adhesives
All
Fig. 2. Clear acrylic disc with attached wire loop and four circular marks to enable the radioactive counts to be monitored. . .
the patient's mouth. The sulcus and posterior palatal regions were checked for any excess of material. The denture was removed and the adhesive coverage on its tissue surface and on the denture-bearing mucosa was examined. The average amount of each adhesive needed to cover the tissue surface of five maxillary complete dentures, without excess of material flowing over the borders, was determined. It was found that 1-4 g of Fixodent®, 0-4 g of Secure® and 1-7 g of Super Polygrip® were required. Radioactive counts and adhesion test Six specimens were prepared for the study, and the same six specimens were used for the 1 h, 3 h and 5 h tests for the three products investigated. This was done in order to control the variation between specimens in each test group. At the start of the test, the skin mounted on the wooden block was cleaned by brushing with a dish-washing detergent. The excess water was evaporated off with a stream of compressed air applied for 30 s. The acrylic disc was placed over the skin and centralized, and the specimen was positioned under the Geiger-Muller counter (Lionel Model 224)* so that the window was 2mm above one of the four marks on the surface of the disc (Fig. 3). The Geiger-Muller counter was connected to the proportional counter (Model PC-3B), and the voltage was set at 775 V. Three 1-min counts of each of the four marked areas were made, and the average of these 12 measurements was obtained. This set of results represented the background radiation, and the data were recorded for each specimen before the tagged adhesive was applied. The disc was then separated from the skin and wiped dry. The test adhesive was applied to the tissue surface of the disc, and was spread evenly over the surface with a plastic spatula. The disc was pressed firmly on to the skin using finger pressure. Excess material flowing out of the border of the disc was removed. The specimen was placed under the Geiger-Mtiller tube for radioactive counts as described above. Upon completion, the specimen was placed in distilled water maintained at 37°C. After 1 h the specimen was removed and the top surface of the disc was rinsed under a gentle flow * Nuclear Measurements Corporation, Indianapolis, Indiana, U.S.A.
,•-
.: ;s;^ r/.'l*>N
C. L. Chew
Fig. 3. Test specimen positioned under the Geiger-Muller tube (Lionel Model 224) for determination of radioactive counts.
of tap water for 5 min, in order to remove any radioactive contamination of the surface of the disc that might have resulted from leaching of tagged adhesive into the storage water. The disc was blotted dry with paper, care being taken not to move the disc. The final radioactive counts were then determined. A reduction in the number of counts indicated the loss of adhesive from beneath the disc. Following the final count, the specimen was subjected to an adhesion test under tensile force. The technique involved was similar to that used by Udagama (1975), except for some modifications. Liquid mercury was used for the load instead of lead shot, the mercury being contained in a 50 ml calibrated burette to the end of which was attached a cut-off valve. A rubber tube led from this valve unit to a plastic container which formed part of the loading assembly. Extending from the centre of the cover was a metal rod, to the end of which was attached a wood disc. The entire loading assembly was connected to the wire loop on the acrylic disc by means of a chain with a hook at each end. The container with the metal rod and wood disc, the connecting chain and the acrylic disc had a total mass of 50 g. The test equipment is shown in Fig. 4. The test specimen was clamped vertically so that the side with the acrylic disc faced downward, and it was positioned with a spirit level to ensure that the specimen was vertical. The loading assembly was carefully attached to the specimen and adjusted so that the wood disc was about 5 mm above the cut-off valve. The valve was opened and the mercury allowed to flow into the container at the rate of 4-0±0-5 ml min~^ until the acrylic disc broke away from the skin. When the loading assembly dropped, the wood disc hit the cut-off valve, thereby closing off the mercury flow. The volume of mercury required to break the bond was read off from the calibrated burette, and the corresponding mass was calculated on the basis of the density of mercury. The tests were also performed on specimens that had been stored in water for 3 h and 5 h.
Retention of denture adhesives
429
Fig. 4. Adhesion test apparatus: S=test specimen consisting of the rat skin on the wood block and acrylic disc, between which was the test adhesive; D=wooden disc for closing the cut-off valve; V=cut-off valve.
Results Loss of adhesives All counts were corrected for background radiation. The standard deviation of the three 1-min counts at each time interval was found to be less than 10%. This was considered to be within the range of acceptability for this type of test (Udagama, 1975). The data, which are the average of twelve 1-min counts, represent the difference between the initial counts when the adhesive was first applied and those measured after each time interval. The initial counts showed wide variation within each group of specimens for each adhesive and also between adhesives. The data were therefore expressed as percentage loss of adhesive. The average loss of each adhesive at different time intervals is shown in Table 1. Factorial analysis of variance showed there to be a significant difference between the percentage loss of each adhesive at the three time intervals (P
Retention of denture adhesives — an in vitro study C.
L.
C H E W Faculty of Dentistry, National University of Singapore, Singapore
Summary
Denture adhesives are being used by patients to aid the retention and stability of their dentures. A number of laboratory and clinical investigations have been conducted to study the effects of such adhesives. This study describes a simple in vitro method for measurement of their retentive effect and its relation to loss of adhesive. The results show that there is a reduction in the effectiveness of adhesives, and that there is also an increase in adhesive loss, with time. There appears to be a correlation between these two properties. Introduction
Denture adhesives are probably the most widely used and least harmful of the overthe-counter denture additives. They were introduced in the early part of the century, and many different types have subsequently been made available. Patients use these materials to improve the retention and stability of their dentures. Studies on the effectiveness of denture adhesives have been conducted by Boone (1962), Kapur (1967), Ow and Beam (1983) and Chew et al. (1985). Their results indicated that adhesives do improve the retention of dentures. Swartz, Norman and Phillips (1967) have measured the loss of denture adhesives under dentures with the aid of radioactive materials. : The purpose of this study was to investigate the retentive effect of denture adhesives, and to determine whether this property is related to loss of the adhesives. Materials and methods
The denture adhesives selected for this study were Fixodent®* and Super Polygrip®!, both of which were in the form of a paste, and also Secure,*, which was in the form of a powder. . . . . . The skin of the rat was selected as a substitute for the oral mucosa. The rat was killed, skinned, and the subcutaneous fat removed. It was then shaved clean of all hair. Rat skin was selected because its surface, which is similar to palatal mucosa, is keratinized and can be kept moist due to its ability to retain moisture. The skin was mounted on the flat surface of a cylindrical block of wood of diameter 35 mm and length 50 mm, and held taut with a ring clamp (Fig. 1). The end surfaces of the wooden block were trimmed flat and parallel to each other, in order to allow vertical * Richardson-Vicks, Wilton, Connecticut, U.S.A. t Block Drug Co. Inc., Jersey City, New Jersey, U.S.A. Correspondence: Dr C.L. Chew, Department of Prosthetic Dentistry, Faculty of Dentistry, National University of Singapore, National University Hospital, Lower Kent Ridge Road, Singapore 0511.
425
426
C. L. Chew
Fig. 1. Rat skin mounted on flat surface of a cylindrical wood block, held taut with a ring clamp.
positioning of the block, with the aid of a spirit level, for the adhesion test. The skin on the block was stored in tap water until needed. A circular, heat-cured, clear acrylic disc of diameter 32 mm and thickness 2 mm was used to represent the denture. A wire loop was attached to one surface of the disc. Four circular marks, of approximately the same size as the window of the miniature Geiger-Muller tube, were made on this surface to enable radioactive counts to be monitored over the same area in each set of measurements (Fig. 2). The other surface was ground flat to ensure even contact of the resin disc with the skin. Adhesive loss was measured using the method described by Swartz et al. (1967). Each adhesive was tagged with the radioisotope "^^P, by dripping a solution of K3P^^O4 on to zinc oxide powder (0-3 |im particle size) in an amount sufficient to yield a concentration of 4 [iCi of ^^P in 0-2 g of zinc oxide. After the powder had been dried under a heat lamp, it was mixed to ensure uniform distribution of the isotope throughout the powder. Enough powder to provide 0-2 g of zinc oxide (4 [xCi of -^^P) per dose was then incorporated into the respective adhesives. Each dose of adhesive was considered to represent the average amount of adhesive required for each clinical application. The zinc oxide and adhesive were mixed with a spatula on a glass slab until the zinc oxide was uniformly dispersed throughout the adhesive. The dose for each material was established by determining the average quantity of adhesive required per application. These values were obtained by trial and error. The maxillary denture was weighed and the adhesive applied to its tissue surface using the procedure specified by the respective manufacturers. The combined mass of the denture and the adhesive was determined, and the denture was then seated firmly in
Retention of denture adhesives
All
Fig. 2. Clear acrylic disc with attached wire loop and four circular marks to enable the radioactive counts to be monitored. . .
the patient's mouth. The sulcus and posterior palatal regions were checked for any excess of material. The denture was removed and the adhesive coverage on its tissue surface and on the denture-bearing mucosa was examined. The average amount of each adhesive needed to cover the tissue surface of five maxillary complete dentures, without excess of material flowing over the borders, was determined. It was found that 1-4 g of Fixodent®, 0-4 g of Secure® and 1-7 g of Super Polygrip® were required. Radioactive counts and adhesion test Six specimens were prepared for the study, and the same six specimens were used for the 1 h, 3 h and 5 h tests for the three products investigated. This was done in order to control the variation between specimens in each test group. At the start of the test, the skin mounted on the wooden block was cleaned by brushing with a dish-washing detergent. The excess water was evaporated off with a stream of compressed air applied for 30 s. The acrylic disc was placed over the skin and centralized, and the specimen was positioned under the Geiger-Muller counter (Lionel Model 224)* so that the window was 2mm above one of the four marks on the surface of the disc (Fig. 3). The Geiger-Muller counter was connected to the proportional counter (Model PC-3B), and the voltage was set at 775 V. Three 1-min counts of each of the four marked areas were made, and the average of these 12 measurements was obtained. This set of results represented the background radiation, and the data were recorded for each specimen before the tagged adhesive was applied. The disc was then separated from the skin and wiped dry. The test adhesive was applied to the tissue surface of the disc, and was spread evenly over the surface with a plastic spatula. The disc was pressed firmly on to the skin using finger pressure. Excess material flowing out of the border of the disc was removed. The specimen was placed under the Geiger-Mtiller tube for radioactive counts as described above. Upon completion, the specimen was placed in distilled water maintained at 37°C. After 1 h the specimen was removed and the top surface of the disc was rinsed under a gentle flow * Nuclear Measurements Corporation, Indianapolis, Indiana, U.S.A.
,•-
.: ;s;^ r/.'l*>N
C. L. Chew
Fig. 3. Test specimen positioned under the Geiger-Muller tube (Lionel Model 224) for determination of radioactive counts.
of tap water for 5 min, in order to remove any radioactive contamination of the surface of the disc that might have resulted from leaching of tagged adhesive into the storage water. The disc was blotted dry with paper, care being taken not to move the disc. The final radioactive counts were then determined. A reduction in the number of counts indicated the loss of adhesive from beneath the disc. Following the final count, the specimen was subjected to an adhesion test under tensile force. The technique involved was similar to that used by Udagama (1975), except for some modifications. Liquid mercury was used for the load instead of lead shot, the mercury being contained in a 50 ml calibrated burette to the end of which was attached a cut-off valve. A rubber tube led from this valve unit to a plastic container which formed part of the loading assembly. Extending from the centre of the cover was a metal rod, to the end of which was attached a wood disc. The entire loading assembly was connected to the wire loop on the acrylic disc by means of a chain with a hook at each end. The container with the metal rod and wood disc, the connecting chain and the acrylic disc had a total mass of 50 g. The test equipment is shown in Fig. 4. The test specimen was clamped vertically so that the side with the acrylic disc faced downward, and it was positioned with a spirit level to ensure that the specimen was vertical. The loading assembly was carefully attached to the specimen and adjusted so that the wood disc was about 5 mm above the cut-off valve. The valve was opened and the mercury allowed to flow into the container at the rate of 4-0±0-5 ml min~^ until the acrylic disc broke away from the skin. When the loading assembly dropped, the wood disc hit the cut-off valve, thereby closing off the mercury flow. The volume of mercury required to break the bond was read off from the calibrated burette, and the corresponding mass was calculated on the basis of the density of mercury. The tests were also performed on specimens that had been stored in water for 3 h and 5 h.
Retention of denture adhesives
429
Fig. 4. Adhesion test apparatus: S=test specimen consisting of the rat skin on the wood block and acrylic disc, between which was the test adhesive; D=wooden disc for closing the cut-off valve; V=cut-off valve.
Results Loss of adhesives All counts were corrected for background radiation. The standard deviation of the three 1-min counts at each time interval was found to be less than 10%. This was considered to be within the range of acceptability for this type of test (Udagama, 1975). The data, which are the average of twelve 1-min counts, represent the difference between the initial counts when the adhesive was first applied and those measured after each time interval. The initial counts showed wide variation within each group of specimens for each adhesive and also between adhesives. The data were therefore expressed as percentage loss of adhesive. The average loss of each adhesive at different time intervals is shown in Table 1. Factorial analysis of variance showed there to be a significant difference between the percentage loss of each adhesive at the three time intervals (P
