Journal of Oral Rehabilitation, 1991, Volume 18, pages 399-401
Evaluation of the level of residual monomer in acrylic denture base materials having different polymerization properties B . K A L I P C I L A R , L . K A R A A G A C L I O G L U and U . H A S A N R E I S06 L U Department of Prosthodontics, Faculty of Dentistry, University of Ankara, Ankara, Turkey
Summary The aim of this study was to evaluate the level of residual monomer in acrylic denture base materials having different polymerization properties. The investigation included a conventional-type acrylic cured under heat and pressure, as well as a pour-type resin polymerized by an injection-moulding technique at room temperature and under pressure. It was found that the residual monomer content ranged from 0.22-0-54% in pour-type resin, and from 0.23-0-52% in routinely used resins when the specimens were analysed by high performance liquid chromatography. These findings revealed that there were no significant differences between the two types of acrylic in terms of their residual monomer content. Introduction
Toxic and allergic reactions to denture-base material may be predicted in patients who present with mucosal damage, hypersensitivity and soreness, when the possibility of mechanical imtation of the candidal denture, denture sore mouth or that of a systemic disease has been eliminated. This could be due to the polymer, the benzoyl peroxide, the hydroquinone, the pigments or the residual monomer, high levels of which are known to have an irritant effect (Anderson, 1976; Craig et al., 1979). The aim of this study was to compare the residual monomer content of a pour-type resin, moulded by an injection technique, with that of a conventional heat-cured acrylic dough moulding system. Materials and methods The two types of material used in this study were QC 20 (DeTrey, Weybridge, UK), a heat-curing resin, classified as Type 1 Class 1 according to the American Dental Association specification, and Intopress (Kulzer Co., GmbH, Bad Homburg, Germany), a pour-type resin classified as Type 2 Class 1 according to the same specification. Twenty standard samples of flat plates, approximately 10 x 10mm, were fabricated, each specimen being prepared by a different flasking procedure. Ten samples of conventional resin were cured, initially in water at 75 f 1"C, and then in boiling water for 30min as described by the American Dental Association (1972-1973). The re-
Correspondence: Prof. Dr Ufuk Hasanreisoglu, Necatibey cad. 104/3,Yenivehir, Ankara, Turkey.
399
400
B. KalipGilar et al.
maining 10 pour-type resin specimens were prepared by injecting the polymer into a flask under constant pressure in an electromechanical Preci-Press unit (Krupp, GmbH, Essen, Germany) at room temperature according to the manufacturers' instructions. After the curing schedule had been completed, the specimens were kept in individual containers, filled with distilled water at 37"C, for 30 days. At the end of this period, specimens were reduced to a powder and melted by placing them in ethylacetate for 24 h at room temperature. High performance liquid chromatography was used to determine the residual monomer content of the polymers. Before the materials were analysed, the wavelength and accuracy of the ultraviolet detector on the chromatograph were adjusted to 254mm and 0.64, respectively. The flow rate of the pump was adjusted to 1ml min-'. The paper speed of the chart recorder was set at 40cm h-'. Initially, the standard solution of 3% monomer was injected into the test unit of the chromatograph, and the standard peaks for methylmethacrylate were recorded. Subsequently, the same procedure was repeated using equal amounts of specimen solutions, and thus the peaks of residual monomer were determined in each sample. The unknown concentration of monomer in the materials was calculated by comparing the peaks of the specimens with those of standard solutions.
Results The concentrations of residual monomer in each specimen, together with the mean value and standard error for each set of replicate determinations, are shown in Table 1. No statistically significant (P > 0.05) differences were found between heat-curing and pour-type resins in terms of their residual monomer content. Discussion In this study, high performance liquid chromatography was employed, since all the procedures were camied out in the liquid at room temperature, thus eliminating heat and yielding more accurate results, as has been advocated previously (Aitzetmiiller and Eckert, 1978). McCabe and Basker (1976) used a gas chromatographic method to analyse the residual monomer content of suspected heat-cured denture bases in two cases, and they reported values of 0.233% and 0.186% which had produced allergic reactions.
Table 1. Percentage content of residual monomer (mg g-') Sample 1 2 3 4
5 6 7 8 9 10
Mean value 2 SEM
Heat-curing resin
Pour type resin
0.49 0.47 0.40 0.38 0.23 0.52 0.36 0.38 0.38 0.33
0.26 0.22 0.54 0.49 0.49 0.51 0.53 0.36 0.35
0.3940 ? 0.0266
0.4260 ? 0.0374
0.51
Residual monomer in acrylic denture base materials
401
Similarly, in two cases reported by Austin and Basker (1980), the levels of residual monomer at which mucosal irritation occurred were 1-7and 3.2%. However, Douglas and Bates (1978) demonstrated for several pour-type resins monomer contents ranging from 2-16-4-99%. Despite these relatively high levels, there appear to have been no reports of rnucosal damage. In view of these findings, it is interesting to note that, although allergic reactions in such patients are apparently due to the presence of residual monomer, predisposition appears to be an important factor since the levels required to induce such reactions vary widely. Recently, researchers have focused their attention on comparisons of the residual monomer contents of pour- and heat-cured resins. According to Kallus (1984), Ruyter and Bysoed obtained a 1% residual monomer level in heat-curing resins, and 3% in pour-type resins in their chromatographic investigations. Similarly, Marx et al. (1983) reported values ranging from 0.5-2.6% for heat-curing resins, and from 0.7-4.4% for pour-type resins. Anderson (1976) has also described a 0-2-0.5% residual monomer, even in perfectly polymerized acrylic resins. All these findings suggest that there is a wide range of variability in the amount of residual monomer in resins, whether they are heat cured or pour type, and our results, namely 0-23-0-52% for heat-curing and 0.22-0.54% for pour-type resins, were well below these values. It was reported that the residual monomer contents of resins that had been polymerized at room temperature by a tertiary amine/benzoyl peroxide system would be higher with regard to heat-curing resins, due to the lower molecular weight of the material, as well as the shorter polymerization time, the undesirable ratios of monomer and polymer and the sudden increase in temperature (Anderson, 1976). However, the pour-type resin used in our study had a residual monomer content similar to those polymerized by curing, although they were polymerized at room temperature by an injection technique. These findings can be attributed to the high molecular weight of the material. References AITZETMULLER, K. & ECKERT,W.R. (1978) High-performance liquid chromatography of methylmethacrylate in intraocular lenses. Journal of Chromatography, 155, 203. AMERKAN DENTALAssocMnoN (1972-1973) Guide to Dental Materials and Devices, 6th edn, pp. 201-215. American Dental Association, Chicago. ANDERSON, J.N. (1976) Applied Dental Materials, 5th edn, pp. 245-270. Blackwell Scientific Publications, Oxford. AUSTIN, A.T. & BASKERR.M. (1980) The level of residual monomer in acrylic denture base materials. British Dental Journal, 149, 281. CRAIG, R.G., O’BREN, W.J. & POWERS,J.M. (1979) Dental Materials, 4th edn, pp. 215-237. C.V.Mosby Co.,St Louis. DOUGLAS, W.H. & BATES,J.F. (1978) The determination of residual monomer in polymethylmethacrylate denture base resins. Journal of Material Science, 13, 2600. KALLUS,T. (1984) Evaluation of the toxicity of denture base polymers after subcutaneous implantation in guinea pigs. Journal of Prosthetic Dentistry, 52, 126. MCCABE,J.F. & BASKER,R.M. (1976) Tissue sensitivity to acrylic resin. British Dental Journal, 140, 347. E. (1983) Zur frage der restmonomeruntersuchung von prothesenMARY,H . , FUKUI,M. & STENDER, kunststoffen. Deutsche Zahnarztliche Zeitschrin, 38, 550.
Evaluation of the level of residual monomer in acrylic denture base materials having different polymerization properties B . K A L I P C I L A R , L . K A R A A G A C L I O G L U and U . H A S A N R E I S06 L U Department of Prosthodontics, Faculty of Dentistry, University of Ankara, Ankara, Turkey
Summary The aim of this study was to evaluate the level of residual monomer in acrylic denture base materials having different polymerization properties. The investigation included a conventional-type acrylic cured under heat and pressure, as well as a pour-type resin polymerized by an injection-moulding technique at room temperature and under pressure. It was found that the residual monomer content ranged from 0.22-0-54% in pour-type resin, and from 0.23-0-52% in routinely used resins when the specimens were analysed by high performance liquid chromatography. These findings revealed that there were no significant differences between the two types of acrylic in terms of their residual monomer content. Introduction
Toxic and allergic reactions to denture-base material may be predicted in patients who present with mucosal damage, hypersensitivity and soreness, when the possibility of mechanical imtation of the candidal denture, denture sore mouth or that of a systemic disease has been eliminated. This could be due to the polymer, the benzoyl peroxide, the hydroquinone, the pigments or the residual monomer, high levels of which are known to have an irritant effect (Anderson, 1976; Craig et al., 1979). The aim of this study was to compare the residual monomer content of a pour-type resin, moulded by an injection technique, with that of a conventional heat-cured acrylic dough moulding system. Materials and methods The two types of material used in this study were QC 20 (DeTrey, Weybridge, UK), a heat-curing resin, classified as Type 1 Class 1 according to the American Dental Association specification, and Intopress (Kulzer Co., GmbH, Bad Homburg, Germany), a pour-type resin classified as Type 2 Class 1 according to the same specification. Twenty standard samples of flat plates, approximately 10 x 10mm, were fabricated, each specimen being prepared by a different flasking procedure. Ten samples of conventional resin were cured, initially in water at 75 f 1"C, and then in boiling water for 30min as described by the American Dental Association (1972-1973). The re-
Correspondence: Prof. Dr Ufuk Hasanreisoglu, Necatibey cad. 104/3,Yenivehir, Ankara, Turkey.
399
400
B. KalipGilar et al.
maining 10 pour-type resin specimens were prepared by injecting the polymer into a flask under constant pressure in an electromechanical Preci-Press unit (Krupp, GmbH, Essen, Germany) at room temperature according to the manufacturers' instructions. After the curing schedule had been completed, the specimens were kept in individual containers, filled with distilled water at 37"C, for 30 days. At the end of this period, specimens were reduced to a powder and melted by placing them in ethylacetate for 24 h at room temperature. High performance liquid chromatography was used to determine the residual monomer content of the polymers. Before the materials were analysed, the wavelength and accuracy of the ultraviolet detector on the chromatograph were adjusted to 254mm and 0.64, respectively. The flow rate of the pump was adjusted to 1ml min-'. The paper speed of the chart recorder was set at 40cm h-'. Initially, the standard solution of 3% monomer was injected into the test unit of the chromatograph, and the standard peaks for methylmethacrylate were recorded. Subsequently, the same procedure was repeated using equal amounts of specimen solutions, and thus the peaks of residual monomer were determined in each sample. The unknown concentration of monomer in the materials was calculated by comparing the peaks of the specimens with those of standard solutions.
Results The concentrations of residual monomer in each specimen, together with the mean value and standard error for each set of replicate determinations, are shown in Table 1. No statistically significant (P > 0.05) differences were found between heat-curing and pour-type resins in terms of their residual monomer content. Discussion In this study, high performance liquid chromatography was employed, since all the procedures were camied out in the liquid at room temperature, thus eliminating heat and yielding more accurate results, as has been advocated previously (Aitzetmiiller and Eckert, 1978). McCabe and Basker (1976) used a gas chromatographic method to analyse the residual monomer content of suspected heat-cured denture bases in two cases, and they reported values of 0.233% and 0.186% which had produced allergic reactions.
Table 1. Percentage content of residual monomer (mg g-') Sample 1 2 3 4
5 6 7 8 9 10
Mean value 2 SEM
Heat-curing resin
Pour type resin
0.49 0.47 0.40 0.38 0.23 0.52 0.36 0.38 0.38 0.33
0.26 0.22 0.54 0.49 0.49 0.51 0.53 0.36 0.35
0.3940 ? 0.0266
0.4260 ? 0.0374
0.51
Residual monomer in acrylic denture base materials
401
Similarly, in two cases reported by Austin and Basker (1980), the levels of residual monomer at which mucosal irritation occurred were 1-7and 3.2%. However, Douglas and Bates (1978) demonstrated for several pour-type resins monomer contents ranging from 2-16-4-99%. Despite these relatively high levels, there appear to have been no reports of rnucosal damage. In view of these findings, it is interesting to note that, although allergic reactions in such patients are apparently due to the presence of residual monomer, predisposition appears to be an important factor since the levels required to induce such reactions vary widely. Recently, researchers have focused their attention on comparisons of the residual monomer contents of pour- and heat-cured resins. According to Kallus (1984), Ruyter and Bysoed obtained a 1% residual monomer level in heat-curing resins, and 3% in pour-type resins in their chromatographic investigations. Similarly, Marx et al. (1983) reported values ranging from 0.5-2.6% for heat-curing resins, and from 0.7-4.4% for pour-type resins. Anderson (1976) has also described a 0-2-0.5% residual monomer, even in perfectly polymerized acrylic resins. All these findings suggest that there is a wide range of variability in the amount of residual monomer in resins, whether they are heat cured or pour type, and our results, namely 0-23-0-52% for heat-curing and 0.22-0.54% for pour-type resins, were well below these values. It was reported that the residual monomer contents of resins that had been polymerized at room temperature by a tertiary amine/benzoyl peroxide system would be higher with regard to heat-curing resins, due to the lower molecular weight of the material, as well as the shorter polymerization time, the undesirable ratios of monomer and polymer and the sudden increase in temperature (Anderson, 1976). However, the pour-type resin used in our study had a residual monomer content similar to those polymerized by curing, although they were polymerized at room temperature by an injection technique. These findings can be attributed to the high molecular weight of the material. References AITZETMULLER, K. & ECKERT,W.R. (1978) High-performance liquid chromatography of methylmethacrylate in intraocular lenses. Journal of Chromatography, 155, 203. AMERKAN DENTALAssocMnoN (1972-1973) Guide to Dental Materials and Devices, 6th edn, pp. 201-215. American Dental Association, Chicago. ANDERSON, J.N. (1976) Applied Dental Materials, 5th edn, pp. 245-270. Blackwell Scientific Publications, Oxford. AUSTIN, A.T. & BASKERR.M. (1980) The level of residual monomer in acrylic denture base materials. British Dental Journal, 149, 281. CRAIG, R.G., O’BREN, W.J. & POWERS,J.M. (1979) Dental Materials, 4th edn, pp. 215-237. C.V.Mosby Co.,St Louis. DOUGLAS, W.H. & BATES,J.F. (1978) The determination of residual monomer in polymethylmethacrylate denture base resins. Journal of Material Science, 13, 2600. KALLUS,T. (1984) Evaluation of the toxicity of denture base polymers after subcutaneous implantation in guinea pigs. Journal of Prosthetic Dentistry, 52, 126. MCCABE,J.F. & BASKER,R.M. (1976) Tissue sensitivity to acrylic resin. British Dental Journal, 140, 347. E. (1983) Zur frage der restmonomeruntersuchung von prothesenMARY,H . , FUKUI,M. & STENDER, kunststoffen. Deutsche Zahnarztliche Zeitschrin, 38, 550.
