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The rheological properties of endodontic sealers
Quarterly
Dental
Review
Over a 3-year period 547 bridges and 162 crowns were cemented with one of three dental cements. At the time of placement of the restoration the type of retainer and biting cement used were noted. The patients were recalled at 6-monthly intervals and the bridge or crown was examined for looseness. The cements investigated were: zinc oxide/eugenol reinforced with EBA and alumina, polycarboxylate and zinc phosphate. The retainer types were: complete crown, three-quarter crown, MOD inlay and pinledge. Statistical analyses of the performance of each type of cement or retainer used and investigation of any interaction between the two groups were carried out. In some groups the numbers of failures were so low that valid comparisons between them could not be carried out. It was found that when EBA-reinforced cements were used, pinledge retainers failed more frequently than either threequarter or complete crowns. When polycarboxylate cements were used, full crowns, three-quarter crowns and pinledges were all equally successful. If only threequarter crowns were compared, the best luting cement was zinc phosphate. G. A. Smith
VERMILYEA S. G., deSlMON L. B. and HUGET E. P. The rheological properties of endodontic sealers, OralSurg. 46 (1978) 711-716. The success of root canal therapy may often be determined by the efficiency with which lateral and accessory canals are obturated. This is usually achieved with a root canal sealer used either singly or in conjunction with a preformed root filling point. The capacity of sealers to adequately fill narrow accessory canals is largely determined by the flow characteristics. Experiments were carried out in this study to investigate the apparent rheological properties of 7 root canal sealers as a function of time and shear rate. Diaket. Kerr’s sealer, Proco-Sol and Roth cement Tvpes 601, 801 and 811 were the commercially available products tested. A volume (about 1 cm3) of each was mixed according to the manufacturer’s directions at a temperature of 23 f 2 “C and at 50
261
per cent relative humidity. The mixed materials were transferred to disposable vials which were suspended in a water bath at 37 ‘C. Commencing 2 min after mixing was complete, the viscosity was measured continuously for a 15-min period using a rotational viscometer at rates varying from 1 to 20 rpm. Five tests were performed on each material at each rate and the viscosity was measured in centipoise. At a rotational speed of 1 rpm the initial viscosities varied from 7000 cp (Roth cement Type 811) to 678 000 cp (Diaket) and the viscosity increased with time in 6 of the preparations. However, the rate of increase in viscosity varied, some undergoing a gradual increase (Roth cement Types 801 and 811 and Proco-Sol), others undergoing an abrupt increase about 10 min after mixing (Roth cement Type 601 and Kerr’s sealers). Diaket underwent an immediate and rapid increase while TubliSeal, after an initial fall, sharply increased in viscosity after 9 min. An increase in rotational speed brought about a considerable decrease in viscosity. At 2 min after mixing and at a rotational speed of 20 rpm, the reduction on the lrpm values ranged from 42 (Roth cement Type 801) to 90 (Diaket) per cent. Roth cement Type 811 was the only product that did not display a significant reduction at the higher shear rate. Clearly there is a need to select a root canal sealer that has a viscosity that will allow its complete but controlled placement in the root canal. Many factors may affect the initial visosity of a product, such as powder particle size, powder : liquid ratio and setting rate, but the contribution made by these is not fully understood and standards have not been established. TubliSeal appeared to demonstrate thixotropic properties. Thixotropy brings about a decrease in viscosity under a constant rate of shear, as may occur during mixing and insertion into the canal. Six materials displaved reduced viscosity at increased rates of shear and therefore high rotational speeds of filling instruments and high condensation pressures might be expected to bring about more effective filling of accessory canals. An examination of viscosity/time behaviour patterns may lead to a more rational selection of root canal sealers by clinicians. J. Cunningham
Dental
Review
Over a 3-year period 547 bridges and 162 crowns were cemented with one of three dental cements. At the time of placement of the restoration the type of retainer and biting cement used were noted. The patients were recalled at 6-monthly intervals and the bridge or crown was examined for looseness. The cements investigated were: zinc oxide/eugenol reinforced with EBA and alumina, polycarboxylate and zinc phosphate. The retainer types were: complete crown, three-quarter crown, MOD inlay and pinledge. Statistical analyses of the performance of each type of cement or retainer used and investigation of any interaction between the two groups were carried out. In some groups the numbers of failures were so low that valid comparisons between them could not be carried out. It was found that when EBA-reinforced cements were used, pinledge retainers failed more frequently than either threequarter or complete crowns. When polycarboxylate cements were used, full crowns, three-quarter crowns and pinledges were all equally successful. If only threequarter crowns were compared, the best luting cement was zinc phosphate. G. A. Smith
VERMILYEA S. G., deSlMON L. B. and HUGET E. P. The rheological properties of endodontic sealers, OralSurg. 46 (1978) 711-716. The success of root canal therapy may often be determined by the efficiency with which lateral and accessory canals are obturated. This is usually achieved with a root canal sealer used either singly or in conjunction with a preformed root filling point. The capacity of sealers to adequately fill narrow accessory canals is largely determined by the flow characteristics. Experiments were carried out in this study to investigate the apparent rheological properties of 7 root canal sealers as a function of time and shear rate. Diaket. Kerr’s sealer, Proco-Sol and Roth cement Tvpes 601, 801 and 811 were the commercially available products tested. A volume (about 1 cm3) of each was mixed according to the manufacturer’s directions at a temperature of 23 f 2 “C and at 50
261
per cent relative humidity. The mixed materials were transferred to disposable vials which were suspended in a water bath at 37 ‘C. Commencing 2 min after mixing was complete, the viscosity was measured continuously for a 15-min period using a rotational viscometer at rates varying from 1 to 20 rpm. Five tests were performed on each material at each rate and the viscosity was measured in centipoise. At a rotational speed of 1 rpm the initial viscosities varied from 7000 cp (Roth cement Type 811) to 678 000 cp (Diaket) and the viscosity increased with time in 6 of the preparations. However, the rate of increase in viscosity varied, some undergoing a gradual increase (Roth cement Types 801 and 811 and Proco-Sol), others undergoing an abrupt increase about 10 min after mixing (Roth cement Type 601 and Kerr’s sealers). Diaket underwent an immediate and rapid increase while TubliSeal, after an initial fall, sharply increased in viscosity after 9 min. An increase in rotational speed brought about a considerable decrease in viscosity. At 2 min after mixing and at a rotational speed of 20 rpm, the reduction on the lrpm values ranged from 42 (Roth cement Type 801) to 90 (Diaket) per cent. Roth cement Type 811 was the only product that did not display a significant reduction at the higher shear rate. Clearly there is a need to select a root canal sealer that has a viscosity that will allow its complete but controlled placement in the root canal. Many factors may affect the initial visosity of a product, such as powder particle size, powder : liquid ratio and setting rate, but the contribution made by these is not fully understood and standards have not been established. TubliSeal appeared to demonstrate thixotropic properties. Thixotropy brings about a decrease in viscosity under a constant rate of shear, as may occur during mixing and insertion into the canal. Six materials displaved reduced viscosity at increased rates of shear and therefore high rotational speeds of filling instruments and high condensation pressures might be expected to bring about more effective filling of accessory canals. An examination of viscosity/time behaviour patterns may lead to a more rational selection of root canal sealers by clinicians. J. Cunningham