Microhardness studies on the setting characteristics of fissure sealants

Abstract

The hardness of five fissure sealants was measured using a Wallace Microhardness Tester and found to continue to increase long after the initial setting. The effect of the intensity of radiation and exposure time on the setting of two u.v. activated sealants (Nuva-seal and Alphaseal) was also investigated, with higher intensities producing both a more rapid set and greater final hardness. Alphaseal required longer exposure at a given intensity of u.v. radiation to achieve the same hardness as Nuva-seal, and displayed relatively slow setting in depth, which could give rise to incomplete polymerization during clinical use, resulting in early sealant loss. Thus special care must be taken to ensure that Alphaseal receives an adequate exposure to u.v. radiation, and sources which are suitable for setting Nuva-seal may not be sufficiently powerful when applying Alphaseal.

Studies on the setting behaviour of sealants using a new acoustic method of determining set

“…Thus the increased setting rate of Alphaseal following a reduction in the catalyst concentration to 1 % w/w, and removal ofthe fiuorescent dye, is probably due to deeper penetration of the radiation into the sealant. These absorption effects can also explain the relatively slow setting of Alphaseal in depth, observed by microhardness measurements in a previous study (Young et al, 1978a). Similarly, the presence of filler particles in Nuva-cote probably caused slower setting in depth by increasing the absorption of radiation at the surface layers.…”

“…Previous studies on the u.v. absorption characteristics of sealants demonstrated that Alphaseal has a much greater absorption coefficient than Nuva-seal (Young et al, 1978b). Further investigation, showed that this was due to the relatively high catalyst concentration used in Alphaseal (5% w/w), and the incorporation of a u.v.…”

Studies on the setting behaviour of sealants using a new acoustic method of determining set

“…Thus the increased setting rate of Alphaseal following a reduction in the catalyst concentration to 1 % w/w, and removal ofthe fiuorescent dye, is probably due to deeper penetration of the radiation into the sealant. These absorption effects can also explain the relatively slow setting of Alphaseal in depth, observed by microhardness measurements in a previous study (Young et al, 1978a). Similarly, the presence of filler particles in Nuva-cote probably caused slower setting in depth by increasing the absorption of radiation at the surface layers.…”

“…Previous studies on the u.v. absorption characteristics of sealants demonstrated that Alphaseal has a much greater absorption coefficient than Nuva-seal (Young et al, 1978b). Further investigation, showed that this was due to the relatively high catalyst concentration used in Alphaseal (5% w/w), and the incorporation of a u.v.…”

An assessment of new dental ultraviolet sources and u.v.‐polymerized fissure sealants

“…Lower intensities, or shorter exposure times may result in the material curing to a lower surface hardness, which nevertheless seems adequate when probed. It is also known that the hardness Distance fron guide i will slowly increase over the subsequent months as demonstrated in study 3 and by Young et al (1978b). However, to fully realize the sealants' potential, the minimum u.v.…”

“…The method was that described by Young et al (1978b). Discs of sealant of varying thickness were exposed to three u.v.…”

Laboratory studies of visible‐light cured fissure sealants: setting times and depth of polymerization

“…(2) Microhardness versus depth "''•'' Measurements of microhardness at various depths in sealant samples were made to give an indication of polymerization at depth. The method used was that of Young et al (1978b). Discs of the three sealants, of varying thickness, were prepared and exposed to the light from a Prisma-Lite source for periods of either 20 or 60s (the UV polymerizing material Nuva-Cote PA was exposed to the light from an Alphalite source).…”

Studies on the setting behaviour of sealants using a new acoustic method of determining set

“…Thus the increased setting rate of Alphaseal following a reduction in the catalyst concentration to 1 % w/w, and removal ofthe fiuorescent dye, is probably due to deeper penetration of the radiation into the sealant. These absorption effects can also explain the relatively slow setting of Alphaseal in depth, observed by microhardness measurements in a previous study (Young et al, 1978a). Similarly, the presence of filler particles in Nuva-cote probably caused slower setting in depth by increasing the absorption of radiation at the surface layers.…”

“…Previous studies on the u.v. absorption characteristics of sealants demonstrated that Alphaseal has a much greater absorption coefficient than Nuva-seal (Young et al, 1978b). Further investigation, showed that this was due to the relatively high catalyst concentration used in Alphaseal (5% w/w), and the incorporation of a u.v.…”

An assessment of new dental ultraviolet sources and u.v.‐polymerized fissure sealants

“…Lower intensities, or shorter exposure times may result in the material curing to a lower surface hardness, which nevertheless seems adequate when probed. It is also known that the hardness Distance fron guide i will slowly increase over the subsequent months as demonstrated in study 3 and by Young et al (1978b). However, to fully realize the sealants' potential, the minimum u.v.…”

“…The method was that described by Young et al (1978b). Discs of sealant of varying thickness were exposed to three u.v.…”

Laboratory studies of visible‐light cured fissure sealants: setting times and depth of polymerization

“…(2) Microhardness versus depth "''•'' Measurements of microhardness at various depths in sealant samples were made to give an indication of polymerization at depth. The method used was that of Young et al (1978b). Discs of the three sealants, of varying thickness, were prepared and exposed to the light from a Prisma-Lite source for periods of either 20 or 60s (the UV polymerizing material Nuva-Cote PA was exposed to the light from an Alphalite source).…”

Studies on the setting behaviour of sealants using a new acoustic method of determining set

“…Thus the increased setting rate of Alphaseal following a reduction in the catalyst concentration to 1 % w/w, and removal ofthe fiuorescent dye, is probably due to deeper penetration of the radiation into the sealant. These absorption effects can also explain the relatively slow setting of Alphaseal in depth, observed by microhardness measurements in a previous study (Young et al, 1978a). Similarly, the presence of filler particles in Nuva-cote probably caused slower setting in depth by increasing the absorption of radiation at the surface layers.…”

“…Previous studies on the u.v. absorption characteristics of sealants demonstrated that Alphaseal has a much greater absorption coefficient than Nuva-seal (Young et al, 1978b). Further investigation, showed that this was due to the relatively high catalyst concentration used in Alphaseal (5% w/w), and the incorporation of a u.v.…”

An assessment of new dental ultraviolet sources and u.v.‐polymerized fissure sealants

“…Lower intensities, or shorter exposure times may result in the material curing to a lower surface hardness, which nevertheless seems adequate when probed. It is also known that the hardness Distance fron guide i will slowly increase over the subsequent months as demonstrated in study 3 and by Young et al (1978b). However, to fully realize the sealants' potential, the minimum u.v.…”

“…The method was that described by Young et al (1978b). Discs of sealant of varying thickness were exposed to three u.v.…”

Laboratory studies of visible‐light cured fissure sealants: setting times and depth of polymerization

“…(2) Microhardness versus depth "''•'' Measurements of microhardness at various depths in sealant samples were made to give an indication of polymerization at depth. The method used was that of Young et al (1978b). Discs of the three sealants, of varying thickness, were prepared and exposed to the light from a Prisma-Lite source for periods of either 20 or 60s (the UV polymerizing material Nuva-Cote PA was exposed to the light from an Alphalite source).…”