Laboratory evaluation of eight pit and fissure sealants.

The penetration coefficients (PCs) and tensile bond strengths of eight pit and fissure sealant materials were determined. The PCs were tested at 22°C with five samples of each resin. Bond strengths were established in a tensile mode using an Instron * testing machine with 10 specimens for each sealant. Despite considerable variation in the PC values, all sealants showed similar tensile bond strengths. Further, the filled sealants, which are very viscous, demonstrated similar bond strengths to the unfilled resins. Epidemiological studies carried out in the 1930s and 1940s showed that nearly 100 per cent of individuals living in western populations suffered from dental caries. 1,~ More recent studies indicate that industrialized nations have a decreasing caries incidence. 3 Despite a slight decline in the overall caries rate, tooth decay remains a major health problem in the United States and other industrialized countries. 3 Longitudinal studies of pit and fissure caries have demonstrated the early onset and rapid rate at which occlusal decay occurs. Lewis and Hargreaves 4 found that 70% of the first: permanent molars of subjects residing in a nonfluoridated area had pit and fissure decay within one year after eruption. This study demonstrated the need for early treatment of all pit and fissure areas. King, Shaw, and Murrays later found that 92% of first molars and 68% of second molars were decayed, missing, or filled by age 15; pits and fissures provide an excellent habitat for opportunistic cariogenic microorganisms. The caries susceptibility of occlusal surfaces and the relative ineffectiveness of fluorides and mechanical plaque control to prevent decay have led to new preventive methods. The technological development of dental resin systems has permitted mechanical obturation of pits and fissures for caries prevention. Clinical trials have * Instron Corp.; Canton, Mass. 02021. demonstrated effective long-term caries reductions with a number of different sealant products. 6,7 The effectiveness of sealants depends on their ability to penetrate fissures before hardening, thus producing a mechanical barrier to caries. To produce bonding and retention, the sealant material must flow over the etched enamel surface and penetrate micropores in the etched surface. Because of this intimate relationship it was felt by some investigators that the penetrative ability of a sealant would affect its ability to bond to enamel. 8,9 Resin penetration, however, was found to be dependent on the underlying etch pattern, wetting ability of the enamel, and the materials’ surface tension, viscosity, and rate of polymerization. 8,9 The purpose of this in vitro investigation was to evaluate eight commercially available sealant materials. The parameters examined were the penetration coefficients (PCs) and tensile bond strengths. Scanning electron microscopy (SEM) was used to examine the fractured tensile bond strength specimens. Methods and Materials The eight sealants are commercially available Bis-GMA resins. Four of the sealants a-d are chemically activated two-component systems. Two of the sealants e,f are polymerized by ultraviolet light, and one of these f contains 64% lithium aluminum silicate filler particles. Two new visible light activated systemsg,h also were examined. One of these materialsg is filled, containing 64% silicate particles. 1° Delton Pit and Fissure Sealant System, Johnson & Johnson; East Windsor, N.J. 08520. Delton Tinted Pit and Fissure Sealant System, Johnson & Johnson; East Windsor, N.J. 08520. Concise White Sealant System, 3M Company; St. Paul, Minn. 55101. Concise Enamel Bond System, 3M Company; St. Paul, Minn. 55101. Nuva Seal, L.D. Caulk Dental Products; Milford, Del. 19963. Nuva Cote, L.D. Caulk Dental Products; Milford, Del. 19963. Prisma Shield, L.D. Caulk Dental Products; Milford, Del. 19963. Visio Seal, Premier; Romano Dr.; Norristown, Pa. 19401. 36 EVALUATION OF PIT AND FISSURE SEALANTS: Wright and Retief Penetration Coefficient The penetration rate of a liquid under its own capillary force into an open, horizontal capillary tube can be derived from Poiseuille’s law.9 The PC of a resin can be calculated from the surface tension of the resin (y), the viscosity of the resin (rl), and the contact angle of the resin on a capillary wall (0). Determination of the parameters ¥, ~1, and 0 is difficult and requires sophisticated instrumentation. As the PC is equal to the square of the distance penetrated into a horizontal capillary tube of unit radius in unit time under capillary pressure, the PC of a sealant can be obtained from the slope of the straight line of the length of the liquid column squared (x2) versus time (t). 9