Comparisons of retention, microleakage, penetration and caries inhibition of fissure sealant and resin infiltration in pit and fissure caries: an in vitro study

The back teeth of children and adults are covered with a landscape of deep grooves and narrow valleys, known as fissures. These natural crevices are difficult to clean, often trapping food and bacteria that produce acid. Over time, this acid eats away at the hard outer shell of the tooth, starting a process called decay. Because the openings to these grooves can be so tiny, a tooth might look healthy on the surface while a cavity begins to form deep inside. To stop this, dentists often apply a protective coating called a fissure sealant. This material flows into the grooves and hardens, acting like a shield that blocks bacteria and acid from reaching the vulnerable tooth structure underneath. However, these shields are not perfect; they can wear away, fall off, or fail to seal the deepest parts of the crack, leaving the tooth vulnerable again.

Researchers have been exploring a different approach called resin infiltration. Instead of just sitting on top of the tooth, this liquid resin is designed to soak deep into the porous, weakened structure of the early decay, hardening from the inside out to strengthen the tooth. While this method sounds promising, it is unclear how well it works on the complex, deep grooves of the back teeth compared to the traditional sealant, or if combining the two offers any extra protection. A team of scientists at the University of Hong Kong set out to test these methods in a controlled laboratory setting to see which approach best prevents leakage and stops decay from progressing.

To answer these questions, the researchers gathered 108 human teeth that had early, non-cavitated decay on their chewing surfaces. They divided these teeth into six groups to test different treatments. One group received the standard resin-based fissure sealant. Another group received the resin infiltration material, but the researchers varied the time they spent etching the tooth surface with acid before applying it, testing durations of 60 seconds, 120 seconds, and 180 seconds. A fifth group received a combination treatment: the resin infiltration followed immediately by the traditional sealant on top. The final group received no treatment at all, serving as a control to show what happens when nothing is done.

After applying the treatments, the team subjected the teeth to a rigorous simulation of years of chewing and temperature changes. They moved the teeth back and forth between hot and cold water thousands of times to see if the materials would crack or fall off. They then checked how well the materials stayed in place and whether gaps had formed where dye could leak in, which would indicate a failure in the seal. The results showed that the retention, or how well the materials stuck, was similar across all groups. No single method was significantly better at staying attached than the others. When looking for leaks, the traditional sealant and the resin infiltration applied for 60 or 120 seconds performed well, showing much less leakage than the untreated teeth. However, extending the acid etching time to 180 seconds or combining the infiltration with a sealant did not improve the seal; in fact, these groups leaked about as much as the untreated teeth.

The researchers also looked closely at how deep the materials penetrated into the cracks using powerful microscopes. They found that the resin infiltration and the traditional sealant both managed to fill the grooves to a similar depth, with about half of the samples in every group achieving complete filling. The depth of the crack did not seem to stop the materials from reaching the bottom. Interestingly, the team observed that when the acid was left on for too long, it altered the shape of the groove edges, causing them to collapse slightly. This created irregular gaps that the liquid resin could not fully fill, explaining why the longer etching time did not help.

To test how well these treatments stopped decay, the researchers exposed the teeth to cycles of acid and saliva, mimicking a high-risk environment where decay is likely to happen. They measured the mineral density of the teeth before and after this challenge. The untreated teeth showed significant loss of minerals, indicating that decay had progressed. In contrast, all the treated groups, whether they had the sealant, the infiltration, or both, showed a similar, much lower level of mineral loss. This suggests that as long as the material stayed in place, both the traditional sealant and the resin infiltration were equally effective at stopping the decay from spreading. Even when the researchers introduced specific bacteria to the teeth, the results remained consistent: the treated teeth fared much better than the untreated ones, and there was no clear advantage to using one method over the other.

The study concludes that for managing early decay in the deep grooves of back teeth, the traditional fissure sealant and the newer resin infiltration technique offer comparable protection. The resin infiltration works just as well as the sealant when applied with a standard etching time, but extending the acid treatment does not provide extra benefits and may even be counterproductive. Combining the two methods also did not yield a superior result. For patients and dentists, this means that both options are valid choices for preventing cavities in these difficult-to-clean areas, and the decision can be based on other practical factors rather than a clear difference in effectiveness.