Cytotoxicity of Chemomechanical Caries Removal Agents on Primary Tooth Fibroblasts at Various Dilutions: A Preliminary Study

In the world of dentistry, the goal has shifted from simply drilling away decay to preserving as much healthy tooth structure as possible. This approach, known as minimally invasive dentistry, is especially vital for children, whose smaller teeth and developing nerves require gentle handling. A key part of this philosophy is removing only the infected, softened part of a cavity while leaving the healthy, firm dentin behind. To do this without a drill, some dentists use chemical gels that contain enzymes. These enzymes act like tiny scissors, specifically cutting up the damaged, denatured collagen fibers that make up the rotting part of the tooth, while ignoring the healthy tissue. Two such gels, one from Brazil and one from Argentina, are used in clinics to soften and remove this decay. However, because these gels are applied so close to the tooth's nerve, scientists must ensure they do not harm the living cells inside the tooth if the gel accidentally touches them.

Researchers at the University of São Paulo set out to test the safety of two popular chemical gels: Papacarie Duo and Brix 3000. Both products rely on papain, an enzyme derived from papaya, to dissolve the infected tooth structure. The team wanted to see how these substances affected human cells taken from the pulp of baby teeth. They grew these cells in a laboratory dish and exposed them to the gels mixed with water at various strengths, ranging from very thick mixtures to very thin ones. To measure the health of the cells, the scientists used two different standard tests. One test checked if the cells were still alive and breathing by looking for a color change in a special dye, while the other measured the energy-producing activity inside the cells' power plants. They observed the results after one day and again after two days.

The study revealed that the two gels behaved very differently depending on how much they were diluted and which test was used. When the gels were mixed with a large amount of water, making them very weak, the Papacarie Duo gel showed a high level of safety. In these weaker mixtures, the cells remained healthy and multiplied well, performing just as well as cells that had not been exposed to any gel at all. This suggests that when used correctly and allowed to dilute slightly in the mouth, this product is gentle on the living tissue inside the tooth. In contrast, the Brix 3000 gel showed a complex safety profile. In the test measuring cell energy, Brix 3000 actually performed better than Papacarie Duo at the strongest concentrations (1:2 and 1:4 dilutions). However, as the gel was diluted further, Papacarie Duo became the safer option, showing significantly higher cell viability at weaker concentrations (1:16 and 1:32), while Brix 3000 remained highly toxic to the cells even when diluted, showing results similar to the negative control in the other test.

The timing of the observation also mattered. The Papacarie Duo gel showed a slight delay in its safety profile; at the strongest concentration, it was harmful to the cells immediately, but as time passed and the mixture was diluted, the cells recovered and thrived. The Brix 3000 gel, however, remained harmful regardless of how much time passed or how much it was diluted in the more sensitive test. The researchers found that the two different lab tests sometimes gave slightly different numbers, but the overall story was clear: Papacarie Duo demonstrated a much better ability to coexist with living tooth cells, especially when not used in its most concentrated form.

These findings suggest that while both products aim to remove tooth decay gently, they have distinct safety profiles. The study indicates that Papacarie Duo has a higher potential for safe clinical use because it allows the cells inside the tooth to survive and function, provided it is not applied in an overly concentrated state. The Brix 3000 product, by comparison, presents a significant risk to the living cells of the tooth pulp, particularly at higher dilutions where it failed to support cell survival. The researchers emphasize that these results come from a controlled laboratory setting using cells from baby teeth, and while the data points to a clear difference in safety, further research is needed to fully understand how these materials interact with the complex environment of a real tooth and the restorative materials used to fill it afterward.