Laser effects on carious dentin of primary molars pretreated with Silver Diamine Fluoride or Nano Silver Fluoride: An In-Vitro Study

Dental decay in young children is a persistent challenge, often progressing quickly and causing pain or infection if left unchecked. For decades, the standard approach involved drilling out the damaged tissue and filling the hole, a method that removes healthy tooth structure and can be frightening for a child. In recent years, dentists have shifted toward gentler, minimally invasive strategies that aim to stop the decay in place rather than removing it. One of the most effective tools for this is a liquid containing silver and fluoride, which kills the bacteria causing the decay and hardens the tooth surface. While this liquid works well, it has a drawback: it turns the treated tooth black, a permanent change that some parents find difficult to accept. A newer version of this treatment uses tiny silver particles to achieve similar results without the dark staining. At the same time, dentists have begun exploring the use of light-based tools, specifically lasers, to help these treatments work better. The question researchers face is whether shining a specific type of blue light on teeth after applying these silver liquids can make the tooth surface harder and more resistant to future decay, without causing damage to the sensitive inner parts of the tooth.

A team of researchers at Mansoura University in Egypt set out to answer this question by conducting a careful experiment in a laboratory. They gathered twenty-six primary molars, the back teeth that children lose naturally, which had been extracted for reasons unrelated to the study. The researchers selected teeth that had clear, visible cavities in the dentin, the softer layer beneath the hard outer enamel. To ensure a fair test, they cut each tooth in half from side to side, creating fifty-two flat surfaces to work with. They then divided these surfaces into two main groups. In the first group, they applied a drop of the traditional silver fluoride liquid to the decayed surface. In the second group, they applied a drop of the newer nano-silver fluoride liquid. Within each of these groups, they split the halves again: one half received only the liquid treatment, while the other half received the liquid followed by a brief exposure to a blue diode laser. This laser, which emits light at a wavelength of 445 nanometers, was set to a power of 700 milliwatts. The researchers applied the laser in two short bursts of ten seconds each, with a thirty-second pause in between to let the tooth cool down, ensuring the heat did not damage the tissue.

After the treatments were complete, the researchers measured two key things: how hard the surface of the tooth had become and what minerals were present inside it. To test the hardness, they used a specialized machine that pressed a tiny diamond tip into the surface with a specific weight and measured the size of the resulting mark. To check the mineral content, they used a powerful microscope that could detect the chemical elements, such as calcium, phosphorus, and fluoride, sitting on the surface of the dentin. The results revealed a clear difference between the two liquids. The traditional silver fluoride liquid made the tooth surface significantly harder and increased the amount of fluoride on the surface more effectively than the nano-silver version. However, when the researchers added the laser treatment, the outcome changed depending on which liquid was used. The laser significantly increased the hardness of the teeth that had been treated with the nano-silver fluoride. In contrast, the laser did not make any noticeable difference to the hardness or mineral content of the teeth treated with the traditional silver fluoride.

The researchers suggest that the reason for this difference lies in how the light interacts with the tooth surface. The traditional silver fluoride leaves behind a dark, silver-rich layer that absorbs the laser light right at the surface, preventing the energy from penetrating deeper into the tooth structure. The nano-silver fluoride, which does not stain the tooth dark, allows the laser energy to distribute more evenly and interact with the dentin in a way that strengthens it. Despite the increase in hardness for the nano-silver group, the laser did not change the actual mineral composition of the tooth; the amounts of calcium, phosphorus, and fluoride remained the same. This indicates that the laser likely altered the physical structure of the tooth's organic material, perhaps by tightening the fibers within the dentin, rather than adding new minerals. The study concludes that while the traditional silver fluoride remains superior for increasing hardness and fluoride levels on its own, adding a blue laser can provide an extra boost to the hardness of teeth treated with the newer, non-staining nano-silver fluoride. This finding offers a potential path forward for treating children's cavities with a method that is both effective and less likely to cause the dark discoloration that often concerns parents.