Femtosecond laser ablation of dental restorative materials toward digitally enabled precision dentistry

Dentistry has long relied on a simple, mechanical truth: to fix a tooth, you must first remove the old filling or the damaged crown. For over a century, this has been done with a spinning drill. The drill bit, a hard, rotating tool, grinds away material through direct contact. While effective, this method is blunt. It creates vibration, noise, and heat, and it often leaves behind a messy smear of debris or tiny cracks in the remaining tooth structure. The challenge is that a dentist must remove the bad material without hurting the healthy tooth underneath or cooking the nerve inside. If the nerve gets too hot, the tooth can die, requiring a root canal.

Recently, scientists have looked to light as a more precise alternative. Instead of a spinning metal bit, they use lasers. Most dental lasers today use pulses that last for a millionth of a second. While fast, these pulses are still long enough to let heat spread into the surrounding tissue, potentially causing the same kind of damage as a drill. A newer type of laser, however, fires pulses that are a million times shorter. These are called femtosecond pulses. Because the energy arrives so quickly, it vaporizes the material before the heat has time to travel anywhere else. This offers the promise of cutting with surgical precision, leaving the surrounding tissue untouched. But while these lasers have been tested on natural tooth enamel, no one knew exactly how they would behave on the wide variety of modern materials used to fill and cap teeth.

A team of researchers at Australian universities set out to map this unknown territory. They wanted to see if a femtosecond laser could safely and efficiently remove the 13 different types of dental restorations currently used in clinics, ranging from simple white fillings to complex ceramic crowns. Their goal was not just to see if the laser could cut, but to find the exact settings where it works best without burning the tooth. They needed to determine how much energy was required to start the cutting, how fast it could remove material, and what the surface looked like afterward. Crucially, they had to measure the heat generated inside the tooth to ensure the nerve would remain safe.

The researchers gathered samples of the most common dental materials. These included direct fillings, which are placed and hardened inside the mouth, and indirect restorations, like crowns and veneers, which are made in a lab and then glued on. They prepared flat blocks of each material and subjected them to the femtosecond laser. The laser fired pulses at the surface, and the team carefully adjusted the energy of each pulse. They started with very low energy and gradually increased it, watching to see the exact moment the material began to disappear. They found that the amount of energy needed to start cutting varied wildly depending on the material. Some white fillings began to vaporize with a very small amount of energy, while the hard ceramic crowns required significantly more power to even begin to break down.

Once they found the starting point, they measured how fast the laser could remove the material. They discovered that for the softer filling materials, the laser became highly efficient at a moderate energy level, removing material quickly and smoothly. For the harder ceramics, the laser needed much higher energy to reach a similar speed, and even then, it removed material more slowly than it did the fillings. The team also looked closely at the surfaces left behind. Under powerful microscopes, the laser-cut surfaces appeared remarkably clean. They showed no signs of the melting, cracking, or smeared debris that typically marks a surface cut by a traditional drill. The laser left behind a precise, well-defined edge, suggesting that the material was removed cleanly rather than torn or crushed.

To ensure this precision did not come at the cost of the tooth's health, the researchers conducted a critical safety test. They took extracted human teeth, cleaned out the nerve tissue, and filled the hollow space inside with water to mimic the living pulp. They placed a tiny temperature sensor inside this water-filled chamber. Then, they attached a block of dental material to the tooth and fired the laser at it. They watched the temperature rise inside the tooth as the laser worked. They found that with a specific cooling system using a stream of air, they could keep the temperature rise well below the dangerous limit that would harm a living nerve. They determined that a power setting of 5 watts was the sweet spot: it was strong enough to remove the material effectively but gentle enough to keep the tooth safe. At this safe power level, the laser could remove a small filling in just a few seconds.

The team did not stop at testing individual blocks. They performed a complete, step-by-step demonstration on a single extracted tooth. First, they used the laser to carve a small, precise cavity into the tooth. Next, they filled that cavity with a standard composite filling material and hardened it. Finally, they used the same laser to remove the new filling. The laser successfully stripped away the filling material, leaving the underlying tooth structure intact and the cavity clean. This proof-of-concept showed that the entire cycle of preparing a tooth, filling it, and then removing that filling could be done with the same laser tool.

The study concluded that femtosecond lasers offer a viable, highly precise method for removing dental restorations, but with an important caveat: the settings must be tailored to the specific material being removed. A single setting does not work for everything. The softer fillings require less energy and cut faster, while the harder ceramics need more power and cut slower. However, when the correct settings are used, the laser produces a cleaner result than a drill and keeps the tooth cool enough to remain healthy. The researchers noted that while this technology is not yet ready for routine use in every dental office, it provides a solid foundation for a future where dentists can remove old work with the same digital precision used to design it. The path forward involves refining the cooling systems and developing tools that can automatically recognize which material they are cutting and adjust the laser power in real time. Until then, this work proves that the dream of a drill-free, heat-free way to fix teeth is moving from theory into reality.