Tsutomu Sugaya

Repairing of Hopeless Teeth

Tsutomu Sugaya , Associate Professor

Graduate School of Dental Medicine (Dentistry, School of Dental Medicine)

High school : Yokohama Municipal Sakuragaoka High School (Kanagawa)

Academic background : School of Dental Medicine, Hokkaido University

Research areas
Research keywords
fractures, adhesion, replantation, operating microscope, ultrasonic waves, regeneration

What is your goal?

Figure 1. Fractured teeth

Figure 2. Extracted fractured teeth

My goal is to repair teeth that are untreatable and need to be extracted. Currently in Japan, more than 10 million teeth are extracted each year. While the major causes thereof are caries and periodontal diseases, in fact, a large number of teeth are extracted due to fractures (Figures 1 and 2), which affect more than 1.5 million teeth per year. When teeth are fractured to the root, symptoms similar to those when developing caries or periodontal diseases normally occur, resulting in many cases being misdiagnosed because these fractures are invisible to the naked eye. Thus, the actual number of such cases is assumed to be several-fold greater. Regarding tooth fractures, 99.99% of dentists around the world abandon treatment even today, opting instead to carry out extraction. However, if the tooth is fractured, what if we can put it back together? This is how this study was initiated.


Figure 3. Periodontal tissue cells attached to the adhesive agent.

What kind of research do you do?

With this treatment, a strongly adhering adhesive agent is necessary so that the tooth does not fracture upon mastication. Moreover, it is important that the adhesive agent have no negative impact on the body. In order to solve these issues, we investigated the toxicity of adhesive agents by cell culturing (Figure 3), the adhesive status to teeth using an electronic microscope (Figures 4 and 5), and the effect on tissues and the repaired status in animal experiments (Figure 6).

Figure 4. Electronic microscope.

Figure 5. Image from an electronic microscope.

Figure 6. Tissue image in an animal experiment.


Figure 8. Operating microscope

Figure 9. Treatment with ultrasonic waves under a microscope

Eventually, this led to an epoch-making treatment in which we extract the fractured tooth once and then replant it in its original position after adhesion, thereby re-attaching the tooth to the bone and enabling the patient to masticate again by creating an artificial tooth, such as a metal tooth (Figure 7). However, in some cases, the tooth is fractured into pieces at the time of extraction and becomes irreparable. Moreover, many patients wish to avoid the pain of extraction. Therefore, we looked at another method, in which, under an operating microscope (Figure 8), the crack in the tooth root is prepared (indicated by the light-blue arrows in Figure 9) by vibrating a metallic chip (250 μm in diameter) (indicated by the white arrow in Figure 9) at an ultrasonic frequency of 25,000 Hz, and repaired with an adhesive agent. This treatment method has also demonstrated significant results, enabling us to repair even more teeth.

More than ten years ago, when we first initiated this research, many researchers were skeptical of this treatment method. At first, treatment did not work well, with gums becoming swollen and causing pain, leading to many teeth having to be extracted. However, professors and graduate students with a strong frontier spirit at Hokkaido University continued to conduct research despite these initial setbacks, and as a result we have had a success rate of more than 80% in the past couple years.


What is your next goal?

While this treatment method is already helping a large number of patients, it still does not allow all cases to be repaired. Regarding cases in which a long time has passed since fracture, inflammation develops and surrounding tissues supporting the tooth are damaged. In order to further increase the success rate, regenerating these tissues is an essential issue. We have already spent a lot of time on regeneration research, but have not yet achieved a clinically effective treatment method. When such treatment is discovered, the number of tooth extractions, not only due to fracture but also due to periodontal diseases will drastically decrease, preventing many patients from having to suffer “not being able to masticate or talk.”

I am looking forward to seeing young dentists with inward smiles as a result of impressed patients who tell them, “I had completely given up and never thought teeth like mine could be repaired.”

Reference Websites

Sugaya, Tsutomu. “Treatment for Vertical Root Fracture Using Super-bond C&B.” General information website for dental professionals: