Ultrasound may help regrow teeth

Hockey players, rejoice! A team of University of Alberta researchers has created technology to regrow teeth--the first time scientists have been able to reform human dental tissue. ... Using low-intensity pulsed ultrasound (LIPUS), Dr. Tarak El-Bialy from the Faculty of Medicine and Dentistry and Dr. Jie Chen and Dr. Ying Tsui from the Faculty of Engineering have created a miniaturized system-on-a-chip that offers a non-invasive and novel way to stimulate jaw growth and dental tissue healing. ... The wireless design of the ultrasound transducer means the miniscule device will be able to fit comfortably inside a patient's mouth while packed in biocompatible materials. The unit will be easily mounted on an orthodontic or "braces" bracket or even a plastic removable crown. The wireless design of the ultrasound transducer means the miniscule device will be able to fit comfortably inside a patient's mouth while packed in biocompatible materials. The unit will be easily mounted on an orthodontic or "braces" bracket or even a plastic removable crown.

... Dr. El-Bialy first discovered new dental tissue was being formed after using ultrasound on rabbits. In one study, published in the American Journal of Orthodontics and Dentofacial Orthopedics, El Bialy used ultrasound on one rabbit incisor and left the other incisor alone. After seeing the surprising positive results, he moved onto humans and found similar results.-  more

This from Wikipedia:

Researchers at the University of Alberta have used LIPUS to gently massage teeth roots and jawbones to cause growth or regrowth, and have grown new teeth. As of June 2006, a large device has been licensed by the Food and Drug Administration (FDA) and Health Canada for use by dentists. A smaller device that fits on braces has also been developed. In order to regrow teeth, the tooth root must be massaged by the LIPUS device for 20 minutes each day for 4 months. It has been approved by both Canadian and American regulatory bodies and a market-ready model is currently being prepared. LIPUS is expected to be commercially available before the end of 2009.

According to Dr. Chen from the University of Alberta, LIPUS may also have medical/cosmetic benefits in allowing people to grow taller by stimulating bone growth.

This from Wiley InterScience:

Constant mechanical stress is essential for the maintenance of bone mass and strength, which is achieved through the cooperative functions of osteoblasts and osteoclasts. However, it has not been fully elucidated how these cell types mediate mechanical signals. Low-intensity pulsed ultrasound (LIPUS) therapy is a recently developed method for application of mechanical stress, and is used clinically to promote bone fracture healing. ...  J. Cell. Physiol. 211: 392-398, 2007. © 2006 Wiley-Liss, Inc.

Here is a specific mention of a frequency:

Vascular endothelial growth factor (VEGF) has been implicated in the regulation of dental pulp and dentine repair. Therapeutic ultrasound was shown to be effective for fracture repair. We investigated whether low frequency ultrasound influences the production of VEGF by odontoblast-like cells. Moreover, we examined the direct effects of VEGF on odontoblast-like cell proliferation. ... Design. MDPC-23, an established odontoblast-like cell line, was exposed to increasing intensities of 30 kHz ultrasound using an ultrasonic tip probe. ... After 24 h cell culture, WST-1 analysis of cell viability and number showed a dose-dependent decrease in the number of viable cells with increasing ultrasound power. However, the relative concentration of VEGF as analysed by ELISA and normalised to cell number was significantly increased in the culture supernatants indicating an ultrasound-induced stimulation of odontoblastic VEGF secretion. ... Results ... Low power ultrasound increased gene expression of all VEGF isoforms. Addition of recombinant VEGF to the cell cultures significantly stimulated cell proliferation. Gene expression of the VEGF receptors Flt1/VEGFR1 and KDR/VEGFR2 was detected in the MDPC-23, suggesting the possibility that VEGF may act on the odontoblast-like cells in an autocrine manner.

Humans can only hear up to about 20kHz. Anything above that, like the 30kHz in this study, is considered ultrasound. Just as with sound you can hear, sounds you can not hear can be at different volumes (intensities).  Sound is a pressure wave.  Intensity of sound can be expressed as "mW/cm2", which is milliWatts per square centimeter.

Different intensities of pulsed ultrasound have distinct biological effects on bone mineralization in the process of bone fracture repair, even across a narrow range (e.g., 30-120 mW/cm₂). The aim of our study was to elucidate the effect of low-intensity (30 mW/cm ) and high-intensity (120 mW/cm₂) pulsed ultrasound on collagen metabolism - inist.fr

Here's another study that used a different frequency.

Low-intensity pulsed ultrasound (LIPUS) has distinct effects on biologic mineralization at intensities of <100 mW/cm². Intensity-dependent differences in the pattern of accelerated mineralization may be due to different alterations in regulation of collagenous matrix formation. However, little is known about the influence of LIPUS on collagen metabolism in the context of mineralization processes. Therefore, we attempted to evaluate differential effects of two intensities of pulsed ultrasound (30 vs. 120 mW/cm²) on collagen post-translational modification and mineralization in osteoblastic MC3T3-E1 cells. Murine osteoblastic MC3T3-E1 cells were exposed to pulsed ultrasound (1.5-MHz, 200-ms burst sine wave at 1.0-kHz frequency, either 30 or 120 mW/cm² SATA, for 20 min/day from Day 14 to Day 35 postconfluence).

In this case, they hit the sample with a 200 millisecond sine wave at 1.5 MHz,  1000 times per second?

I must be having a bone head moment, because I don't get it.. there are 1000 milliseconds in a second, so you could only fit five 200ms bursts in each second, and they'd need some blank space too, so if you went on and off every 200ms, with your vibrations of 1.5MHz, you'd have a pulse rate of about 3 Hz, not 1.0 kHz (1000 Hz). Unless you have multiple sound sources, then they could overlap and you could get 1000 bursts of 200ms in each second.

Update: April 8, 2009:  These things always seem years away. This was said to be two years away in 1996, but nothing is ready yet. Here is a recent mention of it:

Ultrasound could 're-grow' broken teeth in just 12 weeks

... scientists revealed recently that teeth broken in an accident could soon be 'regrown' using an ultrasound machine half the size of a thumbnail.

The process could take just 12 weeks. Ultrasound is already used to help heal broken bones, now the technology is being applied to teeth. Nanotechnology, which can reduce electronic circuitry to one thousandth of the size of a human hair, has enabled scientists to develop an ultrasound device small enough to fit inside the mouth. A wafer-thin ultrasound chip, which is preprogrammed so that it turns on automatically, can be clipped onto the teeth. When it is on, ultrasound waves massage the gums to stimulate and increase blood flow to produce new tooth tissue.

The treatment takes just 20 minutes a day. The current version of the machine has a small handheld device which tells the patient when it is working. Dr Tarek El-Bialy, of the University of Alberta in Edmonton, Canada, discovered the use of ultrasound to form new dental tissue from his research on rabbit incisors. He then moved on to humans and found similar results.

- dailymail.uk

Link to the Department of Dentistry where Dr. El-Bialy is working.

This team includes in addition to Dr. Tarek El-Bialy  (in the Orthodontic Graduate program and Biomedical Engineering), Drs. Jie Chen and Ying Tsui from the Electrical Engineering department. When it was published by Dr. Tarek El-Bialy at the American Journal of Orthodontics for the first time in History that new dental tissue can be reformed after the teeth are grown, this research team and patent was planned for.