Dental caries is a transmissible bacterial disease process, with cavities at the end, and caused by acids from bacterial metabolism. The essence of dental treatment is to clean and disinfect bacterial contamination from the tooth. In this work, we tried to demonstrate the cleaning and disinfecting effects of Nd:YAG laser irradiation on dental carious lesion and root canal in vitro. Acousto-optic Q-switched quasicontinuous and Cr3+:YAG crystal Q-switched pulse Nd:YAG lasers were employed to treat caries lesion and the root canal, respectively. Results showed that acousto-optic Q-switched quasicontinuous Nd:YAG laser irradiation and Cr3+:YAG crystal Q-switched pulse Nd:YAG laser irradiation could rapidly clean decayed material and bacterial contamination from dental carious lesion and the narrow tail end of root canal with minimally invasive in vitro, respectively. It was concluded that acousto-optic Q-switched quasicontinuous laser irradiation may be a rapid and effective alternative caries treatment, and Cr3+:YAG crystal Q-switched pulse Nd:YAG laser irradiation may be an effective method for canal cleaning and disinfecting during root canal therapy.
Dental caries is the most prevalent disease among preschool children (early child caries) [
Dental treatment can prevent and inhibit the dental caries by cleaning and disinfecting the bacterial contamination in tooth or enhancing the caries resistance of tooth at the very beginning of dental caries process [
Thus, it is necessary to develop an alternative caries treatment, which can remove the bacterial containment painless with minimally invasive. Present work is to demonstrate the ability of acousto-optic Q-switched quasicontinuous Nd:YAG lasers and Cr3+:YAG crystal Q-switched pulse Nd:YAG lasers in cleaning of decayed material (pulp and others) speedily and disinfecting of bacteria completely of human tooth in vitro. Laser irradiation treatment may be an ideal alternative dental caries treatment especially preschool children aged 2 to 5 years.
Quasicontinuous laser beam with wavelength of 1064 nm provided by an acousto-optic Q-switched Nd:YAG laser system (Figure
The sketch of quasicontinuous laser system.
The Q-switched laser beam, provided by a Cr3+:YAG crystal Q-switched laser system (Figure
The sketch of Q-switched laser system.
Human teeth with carious lesion on crown surface (one was shown at Figure
Stereomicroscope images of (a) tooth with carious lesion and (b) tail end of root canal.
To demonstrate the cleaning effect of laser treatment, carious lesion tooth samples were exposed to acousto-optic Q-switched quasicontinuous laser irradiation, and tooth canal samples were exposed to Cr3+:YAG crystal Q-switched pulse Nd:YAG laser irradiation, respectively. The cleaning efficiency is evaluated from the difference between pictures of lesion surface before and after laser treated. The disinfecting effect and efficiency of laser treatment is evaluated from the colony counts loss of samples. The experiment samples were scrubbed by swabs with sterile physiological saline before and after laser treatment, respectively. Then, the infected physiological saline of each sample was inoculate to 3 parallel agar dishes and cultivated at 37°C for 24 hours. In order to prevent the bacterial contamination from hands, the medical rubber gloves were necessary during the whole experiment.
Figure
Stereomicroscope images of decayed tooth surface (a) before and (b, c) after acousto-optic Q-switched Nd:YAG quasicontinuous laser treatment.
Figure
Stereomicroscope images of organisms in untreated (a), 20 pulses (b), and 40 pulses (c, d) laser irradiation-treated root canal gap.
The colony counts of experiment tooth samples before and after laser treatment were shown in Figure
The colony counts of carious lesions (samples 1–3) and root canals (samples 4–6).
It is an advantage to choose laser beam with less power density, or less repeated frequency for tooth treatment, because the carbonization showed in Figure
Acousto-optic Q-switched quasicontinuous laser irradiation with big beam size, high average energy density, and repeated frequency was effective for caries lesion treatment, and Cr3+:YAG crystal Q-switched laser irradiation with smaller beam size, shorter pulse width, and higher peak energy density is effective for root canal treatment without any obvious byproducts as carbonization appeared in caries lesion laser treatment. Both acousto-optic Q-switched quasicontinuous laser irradiation and Cr3+:YAG crystal Q-switched laser irradiation had advantages over each other in dental caries treatment and had common advantages such as no pain, no vibrating, overtraditional treatment with drill and spoon. Laser irradiation treatment was very friendly for patient especially for the preschool children patients. It will be a good alternative for early child caries inhibition and readiness to be accepted by child patients.
In conclusion, acousto-optic Q-switched quasicontinuous laser irradiation may be a rapid and effective alternative caries treatment, and Cr3+:YAG crystal Q-switched pulse Nd:YAG laser irradiation may be an effective method for canal cleaning and disinfecting during root canal therapy.
The authors gratefully appreciate the generous help of laser system and stereomicroscope from Professors Xiao Zhu and Pengcheng Li in Wuhan National Laboratory for Optoelectronics.