Danjyo, Atsushi

Goto, Masaaki

Guan, Weimin

Hayashi, Nobuya

Ihara, Satoshi

Satoh, Saburo

Yamabe, Chobei

Yamaguchi, Yoshimasa

Saga University Institutional Repository

Rep. Fac. Sci. Engrg.         Reports of the Faculty of Science and Engineering, 
Saga Univ.                        Saga University, Vol. 33, No.1, 2004 
33-1 (2004)                          
 
 
 
Modification of Hydroxyapatite Crystal Using CO2 Laser 
- The Preliminary Study for FEL Application in Biological Field 
 
By 
  Weimin GUAN*, Nobuya HAYASHI*, Satoshi IHARA*, Saburo SATOH*  
and Chobei YAMABE* 
Masaaki GOTO**, Yoshimasa YAMAGUCHI**, Atsushi DANJYO** 
 
 
Abstract: To remineralize the dental surface, Laser application was concerned in this study. The 
purpose of this experiment was concentrating to investigate crystal structure change of hydroxyapatite 
before and after laser irradiation. The wavelength of incident laser   beam is matching the 
characteristic absorption peak of HAp which ranging around 10μm. As a preliminary study for Free 
Electron Laser (FEL) application in biological field, the results we have got with the 10.6μm 
irradiation indicated that the FEL’s capability of precisely deliver energy over a wide band of infrared 
makes it an attractive tool for further ameliorating of hydroxyapatite crystallization. 
 
Key words: Hydroxyapatite, Remineralization, Dental enamel, X-ray Diffraction. 
 
 
 
1. Introduction 
The first application of laser technology to dentistry 
was for the removal of caries infected material and 
preparation of cavities(1). However, ever since reports of 
laser application on improvement of dental surface were 
emerged, much attention has been focused on the laser’s 
potential to enhance enamel’s hardness and resistance to 
acid(2) (3) (4). 
Although many attempts have been made to alter 
the tooth structure in order to increase its resistance to 
dental caries, little understanding on the physicochemical 
mechanisms involved has been achieved (5). This research 
has pursued the photochemical phenomenon occurred 
during laser irradiation on artificial and biological HAp. 
In order to find a creative method to remineralize the 
demineralized enamel or the exposed coronal of dentine, 
the authors developed a novel procedure during laser 
irradiation (6). 
Free electron laser (FEL) application is also 
intended primarily to realize the same purpose. The 
micro-pulse structure and duration of FEL laser was 
expected to be suitable to modify dental surface 
efficiently (7) (8). 
 
Received May 1, 2004 
*Department of Electrical and Electronics Engineering. 
**Department of Oral and Maxillofacial Surgery.  
© Faculty of Science and Engineering, Saga University 
 
 
In this study, slice samples of sound molar and 
artificial HAp pellet were irradiated with 10.6μm CO2 
laser separately. Various laser parameter and chemical 
conditions were applied in the experiment. Three series 
of samples covered with saturation calcium ion solution 
(Ca(OH)2 and CaHPO4) and their combination were 
compared after irradiation. To investigate the 
micro-crystal morphology of the samples, X-ray 
Diffraction (XRD) pattern were surveyed. The 
comparison of XRD result shows that the chemical 
coating affected the irradiation process evidently. 
2. Experimental Procedure 
2.1 The parameter of incident laser 
-1 0 1 2 3 4 5 6 7 8 9 10
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
Pulse applied in th is experiment
The Irradiation Laser's Pulse Shape
 L
ig
ht
 in
te
ns
it
y 
of
 
la
se
r 
pu
ls
e [
ar
b
.u
n
it
s]
 (µs)
 
Fig. 1 The flexible pulse of TEA-CO2 laser 
 
Weimin GUAN, Nobuya HAYASHI, Satoshi IHARA, Saburo SATOH and Chobei YAMABE 
Masaaki GOTO, Yoshimasa YAMAGUCHI,Atsushi DANJYO 
 
Irradiation was performed with 10.6 μ m 
wavelength TEA-CO2 laser. It gives out pulses around 1
μs (FWHM) at a repetition rate of 0.2Hz. The mean 
output energy was modified from 86mJ to 622mJ. Laser 
beam was focused onto the target surface perpendicularly 
to attain energy density varying from 2J/cm2 to 9J/cm2. 
The average power was ranging from 18mW to 130mW. 
While as the power density from 4.89W/cm2 to 
35.23W/cm2. 
Figure.2 shows the pulse shape that we can modify 
by changing gas ratio in the laser chamber. The pulse, 
which has the shortest FWHM, as it is shown in Fig.1 
was used as the incident beam in this experiment. 
The specific experimental conditions concerned in 
this experiment are following: 
(1) XRD survey of original and CO2 laser irradiated 
artificial HAp. 
(2) XRD survey of dentine and enamel before and after 
CO2 laser irradiation. 
(3) XRD survey of enamel after CO2 laser irradiation 
(covered with saturation chemical solution film). 
 
2.2 The XRD analysis 
 
The X-ray diffraction of the profile breadth and 
relative intensity data were collected from the samples 
on a X-ray diffractometer using CuKα radiation (RINT 
1100, Rigaku, Japan). 
The divergence slit was 1°and the receiving slit was 
0.3mm. The scan range for relative intensities was from 
20°to 70°(2θ) ; the scan rate was 4°(2θ/min). 
  
3. Results and Discussion 
Compared with artificial HAp sample, the (213) 
(202) reflections intensity of dentine was not so intense. 
After irradiation with CaHPO4 solution film, the 
reflection (202) appeared. And the relative intensity 
peaks of artificial HAp pellet sample, (002) (202) (222) 
was modified. Most of the characteristic peaks of HAp 
were decreased. 
Through the result we can suppose that HAp may be 
decomposed due to the thermal effect of laser irradiation 
(9), while as the product of decomposed HAp also exists 
in the dentine and enamel as amorphous calcium 
phosphate phase. The general reaction of HAp infused 
with chemical solution under the photo-thermal effect 
condition is considered as following. 
3Ca3(PO4)2+Ca(OH)2 → 
 Ca10(PO4)6(OH)2+2H2O+4CO2    (1) 
 
Due to the thermal effect during photo ablation 
process, the temperature of the interaction surface should 
raise instantaneously. HAp may be decomposed through 
the reaction as formula (2). 
 
Ca10(PO4)6(OH)2 → 
3Ca3(PO4)2+CaO+H2O         (2) 
 
 
 
 
 
 
Fig. 2 The scheme of irradiation experiment 
Modification of Hydroxyapatite Crystal Using CO2 Laser 
 
  And CaO is easy to react with water, and then 
produce tricalcium phosphate and heat. 
The potential reaction under the irradiation with 
Ca(OH)2 and CaHPO4 mixed saturation solution film 
was considered as following reaction: 
 
4Ca(OH)2+6CaHPO4 → 
Ca10(PO4)6(OH)2+6H2O        (3) 
 
As CaHPO4 is easy to react with Ca(OH)2 to 
produce various calcium phosphate formations. At the 
same time, the reaction will release amount of heat. This 
may delay the heat transmittal and decrease the thermal 
threshold of hard tissue during irradiation. The apparent 
amorphous regions of XRD pattern were considered to 
be connecting with this mechanism. 
 
4. Conclusion 
After CO2 laser irradiation, the (002) reflection was 
increased significantly. It indicates the crystal growth in 
c-axis. On the other hand the (222) reflection was 
reduced both in HAp pellet case and dentine case. It was 
considered relating to the thermal effect during 
high-energy irradiation. 
The laser energy density performs superior role 
during the irradiation process compared with the total 
fluence of energy while fluence is also a very important 
parameter to control the reaction. 
For the Ca(OH)2 solution coated case, obvious 
remineral process occurred via the hydroxyl contained in 
the solution enhanced the pH value of the sample surface. 
The environment should have been modified more 
appropriate for calcium ion to bond with apatite matrix. 
After the irradiation with Ca(OH)2; CaHPO4 
combined saturation solution coating, most of the 
reflection peaks increased except for (310). And the 
pattern of tricalcium phosphate emerged. It should be the 
product of chemical reaction during ablation. We believe 
that the presence of CaHPO4 and Ca(OH)2 could be a 
trace of the original reaction used to produce HAp. 
Fig.2 Comparison of CO2 laser irradiation 
on artificial HAp and dentine sample 
Fig.3 Comparison of CO2 laser irradiation on dentine 
sample, with and without chemical solution 
Weimin GUAN, Nobuya HAYASHI, Satoshi IHARA, Saburo SATOH and Chobei YAMABE 
Masaaki GOTO, Yoshimasa YAMAGUCHI,Atsushi DANJYO 
 
Acknowledgments 
We thank Dr. Ikeda, (Analytical Research Centre for 
Experimental Sciences, Saga University) for the 
measurement of XRD. We also thank Ms. Furuda, (Saga 
Ceramics Research Laboratory.) for her valuable 
technical support. 
 
References 
(1) Myers M. “The effect of laser irradiation on oral tissues”, 
J Prosthet Dent, 66:395-397 (1991) 
(2) Kantola S. “Laser-indued defects on the tooth structure”, 
Acta Odontol Scand, 30:475-484 (1972) 
(3) Melcer J. “Latest treatment in dentistry by means of the 
CO2 laser beam”, Lasers Surg Med, 6:396-398 (1986) 
(4) Miserendino L. “The laser apicoectomy: endodontic 
application of the CO2 laser in apical surgery”, Oral Surg 
Oral Med Oral Pathol, 66:615-619 (1988) 
(5) M. Gonzalez, et al. “Particle-induced X-ray emission and 
scanning electron microscopic analyses of the effects of 
CO2 laser irradiation on dentinal structure”, Journal of 
Dentistry, 27:595-600 (1999) 
(6) Weimin.Guan, Nobuya.Hayashi, Satoshi.Ihara, 
Saburo.Satoh and Chobei.Yamabe, “Modification of 
hydroxyapatite crystallization using IR laser”, Program 
and Abstracts of MAPEES’04, 112 (2004) 
(7) Seiji Ogino, Kunio Awazu, Takio Tomimasu, “The Effect 
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Modification of Tooth Dentine Irradiated by a 9.45μm 
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Modification of Tooth Dentine Irradiated by a 9.45μm 
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Modification of Hydroxyapatite Crystal Using CO_2 Laser : The Preliminary Study for FEL Application in Biological Field

Modification of Hydroxyapatite Crystal Using CO_2 Laser : The Preliminary Study for FEL Application in Biological Field

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