Nagasawa et al.

Int Chin J Dent 2009; 9: 19-22.

Fusion of inorganic materials to enamel and porcelain surfaces
with Nd:YAG laser
Akinori Nagasawa, DDS, PhD,a Hiroyasu Koizumi, DDS, PhD,b,c Daisuke Nakayama,
DDS,b Hiromasa Kazama, DDS,b Hideo Matsumura, DDS, PhD,b,c and Koji Nishikawa,
DDSdaDepartment of Bio-Medical Engineering, School of High-Technology for Human Welfare, TokaibcUniversity, Numazu, Department of Fixed Prosthodontics, and Division of Advanced Dental
dTreatment, Dental Research Center, Nihon University School of Dentistry, Tokyo, and Private Practice,Saitama, Japan
Purpose: The aim of this study was to examine condition concerning fusion of inorganic material to enamel andporcelain surfaces by means of Nd:YAG laser.
Materials and Methods: Iron oxide was added to dental porcelain material in a range from 0.6 to 5.0% byweight. Slurry was placed on the human enamel and dental porcelain surfaces and Nd:YAG laser was exposedwith varying energy and exposure time periods.
Results: Melting of material occurred with the following irradiation condition; 40 W for 4 s for 0.6% iron oxide,
20 W for 2 s for 2.5% and 5% iron oxide. Fusion of the material occurred with specific conditions. However,degeneration or degradation of tooth substrate also was detected with high energy and extended exposure period.
Conclusion: It was possible to fuse an inorganic substance to enamel surface using Nd-YAG laser. Furtherinvestigation is required about materials, type of laser, and irradiation condition.
(Int Chin J Dent 2009; 9: 19-22.)
Key Words: ceramics, enamel, fusion, iron oxide, laser, porcelain.

Introduction
The application to dental practice of laser has increased substantially.1-9 This trend is mainly attributed todevelopment of varying laser apparatus for surgery and dental laboratory.

Neodymium-doped yttrium-aluminum-garnet (Y3Al5O12, Nd:YAG) laser has been used for welding nickel-chromium alloy,10 treating apicalfocus,11 drilling zirconia implant material,12 soft tissue surgery,13 and metal-ceramic bonding.14 It is necessary
for clinicians to keep in mind adequate type of equipment, energy, focus mode, and exposure time period, inapplication of laser devices.

Fusion of inorganic material to tooth surface using laser is novel approachassociated with preventive and restorative dentistry. Although, several reports have been published on fusion ofdental materials to tooth structure, and surface texture of lased enamel,1-3 only limited information is available
about the relation between materials to be fused and exposure conditions of specific type of lasers. This study
aimed to evaluate the relation between composition of inorganic materials and melting condition using aNd:YAG laser apparatus. Behavior of fusion to enamel and porcelain of materials also was examined.

Materials and Methods
Dental porcelain (Dentin A2, Opaque A2), aluminum oxide, hydroxy-apatite as well as two additives,cadmium red and iron oxide were assessed (Table 1). Additives were added to the inorganic materials 0.6-5.0%
by weight. A Nd:YAG laser apparatus (Model 8000, Molectron Medical; currently Coherent Inc., Santa Clara,CA, USA) was used as an energy source. The diameter of the probe was 0.6 mm, and the diameter of thecircular area to be irradiated can be calculated by the following equation; Diameter = DT x tan10˚ x 2 + 6, whereDT is the distance between the aperture of the probe and the surface to be irradiated. According to the equation,
the irradiation diameter can be estimated as 16.6 mm when the distance between the probe aperture and thesurface is 30 mm. Accumulated energy (ACE) can be calculated by the following equation; ACE = PP x PD x

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Int Chin J Dent 2009; 9: 19-22.

NP (Ws), where PP is pulse power (W), PD is pulse duration (s), and NP is number of pulses. The current
experiment used continuous radiation mode instead of pulsed radiation mode.
Table 1.

Materials assessed.

Materials

Composition

Manufacturer

Dental porcelain, VMK Dentin A2
Dental porcelain, VMK Opaque A2
Aluminum oxide
Hydroxy-apatite
Additive, Cadmium red
Additive, Iron oxide (III)SiO2, Al2O3, K2O, MgO
SiO2, Al2O3, K2O, TiO2
Al2O3
Ca10(PO4)6(OH)2
CdS, CdSe
Fe2O3

Vita Zahnfabrik, Säckingen, Germany
Vita Zahnfabrik
Kyocera Inc., Kyoto, Japan
Synthesized
Wako Pure Chemical, Osaka, Japan
Wako Pure Chemical

Two additives were separately added to the three inorganic materials, mixed and slurry was prepared withdistilled water. Approximately 0.05 g of the slurry was placed on either the white ceramic plate made of dental
porcelain material (VMK Dentin A2) or ground human enamel. The laser was irradiated by means of the Model
8000 Nd:YAG apparatus with 0-60 W energy, 2.0-9.9 s exposure period, and 30 mm distance. Formation ofsolid after laser exposure was judged as melted. The specimens judged as fused were cut perpendicularly with alow-speed cutting saw (Isomet, Buhler Ltd., Lake Bluff, IL, USA). The specimens were observed under lightand scanning electron microscope. The specimen without gap formation more than a half-length along theinterface was categorized as fused. In addition, change in temperature on the specimen surface during laser
irradiation was determined with a radiation thermometer with a surface-aperture distance set at 10 cm.

Results
Among the four inorganic materials, opaque porcelain, alumina, and hydroxy-apatite were difficult to melt orfuse under the conditions examined. Solid structure was obtained from the dentin-shade porcelain material withiron oxide. Cadmium red was ineffective as an additive for solid formation of ceramic materials.
Table 2.

Melting and fusion of dentin-shade porcelain with iron oxide (III) after laser irradiation.

Iron oxide (%)

Energy (W)Exposure (s) 2.0

4.0

6.0

8.0

9.9

0.6
0.6
0.6

204060

NNNN
Melt
Melt

N
Melt
MeltN
Melt
Melt

N
Melt
Melt

1.2
1.2
1.2

204060NNNN
Melt
MeltNMelt
MeltN
Melt
MeltN
Melt
Melt

2.5
2.5
2.5

204060

Melt
Melt
Melt

Melt
Melt
Fused

Melt
Fused
Fused

Melt
Fused
Fused

Melt
Fused
Fused

5.0
5.0
5.0

204060

Melt
Melt
Melt

Melt
Melt
Fused

Melt
Fused
Fused

Melt
Fused
Fused

Melt
Fused
Fused

Change of temperature (˚C) at 40 W, 10 cm+9.5+19.0

More than 20.0

Underlying substrate, Dental porcelain material (VMK Dentin A2); N, Not changed; Melt, Solid structure was formed; n=5.
Accumulated energy varied from 40 Ws (20 W by 2.0 s) to approximately 600 Ws (60 W by 10 s).

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Int Chin J Dent 2009; 9: 19-22.

Table 2 shows the change of structure of the dentin-shade porcelainmaterial with iron oxide. Under the condition of the current experiment,
formation of solid occurred when the dentin-shade porcelain material(with 0.6 or 1.2% iron oxide) was irradiated for 4.0 s or more with 40 or
60 W. Also, melting of porcelain material (with 2.5 or 5.0% iron oxide)occurred after 2.0-s irradiation with 20 W.

Fusion to substrate ofporcelain material occurred after 6.0-s irradiation with 40 W or after
4.0-s irradiation with 60 W for the dentin-shade porcelain with 2.5 or
5.0% iron oxide. Fusion to enamel was detected with the same condition
as for the porcelain material (Fig. 1).

The cut surface, however,demonstrated degeneration or degradation of tooth structure especially

200 µmFig. 1.
Scanning electron micrograph of lased
porcelain and enamel.
c; Porcelain material with 2.5% Fe2O3.
e; Enamel.
Irradiation; Nd:YAG, 40 W, 6.0 s.

along the dentino-enamel junction

Discussion
This study evaluated the conditions concerning fusion of inorganic material to enamel and porcelain surface
by means of Nd-YAG laser. Melting, fusion, and other phase transformation of inorganic compound by laser
irradiation are dependent on color of surface to be irradiated. The authors used iron oxide (III) and cadmium red
as coloring agents, i.e., pigments in this experiment. As shown in the results, addition of iron oxide waseffective for melting and fusion of dental porcelain. On the contrary, opaque porcelain, hydroxy-apatite, andalumina were difficult to melt within the conditions employed. One of the reasons for this unfavorable resultwith opaque porcelain is the whitish color of the opaque porcelain. Reflection of laser by white pigment in theopaque porcelain may affect melting of compounds inside the material. In addition, it is likely that color ofmetal oxides and metallic compounds will change to a metallic color after high-energy application. The authors
speculate that metallic colored substances are easier to fuse tooth surface rather than tooth colored substances.
Care must be taken therefore to select inorganic compounds to be fused to tooth structure.
Melting temperature of compound is obviously an important factor for fusion to substrates of materials. Phasetransition temperature of alumina is above 1,000˚C. The temperature is difficult for the material to be fused toother substrates. Hydroxy-apatite and enamel may be easier to decompose by irradiation of high-energy laser,
since it is an ionic compound with two hydroxyl groups. It may be beneficial to use alkaline substance like aflux to reduce melting temperature of compound. Also, basic compounds, if applicable, may reduce acidity of
tooth surface, in which activity of streptococci associated with dental caries will be reduced.
The type of laser apparatus plays a critical role in fusion of material to tooth structure. Several factors,
wavelength, energy, focus setting, and surface temperature etc. should be considered for selection of laser
apparatus in dental practice. Of these, difference between focused and defocused settings, and distance between
aperture and the surface obviously influence characteristics of the irradiated surface. Although attempts at
fusing ceramic material to enamel surface were basically unsuccessful within the limitation of the current
experimental settings, the results of the current study suggested the possibility of fusion of inorganic materials to
tooth structure using laser apparatus. Control of energy distribution of lased surface is another important factor
for laser surgery. In particular, control of temperature around pulp and dentin is important. Irradiation of the21Nagasawa et al.

Int Chin J Dent 2009; 9: 19-22.

40-W Nd:YAG laser for 6.0 s induced degeneration of organic phase of dentin. Further investigation aboutmaterials, type of laser, and irradiation conditions is required.
Acknowledgment, Note
This work was supported in part by a research grant to improve the quality of dental products from the Japan Dental
Association. The first author Akinori Nagasawa passed way before submission of this paper.

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Correspondence to:Dr. Hiroyasu Koizumi
Department of Fixed Prosthodontics, Nihon University School of Dentistry
1-8-13 Kanda-Surugadai, Chiyoda-ku, Tokyo 101-8310, Japan
Fax: +81-3-3219-8351 E-mail: koizumi@dent.nihon-u.ac.jp
Accepted May 20, 2009.

Copyright ©2009 by the International Chinese Journal of Dentistry.

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