Biomedical Engineering Reference
In-Depth Information
4. Discussion
Recently, Er:YAG and Cr:YSGG lasers were introduced in dentistry. For physical and
medical reasons, they are used for the treatment of hard tissue. The advantage of an Erbium
wave is that it is well absorbed by water and dental hard tissue. Although dentin contains a
high proportion of water, the depth is shallow for laser transmission. The strong absorption
of water reduces the level of heat during tooth preparation. As water absorbs laser radiation
better than dental hard tissue, it reduces the increasing temperature of the tissue during the
preparation. Water reaches the boiling point and causes microexposure of the tooth. This
action breaks up the surrounding tissue into small pieces and dissipates them at the same
time. As this explosion occurs in water, it is so-called a preparation induced by water.
Although most radiation is absorbed in water, a certain amount of heat transmission is
unavoidable. Therefore, a water spray is used for cooling. The proper amount of water
spray prevents pulpal damage. As heat transmission normally depends on the pulse shape
and pulse maintenance time, the amount of water varies according to the laser system and
treatment itself. A lack of enough water spray causes pulpal damage.
In contrast to initial studies, there was no immunological difference between the laser
system and conventional etching method. Moreover, the positive effect of the laser to
regenerate pulp was discussed. Essentially, cavity preparation should be performed with
the proper instruments with the "method of minimal pulse energy" according to the
manufacturer's protocol. This is because the preparation should be performed with the
capability to minimize additional damage.
The bond strength of the adhesive system is one of the major factors for the success of
restorations. Therefore, this restoration parameter can be measured accurately by the
bonding test. The bonding of resin composite material to the tooth structure prepared with
different types of lasers has been reported (Visuri et al., 1996; Armengol et al., 1999;
Martínez-Insua et al., 2000; Carrieri et al., 2007; Ekworapoj et al., 2007; Lee et al., 2007; de
Carvalho et al., 2008; Gurgan et al., 2008; Chou et al., 2009). These studies reported variable
results comparing the bond strengths of composite resin to a laser-prepared and acid etched
dentin surface, and suggested that the laser preparation is more effective than etching in
bonding strength of the composite resin to the tooth structure (Obeidi et al., 2010; Turkmen
et al., 2010; Navimipour et al., 2011). This study compared the in vitro SBS of two different
adhesive systems to dentin treated with an Er,Cr:YSGG laser. These results showed that the
type of adhesive system had no effect on SBS, whereas the laser intensity was a criterion to
be considered.
Generally, the manufacturer of Er,Cr:YSGG lasers recommended 2.25 to 2.5 W for laser
etching but other studies used 2 to 3 W referring from their results of a pilot study to obtain
the proper effects (Çalışkan et al., 2010). The data from this study showed that the shear
bond strength (SBS) of dentin treated with 1.4 W, was higher than that of SBS with 2.25 W,
which was recommended by the manufacturer. These results were different from other
study results showing that the shear bond strength of laser etching (1.25 W or 3 W) was
higher than the diamond bur (Gurgan et al., 2008). The distance between the laser tip and
laser irradiated dentin surface may not be strict in this kinds of study designs. On the other
hand, in this experiment, the sweeping motion of the laser irradiation 6 mm away from the
dentin surface was used before the application of adhesive procedures to employ consistent
defocused irradiation with lower intensity. Therefore, the difference in the effect between
