Vol 21 No. 1

J Bagh College Dentistry Vol.21(1), 2009 Microleakage of Class II….
acid etching. However, these systems also have
some disadvantages. The Nd: YAG laser beam
(12)
causes an increase in heat. Cox et al. (13)
studied the effects of pulsed Nd: YAG laser
radiation on enamel and dentin. They observed
melted dentin, crazing on the surface, slight debris
formation, and modification of dentin tubule
structure where the tubule periphery had melted.
The laser irradiation group did not produce a dye
penetration-resistant interface, and the laser group
demonstrated the highest degree of microleakage.
This may be the result of the presence of a fused
layer in which interfibrillar spaces were lacking.
This probably restricted the diffusion of
composite resin into the subsurface of the
intertubular dentin resulting in more leakage.
Ceballo et al. (14) reported similar results using the
Er-YAG laser.
According to stereomicroscope observations,
dye absorption was different in each layer of
composite restorationsThis indicates different
degrees of polymerization and confirms Hellwig’s
theory stating that placing composites in multiple
layers can cause differences in the degree of
polymerization]. (15) Reduced shrinkage may be
due to the small bulk of material in each layer. (15)
In restoration of class II cavities, placing the
spectral output of the curing unit close to the
composite is impossible. Dental tissue or a matrix
band could cause light to become opaque or
shady. In addition illumination of light from
behind a 2mm layer of composite resin can
decrease the amount of transmission. According
to Ruyter and Oysaed (16) , placing the tip of a
curing unit at a 2mm distance from a detector
could cause a 7% decrease in output energy which
could be further reduced to 25% when the
distance is increased to 4mm. When restoring
class II cavities, the marginal ridges and cusps
usually demonstrate a distance of at least 4mm
from the gingival floor. Therefore the exposure
time should be increased in order to achieve
maximum hardness and durability of the filling
material. The recommended distance of a light
source from the composite surface is 1mm.
Various methods and instruments have been
proposed to transmit light to inaccessible areas of
the cavity such as transparent matrix strips, light
conducting wedges, mirror matrix bands and
transparent cones attached to the tip of the curing
unit (17) . However, controlling the exact distance
of the tip of a curing unit would be problematic in
clinical settings. It has been shown that addition
of inserts to composite resins can decrease their
microleakage, which is due to the lower thermal
expansion coefficient of the inserts. (18)
REFERENCES
1. Sazak H, Türkmen C, Günday M. Effects of Nd: YAG
Laser, air-abrasion and acid etching on human enamel
and dentin. Oper Dent 2001; 26: 476-81.
2. Corona SA, Borsatto M, Dibb RG. Microleakage of
Class V resin composite restorations after bur, airabrasion
or Er:YAG laser preparation. Oper Dent 2001;
26: 491-7.
3. Stern RH, Sognnaes RF. Laser effect on dental hard
tissues. A preliminary report. J South Calif Dent Assoc
1965; 33: 17-9.
4. Goldman L, Hornby P, Meyer R. Impact of the laser on
dental caries. Nature 1964; 203: 417.
5. Visuri SR, Gilbert JL, Wright DD. Shear strength of
composite bonded to Er:YAG laser prepared dentin. J
Dent Res 1996; 75: 599-605.
6- Bowen RL, Nemoto K, Rapson JE. Adhesive bonding
of various materials to hard tooth tissues: forces
developing in composite materials during hardening. J
Am Dent Assoc 1983; 106(4): 475-7.
7- Ilie N, Kunzelmann KH, Hickel R. Evaluation of microtensile
bond strengths of composite materials in
comparison to their polymerization shrinkage. Dent
Mater 2006; Jul: 22(7):593-601.
8- Hegdahl T, Gjerdet NR. Contraction stresses of
composite resin filling materials. Acta Odontol Scand
1977; 35(4):191-5.
9- Bausch JR, de Lange K, Davidson CL, Peters A, de Gee
AJ. Clinical significance of polymerization shrinkage of
composite resins. J Prosthet Dent 1982; Jul: 48(1):59-
67.
10. Kytridou V, Gutmann JL, Nunn MH. Adaptation and
sealability of two contemporary obturation techniques
in the absence of the dentinal smear layer. Int Endod J
1999; 32: 464-74.
١١. Moritz A, Schoop U, Goharkhay K. Procedures for
enamel and dentin conditioning: A comparison of
conventional and innovative methods. J Esthet Dent
1998; 10: 84-93.
12. Ariyaratnam MT, Wilson MA, Blinkhorn AS. An
analysis of surface roughness, surface morphology and
composite/dentin bond strength of human dentin
following the application of the Nd:YAG laser. Dent
Mater 1999; 15: 223-8.
13. Cox CJ, Pearson GJ, Palmer G. Preliminary in vitro
investigation of the effects of pulsed Nd:YAG laser
radiation on enamel and dentine. Biomaterials 1994; 15:
1145-51.
14. Ceballo L, Taledano M, Osorio R. Bonding to
Er:YAG-laser-treated dentin. J Dent Res 2002; 81: 119-
22.
15- Hellwig E, Klimek J, Achenbach K. Effects ofan
incremental application technique on the polymerization
of two light-activated composite filling materials. Dtsch
Zahnarztl Z 1991; Apr: 46(4):270-3
16- Ruyter IE, Oysaed H. Conversion in different depths
of ultraviolet and visible light activated composite
materials. Acta Odontol Scand 1982; 40(3):179-92.
17- Yazici AR, Frentzen M, Dayangac B. In vitro analysis
of the effects of acid or laser etching on microleakage
around composite resin restorations. J Dent 2001; Jul:
29(5):355-61.
18- Donly KJ, Wild TW, Bowen RL, Jensen ME. An in
vitro investigation of the effects of glass inserts on the
effective composite resin polymerization shrinkage. J
Dent Res 1989; 68(8): 1234-7.
Restorative Dentistry
48