Sealant Bond Strengths of CO2 Laser-Etched Versus Acid-Etched Bovine Enamel
Sealant Bond Strengths of CO2 Laser-Etched Versus Acid-Etched Bovine Enamel
Sealant Bond Strengths of CO2 Laser-Etched Versus Acid-Etched Bovine Enamel
ner of the square, and ending in the bottom right free, moisture free, compressed air for 5 seconds;
corner. To ensure homogeneity of the etch, the etched with 37% phosphoric acid gel (Bisco Dental
path was then reversed, tracing a left/up/right/up Products) placed with a syringe needle tip;
trajectory inside the square. The total scan was washed for 10 seconds with distilled water; and
composed of 14 passes (7 down and 7 up) in 12–13 then dried with oil-free compressed air until
seconds. The average effective etch time (within chalky white. A gelatin capsule 4.34 mm in diam-
the mask) was 8–10 seconds. The continuous lin- eter (#5, Eli Lilly and Co., Indianapolis, IN) was
ear scan, combined with the helical motion of the filled with the dual curing sealant and bonded to
focus, ensured a homogeneous, stochastic etch. the prepared tooth and cured for 20 seconds by
The use of the mask resulted in a sharp transition using a visible light curing unit (Visiluxll, 3M,
form etched to nonetched surfaces. Minneapolis, MN). The bonded tooth was then
The sealant used (Aelite Seal, Bisco Dental stored in room temperature distilled water.
Products, Itasca, IL) was a dual-cured pit and fis-
sure sealant composed of bisphenol diglycidyl- Acid Etching With Primer
methacrylate with amorphous silica, titanium di- The enamel surface was treated as above ex-
oxide, and benzoyl peroxide (catalyst). The primer cept for the final drying step. Instead of drying
was made of ethyl alcohol and hydroxyethyl meth- with compressed air, the etched enamel surface
acrylate. The bonding procedures given by the was kept moist by using a wet facial tissue
manufacturer’s instructions were as follows. (Kleenex Softique, Kimberly-Clark Corporation,
Acid Etching Without Primer Neenah, WI) to remove only the excess water. The
method of maintaining the moist surface had no
The enamel surface was cleaned with a rub- effect on the bond strength as observed in a pre-
ber cup and pumice for 15 seconds; dried with oil vious study [4]. Two coats of primer were added to
Bond Strengths of CO2 Laser-Etched Versus Acid-Etched Enamel 115
the surface of the enamel as per manufacturer’s Laser Etch With Primer
instructions. The enamel surface was dried with The enamel surface was prepared the same
oil-free compressed air for 10 seconds and then a as the laser-etched and primer placed as above by
gelatin capsule, as above bonded to the surface. using a moist surface. The gelatin capsule was
bonded, and the specimens were stored at room
Laser Etching Without Primer temperature in distilled water.
All of the bonded teeth were stored at room
The enamel surface was cleaned with a rub- temperature in distilled water for 7 days before
ber cup and pumice for 15 seconds and then the shear bond strength test was completed.
etched by using the CO2 laser as described above. Shear bond strength was completed on a material
The etched samples were stored in a 100% humid testing machine (Instron 1152, Instron Corp.,
environment for 12 hours (half an inch of 2 × 2 Canton, MA) at a crosshead speed of 2 mm/min.
nonsterile wet gauze was placed at the bottom of The bond strength was determined by dividing
the container and the etched tooth were placed on the load at fracture by the sealant area.
top of the wet gauze). The etched surface was then Surface roughness (Ra) measurements (1
washed for 10 seconds with distilled water; dried mm in length) were made on an unaltered bovine
with oil-free compressed air until chalky white, incisor, an acid-etched bovine incisor, and a CO2
and a gelatin bonded to the surface. The bonded laser-etched bovine incisor by using a Surftest
tooth was then stored in room temperature dis- 201 surface analyzer (Miutoyo Manufacturing
tilled water. The 12-hour storage time was re- Co., Ltd., Tokyo, Japan). Roughness was mea-
quired because the laser was not housed at the sured parallel and perpendicular to the long axis
same place as the bonding and testing procedures of the tooth to compensate for the dominant ridges
and travel time was required. parallel to the long axis of the tooth. To measure
116 Drummond et al.
the surface roughness at a much smaller scale, an and the laser-etched groups. The two acid-etch
atomic force microscope was used (ARIS-3300 groups were not significantly different from each
Personal Atomic Force Microscope, Burleigh In- other; however, the laser-etched groups were sig-
struments, Inc., Fisher NY) with line scans 1.4 nificantly different from each other.
mm in length. Table 3 presents the result from the rough-
Scanning electron microscopy (SEM) [JOEL ness study. The statistical analysis showed that
35C, JOEL USA, Peabody, MA] was completed for the orientation of the tooth had an effect on the
the control, acid-etched, and laser-etched sur- measured roughness. The laser-etched surface
faces. The specimens were coated with gold- was the roughest followed by the acid-etched and
palladium. then the control. A t-test was then conducted be-
The statistical analysis for the bond strength tween the orientation (parallel vs. perpendicular
and surface roughness consisted of a one-way to the long axis), showing that for both the control
analysis of variance followed by a Tukey multiple and the acid-etched, there was a significant dif-
means comparison test when required. For the ference depending on orientation. For the laser-
comparison between the parallel versus perpen- etched tooth, there was no significant difference
dicular surface roughness within each material in orientation. The roughness from the atomic
(control, acid-etched, and laser-etched), a Stu- force microscope only showed a significant differ-
dent’s t-test was used. ence between the two etched surfaces and the con-
trol. The differences observed between the two
techniques are one of scale. The region measured
RESULTS
by the atomic force microscope is much smaller,
The shear bond strength and statistical between the ridges, than the surface analyzer,
analysis are reported in Table 2. A significant dif- which crossed over the ridges, resulting in the in-
ference existed between the acid-etched groups creased roughness.
Bond Strengths of CO2 Laser-Etched Versus Acid-Etched Enamel 117
SEM photographs of the control, acid-etched, between laser-etched and acid-etched teeth. Most
and laser-etched surfaces are presented in Fig- of literature states that a decrease in bond
ures 1–4. Figure 1 is the unetched surface of bo- strength is observed when enamel was laser-
vine enamel and Figure 2 is the surface after acid treated, but Walsh et al. [6] noted that in their
etching. The surfaces presented were representa- study that a significant increase (P < 0.0001) in
tive of the bovine enamel specimens. Figure 3 is bond strength is seen when enamel was laser
the laser-etched surface with crack formation in treated. It should be noted that these authors had
the re-solidified enamel. No crack formation was used numerous parameters (different power set-
observed in any teeth outside of the region of the tings) for their study and only one of nine showed
laser etching. Figure 4 is a cross-section of the the greater bond strength, whereas all the others
laser-etched surface showing the depth effect of showed a decrease in bond strength. Only one
the laser to be approximately 1–2 mm. power setting was used in our study to measure
shear bond strength and the effect of a primer and
additional research would be needed to determine
DISCUSSION
the most optimal setting, which would mimic the
The results showed that for the parameters characteristics of acid etching and improve the
used, laser etching on the bovine enamel pro- sealant bond strength.
duced a significantly lower bond strength. The Research has shown that lasers can alter the
power settings that were used produced a laser- morphology of enamel to make it less susceptible
etched, re-solidified enamel. The acid-treated to caries. This finding may yet be a more practical
samples revealed a typical morphology observed approach with regard to laser use in preventative
for acid-etched enamel. The decrease in bond dentistry.
strength for the laser-etched teeth may not be a
function of surface roughness, but of the surface
energy of the etched surface. The acid etching pro- ACKNOWLEDGMENTS
cess leaves a high-energy surface that is easily The authors thank Yang-sun Bak for his as-
wetted by the sealant. The laser-etched surface on sistance in the sample preparation and testing,
the other hand, is most likely at a lower surface the Research Resources Center at the University
energy because the surface was melted and then of Illinois at Chicago, for the use of the scanning
re-solidified. Another possibility is that failure of electron microscope, and Laser Industries, Tel
the bond occurred between the re-solidified Aviv, Israel, for use of the laser.
enamel and the unaltered enamel and not be-
tween the sealant and the enamel.
The laser-treated surface would also be ex- REFERENCES
pected to have a lower water content than the 1. Cueto E, Bunocore MG: Adhesive sealing of pits and fis-
original tooth, because the water and organic sures for caries prevention. J Dent Res 1967;44:137.
phase of the tooth would be volatilized during the 2. Feigal RJ, Hitt J, Splieth C. Retaining sealant on salivary
laser etching. With less moisture on the surface, contaminated enamel. J Am Dent Assoc 1993;124:88–97.
the wetting properties of this acetone-based seal- 3. Hitt JC, Feigal RJ. Use of a bonding agent to reduce
sealant sensitivity to moisture contamination: an in vitro
ant system are reduced, limiting sealant penetra-
study. Pediatr Dent 1992;14:41–46.
tion into the enamel surface undercuts, and re- 4. Choi JW, Drummond JL, Dooley R, Punwani I, Soh JM.
sulting in the observed reduced bond strengths. The efficacy of primer on sealant shear bond strength.
This idea is supported because both etched sur- Pediatr Dent 1997;19:286–288.
faces showed an increase in bond strength after 5. Arcoria CJ, Lippas MG, Vitasek BA. Enamel surface
the use of the acetone based primer. The tooth roughness analysis after laser ablation and acid-etching.
J Oral Rehabil 1993;20:213–224.
preparation technique provided a moist surface 6. Walsh LJ, Abood D, Brockhurst PJ. Bonding of resin com-
and not an air-dried surface. posite to carbon dioxide laser-modified human enamel.
The higher surface roughness observed for Dent Mater 1994;10:162–166.
the laser-etched specimens at the micrometer 7. Corpas-Pastor L, Villalba Moreno J, de Dios Lopez-
level did not translate into a higher bond Gonzalez Garrido J, Pedraza Muriel V, Moore K, Elias A.
Comparing the tensile strength of brackets adhered to
strength. The surface roughness at the micron
laser etched enamel vs. acid-etched enamel. J Am Dent
level is attributed to the prominent ridges present Assoc 1997;128:732–737.
on the surface of bovine teeth. At the atomic force 8. Bouvier D, Duprez JP, Nguyen D, Lissac M. Interet du
level of nanometers, the roughness was the same laser CO2 pour lı́adhesion des resines composites sur la
118 Drummond et al.
dentine. Bull Group Int Rech Sci Stomatol Odontol 1994; 12. Hicks MJ, Flaitz CM, Westerman GH, Blankenau RJ,
37:2–5. Powell GL, Berg JH. Caries-like lesion initiation and pro-
9. Shahabi S, Walsh LJ. Effect of bonding agents on adhe- gression around laser-cured sealants. Am J Dent 1993;6:
sion of composite resin following CO2 laser etching of 176–180.
dental enamel. J Clin Laser Med Surg 1996;14:169–173. 13. Wigdor HA, Walsh JT Jr, Featherstone JDB, Visuri SR,
10. Shahabi S, Brockhurst PJ, Walsh LJ. Effect of tooth-
Fried D, Waldvogel JL. Lasers in dentistry. Lasers Surg
related factors on the shear bond strengths obtained with
Med 1995;16:1031–1033.
CO2 laser conditioning of enamel. Aust Dent J 1997;42:
81–84. 14. Visuri SR, Gilbert JL, Wright DD, Wigdor HA, Walsh JT.
11. Ariyaratnam MT, Wilson MA, Mackie IC, Blinkhorn AS. Shear strength of composite bonded to Er:YAG laser-
A comparison of surface roughness and composite/enamel prepared dentin. J Dent Res 1996;75:599–605.
bond strength of human enamel following the application 15. Goodis HE, Marshall GW, White JM, Gee L, Hornberger
of the Nd:YAG laser and etching with phosphoric acid. B, Marshall SJ. Storage effects on dentin permeability
Dent Mater 1997;13:51–55. and shear bond strengths. Dent Mater 1983,9:79–84.