Keywords
cavity disinfection - chlorhexidine - Giomer - laser - microleakage
Introduction
Microbial factors, oral hygiene, and dietary habits may lead to caries formation in
the cervical area of the teeth.[1] Even if the initial lesions are asymptomatic, cervical caries may cause pain, tenderness
and aesthetic defects in later stages. Resin materials are commonly used in the treatment
of cervical caries lesions.[2] Giomer is a resin-based restorative material, developed by adding glass ionomer-filler
particles into composite resins, and indicated for use in Class V cavities. This hybrid
material represents promising aesthetic and physical-mechanical properties similar
to composite resins. Also, the fluoride charging and releasing ability offered by
giomers has been claimed to be close to glass ionomer cements.[3] However, the long-term fluoride release of Giomer is questionable,[3] it has been reported to have demineralization inhibition properties such as glass
ionomers in vitro.[4]
Necrotic and infected dentin tissues are intended to be completely removed from the
cavity to maintain pulp vitality during the cavity preparation.[5] Although most of the bacteria are found in the infected dentin layer, bacteria can
also be found in small amounts in the hard and affected dentin at bottom of excavated
cavity.[1]
[5] Complete removal of infected dentin layers is essential to create a mechanically
and biologically successful restoration. However, in the final stage of caries removal
it is considerably difficult to make a visual diagnosis and distinguish the infected
or affected dentin.[6] Therefore, it is recommended to use an antibacterial cavity disinfectant following
the cavity preparation to eliminate the risk of any pulpal inflammation caused by
the microorganisms that may remain in the affected dentin.[7] Various antibacterial agents and techniques such as chlorhexidine gluconate, potassium iodine, hydrogen peroxide, sodium hypochlorite
(NaOCl), laser, etc. are recommended for this purpose. Chlorhexidine gluconate-based
solutions are the most commonly used materials as cavity disinfectants. Chlorhexidine’s
action mechanism is based on its chemical properties with strong cationic character.
The negative charge on the surface of oral tissues interacts with the positively charged
chlorhexidine molecule and creates a long-lasting antimicrobial effect.[8]
[9] NaOCl, on the other hand, is a broad-spectrum antibacterial agent, which is effective
against both Gram-positive and Gram-negative bacteria. It has organic tissue-dissolving
ability and high efficacy against microorganisms organized in biofilms. NaOCl can
be used to eliminate residual bacteria remaining in dentine tubules and cavity bottom
after cavity preparation.[10] However, there is a possibility that NaOCl as a cavity disinfectant may have adverse
effects on hybrid layer formation or bond strength of composite resins.[11]
Laser irradiation has been recommended for cavity disinfection. Hard tissue lasers
exhibit antibacterial effect, especially by evaporating the cellular liquid that expands
by laser shot, causing the cell wall to break down.[1] Laser irradiation provides reduction or total closure of dentinal tubules and intratubular
fluid flow, which resulted in prevention on microleakage.[12]
Resin restorations show polymerization shrinkage that causes gap formation between
the tooth tissues and the restoration. Bacterial products, oral fluids, and various
ions can penetrate through the interface gap, which is defined as microleakage, and
lead to postoperative sensitivity or discoloration of teeth, secondary caries, or
pulpal pathologies.[13] Besides, thermal expansion, inadequate adhesion of the restorative materials to
the tooth tissues, or dissolution of restorative materials by oral fluids may cause
microleakage.[14]
There are both benefits and drawbacks of using cavity disinfectant according to actual
literature. Some researchers have claimed that cavity disinfectant application may
cause microleakage between the tooth tissue and restoration.[2]
[9] However, others have reported that the disinfections have no effect on the microleakage
of restoration.[6]
[8]
The aim of this study was to investigate the effects of different disinfection methods
on the microleakage of Giomer restorations. The null hypothesis was that cavity disinfectants
did not affect the sealing capability of restorations.
Materials and Methods
In this study, 40 sound permanent bovine central incisors were used. The teeth were
cleaned of debris and residual substances with a rubber-cup and fluoride-free polishing
paste. The teeth were placed in distilled water containing 0.1% thymol for disinfection
and kept there for 24 hours. 3x2x2 mm Class V cavities were prepared in the middle
third of the buccal surfaces of the teeth. This process was done by using a high-speed
head and diamond fissure burs (Diatech Dental AG, Sweden Dental Instrument, CH-9435
Heerbrugg, Switzerland) with water coolant. The depth of the cavities was standardized
by means of a periodontal probe with millimeter markings. Teeth samples were then
randomly divided into four groups (n = 10).
The disinfection procedures were indicated in [Table 1]. After all the four groups were disinfected, BeautiBond (Shofu Inc., Kyoto, Japan)
was applied to all surfaces of the cavities with the help of an applicator in accordance
with the manufacturer's instructions. The bonding agent was polymerized for 20 seconds
by using a LED light source with light intensity of 400 mW/cm2 (Guilin Woodpecker Medical Instrument Co., Ltd, China).
Table 1
Disinfection methods used in the study
|
Group
|
Treatment procedure
|
Manufacturer
|
|
Abbreviations: Er, Cr: YSGG, erbium, chromium: yttrium-scandium-gallium-garnet; NaOCl,
sodium hypochlorite.
|
|
Group 1
|
CHX 2% chlorhexidine gluconate treatment with rinsing and drying
|
Cavity Cleanser, Bisco, Schaumburg, Illinois, United States
|
|
Group 2
|
6% NaOCl treatment with rinsing and drying
|
RC CLEANER, ilchungdental, Seoul, Korea
|
|
Group 3
|
Er, Cr: YSGG laser, 20 Hz; 0.75 W; 15% water, 15% air and drying
|
iPlus; Waterlase, Biolase, California, United States
|
|
Group 4
|
Distilled water with rinsing and drying
|
–
|
Following the conditioning procedures, a single layer of Beautifil II (Shofu Inc.,
Kyoto, Japan) was applied on the cavities. All the samples were polymerized for 20
seconds at a light intensity of 400 mW/cm2. All the restorative procedures were performed by one operator.
The finishing and polishing were performed by using diamond-finishing burs with a
yellow ring and an OneGloss PC (Shofu Inc., Kyoto, Japan). The teeth were immersed
in distilled water for 24 hours at 37°C. Then all the teeth were thermocycled 5,000
times (5–55°C), with a waiting period of 30 seconds and a transfer period of 10 seconds.
The tooth apices, which were then kept at 37°C for 24 hours, were tightly sealed with
wax. The teeth were covered with two layers of nail polish to leave 1-mm thick sound
enamel around the restorations. The teeth were immersed in 0.5% methylene blue at
37°C for 24 hours, after which they were taken out of the dye solution and rinsed
thoroughly under running water until they were clear of dye residuals. The microleakage
levels of the cross-sectioned teeth were examined under a stereomicroscope (Zeiss,
Germany) at 40x magnification.
Statistical Analysis
The results of microleakage evaluation were submitted to statistical analysis using
“SPSS 15.0” computer software (SPSS 15.0; SPSS Inc, United States). Kruskal–Wallis
and Mann–Whitney U tests were performed. Significance was predetermined at p < 0.05.
Results
The examples of cross-sectioned teeth with microleakage were presented in [Fig. 1]. The microleakage scores were determined by using the criteria given in [Table 2]. Distribution of microleakage scores according to groups were shown in [Table 3].
Fig. 1 The arrowheads show microleakage levels between the restoration and tooth surface
of two-dimensional specimens. (A) Score 0, no leakage; (B) Score 1, leakage depth up to one-third of the internal surface; (C) Score 2, leakage depth up to two-thirds of the internal surface. (D) Score 3, leakage into more than two-thirds of the cavity depth up to the axial wall
or toward the pulp.
Table 2
Scoring chart used to evaluate microleakage levels
|
0
|
No microleakage
|
|
1
|
Penetration up to one-third of the cavity depth
|
|
2
|
Penetration between one-third up to two-thirds of the cavity depth
|
|
3
|
Penetration into more than two-thirds of the cavity depth up to the axial wall or
toward the pulp
|
Table 3
Distribution of microleakage scores according to groups
|
Microleakage scores
|
|
0
|
1
|
2
|
3
|
|
Group 1
|
Gingival
|
0
|
0
|
0
|
10
|
|
Incisal
|
1
|
7
|
1
|
1
|
|
Group 2
|
Gingival
|
0
|
1
|
0
|
9
|
|
Incisal
|
2
|
8
|
0
|
0
|
|
Group 3
|
Gingival
|
0
|
0
|
0
|
10
|
|
Incisal
|
2
|
5
|
0
|
3
|
|
Group 4
|
Gingival
|
0
|
0
|
0
|
10
|
|
Incisal
|
1
|
5
|
1
|
3
|
The results of the Kruskal–Wallis test indicated that there was no significant differences
among the microleakage scores of the different groups (p > 0.05). Mann–Whitney U test showed no significant difference in microleakage scores between paired groups
both for incisal and gingival margins (p > 0.05). On the other hand, the microleakage scores of gingival margins were significantly
higher than that in the incisal margins (p < 0.0001).
Discussion
Cervical caries is a common type of caries caused by inadequate oral hygiene, cariogenic
diet and bacteria.[2] After caries removal, the existence of residual bacteria within a restoration may
lead to microleakage and secondary caries.[13] Therefore, disinfection of the dentine surface is recommended before any restorative
material is placed into the cavity.[7] Several agents and techniques, such as chlorhexidine gluconate, potassium iodine, hydrogen peroxide, NaOCl, and
laser, are frequently used for this purpose.[8]
[9] In this in vitro study, we compared four different disinfection methods on the microleakage
of Giomer resin material in Class V restorations of permanent bovine central incisors.
It is recommended to store the extracted teeth in distilled water, glutaraldehyde,
or thymol solutions for in vitro tests.[15]
[16] In the present study, the extracted teeth were first disinfected in distilled water
containing 1% thymol at room temperature for 24 hours after the tooth extraction,
and then kept in distilled water at 37°C for 24 hours following following polishing
procedure.
Eating, drinking, and breathing cause temperature changes within the mouth. Intraoral
temperature changes cause thermal stresses in the adhesive bonding between the tooth
and the restoration interface. Effects of long-term exposure to temperature and humidity
changes can be simulated by means of thermal cycling. Thermal cycling is frequently
used in experiments where the performance of adhesive materials is examined.[17] Also, it is preferred in microleakage studies to age restorations clinically. It
is believed that this method provides rather reliable results in microleakage experiments.[18] In this study, all the teeth were thermocycled 5,000 times (5–55°C) before the microleakage
test.
In vitro microleakage tests are attempt to assess sealing ability of restorative materials.[19] Chemical markers, scanning electron microscope analysis, neutron activation analysis,
autoradiography, and dye leakage methods have been recommended to evaluate microleakage.
Using organic dyes in microleakage studies is one of the oldest methods and still
preferred to other techniques. Silver nitrate (50%), methylene blue (0.2-2%), crystal
violet (0.05%), erythrosine (2%), rhodamine B (0.2%), and basic fuchsine (0.5-2%)
are generally using dye solutions.[2]
[20]
[21] In the present study, 0.5% methylene blue solution was used to assess the microleakage
of restorative materials. This technique is preferred for microleakage studies due
to simple and inexpensive application.
Similar microleakage studies regarding to cavity disinfectants indicated several results.
Türkün et al[8] examined effect of chlorhexidine, benzalkonium chloride, and iodine-based cavity
disinfectants on the sealing ability of different dentin adhesives. They have reported
that the use of chlorhexidine- and benzalkonium chloride-based solutions as cavity
disinfectants had no effect on the microleakage while iodine-based solutions increased
it. Another study investigating the effect of using ethanol, chlorhexidine, and NaOCl
as a cavity disinfectant on microleakage showed that these solutions did not increase
the microleakage.[6] Tulunoglu et al,[9] on the other hand, reported that the use of chlorhexidine-based cavity disinfectant
had a negative effect on dentin adhesive systems. The present study showed that all
samples exhibited microleakage when assessed under the microscope magnification. We
observed that cavities restored with Giomer have similar microleakage scores with
or without different cavity disinfection methods. These results were in accordance
with previous studies.[6]
[8]
The lasers are capable of removing the smear layer which contains residual bacteria
and disinfect the dentinal tubules.[1] The antibacterial effect of lasers is related to many factors including the laser’s
energy output, water content and volume of the cell, cell wall stability, absorption
properties, and movements of bacteria in the dentine tubules.[22] Kouchi et al[23] showed that streptococcus mutans may exist in dentine at depths of 1,050 to 1,150
μm. It was shown that the antimicrobial activity of chlorhexidine gluconate in a 500-μm
thick dentine goes down to 54%,[24] while a diode laser could kill 90.8% of the microorganisms at 5W and 97.7% at 7W
for the same dentine thickness.[22] In a study conducted by Türkün et al,[1] erbium, chromium: yttrium-scandium-gallium-garnet (Er, Cr: YSGG) laser with power
outputs 0.75 W and 1 W and a chlorhexidine-based cavity disinfectant were compared
in terms of antibacterial activity, and it was reported there was no significant difference
between the two methods and lasers could be used for cavity disinfection, but it was
not an economical method. In a study on the effect of potassium-titanyl-phosphate
(KTP) laser radiation, 2% chlorhexidine gluconate, and Clearfil Protect Bond on the
microleakage of Class V composite restorations, KTP lasers were reported to reduce
the microleakage to a statistically significant extent. In the present study, no statistically
significant difference was observed when the microleakage scores related to the use
of Er, Cr: YSGG laser with a power output of 0.75 W were compared with the scores
of the other groups.
Studies examining the microleakage of Class V restorations reported that gingival
edges of cavities showed higher microleakage than the incisal edges,[25]
[26] which were attributed to the fact that the enamel layer in the cervical region is
thinner, and therefore more permeable than the enamel layer at the incisal edge.[25] In fact, in the present study, the microleakage scores of gingival margins showed
were significantly higher than the incisal margins.
Conclusion
The results of present study indicate that the cavity disinfectant application has
no effect on the microleakage of Class V Giomer restorations. These findings should
be supported with long-term clinical trials.
