e66
Effects of Dentin Surface Treatments on Hypersensitivity to Bond Strength of Restorations: An In Vitro Study Ayça Tulga, DDS, PhD1 Duygu Saraç, DDS, PhD2
This study evaluated the effects of desensitizing treatments on the shear bond strength (SBS) of adhesive resin cement (Rely X U100) applied to dentin. Human molars (n = 120) with exposed dentin were divided into 12 groups. In the experimental groups, dentin surfaces were treated with (1) an erbium:yttrium– aluminium–garnet (Er:YAG) laser, (2) a neodymium:yttrium–aluminium–garnet (Nd:YAG) laser, (3) glutaraldehyde (Gluma)–, (4) fluoride (Aqua Prep-F)–, and (5) oxalate (BisBlock)–containing desensitizing agents, (6) Gluma preceding the Er:YAG laser, (7) Aqua Prep-F preceding the Er:YAG laser, (8) BisBlock preceding the Er:YAG laser, (9) Gluma preceding the Nd:YAG laser, (10) Aqua Prep-F preceding the Nd:YAG laser, (11) and BisBlock preceding the Nd:YAG laser, in groups EL, NL, G, F, O, EL-G, EL-F, EL-O, NL-G , NL-F, and NL-O, respectively. Then, lithium disilicate ceramics were cemented to the treated surfaces. Subsequently, an SBS test was performed and the data were statistically analyzed (α = .001). The results suggested that the combined treatment of Gluma preceding Er:YAG laser increased the bond strength of ceramic to the dentin surface using a self-adhesive resin cement. (Int J Periodontics Restorative Dent 2015;35:e66–e74. doi: 10.11607/prd.2194)
Assistant Professor, Department of Prosthodontics, Faculty of Dentistry, Univeristy of Ordu, Ordu, Turkey. 2Professor, Department of Prosthodontics, Faculty of Dentistry, University of Ondokuz Mayıs, Samsun, Turkey. 1
Correspondence to: Ayça Tulga, Department of Prosthodontics, Dental Faculty of Ordu University, 52200 Ordu, Turkey. Fax: +0 (452) 212 12 89. Email: [email protected] ©2015 by Quintessence Publishing Co Inc.
Dentin hypersensitivity is one of the most common complaints in clinical dentistry for which there is still no effective solution. It is particularly after the preparation of teeth for allceramic restorations that patients complain of postoperative sensitivity (POS).1 In addition, restoration and cementation of the adhesive cause POS associated with an increase in dentin permeability and with the residual stresses from shrinkage in adhesive/composite resin restorations. This may cause debonding and/or cusp deformation.2–4 Adhesive resin luting cements are widely used in many restorations. The internal bond between the adhesive luting cement and the dentin is an important factor that prevents microleakage and ensures retention of the restoration. POS is occasionally associated with the use of etch-and-rinse adhesives. In an attempt to reduce sensitivity, selfetching primer systems have been developed. Several desensitizing agents containing oxalate, gluteraldehyde, or resin have been advocated for sealing dentin before cementation of all-ceramic or cast restorations, to decrease POS.5–8 Various types of dentin desensitizers have been used to alleviate pain caused by dentinal sensitivity.4,9–11 These can be classified into several main groups: neural stimulus blockers, anti-inflammatory
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e67 drugs, protein precipitants, tubuleoccluding agents, and tubule sealants and lasers. Generally, the preferred desensitizers in dental clinics are protein precipitants, tubule-occluding agents, and tubule sealants and lasers.9,11 Nowadays, treatments combining chemical desensitizers with lasers are very popular.12–16 Hsu et al13 studied the combined effect of using a fluoride-containing desensitizing agent with an Nd:YAG laser on dentinal tubules. They found a much greater reduction in the number/patency of tubules when compared with either treatment alone. Similarly, in 2005, Kumar and Mehta12 observed that most dentinal tubule orifices were occluded after combined treatment with a neodymium: yttrium-aluminiumgarnet (Nd:YAG) laser and a sodium fluoride varnish. They also showed that the more marked were the occlusions in dentinal tubules, the greater was the decrease in dentin hypersensitivity obtained by using a combination of laser treatment with a desensitizing agent. But what of the effects of combined treatments on the bonding strength between dentin and the restoration? Many previous studies5–8 concluded that desensitizers decrease the bonding strength, but the data in most of these studies were obtained by looking at the desensitizing treatments alone, and not combined with laser treatment. Thus, a considerable need remains for comparison studies on the bonding effects of desensitizing treatments alone and the effects of combined treatments.
The aim of this study was to evaluate the effects of oxalate-, fluoride-, and glutaraldehydecontaining desensitizing agents; Nd:YAG and erbium: yttriumaluminum-garnet (Er:YAG) lasers; and their combinations on the shear bond strength (SBS) of selfadhesive resin cement when used with dentin.
Method and materials Preparation of tooth specimen
One hundred and twenty human molars extracted within a period of 1 month were used. The criteria for choosing the teeth were as follows: (1) maxillary and mandibular molars were used to gain a larger area of dentin, and (2) teeth with caries were excluded to reduce the variability. The collected teeth were cleaned of periodontal tissue residues with a scaler, stored in 0.5% chloramine-T at room temperature for a maximum of 7 days, and then stored in distilled water at 5°C. The clinical crowns were removed up to 2 mm below the buccal cementoenamel junction using a diamond wafering blade (Isomed, Buehler) under a copious water spray. The selected teeth were embedded in acrylic resin (Paladent RR, Heraeus Kulzer) custom-made, cylinder-shaped Teflon (DuPont) molds with a diameter of 30 mm and height of 20 mm. The specimens were prepared until the dentin was exposed using a Model Trimmer (Whip Mix). The teeth were carefully prepared so that
the exposed dentin surface was parallel to the acrylic resin mold, without exposing the pulp. They were ground using wet 320 grit silicon carbide abrasive paper. The prepared teeth were washed with pumice with a low-speed handpiece to remove the contaminants acquired during preparation, and they were immersed in distilled water to supply enough moisture to the exposed dentin surface. The 120 specimens were randomly divided into 12 groups: a control group and 11 experimental groups of 10 teeth each.
Fabrication of all-ceramic specimens
Lithium-based all-ceramic specimens (IPS e.max Press, Ivoclar Vivadent) (N = 120; 5 mm in diameter; 2 mm in height) were fabricated according to the lost-wax technique recommended by the manufacturer, and ingots were injected into an EP 600 furnace (Ivoclar Vivadent). Disc surfaces were ground with 100-, 220-, and 400-grit silicon carbide sandpaper to standardize the bonding surfaces without changing the geometric shape of the discs. Cementation surfaces were air particle–abraded with 110-μm aluminum trioxide at 2 bar air pressure for a period of 10 seconds from a distance of approximately 10 mm, and then ultrasonically cleaned (Sonorex, Bandeline) for 5 minutes in deionized water.
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e68
Table 1 Desensitizing agents used in the study and their application procedures Agent
Composition
Manufacturer
Application procedure
BisBlock
1%–4% oxalic acid
Bisco
Total-etch for 15 seconds, rinse and dry, apply BisBlock for 30 seconds, rinse and leave moist, apply self-etch resin cement
Aqua Prep-F
35% 2-hydroxymetyl Methacrilate (HEMA), 2% sodium fluoride
Bisco
Total-etch for 15 seconds, rinse and dry, apply BisBlock for 30 seconds, rinse and leave moist, apply self-etch resin cement
Gluma
35% (2-hydroxyethyl) methacrylate, water, 5% glutaraldehyde
Heraeus Kulzer
Apply on dried dentin and leave for 30–60 seconds, dry and spray with air, apply self-etch resin cement.
Table 2 Descriptions of the groups Dentin surface treatments Desensitizing agent treatment Test groups (N = 120)
Fluoride Oxalate (Aqua Prep-F) (BisBlock)
Laser treatment
Glutaraldehyde (Gluma)
Er:YAG Laser—60 s/cm2 with 3 Hz and 100 mJ with coolant
Nd:YAG laser—60 s/cm2 with 15 Hz and 1 W laser without coolant
Group C (control)
–
–
–
–
–
Group EL
–
–
–
+
–
Group NL
–
–
–
–
+
Group O
–
+
–
–
–
Group F
+
–
–
–
–
Group G
–
–
+
–
–
Group OEL
–
+
–
+
–
Group FEL
+
–
–
+
–
Group GEL
–
–
+
+
–
Group ONL
–
+
–
–
+
Group FNL
+
–
–
–
+
Group GNL
–
–
+
–
+
EL = Er:YAG; NL = Nd:YAG; O = oxalate; F = fluoride; G = glutaraldehyde; OEL = oxalate preceding EL; FEL = fluoride preceding EL; GEL = glutaraldehyde preceding EL; ONL = oxalate preceding NL; FNL = fluoride preceding NL; GNL = glutaraldehyde preceding NL. + = Procedure was applied. – = Procedure was not applied.
Application of the dentin desensitizer to the tooth specimen
Table 1 lists the dentin desensitizers used for the surface treatment. The dentin desensitizers were applied to the categorized specimens
according to the manufacturers’ instructions. The exposed dentin surfaces of the control group were not treated. Each of these dentin desensitizers was applied to 30 teeth specimens. Thus, a total of 90 teeth were treated with desensitizers.
Laser application
All treatments were done using a Fotona AT Fidelis machine. Four of the experimental groups were irradiated with an Nd:YAG laser; of these, three were combined with desensitizing agents (Table 2). The
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e69 teeth in the Nd:YAG groups (NL, ONL, FNL, GNL) were irradiated twice for 60 seconds/cm2 with 15 Hz and 1 W laser without coolant.17 The other four experimental groups were irradiated with an Er:YAG laser. Three of these were combined with desensitizing agents (Table 2). The teeth in the Er:YAG groups (EL, OEL, FEL, GEL) were irradiated twice for 60 seconds/cm2 with 3 Hz and 100 mJ with coolant, in very low power mode and with an RO7 handpiece.17
Cementation procedure
The ceramic specimens were etched with 5% hydrofluoric acid (Ceramic Etching Gel, Ivoclar Vivadent) for 20 seconds, washed and rinsed thoroughly, air-dried and silanized (Monobond-S, Ivoclar Vivadent). The reaction time of the silane-coupling agent was 60 seconds for both resin groups. Then the self-adhesive resin cement (RelyX U100, 3M Espe) was applied in a thin layer, gently airblown, and photopolymerized with a light-emitting diode photopolymerization unit (Hilux Led-max 550, Benlioglu Dental) for 20 seconds, with a constant distance of 2 mm from the surface. During the polymerization procedure, specimens were processed using a universal testing device (Lloyd LRX, Lloyd Instruments) under 8 kg for 3 minutes. The cemented specimens were then stored in distilled water at 37°C for 24 hours.
Table 3 One-way analysis of variance of force (megapascals) required to debond Empress 2 ceramics from dentin surfaces Sum of squares
df
Mean square
F
Significance
37.921
0.001
Between groups
415.941
11
37.813
Within groups
107.692
108
0.997
Total
523.633
119
SBS test
The specimens were thermocycled 500 times between 5°C and 55°C for a period of 30 seconds. The SBS test was performed with the universal testing device at a crosshead speed of 0.5 mm/second. The SBS values were calculated in megapascals.
Analysis
The specimens were examined under a field-emission scanning electron microscope (SEM) (JSM-6335F, Jeol) at 20.0 kV. The SEM photomicrographs were taken at 2,000× magnification for visual inspection. One-way analysis of variance (ANOVA) was used to determine significant differences among dentin surface treatments. All mean SBS values for treatment combinations were compared using the Tukey multiple comparison test.
Results The results of the one-way ANOVA are shown in Table 3. The mean SBS, minimum and maximum values, and standard deviations (SDs) for each
group are presented in Table 4. The failure modes were all adhesive. The SBS was lowest in the group that received the oxalate (O; BisBlock, Bisco; 4.36 MPa), which showed significantly lower SBS than any of the other groups except the group treated with oxalate preceding the Nd:YAG laser (ONL; 5.03 MPa). The SBS values were highest in the group treated with glutaraldehyde preceding the Er:YAG laser (GEL) (11.22 MPa), which was significantly higher than all of the other groups (P < .001). The SBS values were lower in the groups treated with the Nd:YAG laser (NL), fluoride (F; Aqua Prep-F, Bisco), oxalate preceding the Er:YAG laser (OEL), and fluoride preceding the Nd:YAG laser (FNL) than in the control group (7.51 MPa), but the differences were not statistically significant. The SBS values obtained with the EL, fluoride preceding the Er:YAG laser (FEL), and glutaraldehyde (G; Gluma, Heraeus Kulzer) groups were significantly higher than those of the control group. The differences among the three groups were not statistically significant (9.53 MPa, 9.42 MPa, and 9.36 MPa, respectively).
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e70
Table 4
Mean shear bond strengths, standard deviations (SDs), minimum (Min) and maximum (Max) values for each group (n = 10)
Dentin surface treatment
Group
Mean*
SD
Min
Max
Control
C
7.51 A
1.39
4.60
9.50
Er:YAG laser
EL
9.53 B
0.91
7.80
10.80
Nd:YAG laser
NL
6.66 A
0.65
5.20
7.40
Oxalate
O
4.36 C
0.90
3.10
5.70
Fluoride
F
7.04 A
0.53
6.20
7.70
Glutaraldehyde
G
9.36 B
1.45
7.10
11.90
Oxalate + Er:YAG
OEL
7.24 A
0.99
6.10
8.40
Fluoride + Er:YAG
FEL
9.42 B
0.80
8.30
10.50
Glutaraldehyde + Er:YAG
GEL
1.57
8.60
13.40
Oxalate + Nd:YAG
ONL
5.03 C
0.82
3.80
6.20
Fluoride + Nd:YAG
FNL
7.41 A
0.61
6.50
8.30
Glutaraldehyde + Nd:YAG
GNL
7.80 A
0.70
6.60
8.60
11.22
*Means for groups having the same letters show homogenous subsets, α = .001. EL = Er:YAG; NL = Nd:YAG; O = oxalate; F = fluoride; G = glutaraldehyde; OEL = oxalate preceding EL; FEL = fluoride preceding EL; GEL = glutaraldehyde preceding EL; ONL = oxalate preceding NL; FNL = fluoride preceding NL; GNL = glutaraldehyde preceding NL.
a
b
c
d
Fig 1 SEM images of the dentin after surface treatments with different desensitizing agents. (a) Control group; (b) treatment with Aqua Prep-F; (c) treatment with BisBlock; (d) treatment with Gluma. None of these groups received any laser treatments.
Of the groups using desensitizing agent treatments alone (O, F, G), the SBS value was highest in group G (9.36 MPa) and lowest in group O (4.36 MPa) (P < .001). Of the groups that received the Er:YAG laser treatment (EL, OEL, FEL, GEL), the SBS value was highest in group GEL (11.22 MPa), and lowest in group OEL (7.24 MPa) (P < .001). Of the groups that received the Nd:YAG laser treatment (NL, ONL, FNL, GNL), the SBS value was highest in group GNL (7.80 MPa) and lowest in group ONL (5.03 MPa) (P < .001). The SEM images are shown in Figs 1 to 3. Of the groups that used desensitizing agent treatments alone (O, F, and G), although the control group and group G showed similar surfaces covered with smear layer, dentin tubules were marked in groups F and O because of the application procedures of Aqua Prep-F and BisBlock (Fig 1). Because of the resin contained in Gluma, a resin film layer was seen on the dentin surface of group G (Fig 1d). The SEM images of the groups that received the Er:YAG laser treatment (EL, OEL, FEL, GEL) showed similar figures like flaky irregularities except for the calcification points around the dentin tubules seen in groups OEL and FEL (Fig 2). The photomicrographs of the groups that received the Nd:YAG laser treatments (NL, ONL, FNL, GNL) were similar to those in the groups without laser treatment (C, O, F, G) but the dentin surfaces were smoother in groups treated with the Nd:YAG laser (Fig 3).
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e71 Fig 2 SEM images of the dentin after Er:YAG laser treatments. (a) Treatment with Er:YAG laser alone; (b) treatment with Aqua Prep-F preceding Er:YAG laser irradiation; (c) treatment with BisBlock preceding Er:YAG laser irradiation; (d) treatment with Gluma preceding Er:YAG laser irradiation.
a
b
c
d
a
b
c
d
Fig 3 SEM images of the dentin after Nd:YAG laser treatments. (a) Treatment with Nd:YAG laser alone; (b) treatment with Aqua Prep-F preceding Nd:YAG laser irradiation; (c) treatment with BisBlock preceding Er:YAG laser irradiation; (d) treatment with Gluma preceding Nd:YAG laser irradiation.
Discussion This study revealed that dentin surface treatments used for de-
sensitizing patients before cementation with self-adhesive resin cement increase or do not change the bond strengths of conventional
cementation, except with respect to treatment with BisBlock and the combination treatment using an Nd:YAG laser and BisBlock. Both of
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e72 these showed, by a considerable margin, the lowest values among the surface treatments for desensitization. Although there is no significant difference between group NDL and the control group, the groups in which oxalate-containing desensitizer was used showed lower SBS values than did the control group. When acidic oxalates are applied to the dentin surface, it liberates calcium from the dentin to produce insoluble calcium oxalate crystals that block the dentinal tubules. Pashley and Galloway18 reported that if the dentin surface is treated with an oxalate solution, the hydraulic conductance is decreased, which can efficiently prevent dentin sensitivity. Gillam et al19 examined the surface and subsurface effects of four oxalatecontaining products, using a dentin disc method and qualitative SEM. According to that study, the oxalic acid–containing samples were apparently highly crystalline and did not match with any oxalate standards. Vachiramon et al20 examined BisBlock-containing oxalic acid and concluded that the application of oxalate with an etch-and-rinse twostep bonding system produced significantly lower long-term micro tensile bond strengths and enhanced nanoleakage. The results of the present study may be the result of not having a resin component, such as hydroxyethyl methacrylate (HEMA), as is the case with the other desensitizers used. However, in another study, Huh et al5 concluded that it would be better to limit the use of dentin desensitizers with a resin component when using them
before bonding the restoration with adhesive resin luting cement using self-etching primer. In the present study, however, dentin desensitizers with a resin component (Gluma and Aqua Prep-F) increased or did not change the SBS values of all ceramics cemented with selfadhesive resin cement compared with the control group, because of the HEMA content. Among the Gluma and the Aqua Prep-F groups containing HEMA, the Gluma showed a higher SBS value than the Aqua Prep-F. Sodium fluoride functions to desensitize patients because fluoride ions in the dentinal tubules cause microprecipitation of calcium fluoride crystals, which may act to block hydrodynamically mediated pain-inducing stimuli. Sarac et al21 demonstrated that an increase in the amount of fluoride in desensitizing agents decreased the bond strength of adhesive resin cement to dentin. They stated that an increase in precipitated crystals on the dentin surface, because of a higher amount of fluoride, resulted in lower SBS.21 On the other hand, the desensitizing mechanism of Gluma works by blocking the dentinal tubules through the coagulation of dentin fluid proteins in the dentinal tubules.22 The absence of the formation of precipitated crystals in the group G may explain why it has the highest SBS value among the groups treated with desensitizing agents (O, G, and F). When the laser application procedures were compared, the results showed that the Er:YAG laser was more successful than the Nd:YAG
laser in increasing the SBS of selfadhesive resin cement. Yazici et al23 demonstrated that SBS values did not differ after dentin hypersensitivity treatment with an Nd:YAG laser, whereas Ariyaratnam et al24 reported that the use of a laser did not have a negative influence on SBS. However, other studies showed that dentin irradiation with an Nd:YAG laser before the adhesive procedure resulted in a reduction in SBS with the resin composite.25 This effect was credited to the obliteration of the dentinal tubules by melting and resolidification of the irradiated dentin. On the other hand, Rolla et al26 reported that the irregularities formed by the use of Nd:YAG laser irradiation might have favored greater micromechanical retention for the self-etch adhesives than would be the case with nonirradiated dentin. In the present study, the SBS values did not differ after dentin hypersensitivity treatment with an Nd:YAG laser with a power of 1 W, which was used for the self-adhesive resin cement test. SEM images also proved that the surface of dentins treated with Nd:YAG laser (Fig 3) were smoother than those treated with desensitizing agents alone (Fig 1). However, there were no differences between the groups treated with and without Nd:YAG laser. The Nd:YAG laser reduces dentin hypersensitivity by melting the hydroxyapatite structure without harming the dentinal surface.11 Another suggested laser, the Er:YAG laser, treats hypersensitivity by decreasing fluid movements in dentin tubules by evaporating the superficial layers of the dentinal fluid or by
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e73 sealing the tubule orifices below the ablation threshold. It does this because of the high degree of absorption by water and hydroxyapatite.27 The effects of dentin and resin cements on bonding are as important as their effect on hypersensitivity, and they are able to be used after veneer or crown preparation. Many studies have reported the effect of lasers on bonding systems.24–26 Yazici et al23 studied the effects of Er:YAG and Nd:YAG laser hypersensitivity treatment parameters on the SBS of self-etch adhesives. They concluded that the parameters used for dentin hypersensitivity treatment of both coronal and root dentin substrates, either with an Er:YAG laser or an Nd:YAG laser, did not affect the SBS of the selfetch adhesives. However, the present study showed that although Nd:YAG treatment did not change the SBS of self-adhesive resin cement, the Er:YAG laser enhanced the SBS values, with the same laser parameters used by Yazici et al.23 The present study used self-adhesive resin cement differently. Self-adhesive cements do not require any pretreatment of the tooth surface. The morphologic findings at the cement/dentin interface formed by self-adhesive cements were noticeably different in comparison with the interface formed with resin cements that require pretreatment of the dentin surface.28,29 Self-adhesive cements contain acidic monomers that etch dentin without opening dentin tubules. During this process, the smear layer is incorporated into the shallow hybrid layer, which could reduce POS.28,29
Many studies have evaluated treatments that use the combined effects of a laser and chemical agents.12–16 Most concluded that such treatments produce more marked occlusions in dentinal tubules and increase the duration of the desensitizing effect.12,13,16 Among the combination treatment groups, SBS values of all the Er:YAG treatment groups were higher than those produced by the Nd:YAG laser. The SEM images clearly showed that the dentin surfaces treated with Er:YAG lasers (Fig 2) were flaky and craggy whereas the surfaces treated with Nd:YAG lasers (Fig 3) were smooth and flat. All the SBS values of the Er:YAG combined groups were higher than those produced by treatment with desensitizing agents alone. That is obviously because of water and hydroxyapatite exposure, which results in opening of the tubules made by the Er:YAG laser. On the other hand, among the Nd:YAG combined groups, the SBS values did not change when the teeth were treated with desensitizing agents alone, except for those containing glutaraldehyde. The SBS value of the group treated with Gluma decreased when combined with the Nd:YAG laser. Gluma does not cause microprecipitation of any crystals. Thus, when combined with the Nd:YAG laser, the HEMA contained in Gluma may become effaced, and this may be the reason for the decrease in the SBS value. The present study evaluated the SBS values of desensitizing treatments and compared dentine with self-adhesive resin cement.
According to this study, it cannot be said whether this technique is useful and clinically preferable or not. There is still a considerable need for further clinical studies to evaluate the desensitizing effects of these treatments.
Conclusions Within the limitations of this study, the results seem to suggest that: •
•
•
Among the desensitizing treatments used in the study, Gluma preceding an Er:YAG laser treatment showed the highest increase in bonding between the cement and dentin. All the combined groups with the Er:YAG laser showed higher SBS values than either treatment alone. Thus, combined treatment of desensitizing agents with an Er:YAG laser is preferable to either treatment alone for desensitizing before cementation. When compared with the Nd:YAG laser, the Er:YAG laser increased the SBS values.
Acknowledgments The authors reported no conflicts of interest related to this study.
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e74 References 1. Wat P, Cheung GS. Incidence of postoperative sensitivity following indirect porcelain onlay restorations: Preliminary results. Asian J Aesthet Dent.1995;3:3–7. 2. Chermont AB, Carneiro MK, Lobato MF, Machado SMM, Souza Junior MHS. Clinical evaluation of postoperative sensitivity using self-etching adhesives containing glutaraldehyde. Braz Oral Res 2010;24:349–354. 3. Carvalho RM, Pegoraro TA, Tay FR, et al. Adhesive permeability affects coupling of resin cements that utilise self-etching primers to dentine. J Dent 2004;32:55–65. 4. Mordan NJ, Barber PM, Gillam DG. The dentine disc: A review of its applicability as a model for the in vitro testing of dentine hypersensitivity. J Oral Rehabil 1997;24:148–156. 5. Huh JB, Kim JH, Chung MK, et al. The effect of several dentin desensitizers on shear bond strength of adhesive resin luting cement using self-etching primer. J Dent 2008;36:1025–1032. 6. Johnson GH, Lepe X, Bales DJ. Crown retention with use of a 5% glutaraldehyde sealer on prepared dentin. J Prosthet Dent 1998;6:671–676. 7. Wolfart S, Linnemann J, Kern M. Crown retention with use of different sealing systems on prepared dentine. J Oral Rehabil 2003;30:1053–1061. 8. Yim NH, Rueggeberg FA, Caughman WF, Gardner FM, Pashley DH. Effect of dentin desensitizers and cementing agents on retention of full crowns using standardized crown preparations. J Oral Rehabil 2003;30:1053–1061. 9. Orchardson R, Gillam DG. Managing dentin hypersensitivity. J Am Dent Assoc 2006;137:990–998. 10. Dababneh RH, Khouri AT, Addy M. Dentin Hypersensitivity: An enigma? A review of terminology, epidemiology, mechanisms, aetiology and management. Br Dent J 1999;187:606–611.
11. Kimura Y, Wilder-Smith P, Yonaga K, Matsumoto K. Treatment of dentine hypersensitivity by lasers: A review. J Clin Periodontol 2000; 27:715–721. 12. Kumar NG, Mehta DS. Short-term assessment of the Nd-YAG laser with and without sodium fluoride varnish in the treatment of dentin hypersensitivity: A clinical and scanning electron microscopy study. J Periodontol 2005;76:1140–1147. 13. Hsu PJ, Chen JH, Chuang FH, Roan RT. The combined occluding effects of fluoride-containing dentin desensitizer and Nd-YAG laser irradiation on human dentinal tubules: An in vitro study. Kaohsiung J Med Sci 2006;22:24–29. 14. Al-Saud LM, Al-Nahedh HN. Occluding effect of Nd:YAG laser and different dentin desensitizing agents on human dentinal tubules in vitro: A scanning electron microscopy investigation. Oper Dent 2012; 37:340–355. 15. Femiano F, Femiano R, Lanza A, et al. Efficacy of diode laser in association to sodium fluoride vs Gluma desensitizer on treatment of cervical dentin hypersensitivity. A double blind controlled trial. Am J Dent 2013;26:214–218. 16. Cakar G, Kuru B, Ipci SD, et al. Effect of Er:YAG and CO2 lasers with and without sodium fluoride gel on dentinal tubules: A scanning electron microscope examination. Photomed Laser Surg 2008;6:565–571. 17. Birang R, Poursamimi J, Gutknecht N, Lampert F, Mir M. Comparative evaluation of the effects of Nd:YAG and Er:YAG laser in dentin hypersensitivity treatment. Lasers Med Sci 2007; 22:21–24. 18. Pashley DH, Galloway SE. The effect of oxalate treatment on the smear layer of ground surfaces of human dentin. Archives of Oral Biology 1985;30:731–737. 19. Gillam DG, Mordan NJ, Sınodınou AD, et al. The effects of oxalate-containing products on the exposed dentine surface: An SEM investigation. J Oral Rehabil 2001;28:1037–1044.
20. Vachiramon V, Vargas MA, Pashley DH, et al. Effects of oxalate on dentin bond after 3-month simulated pulpal pressure. J Dent 2008;36:178–185. 21. Sarac D, Kulunk S, Sarac YS, Karakas O. Effect of fluoride-containing desensitizing agents on the bond strength of resinbased cements to dentin. J Appl Oral Sci 2009;17:495–500. 22. Felton D, Bergenholtz G, Cox CF. Inhibition of bacterial growth under composite restorations following Gluma pretreatment. J Dent Res 1989;68:491–495. 23. Yazici E, Gürgan S, Gutknecht N, Imazato S. Effects of erbium:yttrium–aluminum– garnet and neodymium:yttrium–aluminum–garnet laser hypersensitivity treatment parameters on the bond strength of self-etch adhesives. Lasers Med Sci 2010; 25:511–516. 24. Ariyaratnam MT, Wilson MA, Blinkhorn SA. 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;15:223–228. 25. Franke M, Taylor AW, Lago A, Fredel MC. Influence of Nd:YAG laser irradiation on an adhesive restorative procedure. Oper Dent 2006;31:604–609. 26. Rolla JN, Mota EG, Oshimi HMS, Junior LHB, Spohr AM. Nd:YAG laser influence on microtensile bond strength of different adhesive systems for human dentin. Photomed Laser Surg 2006;24:730–734. 27. Schwarz F, Arweiler N, Georg T, Reich E. Desensitizing effects of an Er:YAG laser on hypersensitive dentin: A controlled, prospective clinical study. J Clin Periodontol 2002;29:211–215. 28. Radovic I, Monticelli F, Goracci C, Vulicevic ZR, Ferrari M. Self-adhesive resin cements: A literature review. J Adhes Dent 2008;10:251–258. 29. Burgess JO, Ghuman T, Cakır D. Critical appraisal; Self-adhesive resin cements. J Esthet Restor Dent 2010;22:412–419.
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Effects of Dentin Surface Treatments on Hypersensitivity to Bond Strength of Restorations: An In Vitro Study Ayça Tulga, DDS, PhD1 Duygu Saraç, DDS, PhD2
This study evaluated the effects of desensitizing treatments on the shear bond strength (SBS) of adhesive resin cement (Rely X U100) applied to dentin. Human molars (n = 120) with exposed dentin were divided into 12 groups. In the experimental groups, dentin surfaces were treated with (1) an erbium:yttrium– aluminium–garnet (Er:YAG) laser, (2) a neodymium:yttrium–aluminium–garnet (Nd:YAG) laser, (3) glutaraldehyde (Gluma)–, (4) fluoride (Aqua Prep-F)–, and (5) oxalate (BisBlock)–containing desensitizing agents, (6) Gluma preceding the Er:YAG laser, (7) Aqua Prep-F preceding the Er:YAG laser, (8) BisBlock preceding the Er:YAG laser, (9) Gluma preceding the Nd:YAG laser, (10) Aqua Prep-F preceding the Nd:YAG laser, (11) and BisBlock preceding the Nd:YAG laser, in groups EL, NL, G, F, O, EL-G, EL-F, EL-O, NL-G , NL-F, and NL-O, respectively. Then, lithium disilicate ceramics were cemented to the treated surfaces. Subsequently, an SBS test was performed and the data were statistically analyzed (α = .001). The results suggested that the combined treatment of Gluma preceding Er:YAG laser increased the bond strength of ceramic to the dentin surface using a self-adhesive resin cement. (Int J Periodontics Restorative Dent 2015;35:e66–e74. doi: 10.11607/prd.2194)
Assistant Professor, Department of Prosthodontics, Faculty of Dentistry, Univeristy of Ordu, Ordu, Turkey. 2Professor, Department of Prosthodontics, Faculty of Dentistry, University of Ondokuz Mayıs, Samsun, Turkey. 1
Correspondence to: Ayça Tulga, Department of Prosthodontics, Dental Faculty of Ordu University, 52200 Ordu, Turkey. Fax: +0 (452) 212 12 89. Email: [email protected] ©2015 by Quintessence Publishing Co Inc.
Dentin hypersensitivity is one of the most common complaints in clinical dentistry for which there is still no effective solution. It is particularly after the preparation of teeth for allceramic restorations that patients complain of postoperative sensitivity (POS).1 In addition, restoration and cementation of the adhesive cause POS associated with an increase in dentin permeability and with the residual stresses from shrinkage in adhesive/composite resin restorations. This may cause debonding and/or cusp deformation.2–4 Adhesive resin luting cements are widely used in many restorations. The internal bond between the adhesive luting cement and the dentin is an important factor that prevents microleakage and ensures retention of the restoration. POS is occasionally associated with the use of etch-and-rinse adhesives. In an attempt to reduce sensitivity, selfetching primer systems have been developed. Several desensitizing agents containing oxalate, gluteraldehyde, or resin have been advocated for sealing dentin before cementation of all-ceramic or cast restorations, to decrease POS.5–8 Various types of dentin desensitizers have been used to alleviate pain caused by dentinal sensitivity.4,9–11 These can be classified into several main groups: neural stimulus blockers, anti-inflammatory
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e67 drugs, protein precipitants, tubuleoccluding agents, and tubule sealants and lasers. Generally, the preferred desensitizers in dental clinics are protein precipitants, tubule-occluding agents, and tubule sealants and lasers.9,11 Nowadays, treatments combining chemical desensitizers with lasers are very popular.12–16 Hsu et al13 studied the combined effect of using a fluoride-containing desensitizing agent with an Nd:YAG laser on dentinal tubules. They found a much greater reduction in the number/patency of tubules when compared with either treatment alone. Similarly, in 2005, Kumar and Mehta12 observed that most dentinal tubule orifices were occluded after combined treatment with a neodymium: yttrium-aluminiumgarnet (Nd:YAG) laser and a sodium fluoride varnish. They also showed that the more marked were the occlusions in dentinal tubules, the greater was the decrease in dentin hypersensitivity obtained by using a combination of laser treatment with a desensitizing agent. But what of the effects of combined treatments on the bonding strength between dentin and the restoration? Many previous studies5–8 concluded that desensitizers decrease the bonding strength, but the data in most of these studies were obtained by looking at the desensitizing treatments alone, and not combined with laser treatment. Thus, a considerable need remains for comparison studies on the bonding effects of desensitizing treatments alone and the effects of combined treatments.
The aim of this study was to evaluate the effects of oxalate-, fluoride-, and glutaraldehydecontaining desensitizing agents; Nd:YAG and erbium: yttriumaluminum-garnet (Er:YAG) lasers; and their combinations on the shear bond strength (SBS) of selfadhesive resin cement when used with dentin.
Method and materials Preparation of tooth specimen
One hundred and twenty human molars extracted within a period of 1 month were used. The criteria for choosing the teeth were as follows: (1) maxillary and mandibular molars were used to gain a larger area of dentin, and (2) teeth with caries were excluded to reduce the variability. The collected teeth were cleaned of periodontal tissue residues with a scaler, stored in 0.5% chloramine-T at room temperature for a maximum of 7 days, and then stored in distilled water at 5°C. The clinical crowns were removed up to 2 mm below the buccal cementoenamel junction using a diamond wafering blade (Isomed, Buehler) under a copious water spray. The selected teeth were embedded in acrylic resin (Paladent RR, Heraeus Kulzer) custom-made, cylinder-shaped Teflon (DuPont) molds with a diameter of 30 mm and height of 20 mm. The specimens were prepared until the dentin was exposed using a Model Trimmer (Whip Mix). The teeth were carefully prepared so that
the exposed dentin surface was parallel to the acrylic resin mold, without exposing the pulp. They were ground using wet 320 grit silicon carbide abrasive paper. The prepared teeth were washed with pumice with a low-speed handpiece to remove the contaminants acquired during preparation, and they were immersed in distilled water to supply enough moisture to the exposed dentin surface. The 120 specimens were randomly divided into 12 groups: a control group and 11 experimental groups of 10 teeth each.
Fabrication of all-ceramic specimens
Lithium-based all-ceramic specimens (IPS e.max Press, Ivoclar Vivadent) (N = 120; 5 mm in diameter; 2 mm in height) were fabricated according to the lost-wax technique recommended by the manufacturer, and ingots were injected into an EP 600 furnace (Ivoclar Vivadent). Disc surfaces were ground with 100-, 220-, and 400-grit silicon carbide sandpaper to standardize the bonding surfaces without changing the geometric shape of the discs. Cementation surfaces were air particle–abraded with 110-μm aluminum trioxide at 2 bar air pressure for a period of 10 seconds from a distance of approximately 10 mm, and then ultrasonically cleaned (Sonorex, Bandeline) for 5 minutes in deionized water.
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e68
Table 1 Desensitizing agents used in the study and their application procedures Agent
Composition
Manufacturer
Application procedure
BisBlock
1%–4% oxalic acid
Bisco
Total-etch for 15 seconds, rinse and dry, apply BisBlock for 30 seconds, rinse and leave moist, apply self-etch resin cement
Aqua Prep-F
35% 2-hydroxymetyl Methacrilate (HEMA), 2% sodium fluoride
Bisco
Total-etch for 15 seconds, rinse and dry, apply BisBlock for 30 seconds, rinse and leave moist, apply self-etch resin cement
Gluma
35% (2-hydroxyethyl) methacrylate, water, 5% glutaraldehyde
Heraeus Kulzer
Apply on dried dentin and leave for 30–60 seconds, dry and spray with air, apply self-etch resin cement.
Table 2 Descriptions of the groups Dentin surface treatments Desensitizing agent treatment Test groups (N = 120)
Fluoride Oxalate (Aqua Prep-F) (BisBlock)
Laser treatment
Glutaraldehyde (Gluma)
Er:YAG Laser—60 s/cm2 with 3 Hz and 100 mJ with coolant
Nd:YAG laser—60 s/cm2 with 15 Hz and 1 W laser without coolant
Group C (control)
–
–
–
–
–
Group EL
–
–
–
+
–
Group NL
–
–
–
–
+
Group O
–
+
–
–
–
Group F
+
–
–
–
–
Group G
–
–
+
–
–
Group OEL
–
+
–
+
–
Group FEL
+
–
–
+
–
Group GEL
–
–
+
+
–
Group ONL
–
+
–
–
+
Group FNL
+
–
–
–
+
Group GNL
–
–
+
–
+
EL = Er:YAG; NL = Nd:YAG; O = oxalate; F = fluoride; G = glutaraldehyde; OEL = oxalate preceding EL; FEL = fluoride preceding EL; GEL = glutaraldehyde preceding EL; ONL = oxalate preceding NL; FNL = fluoride preceding NL; GNL = glutaraldehyde preceding NL. + = Procedure was applied. – = Procedure was not applied.
Application of the dentin desensitizer to the tooth specimen
Table 1 lists the dentin desensitizers used for the surface treatment. The dentin desensitizers were applied to the categorized specimens
according to the manufacturers’ instructions. The exposed dentin surfaces of the control group were not treated. Each of these dentin desensitizers was applied to 30 teeth specimens. Thus, a total of 90 teeth were treated with desensitizers.
Laser application
All treatments were done using a Fotona AT Fidelis machine. Four of the experimental groups were irradiated with an Nd:YAG laser; of these, three were combined with desensitizing agents (Table 2). The
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e69 teeth in the Nd:YAG groups (NL, ONL, FNL, GNL) were irradiated twice for 60 seconds/cm2 with 15 Hz and 1 W laser without coolant.17 The other four experimental groups were irradiated with an Er:YAG laser. Three of these were combined with desensitizing agents (Table 2). The teeth in the Er:YAG groups (EL, OEL, FEL, GEL) were irradiated twice for 60 seconds/cm2 with 3 Hz and 100 mJ with coolant, in very low power mode and with an RO7 handpiece.17
Cementation procedure
The ceramic specimens were etched with 5% hydrofluoric acid (Ceramic Etching Gel, Ivoclar Vivadent) for 20 seconds, washed and rinsed thoroughly, air-dried and silanized (Monobond-S, Ivoclar Vivadent). The reaction time of the silane-coupling agent was 60 seconds for both resin groups. Then the self-adhesive resin cement (RelyX U100, 3M Espe) was applied in a thin layer, gently airblown, and photopolymerized with a light-emitting diode photopolymerization unit (Hilux Led-max 550, Benlioglu Dental) for 20 seconds, with a constant distance of 2 mm from the surface. During the polymerization procedure, specimens were processed using a universal testing device (Lloyd LRX, Lloyd Instruments) under 8 kg for 3 minutes. The cemented specimens were then stored in distilled water at 37°C for 24 hours.
Table 3 One-way analysis of variance of force (megapascals) required to debond Empress 2 ceramics from dentin surfaces Sum of squares
df
Mean square
F
Significance
37.921
0.001
Between groups
415.941
11
37.813
Within groups
107.692
108
0.997
Total
523.633
119
SBS test
The specimens were thermocycled 500 times between 5°C and 55°C for a period of 30 seconds. The SBS test was performed with the universal testing device at a crosshead speed of 0.5 mm/second. The SBS values were calculated in megapascals.
Analysis
The specimens were examined under a field-emission scanning electron microscope (SEM) (JSM-6335F, Jeol) at 20.0 kV. The SEM photomicrographs were taken at 2,000× magnification for visual inspection. One-way analysis of variance (ANOVA) was used to determine significant differences among dentin surface treatments. All mean SBS values for treatment combinations were compared using the Tukey multiple comparison test.
Results The results of the one-way ANOVA are shown in Table 3. The mean SBS, minimum and maximum values, and standard deviations (SDs) for each
group are presented in Table 4. The failure modes were all adhesive. The SBS was lowest in the group that received the oxalate (O; BisBlock, Bisco; 4.36 MPa), which showed significantly lower SBS than any of the other groups except the group treated with oxalate preceding the Nd:YAG laser (ONL; 5.03 MPa). The SBS values were highest in the group treated with glutaraldehyde preceding the Er:YAG laser (GEL) (11.22 MPa), which was significantly higher than all of the other groups (P < .001). The SBS values were lower in the groups treated with the Nd:YAG laser (NL), fluoride (F; Aqua Prep-F, Bisco), oxalate preceding the Er:YAG laser (OEL), and fluoride preceding the Nd:YAG laser (FNL) than in the control group (7.51 MPa), but the differences were not statistically significant. The SBS values obtained with the EL, fluoride preceding the Er:YAG laser (FEL), and glutaraldehyde (G; Gluma, Heraeus Kulzer) groups were significantly higher than those of the control group. The differences among the three groups were not statistically significant (9.53 MPa, 9.42 MPa, and 9.36 MPa, respectively).
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e70
Table 4
Mean shear bond strengths, standard deviations (SDs), minimum (Min) and maximum (Max) values for each group (n = 10)
Dentin surface treatment
Group
Mean*
SD
Min
Max
Control
C
7.51 A
1.39
4.60
9.50
Er:YAG laser
EL
9.53 B
0.91
7.80
10.80
Nd:YAG laser
NL
6.66 A
0.65
5.20
7.40
Oxalate
O
4.36 C
0.90
3.10
5.70
Fluoride
F
7.04 A
0.53
6.20
7.70
Glutaraldehyde
G
9.36 B
1.45
7.10
11.90
Oxalate + Er:YAG
OEL
7.24 A
0.99
6.10
8.40
Fluoride + Er:YAG
FEL
9.42 B
0.80
8.30
10.50
Glutaraldehyde + Er:YAG
GEL
1.57
8.60
13.40
Oxalate + Nd:YAG
ONL
5.03 C
0.82
3.80
6.20
Fluoride + Nd:YAG
FNL
7.41 A
0.61
6.50
8.30
Glutaraldehyde + Nd:YAG
GNL
7.80 A
0.70
6.60
8.60
11.22
*Means for groups having the same letters show homogenous subsets, α = .001. EL = Er:YAG; NL = Nd:YAG; O = oxalate; F = fluoride; G = glutaraldehyde; OEL = oxalate preceding EL; FEL = fluoride preceding EL; GEL = glutaraldehyde preceding EL; ONL = oxalate preceding NL; FNL = fluoride preceding NL; GNL = glutaraldehyde preceding NL.
a
b
c
d
Fig 1 SEM images of the dentin after surface treatments with different desensitizing agents. (a) Control group; (b) treatment with Aqua Prep-F; (c) treatment with BisBlock; (d) treatment with Gluma. None of these groups received any laser treatments.
Of the groups using desensitizing agent treatments alone (O, F, G), the SBS value was highest in group G (9.36 MPa) and lowest in group O (4.36 MPa) (P < .001). Of the groups that received the Er:YAG laser treatment (EL, OEL, FEL, GEL), the SBS value was highest in group GEL (11.22 MPa), and lowest in group OEL (7.24 MPa) (P < .001). Of the groups that received the Nd:YAG laser treatment (NL, ONL, FNL, GNL), the SBS value was highest in group GNL (7.80 MPa) and lowest in group ONL (5.03 MPa) (P < .001). The SEM images are shown in Figs 1 to 3. Of the groups that used desensitizing agent treatments alone (O, F, and G), although the control group and group G showed similar surfaces covered with smear layer, dentin tubules were marked in groups F and O because of the application procedures of Aqua Prep-F and BisBlock (Fig 1). Because of the resin contained in Gluma, a resin film layer was seen on the dentin surface of group G (Fig 1d). The SEM images of the groups that received the Er:YAG laser treatment (EL, OEL, FEL, GEL) showed similar figures like flaky irregularities except for the calcification points around the dentin tubules seen in groups OEL and FEL (Fig 2). The photomicrographs of the groups that received the Nd:YAG laser treatments (NL, ONL, FNL, GNL) were similar to those in the groups without laser treatment (C, O, F, G) but the dentin surfaces were smoother in groups treated with the Nd:YAG laser (Fig 3).
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e71 Fig 2 SEM images of the dentin after Er:YAG laser treatments. (a) Treatment with Er:YAG laser alone; (b) treatment with Aqua Prep-F preceding Er:YAG laser irradiation; (c) treatment with BisBlock preceding Er:YAG laser irradiation; (d) treatment with Gluma preceding Er:YAG laser irradiation.
a
b
c
d
a
b
c
d
Fig 3 SEM images of the dentin after Nd:YAG laser treatments. (a) Treatment with Nd:YAG laser alone; (b) treatment with Aqua Prep-F preceding Nd:YAG laser irradiation; (c) treatment with BisBlock preceding Er:YAG laser irradiation; (d) treatment with Gluma preceding Nd:YAG laser irradiation.
Discussion This study revealed that dentin surface treatments used for de-
sensitizing patients before cementation with self-adhesive resin cement increase or do not change the bond strengths of conventional
cementation, except with respect to treatment with BisBlock and the combination treatment using an Nd:YAG laser and BisBlock. Both of
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e72 these showed, by a considerable margin, the lowest values among the surface treatments for desensitization. Although there is no significant difference between group NDL and the control group, the groups in which oxalate-containing desensitizer was used showed lower SBS values than did the control group. When acidic oxalates are applied to the dentin surface, it liberates calcium from the dentin to produce insoluble calcium oxalate crystals that block the dentinal tubules. Pashley and Galloway18 reported that if the dentin surface is treated with an oxalate solution, the hydraulic conductance is decreased, which can efficiently prevent dentin sensitivity. Gillam et al19 examined the surface and subsurface effects of four oxalatecontaining products, using a dentin disc method and qualitative SEM. According to that study, the oxalic acid–containing samples were apparently highly crystalline and did not match with any oxalate standards. Vachiramon et al20 examined BisBlock-containing oxalic acid and concluded that the application of oxalate with an etch-and-rinse twostep bonding system produced significantly lower long-term micro tensile bond strengths and enhanced nanoleakage. The results of the present study may be the result of not having a resin component, such as hydroxyethyl methacrylate (HEMA), as is the case with the other desensitizers used. However, in another study, Huh et al5 concluded that it would be better to limit the use of dentin desensitizers with a resin component when using them
before bonding the restoration with adhesive resin luting cement using self-etching primer. In the present study, however, dentin desensitizers with a resin component (Gluma and Aqua Prep-F) increased or did not change the SBS values of all ceramics cemented with selfadhesive resin cement compared with the control group, because of the HEMA content. Among the Gluma and the Aqua Prep-F groups containing HEMA, the Gluma showed a higher SBS value than the Aqua Prep-F. Sodium fluoride functions to desensitize patients because fluoride ions in the dentinal tubules cause microprecipitation of calcium fluoride crystals, which may act to block hydrodynamically mediated pain-inducing stimuli. Sarac et al21 demonstrated that an increase in the amount of fluoride in desensitizing agents decreased the bond strength of adhesive resin cement to dentin. They stated that an increase in precipitated crystals on the dentin surface, because of a higher amount of fluoride, resulted in lower SBS.21 On the other hand, the desensitizing mechanism of Gluma works by blocking the dentinal tubules through the coagulation of dentin fluid proteins in the dentinal tubules.22 The absence of the formation of precipitated crystals in the group G may explain why it has the highest SBS value among the groups treated with desensitizing agents (O, G, and F). When the laser application procedures were compared, the results showed that the Er:YAG laser was more successful than the Nd:YAG
laser in increasing the SBS of selfadhesive resin cement. Yazici et al23 demonstrated that SBS values did not differ after dentin hypersensitivity treatment with an Nd:YAG laser, whereas Ariyaratnam et al24 reported that the use of a laser did not have a negative influence on SBS. However, other studies showed that dentin irradiation with an Nd:YAG laser before the adhesive procedure resulted in a reduction in SBS with the resin composite.25 This effect was credited to the obliteration of the dentinal tubules by melting and resolidification of the irradiated dentin. On the other hand, Rolla et al26 reported that the irregularities formed by the use of Nd:YAG laser irradiation might have favored greater micromechanical retention for the self-etch adhesives than would be the case with nonirradiated dentin. In the present study, the SBS values did not differ after dentin hypersensitivity treatment with an Nd:YAG laser with a power of 1 W, which was used for the self-adhesive resin cement test. SEM images also proved that the surface of dentins treated with Nd:YAG laser (Fig 3) were smoother than those treated with desensitizing agents alone (Fig 1). However, there were no differences between the groups treated with and without Nd:YAG laser. The Nd:YAG laser reduces dentin hypersensitivity by melting the hydroxyapatite structure without harming the dentinal surface.11 Another suggested laser, the Er:YAG laser, treats hypersensitivity by decreasing fluid movements in dentin tubules by evaporating the superficial layers of the dentinal fluid or by
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e73 sealing the tubule orifices below the ablation threshold. It does this because of the high degree of absorption by water and hydroxyapatite.27 The effects of dentin and resin cements on bonding are as important as their effect on hypersensitivity, and they are able to be used after veneer or crown preparation. Many studies have reported the effect of lasers on bonding systems.24–26 Yazici et al23 studied the effects of Er:YAG and Nd:YAG laser hypersensitivity treatment parameters on the SBS of self-etch adhesives. They concluded that the parameters used for dentin hypersensitivity treatment of both coronal and root dentin substrates, either with an Er:YAG laser or an Nd:YAG laser, did not affect the SBS of the selfetch adhesives. However, the present study showed that although Nd:YAG treatment did not change the SBS of self-adhesive resin cement, the Er:YAG laser enhanced the SBS values, with the same laser parameters used by Yazici et al.23 The present study used self-adhesive resin cement differently. Self-adhesive cements do not require any pretreatment of the tooth surface. The morphologic findings at the cement/dentin interface formed by self-adhesive cements were noticeably different in comparison with the interface formed with resin cements that require pretreatment of the dentin surface.28,29 Self-adhesive cements contain acidic monomers that etch dentin without opening dentin tubules. During this process, the smear layer is incorporated into the shallow hybrid layer, which could reduce POS.28,29
Many studies have evaluated treatments that use the combined effects of a laser and chemical agents.12–16 Most concluded that such treatments produce more marked occlusions in dentinal tubules and increase the duration of the desensitizing effect.12,13,16 Among the combination treatment groups, SBS values of all the Er:YAG treatment groups were higher than those produced by the Nd:YAG laser. The SEM images clearly showed that the dentin surfaces treated with Er:YAG lasers (Fig 2) were flaky and craggy whereas the surfaces treated with Nd:YAG lasers (Fig 3) were smooth and flat. All the SBS values of the Er:YAG combined groups were higher than those produced by treatment with desensitizing agents alone. That is obviously because of water and hydroxyapatite exposure, which results in opening of the tubules made by the Er:YAG laser. On the other hand, among the Nd:YAG combined groups, the SBS values did not change when the teeth were treated with desensitizing agents alone, except for those containing glutaraldehyde. The SBS value of the group treated with Gluma decreased when combined with the Nd:YAG laser. Gluma does not cause microprecipitation of any crystals. Thus, when combined with the Nd:YAG laser, the HEMA contained in Gluma may become effaced, and this may be the reason for the decrease in the SBS value. The present study evaluated the SBS values of desensitizing treatments and compared dentine with self-adhesive resin cement.
According to this study, it cannot be said whether this technique is useful and clinically preferable or not. There is still a considerable need for further clinical studies to evaluate the desensitizing effects of these treatments.
Conclusions Within the limitations of this study, the results seem to suggest that: •
•
•
Among the desensitizing treatments used in the study, Gluma preceding an Er:YAG laser treatment showed the highest increase in bonding between the cement and dentin. All the combined groups with the Er:YAG laser showed higher SBS values than either treatment alone. Thus, combined treatment of desensitizing agents with an Er:YAG laser is preferable to either treatment alone for desensitizing before cementation. When compared with the Nd:YAG laser, the Er:YAG laser increased the SBS values.
Acknowledgments The authors reported no conflicts of interest related to this study.
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