Eur Arch Paediatr Dent DOI 10.1007/s40368-014-0127-y
ORIGINAL SCIENTIFIC ARTICLE
Comparative evaluation in vitro of caries inhibition potential and microtensile bond strength of two fluoride releasing adhesive systems A. R. Prabhakar • K. Dhanraj • S. Sugandhan
Received: 22 January 2014 / Accepted: 1 April 2014 Ó European Academy of Paediatric Dentistry 2014
Abstract Aim To evaluate and compare the caries inhibition potential and tensile bond strength of two commercially available fluoride releasing adhesive systems over conventional adhesive systems. Methods Artificial carious lesions were produced on the buccal surfaces of human molars and treated with experimental adhesive systems: Optibond Solo PlusÒ, One-UpÒ Bond F Plus and G-BONDÒ (control). The caries inhibition potential and the tensile bond strength were measured at 24 h and 3 months, respectively. Results At 24 h and 3 months, Optibond Solo PlusÒ and One-UpÒ Bond F Plus had higher caries inhibition potential over the control group, which was statistically significant. At 3 months, no statistically significant difference was noted between the fluoride releasing adhesives. OneUp Bond F Plus had higher bond strength values than other groups which was statistically significant at 24 h, whereas at the end of 3 months, Optibond Solo Plus had higher bond strength values than other groups which were statistically significant. Statistics The recorded values were statistically analysed using Paired t test, ANOVA followed by Post hoc Tukey’s test. Conclusions Fluoride releasing adhesive systems were effective in caries inhibition and showed comparatively higher bond strength values than the conventional adhesive systems in vitro.
A. R. Prabhakar (&) K. Dhanraj S. Sugandhan Department of Pedodontics and Preventive Dentistry, Bapuji Dental College and Hospital, Davangere 577004, Karnataka, India e-mail: [email protected]
Keywords Caries Fluoride Demineralisation Remineralisation Adhesive systems
Introduction Fluoride is well documented as an anti-cariogenic agent. A variety of mechanisms are involved in the anti-cariogenic effects of fluoride, including the reduction of demineralisation, the enhancement of remineralisation, the interference of pellicle and plaque formation and the inhibition of microbial growth and metabolism (Hamilton and Bowden 1996; Rølla and Ekstrand 1996; ten Cate and Featherstone 1996). Fluoride released from dental restorative materials is assumed to affect caries formation through all these mechanisms and may therefore reduce or prevent demineralisation and promote remineralisation of dental hard tissues (Wiegand et al. 2007). Currently, resin composites combined with an adhesive system are widely used for direct restorations in children because of excellent aesthetics and acceptable mechanical properties. Secondary caries has been reported as being the most common reason for replacement of these restorations. The observation that secondary caries formation rarely being associated with fluoride-containing silicate cement restorations has led to increasing attention on the development of various fluoride releasing products used as restorative materials (De Munck et al. 2005). Recently, fluoride-releasing adhesives have been developed and are available in the market. These adhesives are expected to inhibit secondary caries by simultaneously promoting adhesion to tooth substrate and releasing fluoride ions (Itota et al. 2002). As fluoride releasing adhesives directly contact the cavity wall, fluoride ions released from them easily penetrate and diffuse into the cavity wall
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dentine, Enhancing mineralisation of the dentine and reducing its possible demineralisation. Therefore, penetration by fluoride ions offers resistance against secondary caries attack (Damen et al. 1998). The aim of the present study was to evaluate and compare in vitro the caries inhibition potential and microtensile bond strength of two fluoride-releasing adhesive systems.
Materials and method Two commercially available fluoride-releasing bonding agents, namely Optibond Solo PlusÒ (Kerr & Co., USA), One UpÒ Bond F Plus (Tokuyama Dental Corporation., Tokyo, Japan) were used. The control used was G-Bond (GC Asia, Tokyo, Japan.). Human third molars (60), with no evidence of caries or restorations, freshly extracted for therapeutic reasons were selected and stored in physiological saline solution containing 0.1 % thymol (Shinohara et al. 2009).
photographed at 109 magnification using an Olympus dual stage polarised light microscope (Model BX-51, Dual Mont Corporation, Minneapolis, Minn) (Shinohara et al. 2009). The depth of artificial lesion was quantified at 3 points i.e. from the surface of the lesion to the depth of the lesion, at D1, D2 and D3 to avoid errors so that mean value of the depth of the lesion could be considered for statistical analysis, using a computerised digital imaging system, Image Pro-PlusÒ (Todd et al. 1999). The experimental halves of each tooth specimens were subjected to three commercially available adhesives: Optibond Solo PlusÒ, One Up BondÒF Plus and the control being G-BONDÒ and restored with Filtek Z250. These restored teeth specimens were subjected to the pH cycling regimen of longitudinal sections of the cavity were again quantified for the decrease in the depth of the lesion using computerised digital imaging system, as described for the control specimens. This procedure was performed for a period of 24 h and 3 months, respectively. Microtensile bond strength
Caries inhibition potential Of the 60 human third molars that were free of caries and restorations with no evidence of white spots or cracks on buccal or lingual surfaces 30 were selected. Standardised Class V cavities of dimensions 3 mm 9 2 mm were prepared on the buccal surfaces of the teeth 1 mm from the CEJ. After the application of acid resistant nail varnish except for a window, these teeth were subjected to pH cycling regimen. To simulate dentinal caries, an artificial caries model was designed which consisted of 2.2 mM Ca2?, 2.2 mM PO43-, 50 mM glacial acetic acid at a pH of 4.8. The solution was kept at a constant temperature of 37 °C in an incubator for 4 days and the experimental specimens were exposed to a daily pH cycling regimen for 14 days with 8 h in demineralising and 16 h in remineralising solutions, respectively (Marquezan et al. 2009). The teeth were randomly selected into three different groups of ten each. After subjecting to pH cycling, the specimens were sectioned bucco-lingually such and one half was used for the quantification of depth of the carious lesion (control) and the other half is subjected for the treatment with adhesives (test). Control specimens were embedded on acrylic blocks and sections of 140–160 lm thickness were obtained by cutting through the centre of the cavity using a Silverstone-Taylor hard tissue microtome under constant water irrigation, washed with deionised water and oriented longitudinally on glass cover slides. Sections were
123
Non-carious sound human third molars (30) with no evidence of white spots or cracks on buccal or lingual surfaces were selected. The occlusal surfaces were ground with a diamond saw mounted on a handpiece under running water to expose a flat mid-coronal dentine surface. The dentine surface was ground by a 600 grit silicon carbide abrasive paper under water stream for 60 s to produce a standardised smear layer (Peris et al. 2007). These teeth were randomly divided into 3 groups of 10 each and treated with experimental and control adhesive systems. After the application of adhesive resin as per manufacturer’s instruction, a resin composite, Filtek Z250 (3M ESPE, St. Paul, MN, USA) was built up in increments of approximately 1 mm thick. The specimens were stored in moist environment, under wet cotton, at 37 °C for 24 h. After storage of the restored teeth at 37 °C for 24 h, the bonded samples were embedded in an acrylic resin. These samples were sectioned perpendicularly to the adhesive interface using a diamond saw under water lubrication to produce a series of slabs. Each slab was further sectioned to produce beams with an adhesive area of 0.8 mm2. The specimen lost during preparation was not included in the study. For each group, 15 slabs were subjected to testing. A customised jig was fabricated for the measurement of microtensile bond strength of dental adhesives and subjected to a testing apparatus (Universal testing machine) at a crosshead speed of 1 mm/min and values were measured at a storage period of 24 h and 3 months.
Eur Arch Paediatr Dent Table 1 Comparison of change in lesion depth after treatment with experimental and control groups at 24 h and 3 months Material Optibond solo Plus One Up
Ò
Bond F Plus
TM
G-BOND
Ò
(control)
n
Change in lesion depth at 24 h (lm)
Change in lesion depth at 3 months (lm)
Mean (SD)
t value
p value*
10
18.37 (11.52)
28.89 (15.53)
10.59 (8.6)
3.88
0.004 (HS)
10
20.47 (9.52)
34.06 (21.18)
13.59 (14.7)
2.92
0.01 (S)
10
47.34 (13.70)
52.26 (3.69)
4.92 (6.82)
2.28
0.04 (S)
Lesion depth (in microns)
Lesion depth at 24 hrs and 3 months
differences between the two fluoride releasing adhesives. The statistical difference between the fluoride-releasing adhesives and control group was found to be significant. At 3 months From the observations (Table 1; Fig. 1), post hoc Tukey’s test showed no statistical significant difference between Optibond Solo PlusÒ and One UpÒ Bond F Plus and between One UpÒ Bond F Plus and control. However, there was a significant difference between Optibond Solo PlusÒ and control (p \ 0.01) at the end of 3 months: the mean change in lesion depth at 24 h and 3 months among the experimental and control groups were statistically significant. Microtensile bond strength
Fig. 1 Comparison of change in lesion depth of different experimental groups at 24 h and 3 months
Results Statistical analysis The recorded values are statistically analysed using parametric tests of significance. Paired t test was performed to analyse the changes in the depth of demineralization and remineralisation and changes in tensile bond strength. Oneway ANOVA was used for multiple group comparison followed by post hoc Tukey’s test for pair wise comparisons. For all the tests, a p value of 0.05 or less was considered for statistical significance. Evaluation of caries inhibition potential At 24 h From the observations (Table 1; Fig. 1), Optibond Solo PlusÒ and One UpÒ Bond F Plus exhibited the highest caries inhibition potential, followed by the results for the control group shown by the increased reduction in lesion depth. Post hoc Tukey’s test showed no statistical
At 24 h From the observations (Table 2; Fig. 2) shown, One UpÒ Bond F Plus exhibited a higher mean tensile bond strength followed by control group and Optibond Solo PlusÒ with the mean difference of values between them being statistically significant (p \ 0.01). Inter-group comparisons by post hoc Tukey’s test, showed that there was a no statistical significant difference between experimental and control groups. However, there was a statistically significant difference between Optibond Solo PlusÒ and One UpÒ Bond F Plus. At 3 months From the observations (Table 2; Fig. 3),Optibond Solo PlusÒ exhibited higher mean tensile bond strength than One UpÒ Bond F Plus and control group, the difference being statistically significant (p \ 0.001). Further intergroup comparisons by post hoc Tukey’s test, a statistically significant difference was noted between experimental and control groups. From the observations (Table 2; Fig. 4), there was statistically significant decrease in tensile bond strength among the experimental and control groups at the end of 24 h and 3 months.Thus, at the end of 3 months, it can be inferred that Optibond Solo PlusÒ performed better
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Eur Arch Paediatr Dent Table 2 Comparison of the microtensile bond strength of the two fluoride releasing adhesive systems and non- fluoride releasing adhesive systems at 24 h and at 3 months Material
n
Mean (SD) microtensile bond strength at 24 h
Mean (SD) microtensile bond strength at 3 months
Optibond Solo PlusÒ
10
35.26 (2.1)
30.47 (1.57)
4.78 (2.81)
6.59
\0.001 (HS)
One UpÒ Bond F Plus*
10
37.78 (1.03)
19.02 (1.00)
18.76 (0.73)
98.91
\0.001 (HS)
10
36.23 (1.67)
27.08 (3.69)
9.14 (4.05)
8.73
\0.001 (HS)
TM
G-BOND
(control)
Mean difference (SD) in microtensile bond strength
t value
p value*
S significant, HS highly significant * NS not significant
Microtensile bond strength at 24 hours
Microtensile bond strength at three months
38
35
30.47 30
27.08
37 Bond strengt h (MPa)
Bond strength (MPa)
37.5
36.5 36 35.5 35 34.5
25
19.02
20 15 10 5
34 Optibond Solo One Up® Bond G- BOND TM Plus® F Plus Microtensile bond strength at 24 hours
0 Optibond Solo Plus®
One Up® Bond F Plus
G- BOND TM
Microtensile bond strength at three months
Fig. 2 Comparison of microtensile bond strength of two fluoride releasing adhesive systems and non-fluoride releasing adhesive systems at 24 h
Fig. 3 Comparison of microtensile bond strengths of two fluoride releasing adhesive systems and non-fluoride releasing adhesive system at 3 months
in terms of tensile bond strength than One UpÒ Bond F Plus and control group.
anti-cariogenic effect by increasing the dentine resistance to acids present in the oral cavity. The fluoride ions in these adhesives can easily penetrate the cavity wall and into dentine, thus increasing the mineralisation of dentine and ensuing protection against secondary caries (Savarino et al. 2004). Further, in vivo biodegradation has been suggested as a potential contributor to secondary loss of adhesion, micro leakage and caries. Therefore, the physical and chemical integrity of a composite restoration’s adhesive bond layer—the interface between the restoration and the tooth—is the most significant factor determining long-term clinical restoration success (Kermanshahi et al. 2010). Therefore, an adhesive system with an anti-cariogenic effect and good physical properties would be an effective tool in performing minimally invasive restorations. Incorporating these ideas, our present study was intended to
Discussion The development of adhesive dentistry and scientific progress in understanding the nature of caries has enabled dentists to do more than simply remove and replace diseased tissue (Tyas et al. 2000). Adhesive dental materials make it possible to conserve tooth structure using minimally invasive cavity preparations, because adhesive materials do not require the incorporation of mechanical retention features (Peters and Mclean 2001). Many fluoride-releasing adhesive materials have been developed and introduced into the dental market. It had been shown that the fluoride in these materials induces an
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Microtensile bond strength at 24 hours and 3 months 40 35 Bond strength (MPa)
30 25 20 15 10 5 0 Optibond Solo Plus®
One Up® Bond F Plus
Microtensile bond strength at 24 hours
G- BOND TM
Microtensile bond strength at three months
Fig. 4 Comparison of microtensile bond strength of two fluoride releasing adhesive systems and non-fluoride releasing adhesive system at 24 h and 3 months
compare the caries-inhibition potential and microtensile bond strength of fluoride releasing adhesive systems over conventional adhesive systems. In fluoride-releasing adhesive systems, the presence of a thin layer known as ‘‘acid–base resistant zone’’ (ABRZ) was formed adjacent to the hybrid layer at the adhesive– dentine interface after acid–base challenge (Tsuchiya et al. 2004). ABRZ could resist against acid challenge, hence giving rise to the ability to resist demineralization and prevent secondary caries development. Therefore, in this study, the caries inhibition potential of the adhesive system was measured as the difference between the depth of the inhibition zone and the lesion depth observed before treatment. This was observed as the change in lesion depth. Caries inhibition potential In our study, Optibond Solo PlusÒ and One-Up Bond FÒ Plus showed a significant amount of caries-inhibition at 24 h when compared with that of the control group, indicated by the reduction in the lesion depth. A similar study by (Itota et al. 2002) showed similar caries inhibition potential of fluoride releasing adhesives on decalcified root dentine. They suggested that the decrease in lesion depth was due to the presence of fluoride fillers released from the adhesive system. They proposed that the fluoride released from the adhesive might penetrate into the dentine and react with the calcium ions shifted from solution within the
pulp cavity and enhanced the mineralisation of demineralised dentine, with the deposition of calcium (Itota et al. 2002). Our observations can be further correlated with previous studies which demonstrate that fluoride ions enhance the remineralisation of carious dentine probably via the deposition of inorganic ions such as calcium, calcium fluoride, fluorapatite or hydroxyapatite produced on the demineralised dentine surfaces with increasing F- concentration (TenCate and Van Duinen 1995; Hirose 2000). SEM studies conducted by Ferracane et al. (1998) have also confirmed the presence of fluoride that has leached out from adhesive resin, in the hybrid layer present in the resin–dentine interface, thus corroborating our findings. However, contrary to our results, one study showed that the fluoride in the adhesive system was not capable of inhibiting secondary caries following artificial caries formation. However, that study utilised bovine incisors and the pH cycling used was different from the present study, accounting for the different results (Peris et al. 2007). Further, the decrease in the caries inhibition potential shown by fluoride-releasing adhesive systems at the end of 3 months had been earlier demonstrated by a previous study (Ferracane et al. 1998) which showed a decrease in the fluoride ions being leached out from the adhesive systems. These observations were further confirmed by Castro et al. (1994) which showed that the adhesive layer itself may absorb some amount of fluoride ions released from the restorative materials, thereby reducing the speed of penetration of F- ions into the demineralised dentine. These results also may be due to the low concentration of fluoride present in the adhesive suggesting that a continuous source of fluoride from the oral environment or a slow releasing fluoride adhesive system is essential for the longer durability of the fluoride-releasing adhesive systems. Microtensile bond strength In our study, a composite core of standardised dimensions was built with Filtek Z250 composite in all three groups to avoid the confounding effect of composite. The durability of adhesion was assessed by subjecting the specimens for long-term storage in distilled water at 37 °C for 24 h and 3 months (Shinohara et al. 2009). At the end of 24 h, One-Up Bond FÒ Plus had significant higher bond strengths when compared with OptiBond Solo PusÒ but there was no significant difference between fluoride-releasing and conventional adhesives. Bond strength tests are rough categorising tools for evaluating the durability of adhesive materials. Several factors might influence the bond strength such as nature and origin of the tooth, the dentine surface bonded, the degree of dentine mineralisation and the type of storage media (Vanajasan et al. 2011).
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However, at the end of 3 months, OptiBond Solo PusÒ had significantly higher bond strength values than One UpÒ Bond F Plus and control groups. These results might be due to the fluoride released from the adhesive, as it was suggested that the fluoride in adhesive systems prevents dentine degradation, which results in stability of the adhesive interface. Fluoride could reduce the solubility of calcium phosphate present in the hybrid layer, which stabilises dentine bond strength, accounting for the current results (Ferracane et al. 1998). However, One UpÒ Bond F Plus showed the least bond strength values which may be correlated with the observations of Pashley et al. (1998). They suggested that the monomer component, HEMA, present in the adhesive resin, decreased the vapour pressure of water even more, which may interfere with the removal of the last amounts of water, resulting in excess water in the adhesive resin compromising the bond strength of the adhesives due to entrapment of water blisters (over wet phenomenon), thus corroborating our results. A statistically significant decrease in bond strength among the experimental and control groups was observed during storage for 3 months, which may be attributed to the degradation of resin–dentine interface during storage. (Shono et al. 1999; Armstrong et al. 2001). ‘ However, in the control group (GBP), a single component one step self-etch adhesive non-fluoride releasing adhesive showed higher initial bond strength values. This might have been possible due to incorporation of 4-MET (4-methacryloyloxyethyl trimellitic acid) instead of HEMA in the adhesive monomer, which improves the mechanical properties by forming bonds with calcium ions present in hydroxyapatite. Another reason could be attributed to the acetone solvent present in the adhesive which may account for the initial increase in tensile bond strength values (Nakajima et al. 1995).
Conclusions Fluoride releasing adhesive systems had a significant effect in the inhibition of caries and microtensile bond strength when compared with conventional adhesive systems. At the end of 24 h and 3 months, no significant difference was found between OptiBond Solo PusÒ and One UpÒ Bond F Plus in terms of caries inhibition potential. OptiBond Solo PusÒ proved better in terms of bond strength at the end of 3 months.
References Armstrong SR, Keller JC, Boyer DB. The influence of water storage and C-factor on the dentine-resin composite microtensile bond
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strength and debond pathway utilizing a filled and unfilled adhesive resin. Dent Mater. 2001;17:268–76. Castro GW, Gray SE, Buikema DJ, Reagan SE. The effect of various surface coatings on fluoride release from glass-ionomer cement. OperDent. 1994;19(5):194–8. Damen JJ, Buijs MJ, ten Cate JM. Fluoride-dependent formation of mineralised layers in bovine dentin during demineralisation in vitro. Caries Res. 1998;32(6):435–40. De Munck J, Van Landuyt K, Peumans M, et al. A critical review of the durability of adhesion to tooth tissue: methods and results. J Dent Res. 2005;84(2):118–32. Ferracane JL, Mitchem JC, Adey JD. Fluoride penetration into the hybrid layer from a dentine adhesive. Am J Dent. 1998;11(1): 23–8. Hamilton IR, Bowden GHW. Fluoride effects on oral bacteria. In: Fejerskov O, Ekstrand J, Burt BA (eds) Fluoride in dentistry. Copenhagen: Munksgaard; 1996. p. 230–51. Hirose Y. Effect of fluoride on the surface of sound and demineralised/remineralised dentine. Jpn J Conserv Dent. 2000;43:262 (in Japanese). Itota T, Nakabo S, Iwai Y, et al. Inhibition of artificial secondary caries by fluoride-releasing adhesives on root dentin. J Oral Rehabil. 2002;29(6):523–7. Kermanshahi S, Santerre JP, Cvitkovitch DG, Finer Y. Biodegradation of resin-dentine interfaces increases bacterial micro leakage. J Dent Res. 2010;89(9):996–1001. Marquezan M, Correˆa FN, Sanabe ME, et al. Artificial methods of dentine caries induction: a hardness and morphological comparative study. Arch Oral Biol. 2009;54(12):1111–7. Nakajima M, Sano H, Burrow MF, et al. Tensile bond strength and SEM evaluation of caries-affected dentin using dentine adhesives. J Dent Res. 1995;74(10):1679–88. Pashley EL, Zhang Y, Lockwood PE, Rueggeberg FA, Pashley DH. Effects of HEMA on water evaporation from water–HEMA mixtures. Dent Mater. 1998;14(1):6–10. Peris AR, Mitsui FH, Lobo MM, Bedran-Russo AK, Marchi GM. Adhesive systems and secondary caries formation: assessment of dentine bond strength, caries lesions depth and fluoride release. Dent Mater. 2007;23(3):308–16. Peters MC, McLean ME. Minimally invasive operative care, II: contemporary techniques and materials—an overview. J Adhes Dent. 2001;3(1):17–31. Rølla G, Ekstrand J. Fluoride in oral fluids and dental plaque. In: Fejerskov O, Ekstrand J, Burt BA, editors. Fluoride in dentistry. Copenhagen: Munksgaard; 1996. p. 215–29. Savarino L, Brescgu L, Tedaldi M, et al. Ability of restorative and fluoride releasing materials to prevent marginal dentine demineralisation. Biomaterials. 2004;25:1011–7. Shinohara MS, De Goes MF, Schneider LF, et al. Fluoride-containing adhesive: durability on dentin bonding. Dent Mater. 2009;25(11):1383–91. Shono Y, Terashita M, Shimada J, et al. Durability of resin-dentin bonds. J Adhes Dent. 1999;1:211–8. Ten Cate JM, Featherstone JDM. Physicochemical aspects of fluoride–enamel interactions. In: Fejerskov O, Ekstrand J, Burt BA, editors. Fluoride in dentistry. Copenhagen: Munksgaard; 1996. p. 252–72. TenCate JM, Van Duinen R. Hyper mineralisation of dentinal lesions adjacent to glass-ionomer cement restorations. J Dent Res. 1995;74:1266. Todd AM, Staley NR, Kanellis JM, Donly JK, Wefel SJ. Effect of a fluoride varnish on demineralisation adjacent to orthodontic brackets. Am J Orthod Dentofacial Orthop. 1999;116:159–67. Tsuchiya S, Nikaido T, Sonoda H, Foxton RM, Tagami J. Ultrastructure of the dentin-adhesive interface after acid-base challenge. J Adhes Dent. 2004;6(3):183–90.
Eur Arch Paediatr Dent Tyas MJ, Anusavice KJ, Frencken JE, Mount GJ. Minimal intervention dentistry: a review. FDI Commission Project 1–97. Int Dent J. 2000;50(1):1–12. Vanajasan PP, Dhakshinamoorthy M, Rao CS. Factors affecting the bond strength of self-etch adhesives: a meta-analysis of literature. J Conserv Dent. 2011;14(1):62–7.
Wiegand A, Buchalla W, Attin T. Review on fluoride-releasing restorative materials–fluoride release and uptake characteristics, antibacterial activity and influence on caries formation. Dent Mater. 2007;23(3):343–62.
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ORIGINAL SCIENTIFIC ARTICLE
Comparative evaluation in vitro of caries inhibition potential and microtensile bond strength of two fluoride releasing adhesive systems A. R. Prabhakar • K. Dhanraj • S. Sugandhan
Received: 22 January 2014 / Accepted: 1 April 2014 Ó European Academy of Paediatric Dentistry 2014
Abstract Aim To evaluate and compare the caries inhibition potential and tensile bond strength of two commercially available fluoride releasing adhesive systems over conventional adhesive systems. Methods Artificial carious lesions were produced on the buccal surfaces of human molars and treated with experimental adhesive systems: Optibond Solo PlusÒ, One-UpÒ Bond F Plus and G-BONDÒ (control). The caries inhibition potential and the tensile bond strength were measured at 24 h and 3 months, respectively. Results At 24 h and 3 months, Optibond Solo PlusÒ and One-UpÒ Bond F Plus had higher caries inhibition potential over the control group, which was statistically significant. At 3 months, no statistically significant difference was noted between the fluoride releasing adhesives. OneUp Bond F Plus had higher bond strength values than other groups which was statistically significant at 24 h, whereas at the end of 3 months, Optibond Solo Plus had higher bond strength values than other groups which were statistically significant. Statistics The recorded values were statistically analysed using Paired t test, ANOVA followed by Post hoc Tukey’s test. Conclusions Fluoride releasing adhesive systems were effective in caries inhibition and showed comparatively higher bond strength values than the conventional adhesive systems in vitro.
A. R. Prabhakar (&) K. Dhanraj S. Sugandhan Department of Pedodontics and Preventive Dentistry, Bapuji Dental College and Hospital, Davangere 577004, Karnataka, India e-mail: [email protected]
Keywords Caries Fluoride Demineralisation Remineralisation Adhesive systems
Introduction Fluoride is well documented as an anti-cariogenic agent. A variety of mechanisms are involved in the anti-cariogenic effects of fluoride, including the reduction of demineralisation, the enhancement of remineralisation, the interference of pellicle and plaque formation and the inhibition of microbial growth and metabolism (Hamilton and Bowden 1996; Rølla and Ekstrand 1996; ten Cate and Featherstone 1996). Fluoride released from dental restorative materials is assumed to affect caries formation through all these mechanisms and may therefore reduce or prevent demineralisation and promote remineralisation of dental hard tissues (Wiegand et al. 2007). Currently, resin composites combined with an adhesive system are widely used for direct restorations in children because of excellent aesthetics and acceptable mechanical properties. Secondary caries has been reported as being the most common reason for replacement of these restorations. The observation that secondary caries formation rarely being associated with fluoride-containing silicate cement restorations has led to increasing attention on the development of various fluoride releasing products used as restorative materials (De Munck et al. 2005). Recently, fluoride-releasing adhesives have been developed and are available in the market. These adhesives are expected to inhibit secondary caries by simultaneously promoting adhesion to tooth substrate and releasing fluoride ions (Itota et al. 2002). As fluoride releasing adhesives directly contact the cavity wall, fluoride ions released from them easily penetrate and diffuse into the cavity wall
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Eur Arch Paediatr Dent
dentine, Enhancing mineralisation of the dentine and reducing its possible demineralisation. Therefore, penetration by fluoride ions offers resistance against secondary caries attack (Damen et al. 1998). The aim of the present study was to evaluate and compare in vitro the caries inhibition potential and microtensile bond strength of two fluoride-releasing adhesive systems.
Materials and method Two commercially available fluoride-releasing bonding agents, namely Optibond Solo PlusÒ (Kerr & Co., USA), One UpÒ Bond F Plus (Tokuyama Dental Corporation., Tokyo, Japan) were used. The control used was G-Bond (GC Asia, Tokyo, Japan.). Human third molars (60), with no evidence of caries or restorations, freshly extracted for therapeutic reasons were selected and stored in physiological saline solution containing 0.1 % thymol (Shinohara et al. 2009).
photographed at 109 magnification using an Olympus dual stage polarised light microscope (Model BX-51, Dual Mont Corporation, Minneapolis, Minn) (Shinohara et al. 2009). The depth of artificial lesion was quantified at 3 points i.e. from the surface of the lesion to the depth of the lesion, at D1, D2 and D3 to avoid errors so that mean value of the depth of the lesion could be considered for statistical analysis, using a computerised digital imaging system, Image Pro-PlusÒ (Todd et al. 1999). The experimental halves of each tooth specimens were subjected to three commercially available adhesives: Optibond Solo PlusÒ, One Up BondÒF Plus and the control being G-BONDÒ and restored with Filtek Z250. These restored teeth specimens were subjected to the pH cycling regimen of longitudinal sections of the cavity were again quantified for the decrease in the depth of the lesion using computerised digital imaging system, as described for the control specimens. This procedure was performed for a period of 24 h and 3 months, respectively. Microtensile bond strength
Caries inhibition potential Of the 60 human third molars that were free of caries and restorations with no evidence of white spots or cracks on buccal or lingual surfaces 30 were selected. Standardised Class V cavities of dimensions 3 mm 9 2 mm were prepared on the buccal surfaces of the teeth 1 mm from the CEJ. After the application of acid resistant nail varnish except for a window, these teeth were subjected to pH cycling regimen. To simulate dentinal caries, an artificial caries model was designed which consisted of 2.2 mM Ca2?, 2.2 mM PO43-, 50 mM glacial acetic acid at a pH of 4.8. The solution was kept at a constant temperature of 37 °C in an incubator for 4 days and the experimental specimens were exposed to a daily pH cycling regimen for 14 days with 8 h in demineralising and 16 h in remineralising solutions, respectively (Marquezan et al. 2009). The teeth were randomly selected into three different groups of ten each. After subjecting to pH cycling, the specimens were sectioned bucco-lingually such and one half was used for the quantification of depth of the carious lesion (control) and the other half is subjected for the treatment with adhesives (test). Control specimens were embedded on acrylic blocks and sections of 140–160 lm thickness were obtained by cutting through the centre of the cavity using a Silverstone-Taylor hard tissue microtome under constant water irrigation, washed with deionised water and oriented longitudinally on glass cover slides. Sections were
123
Non-carious sound human third molars (30) with no evidence of white spots or cracks on buccal or lingual surfaces were selected. The occlusal surfaces were ground with a diamond saw mounted on a handpiece under running water to expose a flat mid-coronal dentine surface. The dentine surface was ground by a 600 grit silicon carbide abrasive paper under water stream for 60 s to produce a standardised smear layer (Peris et al. 2007). These teeth were randomly divided into 3 groups of 10 each and treated with experimental and control adhesive systems. After the application of adhesive resin as per manufacturer’s instruction, a resin composite, Filtek Z250 (3M ESPE, St. Paul, MN, USA) was built up in increments of approximately 1 mm thick. The specimens were stored in moist environment, under wet cotton, at 37 °C for 24 h. After storage of the restored teeth at 37 °C for 24 h, the bonded samples were embedded in an acrylic resin. These samples were sectioned perpendicularly to the adhesive interface using a diamond saw under water lubrication to produce a series of slabs. Each slab was further sectioned to produce beams with an adhesive area of 0.8 mm2. The specimen lost during preparation was not included in the study. For each group, 15 slabs were subjected to testing. A customised jig was fabricated for the measurement of microtensile bond strength of dental adhesives and subjected to a testing apparatus (Universal testing machine) at a crosshead speed of 1 mm/min and values were measured at a storage period of 24 h and 3 months.
Eur Arch Paediatr Dent Table 1 Comparison of change in lesion depth after treatment with experimental and control groups at 24 h and 3 months Material Optibond solo Plus One Up
Ò
Bond F Plus
TM
G-BOND
Ò
(control)
n
Change in lesion depth at 24 h (lm)
Change in lesion depth at 3 months (lm)
Mean (SD)
t value
p value*
10
18.37 (11.52)
28.89 (15.53)
10.59 (8.6)
3.88
0.004 (HS)
10
20.47 (9.52)
34.06 (21.18)
13.59 (14.7)
2.92
0.01 (S)
10
47.34 (13.70)
52.26 (3.69)
4.92 (6.82)
2.28
0.04 (S)
Lesion depth (in microns)
Lesion depth at 24 hrs and 3 months
differences between the two fluoride releasing adhesives. The statistical difference between the fluoride-releasing adhesives and control group was found to be significant. At 3 months From the observations (Table 1; Fig. 1), post hoc Tukey’s test showed no statistical significant difference between Optibond Solo PlusÒ and One UpÒ Bond F Plus and between One UpÒ Bond F Plus and control. However, there was a significant difference between Optibond Solo PlusÒ and control (p \ 0.01) at the end of 3 months: the mean change in lesion depth at 24 h and 3 months among the experimental and control groups were statistically significant. Microtensile bond strength
Fig. 1 Comparison of change in lesion depth of different experimental groups at 24 h and 3 months
Results Statistical analysis The recorded values are statistically analysed using parametric tests of significance. Paired t test was performed to analyse the changes in the depth of demineralization and remineralisation and changes in tensile bond strength. Oneway ANOVA was used for multiple group comparison followed by post hoc Tukey’s test for pair wise comparisons. For all the tests, a p value of 0.05 or less was considered for statistical significance. Evaluation of caries inhibition potential At 24 h From the observations (Table 1; Fig. 1), Optibond Solo PlusÒ and One UpÒ Bond F Plus exhibited the highest caries inhibition potential, followed by the results for the control group shown by the increased reduction in lesion depth. Post hoc Tukey’s test showed no statistical
At 24 h From the observations (Table 2; Fig. 2) shown, One UpÒ Bond F Plus exhibited a higher mean tensile bond strength followed by control group and Optibond Solo PlusÒ with the mean difference of values between them being statistically significant (p \ 0.01). Inter-group comparisons by post hoc Tukey’s test, showed that there was a no statistical significant difference between experimental and control groups. However, there was a statistically significant difference between Optibond Solo PlusÒ and One UpÒ Bond F Plus. At 3 months From the observations (Table 2; Fig. 3),Optibond Solo PlusÒ exhibited higher mean tensile bond strength than One UpÒ Bond F Plus and control group, the difference being statistically significant (p \ 0.001). Further intergroup comparisons by post hoc Tukey’s test, a statistically significant difference was noted between experimental and control groups. From the observations (Table 2; Fig. 4), there was statistically significant decrease in tensile bond strength among the experimental and control groups at the end of 24 h and 3 months.Thus, at the end of 3 months, it can be inferred that Optibond Solo PlusÒ performed better
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Eur Arch Paediatr Dent Table 2 Comparison of the microtensile bond strength of the two fluoride releasing adhesive systems and non- fluoride releasing adhesive systems at 24 h and at 3 months Material
n
Mean (SD) microtensile bond strength at 24 h
Mean (SD) microtensile bond strength at 3 months
Optibond Solo PlusÒ
10
35.26 (2.1)
30.47 (1.57)
4.78 (2.81)
6.59
\0.001 (HS)
One UpÒ Bond F Plus*
10
37.78 (1.03)
19.02 (1.00)
18.76 (0.73)
98.91
\0.001 (HS)
10
36.23 (1.67)
27.08 (3.69)
9.14 (4.05)
8.73
\0.001 (HS)
TM
G-BOND
(control)
Mean difference (SD) in microtensile bond strength
t value
p value*
S significant, HS highly significant * NS not significant
Microtensile bond strength at 24 hours
Microtensile bond strength at three months
38
35
30.47 30
27.08
37 Bond strengt h (MPa)
Bond strength (MPa)
37.5
36.5 36 35.5 35 34.5
25
19.02
20 15 10 5
34 Optibond Solo One Up® Bond G- BOND TM Plus® F Plus Microtensile bond strength at 24 hours
0 Optibond Solo Plus®
One Up® Bond F Plus
G- BOND TM
Microtensile bond strength at three months
Fig. 2 Comparison of microtensile bond strength of two fluoride releasing adhesive systems and non-fluoride releasing adhesive systems at 24 h
Fig. 3 Comparison of microtensile bond strengths of two fluoride releasing adhesive systems and non-fluoride releasing adhesive system at 3 months
in terms of tensile bond strength than One UpÒ Bond F Plus and control group.
anti-cariogenic effect by increasing the dentine resistance to acids present in the oral cavity. The fluoride ions in these adhesives can easily penetrate the cavity wall and into dentine, thus increasing the mineralisation of dentine and ensuing protection against secondary caries (Savarino et al. 2004). Further, in vivo biodegradation has been suggested as a potential contributor to secondary loss of adhesion, micro leakage and caries. Therefore, the physical and chemical integrity of a composite restoration’s adhesive bond layer—the interface between the restoration and the tooth—is the most significant factor determining long-term clinical restoration success (Kermanshahi et al. 2010). Therefore, an adhesive system with an anti-cariogenic effect and good physical properties would be an effective tool in performing minimally invasive restorations. Incorporating these ideas, our present study was intended to
Discussion The development of adhesive dentistry and scientific progress in understanding the nature of caries has enabled dentists to do more than simply remove and replace diseased tissue (Tyas et al. 2000). Adhesive dental materials make it possible to conserve tooth structure using minimally invasive cavity preparations, because adhesive materials do not require the incorporation of mechanical retention features (Peters and Mclean 2001). Many fluoride-releasing adhesive materials have been developed and introduced into the dental market. It had been shown that the fluoride in these materials induces an
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Microtensile bond strength at 24 hours and 3 months 40 35 Bond strength (MPa)
30 25 20 15 10 5 0 Optibond Solo Plus®
One Up® Bond F Plus
Microtensile bond strength at 24 hours
G- BOND TM
Microtensile bond strength at three months
Fig. 4 Comparison of microtensile bond strength of two fluoride releasing adhesive systems and non-fluoride releasing adhesive system at 24 h and 3 months
compare the caries-inhibition potential and microtensile bond strength of fluoride releasing adhesive systems over conventional adhesive systems. In fluoride-releasing adhesive systems, the presence of a thin layer known as ‘‘acid–base resistant zone’’ (ABRZ) was formed adjacent to the hybrid layer at the adhesive– dentine interface after acid–base challenge (Tsuchiya et al. 2004). ABRZ could resist against acid challenge, hence giving rise to the ability to resist demineralization and prevent secondary caries development. Therefore, in this study, the caries inhibition potential of the adhesive system was measured as the difference between the depth of the inhibition zone and the lesion depth observed before treatment. This was observed as the change in lesion depth. Caries inhibition potential In our study, Optibond Solo PlusÒ and One-Up Bond FÒ Plus showed a significant amount of caries-inhibition at 24 h when compared with that of the control group, indicated by the reduction in the lesion depth. A similar study by (Itota et al. 2002) showed similar caries inhibition potential of fluoride releasing adhesives on decalcified root dentine. They suggested that the decrease in lesion depth was due to the presence of fluoride fillers released from the adhesive system. They proposed that the fluoride released from the adhesive might penetrate into the dentine and react with the calcium ions shifted from solution within the
pulp cavity and enhanced the mineralisation of demineralised dentine, with the deposition of calcium (Itota et al. 2002). Our observations can be further correlated with previous studies which demonstrate that fluoride ions enhance the remineralisation of carious dentine probably via the deposition of inorganic ions such as calcium, calcium fluoride, fluorapatite or hydroxyapatite produced on the demineralised dentine surfaces with increasing F- concentration (TenCate and Van Duinen 1995; Hirose 2000). SEM studies conducted by Ferracane et al. (1998) have also confirmed the presence of fluoride that has leached out from adhesive resin, in the hybrid layer present in the resin–dentine interface, thus corroborating our findings. However, contrary to our results, one study showed that the fluoride in the adhesive system was not capable of inhibiting secondary caries following artificial caries formation. However, that study utilised bovine incisors and the pH cycling used was different from the present study, accounting for the different results (Peris et al. 2007). Further, the decrease in the caries inhibition potential shown by fluoride-releasing adhesive systems at the end of 3 months had been earlier demonstrated by a previous study (Ferracane et al. 1998) which showed a decrease in the fluoride ions being leached out from the adhesive systems. These observations were further confirmed by Castro et al. (1994) which showed that the adhesive layer itself may absorb some amount of fluoride ions released from the restorative materials, thereby reducing the speed of penetration of F- ions into the demineralised dentine. These results also may be due to the low concentration of fluoride present in the adhesive suggesting that a continuous source of fluoride from the oral environment or a slow releasing fluoride adhesive system is essential for the longer durability of the fluoride-releasing adhesive systems. Microtensile bond strength In our study, a composite core of standardised dimensions was built with Filtek Z250 composite in all three groups to avoid the confounding effect of composite. The durability of adhesion was assessed by subjecting the specimens for long-term storage in distilled water at 37 °C for 24 h and 3 months (Shinohara et al. 2009). At the end of 24 h, One-Up Bond FÒ Plus had significant higher bond strengths when compared with OptiBond Solo PusÒ but there was no significant difference between fluoride-releasing and conventional adhesives. Bond strength tests are rough categorising tools for evaluating the durability of adhesive materials. Several factors might influence the bond strength such as nature and origin of the tooth, the dentine surface bonded, the degree of dentine mineralisation and the type of storage media (Vanajasan et al. 2011).
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However, at the end of 3 months, OptiBond Solo PusÒ had significantly higher bond strength values than One UpÒ Bond F Plus and control groups. These results might be due to the fluoride released from the adhesive, as it was suggested that the fluoride in adhesive systems prevents dentine degradation, which results in stability of the adhesive interface. Fluoride could reduce the solubility of calcium phosphate present in the hybrid layer, which stabilises dentine bond strength, accounting for the current results (Ferracane et al. 1998). However, One UpÒ Bond F Plus showed the least bond strength values which may be correlated with the observations of Pashley et al. (1998). They suggested that the monomer component, HEMA, present in the adhesive resin, decreased the vapour pressure of water even more, which may interfere with the removal of the last amounts of water, resulting in excess water in the adhesive resin compromising the bond strength of the adhesives due to entrapment of water blisters (over wet phenomenon), thus corroborating our results. A statistically significant decrease in bond strength among the experimental and control groups was observed during storage for 3 months, which may be attributed to the degradation of resin–dentine interface during storage. (Shono et al. 1999; Armstrong et al. 2001). ‘ However, in the control group (GBP), a single component one step self-etch adhesive non-fluoride releasing adhesive showed higher initial bond strength values. This might have been possible due to incorporation of 4-MET (4-methacryloyloxyethyl trimellitic acid) instead of HEMA in the adhesive monomer, which improves the mechanical properties by forming bonds with calcium ions present in hydroxyapatite. Another reason could be attributed to the acetone solvent present in the adhesive which may account for the initial increase in tensile bond strength values (Nakajima et al. 1995).
Conclusions Fluoride releasing adhesive systems had a significant effect in the inhibition of caries and microtensile bond strength when compared with conventional adhesive systems. At the end of 24 h and 3 months, no significant difference was found between OptiBond Solo PusÒ and One UpÒ Bond F Plus in terms of caries inhibition potential. OptiBond Solo PusÒ proved better in terms of bond strength at the end of 3 months.
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