Year : 2005 | Volume
: 23 | Issue : 2 | Page : 83--88
Comparative evaluation of tensile-bond strength, fracture mode and microleakage of fifth, and sixth generation adhesive systems in primary dentition
A Stalin1, Balagopal R Varma2, Jayanthi1,
1 Department of Pedodontics and Preventive Dentistry, Ragas Dental College and Hospital, Chennai, India
2 Amrita College of Dentistry, Kochi, India
Balagopal R Varma
Department of Pediatric Dentistry, AIMS Campus, Amrita Lane, Elamakkara, PO Kochi - 682 026
Conservative procedures using dentin-bonding agents are one of the important aspects of pediatric dental practice. The objectives of this in vitro study was to comparatively evaluate the tensile-bond strength, fracture mode (under SEM) and microleakage of total etching single bottle system to self-etching adhesive system in primary dentition. The flat buccal/lingual surfaces of 20 teeth were divided into two groups and treated with Single Bond (Group 1) and Adper Prompt (Group 2) to develop a composite resin cone. Then tensile-bond strength was measured using Instron machine. Fracture mode was evaluated in three specimens from each group under SEM. Microleakage of Class V composite restorations (in 20 teeth) with the above-mentioned adhesives was assessed under stereomicroscope after Basic fuschin dye immersion. Results showed no statistically significant difference between two groups. It was concluded that concerning the single step application with similar efficacy, the self-etching adhesive is better for bonding in primary dentition.
|How to cite this article:|
Stalin A, Varma BR, Jayanthi. Comparative evaluation of tensile-bond strength, fracture mode and microleakage of fifth, and sixth generation adhesive systems in primary dentition.J Indian Soc Pedod Prev Dent 2005;23:83-88
|How to cite this URL:|
Stalin A, Varma BR, Jayanthi. Comparative evaluation of tensile-bond strength, fracture mode and microleakage of fifth, and sixth generation adhesive systems in primary dentition. J Indian Soc Pedod Prev Dent [serial online] 2005 [cited 2020 Feb 23 ];23:83-88
Available from: http://www.jisppd.com/text.asp?2005/23/2/83/16448
The foundation for modern adhesive dentistry was laid in 1955, when Buonocore reported that acids could be used to alter the surface of enamel to 'render it more receptive' to adhesion. Since that time, the dental adhesive systems have evolved through several 'generations' with changes in chemistries, mechanisms, number of bottles, application techniques and clinical effectiveness.
The total etch technique using the fifth generation adhesive system proved its clinical effectiveness with reduction in number of application into two steps. It consisted of a separate etching procedure on dentinal surface before application of single bottle adhesive containing both primer and bonding agent.
A recent development involves the use of acidic or self-etching adhesives which combine acid conditioning with the priming and bonding procedure known as the sixth generation/self-etching adhesive system. Apart from simplification of single step application, the rationale behind this system is to superficially demineralize dentin and simultaneously penetrate it with monomers, which can be polymerized in situ .
While bonding to permanent teeth has been studied extensively, few studies have addressed resin bonding to primary teeth. Studies comparing the same adhesive systems showed results varying from no significant difference to higher or lower bond strength and sealing ability in primary dentition than in permanent dentition., Chemical, physiological and micromorphological differences such as decreased mineralization, small size and lower concentration of dentinal tubules, decreased permeability, more reactivity to acidic conditioner are thought to be responsible for lower bond strength and sealing ability in primary dentition.,,
The objectives of this in vitro study was to evaluate the tensile-bond strength, fracture mode (under SEM) and microleakage of total etching single bottle system to self-etching adhesive system in primary dentition.
Materials and Methods
This study was carried out in Department of Pedodontics, Ragas Dental College, Chennai. The tensile-bond strength was tested at IIT, Chennai and microleakage was tested at GIL Research Institute, Chennai. The SEM study, to know the fracture mode, was done at Annamalai University, Chidambaram, Tamil Nadu, India.
Tensile-bond strength evaluation
A total of 20 freshly extracted caries free, unrestored human primary molars were selected and stored in distilled water. The buccal/lingual surfaces were ground using a water-cooled diamond disc mounted on an air-motor handpiece until enamel was removed. Then 600 grit-Sic paper was used with mandrill to create a flat dentinal surface with enamel at periphery. Then two examiners crosschecked the specimens to confirm that the preparation was on superficial layer of dentin. The opposite side of prepared teeth were embedded into the self-cure acrylic resin and randomly divided into two groups of 10 specimens each.
In Group I (Fifth Generation Group), the exposed surface of specimens were treated with 35% phosphoric acid for 15s and rinsed with water for 10s. Then excess water was dried with oil-free compressed air for 5s. Single Bond adhesive was applied on the etched dentinal surface using a fully saturated brush tip of adhesive for each coat and two consecutive coats were applied and thinned with a gentle stream of air for 2-5s and light cured for 10s.
In Group II (Sixth Generation Group), Adper Prompt solutions were mixed, applied and massaged for 15s according to manufacturer's instructions. A second coating was applied and thinned with a gentle air stream and light cured for 10s.
Specimens of each group were kept separately and the following procedures were done similarly. A hollow metal split dye/mould was held on adhesive-treated surface of specimens and then composite resin of thickness 2 mm was placed inside the mould and condensed. A twisted 26-gauge ligature wire with a loop was placed inside the 2 mm of composite resin, held straightly and light cured for 40s. Another 3 mm thickness of composite resin was placed and light cured incrementally.
Following complete curing, the metal mould was split and removed leaving the 5 mm thickness of resin cone with twisted wire bonded to 2 mm surface area of dentin. The metal mould was reused for other specimens in the same way. A few specimens that showed a spontaneous bond failure during removal of the mould were discarded and not included in the study.
All the specimens were immersed in water for 24 h. Then, tensile-bond strength was measured using an Instron Universal Testing Machine at a crosshead speed of 0.5 mm/min. The values obtained were in 'kg' and bond strength was then converted into 'MPa'. Means and standard deviation (SD) were calculated. The tensile-bond strength data were analysed by Levene's test for equality variance and ' t ' test for equation of means.
After testing the tensile-bond strength, three specimens were selected randomly from both groups. Then, a total of six pairs of 5 mm2 tooth specimen and de-bonded resin cone without any disturbance to the de-bonded surface were prepared. The de-bonded surfaces of specimens were dehydrated, platinum coated and examined under SEM at x50 magnification.
Fracture mode was designed according to the following criteria:
• Resin cohesive - if the resin part was noted on tooth specimen.
• Adhesive - if the adhesive layer was noted on both the specimens.
• Dentin cohesive - if the dentinal part was noted on resin specimen.
• Mixed - if the resin/adhesive parts were noted on tooth specimen.
The fracture modes were not analysed statistically to correlate with tensile-bond strength.
A total of 20 freshly extracted caries free, unrestored human primary molars were selected. One Class V cavity preparation in enamel with rounded outlines -3 mm width, 2 mm height and 2 mm depth was prepared in buccal/lingual surface of all teeth with a No. 330 bur in airotor hand piece.
Two examiners cross-checked all the specimens to confirm that the above-mentioned measurements of Class V cavity preparation were adhered to. Then the specimens were randomly divided into two groups of 10 teeth each.
In Group I (Fifth Generation Group), the cavity walls were treated with 35% phosphoric acid for 15 s, rinsed with water for 10 s, and dried with a gentle air stream for 5 s. Single Bond adhesive was applied to the etched walls according to manufacturer's instructions.
In Group II (Sixth Generation Group), solution from two bottles of Adper Prompt were mixed, applied over the walls of the cavity and massaged for 15 s according to the manufacturer's instructions.
Specimens of each group were kept separately and the following procedures were done similarly. All the cavities were filled with composite resin (Z-100), condensed and light cured for 40 s. Then immersed in water for 24 h.
Teeth were thermocycled in PCR chamber at 5-55°C for 200 cycles with a dwell time of 30 s and a temperature changing time of 3 min in between each cycle. After thermocycling the apices of all teeth were sealed with dental wax and two coatings of nail varnish were done within 1 mm of margins of all restorations.
The specimens were then immersed in 2% aqueous solution of basic fuschin dye for 24 h at room temperature. After removal from the dye, the teeth were washed, dried and sectioned labiolingually through the middle of the restoration using a diamond disc in an airmotor handpiece.
Each section was examined using a stereomicroscope at x40 magnification to assess dye penetration at the margins of the restoration.
The degree of micro leakage was evaluated and scored as follows:
Score 0: No dye penetration.
Score 1: Dye penetration along occlusal or gingival wall up to one-third length.
Score 2: Dye penetration along occlusal or gingival wall up to two-third but not less than one-third length.
Score 3: Dye penetration along whole length of occlusal or gingival wall and along the axial wall.
The maximum score of microleakage was measured in any half of the specimens. Scores of microleakage in two groups were cross-tabulated and analysed by chi-square test.
The tensile-bond strength values for 10 specimens from each group are presented in [Table 1]. The mean value for tensile-bond strength, standard deviation and standard error for mean values are presented in [Table 2]. The Levene's test for equality variances, t test for equality of means and 95% confidence interval of the differences are presented in [Table 3].
There is no statistically significant difference in tensile-bond strength values between these two groups.
De-bonded surfaces of both dentin and resin cone of each specimen were observed under SEM and marked as Adhesive/Mixed/Cohesive type of failure as shown in [Table 4].
Two examiners crosschecked this observation and confirmed the findings. This fracture mode observation was not statistically analysed and correlated with the tensile-bond strength values.
The scores for microleakage of 10 specimens from each group are presented in [Table 5]. The number and percentage of specimens from each group with corresponding microleakage scores are presented in [Table 6]. The chi-square test to find a statistical difference in microleakage of two groups is given in [Table 7]. The obtained P value was higher than 0.05 ( P > 0.05). It indicates that there is no statistically significant difference.
An in vitro study was conducted to comparatively evaluate the tensile-bond strength to primary dentin, fracture mode under SEM and microleakage in Class V cavity preparations of fifth generation adhesive-Single Bond and Phosphoric acid Etchant with that of sixth generation adhesive-Adper Prompt in primary molars. Buccal/Lingual surface of molars were preferred in this study as flat dentin surface could be prepared which would give wider area of dentin to be treated and bonded to resin. In addition, the oblique pattern of tubule orientation in primary molars would not be a variable in bond strength of adhesives.
After applying bonding agents, and curing, a metal mould with inverted hollow (2 mm diameter at lower end, 4 mm diameter at the top and 5 mm in height) was used to develop a resin cone. This mould was used to restrict the bonding surface area only to 2 mm diameter on the dentin. This results in fewer defects occurring in the smaller area of bonding and higher bond strength. During placement of composite inside the mould, incremental technique was used to decrease the polymerization shrinkage.
After complete curing of composite, metal mould was removed and reused for other specimens in the same way. When removing the mould, a spontaneous bond failure occurred in some specimens of both group as noted in a similar study conducted by Agostini et al. It might be due to high water content of these adhesives. These specimens were discarded and not included in the study.
The mean value of the samples for Group 1 was 12.91 ± 1.77 and for Group 2 was 12.46 ± 2.83. Results from t -test showed that the P -value >0.01 so that both adhesive systems performed equally in primary dentin without any statistically significant difference in terms of tensile-bond strength measurement.
Bond strength of self-etch adhesive system have been found higher in enamel, in studies conducted by Hannig et al and Agostini et al. But, results of studies revealing its efficacy in dentin was controversial.,
For effective bond strength in dentin, the adhesive system should produce an intermingled layer of resin monomers and organic portion (collagen fibres) of dentin, known as hybridization zone. The quality of hybrid layer may be varied depending upon the pH of etchant, ability of the resin monomer to flow into the demineralized dentin and chemo-physiological and morphological characteristics of dentin (especially in primary dentin).
Concerning the C-factor, this study was conducted on flat dentin surface. The results were lower in both the group on primary dentin even the C-factor was 1. It may be due to the fact that the area of solid dentin that is available for dentin bonding is significantly reduced in primary teeth. The density and diameter of the dentinal tubules in primary molars were lower than the values reported for permanent teeth and may account for the lower permeability of the primary molars.
Another factor for lower bond strength obtained in both groups may be the fact that both systems are HEMA containing, water-based products from 3 M (ESPE) Dental Manufacturer. Because of higher water content, these systems are very sensitive to water content of demineralized dentin especially during polymerization and formation of hybrid layer. The total etch system (Single Bond) with water was considered more sensitive to over wet and over drying procedure even though it contains ethanol.
The finding that the change in cure was most significant within the 0-0.20 ml water per milliliter of bonding resin range could be of great clinical significance. Consequently, relatively small water contamination could have dramatic effects on the bond strength and render this type of material very technique sensitive.
Incomplete removal of water from the collagen network results in the competition between the monomer and the remaining water inside the demineralized dentin and might inhibit polymerization of the bonding agent. Phase separation of the hydrophobic and hydrophilic monomer components causing blister-like spaces and globule formation of the bonding agent within the hybrid layer has been observed in over wet conditions. In addition, excess water may also dilute the primer and render it less effective.
The self-etch system (Promp-L-Pop) with more water content may be more sensitive when it is applied two or three coats on the dentin. It results in appearance of watery film over the bonded surface of dentin. A possible reason for this phenomenon could be the high water content of these bonding systems released during polimerization. It was suggested by Agostini et al.
In the present study, the self-etching system produced equal strength to that of total etching system. It may be due to the fact that the low pH of the Adper Prompt adhesive dissolved the smear layer completely and formed the hybrid layer without any smear plugs that is very similar to that of total etch system. Tay and Pashley demonstrated more aggressive nature of self-etch system (Prompt-L-Pop), that completely dissolved the smear layer and smear plugs and formed the hybrid layer with a thickness approaching those of phosphoric acid conditioned dentin, in permanent molars.
In the present study, for SEM examination of failure sites, samples were selected from each group, using systematic random sampling method that is every third specimens (third, sixth and ninth) from each group of 10 specimens. It might represent the majority of fracture mode of each group.
In Single Bond group, two of three specimens showed cohesive fracture [Figure 1]a and b in the resin. It might be due to higher bond strength of adhesive on the dentin. In Adper Prompt group, two of three specimens showed mixed type of fracture [Figure 2]a and b and one specimen showed cohesive resin fracture. It may also be considered due to higher bond strength of adhesive. But these findings could not be correlated statistically with bond strength measurements.
Microleakage occurring along the restoration-tooth interface is possibly the greatest deterrent to the development of an 'ideal' restorative material. It poses a particular problem in the pediatric patient in whom the floor of the cavity preparation in primary dentition may be close to the pulp. Hence, sealing of the cavity walls besides its retention remains an important factor while determining the efficacy of a material. Further the microleakage study, together with the bond strength testing, provides good screening methods to determine if adhesive systems will be clinically acceptable.
Many techniques have been devised to test the cavity sealing properties of restorations both in vivo and in vitro . The use of organic dyes as tracers is the most common method detecting leakage in vitro and it is detectable even in dilute concentrations, in expensive, and nontoxic. In this study, basic fuchsin dye was used. Microleakage was studied using a stereomicroscope.
In all types of composite restorations, the sealing ability of bonding agents is the main variable determining the marginal leakage. Recent studies on bonding agents (fifth and sixth) confirmed that none of the adhesives capable of completely stopping microleakage in composite restorations and results were controversial and variable.
After Class V cavity cutting and adhesive treatment in both groups (10 specimens of each), composite resin was placed inside the cavity using bulk filling technique since the cavity depth was only 2 mm. After thermocycling and immersion in 2% basic fuchsin dye for 24 h, teeth were sectioned longitudinally with diamond disks and examined under stereomicroscope. Microleakage was scored by using the scoring criteria used by El Housseiny and Farsi.
Although score 3 was noted in one specimen from self-etch group, the result obtained from chi-square test revealed no statistical difference between the two groups since most of the specimens from both the groups showed score-1 microleakage [Figure 3]. This result correlates with the findings of Gagliardi and Avelar, Gillet et al, Pontes et al. This can be explained by the facts that the monomers that cause etching in sixth generation system are also responsible for the bonding and that the depth of demineralization zone corresponds to the depth of penetration of monomers. As the etching process progresses, the pH of the phosphate esters rises, as dentin buffers the acidic monomers, and this process inhibits further demineralization.
But da Silva Telles et al found more interfacial opening of restoration in Prompt-L-Pop group than in Single Bond group and speculated that the low pH of self-etch adhesive (Prompt-L-Pop) which is required for the etching of tooth structure may have impaired the polymerization of the resin monomer and therefore not allowed for the development of a strong and stable hybrid layer to prevent the opening of interfacial gaps.
In the present study both the systems, were unable to prevent microleakage in Class V cavities. It was demonstrated in studies conducted by Heping Li et al and Ruya Yacizi et al and Pontes et al Heping Li et al found more leakage in Single Bond and Prompt-L-Pop groups than in Clearfil SE Bond and Unifil bond. Ruya Yacizi et al reported more leakage in Gluma one bond (fifth generation total etch adhesive system) and Prompt-L-Pop compared to Optibond FL and Clearfil SL Bond from fifth generation self-etching primer system (with and without acid etching). There is a possibility that the lack of a separate primer may reduce the infiltration depth or the wetability of dentin adhesives, thereby reducing adhesion and sealing capacity of Prompt-L-Pop.
Pontes et al observed less leakage in Prompt-L-Pop group when it is used on enamel, but showed similar leakage to that of Single Bond group in dentin. The total etch system also was not able to prevent microleakage in our study. It may be due to the fact that the single bottle adhesives containing ethanol/acetone are more sensitive to the moisture content of demineralized dentin. It could have profound effect on sealing ability of this system.
Considering the aims with which the present study was undertaken and the results obtained, the following conclusions can be made:
There was no significant difference between two adhesive systems when considering both tensile-bond strength and microleakage in primary molars. Both the systems proved to be equally effective in providing bonding of composite resin restorations in primary dentin.Both the systems showed lower tensile-bond strength and also failed to prevent microleakage in primary molars. It may be due to the chemo-morphological difference in primary dentin or higher sensitivity of water-containing adhesive systems in bonding techniques.
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