Effect of Different Bonding Techniques on Marginal Adaptation of Harmonize Composite Resin at Different Storage Times.

AIM: The aim of this study is to evaluate the outcome of diverse bonding methods on marginal adaptation of harmonize composite at altered times of storage.
MATERIALS AND METHODS: The study was done on 120 upper premolars with two adhesive systems (n = 60), self-etch, and total-etch type. Sixty teeth of each method were stored at three different times (n = 20) 1 day, 3, and 6 months. Class II cavities were made in all teeth restored with Harmonize composite incrementally. Then, each tooth was sectioned into two halves in buccolingual direction and observed with stereomicroscope for detecting any gaps and scanning electron microscope to assess resin-dentin junction.
RESULTS: Mean gap area was more in the self-etch group at the cervical and occlusal margins. Storage period of 6 months revealed significantly highest mean gap area.
CONCLUSIONS: Total-etch system showed better marginal adaptation than the self-etch system and storage of resin in water has unfavorable marginal adaptation. Copyright:

INTRODUCTION

This great popularity of composite resins is mainly associated with esthetics and less tooth structure removal.[1] Any restoration is deemed as successful if the interface of tooth and material is uniform and seals the margins effectively. Obtaining a perfect gap-free interface is difficult in Class II composite restorations.[23] Adhesive systems play a vital role to improve marginal adaptation and also reduce polymerization shrinkage.[4] Many adhesive systems are being developed in recent times.[5] We carried this study to assess the role of diverse bonding techniques on the marginal adaptation of harmonize composite resin at varied times of storage.

MATERIALS AND METHODS

One hundred and twenty maxillary premolar teeth removed for orthodontic treatment or periodontal problems were included in the study. Ethical committee endorsement was attained from the Research Ethical Committee, Al-Farabi Private Colleges in Jeddah-KSA (No. 20-03/8). The sample was randomly categorized into two categories (n = 60), based on the adhesive system, total-etch (A) or self-etch bonding system (B). Using diamond stone (Komet, Lemgo, Germany). Class II cavity was made in all the teeth.

To begin with 37.5% phosphoric acid gel (Kerr etchant gel) was applied to etch the surface of tooth for 15 sec, later the surface was rinsed with water and air-dried. Then, adhesive was applied as two coats on the etched surface, and air-dried gently. Curing of the adhesive was carried out for 20 s using led light-curing unit (Woodpecker Curing Light LED D, having a peak wavelength of around 460 nm).

Using a Teflon instrument, Harmonize composite resin was placed into the cavities in two increments. Curing of each increment was done for 20 s. With a fine finishing tapered stone at low speed, removal of excess resin at margins was done. After finishing, all the teeth were stored in distilled water in an incubator (37°C and 100% humidity) at dissimilar time durations (1 day, 3, and 6 months). After respective periods of storage, the teeth were removed from the incubator and air-dried. Then, teeth were coated with clear nail varnish (excluding restoration and margins of the cavity) and were left to dry.

Then immersion of all the specimen was done in 2% aqueous methylene blue dye solution (freshly prepared, Ph 7.0) at 37°C for 24 h. Afterward, thorough washing of the specimen was carried under tap water. Then, mounting of the teeth was done and with a fine diamond disc at low speed, the specimen were sectioned mesiodistally into two halves. The cut sections were observed under stereomicroscope (Scope Capture Digital Microscope, Guangdong, China) at × 50 and photographs were taken by means of a digital camera attached to the stereomicroscope. Based on Dye penetration criteria, microleakage was evaluated for all the specimen by finding out the degree of dye penetration at the occlusal and the gingival margins [Table 1].[6]

Table 1

Dye penetration criteria

Score	Dye penetration
0	No dye penetration
1	Dye penetration into half of the enamel
2	Dye penetration into more of the half of the enamel
3	Dye penetration into the dentin without extending into the pulpal wall
4	Dye penetration into the pulpal wall

One specimen from each group was randomly picked, and resin-dentin interface was observed under scanning electron microscope (×1500).

Statistical analysis

Mean and standard deviation were recorded and analyzed. By means of the Regression model, three-way analysis of variance, the effect of the adhesive system, storage period and mean gap area were evaluated. When the test was significant, those groups were tested by Tukey's post hoc test for pair-wise comparisons. A value of P ≤ 0.05 was considered as significant.

RESULTS

The self-etch system revealed a significantly higher mean gap area at the gingival and occlusal margins. Significantly, a higher mean gap area was found in teeth which were stored for 6 months [Table 2 and Figure 1]. A hybrid layer with short resin tags was observed under scanning electron microscope observation in self-etch adhesive system with few areas showing the failure of adhesion after 3 months storage period [Figure 2].

Table 2

Mean occlusal and gingival gap area (μm), standard deviation and P of all variable interactions

Storage time		1 day		3 months		6 months		P
Adhesive	Margin	Mean	SD	Mean	SD	Mean	SD
Total etch Adhesive	Occlusal	26.4	5.2	25.6	3.6	33.4	6.9	<0.001*
	Gingival	47.3	7.5	54.5	8	94.5	9.7
Self-etch Adhesive	Occlusal	31.6	4.2	36.1	5.2	58.3	7.3
	Gingival	52.8	6	61	3.4	104	6.9

*Significant at P≤0.05 according to Tukey’s test. SD: Standard deviation

Figure 1

Bar chart showing the difference in mean gap areas among all groups

Figure 2

Scanning electron microscopy showed hybrid layer with short resin tags created by the self-etch adhesive system with few areas of adhesive failure after 3 months storage period

DISCUSSION

Perfect marginal adaptation depends on the composite resin quality and the adhesive system. Marginal imperfections might be seen in the areas with gaps. These gaps favor the accumulation of bacteria leading to secondary caries and in turn resulting in damage to the pulp. To prevent marginal microleakage, proper bond between the adhesive and the tooth surface must be ensured.[789]

Among the adhesives, we found that self-etch adhesive showed significantly higher mean gap area in both occlusal and gingival marginal areas. This difference might be owing to the disparity in the mechanism of action of the adhesive systems. In the case of total-etch adhesives, there is the formation of resin tags on etched tooth surfaces with complete elimination of the smear layer by the usage of strong phosphoric acid. Whereas self-etch adhesives result in deep demineralization chiefly with highly acidic adhesives and the nature of the bonding system of these adhesives is based on diffusion.[4] Thus, two factors affect the outcome of the bonded interface, the dentin structure and acidic monomers aggressiveness.[34]

Gupta et al.[3] and Guéders et al.[4] reported that self-etch adhesive systems are less effectual than the total-etch adhesive systems. According to them, the high acidic nature of the former system weakens the bonding performance significantly. Furthermore, demineralization products are seen in the hybrid layer. Therefore, mechanical adhesion occurs with an abrupt transition of the exposed collagen fibril network to the underlying unaltered dentin. This finding was in accordance with Owens et al.[5] who noticed after the usage of the self-etch adhesives, there was an increase in microleakage due to incomplete etching of the enamel surface by acidic monomer.

Geerts et al.[6] found that total-etch adhesives were superior to the self-etch adhesives. Our findings are in contrast with Osorio et al.[7] who found that both the self-etch adhesives and conventional conditioning of the enamel had comparable marginal integrity on enamel and they also found better marginal integrity on dentin with the former systems in comparison with the conventional procedure. However, the fact that in their study, Class V cavities were made and we did Class II cavities.

Takahashi et al.[8] observed far superior marginal adaptation with the self-etch adhesive system than the etch and rinse adhesive system. Similar findings were reported by Hayakawa et al.[9] This might be owing to the difference in the chemical composition as self-etching primers contain 10-MDP, which causes very low or minimum dissolution of the smear plugs. This results in reduced permeability of the dentin and facilitation of the polymerization penetration, impregnation, and entanglement of the monomers with dentin that is demineralized and forms a fairly thick hybrid layer. The hydroxyl groups of 10-MDP chelates with the calcium present in dental hard tissues.[89]

Most of the studies revealed the superior qualities of etch and rinse technique in respect to the bonding at the dentin restoration interface and we also found similar results. Our finding of the better seal at the occlusal margins than the gingival margins might be owing to the existence of higher organic component, configuration of the tubules, fluid pressure, and the inferior surface energy of dentin and also due to the polymerization shrinkage.[1011] Our findings revealed that 6 months of storage had significantly high mean gap area in both gingival and occlusal margins. We did not observe any significant variation between 1 day and 3 months periods; both showing the least mean gap area values. More microleakage in specimen stored for 6 months at all surfaces may perhaps be due to the water absorption with time in the polymer network that results in hydrolytic degradation of the adhesive.[91011]

Hashimoto et al.[12] suggested that bond efficiency of adhesives is affected on the long run after storage in water due to the property of hydrolytic degradation. This degradation is further assisted by the fact that the adhesives contain 10%–20% Hydroxyethylmethacrylate (HEMA), which penetrates the demineralized dentin in so doing improves the wettability of the adhesive. On the other hand, the hydroxyl groups in the dental adhesives increase their water sorption and results in lowered bond strength with time. With time, the stresses commenced at the resin-dentin interface result in the pulling of the collagen fibers in the hybrid layer, thereby tearing occurs along the bonded interface as the collagen fibers weakens with time due to hydrolysis. These findings were similar to Torkabadi et al.[13] who assessed HEMA free single step adhesive (G bond) and a HEMA-containing adhesive (Tri-s-bond) durability after storage for 1 year in water and they observed a significantly reduced bond strength in HEMA containing group. Similarly, Mousavinasab et al.[11] noticed higher microleakage at 6 months storage than 1 day and they attributed this to the varying concentration of HEMA in the bonding systems.

Yiu et al.[14] evaluated the role of copolymer hydrophilicity on water sorption and durability of the bond and recommended that water sorption has a crucial role in the properties of adhesives. Sadek et al.[15] found that 1 day and 3 months storage period had no major effect on microleakage of the single bond to dentin. Radovic et al.[16] stated that 3 months of storage of specimen did not cause any noticeable microleakage and bond degradation. Li et al.[17] found that observable microleakage occurs after 6 months of storage period.

CONCLUSIONS

The total-etch adhesive system augments marginal adaptation in comparison to the self-etch adhesive system and storing the composite resin in the water had a bad effect on all the teeth in respect to the marginal adaptation.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.