Journal of Conservative Dentistry

ORIGINAL ARTICLE
Year
: 2012  |  Volume : 15  |  Issue : 4  |  Page : 383--387

The effect of surface treatments and bonding regimens on microtensile bond strengths of repaired composite: An in vitro study


Gouri Smita Acharya, MK Manjunath 
 Department of Conservative Dentistry and Endodontics, JSS Dental College, Mysore, India

Correspondence Address:
Gouri Smita Acharya
C/O Dr. Chinmayi Mohapatra, Sr. Doctors Quarters No.3, Medical Road, Ranihat, Cuttack-753007, Orissa
India

Abstract

Aim: To assess the microtensile bond strength of repaired composite resin that was surface treated by diamond point or silicon carbide followed by bonding using either only total- etch bonding regimen or silane coupling agent with adhesive resin. Materials and Methods: Fourteen composite blocks were aged under deionized water for 14 days. The bonding surface was prepared with coarse diamond point or silicon carbide. Two blocks with no surface treatment were used as control groups. The bonding regimen was either total-etch bonding regimen or silane coupling agent and bonding agent. The aged samples were then bonded to new composite. Five sections per block (each 1mm thick) were prepared; cut to obtain an adhesive zone of approximately 1mm 2 and subjected to microtensile bond strength testing. Results: The highest bond strength was obtained by surface treatment by coarse diamond point and total etch bonding regimen and least by silicon carbide and silane. A statistically significant difference was seen in all the four groups. Conclusions: Surface treatment by a coarse diamond point and total-etch bonding regimen provides highest bond strength. Thus, a simpler treatment regimen can contribute to a better bond strength in repaired composites.



How to cite this article:
Acharya GS, Manjunath M K. The effect of surface treatments and bonding regimens on microtensile bond strengths of repaired composite: An in vitro study.J Conserv Dent 2012;15:383-387


How to cite this URL:
Acharya GS, Manjunath M K. The effect of surface treatments and bonding regimens on microtensile bond strengths of repaired composite: An in vitro study. J Conserv Dent [serial online] 2012 [cited 2021 Nov 29 ];15:383-387
Available from: https://www.jcd.org.in/text.asp?2012/15/4/383/101919


Full Text

 Introduction



Resin based dental composites are gaining a wide acceptance in today's dental practice. [1]

In clinical practice, composite is exposed to atmospheric oxygen creating an oxygen-inhibited layer. [2],[3] This layer is viscous and contains unreacted C=C bonds. The unreacted C=C bonds of the functional groups on the surface of a polymerized matrix will allow the monomer of new resin composite to bond, thereby improving adhesion. [4]

But, over time these materials undergo degradation and deterioration in the intra-oral environment. [5] These processes lead to fracture or defects of the composite restoration either at the composite-tooth interface or within the restorative material itself. [6]

For years, the traditional management consisted of replacing entire restorations. [7],[8] More recently a minimally invasive operative philosophy that aims to repair such defects; which is more conservative, less traumatic to pulp, less time consuming and more cost-efficient or at least can be used as an acceptable interim procedure until further treatment has become a viable option. [9]

Due to of limited number of reactive methacrylate groups after polymerization and water sorption into pre-existing composite, the repaired composite cannot effectively bond to the aged composite restoration without adequate surface treatment. [10] In such cases, providing sufficient bonding to the old restoration is important, and can be achieved either mechanically or chemically. [11]

Though studies have been undertaken to find out optimal repair protocols using different bonding techniques; there exists a wide gap between experimental methods and those used in daily restorative practice. [12],[13]

Hence, in the present study surface treatment by Diamond point and Silicon carbide, which are most widely used for finishing composites are compared along with total etch bonding regimen and silane coupling agent with bonding agent.

 Materials and Methods



Fourteen composite blocks of a microhybrid composite resin (Esthet X HD; Dentsply India) {Shade B 2} were made; each measuring 8 mm × 8 mm × 6 mm using Teflon molds. From each block; 5 samples was prepared. They were stored in deionized water at 37°C for 14 days for aging. It was then categorized into 1 control (2 blocks) and 2 experimental groups (6 blocks for each group).

The grouping of samples is as follows:

Group A (Control group) (n=10)-No surface treatment

Subgroup A1 (n=5)- The bonding surface was etched (Frost; Ammdent, India) and bonding agent (Adper Single Bond; 3M, ESPE, USA) applied.

Subgroup A2 (n=5)- Bonding surface was treated with silane primer (Rely X Ceramic Primer; 3M, ESPE, USA) and bonding agent applied.

Group B (Experimental group) (n=30)-Coarse Diamond point {(125 μm to 150 μm); Mani Inc, Japan} was used for surface treatment. Surface was abraded two times for 5 sec by the same operator to maintain standardization.

Subgroup B1 (n=15)- Etching and application of bonding agent.

Subgroup B2 (n=15)- Application of Silane primer and bonding agent.

Group C (Experimental group) (n=30)- Silicon carbide {(Green carborundum stone); Shofu Dental corporation, Japan} was used for surface treatment. Surface was abraded two times for 5 sec by the same operator to maintain standardization.

Subgroup C2 (n=15) - Application of Silane primer and bonding agent.

After surface treatment the blocks were subjected to ultrasonic cleaning for 10 mins to remove surface debris and ensure proper adhesion of composite.

Following the surface treatments and bonding regimen applications, the aged composite blocks (Shade B2) were bonded to new composite (Shade A3.5). An increment of 2 mm was obliquely layered and light cured using a halogen light-curing unit. (Translux Energy, Heraeus KulzerInc, Germany) for 20 sec per increment at 600 mW/cm 2 .

5 Sections per block each (thickness of per section-1mm) were prepared by a slow speed diamond saw (Isomet saw; Buehler Lake Bluff, Illinois, USA). Hourglass shaped specimens with a cross-sectional area of 1 mm 2 were made and subjected to microtensile bond strength in a universal tester (Instron 3365).

Results were statistically analyzed using one way ANOVA and independent t-test

 Results



The results of the microtensile bond strength are summarized in [Table 1]. A comparison between various groups is depicted in [Table 2]. [Table 3], [Table 4], [Table 5], [Table 6], [Table 7], [Table 8] and [Table 9] denote the individual comparisions between two subgroups. [Figure 1] shows the comparative evaluation of all the six subgroups.{Figure 1}{Table 1}{Table 2}{Table 3}{Table 4}{Table 5}{Table 6}{Table 7}{Table 8}{Table 9}

 Discussion



Resin-based composites are widely employed in dentistry since the advent of adhesive technologies. [14] Adhesive dentistry brought into perspective the possibility of a more conservative approach for tooth restoration, based on the reduction of the cavity preparation size and the bonding of the restorative material (resin-based composite) to tooth structure. It led to more cohesive failures rather than adhesive failures. [15]

Hence, a feasible treatment option of such failed restorations can be the repair of just that failed part; rather than the replacement of the entire restoration. Repair preserves the sound tooth structure that would be at risk during replacement of the restoration and also prevents repeated trauma to the pulp-dentin organ.

However, repair of an existing restoration is also not bereft of all flaws. The substrate to be bonded is a chemically degraded one with no free radicals to bond to another layer of fresh composite. Commercially the available bonding systems; rely on primarily adhesion to either enamel or dentin with none, formulated specifically to bond to the non-mineralized aged resin-based composite substrate.

Bonding to this substrate depends on various surface roughening techniques such as with air abrasion, diamond points or acids and the use of intermediary agents such as adhesive resins and Silane primer. [9]

The resin composite used in this study (Esthet X HD) is a microhybrid composite with a particle size of 0.6 to 0.8 μm and loading 77% (by wt %) or 60% (by vol %). It belongs to one of the most commonly used resin composite family, and has been claimed by manufacturers to be used as an universal restorative material (for both anterior and posterior restorations).

Various techniques have been utilized to simulate the intra-oral aging conditions. [12],[16],[17],[18] Among all methods, aging due to immersion in water has generated maximum research and is most commonly seen in oral cavity. [19] Water diffusion through the polymer chains and boundaries with fillers and the hydrolytic deterioration of the polymer chains resulted in elution of components and the plasticization of the composite. Initially, this process would affect surface properties, such as hardness and wear resistance. However, with time, it also interferes with the bulk properties, such as the strength and fracture toughness of the material thereby, compromising the long-term durability of the restoration. [20],[21],[22] Hence, in this study, aging by immersion in water for 14 days was used.

It is rather easy to bond to fresh composite, which is covered by an oxygen inhibition layer, because a covalent bond is established between the uncured surface layer and the newly applied composite material. Aged composite materials lack this zone, and hence other viable alternatives to facilitate bonding of the new materials with the aged composite needs to be investigated.

In this study, three different surface treatments and bonding regimens were applied according to various alternatives; [23],[24],[25]

Creating a micro-mechanical locking substrate using a coarse Diamond point or Silicon carbide.

Forming a potential interpenetrating network using a total-etch bonding regimen.

Creating chemical bond to the surface of exposed glass filler surfaces by application of silane to the surface.

Although, the effect of different contemporary chemical and mechanical treatment procedures on the repair bond strength of aged composite were evaluated previously, the choice of the different chemical and mechanical repairing procedures in this study were aimed to evaluate the validity of the simplest and most common methods that were used in every day clinical practice.

Defects in the old composite resin restorations may be restricted only to the old composite resin or may involve the composite resin and the adjacent tooth structure as well. When such defect involves both the restoration and the tooth, additional preparations in the form of removal of discolored or carious tooth tissues and/or bevel preparation is recommended. In the daily dental practice, such preparations are usually done using rotary cutting instruments.

In this study, two different abrasives have been used:



Coarse diamond point.Silicon carbide.

The micro-mechanical roughening produced by these abrasives depends on the abrasive particle size. Silicon carbide is 29 μm and coarse Diamond point is 125-150 μm. Hence, more surface roughness is expected of the coarse Diamond point. This explains the higher bond strength obtained by groups using coarse Diamond point.

After surface treatment the blocks were subjected to ultrasonic cleaning for 10 mins. This was done to remove any superficial debris produced by the mechanical roughening, which might hinder the bonding to aged composite resin.

The highest repair bond strength obtained by the use of total-etch bonding systems can be attributed to:

The unfilled resins in the bonding agent penetrated into the roughened composite surface, creating a new oxygen inhibited layer.

The bonding agent formed covalent hydrogen bonds to the silane in the inorganic filler particles.

In the present study, silane pretreatment has shown lower bond strength when compared to Total-etch bonding regimen and can be attributed to: [25]

Mechanism through which fillers react when mechanically loaded, aged or abraded is by breaking off in clusters. This loss of fillers might reduce interaction with silanes and thus decrease the bond strength.

Incomplete solvent evaporation during air-drying may occur resulting in increased viscosity of the adhesive blend exerting an adverse effect on the polymerization.

Because of surface treatment; the silane layer on any remaining filler is depleted. Thus, chemical adhesion of the unpolymerized resin matrix to these inorganic particles was unlikely.

Following the surface treatments and bonding regimen applications, the aged composite blocks (Shade B2) were bonded to new composite (Shade A3.5). Contrasting shades were used to obtain an easily recognizable adhesive zone. This made it easier to prepare an hour-glass shaped specimen by cutting along this adhesive zone or interface.

Considering the afore-mentioned facts, surface treatment by coarse Diamond point followed by etching and bonding resin application produces the highest microtensile bond strength in comparison to either surface treatment by silicon carbide or application of Silane primer. From a clinical point of view this might be advantageous, since the use of silane may interfere with composite bond to enamel and /or to dentin exposed at the repair site.

However, in applying the findings of an in vitro study to a clinical situation, it is important to realize that the two situations are widely different and may not co-relate completely. Therefore, further in vivo studies have to be conducted.

I affirm that, I have no financial affiliation (e.g., employment, direct payment, stock holdings, retainers, consultantships, patent licensing arrangements or honoraria), or involvement with any commercial organization with direct financial interest in the subject or materials discussed in this manuscript, nor have any such arrangements existed in the past 3 years. Any other potential conflict of interest is disclosed.

 Conclusion



Within the limitations of this study it can be concluded that:

Bond strength obtained by surface treatment with coarse Diamond point is significantly higher than that obtained by surface treatment with Silicon carbide.

Total-etch bonding regimen produces higher bond strength compared to treatment with Silane primer and Bonding resin application.

The highest bond strength is achieved by surface treatment with coarse Diamond point followed by application of Total-etch bonding regimen.

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