Effect of Aluminum Oxide Air Abrasion on Shear Bond Strength of Composite Resin to Human Dentin Using Two Adhesive Systems

Abstract

Aim:

To evaluate the effect of air abrasion on the bond strength of composite to human dentin using two different adhesive systems and to access the mode of failure using scanning electron microscopy.

Materials and Methods:

In this in vitro investigation, 38 human permanent mandibular molars were extracted so that the dentin was visible through the removal of the buccal and lingual superficial enamel. Buccal surfaces of all teeth were pretreated with air abrasion (50 μm aluminum oxide) while lingual surfaces serve as control without air abrasion before application of adhesive and were divided randomly into two groups (n = 19). GROUP 1- Etch and rinse adhesive; GROUP 2 – Self etch adhesive. Following application of adhesive, 76 “composite cylinders were made and bonded to the tooth (19 buccal and 19 lingual for each group), and light cured. Shear bond strength has been determined by using universal testing machine at crosshead speed of 1.0 mm per min” till failure. Type of failure has been then identified by SEM (scanning electron microscopy).

Results:

Specimens treated with etch and rinse adhesive with air abrasion showed highest shear bond strength with a mean value of 25.8 Mpa when compared to those treated with self-etch adhesive with air abrasion with a mean value of 17.36 Mpa.

Conclusion:

The Etch and Rinse adhesive is recommended for air-abraded dentin because it demonstrated markedly higher bond strengths than the Self-Etch adhesives.

INTRODUCTION

Dentin-bonding adhesive solutions either use the TE (total-etch) technique to eliminate smear layer or SE (self-etch) technique to keep it intact as a component of the bonding substrate.[1] SE adhesives partially incorporate smear layer into hybrid layer rather than completely dissolving or eliminating it like TE adhesives.[2] As it lowers the technique sensitivity of the bonding process, the possibility of partial resin penetration into demineralized dentin will be less, resulting in reduced post-operative sensitivity, thus the SE technique has become more popular.[3,4] Although the precise mechanism is unclear, SE monomers are thought to penetrate beyond the hybrid layer. Their interaction with hydroxyapatite creates an acid-base-resistant zone that strengthens the resin–dentin bond.[5]

Airborne abrasion with aluminum oxide enhances resin tag formation, increases surface area, and strengthens dentin bonding. The particle impact creates microscopic fractures, producing a rougher surface that favors adhesion.[6,7]

After air abrasion, a thinner smear layer remains that is more easily penetrated by acid. In self-etch adhesives, this reduced layer can promote resin tag formation and hybrid layer development.[8,9,10] These elements help to minimize the impacts of polymerization shrinkage, minimize microleakage, and seal the pulp.[11]

This study compared shear bond strength using etch-and-rinse and self-etch adhesives, with and without air abrasion, and analyzed failure modes under SEM to assess clinical relevance.

METHODOLOGY

Sample preparation involved 38 freshly extracted molars, excluding those with caries, cracks, restorations, or defects. Superficial enamel was removed using a diamond bur, surfaces were polished with 600-grit silicon carbide paper, sonicated for 10 minutes, and rinsed with saline. Ethical clearance was obtained (Approval No: ECASM-AIMS-2024-075).

SBS test samples

In total, 38 teeth were randomly assigned into two groups based on the adhesive used: Prime and Bond NT or Single Bond Universal. Buccal surfaces were pretreated with air abrasion, while lingual surfaces served as controls. Composite cylinders were subsequently demolded and adhered to the dentin surface perpendicularly [Figure 1].

Figure 1.

(a) Shear bond strength test setup with chisel loading at the dentin–composite interface; (b) total-etch adhesive without air abrasion showing predominantly cohesive failure; (c) total-etch with air abrasion showing mainly cohesive with some mixed failure; (d) self-etch without air abrasion showing predominantly adhesive failure; (e) self-etch with air abrasion showing mixed cohesive and adhesive failures (SEM, 100×)

Shear bond strength was tested using a universal testing machine (Tinius Olsen H50KL) with a chisel applied at 1.0 mm/min until failure occurred at the dentin–composite interface. After debonding, specimens were examined under a scanning electron microscope (ZEISS EVO 18) at 100× magnification to assess the mode of failure. Failures were classified as adhesive (at the dentin–adhesive or adhesive–composite interface), cohesive (within the adhesive or composite), or mixed (a combination of both).

RESULTS

Specimens bonded with the etch-and-rinse adhesive showed consistently higher shear bond strengths than those with the self-etch system. Air abrasion slightly increased bond strength in the etch-and-rinse group (25.8 ± 6.3 MPa vs. 22.6 ± 6.3 MPa, P = 0.131) and produced a significant improvement in the self-etch group (18.0 ± 6.3 MPa vs. 10.8 ± 4.2 MPa, P < 0.001). SEM analysis revealed mainly cohesive failures with etch-and-rinse adhesives, while self-etch adhesives showed predominantly adhesive failures without air abrasion and more mixed failures when air abrasion was applied, indicating improved interfacial bonding.

Statistical analysis

Statistical analysis was performed by IBMSPSS version 20-0 software. For all analyses, the level of statistical significance was set at P < 0.05 [Table 1].

Table 1.

Paired t-test – Bond strength comparison within groups

Group				n		Mean		Std. Deviation		P
1		Control – etch and rinse		19		22.6		6.3		0.131
		Etch and rinse + air abrasion		19		25.8		6.3
2		Control – self-etch		19		10.8		4.2		<0.001
		Self etch + air abrasion		19		18.0		6.3

DISCUSSION

This study assessed dentin bond strength using total-etch and self-etch adhesives, with and without aluminum oxide air abrasion. Results showed that total-etch, especially with air abrasion, achieved the highest bond strength and outperformed self-etch even without pretreatment. Its superiority is attributed to phosphoric acid demineralization, which exposes the collagen network and enables deeper resin infiltration, forming a strong hybrid layer with effective micromechanical interlocking.[12,13] The self-etch adhesives are easier to apply and don’t require distinct etching and rinsing procedures, which lowers method sensitivity. This study confirmed these findings, as self-etch adhesives showed weaker bonds, while air particle abrasion with aluminum oxide enhanced micromechanical retention by roughening dentin and reducing the smear layer.[14]

This study confirmed that self-etch adhesives showed lower bond strength even after air abrasion. Clinically, the total-etch approach, especially with air abrasion, provides the strongest dentin bond and is useful in high-stress cases or compromised dentin. However, its technique sensitivity and risk of post-operative sensitivity must also be considered.[13,15]

Despite the robust design of this study, certain limitations should be acknowledged. The in vitro study might not accurately represent the intricate oral environment, where variables like ageing, saliva contamination, and pulpal pressure can affect adhesive efficacy. To confirm that the relationships formed via these methods are long-lasting, long-term clinical research is required.[16,17]

CONCLUSION

In comparison to dentin surfaces treated without air abrasion, air abrasion of the dentin considerably strengthened the bonding between the composite and dentin in both “total etch and self-etch adhesives. Bond strength of the composite to” dentin has been considerably enhanced by use of total etch adhesive with air abrasion when compared to self-etch adhesives. Therefore, integrating mechanical surface treatments such as air abrasion will increase the predictability of the bonding to the dentin.

Conflicts of interest

There are no conflicts of interest.

Funding Statement

Nil.