21 March 2024

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How does the universal adhesive’s film thickness affect its ability to effectively bond to dentin?

Lorenzo Breschi, Diego D’Urso

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Introduction: Modern composite restorations rely on increasingly efficient adhesive systems, but sometimes it is not clear how thick the adhesive layer needs to be. The group of professor Van Meerbeek investigated the influence of adhesive resin application modalities on the film thickness and subsequent bonding performance. More precisely, the effectiveness of a two-step universal adhesive (UA) bonded in self-etch (SE) bonding mode to high C-factor class-I cavity-bottom dentin was investigated

Materials and methods: Eighty human third molars were collected, and randomly allocated to eight groups (n = 10), with four subgroups following two aging periods (“immediate” versus “aged”). After the application of the primer G2-Bond Universal (G2B, GC), the adhesive resin was applied into standard class-I cavities following four application modalities: (1) one layer, strongly air-blown; (2) one layer, gently air-blown; (3) two layers, each gently air-blown; (4) one layer, not air-blown. After the composite restorations, upon 1-week storage, all specimens were sectioned using a semi-automated diamond saw to obtain one central rectangular micro-specimen per tooth/cavity. Only the central μ-specimen was tested to standardize the adhesive film thickness and parallelism with the dentin substrate as good as possible, hereby avoiding any potential thickening effects near the cavity corners. The adhesive resin film thickness was measured using optical microscopy. The micro-tensile bond strength (μTBS) was tested immediately and upon 100,000 thermocycles. 

Results: G2B’s μTBS was significantly affected by the adhesive resin application modality and aging. Gently air-blowing the adhesive resin resulted in significantly higher immediate μTBS than strong air-blowing or no air-blowing. No significant difference in μTBS was found between single or double gently air-blown adhesive resin applications. The adhesive resin film thickness significantly varied with the application modalities. 

Conclusion:  The adhesive resin layer thickness influenced the bonding efficiency of the two-step UA to high C-factor class-I cavity-bottom dentin. According to Tang’s study, a film thickness ranging between 36 and 90 μm appeared to favorably influence bonding effectiveness. A too thin or too thick adhesive layer interfered with the dental adhesive’s bonding function. 

Improper air-blowing of the adhesive resin resulted in decreased bonding effectiveness in the two-step UA process, highlighting the importance for dental practitioners to meticulously adhere to the manufacturer's guidelines.

Keywords: Thickness, Universal Adhesives, Application modalities, Air-blown, Bond strength test

For more information:  Does the universal adhesive’s film thickness affect dentin‐bonding effectiveness? C. Tang, B. Mercelis, K. Yoshihara, M. Peumans, B. Van Meerbeek. Clinical Oral Investigations (2024) 28:150 

Source: https://doi.org/10.1007/s00784-024-05523-7