(A-24) Evaluating the Properties of Upgraded and Predecessor Multi-mode Adhesive

Introduction:: Minimally invasive dentistry, which emphasizes the conservation of natural and intact dentition, is rapidly evolving with adhesive biomaterials. The latest trend in recent adhesive dentistry is the multi-mode adhesive system, designed to be versatile and have a broad range of applications, allowing them to be used in various restorative cases. However, due to their complex hydrophilic-hydrophobic formulation, these adhesives are prone to enzymatic degradation or debonding to dental hard tissues, especially when applied to dynamic dentin. Despite such drawbacks, clinicians prefer the multi-mode adhesives because of their less technique sensitivity and broad range of applicability. Consequently, manufacturers constantly release new or improved versions of these adhesives, which can sometimes exhibit unpredictable outcomes and require extensive evaluation. This study evaluates the physical characteristics of two multi-mode adhesives: the upgraded Scotchbond™ Universal Plus adhesive and its predecessor Scotchbond Universal Adhesive (3M™ Oral Care, MN, USA) through rheometry and in-situ degree of conversion (DC) analysis.

Materials and Methods:: To determine the viscosities for the two adhesives in our study, a microfluidic viscometer (microVISC, Rheosense Inc., San Ramon, CA, USA) was utilized. 100 µL solution of each adhesive was introduced into the viscometer using a pipette. The viscosities were measured under a controlled temperature condition of 25°C at a 470 rpm speed with 1 s^-1 shear rate at 15 s run-time. Readings (in mPa·S) were recorded in triplicates for each adhesive. The in-situ degree of conversion (DC) of the solvent-free adhesives was measured using a near-infrared (NIR) spectrometer (NIST SRI 6005b) in transmission. The spectral changes were continuously monitored from immediately before the 10-s curing until 600 s, followed by DC calculation. The DC data were analyzed using an independent samples t-test.


Results, Conclusions, and Discussions:: RESULTS: The viscometry results indicated a notable difference between the two adhesives. The mean viscosity of Scotchbond Universal Plus adhesive was 50.2 ± 0.26 mPa·S, while that of Scotchbond Universal Adhesive was 115.5 ± 0.57 mPa·S. The Scotchbond Universal Adhesive exhibited a viscosity more than double that of its updated counterpart, suggesting a greater fluidity of the new version. Further, a statistically significant increase in-situ DC (p < 0.05) was observed in Scotchbond Universal Plus adhesive (90.8 ± 0.3 %) compared to Scotchbond Universal Adhesive (85.7 ± 0.2 %).

CONCLUSIONS: The recently upgraded Scotchbond Universal Plus adhesive is more fluidic in nature and has a higher polymerization ability than its predecessor Scotchbond Universal Adhesive.

DISCUSSIONS: Scotchbond Universal Plus adhesive has been formulated with a novel cross-linking monomer, replacing the highly viscous resin base oligomer, Bisphenol-A glycidyl methacrylate (Bis-GMA) that had previously formed the resin matrix of Scotchbond Universal Adhesive as outlined in the product safety data sheet. The high molecular weight of Bis-GMA has been suggested to contribute to the low fluidity of the Scotchbond Universal Adhesive, while the absence of this oligomer in Scotchbond Universal Plus may account for the increased fluidity of the product. The lower viscosity might have enhanced the monomer chain mobility resulting in a higher DC of the Scotchbond Universal Plus as demonstrated in our results.


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