Effect of mechanical and chemical surface treatments on the repairing of milled and 3D-printed denture bases

Abstract

Ensuring a strong bond between chairside autopolymerized acrylic resin to denture base is essential for denture repair and reline procedures. However, there is no established protocol to enhance bond strength between autopolymerizing resin and computer-aided design and computer-aided manufacturing (CAD-CAM) denture base materials. The purpose of this study was to determine shear bond strength of CAD-CAM denture bases and autopolymerizing acrylic resin after mechanical and chemical surface treatments compared with heat-polymerized acrylic resin. Heat-polymerized, milled, and 3-dimensional (3D) printed denture bases were divided into 4 surface treatment protocols: none (control), airborne-particle abrasion (APA), tetrahydrofuran, and Vitacoll application. Autopolymerizing acrylic resin cylinders were bonded to denture surface. Shear bond strength and failure modes were determined after thermocycling. Denture base surfaces were assessed for surface roughness, surface morphology, and microhardness before and after surface treatment. Data was analyzed using two-way ANOVA and multiple comparison tests. The results showed that APA significantly increased shear bond strength and surface roughness of all denture base materials. Tetrahydrofuran and Vitacoll application improved shear bond strength of heat-polymerized acrylic resin, but did not reach the level achieved by APA. Conversely, tetrahydrofuran application improved bond strength of 3D-printed denture to the level of APA. Tetrahydrofuran and Vitacoll application significantly reduced denture base hardness, compared with control and APA. In conclusion, mechanical surface treatment using APA enhances the adhesion of autopolymerizing acrylic resin to heat-polymerized and CAD-CAM denture bases. Tetrahydrofuran and Vitacoll chemical surface treatment improved adhesion to heat-polymerized acrylic resin, with only tetrahydrofuran enhancing bond strength of 3D-printed denture to the level of APA. Without surface treatment, the highest bond strength was shown in 3D-printed denture base material.

Keywords: Autopolymerizing acrylic resin; Bond strength; CAD-CAM denture; Milling; Printing.

Fig. 1

Flow diagram of the study.

Fig. 2

Schematic diagram illustrating shear bond strength test. Load was applied perpendicularly to material interface.

Fig. 3

Bar graphs of shear bond strength (MPa) results (n = 10 per group). Different capital letters indicate significant difference between surface treatment protocols within the same denture base material (p < 0.05). Different letters indicate significant difference between denture base materials within the same surface treatment protocol (p < 0.05). THF, tetrahydrofuran.

Fig. 4

Failure modes after shear bond strength test (a) stereomicroscopic images (original magnification 20x); (b) percentage of failure mode (%). APA, airborne-particle abrasion.

Fig. 5

Representative SEM images of heat-polymerized, milled, and 3D-printed specimens with various surface treatments. Original magnification ×5000. APA, airborne-particle abrasion; THF, tetrahydrofuran.