Flexural strength and flexural modulus of repaired 3D-printed denture base resin: Effects of reinforcement and thermal cycling.

PURPOSE: This study evaluated the effects of reinforcement materials and thermal cycling (TC) on the flexural strength and modulus of repaired three-dimensional (3D)-printed denture base resin. METHODS: Specimens were fabricated from a 3D-printed denture base resin and assigned to five groups: positive control (PC; intact), negative control (NC; repaired with autopolymerizing resin only), metal repair (MR), fiber repair-thin (FR-thin), and fiber repair-thick (FR-thick). Each group was further subdivided into no TC (NTC) and TC (10,000 cycles) conditions. Flexural strength and modulus were measured using a three-point bending test. Data (n = 10 per group) were analyzed using nonparametric statistical methods (α = 0.05). RESULTS: Under both NTC and TC conditions, the NC group exhibited the lowest flexural strength and modulus (P < 0.05). The FR-thick group demonstrated the highest flexural strength and modulus, and after TC, its flexural strength was comparable to that of the PC group (P > 0.05). Failure mode analysis showed complete fractures in the PC and NC groups, whereas the MR and FR-thick groups consistently exhibited incomplete fractures regardless of TC. TC significantly reduced the flexural strength and modulus in all groups except the FR-thin group (P < 0.05). CONCLUSIONS: Thick glass fiber reinforcement yielded the greatest improvement in the flexural strength and modulus of the tested vat-photopolymerization-based 3D-printed denture base resin after repair. Following TC, the flexural strength of the FR-thick group was comparable to intact specimens, and its flexural modulus remained the highest among all groups.