EFFECT OF A LOCALLY MANUFACTURED TOOTHBRUSHING SIMULATOR ON THE MONOMER ELUTION OF CAD/CAM RESIN COMPOSITE BLOCK - A PILOT STUDY Objective: This pilot study aimed to calibrate the high-performance liquid chromatography (HPLC) protocol for detection and quantification of monomer that may be eluted from a computer-aided design and computer-aided manufacturing (CAD/CAM) resin composite block (RCB) when subjected to an abrasion test with a toothbrushing simulator. Materials and methods: CAD/CAM RCB (Shofu Block HC) were sectioned and randomly allocated into two groups made up of Control group (CT) group (n = 4), and Toothbrush Abrasion (TA) group (n = 4). CT group was subjected to no surface treatment and TA group was subjected to a toothbrushing wear test following immersion of both groups in artificial saliva for 7 days. High Performance Liquid Chromatography (HPLC) was used to separate and identify urethane dimethacrylate (UDMA) and triethylene glycol dimethacrylate (TEGDMA) that were eluted from the slurry produced following the toothbrushing abrasion test of the TA group and from storage solution of artificial saliva of the CT group. Results: After the toothbrush wear test, 6.192 to 16.937 ng/µL of UDMA eluted from the TA group and no UDMA was detected in the CT group. TEGDMA was not detected from both the CT and TA groups. Conclusion and clinical significance: The HPLC protocol has been calibrated and toothbrushing wear resulted in detectable UDMA released from Shofu HC Block at a level that is not harmful to the patient.