Feasibility study on ultrasonic scaler tooth damage: IOS, interferometry, microscopy

To evaluate ultrasonic scaler-induced tooth surface damage using an intraoral scanner (IOS), green light interferometry (GLI), and optical microscopy (OM). Extracted third molars (n=6) were embedded in acrylic and mounted on a jigsaw mechanism applying a constant 1 N scaling force via a counterweight. A collaborative robotic arm (UR5/CB3, Universal Robots) manipulated an ultrasonic scaler (Varios 970 Lux, NSK) with two tip types (G6 and P20). Four combinations of angulation and orientation were applied robotically to the cervical regions of the teeth, creating four parallel line patterns (5 mm length, 10 s duration, 2.5 mm/s, five cycles). Surface evaluation was conducted using IOS (Trios 4, 3Shape), GLI (ContourGT-K0, Bruker), and OM (Hirox HRX-01). IOS images were processed using surface registration, surface distance measurements, and color-coded visualization. A total of 72 matching sites from IOS and GLI were analyzed using Bland-Altman and Passing-Bablok statistical methods. OM revealed clear surface defects in both P20 and G6 groups. In the P20 group, most defects were <20 µm and below the detection threshold of IOS and GLI, so further analysis focused on the G6 tip. IOS effectively visualized complex surface morphology, whereas GLI struggled with data acquisition and deeper structures but revealed microstructures missed by IOS. OM provided the most intuitive surface visualization. Average defect depths on dentin ranged from 52 to 65 µm and on enamel from 29 to 37 µm (measured by IOS and GLI). A Spearman’s σ of 0.9 indicates strong correlation. Bland-Altman analysis showed a bias of 12.09 µm (standard deviation, 23.53 µm). Passing-Bablok regression indicated a systematic bias (intercept, -2.2; slope, 1.16), suggesting IOS overestimates higher values. IOS, GLI, and OM are complementary. IOS is suitable for assessing complex surface morphology and evaluation of deeper defects, whereas GLI reveals finer micromorphological detail.