Damage of irradiated teeth by ultrasonic scaling: an in vitro study

Purpose To test whether ultrasonic (US) scaling–induced hard-tissue surface loss on irradiated teeth depends on irradiation dose, type of scaler tip, angulation and orientation and tooth region. Methods In vitro study on 24 human molars irradiated with 0, 30, or 70 Gy. US scaling was robot-standardized (force 1 N, tips G6 and P20, angulation 15° and 45°, orientation back and lateral) with medium power and water spray. Surface loss was graded on intraoral scans by three blinded observers on a six-band ordinal 0–5 scale (increasing with loss depth) and analyzed with cumulative-logit ordinal mixed models for median and maximum depth. Results 30 Gy significantly increased the odds of deeper surface loss with the back orientation (median: β = 2.43, p = 0.039; max: β = 2.10, p = 0.022); no 70 Gy contrast reached significance, indicating a dose-threshold effect. The G6 tip increased the odds of deeper damage substantially more than P20 across both depth outcomes (all p < 0.001), and 45° angulation together with the back orientation further amplified peak damage. The root was more susceptible than the crown ( β ≈ 2.95, p < 0.001). Conclusions US instrumentation of irradiated teeth produced dose- and technique-dependent hard-tissue surface loss. Slim periodontal tips (P20) used at shallow angulation (15°) with a lateral orientation were associated with minimal surface loss across all doses and positions, whereas wider tip (G6) at 45° with the back orientation produced consistent measurable wear, amplified on the root and by prior irradiation.