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.