Influence of Staging and Grading and Multiple Factors on the Success of Non-Surgical Periodontal Therapy Performed by Dental Hygienists: A Retrospective Analysis

Objective: To evaluate the incomplete success rate (ISR) of non-surgical periodontal therapy (NSPT) performed by registered dental hygienists, considering periodontitis staging and grading and multiple tooth- and patient-level factors. Methods: Data from patients with periodontitis treated by registered dental hygienists at the University of Michigan were analysed. A complete medical history, periodontal chart and full-mouth radiographs were collected before NSPT (T0), and clinical periodontal parameters were recorded at re-evaluation (T1). Tooth-level ISR (tISR) was defined as the percentage of teeth with residual pocket depth (PD) > 4 mm [Condition 1 (C1)], or PD of 5 mm with bleeding on probing, or PD ≥ 6 mm [Condition 2 (C2)]. Patient-level ISR (pISR) was calculated as the percentage of patients with at least one tooth meeting the criteria for C1 or C2 at T1. Multivariate analyses assessed the impact of staging, grading and other tooth- and patient-level factors on ISR outcomes following NSPT. Results: A total of 1818 teeth from 133 patients were re-evaluated 113.2 ± 85 days after NSPT. The tISR was 28.6% and 20.6% for C1 and C2, respectively; while the pISR was 75.9% and 65.4%. Factors linked to higher tISR for both C1 and C2 included baseline PD and multi-rooted teeth. Smokers and former smokers had more teeth with pathological sites under C1. Higher tISR under C2 was observed in cases presenting radiographic bone loss > 33%. Advanced stage of periodontitis significantly predicted higher pISR for C1, with Stage III-IV patients over twice as likely to exhibit higher pISR than Stage II (OR = 2.35; p = 0.042). Conclusion: Advanced periodontitis stage at T0 significantly predicts higher pISR values, particularly for C1. tISR after NSPT is influenced by baseline PD, number of roots for both conditions and smoking for C1.