[Long-term treatment outcome and influencing factors of teeth receiving modified crown lengthening]

Objective: To observe the long-term clinical treatment outcome and the influencing factors of the outcome for the teeth receiving modified crown lengthening surgery combined with root canal treatment and post-core crown restoration. To summarize the clinical guidelines of modified crown lengthening surgery in selection of indications and for mulation of treatment planning. Methods: Fifty-seven patients with a total of 67 teeth receiving modified crown lengthening surgery combined with root canal treatment and post-core crown restoration for at least a 6 months' follow-up period between July 2004 and July 2013 were recruited in this retrospective study by phone call interviews. The patients' clinical outcomes were evaluated by the combination of clinical examination, radiograph and questionnaire regarding patient-reported outcome of the last follow up (≥9 months post modified crown lengthening surgery and ≥6 months after definite crown restorations). All of the treated teeth were classified into two groups, group A (teeth with good clinical treatment outcome) and group B (teeth with poor clinical treatment outcome), based on the defined criteria including patients' satisfaction with the function and esthetics of the teeth and absence of periodontal, endodontic and prosthodontic complications. The potential influencing factors of clinical treatment outcome were also determined by Logistic regression analysis. Results: Vertical root fracture in 1 tooth was found on its periapical film and the tooth was deemed hopeless. Thus, the survival rate is 99% (66/67) for the multidisciplinary treatment approach. Seventy-two percent (48/67) of the teeth achieved good clinical treatment outcome and 28% (19/67) of the teeth developed one or several complications. In group B (teeth with poor clinical treatment), 16 out of teeth exhibited periodontal complications with bleeding on probing (BOP) positive mostly found. Logistic regression analysis demonstrated that plaque control (OR=21.392, P=0.014), edge form (OR=7.610, P=0.011), and smoking experience (OR=7.315, P=0.018) were the risk factors influencing the clinical treatment outcome of modified crown lengthening surgery combined with root canal treatment and post-core restoration. Conclusions: Modified crown lengthening surgery combined with root canal treatment and post-core restoration has a good and stable clinical effect in the observational time of 6-114 months. Plaque control, smoking status and edge form of the tooth appeared to be the influencing factors of this multidisciplinary treatment approach.