[Evaluation of the clinical effect of the teeth with subgingivally involved defect conserved by crown lengthening surgery].

Purpose: To evaluate the clinical effect of the teeth with subgingivally involved defect which were conserved by crown lengthening surgery.
Methods: 62 teeth, with defect subgingivally from 1.5 mm to 4 mm, mobility degree(MD)</= I degree, appropriate proportion between crown and root, underwent crown lengthening surgery by combining flap surgery and osteoectomy, and restored 4 weeks after operation and followed-up for one year. The parameters of MD, sulcus bleeding index (SBI) and maximal defect probing depth (PD) at different times were measured respectively. 46 anterior teeth were divided into two groups based on PD of pre-operation. The groups were as follows: minor defect group (<2.5mm) and major defect group (2.5 to 4mm). The results were evaluated by student's t test.
Results: The overall effective rate was 83.9%. PD and SBI demonstrated a significant improvement (P<0.01), but MD showed an increasing trend after operation (P<0.01). No significant difference about MD of anterior teeth in two groups was found before operation (P>0.05), but a significant increase about MD occurred in the major defect group one year after restoration (P<0.01), and there was significant correlation between MD of each stage after operation and PD of pre-operation in anterior teeth (r=0.489, 0.526, 0.531, P<0.01).
Conclusions: According to the biological width principle, crown lengthening surgery may conserve these teeth with subgingivally involved defect, and has a good, long-time clinical effect. But MD showed an increasing trend after operation and significant cor.