Evaluation of three-dimensional contraction of the volume of grafts after staged augmentation of the sinus floor, and an analysis of influential factors

Our aim was to evaluate the volume by which grafts contract after augmentation of the sinuses by three-dimensional analysis on cone-beam computed tomographs (CT), and to investigate the factors that influence the outcomes. The sinus floor was augmented with deproteinised bovine bone mineral in 58 patients with 123 edentulous sites related to 67 sinuses. The outcomes of augmentation were analysed by both linear and volumetric measurements on cone-beam CT images taken immediately after operation and six months later. Mathematical models were established to investigate the influence of anatomical characteristics of the sinuses and patient-related factors on contraction of the volume of the grafts. The mean reduction in the height of the grafts on site-based analysis was 17.8% after six months, and the contraction in volume on sinus-based analysis was 22.7 %. Of the edentulous sites 20/123 (16%) could not have implants 10 mm long inserted at the second stage operation because of insufficient bony height. Linear regression indicated that the type of edentulism (single or multiple teeth lost) was significantly associated with contraction in the volume of the grafts (p=0.006). Mixed model regression showed that the reduction in the height of the grafts was significantly influenced by the width of the sinus floor and the angle between the lateral and the medial wall of sinus (p=0.001, p=0.000). The reduction in height of the grafts and contraction in volume on linear and volumetric measurements six months after augmentation were roughly 18% and 22%, respectively. A wide sinus, large lateromedial angle, and loss of multiple teeth under the same sinus strongly predict that large amount of grafts will resorb. The anatomy of the sinus and patients' characteristics should be taken into consideration before treatment.