Original study - ZZI 02/2009

Retrospective radiographic investigation of the long-term stability of xenografts (Geistlich Bio-Oss) in the sinus

H. Ruoff1, H. Terheyden2

The Bio-Oss graft proved to be very stable over a 10-year investigation period. The height reduction over the apex of the implant averaged 0.1 mm per year. Six of the 364 implants in Bio-Oss grafts were lost (two before and four after loading) during the observation period of 0 to 12 years. Therefore, the cumulative survival rate was 98.4 %. Marginal bone loss was monitored for almost six years. Crestal bone resorption in the mesial aspect averaged 0.235 mm per year with a standard error of 0.021 mm per year. In the distal aspect, the resorption rate was 0.211+/-0.018 mm per year. Since the implants were still completely osseointegrated within the follow-up period, even in the case of low preoperative bone levels, it can be concluded that the Bio-Oss graft contributed to the stabilization of the implants.

 

Keywords: Sinus elevation, long-term stability, marginal bone loss, implant survival rate,

1 Introduction

Without further treatment, loss of both molars and premolars in the maxilla leads to a rapid reduction of the horizontal and vertical dimensions of the bone in the posterior maxilla. This process is further reinforced by the increased pneumatisation of the maxillary sinus [17, 28]. The causes of alveolar process resorption after tooth loss are varied and some of them have not yet been fully elucidated. Remodelling processes and atrophy of the empty sockets lead to resorption of 0.1 mm per year on average, though figures of up to 0.5 mm per year can also be reached [2, 22]. Because of the absence of an adequate stimulus originating from the periodontium, more bone is lost than is produced in the course of the physiological alveolar bone remodelling processes. The thickness of the walls of the sinus also diminishes due to the increase in sinus volume after loss of maxillary teeth and the loss of masticatory forces [8, 24]. The expansion of pneumatisation into areas of the maxilla that have become nonfunctioning can hollow out the edentulous alveolar process to a varying degree, sometimes completely, especially in elderly persons. The layer of bone separating the sinus from the oral cavity is often less than 1 mm thick [25].

Rehabilitation of the edentulous posterior maxilla with osseointegrated oral implants when bone volume is insufficient is a standard treatment today. When there is more than 4 mm to 5 mm of residual vertical bone, implants can be placed simultaneously with sinus floor augmentation. If less than 4 mm is available and primary stability cannot be guaranteed, a two-stage procedure is still generally recommended. When there is adequate vertical bone of more than 6 mm, the Summers technique using a crestal approach can also be employed [18].

Sinus lift is a technique-sensitive procedure that demands above-average surgical and prosthetic skills. However, a comparative analysis of the literature with regard to the implant survival rate shows that sinus floor augmentation with Bio-Oss is a reliable long-term method [1]. Although the predictability of the results is linked with the excellent volume stability of the bone that is regenerated in Bio-Oss [14], metrical data on the behaviour of the volume over time are rare.

The present study is the first to investigate radiographically the stability of the augmentation height, the crestal bone level and the duration of implant survival in sinus floor augmentation with Bio-Oss over a period of up to ten years.

 

2 Materials and methods

The study included 112 patients with 364 implants (Camlog and IMZ), which were inserted simultaneously into maxillary sinuses augmented with Bio-Oss (Geistlich). The implant survival rate of all 364 implants was determined. For radiographic evaluation of the time course of augmentation height, 690 digitalised orthopantomographs of 67 patients were measured who had 99 one-stage sinus floor augmentations with pure Bio-Oss and insertion of 186 Camlog and IMZ implants in the period 1995 – 2006. The lengths measured digitally in the orthopantomographs were calibrated, using the known original implant lengths. Calibration errors due to declination of the implant axis, compared with the projection plane, are below 2 % up to an angle of 11°, and were therefore disregarded compared with the standard deviation. Marginal bone loss mesial and distal to each implant was determined in 57 patients with 146 Camlog implants, and the course of the augmentation height was also measured. The investigation period was twelve months in the shortest case and 141 months in the longest case. Orthopantomographs at the following times were used:

on the day of operation or one to two days later,

on the day of incorporation of the superstructure or one to two days later,

orthopantomographs showing the time course at an interval of one to two years.

For quantitative analysis and to measure the augmentation height and crestal bone loss, the radiographs were digitalised either by a scanner or photographically, and were measured using the measuring tool of the Sidexis radiographic software, version 4.2 (Sirona).

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