Three-dimensional evaluation of secondary alveolar bone grafting using a 3D- navigation system based on computed tomography: a two-year follow-up

Abstract

Secondary bone grafting is widely used in the closure of oronasal fistulas and reconstruction of maxillary defects. It often fails from lack of physiological stress or inadequate covering of the transplanted bone with surrounding tissue. The aim of this study was to assess the exact bone volume after secondary alveolar bone grafting over a period of two years using a navigation system based on computed tomography (CT).

We examined 20 patients with complete unilateral cleft lip and palate (UCLP) who had been treated by secondary bone grafting during late mixed dentition. CT scans of the upper jaw were taken immediately preoperatively, and 1 and 2 years postoperatively. The cleft defects and the bony bridges were marked on the monitor. The software of the navigation system created three-dimensional models showing the amount and site of bone resorption.

The mean bone loss after one and two years was 51% and 52%, respectively. There was a significant correlation between the size of the cleft and the success of the alveolar bone grafting (p = 0.01). When the teeth adjacent to the cleft were missing the amount of bone lost was 95% after the first year. There was also significant bone loss in the buccopalatine direction.

Three-dimensional reconstruction of the bony bridges with a navigation system accurately shows the amount of bone within the cleft site. This method is definitely superior to conventional two-dimensional orthopantomography.

Introduction

Primary osteoplasty at the time of initial repair of the lip or shortly afterwards as described by Schuchardt¹ was the common treatment for reconstruction of alveolar cleft defects before the 1970s. During the following period, gingivoperiosteoplasty has been proposed as an alternative to primary bone grafting until secondary autogenous bone grafting was introduced and became the method of choice in the 1980s.² The primary objective of secondary bone grafting is uniting and stabilising the alveolar segments before definitive orthodontic and restorative dental treatment.³ This technique has been standard practice for almost 30 years and has shown favourable results.

Radiographic measurements of bone resorption in relation to interalveolar bone height are the criteria for evaluation of success in most studies.4, 5, 6 The Bergland grading system of measuring the success of a bone graft has remained the gold standard and is used most often.2, 5, 7, 8 It is based on a comparison of the occlusal level of the interdental bone graft with that of the normal site on a four-point scale.

Although bone remodelling and two-dimensional changes can to a certain extent be evaluated by conventional radiographs, the failure of plain films to assess the changes in volume, morphology, and bony architecture are disadvantages inherent in the method. Lawson and Jones⁹ tried to overcome this problem using ultrasound in a porcine experimental model and found it useful when combined with radiography, but unreliable for deep clefts. More recently CT scans have been used to evaluate the outcome of secondary alveolar bone grafting.10, 11

The purpose of the present study was to illustrate the change in bone volume over a period of two years by creating three-dimensional models of the bony bridges on a computer workstation.