MRI for the display of autologous onlay bone grafts during early healing-an experimental study

Abstract

Objectives: Autologous bone grafts are the gold standard to augment deficient alveolar bone. Dimensional graft alterations during healing are not known as they are not accessible to radiography. Therefore, MRI was used to display autologous onlay bone grafts in vivo during early healing.

Methods and materials: Ten patients with alveolar bone atrophy and autologous onlay grafts were included. MRI was performed with a clinical MR system and an intraoral coil preoperatively (t0), 1 week (t1), 6 weeks (t2) and 12 weeks (t3) postoperatively, respectively. The graft volumes were assessed in MRI by manual segmentation by three examiners. Graft volumes for each time point were calculated and dimensional alteration was documented. Cortical and cancellous proportions of bone grafts were assessed. The intraobserver and interobserver variability were calculated. Statistical analysis was performed using a mixed linear regression model.

Results: Autologous onlay bone grafts with cortical and cancellous properties were displayed in vivo in eight patients over 12 weeks. The fixation screws were visible as signal voids with a thin hyperintense fringe. The calculated volumes were between 0.12-0.74 cm³ (t1), 0.15-0.73 cm³ (t2), and 0.17-0.64 cm³ (t3). Median changes of bone graft volumes of -15% were observed. There was no significant difference between the examiners (p = 0.3).

Conclusions: MRI is eligible for the display and longitudinal observation of autologous onlay bone grafts. Image artifacts caused measurements deviations in some cases and minimized the precise assessment of graft volume. To the knowledge of the authors, this is the first study that used MRI for the longitudinal observation of autologous onlay bone grafts.

Keywords: (MeSH): Magnetic Resonance Imaging; alveolar bone augmentation; artifacts; dental implants; diagnostic imaging.

Figure 1.

Inductively coupled intraoral coil with variable capacitor and diodes before (a) and after resin coating (b), and adapted to the individual region of bone augmentation using a silicon coating (c). Figure adapted from previously published work.

Figure 2.

Transversal cross-section through region 16 (FDI) preoperatively (t0) (a), with marked gingival outline (1), cortical bone outline (2), sinus floor (3) and Schneiderian membrane (4), postoperatively (t1) (b), with marked volume of bone graft (purple) and osteosynthesis screw (green) (c), and grafted bone volume by adding marked regions in every slice (d).

Figure 3.

Transversal cross-section in preoperative imaging of atrophic mandible (region 36-FDI) displaying the residual bone with inferior alveolar nerve (1), cortical bone (2), cancellous bone (3) and gingiva (4).

Figure 4.

Transversal cross-section through mandible in region 36 (FDI) displaying the residual bone with inferior alveolar nerve (1), cortical bone (2) and the bone transplant with cortical part (3) and cancellous part (4) covered by the mucoperiostal flap (5).

Figure 5.

Transversal cross-sections through mandible in region 46 (FDI) at t1 (a) and t2 (b) as well as transversal cross-sections through the maxilla in region 21 (FDI) at t2 (c) and t3 (d) displaying the residual bone with inferior with inferior alveolar nerve (1), cortical bone (2) and the bone transplant with cortical part (3) and cancellous part (4) covered by the mucoperiostal flap (5).