Postoperative irradiation after implant placement: A pilot study for prosthetic reconstruction

Abstract

Purpose: On maxillofacial tumor patients, oral implant placement prior to postoperative radiotherapy can shorten the period of prosthetic reconstruction. There is still lack of research on effects of post-implant radiotherapy such as healing process or loading time, which is important for prosthodontic treatment planning. Therefore, this study evaluated the effects of post-implant local irradiation on the osseointegration of implants during different healing stages.

Materials and methods: Custom-made implants were placed bilaterally on maxillary posterior edentulous area 4 weeks after extraction of the maxillary first molars in Forty-eight Sprague-Dawley rats. Experimental group (exp.) received radiation after implant surgery and the other group (control) didn't. Each group was divided into three sub-groups according to the healing time (2, 4, and 8 week) from implant placement. The exp. group 1, 2 received 15-Gy radiation 1 day after implant placement (immediate irradiation). The exp. group 3 received 15-Gy radiation 4 weeks after implant placement (delayed irradiation).

Results: The bone mineral density (BMD) was significantly lower in the immediate irradiation groups. BMD was similar in the delayed irradiation group and the control group. The irradiated groups exhibited a lower bone-to-implant contact ratio, although the difference was not statistically significant. The irradiated groups also exhibited a significantly lower bone volume and higher empty lacuna count than the control groups. No implant failure due to local irradiation was found in this study.

Conclusion: Within the limits of this study, the timing of local irradiation critically influences the bone healing mechanism, which is related to loading time of prostheses.

Keywords: Empty lacuna; Head and neck cancer; Implant; Local irradiation; Postoperative radiotherapy.

Fig. 1. Surgical procedures. (A) Maxillary first molar of the rat (white arrow). (B) Implant was placed in the first molar space after 4-week later (white arrow).

Fig. 2. Local irradiation procedures. (A, B) Verifying radiation fields using an external beam simulator (Nucletron, Veenendaal, the Netherlands). (C, D) Radiation administration using a 6.0-MV linear accelerator (Elekta, Stockholm, Sweden) to marked position (white arrow). Field size of 2 × 2 cm (see light window).

Fig. 3. Microcomputed tomography analysis. (A) Three-dimensional (3D) image reconstruction using OnDemand 3D software. (B) Bone mineral density (BMD) in the region of interest (ROI). Red stars indicate a significant difference between the exp. and control groups (P < .05); orange stars indicate a significant difference between the control groups (P < .05).

Fig. 4. Histologic images of the implant sites. Upper: Hematoxylin-and-eosin (H&E)-stained images at lower magnification (12.5×). Scale bar = 500 µm. A - C: Exp. groups. D - F: Control groups. A, D: 2 weeks after implant placement. B, E: 4 weeks after implant placement. C, F: 8 weeks after implant placement. Black arrows indicate empty lacunae (H&E, original magnification 100×. Scale bar = 200 µm).

Fig. 5. Fluorescence microscopic images of the implant sites. (A) H&E-stained image, green and red emitting regions ofexp. group 3. (B) H&E-stained image, green and red emitting regions of control group 3. Injection time of fluorescence expression agents after implant surgery are shown on the upper left (original magnification 50×. Scale bar = 200 µm).