Research Article Effects of Calcium Phosphate Nanocrystals on Osseointegration of Titanium Implant in Irradiated Bone Jun Yuan Li, 1 Edmond Ho Nang Pow, 1 Li Wu Zheng, 2 Li Ma, 1 Dora Lai Wan Kwong, 3 and Lim Kwong Cheung 4 1 Oral Rehabilitation, Faculty of Dentistry, Te University of Hong Kong, Hong Kong 2 Oral Diagnosis and Polyclinics, Faculty of Dentistry, Te University of Hong Kong, Hong Kong 3 Department of Clinical Oncology, Li Ka Shing Faculty of Medicine, Te University of Hong Kong, Hong Kong 4 Oral and Maxillofacial Surgery, Faculty of Dentistry, Te University of Hong Kong, Hong Kong Correspondence should be addressed to Edmond Ho Nang Pow; ehnpow@hku.hk Received 14 July 2014; Accepted 8 October 2014 Academic Editor: Dong-Wook Han Copyright © 2015 Jun Yuan Li et al. Tis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Radiotherapy may compromise the integration of implant and cause implant loss. Implant surface modifcations have the possibility of promoting cell attachment, cell growth, and bone formation which ultimately enhance the osseointegration process. Te present study aimed to investigate the efects of calcium phosphate nanocrystals on implant osseointegration in irradiated bone. Sixteen rabbits were randomly assigned into control and nano-CaP groups, receiving implants with dual acid-etched surface or dual acid- etched surface discretely deposited of nanoscale calcium-phosphate crystals, respectively. Te lef leg of all the rabbits received 15Gy radiation, followed by implants placement one week afer. Four animals in each group were sacrifced afer 4 and 12 weeks, respectively. Implant stability quotient (ISQ), ratio of bone volume to total volume (BV/TV), bone growth rate, and bone-to-implant contact (BIC) were evaluated. Te nano-CaP group showed signifcantly higher ISQ (week 12,  = 0.031) and bone growth rate (week 6,  = 0.021; week 9,  = 0.001) than that in control group. No signifcant diferences in BV/TV and BIC were found between two groups. Titanium implant surface modifed with CaP nanocrystals provides a potential alternative to improve bone healing around implant in irradiated bone. 1. Introduction Te success of implant osseointegration depends on the quality and quantity of the surrounding bone [1]. Radio- therapy has been considered as one of the predominant factors causing implant loss [2, 3]. It alters the circulation and metabolism of bone. Irradiation injures the small blood vessels leading to persistent hypoxia and reduces the quantity and activity of osteoblasts [4]. A number of studies showed that the failure rate of implants placed in irradiated bone was higher than those in nonirradiated bone [5–7]. Tis fnding was confrmed in our previous study on a rabbit model [8]. Te radiation at 15 Gy demonstrated a signifcantly adverse efect on implant stability and BV/TV. Implant surface modifcations may promote cell attach- ment, cell growth, and bone formation which ultimately enhances the osseointegration process. Te surface modi- fcation includes physical method, chemical method, or a combination of both [9]. Te CaP coated implant has demon- strated enhanced osteoconductive properties in normal bone [10, 11]. However, to our best knowledge no studies have investigated the osseointegration of CaP coated implant in irradiated bone. Te present study investigated the stability and osseoin- tegration of CaP coated implant using our radiation compro- mised rabbit model [8]. 2. Materials and Methods 2.1. Animal Care and Grouping. Te animal experiment was approved by the Committee on the Use of Live Animals Hindawi Publishing Corporation BioMed Research International Volume 2015, Article ID 783894, 6 pages http://dx.doi.org/10.1155/2015/783894