LETTER TO THE EDITOR Dental implants in irradiated patients: which factors influence implant survival? Anke Korfage & Pieter U. Dijkstra & Jan L. N. Roodenburg & Harry Reintsema & Gerry M. Raghoebar & Arjan Vissink Received: 16 May 2014 /Accepted: 30 January 2015 # Springer-Verlag Berlin Heidelberg 2015 Dear Editor, We read the meta-analyses of Schiegnitz et al. [1] on survival of dental implants in irradiated patients with great interest. Although we underline their conclusion that dental implants are a valuable treatment option in oral cancer patients, we would like to make some critical remarks about their data entry and performing a meta-analysis. As such, we question the internal validity of this study. In Table 1, Schiegnitz et al. [1] provide an overview of the studies on dental implants they identified as eligible, and of which, some were included in their analyses. In our opinion, this table includes several errors. For instance, in the studies of Schoen et al. [2] and Korfage et al. [3], mandibular (and not both maxillary and mandibular as reported by Schiegnitz et al. [1]) implants were inserted immediately after the ablative sur- gery as well as that about two thirds of the patients received postoperative radiotherapy. Thus, the implants were inserted pre-irradiation in both studies (and not post-irradiation in the study of Schoen et al. [2] as stated in Table 1). Also, in the study of Schepers et al. [4], the implants were inserted pre- irradiation (and not post-irradiation as stated in Table 1). Furthermore, in the study of Klein et al. [5], implants were inserted post-irradiation instead of pre-irradiation as reported by Schiegnitz et al. [1]. Whether implants inserted before radiotherapy have a dif- ferent survival than implants inserted post-radiotherapy re- mains unclear since most long-term studies on implant surviv- al in irradiated jaws are on implants inserted post-irradia- tion. A major advantage of inserting implants before ra- diotherapy is that osseointegration takes place before the healing capacity of the bone is compromised by radiother- apy. Additionally, more patients can benefit from early oral rehabilitation as it has been shown that patients often are not in favour for implant surgery after completing their ablative surgery/radiotherapy trajectory because they are tired of any new treatment [6]. Schiegnitz et al. [1] state in their discussion that all six eligible studies published in 2007–2013 mention that the sur- vival rate of implants placed in irradiated and non-irradiated bone is comparable, which is not correct. In this respect, it is important to add an analysis on the reasons why implants are lost in irradiated patients: due to loss of osseointegration, due to resection of recurrent tumour, due timing of implant place- ment (before or after radiotherapy), and/or due to implant placement in native or reconstructed bone? When taking these confounders into account, e.g. Korfage et al. [3] and Linsen et al. [7] report a significant lower survival rate for implants placed in irradiated native bone, while in the study of Klein et al. [5], 17 % of the implants were lost in reconstructed bone (22 out of 128) and only 5 % in native bone (3 out of 62). The meta-analysis of recent studies (2007–2013) on im- plants in irradiated and non-irradiated native jaws was, ac- cording to Schiegnitz et al. [1], performed on three studies with a minimal mean follow-up of 60 months. In the study of Linsen et al. [7], the mean follow-up was 42 months. It is not clear how the data of that study is included in the meta- analysis. Furthermore, the number of events in this meta- analysis (lost implants in irradiated versus non-irradiated A. Korfage (*) : P. U. Dijkstra : J. L. N. Roodenburg : H. Reintsema : G. M. Raghoebar : A. Vissink Department of Oral and Maxillofacial Surgery, University of Groningen, University Medical Center Groningen, P.O. Box 30.001, BB70, 9700 RB Groningen, The Netherlands e-mail: a.korfage@umcg.nl P. U. Dijkstra Center for Rehabilitation, University of Groningen, University Medical Center Groningen, P.O. Box 30.001, CB40, 9700 RB Groningen, The Netherlands Clin Oral Invest DOI 10.1007/s00784-015-1435-2