43 Maxillary implant overdentures: surgical templates in atrophic jaws 3.1 INTRODUCTION Surgical templates aim to aid in placing implants in the prosthetically preferred position. They can be used in a flapless approach, supported by teeth or mucosa, or in an open flap approach supported by bone. There are several forms of (non)guidance. Non-guided means the implants are placed free-handed without the use of a template. Semi-guided templates are used to guide cavity preparation and are removed at implant insertion. Fully guided templates are used for both cavity preparation and implant insertion. When considering the use of templates for implant treatment, especially in the atrophic edentulous maxilla, clinical aspects such as the available bone volume are important. Cawood and Howell’s classification1 of edentulous resorption patterns may assist in choosing the type of template: When treating the edentulous maxilla, mucosa-supported templates (MSTs) can enable minimal invasive implant placement with mean accuracies at the implant shoulder varying from 0.8 to 1.7mm and with mean angular deviations of 1.9 to 8.4°2-7. MSTs are often designed using the double scan technique, which, among other things, utilises the patient’s denture as a template base8. Since implant placement inaccuracies are mainly caused by MST positioning error, stability is crucial2 and a safety margin around the implant of 3mm is advised6. Therefore, MSTs may only be suitable for Cawood class II (post-extraction) and III (rounded ridge) cases. An open flap approach is more appropriate for Cawood class IV (knife edge ridge)9,10, using bone-supported templates (BSTs). BST accuracies are similar to MST ones (with an implant shoulder deviation of 0.7 - 1.6mm and a mean angular deviation of 2.4 to 4.6°)11-13. Using an open flap approach any bone dehiscence can be directly noticed and resolved during surgery. The alveolar process offers a bony support which allows for less template displacement compared to a mucosa-supported template. In atrophic bone conditions (Cawood class V and VI) a conventional BST also allows for relatively easy displacement2,3,14, though there can be sufficient bone volume to place implants in the anterior maxilla. To overcome template positioning problems in these cases maxilla, a semiguided template was developed that utilises the nasal aperture as a fulcrum, creating a more forced and exclusive template fit, allowing for more confident and safe implant placement. To the best of our knowledge this is the first study to utilise the nasal aperture to support a surgical template. The aim of this study was to assess the clinical usability of the developed template and corresponding implant placement accuracy in patients with edentulous atrophic maxillae. 3.2 MATERIALS AND METHODS Patients All eligible patients referred between November 2017 and November 2018 to the department of Oral and Maxillofacial Surgery (University Medical Centre Groningen, the Netherlands) with an extremely resorbed maxilla (Cawood class V and VI) and suffering from retention and stability 3
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