10 Chapter 1 GENERAL INTRODUCTION Patients experiencing problems with their conventional maxillary denture can benefit from an implant-retained overdenture (IOD)1-3. For the maxilla, several retention systems for the connection of the overdenture to the implants are available which can be roughly divided into bar retained IODs, in which multiple implants are splinted and the overdenture is attached through retentive clips, and retention systems using non-splinted solitary attachments. Four implants with a bar-clip attachment is currently the favourable treatment option as implant survival rates are high, marginal bone level change is low, patient satisfaction is high, masticatory performance improves and ten years complication rates are low1-7. Therefore, this treatment may be considered the current gold standard. However, treating patients with a maxillary IOD can be challenging, especially in case of severe atrophy of the alveolar process, in which extensive reconstructive surgery using bone augmentation is needed. The implant survival after reconstructive surgery is reliable and predictable, but harvesting of bone grafts is expensive and invasive, can induce morbidity and, due to the extent of the reconstruction needed, it is often performed under general anaesthesia8. Because of these factors, this treatment may be undesirable for certain categories of patients. With an increasingly aging population and subsequent age-associated co-morbidities, the demand for less invasive elective surgical procedures, with a much lower burden, is increasing. Thus, when reconstructive surgery can be avoided, morbidity, treatment costs, invasiveness and treatment-time are also reduced. Furthermore, the procedure can then also be performed in an outpatient treatment setting. The need for a reconstructive procedure could be reduced using 3D virtual surgical planning (3D VSP). Using 3D VSP, a 3D reconstruction is made from the patient’s cone beam computed tomography (CBCT) images, including the patient’s conventional denture9. With this 3D reconstruction, the available maxillary bone volume, and surrounding structures such as the nasal cavity and maxillary sinuses can be inspected virtually. Subsequently, virtual implants can be planned in the prosthetically preferred position where sufficient bone volume is present. Next, the planned position of the implants can then be transferred to the patient using a mucosa supported surgical template. Using a mucosa supported template, the stability can be compromised in case of resilient underlying mucosa, a shallow palate, or alveolar bone resorption. These factors are often present in patients experiencing lacking stability and retention of their conventional denture. Therefore, an open flap approach may be more appropriate10,11. Using an open flap approach, the alveolar process offers a bony support which allows for less template displacement of the surgical template. However, in case of extreme atrophy of the alveolar process, template displacement may still occur12-14. To overcome template positioning problems and enable safe and precise implant placement in atrophied edentulous maxillae, a template with enhanced stabilisation is needed.
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