A guide to implant dentistry part 1: treatment planning

Assessment

Replacement of missing teeth with implant-supported prostheses is a challenging process and each case presents different degrees of complexity and surgical, restorative and aesthetic risk factors.^{4, 8} The SAC Classification system categorizes implant cases as simple, advanced or complex, which aims to assist the clinician with case selection and treatment planning and highlights potential complicating factors (Table 1).⁸

The site (aesthetic versus non-aesthetic), the case complexity and risk factors, such as soft and hard tissue deficiency, presence of keratinized tissues, infection at the implant site, occlusal factors, prosthesis design and laboratory support are the general determinants of the SAC Classification system.^{8, 9} The clinician's experience, patient's medical history and growth considerations are the general modifiers of the SAC Classification system.^{8, 9} The SAC Classification system determines the overall complexity of the case and more detailed assessment can be provided by using the aesthetic, surgical and restorative modifying factors at the implant site (Tables 2–4).^{5, 8, 9}

Systemic diseases can impact implant therapy by affecting healing or susceptibility to disease.^{10, 11} Patients with serious systemic disease (osteomalacia, osteogenesis imperfecta), immunocompromised patients (HIV, immunosuppressive medications), non-compliant patients (psychological and mental disorders) and drug users (alcohol) comprise a very high risk group to implant placement. Patients with irradiated bone (radiotherapy), severe diabetes (especially Type 1) and bleeding disorders (haemorrhagic diathesis, drug-induced anticoagulation) are also a significant risk group to implant therapy.^{10, 11}

Smoking is related to increased risk of implant failure and bone loss. There is increased risk of peri-implantitis in smokers compared to non-smokers (odds ratios from 3.6 to 4.6).^{12, 13} The combination of a history of treated periodontitis and smoking increases further the risk of implant failure and peri-implant bone loss.¹⁴ Implant placement is not an absolute contra-indication in smokers with a history of treated periodontal disease, but should be considered with caution and individualized maintenance is essential to identify any complications at an early stage.^{9, 14}

Age can be a significant modifying factor in implant therapy. Implants placed in jaws of growing patients can present with infra-occlusion, which leads to functional and aesthetic complications.¹⁵ Implant placement in young individuals is advised to be postponed until craniofacial/skeletal growth is complete.¹⁶

Local factors, such as the buccal bone thickness, interproximal bone levels, mesio-distal and inter-occlusal space, hard and soft tissue anatomy, infection at implant site and occlusal factors should be assessed on an individual basis and form the aesthetic, surgical and restorative risk factors at the implant site.^{8, 9}Figures 1–4 illustrate the factors in case assessment of a hypodontia case requiring replacement of upper right canine (UR3) and upper left canine (UL3).¹⁷

Pre-operative planning

Evaluation of patient's expectations and a thorough clinical and radiographic examination are the first and most important stages in pre-operative planning to identify potential complicating factors. Preventive dental care, elimination of any active infection and establishment of healthy soft and hard tissues are imperative prior to the restorative phase of the treatment.¹⁸ Articulated study models for diagnostic wax-up and tooth set-ups are essential for the construction of the radiographic stent which will aid the assessment of regional anatomy and bone volume availability, and the surgical stent which will facilitate the restoratively-driven implant placement.^{4, 19} For single tooth replacement or partially dentate patients with stable occlusion, diagnostic stages follow a conformative prosthodontic approach (Figures 5–8).

For full arch prostheses, extra-oral and intra-oral features will guide the decision towards a fixed or removable prosthesis (Table 5 and Figures 9–12).²⁰ Moreover, implant-retained overdentures will require additional space for the retentive attachments, and consideration for this space should be part of the pre-operative planning and guide decision-making.²⁰ Additionally, treatment outcomes for fixed or removable implant-supported prostheses in the edentulous maxilla show similar patient satisfaction.^{21, 22}

Regarding the provision of implant-retained overdentures, the extension, retention and stability of pre-existing conventional removable prostheses should be assessed prior to the provision of implant therapy (Figures 13 and 14).²³ The neutral zone impression technique should be considered for improving conventional mandibular removable prostheses, since mandibular dentures constructed using this technique show improved retention and stability.²⁴ Patients who fail to adapt to well-constructed conventional removable prostheses should only then be considered for implant treatment.²⁵ Furthermore, existing conventional removable prostheses can be converted to radiographic and surgical stents to assist with implant treatment planning.²⁶

Summary

Implant rehabilitation is a successful treatment modality for the replacement of missing teeth, but careful treatment planning and restoratively-driven surgical implant placement are prerequisites to success to control and minimize technical and biologic complications. The buccal bone thickness and interproximal bone levels for soft tissue stability, the correct implant dimensions for a favourable emergence profile, careful surgical technique, pink and white aesthetic harmony, design of the prosthesis to permit adequate oral hygiene, and planning for long-term maintenance care are the most important elements of treatment planning for implant-supported reconstructions. Attention paid to these factors will result in successful reconstructions with high patient satisfaction levels. The first part of the series focused on new patient assessment and pre-operative planning. The second part of the series will discuss the surgical and prosthodontic considerations and maintenance of implant-supported restorations as part of a successful implant rehabilitation.