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Introduction, History and General Principles

Douglas Deporter, Domenico Baldi, and Mohammad Ketabi

Background

In the 40 plus years since the first reports appeared from Professor P-I Branemark and his colleagues of the clinical use and success of oral rehabilitation using endosseous, root-form, titanium dental implants [1-3], exhaustive laboratory, animal and human clinical research has led to major advancements in their design and use to replace hopeless or missing teeth. Branemark originally used his implant design, a machine-turned, commercially pure titanium screw, to restore long-standing, fully edentulous patients with splinted fixed prostheses meant primarily to provide occlusal function with no great attention being given to esthetic outcomes. Implants were placed in healed edentulous sites and allowed submerged healing for 6?months or more before being uncovered and restored with suitable prostheses. Survival after 10?years was in the high-90th percentile for mandible, but only in the mid-80th percentile for maxilla, likely due to differences in bone density. Subsequent replication studies in university settings (e.g. Leuven, Belgium; Toronto, Canada) and elsewhere then began to define further the prerequisites, indications and contraindications for their use in partially edentulous cohorts. While no mention of any limitations in implant length or diameter were specified by Branemark, the replication studies [4, 5] reported that Branemark's original design had a high risk of failure (=?25%) when used in lengths of less than 10?mm in mandible and less than 13?mm in maxilla, a belief that even today remains in the minds of some clinicians. However, this elevated risk with "short" implants was most likely due to implant design (machined surface topology) and inexperience by the investigators involved, as would later be concluded [6, 7]. The move to implants with moderately rough surface topologies [8] and introduction of titanium alloys containing zirconium to improve material strength [9] was a major advance. Today, we have a wealth of well-designed study results showing that both short (=8?mm) [6] and even ultra-short (<?6?mm) [10], moderately rough-surfaced threaded implants can offer excellent performance when properly used and restored.

The essential need for submerged initial healing in achieving osseointegration of dental implants also came to be challenged since investigators later learned that non-submerged implant placement in healed edentulous sites worked just fine, provided that initial implant stability was adequate [11]. Indeed, even limited, immediate loading in non-submerged cases started to be reported [12], again if appropriate initial stability could be achieved [13].

The Timing of Implant Placement

The original cohort of patients treated by Branemark had long-standing full edentulism and their implants were inserted into healed edentulous sites, often in primarily basal bone and with mature overlying soft tissues. However, we now know that other approaches can be taken including implant placement (IIP) at the time of tooth extraction ("immediate implantation"; type 1) or in some instances within the following 4-8?weeks ("early implantation"; type 2) after tooth removal, during which time initial soft tissue healing has occurred [14-16]. The advantage here is that an additional 3-5?mm of keratinized mucosa, including a significant mid-facial thickening over thin or damaged facial bone walls, can result [17]. There will also be some new bone formation apically in the socket which may accommodate easier implant bed preparation compared with IIP. Both of these "non-traditional" approaches, while challenging, can be suitable for replacement of non-molar teeth [16,18-20]. As will be seen, however, immediate placement via flapless surgery and hard tissue gap grafting with immediate provisionalization is the more heavily researched approach [21, 22]. Type 3 implant placement (after 12-16?weeks of healing) can still be indicated in more challenging situations, such as when the tooth socket is so damaged that it needs to be reconstructed in advance with guided bone regeneration (GBR), while type 4 coincides with the original Branemark approach of placing implants in long-standing, fully healed edentulous sites.

Current thinking is that "immediacy" (type 1) is often the preferred treatment if the condemned tooth or at least its root(s) remains to be extracted, and if so, two possible approaches have been suggested. In the ideal scenario with all socket walls intact, IIP with gap grafting is the usual choice (Figure 1.1). However, if the tooth has suffered extensive bone loss apically and/or buccally due to an endodontic failure or root fracture, provided that the IIP can be placed within the original boney housing with adequate stability, the principles of GBR can be used to regenerate the lost bone during the period of implant integration (Figure 1.2). Finally, if the damage to the bony walls is so extensive so that it is no longer possible to stabilize an implant within the original alveolar housing, immediacy will not be suitable, with the safer approach being socket preservation grafting [23] and delayed implant placement.

Figure 1.1 (a) This patient presented with a hopeless maxillary right central incisor. (b) Preoperative cone beam computed tomography showed the site to have a very thin buccal plate but adequate apical and palatal bone to place an immediate implant. (c) Flapless extraction was followed by implant insertion in a prosthetically ideal location for a screw-retained restoration. A large buccal gap was intentionally left and packed with particulate bone substitute material. (d) Initially a stock, wide body healing abutment was inserted and the soft tissues sutured. (e) A customized transitional crown was placed. (f) The restored implant after 4?years in function showing stable soft tissue morphology. (g) A radiograph taken at the 4-year recall confirming stable crestal bone levels.

Figure 1.2 (a) This patient presented with a failed endodontic treatment with chronic periapical infection and fenestration of the buccal plate at her maxillary right first premolar. (b) Because of the large buccal fenestration, a mucoperiosteal flap was raised to expose it. (c) After thorough debridement of the socket and periapical lesion, an immediate implant was inserted into the original bony housing. (d) Particulate bone substitute was used to graft the apical defect and buccal plate as well as the peri-implant gaps. (e) A collagen membrane was placed over the graft material. (f) Following periosteal release of the flap it was repositioned and sutured. (g) A panoramic radiograph of restored implant 5?years following surgery. (h) The restored implant 5 years in function.

A second case of IIP requiring simultaneous GBR is shown in Figure 1.3a. The patient's maxillary central incisors were extracted revealing major loss of the buccal bone, but it was still possible to secure two implants within the original bony housing of their roots. After ensuring adequate stability of the implants, the large defects were filled with particulate bone allograft, covered with a membrane and allowed 6?months of submerged healing (Figure 1.3b). At that point, cone beam computed tomography (CBCT) revealed significant buccal bone regeneration (Figure 1.3c). To allow wound closure, the large flap had been coronally advanced, which left the buccal covered with alveolar mucosa. Soft tissue grafting was proposed but the patient declined this extra surgery. As a result, it was not possible to regenerate the midline papilla, making it necessary to use a two-unit splinted prosthesis with the interimplant space masked with pink acrylic (Figure 1.3d).

Figure 1.3 (a) Two maxillary central incisors suffered endodontic complications and needed extraction. (b) After implant insertion, the defects were packed with particulate bone allograft material covered with a stabilized collagen membrane.

Source: Courtesy of Dr. Vahid Esfahanian and Dr. Sorena Abrishamkar, Faculty of Dentistry, Islamic Azad University (Isfahan Branch).

(c) Cone beam computed tomography at 6?months of healing revealed regenerated buccal bone and the implants were subsequently restored. (d) The final restoration including pink acrylic to mask the missing midline papilla.

Early Work with Immediate Implant Placement

The earliest report of IIP usage in humans was published in German in 1976 by Schulte and Heimke [24] using ceramic (aluminum oxide, Al3O2), press-fit implants, but this implant design was soon overtaken by Branemark's titanium threaded concept. One of the earliest reports using threaded titanium designs for IIP was a case series published by Richard Lazzara [25], the original founder of the 3i Implant Company. He applied the principle of GBR [26] to allow osseointegration of machine-turned threaded implants placed immediately after...