Since the advent of modern root form osseointegrated implant dentistry in 1952 by Per-Ingvar Brånemark1 and colleagues, clinicians have strived for improvements in implant positioning in the esthetic zone to achieve predictable restorative and esthetic results. Years of clinical experience in congruence with controlled clinical studies have led to established parameters as a guide for these results. Prosthetic treatment planning and establishing a set clinical protocol prior to implant placement are paramount. It is important to note that proper implant positioning is patient and often implant-specific, and that inter-patient generalizations can result in myopic treatment planning and decrease the predictability of an esthetic outcome.
Treatment planning prior to implant placement traditionally begins with comprehensive medical and dental evaluation, articulated diagnostic casts, periapical and panoramic radiographs, cone beam computed tomography (CBCT) scans, and a diagnostic wax-up. Patient demands must always be taken into consideration prior to surgery, and presurgical mockups may be necessary to convey the information to the patient. Prosthetic treatment planning helps the clinician with a restorative-driven implant placement rather than a bone-driven approach, with the latter leading to poor abutment angulations and drastically reduced restorative options. Bone augmentation is often necessary in order to achieve optimal residual ridge dimensions prior to implant placement.
The inventive work of Sir Godfrey Hounsfield2 and the advancement of CBCT technology have led the dental profession into a new realm of dimensional accuracy that is often unattainable with conventional dental radiography. In combination with the use of a surgical or guided stent, proper 3-D positioning of a dental implant has become an attainable goal, leading to increased confidence for the clinician and accurate clinical results. The importance of the implant position can be manifested in the four dimensionally sensitive positioning criteria: mesiodistal, labiolingual, and apico-coronal location, as well as implant angulation.3 The ultimate goal is not only to avoid adjacent sensitive structures, but to respect the biological principles that have been established to achieve esthetic results.
Correct implant position in a mesiodistal orientation allows the clinician to avoid iatrogenic damage to adjacent critical structures. Maintaining adequate distance from adjacent teeth also helps preserve crestal bone and interproximal papillary height. When placing an implant adjacent to a tooth, it has been shown that crestal bone peak is based on and maintained by the bone level of the teeth adjacent to the missing space. A minimum distance of 1.5 mm between implant and existing dentition has been determined to prevent damage to the adjacent teeth and to provide proper osseointegration and gingival contours4-6 (Fig. 1a). Implants placed too closely together can reduce the height of the inter-implant bone crest, and a distance of less than 3 mm between two adjacent implants leads to increased bone loss. It has been shown that a distance of more than 3 mm between two adjacent implants preserves the interproximal bone peak and results in 0.45 mm of resorption on average, giving a better chance of proper interproximal papillary height (Fig. 1b). If the space between implants is 3 mm or less, the average resorption of the interproximal bone peak increases to 1.04 mm, compromising support for the interdental papilla.4,7 As a result, wide-bodied implants less than 3 mm apart in the esthetic zone would compromise the desired outcome.
Labiolingual implant position is often determined by the gingival biotype, occlusal considerations of opposing teeth, and desired emergence profile. An implant placed too far labially can cause bone dehiscence and gingival recession leading to exposure or show-through of the implant collar. An implant placed too far lingually can cause prosthetic difficulties with ridge-lap restorations that can be unhygienic and unesthetic. A thickness of 1.8 mm of labial bone has been determined to be critical in maintaining an implant soft tissue profile and increasing the likelihood of an esthetic outcome8 (Fig. 2). Labially oriented implants compromise the subgingival emergence profile development, creating long crowns and misalignment of the collar with respect to the adjacent teeth.9
Peri-implant crestal bone stability plays a critical role in the presence of interdental papilla.10 Many factors contribute to crestal bone resorption, including existing anatomy, surgical trauma, overloading, peri-implantitis, implant surface characteristics, microgap at the implant-abutment junction, type of connection between implant, and prosthetic components.11 Several factors are cause for concern in the apico-coronal placement of implants. Implants placed too shallow may reveal the metal collar of the implant through the gingiva. Countersinking implants below the level of the crestal bone may give prosthetic advantages with more running room for prosthetic components and tissue contouring, but can lead to crestal bone loss due to the location of a microgap at the implant-abutment interface. The ideal solution to exposure of the implant collar would be the placement of an implant equicrestal or subcrestal to the ridge. However, the existing microgap at the implant-abutment junction leads to bone resorption due to peri-implant inflammation.12 It is suggested that an implant collar be located 2 mm apical to the CEJ of an adjacent tooth if no gingival recession is present13 (Fig. 3). Implant diameter also plays a role in apico-coronal position, with smaller diameter implants needing more space for soft-tissue development and tissue contouring.
Implant angulation is particularly important in treatment planning for screw-retained restorations. Implants angled too far labially compromise the placement of the restorative screw, leaving the clinician with fewer restorative options. Implants angled too far lingually can result in unhygienic and unesthetic prosthetic design. For every millimeter of lingual inclination, the implant should be placed an additional millimeter apically in order to create an optimal emergence profile.14 In general, implant angulation should mimic angulation of adjacent teeth so long as they are in reasonable alignment (Fig. 4). Furthermore, maxillary anterior regions require a subtle palatal angulation to increase labial soft tissue bulk.15
The Inclusive® Tooth Replacement System was developed by Glidewell Laboratories as a complete, prosthetically driven method of restoring missing dentition. The solution comprises treatment planning, implant placement, patient-specific temporization, and the definitive restoration (Figs. 5a, 5b, 5c, 5d, 5e, 5f). When utilizing the comprehensive range of Inclusive Digital Treatment Planning services for guided implant surgeries and restorations, the clinician has absolute and precise control of each step. This results in an efficient and accurate workflow that is beneficial for the clinician and, ultimately, the patient. With the Inclusive Tooth Replacement System, the clinician has control of the four dimensions of implant placement in the esthetic zone, creating a consistently predictable result. Having a single source of services and materials is also advantageous in providing a more affordable yet high-value product for patients.