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Implant Dentistry: Innovations, Improvements Creating an Ever-Advancing Landscape
Advances in implant dentistry have altered the manner in which dental professionals consider and execute treatment in their daily practices. Innovations in implant therapies, designs, and techniques, combined with developments in regenerative materials, have stimulated rapid growth in this segment of dentistry.
Stephen J. Chu, DMD, MSD, CDT; and Maurice A. Salama, DMD
Since the early 1980s when P.I. Bränemark revolutionized the concept of osseointegration and bone integration to a titanium metal surface, dentistry has simply not been the same, and implant dentistry has continued to evolve.
By today’s implant dentistry standards, implant survival and osseointegration are afterthoughts; implant systems that cannot achieve this clinical benchmark consistently will not survive the competitive marketplace.1-3 Primary osseointegration can be thought of as initial stability of the implant offered by the macro-design of the implant body. Many manufacturers have created aggressive thread and pitch patterns to increase primary stability, especially in extraction sockets where initial bone-to-implant contact is a precious commodity. This design shift has allowed immediate or instantaneous temporization (ie, provisional restoration) of the implant placed into healed or augmented edentulous ridges and extraction sockets with consistent results in regards to implant survival.4-7 Secondary osseointegration is provided by the micro-surface texture of the implant, which has an effect over a 2-month healing period during which initial osseointegration is achieved.8,9 Implant position and diameter are key characteristics for complete osseointegration (ie, absence of labial plate dehiscence defects) of implants without placement of a hard-tissue graft.10-12
Immediate Implant Therapy
Immediate single-, partial-, or full-arch implant placement and provisional restoration therapy protocols, whether with healed or augmented ridges and extraction sockets, have become the “norm” because of the aforementioned innovations, enabling many clinical advantages. Consistent survival rate outcomes of 94% to 97% can be attained; such rates are comparable to delayed sites. The most impactful advantage may be the efficiency of treatment whereby the same number of clinical procedures is provided, however in fewer dental appointments, thus reducing overall treatment time. Providing “instantaneous teeth” at the time of implant placement surgery is a tremendous service to the patient, enhancing the transition from a removable to a fixed restoration.
Much effort has been put into esthetic outcomes, especially with esthetic zone implants. Treatment strategies have been devised to maximize mid- and long-term results, particularly with immediate extraction socket implants.
The “dual-zone” bone grafting treatment concept is one of maintaining or preserving existing hard and soft tissues versus recreating and reconstituting the periodontium.13 The “recipe” for success seems to be flapless tooth extraction, having an intact bony socket, use of a smaller-diameter implant, placement with a palatal-biased position, hard-tissue grafting the buccal plate–implant interface “gap” as well as the soft-tissue “zone,” and provisional restoration fabrication to contain, maintain, and protect the graft material during the healing phase of therapy.
In a cone-beam computed tomography study, minimum resorption of 0.1 mm of the buccal plate thickness was shown over a 6-month period.14 Other studies showed similar esthetic results in ridge contour change retrospectively over a 6-month to 4-year recall period.15
The same peri-implant soft-tissue enhancement results can be achieved if a connective tissue graft or bone graft is placed into the soft-tissue zone and contained with the provisional restoration or custom-contoured healing abutment. What remains to be seen is which bone graft would be best from a biologic response standpoint.16
Partial Extraction Therapies (PET)
The pattern and degree of resorption that takes place following the extraction of teeth has been extensively reported in the literature.17 This loss occurs as a result of the destruction of the bundle bone–periodontal ligament (BB–PDL) complex following the removal of a tooth and leads to resorption of these fragile tissues supporting the buccofacial ridge contour.18 Positioning a pontic restoration at a missing tooth site requires bulk of residual ridge tissue and a positive contour to create esthetic harmony between the restoration and the alveolar ridge. It is a well-established concept that to ideally or even adequately restore an edentulous or partially dentate patient in most instances requires management of these extraction sites by careful surgical intervention, either to prevent tissue loss or to augment the already collapsed tissues.19,20 The literature is abundant with these management techniques, which may be divided into pre-ridge collapse interventions, namely ridge preservation techniques, and post-ridge collapse interventions, namely bone augmentation, soft-tissue augmentation, or a combination thereof.19-22 A wealth of literature supports their application, though none of the aforementioned techniques can circumvent the primary cause of resorption, namely the destruction of the vascularized bundle bone and its ultimate effect—partial or total ridge collapse.20
To maintain this tissue complex, the tooth root, its ligament fibers, vascular supply, and attachment to bone need to be retained.23 Thus, the submerging of roots or submerged root technique (SRT) may achieve exactly that and has long since been reported on.24 This concept has been demonstrated with success in the development of pontic sites. An infection-free tooth root, whether treated endodontically or with vital pulp, when submerged, may support the ridge architecture to develop a pontic site.25 The technique is, however, contraindicated by endodontic apical pathology. Endodontic treatment first would need to be successfully carried out or the root would need extraction and an alternative ridge management procedure applied.
The socket-shield technique, in addition to its application as a buccofacial ridge preservation technique at immediate implant placement, overcomes this limitation and provides the clinician with an alternative method to submerge the buccofacial tooth root section, retain the vital periodontal tissues buccofacial to the root, and develop a pontic site with little or no collapse in a buccopalatal dimension.23 This exciting world of partial extraction therapy (PET) for implant and pontic sites may be an optimal solution for extraction site resorption and remodeling and could constitute a paradigm shift in case management, especially within the esthetic zone.
Recent research on implant design, such as connection type (ie, external or internal hex, flat or conical) and platform switching, relative to initial marginal stability indicates that design may not be able to overcome biologic principles and the need for re-establishment of the dentogingival complex (sulcus depth, epithelial and connective tissue attachment = biologic width) first described by Gargiulo et al in 1961 and further delineated by Kois in 1994.26,27 The importance of soft-tissue thickness as a protective barrier of bone has been acknowledged.28-31 When less than 2 mm of soft tissue is present, 1.2 mm to 1.7 mm of bone loss can be anticipated. Conversely, if more than 3 mm of vertical soft-tissue thickness is present, then bone stability can be realized with change of 0.1 mm to 0.4 mm over a 2-year longitudinal period.
Mechanical alternation of the implant or abutment surface (ie, uniform horizontal repeated patterns) has little positive effective or clinical advantage if the soft tissues are thin (≤ 2 mm). Platform switching may have a benefit but only tenths of millimeters due to the ever presence of bacterial plaque and the inability of tissue cells to adhere to contaminated and infected implant–abutment surfaces. It must be understood that the physical diameter of an implant component at the implant–abutment connection is critical for prosthetic stability and “biologic seal” and may be more important than internal shape and fit of such components.
Initial marginal bone stability should not be intermixed or confused with peri-implantitis. However, the lack of initial marginal bone stability could be the “nidus” for peri-implantitis.
CAD/CAM technology has been a “game-changing” innovation in implant dentistry. The so-called digital workflow enhances efficiency and consistency of results—specifically precision fit of extended-span and full-arch fixed dental prostheses frameworks compared to those that are fabricated through casting techniques.32 Zirconia frameworks are resistant to deformation when firing layered ceramics. In addition, luting metal inserts to the zirconia substructure also ensures a passive fit that cannot be achieved with traditional metal-ceramic full-arch bridges.
Peri-implant soft-tissue “physical” support is critical at the time of tooth removal; therefore, future provisional restoration strategies at the soft-tissue level will incorporate prefabricated “shells” or “sleeves” to support these tissues, not unlike prefabricated crown-formers for teeth.33
Surface treatment of implant and abutment components using argon gas-plasma charging devices has underscored the importance of enhanced disinfection and sterilization.34 Enhanced osseointegration and cell adherence to prosthetic components, whether definitive or provisional, to minimize soft-tissue recession and collapse may be beneficial future technologies.
Socket preservation membranes utilizing cross-linked collagen barriers and low-turnover bone graft particulates have been used for years to manage immediate extraction sites with a high degree of partial success. Rarely can the ridge be “preserved” completely (see above) and the remaining deficiencies must then be managed separately at a second stage using additional bone and/or soft-tissue augmentation procedures.
Bone grafting substitutes come in various shapes, sizes, and sources, including allograft (human), xenograft (animal), and synthetics (β-tricalcium phosphate-hydroxyapatite [βTCP-HA]). There appears to be controversy over which bone graft materials would perform best in extraction sites, adjacent to implants, and for contour grafting outside the labial plate to maintain or enhance ridge contour. The decision would be based upon the resorption and replacement rate of each bone graft substitute material. Synthetic and xenograft products seem to have a lower turnover rate and will remain the longest and, therefore, are best suited for contour or sinus grafts where this is preferable. Higher-turnover products like autologous chips and cancellous allograft bone would be ideal in extraction sites slated for future implant placement or adjacent to implants with marginal bone defects. The debate regarding an optimal bone graft material is ongoing, and this continues to be researched. One solution that has been suggested is to utilize a combination of 50:50% high- and low-turnover products in combination. More research is required before a determination can be made with any level of confidence. Therefore, biologics and regenerative materials continue to be rapidly growing arenas in implant dentistry.
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About the Authors
Stephen J. Chu, DMD, MSD, CDT
Clinical Associate Professor
Ashman Department of Periodontology & Implant Dentistry
New York University College of Dentistry
New York, New York
Maurice A. Salama, DMD