February 2014, Volume 10, Issue 2
Published by AEGIS Communications
Dental Implantology: An Evolving Treatment Modality
Technology provides better information earlier in the process
Over the past 30 years, implant dentistry has evolved into a predictable, even conventional, treatment alternative for patients who are missing teeth. In fact, the art and science of implant dentistry has expanded to include many ancillary supporting modalities such as bone grafting, ridge splitting, sinus augmentation, soft-tissue grafting, biologic modifiers, 3-dimensional (3D) imaging technologies, CAD/CAM technologies, guided surgery applications, and enhanced restorative materials.
Diagnosis and treatment planning for dental implants has dramatically improved with the advent of computed tomography (CT), followed by a proliferation of lower dosage cone-beam CT (CBCT) devices. Two-dimensional (2D) periapical radiographs and panoramic radiography are inherently deficient in their ability to provide accurate diagnostic information for dental implant placement and related surgical procedures due to potential distortion and the inability to communicate 3D information related to the maxillo-mandibular anatomy. Advanced imaging technologies and interactive treatment-planning software have now made it a clinical reality for clinicians to be able to assess the individual patient-specific anatomy—before the scalpel ever touches the patient. The quantity and quality of bone can be determined, aiding clinicians in making educated treatment decisions. Implant receptor sites can be evaluated with ever-increasing accuracy, based upon complete visualization of the buccal and lingual cortical plates and intermedullary bone. However, since the goal of implant dentistry is not the implant itself but, rather, mimicking the tooth that is replaced, clinicians striving to achieve restoratively or prosthetically driven implant reconstruction must have a comprehensive understanding of the relationship between the tooth and the underlying bone.
The ideal pre-surgical workflow requires conventional impressions and mounted articulated study casts. A diagnostic wax-up, or duplicate of the patient’s denture representing the desired tooth position, can then be used to fabricate a radiopaque scanning appliance to be worn by the patient during the scan acquisition, providing the clinician unparalleled visualization of the relationship between the tooth and underlying bone. Depending on the interactive treatment planning software, protocols can differ regarding fiducial markers that act to register the digital information to the CBCT scan data.
Additionally, the proliferation of optical scanning devices at dental laboratories, or intraoral optical scanners, can play a role in acquiring this digital information that will be merged with the data from the CBCT scan, enhancing the accuracy of the planning software and allowing the gateway to CAD/CAM or 3D printing processes. Using an interactive treatment-planning software, the virtual implant can then be positioned within the receptor site to fit within the envelope of the desired restoration. It should be noted, however, that the link between the implant and the tooth is the abutment. Thus, it is essential to place a virtual abutment or an abutment “projection” with an appropriate vertical height to visualize the spatial positioning of the abutment as it relates to the tooth to achieve restoratively driven outcomes.
Using the Data
The use of CBCT imaging and interactive treatment planning has been increasing in its adoption for planning both the surgical and prosthetic phases of treatment. Once the scan is taken, regardless of whether a scanning appliance is used, the clinician has several options in using the data: 1) diagnostic-freehand; 2) template-assisted; and 3) full template guidance. Each CBCT device has its own native software, which can provide valuable 3D information about the patient’s anatomical presentation.
The concept of “diagnostic-freehand” can be divided into two applications: a) The surgeon can visualize these data, make measurements, plan the implant positions, communicate with the restorative dentist, and then perform the surgical placement freehand based on his/her personal level of experience; or b) The CBCT data (digital communication in medicine [DICOM]) can be imported into an interactive treatment-planning software where there are additional diagnostic and implant planning tools to enhance the process. The surgeon can then perform the surgery freehand based on the information gleaned from the virtual plan.
The template-assisted protocol can be described as when the information from the interactive treatment-planning software can be used to fabricate a surgical guide. Surgical guides come in several types, including bone-borne, tooth-borne, or soft-tissue/mucosal–borne, and contain guide cylinders that correspond to the drilling sequence for osteotomy creation. Surgical guides can be used in flapless/minimally invasive or flapped surgical procedures, helping to increase accuracy and minimize surgical time and potential patient morbidity.
Encompassing perhaps the most important innovation, the full template guidance method involves a link between the surgical guide and the implant manufacturers’ components. The development of implant specific-hardware allows for full template guidance when it is possible to deliver the implants through the guide with specially designed carriers that provide for the most precise placement. Full template guidance has been made possible by the collaboration between dental implant manufacturers and interactive treatment-planning software companies who have developed innovative solutions for treating patients.
Bone Volume Preservation
3D imaging technologies can identify with great clarity areas that have insufficient bone volume for implant placement. When a tooth needs to be extracted, preservation of the alveolar ridge has become a significant and practical procedure to prevent resorption and to provide enough bone volume for future dental implant placement. If there is not enough bone volume within a designated receptor site to place an implant, many options are now available to enhance deficient anatomy to create a sound foundation for subsequent implant placement.
The area of biologics has greatly expanded the choices for clinicians to determine the appropriate method and materials to rebuild lost soft- and hard-tissue anatomy. Demineralized bone, mineralized bone, bone putties, allografts (human cadaver bone), and zenografts (bovine bone), as well as combinations of particulate and block graft materials, are available as scaffolds to increase volume and promote new bone growth.
There are also a variety of different resorbable and nonresorbable membranes of various materials that can be used in conjunction with grafting procedures with and without tenting screws to preserve space as an aid to the remodeling process. The most popular membranes are made from different configurations of collagen matrices, and can be short acting or long acting, depending on the desired usage.
Use of autologous biomaterials has also been expanded since the development of platelet-rich plasma (PRP) many years ago. Natural bioactive membranes can be fabricated from the patient’s own blood for the purpose of enhancing hard- and soft-tissue healing. PRP protocols are basically enhanced fibrin glues.
Recent advances with platelet-rich fibrin (PRF) create a true fibrin-based biomaterial that can function as a membrane with its improved properties and incorporation of significant growth factors. As a completely autogenous material developed from the patient’s own blood, the membranes derived from this process are easy to handle and inexpensive to produce. These membranes can be used to cover surgical sites, mixed with bone grafting materials, acting as optimized blood clots.
Sinus augmentation procedures were introduced years ago to provide sufficient support to place dental implants in the severely resorbed posterior maxilla. New surgical techniques and instruments have significantly simplified maxillary sinus surgery by decreasing the potential of perforating the Schneiderian membrane through the selective cutting action of hard tissue rather than soft tissue. Creating a piezoelectric bony window osteotomy can be accomplished without damaging the soft tissue, followed by piezoelectric sinus membrane elevation to separate the membrane without causing perforations. The concept of piezoelectric surgery has now been used for ridge splitting, intraoral bone harvesting from the ramus and chin, orthodontic procedures, impactions, distraction osteogenesis, and much more.
Other innovations for sinus grafting include the development of new surgical kits that include a variety of specially designed diamond-coated drills for crestal and lateral approaches to adding bone into the sinus without perforation.
The restorative phase of implant reconstruction has seen significant evolution in components, manufacturing processes, impression methodologies, and materials. Perhaps the most important technological change has been the increased use of CAD/CAM technologies for custom abutments, bars, and prosthesis fabrication. Due to the fact that most implants may not be placed ideally, and that round implants are not true representations of natural tooth morphology, custom abutments are a necessity for the restoration phase. The lost-wax casting method has many issues, including the labor-intensive method of fabricating custom abutments. CAD/CAM technology allows a higher degree of accuracy, consistency, improved emergence design, and morphology, avoiding the porosities and distortion that can occur with analog casting methods. In addition, custom abutments can be fabricated from titanium or more esthetic materials like zirconia. CAD/CAM bars for overdenture applications or as a base for fixed-detachable hybrid restorations have also benefitted from advances in computer design and highly accurate machining to create a significantly improved end product. CAD/CAM technology has been now used to fabricate full-arch restorations from monolithic zirconia, providing enhanced strength without compromising esthetics.
The evolution of dental implants will continue as the industry progresses in combining both the art and science of replacing lost intraoral anatomy and as dentistry remains committed to developing improved methods and materials to treat patients who require these services.
About the Author
Scott D. Ganz, DMD
Prosthodontics, Maxillofacial Prosthetics, and Implant Dentistry
Fort Lee, New Jersey
New Jersey Section of the American College of Prosthodontists