Dental implants allow the clinical dentist an additional tool in the armamentarium of treatment options to offer the patient for the replacement of a missing tooth or teeth. The conventional approach to treatment planning of dental implants includes a thorough clinical examination, review of intra-oral and panoramic radiographs, study models and a diagnostic wax-up. Additionally, diagnostic and therapeutic aids may include ridge mapping and laboratory fabrication of a surgical guide to facilitate the placement of the dental implant (Fig. 1). This last procedure is largely based on a best guess as it is not based upon the true anatomy of the proposed implant site. Traditionally there has been a greater emphasis on the surgical aspect of implant placement, with less consideration for the soft tissues, anatomical contour of the proposed restoration, submergence and emergence profile, occlusion, tooth morphology and final prosthetic outcome.
The demand for dental implants has increased significantly in the past 15 years, placing both the surgical and the restorative dentist continually searching for methods which increase the predictability of the final outcome. Issues of implant failure or patient displeasure are often associated with poor diagnostic and treatment planning methods. Advanced diagnostic aids such as Cone Beam Computerized Tomography (CBCT) not only allow for a comprehensive understanding of the three dimensional anatomy, but the additional use of specific software programs not only allow for virtual implant surgery prior to the actual surgical date. This technology also can facilitate the fabrication of CAD/CAM surgical guides (Fig. 2) and ultimately the fabrication of a definitive final custom abutment prior to the surgery, so that it can be delivered for an immediate non-functional restoration at the time of implant placement.
The conventional panoramic radiograph remains as an excellent tool to assess hard and soft tissues of the oral cavity. However, the two-dimensional panoramic radiograph delivers an inherently distorted image which can lead to incorrect diagnosis leading to incorrect treatment (Fig. 3).1 Certainly the advanced images afforded by the three dimensional CBCT scan offer the clinician further insight into the anatomical structures necessary for proper diagnosis, treatment planning and execution of proposed treatment. To further enhance the practical application of this evolving technology, CBCT scan templates may be fabricated to assist in the planning of endosseous dental implants (Fig. 4). Tooth position should be the ultimate guide in determining implant placement, as implant dentistry is a restoratively driven discipline.2-4
The traditional two-stage approach to dental implant placement requires a closed surgical site, burying the implant under the soft tissues during the healing phase of three to six months prior to activation, or uncovering with a second stage surgical intervention.5-7 Early loading techniques evolved when two stage implants were placed into the bone, a healing collar was attached immediately, and the sort tissue was sutured around the trans-mucosal element, obviating a second stage procedure. While not functionally loaded, the implants did have some stimulation from the oral environment. Immediate loading protocols allowed for the restorative components to be attached at stage-one surgery to support a transitional restoration, whether single, multiple or full arch reconstructions. Success rates for these changes in protocols have demonstrated results as favorable as those achieved with two-stage protocols.8-11
In order to achieve success with immediate or delayed loading, several requirements must be satisfied. These include:
— The presence of sufficient host bone;
— Primary stabilization of the implant;
— Immobility of the interim prosthesis for a minimum of eight weeks;
— Exceptional presurgical prosthetic planning;
— Template guidance for the surgical placement according to the restorative plan;
— Management of the soft tissue.
All six parameters must be met in order to achieve clinical success; if any component is missing then the result may be less than satisfying for the dentist, the patient or both. While all are important, too little emphasis has been placed on the pre-surgical prosthetic planning phase. Ideally, diagnostic study models must be acquired in advance to assess the tooth position and surrounding anatomy. A diagnostic waxup (conventional or digital) or denture tooth setup may be necessary in certain cases to address the desired functional and aesthetic outcomes. It has been stated that the goal of implant dentistry is not the implant, but the tooth that is being replaced.2 Implant dentistry must, therefore, be restoratively driven, and this is of the utmost importance when accelerated treatment protocols are to be implemented.
This article will review concepts that highlight the importance of presurgical prosthetic planning and state-of-the-art tools that can aid the clinician in improving diagnostic and surgical accuracy.
CASE REPORT
A 45-year-old male presented with tooth #12 fracture 1mm subcrestal to the zenith of the buccal soft tissue. The tooth has been previously treated endodontically and the clinical crown had been lost (Figs. 5). The patient’s medical history was unremarkable and on dental examination there were no other significant findings. The patient desired an immediate fixed-type replacement which preserved the healthy teeth and wanted to avoid a removable denture, Essix retainer or Maryland bridge provisional restorations.
After the clinical examination and review of the initial periapical radiograph (Fig. 6), the possibility of an extraction of the remaining root structure of tooth #12 and subsequent implant placement seemed feasible. The patient was advised of the potential benefits (as well as the potential biologic consequence) of a CBCT scan, this information would yield the information necessary to recommend the optimal treatment plan, based upon a comprehensive assessment of the bone for the potential implant placement. Based on this information a decision to take this CBCT scan was made. The CBCT scan was taken with a NewTom VG CBCT unit (QR S.r.l., Verona, Italy.) which provides a medium sized field of view.
The cross sectional CBCT data was initially visualized on tertiary software (InVivo 5, Anatomage. San Jose, CA) which revealed that the buccal plate was intact and there were no deficits in the bony structure around the entire circumference of the residual root (Fig. 7). Additionally within the resolution of the initial scan protocol there were no vertical fractures noted in the root structure. The cross sectional images conveyed the anatomical relationships necessary for diagnosis and treatment planning as well as the existing tooth position in relation to the surrounding bone. The normal tooth trajectory could be appreciated, along with the bony topography on the buccal and palatal aspects of the tooth. Using this interactive software, the clinician could visualize the placement of a proposed implant (manufacturer specific and size specific) in the receptor site within the alveolar housing and the “triangle of bone” as proposed by Ganz (Fig. 8).12
When we viewed the proposed recipient site with this software it was realized that the anatomy was ideal for not only and immediate implant placement, but also an immediate (non-functional) restoration. This determination was made by evaluating the amount of available bone apical to the existing tooth which could be utilized to provide primary stability for the immediately placed implant. A second tertiary software (Simplant 13, Materialise Dental, Dentsply, Glen Burnie, MD) which has powerful treatment planning options was then utilized to further examine the alveolus and potential implant positioning (Fig. 9). A digital copy of the contralateral lateral incisor (#22) was used. Thi
s was mirror and put into position to create a digital wax up. With the red colored implant in position and the green digital wax up of the proposed restoration the two were connected with a blue extension simulating the abutment (Fig. 10). This too was altered to reflect the ideal submergence profile, connecting the round profile of the implant to the triangular cross sectional shape of the crown at approximately the position of the CEJ.
The implant position was virtually positioned using the interactive 3D model and the other available views. This is extremely important when evaluating the planned implant position relative to the final restoration. Using features of the planning software, the virtual maxillary bone can be hidden from view to allow for an unobstructed perspective of the implant, abutment and crown. The implant was evaluated for parallelism to the adjacent roots, position relative to the buccal plate of the alveolus, emergence profile and projection of the abutment. The implant (Ankylos CX A11, Dentsply Implants, Waltham, MA) was selected specifically to be placed sub-crestally, allowing room to develop the submergence profile. The ability to rotate the realistic 3D images granted the clinician the opportunity to review and understand all aspects of the proposed implant position. The virtual planning phase was deemed acceptable.
The next phase of treatment was to translate this virtual plan into reality. The data set was converted so that a CAD/CAM surgical guide (Materialise Dental Inc, Dentsply, Glen Burnie MD) could be created. Not only did this ‘safe’ guide direct our placement of the implant in 3D (bucco-lingual, mesial-distal, apico-coronal) but also in the fourth dimension, timing, or where in 360 degrees of rotation will the implant find itself when positioned at its ideal final location. This is critical as the implant and the abutment are both indexed, and these indexed components must match for this technique to be successful. It was at this time that the prototype customized zirconium abutment was also milled. The design exactly matched what was proposed in the digital treatment plan phase. Additionally a stereolithic model was fabricated so that we could practice the proposed surgery prior to directly performing the procedure in the patient as what was being proposed had not been previously done.
At the date of surgery, the patient was appropriately anesthetized with local anesthetic. The remaining root #12 was atraumatically removed (Benex Extractor, Meisinger USA, Centennial CO). The remaining socket environment was check for any residual granulation tissue, additionally it was verified that there were no dehiscence’s or fenestrations of the buccal plate of bone. The surgical template was firmly seated onto the adjacent dentition. The secure positioning of the tooth-borne position allowed for accurate guidance of the drills in the irregular contours of the fresh extraction socket. Once the drilling sequence was complete, the implant was then placed into the osteotomy and rotated until the marker on the placement head matched the reciprocal marker on the CAD/CAM guide. This surgical guide, the implant driver and the placement head were then disassembled and removed from the surgical site.
A second CAD/CAM designed and fabricated template was then positioned on the incisal edges of the adjacent dentition. This was specifically designed to position the custom fabricated Zirconium abutment. Once the abutment is positioned, the prosthetic screw was tightened according to the manufacture’s specification (15Ncm), the access channel was filled with Teflon tape. A laboratory processed acrylic temporary restoration was seated and adjusted to remove any lateral, protrusive and occlusal interferences. In an attempt to reduce the load on the provisional during the healing phase, no occlusal contact were desired during any jaw movements. The prosthesis was provisionally cemented and remained in place for approximately eight weeks. A conventional periapical radiograph was taken of the area at this time (Fig. 11). After the eight week healing period the provisional restoration was exchanged for a definitive zirconium crown (Fig. 12). This was accomplished without removing the abutment from the implant interface, thereby not disturbing the surrounding gingival tissues. This embodies the clinical ideal minimizing the times an abutment is removed and replaced13 and maximizing the concept of placing a definitive abutment and not removing it throughout the course of treatment.
This case represents the combined use of CBCT planning, CBCT derived tooth-borne templates, digitally designed custom milled abutment and provisional restoration fabrication as well as the definitive crown design and fabrication with a successful result. As implant dentistry has evolved into one of dental sciences most predictable treatment alternatives, there has been a concurrent progression in available diagnostic imaging tools, from the standard periapical radiograph, panoramic radiography, two dimensional tomography and the latest advances in 3D CBCT technology. With recent emphasis on immediate or early loading of implants, the importance of understanding the existing anatomy in all dimensions is paramount to successfully integrating the desired plan with the surgical plan.OH
Dr. Karateew’s practice in Vancouver, Canada focuses on implant supported rehabilitation of the dentition. He has served on the faculties of the University of Pennsylvania, the University of Washington and the University of British Columbia in both post graduate Periodontics and Prosthodontics. He is Key Opinion Leader for Materialise Dental and for Dentsply Implants. www.drkarateew.com
Dr. Sadrameli had practiced general dentistry for 15 years prior to return to the University of Texas health Science Center at San Antonio where she received her Master of Science degree and Certificate in Oral and MaxilloFacial Radiology. She is a Key Opinion Leader for Materialise Dental. She now practices Oral Radiology in Vancouver, Canada. www.ddximaging.com
Oral Health welcomes this original article.
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