CT-Based Oral Implantology

Dov M. Almog, DMD

Clinical Assoc. Prof.,
Dept. of Oral Diagnostic Sciences
University of buffalo
School of Dental Medicine 

From the Spring 2006 AADMRT Newsletter
Dov M. Almog, DMDDov M. Almog, DMD
Background and Significance

Accomplishing predictable prosthetic, aesthetic and functional results for single or multiple tooth replacement with dental implants is challenging. Historically, the overall success rate of dental implants was relatively high(1-6) (with or without the advent of cross-sectional imaging and or surgical guidance systems). However, as dental implants become an increasingly viable treatment option for replacing single and or multiple missing teeth,(7) we are bound to encounter more random anatomic conditions, necessitating complementary diagnostic imaging and surgical solutions. Furthermore, the discipline of oral implantology has become more complex as a result of an exponential increase in the number of practitioners involved in implant surgery, specialists and generalists alike, some experienced and others inexperienced(7, 8).

Historically, residual bone height observed on panoramic radiographs and residual bone trajectory (RBT) or angulation observed during surgery determined clinical parameters such as dental implant size and trajectory. However, this sometimes compromises restorative needs, i.e., mechanical, aesthetic and functional. The final trajectory of an implant, especially in a buccal-lingual direction, does not always conform to that of the natural tooth or the planned prosthetic trajectory (PPT). This may be primarily due to buccal bone loss in the first 1-3 years following tooth loss(9).

While no evidence has yet been established, probably one of the most common problems encountered in treating the dental implant patient is the lack of adequate treatment planning. This becomes a critical issue, especially when implants are placed in aesthetic zones that require precise consideration for final tooth position and distribution.



To date, many practitioners, specialists and generalists alike, are still limiting their dental implants' diagnosis and treatment planning to evaluation of study casts, anesthetizing and probing the depth of the mucosa over the bone, and the use of panoramic and or lateral skull radiographs. The later two are frequently used to determine the appropriateness of the alveolar bone and its relationship to critical anatomical landmarks.

In the same time, over the past couple of decades, a large number of peered reviewed professional manuscripts documented that optimal and critical implant size and orientation can be significantly aided by a cross-sectional, three-dimensional radiographic exam. Some even strongly advocated computed tomography (CT) as the appropriate pre-operative diagnostic modality prior to implant placement(10-35).

Moreover, the complementary use of radiographic guides, designed based on restorative principles, along with cross sectional imaging, was proclaimed to further advance diagnosis and treatment planning.(36-39) The use of cross sectional imaging reveals the outline, width and height of the bone, and relationship to anatomical landmarks. The addition of radiographic surgical guides, provides a precise illustration of the bone-to-implant and bone-to-planned prosthetic trajectory correlation. Different types of radiographic guides have been introduced to market over the years, all consisting of a radiopaque markers, suggestive of the planned prosthetic trajectory (PPT). Patients wear the radiographic guides during the cross-sectional exam. Information obtained from the imaging phase is then transferred to both the surgical and restorative phases of treatment (Figure 1).

Gutta percha
Figure 1: A diversity of imaging guides: Metal sleeve guides; Gutta-percha guides; Lead strip guides; and Circumference lead guides; all delineating the Planned Prosthetic Trajectory (PPT) and or outlining the ultimate prosthetic restoration over the implant site.
The Future of Oral Implantology

In a recent report from Kalorama Information,(7) a complete analysis of the growing dental implant market worldwide is provided. It is estimated that growth in implant-based dental reconstruction products will outstrip other areas of dental devices and products. According to the report, in the industrial world, over 240 million people lack one or more teeth. It is estimated that 40% of the western population is missing at least one tooth. In the United States, roughly 10% of the population is edentulous, and every year approximately two million Americans loose one or more teeth due to sporting accidents.

Additionally, the Kalorama report states that replacing a tooth with the traditional fixed partial bridges (FPB), which consists of a pontic that is attached to two surrounding crowns (abutments), has been shown to be problematic, and newer more permanent solutions are needed.

According to the Kalorama report, one of the most important developments in modern dentistry has been permanent tooth replacement with dental implants. Also, bone grafting and regeneration techniques have expanded the possibilities for implant-based restorative dentistry. These techniques are making it possible to enlarge the candidate pool for implants to include a sizable population who were poor candidates for dental implantation due to severe bone resorption.

What's more, the Kalorama report asserts that with the rapidly aging population trend in the developed world, a large number of companies see the opportunity to move into these sophisticated dental techniques.

In addition, a number of renowned professionals have cautioned our profession not to place a fixed partial bridge (FPB) between "virgin" teeth, that is, unless the patient refused the option of a dental implant, otherwise, the case might end up in court. According to Gordon Christensen if adequate bone is present, implants are state-of-the-art for everything from a single missing tooth to an edentulous case, and in order to serve the American public well and in adequate capacity, many more practitioners should make the effort to become proficient in this area.(40)

Yet, according to another renowned professional like Morton Perel,(41) universal proficiency in the field of oral implantology is lacking. Many implants are misplaced either in poor angulations (48%) and/or distribution (29%). Ironically, and rightfully so, Morton Perel compares placing implants to throwing darts.

How can we Assure more Predictable and Successful Outcomes

As discussed earlier, the use of advanced cross sectional imaging technologies in conjunction with radiographic guides has long been advocated to further enhance the scope of the pre-operative diagnostic information.(10-39) Moreover, in the mid 90s, utilizing different assessment methodologies, two manuscripts(42, 43) forecasted the future of imaging technologies in oral implantology, including the notion of a CT-based surgical guidance system was anticipated the in the 90s (Figures 2-4).

Picture
Figure 2: Cone-Beam CT panoramic slices of the mandibular region (obtained using the i-CATTM 3-D imaging technology, Imaging Sciences International, Hatfield, PA). Note radiographic pins in #30 and 31 positions, representing the planned prosthetic distribution and trajectories.
sagittal slices
Figure 3: Sagital slices of the mandibular #30 and 31 regions. Note alignment of the planned implants in a trajectory that is consistent with the planned prosthetic bucco-lingual trajectories.
Implant Master
Figure 4: Utilizing ImplantMasterTM (I-Dent, Ltd. Hod Hasharon, Israel), a 3-D reconstruction of a patient's anatomy was achieved and a surgical guidance template was designed and e-mailed for computer Rapid Manufacturing with precise drilling holes' distribution and trajectory, in which stainless steal sleeves with the prescribed inner diameter are glued in.
The notion of these methodologies generated an intense professional debate. Shortly after the AAOMR position paper(44) on preoperative implant site assessment was published, many challenged its validity. In a follow-up editorial, Brooks(45) asked the question: "Where's the evidence?" Does CT imaging in the preoperative stage of dental implants have any value, or is it simply another relatively expensive test that has no effect on the outcome in the majority of cases? Other questions raised in the editorial were whether the experience level of the clinician makes a difference in what type of imaging is necessary, does the amount of bone determined clinically make a difference and are there alternative methods to obtain information about undercuts and bone inclination that work better and are less expensive?

A year later, the American Academy of Oral and Maxillofacial Radiology, ad hoc Committee on Parameters of Care, issued an official report regarding parameters of radiologic care, including imaging of dental implant sites.(46) This report stated that panoramic imaging alone is not sufficient for imaging of dental implant sites whereas tomography, either conventional or computed, does provide the necessary radiographic information such as height, density and width of bone.

This report was also followed with a challenging letter to the editor.(47) Shortly after, a rebuttal(48) from the Academy of Oral and Maxillofacial Radiology, ad hoc Committee on Parameters of Care came out, explaining that the Academy's position is one of caution and is derived from adverse effects described in the literature.

Over the years, numerous reports and preliminary clinical studies documented clinical complications with implants and implant prostheses.(49-51) Also, a recent Meta Analysis(52) reported extensively on such complications. In addition, a textbook chapter(53) discusses different implant radiology modalities, their relative strengths and weaknesses, and supplementary imaging guides that might be helpful.

Similarly, the concept of using CT-based dental imaging, coupled with surgical guidance templates is gradually becoming evidence-based through review of recent preliminary clinical studies and case reports.(54-62) These studies describe interactive imaging programs that allow CT studies to be used for planning and constructing a surgical guidance device or navigate the delivery of dental implants at the time of implant placement. The objectives of these preliminary studies were to assess the accuracy of CT-image-based dental implants' planning and surgery. The authors of these studies concluded that these technologies demonstrate progress in oral implantology. However, only one study demonstrated correlating evidence to imaging technology. It showed that the use of conventional cross-sectional tomography before installation of single tooth implants increased the efficacy of periapical plus panoramic images, with respect to the prediction of appropriate implant size, by a factor of 2.5.(63)

Conclusions

Given the recent report from Kalorama Information,(7) the introduction of numerous associated commercial CT-based imaging and surgical guidance platforms and the projected increase in the number of practitioners involved in implant surgery, our profession is bound to go through major changes that will have major effects on the way we view and practice oral implantology. This alone provides sufficient argument for those currently providing services in oral implantology to get gear-up and involved.

While the researchers studying these CT-based imaging and surgical guidance platforms' methodologies agree that more outcomes assessment research has a long term value, in the meantime we must work together to optimize our patient's health.(64)

Many of the authors referenced in this report strongly believe that because dental implants are becoming widespread, careful examination of this pre-operative assessment phase may provide more predictable and successful outcomes, yielding substantial public health benefits. Benefits include preservation of adjacent teeth, lower costs and improved function, to name a few. The impetus to my argument in favor of these new technologies comes from a desire to improve patient care and clinical outcomes. This is a point that many of my colleagues and I have labored over and remain frustrated that our proclamations to this effect are frequently ignored and or present a frequent challenge in dentistry.

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