Untitled Document

Interactive Computerized Tomography For Dental Implants: Treatment Planning From The Prosthetic End Result

Author: Michael Tischler, DDS Woodstock, NY

(Figures at bottom of page)

Abstract:

Dental implant treatment is multidisciplinary and based on the prosthetic end result. Treatment planning for an ideal dental implant prosthetic end result involves gathering as much information as possible. A key tool to successful treatment planning is Computerized Tomography (CT), allowing visualization of a surgical site in a three dimensional aspect. Interactive CT is now available that in conjunction with a surgical guide stent, can help guide dental implant placement into the ideal position with respect to function and esthetics. A further benefit of this process is the information on the CT translates the prosthetic end result for the patient. This article will review the current science and practical applications of interactive CT, utilizing a case example.

Introduction:

With the prosthetic end result driving many parameters of dental implant treatment, it is imperative to treatment plan with the final prosthesis in mind. Traditional diagnostic information via periapical and panoramic radiographs are only two dimensional and offer limited information. Through utilizing an interactive Computerized Tomography (CT) program (Sim/Plant™- Columbia Scientific Inc), the clinician can plan on a computer correct placement of dental implants with respect to position and esthetics in a three dimensional view. With the information from the interactive Sim/Plant program, a computer milled surgical guide stent (Implant Logic Systems., Cedarhurst, NY) can be made which is based on the desired prosthetic end result for the patient. Through following this protocol a surgeon can place dental implants while taking into account such factors as: reducing iatrogenic damage to vital structures, choosing the correct implant size shape and surface, hard tissue density and volume, the relationship of implants to the final prosthesis, and assessment of pre existing pathology.
This article will show through clinical cases, the theory and protocol of the Sim/Plant™ interactive CT software combined with a surgical stent from Implant Logic Systems.

Background.

Computerized tomography has been utilized in medicine since the early 1970's , but it wasn't until 1987 that it was used in dentistry. The superiority over traditional radiographic techniques are numerous. The elimination of distortion allows for increased predictability when planning implant cases. In 1988 Columbia Scientific, Inc. (Columbia Maryland) developed a 3D dental software program that worked with standard GE CT scanners. In 1993 Sim/Plant™ for windows was developed allowing clinicians to utilize their own computers to interactively plan an implant case. The further benefits of the Sim/Plant program is the availability to measure bone density, measure accurately the distance to vital structures, clearly mark vital structures such as the inferior alveolar nerve and sinus, and measure the volume needed for a sinus graft. Further benefits include the availability to see implants from a 3D perspective allowing verification of parallelism therefore reducing offset loading of implants.
The full potential of the program is seen when the position of the final prosthesis is translated to the CT scan, allowing placement of implants to correlate to the final end result.
The Sim /Plant™ software program is easily learned and intuitive. There are 3 basic views available on the Sim/Plant™ screen and a three dimensional view. The Panoramic view is similar to a normal two dimensional panoramic view (Fig 1) The difference being the view can interactively change in a buccal lingual direction. The axial view offers a perspective from a coronal/apical direction. (Fig 2) There is a cross sectional view that allows a mesial/distal cross sectional perspective of the arch. (Fig 3) This is extremely helpful in observing bone thickness and looking for anatomic variations. The cross sectional view also best correlates the position of the prosthesis to the bone. All three of these views correlate to each other, so when a marker is moved on one it corresponds to the other two views. The final perspective is a 3 dimensional view. (Fig 4)
The 3 dimensional view allows the clinician to check for parallelism of implants.
Prior to a patient obtaining a CT, first a radiographic guide stent must be made. If the implant site is a full arch, a duplicate of a denture is made so that a radiographic stent can be made from it. (Fig 5) If the implant site is bordered by teeth, then an impression of the arch is taken. The radiographic stent for a partially edentulous area could either rest on prepared or unprepared teeth. ( Fig 6 )
The CT is taken at any standard Tomography site. The information from the CT now must be translated to the Sim/Plant™ program. If the CT site has the specific Columbia Scientific software, the information is immediately put on to a removable storage disk and can be placed on the doctors computer. If the CT site does not have the software, the CT date must first be processed by Columbia Scientific and then sent to the doctor. The later option simply adds time and a processing cost. Either scenario creates the same result of the CT data being able to be interactively analyzed on the doctor's computer.
After the dentist plans the case and places the implants on the Sim/Plant™ program, the data is sent to Implant/Logic systems for fabrication of a surgical guide stent.
The surgical guide stent contains 2mm guide tubes that direct the placement of the implants during surgery. (Fig7) Specific drills from Implant Logic Systems fit into the 2mm tubes, creating a pilot osteotomy site. The surgical guide stent itself is made from the actual radiographic guide stent. The radiographic guide stent is sent back to Implant Logic Systems with the plan data on a removable storage disk. (ie. Zip disk- Iomega Inc.)
The surgery utilizing the surgical guide stent can be done transmucosal for a full arch case, with flap reflection being done after the initial osteotomy pilot sites are completed. In the case of an edentulous site bordered by teeth, the initial osteotomy pilot drills can be performed after flap reflection. The difference between the two is that in the later scenario, the surgical guide stent can be stabilized with adjacent teeth allowing for direct visualization of the bone.

Clinical Application: Maxillary Full Arch Reconstruction.
Esthetics are a key priority when planning dental implants to replace teeth in an entire maxillary arch. When utilizing an interactive CT with a surgical guide stent for an edentulous arch, the first step is to create an immediate denture that fulfils the ideal criteria for vertical dimension and esthetics. This denture can then be utilized to translate the tooth position to the CT, allowing interactive planning for the case. Once the relationship of the final prosthetic tooth position is seen related to the available bone on the CT, the clinician can then decide first if a fixed bridge is feasible or if a removable implant supported bar overdenture would better suit the patient.
Determination of the need to graft bone, and the location of implant position are other key decisions that can be made when a final prosthetic position is seen on the interactive CT.
A healthy 52 year old male presented with hopeless teeth in the maxillary and mandibular arches. (Fig 8 ) After atraumatic extraction of the remaining maxillary teeth, an immediate denture was delivered. After determining the patient was comfortable with the immediate denture with respect to esthetics and vertical dimension, the immediate denture was then duplicated utilizing a denture duplicator. (Lang Manufacturing Inc.Wheeling, IL) The duplicated denture was then sent to Implant Logic Systems, so that a radiographic guide stent can be made for positioning during the CT scan. The information now obtained on the CT will show a relationship of the final prosthesis position to the available bone. The patient then went for a CT scan utilizing the radiographic stent. Once the CT information is returned via a Zip Disk, it is then loaded into the Sim/Plant™ program on the computer.
Nine implants were planned to support an implant supported fixed prosthesis. The implants were placed in the Sim/Plant™ program with respect to correlation of the final tooth position of the bridge and with respect to bone availability. ( Fig 9) There were a few sites where it was determined that both bone grafting and sinus preparation with osteotomes would be utilized. (Fig 10) This allows for pre surgical planning for time, fees, and informed consent. After the case was planned using Sim/Plant, ™ the information was sent to Implant Logic Systems for fabrication of a surgical guide stent.

Approximately two weeks later, the patient was draped and prepared for surgery.
After delivery of appropriate local anesthesia, the pilot osteotmies were done transmucosaly through the surgical guide stent using the Implant Logic 2mm osteotomy burs. (Fig 11) The correct depth was pre determined and available on report. The depth of the initial pilot osteotomy preparation takes into account the tissue height, stent height, and bone. Often the initial depths are 22-26mm. After the initial pilot osteotomy preparations are done, a full thickness flap was performed, and the osteotomy sites were visualized.
At this point normal osteotomy preparations were done utilizing the implant systems normal osteotomy drills. The implant width and depth being pre determined from the Sim/Plant™ data. Nine Biohorizons dental implants (Biohorizons, Inc. Birmingham AL), were placed , their accompanying cover screws, and primary closure achieved utilizing continuous sutures. The final panograph reveals 9 implants placed in the correct position for esthetics and function. (Fig 16) Each implant correlates to the correct tooth position and is angulated to reduce offset loading. These tasks were accomplished via the aid of the Sim/Plant™ interactive CT program and the corresponding computer milled surgical guide stent.

Conclusion:

Through utilizing the latest technology of an interactive CT, dental implants can be placed in the correct position for esthetics and function. This pre operative planning also allows for a determination of the need for adjunctive grafting procedures. Through including information about the prosthetic end result in the CT scan, the final prosthetic position can dictate the implant placement.
The utilization of this treatment planning technology creates excellence in dental implant treatment and offers simplicity for the practitioner.

Refrences:
Ganz , S.D. "CT Scan Technology- An Evolving Tool for Avoiding Complications and Achieving Predictable Implant Placement and Restoration" International Magazine Of Oral Implantolgy Vol 1 2001 pp 6-13

2 Kopp KC, Koslow AH, Abdo OS. "Predictable implant placement with a diagnostic/surgical template and advanced radiographic imaging"
J Prosthet Dent. 2003 Jun;89(6):611-5

3 Zitzman, NU and Marinello CP, Treatment Planning For Restoring The Edentulous Maxilla With Implant Supported Restorations: Removable Overdenture vs Fixed Partial design. Journal Of Prosthetic Dentistry 1999:82:188-96

4 Klein, M, Cranin ,AN, and Sirakian, A, A Computerized Tomograph (CT) Scan Of Optimal Pre-surgical and Pre-Prosthetic Planning of The Implant Patient. Pract Perio and Aesth Dent 5(6); 1993 :33-39

Figure Legends:

Figure 1
Panoramic view from Sim/Plant™ software