Fabrication of Surgical Templates with 3-D Imaging
The two-step Guide Right™ surgical guide system, which shows two planes, offers an alternative to stereolithographic surgical guides.
Various 3-dimensional (3-D) surgical guides for implant placement are available to dental professionals.1-5 Developed by manufacturers for use with advanced computer tomography and 3-D cone-beam scans, these guides—which include SimPlant® (Materialise, www.materialise.com), Invivo5 (Anatomage, www.anatomage.com), Easy Guide™ Implant Placement (Keystone Dental, www.keystonedetal.com), and Galileos (Sirona Dental Systems, www.sirona.com—assist dental professionals in placing implants in the proper position and angulation.6-9 Although these technologies facilitate the implant process, numerous implants are still positioned in a manner that greatly increases the risk of implant failure and iatrogenic injury to the patient.6-9 While many dentists have purchased guided surgery systems, actual use of the technology in their practice is less than expected due to the time and money dentists must invest into using the technology.10
Dental professionals also have experienced other clinical challenges with these types of surgical guides.1-5 The surgical guides available today require offsite fabrication and have remained costly.6-9 Guides are not easily altered to correct positioning, and dental professionals may experience difficulty when fabricating a properly functioning restoration.6-9 To address these concerns, various methods for fabricating surgical templates have been proposed based on a prosthetic wax-up.1-5 Although this technique may be all that is required to create a perfectly aligned surgical guide, solutions have remained limited for more challenging cases.1-5
Research has shown that implants should be placed between the buccal and lingual bone plates to increase clinical success.11-13 Pre-surgical radiographs can facilitate determining whether the proposed angle of the long axis of the guide sleeve will allow for ideal positioning.11-13 Radiographs also allow dentists to determine if planned implant placement conflicts with the roots of adjacent teeth, the maxillary sinuses, or nerves.11-13 Although conflicts may be visible in single-plane periapical radiographs, greater accuracy is possible using 3-D cone-beam technology showing two-planes.11-13 Using the information obtained from the cone-beam radiograph, conflicts between the axis of the planned implant placement and the anatomy of underlying alveolar bone can be corrected.13
The Guide Right System
When replacing a single tooth with an implant-supported restoration, determining the ideal location for the center of a dental implant is not an extremely difficult task. However, cases requiring multiple implant sites may be challenging. Although there are many surgical guide options, the Guide Right™ (DéPlaque, www.deplaque.com) two-step surgical guide system promotes improved accuracy and efficiency in cases requiring single or multiple implants by serving as an initial diagnostic surgical guide that can be evaluated with cone-beam imaging and corrected in two planes.
The Guide Right system uses open guide sleeves with magnetic guideposts to enhance drilling access and visibility of depth markings in 3-D surgical guides. The open guide sleeves are held in place by the magnetic field of the guidepost, while the surgical guide is fabricated.
Once placed intraorally and radiographs have been taken, the Guide Right system enables alteration of the template in a simple and efficient manner. To correct the guide sleeve angle, a guidepost-bending tool (Generation II Bending Tool, DéPlaque) is provided. Straight and offset guideposts are also available in various sizes for altering the guide sleeve position with or without changing the angle.
The Guide Right surgical guide system allows dentists to clearly see, evaluate, verify, and accurately place implants, with fewer concerns of implant failure due to poor implant placement. Additionally, the Guide Right template can be fabricated in-office by the dentist.
Overall, the Guide Right system provides many benefits over conventional surgical-guide systems. Fabricating the guide in-office requires minutes, not days. The cost of fabricating a Guide Right system is significantly less than having a stereolithic guide made. Further, the Guide Right system provides the opportunity for the dentist to properly communicate case expectations to the rest of the dental team.
A 48-year-old woman presented with a desire to replace the mandibular left second bicuspid and two molars that had been missing for several years, resulting in a resorbed alveolar ridge. She preferred to avoid grafting or ridge augmentation procedures, which would be possible using custom or stock-angled abutments if adequate alveolar bone remained.
Study casts were made of the patient’s jaws, and the spacing of the teeth was determined by measuring the size of the teeth in the contralateral arch. The available interarch space was verified against the opposing dentition to ensure that sufficient room existed for prosthetic construction. The location of the center axis of the crowns was determined and marked on the alveolar ridge on the cast. Three relatively parallel holes were made into the planned implant axis indicator marks on the cast, using a 3/32-inch drill with a laboratory handpiece (Figure 1). This drilled area indicated the proposed long axis of the osteotomy or implant.
Three 3-mm diameter guideposts were placed in the holes drilled in the cast (Figure 2). Three radiopaque cylindrical guide sleeves were placed over the guideposts, with brackets positioned toward the lingual surface. The adjacent teeth on the cast were lubricated with petroleum jelly, and any undercuts were blocked out with wax to prevent the template from being mechanically locked on the cast. Triad® Gel (DENTSPLY Trubyte, prosthetics.dentsply.com) was added to the brackets on the guide sleeve and to the adjacent teeth extending anteriorly around the arch to form the template body and make the template stable (Figure 3). The template was disinfected and placed in the patient’s lower arch.
A cone-beam x-ray was taken, and the location of the mandibular nerve was mapped out (Galileos, Sirona Dental Systems). The long axis of the planned implant positions, represented by the long axis of the guide sleeve images, was evaluated in the mesio-distal and bucco-lingual planes for each site. Using the Galileos software, three virtual implants were superimposed on the x-rays to determine the appropriate size and positions for each of the three implants (Figure 4, FIgure 5, Figure 6, Figure 7, Figure 8 and Figure 9).
The treatment plan was to place three implants above the mandibular nerve without grafting or augmenting the alveolar ridge, using one implant to support each of the three missing teeth. The long axis of the diagnostic cylinders—indicating the long axis of the planned osteotomies—and the long axis of the virtual implants were determined in both the mesio-distal and bucco-lingual plane. A line was drawn through the center of the image of the diagnostic cylinders and the long axis of the virtual implants.
Using Guide Right Features
Angular Correction by Bending the Guideposts
If the line drawn through the center of the diagnostic cylinders is not parallel to the line indicating the long axis of the virtual implants, an angle is formed where the two lines intersect. This angle, which can be calculated with the software or by superimposing a transparent protractor over the image, is used to correct the guide sleeve angle in both planes—mesio-distal and bucco-lingual. The guide-sleeve angle or position can be corrected by bending the guideposts to determine the guide-sleeve angle.
The guideposts have four flat sides on the lower part. A guidepost is placed in the bending tool and a set screw is tightened against one of the flat sides while the bend is being made. The guidepost can be rotated 90º and the set screw retightened to make a second bend in the second plane.
Linear Positioning Using Offset Guideposts
When the linear position of the implant also needs to be changed, offset guideposts can be used to reposition the guide sleeve location in either plane. The offset guideposts are available in 0.5-mm, 1-mm, 1.5-mm, 2-mm, and 3-mm offset configurations (Figure 10).
Use of the Generation II Bending Tool
In this case, the guideposts were bent using a bending plate with a protractor scale (Figure 11). A hex-driver was used to tighten the set screw, and a stylus, which fits over the guidepost, was applied to bend the guidepost. The stylus has a pointed tip directed to the degree to which the guidepost is being bent (Figure 12).
If correction of the guidepost angle is needed in two planes, the guidepost with four flat sides on the lower part is rotated 90º, and the set screw is retightened on the guidepost. A stylus support bar is secured to the plate to support the stylus after making the first corrective bend. The support bar maintains the angle of the first bend while making the second bend.
Analyze and Correct
In this case, the long axes of each of the three guide sleeves were analyzed in the bucco-lingual and mesio-distal planes in the cone-beam images (see Figure 4 through Figure 9), and the following corrections were made. The guide sleeve for the second bicuspid was corrected by bending the guidepost 12º in a mesio-distal plane and 15º toward the lingual in the bucco-lingual plane (see Figure 4 and Figure 5). The guidepost in the first molar position was corrected 33º to the lingual (see Figure 6 and Figure 7), and the guidepost for the second molar was corrected by bending it 30º to the lingual (see Figure 8 and Figure 9).
Three open guide sleeves were used to fabricate the final surgical template. The 3.2-mm open guide sleeves were placed on three magnetic guideposts, which are designed to hold the open guide sleeves by the magnetic field. Triad® Gel (DENTSPLY Prosthetics, prosthetics.dentsply.com) was added to the lingual surface of the guide sleeves and the adjacent teeth to stabilize the surgical guide during the procedures.
Open guide sleeves were used because the long axis of the corrected guideposts was not parallel. If cylindrical guide sleeves had been used, the corrected template would have been locked in place by the divergent guideposts so they could not be removed from the cast. Also, visibility of the depth markings on the drills used to prepare the osteotomy is increased.
The initial osteotomy was made using a 2-mm pilot drill that had an 8.5-mm-long, 2-mm drill shaft with a 2.9-mm diameter stop. The larger diameter stop shaft prevents the 2-mm drill from penetrating deeper into the bone. The stop shaft also fits accurately within the 3.2-mm guide sleeve.
The osteotomy diameter was enlarged using standard drills up to 3.2-mm diameter available from the implant manufacturer and completed by visually centering the larger drills in the arc of the open guide sleeve. The final implant placement is illustrated in Figure 13 radiographically. Impressions were taken 3 months later, and three angled abutments (one 15º and two 25º) with minimal modification were used to restore the case (Figure 14 and Figure 15).
This case would have been very difficult and unpredictable to treat without using 3-D imaging. The diagnostic surgical guide was designed to facilitate implant placement within the envelope of bone to support the final restorations and use of angled abutments, and to eliminate the need for additional bone grafting in positions aligned with opposing teeth. In this case, the cone-beam 3-D images obtained from the x-ray indicated that the three implants would have to be placed 15º to 33º off from the vertical axis of the restorations. If the implants had been placed in an ideal position, according to the original prosthetic planning—without evaluating the positions radiographically—the osteotomies would have perforated the lingual plate, resulting in serious sequelae, including implant failure.
Dr. Meitner is the founder of Guide Right™ by DéPlaque.
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About the Authors
Sean W. Meitner, DDS, MS
Founder, Guide Right™ by DéPlaque
Victor, New York
Department of Periodontology
Eastman Institute for Oral Health
University of Rochester Medical Center
Rochester, New York
Dov M. Almog, DMD
Chief, Dental Service
VA New Jersey Health Care System
East Orange, New Jersey