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Compendium
September 2017
Volume 38, Issue 8
Peer-Reviewed

Myth #6:

In guided surgery, CBCT scans are of equal accuracy and quality to medical CT scans.

Sir Godfrey Hounsfield developed medical multi-slice CT (MSCT) in 1967.5 CBCT was introduced in the European market in 1996 and in the US market in 2001.6 MSCT has long been relied upon for one-to-one accuracy in 3-dimensional (3D) radiography; however, MSCT radiation exposure, as compared with CBCT, has been measured to be 10 to 20 times greater.7 The question is whether the benefit of increased accuracy outweighs the risk for increased radiation exposure.

Abboud and colleagues8 scanned objects of a known diameter with one MSCT scanner and five CBCT scanners. They concluded that MSCT devices provided the most accurate images in the study, but the amount of the differences may not have been of clinical significance for most diagnostic purposes. They did note that fiducial marker localization error caused by some CBCT scanners could be a problem for some guided surgery systems. Liang and coworkers9 compared the geometric accuracy of 3D surface model reconstructions created by images produced by five CBCT scanners and one MSCT system. They concluded that the accuracy of the CBCT 3D surface model reconstruction was somewhat lower as compared with MSCT, but acceptable.

Bone density in MSCT is measured in Hounsfield units (HU). Bone density in CBCT is measured in voxels, a visual gray scale measurement (a 3D pixel). There is no correlation between HUs and voxels. Most dental implant treatment planning software was developed for MSCT, not CBCT. This is why, when using CBCT and importing DICOM image data into proprietary implant planning software, 3D reformation images of less radio-dense areas of bone, such as the maxilla, appear with radiolucent openings, or “holes,” in the bony surfaces (Figure 9 and Figure 10). One could conclude that, when weighing the slight amount of additional inaccuracy along with the potential 3D reformation issues of CBCT against the considerably increased radiation dosage of MSCT, CBCT is an excellent option for dental implant evaluation and placement and guided surgery planning.

Myth #7:

Insertion torque measurements are accurate when using guided surgery.

When using guided surgery for implant insertion, the clinician experiences less tactile sense of the bone density. The surgical guide directs the bur and implant insertion componentry to the planned depth and angulation without consideration of the bone density or tactile resistance. In addition, friction occurs from contact between componentry used in drilling osteotomies (eg, guide sleeves/drill guides and burs) and placing implants (eg, guide sleeves and implant mounts). This all leads to inaccuracy in insertion torque measurements when measuring torque while the surgical guide is in place. Insertion torque of an individual implant can be measured only after the implant has been placed into its final position through the surgical guide, after the guide is removed.

Myth #8:

Bone overheating is of more concern in guided surgery than conventional implant surgery.

Bone overheating is contraindicated in all cases of dental implant surgery. Because of the presence of an intimately fitting surgical guide and insertion instrumentation, questions have arisen about whether cooling irrigation is able to reach the osteotomy site when using guided surgery; if it is not, overheating the bone becomes a concern. Migliorati and colleagues10 studied the internal bone temperature changes registered during guided surgery preparations. They concluded that when using surgical stents, osteotomy preparation generated higher bone temperatures than did conventional drilling. The heat generation, however, did not reach temperature levels that were dangerous to the bone.

Myth #9:

Guided surgery cannot be used in tilted implant/hybrid restoration cases.

The goal of guided surgery is to allow the clinician to avoid vital anatomic structures while placing implants in proper positions, angulations, and depths according to the planned restoration. These two concepts are important considerations in planning and performing “tilted” implant/hybrid restoration cases.

Combining guided surgery and tilted/hybrid cases appears as if it should be a natural marriage of techniques. The questions that arise about the use of guided surgery in these cases are regarding the bone reduction frequently necessary to place implants appropriately, both surgically and restoratively. Some manufacturers have developed bone reduction guides based on virtual treatment plans. Other methods for establishing bone reduction involve using guide pins to mark levels of bone to be removed or the use of the intentional deep placement of the implant to the level of the bone to be reduced (Figure 11 and Figure 12). With proper planning and forethought, guided surgery can be performed relatively easily on tilted implant/hybrid cases.11

Myth #10:

The success rate of guided-placed implants is lower than those placed conventionally.

As stated earlier, many practitioners consider the use of guided surgery only for more difficult implant cases, such as full-arch or multiple-implant cases, or those involving limited bone volume, anatomic issues, difficult prosthetic considerations, trauma, extensive grafting, or cases that encompass medical, orthopedic, or psychological issues with the patient. Given the inherent problems with these types of cases, combined with some of the aforementioned issues associated with guided implant placement, such as the overheating and cooling questions, the inability to accurately measure insertion torque, the diminished clinician tactile sense, and fully guided implant placement with or without a flap being essentially a blind procedure, one might think that the cumulative survival rate (CSR) of implants placed with this technique would be lower than those placed conventionally. This has not been found to be the case, however. In a 7-year retrospective study of 798 implants placed fully guided using different software and implant systems, the authors reported a CSR of 96.98%. Compared with the well-established CSR of 95% to 98% for conventional freehand placement of implants, the CSR of implants placed using fully guided protocol is not lower.12

Conclusion

Guided surgery techniques have been researched and refined for many years and can be used in most clinical scenarios. Attention to detail is necessary in all steps to minimize potential errors, as consistent success requires a solid knowledge and understanding of treatment workflows and armamentarium. The successful integration of guided surgery into practice can lead to improved patient outcomes, which is the ultimate goal of treatment.

About the Authors

Gary Orentlicher, DMD
Section Chief
Division of Oral and Maxillofacial Surgery
White Plains Hospital
White Plains, New York
Private Practice
New York Oral, Maxillofacial, and Implant Surgery
Scarsdale, New York

Andrew Horowitz, DMD, MD
Associate Attending
White Plains Hospital
White Plains, New York
Private Practice
New York Oral
Maxillofacial, and Implant Surgery
Scarsdale, New York

Batya Goldwaser, DMD, MD Attending Oral and Maxillofacial Surgeon,
White Plains Hospital
White Plains, New York
Private Practice
New York Oral
Maxillofacial, and Implant Surgery
Scarsdale, New York

Marcus Abboud, DMD
Associate Dean of Digital Dentistry
University of Kentucky College of Dentistry
Lexington, Kentucky

References

1. Orentlicher G, Horowitz A, Abboud M. Minimally invasive implant surgery using computer-guided technology. In: Minimally Invasive Dental Implant Surgery. Cullum D, Deporter D, eds. Hoboken, NJ: Wiley Publications; 1, 2016:169-189.

2. van Steenberghe D, Glauser R, Blombäck U, et al. A computed tomographic scan-derived customized surgical template and fixed prosthesis for flapless surgery and immediate loading of implants in fully edentulous maxillae: a prospective multicenter study. Clin Implant Dent Relat Res. 2005;7(suppl 1):S111-S120.

3. Sarment DP, Sukovic P, Clinthorne N. Accuracy of implant placement with a stereolithographic surgical guide. Int J Oral Maxillofac Implants. 2003;18(4):571-577.

4. Ozan O, Turkyilmaz I, Ersoy AE, et al. Clinical accuracy of 3 different types of computed tomography-derived stereolithographic surgical guides in implant placement. J Oral Maxillofac Surg. 2009;67(2):394-401.

5. Beckmann EC. CT scanning the early days. Br J Radiol. 2006;79(937):5-8.

6. Hatcher DC. Operational principles for cone-beam computed tomography. J Am Dent Assoc. 2010;141(suppl 3):3S-6S.

7. Carter JB, Stone JD, Clark RS, Mercer JE. Applications of cone-beam computed tomography in oral and maxillofacial surgery: an overview of published indications and clinical usage in United States academic centers and oral and maxillofacial surgery practices. J Oral Maxillofac Surg. 2016;74(4):668-679.

8. Abboud M, Guirado JL, Orentlicher G, Wahl G. Comparison of the accuracy of cone beam computed tomography and medical computed tomography: implications for clinical diagnostics with guided surgery. Int J Oral Maxillofac Implants. 2013;28(2):536-542.

9. Liang X, Lambrichts I, Sun Y, et al. A comparative evaluation of cone beam computed tomography (CBCT) and multi-slice CT (MSCT). Part II: on 3D model accuracy. Eur J Radiol. 2010;75(2):270-274.

10. Migliorati M, Amorfini L, Signori A, et al. Internal bone temperature change during guided surgery preparations for dental implants: an in vitro study. Int J Oral Maxillofac Implants. 2013;28(6):1464-1469.

11. Orentlicher G, Jensen O, Horowitz A, et al. Combining All-on-4 treatment with CT-guided technology: technique and report of three cases. Compend Contin Educ Dent. 2013;34(7):534-542.

12. Orentlicher G, Horowitz A, Goldsmith D, et al. Cumulative survival rate of implants placed “fully guided” using CT-guided surgery: a 7-year retrospective study. Compend Contin Educ Dent. 2014;35(8):590-598,600.

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