Spiral Tomography for Determining Implant Angulation: An In Vitro Study

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1 Original Article Spiral Tomography for Determining Implant Angulation: An In Vitro Study Z. Dalili Kajan 1, H. Neshandar 2, G. Adham Fumani 3, P. Sadr Eshkevari 4 1 Associate Professor, Department of Oral and Maxillofacial Radiology, School of Dentistry, Guilan University of Medical Sciences, Guilan, Iran 2 Assistant Professor, Department of Prosthodontics, School of Dentistry, Guilan University of Medical Sciences, Guilan, Iran 3 Assistant Professor, Department of Oral and Maxillofacial Surgery, School of Dentistry, Guilan University of Medical Sciences, Guilan, Iran 4 Dentist, Private Practice Corresponding author: Z. Dalili Kajan, Department of Oral and Maxillofacial Radiology, School of Dentistry, Guilan University of Medical Sciences, Guilan, Iran zahradalili@yahoo.com dalili@gums.ac.ir Received:12 July 2007 Accepted:14 Nov 2007 Abstract: Objective: To study the accuracy of spiral tomography in the determination of implant angulation. Materials and Methods: Eighteen gutta-percha filled points on dry mandibles were selected for implant placement. A translucent acrylic template was fabricated for each mandible. After preparing tomographic images (2 mm slice thickness, Cranex Tome), the ideal axis of the implant was traced. The angle between the ideal axis and the tangent line on the alveolar crest in the buccal side was measured and transferred to aluminum sleeves by a protractor. After implant placement, tomographic images were taken again and angles of the actual implants were estimated. In addition, the distances from the tip of the actual and the supposed implants to the buccal cortex were measured. The data were analyzed by paired sample t test with 95% confidence. Results: Less than two-degree difference between angles of the supposed and the actual implants was found in 44.4% of the cases, whilst 33.3% revealed more than five-degree difference. There was a significant statistical difference between the angle of the actual and the supposed implants. There was also a significant statistical difference between the linear distances from the tip of the actual and the supposed implants to buccal cortex (P=0.015) Conclusion: Spiral tomography in combination with template may provide acceptable results concerning implant angulation and prediction of cortical perforation risk. Key Words: Dental implants; Tomography, Spiral Computed; Mandible; Surgery, Oral Journal of Dentistry, Tehran University of Medical Sciences, Tehran, Iran (2008; Vol: 5, No.2) INTRODUCTION Basic goals of implant imaging are to assess normal anatomic structures from all aspects, to assign possible surgical path of implant insertion and to provide diagnostic and treatment documentation. The occlusoapical and mesiodistal dimensions of the edentulous area and also the buccolingual dimension along with the angulation of the available bone are all crucial for determining implant size and position during the treatment phase. Moreover, the application of image guidance during the last decade is mainly intended to reflect a preoperative insertion plan into the clinical reality. This method enhances the safety of patients by reducing the risk of violation to the adjacent anatomical structures and also saves the time of surgery [1,2]. Furthermore, the development and application of navigation systems have improved the accuracy of implant insertion 52

2 Dalili et al. regarding its position, angulation and the depth of insertion [3]. Although several image-guide planning systems such as reformatted 2D CT-scan and computer-aided design-like implant models [4] have been introduced, these techniques may not be generally available and also do have some disadvantages like higher exposure and working time. Spiral tomography is an available radiographic method, which provides cross sectional images. Also, there are several studies on the role of spiral tomography in localization of the mandibular canal [5-7], detection of the mental foramen [8], estimation of the alveolar bone height [6,9,10] and determination of the alveolar bone width [6,11,12]. Some argue that the addition of cross sectional tomography and surgical guide leads to a more predictable measure and adequately assessing the bone and its angulation in relation to prosthetic needs [13-20]. To overcome the implant alignment problems, however, several kinds of radiological, surgical, and combined template techniques have been suggested. Few studies have emphasized templates to be only helpful during the surgical phases [21-23]. In contrast, a number of studies have introduced templates for a dual application: first, radiological planning and second, guidance for the surgical implant placement [24-26]. The metal sleeve built in the template serves as both an imaging inclination indicator and a precise surgical osteotomy guide. If a discrepancy is found between the planned prosthetic angulation and anatomical structures, the sleeve can be reoriented using cross sectional images. Thus, the imaging phase may be necessary to be repeated in order to confirm a safe Spiral Tomography for Implant Angulation and suitable trajectory during the osteotomy [27]. The combination of template with image guidance and cross sectional spiral tomography seems to be more effective for multidimensional evaluation of implant sites. It is well known that inappropriate angle of the implant not only impairs the esthetics but also disturbs the even distribution of forces on the implant surface, consequently affecting osseointegration. As a result, given the importance of proper implant insertion, the present study was designed to assess the accuracy of spiral tomography with a diagnostic surgical template in determining implant angulation. MATERIALS AND METHODS In the present study, one completely and two half-dry mandibles were used as phantoms for imaging. A pilot study was first conducted to obtain the optimal exposure factors. In order to achieve a proper density, five aluminum plates (8 10 cm with a total thickness of 7.5 mm), were attached on the tube side on the path of the x-ray beam. Another filter consisting of four 2.25 mm thick aluminum plates with the same size was applied on the slot of the cassette carriage to attenuate beam intensity again. Small one-millimeter deep holes were made by a surgical bur and a micro motor 10 mm far from each other on dry mandibles for implant placement and filled by gutta-percha. A total number of 18 sites were selected. Translucent acrylic fit templates were fabricated for each mandible. The mandibles were then fixed on flat plates using cold cure acrylic resin so that the occlusal plane would be parallel to the horizontal plane. Panoramic views of each mandible were taken Table 1. Mean values of the tomographic angles of the supposed and actual implants. In cross sectional tomographic images N Mean angulation (degree) SD Statistical analysis Angles of supposed implants P=0.002 * Angles of actual implants SD=Standard Deviation, N=number, * Statistically Significant 53

3 Journal of Dentistry, Tehran University of Medical Sciences Dalili et al. Fig 1. Measurement of the buccal angle and linear deviation of supposed implant on cross sectional tomographic image (left). Measurement of the buccal angle and linear deviation of actual implant on cross sectional tomographic image (right). α: angle between ideal axis of supposed implant and the tangent line on alveolar crest in buccal side; β: angle between axis of actual implant and the tangent line on alveolar crest in buccal side; c: axis of actual implant; c': axis of supposed implant; d: distance between the tip of actual implant to buccal cortex; d': distance between the tip of supposed implant to buccal cortex; B: buccal side; L: lingual side using a Cranex Tome Soredex (Helsinki, Finland) (57 kv, 10 ma and 24 s) with a combination of a medium Kodak X-Omat screen (Rochester, NY, USA) and CEA green film (CEADENT, Strängnäs, Sweden). The films were processed using an OPTIMAX 2010 automatic processor (PROTEK Medizintechnik, Obrstenfeld, Germany) with a processing time of 1.5 minutes. For tomography, the program dental tomo was selected, with a slice thickness of two milimeter (57 kv, 56 s, and 3.2 ma) while tomographic images were taken from marked points on the mandible. The tomographic slices showing the sharpest images of the crestal holes were selected for the study. Finally, the ideal axis of the supposed implant was traced and its buccal angle (the angle between the ideal axis and the tangent line on the alveolar crest on the buccal side) was measured (Fig 1). The measured angle was transferred to an aluminum sleeve (ITI 54 guiding for solid screw implant ø 3.3 mm) by a protractor; a triangle and a tooth pick (Fig 2). The protractor was perpendicular to both the buccal and the lingual cortices of the selected point. However, the angle of the sleeve was defined by the protractor and fixed on the template by cold cure acrylic resin. An experienced maxillofacial surgeon was requested to drill the mandibular bone only in the direction of the sleeve hole. After drilling, study implants (ITI, ø 3.3 mm), 12 mm in length, were inserted and tomographic images were taken again (Fig 1). Furthermore, the buccal angles of the axis of the actual implants were measured. In addition, the distances between the tips of the actual and the supposed implants to the buccal cortex were measured as well (Fig 1). To analyze the data, SPSS software was employed. The significant differences of linear and angular measurements between the supposed and the actual implants on

4 Dalili et al. Fig 2. The transfer method of measured tomography angle to the guiding sleeve on the template. tomography slices were detected by paired t test with 95% confidence interval. RESULTS The mean anglulation of the supposed and the actual implants on cross-sectional tomography views were estimated and recorded (Table 1). Significant differences were observed between the values. Differences of less than two degrees between the angles of the supposed and the actual implants were found in 44.4% of the cases while 33.3% of the cases showed a difference of more than five degrees and in 22.2% a difference of two to five degrees was found (Fig 3). Meanwhile, no perforation of the buccal or the lingual cortices was found. Moreover, there was a significant statistical difference between the anglulation of the actual and the supposed implants. In our study, a buccal inclination of the actual implants in comparison to the supposed implants was found in 66.6% of the cases. A comparison between the angulations of the actual and the supposed implants revealed 16.7 Spiral Tomography for Implant Angulation % of the cases to have a lingual inclination and 11.1% of them with no inclination. Whilst, only in 5.6% of the cases, the implants were displaced from their original insertion points however, there was no angulation between the actual and supposed implants. At the tip of the implants, the linear deviation (the difference between the linear distances from the tip of the actual implant to the buccal cortex; and the supposed implant to the buccal cortex) was 1.9 mm (range mm). In Table 2, the distances from the longitudinal axis of the actual and the supposed implants to the buccal cortex at the tip are recorded. There was also a significant difference between the linear distances from the tip of actual and supposed implant to buccal cortex (P=0.015). In 88.9%, this deviation was found to be less than 3.5 mm (Fig 4). DISCUSSION An appropriate method in terms of cost and radiation dose, which provides useful information about the alveolar bone height over the mandibular canal and the angulation of the implant, may grant both esthetics and safety throughout the implant surgery. Tomographic images provide the surgeon with relatively accurate information about the alveolar bone height over the mandibular canal [6,9,11], but to gain proper information about the implant angulation, they can also be combined with guiding templates. The present study was designed to evaluate the role of spiral tomography in determining implant angulation. Results of this study revealed that the buccal inclination of the actual implants is more than the angulation of the supposed implants following the guidance of cross-sectional spiral tomography. Therefore, this inclination seemingly Table 2. Mean distances of the longitudinal axes of the actual and supposed implants at the tip. Distance of implant tip from buccal cortex N Mean distance (mm) SD Statistical analysis Supposed implants P=0.015 * Actual implants SD=Standard Deviation, N=number, * Statistically Significant 55

5 Journal of Dentistry, Tehran University of Medical Sciences Dalili et al % 44.40% < % Fig 3. Frequency of different angles between the axes of supposed and actual implants in cross sectional tomographic views according to degrees. raises the risk of lingual perforation. Although the perforation of the lingual cortex was observed in none of the cases clinically, it was shown that 13 degrees of difference between the axis of the supposed and the actual implants is associated with a six-millimeter displacement of the implant tip to the lingual side. The height of the intrabony part of the implants used in the present study was 12 mm. It is considered that the length of the implant is effective on the amount of the displacement of the implant tip. Thus, the application of shorter implants is likely to reduce the risk of perforation. Although the implant angulation is very influential on the esthetics of a given restoration, the biggest achievement of crosssectional tomography is to assess alveolar bone height, width, and spatial relationship with the mandibular canal, particularly in the posterior zone of the mandible [28]. Therefore, for risk assessment in vertical and horizontal dimensions, it is important to investigate under and over-estimation percentages in measuring the height of the alveolar bone crest over the mandibular canal rather than the exact difference between the actual and the tomographic values [9]. In spite of the significant statistical difference found between the angulations of the actual and the supposed implants, this result may be interpreted in another way as well: It may be stated that displacement probability 2-5 >5 and perforation risk are more important concerns that should be taken into consideration. In a study about implant angulation based on surgical templates, it was shown that 90% of the implants were placed with a difference of less than 10 degrees between the actual and the proposed directions [29]. This difference might be compensated for by a greater access hole of the set-crew and use of an angulated abutment. According to the results of our study, this dif- in more ference was less than eight degrees than 88% of the cases. Thus, it can also be 0.2 to 3.5 mm) [30]. The mean deviation of the implant tip was 1.91 mm (SD=1.43) (ranging from 0 to 6 mm) in the present study and no cortex perforation was observed when using a combination of spiral tomography and guided templates. It has been suggested that the metal sleeve serves as an imaging indicator and a precise surgical osteotomy guide. In addition, it has been stated that if a discrepancy is present be- compensated for by application of angulated abutments. However, it is interesting to note that the greatest differences between the angulations of the supposed and the actual implants were simultaneously observed in the posterior region with buccal inclination of the implants. Probably this difference is related to the reduced accuracy of the images in the posterior region. In other studies on the accuracy of computeraided implant placement, the tip of the inserted implant had a mean deviation of 1.44 mm (SD=0.79) at the buccal cortex (ranging from tween the planned prosthetic angulation and the residual bone angulation or anatomic structures during cross-sectional imaging, the guide can be altered and the sleeve reoriented [27]. In the present study, the metal sleeves were used in order to facilitate transferring of information from cross-sectional tomography to the template as well as radiographic indicators. Moreover, Kramer et al [3] have reported 56

6 Dalili et al. Spiral Tomography for Implant Angulation Percent computer-guided navigation as a threedimensional transferring method improving implant angulation as well as its position and depth; however, availability and cost might be of greater importance than the clinical need when selecting the technique. CONCLUSION Spiral tomography seemingly provides acceptable information in terms of implant angula- and perforation risk in addition to accu- tion racy in the detection of implant insertion depth and localization of the mandibular canal. Furthermore, this method may be helpful in the elimination of esthetic problems due to buccal or lingual inclination of the implant. ACKNOWLEDGMENTS This investigation was supported by Research Grant from Guilan Medical Research Founda- Guilan University of Medical Sciences, tion, Rasht, Iran. REFERENCES 1- Siessegger M, Schneider BT, Mischkowski RA, Lazar F, Krug B, Klesper B, et al. Use of an im- navigation system in dental implant age-guided surgery in anatomically complex operation sites. J Craniomaxillofac Surg 2001 Oct;29(5): Gaggl A, Schultes G, Kärcher H. Navigational mm Fig 4. Frequency of different amounts of linear deviation of actual and supposed implant tips in relation to buccal cortex. precision of drilling tools preventing damage to the mandibular canal. J Craniomaxillofac Surg 2001 Oct;29(5): Kramer FJ, Baethge C, Swennen G, Rosahl S. Navigated vs. conventional implant insertion for maxillary single tooth replacement. Clin Oral Im- plants Res 2005 Feb;16(1): Verstreken K, Van Cleynenbreugel J, Martens K, Marchal G, van Steenberghe D, Suetens P. An image-guided planning system for endosseous oral implants. IEEE Trans Med Imaging 1998 Oct; 17(5): Kim KD, Park CS. Reliability of spiral tomography for implant site measurement of the mandible compared with DentaScan computed tomography. In: Farman AG, Ruprecht A, Gibbs SJ, Scarfe WC, editors. Advances in maxillofacial imaging. Amsterdam: Elsevier Science B.V; pp Lindh C, Petersson A, Klinge B. Measurements of distances related to the mandibular canal in radiographs. Clin Oral Implants Res 1995 Jun;6(2): Ekestubbe A. Conventional spiral and low-dose computed mandibular tomography for dental implant planning. Swed Dent J Suppl 1999;138: Lindh C, Petersson A. Radiologic examination for location of the mandibular canal: a comparison between panoramic radiography and conventional tomography. Int J Oral Maxillofac Implants 1989 Fall;4(3): Bou Serhal C, van Steenberghe D, Quirynen M, Jacobs R. Localisation of the mandibular canal using conventional spiral tomography: a human cadaver study. Clin Oral Implants Res 2001 Jun; 12(3): Ekestubbe A, Grondahl HG. Reliability of spiral tomography with the Scanora technique for dental implant planning. Clin Oral Implants Res 1993;4(4): Dalili Kajan Z, Bavagharian F, Atrkar Roshan Z. Spiral tomography for measuring bone width at different levels from the crest to the inferior border of the mandible in vitro. Oral Radiol 2006;22(2): Lindh C, Petersson A, Klinge B. Visualisation 57

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