Predictability of reformatted computed tomography for pre-operative planning of endosseous implants. R Jacobs1, A Adriansens1, I Naert2, M Quirynen1, ...
Dentomaxillofacial Radiology (1999) 28, 37 ± 41 ã 1999 Stockton Press All rights reserved 0250 ± 832X/99 $12.00 http://www.stockton-press.co.uk/dmfr
Predictability of reformatted computed tomography for pre-operative planning of endosseous implants R Jacobs1, A Adriansens1, I Naert2, M Quirynen1, R Hermans3, D Van Steenberghe1 1
Department Periodontology, 2Department Prosthetic Dentistry, Catholic University of Leuven, Kapucijnenvoer 7, B-3000 Leuven, Belgium and 3Department Radiology, University Hospital Gasthuisberg, Herestraat 49, B-3000 Leuven, Belgium
Objectives: To determine the reliability of reformatted 2D-CT for pre-operative planning of implant placement. Methods: One hundred consecutive partially or fully edentate patients underwent 2-D reformatted CT pre-operative planning and subsequent implant placement. The number, site and size of the implants, the available bone height and anatomical complications were recorded. The pre-operative planning and the outcome at surgery were compared statistically using a percentage agreement and Kendall's correlation coecient. Results: Agreement between the pre- and intra-operative data was good for the number of implants (60%) and the selected sites (70%). From a total of 416 implants planned, 21 implants could not be placed because of intra-operative ®ndings. Agreement was relatively poor for implant size (44%) and anatomical complications (46%). Kendall's correlation coecient was highest for the number of implants (0.80) and implant sites (0.81). It was much lower for implant sizes (0.51) and did not reach signi®cance for anatomical complications (0.09). Conclusions: Reformatted 2D-CT is reliable for the pre-operative assessment of the number and sites of implants in the jaws. It is less predictable for the implant size needed and poor for anatomical complications. Keywords: tomography, X-ray computed; dental implant, endosseous; jaw
Introduction Before considering the actual placement of endosseous implants in the jaws, both the quantity and quality of bone must be assessed radiographically. A variety of imaging techniques are currently available, each with their own strengths and weaknesses and speci®c indications.1 Intra-oral radiography is best suited for single tooth replacement while panoramic radiography is most appropriate for the anterior mandible. However, when there is some doubt about the localisation of adjacent anatomical structures, such as the alveolar nerve, or when the axis or cortical contact of the implant play an important role, cross-sectional imaging with either reformatted CT or tomography is recommended.2 Conventional tomography involves less radiation and is a reliable alternative to CT when
Correspondence to: R Jacobs, Department of Periodontology, Faculty of Medicine, Catholic University of Leuven, Kapucijnevoer 7, B-3000 Leuven, Belgium Received 27 February 1998; accepted 15 September 1998
information is needed on a relatively limited edentulous span.3 An important advantage of CT is the improved visualisation of critical anatomical structures such as the mandibular canal.4 ± 6 Although it is not visualised as such, the combined information from multiplanar CT reconstructions inherently re¯ects the three-dimensional anatomy of the structure imaged. A number of software packages have speci®cally been designed for pre-operative planning of implant placement (Dental CT1, Siemens, Erlangen, Germany; Denta Scan1, Dental Clinical Application Package, ISG Technologies, Missisaugua, Ontario, Canada; ToothPix1, Cemax Inc., Fremont, CA, USA; 3-D Dental1, Columbia Scienti®c Inc., Columbia, MD., USA). Such reformatted images are considered to be highly reliable.7,8 However the ecacy in transferring the 2D-planning data to the 3D-operation site has not yet been assessed. The present study was therefore undertaken to evaluate the predictability of 2D-reformatted CT for implant placement by comparing the pre- and intraoperative ®ndings.
Predictability of 2D-CT R Jacobs et al
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Materials and methods
Table 1 Characteristics of the implants planned and placed in 100 patients
Subjects The study was based on 100 consecutive (partially or fully) edentate patients (59 females, 41 males, age range 15 ± 74 years, mean 53) who, required CT scanning for pre-operative planning of implant placement in the maxilla (n=70) or posterior mandible (n=30) (Table 1). None of the subjects was known to have systemic endocrine, metabolic or skeletal disorders.
Implants
Methods Spiral CT (Somatom Plus S1, Siemens, Erlangen, Germany) was carried out in the Department of Radiology, Leuven University Hospital using the Dental CT1 software package. Pre-operative planning was performed by a periodontologist and a prosthodontist. The periodontologist assessed the scans to decide the number, site and size of the implants. The reconstructed orthogonal and panoramic images and to a lesser extent the axial CT scans, were used for a quantitative estimate of the bone height and width. A transparent template with then available sizes of the BraÊnemark system1 (Nobel Biocare, GoÈteborg, Sweden) was superimposed on the cross-sectional images to decide if implants could be placed. To determine the optimal angulation and length, an implant marked on the template was superimposed on the image of the jaw bone (Figure 1). The bone height available below the sinus or nasal ¯oor and above the mandibular canal, was measured with a digital caliper (Absolute Digimatic Caliper, Mitutoyo (UK), Andover, Hants) allowing for a safety margin of 1.5 mm. The axial CT scans were used for a qualitative estimate of bone quality. The treatment plan reached from the CT scan was modi®ed according to the biomechanical and esthetic requirements of the prosthodontist. The site and angulation of the implants was reproduced on the diagnostic cast which was then used to design a surgical template. The pre-operative planning data recorded for further analysis were the number, site and size of the implants, the bone height at each site and any possible anatomical complications, de®ned as follows: (1) fenestration, the presence of a defect in the buccal or lingual bone overlaying the implant; (2) dehiscence, a lack of buccal or lingual bone overlying the coronal part of the implant; (3) sinus perforation; (4) no primary stability; (5) malposition of the implant in relation to the biomechanical and/or esthetic requirements. Implant placement was performed by a single team of periodontologists at the University Hospital, Leuven following the standard protocol developed by BraÊnemark.9 During surgery, an attempt was made to conform to the pre-operative treatment plan as much as possible. However, it sometimes became evident once the surgical site was inspected that implant placement as planned was impossible. This could
Total Number/patient Site Maxilla Anterior maxilla Posterior maxilla Posterior mandible Length (range) Diameter (range) Complications predicted/found
Planned
Placed
416 395 mean 4.4; range 1 ± 8 mean 4.0; range 1 ± 8 318 117 201 98 6 ± 20 mm 3.75 ± 5.00 mm
304 115 189 91 6 ± 18 mm 3.75 ± 5.00 mm
21%
41%
Figure 1 A transparent template with dierent implant sizes is superimposed on a 2-D reformatted cross-sectional image of the jaw to determine the optimal angulation and length. In this case, a 15 mm implant could be installed (adapted from Jacobs, van Steenberghe1)
occur when the anatomical requirements were not ful®lled, because of intra-operative ®ndings which were overlooked or not identi®able on the CT scans (e.g. inferior bone quality or unfavourable 3-D bone shape, risk of damage to vital anatomical structures or foreign bodies). The number, site and size of the implants placed as well as the presence or absence of anatomical
Predictability of 2D-CT R Jacobs et al
complications were recorded. Post-operatively, actual implant size and angulation were transferred by the system involved to the corresponding cross-sectional image and the distance between the apical end of the implant and the adjacent sinus or nasal ¯oor or mandibular canal measured as described above. The models and surgical templates were used to aid de®ning the angulation. Statistical analysis Agreement between the pre- and intra-operative ®ndings was determined both as a percentage and as Kendall's correlation coecient (t) for the following data: (1) number of implants; (2) size and site of implants; (3) discrepancy between available bone height and implant length; (4) presence of anatomical complications. A paired t-test was performed to determine the discrepancy between the available bone height and the Table 2 Agreement between planning and placement of 395 implants in 100 patients Number Site Size Anatomical complications
Agreement %
t
P
60 70 44 46
0.80 0.81 0.51 0.09
P50.001 P50.001 P50.001 P40.5
implant length at planning and placement. A level of signi®cance of 0.05 was chosen. Results Table 1 shows the characteristics of the implants planned and placed in 100 patients. It should be noted that although 416 implants were planned, only 395 could be placed. There was good agreement between the pre-operative and intra-operative data on the number of implants (60%) and their respective sites (70%) (Table 2). Agreement for length of implants (44%) and presence of anatomical `complications' (46%) was poor. Kendall's correlation coecient (t) was highest for the number of implants (0.8) (Figure 2) and their sites (0.81) (Figure 3), but lower for the length (0.51) of each implant (Table 2). Most implants were planned to have a length of 10, 13 or 15 mm. However, as can be seen in Figure 4, in 110 out of 395 cases, the implants placed were shorter than intended. This represents about 20% of the implants in the upper jaw and 35% in the lower. In 74 cases longer implants were placed, 22% of these in the upper jaw and 12% in the lower. The insertion of longer implants than planned led to complications in 35% of the cases in the upper jaw comprising 20% sinus perforations, 14% dehiscences and 1% fenestrations. Anatomical complications were expected in 21% of the implants, but occurred in 41%
No of implants at planning and placement
Figure 2 Bivariate histogram showing the number of implants planned and placed in each patient. There is a good agreement between the number of implants planned and placed. In the majority of the patients, either 2 ± 3 or 4 ± 6 implants were planned and placed
Figure 3 Bivariate histogram showing the site of the implants planned and placed in 100 patients. There is a good agreement between the site of the implants at planning and placement. The majority of the implants were placed in the premolar region (site 4 ± 5). In the incisor (sites 1 ± 2) and canine (site 3) region, as well as in the molar region (sites 6 ± 8), fewer implants were planned and placed
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Predictability of 2D-CT R Jacobs et al
40
at surgery (Figure 5A). Fenestrations and dehiscences were anticipated in 7%, but arose in 21% (Figure 5B). Similarly, for sinus perforations the ®gures were 1 and 11% respectively. Other complications (malposition and no primary stability of the implant) showed broadly similar pre- and intra-operative values. For the agreement between pre- and intra-operative data on the anatomical complications, the Kendall's correlation coecient (0.09) did not reach the level of signi®cance. There were signi®cant dierences in the discrepancies between the available bone height and the implant lengths at planning and at placement (Table 3).
lower. These discrepancies could be related to the fact that implant planning still requires a mental transformation of the 2D-images to the 3D-operation site. This a
Discussion Radiation exposure to the patient must be justi®ed to the extent that their subsequent management bene®ts. The introduction of spiral CT has led to a reduction in scanning time and thus a reduced patient dose.10 We have con®rmed in the present study, that reformatted 2D-CT is a reliable tool for the pre-operative assessment of the number and sites of implants in the jaws. Its predictability for implant size is somewhat b
Figure 4 Bivariate histogram showing the relation between the implant lengths at planning and placement. The majority of the implants were placed as planned at lengths of 10, 13 and 15 mm, but the overall agreement is poor (see Table 2)
Figure 5 (a) Bivariate histogram showing the relationship between the absence (no) or presence (yes) of anatomical complications at planning and placement. In the majority of the cases, there were no complications at planning or placement. It was however more dicult to predict complications that occured at surgery. (b) Bivariate histogram showing the relationship between the dierent anatomical complications, at planning and placement. In the majority of the cases, there were no complications, but when they occurred, agreement was poor
Table 3 Differences between available bone height and length at planning and in 100 patients placement of 395 implants Difference (s.d.) (mm) Both jaws Upper jaw Lower jaw
Lplanning ± Lplacement
BH ± Lplanning
BH ± Lplacement
0.29 (2.26)* 0.14 (2.32) NS 0.79 (2.00)**
1.49 (1.95)** 1.45 (2.05)** 1.64 (1.60)**
1.79 (2.38)** 1.61 (2.46)** 2.37 (2.03)**
Key: Lplanning, Implant length at planning; Lplacement, Implant length at placement; BH, Available bone height; t-test: NS, not signi®cant; *Signi®cant at P50.01; **Signi®cant at P50.001
Predictability of 2D-CT R Jacobs et al
may also explain the poor predictability of anatomical complications, such as sinus perforations or fenestrations. It is also likely that in dicult cases the surgeon wants to avoid the planned pre-operative complication and instead creates another. With regard to implant length, there was a tendency to place shorter implants than actually planned, particularly in the posterior mandible (35% of the cases). This may be because the surgeon will be cautious and insert a shorter implant to avoid damaging the alveolar nerve. The discrepancy between measured and actual bone height with the reformatted CT images is 0.4 ± 0.5 mm on average.11,12 A safety margin of about 1 ± 2 mm is therefore recommended4 and was incorporated in this study. Table 3 shows that on average the planned implant length was about 1.5 mm less than the available bone height. This discrepancy increased to 2.4 mm in the posterior mandible. Depending on the size of the implant used, the same implant should ®t within dierent cross-sectional views
to avoid fenestrations, dehiscences or damage to anatomical structures. But even then, the planning from 2-D CT images may be dicult and inaccurate. The use of 3D-reconstruction may increase the level of reliability and is currently being investigated. In conclusion, reformatted 2D-CT images are a reliable tool to assess pre-operatively the number and site of implants. It is less good for predicting implant size and poor for predicting anatomical complications at surgery. Surgeons should try to adopt carefully the pre-operative ®ndings to the 3D-operation site. They should also be aware of potential anatomical complications which have not been predicted.
Acknowledgements R Jacobs is a postdoctoral fellow of the Fund for Scienti®c Research (FWO) - Flanders (Belgium). D van Steenberghe is holder of the P-I. BraÊnemark Chair in Osseointegration.
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