| Abstract|| |
Purpose: To evaluate and compare the positional and angular accuracy of virtual implant positions planned on cone-beam computed tomography and final implant positions achieved using a universal open guide system. Materials and Methods: A dual scan of a partially edentulous jaw model along with prosthesis was done, and virtual implant planning was performed. Three implant positions in relation to 35, 36, and 37 were simulated (Group A). In total, 24 implants were placed in eight replaceable bone blocks (Group B) in the same region on the model using an open stereolithographic template. The linear positions and angulation of the placed implants were determined using Vision Measuring Machine. Deviations between virtually planned and surgically placed implants were analyzed in terms of linear and angular measurements. Data were analyzed with the independent-sample t-test with differences P ≤ 0.05 being considered statistically significant. Results: The linear distance (mean ± standard deviation [SD]) in mesiodistal direction between implants in relation to 35 and 36, 36 and 37, 35 and 37 in Group A was 8.79 ± 0 mm, 8.71 ± 0 mm, and 17.50 ± 0 mm, respectively, and in Group B was 7.70 ± 0.58 mm, 8.11 ± 0.30 mm, and 15.80 ± 0.48 mm. All these above values were found to be statistically significant (P ≤ 0.05). The linear distance (mean ± SD) in the vertical direction (mesial) for implants placed in the region of 35, 36, 37 for Group A was 1.51 ± 0 mm, 1.51 ± 0 mm, and 2.47 ± 0 mm, respectively, and for Group B was 1.37 ± 0.32 mm, 1.65 ± 0.48 mm, and 1.79 ± 0.36 mm, respectively. The linear distance (mean ± SD) in the vertical direction (distal) for implants placed in the region of 35, 36, 37 for Group A was 3.37 ± 0 mm, 1.51 ± 0 mm, and 1.51 ± 0 mm, respectively, and for Group B was 1.86 ± 0.48 mm (P ≤ 0.05), 1.56 ± 0.23 mm, and 1.29 ± 0.39 mm (P ≤ 0.05), respectively. The angular deviation (perpendicularity) values for virtually planned implants (Group A) were 90.00° ± 0° and for implants placed in the region of 35, 36, and 37 (Group B) were 84.52° ± 5.4°, 83.57° ± 1.52°, and 80.41° ± 2.37°, respectively, which are highly significant (P ≤ 0.05). Conclusions: The stereolithographic universal open guide used in the study may be considered accurate for placement of implants in mesiodistal position and also in terms of perpendicularity but not in the vertical position. Stereolithographic open guide may be recommended for more accurate implant position, especially for the placement of multiple implants.
Keywords: Dental implant, model, open guide system, stereolithography, universal surgical guide, vision measuring machine
|How to cite this article:|
Sharma A, Agarwal SK, Parkash H, Mehra P, Nagpal A. An in vitro comparative evaluation between virtually planned implant positions on interactive implant software versus actual implant positions achieved using sterolithographic open guide system. Indian J Dent Res 2019;30:254-60
|How to cite this URL:|
Sharma A, Agarwal SK, Parkash H, Mehra P, Nagpal A. An in vitro comparative evaluation between virtually planned implant positions on interactive implant software versus actual implant positions achieved using sterolithographic open guide system. Indian J Dent Res [serial online] 2019 [cited 2020 Apr 5];30:254-60. Available from: http://www.ijdr.in/text.asp?2019/30/2/254/259239
| Introduction|| |
It is well known that the field of oral implantology is prosthetically driven, and keeping the end result in mind, a surgeon is expected to place the implant in the appropriate position, at a safe depth with proper angulation to facilitate an esthetic and functional tooth replacement. Image-guided surgery is a technique involving planning of the surgical and restorative aspects of implant placement using patient's preoperative cone-beam computed tomography CBCT image using specialized computer software and tools.
A computer-generated surgical guide provides a link between the treatment plan and actual surgery, which is made through stereolithography and is preprogrammed with individual depth, angulations, and mesiodistal and labiolingual positioning of the implants. Most of the available systems are close ended which use specific armamentarium and specific type of implants that are unique to their implant planning software and CBCT scanner. Since there is no freedom to use other implant systems with these guides, the dentist is compelled to use their systems.
However, recently, the market has witnessed the emergence of newer open guide systems such as In2Guide used in this study which are not restricted to any one particular implant company or system. Yet, long-term data on these needs to be are tested and validated. This study is a novel approach, to establish the accuracy and reliability of an open guide system for placement of implants, and it can play a pivotal role in laying down standards for guided surgery using any implant system.
The current study was undertaken to evaluate and compare the positional and angular accuracy of implant positions planned virtually using CBCT and final implant positions achieved using a universal open guide system, as determined by vision measuring machine (VMM). The purpose of this study was to determine and compare the precision of three-dimensional image-guided implant rehabilitation in vitro.
| Materials and Methods|| |
The present study was undertaken at Institute of Technology and Science–Center for Dental Sciences and Research, Ghaziabad. For the purpose of this study, a total of 24 implants were placed in eight replaceable bone blocks (Nissin™ Dental, Japan) which simulated the mandibular posterior edentulous bone. In each bone block, three implants were placed.
Preparation of model and fabrication of the radiographic template
A jaw model (Nissin™ Dental, Japan) simulating the mandible (Kennedy Class 1) was used for the study. A polyether impression (Monophase: 3M™ ESPE™, St Paul, MN, USA) of the upper and lower jaw models was made to make duplicate casts, and a radiographic stent was made on the mandibular cast using light-cured custom tray material (ELITE LC tray, Zhermack Spa, Italy). For the planning of implant location, multiple radiographic markers (DIADENT®, Diadent Group International Inc., Vancouver, Canada) were inserted into the flanges of the template. Acrylic teeth were placed in the template representing the desired prosthetic outcome [Figure 1].
|Figure 1: Radiographic guide with fiducial markers (gutta-percha) fabricated on partially edentulous jaw model|
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Preoperative cone-beam computed tomography scanning
Cone-beam scan images of the mandibular model, with the radiographic stent, were acquired using a CS 9300 CBCT Unit (Carestream Dental Systems, Carestream Health Inc., Rochester, NY, USA). Exposure parameters ranged from 85 to 90 kV and 10 to 12 mA. A second scan following the dual scan protocol was followed (two separate scans of the radiographic template and that of the model with template seated in place).
Implant planning stage
The CBCT data were transferred in DICOM format to the planning software (In2Guide™, OnDemand3D™, Cybermed Inc., Seoul, South Korea) in a computer for virtual planning of implants. A total of three implants (Adin Implant Systems Ltd., Israel) for the regions 35, 36, and 37 were virtually planned using OnDemand3D™ software (Cybermed Inc, Seoul, South Korea). The diameter of virtual implant planned in 36 was 3.75 mm × 10 mm and that planned in 36 and 37 was 4.2 mm × 10 mm. The interimplant distances from the center of one implant to the center of the other in horizontal (mesiodistal) direction was 8.71, 8.79, and 17.50 mm between virtual implants in 35 and 36, 36 and 37, and 35 and 37, respectively [Figure 2]. For the vertical measurement of the implants, the implant positions were planned 1.5 mm supracrestal from the highest point on crest of the ridge. This was done as V.M.M. required at least 1 mm of the implant fixture to extend above the crest of the bone for an accurate scanning and precise measurement. The vertical measurements as planned on C.B.C.T were 1.5 mm and 3.37 mm for implant placed in 35, 1.51 mm and 1.51 mm for implant placed in 36, and 2.47 mm and 1.51 mm for implant placed in 37 in mesial and distal directions, respectively [Figure 3]. All three implants were placed perpendicular (90°) to the horizontal axis [Figure 4]. Anchor pin simulation was performed. The data were saved as a stereolithography (.stl) file which was sent to the processing center for the fabrication of the computer-generated surgical guide (In2Guide™, Cybermed Inc., Seoul, South Korea).
|Figure 2: Linear measurements of implants planned on cone-beam computed tomography in mesiodistal dimension|
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|Figure 3: Linear measurements of implants planned on cone-beam computed tomography in vertical dimension|
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|Figure 4: Angular measurements of implants planned on cone-beam computed tomography for implant placed in 35 location|
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The surgical template was disinfected and secured into place on the model using an anchor pin after drilling a hole with anchor drill [Figure 5]. The anchor pin and template were removed, and tissue punch was used to punch out the soft tissue. The template and anchor pin were placed back onto the model. The drilling was started with the 2.0 mm drill and 2.0 mm drill guide was placed into the guide sleeve. It was then switched to the 2.5 mm drill followed by 3.0 mm drill guide and 3.0 mm drill and drilling was continued [Figure 6]. Before the penultimate drill, the surgical guide was removed. In the open universal guide system, the last drilling was free hand using the drill of the implant company (Adin Implant System Ltd., Israel) following the direction of osteotomy site preparations. The osteotomy was done at 800 rpm and the fixture was torqued to 30 Ncm up to the depth of osteotomy site [Figure 7].
|Figure 6: Osteotomy performed through the drill guide placed into the guide sleeve of surgical template in 37 location|
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Testing of samples
Post-in vitro implant these implants were tested for their positional accuracy via V.M.M. for the following criteria:
- Linear distance in horizontal (mesiodistal) axis [Figure 8]
- Linear distance in vertical axis [Figure 9]
- Measurement of angulation (perpendicularity) [Figure 10].
|Figure 8: Measurements obtained in the linear direction using vision measuring machine|
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|Figure 9: Measurements obtained in the vertical direction using vision measuring machine|
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|Figure 10: Angular measurements obtained in terms of perpendicularity using vision measuring machine|
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The measurements recorded were compared to the planned virtual implant positions. For the measurement of vertical distances of the implants, distance of each implant from the crest of the bone till implant platform on both mesial and distal directions was calculated and the discrepancy in these values was compared with the CBCT measurements. For the measurement of angulations for all three implants, a horizontal reference line parallel to the base of the model was marked on V.M.M. 7.5 mm above the base.
The data obtained were analyzed using SPSS software (v20.0; SPSS Inc., Chicago, IL, USA). Descriptive statistics was calculated for each variable of the Group B (Guided Implant placement) with respect to the control Group A CBCT using “one-sample t-test” in relation to each parameter studied, i.e., vertical distance, linear distance, and perpendicularity. Results were expressed in the form of mean, standard deviation (SD), and range. P < 0.05 was considered statistically significant. The measurement denotations of subgroups are summarized in [Table 1].
| Results|| |
Mean and SD of measurements of the three implants I, II, and III in linear, vertical direction and angulation between implants virtually planned using CBCT software (Group A) and those placed through a stereolithographic surgical open guide system (Group B) are described in [Table 2].
|Table 2: Evaluation and comparison of measurements in linear, vertical direction and angulation of the three implants I, II, and III between implants virtually planned using cone-beam computed tomography software (Group A) and those placed through a stereolithographic surgical open guide system (Group B)|
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| Discussion|| |
Buser et al. pointed out that a successful esthetic outcome can only be achieved with “an ideal implant position in all three dimensions.” The angulation of the implant is one of the most important factors in the stresses observed on peri-implant structures. With respect to stress distribution, insertion of the implant parallel to the long axis of occlusal loading is known to be ideal. A recent meta-analysis in which differences in marginal bone loss between straight and tilted implants were evaluated (ranging from 25° to 40°) suggested that regardless of the direction of forces, inclined implants caused higher stresses in peri-implant bone than implants placed parallel to the long axis. Guided surgery is an effective means to achieve this parallelism.
In relation to the angular measurements, significant difference in the final implant position of all three implants was observed after placement through the open guide. These results are in agreement with those of Sarment et al., who concluded that conventional freehand drilling (control guide) allowed for an accuracy of 8° and the test method utilizing a stereolithographic closed-ended system (test guide) achieved an accuracy of 4.5°. This difference was statistically significant (P < 0.001).
Naziri et al. verified that implantation in a free-end dental arch has a statistically significant negative influence on the precision of implant insertion compared to implantation in a tooth supported situation. This is because the surgical guide is only partially tooth supported in free-end dental arch implantation. However, even though the drilling protocol used in our study was partially guided by the template, yet, the guide was made using stereolithography which could have contributed to better results in our study in terms of angular accuracy.
In the present study, there is a significant angular deviation of implant placed in the region with respect to tooth 37 (implant III) as compared to implants placed with respect to tooth 35 and 36 (implant I and II, respectively). This is in consistency with the study performed by Toyoshima et al., who observed that the angular displacement of implant axis in the 47 region was significantly higher than that in the 45 region (P = 0.031). One reason for this could be that the open guide used in our study was supported by mucosa on both sides of jaw as opposed to teeth (Kennedy class I). As the model was a free-end saddle on both ends, there could have been a possible movement of the guide while drilling. Another factor to consider is the placement of anchor pins, which were placed in the region of 35 and 36 (first molar region) on both ends. This could have contributed to the apical displacement of distal part of surgical guide (toward the mucosa) during its movement in posterior direction, because an anchor of the guide could not be set distal to 37 or 47 (distal end of the guide).
In our study, the mean linear deviation (mesiodistal) between implants I and II placed using the stereolithographic open guide was 1.09 mm and between implants II and III was 0.6 mm as compared to the CBCT measurements. Although there is a wide variation among these measurements in the literature, yet it was observed that these values are quite close to the closed-ended guide (0.9–1.38 mm according to the 5th ITI Consensus) systems and even the navigation systems (0.6 mm). Hence, it can be concluded that our stereolithographic open-ended guide is quite accurate especially when compared to manual freehand drillings observed in the literature.,, As for the discrepancy in linear deviation values between I and II implants (1.09 mm) as compared to that of II and III implants (0.6 mm) using the open guide, it could be because of lesser bone width in the region where implants I and II were placed as opposed to the region where implants II and III were placed which had a wider bone. Being an open guide system, there could have been a shift in the implant position during the final osteotomy drilling which was performed manually and as a consequence also while torqueing of the implants in that region of narrower bone.
With respect to the accuracy of open guide system in the vertical direction, significant difference was observed among most of the values when compared to those planned on CBCT, especially at the distal of the first implant and mesial of the third implant.
This could have been attributed to the fact that soft tissue thickness is not picked up as accurately as bony structures in a CBCT unit, particularly in areas where the curvature of the bone changes; hence, the erroneousness between the actual thickness and that observed on a CBCT scan could be a major contributing factor for the above results. It is a well-known fact that gingiva or soft tissues are seen better in CT (multidetector or contrast-enhanced) as opposed to a CBCT. Loubele et al. in their study observed that visualization of soft tissues was more difficult with CBCT because of the low-contrast resolution. In contrast, multislice CT showed much better perception of soft tissues such as gingiva.
The errors in vertical dimension using the surgical guide are significantly lower than those using a freehand approach as shown by various studies, where the values in terms of depth deviation, were significantly lesser for guided surgery (P = 0.05) as compared to free hand. However, the author also pointed out that higher deviation in terms of depth exists only for multiple missing teeth and not for single missing tooth, which is again in accordance with our study where there are three missing teeth.
A notable factor observed from this study is that in clinical situations, guided surgery is usually limited till the first molar region (due to limited mouth opening in the second molar region). Therefore, from a clinical standpoint, these open guides can prove to be quite effective and useful as the anchor pin support in this region can limit the distal or downward movement of the guide that led to the slight errors in position and angulation as seen in the present study in relation to posterior most implant. In addition, it is observed that the accuracy of guide (in vertical direction) used in the present study is questionable, and hence, this should be evaluated in further clinical studies. Further, another line of research could be the comparison of implant positions as achieved by open guides in tooth-supported versus tooth tissue-supported versus completely edentulous situations.
| Conclusions|| |
- The universal open guide system achieved accurate linear placement of implants in terms of horizontal (mesiodistal) distance between implants I and II in comparison to those virtually planned on CBCT
- The linear accuracy of the implants placed using open guide was comparable to the closed-ended guide systems and even the navigation systems
- The open guide system proved to be quite accurate in terms of angulation compared with conventional implant placement although there was a statistically significant difference in the final implant position of all three implants after placement through open guide
- The open guide system did not show an acceptable level of accuracy in terms of vertical distance especially in the distal of the first implant and mesial of the third implant as compared to CBCT measurements
- The open guide used in the study may be considered accurate for placement of implants in horizontal or mesiodistal position, in terms of perpendicularity but not in vertical position.
We would like to express our appreciation and gratitude to the Indian Council of Medical Research (ICMR), New Delhi, India, for lending financial support to this work in the form of Senior Research Fellowship grant.
Financial support and sponsorship
The study was supported by the ICMR.
Conflicts of interest
There are no conflicts of interest.
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Dr. Avni Sharma
Sharma Dental Clinic, 327 A, Pocket A-1, Sector-6, Rohini, Delhi - 110 085
Source of Support: None, Conflict of Interest: None
[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10]
[Table 1], [Table 2]