Original study - ZZI 01/2013

Analysis of the precision of implant templates

F. Petschelt1, M. Millian1, T. Kraußeneck1

Aim: The aim of this study was to evaluate the precision of holes drilled in implant templates, which were analyzed with cone beam computed tomography (CBCT) using suitable planning software.

Material and methods: 40 templates that had been used clinically to enable successful treatment were studied. 17 of the analyzed templates were fabricated with the Med3D program (C. Hafner GmbH, Pforzheim) and 23 templates were made with the ExpertEase software of Dentsply Friadent GmbH. The Scanora Soredex was used for CBCT. Comparative measurements were made on a plaster model with silicone key using an individually fabricated appliance.
3 holes were drilled in each template by 3 different persons. The resulting data were compared to within less than a millimeter.

Results: Maximum deviations of 2.0 mm in the horizontal dimension and 1.0 mm in the vertical dimension were found. Much smaller deviations with more precise positions were found with the ExpertEase version compared with the Med3D-assisted procedure.

There were no significant differences in drilling precision between an experienced implantologist and a dental nurse without any practical experience on patients.

Conclusion: With observation of the basic principles of implantology and use of planning software for template-guided surgery, exact implant placement to within less than a millimeter is possible, even in the most demanding situations.

Keywords: Computer-aided implantology; CBCT; 3D navigation; implant templates; precision; drilling sleeves

Citation

Petschelt F, Millian M. Kraußeneck: Analysis of the Precision of Implant Templates. Z Zahnärztl Implantol 2013;29:58?69. DOI 10.3238/ZZI.2013.0058?0069

Introduction

Implant therapy always forms part of an overall restorative concept. Good preoperative planning is essential to meet the aesthetic and functional demands of implant-borne restorations [6, 8, 20].

Integration of implant-related diagnosis, planning and surgery in this overall concept should therefore be considered carefully, in accordance with DGZMK guidelines.

Radiographic imaging data are imported into the planning software and the implants are placed virtually. There is a wide choice of implant lengths and diameters from different manufacturers and these can be fitted to the bone [2, 7]. Suitable software enables the implant positions in the important anatomical structures to be analyzed and aligned in the axial, sagittal and horizontal dimensions. The usual tomographic views and three-dimensional reconstruction illustrate the planning results. The course of the inferior alveolar nerve, for example, is entered semi-automatically by the user so it can be shown realistically. The guide sleeves of the templates are calibrated so that the different drills can be passed precisely with the exchangeable sleeves [10, 11].

Various procedures for navigated three-dimensional implantology were defined at an early stage. Not least with the introduction of immediate restoration with immediate loading and with the major advances in digital volume tomography, the possibilities of the navigated three-dimensional technique have expanded greatly and are generally highly regarded. [9, 20] An X-ray template is indispensable for backward planning and therefore for well-founded and advanced implant planning [13]. The scan template is the key to success as initial illustration of the functional dental arches incorporating the achievable prosthetic rehabilitation is necessary in every software program to show the situation in the mouth. The software and its special functions can be used optimally only with an X-ray template produced in accordance with certain criteria.

When producing a template, a distinction is made between stereolithography and the model-based implant template, though this has no influence on the actual scan template [2, 5, 8, 11]. In nearly all systems, it must have a radiopaque section with a prosthetic component.

The Dentsply Friadent system, a development of the Simplant system (Materialise, Leuven, Belgium), enables the X-ray template to be produced by optical conversion of the site into the program [2, 16, 17].

The Med3D X-ray template, with the familiar Lego brick, is converted in the dental laboratory from the X-ray template to the subsequent operation template by a suitable calibration system.

With the systems we use, the decision to implant using navigation involves close collaboration with the planning center or laboratory. This provides an opportunity of achieving an optimal result through interdisciplinary collaboration.

Precision depends on the accuracy of transfer from the scan template to the operation template and this is the key to success.

There are several sources of error. Inaccuracy due to conversion of the CT data during production can impair the subsequent fit of the drilling template [14]. Despite precise radiographs, drill play can arise in the drill template sleeves. While these parameters have been investigated in different applications [2, 3, 5, 7, 10, 16, 17, 19, 20, 21], there are no known investigations of how accurate drilling through sleeves can be. This question is addressed in this study.

Intraoperative fixing of drilling templates depends on the residual dentition and the planned surgical procedure. Tooth-supported, mucosa-supported and bone-supported templates are possible [8, 11]. In the cases studies, tooth-supported templates, which are regarded as the most accurate, were used exclusively for analysis.

Dental digital volume tomography (CBCT) is used in guided implantology. This allows much more reliable analysis compared with classical two-dimensional methods. Apart from the three-dimensional view, which allows exact orientation in space, a major advantage of CBCT is the undistorted representation of the volume [14, 15, 19]. The data obtained are transferred to the corresponding planning software by the familiar DICOM data export. The planning software (ExpertEase, Med3D) can convert the imported data on the basis of the DICOM transfer language [8, 11, 14].

Objective: The aim of the study was to investigate how accurately drilling can be performed with the sleeve systems available for navigated implantation by means of holes drilled by 3 different persons following exactly the same procedure with identical templates.

 

Material and methods

40 templates were used in the study. All had previously been used clinically for template-guided navigated implantology. 17 templates were produced with Med3D planning software and 23 with the ExpertEase system.

Using the templates, a plaster model of each situation was produced by the same master dental technician. Perfect fit of the template on the model is ensured as the plaster model was made after the operation template and not the reverse.

The plaster was cut out in the region of the drilling sleeves and 3 absolutely identical silicone keys that could be positioned securely in the plaster model and were exchangeable were made for each template (Fig. 1a and 1b). Holes were drilled in these silicone keys and these drilled cavities were later measured. A new silicone key was used for each drilling by each person. All holes were drilled by the same 3 persons. 2 of these were dentists experienced in oral surgery who used implants frequently and the third was the dental nurse who regularly assists during surgical procedures but has no implant experience (Fig. 2a).

All drilling was performed with the same motor and the same handpiece, the same speed, the same twist drill and the same drilling sleeve. The Xive drill from Dentsply Friadent with a diameter of 3 mm and length of 18 mm was used in all cases (ExpertEase drill, Dentsply Friadent). Drilling depths of 11 mm were analyzed with both Med3D and ExpertEase, so fictive 11 mm implants (Fig. 2b) were selected.

The silicone keys were exchanged by a dental technician. A Lego brick was attached to each drilling template for keying and fixing to the measuring appliance. The Lego locking mechanism, which also provides a reference size for radiographic analysis in Med3D is extremely precise (up to 1/2000 mm)
[1, 8]. A swivel joint is incorporated in this measuring appliance and a transparent film with millimeter divisions can be fitted with this for the respective situation (Fig. 3). The individual parts of the appliance are fixed with Lego bricks. A swivel joint enables the millimeter film to be fitted again to the anatomic situation and the respective template. So as not to endanger the secure position of the appliance, all parts are keyed with self-curing resin (Pattern Resin, GC) so that only the millimeter scale moves in space through the swivel joint and can be fitted to the template (Fig. 3, 4, 5). With this construction, measurement of the deviation of the 3 drillings is possible in the vertical and horizontal or transverse plane. The measurements were assessed by the dental technician using an operating microscope to obtain a neutral assessment even in the submillimeter range and they were checked by the first author. The precision was set at up to a quarter millimeter, which is in the range of what can be measured objectively by the human eye on the underlying millimeter scale at tenfold microscopic magnification.

The measurements were analyzed by the dental technician.

Results

40 templates were selected for the measurements, all of which had been in clinical use previously. Two sleeves, that is, two measurements, were made with three templates, given a total of 43 drilled holes or implant positions for examination and comparison.

The drilling values of one person were chosen as a reference value for the 129 drilled holes, so that the deviation of the holes drilled by one dentist and the dental nurse could be studied.

On vertical measurement (Fig. 4a and 4b), 77 of the 86 drilled holes were without deviation, 2 holes had a deviation of 0.25 mm, 3 had a deviation of 0.5 mm and four holes had a deviation of 1 mm (Fig. 6).

Of the 43 holes drilled by the dentist, 38 were without deviation in the vertical dimension, 2 had a deviation of 0.25 mm, one had a deviation of 0.5 mm and 2 holes
had a deviation of 1 mm, while 39 of the holes drilled by the dental nurse were precise and without deviation, 2 holes had a deviation of 0.5 mm and 2 holes had a deviation of 1 mm (Fig. 7).

The maximum deviation of a drill hole in the vertical dimension was thus 1 mm in 4 cases. An obvious difference in precision can be identified with the different template sleeves in the vertical dimension. All deviations were found with the Med3D method while no deviation was found in the holes drilled with the ExpertEase template.

The drilled holes were also compared and studied in the horizontal plane using the measuring appliance produced by the dental technician and with the operating microscope (Fig. 5a and 5b).

Of the 86 comparable drillings in this plane, 40 were without deviation, the deviation was 0.1 mm with 2 holes, 0.25 mm with 9 holes, 0.5 mm with 10 holes, 0.75 mm with 3 holes, 1 mm with 15 holes, 1.5 mm with 4 holes and the deviation was 2 mm with 3 holes (Fig. 8).

The maximum deviation was 2 mm. The drilling depth in bone and in our in vitro study and in the silicone key was only 11 mm. The error source is therefore smaller with an 11 mm implant length, as the drill length from bone level to the handpiece is more than 11 mm and the excursion is therefore greater.

The holes drilled by the experienced dentist differed hardly at all from those of the dental nurse. 20 of the holes drilled by the dentist and 20 drilled by the dental nurse were without any deviation in the horizontal plane. 3 of the holes drilled by the dentist had a deviation of 0.25 mm, 5 holes had a deviation of 0.5 mm, one had a deviation of 0.75 mm, 9 holes had a deviation of 1 mm, 3 holes had a deviation of 1.5 mm and 2 holes had a deviation of 2 mm.

Of the holes drilled by the dental nurse, 8 had a deviation of up to 0.25 mm, 5 had a deviation of 0.5 mm, 2 holes had a deviation of 0.75 mm, 6 holes had a deviation of 1 mm and 2 holes had a deviation of 2 mm (Fig. 9).

 

Comparison of Med3D and ExpertEase

Two types of templates were included in the study.

One hole drilled by one person was again set as the reference value in both vertical and horizontal dimension so that the work of the second implantologist and of the dental nurse could be analyzed.

34 measurements with the 17 Med3D template, that is, 34 measurements for the vertical and horizontal plane, were compared with the 52 values from the 23 ExpertEase templates (2 drill holes were studied in the case of 3 templates of this type).

In the vertical dimension, much more precise results were found with the ExpertEase-assisted drilling. With the ExpertEase template, 2 deviations of 0.25 mm in the vertical dimension and one deviation of 1 mm were found out of the total of 4 deviations of 1 mm. With Med3D, accordingly, inaccuracy was apparent with a deviation of 0.5 mm 3 times and a deviation of 1.0 mm 3 times.

The 3 greater Med3D deviations (1 mm) in the depth were produced by the experienced dentist and implantologist.

In the horizontal plane, 20 drilled holes were exact with both the ExpertEase produced by stereolithography and with the laboratory-fabricated Med3D template. The two 0.1 mm deviations derive from the ExpertEase template. Six of the 9 deviations with a value of 0.25 mm used the Med3D template as guide and 6 of the 10 imprecise drill holes had a deviation of 0.5 mm. Of the 3 deviations of 0.75 mm, one was produced with the ExpertEase and the rest with the Med3D templates; 6 of the 1 mm deviations were with the ExpertEase and 9 with Med3D; one of the 4 deviations of 1.5 mm arose with the ExpertEase and 3 with Med3D, while the 3 with a deviation of 2 mm all derived from the Med3D templates.

 

Discussion

All deviations were very small, as described in the literature
[2, 3, 5, 7, 10, 16, 17, 19, 20, 21, 22]. In this study, the precision of the relationship between radiographic analysis and the clinical situation was not analyzed, as often before, but rather the precision of the template itself.

The study was not designed to assess or analyze the precision of the imaging, CT or CBCT, and its transfer to the oral situation, that is, the actual use of drilling in the mouth. Examination of the accuracy of data transmission to planning software, conversion of the planned situation to the operating template and ultimately the precision of this fabricated situation in the actual operation is discussed in the available literature and should be the subject of other studies [2, 3, 5, 7, 10, 16, 17, 19, 20, 21, 22].

This study was designed to investigate how accurately holes can be drilled with the twist drills and sleeves provided by the industry and how accurately the position of the implant can then be established. So far there have been no studies in the literature of the possibility of precise and reproducible drilling with one and the same template with the assistance of drilling sleeves. This question is addressed with the data obtained here.

The measurement process was defined. The “treating dentists”, that is, the persons who drilled the holes, all worked under the same conditions with the same material and with the same established calibrated procedure. The analyst was the dental technician. He produced a reproducible report of the results, which was checked by the first author.

The numbers give secure information. Template-guided drilling in the submillimeter range with an operating template produced according to three-dimensional analysis is possible. It was shown that this reproducibility even provides such high precision, thus assisting the work, that even inexperienced persons unfamiliar with drilling in bone can achieve exact drilling geometry. It was not shown clearly that the experienced dentist familiar with dental surgery can achieve better results.

Average error sources of up to 0.5 mm have been discussed in previous publications [3, 5, 7, 9, 16, 17, 19, 20, 21, 22]. Lower errors on average arose with the question of the precision of the sleeve-drill relationship analyzed here.

Many authors have already dealt with the validity of CBCT, transfer of data to planning software, with differences in these programs, with the possibility of transferring the planning to the oral situation and with similar potential sources of error
[1, 2, 7, 16, 17, 19]. These studies are the basis for the precision of template-guided implantology. A new study of the deviations, as shown here, shows the mounting of the drills in the template sleeves.

The digital workflow is easy to manage [15]. However, the operation itself is still performed by human hands. Although guided, inaccuracies, which have not been presented hitherto, cannot be circumvented despite the extremely precise drilling possibilities.

89 % of the total of 86 drilled holes in the study did not deviate in the vertical dimension. About 10 % have a small deviation, all of which occurred with the Med3D-assisted template. The ExpertEase-assisted template with its sleeves exhibits clear advantages. No inaccuracies were identified. No differences were found between the dental nurse and the experienced dentist. These findings were suspected before now but were not yet demonstrated in any study.

Guiding the drilling in the horizontal plane was exact in about half while the other half resulted in a deviation of 0.1 mm to 2 mm. In this case too, no differences were found between the experienced and inexperienced surgeon. However, it should be noted that there was a trend for the precision to increase with each person after several drilling procedures, that is, towards the end of the series of tests. It can be assumed that a learning curve must be overcome and experience leads to better results. In the literature, routine use of implantological measures is frequently evaluated [13, 14].

In the comparison of the numbers, an advantage was found in the precision of the ExpertEase template and the corresponding sleeve system.

A serious difference between the dental nurse and the experienced implantologist was not found in the horizontal dimension when drilling with Med3D and ExpertEase template guidance was compared.

However, a clear trend was noted with advancing practice. Nearly all errors occurred with earlier drillings, while the inaccuracies diminished markedly with the later drillings by both persons. It appears that a learning curve must be overcome in navigated drilling.

In this in vitro study, the difficulties that occur during use in the mouth are absent. Restricted mouth opening, contact between the handpiece and the antagonist teeth, saliva, mucosa and many other factors make procedures in the oral cavity more difficult. With template-guided drilling, particular attention should be paid to the completely submerged precise seating of the individual sleeves in the parent sleeve. With this procedure, the results obtained in vitro are quite applicable to the real situation and provide valid data on drilling precision.

The precision values in our study are confirmed by the literature, which has hitherto analyzed other parameters.

The use of CT or CBCT data allows a precise position in all three dimensions because of the precise determination of the actual bone quantity in the submillimeter range. Precise values can be obtained, especially in the vertical document, where drills with fixed depth stops confer major advantages.

Summary

The aim of this study was to evaluate the precision of holes drilled in implant templates, which were analyzed with digital volume tomography (CBCT) using suitable planning software. 40 templates that had been used clinically to enable successful treatment were studied. 17 of the analyzed templates were fabricated with the Med3D program (C. Hafner GmbH, Pforzheim) and 23 templates were made with the ExpertEase software of Dentsply Friadent GmbH. The Scanora Soredex was used for imaging. Comparative measurements were made on a plaster model with silicone key using a specially fabricated appliance. 3 holes were drilled in each template by 3 different persons. The resulting data were compared to within less than a millimeter.

Maximum deviations of 2.0 mm in the horizontal dimension and 1.0 mm in the vertical dimension were found. Much smaller deviations with more precise positions were found with the ExpertEase version compared with the Med3D-assisted procedure.

In our comparisons, there were no noteworthy differences in drilling precision between an experienced implantologist and a dental nurse without any practical experience on patients. With observation of the basic principles of implantology and use of planning software with template-guided surgery, exact implant placement to within less than a millimeter is possible, even in the most demanding situations.

Conclusion

The holes drilled with a 3 mm diameter twist drill show a high degree of precision, which could probably not have been obtained by free-hand drilling. The “sleeves on drill” technique, using drills with depth stops specially made for navigated implantology appears to confer advantages compared with “normal” drills guided through ordinary sleeves.

 

Citation

Petschelt F, Millian M. Kraußeneck: Analysis of the Precision

of Implant Templates. Z Zahnärztl Implantol 2013;29:58?69.

DOI 10.3238/ZZI.2013.0058?0069

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Correspondence address

Dr. Friedemann Petschelt

Zahnärztliche Gemeinschaftspraxis

Eckertstr. 9

91207 Lauf a. d. Pegnitz

praxis@petschelt.de

Footnote

Zahnärztliche Gemeinschaftspraxis, Lauf

Übersetzung: LinguaDent

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