Abstract
The purpose of this study was to determine the accuracy of depth implant insertion and to describe the frequency of early surgical complications or unexpected events, recorded using a single, totally guided, stereolithographic surgi-guide (bone-, mucosa- and teeth-supported) for both osteotomy site preparation and implant delivery. Ten adults were included in this study. Six patients were treated in both arches, and the number of computer aided implantology (CAI) interventions was 16, which equalled the number of guides used, for a total of 111 implants inserted. Complications and unexpected events occurred during the positioning of the surgical guide and whilst preparing the implant site and installing implants. In order to minimize the risk of complications and unexpected events, attention must be paid to every stage of treatment, including checking computed tomography (CT) images, guide manufacturing, proper guide positioning in the mouth, guide fixation, rotational allowance of drill in tubes, shape and sharpness of the drills, first entry point, mouth opening and guided implant insertion.
Technological developments are increasingly changing the approach to implant therapy. Computer-aided-design/computer-aided manufacturing (CAD/CAM)-generated surgical guides, in conjunction with computed tomography (CT), have widened the realm of pre-surgical treatment planning and accurate implant placement, thus allowing the clinician to satisfy both functional and aesthetic needs, whilst at the same time respecting the fundamental principles of biomechanics . Two different techniques have been developed for computer-aided implant surgery . Computer-guided (static) surgery involves the use of a static surgical template that reproduces the virtual implant position directly from CT data and does not allow for intraoperative modification of the implant position. Computer-navigated (dynamic) surgery involves the use of a surgical navigation system that reproduces the virtual implant position directly from CT data and allows for intraoperative changes in implant position.
There are many advantages in using computer technology in implant surgery and there are several reports of the accuracy of computer-aided implantology (CAI) . There are few papers on in vivo clinical studies reporting the use of stereolithographic surgical guides. Almost all of these studies are aimed at determining the accuracy of stereolithographic surgi-guides, whilst scant information is given about possible intra-operative complications, which must be acknowledged before surgery, in order that they can be dealt with whilst operating. Despite the limited objective data in the literature concerning CAI, unrealistic clinical expectation has led to rapid adoption of this poorly documented technology, which has wrongly been described as effective and easy to apply. A potential risk is the future disuse of a technique which, if properly analysed and applied, can improve the final result in implant-prosthetic rehabilitation .
The purpose of this study is to determine the accuracy of depth implant insertion and to describe the frequency of early (set at 2 weeks postoperatively) surgical complications or unexpected events, recorded using single totally guided, stereolithographic surgi-guides (bone-, mucosa- and teeth-supported) (External Hex Safe ® , Materialise Dental, Leuven, Belgium). The main features of the more recently introduced External Hex Safe ® surgi-guide are the working length, using surgical drills with a physical stop, and guided implant placement using mounting of fixed length. Discussion revolves around whether this new type of surgical template is really characterized by better depth control (unsuccessful implant placement in depth) and lower frequency of complications or unexpected events.
Materials and methods
Implant-prosthetic rehabilitation had to be provided for 10 patients, who were partially (first Kennedy Class) or totally edentate. Their average age was 54 years and the sex ratio was 2:1 (male/female). Patients with unhealthy systemic status, parafunctional habits, poor oral hygiene, severe alveolar bone deficiencies, uncontrolled diabetes, current irradiation to the head or neck, psychological disorders, or alcohol, tobacco or drug abuse were excluded. All patients consecutively treated with CAI between November 2007 and February 2010 were included in this retrospective study. All the patients were informed of the study protocol and signed an informed consent form. The surgical interventions were performed by the same operator of the virtual surgical planning (M.C.), using the SimPlant ® software (Materialise Dental, Leuven, Belgium). The treating clinician was an expert in implant dentistry and in CAI. The protocol employed in this clinical study consisted of an integrated treatment sequence that involved the following steps.
First, the development of a radiopaque diagnostic template, the so-called scanno-guide, which is an exact replica of a temporary, partially or totally removable, prosthesis, was accepted by the patient, and complied with aesthetic and functional principles . In some fully edentulous cases, and in particular in the most recent ones, the ‘double scan technique’ was used. The patient’s complete denture, which satisfied the aesthetic and functional requirements and fitted the supporting tissues, was used as a scanning template, to visualize the teeth setup in CT images and the mucosa surface.
Second, a CT scan of the patient’s arch was carried out with a spiral CT device . The Asteion Multi (Toshiba Medical Systems, Rome, Italy) was used. The scans included the scanno-guide or the patients’ prosthesis to integrate the anatomical data with the functional and aesthetic determinants . When the ‘double scan technique’ was used, the patient’s complete denture was scanned using at least the same scan parameters as for the patient’s scan, but a higher resolution was allowed.
Third, digital three-dimensional CT-based surgical planning was carried out . The computer program used was SimPlant ® (Materialise Dental, Leuven, Belgium), which uses the original CT data, in digital imaging and communications in medicine (DICOM) format, to produce axial, three-dimensional, panoramic and cross-sectional images, all of which are visible at the same time in four interactive windows on the computer monitor. With this software the implants are virtually placed according to bone anatomy and prosthetic design .
Fourth, CAD of the stereolithographic surgical template was carried out. The clinician, in the CAD environment, designs the drilling template according to the prosthetic and anatomical needs of the patient .
Fifth, CAM of the stereolithographic surgical template was carried out, to transfer the digital planning to the surgical environment . The External Hex Safe ® surgi-guide (Materialise Dental, Leuven, Belgium) is a totally guided implant system, allowing for controlled osteotomy site preparation and implant placement in three dimensions . The surgical guides were classified, according to the type of supporting anatomical structure (bone-, mucosa- and teeth-supported). The system uses a single guide for both osteotomy site preparation and implant placement. Specific cylinders are embedded within the acrylic resin guide to accommodate drill handles or similar components that intimately engage the cylinders . The External Hex Safe ® surgi-guide allows for control over the mucotomy and the preparation of the implant site. The first drill used was the mucotome to punch and remove gingival soft tissue . Osteotomy site-specific drills that have vertical stops to control apico-coronal site preparation, were then used . Only two sizes of single-use drills with physical stops were used: a pilot drill (diameter 2.8 mm (bottom)/2.0 mm (top)) and a final drill (diameter 3.00 mm (bottom)/3.15 mm (top)). Drill handle application was chosen depending on the specific needs of the patient and the individualized CT plan. This resulted in different lengths of drills being used varying from 10 to 25 mm. Countersinking was not performed. Implant placement was performed using specific delivery mounts (implant holder length 4–15 mm) to have controlled angulation and apico-coronal depth, which was set by the computerized three-dimensional plan . The method used (External Hex Safe ® surgi-guide-Materialise Dental, Leuven, Belgium) offers the possibility of firmly stabilizing the surgical guide using osteosynthesis screws. In order to determine the real advantage of guide fixation, the use of osteosynthesis screws in some randomly selected patients was planned, in a minimum number of three, arranged in a tripod, to obtain the highest stability. The teeth-supported External Hex Safe ® surgi-guides used were, in all cases, free ending templates and were seated and stabilized with the help of natural teeth. The bone-supported guides required an open flap reflection; the mucosa- and teeth-supported guides did not require flap reflection but used a flapless/transmucosal approach and a special mucotome with an outer diameter of 4.00 mm.
Sixth, computer-aided surgery was carried out . 111 P1H implants (Plan 1 Health-Amaro-Udine-Italia, Italy), cylindrical, with an external hexagon (diameter 3.75–4.00 mm and length 10–18 mm) were inserted in partially and completely edentulous patients, using stereolithographic templates.
Seventh, as described by D’H aese et al. all the patients underwent a postoperative CT and an iterative closest point (ICP) algorithm was used to match the jaw of the preoperative CT with the jaw of the postoperative CT (the software runs until it finds the best overlap between the images) ( Fig. 1 A) . This allowed a comparison of the planned implants with the placed ones ( Fig. 1 B) and the determination and calculation of four parameter deviations (i.e. global apical and coronal, angular, depth, and lateral deviation) by using their three-dimensional coordinates at apical and coronal level ( Fig. 1 C). All parameters except the angular deviation were determined for both the coronal and apical centres . The global deviation (coronal and apical) was defined as the three-dimensional distance between the coronal (or apical) centre of the corresponding planned and placed implants. The global coronal deviation corresponds to the entry point of the surgical drill into the alveolar ridge. Next, the angular deviation was calculated as the three-dimensional angle between the longitudinal axis of the planned and placed implant . To establish the lateral deviation, a plane perpendicular to the longitudinal axis of the planned implant and through its coronal centre was defined and was referred to as the reference plane . The lateral deviation was calculated as the distance between the coronal centre of the planned implant and the intersection point of the longitudinal axis of the placed implant with the reference plane . The depth deviation was calculated as the distance between the coronal centre of the planned implant and the intersection point of the longitudinal axis of the planned implant with a plane parallel to the reference plane and through the coronal centre of the placed implant .
Eighth, during surgery, any unexpected events or complications were recorded and divided into three categories, arising from the following variables: anatomical structures, surgical templates, and implants. Those relating to anatomical structures included uncontrolled removal of keratinized gingiva (lack of attached gingiva around the fixture), mucosal laceration, nerve injuries, abnormal haemorrhages, sinus pathologies, prolonged pain and/or swelling. Surgical template problems included improper or tilted seating of surgical template on the supporting tissues, not enough interocclusal distance to perform implant site preparation and guided implant placement (limited access), overheating of the surgical drill, friction between the inner surface of the master tube and the implant holder surface, detachment of surgi-guide metal tubes, template cracking and breaking, and template cracking without breaking. Problems with implants included unsuccessful placement to depth, limited primary stability of the inserted implants (implant unstable), and alteration of external hexagon of the implant (rounding of the hexagon angles).
Statistical analysis
Data were analysed using SPSS ® software (Statistical Package for Social Science, IBM Corporation, NY, USA). Quantitative data was described using frequency distribution, mean values, standard deviation and median values. Correlations amongst the different deviation parameters (i.e. global, angular, depth and lateral deviation) and between depth deviation and bone density (according to D1–D5 Misch classification) were tested with the Pearson correlation coefficient. The t test was used to determine the influence of surgical variables.
The following influencing variables were defined as categorical factors: External Hex Safe ® support (bone/mucosa/teeth), jaw (maxilla/mandible), type of edentulism (complete/partial). Significance was set to P ≤ 0.05.
Considering the depth deviation data, implants placed more coronally were distinct from those inserted more apically and the accuracy data regarding depth deviation were illustrated using a box plot. Scatter plots were used to evaluate intra-operator variability of depth deviation in relation to the number of surgeries performed and to determine whether a learning curve was present.
The influence of time, as the number of surgeries performed, on the occurrence of early surgical complications or unexpected events was investigated. The frequency data of early surgical complications or unexpected events was categorized into three groups: initial (recorded from first to fourth surgery), middle (recorded from fifth to eighth surgery) and final (recorded from ninth to fourteenth surgery).
The χ 2 test was used to determine the influence of time (experience) on the occurrence of early surgical complications or unexpected events. Significance was set at P ≤ 0.05.
The influence of variables such as arch (maxilla, mandible), type of guide support (bone, mucosa, teeth), type of edentulism (complete, partial) and surgical technique (flapless, open flap; fixed, not fixed) on early surgical complications or unexpected events was determined.
The mean density of the implant site was determined using a specific software function of SimPlant ® software.
Statistical analysis
Data were analysed using SPSS ® software (Statistical Package for Social Science, IBM Corporation, NY, USA). Quantitative data was described using frequency distribution, mean values, standard deviation and median values. Correlations amongst the different deviation parameters (i.e. global, angular, depth and lateral deviation) and between depth deviation and bone density (according to D1–D5 Misch classification) were tested with the Pearson correlation coefficient. The t test was used to determine the influence of surgical variables.
The following influencing variables were defined as categorical factors: External Hex Safe ® support (bone/mucosa/teeth), jaw (maxilla/mandible), type of edentulism (complete/partial). Significance was set to P ≤ 0.05.
Considering the depth deviation data, implants placed more coronally were distinct from those inserted more apically and the accuracy data regarding depth deviation were illustrated using a box plot. Scatter plots were used to evaluate intra-operator variability of depth deviation in relation to the number of surgeries performed and to determine whether a learning curve was present.
The influence of time, as the number of surgeries performed, on the occurrence of early surgical complications or unexpected events was investigated. The frequency data of early surgical complications or unexpected events was categorized into three groups: initial (recorded from first to fourth surgery), middle (recorded from fifth to eighth surgery) and final (recorded from ninth to fourteenth surgery).
The χ 2 test was used to determine the influence of time (experience) on the occurrence of early surgical complications or unexpected events. Significance was set at P ≤ 0.05.
The influence of variables such as arch (maxilla, mandible), type of guide support (bone, mucosa, teeth), type of edentulism (complete, partial) and surgical technique (flapless, open flap; fixed, not fixed) on early surgical complications or unexpected events was determined.
The mean density of the implant site was determined using a specific software function of SimPlant ® software.
Results
For this study, 10 adults were included. Six patients were treated in both arches, and the number of CAI interventions was 16, which equaled the number of guides used, for a total of 112 planned and 111 inserted implants ( Table 1 ). After insertion, one implant showed extreme mobility. It was immediately removed and therefore not included in the evaluation of deviation values.
| Mean | Total | Number of guides | Number of implants | |
|---|---|---|---|---|
| Age | 54 | |||
| Number of implant | 111 | |||
| Number of subjects | 10 | 16 | 111 | |
| Gender | ||||
| Male | 7 | 11 | 84 | |
| Female | 3 | 5 | 27 | |
| Type of edentulism | ||||
| Total | 12 | 94 | ||
| Partial | 4 | 17 | ||
| Arch | ||||
| Maxilla | 9 | 68 | ||
| Mandible | 7 | 43 | ||
| Type of safe guide | ||||
| Fixed | 8 | 67 | ||
| Not fixed | 8 | 44 | ||
| Surgical guide support | ||||
| Mucosa | 11 | 85 | ||
| Bone | 4 | 18 | ||
| Teeth | 1 | 8 | ||
| Surgical technique | ||||
| Flapless | 12 | 93 | ||
| Open-flap | 4 | 18 | ||
Accuracy
Of the 112 implants, 111 were available for a comparison of accuracy via an image registration technique. In this study, the global (apical and coronal), angular, depth and lateral deviations were determined and statistically analysed, but the analysis focused on the assessment of the discrepancy of depth deviation. This value has been proven to be extremely important in achieving optimal clinical results without complications. The depth deviation is, in fact, closely correlated with the preservation of anatomical structures. Mean depth deviation between planned and placed implants of the implants inserted with External Hex Safe ® surgi guide was 0.75 mm. Deviation outcomes are displayed in Table 2 .
| Mean | Max | Min | Standard deviation | |
|---|---|---|---|---|
| Coronal deviation (mm) | 1.52 | 3.00 | 0.13 | 0.61 |
| Apical deviation (mm) | 1.97 | 4.23 | 0.34 | 0.86 |
| Angular deviation (°) | 4.68 | 15.25 | 0.10 | 2.98 |
| Depth deviation (mm) | 0.75 | 2.29 | 0.03 | 0.55 |
| Lateral deviation (mm) | 1.20 | 2.61 | 0.12 | 0.63 |
Regarding the existence of a correlation at the implant level between coronal, apical, angular, depth and lateral deviation, the Pearson correlation coefficient demonstrated that there were significant linear correlations between the depth and coronal deviations ( P = 0.000) and between the depth and apical deviations ( P = 0.016) ( Table 3 ). Angular ( P = 0.608) and lateral ( P = 0.580) deviations were not significantly correlated with depth ( Table 3 ).
| Safe | Coronal deviation (mm) | Angular deviation (°) | Depth deviation (mm) | Apical deviation (mm) | |
|---|---|---|---|---|---|
| Angular deviation (°) | Pearson correlation | 0.132 | |||
| Sig. | 0.168 | ||||
| N | 111 | ||||
| Depth deviation (mm) | Pearson correlation | 0.530 * | −0.049 | ||
| Sig. | 0.000 | 0.608 | |||
| N | 111 | 111 | |||
| Apical deviation (mm) | Pearson correlation | 0.514 * | 0.500 * | 0.228 * | |
| Sig. | 0.000 | 0.000 | 0.016 | ||
| N | 111 | 111 | 111 | ||
| Lateral deviation | Pearson correlation | 0.796 * | 0.157 | −0.053 | 0.438 * |
| Sig. | 0.000 | 0.100 | 0.580 | 0.000 | |
| N | 111 | 111 | 111 | 111 | |
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