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I. Introduction
The surgical guide is a static computer-assisted guidance device used to facilitate appropriate surgical placement and angulation of dental implants1-3. By taking impressions and referring to the patients’ three-dimensional (3D) computed tomography (CT) data of the desired implant site, the surgical guide can be created4,5. During surgery, the surgical guide aids in achieving the designed precise placement position and direction of the implant by guiding surgical instruments and implants to the intended location.
Although there has been extensive research focused on the accuracy analysis of implant surgery using surgical guides6-9, long-term follow-up studies of clinical outcomes with this technology have been relatively limited. While previous studies have demonstrated relatively good accuracy in dental implant surgery using surgical guides10,11, one of the most important things to do to guarantee the long-term effectiveness of dental implants is to maintain the stability and quality of the bone surrounding the implant12. Although the use of surgical guides during implant surgery is critical to assess long-term prognostic outcomes of surgery, relatively few long-term studies of peri-implant bone changes have been reported.
Therefore, being aware of the survival and failure risks associated with implant placement using surgical guides is crucial. In this study, we examined and evaluated the long-term clinical outcomes of implant surgeries performed with surgical guides, utilizing marginal bone loss (MBL) as a measure, and we presented several successful and failed cases.
II. Materials and Methods
1. Case selection
This study investigated patients who underwent implant surgeries using surgical guides at the Department of Oral and Maxillofacial Surgery, Seoul National University Dental Hospital, between July 2009 and February 2011. A single surgeon carried out the treatment. The present research, which involves accessing patient medical records, has obtained ethical approval from the Institutional Review Board (IRB) of Seoul National University Dental Hospital (IRB No. CGE09001). The study adhered to the relevant guidelines and regulations outlined in the Declaration of Helsinki, and written informed consent was procured from all participants. The inclusion and exclusion criteria were as follows:
1) Inclusion criteria
(1) Patients who underwent implant placement using surgical guides
(2) Patients with complete radiographic data, including immediate and periodic follow-up visit panoramic radiographs (at three months post-surgery, and one month, one year, two years, and five years after prosthesis delivery)
2) Exclusion criteria
(1) Patients who were lost during the specified follow-up period
(2) Patients lacking complete clinical records and periodic radiographs
Patient demographic information and implant survival rates of long-term were recorded. Data such as age at surgery, sex, medical history, implant position, diameter, length, prognosis, follow-up period, bone graft procedure, and prosthesis details were collected on electronic charts. Panoramic radiographs were taken right after implant placement using surgical guides, and subsequently three months later. The additional panoramic radiographs were taken one month, one, two, and five years after prosthesis delivery.
2. Surgical procedures
Following the acquisition of the CT scans, the CT images were converted into DICOM (digital imaging and communications in medicine) format and then used OnDemand3D (Cybermed Co.) software to create a 3D virtual model. The lengths and widths of the implants, as well as their sites, were carefully considered. The planning software was used to calculate the implant height and angulation before surgery. In2Guide (Cybermed Co.) surgical guides were fabricated as designed and used accordingly.
Preoperative routine preparations were performed, and the surgical guide was thoroughly disinfected. The surgical procedure was performed under local infiltration anesthesia. A trapezoidal alveolar ridge incision, biased towards the lingual aspect, was created in the edentulous area. The surgical guide was placed and fixed either on top of the mucosa, residual teeth or on the bone after the mucoperiosteal flap was elevated. The drilling procedure was executed to the corresponding length using the Quick Guide Kit (Osstem Implant Co.) system on the surgical guide. After removing the surgical guide and visually verifying the position and spacing of the drill holes, the planned bone level implant fixtures of Brånemark System MK III Groovy (Nobel Biocare AB Co.) were inserted through the metal sleeve to the predetermined position.
During the implant fixture placement, if the instrument encountered resistance, it was adjusted to the height using the ratchet rather than with the handpiece. By maintaining the surgical guide with the installed implant until another implant was placed, the effect of increasing the retention of the surgical guide was achieved. After all the implants were placed, the surgical guide was removed, and the implant position and height were confirmed. Finally, a cover screw or healing abutment was connected, and suturing was performed to reposition the periosteum, minimizing tension to prevent a keratinized gingival recession. Postoperation panoramic radiographs were taken to confirm the direction and position of the fixtures.(Fig. 1)
3. MBL measurement
MBL measurement was conducted by evaluating the radiographs acquired at placement (T0), three months after placement (T1), and one month (T2), one year (T3), two years (T4), and five years (T5) after prosthesis delivery.
Consistent magnification was applied to all placement procedures and follow-up panoramic radiographs during MBL assessments. The distance between the implant platform and the bone’s initial point of contact with the implant surface at the mesial and distal aspects was designated as MBL.(Fig. 2) Every site was measured twice to ensure accuracy, and the mean value was noted. Changes in MBL from the placement time to each follow-up visit, as well as the changes between consecutive follow-up visits, were calculated.
To compensate for radiographic image distortion, a formula was employed—the real implant length divided by radiographic implant length, and then multiplied by radiographic bone loss to obtain real bone loss.
4. Implant survival evaluation
The health scale for dental implants from the 2008 Pisa Consensus Conference of the International Congress of Oral Implantologists (ICOI) served as the foundation for the evaluation of implant survival and failure criteria13. According to the specified failure criteria (clinical or absolute failure), an implant was declared failed if any of the following circumstances were satisfied: pain in function, mobility, radiographic bone loss exceeding half the length of the implant, uncontrolled exudate, or absence from the mouth.
5. Statistical analysis
Data were collected both descriptively and quantitatively. The mean and standard deviation of MBL were calculated for analysis. In this study, paired Student t-tests were used to assess the differences between the follow-up periods. The statistical analysis was conducted using IBM SPSS Statistics software (ver. 26.0; IBM Corp.) with a significance level set at P-value <0.05, indicating statistical significance.
III. Results
1. Patients and implants
After applying the criteria, a cohort of 15 patients with a total of 32 implants, installed using surgical guides, was selected.(Table 1) The study group consisted of eight males and seven females, with a mean age of 57.33 years, ranging from 23 to 72 years, at the time of surgical guide-assisted implant installation surgery. Among these 15 patients, six presented with underlying diseases. The mean follow-up period extended to 10 years and nine months, ranging from six years two months to 13 years 11 months.
Of the 32 implants, five implants were installed in the anterior maxilla, 19 were in the posterior maxilla, and eight were installed in the posterior mandible. All implants belonged to the bone level, external hex type, sourced from Brånemark System MK Ⅲ Groovy (Nobel Biocare AB Co.). The diameters of the 32 implants were 3.30 mm (n=1), 3.75 mm (n=5), 4.00 mm (n=22), and 5.00 mm (n=4). The lengths were varied at 7.0 mm (n=1), 10.0 mm (n=2), 11.5 mm (n=9), 13.0 mm (n=17), and 15.0 mm (n=3). Nine patients underwent guided bone regeneration (GBR) management or bone graft procedures during the implant installation process. Regarding the prosthesis type, eight patients received bridges, six patients received single crowns and one patient received hybrid denture rehabilitation. Notably, all surgical guides utilized were of the tooth-supported guide type.
2. Failure evaluation and survival rate
Out of the 15 patients, five exhibited signs of implant failure during the follow-up period. Among these, three patients with four failed implants displayed evident peri-implantitis symptoms, including pain, exudate discharge, and implant mobility. Subsequently, these four implants underwent removal through implant explantation surgery. The remaining two patients did not exhibit intraoral symptoms with the implants. Two implants loosened naturally during the follow-up period with one loosening five years and four months after placement, while the other implant loosened 11 years and six months postoperatively.(Fig. 3) Following the removal of the failed or naturally loosened implants, replacement procedures were performed for three implants. After the prosthesis was delivered, all three of the replaced implants exhibited positive results and were still operating.
Among the 32 total implants, six implants failed before the last follow-up. There were no instances of early implant failure within the initial three to six months post-implantation evaluation. One implant failed within 10 months postoperatively, while five failures occurred more than five years after surgery. Utilizing the ICOI Pisa consensus implant quality of health scale, the survival rate of implants using surgical guides over a mean of 10 years in this study was determined to be 81.25%.
3. MBL analysis
Three months after placement, the mean MBL was significantly higher compared to the post-installation baseline. Additionally, there was a significant increase in the mean MBL at one month, one, two, and five years following the delivery of the prosthesis.
MBL at one month, one year, and two years following prosthesis delivery, as well as three months after placement, showed a significant increase as compared to the measurements taken during the prior follow-up visit. However, MBL at five years after prosthesis delivery did not differ significantly compared to at two years. The detailed results of MBL radiographic evaluations using panoramas are described in Table 2.
IV. Discussion
This retrospective study presents the clinical outcomes of surgical guide-assisted implant placement, covering a follow-up period of up to 10 years. The primary objective of our study was to evaluate whether implant placement using surgical guides helps preserve peri-implant bone levels and promote long-term implant survival. Following a mean follow-up period of 10 years and nine months, the observed implant survival rate was 81.25%. This rate is relatively lower when compared to a study that reported a 97% implant survival rate over 10 years involving 1,019 dental implants in 333 patients at the Korean maxillofacial surgical unit using the non-guided conventional approach for implant surgery14.
In this study, the comparatively lower survival rate of implants may be attributed to the relatively small sample size. It is important to note that stringent inclusion and exclusion criteria were applied, resulting in the inclusion of only partially edentulous patients. Moreover, all surgical guides used in the study were of the tooth-supported type, introducing certain limitations to this research. Surgical guides can be categorized based on their support type, including tooth-supported guides, mucosa-supported guides, bone-supported guides, and hybrid-supported guides15. Tooth-supported guides are used in areas where several teeth are missing and the remaining teeth exhibit stability. They are retained by adjacent teeth and demonstrate higher accuracy compared to mucosa-supported and bone-supported guides in guided implant placement16,17. Furthermore, it is reported that the number of teeth providing support also affects the accuracy6.
Another contributing factor to the lower implant survival rate is that all of the implants were of the external hex type, possessing inherent characteristics that may unfavorably impact implant survival rates, such as high stress of off-center-loads18, high risk of screw loosening19, undesirable bacterial seal design20, lower anti-rotational capacity due to the misfit between the abutment and fixture when compared to internal connections, and developed by giving priority to surgical placement. The external hex-type implant has been shown to contribute to increased micromovements resulting in improved MBL and decreased peri-implant tissue stability in previous studies21.
Additionally, the limitation of the technique at that time also influenced the long-term implant survival rate. Furthermore, the surgical guide hindered the flexibility to make adjustments to the implant plans. The surgical template also limited proper flushing and irrigation allowing for potential overheating during surgery resulting in peri-implant bone damage22. In addition, the surgeon’s experience could have affected the long-term implant survival rate23.
A previous study demonstrated relatively good accuracy in dental implant surgery using surgical guides10. Despite the advantages of more precise preoperative diagnosis facilitated by computer assistance and surgical templates, deviations remain during the application. These deviations could originate from incomplete information in existing images, the error of the surgical guide fabrication process, and the transfer error of diagnostic data. The inherent instability during the fixation of the surgical guide may also result in tissue deformation during surgery and make it difficult to firmly secure the template. This kind of instability is a crucial factor contributing to changes in implant positioning24.
Despite exhibiting a relatively low long-term implant survival rate with the use of surgical guides in this study, the surgical guide remained a useful and eligible tool for some difficult sites during implant placement. For instance, when implants were placed in the alveolar ridge close to the inferior alveolar nerve or maxillary sinus, preoperative computer-assisted design and measurements could minimize damage to these anatomical structures and reduce postoperative morbidity and bleeding risks9. Additionally, in edentulous patients, the use of surgical guides contributed to the reduction in implant deviation both in the buccal and mesial directions17.
Three months after placement, the mean MBL surrounding dental implants placed with the surgical guide were 0.03 mm on the mesial side and 0.07 mm on the distal side. Subsequently, at one month, one year, two years, and five years after prosthesis delivery, the mean MBL on the mesial side were 0.44, 0.69, 0.82, and 1.00 mm, while on the distal side, they were 0.46, 0.64, 0.75, and 0.92 mm respectively.(Table 2) In comparison to another systematic review25 where the mean MBL was 1.06 mm at the one-year follow-up and 1.48 mm at the three-year follow-up, this study indicated less MBL after placement using surgical guides.
We present three cases of implant placement using surgical guides, one in the anterior maxilla, one in the posterior maxilla, and one in the posterior mandible region. In Patient A, a 70-year-old male with cardiovascular disease underwent the complete extraction of residual roots #11, #12, and #21. Subsequently, the immediate placement of two implants in the socket sites of #11 and #12, and one implant placement in the #23 tooth site were carried out surgically guided. GBR application and bone grafting in the anterior maxilla area were also performed. All three implants were 3.75 mm×15.0 mm in size. At the most recent follow-up visit and following functional loading, all three implants showed minimal MBL and satisfactory stability.(Fig. 4. A) Patient B involved a 56-year-old female who had hyperlipidemia, osteoporosis, and hypothyroidism. Surgical extraction of #16 was performed one year before implant placement. Nine months before implant placement, the patient also underwent sinus lifting surgery in the right posterior maxilla region because of inadequate bone and sinus pneumatization of the edentulous area. Using a surgical guide, a 4.00 mm×13.0 mm implant for implant therapy was placed in the #16 tooth position. During the following follow-up visits, the implant showed minimal MBL and excellent stability.(Fig. 4. B) For Patient C, a 59-year-old male without systemic disease, underwent the extraction of #36 nine months before implant surgery. A surgical guide was used to place a 4.00 mm×10.0 mm implant, taking into account the implant’s proximity to the inferior alveolar nerve. The implant achieved successful osseointegration and exhibited low MBL post-prosthesis delivery up to the latest follow-up visit.(Fig. 4. C)
Digital technology is the crucial development direction of implantology and an inevitable trend. However, for technique users such as surgeons, even with advanced surgical techniques such as the use of surgical guides, it is still critical to grasp potential risks and try to control related factors that cause bias. More research is needed to verify whether the use of surgical guides during implant placement contributes to peri-implant health or good long-term clinical outcomes.
V. Conclusion
In this study, implant rehabilitation assisted by the surgical guide exhibited a favorable survival rate. With the limitation of sample size in this study, further research with larger sample sizes is essential to comprehensively evaluate the long-term clinical effectiveness of using surgical guides. While guided surgery may enhance the predictability and precision of implant placement and reduce surgery time and tissue damage, whether the long-term clinical consequences on implant survival rate and peri-implant tissue state surpass those of implants placed through the conventional non-guided approach remains unclear.
When contemplating the use of surgical guides and external-type implants in implant surgeries, we should not only focus on their surgical advantages in guiding and facilitating implant placement. A more holistic perspective is essential, considering not only the surgical aspects but also the subsequent prosthetic requirements and the long-term survival of the implants for the well-being of patients. Prioritizing patient welfare over operators’ convenience is paramount. Consequently, it is important to develop the surgical guide technique for internal-type implants and conduct further long-term studies on this matter. Such an approach will help strike a balance between the convenience of the surgical procedure afforded by the technique and the long-term longevity of the implants, all while keeping the best interests of the patients at the forefront.
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