Abstract
Background/purpose
The choice between marker-based and marker-free registration in dynamic computer-assisted implant surgery (d-CAIS) presents a trade-off between potential accuracy and workflow efficiency. This study sought to directly compare these two methods by assessing their impact on implant placement precision and overall surgical time, to inform clinical decision-making.
Materials and methods
A retrospective analysis was conducted involving 48 implants placed using d-CAIS, divided into two groups: marker-based and marker-free. Implant placement accuracy was assessed by comparing actual and planned positions using pre- and post-operative cone beam computed tomography scans. Angular and linear deviations at the implant platform and apex were recorded, along with preparation and registration times.
Results
The marker-based group exhibited significantly lower linear deviation compared to the marker-free group, particularly at both the platform and apex. However, the two methods showed no significant difference in angular deviation. The marker-free registration method demonstrated a shorter preparation time but a slightly longer registration time, with no significant difference in overall implant positioning accuracy. The marker-free group showed higher linear deviation, particularly in horizontal measurements at the implant platform and apex.
Conclusion
This study highlights that marker-based registration offers superior precision, especially in linear deviation, during dynamic computer-assisted implant surgery. In contrast, the marker-free approach provides greater efficiency in preparation time, despite requiring slightly longer registration times. By eliminating the need for additional hardware, the marker-free method presents a viable alternative in specific clinical situations. These findings contribute valuable insights into optimizing surgical workflows and enhancing clinical outcomes in implant dentistry.
Keywords: Implant placement accuracy, Dynamic navigation system, Marker-based registration, Marker-free registration, Retrospective
Introduction
Accurate implant placement is critical for ensuring long-term functional and esthetic success in dental implantology.1,2 Dynamic Surgical Navigation Systems (SNS) have gained popularity for their abilities to provide real-time guidance and enhance precision during implant surgeries.3–6 These systems rely on registration methods to align preoperative imaging with the surgical site, which is essential for translating the planned implant position to the clinical setting. Two common approaches to registration are marker-based and marker-free methods, each offering distinct advantages and limitations.7–9
Marker-based registration employs fixed markers as landmarks, such as radiopaque splints or fiducial points, to establish a reference framework in SNS. While this technique is known for its high reliability, it often involves optical occlusion problems and requires additional procedural steps, increasing time and cost.8–10 Marker-free registration, on the other hand, eliminates the need for physical markers by utilizing anatomical landmarks directly.11,12 This approach simplifies the workflow but may introduce challenges in maintaining accuracy and consistency, especially in cases with complex anatomy or limited reference points.8,9,11,12
Despite the growing use of these techniques in clinical practices, direct comparisons of their accuracy and efficiency in dynamic navigation systems in computer-assisted implant surgery remain limited and the results were controversial, particularly regarding the impact of different registration methods.8,9,11–14 The discrepancies highlight the need for further exploration to clarify the factors influencing implant placement accuracy in diverse clinical scenarios. Understanding the differences between registration methods is crucial for optimizing implant surgical outcomes and improving clinical protocols for implantation. By carefully selecting the most appropriate registration technique based on the specific clinical scenario, surgeons can enhance both the accuracy and efficiency of the procedure, ultimately leading to better patient outcomes.
This retrospective study aimed to evaluate and compare the accuracy of marker-based and marker-free registrations in dynamic computer-assisted implant surgery. By analyzing deviations in implant positioning and procedural parameters, this study sought to provide evidence-based insights into the advantages and limitations of each registration method, guiding clinicians in selecting the most appropriate technique for individual cases.
Materials and methods
This retrospective study analyzed partially edentulous patients who received dental implants using dynamic computer-assisted navigation (Yizhimei, Dcarer, Suzhou, China) with either marker-based or marker-free registration between August 2024 and September 2025 (Fig. 1). A total of 26 patients (48 implants) meeting the inclusion criteria were enrolled.
Figure 1.
Workflow of patients’ enrollment.
Inclusion criteria:
Adults aged 18–70 years in good general health
Patients with partial edentulism
Individuals opting against fixed or removable prosthetic dentures
Availability of both pre- and postoperative CBCT imaging
Exclusion criteria:
Presence of uncontrolled systemic conditions
Heavy smoking habit (≥20 cigarettes/day)
Inability to tolerate discomfort or follow clinical instructions
Significant deficiencies in bone or soft tissue
More than 3 missing teeth (leads to registration inaccuracy due to fewer reliable landmarks and greater target distance)
The study adhered to the principles outlined in the Declaration of Helsinki and was approved by the Ethics Committee of the School and Hospital of Stomatology, Wuhan University (HGGC-276). The trial was registered with the Chinese Clinical Trial Registry (ChiCTR2500101713). All participants provided written informed consent. All surgical procedures were performed by clinicians with extensive experience. The study adhered to the STORE checklist.
As a retrospective study, the sample size was determined by the number of eligible cases. A post hoc power analysis using PASS 15 software (NCSS, LLC, Kaysville, UT, USA) was performed. Based on previously reported apex deviations for marker-based15 (1.58 ± 0.56 mm) and marker-free registration12 (1.05 ± 0.34 mm), the estimated effect size16 (Cohen’s d) was 1.144. With 24 implants per group, the statistical power exceeded 0.99 at α = 0.05, indicating adequate power to detect clinically relevant differences.
For marker-based registration, a U-shaped splint with radiopaque markers was fabricated. A silicon elastomer was used to stabilize the splint, covering the implant site and extending bilaterally (Fig. 2A). Patients underwent preoperative CBCT imaging (NewTom VGi, Quantitative Radiology, Verona, Italy) with standardized parameters: 90 kV, 8 mA, 8-s exposure, and a voxel size of 180 μm, with a U-shaped splint in place (Fig. 2B). Using this data, the surgeon determined the appropriate dental implants and formulated a three-dimensional placement plan based on the patient’s specific anatomical and clinical characteristics.17,18 The optical tracking arrays attached to the reference board and implant drill handpiece were calibrated with a long and a short standard round bur (Fig. 3A). To minimize interference from the handpiece, the reference board was fixed to the opposite site of the implantation using self-curing resin (Structure2, VOCO GmbH, Cuxhaven, Germany). During registration, the splint was repositioned on the dentition. A standard short round bur was attached to the handpiece and positioned sequentially on six distributed pits on the splint, ensuring coverage of buccal, lingual, mesial, and distal regions around the implant site (Fig. 3B). The criterion for accepting registration result was that all point errors measured below 0.5 mm. Using the Dcarer® dynamic navigation accuracy verification software (Yizhimei, Dcarer), the markers on the splint were aligned with their counterparts on the reconstructed CBCT images (Fig. 3C). Once registration was completed, the splint was removed. Registration accuracy was confirmed by navigating the drill tip over tooth cusps or surfaces while observing corresponding positional feedback on the display.
Figure 2.
Pre-operative preparations for the marker-based registration. (A) Customized splint containing radiopaque markers made of silicon nitride was securely attached to the dental arch using a silicone elastomer. (B) The CBCT (cone-beam computed tomography) scan was used to capture the relative positioning between the patient’s dental arch and the radiopaque markers.
Figure 3.
Surgical procedures for the marker-based and marker-free registration in dynamic navigated implant surgery. (A) Calibration of the implant drill handpiece using a standard short round bur. (B, C) Marker-based registration: Radiopaque markers on the custom splint were aligned with corresponding reference points on CBCT images. (D) The pointed standard drill used during the registration process. (E, F) Marker-free registration: Selected cusps/fossae were paired with their corresponding anatomical structures visible on CBCT images. (G) Drilling and implant insertion guided by the navigation system. CBCT: Cone-beam computed tomography.
For marker-free registration, CBCT was acquired with cotton rolls maintaining an open-bite position. Registration involved selecting six to eight anatomical reference points on teeth. A pointed drill (Dcarer) was used to touch each reference point during registration (Fig. 3D). The drill was stabilized by the surgeon to maintain contact with the selected points while aligning them with the corresponding anatomical features on the CBCT images (Fig. 3E and F). And registration was accepted only when all point errors were below 0.5 mm.
For both groups, after registration and local anesthesia, implant placement was performed under Dcarer dynamic navigation guidance by an experienced surgeon (Fig. 3G).
Postoperative CBCT scans were obtained. A blinded, calibrated examiner superimposed pre- and postoperative datasets using anatomical landmarks. Software automatically calculated 3D deviations between planned and actual implant positions at the platform and apex,19 including global, horizontal, and vertical linear deviations (mm) and angular deviation (°) (Figs. 4 and 5).
Figure 4.
Measurement of accuracy between planned and actual implant positions. (A) Superimposition of preoperative and postoperative CBCT scans. The gray implant represents the planned position, while the blue implant indicates the actual position post-surgery. (B–D) Axial, coronal, and sagittal views illustrating the deviations between the actual implant position (green) and the planned position. CBCT: Cone beam computed tomography.
Figure 5.
Quantification of three-dimensional implant deviations using seven parameters. (A) Angular deviation, (B) Total linear deviation at the platform, (C) Horizontal deviation at the platform, (D) Vertical deviation at the platform, (a) Illustration of the XYZ coordinate system, (b) Total linear deviation at the apex, (c) Horizontal deviation at the apex, (d) Vertical deviation at the apex.
Statistical analyses were performed by a blinded investigator (C.Y.) using IBM SPSS Statistics 27.0 (IBM Corp., Armonk, NY, USA) and visualizations were generated with GraphPad Prism 10 (GraphPad Software, San Diego, CA, USA). Continuous data were reported as mean ± SD or median (IQR) with 95 % confidence intervals (CI). Normality was assessed with the Shapiro–Wilk test. Between-group comparisons used the student’s t-tests, Welch’s t-test, or Mann–Whitney U test as appropriate. Categorical variables were compared using the chi-square test. A P-value <0.05 was considered significant.
Results
Demographic and clinical characteristics were comparable between the 13 patients (24 implants) in each group (Table 1). No significant differences were found in gender, age, education, implant history, placement timing, jaw distribution, or implant dimensions (diameter, length, morphology).
Table 1.
Demographic and clinical features of the included patients (n = 26) and implants (n = 48).
| Marker-based | Marker-free | P value | ||
|---|---|---|---|---|
| Patient number (n) | 13 | 13 | 1.000 | |
| Implant number (n) | 24 | 24 | 1.000 | |
| Gender | Female | 7 (53.8) | 7 (53.8) | 1.000 |
| Male | 6 (46.2) | 6 (46.2) | ||
| Age (year) | Mean ± SD | 44 ± 11.90 | 44.3 ± 12.5 | 0.949 |
| Educational level | University | 5 (38.5 %) | 7 (53.8 %) | 1.000 |
| High school | 6 (46.2 %) | 5 (38.5 %) | ||
| Middle school | 2 (15.3 %) | 1 (7.7 %) | ||
| First time having implant surgery | No | 2 (15.3 %) | 3 (23.1 %) | 1.000 |
| Yes | 11 (84.7 %) | 10 (76.9 %) | ||
| Implant timing | Immediate | 0 (0 %) | 1 (4.2 %) | 1.000 |
| Delayed | 24 (100 %) | 23 (95.8 %) | ||
| Implant site | Maxilla | 8 (33.3 %) | 12 (50 %) | 1.000 |
| Mandible | 16 (66.7 %) | 12 (50 %) | ||
| Left | 11 (45.8 %) | 10 (41.7 %) | 1.000 | |
| Right | 13 (54.2 %) | 14 (58.3 %) | ||
| Brand | Astra | 1 (4.2 %) | 4 (16.7 %) | 1.000 |
| Straumann | 21 (87.5 %) | 12 (50 %) | ||
| Osstem | 0 (0 %) | 2 (8.3 %) | ||
| Nobel | 2 (8.3 %) | 6 (25 %) | ||
| Diameter | ≥3.3 mm | 3 (12.5 %) | 1 (4.2 %) | 1.000 |
| 3.3 < X ≤ 4.1 mm | 19 (79.2 %) | 16 (66.7 %) | ||
| >4.1 mm | 2 (8.3 %) | 7 (29.1 %) | ||
| Length | ≤8 mm | 7 (29.1 %) | 7 (29.1 %) | 1.000 |
| 8 < X ≤ 10 mm | 12 (50 %) | 12 (50 %) | ||
| >10 mm | 5 (20.9 %) | 5 (20.9 %) | ||
| Morphology of implant apex | Cylindrical | 14 (58.3 %) | 16 (66.7 %) | 1.000 |
| Tapered | 10 (41.7 %) | 8 (33.3 %) | ||
| Preparation time (min) | Mean ± SD | 33.85 ± 4.65 | 24.31 ± 4.8 | <0.0001 |
| Registration time (min) | Mean ± SD | 3.79 ± 0.62 | 5.75 ± 0.68 | <0.0001 |
Note: Bold values indicate statistical significance with a P-value less than 0.05.
Abbreviation: SD, standard deviation.
Preparation time was significantly shorter in the marker-free group (24.31 ± 4.8 min) than the marker-based group (33.85 ± 4.65 min, P < 0.0001). Conversely, registration time was longer in the marker-free group (5.75 ± 0.68 min vs. 3.79 ± 0.62 min, P < 0.0001).
No significant differences were found in registration precision (marker-based: 0.26 ± 0.24 mm (95 % CI: 0.12–0.39); marker-free: 0.26 ± 0.25 mm (95 % CI: 0.1–0.42); p = 0.940) or angular deviation (marker-based: 2.38° ± 1.21°, 95 % CI: 1.87–2.89; marker-free: 3.17° ± 1.85°, 95 % CI: 2.39–3.95; P = 0.252) (Table 2). At the implant platform, the marker-based group showed significantly lower total linear deviation (median 1 mm, IQR: 0.73–1.26; 95 % CI: 0.84–1.27) than the marker-free group (2.19 ± 0.53 mm, 95%CI: 1.96–2.42; P < 0.0001) and lower horizontal deviation (0.53 ± 0.34 mm, 95%CI: 0.42–0.64 vs. 1.58 ± 0.46 mm, 95 % CI: 1.43–1.74; P < 0.0001) (Table 2). Vertical deviation did not differ significantly. At the apex, the marker-based group also demonstrated significantly lower total linear deviation (median 1.04 mm, IQR: 0.78–1.61, 95 % CI: 1–1.38 vs. 2.2 ± 0.64 mm, 95 % CI: 1.67–2.15; P < 0.0001) and horizontal deviation (median 2.55 mm, IQR: 0.31–0.84, 95 % CI: 0.46–0.72 vs. 1.89 ± 0.51 mm, 95 % CI: 1.72–2.06; P < 0.0001) (Table 2). Vertical deviation was not significantly different. Directional deviations at both the implant platform and apex in the mesiodistal, buccolingual, and apicocoronal planes showed no statistically significant differences between the marker-based and marker-free groups (Table 3).
Table 2.
Three-dimensional accuracy assessment of implant position in the marker-based group and marker-free group.
| Group | Marker-based (n = 24) | Marker-free (n = 24) | P value | |||
|---|---|---|---|---|---|---|
|
|
|
|||||
| Mean ± SD/median (IQR) | 95 % CI of mean/median | Mean ± SD/median (IQR) | 95 % CI of mean/median | |||
| Registration precision | 0.26 ± 0.24 | [0.12, 0.39] | 0.26 ± 0.25 | [0.1, 0.42] | 0.94a | |
| Angular deviation (°) | 2.38 ± 1.21 | [1.87, 2.89] | 3.17 ± 1.85 | [2.39, 3.95] | 0.252a | |
| Linear deviation at the platform (mm) | Total | 1 (0.73–1.26) | [0.84, 1.27] | 2.19 ± 0.53 | [1.96, 2.42] | <0.0001 b |
| Horizontal deviation at the platform | 0.53 ± 0.34 | [0.42, 0.64] | 1.58 ± 0.46 | [1.43, 1.74] | <0.0001 a | |
| Vertical deviation at the platform | 0.4 (0.15–0.79) | [0.33, 0.8] | 0.6 (0.2–1) | [0.44, 0.96] | 0.3267b | |
| Linear deviation at the apex (mm) | Total | 1.04 (0.78–1.61) | [1, 1.38] | 2.2 ± 0.64 | [1.67, 2.15] | <0.0001 b |
| Horizontal deviation at the apex | 2.55 (0.31–0.84) | [0.46, 0.72] | 1.89 ± 0.51 | [1.72, 2.06] | <0.0001 b | |
| Vertical deviation at the apex | 0.39 (0.15–0.85) | [0.35, 0.88] | 0.61 (0.17–1.01) | [0.43, 0.96] | 0.5774b | |
Note: Bold values indicate statistical significance with a p-value less than 0.05.
Abbreviation: SD, standard deviation; CI, confidence interval; IQR, interquartile range.
Independent sample t-test.
Mann–Whitney U test.
Table 3.
The directions of deviations in the marker-based group and the marker free group.
| Group | Marker-based (n = 24) | Marker-free (n = 24) | P value | ||
|---|---|---|---|---|---|
|
|
|
|
|
||
| Direction at platform | Mesiodistal | Mesial | 12 (50 %) | 12 (50 %) | 1.000 |
|
|
|
|
|||
| Distal | 12 (50 %) | 12 (50 %) | |||
|
|
|
|
|
||
| Buccolingual | Buccal | 8 (33.3 %) | 10 (41.7 %) | 1.000 | |
|
|
|
|
|||
| Lingual | 16 (66.7 %) | 14 (58.3 %) | |||
|
|
|
|
|
||
| Apicocornal | Apical | 12 (50 %) | 10 (41.7 %) | 1.000 | |
|
|
|
|
|||
| Coronal | 12 (50 %) | 14 (58.3 %) | |||
|
| |||||
| Direction at apex | Mesiodistal | Mesial | 13 (54.2 %) | 12 (50 %) | 1.000 |
| Distal | 11 (45.8 %) | 12 (50 %) | |||
|
| |||||
| Buccolingual | Buccal | 10 (41.7 %) | 11 (45.8 %) | 1.000 | |
| Lingual | 14 (58.3 %) | 13 (54.2 %) | |||
|
|
|||||
| Apicocornal | Apical | 11 (45.8 %) | 9 (37.5 %) | 1.000 | |
| Coronal | 13 (54.2 %) | 15 (62.5 %) | |||
Discussion
Dynamic navigation systems have become increasingly prevalent in implant surgeries, offering enhanced placement accuracy and reducing drilling-related complications.3–8,10,12–14 This retrospective study presents a comparative analysis of marker-based and marker-free registration techniques for dynamic computer-assisted implant surgery across all regions of the oral cavity. The findings reveal that the marker-free registration method exhibited greater linear deviation at both the implant platform and apex compared to the marker-based approach. Despite this, the marker-free method significantly reduced preparation time while increasing registration time. These results provide valuable clinical insights and highlight the need for further research to optimize the accuracy of marker-free registration techniques in implant surgery.
Currently, various dynamic computer-assisted implant surgery (d-CAIS) systems are available for clinical use, yet limited evidence exists regarding their superiority in achieving precise implant positioning across all regions of the oral cavity. Two recent meta-analyses have reported that, irrespective.20,21 In a retrospective study focused on the anterior region, Ma et al. (2023) evaluated implant placement accuracy using the active infrared dynamic navigation system (Yizhimei®).8 Their findings demonstrated an overall angular deviation of 3.29 ± 0.17°, a value consistent with the results observed in the present study, showing no significant differences in directional accuracy.
The accuracy of dynamic navigation systems is heavily dependent on image registration operations, which involves aligning the virtual coordinate system of CBCT information with the physical coordinate system of the patient.22,23 Consequently, the choice of registration method plays a critical role in determining the precision of these systems. Previous in vitro studies have demonstrated the feasibility of both marker-based and marker-free registration techniques using simulated models.24 However, limited clinical data directly compare the performance of these two registration methods in practice.
In a retrospective study, Ma et al. evaluated 99 implants placed using dynamic navigation systems with either marker-based or marker-free registration.8 Their findings revealed no significant differences in angular and linear deviation between the two methods. However, Zhu et al., in a randomized controlled trial, reported that marker-free registration achieved greater angular accuracy in the maxillary anterior region and was associated with higher patient satisfaction post-surgery.9 Notably, both studies focused exclusively on the anterior region, where locating cusps and managing the handpiece during registration are relatively straightforward. These limitations underscore the need for further comprehensive investigations to evaluate the performance of marker-free registration across all regions of the oral cavity.
Dynamic navigation systems introduce several potential sources of error, with registration error being one of the most critical factors affecting navigation accuracy.23,25,26 Marker-based registration is a well-established method, wherein radiopaque markers are integrated into a splint during its fabrication. For example, the Dcar system utilizes silicon nitride in the splint, which minimizes imaging artifacts during CBCT scanning.27 However, this method is not without limitations. Issues such as neglecting to install the splint prior to CBCT scanning, improper placement or loosening of the splint during imaging or registration, and poor tooth stability can all contribute to inaccuracies.28,29 Furthermore, short teeth can make it difficult to securely affix the splint, and deformation of the silicone elastomer material due to prolonged storage can introduce additional errors.9
To address these challenges, Chen et al. developed a marker-free registration method that relies on anatomical landmarks for registration, eliminating the need for additional registration devices.30 This approach offers several advantages: cusp-based registration utilizes natural anatomical points, much like bone-based registration, and is unaffected by edentulous regions.8,9,24,30 While marker-free registration simplifies preparation by bypassing splint fabrication, its accuracy relies heavily on the operator’s ability to precisely identify and register anatomical points.
The main source of error in cusp-based registration lies in point selection, which requires close coordination between the surgeon and the software operator to ensure that the same anatomical point is consistently identified. During this process, the surgeon must maintain the drill tip in a fixed position, a task that is inherently challenging. At the same time, the patient may struggle to remain in an identical position. In practice, even small movements of the drill tip within the cusp region can occur, further contributing to registration errors. These errors can directly affect the accuracy of dynamic navigation surgery, potentially leading to deviations in implant position, angulation, or depth, which may compromise the surgical outcome and increase the risk of complications.
Accuracy in implant placement is primarily assessed through angular and linear deviations. Previous in vitro studies by Wei et al. demonstrated that both marker-based and marker-free registration methods exhibit comparable accuracy in terms of angular and linear deviation.24 Subsequent clinical investigations by the same group confirmed these findings.8 However, Zhu et al. reported that marker-free registration for single implants in the anterior maxilla achieved better angular accuracy, possibly due to issues related to U-tube placement and storage.9 Notably, these in vivo studies focused predominantly on the anterior region, which is more conducive to precise registration due to the visibility of cusps and ease of handling the handpiece. In contrast, our study evaluated implant placement accuracy across the entire dental arch to comprehensively assess the influence of registration methods on navigation accuracy.
Our findings revealed no significant difference in angular deviation between the two methods, suggesting that both marker-based and marker-free registration methods can achieve reliable accuracy. The higher accuracy demands in the anterior region may stem from the thin buccal bone and its predominantly bundle bone composition, necessitating greater caution during implant placement.31,32 Additionally, the U-tube device used in marker-based registration is more prone to displacement in the buccolingual direction during CBCT scanning and registration, particularly in the anterior region.
For linear deviations, the marker-free group exhibited higher errors, particularly in horizontal deviations at both the platform and apex. This discrepancy can be attributed to several factors. Firstly, manual registration operation in the posterior region is more challenging due to limited visibility of cusps and fossae and difficulties in comparing anatomical points with CBCT reference images. Furthermore, operators often need to hold the drill with one hand during posterior registration, reducing stability and increasing the likelihood of error. The choice of anatomical points also plays a significant role. While cusps are easier to locate, they are more difficult to precisely target with the drill. Conversely, fossae are easier to target but harder to identify accurately, especially when CBCT reconstructions lack clarity.25 In contrast, marker-based registration benefits from the stability provided by posterior teeth, making it more effective in the posterior arch.
In addition to implant accuracy, our study evaluated preparation and registration times. Marker-based registration was significantly more time-consuming during preparation due to the fabrication and placement of the U-tube splint—a process taking approximately 10 min—followed by an additional CBCT scan with the splint in place.8 If a CBCT scan had been previously acquired without the splint, repeated scanning was necessary, resulting in additional radiation exposure and prolonged preparation. Conversely, marker-free registration eliminates the need for a splint, allowing direct use of existing open- or closed-bite CBCT data. This “scan-as-you-go” advantage substantially reduced preparation time and avoided extra radiation. However, registration time for the marker-free method is slightly longer due to the difficulty of locating anatomical landmarks and the need for close surgeon-technician coordination to perform registration during the brief contact between the pointed drill and tooth cusps. With accumulated experience, the efficiency of marker-free registration improved noticeably, supporting its potential to enhance clinical workflow and patient experience over time.9,27
Our findings suggest that while marker-based systems may offer superior precision in dynamic computer-assisted implant surgery, marker-free techniques present several advantages in terms of reducing preparation time and material costs. One of the main benefits of the marker-free approach is the elimination of the need for custom-designed U-shaped splints embedded with radiopaque markers. These splints require fabrication in multiple models to fit different areas of the dentition, which increases both time and cost. As a result, the marker-free system can significantly reduce the expenses associated with the splint and the silicon elastomer used for fixation.
Additionally, marker-free registration avoids some of the logistical challenges associated with marker-based methods. For instance, in the marker-based system, clinicians may occasionally forget to install the splint prior to the initial CBCT scan. This oversight often leads to the need for a second CBCT scan with the splint in place, thus adding to the overall cost of the procedure and increasing the patient’s exposure to radiation. These additional steps—requiring extra time, resources, and patient radiation—are mitigated with the marker-free method, making it a more cost-effective and patient-friendly alternative. In clinical settings where time and material efficiency are priorities, the marker-free technique offers significant practical benefits.
Marker-based registration is particularly advantageous in certain scenarios, such as when less experienced surgeons are performing the procedure. In these cases, the surgeon can more easily and steadily position the round bur on the pits of the splint, ensuring accurate alignment. It is also beneficial for patients with periodontitis, where tooth stability is compromised, as the splint helps to stabilize the teeth during the procedure. Additionally, marker-based registration is ideal when there are sufficient teeth to secure the splint and when both the surgeon and patient have adequate time to complete the surgery in a single session.
In contrast, marker-free registration is better suited for more experienced surgeons who are well-versed in dynamic navigation implant surgeries. These surgeons can maintain a steady hand when using the drill to align with the cusps and fossae during the registration process. Marker-free techniques are also appropriate for patients with insufficient or very short teeth, which may not provide enough stability for a U-tube splint. In such cases, the splint may rotate during registration, compromising accuracy. Furthermore, marker-free registration is beneficial when the implant surgery needs to be completed quickly, particularly for patients with temporomandibular joint issues, as the prolonged registration and preparation time required for marker-based systems could hinder the patient’s ability to open their mouth. Lastly, marker-free registration is most effective when the CBCT scan is of high quality and the patient’s teeth have clearly defined cusps and fossae that are easily recognizable.
As a retrospective study, this research has inherent limitations, including potential selection bias and the absence of randomization. Additional factors such as surgeon experience, patient compliance, and variations in bone density were not explicitly controlled, which could influence the results.10,33–36 Future prospective studies with larger sample sizes and a focus on marker-free registration accuracy in the posterior region are necessary to validate these findings and further investigate contributing factors.
In summary, this study demonstrates that marker-based registration achieves higher precision in dynamic computer-assisted implant surgery, particularly in linear deviation, while marker-free registration offers advantages in preparation efficiency. Despite longer registration times, the marker-free approach eliminates the need for additional hardware, making it a viable alternative in certain clinical contexts. These results provide valuable insights for optimizing surgical workflows and improving clinical outcomes in implant dentistry.
Acknowledgments
This work was financially supported by Wuhan Yingcai – Outstanding Young Talents (No. PM0218003), the National Natural Science Foundation of China (No. 82101056) and Science and Technology Program of Hubei Province (No. 2024BCB003).
Funding Statement
This work was financially supported by Wuhan Yingcai – Outstanding Young Talents (No. PM0218003), the National Natural Science Foundation of China (No. 82101056) and Science and Technology Program of Hubei Province (No. 2024BCB003).
Footnotes
Declaration of competing interest: The authors have no conflicts of interest relevant to this article.
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