In Vitro Comparison of Time and Accuracy of Implant Placement Using Trephine and Conventional Drilling Techniques Under Dynamic Navigation

Preparation of an osteotomy site for implant placement requires the use of several drills to expand the osteotomy sequentially before inserting the dental implant. Depending on the size of the implant and the type of bone, it usually varies between 2 and 6 drills. The more drills used for the osteotomy preparation, the higher the risk of overheating the bone and decreasing the accuracy of implant placement. While some studies have established that a shortened drilling sequence reduces the rate of errors in implant-site preparation, albeit requiring a steeper learning curve,¹  most implant surgeons continue to follow the standard osteotomy preparation protocol.

Trephine drills are designed for removing or repositioning implants and, due to their hollowed design can also be used for bone harvesting and biopsy.²  Only a few studies have been reported in the scientific literature regarding the use of trephine drills for implant-site preparation.^3–6  A smaller loading range is needed for an osteotomy with a trephine drill, thus reducing thermal damage to the bone.⁵  The trephine drill also removes less bone marrow than conventional drills, resulting in better primary stability of implants.³  Evidence also suggests that placing an implant in vivo using trephine drills for osteotomy preparation is not inferior to sequential drilling techniques.⁴  No significant difference in bone loss, gingival infection, implant mobility, or chewing discomfort was noted 12 months after implant placement using trephine drills compared with the traditional drilling technique.⁴  Trephine drills can also be used for sinus floor augmentation during immediate implant placement.⁷  However, limited evidence exists regarding the accuracy of implant placement when using trephine drills for osteotomy preparation.⁶ 

Guided surgery or computer-assisted surgery, especially static navigation, is gradually becoming the standard of care due to its precision and predictability. However, dynamic navigation has recently been gaining recognition as an alternative to static guided surgery. In contrast to static guided surgery's use of computer-aided design and manufacturing fabricated guides based on 3-dimensional (3D) and intraoral scans of the patient, dynamic navigation offers the operator continuous real-time tracking on the computer screen of the implant-site anatomy and surgical instruments during implant placement.⁸ 

Implant placement with the assistance of dynamic navigation is more accurate than free-hand placement and at least as accurate as static guided surgery, which is especially beneficial in more demanding anatomic regions.^9,10  Some dynamic navigation systems are highly accurate, with less than 0.73 mm error,¹¹  and thus enable the exact realization of the preoperative plan as well as a decrease in preparation time for the surgical procedure.¹²  Some advantages offered by dynamic navigation systems are real-time positional feedback, accuracy control throughout the procedure, and the possibility to modify the initial plan during the procedure. Other benefits include the possibility of single-visit implant placement, flapless surgery, better visual field, protection of vital anatomic structures, and accessible implant placement in patients with limited mouth opening, especially for posterior sites like second molar sites. Dynamic navigation encourages prosthetically driven implant placement with higher accuracy and fewer complications, resulting in a superior esthetic outcome and more predictable prosthetic rehabilitation.^8,9  The downside to the dynamic navigation system is mostly the cost of the equipment and the learning curve for the operator.

Dentistry has benefited from virtual 3D digital planning, which also offers accuracy and speed in preoperative implant planning and takes into consideration all adjacent anatomic structures and available space.¹³  Digital plans can be accurately executed by means of guidance and use of pre-visualization in the 3D rendering software.¹⁴  A dynamic navigation system incorporates the 3D preoperative planning, followed by visualization used in guidance for implant placement. Using trephine drills for implant-site preparation with a dynamic navigation system could offer advantages over standard methods by reducing the potential for damage to the bone and possibly increasing the accuracy of the execution of the original treatment plan. The aim of this randomized in vitro study was to compare the time involved and accuracy with implant-site preparation and implant placement using trephine vs conventional drilling techniques under dynamic navigation.

Six upper and 6 lower polyurethane Alumilite White (Alumilite) simulation jaw models were made by duplicating a patient's analog impression. Each model was scanned using cone-beam computerized tomography (CBCT; i-CAT). Before scanning, the models were equipped with 3 metallic fiducial sphere markers to be used for accurate superimposition of the preoperative and postoperative CBCT scans (Figure 1). A stent and a dual-arm computerized tomography marker (ClaroNav) were also placed on the model before scanning. Crowns and implants were virtually planned using the Navident software (ClaroNav).

The site preparation and implant placement were performed by 2 surgical residents, both with prior experience using simulation models and dynamic navigation system for implant placement using conventional drilling techniques. The operators were not informed about the exact aim of the study and which measurements would be performed after implant placement. Two different drilling techniques to prepare the implant osteotomies were analyzed and compared. The first technique used a single 3.5-mm trephine drill (Bangkok Bone Harvest) and a final shaping drill (Zimmer Biomet Dental) presented in Figure 2a. This technique was compared with the conventional drilling sequence using 6 drills of sequentially expanding diameter (Zimmer Biomet Dental) presented in Figure 2b.

Each operator placed implants in 6 different jaw models with randomly assigned drilling technique (conventional or trephined) and implant sites. Three implants sites, 3, 7, and 13, were planned for the maxillary models and 4 implant sites, 18, 19, 29, and 30, for the mandibular models for placement of 4.7 × 13 mm size dental implants (Zimmer Biomet; Figure 1). The first operator was assigned 4 maxillary and 2 mandibular models, while the second operator prepared 2 maxillary and 4 mandibular models. Random number generation was used to determine the order of the technique and the order of the implant sites within each attempt. Implants were planned and placed using a dynamic navigation system Navident (ClaroNav) on a standard dental mannequin head with rubber cheeks.

Calibration of the handpiece (Biomet 3i LLC) and drills were made according to the Navident workflow protocol before and during implant placement (ClaroNav). The timing of each attempt was recorded with a digital stopwatch (Apple). After implant placement, a postoperative CBCT scan (i-CAT) was made and superimposed with the aid of the fiducial markers on the planned preoperative CBCT scan using proprietary software Evalunav (ClaroNav). After superimposition, the planned and placed implant positions were compared, and horizontal, vertical, and angulation discrepancies were assessed for both techniques (Figure 3).

The repeated measures analysis of variance test was used to determine if the dependent variables procedure time and deviation of lateral 2-dimensional (2D), apex vertical 2D, overall apex 3D, or overall angle 3D measures (Figure 4) were statistically significantly different between the 2 techniques, trephined and conventional (primary independent variable) while adjusting for jaw (covariate) and accommodating for repeated measures on the same operator. The normality of residuals assumption was tested with the Kolmogorov-Smirnov test. The significance level was set at 0.05 and not adjusted for the familywise error rate. Because all included variables had only 2 levels, post hoc pairwise comparisons did not need to be adjusted for multiple comparisons. The SAS EG v.6.1 (SAS Institute) statistical package was used for all statistical analyses. An independent statistician reviewed the methodology.

A total of 21 implants were placed using the conventional and the same number using the trephine drill. On average, implant placement took 4 minutes and 14.8 seconds using the conventional drill system of sequentially larger drills and 5 minutes and 12.3 seconds using the trephine drill, which included calibration time for the dynamic navigation system. For both methods combined, the average time to place the implant was 4 minutes and 43.6 seconds. The average 2D deviation was 1.56 mm at the platform and 1.43 mm at the apex. The 3D deviation was 2.79° at the apex and 3.43° for the overall implant path. Complete summary statistics are given in Table 1 by the method and combined.

After adjusting for the jaw (maxilla or mandible) and attempt number, and controlling for repeated measures within the operators, the average implant deviation from the planned position was not statistically significantly different based on the drilling technique (conventional vs trephine). The time required to place the implant was also not significantly different (P = .936). Although not statistically significant, operators were more accurate with the conventional technique when assessing lateral 2D deviation, vertical 2D apex deviation, and overall 3D angle. They were less accurate in terms of overall 3D apex deviation and slower (though not statistically significant) with the conventional technique. Complete results are given in Table 2 and Figure 5.

Figure 6 presents the average time to place the implant for each site included in the study based on the method used. Of particular note are the increase in the average time and the standard error (ie, the variability of the time to place the implant) for implant sites 20 and 29. Site 20 required the use of an extender, which likely contributed to the increase in time and variability. The difference in time, based on the combination of drilling technique and implant site, was not statistically significant but did demonstrate the clinical implications and difficulties related to the use of the extender with the single trephine drill.

This is the first study examining the accuracy of dental implant placement using the trephine drill with a dynamic navigation system. While previous studies showed higher accuracy with dynamic navigation than with free-hand implant preparation,^15–17  it has also been established that a reduced number of procedure steps may contribute to increased accuracy and decreased sources of errors.¹  Our study found no statistically significant difference in accuracy between the single trephine drill and shaping drill technique compared with the conventional drilling sequence when using dynamic navigation. Neither of the 2 methods stood out as a more time-efficient technique.

Based on the results from previous studies regarding the benefits of using a trephine drill vs standard drilling sequence,^4–6  we anticipated higher accuracy with the trephine drill since introducing an error in deviation would be less likely as the osteotomy preparation included fewer steps and drills. It should be pointed out that while the conventional drilling method consists of more steps and is, therefore, more prone to error input, it also allows the operator to check and correct drilling direction with each consecutive drill.

Contrary to expectations, there was no significant difference in time between the 2 techniques despite a significant difference in the number of drills, each requiring calibration. Based on the observations in this study, the preparation of osteotomy with a trephine drill presented an unusual and less familiar technique for the operators handling the trephine drill and thus took longer to operate than the more familiar conventional drilling technique. Calibration of the trephine drill likely added to the longer procedure time. The conventional drilling sequence required more drills; however, the calibration process was faster due to their conical shape. The trephine drill's tubular shape and wide open tip made the calibration of the drill more challenging and time consuming. To our knowledge, there is no literature on the topic of trephine drill calibration with a dynamic navigation system, and this study is the first to explore this subject. The tip of the trephine drill had a 3.5-mm diameter opening with non-flat serrated surface rendering stabilization of the bur challenging. During the calibration process, the bur has to stay centered and steadied for several seconds on the calibration spot on the jaw tag until calibration is complete, while conically shaped burrs fit into the slightly concave dip in the calibration spot very securely. The hollow design of the trephine drill is also prone to filling up with debris, impeding its advancement through the model. The inside of the trephine drill had to be cleaned out during the procedure to enable smooth advancement to the depth of the osteotomy, adding time to the procedure. The increased time and increased variability seen in the mandibular premolar sites is likely due to the novelty and added difficulty in handling a trephine drill on an extender. Stabilizing the apparatus of the extender and trephine drill is challenging, especially when the operator needs to focus on both the operating area on the model and the computer screen. Nevertheless, the dynamic navigation system consistently enabled and facilitated repeatable performance with reproducible outcomes by both providers for all implant sites.

Comparison of these 2 techniques should be further tested in clinical settings exploring the applicability of these study findings to clinical scenarios on patients with practitioners with different level clinical skills who have experience with a variety of clinical procedures. Different outcomes may be anticipated as a result of unique patients characteristics and other in vivo clinical challenges that were not present in this in vitro setting. Many factors in an in vivo study may add to the length of the overall procedure, such as the trephine drill not being sharp or becoming filled with debris, the properties of bone, skills of the operator, reduced visibility, and bleeding. Other factors not accounted for on a simulation model include a reflection of the flap and manual stabilization of the drilling apparatus if the patient is moving, which makes tracking with navigation more difficult. Therefore, the findings of this study cannot be generalized. Future in vivo studies should be conducted with more operators, on a large patient sample, in maxillary and mandibular sites, and in different clinical situations to test the findings observed in the simulation model.

This study has some limitations. The simulation jaw models used in this study showed some discrepancies in material homogeneity. Another limitation was the use of graduate students as operators. While they had prior experience placing implants on a simulation model with dynamic navigation using conventional drilling technique, they had no previous experience using a trephine drill. The results likely would be different if operators were experienced surgeons with robust clinical experience and at least some experience using a trephine drill.

Additionally, the sample size was small in this study. An a priori sample-size calculation was not performed due to the lack of any pilot data on such an experiment. Using the observed data, we can determine the necessary sample size to detect statistically significant differences. The most substantial difference between the 2 techniques was lateral 2D platform deviation at 0.35 mm difference. Based on the observed difference, the overall variance, and the correlation between repeated attempts for the same operator, we would need an additional 8 participants to place the 22 implants that each of the 2 operators in the current study placed to have 80% power and test at the .05 significance level. All other measures could be powered to be statistically significant with larger sample sizes, but the differences would likely be clinically irrelevant (ie, effect sizes <0.1). Despite evaluating multiple outcomes, this study did not adjust for the familywise error rate. However, since no significant differences were found, there is no risk for false positives, and an adjustment would not result in differences in the study results.

Within the limitations of this study, it can be concluded that a trephine drill in comparison to a standard implant drilling sequence with dynamic navigation on a simulation model does not provide a less precise or less time-consuming technique for implant-site preparation for novice clinicians.

Within the limitations of this study, implant-site preparation on a simulation model using dynamic navigation with a single trephine drill can be used as accurately and efficiently as a conventional drilling sequence. Further in vitro and in vivo studies are needed to test this novel method with a larger sample of operators.

Abbreviations

2D:

2-dimensional

3D:

3-dimensional

CBCT:

cone-beam computerized tomography

The authors would like to thank Dr Daniel Laskin for the critical review of the manuscript and Dr Leroy Thacker for providing an independent statistical review of the manuscript. Daniel M. Laskin, DDS, MS, is a professor emeritus, Department of Oral and Maxillofacial Surgery, School of Dentistry, Virginia Commonwealth University. Leroy Thacker, PhD, is an associate professor, Department of Biostatistics, School of Medicine, Virginia Commonwealth University.

The authors have no financial interest in this manuscript or any product used in this manuscript.