applied sciences

Technical Note

A Novel Method for Precise Guided Hole Fabrication of DentalImplant Surgical Guide Fabricated with 3DPrinting Technology

Keunbada Son 1,2 and Kyu-bok Lee 2,3,*

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Citation: Son, K.; Lee, K.-b. A Novel

Method for Precise Guided Hole Fab-

rication of Dental Implant Surgical Guide

Fabricated with 3D Printing Technol-

ogy. Appl. Sci. 2021, 11, 49 .

https://dx.doi.org/10.3390/app

11010049

Received: 25 November 2020

Accepted: 21 December 2020

Published: 23 December 2020

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1 Department of Dental Science, Graduate School, Kyungpook National University, Daegu 41940, Korea;sonkeunbada@gmail.com

2 Advanced Dental Device Development Institute, Kyungpook National University, Daegu 41940, Korea3 Department of Prosthodontics, School of Dentistry, Kyungpook National University, Daegu 41940, Korea* Correspondence: kblee@knu.ac.kr; Tel.: +82-053-600-7674

Abstract: A dental implant surgical guide fabricated by 3-dimensional (3D) printing technology iswidely used in clinical practice due to its convenience and fast fabrication. However, the 3D printingtechnology produces an incorrect guide hole due to the shrinkage of the resin materials, and in orderto solve this, the guide hole is adjusted using a trimmer or a metal sleeve is attached to the guidehole. These methods can lead to another inaccuracy. The present method reports a technique tocompensate for a decreased guide hole caused by shrinkage that can occur when a computer-guidedimplant surgical guide is fabricated with a 3D printer. The present report describes a technique toadjust the size of the guide hole using a free software program to identify the optimized guide holesize that is fabricated with the 3D printer.

Keywords: surgical guide; 3D printing; guided hole; dental CAD/CAM; dental implant

1. Introduction

The development of dental digital equipment has made computer-guided implant(CGI) surgery possible [1]. The implant can be positioned using a surgical guide thatis designed according to the patient’s surgical plan [2]. However, the accuracy of thesurgical guide is affected by the manufacturing conditions [2]. The fabrication method(3-dimensional (3D) printing or milling), the properties of the materials (shrinkage and de-formation), and the accuracy of the equipment can affect the final surgical guide, which canlead to incorrect implant positioning [2–4].

Numerous studies have evaluated the accuracy of the surgical guides [2–6]. Previousstudies reported that the inaccuracies in the guided hole of the surgical guide can affectthe accuracy of implant positioning [3,7,8]. Previously, a metal drill key was placed on theguided hole of the surgical guide to prevent inaccuracies [7]. Alternatively, the inaccuracy ofthe guided hole was resolved by fastening a separate metal sleeve to the prepared surgicalguide using an adhesive [8]. However, these methods can lead to another inaccuracy [3,8].

An important factor for accurate implant positioning is the tolerance of the guideholes in the surgical guide [3–9]. Although it would be ideal for the drill and guide hole ofthe surgical guide to be precisely matched, it is impossible to insert the drill into the guidehole without tolerance. Therefore, it is necessary to apply a minimum tolerance. In order toadjust the size of the guide hole with minimum allowable tolerance, either a metal sleeve isapplied or the inside surface of the guide hole is removed using a trimmer bur [9] However,these methods can cause inaccuracies in implant positioning [3]. If there is a large tolerancebetween the guide hole and the drill, the shake during the drilling process and the implantduring the handling may be guided to an inappropriate position [3,9].

The use of dental 3D printers is increasing at a rapid pace. Factors such as the typeof 3D printer, the light-polymerized resin material used, the accuracy of the equipment,

Appl. Sci. 2021, 11, 49 . https://dx.doi.org/10.3390/app11010049 https://www.mdpi.com/journal/applsci

Appl. Sci. 2021, 11, 49 2 of 7

and the layer thickness can affect the result [10–12]. Since no factors are defined in thedental clinical environment, an optimization process is required [13]. The deviation of thedental implant’s position is caused by cumulative errors in the design and manufacture ofthe surgical guide [14,15]. The present technical note describes how to make guided holeswith minimum tolerances using a 3D printer in dental clinical environments.

Inaccuracies in the placement of the placed dental implant can lead to surgical failures,such as nerve damage and complications that may occur in the maxillary sinus [16,17].Therefore, the accuracy of the surgical guide is an important factor for the success ofimplant surgery [18]. In order to improve the accuracy of the surgical guide, there havebeen many studies to improve the accuracy of cone-beam computed tomography andintraoral impressions, and the accuracy of registration in software [19–22]. However,there are still insufficient studies to compensate for the shrinkage of the guide hole due tothe shrinkage of the light-polymerized resin for 3D printing.

Although many software programs and 3D printers for CGI surgery are available,there is still a need for a method that can be optimized for more accurate implant position-ing. This report describes a technique that uses free software to adjust the size of the guidehole in the 3D printing surgical guide. This technical note describes a method for creatinga 3D printing surgical guide with minimal tolerance of guide holes in clinical practice.

2. Materials and Methods

This technical note was performed as shown in Figure 1.

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large tolerance between the guide hole and the drill, the shake during the drilling process and the implant during the handling may be guided to an inappropriate position [3,9].

The use of dental 3D printers is increasing at a rapid pace. Factors such as the type of 3D printer, the light-polymerized resin material used, the accuracy of the equipment, and the layer thickness can affect the result [10–12]. Since no factors are defined in the dental clinical environment, an optimization process is required [13]. The deviation of the dental implant’s position is caused by cumulative errors in the design and manufacture of the surgical guide [14,15]. The present technical note describes how to make guided holes with minimum tolerances using a 3D printer in dental clinical environments.

Inaccuracies in the placement of the placed dental implant can lead to surgical fail-ures, such as nerve damage and complications that may occur in the maxillary sinus [16,17]. Therefore, the accuracy of the surgical guide is an important factor for the success of implant surgery [18]. In order to improve the accuracy of the surgical guide, there have been many studies to improve the accuracy of cone-beam computed tomography and in-traoral impressions, and the accuracy of registration in software [19–22]. However, there are still insufficient studies to compensate for the shrinkage of the guide hole due to the shrinkage of the light-polymerized resin for 3D printing.

Although many software programs and 3D printers for CGI surgery are available, there is still a need for a method that can be optimized for more accurate implant posi-tioning. This report describes a technique that uses free software to adjust the size of the guide hole in the 3D printing surgical guide. This technical note describes a method for creating a 3D printing surgical guide with minimal tolerance of guide holes in clinical practice.

2. Materials and Methods This technical note was performed as shown in Figure 1.

Figure 1. Schematic of the procedure.

2.1. Technical Note: Adjustment of the Virtual Surgical Guide before Fabrication 1. Plan the implant placement according to the patient’s treatment using CGI software

(R2GATE v1.1.1; Megagen, Daegu, Republic of Korea) (Figure 2A). Then, export the CGI surgical guide from the CGI software into a standard tessellation language (STL) format file (Figure 2B).

Figure 1. Schematic of the procedure.

2.1. Technical Note: Adjustment of the Virtual Surgical Guide before Fabrication

1. Plan the implant placement according to the patient’s treatment using CGI software(R2GATE v1.1.1; Megagen, Daegu, Republic of Korea) (Figure 2A). Then, export theCGI surgical guide from the CGI software into a standard tessellation language (STL)format file (Figure 2B).

Appl. Sci. 2021, 11, x FOR PEER REVIEW 3 of 7

Figure 2. Design of the implant surgical guide. (A) Planned implant position with preoperative radiographs. (B) virtual surgical guide.

2. Import the STL format file into a mesh editing software (Meshmixer; Autodesk Co, CA, USA) (Figure 3A).

Figure 3. Method to adjust the size of the guide hole using Meshmixer. (A) Importing virtual surgical guide. (B) Creating a cylinder. (C) Partial segmentation of the cylinder and surgical guide. (D) Setting a reference point at the base of the cylinder. (E) Setting a reference point in the guide hole of the surgical guide. (F) Alignment with the cylinder and surgical guide. (G) Identification of alignment. (H) Cylinder movement. (I) Deletion of the overlapping parts of the cylinder and surgical guide. (J) Identification of the adjusted guide hole.

3. Create the cylinder using a mesh editing software (Figure 3B). Then, adjust the size of the cylinder to a diameter of 5.2 mm by adding 0.2 mm to the original hole-size (5 mm) to compensate for the shrinkage of the resin material.

4. Use the “Face Group” function to separate the base of the cylinder and the guide hole in the surgical guide (Figure 3C).

5. Use the “Create Pivot” function to set up a reference point for alignment. Set the reference point at the base of the cylinder and the guide hole of the surgical guide (Figure 3D,E).

6. Use the “Align” function to superimpose the reference point. Select the reference point of the cylinder and hold down the Shift key while selecting the reference point of the surgical guide (Figure 3F). Make sure it is aligned to the correct posi-tion (Figure 3G).

7. Use the “Transform” function to move the cylinder so it can contact the entire guide hole (Figure 3H).

8. Use the “Boolean Difference” function to adjust the size of the guide hole. Select the surgical guide, hold down the Shift key while selecting the cylinder, and then select the “Boolean Difference” function (Figure 3I).

Figure 2. Design of the implant surgical guide. (A) Planned implant position with preoperativeradiographs. (B) virtual surgical guide.

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2. Import the STL format file into a mesh editing software (Meshmixer; Autodesk Co,San Rafael, CA, USA) (Figure 3A).

Appl. Sci. 2021, 11, x FOR PEER REVIEW 3 of 7

Figure 2. Design of the implant surgical guide. (A) Planned implant position with preoperative radiographs. (B) virtual surgical guide.

2. Import the STL format file into a mesh editing software (Meshmixer; Autodesk Co, CA, USA) (Figure 3A).

Figure 3. Method to adjust the size of the guide hole using Meshmixer. (A) Importing virtual surgical guide. (B) Creating a cylinder. (C) Partial segmentation of the cylinder and surgical guide. (D) Setting a reference point at the base of the cylinder. (E) Setting a reference point in the guide hole of the surgical guide. (F) Alignment with the cylinder and surgical guide. (G) Identification of alignment. (H) Cylinder movement. (I) Deletion of the overlapping parts of the cylinder and surgical guide. (J) Identification of the adjusted guide hole.

3. Create the cylinder using a mesh editing software (Figure 3B). Then, adjust the size of the cylinder to a diameter of 5.2 mm by adding 0.2 mm to the original hole-size (5 mm) to compensate for the shrinkage of the resin material.

4. Use the “Face Group” function to separate the base of the cylinder and the guide hole in the surgical guide (Figure 3C).

5. Use the “Create Pivot” function to set up a reference point for alignment. Set the reference point at the base of the cylinder and the guide hole of the surgical guide (Figure 3D,E).

6. Use the “Align” function to superimpose the reference point. Select the reference point of the cylinder and hold down the Shift key while selecting the reference point of the surgical guide (Figure 3F). Make sure it is aligned to the correct posi-tion (Figure 3G).

7. Use the “Transform” function to move the cylinder so it can contact the entire guide hole (Figure 3H).

8. Use the “Boolean Difference” function to adjust the size of the guide hole. Select the surgical guide, hold down the Shift key while selecting the cylinder, and then select the “Boolean Difference” function (Figure 3I).

Figure 3. Method to adjust the size of the guide hole using Meshmixer. (A) Importing virtual surgical guide. (B) Creating acylinder. (C) Partial segmentation of the cylinder and surgical guide. (D) Setting a reference point at the base of the cylinder.(E) Setting a reference point in the guide hole of the surgical guide. (F) Alignment with the cylinder and surgical guide.(G) Identification of alignment. (H) Cylinder movement. (I) Deletion of the overlapping parts of the cylinder and surgicalguide. (J) Identification of the adjusted guide hole.

3. Create the cylinder using a mesh editing software (Figure 3B). Then, adjust the sizeof the cylinder to a diameter of 5.2 mm by adding 0.2 mm to the original hole-size(5 mm) to compensate for the shrinkage of the resin material.

4. Use the “Face Group” function to separate the base of the cylinder and the guide holein the surgical guide (Figure 3C).

5. Use the “Create Pivot” function to set up a reference point for alignment. Set thereference point at the base of the cylinder and the guide hole of the surgical guide(Figure 3D,E).

6. Use the “Align” function to superimpose the reference point. Select the reference pointof the cylinder and hold down the Shift key while selecting the reference point of thesurgical guide (Figure 3F). Make sure it is aligned to the correct position (Figure 3G).

7. Use the “Transform” function to move the cylinder so it can contact the entire guidehole (Figure 3H).

8. Use the “Boolean Difference” function to adjust the size of the guide hole. Select thesurgical guide, hold down the Shift key while selecting the cylinder, and then selectthe “Boolean Difference” function (Figure 3I).

9. Check the adjusted guide hole (Figure 3J). Then, export the surgical guide with aguide hole of 5.2 mm diameter from the mesh editing software into a STL format file.

2.2. Technical Note: Identification of the Surgical Guide for the Optimized Guide Hole Size

1. Fabricate the surgical guides with guide hole sizes of 5.0 mm (original size) and 5.2 mm(+0.2 mm) in diameter using a 3D printer (MegPrinter; Megagen, Daegu, Republic ofKorea) with photosensitive liquid resins (RAYDENT SG; Ray, Seoul, Republic of Korea).

2. Assess the size of the hole by inserting an implant surgical guide drill (R2GATE;Megagen, Daegu, Republic of Korea) into the hole of the surgical guides with guidehole sizes of 5.0 mm and 5.2 mm in diameter (Figure 4). The insertion of the drill wasimpossible at 5.0 mm (Figure 4A), while it was possible at 5.2 mm (Figure 4B).

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9. Check the adjusted guide hole (Figure 3J). Then, export the surgical guide with a guide hole of 5.2 mm diameter from the mesh editing software into a STL format file.

2.2. Technical Note: Identification of the Surgical Guide for the Optimized Guide Hole Size 1. Fabricate the surgical guides with guide hole sizes of 5.0 mm (original size) and 5.2

mm (+0.2 mm) in diameter using a 3D printer (MegPrinter; Megagen, Daegu, Re-public of Korea) with photosensitive liquid resins (RAYDENT SG; Ray, Seoul, Re-public of Korea).

2. Assess the size of the hole by inserting an implant surgical guide drill (R2GATE; Megagen, Daegu, Republic of Korea) into the hole of the surgical guides with guide hole sizes of 5.0 mm and 5.2 mm in diameter (Figure 4). The insertion of the drill was impossible at 5.0 mm (Figure 4A), while it was possible at 5.2 mm (Figure 4B).

Figure 4. Evaluation of the fabricated surgical guides. (A) Surgical guide template with 5.0 mm diameter. (B) Surgical guide template with 5.2 mm diameter.

3. Perform ‘Adjustment of the virtual surgical guide’ steps for the fabrication of surgical guides with guide hole sizes of 5.19 mm, 5.18 mm, and 5.17 mm in diameter. Using this process, it is possible to determine the minimum usable clearance between the hole and the drill.

4. Perform the 2 steps for assessment of the surgical guides with guide hole sizes of 5.19 mm, 5.18 mm, and 5.17 mm. The insertion of the drill was possible at 5.19 mm and 5.18 mm (Figure 5A,B), but was not possible at 5.17 mm (Figure 5C). Therefore, the value of 5.18 mm between 5.19 mm and 5.17 mm was determined as the minimum usable tolerance.

Figure 5. Evaluation of the fabricated surgical guides. (A) Surgical guide with 5.19 mm diameter. (B) Surgical guide with 5.18 mm diameter. (C) Surgical guide with 5.17 mm diameter.

5. Fabricate 10 surgical guides with guide holes of 5.18 mm for repeatability. Then, as-sess the size of the hole by inserting an implant surgical guide drill.

6. Measure the size of the guide holes using a digital vernier caliper (500-197-20; Mi-tutoyo, Tokyo, Japan).

Figure 4. Evaluation of the fabricated surgical guides. (A) Surgical guide template with 5.0 mm diameter. (B) Surgical guidetemplate with 5.2 mm diameter.

3. Perform ‘Adjustment of the virtual surgical guide’ steps for the fabrication of surgicalguides with guide hole sizes of 5.19 mm, 5.18 mm, and 5.17 mm in diameter. Using thisprocess, it is possible to determine the minimum usable clearance between the holeand the drill.

4. Perform the 2 steps for assessment of the surgical guides with guide hole sizes of5.19 mm, 5.18 mm, and 5.17 mm. The insertion of the drill was possible at 5.19 mmand 5.18 mm (Figure 5A,B), but was not possible at 5.17 mm (Figure 5C). Therefore,the value of 5.18 mm between 5.19 mm and 5.17 mm was determined as the minimumusable tolerance.

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9. Check the adjusted guide hole (Figure 3J). Then, export the surgical guide with a guide hole of 5.2 mm diameter from the mesh editing software into a STL format file.

2.2. Technical Note: Identification of the Surgical Guide for the Optimized Guide Hole Size 1. Fabricate the surgical guides with guide hole sizes of 5.0 mm (original size) and 5.2

mm (+0.2 mm) in diameter using a 3D printer (MegPrinter; Megagen, Daegu, Re-public of Korea) with photosensitive liquid resins (RAYDENT SG; Ray, Seoul, Re-public of Korea).

2. Assess the size of the hole by inserting an implant surgical guide drill (R2GATE; Megagen, Daegu, Republic of Korea) into the hole of the surgical guides with guide hole sizes of 5.0 mm and 5.2 mm in diameter (Figure 4). The insertion of the drill was impossible at 5.0 mm (Figure 4A), while it was possible at 5.2 mm (Figure 4B).

Figure 4. Evaluation of the fabricated surgical guides. (A) Surgical guide template with 5.0 mm diameter. (B) Surgical guide template with 5.2 mm diameter.

3. Perform ‘Adjustment of the virtual surgical guide’ steps for the fabrication of surgical guides with guide hole sizes of 5.19 mm, 5.18 mm, and 5.17 mm in diameter. Using this process, it is possible to determine the minimum usable clearance between the hole and the drill.

4. Perform the 2 steps for assessment of the surgical guides with guide hole sizes of 5.19 mm, 5.18 mm, and 5.17 mm. The insertion of the drill was possible at 5.19 mm and 5.18 mm (Figure 5A,B), but was not possible at 5.17 mm (Figure 5C). Therefore, the value of 5.18 mm between 5.19 mm and 5.17 mm was determined as the minimum usable tolerance.

Figure 5. Evaluation of the fabricated surgical guides. (A) Surgical guide with 5.19 mm diameter. (B) Surgical guide with 5.18 mm diameter. (C) Surgical guide with 5.17 mm diameter.

5. Fabricate 10 surgical guides with guide holes of 5.18 mm for repeatability. Then, as-sess the size of the hole by inserting an implant surgical guide drill.

6. Measure the size of the guide holes using a digital vernier caliper (500-197-20; Mi-tutoyo, Tokyo, Japan).

Figure 5. Evaluation of the fabricated surgical guides. (A) Surgical guide with 5.19 mm diameter. (B) Surgical guide with5.18 mm diameter. (C) Surgical guide with 5.17 mm diameter.

5. Fabricate 10 surgical guides with guide holes of 5.18 mm for repeatability. Then, assessthe size of the hole by inserting an implant surgical guide drill.

6. Measure the size of the guide holes using a digital vernier caliper (500-197-20;Mitutoyo, Tokyo, Japan).

3. Results

The actual hole size of the surgical guide fabricated under the 5.18 mm diameterguide hole was measured to be a mean 5.06 ± 0.03 mm. Since no errors were observed indrill insertion, a 5.18 mm diameter guide hole was suggested as the size with minimumtolerance suitable for the conditions presented in this method.

4. Discussion

The size of the hole with minimum tolerance was proposed as 5.18 mm when prepar-ing the surgical template as described in this technical note. These results may varydepending on the manufacturing conditions (equipment, material). If the described tech-nique was used to fabricate surgical templates with minimum tolerance in the clinicalenvironment with various manufacturing conditions, it will have a positive effect on the ac-

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curacy of implant positioning. If the equipment and materials do not change, the proposedhole size can be applied to other patients. Therefore, through this technical note, a dentalclinician can create a surgical guide optimized for 3D printers and materials owned by thedental clinic.

Schneider et al. [9] reported that drill tolerance was reduced by decreasing the sleevediameter of the surgical guide. Apostolakis et al. [5] reported that the maximum errors thatcould be caused by drill tolerance were 2.8 mm and 5.9◦ at the apex of the implant andimplant axis, respectively. Koop et al. [6] reported that the maximum errors that could becaused by the type of sleeve were 1.3 mm, 2.4 mm, and 5.2◦ at the implant apex, implantshoulder, and implant axis, respectively. Therefore, minimum tolerance between the sleeveand the drill can improve the accuracy of the computer guide implant.

In a systematic review, the reliability, accuracy, and precision of implant surgicalguides were reported [23,24]. It was concluded that the average deviations from the entryand apex of the implant placed using the surgical guide were 1.2 mm and 1.4 mm, and themaximum deviations were 4.5 mm and 7.1 mm [23,24]. Each step in computer-assistedguided surgery, from examination to planning and execution, has been reported to affectthe final accuracy of implant placement [23,24]. The large tolerance between the guide holeand the drilling bur guides the implant to the wrong position [3,9]. In this technical note,a way to minimize tolerances was presented.

This technical note explains how to make a surgical guide with a guide hole ofminimum tolerance. Guide holes with minimal tolerances prevent inadequate horizontalmovement and allow the implant to be accurately guided to the planned position [3,9].The minimum tolerance guide hole made with this technical note can minimize horizontalmovement, but the vertical movement is associated with the stopper of the surgical guide,which can control the drilling bur vertically [25].

The spread of dental 3D printers is increasing, and the use of guides during implantsurgery is being made and applied at the dental chairside environment [1–9]. The methodpresented in this technique is proposed to fabricate a surgical guide with minimum toler-ance without the use of a metal drill key or a separate metal sleeve with the equipment(implant planning software and 3D printer) and printing materials readily available to clin-icians. This technical note can also allow the clinicians to eliminate the need for pretreatingthe sleeve, which saves cost and time.

There is a limitation in that additional in vitro or clinical studies are required to verifythe improvement of the accuracy of the computer guide implant with the present technique.In addition, the lack of visibility and small mouth opening may be a limitation of thisnote during implant placement. This technical note can be used as information for moreaccurate placement for clinicians who use 3D printers to create surgical guides and usethem for surgery.

5. Conclusions

The method presented in this technical note allows the use of free software to fabricatethe 3D printing surgical guide with minimal tolerances between the guided hole anddrill without metal guide keys or metal sleeves. The present technical note gives baselineinformation that will be valuable for future investigations.

Author Contributions: Conceptualization, K.S.; methodology, K.S.; software, K.S.; validation, K.S.;formal analysis, K.S.; investigation, K.S.; writing—original draft preparation, K.S.; writing—reviewand editing, K.S.; visualization, K.S.; supervision, K.-b.L.; project administration, K.-b.L.; fundingacquisition, K.-b.L. All authors have read and agreed to the published version of the manuscript.

Funding: This work was supported by the Industrial Strategic Technology Development Program(10062635, New hybrid milling machine with a resolution of less than 10 µm development, using openCAD/CAM S/W integrated platforms for one-day prosthetic treatment of 3D smart medical caresystem) funded by the Ministry of Trade, Industry and Energy (MOTIE, Korea).

Institutional Review Board Statement: Not applicable.

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Informed Consent Statement: Not applicable.

Data Availability Statement: Data is contained within the article.

Acknowledgments: The authors thank the researchers of the Advanced Dental Device DevelopmentInstitute, Kyungpook National University for their time and contributions to the study.

Conflicts of Interest: The authors declare no conflict of interest. The funders had no role in thedesign of the study; in the collection, analyses, or interpretation of the data; in the writing of themanuscript; or in the decision to publish the results.

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