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Review
3D Printed Surgical Guides
By: Jason Frankel

Abstract

There are several methods of restoring missing teeth. The most ideal restorative method is a dental implant. Some surgeons prefer to use dental surgical guides to perform more efficient surgeries when placing these implants. 3D printed guides produce similar accuracy to other guides at a reduced cost. Additionally, consumer-level 3D printers provide similar accuracy as high-end 3D printers, making accurate guides for implant placement both cheap and accessible.

Introduction

Tooth decay is prevalent at some point in most people’s lives.1 When sugars and starches aren’t cleaned from the teeth, bacteria begin to feed on them and form plaque. Plaque contains acids that remove some minerals from the tooth’s enamel (the outer layer of the tooth), causing cavities. A simple dental filling may restore a cavity.2 Once holes are formed in the enamel, the acids attack the dentin (the middle layer of the tooth), which contains tubes that connect to the blood vessels and nerves in the pulp, providing sensitivity to the tooth.3 If the damage reaches the pulp (the inner layer of the tooth), the method of restoration may be a root canal, in which the endodontist removes the affected pulp, including the nerves and blood vessels, fills and seals the space, and usually places a restorative crown on top.4 If there is substantial damage beyond the root end of the tooth, a root canal may not be sufficient to correct the damage. In that situation, an apicoectomy may be done for the patient as well.5 During an apicoectomy, the surgeon cuts a flap in the gums and drills into the bone until they reach the root of the tooth. At that point, they repair the damage from the apex (root side) of the tooth without touching the crown and then suture the flap closed.

 

If an entire tooth is missing, a fixed partial denture (bridge) may fill the gap between teeth.6 Bridges are made by shaving down the adjacent teeth. Crowns made of porcelain are then put onto these teeth, with a connected crown taking the place of the missing tooth. However, if the tooth to which the bridge is attached decays, it may become unstable and nonfunctional as the foundation for the bridge.7 In this case, the patient may now end up with additional damaged teeth. An alternative, more ideal restorative method to fill the gap between teeth may be dental implants, which are sometimes placed using surgical guides. New technological innovations, such as 3D printed guides, provide accurately placed implants at a reduced cost.


 

Use and Placement of Dental Implants

A dental implant is a piece of titanium, surgically placed below the gum line that acts as a substitute for the root of a tooth. An abutment is then attached to the top of the implant, and the restorative dentist builds a crown placed upon the abutment.8 Dental implants rely on osseointegration, the direct contact between the titanium implant and the surrounding bone.9 The osseointegration gives them similar strength as natural teeth in the bone.10

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Figure 1

Dental implants are frequently done in multiple steps to ensure the most vital foundation for a new “tooth” (Figure 1). The first step is the extraction of the damaged tooth. If the implant cannot be placed right away,11 the bone would shrink, resulting in significant bone loss. Too much bone loss in the implant’s intended site may mean there is not enough bone for the implant to be placed correctly. In this case, the surgeon will rebuild the extraction socket with a bone graft and allow the bone to heal.12 The surgeon will also take a CBCT (Cone-Beam Computed Tomography) scan to show the amount of bone available in the jaw where the implant will be placed. It also shows the adjacent anatomy to prevent damage to vital structures.13 After the first waiting period, the patient returns for a second surgery. In this procedure, the surgeon may take an updated CBCT scan, and then will cut a flap in the gums, drill a hole into the bone, thread a titanium implant tightly into place, and finally suture the flaps to reseal them. Alternatively, surgeons can place the implant with flapless surgery, in which the drill goes straight through the soft tissue and into the bone for the implant to be threaded.14 If there is not enough bone in the posterior upper jaw in the maxillary sinus region, a sinus augmentation may be performed, which adds bone to the base of the sinus.15 After the second surgery, the bone is allowed to heal, and then the patient is sent back to the restorative dentist.

 

Dental Surgical Guides

Many surgeons prefer surgical guides (Figure 2) for these operations, while others prefer to free-hand. Dental implants have been proven highly effective, with low failure percentages. A surgical guide is a tool that is made to fit perfectly over the patient's targeted implant site to assist surgeons in the accurate placement of dental implants. The guides are designed for a metal sleeve to fit in the holes, enabling the implant to be placed at the right angle, depth, and direction into the bone.

 

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Figure 2

A surgical guide is made by first taking an impression or scanning the patient’s desired implant site. The surgeon can then use a computer-guided implant planning system to map out the exact location of the implant in the bone. Guides can be made to either fit over the soft tissue of the implant site (for a flapless surgery) or directly over the bone (for a flapped surgery). In either case, the guides are made to fit adequately into their respective positions and allow for precision when assisting the surgeon in placing the implant.16

 

A study comparing the results from free-hand and surgical guided surgeries determined a difference between these methods. They found that free-hand surgery had a 6.42% failure rate, while guided surgeries had a 2.25% failure rate, emphasizing the effectiveness of using a surgical guide.17 

 

In addition to the low failure rates, surgeries using guides have been proven to be highly accurate. Another study was done in which patients were split into three test groups. One group had a guided surgery done with a flap approach, the second had a guided surgery done with a flapless approach, and the third had their surgery also done with a flap approach, but entirely free-hand. For all three groups, their surgeries were planned based on preoperative CBCT images and allowed for pre-planning of how the surgery would take place. Then, after each patient had their surgeries done respective to their group, they had a postoperative CBCT. The surgeons then used an Osstell Mentor, a device that vibrates and calculates the frequency,18  to determine the implant’s stability19 and found that the free-handed group was not significantly different from the guided surgeries. The preoperative and postoperative CBCTs were then compared to determine the accuracy of implant placements based on the methods used for the different groups. They also compared the distance from the planned entry point and the insertion angle into the entry point from the planned implant placement based on the preoperative CBCT and the postoperative CBCT. The results showed that the deviation of the position of the implants was more prominent in the guided flapped surgery than in the guided flapless surgery. However, both guided surgeries didn’t have nearly as much deviation as the free-handed surgeries for distance from the projected entrance point and the entrance angle.20 Although implants may fail for several reasons regardless of the placement method,21 22 research reveals that guided implant surgeries have proven more effective and accurate than free-hand surgeries. 

 

Novice surgeons generally have less accurate results than experienced surgeons. However, a study found that the deviation between novice and experienced surgeons is much lower when using surgical guides than in free-handing surgeries.23 This study further indicates the accuracy of surgical guides. 

 

Additionally, aside from the extreme accuracy and effectiveness of using surgical guides, other benefits include reducing trauma, time of the procedure, swelling, and pain, resulting in a quicker recovery period for the patient.16

 

Potential Problem of Placing Implants with Guides

While there are many benefits of using surgical guides in assisting surgeons in placing implants, there are still some significant problems with the method. Generally, when placing dental implants, the dental assistant will irrigate the implant site as the surgeon drills into the bone. Irrigation is performed to reduce the temperature and avoid thermal osteonecrosis (the death of bone tissue due to high temperatures),24 which would inhibit osseointegration. That being a concern, a study determined that the use of surgical guides blocks the irrigation, making it more difficult to control the temperature of the implant site while drilling.25 However, a different study, which utilized routed irrigation (customized channels to direct the water directly to the implant site), found that the temperature was able to be held consistently below 47ºC, preventing thermal osteonecrosis.26

 

Types of Dental Surgical Guides

Surgical guides have thus far been proven to be the most effective and accurate route for placing dental implants. However, there are multiple types of surgical guides. Thermoforming is a traditional method used in the production of dental surgical guides. The first step in producing these guides is by either taking an impression of the patient’s teeth and casting it to form a model or taking an intraoral digital scan to print a model. A thermoplastic sheet is then heated and pressed over the model, sleeves are then placed in the guides to increase strength and ensure the implant is placed in the precise position.27

 

An alternative to thermoplastic surgical guides is 3D printed surgical guides. The first step in producing these guides is to take a CBCT scan to get a 3D image of the region.28 In turn, the surgeon can visualize the amount of bone they are working with for the implant to be placed,29 as well as the surrounding structures such as roots of adjacent teeth,30 the maxillary sinus,31 and the mandibular nerve32 (Figure 3). Along with the CBCT, a surface scan of the teeth is also required to be converted into an STL file. The intraoral surface scan is created because some of the x-ray photons from the CBCT do not penetrate radiopaque restoration; instead, they reflect at the surface.33 These two scans are brought together to provide a complete visual of the implant site. The surgeon then decides the length and width for the implant based on the available bone and digitally places it (in a guided implant surgery planning software) in the most optimal orientation and depth for the crown to be placed after healing.34 After it is known where and how the implants should be placed, another STL (the guide itself) is designed to be offset from the model of the teeth (or bone, depending on the type of guide)35 and provide holes for the sleeves36 to place the implant in the correct position. The guide is then printed, sterilized, and ready for use (Figure 3).37    

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Figure 3

3D printed surgical guides are cheaper and faster to produce than thermoplastic surgical guides. However, the most critical variable to compare the two methods is their accuracy. A study was done where some patients had implants placed with thermoplastic surgical guides while others had implants placed with 3D printed surgical guides. The results found that implants placed with 3D printed guides were more accurate in the angle of insertion and the measured distance from the planned placement of the implant than compared with those placed with thermoplastic guides.38 The difference in cost and time of production, as well as the significantly greater accuracy of the 3D printed guides, makes them the far more efficient choice.

 

Surgical Guides Produced by High-End vs. Consumer-Level 3D Printers

It is inconvenient to send out the 3D-designed models and surgical guides to professional high-end printers, but it may not be necessary. A study conducted used surgical guides that were digitally designed using the same software. They then printed some guides using consumer-level 3D printers and others using a high-end professional 3D printer and compared the accuracy guides from their respective printers. The results showed that although the measured differences in accuracy between the printers were statistically significant, from a clinical point of view the deviations were negligible.39

 

Conclusion 

Dental implants are the most efficient way to restore a missing tooth. Though some surgeons prefer to free-hand their surgeries, studies have proven implants placed with the help of surgical guides to be more accurate with lower failure rates. Some surgical guides can be costly, but 3D printed guides are a cheaper option with similar accuracy. 3D printers in a dental office can produce nearly as accurate guides as high-end printers, making cheap dental surgical guides easily accessible.

References

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25. Liu, Yun-feng, et al. “Numerical and Experimental Analyses on the Temperature Distribution in the Dental Implant Preparation Area When Using a Surgical Guide.” Journal of Prosthodontics, vol. 27, no. 1, 2016, pp. 42–51., https://doi.org/10.1111/jopr.12488. 

26. Teich, Sorin, et al. “3D Printed Implant Surgical Guides with Internally Routed Irrigation for Temperature Reduction during Osteotomy Preparation: A Pilot Study.” Journal of Esthetic and Restorative Dentistry, 2021, https://doi.org/10.1111/jerd.12847. 

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33. TI, Dental. “Creating a Surgical Guide with Your CBCT (and without an Intraoral Scanner).” Dentalti, Dentalti, 8 Mar. 2021, https://www.dentalti.com/post/creating-a-surgical-guide-with-your-cbct-and-without-an-intraoral-scanner. 

34. Justin Moody, The Basics of 3D Printing Surgical Guides, Henry Schein Dental, 27 Jan. 2021, https://www.youtube.com/watch?v=v3jGvi1QiEQ. Accessed 2022. 

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36. Ozan, Oğuz, et al. “Effect of Guide Sleeve Material, Region, Diameter, and Number of Times Drills Were Used on the Material Loss from Sleeves and Drills Used for Surgical Guides: An in Vitro Study.” The Journal of Prosthetic Dentistry, 2021, https://doi.org/10.1016/j.prosdent.2020.12.036. 

37. van Dal, Vito. “Effect of Sterilization on 3D Printed Patient-Specific Surgical Guides.” TU Delft Repositories, 1 Jan. 1970,

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38. Bell, Caitlyn, et al. “Accuracy of Implants Placed with Surgical Guides: Thermoplastic versus 3D Printed.” The International Journal of Periodontics & Restorative Dentistry, vol. 38, no. 1, 2018, pp. 113–119., https://doi.org/10.11607/prd.3254. 

39. Wegmüller, Lukas, et al. “Consumer vs. High-End 3D Printers for Guided Implant Surgery—an in Vitro Accuracy Assessment Study of Different 3D Printing Technologies.” Journal of Clinical Medicine, vol. 10, no. 21, 2021, p. 4894., https://doi.org/10.3390/jcm10214894. 

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