Implant Surgical Guides: Types, Designs & Production Methods
In this article:
Implant surgical guide design concepts
Immediate implant placement after teeth extraction in patients with failing dentition can be tricky. In full arch rehabilitation cases, large-scale alveoplasty (i.e. bone reduction) may be required. The purpose of this procedure is to provide enough space between the jaws to accommodate the preplanned prosthesis of choice.
In some cases, alveoplasty is done to widen the thin bony ridge enough to enhance the implant-recipient area by creating an architecturally sound base for implant placement. Too much or too little bone reduction will create unfavorable restorative space and compromise the positioning of the dental implants. You can can read about this topic more in depth in our article. “Why do implant-supported fixed dental prostheses (ISFDP) sometimes fail?“
CAD/CAM technology offers increased accuracy with regard to the outcome of the treatment of choice. Currently, there are 3 main categories of CAD/CAM implant surgical guides; namely, tooth-supported, mucosa-supported, and bone-supported.
Both mucosa- and bone-supported implant surgical guides are indicated for completely edentulous patients, and issues related to their stability have been reported in a number of studies. One solution to increase their stability is the use of anchoring pins which stabilize the guide inside the patient’s mouth. With that said, tooth-supported implant surgical guides are the most stable among the CAD/CAM guides.
The most stable among bone reduction guides is currently the 360Imaging Anatomic Guide. With it titanium screw-locking system, Anatomic Guide is locked into the cortical bone by means of 4 short titanium screws after a facial/labial flap has been raised. This ensures maximum support, placement accuracy and eliminates both rocking and cantilever effects almost entirely.
The anatomical accuracy of this guide helps with the fit and intimate seating, allowing it to sit flat on the bone and engage the often neglected bony undercut area. Its small size and transparency facilitates irrigation and maximizes visibility and accessibility during surgery.
Implant surgical guide design concepts
- Non-guided technique
- Partially-guided technique
- Fully-guided technique
This design indicates the location of the prospective prosthesis is in relation to the planned implant-recipient area. The proper position of the dental implant is marked with no emphasis on drill angulation, which gives more leeway when it comes to the final implant placement. A guiding pin hole is first drilled through a transparent matrix formed by a vacuum. This points to the ideal location of the implant. Then, drill angulation is positioned relative to the neighboring teeth.
Evidently, such implant surgical guides can lead to inadequate positioning of the guiding pin hole and improper angulation of the implant. Therefore, these surgical templates can be used as imaging indicators during the surgical phase of implant placement.
In this technique, the drill used is guided by the implant surgical guide, with osteotomy and implant placement done freehand by the oral surgeon. This requires a radiographic template to be prepared, then turned into a surgical template using radiographic landmarks. A number of variations have been suggested, such as using different implant surgical guide material, radiographic marker, imaging system, and conversion procedure (i.e. converting the radiographic template into a surgical template). However, although this technique is partially-limiting, it still does not control the angle of surgical drills entirely.
This design limits the drilling buccolingually and mesiodistally. Drill stops determine the depth of the osteotomy, as well as the subsequent prosthetically-driven implant placement. The more restricting the technique, the fewer decisions the surgeon has to make mid-operation. This completely-limiting technique reduces stress on the day of surgery and increases success rate of the treatment.
1. Cast-based surgical guides
This is an analog design done using bone sounding (i.e. transgingival probing) and periapical radiographs in flapless guided implant surgery. Radiographs are altered with digital software in order to transpose root anatomy onto the model. Following that, the model is sectioned at the proposed implant-recipient area, and transgingival probing measurements are taken to determine the drilling angulation. A lab-made analog is positioned on the model, then a guide sleeve that corresponds to the implant diameter is fabricated with wires, creating a framework around the teeth. Occlusal registration material, such as vinyl polysiloxane is used to make the superstructure.
2. CAD/CAM surgical guides
In this design, data from a CT scan (i.e. computerized tomography) is utilized to plan implant placement. CT scan images are transformed into recognizable form to be read by an implant planning software.
The advantages of this technique include:
- Bone anatomy can be virtually viewed in 3D
- Visualization of the surgical area of interest before surgery
- Minimizing the chances of insufficient remaining bone compromising intraoral structures
- Prosthetically-driven implant planning using a digital template which leads to biomechanically-sound final treatment outcome
- The option of flapless surgery with pre-surgical cast and provisional prosthesis fabrication
- Immediate loading of temporary restoration
However, this method does not come without its own challenges, such as:
- Experience and skill are required to master the system and its workflow
- Complications related to inaccurate treatment planning, radiographic stent error, scanning errors, rapid prototyping of the guide stent, and fabrication methods.
CAD/CAM surgical guides manufacturing process generally follows these steps:
- Radiographic template preparation
- CT scanning
- Implant planning with dental planning software
- Stereolithographic surgical guide fabrication
The radiographic template has to be guided by the desired prosthetic end result. The template helps the dentist evaluate implants’ positions from an esthetic and biomechanical view points. Following that, the inter-arch index is fabricated, allowing accurate placement of the scan template. Double scanning is then performed; the patient is scanned wearing the radiographic template and inter-arch index during the first scan. The index is removed for the second scan. This is done to get an accurate representation of intraoral structures.
STL and DICOM data sets are then superimposed on top of each other guided by the radiographic markers. They are then converted into a file format compatible with a dental planning platform. The result is a 3D image of the patient’s intraoral anatomy. In this stage, implant placement procedure can be carried out virtually using the software. Digitally planning the position, angle, depth, and diameter of the implants is performed. The plan can be evaluated in different views simultaneously; axial, panoramic, and cross-sectional.
After digital planning, the file is exported into an appropriate format and sent to the fabrication facility for processing. Stereolithography is a computer-assisted, rapid prototyping polymerization process which recreates the patient’s anatomic landmarks in a polymer layer producing a clear resin 3D model. After the material solidifies, spaces for stainless steel or titanium sleeves can be inserted. The sleeves help guide the osteotomy drills accurately and with little deviation.
Generally speaking, implant surgical guides can be produced by either additive or subtractive fabrication techniques.
1. Additive fabrication
This method describes a number of technologies which create 3D objects by adding layers of material on top of each other. An additive-manufacturing machine transforms data obtained from the previously described CAD file into various types of materials. This is an umbrella term that includes methods such as, rapid prototyping, direct digital manufacturing, layered manufacturing and 3D Printing.
Various materials can be used like plaster, silica, PLA filament, and acrylic resin. 3D-printing is a relatively quick process that uses low-cost materials. However, surface finish and the material options are limited– the printed objects can be fragile as well.
Fine powder particles are fused together by laser, incrementally building up the framework. The laser welds the grains together to form a layer. This is done repeatedly until the implant surgical guide is formed.
A wider range of material options are available and the final product can be sterilized in an autoclave. Due to the porosity of some materials, distortion by shrinkage or wrapping of certain parts is possible due to heat. The objects are less accurate than those made using stereolithography. Plus, this method can be costly as it needs to be performed under certain conditions such as compressed air.
2. Subtractive fabrication
In this computer-aided manufacturing (CAM) process, a block of material is cut into the desired shape and size by a computer-aided milling process. Materials such as wax, resin, ceramic or metal can be used. The milled objects seem to be more durable but need continuous cooling to counteract the heat resulting from milling power. Surface defects such as chipping and microfractures may occur, particularly in brittle milling materials. However, this can be avoided by employing a two-step milling process where low cutting force is used in the second phase resulting in a smooth surface.
Fully-guided implant placement protocols are reported to give consistently accurate treatment outcomes. That said, many clinicians perceive such protocols as costly as well as requiring extensive training and skill. Many implant placement protocols are being developed constantly but not all systems are one-size-fits-all. With continuous innovation, we now have many affordable and reliable options that are accessible to dental practitioners of all skill levels. The smallest deviation in implant placement or alveoplasty can negatively affect the final prosthesis. Therefore, clinicians have to be discerning with regard to which solutions they choose, as well as who they depend on when it comes to treatment planning.