Computerized implant-dentistry: Advances toward automation.

Advancements in the field of implantology such as three-dimensional imaging, implant-planning software, computer-aided-design/computer-aided-manufacturing (CAD/CAM) technology, computer-guided, and navigated implant surgery have led to the computerization of implant-dentistry. This three-dimensional computer-generated implant-planning and surgery has not only enabled accurate preoperative evaluation of the anatomic limitations but has also facilitated preoperative planning of implant positions along with virtual implant placement and subsequently transferring the virtual treatment plans onto the surgical phase via static (guided) or dynamic (navigated) systems aided by CAD/CAM technology. Computerized-implant-dentistry being highly predictable and minimally invasive in nature has also allowed implant placement in patients with medical comorbidities (e.g. radiation therapy, blood dyscrasias), in patients with complex problems following a significant alteration of the bony anatomy as a result of benign or malignant pathology of the jaws or trauma and in patients with other physical and emotional problems. With significant achievements accomplished in the field of computerized implant-dentistry, attempts are now been made toward complete automation of implant-dentistry.

INTRODUCTION

Traditionally, determining implant position, size, number, direction, and placement depended on the presurgical diagnostic imaging, which often, was limited to two-dimensional radiographs, and on the guiding acrylic stents usually prepared over duplicated casts of diagnostic wax-up. However, limitations of two-dimensional imaging and inaccuracies in the stent fabrication or guide channels often lead to erroneous implant placement, which results in complications and implant failure, especially in anatomically complicated situations. To overcome these limitations, many advancements have taken place, which have computerized the implant-dentistry. These include:

Three-dimensional computed tomography (CT) imaging

CT-based implant-planning software

Computer-aided-design/computer- aided-manufacturing (CAD/CAM) technology

Computer guided implant surgery (CGIS)

Computer navigated implant surgery (CNIS)

Robotic-implant-dentistry.

THREE-DIMENSIONAL COMPUTED TOMOGRAPHY IMAGING

Two-dimensional imaging techniques like orthopantomogram and intra oral periapical radiography are affordable, economical and easy means of implant site selection. Yet, they tend to produce errors as they have many shortcomings like image superimposition, limited reproducibility, and production of a projected image of three-dimensional object onto a two-dimensional plane as well as distortion and variable magnification of the image. Considering these shortcomings of two-dimensional imaging techniques, three-dimensional imaging has become an essential diagnostic tool and is considered the gold standard in implant-dentistry, for it:[12]

Allows three-dimensional views of the region of interest and relevant jaw anatomy such as the maxillary sinus and mandibular nerve

Can also be utilized for the estimation of alveolar bone density

Overcomes the limitations of traditional two-dimensional imaging modalities and provides uniform magnification, multiplanar views, and simultaneous study of multiple implants.

Yet, certain limiting factors as follows are also associated with CT:[3]

Beam hardening artifact or scatter due to adjacent metal structures

High costs associated with CT examinations

Relatively high radiation dose to the patient.

Considering these limitations, cone-beam computed tomography (CBCT) imaging might be a viable, more practical and perhaps even better alternative to CT in the preoperative radiographic assessment of potential dental implant sites. Recently, Esmaeili et al. 2013 compared CBCT and a 64-slice CT scanner for the beam hardening artifacts produced by dental implants and suggested that given the higher resolution of the images produced by CBCT and its lower doses and costs compared with CT scanner, CBCT should be recommended in order to produce images of higher diagnostic values, especially in patients with extensive restorations, multiple prostheses or previous implant treatments.[4] Furthermore in 2012, Pires et al. in his study demonstrated that presence, location, and dimensions of the mandibular incisive canal are better determined by CBCT imaging than by panoramic radiography.[5]

The patient is thenceforth, scanned with either fiducial (artificial) radiographic markers that are placed in stent, jaws etc., or with anatomic (natural) markers such as teeth or bony landmarks and then the digital images, in digital imaging and communications in medicine format, which are derived this way are imported into one of the implant-planning software programs and converted into a virtual three-dimensional model of the treatment area to provide a realistic view of the patient's bony anatomy, thus permitting a virtual execution of the surgery in an ideal and precise prosthetically driven manner.[678] Yet, whichever diagnostic scan is advised, a risk/benefit analysis must be carried out before.

COMPUTED TOMOGRAPHY BASED IMPLANT-PLANNING SOFTWARES

The implant-planning software not only allows an undistorted three-dimensional visualization of the jawbone in axial, sagittal, coronal, panoramic and cross-sectional views it even produces three-dimensional reformatted reconstructions. The implant-planning software has the following advantages as well:[91011]

Digital planning and fabrication of a virtual wax-up, implant position, abutment design, surgical guide, provisional restoration, and as well as final restoration [Figures 1 and 2]

Figure 1

Digital imaging and communications in medicine images visualized when loaded into the software

Figure 2

After virtually placing implant (size: 4.1 mm × 10 mm)

Allows predetermination of the size of the implant, the abutment and the provisional restoration

Averts any possible complications by highlighting the inaccuracies in the selection of implant size or position, during virtual planning, which, can then be easily rectified using the software [Figure 3]

Figure 3

Any inaccuracy in selection of implant-size (size: 4.1 mm × 13 mm) highlighted by the software

Assists in anticipation, guiding and planning of procedures like alveolectomy, alveoplasty, implant positioning in situations with anatomical limitations, visualization of the amount of available bone in each area and aids in selecting the ideal donor site for osseous grafts, graft location, shape and volume of graft, sinus lift technique and placement of implants in one step surgery, treatment of atrophic maxillae as well as placement of transzygomatic implants etc.

Allows for the storage of the treatment plan and all other data of the patients on the computer

Demonstration of the virtual treatment plan to the patient is possible.

Though these software programs have facilitated accurate implant placement, yet, there also are certain limitations associated with them:

Requires time to understand how the software functions

High investment cost

Requires an exact localization of natural or fiducial markers in image data and reality for an accurate registration of the patient.[12]

Some of the software programs commercially available are:[8]

Procera-Software® (Nobel Biocare, Göteborg, Sweden)

coDiagnostiX® (IVS Solutions AG, Chemnitz, Germany)

Easy Guide (Keystone-Dental, Burlington, MA, USA)

SICAT (SICAT GmbH and Co. KG, Brunnenallee, Bonn, Germany)

Virtual Implant Planning (BioHorizons, Birmingham, USA)

ImplantMaster TM (I-Dent Imaging Ltd., Hod Hasharon, Israel)

Simplant®, SurgiCase® (Materialize Inc., Leuven, Belgium)

Implant3D Media Lab Software (Media Lab Srl, Follo (SP), Italy)

DentalSlice (Bioparts, Brazil)

Scan2Guide or S2G (iDent, Ft. Lauderdale, Florida)

Tx Studio software (i-CAT, Imaging Sciences International, Hatfield, PA) etc.

Martins and Lederman in 2013, evaluated the efficacy of virtual planning using DentalSlice software and revealed that a prototype guide planned on DentalSlice was efficient for positioning implants and for quantifying and locating the bone graft, which also aided in the achievement of 100% success rate.[13] In 2012, Nkenke et al. even promoted the implementation of virtual dental implant-planning software in dental undergraduate curriculum based on their assessment of positive acceptance of the software by the students.[14]

COMPUTER-AIDED-DESIGN/COMPUTER-AIDED-MANUFACTURING TECHNOLOGY

Transferring the virtual treatment plan into actual patient treatment has been made possible by the revolutionary CAD/CAM technique, which is used in two guided surgery systems that is, (1) “Static” or “template-based system,” that communicates predetermined sites using “surgical templates” or implant guides in the operating field, manufactured via rapid prototyping technologies such as three-dimensional printing and stereolithography or “computer-driven drilling” and (2) dynamic system or “surgical navigation/computer-aided navigation” technology, which communicates virtual treatment plan to the operative field with visual imaging tools on a computer monitor, rather than the intraoral guides.[7]

Advantages of CAD/CAM technology are:[1516]

It facilitates minimally invasive surgical procedures with surgical guides (CGIS) along with greatly improving the predictability of implant surgery

It allows immediate loading by enabling the presurgical construction of master cast and accurately fitting, custom designed restorations.

COMPUTER GUIDED IMPLANT SURGERY (STATIC SYSTEM)

The static system, which employs use of a static surgical template/guide to reproduce virtual implant position in the surgical field, can be categorized into two types based on the CAD/CAM technology used for the surgical guide production. Examples of some of these available systems are given in Table 1.[17]

Table 1

Computer guided implant surgery

The computer guided implant surgery employing surgical template has the following advantages:[151618]

It precisely guide the osteotomy drills

Directs the surgeon in the exact location and angulation to place the implant based on virtual treatment plan

It allows flapless surgery, which entails less bleeding, less swelling, decreased healing time and postoperative pain

Aids in the preservation of hard and soft tissue and maintains blood circulation to the surgical site

Considerably increased accuracy of implant placement

Avoidance of vital structures

Shorter period required for surgery.

Out of the various types of surgical guides (classified according to the type of support: Bone, mucosa, tooth, or combination tooth-mucosa), Arisan et al. in 2010, demonstrated that Implants that were placed by bone-supported guides had the highest mean deviations (1.70 ± 0.52 mm for implant shoulder), whereas the lowest deviations (0.7 ± 0.13 mm for implant shoulder) were measured in implants that were placed by mucosa-supported guides fixed with osteosynthesis screws.[19] Though implant placement through the static surgical guide system is significantly more accurate than freehand, a higher accuracy can be achieved by sleeve-in-sleeve concept in which multiple sleeves are placed in the guide to properly orient the implant drills with increasing diameters and also by the fixation of the guide onto the surrounding alveolar ridge or mucosa for the stabilization.[2021] In 2007, Nickenig and Eitner had demonstrated that virtual plans based on CBCT scans could be reproduced during implant placement surgery, and hence, validated the reliability of the CGIS method for safe and predictable implant placement, and enabling wider use of flapless surgery.[22] Based on the systematic review regarding accuracy and clinical application of computer-guided template-based implant-dentistry, Schneider et al., in 2009 showed high implant survival rates ranging from 91% to 100%, following CGIS method.[23] The meta-regression analysis also revealed a reasonable accuracy with a mean deviation of 1.07 mm (95% confidence interval [CI]: 0.76-1.22 mm) at the entry point and 1.63 mm (95% CI: 1.26-2 mm) at the apex.[23] Precise transfer of implant replica position by means of simulated guided implant insertion, into a preoperative cast and a postoperative cast has also been demonstrated by Platzer et al., in 2013.[24] Vasak et al., (2014) also verified the viability of the CGIS concept and revealed a cumulative survival rate and success rate of 98.8% and 96.3% of immediate and delayed loaded implants respectively, placed using CGIS technique.[25] Recently, Meloni et al. conducted a clinical trial where in 23 edentulous jaws were treated with three-dimensional software planning, guided surgery, and immediate loading and restored with CAD-CAM full arch frameworks and concluded that computer-guided surgery and immediate loading seem to represent a viable option for the immediate rehabilitations of completely edentulous jaws with fixed implant supported restorations.[26] Though CGIS technique has been proven as an accurate and viable technique, it also has certain drawbacks and limitations, which have to be considered as well. The most common drawbacks and limitations associated with CGIS include:[7202728]

Error in data acquisition or incorrect processing of the image

Deviations from planned implant positions especially in the coronal and apical portions of the implants as well as with implant angulation

Inaccurate fixation of the guide resulting in displacement during perforation

Mechanical errors caused by angulation of the drills during perforation

Changed positioning of surgical instruments due to reduced mouth opening

Fracture of the surgical guide

Complexity of the whole system

The total cost of tools needed including the software program and surgical templates

The potential for thermal injury secondary to reduced access for external irrigation during osteotomy preparation during flapless implant placement with surgical guides

Does not allow intraoperative modification of implant position.

Hence, care should be taken whenever applying this technique on a routine basis. Yet, with the progression towards CNIS many of the limitations and drawbacks of CGIS technique have been evaded.

COMPUTER NAVIGATED IMPLANT SURGERY (DYNAMIC SYSTEM)

Computer navigated implant surgery involves the use of a surgical navigation system that reproduces virtual implant position directly from CT data with the optical bur tracking system without the requirement of an intraoral surgical guide. There are several navigation or positional tracking systems available in implant-dentistry [Table 2],[17] but few meet the computer-aided-surgery requirements in terms of accuracy (about 1 mm in 1 m3), reliability, and clinical usability.[6] In CNIS, the natural and fiducial markers that were used during the radiological scan as reference points are needed for the registration of the instruments.[20] Watzinger et al. In his case report promoted the use of optical tracking system for the intraoperative transfer of preoperative planning on CT scans, in real-time, since, the motor of the implant drill produced considerable distortion of the magnetic field and hindered the direct visualization of implant socket drilling when the electromagnetic tracking system were employed formerly.[29] Sensors attached to both the patient and the surgical hand-piece transmit three-dimensional positional information to a camera or detector that allows the computer to instantaneously calculate and display the virtual position of the instruments relative to the image data and also allows the visualization of the movements of the instruments in real-time to the surgeon via side-viewers or advanced see-through viewers.[17]

Table 2

Computer navigated implant surgery

Computer navigated implant surgery has many advantages over CGIS in that:[7]

It allows intraoperative changes in implant position that is, the virtual surgical plan can be altered or modified during surgery and the clinician can use the navigation system to concurrently visualize the patient's anatomy, permitting the surgeon to steer around obstacles, defects etc., that were not apparent on the presurgical scan

Bur tracking allows the drill to be continuously visualized on a computer screen in all three-dimensions (x, y and z)

It overcomes other limitations of CGIS like secondary thermal injury, displacement or fracture of guide etc.

The image guided implantology (IGI) system, which is a CNIS system, has been shown to provide highly accurate navigation with overall mean spatial navigation error of 0.35 mm, which is acceptable in dental implantology.[30] The accuracy in implant placement by the CNIS system (IGI) has also been illustrated in a recent study by Elian et al. who demonstrated a mean linear accuracy of less than 1 mm at both the implant neck and apical tip and the reported mean angular deviation of less than 4° for the implants placed via CNIS system that is, an accurate match between the planned implant and final implant was revealed.[31] In contrast, a mean linear accuracy ranging between 1.1 mm and 1.45 mm at the implant neck and between 1.41 mm and 2.99 mm at the implant apical tip along with a mean angular deviation ranging between 2° and 7.25° in the implants placed with stereolithographic guides has been reported.[3233] Based on the preceding studies, it can be assumed that CNIS system provides higher accuracy than the CGIS system. Yet, in one of the studies evaluating the accuracy of optical tracking versus stereolithographic system for implant placement, no statistically significant differences were found between the two systems.[34] Recently in 2014, accuracy of a dynamic CNIS system was compared with three commercial CGIS static systems and the use of an acrylic stent for implant osteotomy preparation. It was revealed that the dynamic and static systems provided superior accuracy versus a laboratory-made acrylic guide and that both dynamic and static systems showed an average error of <2 mm and 5°.[35]

Though CNIS technology (using optical tracking systems) has been widely used with superb accuracy but it also suffers the following limitations:[63637]

They are sensitive to reflections and interference with the line of sight between the sensors and the cameras that is, a line-of-sight between the tracking device and the instrument to be tracked has to be maintained, which is not always convenient especially with the typical seating arrangement of dental surgeon and assistant and hence may preclude tracking of instruments

More expensive and requires an expensive hardware

Requires rigorous intraoperative referencing

Significant learning curve.

However, compared with CNIS that can cost about $60,000-$200,000 (Rs. 75 lakhs to Rs. 118 lakhs), CGIS is less expensive and outsourcing is possible with CGIS, as a remote company can fabricate surgical template, omitting the need to purchase expensive hardware by the clinician.[37] In India, a computer guided surgical guide (excluding the cost of implant being placed) costs Rs. 20,000/- approximately, though the prices can vary depending on the complexity of situation. However, based on the 7 years of clinical experience in CNIS, Ewers et al., in 2004 revealed that handling of the software is quite easy due to a logical, self-explanatory menu structure which can be learned within a short time.[38] The authors also validated that CNIS is a promising technology, already successfully tested in routine clinical application, that can substantially contribute to an increase in quality and intraoperative safety for the insertion of implants.[38] Computerization of implant-dentistry has opened up new vistas and has eased implant placement in patients with complex problems following a significant alteration of the bony anatomy as a result of benign or malignant pathology of the jaws or trauma and in patients with physical and emotional problems (that limited the amount of time a patient could sit in a dental chair). Computerized-implant-dentistry being minimally invasive in nature has also enabled implant placement in patients with medical comorbidities (e.g. radiation therapy, blood dyscrasias).[39]

ROBOTIC-IMPLANT-DENTISTRY

Robots are expected to be more accurate and more reliable than a human being and can work as part of an interactive system, are immune to radiation and can be automatically programmed for documentation, evaluation and training protocols. As such, in the cranial area, robotic systems have already been considered for defined drilling of holes or implant beds with an automatic stop, for milling of the bone surfaces, for performing deep saw-cuts for osteotomies and allowing for the precise three-dimensional transportation of the subsequent bone segments or CAD/CAM transplant etc.[40] In fact, a partial section of robot-assisted dental surgery project has already been attempted to develop fully aided system on navigated, guided and assisted surgical performance.[41]

CONCLUSION

With significant achievements accomplished in the field of computerized implant-dentistry implant placement has become highly predictable, even in patients where implant surgery was contra-indicated formerly. As a result, attempts are now been made toward complete automation of implant-dentistry. Yet, keeping the limitation of high radiation dose, computerized implant-dentistry must be limited to anatomically complicated cases. Future tasks include advanced intraoperative imaging techniques for navigated surgeries along with sophisticated mechanized surgical tools and new robotic developments, which will revolutionize the field of implantology.