Exploring Effectiveness of Computer-Aided Planning in Implant Positioning for a Single Immediate Implant Placement

Single tooth immediate implant placement can be difficult due to the anatomy of the extraction socket, in particular the remaining buccal or facial alveolar bone.^1–3  The integrity of the facial alveolar bone and the primary stability of the immediate placed implant are perhaps two of the most essential factors in the short-term survival and longevity of immediate implants.^4,5  The facial alveolar bone, anatomically known as bundle bone, is a cortical bone that has limited intrinsic vasculature.^3,6–8  It is recommended that the implant fixture be placed lingual to the facial alveolar bone because contacting the facial alveolar bone or placing an implant too close to the facial alveolar bone can result in resorption of the facial alveolar bone.^2,3,9  On average, the thickness of the facial alveolar bone in the esthetic area is approximately 1 mm.¹⁰  Immediate extraction and implant placement can also present challenges to clinicians due to the close proximity of the roots of the adjacent teeth and anatomical structures such as the incisive canal, maxillary sinuses, mental foramen, and inferior alveolar canal.

Rapid advancement of cone-beam computed tomography (CBCT) scans^11–14  and computer-aided implant planning programs is believed to enhance CBCT technology and improve the accuracy of implant placement.¹⁵  Planning implant positions in silico (using computerized implant planning software) allows clinicians to visualize the implant positions in relation to the extraction socket and adjacent anatomical structures in 3 dimensions. The in silico planning allows the surgical operator to examine and evaluate the existing anatomical structures along with the positions of implant fixtures and definitive prostheses. Implant-guided surgery, using computer-aided design/computer-aided manufacturing or stereolithographic technology to fabricate a surgical guide, would allow an accurate placement of an implant into the planned position.^14,15  However, for a single immediate implant, in most cases, guided surgery can be difficult due to the available space between the adjacent teeth that can limit the use of a metal tube or cylinder that is required to guide the implant drills.^16–18  Financial constraint can also prohibit the use of guided surgery for a single tooth implant. The objective of this study is to determine whether immediate single implant placement can be performed accurately using a 3-dimensional (3D) computer implant planning program. Accuracy was determined by using measurements the variations between the planned immediate implant position and the actual implant position in the pre- and postoperative CBCT scans.

Subjects were part of the study previously described.³  The study clinical protocol was approved by the Institutional Review Board (IRB study 10-0286). Written consent was obtained from all subjects. Twenty subjects were initially recruited at the University of North Carolina (UNC) School of Dentistry; however, 1 subject was lost in the follow-up and another subject's implant failed. The inclusion and exclusion criteria were described in our previous studies^2,3  and are summarized in Table 1.

The details of the treatment protocol were described previously (Figure 1).^2,3  The planning of implant positioning and implant size was performed using SimPlant Pro 15 (Dentsply, Waltham, Mass). Immediately after the surgery, a postoperative periapical radiograph was taken. Postoperative CBCT scans were taken immediately after surgery for 4 cases that required immediate determination of the implant position (eg, close to adjacent structures or teeth). In all cases, follow-up CBCT scans were taken 12 months after the implant was placed. The distribution of implant locations is described in Table 2.

Using the adjacent teeth as the point of reference, the pre- and postoperative CBCT scans were examined, and the relationships between the planned implant fixture and actual implant position and adjacent teeth were evaluated using SimPlant Pro 15. The brief protocol for implant planning using the preoperative CBCT scans is described here. A 3D model was created in SimPlant using DICOM files from preoperative CBCTs. First, the panoramic curve was made approximately in the middle of the remaining teeth and implant site, facio-lingually, and in the middle of the root of the remaining natural teeth, and the designated extracted tooth was examined. An appropriate implant type, width, and length was chosen and placed in silico using SimPlant. The planned implant position was determined.³  Attempts were made to avoid adjacent roots and important anatomical structures. Appropriate mesio-distal dimensions from adjacent teeth were determined and measured. The angulation of the implant fixture in relation to the clinical crown was also determined and measured (Figure 2). Most importantly, all implants were planned to have at least 1–2 mm or more of a gap between the cervical portion of the implant fixture and the facial alveolar bone plate. To determine the actual positioning of the placed implant, the postoperative CBCT scans were used to create the follow-up 3D model (Figure 3). A similar panoramic curve to the planning curve was made. Attempts were made to position the panoramic plane in the similar plane as in the preoperative model.

The facial-lingual or axial angulation profile of the planned or actual implant fixture was measured using the angulation of the long axis of the implant and the long axis of the crown. We used the incisal edge for the incisors and tip of the cusp for the canines. For the premolars, we used the midpoint between the facial and lingual cusps as a reference point (Figures 2a and 3a). The facio-lingual positioning of the planned or actual implant was determined using the horizontal plane at the most cervical part of the implant to the plane made by the most lingual part of the adjacent teeth (Figures 2b and 3b). The mesio-distal distances of the planned or actual implant fixture were evaluated using the distance from the most cervical portion of the implant fixture to the plane of the adjacent teeth (Figures 2c and 3c). Differences between pre- and postoperative measurements were summarized with box plots and 95% CIs for means of within-subject paired differences.

Table 3 provides the mean and 95% CI of all measurements made. As the CI contains zero in every case, there was no statistically significant difference between the planned and actual implant positions in all dimensions. Figure 4 shows the box plots of the 3 distance measurements. The circles in the box plots denote a total of 3 outliers from 3 different subjects.

This study is one of a few studies to look at the planned position of an implant fixture compared with the actual implant fixture position in a single tooth immediate implant placement.¹²  Most studies have been done on the accuracy of guided surgery in multiple implant placement cases.^15,19,20  Limited information exists to date on the accuracy of implant placement using implant planning software without a surgical guide in limited situations. Implant planning software can help clinicians plan their cases in a 3D manner. This allows surgeons to practice their implant placement and examine the relationship between clinical anatomy seen in the oral cavity (eg, clinical crowns of the affected tooth and adjacent teeth) and the osseous structures seen in the 3D radiographic model. 3D in silico planning, in theory, should help surgeons to achieve a more accurate implant positioning.^{16,17,19–23}  This study demonstrates that computer-aided implant planning of a single tooth may be beneficial even without guided surgery.^20,24 

We hypothesized that the actual implant position would be displaced facially and would have a different facio-lingual angulation from the planned position.^{1,12,19,24,25}  The facial displacement of an immediately placed implant was thought to be the result of 2 factors: the smaller diameter of the final osteotomy drill and the lack of contact on the facial aspect of the implant fixture. However, there was no statistical difference between the positions of the planned implant and the placed implants. Our study (Table 1 and Figure 4) shows that the majority of implant displacements are within 0.5 mm in the mesio-distal. In the facial-lingual dimension, while there is no statistical difference, the majority of actual implant positions are slight lingual, within 1 mm. For the angulation difference, there is a slight trend that the implant will flare a little facially. Note that CBCT imaging for postimplant placement can produce artifacts that may be difficult to visualize and measure the peri-implant bone. We therefore used the adjacent teeth as a landmark for all our measurements to minimize the artifact effects of implant metal fixture.

The implant fixture is almost always larger than the final drill used to prepare the implant osteotomy site. For instance, in the Zimmer system (Zimmer Dental, Carlsbad, Calif), an implant with 4.7-mm coronal width would be placed after the final drill with 3.8-mm width. Therefore, when placing an implant into the site with no contact facially, the implant would in theory be displaced slightly facially. To prevent the expected facial displacement, we used only the final 1–2 drills to prepare the osteomy site and based the angulation of the implant site as planned in silico. Using multiple smaller drills can potentially create more displacement or an overly lingually corrected implant positioning. In the case of thick lingual bone (at least 1.5–2 mm), we also used the implant osteotomy tap to create threads in an appropriate angulation and position for the implant fixture. We believe that this final 1–2 drill protocol and implant osteotomy site thread tapping are perhaps the key factors in ensuring implant position closest to the planned position. Although this technique appears to work well in our hand with a taper screwed–type implant, we do not know whether it will be applicable to implant fixtures with different configurations. In contrast to the facio-lingual positioning, we examined the mesio-distal position of the implant as a control. In the esthetic zone, positioning the implant in the mesio-distal dimension is relatively simple. The adjacent teeth provide a substantial framework for the osteotomy preparation. Our results are therefore consistent with this idea. Note also that all implant surgeries in this study were done by 2 practitioners (S.B. and B.H.). Having 2 experienced implant surgeons performing the surgery for each case might have improved the accuracy of our implant positioning.

Placing an immediate implant can be further complicated by the proximity of the adjacent teeth and important anatomical structures, such as inferior alveolar canals and maxillary sinuses. Although postoperative CBCTs have become more popular in the evaluation of peri-implant bone after healing,^{11–13,15,26,27}  we believe that for immediate postimplant placement, small volume CBCTs can be helpful in such cases. Two-dimensional radiographs such as panoramic and periapical radiographs may not provide sufficient information when several structures are superimposed over the implant area. Immediate postoperative CBCTs can therefore allow immediate repositioning of the implant and may prevent future complications due to the violation of an immediate implant to adjacent structures.

Computer-aided implant planning can be useful in the diagnosis and treatment planning for immediate single implant therapy. Careful examination of the CBCT scans using computer-aided 3D coupled with 1-to-2 drill osteotomy preparation protocol may allow appropriate placement of immediate taper screwed implants and reduce the displacement of the implant fixture without guided surgery. Creating an implant thread may also help control the implant positioning. Small volume CBCT scans can be an effective tool in treatment planning and evaluating the position of a single immediate implant after placement.

Abbreviation

CBCT

cone-beam computerized tomography

There was no direct compensation for this study. Zimmer Dental, Inc provided the implant fixtures for this study; however, the sponsor had no role in the writing and publication of this manuscript. However, S.B. is a Zimmer Institute lecturer. In addition, Zimmer Dental, Inc does not directly support salary for any authors; however, Zimmer Dental, Inc was supporting the work of S.B. through unrestricted research and educational grants.

This work was partly supported by the American Academy of Implant Dentistry (AAID) Foundation with a grant to S.B.