Diagnosis and Treatment Planning for Implant Prostheses
Prior to planning implant restorations, it is critical to assess the medical and dental history and ensure that there are no contraindications to the placement of dental implants. For any implant restoration to be successful, it is critical to plan and place implants accurately.69,70 Ideally a treatment prosthesis should be fabricated for every patient. This prosthesis helps the dentist gauge the restorative space (Figure 9), the lip support, phonetics, OVD, the relationship between the edentulous ridge and the intended position of the prosthetic teeth, the intended design of the definitive restoration, esthetics and expectations of the patient. The restorative dentist should decide the type and the design of the prosthesis before implant placement. If the patient is satisfied with the treatment prosthesis, it can be converted into a radiographic guide (by adding fiduciary markers or painting radiopaque ink) (Figure 10) and used to plan implant positions and angulations based on the intended position of the prosthetic teeth.70
Boley gauge used to evaluate the vertical restorative space at the location of the right first premolar.
Fiduciary markers incorporated in the treatment prosthesis.
CBCT Assisted Implant Planning
It is beneficial to plan implants using the data generated from 3-dimensional (3-D) Cone beam computed tomography (CBCT) scans and guided implant planning software.70-72 Usually two CBCT scans are made (Dual scan protocol). The first scan is made of the patient with the radiographic guide placed in the oral cavity, and the other scan is made of the radiographic guide itself. Using the implant planning software, the raw data is converted into DICOM (Digital Imaging and Communications in Medicine) data and the data from the two scans is combined into one to treatment plan the implants in relation to the bone and prosthesis. This has helped change the osseous-driven approach to a combination of osseous- and prosthetic-driven approach for implant placement.70-73
The planning and placement of the implants should vary depending on the design of the prosthesis. For an implant-supported removable restoration, the long axis of the implants should emerge from the lingual aspect of the prosthetic teeth since it is the bulkiest part of the prosthesis. For a fixed implant restoration, the implants should emerge (the long axis of the implant) through the center of the prosthetic teeth. Implants should be planned such that they are parallel to each other and perpendicular to the occlusal plane (Figure 11).
Implants planned parallel to each other.
The anteroposterior (A-P) spread is the mesiodistal distance between the posterior edges of the distal implants and the midpoint of the most anterior implant in an arch.74,75 An A-P spread that minimizes the distal cantilevers and establishes stability may contribute to implant and prosthesis success.74,75 Hence, it is recommended to maximize the A-P spread of implants.74,75 When adequate A-P spread of the implants cannot be achieved (due to inadequate bone) implants can be tilted posteriorly to optimize the A-P spread. Multi-unit angle correction abutments can be used to correct the angulation of the tilted implants.
A minimum of 4 and 6 implants are required for a maxillary removable and a fixed implant prosthesis, respectively. A minimum of 1 (or 2) and 4 implants (with a good anteroposterior spread) are required for mandibular removable and fixed implant prosthesis, respectively. Incorporating additional implant/s than the bare minimum requirement is advantageous as it aids in providing extra support and also prevents the need for a subsequent surgical procedure if an implant is lost.
Another factor that must be evaluated during implant planning is the available vertical restorative space.28,29 Vertical restorative space can be calculated on the CBCT scan by measuring the distance between the platform of the planned implant and the occlusal surface of the prosthetic tooth (Figure 12).29 Fabrication of a prosthesis in the presence of inadequate restorative space may lead to physiologically inappropriate contours, structurally weak prostheses, esthetic compromise, encroachment into freeway space, and/or suboptimal retention and stability of the treatment result.28,29 When the restorative space is inadequate, clinical procedures may be implemented to improve vertical space availability. These procedures include alveoloplasty, intentional increase in OVD, occlusal plane repositioning, and management of attachment selection.28 These procedures should be implemented prior to implant placement when treatment options are being considered.28
Vertical restorative space calculated on the CBCT cross-sectional image.
Surgical Guide and Guided Surgery
Anchor pins may be planned to help stabilize the surgical guide during the osteotomy procedures. Combining the CAD/CAM technique, digital implant planning can be applied to clinical practice using 3-D surgical guides.71-73 Once the plan has been approved the CAD (computer-assisted design) files may be sent to the 3D surgical guide manufacturer for the fabrication of the 3D surgical guide (Figure 13).
3D surgical guide.
The surgical guide should be tried in the mouth and adjusted to ensure that it completely seats in the mouth. The osteotomy, as well as implant placement, can be accomplished through the 3D guide following the manufacturers’ recommended protocol (Figure 14). The surgical guide directs the osteotomies and placement of implants in the X, Y, and Z-axis. Following implant placement, cover screws (requires second-stage surgery) or healing abutments may be attached to the implants. At this time, the treatment denture may be adjusted as needed and then relined with a soft lining material.
Implants placed through the 3D surgical guide.
Note: The implant placement through the guide is exactly as planned in the software. It is so accurate that a cast may be retro engineered using the surgical guide and a transitional restoration can be fabricated on the cast prior to the placement of implants. If a transitional fixed restoration (pre-fabricated by the laboratory) is planned, the prosthesis is adjusted, the temporary abutment cylinders are picked up clinically, the prosthesis is finished and polished, screws are tightened and screw access holes are plugged with Teflon tape and sealed with composite resin.