By Robert Waugh, DMD, MS, Athens, Ga
When it comes to placing TADs in difficult areas, CBCT technology and radiopaque markers provide the diagnostic views necessary for 3D treatment planning and sequencing. In cases involving the temporary replacement of a missing maxillary lateral incisor, my overall three-stage treatment sequence includes:
- A focused-field CBCT scan of the patient’s anterior maxilla while wearing a flipper prepared with a barium-laced acrylic marker;
- TAD placement and analogue impressions; and
- Delivery of an acrylic pontic over the TAD to restore the space for the missing lateral.
The focus here deals largely with the first of these three steps.
|Figure 1: The hole is filled with an acrylic mixed with barium sulfate to create a radiopaque 3D cylindrical marker for the scan. Figure 2 and 3: The radiopaque marker is located on the 3D volume to provide a reference for length and width measurements as well as for simulation of the virutal TAD insertion.|
For patients with congenitally missing anterior teeth approaching the final stages of orthodontic treatment, a consultation is scheduled to review treatment options. Among the options available are single tooth implants for non-growing patients and non-integrating miniscrew TAD replacement for growing patients. Given that most of my patients are still growing when they finish treatment, there is a demand for temporary implants or TADs until a definitive implant can be placed and permanently restored. Once the recommendations and risks of interim TAD-based anterior tooth replacement are understood, the braces are removed and an immediate-insertion Essix retainer containing an acrylic pontic is delivered.
A second impression is also taken for a modified flipper appliance (acrylic removable partial denture) fabrication. This is initially an acceptable solution to the patient for esthetics and retention, although a non-removable replacement is expected for the next few years before the eventual implant restoration.
The acrylic appliance was originally fabricated by a dental prosthetics lab with the addition of a radiopaque marker. The lab technician modifies the appliance by preparing a 2-mm-diameter hole over the highest point of the alveolar ridge, centered in the space for the missing tooth. The hole is filled with a plug of acrylic mixed with barium sulfate to create a radiopaque three-dimensional cylindrical marker for the scan (Figure 1).
Next, a focused-field scan (CS 9000C 3D system, .076 voxel) is taken of the patient’s anterior maxilla with the modified flipper. Using Carestream Dental’s 3D software, the radiopaque marker is located on the 3D volume to provide a reference for length and width measurements (Figure 2) as well as for the simulation of the virtual insertion of the TAD (Figure 3). The appliance thickness or marker height references the occlusal clearance of the TAD head and measurements show the soft-tissue thickness, located spatially between the apical limit of the marker and the height of the bony alveolar ridge. In the absence of magnification, these measurements are made accurately using the trans-axial view on the Curved Slicing tab for the precise selection of the ideal TAD dimensions. Virtual TAD placement is accomplished using the same software on the 3D surface volume to create custom implants for the simulation of the intended labio-lingual position and axial inclination of the TAD(s) (Figure 4).
Making a difficult procedure easier for patients and practitioners requires the correct materials and technologies. I have found the creative use of CBCT technology to be an extremely valuable tool in developing predictably successful clinical procedures for my patients. OP