Miniscrew impants as temporary anchorage devices (TADs) are becoming more popular in orthodontic tretment. Their ease of use allows orthodontists to place them in locations in the mouth that are convenient for orthodontic treatment mechanics. The aims of this study were to evaluate the location of TADs placed during orthodontic treatment and to relate the placement to the surrounding dentoalveolar structures.
Three-dimensional cone-beam computed tomography scans were taken before and after placement of the TADs over a 6-month period as part of routine clinical protocol. The following parameters were recorded: placement site, length of the TAD in the alveolar bone, amount of contact with the periodontal ligament, and interroot distance between TADs.
Thirty-five TADs (19 in the maxilla, 16 in the mandible) were evaluated. The mean lengths of the TADs in alveolar bone were 5.29 ± 1.39 mm in the maxilla and 4.60 ± 0.86 mm in the mandible. The amounts of contact with the periodontal ligaments were 2.54 ± 0.81 mm (n = 13) in the maxilla and 2.72 ± 0.49 mm (n = 10) in the mandible. The interroot distance measurements were 2.78 ± 0.76 mm (n = 15) and 5.19 ± 4.42 mm (n = 16) in the maxilla and the mandible, respectively. Paired t tests indicated a significant difference in the interroot distance for mandibular teeth.
Three-dimensional cone-beam computed tomography technology allows better visualization of TAD placement. Clinicians can expect 71.2% of the length of the screw section of the TAD to be embedded in the alveolar bone; the percentage is often higher in the maxilla than in the mandible. Of the 35 TADs, 65.2% were in contact with the periodontal ligament. There appears to be more space for TAD placement in the mandible than in the maxilla.
Temporary anchorage devices (TADs) are biologically compatible devices used in orthodontics to provide absolute anchorage to facilitate the movement of teeth. They are mechanically retained in bone and removed after they have served their purpose. They can be placed transosteally, endosteally, or subperiosteally, and are either anchored in cortical bone, providing mechanical retention, or allowed to osseointegrate, providing biochemical anchorage. In 1945, Gainsforth and Higley used vitallium screws in dogs in an attempt to retract their canines; although the experiment was not successful, it suggested the possibility of using metallic screws for anchorage to aid in tooth movement. The current use of TADs came about after the evolution of osteointegrated implants by Brånemark et al. The first successful clinical TAD placement was done in 1983 by Creekmore and Eklund, with vitallium screws used to treat a patient with an overbite. Today, TADs are used for restorative procedures and in many procedures that previously required orthognathic surgery. Some authors have proposed that the use of TADs decreases orthodontic treatment time and also provides clinicians a choice of extracting compromised teeth instead of healthy premolars. A previous study attempted to quantify the amount of bone for the placement a TAD, but, despite extensive use in orthodontics, little has been recorded in the literature to determine the position of the TAD immediately after its placement.
Since its development in the early 1990s, cone-beam computed tomography (CBCT) has been used extensively in orthodontics, oral maxillofacial surgery, and several other specialties of both dentistry and medicine. In orthodontics, 3-dimensional (3D) CBCT imaging has been used to assess pretreatment and posttreatment dentoskeletal relationships, the location of impacted canines, and airway analysis. In dentistry, it is used extensively in implant planning and stent fabrication. Some experts have argued that the use of this imaging modality could be routine in orthodontics for diagnosis and treatment planning because of the number of conventional 2-dimensional radiation exposures and the amount of clinical information available from 3D views.
The aims of this study were to evaluate the location of TADs placed during orthodontic treatment and to relate TAD placement to the surrounding dentoalveolar structures.
Material and methods
Three-dimensional CBCT records were obtained in the Houston area immediately after TAD placements in all patients who required them. Records were collected over 6 months comprising all patients treated during that period of time.
This was made possible because a clinical protocol had been established so that patients who were accepted for orthodontic treatment had pretreatment, midtreatment, and posttreatment CBCT records for all orthodontic diagnoses and treatment evaluations. The evaluations of TAD placements were obtained as part of this routine clinical protocol.
Ethical approval to retrospectively analyze the data was obtained from the Institutional Review Board of the University of Texas Health Science Center; local consent was obtained as part of chart records.
The TAD used in this study was the Quattro from Mondeal Orthodontic Anchorage System (GAC International, Bohemia, NY). It is a self-drilling, self-tapping, polished titanium screw with a tube slot on the head that allows for 3D control. The dimensions of the screw were diameter, 1.5 mm, and length, 7 mm. All TADs were placed under the supervision of experienced clinicians. The TAD placement site was marked after measurements were made on panoramic projection radiographs obtained from the CBCT. Topical anesthetic was used, and the TAD was placed by a clinician who was either supervising faculty and a resident.
The CBCT imaging device was the Galileos (Sirona, Bensheim, Germany). This system emits a radiation dose between 29 and 68 μSv according to the manufacturer. It has a scan time of 14 seconds and captures the maxillomandibular region in a 180° rotation within a radiation-detector configuration. The field of view has a spherical diameter of 16 cm. The voxel size is between 0.15 and 0.30 mm, and the grayscale is 12 bit.
The reconstruction program calculated the entire image volume from the data of the 200 exposures generated from a pulsed scan; after 3 minutes, the image appeared on the screen platform for comprehensive diagnostics. Image manipulation was carried out with the proprietary software, Galaxis (Sirona). To increase the accuracy of the assessment, all 3 planes (sagittal, axial, and coronal) were used.
The following parameters were measured from the CBCT volumes.
Placement site: the regions for the placement of TADS were marked as (I) anterior incisal region, (II) distal region from the canine, (III) premolar region (between 2 premolars and distal of the second premolar), and (IV) molar region.
Length of TAD (LT) placement in alveolar bone. This measurement was made from the point of embedment of the tip of the TAD in the alveolar bone to the cortical margin of the alveolar bone as shown on the CBCT.
Amount of contact with the periodontal ligament (CPDL). This measurement was made of the TAD in direct contact with the periodontal ligament (PDL). Measurements were made on the visible portion where the TAD touched the PDL space.
Interroot (IR) distance between TADS. This was made from the outline of the roots at the level of TAD placement.
Figure 1 illustrates these parameters. Further analysis of the measurements was made to determine whether there were any differences in parameters 2 through 4 for the maxilla and the mandible.
The data were tested for significant differences by using independent-sample, 2-tailed Student t tests with SPSS software for Windows (version 16.0, SPSS, Chicago, Ill).
The results were obtained by 2 trained evaluators (M.G.M. and H.H.). Paired t tests to determine interexaminer variability carried out on a random sample of 10 TAD measurements showed no significant differences ( P <0.05) between recordings, indicating good consistency between the evaluators and also that the parameters could be measured reliably.
Once all the results were obtained, a mean score for each parameter was calculated. These are summarized in Tables I to III .
|Region I||Region II||Region III||Region IV||Total|
|n||Location||Mean (mm)||SD (mm)|