The validity of two methods of mandibular superimposition: a comparison with tantalum implants

Sagittal and Vertical Growth of the Maxillo-Mandibular Complex in Untreated Children: A Longitudinal Study on Lateral Cephalograms Derived from Cone Beam Computed Tomography

The aim of this longitudinal study was to evaluate the sagittal and vertical growth of the maxillo–mandibular complex in untreated children using orthogonal lateral cephalograms compressed from cone beam computed tomography (CBCT). Two sets of scans, on 12 males (mean 8.75 years at T1, and 11.52 years at T2) and 18 females (mean 9.09 years at T1, and 10.80 years at T2), were analyzed using Dolphin 3D imaging. The displacements of the landmarks and rotations of both jaws relative to the cranial base were measured using the cranial base, and the maxillary and mandibular core lines. From T1 to T2, relative to the cranial base, the nasion, orbitale, A-point, and B-point moved anteriorly and inferiorly. The porion moved posteriorly and inferiorly. The ANB and mandibular plane angle decreased. All but one subject had forward rotation in reference to the cranial base. The maxillary and mandibular superimpositions showed no sagittal change on the A-point and B-point. The U6 and U1 erupted at 0.94 and 1.01 mm/year (males) and 0.82 and 0.95 mm/year (females), respectively. The L6 and L1 erupted at 0.66 and 0.88 mm/year (males), and at 0.41 mm/year for both the L6 and the L1 (females), respectively.

3D Mandibular Superimposition: Comparison of Regions of Reference for Voxel-Based Registration

Introduction

The aim was to evaluate three regions of reference (Björk, Modified Björk and mandibular Body) for mandibular registration testing them in a patients’ CBCT sample.

Methods

Mandibular 3D volumetric label maps were built from CBCTs taken before (T1) and after treatment (T2) in a sample of 16 growing subjects and labeled with eight landmarks. Registrations of T1 and T2 images relative to the different regions of reference were performed, and 3D surface models were generated. Seven mandibular dimensions were measured separately for each time-point (T1 and T2) in relation to a stable reference structure (lingual cortical of symphysis), and the T2-T1 differences were calculated. These differences were compared to differences measured between the superimposed T2 (generated from different regions of reference: Björk, Modified Björk and Mandibular Body) over T1 surface models. ICC and the Bland-Altman method tested the agreement of the changes obtained by nonsuperimposition measurements from the patients’ sample, and changes between the overlapped surfaces after registration using the different regions of reference.

Results

The Björk region of reference (or mask) did work properly only in 2 of 16 patients. Evaluating the two other masks (Modified Björk and Mandibular body) on patients’ scans registration, the concordance and agreement of the changes obtained from superimpositions (registered T2 over T1) compared to results obtained from non superimposed T1 and T2 separately, indicated that Mandibular Body mask displayed more consistent results.

Conclusions

The mandibular body mask (mandible without teeth, alveolar bone, rami and condyles) is a reliable reference for 3D regional registration.

Assessing lower incisor inclination change: a comparison of four cephalometric methods

OBJECTIVE

Cephalometric inclination change of the lower incisors during orthodontics is used to assess treatment outcome. The lower border of the mandible is commonly used for measuring inclination change, despite it being subject to remodelling in growing patients. Superimposition of radiographs using Björk's 'stable structures' is intended to exclude these growth changes. We tested whether there is a significant difference for three commonly used methods to assess inclination change induced by orthodontic treatment (Me-Go, Go-Gn, the tangent to the lower border of the mandible) when comparing it to Björk's 'stable structures'.

METHODS

Björk's superimposition does not allow measuring incisor inclination changes directly; hence, one pre- and mid-treatment cephalogram of 39 growing orthodontic patients were superimposed in this retrospective study. The radiographs were taken at least 1 year apart (120 weeks; SD = 34.4). Patients undergoing growth modification treatment were excluded. Standardized cephalograms were hand traced and changes in lower incisor inclination, using the three mandibular planes, were compared to the changes obtained by anatomical superimposition of Björk's 'stable structures'.

RESULTS

Linear regression showed good intra-class correlation (ICC) between all methods. ICC was 0.96 for Me-Go, 0.94 for Go-Gn, and 0.92 for the lower border tangent. ICC for operator reliability was 0.99.

LIMITATIONS

Measurement errors affect all investigations of both analogue and digital radiographs, but movement artefacts particularly apply to the latter. Cephalometry uses two-dimensional measurements of a three-dimensional subject, which can lead to further inaccuracies. These limitations have to be taken into account when interpreting the results of our investigation.

CONCLUSION

Data obtained from Björk's superimposition did not vary significantly from the other more commonly used techniques (Me-Go, Go-Gn, and the tangent to the lower border of the mandible). Remodelling of the lower border of the mandible was insignificant for the time period investigated.

A reflection on radiographic cephalometry: the evaluation of sagittal discrepancy

A critical review is presented of the basic properties and applications of cephalometry as a clinical tool with a focus on the evaluation of sagittal discrepancy. Diagnostic cephalometric assessments are subjective and not based on evidence. To assess individual skeletal and/or facial soft tissue form subjectively, selected norms are used. Norms have been developed for various ethnical groups to improve clinical applicability, but subjectivity remains. That subjectivity precludes application of a modern review system, making the present review a personal account. The cephalometric evaluation of sagittal discrepancy finds its historic origin in the Angle classification. Recent publications try to improve accuracy in classifying sagittal discrepancy. It remains unclear in what sense such efforts influence treatment decisions and/or treatment effect. Almost all selected landmarks are located on or dependent upon periosteal/endosteal bone image contours. Their homology is based on circumstantial reasoning and stability over time, which is implicitly assumed. However, implant growth studies and histological investigations show most landmarks to be unstable, as they are involved in displacement and bone remodelling. These landmarks are therefore heterologous when used for individual evaluation of change over time. Notwithstanding the above-indicated limitations, diagnostic cephalometric assessments are clinically useful and help to develop perceptions of balance and harmony and communication between colleagues and patients. There is no evidence-based method to prefer one particular diagnostic method. Landmark location accuracy and geometric issues do not play a decisive role. The subjective characteristic of diagnostic evaluations limits their power to size/shape comparisons. Structural superimposition is the valid biologically evidence-based method to provide advanced insight in individual growth and/or treatment changes and their variations.

Trabecular metal endoprosthetic limb salvage reconstruction of the lower limb

Currently, porous tantalum (trabecular metal) implants are widely accepted and frequently used for primary and revision hip and knee replacement surgery. This study examines the results of porous tantalum endoprostheses used to reconstruct large skeletal defects following resection of bone tumors. Seven custom tantalum implants were used to reconstruct 7 patients following resection for skeletal sarcomas in the femur and proximal tibia. Patient ages ranged from 13 to 71, with a mean of 34 years. Minimum patient follow-up was 6 years. The average Musculoskeletal Tumor Society functional evaluation score was 95 % of normal. There were no infections, hardware failures, or adverse events. One implant was revised 98 months post insertion because of fibrosis, loss of motion and loosening. In this small clinical series, the use of porous tantalum for limb salvage reconstruction is shown to be safe, to successfully provide osteointegration and soft tissue ingrowth, and to facilitate return of limb girdle muscle function.

Cephalometric superimpositions

OBJECTIVE

To test the hypothesis that there is no difference between the information produced by superimposition of serial lateral headfilms on anatomical structures and that produced by superimposition on metallic implants according to the protocols of Björk.

MATERIALS AND METHODS

Serial cephalograms of 10 untreated subjects who had tantalum implants placed in the maxilla and mandible during childhood were analyzed. Headfilms taken at six consecutive stages of cervical vertebral maturation (CS1-CS6) for six female and four male subjects were used. Tracings were superimposed according to the methods of superimpositions advocated by the American Board of Orthodontics (ABO). In addition, superimpositions along the inferior border of the mandible were performed. Finally, superimpositions of serial tracings on stable intraosseous implants were made to determine the actual growth and remodeling patterns of the maxilla and mandible.

RESULTS

The ABO maxillary superimposition method underestimates the vertical displacement and overestimates the forward movement of maxillary landmarks. Superimposing on the internal cortical outline of the symphysis and the inferior alveolar nerve canals generally approximates the mandibular superimposition on implants, although the lower anterior border of the symphysis may be a preferable area of superimposition. Superimposition on the lower border of the mandible does not reflect accurately the actual pattern of growth and remodeling of the mandible.

CONCLUSIONS

When analyzing serial headfilms, erroneous information concerning patterns of bone growth and remodeling can be obtained if convenient, but biologically incorrect superimposition protocols are used. In addition, tooth movements measured can be distorted significantly depending on the method of superimposition.

The validity of superimposing oblique cephalometric radiographs to assess tooth movement: an implant study

Assessment of the exact position of the posterior teeth on lateral headfilms is of limited validity because of the superimposition of the 2 sides. Lateral headfilms are also of limited use for evaluating orthodontic tooth movement, especially in cases of asymmetric mechanics. To solve this problem, the oblique cephalometric radiograph, which brings only 1 side of the image into focus, was introduced. We evaluated whether the projection of the cranial base could be used for evaluating facial growth and whether structures that were stable relative to the implants could be identified and thus replace the implants in future evaluations. Thirty sets of headfilms from growing patients with metallic implants were analyzed. Three types of superimpositions were performed. Displacement of the metallic implants in the maxillary complex and the mandible with respect to the superimposed structures of the cranial base was evaluated. When the development of the lateral parts of the facial skeleton was evaluated in relation to the cranial base, the reproducibility of the superimpositioning was significantly better in the vertical-S(e) = 0.41-than in the horizontal plane of space-S(e) = 1.35). The error of the method when superimposed on the stable structures in the maxillary complex varied between 0.31 and 0.72 and did not differ in the vertical and sagittal directions. In the mandible, the stable structures suggested for superimposition of the lateral headfilms were applicable on the oblique cephalometric radiograph-S(e) = 0.33-0.57. Oblique projection is recommended when individual analysis of the 2 sides is needed.