Glenn T. Sameshima

Assessment of root resorption and root shape: periapical vs panoramic films.

A radiographic examination is an essential part of the diagnostic process in orthodontics. However, what radiographs are needed to properly evaluate root shape and position? Most clinicians order panoramic or periapical radiographs in addition to the cephalometric radiograph. The purpose of this study was to find out whether one type of film is more accurate than the other in the pretreatment evaluation of root shape and the posttreatment computation of apical root resorption. Pretreatment and posttreatment panoramic films and full-mouth periapical films from 42 patients who completed fixed orthodontic treatment were assessed for tooth length and root shape. Panoramic films showed significantly greater average apicaL root resorption than periapical films for the 743 teeth surveyed. The greatest differences were found in the lower incisors, the least in the maxillary incisors. Classification of root shape was significantly different between the 2 types of radiographs. Root dilacerations and other abnormal shapes, clearly visible on periapical films, often appeared normal on panoramic films. The findings strongly suggest that root shape is much harder to assess on panoramic films. We conclude that, in cases where the apices are obscured or other factors are present that might suggest higher risk for root resorption or vertical bone loss, periapical films should be ordered. The use of panoramic films to measure pre- and posttreatment root resorption may overestimate the amount of root loss by 20% or more.

Two- and Three-dimensional Orthodontic Imaging Using Limited Cone Beam–Computed Tomography

Considerable progress has been made in diagnostic, medical imaging devices such as computed tomography (CT). However, these devices are not used routinely in dentistry and orthodontics because of high cost, large space requirements and the high amount of radiation involved. A device using computed tomography technology has been developed for dental use called a limited cone beam dental compact-CT (3DX). The aim of this article is to demonstrate the usefulness of 3DX imaging for orthodontic diagnosis and treatment planning. We present three cases: (1) one case shows delayed eruption of the upper left second premolar, (2) the second case shows severe impaction of a maxillary second bicuspid; and (3) the third case shows temporomandibular joint disorder (TMD). In the tooth impaction cases, the CT images provided more precise information than conventional radiographic images such as improved observation of the long axis of the tooth, root condition, and overlap with bone. In the TMD case, clear and detailed temporomandibular joint images were observed and pre- and posttreatment condylar positions were easily compared. We conclude that 3DX images provide useful information for orthodontic diagnosis and treatment planning.

A Finite Element Model of Apical Force Distribution From Orthodontic Tooth Movement

This study was undertaken to determine the types of orthodontic forces that cause high stress at the root apex. A 3-dimensional finite element model of a maxillary central incisor, its periodontal ligament (PDL), and alveolar bone was constructed on the basis of average anatomic morphology. The maxillary central incisor was chosen for study because it is one of the teeth at greatest risk for apical root resorption. The material properties of enamel, dentin, PDL, and bone and 5 different load systems (tipping, intrusion, extrusion, bodily movement, and rotational force) were tested. The finite element analysis showed that purely intrusive, extrusive, and rotational forces had stresses concentrated at the apex of the root. The principal stress from a tipping force was located at the alveolar crest. For bodily movement, stress was distributed throughout the PDL; however, it was concentrated more at the alveolar crest. We conclude that intrusive, extrusive, and rotational forces produce more stress at the apex. Bodily movement and tipping forces concentrate forces at the alveolar crest, not at the apex.

Oropharyngeal airway changes after rapid palatal expansion evaluated with cone-beam computed tomography

INTRODUCTION The aims of this retrospective study were to use cone-beam computed tomography (CBCT) to assess changes in the volume of the oropharynx in growing patients with maxillary constriction treated by rapid palatal expansion (RPE) and to compare them with changes in age- and sex-matched orthodontic patients. METHODS The experimental group consisted of 24 patients (mean age, 12.8+/-1.88 years) with maxillary constriction who were treated with hyrax palatal expanders; the control group comprised 24 age- and sex-matched patients (mean age, 12.8+/-1.85 years) who were just starting regular orthodontic treatment. Beginning and progress CBCT scans, taken in the supine position, were analyzed with software to measure volume, length, and minimal cross-sectional area of the oropharyngeal airway. The 2 groups were compared with paired t tests. RESULTS Only retropalatal airway volume was found to be significantly different between groups before treatment (P = 0.011), and this difference remained after treatment (P = 0.024). No other statistically significant differences were found relative to changes in volume, length, or minimum cross-sectional area of the oropharyngeal airway between the groups, but the molar-to-molar width after RPE increased significantly compared with the controls (P <0.001). CONCLUSIONS Narrow oropharyngeal airways in growing patients with maxillary constriction was demonstrated. But there was no evidence to support the hypothesis that RPE could enlarge oropharyngeal airway volume.

Mesiodistal Root Angulation Using Panoramic and Cone Beam CT

OBJECTIVE To determine if the panoramic projection can accurately determine mesiodistal root angulations. MATERIALS AND METHODS A plaster study model of the dentition of each of five patients was prepared. A radiographic stent containing radiopaque markers was fabricated for each of the models. Panoramic and cone beam computed tomography (CBCT) scans were taken on each patient with the radiographic stent seated on the dentition. Root angulations for each of the radiographic images were measured and compared. RESULTS Root angulation was measured by three independent individuals and good reliability between measurements was demonstrated. Compared to plaster model measurements (the gold standard), the CBCT scan produced very accurate measurements of root angulation. Compared to CBCT images, panoramic projections did not provide reliable data on root angulation. CONCLUSION Panoramic images did not accurately represent the mesiodistal root angulations on clinical patients.

Predicting soft tissue changes in mandibular advancement surgery: a comparison of two video imaging systems.

The purpose of this study was to evaluate the accuracy of two video imaging systems, Prescription Portrait and Orthognathic Treatment Planner, in predicting the soft tissue profiles of 39 patients who underwent mandibular advancement surgery. Presurgical cephalograms and profile photographs were entered into a computer. Computerized cephalometric line and video image predictions were generated and compared with the actual postsurgical results. The results indicate that both programs were equally accurate clinically in their line drawing and video image predictions. In the line drawings, clinically acceptable accuracy was shown in approximately 80% of the upper lip and chin predictions and in less than 50% of the lower lip predictions. The video images produced by both programs received fair to good ratings from a panel of professional and lay judges. Orthodontists and surgeons rated all aspects of the images similarly, while lay people were most critical of the chin and submental areas and least critical in their overall evaluation.

The long-term stability of LeFort I maxillary downgrafts with rigid fixation to correct vertical maxillary deficiency

This study evaluated the long-term stability of LeFort I maxillary downgrafts with rigid fixation in 28 patients with vertical maxillary deficiency. Preorthodontic, presurgical, immediate postsurgical, and an average of 16 months postsurgical cephalometric radiographs were evaluated. The results indicated that overall vertical maxillary stability after downgraft was good with 80% of the cases showing superior relapse of 2 mm or less. The mean amount of postoperative relapse represented 28% of the surgical downgraft. No correlation was found between the amount of the maxillary downgraft and the subsequent postsurgical vertical stability of the maxilla. No difference was found in the vertical stability of the maxilla comparing one-jaw and two-jaw procedures. It was also found that there was no difference in the vertical stability of the maxilla between single-segment and multiple-segment maxillary procedures, and also when comparing standard and high LeFort I osteotomy techniques. In addition, occlusal plane rotation of surgery, as well as the type of presurgical orthodontic movement, were both found to have no influence on postoperative stability of the maxilla.

Predicting soft tissue changes in maxillary impaction surgery: a comparison of two video imaging systems.

The purpose of this retrospective study was to investigate the accuracy of two video imaging systems, Orthognathic Treatment Planner (OTP) and Prescription Portrait (Portrait), in predicting soft tissue profile changes after maxillary impaction surgery. Computer-generated line drawing predictions were compared with actual postsurgical profiles. Neither program was very accurate with vertical measures and lower lip contour. Portrait was more accurate at pronasale, inferior labial sulcus, and pogonion in the y-axis direction (P < 0.05). Video image predictions produced from the presurgical photographs were rated by orthodontists, surgeons, and lay people, who compared the predictions with the actual postsurgical photographs using a visual analog scale. Portraits prediction images were scored higher than OTPs for five of eight areas. Orthodontists were most critical of the lips and the overall appearance. Lay people were most critical of the chin and submental areas.

A new method to measure mesiodistal angulation and faciolingual inclination of each whole tooth with volumetric cone-beam computed tomography images

INTRODUCTION The purpose of this study was to develop a methodology to measure the mesiodistal angulation and the faciolingual inclination of each whole tooth (including the root) by using 3-dimensional volumetric images generated from cone-beam computed tomography scans. METHODS A plastic typodont with 28 teeth in ideal occlusion was fixed in position in a dry human skull. Stainless steel balls were fixed to the occlusal centers of the crowns and to the apices or bifurcation or trifurcation centers of the roots. Cone-beam computed tomography images were taken and rendered in Dolphin 3D (Dolphin, Chatsworth, Calif). The University of Southern California root vector analysis program was developed and customized to digitize the crown and root centers that define the long axis of each whole tooth. Special algorithms were used to automatically calculate the mesiodistal angulation and the faciolingual inclination of each whole tooth. Angulation measurements repeated 5 times by using this new method were compared with the true values from the coordinate measuring machine measurements. Next, the root points of 8 selected typodont teeth were modified to generate known angulation and inclination values, and 5-time repeated measurements of these teeth were compared with the known values. RESULTS Intraclass correlation coefficients for the repeated mesiodistal angulation and faciolingual inclination measurements were close to 1. Comparisons between our 5-time repeated angulation measurements and the coordinate measuring machines true angulation values showed 5 teeth with statistically significant differences. However, only the maxillary right lateral incisor showed a mean difference that might exceed 2.5° for clinical significance. Comparisons between the 5-repeated measurements of 8 teeth with known mesiodistal angulation and faciolingual inclination values showed no statistically significant differences between the measured and the known values, and no measurement had a 95% confidence interval beyond 1°. CONCLUSIONS We have developed the novel University of Southern California root vector analysis program to accurately measure each whole tooth mesiodistal angulation and faciolingual inclination, in a clinically significant level, directly from the cone-beam computed tomography volumetric images.

Measurements of the torque moment in various archwire- bracket-ligation combinations

The torque moment generated by third-order bends is important for tooth movement. The purpose of this study was to measure the torque moment that can be delivered by various archwire and bracket combinations at the targeted tooth. Stainless steel (SS) upper brackets with 0.018 and 0.022 inch slots, two sizes of nickel-titanium (Ni-Ti) alloy wires, and three sizes of SS wires for each bracket were used. The wire was ligated with elastics or wire. The torque moment delivered by the various archwire-bracket-ligation combinations was measured using a torque gauge. Statistical analysis was undertaken using analysis of variance (multiple comparison tests and post hoc using Tukeys honestly significant difference test. The torque moment increased as the degree of torque and wire size increased. There was no significant difference in torque moment between the SS and Ni-Ti wires at lower or higher than 40 degrees torque. The torque moment with wire ligation was significantly larger than that with elastic ligation with 0.016 × 0.022 and 0.017 × 0.025 inch Ni-Ti wires in the 0.018 inch slot brackets and the 0.017 × 0.025 and 0.019 × 0.025 inch SS and Ni-Ti wires in the 0.022 inch slot brackets. However, there was no significant difference in torque moment between either ligation method when using the full slot size wires.