Buccolingual inclination measurements of canines and first molars through cone-beam computed tomography
Shewinvanakitkul W, Hans MG, Narendran S, Palomo JM. Measuring buccolingual inclination of mandibular canines and first molars using CBCT. Orthod Craniofac Res 2011;14:168-74
One of Andrews’ 6 keys of occlusion, and also a grading criteria for the American Board of Orthodontics, states that the teeth must display correct buccolingual inclination to achieve proper occlusion. These researchers wanted to develop a reliable method to measure the buccolingual inclination of the mandibular canines and first molars, evaluate a possible correlation between canine and molar buccolingual inclination with their respective interdental width, and describe such inclinations in an untreated sample of preorthodontic patients. The sample consisted of 78 untreated patients (37 boys, 41 girls) with an average age of 13 years. The buccolingual inclination measurements were taken between the long axis of the tooth and a tangent line to the inferior border of the mandible. The mean inclination of the mandibular canines was 98°, and the mean intercanine width was 26 mm. The mean inclination of the mandibular molars was 74.6°, and the mean intermolar width was 40.9 mm. The study showed that the best approach to correctly indentifying the buccolingual inclination was by using the inferior border of the mandible as a reference plane because it is reproducible and less likely to be influenced by orthodontic tooth movement. There was a low correlation between arch width and inclination, suggesting that tooth inclination is independent of width. Before treatment, the mandibular canines also appeared to be buccally inclined, whereas the mandibular molars were lingually inclined. Tooth inclination also seems to be influenced by dental adaptation or compensation to skeletal discrepancies; when we know the inclinations before treatment, a more detailed treatment plan can be used.
Reviewed by Patrick O’Neil
Molar distalization with buccal mini-implants and palatal plate
Yu IJ, Kook YA, Sung SJ, Lee KJ, Chun YS, Mo SS. Comparison of tooth displacement between buccal mini-implants and palatal plate anchorage for molar distalization: a finite element study. Eur J Orthod 2011 Nov 2 [Epub ahead of print]
Headgear and noncompliance appliances have been used to treat Class II malocclusions through molar distalization. The disadvantages of these appliances include the need for patient compliance, molar tipping, molar extrusion, anchorage loss, and incisor flaring. Today, skeletal anchorage is becoming more popular to help control the negative side effects and disadvantages of these appliances. The purpose of this study was to analyze the displacement of the central incisors and the molars with distalization through skeletal anchorage by using finite element analysis. Finite element models were created by scanning tooth models and producing 3-dimensional virtual models. These models were aligned on an arch form with passive brackets and archwires. Three treatment modalities were then installed on the finite element models. Modality 1 was indirect anchorage to a buccal mini-implant with an open-coil spring placed between the first premolar and the first molar to apply the distalization force. Modality 2 was direct anchorage to a buccal mini-implant with an open-coil spring between the first premolar and the first molar. Modality 3 was direct anchorage to a palatal plate at the level of the molars with lever arms for distalization. Both buccal implant modalities resulted in mesial-out molar rotation, molar extrusion, and uncontrolled distal tipping with incisor intrusion and flaring. The palatal plate modality resulted in bodily molar distalization and insignificant incisor flaring when the lever arm was close to the midpalatal suture. These findings can be used as a guide for clinicians when deciding to use mini-implants for molar distalization. Some limitations of this study include measuring only initial tooth movement and making comparisons on virtual rather than biologic models.
Reviewed by Leslie Talbert