Orienting 3-dimensional models to natural head position
Xia JJ, McGrory JK, Gateno J, Teichgraeber JF, Dawson BC, Kennedy KA, et al. A new method to orient 3-dimensional computed tomography models to the natural head position: a clinical feasibility study. J Oral Maxillofac Surg 2011;69:584-91
Natural head position (NHP) is defined as the natural physiologic position of the head when a relaxed subject looks at an infinite horizon. An accurate recording of this position is crucial for the diagnosis and treatment of patients with craniofacial deformities. The authors wanted to record an accurate and reproducible NHP that could be transferred to a patient’s 3-dimensional (3D) computed tomography (CT) model for surgical planning. Fifteen patients with craniofacial deformities were included in the study, and each patient’s NHP was recorded 3 times. NHP was first recorded with a laser scan without a digital orientation device (orientation 1). The digital orientation device was then used for the second NHP (orientation 2), and a third NHP (orientation 3) was simultaneously recorded with the laser scanning method. Each recorded position was transferred to the patient’s 3D CT facial model; this resulted in 3 different orientations for each patient. The results showed that in each pair (orientations 1 and 2, and orientations 2 and 3) the difference between the measurements (pitch, roll, and yaw) was not statistically significantly different from 0°. Additional factors such as the ability to detach the digital orientation sensor (to prevent artifacts during the CT scan), cone-beam CT compatibility, and the ability of the bite jig and facebow to be used for multiple purposes (eg, to create composite skull models for computer-aided surgical simulation) are additional benefits of this technique. This study showed that the authors’ technique can accurately recorded NHP in all 3 dimensions, and that this position could be transferred to a 3D model to be used for surgical planning to correct craniofacial deformities.
Reviewed by Steven Machicek
Closing spaces without skeletal anchorage
Jacobs C, Jacobs-Muller C, Luley C, Erbe C, Wehrbein H. Orthodontic space closure after first molar extraction without skeletal anchorage. J Orofac Orthop 2011;72:51-60
The purpose of this study was to analyze the effects of space closure after first molar extractions by using the anterior dentition and the premolars as anchorage. The records of 35 patients who had undergone unilateral or bilateral maxillary or mandibular permanent first molar extractions because of caries were studied. The patients had the spaces closed with elastic chains on both the buccal and lingual aspects of the second molar and the canine, and supported by an edgewise stainless steel wire, with the teeth anterior to the space tied together with a continuous ligature as anchorage. The results were evaluated by using lateral cephalograms, orthopantomograms, and images of the patients’ study casts before and after treatment. This study showed that the second molars were mesialized primarily by bodily movement. Bilateral space closures led to 3.6° of uprighting and 2.8 mm of lingual translation of the anterior teeth in the maxilla, and 4.2° of uprighting and 2.2 mm of lingual translation of the anterior teeth in the mandible. Less than 50% of the unilateral extraction patients had slight midline deviations toward the extraction site. These authors found that attempting to close first molar extraction spaces caused lingual displacement of the anterior teeth used as anchorage and had a corresponding effect on the soft tissues over those incisors. This article highlights that, although first molar space closure can be accomplished without supplemental anchorage devices such as skeletal anchorage, the effect on the profile must be considered. A future study on the effects of space closure with skeletal anchorage devices placed in different locations would be a valuable addition to the information covered in this article.
Reviewed by Sebastian Paige
Closing spaces without skeletal anchorage
Jacobs C, Jacobs-Muller C, Luley C, Erbe C, Wehrbein H. Orthodontic space closure after first molar extraction without skeletal anchorage. J Orofac Orthop 2011;72:51-60
The purpose of this study was to analyze the effects of space closure after first molar extractions by using the anterior dentition and the premolars as anchorage. The records of 35 patients who had undergone unilateral or bilateral maxillary or mandibular permanent first molar extractions because of caries were studied. The patients had the spaces closed with elastic chains on both the buccal and lingual aspects of the second molar and the canine, and supported by an edgewise stainless steel wire, with the teeth anterior to the space tied together with a continuous ligature as anchorage. The results were evaluated by using lateral cephalograms, orthopantomograms, and images of the patients’ study casts before and after treatment. This study showed that the second molars were mesialized primarily by bodily movement. Bilateral space closures led to 3.6° of uprighting and 2.8 mm of lingual translation of the anterior teeth in the maxilla, and 4.2° of uprighting and 2.2 mm of lingual translation of the anterior teeth in the mandible. Less than 50% of the unilateral extraction patients had slight midline deviations toward the extraction site. These authors found that attempting to close first molar extraction spaces caused lingual displacement of the anterior teeth used as anchorage and had a corresponding effect on the soft tissues over those incisors. This article highlights that, although first molar space closure can be accomplished without supplemental anchorage devices such as skeletal anchorage, the effect on the profile must be considered. A future study on the effects of space closure with skeletal anchorage devices placed in different locations would be a valuable addition to the information covered in this article.
Reviewed by Sebastian Paige
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