Posterior Arch Length Research Articles

Atlantoaxial fixation using C1 posterior arch screws: feasibility study, morphometric data, and biomechanical analysis.

OBJECTIVEC1-2 is a highly mobile complex that presents unique surgical challenges to achieving biomechanical rigidity and fusion. Posterior wiring methods have been largely replaced with segmental constructs using the C1 lateral mass, C1 pedicle, C2 pars, and C2 pedicle. Modifications to reduce surgical morbidity led to the development of C2 laminar screws. The C1 posterior arch has been utilized mostly as a salvage technique, but recent data indicate that this method provides significant rigidity in flexion-extension and axial rotation. The authors performed biomechanical testing of a C1 posterior arch screw (PAS)/C2 pars screw construct, collected morphometric data from a population of 150 CT scans, and performed a feasibility study of a freehand C1 PAS technique in 45 cadaveric specimens.METHODSCervical spine CT scans from 150 patients were analyzed to determine the average C1 posterior tubercle thickness and size of C1 posterior arches. Eight cadavers were used to compare biomechanical stability of intact specimens, C1 lateral mass/C2 pars screw, and C1 PAS/C2 pars screw constructs. Paired comparisons were made using repeated-measures ANOVA and Holm-Sidak tests. Forty-five cadaveric specimens were used to demonstrate the feasibility and safety of the C1 PAS freehand technique.RESULTSMorphometric data showed the average craniocaudal thickness of the C1 posterior tubercle was 12.3 ± 1.94 mm. Eight percent (12/150) of cases showed thin posterior tubercles or midline defects. Average posterior arch thickness was 6.1 ± 1.1 mm and right and left average posterior arch length was 28.7 mm ± 2.53 mm and 28.9 ± 2.29 mm, respectively. Biomechanical testing demonstrated C1 lateral mass/C2 pars and C1 PAS/C2 pars constructs significantly reduced motion in flexion-extension and axial rotation compared with intact specimens (p < 0.05). The C1 lateral mass/C2 pars screw construct provided significant rigidity in lateral bending (p < 0.05). There was no statistically significant difference between the two constructs in flexion-extension, lateral bending, or axial rotation. Of the C1 posterior arches, 91.3% were successfully cannulated using a freehand technique with a low incidence of cortical breach (4.4%).CONCLUSIONSThis biomechanical analysis indicates equivalent stability of the C1 PAS/C2 pars screw construct compared with a traditional C1 lateral mass/C2 pars screw construct. Both provide significant rigidity in flexion-extension and axial rotation. Feasibility testing in 45 cadaveric specimens indicates a high degree of accuracy with low incidence of cortical breach. These findings are supported by a separate radiographic morphometric analysis.

Morphological and dimensional characteristics of dental arch in children with beta thalassemia major.

The aim of this study was to examine the arch dimensions of beta thalassemia major patients in comparison with normal individuals. Dental arch dimensions were compared between thalassemic patients and normal individuals in the age group of 12-16 years in the maxillary and mandibular arch corresponding to each other regarding age, sex and Angle's molar relationship. A total number of sixty cases in each group were taken. Maxillary and mandibular impressions were made with alginate for all the sixty participants in each group and poured with die stone. Measurement of inter incisor, inter canine, inter premolar and intermolar arch width, arch depth, right anterior, right posterior, left anterior, and left posterior arch length was carried out from each cast using digital Vernier caliper. Unpaired t-test was used for comparison between the two groups. Statistically, a significant difference was found between the case and control groups in the maxillary arch in intercanine width, inter premolar width, intermolar width, right anterior arch length, right posterior arch length, and left anterior arch length. However, no statistically significant difference was found between the groups in inter incisor width, left posterior arch length, and arch depth in the maxillary arch. In the mandibular arch, statistically significant difference was found between the case and control groups in inter canine width, inter premolar width, inter molar width, and left anterior arch length. However, no statistically significant difference was found between the case and control groups in the mandibular arch in interincisor width, right anterior arch length, right posterior arch length, and left posterior arch length. Dental arch widths and arch lengths were significantly reduced in thalassemic patients as compared to normal individuals for the maxillary and mandibular arches.

Functional analyses of the primate upper cervical vertebral column

Recent work has highlighted functional correlations between direct measures of head and neck posture and primate cervical bony morphology. Primates with more horizontal necks exhibit middle and lower cervical vertebral features that indicate increased mechanical advantage for deep nuchal musculature and mechanisms for column curvature formation and maintenance. How features of the C1 and C2 reflect quantified measures of posture have yet to be examined. This study incorporates bony morphology from the upper cervical levels from 20 extant primate species in order to investigate further how posture correlates with cervical vertebrae morphology. Results from phylogenetic generalized least-squares analyses indicate that few vertebral features exhibit a significant relationship with posture when accounting for differences in size. When size-adjusted traits were correlated with posture, vertebral variation had a stronger relationship with neck posture than head posture variables. Two C1 traits—relative posterior arch length and superior facet curvature—were correlated with neck posture variables. Relative posterior arch length exhibits a positive relationship with neck posture, while superior articular facet curvature demonstrates a negative relationship, such that as the neck becomes more horizontal, the greater the facet curvature. Four C2 features were also correlated with neck posture: relative pedicle and lamina lengths, relative superior facet orientation, and dens orientation. Relative pedicle and lamina lengths become craniocaudally longer as the neck becomes more horizontal. Relative C2 superior facet orientation and dens orientation exhibit negative correlations with posture, such that as the neck becomes more horizontal, the superior facet becomes more caudally inclined and the dens more dorsally inclined. These results produce a similar functional signal observed in the middle and lower cervical spine. Modeling the cervical vertebrae of more pronograde taxa within a sigmoidal spinal column model is further discussed and may prove useful in refining and testing future hypotheses of primate cervical mechanics.

Reliability and validity of intraoral and extraoral scanners.

BackgroundThis study evaluated the reliability and validity of one extraoral [Ortho Insight 3D™ (Motionview Software, Hixson, TN/USA)] and two intraoral [ITero™ (Align Technologies, San Jose, CA/USA) and Lythos™ (Ormco Corp., Orange, CA/USA)] scanners.MethodsFifteen dry human mandibles were scanned twice with each of the scanners, and digital models were generated. Five measurements were made on the dry mandibles and on each of the generated models, including intermolar width, intercanine width, posterior arch length, premolar crown diameter, and canine height. Systematic and random errors were evaluated based on replicate analyses. Differences were assessed using paired Student’s t tests.ResultsReplicate analyses showed statistically significant systematic errors for only one measure (intermolar width measured from Ortho Insight 3D scans). Measurements taken from all three scanners were highly reliable, with intraclass correlations ranging from .926 to .999. Method errors were all less than 0.25 mm (averaged ≈0.12 mm). Posterior arch length and canine height were significantly smaller when measured on the Ortho Insight 3D scans than when measured on the dry mandibles and significantly smaller than when measured from the ITero and Lythos models.ConclusionsWhile all three scanners produced reliable measures, Ortho Insight 3D systematically underestimated arch length and canine height.

Morphological Asymmetry of the Atlas and Its Clinical Implications

Objective The aim of this study was to investigate the asymmetry of the adult atlas by deviation frequencies using 3-dimensional (3D) computer models based on the computed tomographic (CT) spine data from healthy patients. Methods Sixty adult atlas computer models were reconstructed from CT data of the cervical spine. The morphological asymmetries were investigated and measured with 3D software. Asymmetry in the morphology of the vertebral artery groove was observed, and the angles between the lines connecting the apices of transverse processes and the apices of anterior and posterior tubercles were measured. The lengths of the left and right posterior arches were measured, and the differences in values were categorized. Results We observed 7 cases (11.67%) with asymmetrical vertebral artery groove forms. There were 4 different categories: foramen-shaped, semi-foramen–shaped, deep, and superficial grooves. The asymmetry was of different shapes on both sides. Relative to the lines connecting the apices of anterior and posterior tubercles, the asymmetry frequency of the transverse processes and the posterior arch length was 6.67% and 16.67%, respectively. Conclusions For the specimens in this study, variation in morphology of the atlas was common. Asymmetry of apices of transverse processes, posterior arches, and vertebral artery grooves should be taken into account during clinical palpation, diagnostic imaging, and treatment including spinal manipulation.

Evaluation of Maxillary Permanent Molars in Patients With Syndromic Craniosynostosis After Monobloc Osteotomy and Midface Advancement With Rigid External Distraction (RED)

This retrospective study was conducted to analyze changes in the maxillary permanent molars after monobloc advancement with rigid external distraction (RED).University hospital-based craniofacial center.Fourteen patients, three in primary, eight in mixed, and three in permanent dentition underwent monobloc advancement with RED. After a latency period of 6 days, distraction was carried out for 18 days. Lateral cephalometric radiographs were taken before surgery (T1) and an average of 3.72 months after the removal of the distractor (T2). Panoramic radiographs were taken at T1, T2, and T3 (an average of 14.87 months after RED removal), to search for surgical tooth trauma, arrested crown/root development, impaction, tooth germ displacement, dilacerations, and other possible dental abnormalities. Vertical and horizontal displacement and angulations of the permanent maxillary molars were evaluated before and after surgery.A paired t test was used to analyze significant changes in molar position after distraction.Distraction created posterior arch length with significant horizontal forward movement of the first and second molars (p<.05) and minimal vertical displacement (p>.05). The procedure disrupted the development of one of the first molars, three of the second molars, and two of the third molars. Incidence of molar damage was increased in patients operated on during primary dentition. Careful surgical technique during pterygomaxillary disjunction, especially in young children, and long-term radiographic follow-up of maxillary molars is strongly recommended.

Evaluation of Maxillary Permanent Molars in Patients with Syndromic Craniosynostosis after Monobloc Osteotomy and Midface Advancement with Rigid External Distraction (RED)

This retrospective study was conducted to analyze changes in the maxillary permanent molars after monobloc advancement with rigid external distraction (RED). University hospital-based craniofacial center. Fourteen patients, three in primary, eight in mixed, and three in permanent dentition underwent monobloc advancement with RED. After a latency period of 6 days, distraction was carried out for 18 days. Lateral cephalometric radiographs were taken before surgery (T1) and an average of 3.72 months after the removal of the distractor (T2). Panoramic radiographs were taken at T1, T2, and T3 (an average of 14.87 months after RED removal), to search for surgical tooth trauma, arrested crown/root development, impaction, tooth germ displacement, dilacerations, and other possible dental abnormalities. Vertical and horizontal displacement and angulations of the permanent maxillary molars were evaluated before and after surgery. A paired t test was used to analyze significant changes in molar position after distraction. Distraction created posterior arch length with significant horizontal forward movement of the first and second molars (p<.05) and minimal vertical displacement (p>.05). The procedure disrupted the development of one of the first molars, three of the second molars, and two of the third molars. Incidence of molar damage was increased in patients operated on during primary dentition. Careful surgical technique during pterygomaxillary disjunction, especially in young children, and long-term radiographic follow-up of maxillary molars is strongly recommended.

Dental arch morphological and dimensional characteristics in Jordanian children and young adults with β‐thalassaemia major

The aim of this study was to examine the arch dimensions of Jordanian patients with beta-thalassaemia major in comparison with an unaffected control group. The sample consisted of 24 patients who suffered from beta-thalassaemia major (mean age = 13.9 +/- 3.1 years) and an unaffected control group (mean age = 13.5 +/- 2.9 years) matched for dental age, sex, and incisor and molar relationships. The unaffected control group was randomly selected from four public schools in the Governate of Irbid-Jordan. Alginate impressions were taken of the maxillary and mandibular dental arches of all participants. All measurements of the arch dimensions were made on the casts using an electronic digital sliding calliper. In the mandibular arch, when compared with the patients with thalassaemia, the unaffected control group subjects showed a (statistically) significantly larger incisor width, larger arch depth, and larger left and right anterior arch lengths (1.18, 2.58, and 1.85 and 1.12 mm, respectively). In the maxillary arch, there was a statistically significant difference in the mean incisor width (+/- 2.16 mm), arch depth (+/- 3.14 mm), inter-molar width (+/- 1.21 mm) and in the left anterior arch length (+/- 1.97 mm). The canine widths, premolar widths, left and right posterior arch length, and curve of Spee of both arches showed no statistically significant differences between the two groups. When compared to unaffected subjects, patients with beta-thalassaemia major exhibited: a narrower maxilla; a shorter maxilla and mandible; and smaller incisor widths for the maxillary and mandibular arches.