ABSTRACT
OBJETIVO: determinar o perímetro de arco adicional necessário para o nivelamento da curva de Spee através de uma técnica laboratorial em modelos de estudo. MÉTODOS: foram utilizados 70 modelos inferiores nos quais se mediu a profundidade da curva de Spee e o perímetro do arco (de segundo molar a segundo molar). Nos mesmos modelos, após a simulação do nivelamento da curva de Spee, o perímetro de arco foi novamente avaliado, mantendo sua forma e comprimento. RESULTADOS: foi confirmada a correlação entre a profundidade da curva de Spee e o perímetro de arco adicional, sendo deduzida a fórmula [Paa = 0,21 CSmax - 0,04]. CONCLUSÃO: a técnica proposta permitiu, através da avaliação do perímetro de arco com curva de Spee nivelada, a determinação do espaço disponível para o alinhamento dentário.
AIM: To determine the additional arch perimeter needed for leveling the curve of Spee by means of a laboratory technique using dental casts. METHODS: Seventy lower dental models were used for measuring the depth of the curve of Spee and assessing the arch perimeter from second molar to second molar. In these dental casts, after simulation of leveling the curve of Spee, arch perimeter was reevaluated, after maintaining its form and length. RESULTS: The correlation between the depth of the curve of Spee and the additional arch perimeter was ratified, as can be shown by the formula [Paa = 0,21 CSmax - 0,04]. CONCLUSION: The proposed technique allowed, through the assessment of the arch perimeter with the leveled curve of Spee, the determination of the space available for tooth alignment.
Subject(s)
Dental Arch , Dental Occlusion , Tooth Movement Techniques , Casts, SurgicalABSTRACT
Although C1-C2 transarticular screw fixation has become a popular surgical method of treating atlantoaxial instability, we remain concerned about the potential for injury to the vertebral artery. Because of the lack of an objective measuring method, surgical unsuitability has been decided on the basis of individual experiences as reported in 18-23% of cases. In this study, the point of screw intersection(the passing points) on the superior articular surface of C2 were measured and the directions of these were thus objectified. Sixty-four healthy volunteers underwent 1mm fine-slice C1-C2 CT scanning, and sagittal images were reconstructed at 3.5mm(3.5mm lateral image) and 6mm(6mm lateral image) lateral to the spinal canal. The C1/2 transarticular screw trajectories making the longest paths or violating the transverse foramen(dangerous trajectory) were drawn and the distance from their points of screw intersection on the superior articular surface of C2 were measured from the posterior rim of the superior articular surface of C2. When the space available for screw(SAS) posterior to the passing point of the dangerous trajectory was equal to or less than 3.5mm(major diameter of the commonly used screw), the case was considered unacceptable, when SAS was over 3.5mm but equal to or less than 4.5mm, screw placement were considered risky. The trajectories made the longest paths when they passed 3.6+/-1.6mm(mean+/-S.D.) and 2.8+/-1.7mm(mean+/-S.D.) anterior to the posterior rim of the posterior articular surface of C2 as seen on 3.5mm lateral images and 6mm lateral images, respectively. While four of 64 cases(6.3%) were unilaterally unacceptable or risky on 3.5mm lateral images, 21 cases(32.8%) were unacceptable or risky on 6mm lateral images(unilateral, 15cases; bilateral, 6 cases). When the trajectories inclined forward to 0%, 25%, 50%, 75% and 100% points of AP diameter of the superior articular surface of C2 from the posterior rim, the respective risks of the involvement of the transverse foramen increased to 0.78%, 1.5%, 25%, 74% and 100%, as seen on 3.5mm lateral images and 10.9%, 14%, 62.5%, 95% and 100%, on 6mm lateral images.
Subject(s)
Healthy Volunteers , Spinal Canal , Tomography, X-Ray Computed , Vertebral ArteryABSTRACT
The authors analyzed 17 cases of os odontoideum. a very rare condition and one of the causes of atlantoaxial instability. We investigated the radiographic findings of os odontoideum and classified the patients according to clinical grade, radiographic findings and direction of atlantoaxial instability. Their mean age was 33.4 years, and the male to female ratio was. 7: 10. Thirteen patients(76.5%) were classified as clinical grade 3, indicating fixed or progressive myelopathy. They were classified as one of two types, according to the location of the os, five were dystopic and ten were orthotopic. In remaining two patients, it was difficult to classify. We measured SAC(space available for cord) laterally, using plain film, and sagittally, using MR imaging, and compared the results with clinical symptoms. SAC as seen on cervical MRI, correlated more closely with severity of cord compression than did SAC seen on plain film. The 15 patients underwent various operative methods including C1/2 fixation, occipito-cervical fusion, and transoral decompression; because of postoperative hardware failure, two required further surgery. Postoperatively, twelve patients showed excellent or good neurologic improvement. In this retrospective study, SAC seen on cervical MRI was a very good indicator of the need for surgery, and surgery should be considered in patients whose clinical grade is higher than 2.
Subject(s)
Female , Humans , Male , Decompression , Diagnosis , Magnetic Resonance Imaging , Retrospective Studies , Spinal Cord DiseasesABSTRACT
PURPOSE: To evaluate the degree of injury of the spinal cord in relation with the space available for the spinal cord at the level of injury, the sagittal diameter of the spinal canal at the uninjured levels, and the Pavlov ratio at the uninjured levels in fractures and dislocations of the lower cervical spine. MATERIALS AND METHODS: We retrospectively reviewed the records and radiographs of patients who had sustained an acute fracture or dislocation of the cervical spine from 1990 to 1995. We collected patients from Orthopedic and Neurosurgical department of Chonbuk University Hospital and at Orthopedic department of Presbyterian Medical Center. Of the 69 patients analyzed, twelve had no neurological deficit, eleven had an isolated nerve-root injury, twenty-two had an incomplete injury of the spinal cord, and twenty-four had a complete injury. We measured above three parameters from the plain lateral radiographs and assessed the difference by one-way ANOVA and unpaired t-test. RESULTS: 1. The mean space available for the spinal cord at the level of injury was 12.9 millimeter for the complete injury of the spinal cord,13.8 millimeter for the incomplete injury, 14.7 millimeter for an isolated nerve-root injury, and 15.7 millimeter for no neurological deficit group. The overall difference among the groups was significant (F=6.98, P=0.0004). The patients who had a complete injury of the spinal cord and those who had an incomplete injury of the spinal cord were significantly different from the patients who had an isolated nerve-root injury and those who had no neurologic deficit (P=0.002). 2. The mean sagittal diameter of the canal at the proximal and distal uninjured level was 14.3 and 14.6 millimeter for the complete injury of the spinal cord, 14.9 and 14.9 millimeter for the incomplete injury, 15.5 and 16.6 millimeter for an isolated nerve-root injury, and 16.9 and 16.5 millimeter for no neurological deficit group. The patients who had a complete injury of the spinal cord and those who had an incomplete injury of the spinal cord were significantly different from the patients who had an isolated nerve-root injury and those who had no neurologic deficit (P=0.001). 3. The mean Pavlov ratio at the proximal and distal uninjured level was 0.90 and 0.86 for no neurologic deficit group, 0.85 and 0.87 for an isolated nerve-root injury, 0.76 and 0.75 for the incomplete injury of the spinal cord, and 0.76 and 0.76 for the complete injury. The patients who had a complete injury of the spinal cord and those who had an incomplete injury of the spinal cord were significantly different from the patients who had an isolated nerve-root injury and those who had no neurologic deficit (P=0.001). CONCLUSIONS: The patients who sustained a permanent injury of the cord usually had had a narrower sagittal diameter (<14mm) and a lower Pavlov ratio (<0.80) of the spinal canal before injury. Patients who had a large sagittal diameter of the canal may be more likely to be spared a permanent injury of the spinal cord following a fracture or dislocation of the cervical spine compared with patients who have a narrow canal. These findings demonstrated that the severity of the injury of the spinal cord was in part associated with the space available for the cord (at risk:<13mm) after the injury, as measured on plain lateral radiographs.