Changes of axial length in primary and secondary school students in Yunnan and associated factors / 中国学校卫生

Objective@#To explore the pattern of change of axial length/curvatrue radius ratio (AL/CR) and associated factors in primary and secondary school students in Yunnan, so as to provide scientific basis and prospective guidance for early myopia intervention and control.@*Methods@#A total of 685 students from grades 2 to 3 and grade 7 in 2 cities/counties in Yunnan Province were selected by multi stage stratified random cluster sampling method in 2020. All the participants were followed up twice with questionnaire of myopia related factors, uncorrected distance visual acuity, and refractive parameter measurement from October,2021 and March,2023,respectivelty. The distribution and change of AL/CR in different classes and groups were analyzed, and the influencing factos of AL/CR cumulative progression were explored using generalized linear model.@*Results@#AL/CR ratio in primary school students was (2.95±0.09) at baseline, increased to (2.99±0.11) at the first follow up and (3.04±0.12) at the second follow up. AL/CR ratio in middle school students(3.08±0.13) at baseline, increased to (3.12±0.15) at the first follow up and (3.15±0.14) at the second follow up. The generalized linear model showed that after controlling for environmental factors, ethnicity ( β =-0.017) , cumulative progression of the SE ( β =-0.027) influenced the changes of AL/CR ratio among the primary school students, whereas the changes of AL/CR ratio were associated with baseline AL ( β =-0.005), baseline corneal curvatrue radius ( β =0.032) and cumulative progression of SE( β =-0.035) among middle school students ( P <0.05).@*Conclusions@#The AL/CR ratio of primary and secondary school students in Yunnan can be used to judge different refractive status types, but its variation is not only related to SE progression, but also affected by different ethnic groups and baseline ocular biological parameters. so the value of AL/CR application in assessing the progression of myopia needs to be further confirmed.

Numerical Simulation for the Safe Retention Value of Residual Stromal Bed Thickness in Laser-Assisted in situ Keratomileusis / 医用生物力学

Objective To study the effects of different residual stromal bed thickness (RSBT) in laser-assisted in situ keratomileusis (LASIK) surgery on geometric deformation and stress changes of the cornea under different intraocular pressures (IOP), and evaluate safety of the three retention values (250, 280, 300 μm). Methods The models of normal cornea and corneas with different RSBT after surgery were established by the finite element software ABAQUS. Appropriate loading and boundary conditions were set and then the corresponding displacement and stress were calculated. Results The apical displacement of the postoperative cornea (RSBT=250 μm) under IOP=2.66 kPa was basically the same as that of the normal cornea (RSBT=550 μm) under IOP=5.32 kPa. RSBT=280 μm was in the low risk area of keratoconus, while RSBT=250 μm was in the high-risk area. At a value between 280 μm and 300 μm of RSBT, the stress distribution was nearly consistent with that of the normal cornea. With RSBT=300 μm, the stromal layer of the cornea lost 40% of the strongest strength against tissue tension. Conclusions RSBT=250 μm is the minimum retention value for LASIK surgery. RSBT=250 μm is the high risk value. With RSBT=330-340 μm, LASIK surgery is safe enough for most patients.

Identification of Apical and Cervical Curvature Radius of Human Molars

To determine the frequency of apical and cervical curvatures in human molars using the radius method and cone-beam computed tomography (CBCT) images. Four hundred images of mandibular and maxillary first and second molars were selected from a database of CBCT exams. The radius of curvature of curved root canals was measured using a circumcenter based on three mathematical points. Radii were classified according to the following scores: 0 - straight line; 1 - large radius (r>8 mm, mild curvature); 2 - intermediate radius (r>4 and r<8 mm, moderate curvature); and 3 - small radius (r≤4 mm, severe curvature). The frequency of curved root canals was analyzed according to root canal, root thirds, and coronal and sagittal planes, and assessed using the chi-square test (significance at α=0.05). Of the 1,200 evaluated root canals, 92.75% presented curved root canals in the apical third and 73.25% in the cervical third on coronal plane images; sagittal plane analysis yielded 89.75% of curved canals in the apical third and 77% in the cervical third. Root canals with a large radius were significantly more frequent when compared with the other categories, regardless of root third or plane. Most root canals of maxillary and mandibular first and second molars showed some degree of curvature in the apical and cervical thirds, regardless of the analyzed plane (coronal or sagittal).

Determinar a frequência de curvaturas apicais e cervicais em molares humanos usando o método do raio de curvatura e imagens de Tomografia Computadorizada de Feixe Cônico (TCFC). Quatrocentas imagens de primeiros e segundos molares superiores e inferiores foram selecionadas a partir de um banco de dados de exames de TCFC. O raio de curvatura dos canais foi medido usando um circuncentro com base em três pontos matemáticos e classificado de acordo com os seguintes escores: 0 - linha reta; 1 - raio grande (r > 8 mm, curvatura suave); 2 - raio intermediário (r > 4 e r < 8, curvatura moderada); 3 - raio pequeno (r ≤ 4 mm, curvatura severa). A frequência de curvaturas foi analisada em função do canal radicular, dos terços da raiz, e dos planos de avaliação (coronal e sagital); e avaliados usando o teste Qui-Quadrado (significância de α=0.05). Dos 1200 canais radiculares avaliados, 92,75% apresentaram curvatura no terço apical e 73,25% no terço cervical quando da análise no plano coronal; a análise do plano sagital revelou 89,75% de canais curvos no terço apical e 77% no terço cervical. Canais radiculares com curvatura suave foram significantemente mais frequentes quando comparados com as demais categorias, independentemente do terço radicular ou do plano. A maioria dos canais radiculares dos primeiros e segundos molares superiores e inferiores apresentou algum grau de curvatura nos terços apical e cervical, independentemente do plano analisado (coronal ou sagital).

Piecewise straight line approximation of curve existing in slightly curved mesiobuccal root canal of mandibular first molar: a radiographic investigation / Aproximación a segmentos de línea recta en la curva existente del canal radicular mesiobucal ligeramente curvado del primer molar inferior: una investigación radiográfica

The aim of this study was to radiographically investigate the curve existing in slightly curved mesiobuccal canal of mandibular first molar by applying Piecewise straight line approximation. Extracted human mandibular molars were radiographed and one hundred radiographs were selected whose mesiobuccal canal showed slight curvature (10-20°) according to Schneider's method. The curves were traced and analyzed using Piecewise straight line method. Each curve was considered as a unit consisting of six different pieces of straight lines joining at seven specific points and the angle of curvature at these points was determined using the slope formula. All curves analyzed in this study had varying degrees of curvatures at different points on the curve. Maximum curvature (0.40°) was recorded at the middle third of the root canal. Within the limitation of the study, significant curvature occurs through out the curve existing in the mesiobuccal canal of mandibular first molar and the middle third of the curve showing greater degree of curvature. There is a possibility of greater curvature occurring in the coronal third of the curve. Though three dimensional studies would be more appropriate, Piecewise straight line approximation may be a better method than existing methods to simulate canal geometry.

El objetivo de este estudio fue investigar radiográficamente la curva existente en el canal radicular mesiobucal ligeramente curvado del primer molar inferior mediante la aplicación de aproximaciones a segmentos de línea recta. Se utilizaron molares inferiores humanos extraídos que fueron radiografiados. Fueron seleccionadas, según el método de Schneider, 100 radiografías cuyo canal mesiobucal mostró una ligera curvatura (10-20°). Las curvas fueron delineadas y analizadas mediante el método de aproximación a segmentos de línea recta. Cada curva se consideró como una unidad que consta de seis diferentes segmentos de línea recta que unen a siete puntos específicos y el ángulo de curvatura en estos puntos se determinó utilizando la fórmula de la pendiente. Todas las curvas analizadas en este estudio tenían diversos grados de curvaturas en diferentes puntos de la curva. La curvatura máxima (0,40°) se registró en el tercio medio del canal radicular. Dentro de la limitación del estudio, una curvatura significativa se produce a través de la curva existente en el canal mesiobucal del primer molar inferior y el tercio medio de la curva que muestra un mayor grado de curvatura. Existe la posibilidad que ocurra una mayor curvatura en el tercio coronal de la curva. Aunque un estudio tridimensional sería más apropiado, la aproximación a segmentos de línea recta puede ser un mejor método que los existentes para simular la geometría del canal.

Radios de curvatura corneal encontrados en diferentes condiciones corneales de carácter hereditario, genético o iatrogénico / Radios of corneal curvature found in different corneal conditionsof hereditary, genetic or iatrogenic character

En este artículo de revisión se pretende determinar los radios de curvatura que se pueden presentar en patologías y en alteraciones corneales de carácter hereditario, genético o iatrogénico, tanto en córneas planas y en córneas curvas como la esclerocórnea, microcórnea, megalocórnea, queratocono, queratoglobo, miopía de curvatura y otros. Se hizo una revisión bibliográfica de artículos con la información necesaria para identificar las alteraciones corneales más frecuentes que se pueden presentar en pacientes con córneas planas y córneas curvas diferentes a las queratometria, consideradas medidas promedio comprendidas entre 42,00 y 45,00 D. Se concluyó que los pacientes con córneas planas presentaban una refracción corneal entre 20,00 D y 41,50 D, siendo 32,25 D el promedio encontrado en la revisión; en las córneas curvas se encontraron refracciones corneales entre 51,00 D y 59,75 D, con un promedio de 55,50 D.

In this review there was tried to determine the curvature radius present in some pathologies and corneal diseases of hereditary, genetic or iatrogenic character, in flat corneas and steep corneas as esclerocornea, microcornea, megalocornea, Keratoconus, keratoglobus, curvature myopia and others. An article review was made to identify frequent corneal alterations that can be found in patients with flat and steeper curves different from corneal measures average between 42.00 and 45.00 D. It was concluded that in the patients with on flat corneas the corneal refraction was from 20.00 D to 41.50 D being the average value in the review 32.25 D; in steeper corneas, corneal refractions were from.

Method for determination of root curvature radius using cone-beam computed tomography images

This article describes and discusses a method to determine root curvature radius by using cone-beam computed tomography (CBCT). The severity of root canal curvature is essential to select instrument and instrumentation technique. The diagnosis and planning of root canal treatment have traditionally been made based on periapical radiography. However, the higher accuracy of CBCT images to identify anatomic and pathologic alterations compared to panoramic and periapical radiographs has been shown to reduce the incidence of false-negative results. In high-resolution images, the measurement of root curvature radius can be obtained by circumcenter. Based on 3 mathematical points determined with the working tools of Planimp® software, it is possible to calculate root curvature radius in both apical and coronal directions. The CBCT-aided method for determination of root curvature radius presented in this article is easy to perform, reproducible and allows a more reliable and predictable endodontic planning, which reflects directly on a more efficacious preparation of curved root canals.

O objetivo deste estudo foi discutir um método para obter o raio de curvatura a partir de imagens de tomografias computadorizadas cone beam (CBCT). A severidade da curvatura do canal radicular é essencial para selecionar o instrumento e a técnica de instrumentação. O diagnóstico e o planejamento do tratamento endodôntico tem sido feito com o auxílio da radiografia periapical. Contudo, a precisão da imagem obtida por CBCTpara identificar alterações anatômicas e patológicas reduz os resultados falso-negativos. Em imagens com alta qualidade de resolução a mensuração do raio de curvatura pode ser obtida a partir do circuncentro. Baseado em três pontos matemáticos com a ferramenta de trabalho de um software (Planimp®) pode-se calcular o raio de curvatura em ambas as direções, tanto para frente em sentido apical, como para trás em direção cervical. Este método para se determinar o raio de curvatura auxiliado por imagens de tomografia computadorizada é fácil, reprodutível e favorece o planejamento do tratamento endodôntico o que influencia na eficácia do preparo de canais radiculares curvos.