Photoelastic Analysis of Two Maxillary Protocols Using Zygomatic Implants / Análisis Fotoelástico de Dos Protocolos Maxilares con Uso de Implantes Cigomáticos

The aim of this study was to analyse the in vitro the stress distribution in craniofacial structures around zygomatic implants. Synthetic polyurethane skulls replicas were used as templates for installation of standard and zygomatic implants performing two techniques using rehabilitation with using one zygomatic implant in the right and left side in combination with 2 and 4 standard implants in the anterior maxilla (group 1 and group 2). The skull replicas of photoelastic resin were subjected to photoelastic analysis after linear loading using an Instron 4411 servohydraulic mechanical testing, with a 2 mm displacement. The stress distribution showed the fringes with concentration in the body and the frontal process of zygomatic bone. In the case of model 1, higher concentrations of stress were found around the standard and zygomatic implants and surrounding bone. Under this condition, the rehabilitation with 2 zygomatics implants and 4 standard implants (group 2) provided the most favorable behavior.

El objetivo de este estudio fue analizar el estrés in vitro y la distribución de tensiones en la estructura craneofacial a partir de los implantes cigomaticos. Réplicas de cráneo de poliuretano fueron usados como modelos para la instalación de implantes cigomáticos estándar utilizando dos modelos de distribución de implantes. Estos modelos fueron usados como modelos utilizando 1 implante en cada lado con dos o cuatro implantes convencionales en la región anterior maxilar (grupo 1 y grupo 2); posteriormente, se realizó una carga compresiva unilateral en la máquina Instrom 4411 utilizando 2 mm de desplazamiento máximo. La distribución de estrés se concentró principalmente en la región de cuerpo de hueso cigomático y en la región frontal del proceso cigomático; el modelo 1, con dos implantes convencionales, mostró mayor distribución de estrés en la región cigomática al comparase con el grupo 2; bajo estas condiciones, se concluye que la distribución con cuatro implantes convencionales entrega mejores condiciones de distribución de tensiones.

Distribuição das tensões promovidas por implantes cone morse inseridos em diferentes níveis ósseos: análise fotoelástica e método dos elementos finitos / Stress distribution promoted by morse taper connection implants inserted in different bone levels: photoelastic analysis and finite element method

Ainda não existe um consenso sobre o nível em que os implantes cone Morse devem ser inseridos em relação à crista ósse alveolar. A literatura mostra diversas pesquisas em animais e laboratoriais com implantes posicionados acima, abaixo ou ao nível da crista. Contudo, diferentes metodologias e técnicas dificultam a definição do melhor nível de localização. O presente trabalho optou por analisar qualitativa e quantitativamente por meio da fotoelasticidade e do método dos elementos finitos (MEF), implantes em diferentes níveis de inserção sob carga compressiva estática, visando elucidar esse tema. Quatro níveis foram simulados: 1 mm acima da crista (AC); ao nível da crista (AN); 1 mm abaixo da crista sem aposição óssea sobre a plataforma (AB-S); e 1 mm abaixo da crista com aposição óssea sobre a plataforma (AB-C). Os resultados fotoelásticos demonstraram maiores valores de ordem de franja na região apical e menores na região cervical, em todos os modelos, independente do tipo de carga. No MEF verificou-se que o aprofundamento do implante da posição AC para AB-S reduziu progressivamente as tensões de von Mises na região cortical independente do tipo de carga, respectivamente, 0,5595 - 0,3842 Mpa nas cargas cêntricas e 1,5261 - 0,9787 MPa nas excêntricas. Concluiu-se que houve redução na concentração de tensões posicionado-se o implante abaixo do crista óssea e uma tendência de aumento de tensão nas amostras AB-C, provavelmente devido à tração do osso existente sobre a plataforma do implante.

There is still no consensus on the level that the Morse taper implants should be inserted in relation to the alveolar crestal bone. The literature shows several studies in animals and laboratory implant positioned above, at level or subcrestal. However, different methodologies and techniques make it difficult to define the best level of the implant. This study analyzes qualitatively and quantitatively by using photoelastic analysis and the finite element method (FEM), implants at different levels under static compressive load, to elucidate this issue. Four levels were simulated: 1 mm above the crest (AC); the crest level (AN); 1 mm below the crest free bone apposition on the platform (AB-S); and 1 mm below the crest with bone apposition on the platform (ABC). Photoelastic results demonstrated higher fringe order of values in the apical region and lower in the cervical region, in all models, regardless of the loading type. In MEF found that the deepening of the implant position from AC to AB-S progressively reduced von Mises equivalent stresses in cortical region independent of the load type, respectively, 0.5595 - 0.3842 MPa in centric loads and 1.5261 - 0.9787 MPa in eccentric loads. It was concluded that there was a reduction in stress concentration on the implant positioned below the alveolar crest and a tendency of an increase in tension in the AB-C samples, probably due to traction on the existing bone implant platform.

Photoelastic stress analysis of the mandibular unilateral free-end removable partial dentures according to the design / 대한치과보철학회지

STATEMENT OF PROBLEM: There are common clinical cases in which the mandibular first and second molars are missing unilaterally. PURPOSE: This study was designed to compare and evaluate the magnitude and distribution of stress produced by four kinds of mandibular unilateral free-end removable partial dentures that could be applied clinically in Kennedy class II cases. MATERIAL AND METHODS: Four unilateral free-end removable partial dentures using clasp, Konus crown, resilient attachment, and flexible resin were fabricated on the photoelastic models of the Kennedy class II cases. The vertical load of 6kg was applied on the central fossa of the first molar of every removable partial denture in the stress freezing furnace and the photoelastic models were frozen according to the stress freezing cycle. After these models were sliced mesio-distally to a thickness of 6mm, the photoelastic isochromatic white and black lines of the sliced specimens were examined with the transparent photoelastic experiment device and photographs were taken with a digital camera. The fringe order numbers at eight measuring points in the photograph were measured with the naked eye. RESULTS: The maximum fringe order number of each sliced specimen and the fringe order number at the residual ridge just below the loading point were in the decreasing order of the unilateral removable partial dentures using flexible resin followed by clasp, resilient attachment, and Konus crown. The fringe order number at the root apex of the second premolar was in the decreasing order of the unilateral removable partial dentures using clasp followed by flexible resin, Konus crown, and resilient attachment. CONCLUSION: The removable partial denture using Konus crown showed the most equalized stress distribution to the supporting alveolar bone of abutment teeth and residual ridge under the vertical loads. The removable partial denture using flexible resin can be applied to the case that has a better state of residual ridge than abutment teeth.

A photoelastic study of the stress distribution on canine retraction by segmented TMA T-loop spring / 대한치과교정학회지

The segmented TMA T-loop spring, used for reciprocal space closure and described by Burstone, was used to achievebodily movement of canine. Photoelastic analysis is a technique for the transformation of internal stress into visible light patterns. The two-dimensional photoelastic stress analysis was performed, and stress distribution was recorded by photography. The purpose of this study was to visualize photoelastically the distribution of forces transmitted to the alveolus and surrounding structures using new segmented TMA T-loop spring for canine retraction. The results were as follows: 1. Decreased activation produced decreased stress of upper 1st. premolar extraction site and increased intrusive stress of upper 1st. molar, regardless of T-loop position. 2. At 5mm activation, More posterior positioning of T-loop produced an increased stress in upper 1st. premolar extraction site. 3. At 3mm activation, More posterior positioning of T-loop produced an increased stress in upper 1st. premolar extraction site and mesial lower half of upper 1st. molar mesio-buccal root. 4. At 1mm activation, More anterior positioning of T-loop produced an increased stress in upper mesial and blew apex area of upper canine root. 5. 0.25 B/L ratio and 3mm activation produced bodily movement of canine. To summarize, desired tooth movement and anchorage requirement is possible by altering the activation and mesio-distal position of the T-loop spring.

A photoelastic study on the initial stress distribution of the upper anterior teeth when intrusive force applied (by utility archwire. burstone intrusion archwire. and "J" hook headgear) / 대한치과교정학회지

The purpose of this study was to analize the initial stress distribution around apex and the alveolar bone of the upper anterior teeth when applying intrusive force by the use of utility archwire, Burstone 3-piece intrusion archwire, and "J" hook headgear which is usually used in clinical practice. By the use of the polarization plate, initial stresses were analized when 80g and 150g force applied. The results were as follows. 1. With the utility archwire, moderate levels of stress were evenly distributed on the apical areas of the anterior teeth and concentrated on the apical areas of the first molars. 2. With the Burstone's 3-piece intrusion archwire, moderate levels of stress were evenly distributed on the apical areas of the anterior and posterior teeth. 3. With the "J" hook headgear, severe levels of stress were widely distributed on, the alveolar- bone and apical areas of the upper anterior teeth, and concentrated on the apical area between the central and the lateral incisors. Especially. weak levels of stress appeared along the periodontal ligament space of all teeth.

A photoelastic study on the stress distribution of the upper anterior teeth when retract with high pull J-hook headgear / 대한치과교정학회지

This study was designed to inveatigate the stress intensity and distribution produced by 1mm activation of retraction archwire with 0degrees, 7degrees, 14degrees torque and application of high pull J-hook headgear during retraction of four maxillary incisors using the photoelatic stress analysis. The photoelastic model was made with a PL-3 type epoxy resin which was substituted by alveolar bone portion. Each retraction archwire was fagricated from .020" x .025" stainless steel wire which had vertical loops in 7mm height and hook for high pull J-hook headgear between central and lateral incisors. The high pull J-hook headgear was applied 35 degree backward and upward to occlusal plane with 200mg per each side. The findings of study as follows : 1. In case of 0degrees torque, the stress was distributed from cervical 1/3 to apex of root of central and lateral incisors which were the froms of arc mode. When the high pull J-hook headgear was applied, the stress disrtrbuted by following by arc mode was presented from cervical 1/2 to apex of roots of central and lateral incisors. And the stress distributed by following the root surface was presented from alveolar crest to cervical 1/2 of central and lateral incisors. The stress between apecies of central and lateral incisors was presented also. 2. In case of 7degrees torque, the stress distributed by arc mode was presented from cervical 1/2 to apex of roots of central and lateral incisors. And the stress distributed by following the root surface was presented from alveolar crest to cervical 1/2 of roots of central and lateral incisors. When the hight pull J-hook headgear was applied, the stress distributed by following the root surface was presented more apically than without headgear. The stress between apecies of central and lateral incisors was presented also. 3. In case of 14degrees torque, the stress distributed by following the root surface was presented from alveolar crest to apex of roots of central and lateral incisors. When the high pull J-hook headgear was applied, the stress distributed by following the root surface was presented stronger than without headgear. The stress between apecies of central and lateral incisors was presented also.