Stress analysis of the supporting tissues for mandibular Kennedy ClassⅠ defect repaired with removable partial dentures supported by implants / 上海交通大学学报（医学版）

Objective·To compare the stress distribution at abutments, edentulous ridge, and peri-implant tissue under the vertical load between the RPI-type removable partial denture supported by implants with different diameter and the conventional RPI-type removable partial denture using a three-dimensional photoelastic method. Methods·The mandibular Kennedy I type denture defect models were fabricated according to the standard mandibular model. Four Straumann system soft tissue level implants with different diameters (two 4.1 mm implants and two 3.3 mm implants) were implanted into the bilateral first molar areas. Planting nails and epoxy resin teeth were inversely put into the mandibular silicone rubber molds to fabricate the epoxy resin photoelastic models and the regular neck (RN) healing abutments were screwed into the implants. A simulated alveolar mucosa with thickness of 2mm and a conventional RPI-type removable partial denture were placed on the epoxy resin models with or without implants. Then a force of 1 kg was vertically applied by a bite force loading device which fixed the model and denture in the centric occlusion. After the stress was frozen, model slices at different areas were cut and the stress fringes were observed. The stress was calculated according to the fringe value of per unit thickness. Results·For the conventional RPI-type removable partial denture, the maximum stress of distal abutment was mainly concentrated on the apical regions and the maximum stress of edentulous ridge was concentrated on the first molar area, particular on the lingual side of alveolar bone. For the implant-supported RPI-type removable partial denture, the maximum stress of distal abutment was lower than that of the conventional RPI-type removable partial denture, and the maximum stress of edentulous ridge (without the implants) was similar to that of abutment and supporting tissues and was lower than that of the conventional RPI-type removable partial denture. The stress around the implant was the largest and the peri-apical stress of implant was greater than the neck stress of implant. Meanwhile, the maximum stress around the implant was increased with the decrease of implant diameter. Conclusion·Compared to the conventional RPI-type removable partial denture, removable partial dentures supported by implants are more stable with a more balanced stress distribution in supporting tissues, thus benefit the health of abutments and supporting tissues.

Stress analysis in maxillary all-on-four model / Análisis del estrés en un modelo maxilar del concepto all-on-four

The aim of this research was to evaluate the load distribution in tilted distal implants used in the all-on-four system. Two implant schemes were used. In both, two vertical anterior implants and tilted posterior implants were installed, one group with an angulation of 15 and another with an angulation of 35. The implants were installed together with a bar binding them all in a photoelastic model obtained from a replica of an edentulous maxilla. In this model, loads were produced in the sector of the bar cantilever, the abutment of the tilted implants and over the four implants using devices specially designed for this purpose. The bands were recorded with a digital camera, and the qualitative and quantitative analyses were carried out by means of student's t-test and the Mann-Whitney test in Biostat v. 5.0, considering a level of p<0.05 to establish a statistically significant relation. In the qualitative analysis, the implant with 35 presented the greatest amount of stress on the cantilever forces at cervical level. The quantitative studies showed fewer differences in all aspects assessed, although significant differences were observed between the two systems when loads were applied at cantilever level. It can be concluded that there are minimal differences in the stress distribution when comparing implants with angulations of 15 or 35. However, there is a greater concentration of stress at the cervical level in implants tilted to 35.

El objetivo de esta investigación fue evaluar la distribución de cargas en implantes angulados distales utilizados en el sistema "All-On-Four". Dos esquemas de implantes fueron empleados. En ambos, dos implantes verticales en el área anterior y dos implantes angulados en el sector posterior fueron instalados, utilizando angulaciones de 15 y 35 o en estos últimos. Los implantes fueron instalados de forma conjunta mediante una barra unida al sistema de resina fotoelástica obtenida de una replica de una maxila edéntula. En este modelo, las cargas fueron producidas en el sector del cantiléver de la barra, el pilar del implante angulado y, mediante un sistema genérico, sobre la totalidad de los implantes. Las bandas de estrés fueron reconocidas en una cámara digital donde los análisis cualitativos y cuantitativos fueron realizados utilizando las pruebas t de Student y Mann-Whitney en el programa computacional Biostat v. 5.0, considerando un valor de p<0,05 para establecer diferencias significativas. En el análisis cualitativo, los implantes con 35 presentaron una gran cantidad de estrés en el área de cantiléver, principalmente a nivel cervical. Los estudios cuantitativos mostraron limitadas diferencias en todos los aspectos, aunque diferencias significativas fueron alcanzadas cuando se compararon ambos sistemas después de la carga a nivel del cantiléver. Se puede concluir que hay diferencias menores en la distribución de estrés cuando se comparan implantes dentales con angulación de 15 y 35. Sin embargo, existe una mayor cantidad de concentraciones de estrés a nivel cervical en los implantes con 35 de angulación.

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.

CAD fabrication of the mandible All-on-4 implant photoelastic model / 实用口腔医学杂志

Objective:To explore the method of the establishment of edentulous mandible All-on-4 implant photoelastic model with various distally tilted implants by computer-aided design(CAD).Methods:The edentulous mandible specimen was scanned by CT. Three-dimensional models of the mandible consisting of implant location were reconstructed and edited with Mimics and Geomagic Stu-dio software.Each of the four models had four implant sockets in the interforaminal area.In the first model,the bilateral distal im-plants were placed vertically.In the other models,the posterior implants were respectively inclined by 1 5°,30°and 45°distally.The four models were manufactured by RP and then the All-on-4 photoelastic models were made by traditional ways.Results:The ob-tained ethoxyline resin models featured bright surface,homogeneous structure,faintly yellowish,high optical sensibility,precision im-plants location and with no natural stress.The model offered a good experimental basis for the stress measurement.Conclusion:The method of fabricating ethoxyline resin models by CAD is reproducible,which simplifies the operating process.

Osteotomía sagital de rama mandibular con osteosíntesis en L invertido: estudio mecánico con fotoelasticidad / Sagittal split ramus osteotomy with L inverted osteosynthesis: A mechanical study with photoelasticity

El objetivo de esta investigación es identificar las tensiones presentes en tornillos de osteosíntesis utilizados en la fijación de la osteotomía sagital de rama mandibular (OSRM). Se utilizaron dos modelos de OSRM realizados con resina fotoelástica donde el grupo 1 presentaba una osteotomía basilar recta mientras que el grupo 2 presentaba una osteotomía basilar angulada; en ambos se utilizo el sistema de L invertido para la osteosíntesis con tornillos 2.0 de 13 mm de longitud. Posteriormente el sistema fue instalado en un pilar sobre la maquina Instrom, donde se aplico una carga vertical de 1 mm/minuto hasta conseguir el desplazamiento de 3 mm; el punto de carga estuvo en la fosa central del primer molar. La distribución de franjas mostro mayor tensión en el tornillo mas próximo de la osteotomía en ambos grupos; en el grupo 2 se produjo una diseminación de fuerzas levemente hacia la basilar y en el grupo 1 se mantuvo la diseminación a través de la línea oblicua. Se puede concluir que ambas osteotomías mandibulares son eficientes en la distribución de cargas y que no se observan diferencias cualitativas entre tornillos en términos de cantidad de diseminación de energía

The aim of this research was to analyzed the tension in osteosynthesis screw used for fixation of sagittal split ramus osteotomy (SSRS). Was used two model of SSRS made in photoelastic resin; in one of them was include a basilar osteotomy and the another one only SSRS without basilar osteotomy; for both system was used inverted L osteosynthesis with 13 mm screw of 2.0 system. Posteriorly, the hemimandible was installed in Instrom machine with a vertical load of 1 mm/min until the displacement of 3 mm; the load point was on first molar. The fringe distribution show more tension in the screw close to osteotomy in both groups; when SSRS was united to basilar osteotomy was produced a inferior distribution of force and in the SSRS without basilar osteotomy group was maintained a distribution into the oblique line. It's was conclude that both mandibular osteotomies was efficient in load distribution and was not observed important differences between screw related to distribution of load

Macro design effects on stress distribution around implants: A photoelastic stress analysis.

Objectives: Biomechanics is one of the main factors for achieving long-term success of implant supported prostheses. Long-term failures mostly depend on biomechanical complications. It is important to distinguish the effects of macro design of the implants. Materials and Methods: In this study, the photoelastic response of four different types of implants that were inserted with different angulations were comparatively analyzed. The implant types investigated were screw cylinder (ITI, Straumann AG, Basel, Switzerland), stepped cylinder (Frialit2, Friadent GmbH, Manheim, Germany), root form (Camlog Rootline, Alatatec, Wilshelm, Germany), and cylindrical implant, with micro-threads on the implant neck (Astra, AstraTech, Mölndal, Sweden). In the test models, one of the implants was inserted straight, while the other one was aligned mesially with 15° angles. The superstructures were prepared as single crowns. A 150N loading was applied to the restorations throughout the test. Results: A comparison of the implant designs showed that there were no significant differences between the straight implants; however, between the inclined implants, the most favorable stress distribution was seen with the stepped cylinder implants. The least favorable stress concentration was observed around the root formed implants. Microthreads around the implant neck appeared to be effective in a homogenous stress distribution. Observations showed that misaligned implants caused less stress than straight implants, but the stress concentrations were not homogenous. Conclusion: As there were observable differences between the implant types, straight placed cylindrical implants showed better stress distribution characteristics, while inclined tapering implants had better stress distribution characteristics.

Estudo qualitativo fotoelástico do sistema de forças gerado pela mola "T" de retração com diferentes pré-ativações / Qualitative photoelastic study of the force system produced by retraction T-springs with different preactivations

OBJETIVO: avaliar o sistema de forças gerado pela mola T utilizada para fechamento de espaços. MÉTODOS: por meio do método experimental fotoelástico, avaliou-se a mola T utilizada no fechamento de espaços com duas variações de pré-ativação em sua porção apical, sendo uma com 30º e a outra com 45º. As molas foram confeccionadas com fio retangular de titânio-molibdênio (TMA) de secção 0,017" x 0,025", centralizadas no espaço interbraquetes de 27mm e ativadas em 5,0mm, 2,5mm e posição neutra. Para melhor confiabilidade dos resultados, os testes foram repetidos em três modelos fotoelásticos igualmente reproduzidos e confeccionados pelo mesmo operador. Para compreensão dos resultados, as franjas fotoelásticas visualizadas no polariscópio foram fotografadas e analisadas qualitativamente. RESULTADOS: por meio da análise qualitativa da ordem de franjas no modelo fotoelástico, notou-se que, nas extremidades de retração e ancoragem, a mola T com 30º de ativação apical apresentou um acúmulo de energia discretamente maior para o sistema de forças liberado.

OBJECTIVE: Evaluate the force system produced by the T-spring used for space closure. METHODS: By means of the experimental photoelastic method, we evaluated the T-spring-used for space closure-with two different preactivations on its apical portion, i.e., one with 30º and one with 45º. The springs were fabricated with rectangular 0.017 X 0.025-in titanium-molybdenum alloy (TMA), centered in a 27.0 mm interbracket space and activated at 5.0 mm and 2.5 mm, and in a neutral position. For more reliable results, tests were repeated on three photoelastic models duplicated and prepared by the same operator. To better understand the results, the fringes seen in the polariscope were photographed and analyzed qualitatively. RESULTS: Through qualitative analysis of the fringe order in the photoelastic model it was noted that at the retraction and anchoring ends the T-spring with 30º apical activation showed a slightly greater accumulation of energy relative to the force system that was generated.

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.

Development of the Photoelastic Model for the Tooth and Periodontal Tissue of Mandibular First Molar after Hemisection / 中国康复理论与实践

@#ObjectiveTo discuss the design and fabrication of the photoelastic model of mandibular first molar after hemisection.MethodsAccording to principles of similarity, different materials were used to manufacture the photoelastic model of mandibular first molar with hemisection, which included teeth, alveolar bone and pericementum.ResultsThe photoelastic modle of mandibular first molar with hemisection was manufactured, which was as similar as noumenon in appearance, parameter and boundary condition.ConclusionThe photoelastic model can be applied in qualitative analysis of the stress distribution in the periodontal supporting tissues of mandibular first molar with hemisection.

Photoelastic Stress Analysis of Two Kinds of Rigid Fixed Bridge Design after Hemisection of Mandibular First Molar / 中国康复理论与实践

@#ObjectiveTo observe the effects of the two kinds of rigid fixed bridge design on the stress of the alveolar bone of mandibular first molar after hemisection.MethodsThe normal mandibular first molars were selected as control group. The two-abutment teeth and three-abutment teeth rigidly fixed bridge designs were selected as trial group. Stress distributions in the remaining sections of the alveolar bone models were evaluated with photoelastic stress analysis method.ResultsThe stress values of two kinds of rigid fixed bridge design were higher than the control group but still below the twice. There was no significantly difference between two-abutment teeth rigidly fixed bridge design and three-abutment teeth rigidly fixed bridge design (P>0.05).ConclusionTwo-abutment teeth rigidly fixed bridge of mandibular first molar should be chosen after hemisection.

Photoelastic stress analysis of implants according to fixture design / 대한치과보철학회지

PURPOSE: The purpose of this study was to evaluate the pattern and the magnitude of stress distribution in the supporting tissues surrounding three different types of implants(ITI, 3i, and Bicon implant system). MATERIAL AND METHOD: Photoelastic models were made with PL-2 resin(Measurements Group, Raleigh, USA) and three implants of each kind were placed in the mandibular posterior edentulous area distal to the canine . For non-splinted restorations, individual crowns were fabricated on three titanium abutments. For splinted restorations, 3-unit fixed partial dentures were fabricated. Photoelastic stress analyses were carried out to measure the fringe order around the implant supporting structure under simulated loaded conditions(15 lb, 30 lb). CONCLUSION: The results were as follows; 1. Regardless of the implant design, stresses were increased in the apex region of loaded implant when non-splinted restorations were loaded. While relatively even stress distribution occurred with splinted restorations. Splinting was effective in the second implant. 2. Strain around Bicon implant were lower than those of other implants, which confirmed the splinting effect. The higher the load, the more the stress occurred in supporting tissue, which was most obvious in the Bicon system. 3. Stress distribution in the supporting tissue was favorable in the ITI system, while the other side of 3i system tended to concentrate the stress in some parts.

Photoelastic stress analysis of implants according to fixture design / 대한치과보철학회지

PURPOSE: The purpose of this study was to evaluate the pattern and the magnitude of stress distribution in the supporting tissues surrounding three different types of implants(ITI, 3i, and Bicon implant system). MATERIAL AND METHOD: Photoelastic models were made with PL-2 resin(Measurements Group, Raleigh, USA) and three implants of each kind were placed in the mandibular posterior edentulous area distal to the canine . For non-splinted restorations, individual crowns were fabricated on three titanium abutments. For splinted restorations, 3-unit fixed partial dentures were fabricated. Photoelastic stress analyses were carried out to measure the fringe order around the implant supporting structure under simulated loaded conditions(15 lb, 30 lb). CONCLUSION: The results were as follows; 1. Regardless of the implant design, stresses were increased in the apex region of loaded implant when non-splinted restorations were loaded. While relatively even stress distribution occurred with splinted restorations. Splinting was effective in the second implant. 2. Strain around Bicon implant were lower than those of other implants, which confirmed the splinting effect. The higher the load, the more the stress occurred in supporting tissue, which was most obvious in the Bicon system. 3. Stress distribution in the supporting tissue was favorable in the ITI system, while the other side of 3i system tended to concentrate the stress in some parts.

Analysis on mechanical property of remedy for scoliosis by PRSS / 中国矫形外科杂志

[Objective] Scoliosis with wedging of vertebra and open-up disc space over convex side can be reversed when PRSS(plate-rod system for scoliosis)was applied.In order to study the mechanical properties of the remedy for the scoliosis by PRSS,the photoelastic test was performed.[Method] The model that consists of five vertebra bodies and four intervertebral discs was built with aluminum and polycarbonate,thus the situation of low-grade scoliosis was simulated.The axial stress was loaded 0 kg,5kg,10 kg,15 kg,20 kg respectively,and the lateral side load was 0 kg,3 kg,6 kg,9 kg,and 12 kg respectively over the spinal column.According to the factual situation,the in-situ stress was measured by using photoelastic and strain gage method.ANSYS9.0 method was also applied to simulate the experiment process and evaluate the reliability of measurement.[Result]When PRSS was placed in,compressive stress was found to exert on the convex side whereas tensile stress was found on the concave side of the curvature,thus modulating bony growth of spinal vertebra,resulted in spinal column realignment.[Conclusion]The PRSS is an effective device to treat the scoliosis of the patients,especially in young children,because it not only can correct the deformity but also allows extension along with the children's growth.

Photoelastic stress analysis of implant supported fixed prostheses with different placement configurations in mandibular posterior region / 대한치과보철학회지

STATEMENT OF PROBLEM: More than 70% of patients who need the implant supported restoration are parially edentulous. The principles of design for implant supported fixed partial denture in mandibular posterior region are many and varied. Jurisdiction for their use is usually based on clinical evaluation. There are several areas of interest regarding the design of implant supported fixed partial denture in mandibular posterior region. 1) Straight and tripod configuration in implant placement, 2) Two restoration types such as individualized and splinted restorations. PURPOSE: The purpose of this study was to compare the amount and distribution of stress around the implant fixtures placed in the mandibular posterior region with two different arrangements and to evaluate the effects of splinting using the photoelastic stress analysis. MATERIALS AND METHODS: 1) Production of study model: Mandibular partially edentulous model was waxed-up and duplicated with silicone and two models were poured in stone. 2) Fixture installation and photoelastic model construction: Using surveyor(Ney, USA), 3 fixtures(two 4.0x13 mm, one 5.0x10 mm, Lifecore, USA) were installed in straight and tripod configurations. Silicone molds were made and poured in photoelastic resin (PL-2. Measurements group, USA). 3) Prostheses construction: Four 3-unit bridges (Type III gold alloy, Dongmyung co., Korea) were produced with nonhexed and hexed UCLA abutments and fitted with conventional methods. The abutments were tightened with 30 Ncm torque and the static loads were applied at 12 points of the occlusal surface. 4) Photoelastic stress analysis: The polarizer analyzer system with digital camera(S-2 Pro, Fujifilm, Japan) was used to take the photoelastic fringes and analysed using computer analysis program. RESULTS: Solitary hexed UCLA restoration developed different stress patterns between two implant arrangement configurations, but there were no stress transfer to adjacent implants from the loaded implant in both configurations. However splinted restorations showed lesser amount of stresses in the loaded implants and showed stress transfer to adjacent implants in both configurations. Solitary hexed UCLA restoration with tripod configuration developed higher stresses in anterior and middle implants under loading than implants with straight configurations. Splintied 3 unit fixed partial dentures with tripod configuration showed higher stress development in posterior implant under loading but there were no obvious differences between two configurations. CONCLUSIONS: The tripod configuration of implant arrangement didn't show any advantages over the straight configuration. Splinting of 3 unit bridges with nonhexed UCLA abutments showed less stress development around the fixtures. Solitary hexed UCLA restoration developed tilting of implant fixture under offset loads.

A photoelastic stress analysis of fixed partial dentures with bicon implants on mandibular posterior area / 대한치과보철학회지

STATEMENT OF PROBLEM: Several prosthetic options are available for the restoration of multiple adjacent implants. A passively fitting prosthesis has been considered a prerequisite for the success and maintenance of osseointegration. Passivity is a particular concern with multiple implants because of documented inaccuracies in the casting and soldering process. One way to avoid this problem is to restore the implants individually, however, the restorations of individual adjacent impants requires careful adjustment of interproximal contacts. PURPOSE: The purpose of this study was to compare the stress distribution pattern and amount surrounding Bicon implants with individual crowns and splinted restorations. MATERIAL AND METHOD: A photoelastic model of a human partially edentulous left mandible with 3 Bicon implants(4*1 mm) was fabricated. For non-splinted restorations, individual crowns were fabricated on 3 abutments (4.0*6.5 mm, 0 degree, 2.0 mm post, Bicon Inc., Boston, USA) After the units were cemented, 4 levels of interproximal contact tightness were evaluated: open, ideal (8 micrometershim stock drags without tearing), medium(40 micrometer), and heavy(80 micrometer). Splinted 3-unit fixed partial dentures were fabricated and cemented to the model. Changes in stress distribution under simulated non-loaded and loaded conditions(7.5, 15, 30 lb) were analyzed with a circular polaricope. RESULTS: 1. Stresses were distributed around the entire body of fin in Bicon implants. 2. Splinted restorations were useful for distribution of stress around implants especially with higher loads. 3. By increasing the contact tightness between the individually restored three implants, the stress increased in the coronal portion of implants. CONCLUSIONS: Ideal adjustment of the contact tightness was important to reduce the stresses around individually restored Bicon implants.

A photoelastic stress analysis of fixed partial dentures with endopore implants according to splinting, contact tightness, and crown length / 대한치과보철학회지

STATEMENT OF PROBLEM: A difficulty in achieving a passive-fitting prosthesis can be overcome by individual crown restoation of multiple implants. But individualized crown has another difficulty in control of contact tightness and stress distribution. PURPOSE: This in vitro study is to evaluate the stress distribution and the magnitude in the supporting tissues around Endopore implants with different crown lengths, interproximal contact tightness, and the splinting effects. MATERIAL & METHODS: Three Endopore implants(4.1*9 mm) were placed in the mandibular posterior edentulous area distal to the canine and photoelastic model was made with PL-2 resin(Measurements Group, Raleigh, USA). Restorations were fabricated in two crown lengths: 9, 13 mm. For non-splinted restorations, individual crowns were fabricated on three custom-milled titanium abutments. After the units were cemented, 4 levels of interproximal contact tightness were evaluated: open, ideal(8 micrometershim stock drags without tearing), medium(40 micrometer), and heavy(80 micrometer). For splinted restorations, 3-unit fixed partial dentures were fabricated. This study was examined under simulated non-loaded and loaded conditions(6.8 kg). Photoelastic stress analysis was carried out to measure the fringe order around the implant supporting structure. RESULTS: 1. When restorations were not splinted, the more interproximal contact tightness was increased among the three implants, the more stress was shown in the cervical region of each implant. When crown length was increased, stresses tended to increase in the apex of implants but there were little differences in stress fringes. 2. When nonsplinted restorations were loaded on the first or third implant, stresses were increased in the apex and cervical region of loaded implant. Regardless of interproximal contact tightness level, stresses were not distributed among the three implants. But with tighter interproximal contact, stresses were increased in the cervical region of loaded first or third implant. 3. When the nonsplinted restorations were not loaded, there were little stresses on the supporting structure of implants, but low level stresses were shown in the splinted restorations even after sectioning and soldering. 4. With splinted restorations, there were little differences in stresses between different crown lengths. When splinted restorations were loaded, stresses were increased slightly on the loaded implant, but relatively even stress distribution occurred among the three implants. CONCLUSIONS: Splinting the crowns of adjacent implants is recommended for Endopore implants under the overloading situation.

A photoelastic evaluation of stress distribution during distal movement of upper molar / 대한치과교정학회지

The purpose of this study was to photoelastically visualize the distribution of forces transmitted to the alveolus and surrounding structures using three different types of headgear for the distal movement of the upper molars. A photoelastic maxillary model was made and three different directional forces applied, which were high-pull, straight- pull, and cervical-pull. Stress distribution was recorded through circular polariscope, and two-dimensional photoelastic stress analysis was performed according to isochromatic fringe characteristics. The results were as follows: 1. In the case of high-pull headgear, bodily movement occurred in the medium-length outer bow, stress distribution in the apical region was 1st molar, 2nd premolar, 1st premolar in sequence and there was no apparent difference. 2. In the case of straight-pull headgear, bodily movement occurred in the long outer bow and stress distribution in the apical region was heavy in the 1st molar, 2nd premolar, 1st premolar in sequence. But, there were no apparent differences according to the length of the outer bow. 3. In the case of cervical-pull headgear, bodily movement also occurred in the long outer bow, and apical stress of the premolar region was heaviest among other cases and apical stress of the 2nd premolar was heaviest in the short outer bow. In clinical situations, to achieve bodily movement of the upper 1st molars without modifying outer bow height, applying an outer bow length as long as the inner bow length in high-pull headgear and applying an outer bow length longer than the inner bow length in straight-pull, cervical-pull headgear are recommended.

A photoelastic study on the initial stress distribution of the upper anterior teeth retraction using combination loop archwire and sliding mechanics / 대한치과교정학회지

An unfavorable tipping movement can occur during the retraction of anterior teeth because orthodontic force is loaded by brackets positioned far from the center of resistance. To avoid this unfavorable movement, a compensating curved wire or lingual root torque wire is used. The purpose of this study is to investigate, using photoelastic material, the distribution of initial stress associated with the retraction of the incisors according to the degree of the compensating curve, to model changes associated with tooth and alveolar bone structure. The following results were obtained by analysis of the polarizing plate of the effects of initial stress resulting from retraction of the anterior teeth: 1. When the incisors were retracted using combination archwire or sliding mechanics, the maximal polarizing pattern of the apical area decreased as the degree of the compensating curve increased from 0 to 15 to 30. 2. When the incisiors were retracted by the combination archwire or sliding mechanics, the maximal polarizing pattern of t he canine and premolar area increased as the degree of the compensating curve increased from 0to 15to 30. 3. A lower degree of polarizing patterns were associated with the combination archwire technique than the sliding mechanics technique at a given force. The above results indicate that there is no significant difference between the combination loop archwire technique and sliding mechanics, for the retraction of maxillary anterior teeth with decreased lingual tipping tendency by a compensating curve on the arch wire. However, the use of sliding mechanics is more effective for the prevention of lingual inclination of the anterior teeth, because the hook used in sliding mechanics is closer to the center of resistance of the maxillary anterior teeth.

Three dimensional photoelastic study on the initial stress distributions of alveolar bone when retracted by lingual K-loop archwire / 대한치과교정학회지

This study was designed to investigate the stress distribution of alveolar bone in case of en masse retraction with lingual K-loop archwire using the 3-dimensional photoelastic stress analysis followed by stress freezing process. Lingual K-loop archwire which had loop in 15mm height was used and activated by retraction force of 350gm per each side. The results were as follows: 1. Central incisor: As the closer side to crown, the larger tensile stress was distributed at both mesial and labial surfaces and the larger compressive stress was distributed at distal surface. As the closer side to root apex, the larger compressive stress was distributed at lingual surface. The compressive stress was distributed at root apex. 2. Lateral incisor: The tensile stress was distributed at the coronal side of mesial surface. The compressive stress was distributed at distal surface. As the closer side to crown, the larger tensile stress was distributed at labial surface. The tensile stress was distributed at coronal side and the compressive stress was distributed at apical side of lingual surface. The compressive stress was distributed at root apex. 3. Canine: The tensile stress was distributed at coronal side and the compressive stress was distributed at apical side of mesial surface. The tensile stress was distributed at distal surface. As the closer side to crown, the larger tensile stress was distributed at both mesial and distal surfaces. The compressive stress was distributed at root apex. 4. Second premolar: The tensile stress was distributed at mesial surface. The compressive stress was distributed at coronal side and the tensile stress was distributed at apical side of distal surface. The compressive stress was distributed at coronal side of buccal surface. As the closer side to crown, the larger tensile stress was distributed at lingual surface. The compressive stress was distributed at root apex. 5. First molar: As the closer side to crown, the larger tensile stress was distributed at both mesial and distal surfaces. No stress was distributed at buccal surface and palatal root apex. As the closer side to crown, the larger tensile stress was distributed at both lingual surfaces. The compressive stress was distributed at buccal root apexes. 6. Second molar: The compressive stress was distributed at all root apexes. As the closer side to crown, the larger compressive stress was distributed at both mesial and lingual surfaces, and the larger tensile stress at both distal and buccal surfaces. Transverse bowing effect was observed in en-masse retraction with lingual K-loop archwire, however vertical bowing effect was not. Rather, reverse vertical bowing effect was developed.