Intrusion of overerupted periodontally compromised posterior teeth using orthodontic mini implants: A mechanobiological finite element study.

INTRODUCTION: The intrusion of posterior teeth had been considered challenging up to the development of orthodontic mini implants. In periodontally compromised teeth, the challenge is even greater, because of the root resorption risk due to periodontal ligament over-compression. Still, the precise strategy to determine the force reduction level remains uncertain. OBJECTIVE: The objective of the study was to determine, by a finite element analysis (FEA), the force reduction needed to avoid root resorption and maintain the efficiency of orthodontic mechanics of periodontally compromised teeth similar to the sound one. METHODS: An anatomical model was constructed representing a premolar inserted into a maxillary bone. Based on the initial model (R0), three bone height loss conditions were simulated (R2 = 2 mm, R4 = 4 mm, and R6 = 6 mm). Two intrusive movements were simulated: pure intrusion (bilateral mini implant) and uncontrolled-tipping intrusion (buccal mini implant). The hydrostatic stress at the periodontal ligament was used to evaluate the risk of root resorption due to over-compression. RESULTS: For bilateral mini implant intrusion, the force had to be decreased by 16%, 32% and 48% for R2, R4 and R6, respectively. For buccal mini implant intrusion, the required reductions were higher (20%, 36% and 56%). A linear relationship between the intrusive force reduction and the alveolar bone height loss was observed in both intrusion mechanics. CONCLUSIONS: According to the FE results, 8% or 9.3% of force reduction for each millimetre of bone height loss is suggested for intrusion with bilateral or buccal mini implant, respectively. The buccal mini implant anchorage must be associated with a supplemental strategy to avoid buccal crown tipping.

Can maxilla and mandible bone quality explain differences in orthodontic mini-implant failures?

Purpose: This study aimed to compare the risk of orthodontic mini-implant (OMI) failure between maxilla and mandible. A critical analysis of finite-element studies was used to explain the contradiction of the greatest clinical success for OMIs placed in the maxilla, despite the higher quality bone of mandible. Materials and Methods: Four tridimensional FE models were built, simulating an OMI inserted in a low-dense maxilla, control maxilla, control mandible, and high-dense mandible. A horizontal force was applied to simulate an anterior retraction of 2 N (clinical scenario) and 10 N (overloading condition). The intra-bone OMI displacement and the major principal bone strains were used to evaluate the risk of failure due to insufficient primary stability or peri-implant bone resorption. Results: The OMI displacement was far below the 50-100 µm threshold, suggesting that the primary stability would be sufficient in all models. However, the maxilla was more prone to lose its stability due to overload conditions, especially in the low-dense condition, in which major principal bone strains surpassed the pathologic bone resorption threshold of 3000 µstrain. Conclusions: The differences in orthodontic mini-implant failures cannot be explained by maxilla and mandible bone quality in finite-element analysis that does not incorporate the residual stress due to OMI insertion.

Effect of three different attachment designs in the extrusive forces generated by thermoplastic aligners in the maxillary central incisor.

INTRODUCTION: Orthodontic aligners use have increased in dentistry. The resolution of complex movements such as extrusion demands the use of attachments to reach the aimed force, but just a few studies have been developed to evaluate the biomechanical performance of the aligners and their accessories. OBJECTIVE: The objective of this study was to evaluate on the three axes (X, Y and Z) the forces generated by three different attachment designs for the extrusion of the maxillary central incisor using esthetic orthodontic aligners. METHODS: Three prototypes of maxillary models were developed, each one with a specific attachment inserted in the central incisor. Three aligners were manufactured for each of the three attachment designs, with 0.33-mm activation in the direction of the extrusion. An analytical device was used to evaluate the forces applied to the three axes by each aligner/attachment. The data were assessed by one-way ANOVA and Tukey's test (α = 0.05). RESULTS: All of the studied attachment designs could satisfactorily perform the extrusion movement. However, force intensities were different in the three designs (design 1 = 2.5 N; design 2 = 2.2 N, and design 3 = 1.1 N). Furthermore, two of the three attachment designs (designs 1 and 2) eventually exerted significant forces on the X (mesiodistal) and Y (buccopalatal) axes. CONCLUSION: The attachment design 3 presents the best distribution of forces for extrusion movement, generating almost null forces on X and Y axes, and lower intensity of force on the Z axis.

Effect of three different attachment designs in the extrusive forces generated by thermoplastic aligners in the maxillary central incisor

ABSTRACT Introduction: Orthodontic aligners use have increased in dentistry. The resolution of complex movements such as extrusion demands the use of attachments to reach the aimed force, but just a few studies have been developed to evaluate the biomechanical performance of the aligners and their accessories. Objective: The objective of this study was to evaluate on the three axes (X, Y and Z) the forces generated by three different attachment designs for the extrusion of the maxillary central incisor using esthetic orthodontic aligners. Methods: Three prototypes of maxillary models were developed, each one with a specific attachment inserted in the central incisor. Three aligners were manufactured for each of the three attachment designs, with 0.33-mm activation in the direction of the extrusion. An analytical device was used to evaluate the forces applied to the three axes by each aligner/attachment. The data were assessed by one-way ANOVA and Tukey's test (α = 0.05). Results: All of the studied attachment designs could satisfactorily perform the extrusion movement. However, force intensities were different in the three designs (design 1 = 2.5 N; design 2 = 2.2 N, and design 3 = 1.1 N). Furthermore, two of the three attachment designs (designs 1 and 2) eventually exerted significant forces on the X (mesiodistal) and Y (buccopalatal) axes. Conclusion: The attachment design 3 presents the best distribution of forces for extrusion movement, generating almost null forces on X and Y axes, and lower intensity of force on the Z axis.

RESUMO Introdução: O uso de alinhadores ortodônticos tem aumentado na Odontologia. Porém, para a realização de movimentos complexos, como a extrusão, é necessário usar attachments para se obter as forças desejadas. Apesar disso, há poucos estudos que tenham avaliado o desempenho biomecânico dos alinhadores e de seus attachments. Objetivo: O objetivo do presente estudo foi avaliar nos três eixos (X, Y e Z) as forças geradas por três diferentes designs de attachments para extrusão de um incisivo central superior usando alinhadores ortodônticos. Métodos: Foram confeccionados três modelos superiores prototipados, cada um com um tipo de attachmentinserido no incisivo central. Três alinhadores foram fabricados para cada um dos três designs de attachment, com ativação de 0,33 mm na direção da extrusão. Foi, então, utilizado um equipamento de análise para mensurar, nos três eixos, as forças aplicadas por cada alinhador/attachment. Os dados foram submetidos à ANOVA de fator único e ao teste de Tukey (α?#8197;= 0,05). Resultados: Todos os designs de attachments utilizados foram capazes de exercer satisfatoriamente o movimento de extrusão. Entretanto, a intensidade das forças foi diferente nos três designs (attachment 1 = 2,5 N; attachment 2 = 2,2 N e attachment 3= 1,1 N). Além disso, dois dos três designs (attachments 1 e 2) exerceram forças significativas nos eixos X (mesiodistal) e Y (vestibulopalatino). Conclusões: o design do attachment 3 apresentou a melhor distribuição de forças para o movimento de extrusão, sendo o mais próximo de forças nulas nos eixos X e Y e força de baixa intensidade no eixo Z.

Improvement of full-thickness rat skin wounds by photobiomodulation therapy (PBMT): A dosimetric study.

Basic dosimetric studies are necessary to support the use of photobiomodulation therapy (PBMT), since the great variety of laser parameters that are reported in the literature have created an obstacle to identifying reproducible results. Thus, the present study evaluates the process of tissue repair after the photobiomodulation therapy, taking into consideration the dose, frequency and the mode of energy delivery used. For this, 6 mm diameter wounds were created on dorsal skin of Wistar rats, and the animals were divided in control and irradiated groups, where L1 and L4 (irradiated with 1 point of 10 J/cm2), L2 and L5 (5 points of 10 J/cm2), L3 and L6 (1 point of 50 J/cm2), respectively for one or multiple days of irradiations. A diode laser, λ 660 nm, 40 mW of power and 0.028 cm2 of spot area was used. Our data showed that the group receiving multiple treatments over the first week post wounding, applied at 10 J/cm2 at each of 5 points on and around the wound (group L5) presented the best improvement of wound closure, higher cytokeratin 10, lower macrophage infiltration, and greater tissue resistance to rupture. We conclude that PBMT improves the skin wound healing process, and the outcomes were directly related to the chosen laser parameters and irradiation mode.

Biomechanical evaluation of the sheep mandible as a model for studying fixation methods / Evaluación biomecánica de la mandíbula de oveja como modelo para estudiar los métodos de fijación

Recently, there has been increased interest in the use of natural jaws for better results in bone fixation studies. Thus, the sheep mandible has been chosen for such studies. The aim of this study was to evaluate the length and resistance of the sheep mandible when submitted to a compression test with freedom in the three axes of space. Seventy fresh sheep (Ovis aries) mandibles were used in this study. Initially, the soft tissues were removed, and measurements of the mandible size were performed. Fifty mandibles were selected for mechanical testing based on the mean values from this assessment. The mandibles were joined by fixation in the symphyseal region and were tridimensionally deformed. A metallic support suitable for study of the mandible under efforts with freedom in the three axes in space was used. For this test, three displacement cycles were applied. Based on the mean stiffness, 35 mandibles were selected. The mean value of the sheep mandible mensuration was 13.6 cm ± 0.53 cm. The mean value of the sheep mandible stiffness was 153.5N ± 54.0 N. These data are useful for future studies on fixation systems for fractures and orthognathic surgery.

Recientemente, ha aumentado el interés en el uso de mandíbulas naturales para obtener mejores resultados en estudios de fijación ósea. Por lo tanto, la mandíbula de las ovejas se ha elegido para tales estudios. El objetivo de este estudio fue evaluar la longitud y la resistencia de la mandíbula de oveja al ser sometida a una prueba de compresión con libertad en los tres ejes del espacio. Se utilizaron 70 mandíbulas de oveja fresca (Ovis aries). Inicialmente, se extirparon los tejidos blandos y se realizaron mediciones del tamaño de la mandíbula. Cincuenta mandíbulas fueron seleccionadas para pruebas mecánicas basadas en los valores promedio de esta evaluación. Las mandíbulas se unieron por fijación en la región sinfisial y se deformaron tridimensionalmente. Se utilizó un soporte metálico adecuado para el estudio de la mandíbula bajo esfuerzos con libertad en los tres ejes en el espacio. Para esta prueba, se aplicaron tres ciclos de desplazamiento. En base a la rigidez media, se seleccionaron 35 mandíbulas. El valor medio de la medición de la mandíbula de oveja fue de 13,6 cm ± 0,53 cm. El valor medio de la rigidez de la mandíbula de oveja fue 153,5 N ± 54,0 N. Estos datos son útiles para futuros estudios sobre sistemas de fijación para fracturas y cirugía ortognática.

Comparative analysis of polymerization shrinkage of different resin composites.

This study sought to compare the shrinkage of 3 resin composites after polymerization, using different curing modes and 2 methods of analysis, with 45 samples in each group. To evaluate free linear shrinkage, specimens were prepared in Teflon molds (8 mm diameter x 2 mm thick) with 1 of 2 methacrylate-based resins or a silorane-based resin. To evaluate wall-to-wall shrinkage, cavities (1.5 mm thick x 3 mm diameter) were prepared in 45 healthy bovine incisors and then restored. In both tests, the same curing lights were used: conventional quartz-tungsten-halogen, a conventional light-emitting diode (LED), and an exponential LED. Gaps were measured microscopically, and the gap percentage was calculated. The results were analyzed by 2-way ANOVA and Tukey's test (α = 0.05). Curing modes differed significantly in the free linear shrinkage test group, while resin composites did not. In the wall-to-wall shrinkage group, there were significant differences between the resin composites.

Clinical, biochemical and histological study of the effect of antimicrobial photodynamic therapy on oral mucositis induced by 5-fluorouracil in hamsters.

Oral mucositis (OM) is a debilitating side effect of chemotherapy, which can be relieved by phototherapy. Antimicrobial photodynamic therapy (aPDT) may be used for the treatment of OM, when infection is present. However, there are no studies showing that aPDT affects tissue repair process when used in the treatment of lesions caused by OM. This work aims to evaluate the effect of aPDT in healing OM induced by 5-Fluorouracil (5-FU). Two hundred forty-five hamsters were divided into two groups, control (C) and experimental, which were subdivided into 4 subgroups (Ch, ChP, ChL, aPDT). C group received only the vehicle of chemotherapy and anesthesia, whereas all animals of the experimental groups received anesthesia and chemotherapy agent 5-FU to induce OM. Ch group received no OM treatment; ChP group received an application of methylene blue (MB) 0.01%; ChL received irradiation with low-power-laser (LPL-660 nm/120 J /cm(2)/40 mW/4.4 J per point); and aPDT received MB and LPL irradiation. OM Clinical severity were daily assessed by a blinded examiner. The animals were sacrificed after 5, 7 and 10 days of experiment and their oral mucosa were removed for biochemical (enzymatic activity of SOD and catalase) and histological analyzes (light microscopy). After statistical analysis was performed, results showed that aPDT reduced the severity of OM on the tenth day of the experiment, when compared to the initial OM score (p < 0.05), as well as increased keratinization with organized collagen deposition in the lamina propria. In conclusion, aPDT can be safely used in animals with infected OM because it does not affect lesion-repairing processes.

Does self-ligating brackets type influence the hysteresis, activation and deactivation forces of superelastic NiTi archwires?

OBJECTIVE: To compare hysteresis, activation and deactivation forces produced by first-order deformation of Contour 0.014-in NiTi wire (Aditek, Brazil) in four brands of self-ligating brackets: Damon MX, Easy Clip, Smart Clip and In-Ovation. METHODS: Activation and deactivation forces were measured in an Instron universal tensile machine at 3 mm/minute speed to a total displacement of 4 mm. Tests were repeated eight times for each bracket/wire combination. Statistical analysis comprised ANOVA and Tukey's multiple comparisons test. RESULTS: Using a 4-mm deformation, mean activation forces increased in the following order: Damon = 222 gf, Easy Clip = 228 gf, In-Ovation = 240 gf and Smart Clip = 306 gf. The same order was observed for mean hysteresis values, i.e., 128 gf, 140 gf, 150 gf and 206 gf, respectively. The respective values of deactivation forces for the Damon, Easy Clip, In-Ovation and Smart Clip brackets were 94 gf, 88 gf, 90 gf and 100 gf. CONCLUSIONS: Brackets with higher activation forces were accompanied by higher hysteresis values, which resulted in clinically similar deactivation forces, regardless of the type of self-ligating brackets used.

Mechanical properties of nanofilled and microhybrid composites cured by different light polymerization modes.

This study compared nanofilled and microhybrid composites polymerized by different light polymerization modes, and the effects these modes had on the mechanical properties of the composites. The following mechanical properties were measured: Vickers microhardness numbers, diametral tensile strength, flexural strength, and flexural modulus. The filler content (Wt%) present in the resins was investigated. Data were treated statistically by ANOVA and Tukey's test (P ≤ 0.05) and the interaction of the inorganic content with the mechanical properties was analyzed by Pearson's correlation (P ≤ 0.05). The nanofilled material showed a higher percentage of inorganic filler and better mechanical properties when compared to the microhybrid composite. The correlation of Wt% with the tested properties was positive for all but the flexural strength test. Different light polymerization modes were shown not to have a significant influence on the mechanical properties of the composites in this study.

Flexural properties of resin composites: influence of specimen dimensions and storage conditions.

This study evaluated the influence of specimen dimensions and storage medium and temperature on the flexural properties of one dental resin composite. The material utilized throughout the study was Clearfil AP-X. Eighty specimens were built with dimensions of either 10×2×2 mm or 25×2×2 mm, stored dry or in distilled water, at 25 or 37ºC, for 24 h. Flexural strength and modulus were tested in three-point bending. Results were evaluated with three-way ANOVA and Tukey's test (α=0.05). Statistical significance was observed for all three factors: temperature (37ºC=190.8 MPa, 25ºC=165.3 MPa; p<0.01), storage medium (water=167.7 MPa, Dry=188.4 MPa; p<0.01) and specimen dimensions (10×2×2 mm=197.9 MPa, 25×2×2 mm=158.2 MPa; p<0.01). None of the interactions were significant. Within the limitations of this study, it can be concluded that factors such as specimen dimensions, storage medium and temperature significantly affect flexural strength results, which invalidates comparisons of results from studies that use different methodologies.

Does self-ligating brackets type influence the hysteresis, activation and deactivation forces of superelastic NiTi archwires?

OBJECTIVE: To compare hysteresis, activation and deactivation forces produced by first-order deformation of Contour 0.014-in NiTi wire (Aditek, Brazil) in four brands of self-ligating brackets: Damon MX, Easy Clip, Smart Clip and In-Ovation. METHODS: Activation and deactivation forces were measured in an Instron universal tensile machine at 3 mm/minute speed to a total displacement of 4 mm. Tests were repeated eight times for each bracket/wire combination. Statistical analysis comprised ANOVA and Tukey's multiple comparisons test. RESULTS: Using a 4-mm deformation, mean activation forces increased in the following order: Damon = 222 gf, Easy Clip = 228 gf, In-Ovation = 240 gf and Smart Clip = 306 gf. The same order was observed for mean hysteresis values, i.e., 128 gf, 140 gf, 150 gf and 206 gf, respectively. The respective values of deactivation forces for the Damon, Easy Clip, In-Ovation and Smart Clip brackets were 94 gf, 88 gf, 90 gf and 100 gf. CONCLUSIONS: Brackets with higher activation forces were accompanied by higher hysteresis values, which resulted in clinically similar deactivation forces, regardless of the type of self-ligating brackets used.

OBJETIVO: comparar as forças de ativação, desativação e histerese produzidas por deformação de primeira ordem do fio superelástico Contour NiTi 0,014" (Aditek®) em quatro modelos de braquetes autoligáveis: Damon MX, Easy Clip, Smart Clip e In-Ovation. MÉTODOS: as forças de ativação e desativação foram medidas em máquina universal de tração Instron com velocidade de 3mm/minuto e deslocamento de 4mm. Em cada combinação braquete/fio foram executadas oito repetições. A análise estatística empregou ANOVA e o Teste de Comparações Múltiplas de Tukey. RESULTADOS: com 4mm de deformação, as forças médias de ativação foram, em ordem crescente, Damon = 222gf, Easy Clip = 228gf, In-Ovation = 240gf e Smart-Clip = 306gf; a mesma ordem foi observada nas histereses médias, cujos valores foram, respectivamente, 128gf, 140gf, 150gf e 206gf; os valores das forças de desativação foram, respectivamente, 94gf, 88gf, 90gf e 100gf. CONCLUSÃO: os braquetes com maiores valores nas forças de ativação foram acompanhados por maiores valores na histerese, o que resultou em forças de desativação clinicamente semelhantes, independentemente do tipo de braquete autoligável utilizado.

A novel vibratory stimulation-based splint for chronic and untreatable masticatory myofascial pain: a case-series.

AIM: This clinical report aimed to introduce a novel vibratory stimulation-based occlusal splint (VibS) for management of chronic and untreatable masticatory myofascial pain (MMFP). METHODS: This study was conducted on four chronic MMFP patients (mean age: 27.5±5.56 years, females) who were diagnosed according to the research diagnostic criteria for temporomandibular disorders (RDC/TMD), and who were using stabilization splints for more than 6 months and still complained of pain above 40 mm in a 100-mm VAS scale. The included subjects utilized the active VibS and subsequently the inactive VibS during 30 days in each trial, separated by a wash-out period of at least 8 months. VAS pain levels were the only measured dependent variable, and were recorded before and after the use of active VibS and inactive VibS. RESULTS: At baseline, mean VAS pain levels before using the active or inactive splint were 54.5±19.8 mm and 44.0±13.6 mm, respectively. After using the active VibS, mean pain level decreased by 77% (VASpos-pre=-42.0±30.3 mm). On the other hand, after using the inactive VibS, severe pain aggravation of 67% in magnitude was observed (VASpos-pre=+29.5±21.5 mm). CONCLUSION: This case-series study demonstrated a good tendency of this novel VibS in chronic MMFP alleviation after a 4-week management period compared to a control inactive VibS.

Comparative study of frictional forces generated by NiTi archwire deformation in different orthodontic brackets: In vitro evaluation / Estudo comparativo da força de atrito produzida pela deformação de arco NiTi em diferentes braquetes ortodônticos: avaliação in vitro

INTRODUCTION: The purpose of this study was to compare the frictional forces between 0.014-in NiTi wires (Aditek) with 4 mm horizontal deflection and brackets with different archwire ligation systems. METHODS: Four types of self-ligating brackets (Damon MX, Easy Clip, Smart Clip and In-Ovation), a triple bracket (Synergy) and a twin bracket with 8-shaped ligature (Tecnident) were tested. Twin brackets with conventional elastomeric ligatures (Morelli) were used as control group. Tests were repeated 10 times for each bracket/archwire combination. Frictional forces were measured in an Instron universal tensile machine at 3 mm/minute speed and a total displacement of 6 mm. Statistical analysis comprised ANOVA and Dunnett's multiple comparison post hoc test. RESULTS: Deflection-induced frictional (DIF) forces increased in the following order: Synergy, Damon, 8-shaped Ligature, Easy Clip, In-Ovation, Smart-Clip and conventional ligatures. The differences among groups were significant, with the exception of the 8-shaped ligature groups which was equal to the Damon and Easy Clip groups. CONCLUSIONS: Compared to conventional ligatures, all ligation systems tested reduced frictional forces. However, such reduction varied according to the ligation system employed.

OBJETIVO: o objetivo desse trabalho foi comparar as forças de atrito entre fios NiTi 0,014" (Aditek) com deformações horizontais de 4mm, e braquetes com diferentes sistemas de ligação dos arcos. MÉTODOS: foram testados 4 tipos de braquetes autoligáveis (Damon MX, Easy Clip, Smart Clip e In-Ovation), um braquete triplo (Synergy) e um braquete gêmeo com amarrilho 8 (Tecnident). Como grupo controle, foi utilizado braquete gêmeo com ligadura elástica convencional (Morelli). Foram executadas 10 repetições em cada combinação arco/braquete. As forças de atrito foram medidas em máquina de tração universal Instron, com velocidade de 3mm/minuto e deslocamento total de 6mm. Para análise estatística, usou-se a ANOVA e o Teste de Comparações Múltiplas de Dunnett. RESULTADOS: as forças de atrito por deformação do fio se mostraram crescentes na seguinte ordem: Synergy, Damon, amarrilho 8, Easy Clip, In-Ovation, Smart-Clip e ligadura convencional. As diferenças entre todos os grupos foram estatisticamente significantes, com exceção do Amarrilho 8 em relação aos grupos Damon e Easy Clip. CONCLUSÃO: em relação à ligadura convencional, todos os sistemas de fechamento das canaletas testados são eficientes em reduzir a força de atrito, porém, tal redução varia significativamente de acordo com o sistema de fechamento da canaleta selecionado.

Comparative study of classic friction among different archwire ligation systems

OBJECTIVE: To describe and compare three alternative methods for controlling classical friction: Self-ligating brackets (SLB), special brackets (SB) and special elastomeric ligatures (SEB). METHODS: The study compared Damon MX, Smart Clip, In-Ovation and Easy Clip self-ligating bracket systems, the special Synergy brackets and Morelli's twin bracket with special 8-shaped elastomeric ligatures. New and used Morelli brackets with new and used elastomeric ligatures were used as control. All brackets had 0.022 x 0.028-in slots. 0.014-in nickel-titanium and stainless steel 0.019 x 0.025-in wires were tied to first premolar steel brackets using each archwire ligation method and pulled by an Instron machine at a speed of 0.5 mm/minute. Prior to the mechanical tests the absence of binding in the device was ruled out. Statistical analysis consisted of the Kruskal-Wallis test and multiple non-parametric analyses at a 1% significance level. RESULTS: When a 0.014-in archwire was employed, all ligation methods exhibited classical friction forces close to zero, except Morelli brackets with new and old elastomeric ligatures, which displayed 64 and 44 centiNewtons, respectively. When a 0.019 x 0.025-in archwire was employed, all ligation methods exhibited values close to zero, except the In-Ovation brackets, which yielded 45 cN, and the Morelli brackets with new and old elastomeric ligatures, which displayed 82 and 49 centiNewtons, respectively. CONCLUSIONS: Damon MX, Easy Clip, Smart Clip, Synergy bracket systems and 8-shaped ligatures proved to be equally effective alternatives for controlling classical friction using 0.014-in nickel-titanium archwires and 0.019 x 0.025-in steel archwires, while the In-Ovation was efficient with 0.014-in archwires but with 0.019 x 0.025-in archwires it exhibited friction that was similar to conventional brackets with used elastomeric ligatures.

Photoelastic stress analysis surrounding implant-supported prosthesis and alveolar ridge on mandibular overdentures.

The purpose of this research was to evaluate the maximum stress around osseointegrated implants and alveolar ridge, in a mandible with left partial resection through a photoelastic mandibular model. The first group consisted of two implants: traditional model (T), implants placed in the position of both canines; fulcrum model (F), implants placed in the position of left canine CL and right lateral incisor LiR. Both models linked through a bar and clips. The second group was consisted of three implants, with implants placed in the position of both canines (CR and CL) and the right lateral incisor (LiR), which composed four groups: (1) model with 3 "O" rings, (2) model 2 ERAs, bar with clips, (3) model 2 ERAs bar without clips; (4) model "O" ring bar and ERA. An axial and an oblique load of 6.8 kgf was applied on a overdenture at the 1st Pm, 2nd Pm, and 1st M. Results showed that the area around the left canine (CL) was practically free of stress; the left lateral incisor (LiL) developed only small tensions, and low stress in all the other cases; the right canine tooth suffered the largest concentrations of stress, mainly with the ERA retention mechanism.

Análise biomecânica de dentes restaurados com retentor intrarradicular fundido, com ou sem férula / Biomechanical analysis of teeth restored with cast intra-radicular retainer, with or without ferrule

Objetivo: Avaliar a influência de variações no formato da férula dada por núcleo estojado sobre as tensões desenvolvidas na raiz. Métodos: Seis modelos 3D de um segundo pré-molar superior foram confeccionados a partir das dimensões médias obtidas na literatura. Simulou-se uma carga mastigatória (291,36N) com resultante paralela ao longo eixo do dente. Em quatro modelos, variou-se o tamanho do espelho (E): 1/3 da espessura da parede radicular (E1) ou 2/3 (E2). A altura (A) do bisel foi equivalente a E1 (A1) ou a E2 (A2), ou seja: férula E1A1 e E2A2 com inclinação de 45º. Um modelo representou o dente hígido, outro modelo simulou núcleo apenas, com espelho, sem férula (E2A0). Todos os casos mantiveram a mesma restauração coronária. Todas as estruturas foram consideradas homogêneas, isotrópicas e lineares elásticas. O aumento da altura do estojo (de E2A1 para E2A2 ou de E1A1 para E1A2) provocou mudança das tensões compressivas para trativas na dentina radicular sobre o estojo. Resultados: Os melhores resultados foram obtidos pelo modelo E1A2, que minimizou as tensões trativas na dentina radicular cervical e na dentina radicular próxima ao ligamento periodontal, seguido do modelo E1A1, E2A1 e E2A2. Conclusão: Para distribuir, de melhor modo possível, a tensão na dentina radicular sobre o espelho é imprescindível que exista férula. A férula protege a dentina radicular sob o espelho (quanto mais alta, melhor) e a inclinação de 45º resulta em efeito protetor mais eficiente para a dentina sobre o espelho.

Objective: To evaluate the influence of variations in ferrule shape given by the core placed, on stresses developed in the root. Methods: Six 3D models of a maxillary second premolar were made according to the mean dimensions obtained in the literature. A masticatory load (291.36N) was simulated with result parallel to the long axis of the tooth. In four models, the size of the plate (E) was varied: 1/3 of the root wall thickness (E1) or 2/3 (E2). The height (A) of the bevel was equivalent to E1 (A1) or E2 (A2), that is: ferrule E1A1 and E2A2 with an inclination of 45º. One model represented a healthy tooth, another model simulated the core only, with plate, without ferrule (E2A0). All the cases had the same coronal restoration. All the structures were considered homogenous, isotropic and linear elastic. The increase in the height of the recess (from E2A1 to E2A2 or from E1A1 to E1A2) caused changes in the compressive sheer stresses in the root dentin over the recess. Results: The best results were obtained by model E1A2, which minimized the sheer/ stresses in the cervical root dentin and in the root dentin close to the periodontal ligament, followed by models E1A1, E2A1 and E2A2. Conclusion: To distribute the stress on the root dentin on the plate in the best possible manner, it is imperative to have the ferrule. The ferrule protects the root dentin under the plate (the higher the better) and the inclination of 45º results in a more efficient protective effect for the dentin over plate.

Does adhesive thickness affect resin-dentin bond strength after thermal/load cycling?

This study evaluated the influence of adhesive layer thickness (ADL) on the resin-dentin bond strength of two adhesive systems (AS) after thermal and mechanical loading (TML). A flat superficial dentin surface was exposed with 600-grit SiC paper on 40 molars. After primer application, the adhesive layer of Scotchbond Multipurpose (SBMP) or Clearfil SE Bond (CSEB) was applied in one or two layers to a delimited area (52 mm2) and resin blocks (Filtek Z250) were built incrementally. Half of the sample was stored in distilled water (37 degrees C, 24 hours) and submitted to thermal (1,000; 5 degrees -55 degrees C) and mechanical cycles (500,000; 10kgf) [TML]. The other half was stored in distilled water (72 hours). The teeth were then sectioned to obtain sticks (0.8 mm2) to be tested under tensile mode (1.0 mm/minute). The fracture mode was analyzed at 400x. The BS from all sticks from the same tooth was averaged for statistical purposes. The data was analyzed by three-way ANOVA. The chi2 test was used (p < 0.05) to compare the frequency of pre-testing failure specimens. Higher BS values were observed for SBMP regardless of the ADL. The TML reduced the BS values irrespective of the adhesive employed and the ADL. A higher frequency of pre-testing failure specimens was observed for the cycled groups. A thicker adhesive layer, acting as an intermediate flexible layer, did not minimize the damage caused by thermal/mechanical load cycling for a three-step etch-and-rinse and two-step self-etch system.

Shear versus micro-shear bond strength test: a finite element stress analysis.

OBJECTIVES: This study aimed at comparing the stress distribution in shear and micro-shear test set-ups using finite element analysis, and suggesting some parameter standardization that might have important influence on the results. METHODS: Two-dimensional plane strain finite element analysis was performed using MSCPatran and MSCMarc softwares. Model configurations were based on published experimental shear and micro-shear test set-ups and material properties were assumed to be isotropic, homogeneous and linear-elastic. Typical values of elastic modulus and Poisson's ratios were assigned to composite, dentin and adhesive. Loading conditions considered a single-node concentrated load at different distances from the dentin-adhesive interface, and proportional geometry (1:5 scale, but fixed adhesive layer thickness in 50microm) with similar calculated nominal strength. The maximum tensile and shear stresses, and stress distribution along dentin-adhesive interfacial nodes were analyzed. RESULTS: Stress distribution was always non-uniform and greatly differed between shear and micro-shear models. A pronounced stress concentration was observed at the interfacial edges due to the geometric change: stress values farther exceeded the nominal strength and tensile stresses were much higher than shear stresses. For micro-shear test, the relatively thicker adhesive layer and use of low modulus composites may lead to relevant stress intensification. An appropriate loading distance was established for each test (1mm for shear and 0.1mm for micro-shear) in which stress concentration would be minimal, and should be standardized for experimental assays. SIGNIFICANCE: The elastic modulus of bonded composites, relative adhesive layer thickness and load application distance are important parameters to be standardized, once they influence stress concentration.

Morphological characterization of the tooth/adhesive interface.

The purpose of this study was to assess the morphological characteristics of the tooth/adhesive interface using different adhesive systems in MOD restorations under scanning electron microscopy (SEM). The tested hypothesis was that the morphology of the bonding interface would vary in different areas of MOD restorations for the three adhesive systems. MOD cavities were prepared in 12 sound extracted human third molars and restored with Filtek Z250 composite resin and one of the following adhesive systems: Experimental ABF (n=4), Clearfil SE Bond (n=4) self-etching primers and Single Bond etch-and-rinse adhesive system (n=4). After 24-h storage in distilled water at 37 degrees C, teeth were sectioned and prepared for SEM. The interfacial morphology varied depending on the adhesive system and also on the evaluated area. The null hypothesis was accepted because the morphology of the tooth/adhesive interface reflected the characteristics of both the dental substrate and the adhesive systems.