A finite element study on the risk of bone loss around posterior short implants in an atrophic mandible.

PURPOSE: This study aimed to evaluate the risk of bone loss around single short molar crown-supporting implants in an atrophic mandible. METHODS: Implants of different lengths (L = 4 or 6 mm) and diameters (Ø = 4.1 or 4.8 mm) were placed in the molar area of an atrophic mandible. Additional control mandible models were simulated for 4.1 mm diameter implants (L = 4, 6, 8, and 10 mm). A vertical masticatory load of 200 N was applied to three or six occlusal contact areas (3ca or 6ca) of the prosthetic crown. The bone strain energy density (SED) of 109.6 µJ/mm3 was assumed to be the pathological threshold for cortical bone. The peri-implant bone resorption risk index (PIBRri) was calculated by dividing the maximum SED of the crestal cortical bone by the SED pathological threshold. RESULTS: Increasing the implant length from 4 to 6 mm, implant diameter from 4.1 to 4.8 mm, and number of contact areas from 3 to 6 reduced the SED and PIBRri values by approximately 20%, 35%, and 40%, respectively, when comparing pairs of models that isolated a specific variable. All models with 6ca had a low bone resorption risk (PIBRri<0.8), while the Ø4.1 short implant with 3ca had a medium (0.8≤PIBRri≤1.0) or high (PIBRri>1.0) resorption risk. CONCLUSIONS: Increasing the diameter or occlusal contact area of a 4 mm short implant in an atrophic mandible resulted in reduced bone resorption risks, similar to or lower than those observed in a regular mandible with standard-length implants.

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.

Effect of processing methods on the chipping resistance of veneered zirconia.

OBJECTIVES: To evaluate the edge chipping resistance (ReA) and the fracture toughness (KC) of 3Y-TZP bilayers produced with the following materials/processing combinations: fluorapatite glass-ceramic applied on zirconia using the traditional layering and hot-pressing (press-on) techniques; feldspathic porcelain using rapid layer technology (RLT); and lithium disilicate glass-ceramic using CAD-on method. The influence of the cooling rate (slow and fast) was analyzed for layering and hot-pressing. METHODS: Bilayer bars (25x4x2 mm) were made following manufacturers' instructions. The edge chipping test was performed in an universal testing machine, using a coupled Vickers indenter. ReA was calculated dividing the critical load at fracture by the edge distance. Fracture toughness was calculated by a regression fit with a fixed slope of 1.5 correlating the critical chipping load regarding edge distance and also with indentation fracture (IF) method. Data were statistically analyzed using ANOVA and Tukey's test (α = 5%). RESULTS: ReA and KC was significantly higher for the CAD-on bilayers. RLT showed intermediate ReA means, and layering and hot-pressing techniques showed the lowest ReA values. For both processing methods there was no effect of the cooling protocol on the ReA and fracture toughness. CONCLUSIONS: There is a significant effect of the material/processing association on the edge chipping resistance and fracture toughness of the bilayers. There was no effect of the cooling protocol on the edge chipping resistance and fracture toughness for the specimens processed by both the layering and hot-pressing techniques.

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.

Influence of physical assessment of different light-curing units on irradiance and composite microhardness top/bottom ratio.

The aim of this study was to evaluate the influence of the physical assessment of different light-curing units from 55 dental offices on the irradiance and composite microhardness top/bottom ratio, and the influence of the radiometers for LED or QTH light sources on irradiance measurement. The irradiance of each light-curing unit was evaluated with two radiometers, either for LED or QTH light. A questionnaire regarding the type of source (LED or QTH), time of use, date of last maintenance and light-curing performance assessment applied. The physical assessments were evaluated regarding damage or debris on the light tip. For each light-curing unit, three composite specimens were made (diameter = 7 mm; thickness = 2 mm) with polymerizing time of 20 s, in order to perform the microhardness (Knoop) test. Data were analyzed by Kruskal-Wallis and Dunn test (α = 0.01). There was wide variation in irradiance (0-1000 mW/cm(2)). Approximately 50 % of the light-curing units presented radiation lower than 300 mW/cm(2); 10 % of light-curing units, especially those with LED source, presented values higher than 800 mW/cm(2), and 43 % of light-curing units worked with adequate irradiance between 301 and 800 mW/cm(2). In almost 60 % of cases, no maintenance of light-curing units was performed in a period of 3 to 10 years. The age of the light-curing units and the use of inadequate tips interfered negatively in irradiance. The data emphasize the importance of periodic maintenance of light-polymerizing, light-curing units.

Experimental and FE displacement and polymerization stress of bonded restorations as a function of the C-Factor, volume and substrate stiffness.

OBJECTIVES: To determine the free surface displacement of resin-composite restorations as a function of the C-Factor, volume and substrate stiffness, and to compare the results with interfacial stress values evaluated by finite element analysis (FEA). METHODS: Surface displacement was determined by an extensometer using restorations with 4 or 6mm diameter and 1 or 2mm depth, prepared in either bovine teeth or glass. The maximum displacement of the free surface was monitored for 5 min from the start of photoactivation, at an acquisition rate of 1s(-1). Axisymmetric cavity models were performed by FEA. Structural stiffness and maximum stresses were investigated. RESULTS: For glass, displacement showed a stronger correlation with volume (r=0.771) than with C-Factor (r=0.395, p<0.001 for both). For teeth, a stronger correlation was found with C-Factor (r=0.709; p<0.001) than with volume (r=0.546, p<0.001). For similar dimensions, stress and displacement were defined by stiffness. Simultaneous increases in volume and C-Factor led to increases in stress and surface displacement. Maximum stresses were located at the cavosurface angle, internal angle (glass) and at the dentine-enamel junction (teeth). The displacement of the restoration's free surface was related to interfacial stress development. CONCLUSIONS: Structural stiffness seems to affect the shrinkage stress at the tooth/resin-composite interface in bonded restorations. Deep restorations are always problematic because they showed high shear stress, regardless of their width. FEA is the only tool capable of detecting shear stress due to polymerization as there is still no reliable experimental alternative.

Influence of fiber post cementation length on coronal microleakage values in vitro and finite element analysis.

AIM: This study aims to evaluate, the Influence of different fiber posts cementation lengths by finite element analysis (FEA) and coronal microleakage. MATERIALS AND METHODS: Fifty anterior bovine teeth were sectioned to obtain roots with 16 mm length. The coronal length of the post was 6 mm for all groups, while the radicular length were varied 6, 8, 10 or 12 mm. The fiber posts surfaces were cleaned with alcohol and silanized. Then the posts were cemented using a two steps total etch-and-rinse adhesive system + conventional resin cement. Forty teeth were submitted to mechanical cycling (45°; 2.000.000 cycles; 90N; 4Hz; 37°C) and ten teeth with radicular length of 12 mm was not submitted, ser ving as c ontrol. So, the experimental design was composed by different ratios of post coronal length/post radicular length and mechanical cycling (MC): Gr1- 1/1 + MC; Gr2- 3/4 + MC; Gr3- 3/5 + MC; Gr4- 1/2 + MC. All groups were immersed in a 1% toluidine blue solution. After 24 hours, the teeth were longitudinally sectioned and the microleakage scores was given by a blind operator. Data were submitted to Kruskal-Wallis test (p = 0.05). The experimental variables were simulated in two-dimensional finite element analysis (2D-FEA). The maximum principal stress distributions were compared. RESULTS: No difference was observed in microleakage values between the cycled groups, whilst the control groups showed the lowest values. FEA analysis showed similar maximum principal stress distribution between the groups. CONCLUSION: Mechanical cycling affected the values of coronal microleakage and different cementation length generated similar values of coronal microleakage and stress distribution. CLINICAL SIGNIFICANCE: These results showed that from the microleakage point of view, more conservative cementation lengths have the same effect as longer cementation lengths.

Assessment of nose protector for sport activities: finite element analysis.

There has been a significant increase in the number of facial fractures stemming from sport activities in recent years, with the nasal bone one of the most affected structures. Researchers recommend the use of a nose protector, but there is no standardization regarding the material employed. Clinical experience has demonstrated that a combination of a flexible and rigid layer of ethylene vinyl acetate (EVA) offers both comfort and safety to practitioners of sports. The aim of the present study was the investigation into the stresses generated by the impact of a rigid body on the nasal bone on models with and without an EVA protector. For such, finite element analysis was employed. A craniofacial model was constructed from images obtained through computed tomography. The nose protector was modeled with two layers of EVA (1 mm of rigid EVA over 2 mm of flexible EVA), following the geometry of the soft tissue. Finite element analysis was performed using the LS Dyna program. The bone and rigid EVA were represented as elastic linear material, whereas the soft tissues and flexible EVA were represented as hyperelastic material. The impact from a rigid sphere on the frontal region of the face was simulated with a constant velocity of 20 m s(-1) for 9.1 µs. The model without the protector served as the control. The distribution of maximal stress of the facial bones was recorded. The maximal stress on the nasal bone surpassed the breaking limit of 0.13-0.34 MPa on the model without a protector, while remaining below this limit on the model with the protector. Thus, the nose protector made from both flexible and rigid EVA proved effective at protecting the nasal bones under high-impact conditions.

Fraturas nasais em esportes: sua ocorrência e importância / Nasal fracture in sports: its occurrence and importance

Introdução: O aumento do número de participantes nas mais variadas modalidades desportivas e de praticantes em recinto fechado trouxe também um aumento significativo de traumas orofaciais nos esportes, principalmente fraturas nasais, que ocupam o terceiro lugar em ocorrência em todas as modalidades desportivas. Objetivo e revisão de literatura: Trazer conhecimento das causas, da ocorrência e da importância da fratura nasal no esporte, já que é de responsabilidade do cirurgião-dentista confeccionar meios de proteção bucomaxilofaciais nos esportes, área em que a Odontologia do Esporte vem se sedimentando. Conclusão: Um afastamento prolongado do atleta acarreta a ele grande prejuízo físico e psicológico, assim como prejuízo financeiro para seu clube. Deve-se ter atenção para meios de proteção para o atleta.

Introduction: The increasing number of participants in various sports, mainly those practiced indoors, brought a significant increase of orofacial injuries in sports, especially nasal fractures, which rank third in incidence in all sports. Objective and literature review: To study the causes, occurrence and importance of nasal fracture in sports, as providing ways of protecting the maxillofacial area in sports is the responsibility of the dentist, area in which Sports Dentistry is establishing itself. Conclusion: A long athlete withdrawal carries great physical and psychological damage, as well as financial loss to his club. Attention in providing ways of protection for the athlete is required.

Efeitos da contração e do módulo de elasticidade de compósitos sobre a tensão de polimerização em sistemas com diferentes complacências: análise por elementos finitos / Effects of composite shrinkage and elastic modulus on polymerization stress in systems with different compliances: finite element analysis

O objetivo deste trabalho foi simular, por análise de elementos finitos, o ensaio de tensão de polimerização com vistas a um melhor entendimento da mecânica do teste que permita explicar divergências encontradas entre estudos que utilizaram montagens experimentais semelhantes, porém com diferentes substratos de colagem. Com base em dados extraídos da literatura, foi formulada a hipótese que o efeito da contração volumétrica e do módulo de elasticidade do compósito sobre a tensão de polimerização depende da complacência do sistema. Em sistemas de teste com alta complacência, os valores de tensão estariam diretamente relacionados à contração do compósito, enquanto que a utilização de sistemas menos complacentes realçaria a influência do módulo de elasticidade do compósito. Um ensaio de tensão de polimerização frequentemente utilizado foi simulado pelo método por elementos finitos. Devido à simetria geométrica e de carregamento, apenas um oitavo do modelo foi representado. Foram simulados quatro diferentes complacências do teste, correspondentes a diferentes materiais dos bastões: aço, vidro, compósito e acrílico. A contração de polimerização foi simulada através de analogia térmica. A temperatura foi reduzida em 1°C e o coeficiente de expansão térmica foi ajustado para conferir a contração volumétrica desejada. A polimerização foi simulada em duas fases: pré-gel e pós-gel. Na fase pré-gel os elementos do compósito apresentavam módulo de elasticidade bastante baixo, para simular o alívio de tensões decorrente do escoamento do compósito nos estágios iniciais da polimerização...

The purpose of the present study was simulate, using finite element analysis, the polymerization stress test aiming at a better understanding of the test mechanics that could explain the divergences among studies using similar experimental set-ups but different bonding substrates. Based on literature data, a hypothesis was formulated stating that the effects of composite volumetric shrinkage and elastic modulus on polymerization stress depend upon the compliance of the testing system. In high compliance systems, stress values would be directly related to shrinkage, while low compliance systems would emphasize the influence of the composite elastic modulus. A frequently used testing apparatus was simulated by finite element method. Due to the geometry and loading symmetry, only one-eighth of the model was represented. Four different compliance levels were simulated, corresponding to different rod materiais: steel, glass, composite and acrylic. Polymerization shrinkage was simulated by thermal analogy. Temperature was reduced by 1°C and the coefficient of thermal expansion was adjusted to result in the desired shrinkage. Polymerization was simulated in two stages, pre-and post-gel. In the pre-gel phase, the elements representing the composite presented very low modulus to simulate the stress relief resulting from viscous flow occurring in the early stages of the reaction. In the post-gel phase, composite elements presented its final elastic modulus. Different composites were simulated with modulus between 1 and 12 GPa (in 1 GPa increments) and total volumetric shrinkage between 0.5% and 6% (in 0.5% )...

Expansion of high flow mixtures of gypsum-bonded investments in contact with absorbent liners.

OBJECTIVES: To evaluate the expansion of high flow mixtures of gypsum-bonded investments in contact with two dry absorbent liners since early setting. METHODS: Cristobalite-Dentsply and Cristobalite-Polidental gypsum-bonded investments were tested under 10 setting conditions (n=4): Normal and Hygroscopic (controls); four conditions of 'Dry-Lining' (set in contact with 3 different amounts of dry cellulose liner: 0.2, 0.4 or 0.8 g and with 0.1 g of a granulated Super Absorbent polymer liner) and four conditions of 'Dry-Lining with hygroscopic expansion' (initially setting in contact with dry absorbents, as 'Dry-Lining' conditions, followed by water immersion immediately after loss of gloss). The percent of expansion at 2h was analyzed. RESULTS: The 'Dry-Lining' condition, with 0.4 and 0.8 g of cellulose, for brand Dentsply (1.41+/-0.13 and 1.42+/-0.16) and Polidental (1.14+/-0.17 and 1.01+/-0.22) allowed a significant higher expansion than the controls Normal (Dentsply=0.30+/-0.04, Polidental=0.31+/-0.05) (P<0.05). The 'Dry-Lining with hygroscopic expansion' condition with 0.8 g of cellulose expanded significantly more (3.57+/-0.55) than the control Hygroscopic (2.63+/-0.31) in brand Dentsply (P<0.05). Super Absorbent did not produce different expansion (Dentsply=0.86+/-0.02, Polidental=0.79+/-0.18) than the controls Normal and Hygroscopic (Dentsply=2.93+/-0.17, Polidental=2.12+/-0.40). SIGNIFICANCE: The water removal with dry cellulose absorbent liner before loss of gloss increased the potential of setting expansion for Normal and Hygroscopic conditions. Thus, when using high fluid mixtures, which are more desirable for investment pouring, it will be possible to obtain enough setting expansion potential in order to adequately compensate for wax and alloy shrinkage in the casting process.

O mercúrio no consultório dentário – minimizando os riscos / Mercury in the dental office – risk reduction

Apresentamos um resumo dos perigos que comporta o uso do mercúrio em consultórios dentários e o protocolo de uso que visa minimizar os riscos inerentes ao uso de amálgama e à manipulação dos resíduos gerados por ele. O amálgama é um material seguro para o paciente, para a equipe odontológica e para o ambiente desde que sejam tomados os cuidados assinalados neste protocolo

Color unit differences (AE) of acrylic resins related to powder-to-liquid ratio, sample thickness and trade marks / Diferenças de unidades de cor (AE) de resinas acrílicas em função de proporções, espessuras e marcas

O objetivo da pesquisa foi determinar as diferenças de cor de resinas acrílicas, empregando corpos-de-prova em peça única, com as espessuras de 6, 4 e 2mm. As resinas ensaiadas foram: duas de cor rosa médio (Clássico e Vipi) e três de cor 66, Dencor (Clássico), Vipi-cor (Vipi) e Duralay (Reliance). Com um espectrifotômetro foram determinados os parâmetros de cor (L*,a*,b*) e calculados as diferenças entre condições diferentes. As diferenças de cor foram determinadas pelo emprego dos seguintes padrões: 1) Proporção pó/líquido normal (do fabricante), à qual foram comparadas aquelas de (em porcentagem): +10, -10 e -20; 2) espessuras de 4 a 2mm, em relação ao padrão de 6mm; 3)comparação entre duas resinas cor de rosae entre as três de cor 66. Os resultados permitiram concluir que: a variação na proporção pó/líquido em relação à normal influenciou pouco na alteração de cor, do ponto de vista clínico, com o maior valor (diferença de cor = 1.6) não perceptível por um grande número de observadores; a comparação, em relação ao padrão de 6mm de espessura, mostrou que a de 4mm não foi grande (diferença de cor = 1.7 no máximo), entretanto, a de 2mm de espessura em relação ao mesmo padrão, apresentou alterações insatisfatórias, que, dependendo da resina e proporções, chegou a diferença de cor = 8.4 entre as resinas cor de rosa, a semelhança de cor foi boa, contudo entre as resinas de cor 66, as diferenças foram insatisfatórias

Marginal fit of cast titanium copings related to investments and casting techniques

The purpose of this study was to evaluated marginal fit of cast titanium coping according to the following conditions: 1) three investment types, 2) use of a doll made up with the three investments and the ring filling with conventional phosphate investment; 3) use of die relief; 4) surface treatment. Casting was made using appropriate equipment for titanium alloys. The results obtained led us to conclude that it is possible to obtain titanium casts with satisfactory marginal it using adequate techniques; rematitan investment led to good results, although they may not used without die relief, especially when the cover technique is employed; Ticoast S + L was the least critical regarding casting techniques, but requires drilling to obtain good fit

Concentraçäo de tensöes em teste de micro-traçäo / Stress concentration factor in microtensile tests

O objetivo deste estudo foi determinar, através do método de elementos finitos, o fator de concentraçäo de tensöes (`K IND. t`) para espécimes com formato de ampulheta e dimensöes mais freqüentemente utilizadas em teste de micro-traçäo. Foram simulados oitenta casos, com modelos tridimensionais, mudando o modo de fixaçäo do espécime na garra [f=1 ou 2 lados] a altura da regiäo fixada [h=1 ou 2,75mm], largura do espécime [D=1,5; 2; 3; 4 ou 5mm] e raio de curvatura do entalhe (r = 0,2; 0,5; 0,7 ou 1 mm). Para todos os casos foi constante a área de seçäo transversal (1 mm²). Foram registrados os valores de tensäo máxima e calculado o K(t) IND. t` (tensäo máxima/tensäo nominal). Os resultados indicam que o parâmetro geométrico mais influente sobre o K(t) é o raio (variaçäo de até 47,4 por cento) e, para espécimes fixados por apenas um lado, também a altura (27,3 por cento) e largura (26,9 por cento). O grupo flh1r0,2 (f1 = um lado de fixaçäo, h1 = 1 mm de altura da regiäo de colagem; r0,2 = 0,2mm de raio de curvatura) obteve os mais altos valores de K(t) (3,0 ñ 0,15); e f2r1 apresentou os menores valores (1,3 ñ 0,04), enquanto f1h2,75r0,2 obteve valores intermediários (2,5 ñ 0,05). Para os espécimes fixados por dois lados a variaçäo do K(t) esteve ao redor de 3 a 4 por cento enquanto que para os espécimes fixados por apenas um lado a variaçäo foi entre 11 e 15 por cento. A fixaçäo dos espécimes por dois lados é um modo eficiente para reduzir o fator de concentraçäo de tensöes e a variabilidade do K(t) decorrente das variaçöes geométricas do espécime