Polymerization Contraction Research Articles

Air Pollution Exposure Duration and Its Correlation with Triglyceride, HDL, and Atherogenic Index in Online Motorcycle Drivers

Background: The most restoration material used currently in dentistry was composite resin. The newest generation of composite resin was bulk-fill composite resin. The bulk-fill composite resin had advantages of lower polymerization contraction and a more straightforward and faster restoration technique. One of the factors which could affect the hardness of composite resin was the consumption of acidic drinks. The acidic beverage that people often consumed is coffee. A few coffee brewing methods were espresso and drip brewing.Objective: This research aimed to identify the effects of coffee soaking through espresso and drip brewing methods on bulk-fill composite resin's hardness.Methods: his research was experimental research, with a post-test control group design and a total sample of 27 samples. The soaking process was taken for seven days at a temperature of 37˚C on artificial saliva, espresso, and drip brewing coffee methods. The hardness of bulk-fill composite resin was measured after seven days by using Vickers hardness. The statistic test exerted One-Way ANOVA.Results: This research found a significant difference in bulk-fill composite resin's hardness among all groups, p-value = 0.00 (p<0.05). The result of the post-hoc LSD test showed a significant difference in the change of bulk-fill composite resin hardness between the artificial saliva group and espresso group (p=0,00) and no significant difference found between the artificial saliva group and drip brewing group (p=0.85).Conclusion: Soaking with espresso coffee has the smallest hardness value compared to soaking with drip brewing coffee and artificial saliva, so soaking with espresso coffee is the most influential on the hardness of the bulk fill composite resin.

The Effect of Espresso and Drip Brewing Coffee Methode to The Hardness of Bulk-Fill Composite Resin

Background: The most restoration material used currently in dentistry was composite resin. The newest generation of composite resin was bulk-fill composite resin. The bulk-fill composite resin had advantages of lower polymerization contraction and a more straightforward and faster restoration technique. One of the factors which could affect the hardness of composite resin was the consumption of acidic drinks. The acidic beverage that people often consumed is coffee. A few coffee brewing methods were espresso and drip brewing.Objective: This research aimed to identify the effects of coffee soaking through espresso and drip brewing methods on bulk-fill composite resin's hardness.Methods: his research was experimental research, with a post-test control group design and a total sample of 27 samples. The soaking process was taken for seven days at a temperature of 37˚C on artificial saliva, espresso, and drip brewing coffee methods. The hardness of bulk-fill composite resin was measured after seven days by using Vickers hardness. The statistic test exerted One-Way ANOVA.Results: This research found a significant difference in bulk-fill composite resin's hardness among all groups, p-value = 0.00 (p<0.05). The result of the post-hoc LSD test showed a significant difference in the change of bulk-fill composite resin hardness between the artificial saliva group and espresso group (p=0,00) and no significant difference found between the artificial saliva group and drip brewing group (p=0.85).Conclusion: Soaking with espresso coffee has the smallest hardness value compared to soaking with drip brewing coffee and artificial saliva, so soaking with espresso coffee is the most influential on the hardness of the bulk fill composite resin.

Full mapping tensile bond strength of luting in search for differences due to centripetal curing shrinkage

Objectivestesting if hypothetical transverse centripetal strains due to polymerization contraction of luting materials produce differential alterations in its bonding to luted structures, depending on distances to the center of the luting mass, and if this effect is C-factor related. Two hypotheses were tested: (1) there is a statistically significant decreasing relationship between the bonding strength and the transverse distances to the center of the luting material, and (2) there is a statistically significant difference between bonding strengths among luting spaces with different configuration factors. Methods10 PMMA (15 mm Ø) pairs of cylinders were cemented (Scotchbond Universal adhesive & Relyx Universal, both chemically cured) in a compliant setup under two (20 and 70 N) luting forces forming 2 groups (5 samples each), resulting in different C-factors. Whole samples were sectioned in x and y directions obtaining non-trimmed beams from all along the luting surfaces. Their relative positions in each sample were assessed before separating and categorized (10 categories) according to their distances to the center of the sample. All beams were tested in tension and, because of their uneven bonding areas and to balance its influence, UTS results were transformed into UTSres. First hypothesis was tested trough a linear relationship between UTSres and distances to vertical centers per samples. Second hypothesis was tested using Mann-Whitney U tests to compare UTSres between groups, along all categories. Further Weibull analysis was applied. ResultsANOVA’s p of the regression UTSres – categories were statistically significant for all samples in group 70 N and for all except one in group 20 N: first hypothesis is partially maintained. Although Mann-Whitney tests p comparing UTSres of both groups for all categories but the first were statistically significant this hypothesis was maintained relying in Weibull analysis. Significance: bonded attachment of cemented materials decreases from centers to outbounds in plane, extensive surfaces, and this decrease is C-factor related.

Improvement of Quality of Life through Nanoparticles in Restorative Dentistry

Dental methods aimed at dental rehabilitation, regional anesthesia, orthodontic realigning, permanent hypersensitivity treatment, covalent bonding diamondized enamel, dental health preservation using mechanical dentifrobots, and the formation of artificial bone and teeth are among the possible uses of nanotools in dentistry. The evaluation and treatment of problems affecting the teeth and their surrounding tissues are the focus of restorative dentistry. For the restoration of tooth function and the repair and replacement of damaged tooth structures as well as better aesthetics, advanced procedures are required. In the past few years, resin-based dental restorative materials have made significant progress. Dental composite resin's mechanical performance, minimal polymerization contraction, strong wear resistance, and surface hardness can all be considerably improved by adding nanoparticles to the matrix. To date, nanocomposites for the repair of tooth structure have made one of the most significant contributions to restorative and cosmetic dentistry. Nanocomposites' characteristics aid in minimizing polymerization loss. Their microhardness is higher than that of already employed posterior resin-based composites, and the improved polishability properties in turn result in a smoother surface with better shade qualities. Nanocomposites have a number of benefits, including reduced weight, excellent thermal and electrical properties, antimicrobial activity, and the ability to remineralize dental defects. The other nanotools used in restorative dentistry are nanoadhesives, nanoionomers and nanoendodontic sealants. Nanoadhesives protect against failure of a restoration from bacterial invasion occurs due to spaces between restorative material and preparation margins. Nanoionomers chemically adhere to the surface of the tooth and offer advantages of enhanced bond strength, chemical stability, and insoluble nature. Nano endodontic sealers have the advantage of sealing better than conventional sealers and employing nanoparticles effectively acts as an antibacterial agent. Due to its potential uses and advantages, there is a growing demand for and interest in nano-based dental materials.

Polymerization Shrinkage of Short Fiber Reinforced Dental Composite Using a Confocal Laser Analysis.

The purpose of this study was to investigate the polymerization shrinkage of short fiber reinforced composite (SFRC) using a multicolor confocal displacement laser that can measure the polymerization shrinkage with high accuracy. The three types of SFRCs used in this study were XD (Ever X Flow Dentin), XB (Ever X Flow Bulk), and XP (EverX Posterior). In addition, CF (Clearfil majesty ES Flow) with hybrid type filler was used as a control. The measured values of the final polymerization shrinkage rate and amount of polymerization shrinkage rate when the polymerization shrinkage rate became constant (less than 0.1 µm/s) were approximated for all SFRCs. XP had a large aspect ratio of glass fiber filler and showed a significant difference from XD with a small aspect ratio (p < 0.05). There was no significant difference in the measured value of time when the polymerization contraction reached a constant speed (0.1 µm/s or less) for all SFRCs (p > 0.05). There was no significant difference in the measured values of polymerization shrinkage rate after the polymerization shrinkage reached a constant rate for all SFRCs (p > 0.05). These results show that glass fiber with large aspect ratio can alleviate polymerization shrinkage stress. The polymerization behavior of SFRC was found to be dependent on the amount of glass fiber filler, aspect ratio, and orientation.

Microleakage of Direct Restorations-Comparisonbetween Bulk-Fill and Traditional Composite Resins:Systematic Review and Meta-Analysis.

Since the bulk-fill composites were produced, there was a progressive diffusion of their use for direct conservative treatment in posterior teeth. Their chemical structure increases the depth of cure and decreases the polymerization contraction; in this manner, bulk-fill composites can be placed in 4 mm single layers and the treatment times are considerably reduced. However, aesthetic and mechanical properties and impact on microleakage of bulk-fill resins are still unclear.This systematic review and meta-analysis aimed to assess the risk of microleakage of direct posterior restorations made of bulk-fill versus conventional composite resins.Researches were performed on PubMed and Scopus databases. Eligible in vivo studies, published since 2006, were reviewed. Outcomes of marginal discoloration, marginal adaptation, and recurrent caries were considered to conduct the systematic review and meta-analysis. Secondary data were examined to implement additional analysis and assess the risk of bias.Eight randomized clinical trials were analyzed, involving 778 direct restorations. The summary of RCTs led to significant but inconsistent results; the marginal discoloration and recurrent caries were found to be improved respectively by 5.1 and 1.4%, whereas the marginal adaptation was reduced of 6.5%. Secondary analyses revealed that follow-up periods, the adhesive system used and the class of carious lesions evaluated are confounding factors, and they result in a risk of bias across studies.Bulk-fill composites are innovative materials for conservative dentistry and they can be used to reduce treatment steps and duration of operative times. There are insufficient data to explore the relationship between bulk-fill composites and microleakage and further investigations are needed.

Effects of the lining material, thickness and coverage on residual stress of class II molar restorations by multilayer technique

ObjectiveThis study aims to analyse the influence of different lining material, thickness and coverage on residual stress of class II molar restoration by the multilayer technique through the three-dimensional (3D) finite element (FE) method. The objective is to reveal the correlations between the base layer configurations and the residual stress distributions of the tooth. MethodsA 3D reconstructed model of an extracted first molar was built through micro-CT images and a class II mesio-occlusal-distal cavity was prepared using computer-aided engineering (CAE) software. A bilayer technique was then applied, and 3D FE analyses were performed under polymerization contraction loading. Glass ionomer composites (Vitrebond and Ionosit) and flowable composite resin (Luxa Flow and Z350 Flowable Restorative) were used as lining materials. Moreover, several sensitivity analyses with dozens of hypothetical lining materials were conducted to provide definitive results. The thickness of the base layers was set to be distinct (0.5 mm or 1 mm) so as to reveal its effect on the stress alleviation. Various lining strategies with the liner covering different areas of the cavity walls (Closed Sandwich, Open Sandwich and Special Open Sandwich) were adopted to determine the effects of the base layers. ResultsAdoption of an appropriate liner could effectively reduce the polymerization shrinkage stress. The mechanical properties of the base layer can affect the residual stresses, basically a lower Young's modulus and lower Poisson's ratio (of lining material) result in better stress mitigation, therefore reducing the stress transmitted to the dentin. Increase of the lining thickness within a certain range could lead to a decrease in the probability of stress concentration formation. Lining strategies had the strongest influence on the stress distributions. Different lining coverage could cause various stress responses, and covering all cavity walls with the lining material had the optimal performance among all the simulations in this study. SignificanceThe multilayer technique is an effective way to prolong the service life of resin composites restorations. A thorough evaluation of the sandwich technique through the FE method can provide a better understanding of the stress distributions of the restoration, and reveal its internal mechanisms.

Desenvolvimento de instrumental para a padronização do volume e da forma dos incrementos de resina composta direta e relato de caso clínico

Objetivo: O presente trabalho teve por objetivo desenvolver um protótipo de instrumental clínico que possibilita a padronização do volume e forma da massa de resina composta para o uso em procedimentos restauradores direto, além de relato de caso demonstrando a aplicabilidade do protótipo. Para isso, foi selecionada uma empresa produtora de instrumentos odontológicos e ativa no mercado nacional com registro na ANVISA. Tendo como base um calcador de Holemback número 6, esse, foi reconfigurado geometricamente afim de atingir os requisitos necessários para o desenho pretendido. Após a etapa de desenvolvimento, esse novo instrumento foi utilizado para o relato de um caso clínico de restauração direta de resina composta envolvendo esmalte e dentina das superfícies ocluso-distal do dente 15 e oclusal do dente 16. Os tecidos dentais foram hibridizados pela técnica adesiva associada de condicionamento seletivo do esmalte com ácido fosfórico e aplicação de sistema adesivo auto-condicionate (Clearfil SE Bond, Kuraray, Japão) em esmalte e dentina. A restauração foi realizada com a resina composta Z350 XT (3M ESPE, USA) nas cores A1 e A2B. Conclusão: A utilização do protótipo de instrumental auxilia na execução de restaurações direta de resina composta com o favorecimento ao controle das tensões geradas pela contração de polimerização e poderá ter papel importante no treinamento restaurador dos profissionais.

Current perspectives on dental adhesion: (3) Adhesion to intraradicular dentin: Concepts and applications

Adhesion science is one of the greatest contributions to restorative dentistry. Adhesion not only established the current principles of tissue preservation, but also allowed for the production of more hermetic and long-lasting restorations. Although adhesive strategies are routinely used in most clinical situations, adhesion to root dentin is still a major challenge. The presence of humidity together with less intertubular dentin are factors that limit the adhesive potential of root dentin. This situation is more unfavorable in endodontically treated teeth prepared for prefabricated or custom-made intraradicular posts; these procedures may alter the mechanical properties of teeth by modifying the viable dentin surface for adhesion. Also, contaminants deposited on the dentin surface are difficult to remove through conventional techniques. Moreover, root canal morphology has a very unfavorable C-factor, bringing undesirable effects resulting from polymerization contraction of resin-based materials. However, the differences between coronal and root dentin are not a barrier for dentin adhesion. Standardization of procedures and care during clinical steps are fundamental to the success of adhesion to coronal or intraradicular dentin. Thus, it is essential to know the anatomy of the root structure, the factors that interfere with intraradicular adhesion, as well as the current adhesive materials and techniques.

Bulk Fill flow resin contraction using 3D finite element model and calibration by Fiber Bragg Grating measurement

Contraction due to polymerization of dental resin can cause failure on the adhesive interfaces, can lead to problems such as the appearance of gaps in the interfaces, postoperative sensitivity, pulp damage and the return of the caries. The objective of this work is the study of stresses on the dental adhesive that are generated by the process shrinkage of resin associated with biting forces. A laboratory experiment measured the strains and temperature inside the FiltekTM Bulk Fill Flow resin during the process of polymerization using Fiber Bragg Grating sensors in an ex vivo tooth. From tomographic images a three-dimensional geometric model of the tooth was reconstructed. A pre-tension was calibrated to simulate the residual contraction on the resin 3 D model. Finally, an Finite Element Method analysis was performed to access the adhesive stresses at the interface enamel/dentin with the adhesive, considering as loading the residual polymerization contraction of the dental resin and also biting loads. The model was able to represented the strain obtained in the laboratory experiment. The results of the stress analysis shows that the outer regions of adhesive are more prone to failure, as veried by dental surgeons in clinical practice.

COMPARATIVE EVALUATION OF THE MARGINAL ADAPTATION OF FOUR DIFFERENT COMPOSITE RESINS WITH OR WITHOUT PREHEATING – AN IN VITRO STUDY

Background: Resin composites as direct posterior restorative material was associated with the polymerization contraction and microleakage. Different methods have been introduced to overcome these drawbacks by increasing the degree of monomer conversion and to minimize the polymerization shrinkage. Composite preheating is an innovative method to improve the handling and physical properties. So this study was done to evaluate the effect of prepolymerization warming of different composites on the marginal adaptation. &#x0D; Materials and Methods: This in vitro study was conducted on 80 extracted human maxillary premolars. Class II cavities on the proximal surface were prepared with the dimensions of 4 mm buccolingual width, 2 mm axial depth, and gingival margin at the cementoenamel junction. They were divided into four groups of 20 teeth each and were restored accordingly: Group I – Bulkfill nanohybrid; Group II – Nanofill; Group III – Ormocer; Group IV – microhybrid composites. Each group was further sub - divided into subgroups of 10 teeth, according to the preheated composites and room temperature composites used. After restorative procedures, samples were sectioned in the mesiodistal direction through the centre of the restoration and analysed using Scanning Electron Microscope at 200x magnification and marginal gap width was measured in three areas at the axial wall using Image Processing and Analysis in Java (ImageJ 1.5 2a) software.&#x0D; Statistical Analysis: Data was entered in Statistical Package for Social Sciences version 21 Software for Windows. The comparisons of four different composite materials with two subgroups were analyzed using Kruskal Wallis test. The level of significance was kept at p &lt; 0.05.&#x0D; Results: Preheating results in more gap formation with the bulk fill nanohybrid and Ormocer showed higher MQ4 scores than the room temperature composites. No statistically significant results were found. But the percentage of gap formation was comparatively higher in preheated composite group.&#x0D; Conclusion: Within the limitations of the present study, it could be concluded that preheated composites showed poor internal marginal adaptation with increased frequency of gap formation.&#x0D; Key words: Internal marginal adaptation, Ormocer, Filtek nanofill, Microhybrid, Tetric bulk fill

Aspectos gerais das resinas bulk fill: uma revisão da literatura

As resinas Bulk Fill, ou resinas de preenchimento único podem ser classificadas de acordo com a consistência bem fluidas ou resinas de consistência regular. De forma geral, têm como principal vantagem à facilidade da técnica, o que reduz muito o tempo clinico; além disso, apresentam como característica principal a diminuição da contração de polimerização, quando comparadas as resinas convencionais, o que possibilita a utilização destes materiais em camadas de 4-5 mm.Os objetivos da presente revisão foram de avaliar a composição das resinas Bulk Fill, verificar suas propriedades gerais, descrever sobre a dinâmica de polimerização bem como relatar seu desempenho clinico. Foi realizada uma revisão da literatura através de uma busca online nas bases de dados: PubMed, Google acadêmico, biblioteca virtual de saúde (BVS), LILACS, SCIELO E BIREME, utilizando os descritores: resinas Bulk Fill, estética e propriedades, que foram selecionados de acordo com os critérios de inclusão e exclusão. A partir da análise bibliográfica foi possível perceber que as resinas apresentaram boas propriedades físico-químicas, como dureza, resistência e em relação a sua composição as resinas Bulk Fill são constituídas por uma porcentagem minimizada de partículas inorgânicas e maior quantidade de matriz orgânica, além disso, estas apresentam uma contração de polimerização diminuída. Em relação ao seu uso na clínica odontológica constatou-se que essas resinas apresentam um menor tempo clínico.

Microporosity and polymerization contraction as function of depth in dental resin cements by X-ray computed microtomography.

This research aimed to obtain the depth dependence of polymerization contraction and microporosity from irradiated dental resin cements by X-ray computed microtomography (μCT). Samples (n = 5) of commercial Relyx U200 (RU) and AllCem Core (AC) dual-cure resin cements were injected in a cylindrical Teflon sampler (25 mm3 ) and separated according to polymerization mechanism: self-cured (not irradiated) and dual-cured (irradiated from the top surface with a LED device). The cement's volume was scanned with the μCT scanning conditions kept constant. To assess the depth dependence of polymerization contraction, it was measured the displacement of the cement mass from the sample holder at 30 vertical cuts (0.1 mm distant). To probe the microporosity, the percentage of area with presence of porosity by slice was obtained. All data were statistically treated. It was observed a positive linear correlation between depth and polymerization contraction in the irradiated groups. In the other hand, the concentration of micropores decreased with increasing depth. Furthermore, the composition of the resin cement was determinant for the correlation's coefficients of these physical properties with depth. The μCT technique showed to be useful to probe physical properties of dental restorative materials that influence in the clinical outcomes, revealing that, for thin specimens, when light cured the RU cement presented mechanical behavior more favorable for clinical applications.

Comparative study of the bond strength of composite resins in the cementation of indirect restorations

Introduction: Nowadays there is an increasing development of materials capable of reducing the time of appointment, as is the case of multi-mode adhesive systems. The same occurs with composite resins as the creation of bulk-fill resins. This new type of resin can be classified, for its properties, between the fluid resins and the nanohybrid and microhybrid resins [1]. As for their mechanical properties, these materials have been shown to be stiffer (higher modulus of elasticity) and more plastic (greater plastic deformation) than conventional fluid resins. However, they have lower mechanical properties when compared with conventional nano-hybrid and microhybrid resins [1]. The new generation of bulk-fill resins has a low polymerization contraction value when compared to both nanohybrid and microhybrid fluid and non-flowing resins [2–4], so the aim of this study is to evaluate if it is possible to cement indirect restorations with Filtek™ Bulk Fill. Materials and methods: This work was approved by the IUEM Ethics Committee (nº572). Eighteen healthy molars were submitted to immediate dentin sealing (IDS) after exposure of the middle dentin. After 24 hours, they were randomly divided into two groups according to the type of restorative material, composite resin (Filtek™ Z100 3M ESPE) or lithium dissilicate (IPS e.max CAD - Ivoclar Vivadent). Each group was subdivided into three subgroups according to the adhesion material. 9 disks were obtained through a calibrated cylinder in 4x4 mm composite resin (Filtek™ Z100 3M ESPE) and adhered to the crowns with Filtek™ Z100 (3M ESPE), Filtek™ Bulk Fill (3M ESPE) and RelyX™ Veneer (3M ESPE). 9 ceramic blocks (IPS e.max CAD - Ivoclar Vivadent) with similar dimensions were produced and adhered with the same materials. The samples were stored for 24 hours at 37 °C and sectioned in beams. The specimens were pulled in a universal testing machine at 1 mm/min speed. The resulting fractures were classified stereoscopically. The adhesive interfaces were morphologically evaluated with SEM. Statistical analysis was performed using Student’s t tests, Anova One-Way (p ≤ 0.05). Results: The differences between the materials used in the adhesion of indirect restorations are not statistically significant, so Filtek ™ Bulk Fill can be used as cementing material. The highest adhesion values were obtained by the RelyX™ Veneer resin cement (Table 1, p = .385; Table 2, p = .158). Discussion and conclusions: This investigation tested the adhesive strength of three composite resins when cemented to two different types of indirect restorations. No statistically significant differences were obtained between the different adhesion materials, regardless of restorative material, so any of the materials can be used in adhesion of indirect restorations to composite resin or ceramic. Indirect restorations in both composite resin and lithium disilicate can be adhered with either Filtek ™ Z100, Filtek ™ Bulk Fill or RelyX ™ Veneer, as no statistically significant differences were obtained when indirect restorations are adhered with these materials. RelyX ™ Veneer resin cement was the adhesion material that achieved best adhesive strength results and the highest adhesive strength results were obtained in the indirect composite resin restoration.

Influence of Temperature and Relative Humidity on Dentin and Enamel Bonding: A Critical Review of the Literature. Part 1. Laboratory Studies

The aim of this literature review was to investigate the results from in vitro laboratory studies on the influence of temperature and relative humidity present before polymerization on enamel and dentin bonding systems. A systematic search was carried out including articles published in English, in peer reviewed journals, and indexed in MEDLINE/PubMed database. The search was carried out using the terms: relative AND humidity AND dental. In vitro studies were retrieved and divided into laboratory simulation studies and studies on physical properties. Laboratory simulation studies were addressed by subtopic: resin-enamel bond strength, resin-dentin bond strength, and dentin-enamel microleakage. Studies on physical properties tested the influence of humidity and temperature through polymerization contraction, flexural strength, and dentin wettability. Laboratory simulation studies demonstrated a strong influence of humidity and temperature on dentin and enamel bond strength and microleakage with dental adhesives systems. The studies on physical properties failed to demonstrate any influence of humidity on the adhesion performance, except for wettability measurement. The clinical relevance of these in vitro results remains to be demonstrated. A review of in vivo clinical studies will complete the literature data presented here.

Influence of volume on polymerization contraction force of bulk-fill-composites

Influence of volume on polymerization contraction force of bulk-fill-composites

µCT-3D visualization analysis of resin composite polymerization and dye penetration test of composite adaptation.

This study evaluated the effects of the light curing methods and resin composite composition on composite polymerization contraction behavior and resin composite adaptation to the cavity wall using μCT-3D visualization analysis and dye penetration test. Cylindrical cavities were restored using Clearfil tri-S Bond ND Quick adhesive and filled with Clearfil AP-X or Clearfil Photo Bright composite. The composites were cured using the conventional or the slow-start curing method. The light-cured resin composite, which had increased contrast ratio during polymerization, improved adaptation to the cavity wall using the slow-start curing method. In the μCT-3D visualization method, the slow-start curing method reduced polymerization shrinkage volume of resin composite restoration to half of that produced by the conventional curing method in the cavity with adhesive for both composites.μCT-3D visualization method can be used to detect and analyze resin composite polymerization contraction behavior and shrinkage volume as 3D image in the cavity.

The influence of delayed light curing on the degree of conversion and polymerization contraction stress in dual-cured resin luting agents

The aim of the study was to assess the effect of delayed photo-initiation on the polymerization contraction stress (PCS) and degree of conversion (DC) of a dual-cure resin-luting agent. Thirty-five disk (6 mm × 1 mm) samples (n = 10 each group) of dual cure resin luting agent for PCS assessment were fabricated and polymerized using two illuminated quartz rods. Based on the delay in photo-initiation, 30 disks were divided among six groups [group A-0 min (min) delay, group B-2 min, group C-4 min, group D-6 min, group E-8 min and group F-10 min]. A non-photoinitiated group (group G – chemical cure – n = 5) was included as control. The PCS for all specimens was assessed using a Tensometer. For DC evaluation thirty-five specimens were divided into seven groups with delays in photo-initiation (group H-0 min, group I-2 min, group J-4 min, group K-6 min, group L-8 min and group M-10 min, group N-chemical cure). DC was assessed using attenuated total reflectance spectroscopic technique. Statistical comparison among groups was performed using analysis of variance (α = 0.05). The maximum and minimum PCS and DC values with delayed photo-initiation was observed in group-C (3.34 MPa) & group-F (2.44 MPa); and group-M (0.78 MPa) and group-H (0.55 MPa) respectively. Chemically cured samples showed the least PCS (group-G, 1.94) and DC (group-N, 0.53) values in their respective categories. PCS significantly decreased with delayed photo-initiation. A significant increase in DC was noticed when photo-initiation was delayed in the dual cure resin luting agent.

Abstract LB-021: Impaired formation of homotypic cell-in-cell structures in human tumor cells lacking alpha-catenin expression

Abstract Majority of internal lumens in our bodies are covered with a layer of epithelial cells, whose integrity is critical for the organs to function properly. The integrity of epithelial tissues depends on intact adherens junctions (AJs), which is a multiple-components complex comprising cadherins, the transmembrane adhesion receptors, and their cytoplasmic binding proteins such as p120-catenin and b-catenin etc. Functional AJs is coupled with actin filaments through linker molecules, of which a-catenin and EPLIN are best characterized. Actin polymerization and actomyosin contraction regulated by Rho GTPases and their effectors play important role in AJs maintenance and remodeling. Aberrations, structural or functional, in AJs were associated with a number of pathological conditions, such as infection, inflammation and tumors and the like. Recent studies indicated that AJs mediated the formation of cell-in-cell structures (CICs). CICs refer to the cellular structures formed between viable cells, in which one or more cells exist inside other ones. Early records on CICs could be dated back to last century, when pathologists identified this type of unusual structures in human tumor samples10. Recent progress showed that cell-in-cell structures are rather complex than initially described, and could be classified into homotypic or heterotypic CICs based on the cells involved. Heterotypic CICs are usually formed by penetration of lymphocytes into tumor cells through processes like emperitosis. Homotypic CICs are formed between cells from same type, for example, epithelial cells inside epithelial cells. Mechanisms like entosis and homotypic cell cannibalism (HoCC) are responsible for this type of CICs formation. Once formed, CICs usually result in death of the internalized cells, which lead to the conception that CICs formation is a process of cell death. Limited researches identified extensive involvement of CICs in several important biological processes including development, immune homeostasis and tumor development and evolution etc. Recently, we and others found that formation of homotypic CICs by entosis was dependent on intact AJs and polarized actomyosin contraction. Tumor cells lacking epithelial cadherins (E and P-cadherin) failed to form CICs, moreover, re-expression of E- or P-cadherin could efficiently induce CICs in these cells, suggesting that disrupting AJs is a mechanism whereby tumor cells escape entosis-mediated CICs formation. In this work, we found that tumor cells deficient of a-catenin, a key component of functional AJs, also displayed impaired CICs formation, which could be fixed by restored expression of a -catenin. Therefore, tumor cells could escape entotic CICs formation by targeting multiple AJs components including E-/P-cadherin and a-catenin, and CICs formation by entosis may constitute a novel mechanism underlying the tumor suppressive function imposed by a -catenin. Note: This abstract was not presented at the meeting. Citation Format: Manna Wang, Xiangkai Ning, Ang Chen, Hongyan Huang, Qiang Sun, Zhaolie Chen, Li Ma, Xiaoning Wang. Impaired formation of homotypic cell-in-cell structures in human tumor cells lacking alpha-catenin expression [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr LB-021. doi:10.1158/1538-7445.AM2017-LB-021

Clinical evaluation of prefabricated ceramic inlays

Background: One of the methods to overcome the problem of polymerization contraction of posterior composites is to use prefabricated ceramic inlays in combination with composites. Several studies have shown that these pre fabricated ceramic inlays act as mega fillers which allow a reduction in resin based composite volume by 50-75% and a concomitant reduction in polymerization shrinkage and marginal micro leakage. Moreover the integration of pre fabricated ceramic inlays into composites reduces the overall coefficient of thermal expansion. Aims and Objectives: The performance of cerena prefabricated inlay system was evaluated. Material and Methods: 20 proximo occlusal cavities were restored with cerana prefabricated inlay system in patients. The performance of cerena pre fabricated inlay system in the oral cavity was recorded at base line follow up using Modified USPHS Ryge criteria at the end of 3, 6, and 12 months. Results: The alpha and Bravo values for the anatomic form, marginal integrity and caries assessment was evaluated. Alpha values were ideal. The Cerena pre- fabricated inlay system showed good fracture resistance, good marginal integrity and maintenance of antomic forms at end of 12 months period. Conclusion: The cerena pre-fabricated inlay system is a good treatment modality and provides a good restorative material at the end of 12 months too.