Dynamic and static elastic moduli of packable and flowable composite resins and their development after initial photo curing

Study on the Restoration of Class II Carious Cavities by Virtual Methods: Simulation of Mechanical Behavior

The restoration of class II cavities is predominantly carried out with composite materials. Due to the high failure rate in restoring this type of cavity, composite materials with much-improved properties and new application techniques have been promoted. The study aimed to analyze the mechanical behavior of several topical composite materials (nanocomposites, nanohybrids and ormocer) using different application techniques. In a lower second molar, a class II occlusal cavity was prepared. As filling materials, we used the following combinations: Admira Fusion and Admira Fusion Flow, Grandio and Grandio Flow, Filtek Supreme XT and Filtek Supreme Flow. These were applied using a snow plow, injection molded and Bichacho techniques. Three-dimensional scanning of the molar with the prepared cavity was performed, and then scanning of each layer of added composite material was performed, obtaining three-dimensional models. The virtual molar models were analyzed with software specific to the finite element analysis method, where their physical-mechanical properties were entered and assigned to the components of the virtual molar. Simulations at high forces specific to bruxism were then carried out and analyzed, and compared. The values of displacements and strain, for all six analyzed situations, are relatively small (range from 5.25 × 10^-6-3.21 × 10^-5 for displacement, 6.22 × 10^-3-4.34 × 10^-3 for strain), which validates all three methods and the materials used. As far as the stress values are concerned, they are similar for all methods (250-300 MPa), except for the snow plow and injection-molded techniques using Grandio and Grandio Flow composites, where the maximum von Mises stress value was more than double (approximately 700 MPa). When using the combination of Grandio and Grandio Flow materials, the 1 mm thickness of the fluid composite layer was found to have a major influence on occlusal forces damping as opposed to 0.5 mm. Therefore, the Bichacho technique is indicated at the expense of the snow plow and injection-molded techniques. The composite materials used by us in this study are state-of-the-art, with clear indications for restoring cavities resulting from the treatment of carious lesions. However, their association and application technique in the case of Class II cavities is of clinical importance for resistance to masticatory forces.

Effect of post-irradiation polymerization on selected mechanical properties of six direct resins

This study evaluated the post-irradiation mechanical property development of six resin composite-based restorative materials from the same manufacturer starting at 1 h post irradiation, followed by 24 h, 1 week, and 1 month after fabrication. Samples were stored in 0.2M phosphate buffered saline until testing. Flexural strength, flexural modulus, flexural toughness, modulus of resiliency, fracture toughness, and surface microhardness were performed at each time interval. Mean data was analyzed by Kruskal Wallis and Dunn's post hoc testing at a 95% level of confidence (α=0.05). Results were material specific but overall, all resin composite material mechanical properties were found to be immature at 1 h after polymerization as compared to that observed at 24 h. It may be prudent that clinicians advise patients, especially those receiving complex posterior composite restorations, to guard against overly stressing these restorations during the first 24 h.

Functional fillers for dental resin composites

Dental resin composites (DRCs) are popular materials to repair caries. Although various types of DRCs with different characteristics have been developed, restoration failures still exist. Bulk fracture and secondary caries have been considered as main causes for the failure of composites restoration. To address these problems, various fillers with specific functions have been introduced and studied. Some fillers with specific morphologies such as whisker, fiber, and nanotube, have been used to increase the mechanical properties of DRCs, and other fillers releasing ions such as Ag⁺, Ca²⁺, and F^-, have been used to inhibit the secondary caries. These functional fillers are helpful to improve the performances and lifespan of DRCs. In this article, we firstly introduce the composition and development of DRCs, then review and discuss the functional fillers classified according to their roles in the DRCs, finally give a summary on the current research and predict the trend of future development.

A Comparative Clinical Study of the Self-Adhering Flowable Composite Resin Vertise Flow and the Traditional Flowable Composite Resin Premise Flowable

Background. The aim of this research was to carry out a comparative clinical study of a self-adhesive, light-curing composite material called Vertise Flow and a traditional flow material called Premise flowable used in combination with dedicated bonding systems. In order to standardize the clinical environment, the stability of oral hygiene (analyzed with the oral hygiene index and the approximal plaque index) was taken into consideration. Methods. The study involved 37 patients with 64 fillings. They were distributed into three groups: 22 fillings in Group I, 22 fillings in Group II and 20 fillings in Group III. In Group I (G I), Vertise Flow material was applied without the use of an etching agent or a bonding system; in Group II (G II), Premise flowable material was applied without the use of an etching agent, but with the use of the OptiBond All-In-One seventh-generation bonding system; in Group III (G III), Premise flowable material was applied after etching and treatment of the hard tooth tissues using a fifth-generation OptiBond Solo Plus bonding system. Then, at appropriate time intervals (0, i.e., right after filling and after 6, 12 and 24 months), the fillings were subjected to clinical evaluation, conducted according to the Ryge scale criteria with the use of registration by means of a fluorescent high-intensity visible light beam produced by a camera (Vista Proof). Results. The quality of fillings performed with the use of comparable materials was subjected to clinical evaluation using the Ryge scale of fillings after 6, 12, and 24 months; the examination showed significant differences between the tested materials. The Vertise Flow material used without an etching agent or a bonding system (G I) presented the weakest results with respect to marginal adaptation and smoothness among those evaluated in this study. The intensification of the degradation continued over time until the final clinical observation at 24 months. The results confirmed that the best quality was achieved with the Premise flowable material after etching and treatment of the hard tooth tissues using a fifth-generation OptiBond Solo Plus bonding system (G III) relative to others for all time points during the observation. Conclusions. The used preparation scheme and bonding system have an impact on the final quality of the composite filling. There is a need to carry out a qualitative clinical evaluation of dental restorative materials under uniform conditions using evaluation scales.

Clinical evaluation of a self-adhering flowable composite as occlusal restorative material in primary molars: one-year results

Purpose:

The aim of this study was to evaluate and compare the 1 year clinical performances of a self-adhering flowable composite and a commercially available self-etch adhesive/composite system in occlusal restorations of primary second molars.

Materials and methods:

Thirty-one patients (10 male, 21 female) were recruited into the study. A total of 62 occlusal cavities were restored with either a universal composite or a self-adhering flowable composite according to manufacturers' instructions. The restorations were clinically evaluated 1 month after placement as baseline, and after 3, 6 months and 1 year post-operatively using modified USPHS criteria by two operators.

Results:

Lack of retention was not observed in any of the restorations. With respect to color match, marginal adaptation, secondary caries and surface texture, no significant differences were found between two restorative materials tested after 1 year. None of the restorations had marginal discoloration and anatomic form loss on the 1 year follow-up. Restorations did not exhibit post-operative sensitivity at any evaluation period.

Conclusion:

The clinical assessment of self-adhering flowable composite exhibited good clinical results with predominating alpha scores after 1 year. Advantage of the application convenience for children is promising for self-adhered flowable composite materials in pediatric use.

Impact of substrate stiffness on dermal papilla aggregates in microgels

Interaction between cells and the extracellular environment plays a vital role in cellular development. The mechanical property of a 3-dimensional (3D) culture can be modified to mimic in vivo conditions. Dermal papilla (DP) cells are shown to gradually lose their inductivity in hair cycle development in a 2-dimensional culture. They are shown to partially restore their inductivity when transferred into a 3D microenvironment. In this study, a microarray fabricated from three different concentrations of poly-ethylene-glycol-diacrylate 3500, namely 5%, 10% and 15% w/v, yielded increasing substrate stiffness. The impact of varying substrate stiffness was tested for DP cell viability, attachment, and selected hair inductive markers. DP aggregates were shown to be viable and exhibited greater spreading with increasing substrate stiffness. Moreover, DP aggregates cultured on a softer substrate showed a greater fold change of gene and protein expressions than those cultured on a harder substrate.

Microshear bond strength of self-adhesive composite to ceramic after mechanical, chemical and laser surface treatments

Objectives

This study aimed to assess the microshear bond strength of a repairing self-adhesive flowable composite to ceramic after mechanical, chemical and laser treatment of the ceramic surface.

Materials and Methods

Forty zirconia and forty feldspathic ceramic blocks measuring 8 x 8 x 2 mm were fabricated. Feldspathic blocks were divided into four groups of control (1), laser (2780 nm) (2), sandblasting + hydrofluoric (HF) acid + silane (3) and laser (2780 nm) + HF acid + silane (4). Zirconia blocks were also divided into four groups of control (1), laser (2780 nm) (2), sandblasting + Z-Prime Plus (3) and laser (2780 nm) + Z-Prime Plus (4). Vertise Flow composite was bonded to treated ceramic surfaces as a repairing material, then the samples were subjected to 1000 thermal cycles. Repair bond strength was measured by Instron machine and data were analyzed using one-way ANOVA and post hoc test (P < 0.05).

Results

Maximum and minimum bond strength values were observed in zirconia-control (22.57 ± 4.76 MPa) and feldspathic-control (8.65 ± 6.41 MPa) groups, respectively. There was no significant differences between subgroups within the zirconia or feldspathic groups (P > 0.05), however the bond strength of zirconia subgroups was significantly higher than that of feldspathic subgroups.

Conclusion

Vertise Flow provides relatively good bond strength to ceramic even with no surface treatment.

Flowable Resin Composites: A Systematic Review and Clinical Considerations

BACKGROUND

Little is known about flowable composite materials. Most literature mentions conventional composite materials at large, giving minimal emphasis to flowables in particular. This paper briefly gives an in depth insight to the multiple facets of this versatile material.

AIM

To exclusively review the most salient features of flowable composite materials in comparison to conventional composites and to give clinicians a detailed understanding of the advantages, drawbacks, indications and contraindications based on composition and physical/mechanical properties.

METHODOLOGY

DATA SOURCES

A thorough literature search from the year 1996 up to January 2015 was done on PubMed Central, The Cochrane Library, Science Direct, Wiley Online Library, and Google Scholar. Grey literature (pending patents, technical reports etc.) was also screened. The search terms used were "dental flowable resin composites".

SEARCH STRATEGY

After omitting the duplicates/repetitions, a total of 491 full text articles were assessed. As including all articles were out of the scope of this paper. Only relevant articles that fulfilled the reviewer's objectives {mentioning indications, contraindications, applications, assessment of physical/mechanical/biological properties (in vitro/ in vivo /ex vivo)} were considered. A total of 92 full text articles were selected.

CONCLUSION

Flowable composites exhibit a variable composition and consequently variable mechanical/ physical properties. Clinicians must be aware of this aspect to make a proper material selection based on specific properties and indications of each material relevant to a particular clinical situation.

In Situ Surface Biodegradation of Restorative Materials

This study aimed to evaluate the surface characteristics of restorative materials (roughness, hardness, chemical changes by energy-dispersive spectroscopy [EDX], and scanning electron microscopy [SEM]) submitted to in situ biodegradation. Fifteen discs of each material (IPS e.max [EM], Filtek Supreme [FS], Vitremer [VI], Ketac Molar Easymix [KM], and Amalgam GS-80 [AM]) were fabricated in a metallic mold (4.0 mm × 1.5 mm). Roughness, hardness, SEM, and EDX were then evaluated. Fifteen healthy volunteers used a palatal device containing one disc of each restorative material for seven days. After the biodegradation, the roughness, hardness, SEM, and EDX were once again evaluated. Data obtained from the roughness and hardness evaluations were submitted to Kolmogorov-Smirnov and Tukey-Kramer tests (p&lt;0.05). All esthetic restorative materials showed a significant increase in the roughness after biodegradation. Before biodegradation, significant differences in the hardness among the materials were seen: EM&gt;AM&gt;FS&gt;KM&gt;VI. After biodegradation, the hardness was significantly altered among the materials studied: EM&gt;AM&gt;FS=KM&gt;VI, along with a significant increase in the hardness for AM, KM, and VI. SEM images indicated degradation on the surface of all materials, showing porosities, cracks, and roughness. Furthermore, after biodegradation, FS showed the presence of Cl, K, and Ca on the surface, while F was not present on the VI and KM surfaces. EM and AM did not have alterations in their chemical composition after biodegradation. It was concluded that the dental biofilm accumulation in situ on different restorative materials is a material-dependent parameter. Overall, all materials changed after biodegradation: esthetic restorative materials showed increased roughness, confirmed by SEM, and the ionomer materials and silver amalgam showed a significantly higher hardness. Finally, the initial chemical composition of the composite resin and ionomer materials evaluated was significantly altered by the action of the biofilm in situ.

An inset CT specimen for evaluating fracture in small samples of material

In evaluations on the fracture behavior of hard tissues and many biomaterials, the volume of material available to study is not always sufficient to apply a standard method of practice. In the present study an inset Compact Tension (inset CT) specimen is described, which uses a small cube of material (approximately 2×2×2mm(3)) that is molded within a secondary material to form the compact tension geometry. A generalized equation describing the Mode I stress intensity was developed for the specimen using the solutions from a finite element model that was defined over permissible crack lengths, variations in specimen geometry, and a range in elastic properties of the inset and mold materials. A validation of the generalized equation was performed using estimates for the fracture toughness of a commercial dental composite via the "inset CT" specimen and the standard geometry defined by ASTM E399 (2006). Results showed that the average fracture toughness obtained from the new specimen (1.23±0.02MPam(0.5)) was within 2% of that from the standard. Applications of the inset CT specimen are presented for experimental evaluations on the crack growth resistance of dental enamel and root dentin, including their fracture resistance curves. Potential errors in adopting this specimen are then discussed, including the effects of debonding between the inset and molding material on the estimated stress intensity distribution. Results of the investigation show that the inset CT specimen offers a viable approach for studying the fracture behavior of small volumes of structural materials.

Bonding and sealing ability of a new self-adhering flowable composite resin in class I restorations

OBJECTIVES

The aim of this study is to assess by means of shear bond strength tests (SBS), microleakage analysis (μLKG), and scanning electron microscopy (SEM) the bonding potential and sealing ability of a new self-adhering composite resin.

MATERIALS AND METHODS

SBS and μLKG of Vertise Flow (VF, Kerr) were measured and compared to the all-in-one adhesive systems G-Bond (GB, GC), AdheSE One (AO, Ivoclar Vivadent), Adper Easy Bond (EB, 3M ESPE), Xeno V (XV, Dentsply), and iBOND (iB, Heraeus Kulzer). For each system, 20 molars were tested for SBS on dentin (n = 10) and enamel (n = 10). For μLKG assessment, 12 premolars per group were selected and small, box-shaped cavities were made. After restoration, the teeth were immersed in 50 wt% silver nitrate solution for 24 h. For each group, 10 randomly selected specimens were processed for leakage calculations, while two of the specimens were examined under SEM. Between-group differences in SBS to dentin and μLKG were assessed using Kruskal-Wallis analysis of variance followed by the Dunn's Multiple Range test. Enamel SBS data were analyzed with one-way ANOVA, followed by the Tukey test.

RESULTS

On dentin and enamel, VF recorded the lowest SBS values that were statistically comparable to those measured by GB, iB, and AO. μLKG analysis showed the lowest percentage of stained interface for VF. Significantly greater extent of infiltration was seen for iB and EB.

CONCLUSIONS

Although VF resulted in lower bond strengths values on either dental substrate, better marginal sealing ability was visualized in comparison with all-in-one adhesive systems.

CLINICAL RELEVANCE

The results of the present study demonstrated satisfactory in vitro outcome of the self-adhering flowable composite resin VF when used to restore class I cavities.

Impulse-Based Rendering Methods for Haptic Simulation of Bone-Burring

Bone-burring is a common procedure in orthopedic, dental, and otologic surgeries. Virtual reality (VR)-based surgical simulations with both visual and haptic feedbacks provide novice surgeons with a feasible and safe way to practice their burring skill. However, creating realistic haptic interactions between a high-speed rotary burr and stiff bone is a challenging task. In this paper, we propose a novel interactive haptic bone-burring model based on impulse-based dynamics to simulate the contact forces, including resistant and frictional forces. In order to mimic the lateral and axial burring vibration forces, a 3D vibration model has been developed. A prototype haptic simulation system for the bone-burring procedure has been implemented to evaluate the proposed haptic rendering methods. Several experiments of force evaluations and task-oriented tests were conducted on the prototype system. The results demonstrate the validity and feasibility of the proposed methods.

Effect of aging on coronal microleakage in access cavities through metal ceramic crowns restored with resin composites

PURPOSE

The purpose of this in vitro study was to determine if packable resin composite with/without flowable resin composite has the ability to prevent coronal leakage in restored endodontic access openings following aging.

MATERIALS AND METHODS

Eighty simulated standardized access cavities of metal-ceramic crowns were fabricated and fixed on Vitrebond cavities filled with an epoxy resin. The specimens were randomly divided into two main groups: (1) Group A-Access cavities filled with only packable composite (Filtek P60); (2) Group B-Access cavities filled with Filtek P60 and a flowable composite (Filtek Z350) as liner. Each main group was further subdivided randomly into four subgroups according to water storage and thermocycling periods. All specimens were immersed in blue ink solution for 24 hours and then sectioned into quadrants. The extension of blue ink along the metal-ceramic crown/composite resin interface was measured linearly using image analyzer and then analyzed by three-way ANOVA and independent t-test with a Mann-Whitney test. The level of significance was set at p < 0.05.

RESULTS

All tested subgroups demonstrated different levels of microleakage. There was no significant difference related to restorative technique; however, there was a significant difference related to water storage and thermocycling.

CONCLUSIONS

All tested techniques and materials in this study showed microleakage. Packable composite while a flowable liner showed a marginally better result than packable composite alone. Excessive thermocycling resulted in significant differences among the test groups.

Shrinkage Stresses Generated during Resin-Composite Applications: A Review

Many developments have been made in the field of resin composites for dental applications. However, the manifestation of shrinkage due to the polymerization process continues to be a major problem. The material's shrinkage, associated with dynamic development of elastic modulus, creates stresses within the material and its interface with the tooth structure. As a consequence, marginal failure and subsequent secondary caries, marginal staining, restoration displacement, tooth fracture, and/or post-operative sensitivity are clinical drawbacks of resin-composite applications. The aim of the current paper is to present an overview about the shrinkage stresses created during resin-composite applications, consequences, and advances. The paper is based on results of many researches that are available in the literature.

Flowability of composites is no guarantee for contraction stress reduction

OBJECTIVES

The purpose of this study was to measure the contraction stress development of three flowable resin-composite materials (Grandio Flow, VOCO GmbH, Cuxhaven, Germany; Tetric Flow, Ivoclar Vivadent, Schaan, Liechtenstein; Filtek Supreme XT Flowable Restorative, 3M ESPE, ST. Paul, MN, USA) and an universal micro-hybrid composite resin (Filtek Z250, 3M ESPE, St. Paul, MN, USA) during photopolymerization with a halogen curing light, using a novel stress-measuring gauge.

METHODS

Curing shrinkage stress was measured using a stress-analyzer. Composites were polymerized with a halogen curing unit (VIP, Bisco Inc., Schaumburg, IL, USA) for 40s. The contraction force (N) generated during polymerization was continuously recorded for 180s after photo-initiation. Contraction stress (MPa) was calculated at 20s, 40s, 60s, 120s and 180s. Data were statistically analyzed.

RESULTS

Filtek Supreme XT Flowable Restorative exhibited the highest stress values compared to other materials (p<0.05), while the lowest values were recorded with Tetric Flow (p<0.05). Tetric Flow was also the only flowable composite showing stress values lower than the conventional composite Filtek Z250 (p<0.05).

SIGNIFICANCE

Flowable composites investigated with this experimental setup showed shrinkage stress comparable to conventional resin restorative materials, thus supporting the hypothesis that the use of flowable materials do not lead to marked stress reduction and the risk of debonding at the adhesive interface as a result of polymerization contraction is similar for both type of materials.

Class I and Class II restorations of resin composite: An FE analysis of the influence of modulus of elasticity on stresses generated by occlusal loading

OBJECTIVES

It was the aim of the study to analyze by the FE method stresses generated in tooth and restoration by occlusal loading of Class I and Class II restorations of resin composite. On the basis of available information on the influence of the modulus of elasticity, the research hypothesis was that the marginal stresses would decrease with increasing modulus of elasticity of the restoration.

METHODS

A cylindrical tooth was modelled in enamel and dentin and fitted with a Class I or a Class II restoration of resin composite. In one scenario the restoration was bonded to the tooth, in another the restoration was left nonbonded. The resin composite was modelled with a modulus of elasticity of 5, 10, 15 or 20 GPa and loaded occlusally with 100 N. By means of the soft-ware program ABAQUS the von Mises stresses in enamel and dentin were calculated.

RESULTS

In the bonded scenario, the maximum stresses in the enamel were located at the occlusal margins (range 7-11 MPa), and in the dentin centrally at the pulpal floor (range 3.4-5.5MPa). The stresses decreased with increasing modulus of elasticity of the resin composite. In the nonbonded scenario, the stresses were higher in the dentin and lower in the enamel than in the bonded cases, and the influence of the modulus of elasticity was less pronounced. The marginal stresses in the restoration were below 6 MPa in the bonded scenario and below 3 MPa in the nonbonded scenario.

SIGNIFICANCE

Occlusal restorations of resin composite should have a high modulus of elasticity in order to reduce the risk of marginal deterioration.

Time-dependent visco-elastic creep and recovery of flowable composites

Creep behaviour of flowable composites was evaluated in relation to their filler fraction and the postcure period. Solid cylindrical specimens were prepared (4 x 6 mm) using steel moulds, with thorough light curing from multiple directions at 600 mW cm(-2). The specimens were divided into two groups (n=3/material) as follows: group I, loaded 5 min after preparation; and group II, loaded after storage for 1 month in water at 37+/-1 degrees C. A constant compressive stress of 36 MPa was applied to each specimen for 2 h followed by removal of the weight for 2 h of strain recovery. Axial strain measurements were obtained continuously over the total analysis time of 4 h. The maximum creep strain ranged from 2.04 to 7.69% and from 1.03 to 6.12% for groups I and II, respectively. Flowables that had the highest percentage of filler produced the lowest creep strain. The creep response decreased with 1 month of preload storage. Clinically, the finding of this study suggests that flowable composites are unsuitable for stress-bearing areas.