Objective . This study determined the ultimate tensile strength (UTS) of enamel (E), dentin (D) and dentin–enamel junction (DEJ) using the microtensile technique. It was hypothesized that the UTS of dental structures varies according to location and nature. Methods . Intact occlusal enamel surfaces from extracted human third molars were etched with 37% phosphoric acid and bonded with a one-bottle adhesive system. The bonded occlusal surfaces received a resin composite build-up and teeth were serially, vertically sectioned into several 0.7 mm thick slabs. Each slab was then trimmed to a dumbbell-shaped specimen with irrigated diamond burs to reduce the cross-sectional area to approximately 0.5 mm 2 at E, D or DEJ. E was tested according to its prismatic orientation (parallel, EP; and transversally, ET) and D as function of depth (superficial, DS; middle, DM and deep, DD). Specimens were tested in tension in an Instron testing machine at 0.5 mm/min. Results were analyzed by one-way ANOVA and Duncan's Multiple Range test. Results. UTS mean values ( N =20) were, MPa (SD): DEJ, 46.9 (13.7) b ; EP, 42.1 (11.9) b ; ET, 11.5 (4.7) d ; DS, 61.6 (16.2) a ; DM, 48.7 (16.6) b and DD, 33.9 (7.9) c . Enamel stressed transversally to its prismatic orientation was significantly weaker ( p p p >0.05). Significance . The UTS of dental structures varies according to its nature and location.

Ultimate tensile strength of tooth structures

https://www.cell.com/trends/biotechnology/pdf/S0167-7799(15)00191-2.pdf

Advances in Dental Materials through Nanotechnology: Facts, Perspectives and Toxicological Aspects.

Biomechanical Properties of First Maxillary Molars with Different Endodontic Cavities: A Finite Element Analysis.

Poly methyl methacrylate (PMMA) resin is the most widely used material for fabrication of dentures since 1937 as it exhibits adequate physical, mechanical and esthetic properties. But one of the major problems faced using this material is that, it is highly prone to plaque accumulation due to surface porosities and its food retentive properties. This in turn increases the bacterial activity causing denture stomatitis. In efforts to impart antimicrobial property to these resins, various nanoparticles (NP) have been incorporated viz. Silver, Zirconia oxide, Titanium dioxide (TiO2), Silica dioxide (SiO2) etc. However, as additives they can affect the mechanical properties of the final product. Therefore, the aim of the present study was to evaluate and compare the effect of different concentration of TiO2 NP on the flexural strength of PMMA resins. Specimens made from heat polymerizing resin (DPI) without NP were used as a control group (Group A). The two experimental groups, (Group B and Group C) had 0.5 and 1 % concentration of TiO2 NP respectively. The specimens were stored in 37 °C distilled water for 50 ± 2 h. A three-point bending test for flexural strength measurement was conducted following ADA specification no. 12. The maximum mean flexural strength (90.65 MPa) belonged to the control group; and acrylic resin with 1 % TiO2 NP demonstrated the minimum mean flexural strength (76.38 MPa). But, the values of all the three groups exceeded the ADA Specification level of 65 MPa. Conclusion may be drawn from the present study that addition of TiO2 NP into acrylic resin can adversely affect the flexural strength of the final product and is directly proportional to the concentration of NP.

Effect of Anatase Titanium Dioxide Nanoparticles on the Flexural Strength of Heat Cured Poly Methyl Methacrylate Resins: An In-Vitro Study

Clinical Relevance In vitro research remains of primary importance to selecting and validating the techniques and products to be used in vivo. However, the clinical predictive value of such tests n...

In Vitro Performance of Class I and II Composite Restorations: A Literature Review on Nondestructive Laboratory Trials—Part I

In the recent years, there has been an increasing interest in the research of biomechanical aspects of biomaterials and human tissues (1-3). Although studies conducted in vivo and in vitro have provided some of the answers in this field, dental and medical research is usually costly, and may be ethically questionable and time-consuming (4,5). Because of this, the use of numerical models and in vitro simulations became a valuable tool for saving time and money associated with laboratory and clinical research (6). Previous studies have reported different techniques for generating three-dimensional (3D) solid models of the teeth (7-9). Nowadays, technological development brings new possibilities for efficient generation of sophisticated 3D solid models. For example, using specialized software, these models can be generated based on computed-tomography (CT) scan data (5,10-12). In addition, the application of finite element analysis (FEA) allows calculation of stress and strain within tooth structure and biomaterials, which can hardly be measured in vivo (13).

Cavity design preparation has a great impact on stress values and fracture resistance of a tooth (7,14-16). It is a factor of a paramount importance, especially in cases of restoring maxillary premolars with extensive mesio-occlusal-distal (MOD) cavities (14,17,18). From the biomechanical point of view, different opinions have been reported on the most appropriate restorative procedure in such cases. Kuijs et al have found that ceramic, indirect resin composite and direct resin composite provide comparable fatigue resistance in a cusp replacing restorations (19). These findings were supported by clinical trials performed by van Dijken and Hickel et al (20,21). On the other hand, Soares et al found that MOD cavities restored with resin composite placed with direct technique attained better biomechanical performance than those restored with laboratory processed resin and ceramic restorations (15,16). Another study also confirmed that in comparison with ceramic restorations, resin composite restoration had higher fatigue resistance (17). As opposed to preparation for direct restoration, cavity preparation for indirect restorations requires removal of additional amount of tooth structure (22). The situation is the same with the cavity preparation for the amalgam (23). Since the quantity of the tooth structure removed while doing cavity preparation affects the biomechanical characteristics of the restored tooth, the use of adhesive direct restorations should be recommended for reinforcing the remaining dental structure (2,16).

When planning the design of MOD cavity preparation, cavity wall thickness and cusp reduction should be carefully considered. Usually, cusp reduction is recommended when cavity isthmus width is 2/3 of intercuspal width (7,24). Although this promotes more dental tissue reduction (25), it was shown that the reduction of cuspal height by 2.0 mm increases fracture resistance of a premolar when restored with direct resin composite (26,27). On the other hand, cavity wall thickness is not well defined. Macpherson et al found that 2.25 mm wall thickness is critical for restoring fracture resistance of tooth with MOD cavity (28), but another study, which investigated 1.0-3.0 mm wall thicknesses, reported that the thickness of remaining cavity walls was not relevant to fracture resistance (27).

The aim of this study was to investigate the effect of cavity design preparation on stress values in remaining tooth structures restored with resin composite. The null hypothesis was that stress values were not significantly influenced by the cavity wall thickness and cusp reduction.

/pdf/influence-of-cavity-design-preparation-on-stress-values-in-39ix2j1axs.pdf

Influence of cavity design preparation on stress values in maxillary premolar: a finite element analysis.

An experimental technique to reveal the effects of dental polymer contraction is established to choose the most appropriate polymerization technique. Tooth deformation following a dental filling polymerization is analyzed using double-exposure holographic interferometry. A caries-free, extracted human molar is mounted in dental gypsum and different cavity preparations and fillings are made on the same tooth. Dental composite fillings are polymerized by an LED light source especially designed for this purpose. Holographic interferograms are made for occlusal (class I), occlusomesial (class II), and mesioocclusodistal (class II MOD) cavities and fillings. Maximum intercuspal deformation ranges from 2 microm for the class I cavity to 14 mum for the MOD class cavity. A finite element method (FEM) is used to calculate von Mises stress on a simplified tooth model, based on experimental results. The stress varies between 50 and 100 MPa, depending on the cavity type.

https://www.spiedigitallibrary.org/journals/Journal-of-Biomedical-Optics/volume-12/issue-02/024026/Holographic-detection-of-a-tooth-structure-deformation-after-dental-filling/10.1117/1.2714056.pdf

Holographic detection of a tooth structure deformation after dental filling polymerization

We describe a real-time holographic technique used to observe dental contraction due to photo-polymerization of dental filling during LED lamp illumination. An off-axis setup was used, with wet in-situ processing of the holographic plate, and consequent recording of interference fringes using CCD camera. Finite elements method was used to calculate internal stress of dental tissue, corresponding to experimentally measured deformation. A technique enables selection of preferred illumination method with reduced polymerization contraction. As a consequence, durability of dental filling might be significantly improved.

Real-time measurement of internal stress of dental tissue using holography.

Nanotechnology has been considered as multidisciplinary field of scientific
 research about different types of nanoparticles as well as the application of
 new nanomaterials and nanodevices in numerous areas of human interest. It
 offers advances in industry, engineering, information and communication
 technology, electronics, environmental science and energy savings, economics
 etc. New nanoproducts and nanotehnology could be applied in almost all fields
 of human activity. Potential benefit of nanomaterials and nanorobots applied
 in medicine and dentistry is of main concern when thinking about
 nanoadvances. However, nanotechnology has become a controversial issue
 between scientific and public opinions due to the insufficient knowledge of
 potential hazard to human health and environment. Some of the raised
 questions are what are the advantages and disadvantages of nanotechnological
 evolution, and what kind of future can be expected when changes gain wider
 scale? The aim of this study was to present the importance of nanotechnology
 in various areas, especially in medicine and dentistry, and to point out
 possible consequences of their use to human health and environment.

/pdf/nanotechnology-in-dentistry-current-state-and-future-2lqjsfnsxo.pdf

Nanotechnology in dentistry: Current state and future perspectives

Adhesion to enamel has become a routine technique in restorative dentistry. Adhesion to dentin, however, is still under investigation. Except structural elements of the dentin, smear layer has been one of the reasons that the interaction between the adhesive system and this tissue is difficult. The smear layer tissue created by cutting a tooth. It varies in thickness, roughness, density and degree of attachment andoccludes tubules and reduces the dental permeabilita. Dentin adhesivesystems can react with intertubular and peritubular dentin only when this smear layer is removed or when the adhesive system is capable of diffusion through layer of debris. As part of restorative procedures required by adhesive dentistry, the smear layer must be removed, modified or impregnated by the resin to allow for bonding between the tooth and the restorative material. For remove and dissolve of smear layer acid conditioners on total etch and self-etching primers were used. Self-etching primer systems are undergoing rapid evolution; their results are not yet sufficiently predictable overall, but some systems have achieved positive results in both enamel and dentin bonding. Further studies are necessary to confirm the long-term efficiency of these self-etching primers.

/pdf/smear-layer-on-dentin-in-restorative-dentistry-4rn1m82seh.pdf

Larisa Blazic

Papers

Influence of cavity design preparation on stress values in maxillary premolar: a finite element analysis.

Holographic detection of a tooth structure deformation after dental filling polymerization

Real-time measurement of internal stress of dental tissue using holography.

Nanotechnology in dentistry: Current state and future perspectives

Smear layer on dentin in restorative dentistry