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

Introduction Based on literature data it is obvious that there is a connection between smoking and periodontal diseases. Alveolar bone loss increases with smoking. Tobacco smoking affects the proportion of subgingival bacterial flora by influencing oxidoreduction potential of dental plaque and thus making conditions for development of anaerobic bacteria. According to some researchers, smoking affects the mineral component of bone tissue. Orthopantomograms show higher level of alveolar bone loss in smokers than in nonsmokers with the same level of oral hygiene. The aim of this study was to establish if smoking affects alveolar bone loss in complete denture wearers. Material and methods Our clinical investigation included 60 patients of both sexes (30 smokers and 30 nonsmokers) all complete dentures wearers. All patients met study criteria: jaw relation and smokers who smoke over 20 cigarettes per day. All subjects were interviewed, and after that orthopantomograms were made. They were used to calculate the degree of alveolar bone loss. Results The examined subjects were approximately of the same age. Mean age of smokers was 59.9 and nonsmokers 61.8. It was established that differences regarding resorption in men were not significant. The degree of resorption in women smokers and women nonsmokers was different, but differences were not significant. Discussion It has been proven that the number of cigarettes smoked per day is very important. It is considered that the risk of oral epithelial dysplasia increases when smoking more than 20 cigarettes per day. Considering our results regarding resorption of edentulous alveolar ridge in smokers and nonsmokers, we concluded that there were no significant differences. There are opinions in literature that smoking is not an etiological factor in resorption, but there are some opinions that smoking is connected with the degree of resorption in periodontium. The analyses of resorptive changes in edentulous smokers were done only around implants and it was estimated that smoking has more influence than other clinical risk factors. Conclusion On the bases of our research we may conclude that smoking does not directly affect the degree of resorption of edentulous alveolar ridge with complete denture wearers.

/pdf/effects-of-smoking-on-resorption-of-the-residual-alveolar-4fwt040nsi.pdf

Effects of smoking on resorption of the residual alveolar ridges in complete denture wearers

Introduction Dimensional stability of polymer-based dental materials is compromised by polymerization reaction of the monomer. The conversion into a polymer is accompanied by a closer packing of molecules, which leads to volume reduction called curing contraction or polymerization shrinkage. Curing contraction may break the adhesion between the adhesive system and hard tooth tissues forming microgaps which may result in marginal deterioration, recurrent caries and pulp injury. POLYMERIZATION SHRINKAGE OF RESIN-BASED RESTORATIVE DENTAL MATERIALS: Polymerization of the organic phase (nonomer molecules) of resin-based dental materials causes shrinkage. The space occupied by filler particles is not associated with polymerization shrinkage. However, high filler loading within certain limits, can contribute to a lesser curing contraction. Polymerization shrinkage stress and stress reduction possibilities Polymerization shrinkage stress of polymer-based dental resins can be controlled in various ways. The adhesive bond in tooth-restoration interface guides the contraction forces to cavity walls. If leakage occurs, complications like secondary caries and pulpal irritation may jeopardize the longevity of a restoration. Stress relieve can be obtained by modifications of the monomer and photoinitiator, or by specially designed tooth preparation and application of bases and liners of low modulus of elasticity. The polymerization contraction can be compensated by water absorption due to oral cavity surrounding. The newest approach to stress relief is based on modulation of polymerization initiation. Conclusion This work deals with polymerization contraction and how to achieve leak-proof restoration. Restorative techniques that may reduce the negative effect of polymerization shrinkage stress need further research in order to confirm up-to-date findings.

/pdf/light-induced-polymerization-of-resin-composite-restorative-hb7htlq227.pdf

Light induced polymerization of resin composite restorative materials

The dental profession increase utilization of light-curable restorative materials nowadays. Conventional halogen light sources with newly developed, high-tech light activating units are simultaneously present in modern dentistry. The present study was conducted in order to characterize the degree of light irradiation absorption, and according to absorbed energy spectral distribution estimate the opportunity for application of the most compatible polymerization light source. As a material in this work six composite resins were tested: Admira (VOCO), Admira Flow (VOCO), Filtek P60 (3M), Helio Progress (Vivadent), Tetric Ceram (Vivadent) and Tetric Flow (Vivadent). Absorption spectra analysis pointed out the absorbance values of all tested composite resin materials were very close to absolution peak of Camphorquinone (468 nm). The most similar absorbance values (%) in relationsliip to wavelenght (nm) in comparasion to Camphorquinone absorption maximum were as follows: 99,47 % for Admira; 98,02 % for Filtec P60; 97,72 % for Tetric Ceram; 97,51 % for Helio Progress, and a bit smaller values were found for Admira Flow (96,21 %) and for Tetric Flow (94,21 %). The results in this analysis which was done by using a spectrophometer pointed out high degree absorption of light for tested materials could have significant influence on polymerization process, and also on proper choice of polymerization light source.

/pdf/absorption-spectar-of-six-composite-resins-analyzed-by-using-42yb1a98li.pdf

Larisa Blazic

Papers

Effects of smoking on resorption of the residual alveolar ridges in complete denture wearers

Light induced polymerization of resin composite restorative materials

Absorption spectar of six composite resins analyzed by using a spectrophotometer