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news 2021/10/31

Composite’s mechanical activation (pt.1)


Composite’s mechanical activation (pt.1)

Mechanical activation by M. Melikyan and its influence of on the strength properties of composite materials (pt.1)

Composites materials (synthetic resins) have been extensively used in dentistry as restorative composites to eliminate defects in hard dental tissues. It is well known, from literature and practical tests, that during the restoration of hard dental tissue the composites materials applied by several layers to form special shapes of the teeth.  The ultimate load of composite samples made of micro-hybrid composite material depends essentially on mechanical activation in particular, for example, at initial arrangement of composite materials in the form of spherical shape the ultimate load increases up to 5,7%, while at cylindrical shape the ultimate load increases up to 7,3% with comparison of control samples.

Purpose of the study: to study the effect of mechanical activation on the strength of composite specimens during three-point bending tests. Here we are sharing our analysis of the strength properties of the micro-hybrid composite samples on a three-point bend test according to preliminary mechanical activation of the material.


The three-point static bend fixture test of the all composite samples revealed that their integrity of structure fails causing cracks on the underside of the sample on strain tension zone. In the process of crack development, the fracture grows to be arterial by propagating throughout of the entire sample thickness from strain tension zone to neutral zone and completed in the compression zone, thereby separating the sample by about two parts. It was established that during the process of preparation of composite samples, by applying sections of composite materials to manually form spherical or cylindrical shapes, (using not powdered natural latex gloves), increases the ultimate load on 5,7-7,3%, while the color of samples was not changed with comparison of samples prepared by metal plugger.

In clinical practice, defects of the incisal edge of the tooth of carious and non-carious origin are observed quite often. In numerous classifications, destruction of up to 1/3 of the length of the coronal part, which is 3-4 mm, is considered under the defect of the incisal edge. The height of the coronal part of the anterior incisors of the upper jaw is 9.0-12.0 mm, and the height of the coronal part of the incisors of the lower jaw is 6.3-11.6 mm. According to histological studies, the thickness of the enamel layer at the level of the incisal edge of the tooth is 1.5-1.7 mm. When the incisal edge of the tooth is destroyed, up to 2 mm deep, dentin is exposed at the level of the enamel-dentin border. Dr. Melikian et al. developed a classification of defects in the coronal part of anterior teeth for reinforced composite restorations and methods for their elimination that meet the requirements of the concept of minimal invasion (MI). Taking into consideration that the length of the incisal edge of the tooth is 3-4 mm, in the presented classification, the defects of the incisal edge are divided into 2 classes; defect of the incisal edge of the tooth, up to 2 mm deep, is allocated in a separate class.

We have developed and patented an atraumatic method for eliminating the incisal edge defect, up to 2 mm deep, using composite materials. To restore the integrity of the incisal edge, a composite material was used. It is known from literary sources that when various defects of dental hard tissues are eliminated with the use of a composite material, portions of the composite material are given a different shape during the restoration process. Considering the peculiarities of the defect of the incisal edge of the tooth, up to 2 mm deep, in the process of restoration, the composite material was given the form of a ball by the method of manual mechanical action (mechanical activation), and then - the shape of a roller. The length of the composite beads was formed according to the length of the incisal edge of the damaged tooth in the medio-distal direction. Mechanical activation, in the broadest sense of this term, should be understood as any acceleration of technological processes leading to an increase in the quality of a product through mechanical influences (see continuation in the next article).

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