[Acoustic microscopy application for the evaluation of restorative materials bonding quality. Experimental investigation].

Ultrasound transmission and reflection at the interface between restorative material and tooth tissue have been investigated using experimental flat-parallel models and whole extracted human teeth with restorations. It has been found that in the case of good bonding the ultrasound wave energy practically does not reflect at the cement/dentin interface and propagates into dentin layer. If any microscopic cavity had been formed between cement and dentin, the most part of the acoustic energy would be reflected from the interface between cement and gaseous or liquid contents of that cavity. The results acquired have been used for the interpretation of morphological peculiarities of the adhesive bonding area in visual images, non-destructively obtained in acoustic microscope ultrasound frequency - 50 MHz. The differences discovered could be used as a base for the design and development of new ultrasound methods for the restorative materials bonding evaluation as well as for secondary caries revealing.

The use of acoustic microscopy to study the mechanical properties of glass-ionomer cement.

OBJECTIVES: The aim of the study was to investigate the relationship between microstructure, acoustic and mechanical properties of hardened dental cement samples, prepared with different powder/water ratios. METHODS: Glass-ionomer dental cement samples, prepared with a standard amount of cement powder and different amounts of water have been examined after being hardened. Surface microstructure and ultrasound, longitudinal and shear velocities were obtained with a scanning acoustic microscope. Conditional effective elastic modulus and Poisson's ratio have been calculated using longitudinal and shear sound velocity values. Then on the same samples elastic modulus and microhardness have been determined by standard tests. Additional samples have been used to determine compressive strength. RESULTS: Density; conditionally instantaneous elastic modulus; high-elasticity modulus and compression strength of the samples decrease when large amounts of water were used for their preparation. At the same time porosity and microhardness of the cement matrix increase. Acoustic parameters and parameters of elasticity, calculated on the basis of sound velocity, demonstrated changes, similar to those obtained in standard mechanical tests. SIGNIFICANCE: The established relation between microstructure, acoustic and mechanical parameters demonstrated a high capacity of acoustic microscopy application for non-destructive characterization of dental materials. A particular advantage of the acoustic microscopy is the opportunity to evaluate microstructure and mechanical properties on the same sample.

[Acoustic microscopy methods in studies of the filling materials microstructure]. / Ispol'zovanie metodov akusticheskoi mikroskopii dlia issledovaniia mikrostruktury plombirovochnykh materialov.

The structure of filling materials (kemfil, polyacrylate cement, and Dentis, material produced by Stomadent Firm in Russia) at the interface with human dentin was studied in teeth subjected to retrograde filling with preliminary appendectomy. A prototype of table wide-field short pulse scanning acoustic microscope (50 mHz) (Acoustic Microscopy Center, Institute of Biochemical Physics of Russian Academy of Sciences) and Elsam acoustic microscope (200 mHz) (Leitz, Germany) were used. The results indicate that analysis of acoustic characteristics, including the data of acoustic microscopy, helps investigate the cement microstructure and evaluate the compactness and elasticity of samples; moreover, structural elements of the material, which are undetectable by other methods, are seen on acoustic images. These data can be used for evaluating the relationship between the microstructure and formation of mechanical properties, and, maybe, the patterns of cement interactions with dental tissues.