Djordje Antonijevic

In vitro radiographic detection of cement overhangs on cement-retained implant restorations.

PURPOSE The aim of this in vitro study was to investigate the potential of digital and conventional radiography to detect small amounts of residual dental luting cements around implant abutments. MATERIALS AND METHODS Artificial cement and aluminum overhangs in varying thicknesses, heights, and depths were radiographed adjacent to implant restorations with a radiovisiography sensor. Five trained evaluators were asked to identify the smallest depth of overhang that could be detected on radiographs. RESULTS For detection of cement overhangs adjacent to implant abutments, a luting agent must have greater radiopacity than what is recommended by relevant International Organization for Standardization directives. To detect a 0.1-mm-thick portion of excess cement adjacent to an implant abutment, the cement should have a radiopacity of at least 1.7 mm of aluminum for high-resolution digital radiographs and 2.2 mm of aluminum for film-based radiographs. Two-way analysis of variance revealed that the thickness of the specimens, type of imaging detector, and type of cement all affected the radiopacity threshold for artificial cement excess (P < .05). The height of the specimens and the surrounding structures were not statistically significant factors in cement detection. CONCLUSIONS Digital radiography offers better possibilities for visualization of cement excess than conventional radiography.

Porotic paradox: distribution of cortical bone pore sizes at nano- and micro-levels in healthy vs. fragile human bone

Bone is a remarkable biological nanocomposite material showing peculiar hierarchical organization from smaller (nano, micro) to larger (macro) length scales. Increased material porosity is considered as the main feature of fragile bone at larger length-scales. However, there is a shortage of quantitative information on bone porosity at smaller length-scales, as well as on the distribution of pore sizes in healthy vs. fragile bone. Therefore, here we investigated how healthy and fragile bones differ in pore volume and pore size distribution patterns, considering a wide range of mostly neglected pore sizes from nano to micron-length scales (7.5 to 15000 nm). Cortical bone specimens from four young healthy women (age: 35 ± 6 years) and five women with bone fracture (age: 82 ± 5 years) were analyzed by mercury porosimetry. Our findings showed that, surprisingly, fragile bone demonstrated lower pore volume at the measured scales. Furtnermore, pore size distribution showed differential patterns between healthy and fragile bones, where healthy bone showed especially high proportion of pores between 200 and 15000 nm. Therefore, although fragile bones are known for increased porosity at macroscopic level and level of tens or hundreds of microns as firmly established in the literature, our study with a unique assessment range of nano—to micron-sized pores reveal that osteoporosis does not imply increased porosity at all length scales. Our thorough assessment of bone porosity reveals a specific distribution of porosities at smaller length-scales and contributes to proper understanding of bone structure which is important for designing new biomimetic bone substitute materials.Graphical Abstract

“Dangerous duo”: Chronic nicotine exposure intensifies diabetes mellitus-related deterioration in bone microstructure - An experimental study in rats

Aims: Bony complications of diabetes mellitus (DM) are still insufficiently understood. Our aims were to analyze the individual and combined effects of chronic hyperglycemia and nicotine exposure on the femoral trabecular and cortical microarchitecture on a rat experimental model. Main methods: The micro‐computed tomography based bone microstructural evaluation was performed on male Wistar rats divided into four groups: control (n=7), experimentally‐induced DM (n=8), chronically exposed to nicotine (n=9) and the DM group exposed chronically to nicotine (n=9). Key findings: Chronic hyperglycemia caused mild trabecular deterioration; yet, the combination of hyperglycemia and nicotine exposure showed more deleterious effects on the trabecular bone. Namely, the DM+nicotine group had significantly lower bone volume fraction, fewer and more rod‐like shaped trabeculae, along with higher trabecular separation and lower connectivity than the control group (p<0.05). Nicotine alone did not show any significant deterioration compared to the control group. DM and DM+nicotine groups had lower cortical porosity than control and nicotine groups (p<0.05). Cortical thickness did not show any significant intergroup differences, whereas bone perimeter and the mean polar moment of inertia were reduced in DM+nicotine group. Significance: Mild effects of chronic hyperglycemia on bone structure were accentuated by the chronic nicotine exposure, although nicotine alone did not cause any significant bone changes. That suggests a synergistic effect of hyperglycemia and nicotine on bone deterioration and increased propensity to fracture. Indeed, better understanding of risk factors driving bone structural deterioration is a precondition to limit the complications associated with DM.

Extracting Cross-Sectional Clinical Images Based on Their Principal Axes of Inertia

Cross-sectional imaging is considered the gold standard in diagnosing a range of diseases. However, despite its widespread use in clinical practice and research, no widely accepted method is available to reliably match cross-sectional planes in several consecutive scans. This deficiency can impede comparison between cross-sectional images and ultimately lead to misdiagnosis. Here, we propose and demonstrate a method for finding the same imaging plane in images obtained during separate scanning sessions. Our method is based on the reconstruction of a “virtual organ” from which arbitrary cross-sectional images can be extracted, independent of the axis orientation in the original scan or cut; the key is to establish unique body coordinates of the organ from its principal axes of inertia. To verify our method a series of tests were performed, and the same cross-sectional plane was successfully extracted. This new approach offers clinicians access, after just a single scanning session, to the morphology and structure of a lesion through cross-sectional images reconstructed along arbitrary axes. It also aids comparable detection of morphological and structural changes in the same imaging plane from scans of the same patient taken at different times—thus potentially reducing the misdiagnosis rate when cross-sectional images are interpreted.

Application of reference point indentation for micro-mechanical surface characterization of calcium silicate based dental materials

The objective of this study was to elucidate micromechanical properties of Biodentine and two experimental calcium silicate cements (CSCs) using Reference Point Indentation (RPI). Biomechanical characteristics of the cement type and the effects of a radiopacifier, liquid components, acid etching treatment and bioactivation in simulated body fluid (SBF) were investigated by measuring the microhardness, average unloading slope (Avg US) and indentation distance increase (IDI). Biodentine had a greater microhardness than the experimental CSCs, while the Avg US and IDI values were not significantly different among investigated materials. There was a statistically significant difference in microhardness and IDI values between pure CSCs and radiopacified cements (p < 0.05). Micromechanical properties were not affected by different liquid components used. Acid-etching treatment reduced Biodentine’s microhardness while cements’ immersion in SBF resulted in greater microhardness and higher IDI values compared to the control group. Clearly, the physiological environment and the cements’ composition affect their surface micromechanical properties. The addition of calcium chloride and CSCs’ immersion in SBF are beneficial for CSCs’ micromechanical performance, while the addition of radiopacifiers and acid etching treatment weaken the CSCs’ surface. Application of RPI aids with the characterization of micromechanical properties of synthetic materials’ surfaces.

Novel calcium silicate based dental material with the addition of biologically active soy compound

Calcium silicate cements (CSC) present numerous properties that favor its use in dentistry. The purpose of this study was to investigate how the addition of soy extract affects porosity and wettability of the CSC. Soy was added to commercially available CSC named Portland cement (Italcementi, Spa Bergamo, Italy) at 10 weight % Pure Portland cement was used as a control material. Particle cement size was determined using scanning electron microscopy (TESCAN Mira3 XMU, USA Inc). Porosity of the cement was measured using micro computed tomography (μCT) (Skyscan 1172, Bruker, Belgium) at 10 μm isotropic resolution. Wettability of the cements was tested using contact angle analyzer and Endomethasone (Saint Maur, Cedex, France). Scanning electron microscopy has shown that Portland cement is composed of spherical and rods like particles ranging in size from 1 μm to 10 μm. The μCT analysis revealed that the addition of soy leads to an increased cements porosity. Both open and closed porosity values were higher in Portland cement with soy addition than in pure Portland cement. More than 70% of pores were in the range of 20-57 μm in both investigated groups. The addition of soy resulted in lower contact angles of Endomethasone on the cement surface, suggesting that this cement formulation possesses superior wettability. It can be deduced that soy is a promising candidate for Portland cement adhesive properties improvements.