An approach to investigate the crystallographic unit cell of human tooth enamel.

Human tooth enamel (HTE) is the hardest tissue in the human body and its structural organization shows a hierarchical composite material. At the nanometric level, HTE is composed of approximately 97% hydroxyapatite [HAP, Ca10(PO4)6(OH)2] as inorganic phase, and of 3% as organic phase and water. However, it is still controversial whether the hexagonal HAP phase crystallizes in P63/m or another space group. The observance in HTE of Ca2+, Mg2+ and Na+ ions using X-ray characteristic energy-dispersive spectroscopy in the scanning electron microscope has been explained by substitutions in the HAP unit cell. Thus, Ca2+ can be replaced by Na+ and Mg2+ ions; the PO43- group can be replaced by CO32- ions; and the OH- ions can also be replaced by CO32-. A unit-cell model of the hexagonal structure of HTE is not fully defined yet. In this work, density functional theory calculations are performed to study the hexagonal HAP unit cell when substitution by OH-, CO32-, Mg2+ and Na+ ions are carried out. An approach is presented to study the crystallographic unit cell of HTE by examining the changes resulting from the inclusion of these different ions in the unit cell of HAP. Enthalpies of formation and crystallographic characteristics of the electron diffraction patterns are analysed in each case. The results show an enhancement in structural stability of HAP with OH defects, atomic substitution of Mg2+, carbonate and interstitial Na+. Simulated electron diffraction patterns of the generated structures show similar characteristics to those of human tooth enamel. Hence, the results explain the indiscernible structural changes shown in experimental X-ray diffractograms and electron diffraction patterns.

Opalescence and color stability of composite resins: an in vitro longitudinal study.

OBJECTIVES: This study aims to evaluate the opalescence (OP) and color stability of composite resins over a period of 180 days and to compare composite resins' OP with enamel's OP. MATERIALS AND METHODS: Twenty human enamel specimens (5.0 × 0.3 mm) and 9 specimens (10.0 × 1.0 mm) of 10 colors of 4 different composite resins (3 M ESPE, FGM, Ivoclar-Vivadent, Miscerium) and one brand of adhesive (3 M ESPE) were made. The results were obtained by measuring the reflectance and transmittance spectra in the visible region. After baseline measurement, composites and adhesive were analyzed after 2, 7, 30, 60, 120, and 180 days. The Lab color coordinates were used in the calculations of the OP parameter and color differences in the CIELab and CIEDE2000 methods. The data were analyzed statistically. RESULTS: The materials tested showed variation and an increase in OP over time. The OP found for enamel was 18.06 ± 2.99, and some resins showed higher results. There was a strong correlation between the coordinate b*T and the OP over time. Enamel Plus was the only one material that presented no color changes during all periods in both color analyses. Filtek Z350 XT, AT, and BT did not show differences in any time when analyzed by CIELAB. CONCLUSIONS: The OP of most composite resins changed during the period of 180 days and was different from the OP of tooth enamel. In general, composites demonstrated small color changes over the period tested, being this characteristic material dependent. CLINICAL RELEVANCE: Natural teeth present different optical properties. Composite resins restorations should present properties similar to natural teeth and it is important that characteristics like color and opalescence remain stable over time.

Effect of reciprocating instrumentation on chlorhexidine substantivity on human dentin: chemical analysis followed by confocal laser microscopy

The present research analyzed the reciprocating instrumentation associated to chlorhexidine (CHX) substantivity as its correlation with E. faecalis viability in ex vivo root canals. Eighty extracted single-rooted human teeth were used, being 40 to high-performance liquid chromatography (HPLC) and 40 to confocal laser scanning microscopy (CLSM). In both, teeth were decoronated and the cervical third was prepared. In the CLSM analysis, the root canals were inoculated with E. faecalis for 14 days. Samples were divided into 4 groups (n=10) according to instrumentation technique: no instrumentation and irrigation with distilled water (control); manual instrumentation (K-File); rotary instrumentation (ProTaper Next); and reciprocating instrumentation (Reciproc R25). Two percent chlorhexidine was applied as irrigating substance in experimental groups. Longitudinal grooves resulted in 2 halves root and 20 proof bodies in each group. Samples were divided by chance in two groups (n=10) and the outcomes were evaluated after two days and one week. The retained chlorhexidine and live cells after instrumentation techniques in each evaluation time was measured by HPLC and CLSM, respectively. Specific analysis was applied for experimental tests (p≤0.05). Both rotary as well as reciprocating techniques significantly reduced the amount of chlorhexidine on dentin in all observation periods (p<0.05). After evaluation times, all experimental groups presented lower live cells compared to control, but without statistically difference. Intragroup comparisons in times of evaluation showed no differences in instrumentation techniques, in chlorhexidine retention and number of live cells (p>0.05). Reciprocating instrumentation does not interfere on chlorhexidine substantivity.

Caracterización estereológica de odontoblastos en pulpas dentarias humanas sanas y con pulpitis reversible / Stereological characterization of odontoblasts in normal healthy and reversible pulpitis in human dental pulps

La reacción y reparación dentinaria depende del número de odontoblastos. Los métodos para obtener estimaciones fiables sobre la cantidad de odontoblastos en la pulpa dental han sido subjetivos y sesgados, sobre todo al evaluar los cambios cuantitativos y la potencial capacidad reparativa en presencia de caries. El objetivo de este trabajo fue estimar y comparar cuantitativamente el número, densidad y volumen de odontoblastos en dientes sanos y con diagnóstico de pulpitis reversible producto de caries a través de herramientas estereológicas. Se utilizaron dientes premolares humanos obtenidos de exodoncias, divididos en un grupo sano y otro cariado. Fueron fijados y descalcificados con ácido nítrico al 5%. Siguiendo el protocolo del orientator se obtuvieron 5 secciones de 5 mm teñidas por H-E de cada diente. Se aplicó el recuento estereológico de los odontoblastos con el test multipropósito M42. Se estimaron las densidades de número (Nv), volumen (Vv) y superficie (Sv), y calcularon las Medias (±DE) por diente, y Medias (±EE) por grupo. Las diferencias entre grupos se analizaron mediante la prueba T, con un valor p 0,05 de significación estadística. En dientes sanos, la Media (±EE) para Nv de odontoblastos fue 0,409x105/mm3 (±0,018x105/mm3), para Vv 19,714% (±1,43%) y para Sv 21,016 mm2/mm3 (±1,425 mm2/mm3). En dientes cariados, la Nv fue 0,521x105 /mm3 (±0,023x105/mm3), la Vv 24,686% (±1,625%) y la Sv 23,203 mm2/mm3 (±1,364 mm2/mm3). Al comparar las Nv, los odontoblastos del grupo con caries aumentaron significativamente (p=0,0062), al igual que la Vv (p=0,0197). Existe un aumento del número de odontoblastos en los dientes con pulpitis reversible, lo que condicionaría su capacidad de respuesta. La metodología empleada puede ser aplicable para determinar el comportamiento pulpar y cuantificar variables de respuesta odontoblástica en tratamientos restauradores atraumáticos de manera imparcial y reproducible.

Dentinal reaction and repair depends on factors like the amount of odontoblasts. Methods for obtaining reliable estimates of the number of odontoblasts in the dental pulp have been subjective and biased, especially when assessing the potential quantitative changes and reparative capacity in the presence of cavities. The aim of this study was to estimate and quantitatively compare, through stereological tools, the number, density and volume of odontoblasts in healthy teeth, diagnosed with reversible pulpitis due to caries. We used human premolars obtained from extractions, divided into groups of healthy teeth and teeth with caries, fixed and decalcified in 5% nitric acid. Following the orientator protocol, five 5-µm-thick sections stained by HE were obtained from each tooth. Stereological counting for odontoblast with M42 multipurpose test was applied. Numerical density (Nv), volume density (Vv) and surface density (Sv) were estimated, and the mean (± SD) for each tooth, and Mean (± SE) per group were calculated. Differences between groups were analyzed by t test, with p 0.05 for statistical significance. In the healthy teeth group, the mean (± SE) for Nv was 0.409x105/mm3 (±0.018x105/mm3), Vv 19.714% (±1.43%) and to Sv 21.016 mm2/mm3 (±1.425 mm2/mm3) odontoblast cells. In the caries teeth group, the Nv was 0.521x105 /mm3 (±0.023x105/mm3), Vv 24.686% (±1.625%) and Sv 23.203 mm2/mm3 (±1.364 mm2/mm3). When comparing Nv, an increased in odontoblasts significantly (p = 0.0062), as well as Vv (p = 0.0197) in caries teeth group. There is an increased number of odontoblasts in teeth with reversible pulpitis, which would condition its responsiveness. The methodology can be applied to determine pulp behavior, and quantify variables of odontoblastic response in atraumatic restorative treatments in an impartial and reproducible form.

Radiodensity evaluation of dental impression materials in comparison to tooth structures

In the most recent decades, several developments have been made on impression materials' composition, but there are very few radiodensity studies in the literature. It is expected that an acceptable degree of radiodensity would enable the detection of small fragments left inside gingival sulcus or root canals. OBJECTIVE: The aim of this study was to determine the radiodensity of different impression materials, and to compare them to human and bovine enamel and dentin. MATERIAL AND METHODS: Twenty-five impression materials, from 5 classes, were studied: addition and condensation silicones, polyether, polysulfides and alginates. Five 1-mm-thick samples of each material and tooth structure were produced. Each sample was evaluated 3 times (N=15), being exposed to x-ray over a phosphor plate of Digora digital system, and radiodensity was obtained by the software Digora for Windows 2.5 Rev 0. An aluminum stepwedge served as a control. Data were subjected to Kruskal-Wallis and Dunn's method (α=0.05). RESULTS: Different materials and respective classes had a different behavior with respect to radiodensity. Polysulfides showed high values of radiodensity, comparable to human enamel (p>0.05), but not to bovine enamel (p<0.05). Human dentin was similar only to a heavy-body addition silicon material, but bovine dentin was similar to several materials. Generally, heavy-body materials showed higher radiodensity than light-body ones (p<0.05). CONCLUSION: Impression materials' radiodensity are influenced by composition, and almost all of them would present a difficult detection against enamel or dentin background in radiographic examinations.