EFFECT OF CHICKEN EGGSHELL PASTE ON ENAMEL SURFACE MICROHARDNESS AND COLOUR CHANGE OF ARTIFICIAL CARIOUS LESIONS CREATED ON PERMANENTLY EXTRACTED TEETH

Remineralizing agents such as fluoride and hydroxyapatite (HA) (Ca5 (po4)3OH) are well-known treatment choices for incipient enamel lesions. Hydroxyapatite has been newly presented to return the color of such enamel lesions. The purpose of this prospective in vitro study was to compare commercial sodium fluoride paste to hydroxyapatite paste (HA) made from chicken eggshells powder (CESP) in terms of how it affected the microhardness and color of the enamel surface of artificially demineralized permanent teeth. Fifty healthy maxillary premolars were gathered, decoronated, and the crowns were placed in acrylic moulds with the buccal enamel surfaces exposed. Baseline microhardness evaluation was done for the baseline group, while the colour assessment was done at baseline to three treatment groups. Then specimens were randomly divided into the following five groups (n = 10) based on the treatment of enamel surface: Group 1: Baseline group; Group 2: Acid group demineralized only; Group 3: demineralized followed by the application of hydroxyapatite paste (HA); Group 4: demineralized followed by the application of sodium fluoride toothpaste (Naf); and Group 5: demineralized followed by application of combination treatments (HA paste at morning and Naf paste at evening. The specimens were stored in deionized water at room temperature during treatments, after one week they were subjected to a Vickers microhardness test, and colour assessment to three treatment groups after treatment. One‑way ANOVA and Tukey's post hoc multiple comparison tests were used for statistical analysis (P < 0.05). After artificial demineralization, the enamel's surface microhardness was greatly reduced, and after management, it dramatically increased. The combination group had the greatest mean microhardness value when compared to the HA paste group and the Naf paste group. Statistically, there was no significant variance in microhardness values among the Naf paste and HA paste groups. Hydroxyapatite sourced from chicken eggshell was as effective as Naf paste in remineralizing and restoring the lost microhardness of artificially demineralized enamel, hydroxyapatite paste changed tooth color, while sodium fluoride paste, a combination group neither changed nor masked color of early caries lesion.

Influence of Carbon Nanotubes on Phase Composition, Thermal and Post-Heating Behavior of Cementitious Composites

This paper experimentally investigates the influence of carbon nanotubes (CNTs) on phase composition, microstructure deterioration, thermal behavior, and residual mechanical strengths of cementitious composites exposed to elevated temperatures. Cement mortars with small dosages of CNTs, 0.05% and 0.2% by weight of cement, were prepared and then heated at 25 °C, 150 °C, 200 °C, 450 °C, and 600 °C for two hours before being tested. The results show positive impact of the CNTs on the hydration process of cement mortar at room temperature and at higher temperatures up to 200 °C. Decomposition of the hydration products is obvious at 450 °C, whereas sever deterioration in the microstructure occurs at 600 °C. The nano reinforcement and bridging effect of the CNTs are obvious up to 450 °C. Thermal behavior characterization shows that CNTs incorporation enhances the thermal conductivity of the unheated and heat-treated mortar specimens. The decomposition of the hydration products needs more heat in the presence of CNTs. Finally, presence of CNTs significantly enhances the residual compressive and flexural strengths of heated mortar specimens for all studied temperatures.

The Role of Polypropylene Microfibers in Thermal Properties and Post-Heating Behavior of Cementitious Composites

This paper experimentally studied the effect of polypropylene (PP) microfibers on thermal and post-heating mechanical behaviors of cementitious composites. Cement mortars with small dosage of polypropylene fibers were prepared, heated at various temperatures (150 °C, 200 °C, 450 °C, and 600 °C), and then tested. The investigated parameters include residual compressive and flexural strengths, elastic modulus, fracture energy, stress intensity factors, failure modes, microstructure (scanning electron microscopy (SEM) imaging), thermal conductivity, heat flow (differential scanning calorimetry (DSC) test), mass loss (thermogravimetric analysis (TGA) test), and chemical composition (XRD analysis). The results showed the efficiency of PP fibers to enhance the post-heating behavior and the residual mechanical properties of cement mortar after heating. The presence of PP fibers did not affect the heat flow and the mass loss of cement mortar at room temperature. However, heating cement mortar at temperature beyond the melting point of the fibers negatively affected its thermal behavior. The presence of PP fibers played a major role in bridging the cracks and mitigating their propagation. Once the melting point of the polypropylene fibers is exceeded, the fibers melted and created extra voids in the microstructure of concrete.

A prospective study on the effect of coronal tooth structure loss on the 4-year clinical survival of root canal retreated teeth and retrospective validation of the Dental Practicality Index

AIM

First, to examine the impact of the residual volume of coronal tooth structure in posterior teeth measured with an intra-oral scanner on the 4-year clinical survival of root canal retreated teeth. Secondly, to assess retrospectively the effectiveness of the Dental Practicality Index (DPI) in predicting the survival of root canal retreated teeth.

METHODOLOGY

A total of 156 posterior root canal treated teeth (140 patients) had baseline periapical radiographs (PA) and cone-beam computed tomography (CBCT) scans taken prior to root canal retreatment. These teeth were followed up with a clinical examination at 1, 2, 3 and 4 years (T12, T24, T36 and T48) with periapical radiographs and CBCT images taken at T12, and PA taken at T24, T36 and T48 where appropriate. Root canal retreated teeth were dichotomized into 'survived' versus 'extracted'. Fisher's exact test was used to determine the association between the volume of remaining coronal tooth structure and the 4-year tooth survival. The Dental Practicality Index for each tooth was established using the preoperative clinical and radiographical data. Fisher's exact test was used to establish a relationship between categorical variables, the total score of DPI vs tooth outcome.

RESULTS

The percentage of extractions associated with teeth with <29.5% remaining coronal tooth structure was 3 times higher (12.5%) compared to that of teeth with a residual tooth structure > 29.5% (3.5%), but with no significant difference (P = 0.073). There was a significant correlation between the outcome of root canal retreatments at 1 year, assessed by both PA and CBCT, and the 4-year survival (Fisher's exact test, P = 0.007 and P = 0.001, respectively). Teeth with DPI scores ≥ 6 were more likely to be extracted than teeth with DPI score < 6 (18.8% vs. 3.9%) (Fisher's exact test, P = 0.045).

CONCLUSION

Teeth with <30% of remaining tooth structure were associated with a survival rate above 80% and teeth with more than 30% of residual tooth structure survived in more than 94% of the cases. The radiographic outcome of root canal treatment can also help to predict tooth survival with teeth having an unfavourable outcome at 1 year more likely to be extracted within 4 years of completion of treatment. The DPI score can potentially be used to identify teeth with failed root canal treatment, which are likely to be extracted following retreatment and cuspal coverage.

Purification of the cytoplasmic oestrogen receptor from mammary tumours induced in rats with dimethylbenzanthracene

The oestrogen receptor from mammary tumours induced in rats by dimethylbenz(a)-anthracene has been extensively purified by affinity chromatography and isoelectric focusing. The unpurified cytoplasmic 8 S oestrogen receptor had a molecular weight of 240,000, a Stokes radius of 5.4 nm and a frictional ratio of 1.32; the Km (dissociation constant) at 4 degrees C for [3H]oestradiol-17 beta was 0.184 nmol/l. At the end of affinity chromatography the molecular weight was still 240,000 but under the conditions of isoelectric focusing it was reduced to 110,000, with a Stokes radius of 4.0 nm, a frictional ratio of 1.26 and an isoelectric point of 6.4.