High-speed atomic force microscopy of dental enamel dissolution in citric acid

High-speed atomic force microscopy (HS AFM) in 'contact' mode was used to image at video rate the surfaces of both calcium hydroxyapatite samples, often used as artificial dental enamel in such experiments, and polished actual bovine dental enamel in both neutral and acidic aqueous environments. The image in each frame of the video of the sample was a few micrometers square, and the high-speed scan window was panned across the sample in real time to examine larger areas. Conventional AFM images of the same regions of the sample were also recorded before and after high-speed imaging. The ability of HS AFM to follow processes occurring in liquid on the timescale of a few seconds was employed to study the dissolution process of both hydroxyapatite and bovine enamel under acidic conditions. Buffered citric acid at pH values between 3.0 and 4.0 was observed to dissolve the surface layers of these samples. The movies recorded showed rapid dissolution of the bovine enamel in particular, which proceeded until the relatively small amount of acid available had been exhausted. A comparison was made with enamel samples that had been treated in fluoride solution (1 h in 300 ppm NaF, pH 7) prior to addition of the acid; the speed of dissolution for these samples was much less than that of the untreated samples. The HS AFM used an in-house designed and constructed high-speed flexure scan stage employing a push-pull piezo actuator arrangement. The HS AFM is able to follow the large changes in height (on the micrometer scale) that occur during the dissolution process.     

Inhibition of angiogenesis and suppression of colorectal cancer metastatic to the liver using the <Emphasis Type="Italic">Sleeping Beauty</Emphasis> Transposon System

Background  

Metastatic colon cancer is one of the leading causes of cancer-related death worldwide, with disease progression and metastatic spread being closely associated with angiogenesis. We investigated whether an antiangiogenic gene transfer approach using the Sleeping Beauty (SB) transposon system could be used to inhibit growth of colorectal tumors metastatic to the liver.     

Risk factors for meningioma in postmenopausal women: results from the Iowa Women's Health Study

Few risk factors for meningioma, aside from increasing age and female sex, have been identified. We investigated risk factors for meningioma in elderly women, a group with a high incidence. We evaluated associations of demographic, lifestyle, medical history, and anthropometric variables with risk of meningioma in the Iowa Women's Health Study (IWHS), a population-based, prospective cohort study. Risk factors were collected via questionnaires mailed in 1986 and 1992. Incident meningiomas were identified via linkages to Medicare. Cox regression models were used to examine the association of risk factors with meningioma incidence. The mean age at baseline of the 27,791 women in the analysis cohort was 69.3 years (range, 65.0-84.6 years). During 291,021 person-years of follow-up, 125 incident meningiomas were identified. After adjusting for age, lower levels of physical activity (relative risk [RR] , 0.68 for high versus low; P for trend = .039), greater body mass index (BMI; RR, 2.14 for ≥35 versus 19.5-24.9 kg/m(2); P for trend = .0019), greater height (RR, 2.04 for >66 versus ≤62 inches; P for trend = .013), and a history of uterine fibroids (RR, 1.72; 95% confidence interval, 1.19, 2.50) were positively associated with meningioma risk in multivariate analysis. BMI at age 18 and 30 years were not associated with risk. There were no associations with menstrual or reproductive factors or other medical history and lifestyle factors. Physical activity, BMI, height, and history of uterine fibroids were associated with meningioma risk in older women. The positive association with height suggests a role for early life influences on risk, whereas the associations with BMI and physical activity suggest a role for modifiable factors later in life.     

PARP inhibitors: its role in treatment of cancer

PARP is an important protein in DNA repair pathways especially the base excision repair (BER). BER is involved in DNA repair of single strand breaks (SSBs). If BER is impaired, inhibiting poly(ADP-ribose) polymerase (PARP), SSBs accumulate and become double stand breaks (DSBs). The cells with increasing number of DSBs become more dependent on other repair pathways, mainly the homologous recombination (HR) and the nonhomologous end joining. Patients with defective HR, like BRCA-deficient cell lines, are even...     

Influence of the degree of dentine mineralization on pulp chamber temperature increase during resin-based composite (RBC) light-activation

Objectives

To analyse the influence of the degree of dentine mineralization on the pulp chamber temperature increase during composite light-activation.

Methods

Dentine discs (2 mm thick) obtained from recently extracted teeth or those with extensive dentine sclerosis were analysed by FT-IR spectrometry in order to choose the two discs with the greatest difference in the degree of mineralization. A model tooth was set up with the dentine discs between a molar with the pulp chamber exposed and a crown with a standardized class II cavity. A K-type thermocouple was introduced into the molar root until it came into contact with the dentine discs and the cavity was filled with P60 resin composite. The temperature rise was measured for 120 s after light-activation began: Standard (S) 600 mW/cm²/40 s; Ramp (R) 0 → 800 mW/cm²/10 s + 800 mW/cm²/10 s; Boost (B) 850 mW/cm²/10 s and LED (L) 1.300 mW/cm²/40 s (n = 10). The same protocol was repeated after grinding the dentine discs to 1.0 and 0.5 mm thickness.

Results

The temperature increase was significantly higher in dentine with high degree of mineralization (p < 0.05). With respect to the dentine thickness, the following result was found: 2 mm < 1 mm < 0.5 mm (p < 0.05). The light-activation mode also presented significant difference as follows: S > R = L > B (p < 0.05).

Conclusions

The higher the degree of dentine mineralization the greater the increase in pulp chamber temperature. The temperature increase was influenced by the light-polymerization mode and dentine thickness.