Comparative evaluation of the fracture resistance of newly developed prefabricated fibreglass crowns and zirconium crowns.

BACKGROUND: Prefabricated fibreglass crowns (PFCs) require less tooth structure reduction than prefabricated zirconium crowns (PZCs) for restoring primary molars. Little is known, however, about their mechanical properties. AIM: To investigate the fatigue survival and fracture resistance of PZCs and PFCs cemented with two different types of luting cement [glass-ionomer cement (GIC) and resin-modified GIC (RMGIC)]. DESIGN: One hundred and twenty extracted human primary molars were randomly divided into subgroups (n = 15) according to the crown type (PFCs/PZCs), the luting cement (GIC/RMGIC) and crowns subjected to the chewing simulation test with thermocycling mechanical loading (CSTTML). The surfaces of the teeth were reduced by approximately 2 mm in the PZC group and 1 mm in the PFC group. All the samples were subjected to fracture tests. RESULTS: None of the samples subjected to CSTTML exhibited signs of surface damage, fracture or premature debonding. The forces required to fracture PFCs were higher than those required for PZCs in all groups (p = .001). The highest mean fracture resistance values were obtained from the group of PFCs cemented with GIC that were subjected to the CSTTML (2515.8 N ± 619.2 N). CONCLUSIONS: PFCs presented high fatigue survival and could be used as alternatives to PZCs as they require less tooth structure reduction. Crowns cemented with GIC had a similar fracture resistance value when compared with RMGIC.

Effects of Wi-Fi (2.45 GHz) and Lactic Acid Bacteria on Oral Pathogens and Caries Development in Rats.

PURPOSE: To evaluate the effects of Wi-Fi and lactic acid bacteria on salivary mutans streptococci and caries formation. MATERIALS AND METHODS: Wistar rats and their offspring were equally divided into two main groups and seven subgroups. Experimental groups were exposed to Wi-Fi during pregnancy and lactation. Subgroups were divided according the administration of the beneficial bacteria L. plantarum 167.P6.5 and L. rhamnosus M17-10.2. In the 8-week experimental period after weaning at 21 days, Mutans streptococci counts and the number of carious lesions were determined. RESULTS: The MS count ratios at the end of 8 weeks were statistically significantly lower than those at the end of 4 weeks in all groups given L. rhamnosus (p < 0.05). A strong correlation was found between the total MS count and sulcal caries scores (r = 0.507). No statistically significant difference was observed between groups exposed to Wi-Fi and other groups in terms of microorganism count and caries scores (p < 0.05). CONCLUSIONS: These results suggest that lactic acid bacteria, especially those originating from an oral source, may be of benefit as probiotics for the prevention of oral pathogens and dental caries. Perinatal and lactational exposure to Wi-Fi does not predispose to caries development in rats.

Fracture Resistance of Prefabricated Primary Zirconium Crowns Cemented with Different Luting Cements.

Purpose: The purpose of this study was to determine the retention of prefabricated primary zirconium crowns (PPZCs) and the fracture resistance of samples cemented with four different luting cements subjected to a chewing simulation test with thermocycling mechanical loading (CSTTML). Methods: A total of 120 extracted primary molar teeth were selected and allocated into four groups, according to luting cement materials (bioactive cement, resin cement, glass ionomer cements [GICs], resin-modified GICs). After half of each group was subjected to CSTTML, all the samples were subjected to fracture tests and the mean force required to fracture the PPZCs was recorded. Results: After the CSTTML test, corresponding to a simulated one-year aging, none of the sample materials were found to be cracked, fractured, chipped, or non-retained. Resin cements in all groups showed the highest fracture resistance, whereas bioactive cement, subjected to CSTTML and resin-modified GIC in all tests, showed the lowest values. However, no statistically significant differences were found. Conclusions: The prefabricated primary zirconium crowns were found to be successful after almost one year of simulated aging. The results of all of groups showed that the PPZCs cemented with resin and glass ionomer cements were more successful. However, further in vitro and in vivo studies are needed to determine their potential for clinical success.

Effects of prenatal and postnatal exposure of Wi-Fi on development of teeth and changes in teeth element concentration in rats. [corrected].

The present study determined the effects of prenatal and postnatal exposure to Wi-Fi (2.45 GHz)-induced electromagnetic radiation (EMR) on tooth and surrounding tissue development as well as the element levels in growing rats. Twenty-four rats and their offspring were equally divided into two separate groups identified as experiment and control. The experiment group was exposed to 2.45 GHz EMR for 2 h/day during the periods of pregnancy (21 days) and lactation (21 days). The offspring of these dams were also exposed to EMR up to decapitation. The control group was exposed to cage stress for 2 h per day using the same protocol established for the experimental group. On the 7th, 14th, and 21st days after birth, 8 male offspring rats from each of the two groups were decapitated, and the jaws were taken for histological and immunohistochemical examination. Caspase-3 (1/50 dilution) was used in the immunohistochemical examination for apoptotic activity. On the last day of the experiment, the rats' incisors were also collected. In samples that were histologically and immunohistochemically examined, there was an increase in apoptosis and caspase-3 in both the control and the Wi-Fi groups during the development of the teeth. However, no significant difference was observed between the two groups in terms of development and apoptotic activity. Results from the elemental analysis showed that iron and strontium concentrations were increased in the Wi-Fi group, whereas boron, copper, and zinc concentrations were decreased. There were no statistically significant differences in calcium, cadmium, potassium, magnesium, sodium, or phosphorus values between the groups. Histological and immunohistochemical examinations between the experimental and control groups showed that exposure to 2.45 GHz EMR for 2 h per day does not interfere with the development of teeth and surrounding tissues. However, there were alterations in the elemental composition of the teeth, especially affecting such oxidative stress-related elements as copper, zinc, and iron, suggesting that short-term exposure to Wi-Fi-induced EMR may cause an imbalance in the oxidative stress condition in the teeth of growing rats.