Robert E. Chapin, Jane Adams, Kim Boekelheide, L. Earl Gray Jr, Simon W. Hayward, Peter S.J. Lees, Barry S. McIntyre, Kenneth M. Portier, Teresa M. Schnorr, Sherry G. Selevan, John G. Vandenbergh, and Susan R. Woskie Pfizer, Inc., Groton, CT University of Massachusetts, Boston, MA Brown University, Providence, RI U.S. Environmental Protection Agency, Research Triangle Park, NC Vanderbilt University Medical Center, Nashville, TN Johns Hopkins University, Baltimore, MD Schering Plough Research Institute, Summit, NJ American Cancer Society, Atlanta, GA National Institute for Occupational Safety and Health, Cincinnati, OH U.S. Public Health Service (Ret), Silver Spring, MD North Carolina State University, Raleigh, NC University of Massachusetts, Lowell, MA

https://onlinelibrary.wiley.com/doi/pdf/10.1002/bdrb.20147

NTP‐CERHR expert panel report on the reproductive and developmental toxicity of bisphenol A

Sodium hypochlorite in endodontics: an update review.

The specific biomechanical alterations related to vitality loss or endodontic procedures are confusing issues for the practitioner and have been controversially approached from a clinical standpoint. The aim of part 1 of this literature review is to present an overview of the current knowledge about composition changes, structural alterations, and status following endodontic therapy and restorative procedures. The basic search process included a systematic review of the PubMed/Medline database between 1990 and 2005, using single or combined key words to obtain the most comprehensive list of references; a perusal of the references of the relevant sources completed the review. Only negligible alterations in tissue moisture and composition attributable to vitality loss or endodontic therapy were reported. Loss of vitality followed by proper endodontic therapy proved to affect tooth biomechanical behavior only to a limited extent. Conversely, tooth strength is reduced in proportion to coronal tissue loss, due to either caries lesion or restorative procedures. Therefore, the best current approach for restoring endodontically treated teeth seems to (1) minimize tissue sacrifice, especially in the cervical area so that a ferrule effect can be created, (2) use adhesive procedures at both radicular and coronal levels to strengthen remaining tooth structure and optimize restoration stability and retention, and (3) use post and core materials with physical properties close to those of natural dentin, because of the limitations of current adhesive procedures.

/pdf/biomechanical-considerations-for-the-restoration-of-20ki607nts.pdf

Biomechanical considerations for the restoration of endodontically treated teeth: a systematic review of the literature--Part 1. Composition and micro- and macrostructure alterations.

Exposure measurements from several countries indicate that humans are routinely exposed to low levels of bisphenol A (BPA), a synthetic xenoestrogen widely used in the production of polycarbonate plastics. There is considerable debate about whether this exposure represents an environmental risk, based on reports that BPA interferes with the development of many organs and that it may alter cognitive functions and mood. Consistent with these reports, we have previously demonstrated that BPA antagonizes spine synapse formation induced by estrogens and testosterone in limbic brain areas of gonadectomized female and male rats. An important limitation of these studies, however, is that they were based on rodent animal models, which may not be representative of the effects of human BPA exposure. To address this issue, we examined the influence of continuous BPA administration, at a daily dose equal to the current U.S. Environmental Protection Agency's reference safe daily limit, on estradiol-induced spine synapse formation in the hippocampus and prefrontal cortex of a nonhuman primate model. Our data indicate that even at this relatively low exposure level, BPA completely abolishes the synaptogenic response to estradiol. Because remodeling of spine synapses may play a critical role in cognition and mood, the ability of BPA to interfere with spine synapse formation has profound implications. This study is the first to demonstrate an adverse effect of BPA on the brain in a nonhuman primate model and further amplifies concerns about the widespread use of BPA in medical equipment, and in food preparation and storage.

/pdf/bisphenol-a-prevents-the-synaptogenic-response-to-estradiol-4yt48ubfi9.pdf

Bisphenol A prevents the synaptogenic response to estradiol in hippocampus and prefrontal cortex of ovariectomized nonhuman primates.

Bisphenol A (BPA) is an estrogenic chemical that is widely used in the manufacture of plastics and epoxy resins. Because BPA leaches out of plastic food and drink containers, as well as the BPA-containing plastics used in dental prostheses and sealants, considerable potential exists for human exposure to this compound. In this article we show that treatment of ovariectomized rats with BPA dose-dependently inhibits the estrogen-induced formation of dendritic spine synapses on pyramidal neurons in the CA1 area of the hippocampus. Significant inhibitory effects of BPA were observed at a dose of only 40 μg/kg, below the current U.S. Environmental Protection Agency reference daily limit for human exposure. Because synaptic remodeling has been postulated to contribute to the rapid effects of estrogen on hippocampus-dependent memory, these data suggest that environmental BPA exposure may interfere with the development and expression of normal sex differences in cognitive function, via inhibition of estrogen-dependent hippocampal synapse formation. It may also exacerbate the impairment of hippocampal function observed during normal aging, as endogenous estrogen production declines.

The environmental estrogen bisphenol a inhibits estradiol-induced hippocampal synaptogenesis.

Bisphenol A (BPA) is an endocrine disruptor, and is used as a raw material for bisphenol A diglycidyl methacrylate and polycarbonate, that are used in the dental materials. In this study, the total and released amounts of BPA from polycarbonate-based dental materials were measured with high-pressure liquid chromatography (HPLC). The specimens used were orthodontic brackets and denture base resins in the same condition as when obtained commercially were cut into 3 x 3 x 4 mm pieces and crushed into powder. The HPLC analysis was carried out after immersion of the specimens in water or ethanol for a determined time. The total amount of BPA in the specimens was analyzed after dissolution in chloroform. The amount of BPA released after immersion in water for 1 hr was 0.01-0.4 microgram/g for the block samples and 0.14-4.22 micrograms/g for the crushed samples, while that in ethanol for 1 hr was 0.12-9.42 micrograms/g for the block samples and 0.42-22.24 micrograms/g for the crushed samples. The control of BPA in the denture preform resin was 78.9 micrograms/g and this increased to 90.2 micrograms/g after heating to form dentures and then to 250 micrograms/g with mechanical crushing. The results of this study indicate that BPA is released from polycarbonates used in dentistry, and that the thermal conditions during the manufacturing of restorations may cause polymer decomposition resulting in the formation of BPA.

/pdf/content-and-release-of-bisphenol-a-from-polycarbonate-dental-50l9x9nvaw.pdf

Content and release of bisphenol A from polycarbonate dental products.

The purposes of this study were to investigate the reliability and efficiency of a new evaluation method for resin bonding to root canal dentin, which measures both marginal adaptation and shear bond strength simultaneously, and to determine the effects of root canal irrigants on resin bonding. A wet bonding system (Single Bond) and a self-etching primer system (Clearfil Mega Bond) were employed; NaClO was used as a root canal irrigant. No gaps or changes in bond strength were observed despite the NaClO treatment when the wet bonding system was employed, while the gap formation ratio increased, and bond strength decreased with longer NaClO treatment time when the self-etching primer system was employed. These findings suggested that this new experimental method was effective for evaluating resin systems to the root canal wall dentin which is affected by irrigation with NaClO.

Effect of NaClO treatment on bonding to root canal dentin using a new evaluation method.

The purpose of this study was to investigate the effects of the location and orientation of dentinal tubules in the tooth on tensile strengths of the dentin. Dumbbell-shaped specimens of 12 groups from various locations and dentinal tubule orientations were prepared. The tensile test was performed in distilled water at a temperature of 37°C. The tensile strengths of the parallel to the orientation were significantly greater than those of the perpendicular to the orientation; the tensile strengths of the radicular dentin were significantly greater than those of the coronal dentin. Nevertheless, in the radicular dentin, the tensile strengths of the perpendicular to dentinal tubules differ with respect to tensile forces. These results suggest that tensile strength of the dentin varies according to the location and orientation of dentinal tubules in the tooth.

Anisotropy of tensile strengths of bovine dentin regarding dentinal tubule orientation and location.

Bovine teeth are used for dental research as a substitute for human teeth. In the present study the effects of storage on the tensile strength of bovine dentin were investigated. Storage conditions selected were frozen storage for 1 week, 4 weeks, and 1 year. Boiling in water for 45 minutes was also employed to clarify the effect of heat. Dumbbell-shaped specimens were prepared from teeth of each condition and tensile tests were performed immediately. The same tests were also performed on specimens, as a control, prepared from bovine teeth within 8 hours of extraction. The tensile strength of the control was 76.1 MPa; 1 week frozen storage, 78.7 MPa; 4 weeks, 79.9 MPa; 1 year, 79.0 MPa. The tensile strength of bovine dentin remained unchanged during one year frozen storage. On the other hand, the tensile strength of bovine dentin after boiling was 70.3 MPa, showing that tensile strength had decreased.

Effect of frozen storage and boiling on tensile strength of bovine dentin.

The biaxial flexural strength and cyclic fatigue biaxial flexural strength of CAD/CAM ceramics polished with #220, 400, 600 and 1000 diamond pads were measured in an effort to determine the effect of surface roughness on fatigue behavior of dental ceramics. The surface roughness was improved after polishing with a smaller diamond grain pad. The flexural strengths of the specimens polished with #220, 400, 600 and 1000 diamond pad were 75.2, 76.6, 82.2, and 83.3 MPa, respectively; the fatigue flexural strength of those with #220, 400, 600 and 1000 were 53.0, 58.1, 60.0, and 61.5MPa, respectively. Both the flexural and fatigue flexural strengths increased with improvement of surface profile. These results suggest the importance of polishing of dental ceramics for not only the static strength but also the cyclic fatigue strength.

Fumio Nishimura

Papers

Content and release of bisphenol A from polycarbonate dental products.

Effect of NaClO treatment on bonding to root canal dentin using a new evaluation method.

Anisotropy of tensile strengths of bovine dentin regarding dentinal tubule orientation and location.

Effect of frozen storage and boiling on tensile strength of bovine dentin.

Effect of Polishing on Cyclic Fatigue Strength of CAD/CAM Ceramics