Synthesis, characterization, shrinkage and curing kinetics of a new low-shrinkage urethane dimethacrylate monomer for dental applications.

OBJECTIVES: The aim of the study was to synthesize and characterize an isophorone-based urethane dimethacrylate (IP-UDMA) resin-monomer and to investigate its shrinkage and curing kinetics. METHODS: The IP-UDMA monomer was synthesized through the reaction of polyethylene glycol 400 and isophorone diisocyanate followed by reacting with HEMA to terminate it with methacrylate end groups. The reaction was followed using a standard back titration method and FTIR spectroscopy. The final product was purified and characterized using FTIR, (1)H NMR, elemental analysis and refractive index measurement. The shrinkage-strain of the specimens photopolymerized at circa 700mW/cm(2) was measured using the bonded-disk technique at 23, 35, and 45 degrees C. Initial shrinkage-strain-rates were obtained by numerical differentiation of shrinkage-strain data with respect to time. Degree-of-conversion of the specimens was measured using FTIR spectroscopy. The thermal curing kinetics of the monomer were also studied by differential scanning calorimetry (DSC). RESULTS: The characterization methods confirmed the suggested reaction route and the synthesized monomer. A low shrinkage-strain of about 4% was obtained for the new monomer. The results showed that the shrinkage-strain-rate of the monomer followed the autocatalytic model of Kamal and Sourour [Kamal MR, Sourour S. Kinetic and thermal characterization of thermoset cure. Polym Eng Sci 1973;13(1):59-64], which is used to describe the reaction kinetics of thermoset resins. The model parameters were calculated by linearization of the equation. SIGNIFICANCE: The model prediction was in a good agreement with the experimental data. The properties of the new monomer compare favorably with properties of the commercially available resins.     

The effect of aspirin on gingival crevicular fluid levels of inflammatory and anti-inflammatory mediators in patients with gingivitis

BACKGROUND: Inflammatory and anti-inflammatory mediators may play a significant role in patients with gingivitis. The purpose of this study was to assess the short-term effects of the systemic administration of two different concentrations of aspirin (81 and 325 mg/day, by mouth) on clinical periodontal parameters and gingival crevicular fluid (GCF) levels of 15-epi-lipoxin A4 (15-epi-LXA4), lipoxin A4, leukotriene B4 (LTB4), prostaglandin E2 (PGE2), and interleukin (IL)-6 and -1beta in a sample of naturally occurring gingivitis patients. METHODS: At day 0, after initial screening for entry, baseline periodontal parameters, including bleeding on probing (BOP), periodontal probing depths (PDs), and plaque index (PI) were measured, and GCF was sampled from 12 intrasulcular sites with filter paper strips for the measurement of six types of inflammatory and anti-inflammatory mediators using competitive enzyme immunoassay and enzyme-linked immunosorbent assay (prevalues). Forty-seven subjects were assigned randomly to one of three treatment groups: placebo (15 subjects); aspirin, 81 mg (16 subjects); and aspirin, 325 mg (16 subjects) once daily. On day 7, subjects were recalled for the measurement of periodontal parameters and collection of GCF samples for the measurement of six types of mediators (postvalues). RESULTS: Changes in inflammatory and anti-inflammatory mediator levels were not statistically significant for any of the three treatment groups. However, when pre- and postvalues were compared in the subjects receiving aspirin, 325 mg, there was a negative trend in the relationship between 15-epi-LXA4 and PGE2, whereas the relationship between LTB4 and PGE2 was not as strong. This might indicate that the subjects responding to aspirin-mediated PGE2 suppression effects produced higher 15-epi-LXA4 in GCF than non-responders. No statistically significant differences in PD and PI between pre- and postvalues were found for any of the three treatment groups. However, the results demonstrated a significant increase in BOP when aspirin, 325 mg was compared to placebo (P <0.001) and aspirin, 81 mg (P = 0.001). CONCLUSIONS: Aspirin can have an affect on BOP in naturally occurring gingivitis patients. Although most of the inflammatory mediators did not show significantly detectable changes after aspirin treatment for 7 days, the trend of aspirin-associated increases of 15-epi-LXA4 implied that this recently discovered aspirin-dependent eicosanoid may be associated with the increased incidence of BOP observed in the subjects who received aspirin therapy.     

Clinical measurement of palatal tooth wear following coating by a resin sealing system

This study investigated the hypothesis that coating eroded teeth with a resin-based dentin bonding agent gave protection from tooth wear. Nineteen adults with palatal tooth wear exposing dentin were recruited, following referral by their general dental practitioner. Alternate teeth were coated with the resin adhesive, while the uncoated teeth acted as controls. Accurate impressions of the eroded teeth, onto which were cemented machined stainless steel discs to act as reference areas, were scanned with a non-contacting laser profilometer at 3, 6, 12 and 24 months. The mean thickness of resin at baseline application was 0.15 mm and, from 0 to 6 months, the rate of wear of the control teeth was higher than those covered with Seal & Protect. There was a statistically significant difference in "wear" measured between resin covered and control teeth at three months. The Inter Class Correlations (repeated measurements) for the step heights obtained for the original and repeat impressions was excellent at 0.99. This study shows that coating eroded teeth with a resin-based adhesive has the potential to prevent further tooth wear.     

Children's drawings about dentistry

Abstract Drawings about the dentist at work were solicited from 1,101 children in grades 2, 4, 6 and 8 in an urban school district. A system to classify the contents of these drawings was developed. The frequency of various items occurring in the children's drawings was determined. The “typical” or most frequent child's drawing of the dentist at work was described. This drawing contained a normal dental chair, dentist, a patient in the chair and dental cabinetry or furniture. The picture was a very matter-of-fact representation. Abnormal or bizarre pictures occurred infrequently. A few children drew pictures that did not relate to dentistry.     

Susceptibilties of two Enterococcus faecalis phenotypes to root canal medications

This study aimed to investigate and compare the efficacy of selected root canal irrigants and a medicament on a clinical isolate of Enterococcus faecalis grown as biofilm or planktonic suspension phenotype. A cell-dense pellet "presentation" prepared from planktonic phenotype was also tested. Each bacterial presentation was exposed to calcium hydroxide (pH 12.3), 0.2% chlorhexidine gluconate, 17% ethylene-diamine-tetra-acetic acid, 10% povidone iodine, or 3.0% sodium hypochlorite (NaOCl) for a range of time periods (1, 2, 4, 8, 15, 30, and 60 min). Phosphate buffered saline was used as a control agent. The difference in gradients of bacterial killing among the biofilm, planktonic suspension or pellet presentation was significant (p < 0.05) and dependent upon the test agent except in the case of NaOCl and calcium hydroxide where no difference could be detected. NaOCl was the most effective agent and achieved 100% kills for all presentations of E. faecalis after a 2 min contact time.     

EDTA or H3PO4/NaOCl dentine treatments may increase hybrid layers’ resistance to degradation: A microtensile bond strength and confocal-micropermeability study

Objectives

The aim of this study was to reduce hybrid layer degradation created with simplified dentine adhesives by using two different methods to condition the dentine surface.

Methods

A smear-layer was created on flat dentine surfaces from extracted human third molars with a 180-grit/SiC-paper. Dentine specimens were conditioned before bonding with the following procedures: 37% H₃PO₄; H₃PO₄/0.5% NaOCl; 0.1 M EDTA; 0.1 M EDTA/0.5% NaOCl. Two etch-and-rinse adhesives: (Scotchbond 1XT or Optibond Solo Plus) were applied and light-cured. Composite build-ups were constructed. The bonded teeth were sectioned into beams, stored in distilled water (24 h) or 12% NaOCl solution (90 min) and finally tested for microtensile bond strengths (μTBS). Additional dentine surfaces were conditioned and bonded as previously described. They were prepared for a pulpal-micropermeability confocal microscopy study and finally observed using confocal microscopy.

Results

μTBS results revealed that both adhesives gave high bond strengths to acid-etched dentine before, but not after a 12% NaOCl challenge. Bonds made to acid-etched or EDTA-treated dentine plus dilute NaOCl, gave high μTBS that resisted 12% NaOCl treatment, as did EDTA-treated dentine alone. A confocal micropermeability investigation showed very high micropermeability within interfaces of the H₃PO₄, etched specimens. The lowest micropermeability was observed in H₃PO₄ + 0.5% NaOCl and 0.1 M EDTA groups.

Conclusions

The use of dilute NaOCl (0.5%) after acid-etching, or the conditioning of dentine smear layers with 0.1 M EDTA (pH 7.4) produced less porous resin–dentine interfaces. These dentine-conditioning procedures improve the resistance of the resin–dentine bond sites to chemical degradation (12% NaOCl) and may result in more durable resin–dentine bonds.     

The origins of fear of occupational exposure in the clinical dental setting

Although there is a growing literature on the incidence of occurrence and reporting of occupational exposures in clinics in dental schools, the contributing factors to fear of such injuries and their dynamic evolution over time remain unstudied. It is hypothesized that fear of occupational exposures is a function of estimated likelihood of such events and their perceived importance. Individual personality factors and situational circumstances are also thought to play a role, although it is believed that these factors recede in importance as students gain direct knowledge through clinical experience. Path analysis methods are applied to longitudinal survey data in a single dental school to confirm these hypotheses.     

How to increase the durability of resin-dentin bonds

Resin-dentin bonds are not as durable as was previously thought. Microtensile bond strengths often fall 30% to 40% in 6 to 12 months. The cause of this poor durability is a combination of the activation of matrix metalloproteinases (MMPs) by weak acids such as lactic acid released by caries-producing bacteria, and acid-etchants used in adhesive bonding systems. These acids uncover and activate matrix-bound MMPs. The other contributing factor is incomplete resin infiltration. If all exposed collagen fibrils were enveloped by resin, the MMPs would not have free access to water, an obligatory requirement of these enzymes. Recently, several inhibitors of MMPs have been added to adhesive primers. Examples include chlorhexidine (CHX), benzalkonium chloride (BAC), and MDPB, an antibacterial monomer used in a two-step self-etching primer adhesive. The advantage of MDPB over CHX and BAC is that it polymerizes with adhesive resins and cannot leach from the hybrid layer. This is an example of what can be termed a "therapeutic adhesive system" that provides anti-MMP activity along with antibacterial qualities.     

Advancement of women in dental education: expanding opportunities, enriching the pool

In the recent past, we have seen both the dental student applicant and enrollment pools of women in the United States increase. There has been an increase in both women applicants and first-year enrollees from the year 2000. The advancement of women in advanced educational programs and into dental faculty positions has likewise seen a trend of increase. The challenge to dental education is to ensure that the recruitment and advancement of women to careers in dental education and research in the future are consistent with their talent, expertise, and career expectations. Within this pool of women are our future leaders, deans, and researchers. As we consider future faculty needs for all dental faculty members, we must consider the unique needs of women who must balance their careers with other societal demands related to their gender.