News of the Week herbicides being developed by FMC chemists (C&EN, April 23, 1984, page 26). Donald Bissing, director of R&D for FMCs agricultural chemicals group, says the mechanisms aren't understood yet but Command works by inhibiting the synthesis of chlorophyll and carotenoids. Weed seedlings exposed to Command emerge bleached, rather than green, and most die. Soybeans are immune to the effect; most other crop plants are susceptible. However, it's that broad spectrum of activity that makes the compound useful as an herbicide. It works in very small amounts. "We don't find residues even in plants that are bleached completely white," Bissing says. In addition, toxicological studies indicate that Command is nonteratogenic, noncarcinogenic, and relatively nontoxic. C o m m a n d is a powerful preemergent herbicide, Bissing says, but it isn't a good postemergent herbi-
cide. Although it travels up from roots to leaves, it tends not to travel through the plant the other way. Thus drift effects tend to be localized. And although those effects New ways to remove decayed pormay be highly noticeable, they're tions of teeth and new materials probably no worse than with other with which to fill the resulting cavherbicides. "The impact is spectac- ities are among the advances in denular but short-lived," Bissing ex- tal technology described at the replains. Most plants will recover from cent International Association for the exposure within days or weeks. Dental Research sessions in The Frank Sanders, the Environmen- Hague, the Netherlands. tal Protection Agency's head of herDanish researchers at the Royal bicide registration, says no changes Dental College, Aarhus, use a highin Command's registration status are pressure stream of air, water, and contemplated. Just the same, his of- fine particles of sodium bicarbonfice is encouraging FMC to take ate to abrade damaged tooth matesteps to minimize the off-target rial from healthy dentin and enammovement. Bissing says FMC is stud- el. The method is selective for damying a number of approaches, in- aged tissue. It causes only minor cluding changing the formulation changes in the surface structure of to minimize vaporization. There healthy tooth enamel but much likely also will be labeling changes, more severe abrasion of caries leincluding a recommendation that sions. the herbicide be incorporated into Sound dentin is somewhat abradthe soil at the time of application. D ed by their procedure, but carious dentin is abraded at a much faster rate so that, with care, it's possible to remove only the diseased tissue, the researchers say. The technique, drug-delivery system, drug-impreg- they say, removes decayed tooth manated microspheres of the homo- terial almost painlessly, even in papolyanhydrides degrade from the tients whose teeth were extremely surface inward, releasing drugs at sensitive to air-blasting and probing before treatment. constant rates over long periods. Meanwhile, Rafael L. Bowen and Under the formal terms of the agreement, Nova will bring the coworkers at the American Dental brain-drug-delivery system to the Association Health Foundation have joint venture. The two companies come up with a new technique for have not yet worked out whether filling cavities on tooth surfaces that other Nova drug-delivery system receive a lot of wear but where the work also will go over to NovaCel, appearance of the filling material is says Lloyd H. Schloen, vice presi- important. They combine a convendent of corporate development at tional polymer composite dental maNova. Celanese will contribute its terial with glass inserts that improve polymer technology expertise, and the polymer's wear resistance. Nova will manage technical develCavities in teeth are partially filled opment of products. Other terms of with the unhardened polymer comthe agreement have not been dis- posite paste, then inserts of a speclosed. NovaCel expects to begin cial aluminoborosilicate glass are human clinical tests of the system pressed into the soft composite reslater this year. in so that the insert material makes The formation of NovaCel follows up as much as possible of the finseveral business arrangements made ished restoration and its surface, by Celanese in the advanced tech- Bowen explains. Excess material is nology area in recent months, in- removed and the filling material is cluding an agreement with Kuraray cured with a dental curing light. of Japan to study commercialization "The advantage of the inserts in of a new high-strength fiber, and an composite restorations is that glass increased stake in Endotronics, Coon materials have wear and other propRapids, Minn., which is developing erties that more closely match those automated tissue-culture processes. D of natural teeth," Bowen explains. D
Celanese and Nova form joint venture In its first foray into the human health arena, Celanese last week formed a 50-50 joint venture with Nova Pharmaceutical to develop controlled-release drug-delivery systems. The agreement deepens Celanese's relationship with Baltimorebased Nova, of which Celanese purchased a 4% equity stake for $10 million in March. The initial product of the new firm, called NovaCel, will be a polymer drug-delivery system for treatment of brain cancer. The system is based on a biodegradable polymer developed by scientists at Massachusetts Institute of Technology. Last week, Nova obtained exclusive worldwide rights to all pharmaceutical applications of the system, which could include treatment of other cancers and various diseases. Under a previous agreement, Nova had rights to brain therapy uses only. The polymers covered under the new agreement are biodegradable polyanhydrides of such acids as 4,4'isopropylidenedioxybenzoic acid and its copolyanhydrides with acids like sebacic acid. According to Robert Langer, who led the MIT research group that developed the 8
July 7, 1986 C&EN
New treatments for tooth cavities developed
