Show F i r Better Stop Chewing Chew in I On Ice A hot toddy may be better for you than a cold glass of punch or a dish of ice cream at least as far as your teeth are concerned And breathing through your teeth on a cold coldwin win winter er day or crunching on onIce onice onice ice may be a good invitation invitation invitation tion to visit your dentist Tl THIS S WAS the report of a group of scientists from the University of Utah today following following following fol fol- fol- fol lowing an extensive year two-year study of the thermal stresses on human teeth caused used by the constant temperature changes inside the mouth Since man heats and cools food his teeth are subjected to higher thermal stresses than other animals says Dr Wayne S S. Brown professor of mechanical engineering and principal investigator in the dental research This may be bea a contributing factor to tooth decay THE STUDY of what happens happens happens hap hap- pens to teeth under thermal stress is financed by a annual grant from the National National National Na Na- Institute of Dental Research Research Research Re Re- search to Dr Brown and Dr Harold R. R Jacobs associate professor of mechanical en en- It is one of a series of dental dental dental den den- tal research projects under underway underway underway way in the University's Institute Institute Institute tute for Biomedical Engineering Engineer Engineer- ing which is rapidly gaining national stature in probing unknown unknown unknown un un- un- un known factors in dentistry TWO LOCAL dentists Dr Richard Despain and Dr Elbert Elbert Elbert El- El bert 0 O. Thompson serve as research consultants Working with hundreds of extracted teeth collected from the offices of Salt Lake City oral surgeons and with cattle teeth gathered at stockyards the U researchers have discovered discovered discovered dis dis- dis- dis covered that tooth enamel can suffer thermal fatigue when subjected to the constant hot and cold cycling that goes on inside the mouth THE TIlE RESULT is the appearance appearance appearance appear appear- ance of tiny cracks in the enamel surface which the engineers believe collect food invite decay and increase the possibility of fracture Dr Brown and Dr Jacobs say their research showed enamel is quite strong during thermal compression which occurs when the tooth is heated as in the intake of a hot drink BUT WHEN the tooth surface is subjected to sudden temperature tempera tempera- ture drops like drinking or orf r eating something cold the enamel tends to contract and andis andis is more susceptible to cra crack crack- k- k P ing jag Tooth materials are relatively poor thermal conductors the two engineers continued because because because be be- cause the dentin beneath the enamel surface does not experience experience experience ex ex- the same temperature changes In cooling it retains its original dimensions causing tensile stress on the contracting contracting contracting ting outer enamel Cracking results ONE OF the worst things a person can do to his teeth they added is to chew on ice Not only are the teeth subjected subjected subjected sub sub- to thermal stresses but at the same time they must withstand the physical stresses brought about by crush crush- ng hard ice The U researchers fashioned a special set of false teeth actually thin plastic upper and lower plates with thermocouples thermocouples thermocouples thermo thermo- couples wired them to a recorder and measured the temperature changes inside a persons person's mouth THEY DISCOVERED a fluctuation fluctuation fluctuation from degrees hot toddy coffee and other hot drinks to 35 degrees soft ice cream They also built a special thermal cycling machine in which extracted teeth could be subjected to alternate hot and cold temperatures every 30 seconds This was accomplished accomplished accomplished by running streams of controlled temperature water over the enamel surfaces WE FOUND that repeated exposure to temperature cycling cycling cycling cyc cyc- ling increased the probability of fracture Dr Jacobs said Small cracks appeared after fewer than 2000 cycles and those already present continued to grow Teeth sliced into sections by a tiny thin-blade thin diamond saw clearly showed that the cracks penetrated the enamel but not the underlying dentin THE RESEARCH team worked worked worked work work- ed with computer models of the cracking process to trace the evolution of thermal fa fa- fa- fa tigue The also noted that stresses in excess of 2000 pounds per square inch could be expected when drinking or eating cold foods The tensile strength of enamel is only to pounds per square inch Teeth are arc also subjected to thermal stresses during dental dental dental den den- tal drilling the U researchers reported and unless this heat can be dissipated in some cooling medium teeth can be weakened around the filling ONE OF the dentists engaged engaged engaged en en- in the research Dr Elbert 0 O. Thompson reported at a meeting of the American Association of Dental Res- Res searchers Tuesday November 10 in Las Vegas that cold coldwater coldwater coldwater water and cold water air-water sprays can cause severe temperature temperature temperature tem tem- cycling during the drilling process thus weakening weakening weakening weaken weaken- ing the surrounding enamel He said tests conducted by him have shown a warm water water water wa wa- wa- wa ter controlled at body temperature is a good way to eliminate thermal stress during drilling Whenever you find the word therefore in the Bible it is isa isa a good go d thing to ask Wherefore Wherefore Wherefore Where fore the thc therefore One of old wrote in Psalm and 3 Therefore will not ue we fear though the earth be removed and though the mountains be carried into the midst of the sea though the waters thereof roar and be troubled Since there is a therefore let us ask the wherefore The wherefore therefore is found in inthe inthe inthe the first verse of this Psalm God is our refuge and strength a aery very ery present help in trouble ACCORDING TO the U research research research re re- re- re search team teeth with amalgam amalgam amalgam amal amal- gam fillings are more susceptible susceptible susceptible tible to thermal stress than unfilled teeth These teeth 0 a a also weakened because dentists dentists dentists den den- must undercut the holes they drill to keep the amalgam amalgam amalgam amal amal- gam in place One of the aims of our research says Dr Brown will be to look for a better way to shape the holes dentists dentists dentists den den- drill to fill cavities WERE WE'RE ALSO looking for better restorative materials that can withstand thermal expansion and contraction Most of the previous dental research has stressed the search for better filling mae ma- ma e nsF 5 elf f f engineering analysis of the teeth themselves them them- selves t tIN IN THE past there has been less concern for finding causes than in refining the the cures Dr Jacobs added But we think there is a natural natural al wedding between dentistry and engineering Repair and restoration of teeth is after all actually a miniaturized engineering project |