Why are teenagers getting taller?
 Dentistry
A 成人大片 PhD student has uncovered some startling research results - today's teenagers are one to two centimetres taller on average than children of the same age a little over a decade ago. The research by dental graduate and PhD student Sarbin Ranjitkar, recently published in the Australian Orthodontic Journal, compares the heights of about 5000 children aged between nine and 18 over two different time periods, 1987 to 1994 and 1995 to 2005. The measurements, along with hand and wrist x-rays to assess skeletal maturation, came from data collected by Adelaide specialist oral and maxillofacial radiologist Dr Ross Macdonald during orthodontic treatment referral over the 18 years. Dr Ranjitkar did his research with Professor Grant Townsend, who heads the University's Craniofacial Biology Research Group within the School of Dentistry. The group's research centres on the growth and development of teeth and faces, and it is involved in two major studies on genetic influences in dental development using twins. "This study is important to our work because orthodontists need to understand how children grow in order to predict when they go into their growth spurts," Professor Townsend said. "Generally the best time to intervene with orthodontic treatment is during the growth spurt - that's when there is most response to treatment." Dr Ranjitkar found the children from the more recent group were on average taller than the earlier group, with the difference more pronounced in boys. Although there was some trend towards earlier skeletal development in boys, this didn't account for the height difference. The results have placed the use of standard growth charts - set in the 1970s - in question. These charts predict children will be 3-5cm shorter than Dr Ranjitkar found. They have also provoked comment and questioning. Although past upwards growth trends have been put down to improved nutrition and less disease, differences since the late 1980s are less clear-cut. "It is a controversial area," said Professor Townsend. "These patterns of secular trends in growth are not the same everywhere in the world." Dr Ranjitkar added: "In many countries there were clear positive trends in height after the Second World War but that has slowed down in developed countries in recent years. In some developing countries, it is believed the trends could be negative because of war and famine." "We have no real answers as to why it's still happening," said Professor Townsend. "When you look at variations in stature there is a strong genetic component, and some influence from environmental factors. Just how genetic and environmental factors interact for an individual is difficult to assess. There could be dietary factors involved in this trend, but that is still speculation. "What's causing them and how long these trends can continue - that's the fascinating question." Story by Robyn Mills
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