Rotten roots of dentistry
QUESTION description of a dental procedure? Who was the first professional dentist? What is the earliest
THE earliest known patient who was treated for dental caries (tooth decay) was Villabruna, a late upper Palaeolithic man from 14,000 years ago.
This is the name given by archaeologists for remains found in an ancient burial site in northern Italy. He appears to have had tooth decay scratched away using a flint scraper.
The Mehrgarh burial site in western Pakistan dates back to between 7,500 and 9,000 years ago, and is believed to be the oldest Stone Age complex in the Indus River valley. There is evidence of 11 drilled molars from a sample of 300 individuals. The budding dentists used a flint point attached to a bow to make a Stone Age version of a high-speed drill.
A beeswax filling was discovered in a 6,500-year-old human tooth in Slovenia.
Dentistry was performed widely in Egyptian times. Hesy-Re, an Egyptian scribe from 2600 BC, is described as being the first true dentist. The Ebers papyrus dated 1700 BC to 1550 BC describes various remedies for toothache.
A Babylonian tablet, The Legend Of The Worm, talks of tooth worms which drink the blood and eat the roots of teeth. This may have been an ancient way of describing a bacterial infection, though artistic models of teeth featuring worms suggest it was often taken literally.
In the West, dentistry became a profession in the Middle Ages. A Guild of Barbers was established in France in 1210, and barber-surgeons performed routine hygienic services including shaving, bleeding and tooth extraction.
In 1530, the first dental book for barbers was published by Artzney Buchlein in Germany. It contained practical information on extraction, drilling and fillings.
Professional dentistry began to develop in the 18th century, with many significant advances made in the 19th century.
The American Journal of Dental Science began publication in 1839. The world’s first dental school, the Baltimore College of Dental Surgery, was founded in 1840, and its graduates were given the Doctor of Dental Surgery (DDS) degree.
Charles Avery, Shrewsbury, Shropshire.
QUESTION
What determines the spacing and speed of the ripples produced when a stone is dropped into a still pond?
THE processes that govern the movement of ripples in a pond are complex. Waves disperse at a set speed due to gravity, the depth of the water, and the density and surface tension of the water. The amplitude of the wave is affected by the size of the stone.
Two types of wave are generated when a stone is dropped into water. Gravity waves are the most visible. Dropping a stone into a pond causes water to rise above the equilibrium surface level, gravity pulls it back down, inertia acquired during the falling movement causes the water to penetrate below its level of equilibrium and a bouncing motion results.
Gravity waves move horizontally because when a parcel of water rises somewhere above the surface, the added weight of this water creates a pressure that is locally higher than normal.
This pressure anomaly accelerates the fluid away from that place and piles it up a little further, generating another surface rise some distance away.
Water motion under a surface wave is nearly oscillatory, with almost no net displacement.
Surface waves are a mechanism by which the fluid moves energy from one area to another without involving any significant movement of the fluid itself.
A leaf suspended in the water will not move outwards with the apparent wave motion.
Capillary waves are also formed when a stone deforms the surface layer of the water, which acts like an elastic membrane that pushes back against the falling object. Surface tension supplies the restoring force that strives to flatten the surface of the water.
A combination of gravity and capillary waves creates the familiar ripple effect.
H. D. Singh, Bedford.
QUESTION
What is the average lifespan of a thatched roof?
FURTHER to the earlier answer, I been a grower of thatching straw for 40 years. Four main types of thatch are used for roofs.
Long straw thatch is made from wheat, usually older, taller varieties popular before the advent of modern short-strawed, high-grain-yielding types. A threshing machine is used on the sheaves.
With combed wheat reed, the sheaves are fed through a reed comber mounted on top of a threshing machine.
The straw does not pass through the mechanism.
The third and fourth types, water reed and heather thatch, are rarely used nowadays.
The average lifespan of each type of thatch varies and depends on the position of the property, the micro-climate, the angle or pitch of the roof, the quality of the thatching material and the skill of the thatcher. In areas of lower, cooler humidity, the style is for steep roofs. The thatch would be expected to last longer than in areas of relatively high humidity, and shallow pitched roofs can lead to fungal decay and wear.
Long straw thatch performs well on steeper roofs. If thatched to good specifications of 300mm thickness, you would expect a lifespan of between 30 and 40 years, with ridge replacement every 15 to 20 years.
Combed wheat reed was used only on shallow roofs until the late 20th century. It performs well when thatched at between 250mm and 300mm thickness and has an average lifespan of 35 to 45 years.
Water reed thatch can last 50plus years. However, it can fail prematurely if the reed has been clamped too tight near the surface, leading to trapped moisture and a white fungus and decay.
But that doesn’t altogether answer the question as to the lifespan of a thatched roof. In the case of some long straw thatched houses where a new coat is applied over the worn straw below, there can be the remnants of many layers. There are many records of smoke-blackened thatch where the first coat would have been laid down when open hall houses were common in late medieval times. Smoke would rise from the open hearth and filter through the roof, so there are some straw roofs that are 500 years old.
Paul Watkin, Bungay, Suffolk.