Eye for a Tooth

Desmond Eccles

Description

Why do our faces look so different from those of our ancestor - Early Man? Do animals' teeth wear out? Why are they sometimes such funny shapes like tusks and fangs? An Eye for a Tooth: The teeth of animals aims to fill a gap in the genre of popular science. It explains and describes in everyday language how important teeth are to animals, how they function and why they are different shapes. It also looks at all aspects of the jaw system. The book deals with the dentitions of dinosaurs, primitive animals, sharks and rays, lizards, snakes, crocodiles and alligators. There is an extensive section on mammals, covering many different creatures of different shapes and sizes, including whales, herbivores and carnivores. An Eye for a Tooth is not a comprehensive survey, but examples of each Order are considered and some unusually interesting dentitions are mentioned. The book concludes with sections on human evolution, evolutionary niches and the future of teeth. This book is an ideal companion for any fans of popular science who are looking to expand their knowledge, as well as those interested in evolution.

Sujets

• Médecine
• Popular science
• Anatomy

Informations

• Publié par: Troubador Publishing Ltd
• Date de parution: 28 janvier 2015
• Nombre de lectures: 0
• EAN13: 9781784627645
• Langue: English

Extrait

AN EYE FOR A TOOTH
The teeth of animals
DESMOND ECCLES
Copyright 2015 Desmond Eccles
The moral right of the author has been asserted.
Apart from any fair dealing for the purposes of research or private study, or criticism or review, as permitted under the Copyright, Designs and Patents Act 1988, this publication may only be reproduced, stored or transmitted, in any form or by any means, with the prior permission in writing of the publishers, or in the case of reprographic reproduction in accordance with the terms of licences issued by the Copyright Licensing Agency. Enquiries concerning reproduction outside those terms should be sent to the publishers.

Matador 9 Priory Business Park Kibworth Beauchamp Leicester LE8 0RX, UK Tel: [phone] Fax: [phone] Email: [e-mail] Web: www.troubador.co.uk/matador

ISBN 978 1784627 645
British Library Cataloguing in Publication Data.
A catalogue record for this book is available from the British Library.

Matador is an imprint of Troubador Publishing Ltd
To Bridget
CONTENTS
Introduction
Dinosaurs
Recently Extinct Animals
The Jaw System
Living Animals
Reptiles
Mammalians
Carnivores
Herbivores
Omnivores
What Animal Does This Skull Belong To?
Primates
Conclusions
General Outline of Dentitions
Acknowledgement
INTRODUCTION
When I was a student I read a book on the comparative anatomy of teeth. It was as dull as ditchwater with poor illustrations and lots of boring dental formulae. The only thing I remember about it is a description of whales as Mammals that never set foot on land. I thought, Some day I will do better than this!
The importance of teeth
How often do you think about your teeth? At least three times a day, I hope, when you brush them. Have you ever thought what would happen if you had no teeth at all? You couldn t speak properly and you couldn t chew. You would find it hard to get a date. You would get thin and might not have enough energy to work or play games. But you could mince your food, choose a diet of soups and soft foods and a dentist could make you artificial dentures. Very rarely a person is born who never forms any teeth at all and this can be a serious problem socially and very difficult to treat.
Healthy teeth can look beautiful and in humans, male or female, a regular, healthy dentition can add greatly to a person s attractiveness. The way in which we display our teeth carries a message to others, just think of the powerful effects of a wide beaming smile. Missing, damaged, unhealthy or irregular teeth are a social handicap in some circles. They are necessary for articulating certain sounds, particularly f and v . They tend to get more yellow with age which may explain the present popularity of whitening.
For a person, life without teeth would be difficult but for an animal teeth are not just important, they are a matter of life and death. An animal that no longer has a good working dentition will be able to eat less and less until it weakens and starves to death or becomes a soft target for any hungry predator. Life in the wild for many animals is a constant battle to compete with others of its own species, and other species, that eat the same foods and to resist attack from predators; strong healthy teeth are an essential weapon in this struggle.
Teeth are marvels of design and construction, with a strong core of dentine firmly bonded to wear-resistant enamel on the outside and held in their sockets by many fibres of collagen running between the roots and the surrounding bone of the socket. With care our teeth should last a lifetime.
How animals use teeth
Except for birds most vertebrates have teeth. Carnivores (meat-eaters) use their teeth to grasp their prey, hold it until it suffocates and dies and then to tear it open to get at the meat. Herbivores (vegetation eaters) need teeth which can collect vegetation and grind it into small pieces. In each case food must reach the stomach in a form which the animal can digest.
Many animals use teeth for fighting, males for keeping off competitors during the mating season and females for defending their young against attackers, animals with antlers or horns don t need such teeth. Some use teeth to comb their hair or fur to keep it in good condition. The four large canine teeth of predators give them a ferocious appearance and discourage others from attacking them, I know they scare me!
The shape of teeth and jaws
The teeth and jaws of an animal have evolved over millions of years to a form where they are able to to secure food from available sources and change it in the mouth to a state when it can be swallowed and digested. Evolution acts by the principle, discovered by Charles Darwin, of survival of the fittest if an animal fails to meet these requirements it won t survive. Furthermore, it must continue to meet new changes in its environment by further evolution. If a species fails to adapt in time to such changes it will go the way of the mastodon, the mammoth and the sabre-tooth tiger and become extinct.
What are teeth made of?
The teeth of animals such as sharks and rays, with skeletons made of cartilage, are derived from the scales that cover their skin. In other toothed animals the teeth are made up of three hard tissues: dentine, enamel and cementum, and one soft tissue, the dental pulp.

Figure 1
Figure 1 shows (a) enamel, (b) dentine, (c) dental pulp, (d) root canal and (e) alveolar bone. Note the bulge on each side of the crown which deflects food from this area of potential weakness, and protects the gums during chewing.
Enamel covers the crown of the tooth and is bonded to the dentine, the bond is absolute - enamel never separates from dentine in a healthy tooth. Dentine forms the bulk of the tooth and gives it toughness. Inside the pulp a row of specialised cells (odontoblasts) have extensions running into fine tubules which extend outwards the full thickness of the dentine. Odontoblasts also have connections with nerves in the pulp and it is these which make dentine sensitive to stimulation.
The part of the tooth covered by enamel is called the anatomical crown, it is established when enamel stops forming, the part visible in the mouth is the clinical crown. As the tooth erupts the clinical crown increases in size. In later life the gums may recede exposing part of the root and cause sensitivity to hot and cold stimuli.
The roots of the teeth are covered by a thin layer of cementum, a bone-like substance which attaches the periodontal fibres to the roots. Most mammalian teeth are composed of enamel and dentine but others, like the elephant s tusks, are of dentine (ivory) only.
The hard dental tissues are composed of combinations of collagen, calcium phosphate and water. Enamel, the hardest tissue in the animal body, is about 96 per cent calcium phosphate, dentine and cementum are about 70 per cent and the remainder collagen, and the fibres of the periodontal ligament are entirely collagen. The part of the jaw bone which encloses the teeth and forms the sockets is the alveolar bone.