Forensic odontology to determine age – The alveolar cavities which contain teeth are formed around the third or fourth month of intrauterine life. Development of the tooth begins with the formation of cellular tooth germ within the alveolar bone, in the shape of the crown. Apposition and calcification of enamel and dentin take place within this germ, and the crown is completely formed and calcified before any positional changes occur.
At birth, the rudiments of all the temporary and of the first permanent molars may be found in the jaws. Root formation begins after completion of the crown, and as the root becomes longer, the crown erupts through the bone, and finally comes out of the jaws.
The root is completed sometime after the tooth is in full functional occlusion. The calcify from crown to neck to roots. During eruption of a permanent tooth, the overlying root of its deciduous predecessor simultaneously undergoes absorption until only the crown remains. The unsupported crown then falls off.
Teeth are useful for age determination in forensic odontology (a) by the state of development, and (b) by secondary changes.
Temporary, deciduous or milk teeth are 20 in number: 4 incisors, 2 canines, and 4 molars in each jaw. In ill-nourished children, and especially in rickets, and in hypothyroidism, dentition may be delayed, while in syphilis, teeth may be premature or even present at birth.
At about four years, there is usually spacing between the deciduous teeth. About the sixth or seventh year, first permanent molar erupt behind the second temporary molars. After this, the temporary begin to fall off. Between 7 to 12 years, 24 teeth are present.
At age nine, 12 permanent teeth are in the mouth; 8 incisors and 4 first molars. Deciduous molars and canines are present. At the age 11, there are 20 permanent: 8 incisors, 8 premolars and 4 molars. Mixed dentition is seen up to 12 years. Between 7 to 12 years 24 teeth are present. At the age 14, there are 28 permanent, and no deciduous teeth.
If there is doubt whether a particular tooth is temporary, take an X-ray. If it is temporary tooth, germ of the permanent tooth can be seen underneath.
Permanent are 32 in number: 4 incisors, 2 canines, 4 premolars, and 6 molars in each jaw. Developmentally, They are divided into two sets
(1) Superadded permanent teeth are those which do not have deciduous predecessors. They erupt behind the temporary. All the permanent molars are super-added permanent. The first permanent molar tooth of each side erupts, while all the other deciduous are present in the jaw. Superadded permanent are six in each jaw. (2) Successional permanent are those which erupt in place of deciduous. Permanent premolars erupt in place of deciduous molars. Successional are ten in each jaw.
MORPHOLOGY OF PERMANENT TEETH in Forensic odontology
Each tooth has a crown, a neck and a root embedded in the jaw bone. Teeth are composed of dentin, covered on the crown by enamel and on the root by cementum, which is attached to the alveolar bone by periodontal membrane.
The crown is shaped like chisel and is convex on its labial surface and concave on its lingual surface, except near the neck, where the surface becomes convex. The neck is slightly constricted. The root is single.
They are larger than the incisors. The crown is large and conical, very concave on its labial surface and slightly concave on its lingual surface. Its masticatory edge tapers to a blunt point, which projects slightly beyond the level of the other teeth. The root is single, larger and thicker than that of an incisor.
PREMOLARS OR BICUSPIDS
They are smaller and shorter than the canines. The crown of each is nearly circular in cross-section and slightly compressed mesio-distally. The chewing surface has two cusps.The root is usually single, but may be double.
They are largest with broad crown. The crown is cubical; convex on its labial and lingual surfaces, and flattened on its mesial and distal surfaces. It has three, four or five cusps. Each upper molar has three roots and lower two.
They resemble in form the teeth which bear the same names in the permanent set thus helping in Forensic odontology.
Eruption is defined as the superior part of the crown of the tooth appearing level with the surface of the alveolar bone in both deciduous and permanent teeth, dentition occurs earlier in lower jaw except for the lateral incisors which erupt earlier in upper jaw. The lower permanent incisors, premolars and molars erupt about one year earlier than do the corresponding teeth in the upper jaw.
Wisdom tooth first erupts in the lower and on the left side and then on the right side. The number and eruption of deciduous teeth is more regular than the permanent dentition. Eruption is not always bilaterally symmetrical. Tooth eruption in female may be one year before that of males. Females have smaller ones (esp. lower canines) than males.
In general, the dental and skeletal ages, correspond closely in the male, but in the female the skeletal age is generally one year ahead of the dental age. The ethnic, cultural, hereditary, environmental, endocrine reactions and nutrition all play a part in the eruption and calcification. Eruption tends to occur earlier in warmer climates and in urban areas.
From birth to fourteen years of age, the degree of formation of root and crown structures, the stage of eruption and the inter-mixture of temporary and permanent teeth are useful in age estimation in forensic odontology. It is generally accepted that in a child estimation of age from teeth gives better results than skeleton.
Dental X-rays show the developmental status of un-erupted teeth and the degree of root completion in erupted teeth. From 14 to 20 years, dental age estimation in forensic odontology is based upon the stage of development of the third molar. There is much variation in these, and the accuracy of dental age estimation during this period varies by about plus/minus three years. The body of the jaw grows posteriorly, and the ramus is elongated after eruption of second molar.
If third molars are absent, it should be noted whether there is a space in the jaw behind the second molar. If third molars are fully erupted, it indicates that an individual is above 17 years of age. In some persons due to inadequate jaw space, the third molars never erupt into the oral cavity, particularly the mandibular third molars. Such trapped teeth are known as impacted teeth. All can be visualized by single X-ray by dental panoramic tomograph (orthopantogram).
GUSTAF-SON’S METHOD in Forensic odontology
The age estimation in forensic odontology of adult over 21 years depends on the physiologic age changes in each of the dental tissues.
Due to wear and tear from mastication, occlusal (upper) surface of the teeth is destroyed gradually, first involving the enamel, then dentin and at last pulp is exposed in old age. It depends on the functional use of them and also upon the hardness of the enamel.
Regression of the gums and periodontal tissues surrounding the teeth takes place in advancing age, gradually exposing the necks and the adjacent part of roots, due to which the teeth become loose and fall off. Poor oral hygiene increases paradentosis. This feature helps in Forensic odontology.
(3) Secondary dentin
It may develop from the walls within the pulp cavity, and decrease the size of the cavity. First it is deposited at the pulp chamber and gradually extends downwards to the apex, and may completely fill the pulp cavity. This is partly due to aging and partly due to pathological conditions like caries, and paradentosis.
(4) Cementum apposition
The cementum increases in thickness particularly due to changes in the tooth position, especially near the end of the root. Secondary cementum is slowly and continuously deposited throughout life, and forms incremental lines.
Incremental lines appear as cross-striations on the enamel of teeth due to cementum apposition, and are thought to represent daily increments of growth. They can be seen on histological section. The age can be calculated in forensic odontology by counting the number of lines from the neonatal line onwards. This is mainly applicable to infants.
(5) Root resorption
It involves both cementum and dentin which show characteristically sharp grooves. Absorption of the root starts first at the apex and extends upwards. It usually occurs in late age. it may be due to pathological process.
(6) Transparency of the root
It is not seen until about 30 years of age. The canals in the dentin are at first wide. With age they are filled by mineral, so that they become invisible and the dentin becomes transparent. It is the most reliable of all criteria.
Before the tooth is extracted from a body, the degree of paradentosis is estimated. The tooth is ground down on glass slabs from both sides of the tooth to about one mm. which allows the estimation of transparency. Then the section is ground further down to about one-fourth mm. for microscopic examination.
Anterior are more suitable than the posterior teeth, and the merit decreases from incisors to premolars, while third molar is quite unsuitable. All changes are absent at 15 years. Arbitrarily, 0 to 3 points are allotted to indicate the degree of any of these changes.
Stage 0 indicates no change; I beginning of change; 2 obvious change; and stage 3 maximum change, occurring in the dental tissues. The result corrected for standard deviation, etc., gives an estimate of the age of the person in forensic odontology. The error is said to be ± 4 to 7 years. The limit of error increases above 50 years of age.
Further modifications of this method is known as Gustafson‘s formula. Age can also be determined by directly reading from the graph on which the regression line is plotted.
Cross striations develop in the enamel of teeth, till the complete formation of enamel. They represent daily incremental lines. The age of an individual can be calculated in forensic odontology in terms of days by counting the number of lines from the neonatal line onwards. Neonatal line is formed very soon after birth and can be seen in about three weeks or by electron microscopy within one to two days after birth. It is useful to estimate the age of a dead infant.
Stack’s method: Stack evolved a method to know the age of infants from the weight and height of the erupting teeth of child. Forensic odontology can be used on both deciduous and permanent during their erupting phase.