Human Dentition: Types of Teeth, Age Estimation and Bite Marks

A tooth has two anatomical parts. The crown sits above the gum and is covered by enamel the hardest tissue in the human body (about 96 per cent inorganic, predominantly hydroxyapatite). The root is embedded in the alveolar bone of the maxilla or mandible and is covered by cementum a bone-like tissue that anchors the periodontal ligament. The crown and root meet at the neck (cervix)marked by the cement-enamel junction. Under the enamel and cementum lies dentine a yellowish calcified tissue that forms the bulk of the tooth and contains tubules running from the pulp outward. At the centre of the tooth is the pulp cavity holding nerves and blood vessels that enter through the apical foramen at the root tip.

Humans are heterodont(four tooth shapes),diphyodont(two successive dentitions) and thecodont(teeth set in bony sockets). The four functional types map cleanly onto stems.Incisors are chisel-shaped and used for cutting.Canines (cuspids)are single-cusped and used for tearing and gripping; they are the longest-rooted teeth and the most stable in old age.Premolars (bicuspids)are two-cusped and used for grinding and tearing; they exist only in the permanent dentition.Molars are large, multi-cusped grinders; the permanent third molar is the wisdom tooth. India-specific anchor: undergraduate dental anatomy is taught from the standard reference, Modi's Medical Jurisprudence and Toxicology alongside the BDS curriculum in institutions such as Government Dental College Mumbai and Government Dental College and Hospital Kolkata, which is also where many Indian forensic-odontology consultants train.

The two dentitions compared:

• Deciduous dentition.20 teeth in total, 5 per quadrant (2 incisors, 1 canine, 0 premolars, 2 molars). Dental formula per quadrant:2.1.0.2. No premolars exist in the milk set. Eruption begins with the lower central incisor at 6 to 8 months and completes by 2 to 3 years. Shedding starts around 6 years.
• Permanent dentition.32 teeth in total, 8 per quadrant (2 incisors, 1 canine, 2 premolars, 3 molars). Dental formula per quadrant:2.1.2.3. The first permanent molar erupts at 6 years and is called the six-year molar the second molar erupts around 12 years; the third molar (wisdom tooth) erupts between 17 and 25 years and may remain impacted in many adults.

Eruption sequence, per the Schour-Massler chart (1941, with later updates): lower central incisor 6 to 8 months, upper central incisor 8 to 12 months, first deciduous molars 12 to 16 months, deciduous canines 16 to 20 months, second deciduous molars 20 to 30 months, complete deciduous set by 2.5 to 3 years. For the permanent set: first molar 6 years, central incisor 6 to 7 years, lateral incisor 7 to 8 years, first premolar 9 to 11 years, canine 9 to 12 years, second premolar 10 to 12 years, second molar 11 to 13 years, third molar 17 to 25 years. Indian population studies from AIIMS Delhi and various state dental colleges report mild local variation from these global landmarks.

Forensic odontology splits age estimation into three life stages, each requiring a different methodological approach.

Pre-natal and infancy. Fetal dental development begins at about 6 weeks of intrauterine life with the dental lamina. Calcification of the deciduous central incisor starts around 14 weeks in utero. Useful for foetal-remains casework but rarely the answer in MCQs unless the stem says "infant" or "neonate".

Childhood and adolescence. Two methods dominate.Demirjian (1973)uses eight stages (A to H) of crown and root calcification, applied to the seven permanent left mandibular teeth visible on a panoramic radiograph; each tooth gets a stage score, the scores are summed and converted to dental age through Demirjian's tables.Nolla (1960)is the alternative ten-stage radiographic scoring system. Both are radiographic and non-destructive. The Schour and Massler chart (1941)remains the classic eruption-sequence reference that examiners shows in figure-based questions. Indian-population adaptations exist but the original tables are still the examined ones.

Adult age estimation. Once tooth eruption is complete, examiners switch to degenerative-change methods.Gustafson (1950)is the landmark adult method and the single most testable item in this section. Six criteria, each scored on a 0 to 3 scale (0 = no change, 3 = severe change), are summed and put through a linear regression of the form Age = a + b × (sum of scores). The six criteria, in Gustafson's original order, are:

1. Attrition (A)of the occlusal surface from chewing.
2. Periodontosis (P)recession of the periodontal attachment, measured along the root.
3. Secondary dentine (S)deposition inside the pulp cavity.
4. Cementum apposition (C)at the root apex.
5. Root resorption (R)by osteoclastic activity.
6. Transparency (translucency) of the root (T)caused by hydroxyapatite filling of dentinal tubules; the most reliable of the six.

Maximum sum is 18, and the standard error of the original regression is about ±3.6 years. The mnemonic for the six is APSCRT(sometimes rearranged to TRACPS for ease of recall). Gustafson's method requires a longitudinal section of the tooth, so it is destructive; later workers (Johanson 1971, Kashyap and Koteswara Rao 1990, Kvaal 1995) refined the scoring or moved it onto radiographs.Kvaal (1995)uses pulp and tooth length ratios on periapical radiographs and is non-destructive.Cameriere (2007)uses the pulp-to-tooth area ratio (most often on canines) and has been validated in Indian populations by AIIMS Delhi and several state dental colleges.Aspartic acid racemisation in dentine is a biochemical method with low standard error (about ±3 years) but needs specialist laboratory facilities.

India-specific anchor: the All India Institute of Medical Sciences (AIIMS) Delhi the Centre for Forensic Odontology at the Faculty of Dental Sciences in several state government dental colleges, and the National Forensic Sciences University (NFSU) Gandhinagar Forensic Odontology unit handle most live age-estimation casework, especially the contested juvenile-vs-adult age determinations referred under the Juvenile Justice (Care and Protection of Children) Act 2015, where dental and skeletal age together drive the bench's decision.

A bite-mark is the American Board of Forensic Odontology (ABFO)defines as "a representative pattern left in an object or tissue by the dental structures of an animal or human". On human skin a complete bite typically shows two opposing curved or U-shaped marks (upper and lower arches) made by the six anterior teeth (incisors and canines) of each jaw. The space between the two arches gives the inter-canine distance typically 25 to 40 mm in an adult.

Bite-marks are classified along three axes. By certainty definite, probable, or possible bite (ABFO 1986 guidelines). By mechanism abrasion, contusion, laceration, avulsion, incision, or pattern impression. By origin self-inflicted (often in mental-health contexts), animal (dog and cat bites have distinct canine spacing), or human inflicted by another. Bite-marks recovered from food substrates (cheese, chocolate, fruit) are sometimes the strongest evidence because the substrate holds a sharper impression than skin.

The collection protocol is the workflow you should commit to memory:

1. Photograph the bite from three directions (perpendicular, plus two oblique angles) using the ABFO No.2 reference scale placed coplanar with the bite. Use ultraviolet (UV) and infrared (IR) photography to enhance bruising days after the event (a topic that connects directly to the specialised photography topic).
2. Swab the bite-mark for salivary DNA before any washing or examination touches the site. The double-swab technique (one wet, one dry) is standard. Salivary amylase confirms saliva; STR profiling identifies the biter.
3. Cast the bite-mark by silicone or polyvinylsiloxane impression if the substrate is firm enough (food items, less often skin).
4. Take dental exemplars from suspects (impressions of upper and lower arches in alginate, plus study casts and bite-print on wax) under a magisterial direction analogous to a voice or fingerprint sample.
5. Compare by transparent overlay (acetate overlays traced from the suspect's cast), computer-generated digital overlay, or direct cast comparison.Individual features that drive a match: rotated teeth, missing or fractured teeth, distinctive cuspal wear, restorations and prosthetics.

The ABFO Guidelines(1986, with major revisions in 2018) are the international reference. The 2018 revision explicitly retreated from categorical "this suspect bit this victim" conclusions following a wave of US exonerations and now prefers narrower opinions such as "the suspect cannot be excluded as the biter" or "the pattern is consistent with a human bite".

Krishan Kumar Malik v State of Haryana (2011, Supreme Court of India). A rape case in which bite-mark evidence on the victim formed part of the prosecution. The Supreme Court used the case to remind trial courts that bite-mark evidence has to be collected, photographed and compared by qualified experts with proper documentation, and that the prosecution must lead the dental expert's testimony rather than rely on the investigating officer's untrained opinion. The bench's caution mirrors the wider international scepticism around bite-marks. Krishan Kumar Malik v State of Haryana is the leading Indian authority on bite-mark evidence.

Mohd. Aman v State of Rajasthan (1997). Cited often in identification jurisprudence; useful background on the standards required for forensic opinion evidence. The principles read across to forensic odontology even though the case itself dealt with fingerprint evidence.

State (Delhi Administration) v Pali Ram and the wider Section 45 IEA (now BSA 2023 Section 39)line of cases govern how the dental surgeon's report is admitted.BSA 2023 Section 39 treats forensic odontology as expert opinion on a matter of "science or art" and integrates with the wider forensic evidence framework under the Bharatiya Sakshya Adhiniyam.BNSS 2023 Section 194 governs post-mortem and medico-legal examination reports, which is where dental findings from an autopsy enter the record.

Historical international anchor (background only). The American serial-murder case State v Bundy (1979)is the most cited bite-mark conviction in the global literature; it is useful as illustrative context but not Indian law. examiners sometimes uses it as A common point of confusion.

Institutional anchors in India.

• AIIMS Delhi Department of Forensic Medicine and Toxicology, handles complex age-estimation and bite-mark reference work.
• NFSU Gandhinagar runs a dedicated forensic-odontology teaching and research unit and a short-course programme for dental graduates.
• Government Dental College Mumbai and Government Dental College and Hospital Kolkata are the longest-running institutional centres for forensic odontology training in India.
• Anthropological Survey of India (AnSI)holds dental anthropology reference collections used in population-specific eruption-table studies.
• Indian Association of Forensic Odontology (IAFO)is the professional body that publishes Indian guidelines and runs continuing-education programmes.

The interplay of bite-mark and DNA evidence connects this topic to the DNA structure, extraction and profiling techniques topicbecause salivary swabs from bite-marks are now routinely the stronger evidence than the dental overlay itself.

Forensic odontology casework frequently involves oral-identification adjuncts that extend beyond teeth alone.

Cheiloscopy is the study of lip prints.Suzuki and Tsuchihashi (1970)classified lip-print patterns into six types (Type I straight vertical grooves, Type I' partial vertical, Type II branched, Type III intersected, Type IV reticular, Type V undetermined). Lip prints are claimed to be individual and stable from before birth to death, and they appear on cups, cigarette butts, glassware and clothing at scenes. Indian studies from various dental colleges have reported regional pattern frequencies useful in population databases.

Palatoscopy (rugoscopy)is the study of palatal rugae the transverse ridges on the anterior hard palate. Rugae patterns are individual, stable after age 12, and survive most forms of trauma and decomposition because they sit inside the oral cavity protected by the cheeks and lips. They are particularly useful in mass-disaster victim identification when soft-tissue facial features are destroyed.

Both adjuncts come under expert opinion within the meaning of BSA 2023 Section 39 and are reported alongside dental findings in many Indian medico-legal post-mortems, particularly in fire and explosion disasters where the skull superimposition and facial reconstructionteam and the dental surgeon work the same set of remains.