WEEK 7

1. Learning Objectives

  • By the end of this lesson, you should be able to:

    • Visually and verbally identify various teeth.

    • Have a working knowledge of dental eruption patterns and their use in juvenile age estimation.

    • Comment on occlusion variations.

    • Understand the forensic value of teeth.

    • Appreciate the use of, and obstacles to, bite mark analysis.

2. Dentition

  • Visual Identification of Tooth Types: You are expected to visually identify different tooth types without distinguishing upper/lower or left/right.

  • Deciduous Teeth Appearance:

    • Deciduous teeth are smaller in size with a reduced root length compared to permanent teeth.

    • They lack premolars and third molars.

  • Numbering Conventions for Teeth:

    • Specific teeth are annotated in a standardized format (e.g., Upper left I2, lower right Pm1).

2.1. Dental Eruption Patterns

  • Significance: Dental eruption patterns are one of the most precise methods for estimating age in adolescents.

  • Reference: London Atlas of Human Tooth Development and Eruption (AlQahtani et al., 2010).

2.2. Occlusal Patterns

  • Definition: The occlusal surface refers to areas where teeth touch each other while biting.

  • Types of Occlusion Patterns:

    • Orthognathism: Normal alignment of the jaw and teeth.

    • Retrognathism: A condition where the lower jaw is positioned further back than the upper jaw.

    • Prognathism: A condition where the lower jaw protrudes beyond the upper jaw.

3. Forensic Odontology

  • Definition: Forensic odontology encompasses all aspects related to the mouth and teeth in a forensic context.

  • Applications:

    • Often utilized to identify unknown deceased persons.

    • Sometimes serves as evidence against perpetrators.

    • Encompasses age, sex, and ancestry estimations as well as bite mark analysis.

    • Teeth are also valuable for DNA extraction and analysis due to their protective enamel layers and enclosed pulp cavities.

3.1. Age Estimation

  • Methods:

    • Dental Eruption Patterns: A reliable method for age estimation in juveniles.

    • Gustafson Method (1950):

    • Involves scoring six characteristics:

      • Attrition

      • Secondary dentine

      • Periodontosis

      • Cementum

      • Root resorption

      • Root transparency.

    • The total score is calculated and inserted into a regression formula similar to TBS scores.

    • Lamendin Technique (Lamendin et al., 1992):

    • Measures root transparency (RT) and periodontosis (P) in single-rooted teeth (incisors, canines, premolars).

    • Formula:

      • Aext(age)=(0.18imesP)+(0.42imesRT)+25.53A ext{ (age)} = (0.18 imes P) + (0.42 imes RT) + 25.53 where:

      • P=racextperiodontosisheightimes100extrootheightP = rac{ ext{periodontosis height} imes 100}{ ext{root height}}

      • RT=racextroottransparencyimes100extrootheightRT = rac{ ext{root transparency} imes 100}{ ext{root height}}

    • Suitability: Found to work well for both sexes and all single-rooted teeth.

    • Reported mean error for estimated age: ± 10 years for the working sample and ± 8.4 years for the control sample. However, it noted larger errors for individuals under 40 and over 80.

    • Incremental Lines in Root Cementum:

    • Method involves viewing transverse root slices under a microscope and counting concentric circles formed over a lifetime.

    • Although theoretically applicable to all teeth, slicing requirements are intensive and costly.

3.2. Sex Estimation

  • Measurement Techniques:

    • Various combinations of tooth crown measurements are used to estimate sex.

    • Discriminant function formulas are utilized where measurements input provide a sex estimate:

    • Common measurements include:

      • Mesiodistal (MD) Crown Diameter: The distance between two parallel lines measuring left to right across the tooth axial plane.

      • Buccolingual (BL) Crown Diameter: The greatest distance measured from the buccal/labial surface to the lingual surface of a tooth crown.

    • Challenges:

    • Measurement accuracy can be complicated due to shape variations and small sizes.

    • Discriminant function analyses' accuracies can range from 58% to 94%, often population-specific;
      thus, unknown ancestry complicates analysis.

3.3. Ancestry Estimation

  • Challenges in Estimation with Teeth:

    • The accuracy of ancestry estimation from dental features is generally lower compared to other skeletal elements.

  • Utilized Measurements and Features:

    • Measurements of teeth and distances between particular teeth (especially canines) can be used.

    • Morphological features can exhibit frequency variations in different population groups (e.g., four molars, dental size, shovel-shaped traits).

    • Caution is advised due to the dearth of focused studies in the South African context.

3.4. Bite Mark Analysis

  • Overview: Bite mark analysis is a significant component of forensic odontology.

  • Legal Context: Recent studies indicate bite marks are admissible in South African courts, but such acceptance varies internationally.

  • Analysis Factors:

    • Bite imprints can be measured and compared against reference samples to assist in eliminating suspects.

    • Saliva often provides another medium for DNA collection from the bite mark surface, enhancing its forensic utility.

  • Unique Patterns: The more unique a person's dental pattern (e.g., slightly skewed or missing teeth), the more valuable the evidence.

  • Challenges: The physical characteristics of the surface on which the bite mark is left can distort measurements and traits:

    • Brittle or elastic surfaces may warp when subjected to biting force, complicating comparative evaluations.

  • Conclusion: The evidentiary role of bite marks remains controversial and is not universally accepted within legal frameworks.