Preclinical Paediatrics · MU Sofia

29. Anatomical and physiological differences between primary and permanent dentition.

Covers how primary and permanent dentitions differ in tooth number, successional and accessional teeth, crown size and shape, enamel and dentin thickness, pulp chamber and horn form, root length and divergence, and arch shape. It includes the leeway space figures for each arch and the concept of incisor liability, and explains that the crowns of primary molars resemble no premolar they succeed.

Inside: 5 sections · 15 flashcards · 5 min

Topic 29 of 40 in the MU Sofia syllabus for Preclinical Paediatrics (Dental Medicine, Year 3). The free AceMed note covers it in 5 sections, about 691 words (5 min of reading), with 15 flashcards.

In this note

  1. ANATOMICAL AND PHYSIOLOGICAL DIFFERENCES BETWEEN PRIMARY AND PERMANENT DENTITION
  2. DIFFERENCES IN THE PULP
  3. DIFFERENCES IN ROOT
  4. DIFFERENCES IN TOOTH STRUCTURE
  5. ARCH SHAPE

ANATOMICAL AND PHYSIOLOGICAL DIFFERENCES BETWEEN PRIMARY AND PERMANENT DENTITION

Humans are diphyodont as they have two dentitions: primary and permanent

  • Humans are also heterodonts as they have different tooth groups
  • Primary dentition consists of 20 teeth and permanent dentition consisting of 32 teeth
  • Permanent teeth replacing the primary teeth are called successional teeth
  • Permanent teeth with no predecessors are called accessional teeth

MAIN DIFFERENCE BETWEEN PRIMARY AND PERMANENT TEETH is that there are 4 premolars and 6 molars in each arch. Each jaw consists of specific teeth, which are incisors (Cutting teeth), canines (tearing teeth) and molars (grinding teeth)

DIFFERENCES IN SIZE AND FORM

  • Crowns of primary teeth are smaller than permanent
  • Crowns of permanent incisors and canines are larger than the primary variants
  • Difference between the cumulative mesiodistal diameters of primary molars and canines those of permanent variants is called the leeway space
  • 1.3mm in maxillary arch and 3.1mm in mandibular arch
  • Primary teeth resemble permanent teeth
  • Both permanent and primary incisors have single roots and incisal edge
  • Both permanent and primary canines have single roots and cusps
  • Primary molars bear no resemblance to the premolars that succeeds them
  • Crowns of permanent molars are larger than the crowns of primary molars
  • Primary molars have a larger mesiodistal diameter than the crowns of succeeding premolars

DIFFERENCES BETWEEN CROWNS

  • Shape of crowns of two dentitions is similar
  • Exception is the form of primary molars and permanent premolars which erupt in their place
  • Primary teeth have shorter crown than permanent teeth. Difference in colour as primary ones are bluish-white and permanent ones are more yellowish
  • Due to thinner enamel of primary and thicker and more mineralised enamel of permanent teeth
  • Occlusal surface of primary molars is narrower than the permanent teeth
  • Primary teeth are much more constricted in the cervical portion of the crown than permanent teeth
  • Marginal ridge is linear, rounded border of enamel that forms the mesial and distal margins of anterior teeth as viewed from lingual and mesial and distal edges of occlusal surfaces of posterior teeth
  • Primary teeth have pronounced cervical ridge. Most pronounced is buccal ridge of 1ˢᵗ primary molar
  • Enamel and dentin layers are thinner in primary tooth. Enamel is equally thick in all areas of crown-1mm
  • Enamel rods in gingival third extends in a slightly occlusal direction from DEJ in primary teeth but continue slightly apically in the permanent dentition
  • Contact areas between primary molars are broad and flat

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