Morphological Differences Between Primary and Permanent Teeth: A Comprehensive Guide

Posted on Aug 7, 2024 in Biology

Morphological Differences Between Primary and Permanent Teeth

Crown Characteristics

  • Primary teeth have wider crowns mesiodistally compared to their length.
  • Anterior primary teeth are narrower and shorter than permanent teeth.
  • Primary molars have relatively longer and more slender roots than permanent molars.

Enamel and Cervical Ridge

  • The cervical ridge of enamel is more prominent in primary teeth, especially on the labial and lingual surfaces.
  • Primary molars have more slender crowns and roots mesiodistally at the cervical third than permanent molars.
  • The cervical ridge on the buccal aspect of primary molars is more definite, particularly on the maxillary and mandibular first molars.

Occlusal Surface

  • The buccal and lingual surfaces of primary molars are flatter above the cervical curvatures than those of permanent molars.
  • This makes the occlusal surface narrower in primary teeth compared to permanent teeth.

Color

  • Primary teeth are usually lighter in color than permanent teeth.

Considerations Due to Morphological Differences

  • Special care is required during gingival floor formation in Class 2 restorations due to the constriction of the neck in primary teeth.
  • There is a greater chance of pulp exposure during cavity preparation due to the large pulp chamber in primary teeth.
  • The enamel of primary teeth is thin but of uniform thickness.
  • The bulbous crown of primary molars can make matrix placement more difficult.
  • Porosity in the pulpal floor of primary teeth is more common than in permanent teeth.

Specific Tooth Morphology

Maxillary Canine

  • Well-developed sharp cusp
  • Straight incisal edge
  • Long, slender, tapering root

Mandibular Central Incisor

  • Labiolingual measurement is usually only 1mm less than the mesiodistal measurement.
  • Flat labial aspect without developmental grooves
  • Root is twice the length of the crown

Mandibular Lateral Incisor

  • Larger than the mandibular central incisor in all dimensions except labiolingually.
  • Greater concavity between the marginal ridges on the lingual surface.
  • Incisal edge slopes toward the distal aspect of the tooth.

Mandibular Canine

  • Similar to the maxillary canine with a few exceptions.
  • Crown is slightly shorter.
  • Not as large labiolingually as the maxillary canine.

Mandibular First Molar

  • Does not resemble any other teeth.
  • Crown height is greater on the mesial side than the distal side.
  • Mesial marginal ridge is very well developed.
  • Prominent mesiobuccal cervical ridge.
  • Rhomboid outline.

Mandibular Second Molar

  • Resembles the mandibular first permanent molar.
  • Five cusps: 3 buccal and 2 lingual.
  • Three buccal cusps are more equal in size.

Periods of Dental Development

Pre-Dentition Period

  • From birth to the eruption of the first primary tooth.
  • Alveolar processes are covered with gum pads.
  • Gum pads are divided into labial and lingual portions by lingual grooves.
  • Gum pads are segmented into 20 segments by transverse grooves.

Primary Dentition

  • Tooth eruption begins at about 6-7 months.
  • Variables that influence eruption include genetics, environmental factors, and systemic factors.

Mixed Dentition

  • Period where both primary and permanent teeth are present in the mouth.
  • From 6-12 years of age.
  • Sequence of eruption: Moyers in the mandible and maxillary.
  • Problems associated with eruption include difficult eruption, eruption cyst, eruption hematoma, and eruption sequestrum.

Types of Examination Appointments

  • Complete
  • Recall
  • Emergency

Aims of the First Session with a Child Patient

  • Establish good communication with the child and parent.
  • Obtain important background information.
  • Examine the child and obtain X-rays if required.
  • Introduce the child to a simple treatment procedure.
  • Explain treatment aims to the child and parent.

Steps of First Appointment

  • Initial interview and case history
  • Extraoral examination
  • Intraoral soft tissue examination
  • Intraoral hard tissue examination
  • Radiographic examination
  • Special investigations

Radiographs Used in Pediatric Dentistry

  • Bitewing
  • Periapical
  • Panoramic
  • Occlusal films
  • Extra-oral facial films

Guidelines for Treatment Planning

  • Treatment sessions should be planned efficiently and effectively.
  • Use quadrant dentistry.
  • Treat posterior teeth before anterior teeth.
  • Incipient lesions should always be restored in caries-active children.
  • The last restorative visit should be minimal.
  • Always treat the area that is painful to the patient.

Treatment Plan

Medical Phase

  • Patients with positive medical history are referred to a pediatrician for evaluation and consent.

Systemic Phase

  • Any medication given to modify the dental treatment is included in this phase.

Preventive Phase

  • Oral hygiene consultation
  • Oral prophylaxes
  • Pit and fissure sealants
  • Diet consultation

Corrective Phase

  • Operative dentistry
  • Extraction and minor surgery
  • Space maintainers
  • Orthodontics

Maintenance and Recall

  • No treatment plan is complete without a recall appointment and follow-up.