Differences Between Primary and Permanent Dentition

Introduction

• Primary teeth are also called deciduous teeth because they shed off.
• Present in the mouth from 6 months to 6 years, then replaced by permanent teeth which complete by age 21.

Key Differences

Number of Teeth

• Primary Teeth: 20 total (10 in each arch, 5 in each quadrant)
• Permanent Teeth: 32 total (16 in each arch, 8 in each quadrant)

Size

• Primary teeth are smaller in all dimensions compared to permanent teeth due to smaller arches in children.

Color

• Primary Teeth: Bluish-white due to thinner dentin and no exposure to environmental factors during formation.
• Permanent Teeth: Gray or yellow-white due to thicker dentin and environmental exposure.

Crown Morphology

• Incisors: Primary incisors are wider mesio-distally, permanent incisors are taller cervico-incisally and have mamelons.
• Canines: Primary canines are thin and conical with a prominent cingulum; permanent canines are bulkier and less conical.
• Molars: Primary molars have more bulbous crowns, flat buccal and lingual surfaces, marked cervical constriction; permanent molars are less bulbous with more rounded surfaces.

Roots

• Primary Teeth: Longer, slender, more divergent, and physiologically resorb as they shed.
• Permanent Teeth: Shorter, robust, less divergent with a larger root trunk.

Histological Differences

Enamel

• Primary Teeth: Thinner (~1mm), more organic, consistent thickness, bluish-white color, neonatal lines present.
• Permanent Teeth: Thicker (2-3mm), varied thickness, more mineralized, neonatal lines only in first molars.

Dentin

• Primary Teeth: Thinner, irregular tubule arrangement, no interglobular dentin, flat dentino-enamel junction.
• Permanent Teeth: Thicker, regular S-tubules, interglobular dentin present, scalloped dentino-enamel junction.

Pulp

• Primary Teeth: Larger pulp chambers, higher pulp horns, high vascularity, and cellularity.
• Permanent Teeth: Smaller pulp chambers, lower vascularity, and cellularity.

Root Canals

• Primary Teeth: Thin, tortuous, branching, porous pulp chamber floor.
• Permanent Teeth: Well-defined, less branched, pulp chamber floor less porous.

Cementum

• Primary Teeth: Thinner primary cementum, no secondary cementum.
• Permanent Teeth: Thicker, secondary cementum present, stronger attachment to alveolar bone.

Clinical Importance

1. Treatment Planning: Identifying teeth correctly is crucial for diagnosis and treatment.
2. Dental Age Estimation: Helps estimate the age of the patient.
3. Eruption Status: Insight into the eruption stage of the child.
4. Forensic Odontology: Important for age and identity estimation in forensic cases.