Chapter 24. Dentistry
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2. Tooth Growth
a. Chemical Action of Toothpaste
1. Structure of Teeth
⑴ Chemical Composition
① Teeth have a denser crystal structure than bones and lower moisture content.
⑵ Tooth = Crown + Root
① Crown: The visible part outside the gum.
② Root: The part within the gum.
⑶ Tooth Tissues = Enamel + Dentin + Pulp
① Enamel: The outermost layer of the tooth.
○ 96% of enamel is composed of hydroxyapatite, a mineral crystal.
○ Hardest tissue in the human body, harder than bones.
○ Can withstand forces of 60 kg to 70 kg.
○ Avascular tissue. Non-living tissue.
② Dentin: The main bulk of the tooth, under the enamel.
○ 70% of dentin is composed of hydroxyapatite, a mineral crystal.
○ Dentinal tubules: Microscopic holes in dentin.
○ Function: Absorbs mechanical shocks to enamel (acts as a cushion).
○ Odontoblasts: Cells in dentin. Synthesize dentin, extend into dentinal tubules.
○ Vascular tissue. Living tissue due to odontoblasts.
○ (Note) Factors in dentin formation: OP-1 (osteogenic protein), BMP-2, BMP-4.
③ Dental Pulp
○ Mature teeth can survive without dental pulp. Reason for root canal therapy.
○ Core: Fibroblasts + GAG + collagen. Contains blood vessels and nerves. Supplies nutrients and detects stimuli.
○ Periphery: Presence of odontoblasts. Dentin formation and repair when dentin is damaged.
⑷ Gingiva (Gums): Tissues around the teeth
① Cementum: Tissue surrounding the tooth root.
○ 50% of cementum is composed of hydroxyapatite, a mineral crystal.
○ Anchors collagen fibers of the periodontal ligament to the tooth.
○ Composed of hydroxyapatite, protein, collagen.
② Alveolar Bone: Bone supporting teeth
○ Contains osteoblasts on its surface.
③ Gingiva: Pink mucous membrane beneath the crown of the tooth.
○ Protects alveolar bone.
④ Periodontal Ligament: Thin membrane connecting cementum and alveolar bone.
○ Function: Cushions impact. Implants without this ligament can’t absorb shocks.
○ Composed of fibroblasts.
○ Contains blood vessels and nerves.
○ Tension on the ligament → ligament cells differentiate into osteoblasts → alveolar bone formation.
○ Loss of function leads to alveolar bone resorption.
2. Tooth Growth
⑴ Number of Teeth = 4 × (Incisors × 2 + Canines × 1 + Premolars × 2 + Molars × 3) = 32
⑵ Timing of Tooth Eruption
Table 1. Timing of Tooth Eruption
⑶ (Note) Tooth Growth from Birth to Adulthood
① Birth: Deciduous and some permanent teeth present but not visible.
② 6 to 8 months: First tooth erupts, usually lower central incisors.
③ 2.5 years: All 20 deciduous teeth present.
④ 6 to 8 years: First permanent molars appear, followed by permanent incisors.
⑤ 10 years: Premolars and canines erupt after incisors.
⑥ 12 years: Second permanent molars appear.
⑦ 17 to 21 years: Third molars (wisdom teeth) erupt. (Origin) Eruption coincides with the time of falling in love.
3. Dental Diseases
⑴ Gingivitis (Gum Inflammation): Inflammation of gum tissue
① Cause: Plaque (bacterial colony)
○ Plaque: Bacterial mass in the oral cavity
○ Plaque bacteria survive on carbohydrates from food.
○ Plaque → Invades periodontal tissues (gingivitis) → Turns into tartar (calculus).
② Gingivitis can occur even in a healthy body. Plaque needs physical removal, not just immunity.
⑵ Dental Caries (Tooth Decay)
① 85% of the general population has it.
② Cause
○ Carbohydrates + Plaque → Acid formation
○ Acid + Tooth → Decay: Acid dissolves minerals.
○ Streptococcus mutans: Forms dextran from carbohydrates. Dextran is essential for plaque formation.
③ Stages
○ Grade 1 Dental Caries: Limited to enamel. Remove decay and fill with amalgam or gold.
○ Grade 2 Dental Caries: Reached dentin. Remove decay and fill with amalgam or gold.
○ Grade 3 Dental Caries: Reached the pulp. Root canal therapy + (if necessary) extraction.
⑶ Oral Cancer: Malignant tumor in the oral cavity and surrounding tissues
① 5% of all cancers. 7th to 8th leading cause of cancer-related deaths.
② Causes: Smoking, alcohol consumption, poor oral hygiene, syphilis virus, drugs, weakened immune function, oral mucosal irritation.
③ Treatment: Surgery, radiation therapy, chemotherapy
Input: 2019.11.29 16:40