ERUPTION OF TEETH Tooth eruption is defined as the physiological movement of tooth from its site of development within the jaw to its position of function within the oral cavity.

Eruption of mandibular incisor 5 months At birth 1 year 2 years 3.5 years 4.5 years Figure Source: Dr. Sandra Meyers

Mixed dentition

Dentition: Diphodont: two sets of dentition in humans Primary vs Secondary dentition Deciduous vs Permanent dentition Mixed dentition: presence of two dentition Teeth in primary dentition are smaller and fewer in number than permanent dentition to conform to the smaller jaw size Primary dentition: ~ 2 to 6 years of age Mixed dentition: ~ 6 to 12 years Permanent dentition: > 12 years

Source: http://www.columbia.edu/itc/hs/dental/d9903/lectures/lecture4.pdf

Mixed Dentition Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6th edition

Mixed Dentition: Presence of both dentitions Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6th edition

The rate of tooth eruption depends on the phase of movement Intraosseous phase: 1 to 10 µm/day Extraosseous phase: 75 μm/day Environmental factors affecting the final position of the tooth: Muscular forces Thumb-sucking

Directions and rates of tooth eruption Main direction is axial (i.e. long axis of the tooth) Also movement in other planes – resulting in tilting and drifting Eruption rates are greatest during times of crown emergence Rates will differ based on tooth type – balance between eruptive forces and resistive forces permanent maxillar y incisors – 1mm/month mandibular second molars – 4.5 mm in 14 weeks permanent third molars – 1 mm in 3 months eruption rates can slow to 1 mm/6 months in crowded dentitions

Clinical crown: Anatomic crown: During eruption, the exposed crown extending from the cusp tip to the area of the gingival attachment Anatomic crown: Entire crown, extending from cusp tip to the cementoenamel (CE) junction

Eruption Active eruption :Is the movement of the tooth from its development site to its position in the dental arch. Passive eruption does not involve tooth movement but occurs due to apical recession of gingival tissues exposing more tooth structure into the oral cavity.

PASSIVE ERUPTION Gingival recession onto & down the cementum with loss of alveolar-crest bone Raising the banana, then peeling the banana

Tooth eruption Eruption takes place in chronological order involves active eruption – vertical movement of the tooth as opposed to passive eruption – recession of the gingiva. root growth, hormonal action, contractile collagen, vascular pressure?? no requirement for the root Three distinct phases to the development of the dentition 1. pre-eruptive – initiation of tooth development 2. tooth eruption – prefunctional phase begins as the roots begin to form 3.Posteruptive: development and maintenance of occlusion – functional phase after the teeth have emerged into the oral cavity

END OF CROWN FORMATION Ameloblasts will finish full thickness of cusp enamel & reduce in height Dentine widens DENTAL PAPILLA become pulp process proceeds downs Stellate reticulum follows Cervical loop down then stops: Crown defined Odontoblast recruitment site Cervical loop:

Types of movements of tooth during three phases of eruption 1.Axial or occlusal 2.Bodily 3.Tilting 4.Rotation Excentric

covering the recently formed crown Eruptive phase starts at the beginning of root formation Note the reduced enamel epithelium covering the recently formed crown Essentials of Oral Histology and Embryology. James Avery, 2nd edition

Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6th edition

Eruption of mandibular incisor 5 months At birth 1 year 2 years 3.5 years 4.5 years Figure Source: Dr. Sandra Meyers

Eruption: tooth in bony crypt

Eruption phase

Eruption phase

Post eruption phase

The cervical portion of the reduced enamel epithelium is still attached to the neck of the tooth . -this fused tissue serves as the initial junctional epithelium (thin dotted line) and creates a seal between the tooth and the surrounding tissue

Histological phases of eruption: 1) Pre-eruptive phase: It starts at the beginning of tooth development and ends when the crown formation is completed. It is characterized by: a) Growth of tooth germ i.e. dental (enamel) organ, dental papilla and dental sac. b) Formation of bony crypt. c) Movement of developing tooth within the growing jaw. Different types of movement occurs: bodily, axial, rotational and eccentric( i.e. shifting the long axis of the developing tooth).

2)Prefunctional ( Eruptive) phase: It starts at the beginning of root formation and ends when the tooth reaches occlusion. It is characterized by: a) Formation of the root. b) Bone apposition especially at the fundus of the crypt. c) Initial organization of periodontal ligament. d) Rapid active eruption

3) Functional ( Posteruptive ) phase: It starts when the erupting tooth reaches occlusion with its antagonists and lasts throughout the life of the tooth. It is characterized by: a) Occlusal active eruption (more cementum and alveolar bone apposition). b) Occlusomesial physiological drift . c) alveolar bone remodeling. d) Organization of periodontal ligament principal fibers.

Two types of tooth movement in pre-eruptive phase: Total bodily movement Movement where one part remains fixed while the rest continues to grow leading to change in the center of the tooth germ

Eruptive Tooth Movement 4 major events occur: Root formation. Space is required for root formation Proliferation of epithelial root sheath Initiation of root dentin and pulp Increase in fibrous tissue of the follicle Movement. Occurs incisally or occlusally The main reason for movement is so that the roots can form normally Reduced enamel epithelium fuses and contacts the oral epithelium Penetration of the tooth’s crown tip through the fused epithelial layers allowing entrance of the crown into the oral cavity Intraoral incisal or occlusal movement of the erupting tooth continues until clinical contact with the opposing crown occurs

Post Eruptive Tooth Movement Movements to accommodate the growing jaws. Mostly occurs between 14 and 18 years by formation of new bone at the alveolar crest and base of socket to keep pace wit increasing height of jaws. Movements to compensate for continued occlusal wear. Compensation primarily occurs by continuous deposition of cementum around the apex of the tooth. However, this deposition occurs only after tooth moves. Similar to eruptive tooth movement. Movements to accommodate interproximal wear. Compensated by mesial or a proximal drift. Mesial drift is the lateral bodily movement of teeth on both sides of the mouth. Very important in orthodontics.

Why hemorrhage does not occurs during eruption Degeneration of connective tissue (decrease in blood vessels and degeneration of nerves) immediately overlying the erupting teeth Eruption pathway – altered tissue area overlying the teeth Macrophages destroy cells and fibers by secreting hydrolytic enzymes

Essentials of Oral Histology and Embryology. James Avery, 2nd edition

Mechanism(Theories )of tooth eruption 1.Bone remodeling 2.Root formation theory 3.Vascular hydrostatic pressure 4.PDL traction 5.Dental follicle Multifactorial process but the most important factor is the PDL traction

MECHANISMS OF ERUPTION Construction & Reorganization of PDL Formation of the root Deposition of alveolar bone? Remodelling of bone overall FURTHER INFLUENCES from: tooth/teeth in occlusion; muscle actions

Mechanism of eruption: Theories 1- Root growth ( increase in root length ): Root growth seems to generate a force but it does not cause eruptive tooth movement. Evidence against this theory is that teeth without roots erupt, also some human teeth during eruption move a greater distance than the length of their fully formed roots. Further, teeth continue to erupt after root formation is completed and when root forming tissues were surgically removed in experimental animals, those teeth continued to erupt.

2- Hydrostatic pressure from tissue fluid and blood vessels in periapical tissues: Experimental evidence indicates that tissue pressure occlusal to an erupting tooth is less than that in the tissues apical to it. This pressure differential seems to favor axial eruptive movements.

3. Bone remodeling theory Experimental studies using bone markers clearly showed that bone apposition at the bottom of the bony crypt housing an erupting tooth is a result of the occlusal movement of the tooth not a cause for eruption.

PDL traction theory Linked to contractility of fibroblasts Tractional forces are associated with pulling properties of fibroblasts The tractional force of fibroblast is mediated through collagen fibers of the PDL Explained as a sailor pulling a rope Sail=tooth PDL collagen fiber= a rope Sailor=fibroblast

A sailor pulling a sail Sailor =Fibroblast Sail = Erupting tooth Rope = Collagen fibers

Dental follicle This theory suggests that the dental follicle has an important participation in tooth eruption.

Eruption of permanent teeth Same as the primary teeth Additional force generated by fibrous tissue containing remnants of the dental lamina, known as gubernacular cord The gubernacular cord is the connective tissue link between the crypt and the oral mucous membrane. Gubernacular cord provides a specific promoting role or a guiding path for eruption of the permanent teeth

Eruption of secondary tooth Loss of primary teeth should occur first Gubernacular cord: The connective tissue overlying a successional tooth that connects with the lamina propria of the oral mucosa by means of a strand of fibrous connective tissue that contains remnants of dental lamina Gubernacular canal: Holes noted in a dry skull noted lingual to primary teeth in jaws that represent openings of gubernacular cord . As the successional teeth erupt, gubernacular canal Widens enabling tooth to erupt .

Essentials of Oral Histology and Embryology. James Avery, 2nd edition Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6th edition

Essentials of Oral Histology and Embryology. James Avery, 2nd edition

Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6th edition

ERUPTION: Problems Delayed eruption Early eruption Missing tooth Impaction - failure to erupt e.g., from too little gap after premature loss of deciduous tooth Retained root fragment Malocclusion Infra-occlusion (not high enough) Excessive drift Tilting (can occur early from germ rotation)

Problems of Premature Tooth Eruption Natal and Neonatal Teeth

Congenitally Missing Teeth