Craniofacial Growth, Developing Dentition and Occlusion Flashcards
Period of the ovum
- Day 0 to 10-14
- Fertilization to implantation
- Cell division (proliferation)
Period of the embryo
- Week 2 to 8
- Remainder of 1st trimester
- Cell differentiation
Period of the fetus
- Week 8 to 40
- 2nd and 3rd trimester
- Maturation of organ systems
Branchial arch structure
Cartilage, a nerve, and blood vessels surrounded by mesenchyme
Palate formation
- Initially palatal shelves grow vertically on either side of the developing tongue
- Palatal shelf elevation occurs rapidly bringing the shelves into proximity
- Fusion of the shelves to each other and to the nasal septum follows
Definition of growth
- an increase in size or number
- anatomical phenomenon
Definition of development
- an increasing degree of organization, complexity, and specialization
- physiological and behavioral phenomenon
Hypertrophy
Increase in size
Hyperplasia
Increase in number
Interstitial growth
- Occurs throughout the tissue
- Soft tissues
- Uncalcified cartilage
Appositional growth
- Occurs only on the surface of the tissue
- Hard tissues
- Calcified tissues
Growth of cartilage
- Grows by appositional and interstitial growth
- Appositional growth: new cartilage is added to the surface of the cartilage by chondroblasts from the inner layer of the perichondrium
- Interstitial growth: new cartilage is formed within the cartilage by chondrocytes that divide and produce additional matrix
Intramembranous
- No structural precursor
- Secretion of bone matrix directly within connective tissues
- Cranial vault, maxilla, mandible
Appositional
- Cartilaginous precursor
- Replacement of cartilage with centers of ossification
- Axial and appendicular skeleton, cranial base
AKA endochondral ossification? Needing a cartilage precursor
Condylar cartilage
- Arises independently as secondary cartilage
- Initially separated from the body of the mandible, but eventually fuses in fetal life
- Both endochondral and intramembranous ossification contribute to the origin of the mandible **
Craniofacial complex
1) Cranial vault
2) Cranial base
3) Nasomaxillary
4) Mandible
Differential growth patterns
- Neural is the majority at first, then plateaus
- Lymphoid tissue increases then decreases
- Mandible follows the general curve
Cranial vault
- Intramembranous, no interstitial growth
- Anterior fontanelle, mastoid fontanelle, sphenoid fontanelle, posterior fontanelle
Cranial base
- Endochondral growh
- Frontal bone, sphenoid bone, temporal bone, occipital bone
Maxilla
- Intramembranous
- Sutures connects the maxilla to the rest of the cranium
- Apposition occurs upward and backward, however, it results in downward and forward net effect.
Maxillary growth
- Apposition of the bone at the sutures –> displaces maxilla downward and forward
- Apposition of bone at the maxillary tuberosity –> increases arch depth
- Resorption at anterior surface of maxilla –> maintains position of anterior surface
Mandible
Mix of both intramembranous and endochondral
Mandibular growth
- Endochondral growth at the condyle –> displaces mandible downward and forward
- Apposition at posterior border, resorption at anterior border of ramus –> relocates ramus posteriorly, displaces mandible downward and forward
Primary germ layers
- Ectoderm –> Epidermis (skin), oral mucosa, enamel
- Mesoderm –> Skeletal muscle
- Endoderm –> Lining of the gut (pharynx)
- Neural crest –> Connective tissue proper, cartilage, bone, dentin, cementum, pulp, PDL
___ is from the ectoderm, while the rest of the dental tissues comes from the ____
Enamel; neural crest
Stages of tooth development
A) Bud B) Cap C) Bell D) Dentinogenesis E) Amelogenesis F) Crown formation G) Root formation and eruption H) Root completion
Root formation timeline
Root formation begins BEFORE eruption, but finishes 2-3 years AFTER
Life cycle of the tooth
1) Growth
- Initiation
- Proliferation
- Histodifferentiation
- Morphodifferentiation
- Apposition
2) Calcification
3) Eruption
4) Attrition
Stage of tooth development: Initiation
Initial formation of the bud
Stage of tooth development: Proliferation
Proliferation of the cells of the bud to proceed through the cap stage
Stage of tooth development: Histodifferentiation
Differentiation of the cells of the tooth germ into inner and outer epithelium and dental papilla (bell)
Stage of tooth development: Morphodifferentiation
Tooth germ begins to take on the morphology of the tooth (advanced bell)
Stage of tooth development: Apposition
Tissue matrix is deposited
Tooth germ composition
- Enamel organ –> from the ectoderm, surrounded by ectomesenchyme forming the dental sac and papilla
- Dental papilla
- Dental sac
Dental papilla becomes?
Dentin and pulp
Dental sac becomes?
PDL and cementum
Enamel organ
- Differentiates into 4 layers: outer enamel epithelium (OEE), inner enamel epithelium (IEE), stellate reticulum, stratum intermedium
- IEE becomes ameloblasts that produce enamel
- Stellate reticulum and stratum intermedium are the supporting structures for the IEE
Histodifferentiation and apposition
- Odontoblasts are signaled by preameloblasts to make predentin – beginning the first dentin at the DEJ
- Preameloblasts differentiate into mature ameloblasts when stimulated by dentin laid down by odontoblasts
Basement membrane or basal lamina
- Microscopic interface between epithelial and mesenchymal tissues
- Product of both tissues
- Mediator of molecular signaling that controls differentiation
- Becomes the dentino-enamel junction
Root formation
- Begins towards the end of crown formation, and will not complete until 2-3 years after tooth eruption
- Outer enamel epithelium + inner enamel epithelium = Hertwig’s epithelial root sheath –> function is to GUIDE the SHAPE and NUMBER of roots
Cementogenesis
- Breakup of hertwig’s epithelial root sheath allows cells of dental sac to contact root dentin and differentiate into cementoblasts.
- These cells produce cemented which mineralizes to form cementum.
- The root sheath thus directs the cementoblasts where to go.
PDL and tooth eruption
- Root formation is not complete until 2-3 years after eruption
- Cementum of the root is connected to the alveolar bone via connective fibers called the Periodontal Ligament (PDL)
- As the tooth erupts –> more and more PDL will form
Three phases of tooth eruption
1) Preeruptive –> root formation begins and tooth is moving toward bony surface
2) Eruptive (prefunctional) –> development of tooth root through gingival emergence; most roots are 1/2 to 2/3 developed upon gingival emergence
3) Eruptive (functional) –> From gingival emergence to the point where the tooth meets its antagonist
Developmental events of dentition
- Primary dentition stage (6 months to 6 years) –> first inter-transitional period
- Mixed dentition stage (6 to 12 years)
- First transitional period
- Second inter-transitional period –> ugly ducking stage
- Second transitional period
- Permanent dentition stage (12 years to adult)
Eruption of primary teeth
Maxillary:
Central (10 mo) –> Lateral (11 mo) –> First molar (16 mo) –> Canine (19 mo) –> Second molar (29 mo)
Mandibular:
Central (8 mo) –> Lateral (13 mo) –> First molar (16 mo) –> Canine (20 mo) –> Second molar (27 mo)
General features of the primary dentition
- Developmental spacing
- Flush terminal plane molar relationship
- Dental arches ovoid in shape
- Deep bite present initially that changes to edge-to-edge
- Flat curve of spee
Developmental spacing
- Maxillary spacing – 70% of children
- Mandibular spacing - 63% of children
- *Primary dentition without spacing will be followed by crowding of the permanent dentition in 40% of children
- Baume type 1: spacing
- Baume type 2: no spacing
Primate space
Maxillary: between lateral incisors and canine
Mandibule: between canine and first primary molar
Primary molar relationship
Flush terminal plane –> 76% of children (distal of maxillary primary second molar flush with distal of mandibular primary second molar)
Mesial step –> 14% of children
Distal step –> 10% of children
Early mesial shift
- Closing of interdental space between primary molars prior to eruption of first permanent molars
- Affects mandibular primate space
- Convert flush terminal plane to mesial step
- Approximately age 4
First inter-transitional period (primary dentition)
- The period between the completion of the primary dentition and the emergence of the first permanent tooth
- Vertical skeletal growth
- Deepening of the bite due to attrition of the primary incisors
Orthodontic implications of first inter-transitional period (primary dentition)
- Close/non-spaced dentitions have increased risk of crowding
- Distal step molar relationship should be evaluated for class II malocclusion
- Mesial step molar relationship should be monitored for the development of class III malocclusion
- Closed/non-spaced dentitions have a decreased probability of converting to class I molar relationship if initially distal step or flush terminal plane
Eruption sequence of permanent dentition
Maxillary: First molar (6-7 years) –> central (7-8 years) –> lateral (8-9 years) –> first premolar (10-11 years) –> second premolar (10-12 years) –> canine (11-12 years) –> second molar (12-13 years)
Mandibular: First molar (6-7 years) –> central (6-7 years) –> lateral (7-8 years) –> canine (9-10 years) –> first premolar (10-12 years) –> second premolar (11-12 years) –> second molar (11-13 years)
First transitional period (mixed dentition)
- From ages 6-8 years
- Eruption of first permanent molars
- Replacement of incisors
Incisor liability
- Permanent incisors are larger than primary incisors
- 7.6 mm in maxilla
- 6 mm in mandible
Compensation for incisor liability
- Interdental spacing in primary dentition –> maxillary primate space
- Labial eruption of permanent incisors –> Increased proclination of permanent incisors
- Increased intercanine width –> 4mm in maxilla, 2-3mm in mandible
Orthodontic implications of first transitional period (mixed dentition)
- “Shark teeth”
- Lingually erupting mandibular incisors –> 10-20% prevalence
- Closed primary dentition
Second inter-transitional period (mixed dentition)
- From age 8 to 9 or 10 years
- From the complete eruption of incisors until the beginning of replacement of primary canines and molars
- Maxillary arch –> 1) “ugly duckling” stage, 2) diastema, 3) loss of primate space, 4) excess overjet
- Mandibular arch –> 1) transitional crowding, 2) loss of primate space
- Vertical skeletal growth
- Bone remodeling in maxillary tuberosity and mandibular ramus
- Development of maxillary canines
Orthodontic implications of second inter-transitional period (mixed dentition)
- Mild mandibular crowding (<2mm) can resolve spontaneously
- Maxillary diastema has a high likelihood of resolving spontaneously –> wait until maxillary canines erupt to reassess
Second transitional phase (mixed dentition)
- Occurs between 10-12 years of age
- Replacement of primary canines and molars
- Leeway space
- Late mesial shift
- Closure of maxillary diastema
Leeway Space
Difference in the mesiodistal dimension between primary canine and molars and permanent canines and premolars
Average values for leeway space
Maxillary leeway space
- 2.2 mm (Bishara)
- 1.8 mm (Nance)
Mandibular leeway space
- 4.8 mm (Bishara)
- 3.4 mm (Nance)
Late mesial shift
** Late mesial shift = Leeway space
- Mesial movement of first permanent molars after exfoliation of the primary molars
- Closure of the leeway space
Late mesial shift and arch length
Maxilla: arch length greatest in mixed dentition (8-10 years), then decreases
Mandible: arch length greatest before early mesial shift (age 4 then continues to drop off
**Arch length decreases 2-3 mm
Closure of maxillary diastema
Arch length greatest before early mesial shift (age 4) then continues to drop off
Orthodontic implications of second transitional phase (mixed dentition)
- Leeway space may be used to address incisor liability
- Late mesial shift can help transition to a class I molar relationship from end on
- Maxillary diastema should be reassessed once permanent canines have erupted
- Moderate to severely crowded mixed dentition cases will have a lower likelihood of transitioning from class I molar relationship from class II
Permanent dentition
- From age 12 to adulthood
- Onset of adolescent growth spurt
- Finalization of molar relationship
Transverse dimension and adolescent growth spurt
Completed prior to growth spurt
Vertical dimension and adolescent growth spurt
Continues beyond growth spurt
Anterior-posterior dimension and adolescent growth spurt
Continues throughout growth spurt
Adolescent growth spurt additional changes
- Profile changes occur as changes in specific locations take place
- Frontal bone, brow, nose, and chin becomes more prominent
- Continued lowering of the palatal vault
- Vertical maxillary growth is often greater in females
Context of adolescent growth spurt
Modifying growth of the craniofacial structures might help to address malocclusion of skeletal origin
Implications of growth spurt
- Skeletal malocclusion
- Timing of growth modification
- Timing of surgery
- Dental interventions
- Timing of implant placement
Mandible and growth spurt
- Mandible demonstrates a pubertal growth peak
- Allows for additional change in molar relationship
Distal step can develop into
- Class II
- End to End
Flush terminal plane can develop into
- Class I
- End to end
Mesial step can develop into
- Class I
- Class III