Growth and Development Flashcards
Period of the Ovum
0-10/14 days
Fertilization to implantation
Cell division (proliferation)
Period of the Embryo
Week 2-8
Remainder of first trimester
Cell differentiation
Period of the Fetus
Weeks 8-40
2nd and 3rd trimester
Maturation of organ systems
Overall structure components of a branchial arch
Cartilage
Nerve
Blood vessels
Surrounded by mesenchyme
Merging of the two medial nasal processes gives rise to what structures?
Tip of nose Columella Philtrum Primary palate Maxillary incisor teeth
Merging of the maxillary process + medial nasal process gives rise to what?
Lateral aspect of upper lip
Cheek
Rest of maxillary teeth and secondary palate
Merging of the maxillary process + lateral nasal process gives rise to what?
Nasolacrimal duct
Overview of palate formation
Initially palatal shelves grow vertically on either side of developing tongue
Palatal shelf elevation occurs rapidly bringing the shelves into proximity
Fusion of shelves to each other and nasal septum follows
Definition of growth
Increase in size or number
Anatomical phenomenon
Definition of behavior
Increasing degree of organization, complexity and specialization
Physiological and behavioral phenomena
Hypertrophy
More cell size
Hyperplasia
More cell number
Interstitial vs appositional growth
Interstitial: occurs throughout the tissue; soft tissues and cartilage
Appositional: occurs on surface of tissue only; hard tissues
Intramembranous vs Endochondral growth
Intramembranous: secretion of bone matrix directly with connective tissues; radiating mesenchyme
Endochondral: cartilaginous precursor, replacement of cartilage with centers of ossification
Fetal skull growth
By week 8 in utero, cartilage of chondrocranium has begun to develop
By week 12, midline cartilage has begun to ossify and bones of the cranial vault, maxilla and mandible have begun to form
Mandible growth
Formed by both intramembranous and endochondral ossification
At 7 weeks, intramembranous ossification of the body of the mandible has begun lateral to Meckel’s cartilage
Condylar cartilage arises independently as a secondary cartilage, initially separated from the body of the mandible, but fuses in fetal life (endochondral)
Cephalocaudal gradient of growth
Growth is prioritized towards the skull, then proceeds towards caudal (tail) area
Scammon’s Growth Curve
Growth of different tissues (lymphoid, neural, general, genital)
Lymphoid: rapid acceleration and highest peak at age 10 then decreases
Neural: slow rise and plateaus around age 5 with everything done by 10
General: steady consistent rise
Genital: slow flat rise until about 12, which then has rapid rise
Definition of remodeling
Balance of apposition and resorption
Definition of relocation/drift
Movement of a component part of bone in response to remodeling
Definition of displacement/translation
Movement of a whole bone in response to remodeling
Cranial Vault Growth
Intramembranous ossification
Flat bones of skull
Fontanelles eventually beome sutures
Cranial Base Growth
Endochondral ossification
Frontal bone, sphenoid bone, temporal bone, occipital bone
After ossification takes place, synchondroses are leftover
Growth of maxilla
Maxilla forms through intramembranous ossification
Apposition of bone in the suture (superior and posterior) leads to displacement of the maxilla down and forward
Growth of mandible
Mixed endochondral and intramembranous ossification
Main sites of remodeling are resorption at anterior surface of ramus, apposition at posterior of ramus
Overall effect is down and forward translation/displacement
Primary Germ Layers
Ectoderm: epidermis, oral mucosa, enamel
Mesoderm: skeletal muscle
Endoderm: lining of gut
Neural crest: connective tissue cartilage, bone, dentin, cementum, pulp, PDL
Where germ layers do the structures of teeth come from?
Enamel comes from ectoderm
The rest comes from neural crest
When do primary tooth buds appear in utero?
6 weeks
Tooth buds
Primary incisor, canine, molar buds each have successional lamina for permanent successors
Permanent molar buds develop from the dental lamina that extends distally from primary second molar
Stages of tooth development - how it looks
Bud Cap Bell Dentinogenesis Amelogenesis Crown formation Root formation Eruption Root completion
Stages of tooth development - what activities happen
Initiation Proliferation Histodifferentiation Morphodifferentiation Apposition Calcification Eruption
Cap Stage
Enamel organ forms from ectoderm, surrounded by condensation of ectomesenchyme
Ectomesenchyme forms the dental sac and papilla
Dental sac will become PDL and cementum
Dental papilla will become dentin and pulp
Enamel organ differentiates into 4 layers (OEE, IEE, stellate reticulum and stratum intermedium)
-IEE becomes ameloblasts
Bell Stage
Histodifferentiation of cells of tooth germ into inner ane outer epithelium and dental papilla
Morphodifferentiation of tooth germ that takes on morphology of tooth
Apposition of tissue matrix
Formation of enamel and dentin (histodifferentiation and apposition)
Odontoblasts are signaled by preameloblasts to make predentin - beginning the first dentin at the DEJ
Preameloblasts differentiate into mature ameloblasts after dentin is formed
Enamel and dentin matrices are deposited simultaneously from incisal portion to CEJ
Root formation
Begins toward end of crown formation and does not complete until 2-3 years after eruption
OEE and IEE form Hertwig’s Epithelial Root Sheath - guides the shape and number of roots
Breakup of HRS allows cells of dental sac to contact root dentin and differentiate into cementoblasts
Eruption
Root development correlates with eruption
PDL completes as tooth erupts
Three phases of eruption
Pre-eruptive: root formation begins and tooth is moving toward surface
Eruptive (prefunctional): development of tooth root through gingival emergence
-most roots 1/2-2/3 developed upon gingival emergence
Eruptive (functional): from gingival emergence to point where tooth meets antagonist
Eruption of primary incisors
6-12 months
Eruption of primary first molars
12-16 months
Eruption of primary canines
18-20 months
Eruption of primary 2nd molars
16-30 months
General features of primary dentition
Developmental spacing Baume Type I: spacing Baume Type II: no spacing Dental arches are ovoid shaped Deep bite initially that changes to edge to edge Flat curve of Spee Flush terminal plane in most
Primate space
Distal to maxillary lateral
Distal to mandibular canine
First inter-transitional period
Period between completion of primary dentition and emergence of first permanent tooth
Early mesial shift
Deepening of bite due to attrition
Early mesial shift
Closing of interdental space between primary molars prior to eruption of first permanent molars
Affects mandibular primate space
Occurs around 4 years
Converts flush terminal plane to mesial step
First Transitional Period
6-8 years
Replacement of incisors and eruption of permanent molars
Incisor liability
Shark teeth
Incisor liability
Permanent incisors are larger than primary incisors
7.6mm in maxilla, 6mm in mandible
Interdental spacing helps compensate
Labial eruption path of permanent incisors leads to increased proclination of permanent incisors (increases arch perimeter)
Canines move distally to increase intercanine width
Second Inter-Transitional Period
8-10 years
Ugly duckling stage
From complete eruption of permanent incisors to beginning of replacement of primary canines ad molars
Spacing in maxilla, excess overjet, loss of primate space in maxilla
Second Transitional Phase
10-12 years
Replacement of primary molars and canines
Leeway space
Late mesial shift
Closure of maxillary diastema
Leeway space
Difference in MD dimension between primary canine and molars and permanent canine and premolars
Maxillary 2.2mm (Bishara), 1.8mm (Nance)
Mandibular 4.8mm (Bishara), 3.4mm (Nance)
Late mesial shift
Mesial movement of first permanent molars after exfoliation of primary molars
Arch length decreases 2-3mm
Permanent dentition stage
12 years to adult
Which dimension is last to complete growth? (vertical, transverse, anterior/posterior)
Vertical
Transverse dimension is completed before permanent dentition stage
AP dimension finishes before vertical
Does dental age generally correlate with developmental age?
No
Variation in timing of eruption
Skeletal age
More highly correlated with menarche than height, weight or growth velocity
Skeletal age staging methods
Carpal Index (Hand-Wrist Image) - seeing if epiphyses have ossified
Cervical vertebrae maturation stages - 5 stages of vertebra morphology
Prepubertal growth peak
Age 6-7
Pubertal growth peak
- 5 females
14. 5 males
AP Dimension Changes
Decreases in maxilla when first molar erupts, then increases with incisors, and decreases once premolars erupt
Decreases in mandible when first molar erupts, stays stable, then decreases
When is arch length the greatest in the mandible?
Early mixed dentition, before early mesial shift
What does distal step primary molar relationship usually go to in permanent molars?
Class II
Can go to flush
What does flush terminal plane go to in permanent molar relationship?
56% class I 44% class II
What does mesial step go to in permanent molars?
68% class I 13% class II 19% class III
Overall population permanent molar relationships
61% class I 34% class II 4% class III
Transverse dimension changes
As incisors erupt, increase in dimension and levels off with canine eruption
Intercanine width increase is not as great in the mandible as the maxilla
When is intercanine width complete?
Mandible: 9-10 years (early for girls than boys)
Maxilla: 12 years (girls), 18 years (boys)
Angle Classification
Class I: MB cusp of upper 1t molar occludes in buccal groove of lower 1st molar
Class II: lower molar distally positioned
Class III: lower molar mesially positioned
Overjet
Normal = 2-3mm
Measured from labial surface of lower incisor to incisal tip upper incisors
Division 1: flared incisors
Division 2: retroclined incisors
Components of AP direction
Angle molar class
Overjet
Incisor Angulation
AP incisor position
Components of Vertical Dimension
Overbite
Incisor display
Curve of Spee
Occlusal Cant
Overbite
Normal is 1-2mm or 20-30%
Components of Transverse Dimension
Midlines Posterior crossbites Arch width Arch symmetry Curve of Wilson
Prediction of Alignment
Crowding and arch length deficiency Missing teeth Supernumerary teeth Impacted, transposed, ankylosed teeth Diastema
Bolton Analysis
Tooth size discrepancy
Ideal sizes of maxillary and mandibular teeth ratio
Only done in permanent dentition (not mixed)
Mixed dentition analysis
Compares space available as measured in permanent dentition to space required as measured in erupted permanent incisors or unerupted permanent canines and premolars
Direct measurement of mixed dentition analysis
Measure unerupted teeth on radiographs
Account for magnification errors
Compare space required with space available
Tanaka and Johnston
Mandibular incisors must be erupted
Predicts unerupted permanent canines and premolars
1/2 the MD width of four lower incisors + 10.5mm = estimated width of mandibular canine and premolars of one quadrant
1/2 the MD width of four lower incisors + 11.0mm = estimated width of maxillary canine and premolars in one quadrant
Moyers analysis
Uses prediction values for unerupted canine and premolars for one quadrant based on width of mandibular incisors
Most commonly used
Tooth Size Discrepancy
5% of population have some degree of tooth size discrepancy
Most common teeth are upper lateral incisors and 2nd premolars
Purpose of cephalometric analysis
Compare patient to normal reference group
Diagnose skeletal discrepancy
Steiner analysis
First modern cephalometric analysis
Displayed measurements in a way that emphasized not just individual measurements but patterns
Offered specific guides for use of cephs
Most widely used analysis today
SNA
Sella Turcica - Nasion - A point
Normal is 82 degrees
Relates cranial base to maxilla
Greater = prognathic maxilla Lesser = retrognathic maxilla
SNB
Sella Turcica - Nasion - B point
Normal is 80 degrees
Relates cranial base to mandible
Greater = prognathic mandible Lesser = retrognathic mandible
ANB
A point - Nasion - B point
Normal is 2 degrees
Relates maxilla to mandible
Greater = class II skeletal Lower = class III skeletal
Does not specify which jaw is at fault
Relationship of upper incisor to NA line
Normal is 4mm and 22 degrees
Greater = proclined and protrusive Lesser = retroclined and reclusive
Relationship of lower incisor to NB line
Normal is 4mm and 25 degrees
Interincisal angle
Normal is 131 degrees
Smaller = acute angle, proclined
Doesn’t tell which incisor is at fault
Mandibular plane to Sella-Nasion plane
GoGn - SN angle
Normal is 32 degrees
Greater = steep mandibular plane angle (dolichofacial) Lower = shallow mandibular plane angle (brachyfacial)
Occlusal plane to SN
Norm = 14 degrees
Greater = dolichofacial
Management of Skeletal Problems
Skeletal solutions for skeletal problems
Dental solutions for skeletal problems = camoflauge
Growth modification and surgery
Growth Centers and Growth Sites
Growth Center: area considered to be under genetic control that exhibit tissue-separating capabilities
Growth Site: area where active skeletal growth occurs in a secondary, compensatory manner
All growth centers are growth sites, but not all growth sites are growth centers
Nasal Septum Theory (1950s)
Proposed by Scott
Cartilage is primary target of genetic activity
Cranial base, nasal septum, mandibular condyles drive growth (growth centers)
Pretty accurate, but difficultt o modify these growth centers
Functional Matrix Hypothesis (1960s)
Proposed by Moss
Main idea = form follows function
Soft tissues are primary targets of genetic activity
Skeletal structures grow in response to their extrinsic environment (bone is growth site, soft tissue is growth center)
Functional cranial components - cranial bones respond to growth of brain
Not considered 100% accurate, but some elements are true as a lot of skeletal growth is driven by soft tissues
Servosystem Theory (1970s)
Proposed by Petrovic
Nasal septum and cranial base are primary targets of genetic activity
Condylar growth is secondary
Midface growth is driven by sutures
Occlusal deviation leads to mandibular growth
Mandibular growth proprioception sends back information
Modification of growth at anatomical sites
Periosteal tissues: difficult to modify
Sutures: susceptible to pressure and tension (easiest to modify)
Cartilage (difficult to modify)
Synchondroses: questionable susceptibility to pressure and tension
Transverse growth modification of maxilla
Create tension at midpalatal suture
RPE: Hyrax (more force), Haas (acrylic; hygiene not good)
Quad helix: springs, less force
W arch: stronger than quad helix, but not as much as RPE
Schwartz: removable; takes longer
AP growth modification of maxilla
Create tension at circum-maxillar sutures
Face mask (reverse pull headgear): used for early class III - tries to pull maxilla forward via fixed appliance in maxilla and pad on forehead and chin
AP restriction modification of maxilla
Create pressure at circum-maxillary sutures
Parietal pull headgear (up and back): used for dolichofacial
Cervical pull headgear (down and back): used for brachyfacial
Occipital headgear: normocephalic
AP growth modification of mandible
Modify function of mandible
Difficult to achieve much growth, produces teeth movements
Should be done right before puberty
AP growth of mandible appliances
Bionator: removable appliance, makes it uncomfortable to bite unless mandible is forward
Twin block: removable appliance, inclined plane to force mandible forward
Herbst: fixed appliance, pin and tube apparatus pulls mandible forward (can be removable)
Mandibular Anterior Repositioning Appliance (MARA): one element on maxilla, one on mandible similar to Herbst
AP growth restriction of mandible
Restrain growth in condylar cartilage at periosteum
Chin cup: not a ton of success, requires a lot of compliance
Timing of growth modification
RPE and Facemasks should be done in childhood, before pre-pubertal minimum
Functional appliances are done at pubertal maximum (preteen)
Management of over-retained teeth
Problems = gingival inflammation, deflected eruption
Solutions = self-exofliation if mobile, extraction if not
Management of ectopic lateral incisors
Problems = premature loss of primary canine (indication for space analysis)
Solutions = lingual arch with or without spur to prevent midline shift and prevent lingual tipping
Management of ectopic maxillary first molars
Problems = blockage of eruption
Solutions = active survillance or intervention
2/3 self-correct
Observe for 6 months, and if no change, intervention necessary
Intervention for ectopic maxillary first molars
Halterman (fixed appliance)
Brass wire
Ortho separator
Arkansas separator
Management of ectopic maxillary canines
Problems = retention of primary canines, impaction
Solutions = extraction of primary canines, maxillary expansion
Often associated with small lateral incisors
If canine is behind midline of maxillary incisor (sector I or II), 91% self-correct
If past the midline of lateral, 64% self-correct (sector III)
Management of ankylosed teeth
Problems = effect on eruption of permanent successor, mesial tipping of distal tooth, supraeruption of opposing tooth, vertical bone defect
Solutions = buildup with composite, anesthetize and subluxate
If no successor, treatment could be extract and allow mesial drift, or decoronation and maintenance of bone
Factors associated with prolonged sucking habits
Older maternal age
Higher maternal education level
No older siblings
How many children have oral habit in first year of life?
> 90%
Outcomes of prolonged NNSH
Anterior open bite
Posterior crossbite
Excess overjet
What type of NNSH is more common in posterior crossbite?
Pacifier habit
What type of NNSH is more common for excess overjet?
Digit sucking
Timing of intervention for NNSH
Intervene before eruptio nof permanent teeth (start 3-4 years)
Options for intervention for NNSH
Psychosocial health Counseling Reminder therapy Reward system Adjunctive therapy (tongue crib, quad helix, etc.)
Tongue thrust
Outcome: Anterior open bite
Treatment: tongue crib, myofunctional therapy
Mouth breathing
Outcome: longer lower face, maxillary constriction, adenoid facies
Normal for 3-6 year olds to be lip incompetent
Treat with T&A if from airway obstruction
Nail biting
Rare in children under 3
Suggested as manifestation of stress
Impact: no evidence of impact on occlusion, possible enamel fractures
No treatment recommended
Bruxism
Impact: wear of primary canines and molars 9rare effect on pulp), muscle soreness, TMJ pain
Causes: stress, localized causes, medical causes
Treatment: equilibrium of occlusal interferences, rule out systemic problems, mouthguard, stainless steel crowns as needed, therapy
Etiology of Premature Tooth Loss
Caries Trauma Ectopic eruption Congenital disorders Arch length deficiencies resulting in resorption
Early loss of primary incisors
Usually due to caries or trauma
Minimal loss of arch length
<2 years, possible space loss
Minimal impact on masticatory function
Possible impact on speech (lingual-dental sounds like s, z, th)
Early loss of canines
Usually due to arch length deficiencies
No detectable relationship with posterior alignment
Accompanied by lateral shift of incisors and midline shift
Early loss of primary first molars
Usually due to caries
Canine and incisor dislocation toward extraction site
Mesial movement of second molar
No statistically significant loss of arch width, length and perimeter in primary dentition
-less space loss after eruption of permanent molars
Early loss of second primary molars
Usually due to caries, sometimes due to ectopic eruption of permanent first molar
Arch length reduction
When does the greatest space loss occur after loss of tooth?
First 4-8 months after extraction
Impact of early tooth loss on occlusion
Mandibular effects worse than maxillary
Second primary molar effects worse than first
Earlier tooth loss worse than later
Tooth loss in crowded arch worse than in spaced
Summary of early tooth loss
Premature loss of primary teeth correlates with increasing likelihood of ortho treatment
Premature loss of primary incisors and canine does NOT affect posterior occlusion
Premature loss of primary canines MAY affect anterior alignment
Premature loss of primary molars MAY affect posterior occlusion
Treatment options for crowding
Mild: 0-4mm; maintain space available
Moderate: 4-8mm; increase space available
Severe: >8mm; decrease space required
Serial Extraction
Planned sequence of tooth removal to reduce crowding and irregularity during transition from the primary to permanent dentition
Extraction of primary canines, primary first molars, first premolars
Allows permanent teeth to erupt through keratinized tissue rather than displaced buccal or lingual
Key concepts of space management
In mixed dentition, space available is measured the same way as in permanent dentition
In mixed dentition, space required must be estimated to predict the size of unerupted teeth
The serial extraction protocol is initiated in the mixed dentition
