ILA Flashcards
What has been affected for a cleft lip / palate to develop?
CLP occurs when the normal fusion processes of the facial prominences or palatal shelves fail. A cleft results from failure of fusion:
- Cleft lip: failure of fusion between the medial nasal and maxillary processes (around 4~6 weeks gestation).
- Cleft palate: failure of the palatal shelves (outgrowths of the maxillary processes) to elevate, grow, or fuse at the midline (around 6~12 weeks gestation)
What is the normal timing of development of lip and palate?
lip: 4~7 weeks of embryonic life
primary palate: 6 weeks
secondary palate: 7~12 weeks
What genes are involved in directing / controlling the development of the orofacial complex?
Hox Genes (homeobox genes): these transcription factors establish rostro-caudal patterning but are notably absent in the first branchial arch, which forms most of the face. They indirectly influence orofacial development by patterning adjacent cranial structures.
What other structures that are derived from the same embryological processes are commonly be affected and in turn have medical or functional implications (teeth and other derivatives of thebrai branchial arches)
The first and second pharyngeal (branchial) arches give rise to several craniofacial and oral structures:
- Dental anomalies: hypodontia, supernumerary teeth, malformation, displaced teeth
- Eustachian tube, middle ear defects: hearing problems due to ossicle malformation (from first and second arches
- Muscles of mastication, facial expression: functional issues (e.g., feeding, speech)
- Jaw and facial bones: may show asymmetry or underdevelopment
- Facial nerve and muscle abnormalities (e.g., in hemifacial microsomia)
These structures can have medical and functional implications such as speech delay, dental malocclusion, and recurrent ear infections.
What are the things needed to answer for: “What is the normal process of development of the lip and palate and related orofacial region?”
- What has been affected for a cleft lip / palate to develop?
- What is the normal timing of development of lip and palate?
- What genes are involved in directing the development of the orofacial complex?
- What other structures are derived from the same embryological processes are commonly be affected and in turn have medical or functional implications (teeth and other derivatives of the branchial arches)?
What factors, genetic and environmental influence / alter the normal process of development of the orofacial complex?
- What are the types of CLP?
- How do the various aetiological factors cause the cleft? What goes wrong in the tissues for a cleft to develop?
- How do these various factors influence development of the orofacial compelx?
What are the different types of CL? And their incidence, prevalence
Cleft Lip (CL)
Unilateral: One side of the lip is affected
Bilateral: Both sides are affected
Complete: Extends into the nostril
Incomplete: Does not reach the nostril
Cleft lip with or without cleft palate (CL ± P): ~ 1 in 1,000 live births => More common in males
What are the different types of CP? And their incidence, prevalence
Cleft Palate (CP)
Soft palate only
Hard and soft palate
Submucous cleft palate: Palate appears intact but has a muscular defect beneath the mucosa
Cleft palate only (CP): ~ 1 in 2,000 live births => More common in females
What are the different types of CLP? And their incidence, prevalence
Cleft Lip and Palate (CLP)
A combination of cleft lip and cleft palate, may be:
- Unilateral or bilateral
- Complete or incomplete
How do the various aetiological factors cause the cleft? What goes wrong in the tissues for a cleft to develop?
- Genetic mutations in developmental genes like IRF6, MSX1, PAX9, TGF-β3, FGFR1, SHH, and TBX22 disrupt cellular communication, migration, or differentiation, preventing proper epithelial seam breakdown or alignment between facial prominences, leading to persistent clefts.
- Environmental teratogens such as maternal smoking, alcohol, certain medications (e.g., anticonvulsants, retinoic acid), and folic acid deficiency interfere with molecular pathways or induce apoptosis in developing facial tissues, impairing lip or palate fusion.
- Mechanical obstructions, such as macroglossia, mandibular hypoplasia, or amniotic bands, physically prevent palatal shelves from elevating or meeting at the midline, resulting in a cleft palate despite normal shelf growth.
- Clefts associated with syndromes like Pierre Robin Sequence, Van der Woude Syndrome, or Treacher Collins Syndrome arise from specific genetic disruptions (e.g., IRF6 mutations or first arch developmental failures), manifesting as part of broader craniofacial abnormalities.
How do these various factors influence development of the orofacial complex? eg, do they alter proliferation and /or differentiation of tissues by altering expression of growth/differentiation factors or can a physical obstruction interfere with growth of tissues?
Genetic Mutations: Mutations in genes like IRF6, TP63, PAX9, TGF-β, BMP, and SHH disrupt expression of growth/differentiation factors, impairing mesenchymal proliferation, epithelial differentiation, and neural crest cell migration, preventing facial prominence or palatal shelf fusion.
Environmental Teratogens: Maternal smoking, alcohol, folate deficiency, or drugs (e.g., phenytoin) inhibit DNA synthesis, increase oxidative stress, or alter signaling (e.g., SHH, TGF-β), reducing tissue growth and ECM remodeling critical for fusion.
Mechanical Obstructions: Abnormal tongue positioning (e.g., Pierre Robin sequence) or amniotic bands physically block palatal shelf elevation or prominence alignment, halting epithelial seam breakdown and mesenchymal consolidation.
Multifactorial Synergy: Genetic predispositions (e.g., IRF6 variants) lower developmental thresholds, amplifying susceptibility to environmental or mechanical disruptions, exacerbating tissue fusion failures.
Proliferation Disruption: Altered growth factor expression (e.g., TGF-β, BMP) reduces mesenchymal cell proliferation, leading to insufficient tissue for lip or palate formation.
Differentiation Impairment: Defective epithelial differentiation (e.g., via TP63 mutations) prevents proper tissue fusion, maintaining epithelial seams and causing clefts.
Migration Defects: Disrupted neural crest cell migration (e.g., via SHH dysregulation) limits mesenchymal contributions to facial prominences, hindering orofacial development.
What are the normal processes for swallowing (muscles and movements) and speech (muscles and movements) in baby/child/adult with an intact lip/palate? How are these processes altered if there is a cleft of lip or palate?
- What are the normal processes/mechanisms (muscles and movements) for feeding/suckling in a baby/child/adult?
- What are the common functional problems do babies, children, adolescents, adults experience if they have a cleft lip/palate in terms of mastication, swallowing, speech?
What are the normal processes/mechanisms (muscles and movements) for feeding/suckling in a baby?
Baby Suckling:
* Mechanism: Suckling is driven by innate reflexes (rooting, suck-swallow, gag) that facilitate breastfeeding or bottle-feeding; the rooting reflex prompts head turning toward tactile stimuli (e.g., breast), while the suck-swallow reflex coordinates milk extraction and swallowing.
* Muscles: The orbicularis oris and buccinator muscles form a tight lip seal around the nipple/teat, creating negative intraoral pressure; extrinsic tongue muscles (genioglossus, hyoglossus) press the nipple against the hard palate, initiating an antero-posterior tongue wave to extract milk, stabilized by buccal fat pads.
* Movements: The tongue oscillates rhythmically, and the mandible (via masseter, temporalis) moves slightly to expand oral volume, drawing milk into the mouth; swallowing follows as milk fills the oral cavity, coordinated with breathing to prevent aspiration.
* Context: This process ensures efficient nutrient intake, with the gag reflex (triggered by posterior tongue stimulation) protecting against choking, as described by WHO (2009).
What are the normal processes/mechanisms (muscles and movements) for feeding/suckling in a child?
Child Feeding:
* Mechanism: From 6 months, weaning introduces solids as reflexes transition to voluntary actions; early chewing (6–12 months) involves vertical jaw and tongue movements, evolving into a mature rotary pattern by 24–30 months, supporting bolus formation and propulsion.
* Muscles: Masseter and temporalis elevate the mandible for biting, while lateral pterygoid enables jaw opening and lateral movements; intrinsic tongue muscles (longitudinal, transverse) facilitate lateral bolus manipulation, and buccinator stabilizes food within the oral cavity.
* Movements: Initial vertical mandibular movements (antagonistic muscle activation) progress to rotary jaw excursions with coordinated lateral tongue movements, refining bolus formation; by age 4, chewing mirrors adult patterns, as noted by Wilson and Green (2009).
* Context: Developmental readiness (e.g., head control) is critical, with gag reflex diminishing to allow solid food tolerance, per Australian Breastfeeding Association (2023).
What are the normal processes/mechanisms (muscles and movements) for feeding/suckling in an adult?
- Mechanism: Feeding encompasses liquid and solid consumption via four stages: oral preparatory, oral propulsive, pharyngeal, and esophageal; solids require mastication, while liquids follow a streamlined propulsion process.
- Muscles: Masseter, temporalis, medial/lateral pterygoids drive cyclic jaw movements (elevation, depression, lateral excursion) for mastication; intrinsic/extrinsic tongue muscles shape and propel the bolus; buccinator and soft palate muscles (tensor/levator veli palatini) stabilize bolus position and close the nasopharynx.
- Movements: In the oral preparatory stage, the tongue and cheeks position food/liquid for mastication or holding; the oral propulsive stage involves tongue elevation against the hard palate to push the bolus to the oropharynx; pharyngeal/esophageal phases follow involuntarily, as detailed by Matsuo and Palmer (2008).
- Context: Coordinated movements of the jaw, tongue, hyoid, and soft palate ensure efficient bolus processing, with liquids confined to the anterior oral cavity and solids masticated in the post-canine region.
Describe the process of deglutition.
Oral/buccal: Voluntary phase
* Tongue carries ingested food to post-canine region and rotates to the side.
* Food is placed on occlusal surface of lower teeth for mastication
* Muscles of mastication depress mandible, move mandible laterally and then elevate to meet the maxillary arch
* Cyclic jaw movement coordinated with movements from tongue, cheek, soft palate, hyoid bone to tenderise food and form bolus
* Food propelled to oropharynx as anterior tongue contracts in contact with hard palate
Pharyngeal: Involuntary phase
* Soft palate elevates to prevent regurgitation into nasal cavity;
* Medullary swallowing centre (mechanoreceptors) in the brain initiates involuntary process of swallowing.
* Lateral and posterior walls of pharynx contract –> Nasopharynx closed as bolus head enters pharynx
* Base of tongue retracts to push bolus against pharyngeal walls
* Pharyngeal constrictor muscles contract via peristalsis, pushing the bolus downwards
Oesophageal phase
* Lower oesophageal sphincter normally tensioned at rest to prevent stomach regurgitation. Relaxes during swallow to allow bolus to pass to stomach via peristalsis wave
Swallowing and Feeding/Suckling (intact lip/palate) in baby
Baby
Main reflexes; Liquid intake from breast / bottle
Rooting reflex: Mechanism allowing babies to find and latch onto a milk bottle or breast for feeding
1. Baby receives tactile stimuli on lips / cheek, i.e. breast
2. Turns to find stimulus
3. Opens mouth
Tongue thrust; Suck-swallow reflex:
Suckling reflex: Oscillating movement of tongue and jaw to extract milk (for nutrients)
Swallow: Movement of milk from the oropharynx to the oesophagus and coordinated with breathing (preventing aspiration of milk into nasal cavity)
- Same as adult
1. Baby receives tactile stimuli on lips
2. Tongue moves forward out of the mouth using extrinsic muscles of tongue, to protect against choking
3. The lips curl outwards to seal around the areola. Buccal fat pads stabilise teat in mouth – need a negative pressure to draw milk in from teat and close off the nasal passage
4. Baby begins to suck: Antero-posterior wave passes along tongue. Teat pressed against hard palate, with milk into mouth
5. Baby swallows as mouth is filled with milk
Gag reflex
Any hard object placed posteriorly in the mouth will trigger reflexive movement of the tongue to expel the object. Protects against choking.
- Prevents the infant from choking (milk entering airway) and ensures the safe swallowing of food
Swallowing and Feeding/Suckling (intact lip/palate) in Baby to toddler to child
- Weaning, recommended age 6 months onwards or with signs of developmental readiness, e.g. good head control
- Reflexes transition to a voluntary action. Gag reflex diminishes around 6 months, triggered by objects on posterior third of tongue. Tongue thrust diminished or gone
Early chewing pattern: Seen 6 months onwards
- Vertical movements of mandible / tongue, with little lateral movement
- Antagonistic muscles of mastication may activate to some extent simultaneously, though still in alternating fashion
Mature chewing pattern: Varies in first appearance. Usually established by 24-30 months of age. Refinement and maturation continue till at least age 4
- Rotary jaw movements: Vertical mandibular movements are alternated with lateral excursion, along with lateral tongue movements with intrinsic muscles
- Simultaneous activation of antagonistic muscles diminishes, while elevator muscles begin to act together.
Similar deglutition process to adults, refining over time
Swallowing and Feeding/Suckling (intact lip/palate) in Adult
Mastication and deglutition: Occurs in phases
FOR LIQUID: Oral Preparatory Stage (L)
- Lip is sealed
- Liquid bolus is blocked from entering the oropharynx, but may leak into the pharynx
FOR LIQUID: Oral Propulsive Stage (L)
- Tongue moves upwards and increases contact with the hard/soft palate and pushes the liquid bolus posteriorly to the pharynx
- Pharyngeal phase begins during the oral propulsive stage for liquids
- Oral/buccal: Voluntary phase
- Tongue carries ingested food to post-canine region and rotates to the side.
- Food is placed on occlusal surface of lower teeth for mastication
- Muscles of mastication depress mandible, move mandible laterally and then elevate to meet the maxillary arch
- Cyclic jaw movement coordinated with movements from tongue, cheek, soft palate, hyoid bone to tenderise food and form bolus
- Food propelled to oropharynx as anterior tongue contracts in contact with hard palate - Pharyngeal: Involuntary phase
- Soft palate elevates to prevent regurgitation into nasal cavity;
- Medullary swallowing centre (mechanoreceptors) in the brain initiates involuntary process of swallowing.
- Lateral and posterior walls of pharynx contract –> Nasopharynx closed as bolus head enters pharynx
- Base of tongue retracts to push bolus against pharyngeal walls
- Pharyngeal constrictor muscles contract via peristalsis, pushing the bolus downwards
To prevent aspiration to the trachea:
o Vocal cords close
o Larynx shifts superiorly and anteriorly
o Epiglottis folds down blocking the trachea entrance
- Oesophageal phase
- Lower oesophageal sphincter normally tensioned at rest to prevent stomach regurgitation. Relaxes during swallow to allow bolus to pass to stomach via peristalsis wave
Describe the muscles of mastication
Describe the normal process for speech
Baby
- Can mimic facial expressions, gestures
- Attempt to imitate vocal sound when interacting with speaking companions.
Around 2-3 months of age, newborns produce non-syllabic babbling (“gooing”) using simple tongue or lip movements.
Baby to toddler to child
Within 1 year: transition from non-syllabic babbling to syllabic babbling
Around 7 months: start to consistently produce clear syllables (canonical babbling)
- Canonical babbling is an essential part for the foundation of human speech and involves some learning and interaction with others who speak, such as the baby’s mother.
The neural network involved in speech, contains two motor neuron groups:
1. Agonist group
2. Antagonist group
Function: control the masseter and orbicularis oris muscles to increase or decrease mouth closure.
- <1yr: parts of the motor cortex may develop the capability to directly produce movements of the vocal tract articulators, leading to syllabic vocalizations.
Adult
Speech involves four stages: respiration, phonation, resonance, and articulation.
- Respiration: breathing and the lungs provide energy/power behind our voice
- During speech, exhalation is active movement => abdominal muscles actively contract/the lungs, diaphragm and external intercostal muscles passively recoil, to force the air out
- Strengthening these muscles increases speech loudness
- Without air, vocalisations are soundless - Phonation
- Laryngopharynx (contains the vocal cords) => vibrate to produce sound or voice when air is exhaled from the lungs during speech
- Infrahyoid muscles move the larynx and the hyoid during speech and swallowing - Resonance
- Sound flowing through cavities in head e.g. in the throat, mouth and nasal cavity
- Changing the size of these cavities changes how the voice sounds
- Oropharynx contains the posterior and lateral pharyngeal walls => close off the nasopharynx by moving upward and backward with the soft palate, while the lateral walls move inward => directs air into the oral cavity for oral resonance
- During quiet breathing, the soft palate rests on the tongue, allowing air into the nasopharynx and nasal cavity. The soft palate, closes the nasopharynx for oral sounds and opens for nasal sounds, controlling air flow for proper resonance in speech. Velopharyngeal competence ensures appropriate resonance in connected speech. - Articulation
- Articulation refers to how we shape sounds with our mouths to form words
- The parts of the mouth involved in articulation (articulators) include the tongue, lips, cheeks, vocal cords, uvula, palate, teeth, tongue, and mandible —work together to produce speech sounds in various languages.
