How chewing works

Question 1

Explain in general, how the process of chewing works

Answer 1

• Incision: Depression and protrusion of mandible, elevation of mandible. Incisors are slicing through food
• Stage 1 Transport: Keeping the lips closed while chewing helps create a seal. The severed food at tip of tongue it transferred posteriorly to the working/ chewing side. This is aided by buccinators

Question 2

List the phases of the chew cycle

Answer 2

Opening stroke

Closing stroke

Power stroke

Question 3

Describe the opening stroke of the chew cycle in terms of:

• Mandibular movement
• Tongue role
• Muscles

Answer 3

Mandibular movement:
• The mandible needs to be depressed so the mouth is open, and the mandible needs to needs to swing to the chewing side.

Tongue role:
• Positions food on working side

Muscles:
• This is guided by the rapid contraction of the lateral pterygoids on the non dominant side, causing the mandible to swing towards to the chewing side (the lateral pterygoid will activate afterwards on this side).
• Assisted by digastrics and suprahyoid muscles (mylohyoid)

Question 4

Describe the closing stroke of the chew cycle in terms of:

• Mandibular movement
• Food
• Muscles

Answer 4

Mandibular movement:
• Elevation needs to occur, though the mandible still needs to swing side to side

Food:
• Food is trapped between the teeth in the working side

Muscles:
• This is guided by the rapid contraction of the medial pterygoids on the non dominant side, causing the mandible to swing towards to the chewing side (the medial pterygoid will activate afterwards on this side)
• The masseter and anterior temporalis contracts

Question 5

Describe the power stroke of the chew cycle in terms of:

• Mandibular movement
• Food
• Muscles

Answer 5

Mandibular movement:
• Clenching occurs.
The mandible needs to swing towards the non dominant side

Food:
• Food is grinded between the occlusal surfaces teeth

Muscles:
• Medial pterygoid and masseter need to be contracted
• Posterior temporalis on non- dominant slide side

Question 6

State 3 things that influence the number of chew cycles an individual

Answer 6

• Food consistency
• Food volume
• Individual variation in speed of chew cycles, especially in the power stroke e.g. slow versus fast chewer

Question 7

Describe the neural control of mastication and swallowing

Answer 7

• Primarily automatic (conducted in the central pattern generator in the stem) but can be conducted by the higher brain/ cerebral cortex
• Input from muscles of mastication that there is food, its hardness etc -> travels through the trigeminal ganglion -> central pattern generator in the brain stem -> motor nuclei to muscles of mastication informing them to conduct a chew cycle

Question 8

Describe the role of saliva in mastication and swallowing of food

Answer 8

• Food and mastication help stimulate saliva
• Saliva enables bolus formation. The H20 in saliva helps moistens food particles, while the mucins binds food particles (like a glue). This results in a coherent and slippery bolus so the food can get down the throat
• Digestion: α – amylase (carbs) and lingual lipase (fats)

Question 9

Describe the three phases of SWALLOWING food

Answer 9

1. Oral Phase: Voluntary. Bolus squeezed against hard palate by tongue, and the tongue is elevated (stylo- and palatoglossus)
2. Oropharynx/ pharyngeal phase: Automatic (Glossopharyngeal and Vagus nerve to swallowing centre). At this stage, the soft palate is raised so that the nasopharynx is closed, and epiglottis is raised so that the larynx is closed. This prevents food from entering the airways when swallowing
3. Oesophagus: Automatic, with the peristalsis action

Question 10

State the 6 factors that can impact proper mastication and swallowing

Answer 10

• State of dentition. Having less teeth leads to less muscle and soft tissue control, which can go onto impacting the chew cycle
• Occlusion contact
• Bite force
• Muscle control
• Soft tissue control
• Salivary gland function. Cannot create a food bolus, and therefore swallowing and eating food can become difficult