The orofacial skeletal and dental development are intimately interdependent on the development of functions of the orofacial structures. When a child is born, the neuromuscular components of the oral cavity primarily serve to fulfil the most basic needs of feeding, airway maintenance and gratification of emotional needs. Maturation of these oral functions occurs from anterior to posterior of the mouth; at birth, lip functions develop relatively early, followed by the posterior part of the tongue and, lastly, the pharyngeal structures. Prolonged retention of primitive functions or the development of an abnormal function adversely affects the growth of the jaw and teeth.

This chapter will focus on how orofacial functions stimulate normal development of the associated structures and the orthodontic implications of abnormal functions.

The human foetus begins swallowing movements very early during intrauterine life, at 11 weeks into gestation. The sucking movements become more intricate and evolve between weeks 18 and 20.

Although earlier it was believed that suckling and swallowing movements were fundamental to post-birth survival, research conducted on foetal development performed with advanced sonographic visualisation has proved that intrauterine development of the gastrointestinal tract and foetal growth are intimately linked with swallowing.

The act of swallowing is a fundamental process that maintains the equilibrium of foetal and amniotic fluids during intrauterine life. Additionally, it plays a pivotal role in the development of the foetus’s somatic and gastrointestinal systems. Notably, human foetus exhibits increased swallowing activity throughout gestation, closely linked to their ingestive behaviour.

The newborn, at the time out of the womb, carries an innate suckling reflex or a congenital neuromuscular behaviour shown as sucking in the rhythmical pattern. The rhythmical suckling pattern is essentially governed by the sensory-motor pathways in the spinal cord—brain stem and through the rhythmic firing of ‘central pattern generators’ (CPGs) located in the central nervous system. The newborn, although new in the world out of the womb, can attach to the maternal nipple and begin suckling through this ‘innate’ behaviour. Swallowing and feeding continue throughout infancy and early childhood.

The period after 6 months of birth involves oral sensitisation and the differentiation of the texture and consistency of foods. As babies grow, they learn to use their oral muscles and develop skills to handle different types of food with varying textures and consistencies. This skill development is primarily observed in the second half of the first year, as babies move from semi-solid to solid foods. During this time, they learn to chew and manipulate food with their deciduous teeth and tongue, coordinating breathing and swallowing to eat safely and efficiently. This crucial developmental process sets the foundation for a lifetime of healthy eating habits and overall well-being.

When an infant learns to take solid food, the muscles of the cheek, tongue and lips get involved, but the activity of the lips is reduced. Lips keep the food from falling out of the mouth during the peristalsis actions of the tongue and cheeks as the bolus is pushed towards the pharynx. The bolus of food is mixed with saliva by the tongue activity and is forced between the gum pads or the erupting teeth. The eruption of primary teeth and establishment of occlusion facilitates mastication and deglutition.

In the infantile or visceral swallow, the mandible is stabilised by placing the tongue forward and between the gum pads and facial muscles innervated by the seventh cranial, that is facial nerve. In adult swallowing, also called somatic swallowing, the mandible is stabilised by teeth contact, which is controlled by muscles of mastication, innervated by the fifth cranial nerve ( Fig. 48.1 A and B; Table 48.1 ).

(A) Infantile swallow, (B) mature swallow, (C) persistent infantile swallow.

A mature swallow is well-developed by 18 months. The act of suckling and the manner in which infants swallow persist for approximately a year post-birth. This pattern slowly diminishes as solid food is gradually introduced and the molar teeth emerge. Around 18 months of age, a transitional swallowing pattern emerges, which is commonly observed in children aged 3–10. At this stage, lip contraction and tongue-to-lower lip posture may or may not be present.

Typically, the adult swallowing pattern in which the tongue is contained in the oral cavity is established by the age of 9 or 10. However, some 10%–15% of individuals may continue with a transitional or immature swallowing pattern ( Fig. 48.1 C).

The adult swallow is characterised by swallowing with the teeth occluding together, the tongue against the palate, and the lips relaxed. The change from infantile to adult swallow is gradual. A delay in the normal swallow transition can be expected when a child has a sucking habit.

The process of swallowing, also known as deglutition, involves how, within the oral cavity, the substances flow and travel to the stomach via the pharynx and oesophagus. Swallowing is a crucial and intricate behaviour for survival that is learned very early in foetal development. The anatomical pathway travelled is common with the airway. Therefore, in addition to directing food into the digestive tract, the swallowing mechanism should have the arrangement to protect the entry of food into the airway. The act of swallowing and transferring food in the stomach, protecting the airway, entails a complex coordinated movement affected by 30 nerves. The act of swallowing involves reflexive and voluntary actions.

Swallowing or deglutition is a series of coordinated voluntary, involuntary and reflex muscular activity that moves the prepared food bolus in the oral cavity through the oesophagus to the stomach. Stabilisation of the mandible is necessary for swallowing. The mandible must be stabilised so that contraction of the suprahyoid and infrahyoid muscles can control the proper movement of the hyoid bone needed for swallowing.

The average tooth contact during swallowing is about 683 ms, more than three times the average mastication. The force applied to the teeth during swallowing is approximately 66.5 lb, 7.8 lb more than during mastication.

The swallowing cycle occurs 590 times during 24 h: 146 cycles during eating, 394 cycles between meals while awake and 50 cycles during sleep. Lower levels of salivary flow during sleep result in less need to swallow.

Non-nutritive sucking habits include thumb sucking, finger sucking and lip sucking. Occasionally cases of cheek sucking are also seen though very rare. Non-nutritive sucking habits may continue till 2 years of age, when these practices usually stop with a transition to mature swallow.

Thumb sucking starts as early as 15 weeks of intrauterine life and is considered a normal act till 4 years of age. Beyond this age, thumb sucking, if continued, would hinder normal development of occlusion. Thumb sucking refers to placing the thumb or fingers into the mouth many times every day and night, exerting a definite sucking pressure. The habit can be repetitive and forceful, associated with strong cheek and lip contractions ( Figs 48.2 and 48.3 ).

Thumb sucking habit and its affects on developing occlusion.

(A–C) Intensive thumb sucking at the age of 3 years. (D) The thumb used is cleaner due to the frequent use of the mouth. Continuous irritation from the teeth may lead to the formation of calluses on the skin. (E) The untoward effects of thumb sucking are influenced by the intensity, frequency and duration of the habit. Thumb sucking leads to an open bite. It can also lead to maxillary protrusion and a recessive chin, resulting in class II malocclusion. (F) The pulp side of the thumb used for sucking that rests on incisal edges shows injury caused due to continued rubbing by the incisors.

Interceptive orthodontics, psychological guidance for the child and family counselling can help to discontinue the habit, which may normalise facial growth at this age.

Thumb sucking in a young girl.

(A and B) Placement of thumb and abnormal perioral muscle behaviours. (C) Thumb sucking caused a retrognathic mandible and superior protrusion. (D and E) Class II malocclusion caused by thumb sucking.

Note: Proclination of maxillary anterior teeth and large overjet was contributed by the backwardly held mandible by the wrist resting on the chin resulting in Class II malocclusion.

Several theories have been put forward to explain thumb sucking habit.

• •

  Freudian theory of psychoanalysis is linked to the psychosexual development of humans. This theory regards thumb sucking as a symptom of a more profound emotional disturbance or neurosis.

• •

  Eysenck’s learning theory views it as a form of neurotic symptom itself and not caused by underlying neurosis. If the symptom (habit) is eliminated, the child’s associated neurosis will also be reduced. Most habit-breaking appliances work on the learning theory.

• •

  Palermo theory regards thumb sucking as arising out of a progressive stimulus and rewards reaction, which would spontaneously disappear unless it becomes an attention-getting mechanism.

• •

  Sear’s oral drive theory believes that the thumb sucking habit is intimately related to the prolongation of breast feeding. The longer the baby is breastfed, the stronger will be its oral drive and the more prone it is to thumb sucking.

Types of thumb sucking

How children place their thumb has been studied using:

• Group A The thumb is generally inserted into the mouth considerably beyond the first joint or knuckle. It occupies a significant portion of the palate, pressing against the palatal mucosa and alveolar tissue. The lower incisors press against the thumb in the region of the first joint. Nearly 50% of the children fall into this pattern.

• Group B The thumb does not fully enter the vault area of the hard palate. However, it extends into the mouth up to and around the first joint, or just anterior to it. Nearly 24% of the thumb sucking children fall in this pattern.

• Group C The thumb is typically placed in the oral cavity and approaches the vault of the hard palate, similar to Group A. However, the lower incisors do not touch or make contact with the thumb. Nearly 20% of the thumb sucking children fall in this pattern.

• Group D The thumb does not advance significantly into the mouth. The contact of the lower incisors occurs at a level near the thumbnail. Only a small 6 of thumb sucking children fall in this pattern.

The adverse effects of any pressure habit are dependent upon the trident of the

• a.

  Duration

• b.

  Frequency and

• c.

  Intensity of the pressure habit.

The pathophysiology of the thumb sucking habit and its effects on the face and occlusion are explained in Fig. 48.4 .

• •

  Exaggerated mentalis muscle activity may be seen because of the effort of the lower lip to attain a lip seal with the upper lip.

• •

  The maxillary arch shows constriction due to abnormal and excessive pressure from the buccal musculature, which is not balanced by the tongue on the palatal side, and oral space is occupied by the thumb during the sucking habit. Posterior cross bite tendency may occur.

• •

  Mandibular incisors may be retroclined or upright.

• •

  The mandible shows downward and backwards rotation due to lowered position while sucking.

• •

  An increase in the ANB (A point, nasion, B point) angle is seen, which is contributed by maxillary prognathism and mandibular retrognathism.

• •

  The patient may develop tongue thrusting in an anterior open bite-like situation created by thumb sucking.

Pathophysiology of thumb sucking induced class II division 1 malocclusion and tongue thrust swallow.

Thumb and digit sucking results in the development of features of class II malocclusion. Proclination of the upper incisors is the first and the most common sign of persistent thumb sucking ( Fig. 48.5 ). The proclination is self-maintaining because of the cushioning effect of lower lips, and the upper lip becomes redundant. These proclined incisors are more prone to traumatic dental injuries compared to normally inclined incisors. The fist being held against the chin during thumb/finger sucking prevents forward growth of the mandible, thus contributing to the development of skeletal class II malocclusion.

Anterior open bite caused by tongue thrusting habit.

(A) At rest (B) initiating of swallowing (C) tongue thrust position, tip of the tongue resting on lower incisor and protruding through the open bite.

The tongue is a powerful muscular organ which exerts tremendous pressure during swallowing at frequent intervals, 24 h a day, during sleep time and during the day.

In tongue thrusting habit, a normal-sized tongue or enlarged tongue thrusts itself between the occlusal tables of the upper and lower teeth each time the patient swallows, producing an anterior open bite ( Fig. 48.5 ). Sometimes, the patient allows the tongue to rest in the open bite space between the act of deglutition, preventing the buccal bite from closing. Tongue thrusting leads the molars to supra erupt, further complicating the problem in correcting the open bite, even if tongue thrusting habits have been corrected.

Rix recognised two sharply contrasting types of tongue behaviour:

• a.

  The non-dispersing behaviour of the tongue: The tongue’s non-dispersing behaviour is observed in cases where it refrains from exerting any force on the lingual surface of the upper and lower incisors. The lips may or may not contract excessively. The upper and lower incisors are upright or retroclined.

• b.

  Dispersing behaviour of the tongue: Those cases in which the actions of the tongue and lips are associated with a dispersal of upper and lower incisor relations.

Types of tongue thrusting

Moyers classified tongue thrusting into three types:

• a.

  Simple tongue thrusting: Characterised by teeth together swallow.

• b.

  Complex tongue thrusting: Characterised by teeth apart swallow.

• c.

  Retained infantile swallow.

The clinical features seen in the tongue thrusting condition vary according to the type of tongue thrusting. (Figure 48.1)

Simple tongue thrusting

Generalised spacing and proclination may be seen in the upper and lower anterior teeth. An increased overjet, reduced overbite or an anterior open bite are signs associated with tongue thrust. A simple tongue thrust is usually associated with a history of digit sucking. Exaggerated perioral musculature activity is observed during the swallowing action ( Fig. 48.6 ). The correction of malocclusion will settle the tongue behaviour to a normal swallowing pattern.

Abnormal tongue posture.

(A and B) Mild spacing in the upper anterior due to abnormal tongue posture. (C) Saliva drooling out during swallowing habit.

Complex tongue thrusting

Complex tongue thrust is a more complicated swallowing pattern associated with chronic naso-respiratory issues such as mouth breathing, tonsillitis or pharyngitis.

When the tonsil is inflamed and enlarged, the root of the tongue exerts a force on the tonsil and causes pain. The tongue is postured forward to avoid pain, facilitating the airway space for breathing. In the complex tongue thrust, the mandible is stabilised by the tongue. Hence, combined contractions of the lip, facial and mentalis muscles, and a lack of contraction of the mandibular elevators are found. The tongue spreads laterally in between the occlusal tables of the upper and lower teeth. The malocclusion with a complex tongue thrust has a poor occlusal fit and a generalised anterior open bite.

Retained infantile swallow

The transition from the infantile swallowing pattern to an adult swallowing behaviour occurs after 6 months, with tooth eruption. The immature swallow is retained, suggesting that the transition to an adult swallowing behaviour has not happened. An open bite may not conform to the anterior segment alone, extending to buccal segments, and ordinarily, they occlude on only one molar in each quadrant ( Fig. 48.1 C).

Interception and treatment of tongue thrusting

The approach to interception and treatment of tongue thrusting are age and severity dependent. No active intervention is instituted in children below 3 years, while children above this age can be trained for tongue swallowing exercises. Tongue thrusting treatment would necessitate those anatomic obstructions like enlarged tonsils be handled by appropriate therapy in consultation with an ENT surgeon. An abnormally enlarged tongue could be associated with a tumour/cyst in the floor of the mouth. These conditions should be investigated and treated accordingly.

Treatment of tongue thrusting requires a positive attitude and a strong desire by the patient to overcome abnormal habits supported with suitable mechanotherapy instituted by the orthodontist. Some commonly used removable appliances include upper Hawley’s plate with tongue cribs and roller balls for tongue exercise ( Fig. 48.7 ). Modalities of treatment for tongue thrusting are outlined in Table 48.3 .

Fixed habit breaking appliances

(A) . Fixed appliance soldered on molar bands for tongue thrusting/thumb sucking (B) . Pearl exerciser fixed on molar bands for tongue thrusting (C) . Lip bumper for lower lip sucking.

TABLE 48.3

Management of tongue thrusting

	Modalities
a. Reminder therapy	Palatal appliances Palatal cribs, spurs, palatal rolling ball
b. Corrective therapy	(i) Removal of obstruction Surgery for adenoids and macroglossia (ii) Closure of anterior open bite, posterior open bite and/or anterior spaces with either a fixed or removable orthodontic appliance (iii) Tongue exercises a. Elastic band swallow The elastic band is kept on the tip of the tongue against the palate, and swallowing is practised. b. Water swallow Keep water in the mouth and a mirror in hand, and swallowing is practised daily. c. Candy swallow A candy is placed between the tongue and palate, and swallowing is practised. d. Speech exercises The patient practises syllables like c, g, h and k while keeping an elastic band between the tongue and the palate. (iv) Lip exercises Patient practises stretching of lips to achieve anterior lip seal

Mastication is a complex function that utilises the muscles, teeth, supportive structures, lips, cheeks, tongue, palate and salivary glands. The four major contributors of the masticatory apparatus are the bones, muscles, teeth and soft tissues and their neurologic control and coordination. The masticatory apparatus is a dynamic organ that attains a complex functional and developmental maturity level from birth to life cycle. Thus, morphological, functional and behavioural changes occur with age, affecting occlusion, muscle behaviour and chewing efficiency.

Dental hard tissue conditions, oral health, contact area of occlusion, bite force, ability to control masticatory muscles for effective contraction and ability to manipulate soft tissues, lips and cheeks can affect masticatory efficiency. During mastication, the entire stomatognathic system contributes to the process, including oral tissues such as the lips, teeth, cheeks, tongue and palate that prepare the food for swallowing. A series of biophysical and biochemical processes occur, including rhythmic separation and apposition of jaws, salivary secretions with temporomandibular joint (TMJ) functions being significant. The tongue and cheek muscles also play an essential role in chewing by holding the bolus of crushed food between the occlusal surfaces of the teeth.

The process of chewing relies on a significant amount of sensory information to ensure that it remains within the narrow limits of the mouth. The sensory inputs from the teeth, tongue and cheeks all contribute to the coordination of the chewing process. The teeth and many other parts of the masticatory apparatus can be harmed by non-functional or parafunctional habits like bruxism and clenching due to repeated or continuous trauma to dental structures and occlusion.

Chewing centre

The chewing process is a cyclic and patterned behaviour that relies on a subcortical centre known as the brain stem ‘chewing centre’. Chewing contains a central neural pattern generator influenced by descending regulatory signals from higher brain centres and sensory inputs from oral-facial receptors. The sensory inputs are crucial for learning the skills of chewing, guiding masticatory movements and determining the jaw’s position during occlusion and at rest ( Fig. 48.8 ).

Neurological and sensory control of mastication.

Mastication is programmed in the lower brainstem. Rhythmical movement of the jaw and tongue is regulated by the lower brainstem, mainly as a mechanism of rhythm formation based on information generated during mastication from sensory receptors in the oral cavity and masseter muscles.

Source: Y. Watanabe, Age Changes in Oral Function, Reference Module in Biomedical Sciences, Elsevier, 2014, ISBN 9780128012383, https://doi.org/10.1016/B978-0-12-801238-3.00041.

The sensory inputs, in combination with central influences, are also believed to play a role in the development of temporomandibular disorders and bruxism.

Chewing patterns

The chewing follows a complex pattern of strokes. The movement pattern of the chewing stroke is tear shaped ( Fig. 48.9 ). Two phases are an opening phase and a closing phase. The closing phase is further performed in two stages: the crushing phase and the grinding phase. Mandibular frontal plane tracing indicates that during the mouth opening phase, the single chewing stroke drops downwards from the first contact at an intercuspal position to a point where the incisal edges of the teeth are approximately 16–18 mm apart. It moves 5–6 mm laterally from the midline as the closing movement begins. The first stage of the chewing process is the crushing phase, during which food gets trapped between the teeth. At this juncture, the positioning of the teeth results in the buccal cusps of the mandibular teeth being nearly under the buccal cusps of the maxillary teeth on the side towards which the mandible has shifted. Subsequently, as the mandible progresses with closure, the alimentary bolus becomes ensnared between the teeth and the grinding phase starts to shear and pulverise the bolus of food ( Fig. 48.9 ).

The envelop of chewing pattern cycle.

Like mastication and swallowing, respiration is an inherent innate reflex activity. Studies show that in the infant, respiration is carried out through the nose, with the tongue in proximity to the palate, obturating the oral passageway. Infants are obligate nasal breathers, and respiration maintains the patency of the pharyngeal airway. At birth, the infant’s airway must be established immediately on delivery and retained for life. Humans are primarily nasal breathers, but in some physiological conditions, like during exercises, we also partially breathe through the mouth. There is a transition to partial oral breathing when ventilator exchange rates above 35.3 ± 10.8 L/min are reached. If the nose is partially obstructed, the work associated with nasal breathing increases, and at a certain level of resistance to nasal airflow, the individual switches to partial mouth breathing. This crossover point varies amongst individuals but is usually reached at resistance levels of about 3.5–4 cm H ₂ O/L/min.

Nasal obstruction for an extended period leads to developing a mouth breathing pattern. The anatomical structures of the upper airway may contribute to obstruction in the airway. The upper airway includes the hypopharynx, oropharynx, nasopharynx and nasal cavity ( Table 48.4 ).

TABLE 48.4

Common causes of upper airway obstruction and their treatment

Area of obstruction	Structure involved	Treatment procedure
Nasal cavity	Hard tissue • Nasal septal deviation • Turbinate hypertrophy	Septoplasty Turbinoplasty
	Soft tissue • Allergic rhinitis • Nasal polyp	Mild-to-moderate allergic rhinitis: H 1 antihistamines Severe allergic rhinitis: Intranasal steroids Surgical removal
Nasopharynx	Adenoid hypertrophy Maxillary retrognathia	Adenoidectomy Maxillary advancement
Oropharynx	Tonsillar hypertrophy Soft palate redundancy Retrognathia	Tonsillectomy Uvulopalatopharyngoplasty (UPPP) Mandibular advancement Genioglossal advancement

Only gold members can continue reading. Log In or Register to continue

Share this:

• Click to share on Twitter (Opens in new window)
• Click to share on Facebook (Opens in new window)

Related

Related posts:

1. Psychological implications of malocclusion and orthodontic treatment
2. Downs’ analysis
3. Digital and computerised cephalometrics
4. Diagnostic records, their evaluation and integration in treatment planning
5. Role of removable appliances in contemporary orthodontics
6. Orthodontic treatment with contemporary fixed appliance phase III: Finishing and detailing

Stay updated, free dental videos. Join our Telegram channel

Join