Development of Human Face- Nose and Mouth

The nose and mouth of a baby develop between the 5th and 12th weeks of life inside the mother’s womb.

There are two important tissue structures involved in development of the nose and face – the pharyngeal arches and neural crest cells.

In the developing embryo, there are six pharyngeal arches. They arise in the fourth week of development as out-pocketings of mesoderm on both sides of the pharynx. Each pharyngeal arch has a branch of the aorta, a cranial nerve and a cartilage bar associated with it.

Neural crest cells are a specialised cell lineage which originate from neuroectoderm. As the neural tube forms, cells from the lateral border of the neuroectoderm are displaced into mesoderm, and from there they migrate throughout the body to form various structures. Of relevance to the head and neck, these cells enter the pharyngeal arches to help contribute to their derivatives.

Development of human face

During week 3 of embryonic development, an oropharyngeal membrane initially appears at the site of the future face. It is comprised of ectoderm and endoderm – externally and internally, respectively.

During the 4th week, the oropharyngeal membrane begins to break down in order to become the future oral cavity, and sits at the beginning of the digestive tract.

The structures of the external face are derived from two sources:

Frontonasal prominence – formed by the proliferation of mesenchymal neural crest cells ventral to the forebrain.

Mandibular and maxillary prominences – parts of the 1st pharyngeal arch.

A space lies between the maxillary prominences, covered by the oropharyngeal membrane; this is known as the stomatodeum, the precursor to the mouth and pituitary gland.

Nasal development is instigated by the appearance of raised bumps called nasal placodes on both sides of the frontonasal prominence. These then invaginate to form nasal pits, with medial and lateral nasal prominences on either side.

As the maxillary prominences expand medially, the nasal prominences are ‘pushed’ closer to the midline. The maxillary prominences then fuse with the nasal prominences – and soon after fuse in the midline to form a continuous central structure.

Prominence	Derivatives
Frontonasal	Forehead, bridge of nose, medial and lateral nasal prominences
Medial nasal	Philtrum, primary palate, upper 4 incisors and associated jaw
Lateral nasal	Sides of the nose
Maxillary (1st pharyngeal arch)	Cheeks, lateral upper lip, secondary palate, lateral upper jaw
Mandibular (1st pharyngeal arch)	Lower lip and jaw

Development of the Palate

Initially, the nasal cavity is continuous with the oral cavity. A series of steps lead to their separation, and the establishment of the palate.

As the nose forms, the fusion of the medial nasal prominence with its contralateral counterpart creates the intermaxillary segment – which forms the primary palate (becomes the anterior 1/3 of the definitive palate). The intermaxillary segment also contributes to the labial component of the philtrum and the upper four incisors.

The maxillary prominences expand medially to give rise to the palatal shelves. These continue to advance medially, fusing superior to the tongue. Simultaneously, the developing mandible expands to increase the size of the oral cavity; this allows the tongue to drop out of the way of the growing palatal shelves. The palatal shelves then fuse with each other in the horizontal plane, and the nasal septum in the vertical plane, forming the secondary palate.

Mouth anatomy

The main structures of the mouth include:

Lips – two mobile and muscular structures that form the entrance to the mouth. The lips mark the transition from skin to moist mucous membrane.

The vestibule – the space between the soft tissue (lips and cheeks), and the teeth and gums. The vestibule is kept moist by secretions from the parotid salivary glands, which are located in front of the ears and behind the angle of the jaw.

Mouth cavity – the mouth cavity is bounded by several structures. The alveolar arches (bony structures that contain the teeth) surround the mouth cavity at the front and on the sides – overhead are the hard and soft palates and below is the tongue. The mouth cavity is kept moist by secretions from the submaxillary and sublingual salivary glands located in the floor of the mouth beneath the tongue.

Gums – are made up of the fibrous and dense tissue that lines the alveolar arches and hugs the teeth.

Teeth – a person has two sets of teeth over the course of a lifetime. The average child has their full set of 20 primary (or milk or baby or Deciduous teeth) teeth by the age of three years. The primary teeth start to fall out between the ages of about six and seven years, and are gradually replaced by permanent (or secondary or adult) teeth. By about 21 years, the average person has 32 permanent teeth – 16 in the upper jaw and 16 in the bottom jaw.

Palate – consists of the hard and soft palates. The hard palate is the bony roof of the mouth. The soft palate is a fold of membrane that hangs between the mouth cavity and the back of the throat. The little dangling bit you can see when you stick out your tongue and say ‘ah’ is called the uvula.

Tongue – the tongue is made up almost entirely of muscle fibres. It is divided into an oral portion (tip, blade, front, centre and back) and a pharyngeal (throat) section. The tongue helps us to taste, speak and swallow.

Minor salivary glands – make the clear fluid (saliva) that keeps the mouth moist and contains enzymes to break down food. These glands are found in various locations around the mouth, including the inner cheeks.

Trigeminal nerve

The trigeminal nerve is the major nerve of the face. Its roles include sensation and some motor functions such as biting, chewing and swallowing. Also known as the fifth cranial nerve, it has three main branches, including:

Upper branch – services the scalp and forehead.

Middle branch – services the cheeks, top lip, upper jaw, top teeth and gums, some areas of the nose.

Lower branch – services the bottom lip, bottom jaw, bottom teeth and gums.

The lips and palate originate from three areas of the baby’s developing face:

Central or Frontal Nasal Prominence: normally grows to become the forehead, nose, middle portion of the upper lip (philtrum or Cupid’s bow) and the primary palate (part of the upper jaw that holds the middle four teeth)

Left and Right Maxillary Prominences: grow and become the lower face, lower lip and jaw, all but the middle portion of upper lip and jaw, and the secondary palate (behind the four upper middle teeth to back of mouth.

These three prominences on the child’s developing face grow towards the center of the face and fuse together during the 6th to 13th weeks of pregnancy. When this happens correctly, the child’s lips, mouth, and palate develop normally. But sometimes this growth process is disturbed in some way and the prominences do not meet. When this happens, the lips and mouth do not form properly, leaving a cleft or split in the lip.

The prominence’s grow and come together, fusing to create the nose, the mouth, the lips and the front part of the palate.

Next to the prominence’s are the palatine shelves which start out as ledges on either side of the mouth. As the fetus grows, these ledges lengthen and join in the middle to form the back of the palate in the same way that a zipper closes. The joining process, or “closing of the zipper” starts up front by the teeth and moves backwards towards the throat.

If the process of growth and joining is interrupted at any stage, a gap or split will develop, resulting in a cleft of either the lip or the palate. The type of cleft that develops in the lip and/or palate depends upon when the joining process is interrupted.

Teeth

Deciduous teeth, otherwise known as milk teeth, baby teeth, or primary teeth, are the first set of teeth in the growth development of humans and many other animals. They develop during the embryonic stage of development and erupt - become visible in the mouth - during infancy. They are usually lost and replaced by permanent teeth, but in the absence of permanent replacements, they can remain functional for many years.

Deciduous teeth start to form during the embryo phase of pregnancy. The development of deciduous teeth starts at the sixth week of development as the dental lamina. This process starts at the midline and then spreads back into the posterior region. By the time the embryo is eight weeks old, there are ten areas on the upper and lower arches that will eventually become the deciduous dentition. These teeth will continue to form until they erupt in the mouth. In the deciduous dentition there are a total of twenty teeth: five per quadrant and ten per arch. In most babies the eruption of these teeth begins at the age of six months and continues until twenty-five to thirty-three months of age. The first teeth seen in the mouth are the mandibular centrals and the last are the maxillary second molars. 

The deciduous dentition is made up of centrals, laterals, canines, first molars, and second molars; there is one in each quadrant, making a total of four of each tooth. All of these are replaced with a permanent counterpart except for the first and second molars; they are replaced by premolars. These teeth will remain until the age of six. At that time, the permanent teeth start to appear in the mouth resulting in mixed dentition. The erupting permanent teeth causes root resorption, where the permanent teeth push down on the roots of the deciduous teeth causing the roots to be dissolved and become absorbed by the forming permanent teeth. The process of shedding deciduous teeth and the replacement by permanent teeth is called exfoliation. This will last from age six until age twelve. By age twelve there are only permanent teeth remaining.

Parts of the tooth

Each tooth has 4 main parts, including:

Enamel. The outer layer of the tooth and the hardest material in the body.

Dentin. The inner layer and the main part of the tooth, and the largest dental tissue.

Pulp. Soft tissue on the inside of the tooth that contains the nerve, blood supply, and the ability to produce dentin.

Root. The part of the tooth that secures it into the jaw.