Basic Guide to Oral Health Education and Promotion. Alison Chapman
Chapter 1 The oral cavity in health
Learning outcomes
By the end of this chapter you should be able to:
1 Describe how the oral cavity, jaws, and face develop in utero.
2 Explain the structures and functions of the tissues and fluid of the oral cavity, including teeth, supporting structures, the tongue, and saliva.
3 Distinguish between the different types of cleft lip and cleft palate.
4 List primary and secondary dentition eruption dates.
INTRODUCTION
Before oral health educators (OHEs) can deliver dental health messages to patients and confidently discuss oral care and disease with them, they will need a basic understanding of how the mouth develops in utero (in the uterus), the anatomy of the oral cavity (Figures 1.1, 1.2, 1.3, and 1.4), and how the following structures function within it:
Teeth (including dentition).
Periodontium (the supporting structure of the tooth).
Tongue.
Salivary glands (and saliva).
Figure 1.1 Structure of the oral cavity.
Source: From [1]. Reproduced with permission of Elsevier.
Figure 1.2 A healthy mouth (white person).
Source: [2]. Reproduced with permission of Blackwell.
Figure 1.3 A healthy mouth (black person).
Source: Alison Chapman.
Figure 1.4 A healthy mouth (Asian person).
Source: Alison Chapman.
ORAL EMBRYOLOGY
A basic understanding of the development of the face, oral cavity, and jaws in the embryo and developing foetus will help enable the OHE to discuss with patients certain oral manifestations of conditions that stem from in utero development; notably cleft lip and palate.
An embryo describes the growing organism up to 8 weeks in utero; a foetus describes the growing organism from 8 weeks in utero.
Development of the face
At approximately week 4 in utero (Figure 1.5), the embryo begins to develop five facial processes (or projections), which eventually form the face, oral cavity, palate, and jaws by week 8 [3]:
Frontonasal process – forms the forehead, nose, and philtrum (groove in upper lip).
Maxillary process (two projections) – forms the middle face and upper lip.
Mandibular process (two projections) – forms the mandible (lower jaw) and lower lip.
Figure 1.5 Facial development at 4 weeks in utero.
Source: From [3]. Reproduced with permission of Wiley‐Blackwell.
Development of the palate and nasal cavities
Week 5
The frontonasal and maxillary processes begin to form the nose and maxilla (upper jaw). However, if the nasal and maxillary processes fail to fuse, then a cleft will result. This is the most common craniofacial (skull and face) abnormality that babies are born with, and is thought to commonly result from a combination of genetic and environmental factors, or as part of a wider syndrome [4].
A baby can be born with a cleft lip, a cleft palate, or both. Cleft lip and/or palate occurs in 1–2 births out of every 1000 in developed countries [5]. Submucous cleft palate can also occur, which is a cleft in the soft palate and includes a split in the uvula. Surgery to close a gap is often undertaken when a baby is less than a year old.
A cleft lip can be anything from a small notch in the lip (incomplete cleft lip) to a wide gap that runs up to the nostril (complete cleft lip). It can also affect the gum, which, again, can be a small notch or complete separation of the gum.
A cleft lip can be either (Figure 1.6):
Unilateral – affects one side of the mouth (incomplete or complete).
Bilateral – affects both sides of the mouth (incomplete or complete).
A cleft palate is a gap in the roof of the mouth. A cleft can affect the soft palate (towards the throat) or the hard palate (towards the lips), or both. Like a cleft lip, a cleft palate can be unilateral or bilateral, and complete or incomplete (Figure 1.6)
Week 6
By week 6, the primary palate and nasal septum have developed. The septum divides the nasal cavity into two.
Week 8
By week 8, the palate is divided into oral and nasal cavities.
Development of the jaws (mandible and maxilla)
Week 6
By week 6, a band of dense fibrous tissue (Meckel’s cartilage) forms and provides the structure around which the mandible forms.
Week 7
By week 7, bone develops, outlining the body of the mandible.
As the bone grows backwards two secondary cartilages develop; these eventually become the condyle and coronoid processes.
As the bone grows forward, the two sides are separated by a cartilage called the mandibular symphysis. The two sides will