Tongue

Introduction and Landmarks

Around the end of the fourth week of gestation, a median, somewhat triangular elevation appears in the floor of the pharynx just rostral to the foramen caecum. This elevation, the median tongue bud, gives the first indication of tongue development. Soon, two oval distal tongue buds (lateral lingual swellings) develop on each side of the median tongue bud. These elevations result from proliferation of mesenchyme in the ventromedial parts of the first pair of branchial arches. The distal tongue buds rapidly increase in size, merge with each other, and overgrow the median tongue bud. The merged distal tongue buds form the anterior two thirds or oral part of the tongue. The posterior third or pharyngeal part of the tongue is initially indicated by two elevations that develop caudal to the foramen caecum, the copula from the second branchial arches, and the hypobranchial eminence from the third and fourth branchial arches. Branchial arch mesenchyme forms the connective tissue and the lymphatic and blood vessels of the tongue and probably some of its muscle fibers. Most of the tongue musculature, however, is derived from myoblasts that migrate from the myotomes of the cervical somites. The hypoglossal nerve accompanies the myoblasts during their migration and innervates the tongue musculature when it develops.

The papillae of the tongue appear at about 54 days of gestation. All the papillae will develop taste buds.

Tongue landmarks are outlined in Figure 7-88.

Remarks Congenital malformations of the tongue include congenital cysts and fistulae derived from remnants of the thyroglossal duct, anky-loglossia (tongue-tie), in which the frenulum from the inferior surface of the anterior part of the tongue extends to near the tip of the tongue and interferes with free protrusion; cleft tongue, caused by incomplete fusion of the distal tongue buds posteriorly; and bifid tongue, in which there is complete failure of fusion of the distal tongue buds.

There is variation in the size of the tongue among individuals, and no normal measurements have been established. Most pediatricians, however, have established their own norms for children. Detection of a large tongue or macroglossia is important, particularly in the neonatal and infantile periods, to allow early diagnosis of certain conditions such as congenital hypothyroidism. An illusion of a large tongue may be seen in a disorder

Pharyngeal part of tongue

Oral pa of tong

Pharyngeal part of tongue

Oral pa of tong

Median sulcus Fungiform papilla

Circumvallate papillae Terminal sulcus Foramen caecum

Epiglottis

Median sulcus Fungiform papilla

Circumvallate papillae Terminal sulcus Foramen caecum

Epiglottis

Figure 7.88 Landmarks of the tongue.

that is characterized by a small oral cavity as in Beckwith-Wiedemann or Down syndrome. The tongue may be large if it is the site of a congenital vascular malformation. Acquired forms of macroglossia include trauma and allergic reactions, for example, angioneurotic edema. When considering the tongue in facial diagnosis, one should remember that largeness is not necessarily the same as protrusion.

Diminished bulk of the tongue may be associated with an atrophic process. Tongue atrophy is a very important clinical sign and usually indicates a lower motor neuron lesion or disturbance if the intrinsic tongue musculature. One should distinguish between bilateral atrophy and unilateral atrophy. The term aglossia refers to absence of the tongue, although usually some rudiments of the tongue are present. Aglossia may be seen in association with limb anomalies.

One should look for abnormal postures of the tongue or an inability to protrude the tongue. Topographic tongue abnormalities, such as a furrowed tongue or geographic tongue, should be noted.

Teeth

Introduction

The teeth develop from ectoderm and mesoderm. The enamel is produced by cells derived from oral ectoderm. All other dental tissues develop from mesenchyme. The mandibular teeth usually erupt before the maxillary teeth, and girls' teeth usually erupt sooner than boys' teeth. As the root of the tooth grows, the crown gradually erupts through the oral mucosa. The part of the oral mucosa around the erupted crown becomes the gum or gingiva.

Eruption of the deciduous teeth usually occurs between 6 and 24 months after birth (Fig. 7.89). The permanent teeth develop in a manner similar to that just described. As a permanent tooth grows, the root of the corresponding deciduous tooth is gradually resorbed by osteoclasts. Consequently, when the deciduous tooth is shed, it consists only of the crown and the uppermost portion of the root. The permanent teeth usually begin to erupt during the sixth year and continue to appear until early adulthood. They are often serrated initially and become smooth with time. The chronology of onset of prenatal and postnatal enamel formation is illustrated in Figure 7.90. Details of dental age are provided in Chapter 13.

Remarks Defective enamel formation results in grooves, pits, or fissures on the enamel surface. These defects result from temporary disturbances in enamel formation. Various factors may injure the ameloblasts, for example, nutritional deficiency, tetracycline therapy, and diseases such as

Figure 7.89 Tooth eruption.

Lateral

1. Molar

Maxilla

Lateral

1. Molar

Maxilla

4-5 Months | 6-7 Months 8-9 Months ] 10-12 Months j

Primary teeth Primary teeth

Primary teeth Primary teeth

CusDÍd

2nd biscupid 2nd deciduous

CusDÍd

2nd biscupid 2nd deciduous

Central Lateral incisor incisor lstbiscuspid 1st deciduous molar

1st 2nd permanent permanent

Central Lateral incisor incisor lstbiscuspid 1st deciduous molar

1st 2nd permanent permanent molar molar molar molar

Figure 7.90 Tooth enamel development.

measles. Rickets is probably the most common cause of enamel hypoplasia. In amelogenesis imperfecta, the enamel is soft and friable because of hypocalcification, and the teeth are yellow to brown in color. This genetic trait affects about one in every 20,000 children. In dentinogenesis imperfecta, a condition relatively common in Caucasian children, the teeth are brown to gray-blue with an opalescent sheen. The enamel tends to wear down rapidly, exposing the dentin. Foreign substances incorporated into the developing enamel will cause discoloration of the teeth. Hemolysis and tetracycline therapy are among the causes of tooth discoloration. The primary teeth are affected if tetracyclines are given from 18 weeks of gestation to 10 months postnatally, and the permanent teeth may be affected if exposure occurs between 18 weeks prenatally and 16 years of age.

Abnormally shaped teeth are relatively common. Occasionally, spherical masses of enamel called enamel pearls or drops are attached to the tooth. They are formed by aberrant groups of ameloblasts. The maxillary lateral incisor teeth may assume a slender tapering shape (peg-shaped lateral incisors). Congenital syphilis affects the differentiation of the permanent teeth, resulting in screwdriver-shaped incisors with central notches in their incisive edges, called Hutchinson teeth.

The most common dental anomaly present at birth is premature eruption of one or more of the deciduous teeth, usually the mandibular incisors. One or more supernumerary teeth may develop, or the normal number of teeth may fail to form. Supernumerary teeth usually appear in the area of the maxillary incisors, where they disrupt the position and eruption of normal teeth. The extra teeth commonly erupt posterior to the normal ones. In partial anodontia, one or more teeth are absent. In total anodontia, no teeth develop. This very rare condition is usually associated with an ectodermal dysplasia.

Disturbances during the differentiation of teeth may result in gross alterations in dental morphology, for example, macrodontia (large teeth) and microdontia (small teeth). Taurodontia is a variation in tooth form involving all or some of the primary and secondary molars, marked by elongation of the body of the tooth producing large pulp chambers and small roots. Taurodontia is found in association with several chromosomal abnormalities.

Maxilla

Introduction

The lateral parts of the upper lip, most of the maxilla, and the secondary palate form the maxillary prominences of the first branchial arch. These prominences merge laterally with the mandibular prominences.

Unilateral maxillary absence is a rare condition and is due to failure of development of one maxillary process. Absence of the premaxillary area is found in cyclopia when the frontonasal process does not form. Subtle hypoplasia of the maxilla is best appreciated on X-ray and is an important feature to be looked for in first-degree relatives of patients with Treacher Collins syndrome.

In the measurement section that follows, the maxilla is chiefly evaluated by cephalometric means. Clinical evaluation of the maxilla is extremely subjective and is best performed in profile, looking at the prominence of the maxilla in comparison to the prominence of the supraorbital ridges, malar area, and mandible. No objective clinical measurements appear to be available.

Effective Midfacial Length: Cephalometric

Definition Size and prominence of the maxilla (Fig 7.91).

Fig. 7.91 Effective midfacial length (mm), both sexes, 6 to 18 years
Pregnancy And Childbirth

Pregnancy And Childbirth

If Pregnancy Is Something That Frightens You, It's Time To Convert Your Fear Into Joy. Ready To Give Birth To A Child? Is The New Status Hitting Your State Of Mind? Are You Still Scared To Undergo All The Pain That Your Best Friend Underwent Just A Few Days Back? Not Convinced With The Answers Given By The Experts?

Get My Free Ebook


Post a comment