D–E

deafness See HEARING LOSS.

dental caries The clinical term for cavities, ero-
sions through the enamel of the TEETHthat expose
the inner pulp and sometimes the NERVEof the
tooth. A dentist is the health-care provider who
diagnoses and treats dental caries. Untreated den-
tal caries can lead to INFECTIONof the tooth’s root
structure and potentially an ABSCESSof the nerve
canal, health conditions that require treatment
with ANTIBIOTIC MEDICATIONSas well as dental care.
The accumulation of BACTERIAcan contribute to
HALITOSIS (bad breath). A cavity that penetrates
into the inner tooth often causes TOOTHACHE.
Appropriate ORAL HYGIENEand routine dental care
can help prevent dental caries.
See also GINGIVITIS; PERIODONTAL DISEASE.

ear The structures of the ear support the func-
tions of hearing and balance. The ear has three
divisions:

• The outer ear consists of the auricle (pinna)
  and auditory canal, structures that collect,
  focus, and channel sound waves.


• The middle ear consists of the auditory ossicles,
  three tiny bones that vibrate in sequence to
  focus and amplify sound.


• The inner ear contains the COCHLEA, which con-
  verts sound waves to NERVEimpulses, and the
  structures of the vestibular system that regulate
  balance, the bony labyrinth, and the semicircu-
  lar canals.

The TYMPANIC MEMBRANE, or eardrum, separates
the outer ear and the middle ear; the EUSTACHIAN
TUBEconnects the middle ear with the THROATto
equalize pressure on both sides of the eardrum.

Many causes of HEARING LOSSarise as a result of

damage to or dysfunction of the structures of the

outer and middle ear. The inner ear is entirely

sealed from the external environment. Fluid

bathes the delicate structures of the inner ear,

helping protect them as well as isolate them from

external stimuli that could affect their functions.

Most disturbances of balance, often called vestibu-

lar dysfunction, stem from problems with the

inner ear.

COMMON CONDITIONS AFFECTING

THE EAR, HEARING, AND BALANCE

ACOUSTIC NEUROMA BAROTRAUMA

CHOLESTEATOMA HEARING LOSS

LABYRINTHITIS MÉNIÈRE’S DISEASE

MYRINGITIS OTITIS(INFECTION)

OTOSCLEROSIS OTOTOXICITY

TINNITIS VERTIGO

For further discussion of the ear within the

context of otolaryngologic structure and function,

please see the overview section “The Ear, Nose,

Mouth, and Throat.”

See also AUDIOLOGIC ASSESSMENT; COCHLEAR

IMPLANT; HEARING AID.

earache A generalized term for sensations of

pressure, discomfort, and PAINin the area of the

EAR. Pain messages from other structures of the

head and neck, such as the NOSEand THROAT, also

sometimes appear to come from the ear (referred

pain). A common cause of earache in children is

OTITISmedia (INFECTIONof the middle ear).

Congestion in the eustachian tubes can cause

fluid to accumulate between the TYMPANIC MEM-

BRANE (eardrum) and the inner ear, creating

increased pressure, which causes pain. A child

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