"I will praise Thee; for I am fearfully and wonderfully made: marvelous are Thy works; and that my soul knoweth right well." Ps. 139:14.
The infinite wisdom of God in the creation of the human body is demonstrated in all its many members and their individual functions. Among these members the oral cavity occupies an important place. And here, even as in the construction and function of other parts of the body, the result of a beautiful and perfect plan is displayed.
Little study is given, and therefore little knowledge is acquired, regarding the oral cavity, save by those few specialists who are trained in the care and treatment of oral structures. Too little is known by the average layman either of the normal development of the teeth or of proper oral hygiene. Most people have had teeth as far back as they can remember. Somewhere between six and twelve years of age they have gone through the somewhat disfiguring and unlovely process of losing their deciduous teeth and acquiring their permanent set. Aside from that, they have given them little thought or care until they have been painfully reminded by a toothache. A little education on this important part of the human body would, without doubt, stimulate an interest in its proper care.
DECIDUOUS DENTITION.—At birth there is seldom any evidence of the presence of twenty little teeth, although they are there, in various stages of development, each type of tooth being found in its own peculiar form to best perform its appointed work.
As the child develops and becomes capable of changing from a milk diet to food which requires cutting, four pairs of incisors will make their appearance, and become firmly fastened in position in the baby jaws. Growth and development being normal, the upper teeth will overlap the lower, thus preventing involuntary biting of the lips. This plan places the upper teeth in a curve of greater dimension than the lower. In order to compensate for this difference the upper teeth are wider. As development progresses and the need for crushing and grinding arises, usually about six months after the eruption of the incisors, two pairs of molars appear.
The jaws are continually acquiring larger dimensions, but the dimensions of the teeth, once determined, remain unchanged. Were not some provision made to compensate for the larger jaws in which teeth of fixed size are attached, there would be wide spacing of the teeth. Acting as a filler to prevent this unattractive spacing, two pairs of wedge-shaped teeth, called cuspids, find their places at the "corners" of the arches. These have been called canine teeth by some, since they are pointed and resemble somewhat the front teeth found in the canine family.
The jaws now possess teeth adapted to cutting or incising, to tearing, crushing, and grinding. The jaws continue to grow, and this increase in growth makes room for two more pairs of molars to increase the grinding surface. The full complement of deciduous teeth now being in place, let us observe the normal operation of the jaws.
The upper incisors are not the only teeth which overlap the lower. The upper cuspids and molars, as they glide up and down against the inner surface of the cheek, prevent that structure from being pinched between the teeth, by pushing it just beyond the reach of the lower teeth.
Nearly all the teeth contact two teeth in the opposing arch, the exceptions being the lower central incisors and the upper second molars. These contact only one opposing tooth each, since in each case they are smaller than the teeth opposite. This plan spreads the force of biting more evenly, and in the event an opposing tooth is lost, contact is still made between opposing teeth, preventing the antagonist from becoming too long.
When the teeth glide from side to side, the pointed parts, called cusps, in one arch glide either between two teeth, or in and out of grooves in the teeth of the opposing arch. Thus, the food is pulverized or ground, much as corn is ground with a mortar and pestle.
To the casual observer it might seem that chewing is the sole function of the masticatory system. This, however, is far from the truth. As the system is used for mastication, the face and jaws are assisted in their development, these gradually taking on more mature proportions. In this development of the jaws, room is gradually being made for the larger teeth which will replace the deciduous teeth, and which are necessary to give form and interest to the adult face.
Soon, and with little warning, two pairs of larger, more durable teeth make their appearance behind each second deciduous molar. These are the keystones to the so-called permanent set, which, alas, is often not permanent, since in too many cases the care of the keystones is neglected, and thus the plan is destroyed because of their loss or mutilation.
There are certain unfortunate factors which may destroy or distort the symmetry of the perfect plan. Beauty of proportion and form may be lost, and actual deformity result through neglect to correct certain childhood habits. Perhaps foremost among these are thumb-sucking, tongue-sucking, biting of the lips or fingernails. Habits of sleeping which place pressure on a limited area of the supporting structure may result in distortion of the face or jaws. Mouth breathing, regardless of cause, tends to distort the pattern. The premature loss of a tooth may result in locking a succeeding tooth, thus destroying proper balance in the dentition. Deciduous teeth too long restrained may also destroy the symmetry.
Since the deciduous teeth are an essential aid in the development of the face and jaws, as well as for mastication, aesthetics, and speech, they should be given adequate care.
PERMANENT DENTITION.—Before the deciduous teeth are all completely formed, some of them begin to be resorbed at the tips of the roots to make way for the permanent teeth. Hence, at no time is the deciduous dentition complete.
About the same time that the six-year or first permanent molars erupt, the lower deciduous incisors are lost, to be replaced inimediately by new teeth which are wider and more durable. This process is soon repeated by the upper incisors. Since the child's face is not yet completely developed, these large teeth, which appear to be all out of proportion, produce that awkward appearance so characteristic to children of this age.
The lower deciduous cuspids are the next to be replaced. The upper permanent cuspids do not usually appear until the bicuspids are erupting.
In the deciduous set of teeth there are only incisors, cuspids, and molars. With the permanent molar and the anterior teeth in position, it would seem that there might be a locking out of the teeth to fill the space between. However, this eventuality has been provided for with the appearance of narrow bicuspids to replace the deciduous molars. So it is that, although space is lost during the eruption of these intermediate teeth, adequate space is provided for them.
The child's face is now rapidly assuming adult proportions, and the jaws which accommodated the deciduous dentition are somewhat larger. Again, to provide for more chewing surface, second molars are added, behind the first permanent molars.
Sometime later third molars, or the so-called wisdom teeth, attempt to find their places, but they are usually blocked in one way or another, and, in most instances, only develop to become troublemakers. There are a few fortunate individuals in whose jaws third molars never form, and hence, are spared the discomfort so often occasioned by these problem teeth.
The permanent set of teeth functions much as does the deciduous set, but the teeth are harder and larger. As time goes on and the teeth are worn down, the nerve space is gradually filled in with dentine, to protect the nerve from irritation by heat or cold. This process may continue until the nerves and blood vessels are completely crowded out of the teeth.
When properly aligned in the dental arches, well-formed teeth may, with proper care, be retained for years. But proper care alone will not ensure healthy teeth. A well co-ordinated and healthy body are prime essentials, for the teeth are organs of the body and perform their functions best and most effectively when in full co-operation with other body organs.
How we all admire teeth well formed and properly cared for, for what is a smile without teeth but a tragedy? He who takes time to familiarize himself with the beauty and symmetry of the oral structures, and the perfect co-ordination of the dental arches can but pause in admiration and exclaim, "I am 'fearfully and wonderfully made."
BIBLIOGRAPHY
McBride, Juvenile Dentistry, Lea and Febiger, Philadelphia.
Dewey and Anderion, Practical Orthodontla, C. V. Mosby Company, St. Louis.
Noyes, Schour, Noyes, Dental Histology and Embryology, Lea and Febiger, Philadelphia.
