Molar relationship in primary dentition anatomy

Occlusion (Dental Anatomy, Physiology and Occlusion) Part 1

molar relationship in primary dentition anatomy

Molar Relationship The molar relationship in the primary dentition can be classified into . Dental Anatomy, Physiology & Occlusion: Wheeler. The primary molars are replaced by permanent premolars. No premolars The molar relationship, both deciduous and permanent, is accented here. C, This is a . Occlusal Relationship of Primary & Permanent Molars; . References CONCISE DENTAL ANATOMY & MORPHOLOGY: JAMES L.

Primary Dentition Any consideration of the development of the occlusions should begin with the primary dentition. It is during this period in the development of the oral-facial complex that oral motor behavior reflects learning related to the advent of the teeth. Human oral functions that are acquired or modified during the natural progression from birth through infancy to adulthood are in part related to the development of occlusion, both of the deciduous and permanent teeth i.

molar relationship in primary dentition anatomy

Perhaps many of the reflex mechanisms of the oral-facial area and sensory and higher-center influences are important for the acquisition of masticatory skills, just one of the many motor behaviors that come under the phrase oral motor function.

The development of the muscle matrix and the active growth of the facial skeleton occur at a very strategic time for the maturation of the nervous system and the development of oral motor functions involving the teeth and chewing. It is also at this time that jaw positions and posturing of the mandible in relationship to the teeth takes place. An outline following the labial and buccal surfaces of the maxillary teeth describes the segment of an ellipse and is larger than the segment following the same surfaces on the mandibular teeth see FigureA.

The relation between the maxillary and mandibular primary teeth when in occlusion is such that each tooth, with the exception of the mandibular central incisor and the maxillary second molar, occludes with two teeth of the opposing jaw.

The primary teeth should be in normal alignment and occlusion shortly after the age of 2, with all the roots fully formed by the time the child is 3 years old. A year or so after the teeth have fully erupted and have assumed their respective positions in the arches, the rapid development of the jaws is sufficient to create an interdental space, or diastema, between some of them.

The anterior teeth separate and usually show greater separation as time goes on by a process that is caused by the growth of the jaws and the approach of the permanent teeth from the lingual side.

This separation usually begins between the ages of 4 and 5 years. The canines and molars are supposed to keep their positive contact relation during all the jaw growth. However, some shifting and separation are seen quite often. Because the teeth do not hold their relative positions for long, they are worn off rapidly on incisal ridges and occlusal surfaces. As an example, when a primary canine is lost 8 years or more after its eruption, its long, sharp cusp has in most instances been worn down.

If the primary teeth are in good alignment, the occlusion is most efficient during the time that these teeth are in their original positions.

This situation exists for only a relatively short time. After normal jaw growth has resulted in considerable separation, the occlusion is supported and made more efficient by the eruption and occlusion of the first permanent molars immediately distal to the primary second molars. The child is now approximately 6 years of age and will use some of the primary teeth for 6 more years.

Occlusion (Dental Anatomy, Physiology and Occlusion) Part 1

According to Falkner12 the development and eruption of the primary dentition are quite independent of the development and maturation of the child as a whole. The significance of local environmental factors for the development of occlusion considered in its broadest sense is relatively unknown.

These terms are improper because they foster the implication that these teeth are useful for a short period only. It is emphasized again that they are needed for many years of growth and physical development. Premature loss of primary teeth because of dental caries is preventable and is to be avoided.

molar relationship in primary dentition anatomy

The first permanent molar, commonly called the 6-year molar, makes its appearance in the mouth before any of the primary teeth are lost. It comes in immediately distal to the primary second molar see Figure The primary dentition is complete at about 2. The position of the incisors is usually relatively upright with spacing often between them. Attrition occurs, and a pattern of wear may be present. The primary molars are replaced by permanent premolars.

No premolars are present in the primary set, and no teeth in the deciduous set resemble the permanent premolar. However, the crowns of the primary maxillary first molars resemble the crowns of the permanent premolars as much as they do any of the permanent molars. Nevertheless, they have three well-defined roots, as do maxillary first permanent molars. The deciduous mandibular first molar is unique in that it has a crown form unlike that of any permanent tooth see FigureC.

The Primary (Deciduous) Teeth (Dental Anatomy, Physiology and Occlusion) Part 1

It does, however, have two strong roots, one mesial and one distal—an arrangement similar to that of a mandibular permanent molar. These two primary teeth, the maxillary and mandibular first molars, differ from any teeth in the permanent set when crown forms are compared, in particular see Figures and The primary first molars, maxillary and mandibular, are described in detail later in this topic. Major Contrasts between Primary and Permanent Teeth In comparison with their counterparts in the permanent dentition, the primary teeth are smaller in overall size and crown dimensions.

They have markedly more prominent cervical ridges, are narrower at their "necks," are lighter in color, and have roots that are more widely flared; in addition, the buccolingual diameter of primary molar teeth is less than that of permanent teeth.

The crowns of primary anterior teeth are wider mesiodistally in comparison with their crown length than are the permanent teeth. The roots of primary anterior teeth are narrower and longer comparatively. Narrow roots with wide crowns present an arrangement at the cervical third of crown and root that differs markedly from that of the permanent anterior teeth. The roots of the primary molars accordingly are longer and more slender and flare more, extending out beyond projected outlines of the crowns.

This flare allows more room between the roots for the development of permanent tooth crowns see Figures and The cervical ridges of enamel of the anterior teeth are more prominent. These bulges must be considered seriously when they are involved in any operative procedure see Figure The crowns and roots of primary molars at their cervical portions are more slender mesiodistally.

The cervical ridges buccally on the primary molars are much more pronounced, especially on the maxillary and mandibular first molars see Figures through The buccal and lingual surfaces of primary molars are flatter above the cervical curvatures than those of permanent molars, which narrows the occlusal surfaces. The primary teeth are usually less pigmented and are whiter in appearance than the permanent teeth. Figure A, This is a specimen of a 5- to 6-year-old child prepared to show a full complement of primary teeth, the beginning of resorption of deciduous roots in some, and no apparent resorption in others.

This front view shows the relative positions of the developing crowns of the permanent anterior teeth. The maxillary central and lateral incisors and the canine are shown overlapped in a narrow space, waiting for future development of the maxilla that will allow them to develop roots and improve the alignment.

Unless they were lost in preparation, no development shows of mandibular permanent premolars. The tiny cusps formed at this age would be lost easily in preparation.

The Primary (Deciduous) Teeth (Dental Anatomy, Physiology and Occlusion) Part 1

Note the crowns of permanent maxillary premolars located between the roots of the first and second primary molars, with their roots still intact.

Note the well-developed first permanent maxillary molar entirely erupted with half its roots formed. Ordinarily, the mandibular first permanent molar comes in and takes its place first, the maxillary molar following. The specimen shows the mandibular molar still covered with bone and no roots in evidence. The maxillary second molar crown is well developed and located in a place that is about level with the present root development of the permanent maxillary first molar. Pulp Chambers and Pulp Canals A comparison of sections of primary and permanent teeth demonstrates the shape and relative size of pulp chambers and canals Figurewhich is noted here: Crown widths in all directions are large in comparison with root trunks and cervices.

The enamel is relatively thin and has a consistent depth.

  • Modified Angle's Classification for Primary Dentition

The dentin thickness between the pulp chambers and the enamel is limited, particularly in some areas lower second primary molar. The pulp horns are high, and the pulp chambers are large FigureA and B. Primary roots are narrow and long when compared with crown width and length.