DESCRIPTION OF DECIDUOUS TEETH
The deciduous teeth or primary, milk, baby and temporary teeth are twenty in number,10 in each jaw ( 4 incisors, 2 canines and 4 molars).
They start to erupt at the age of six month by the appearance of the first deciduous mandibular incisors in the oral cavity. At about 2 years old, the last deciduous tooth which is the second molar, starts to appears. At three year of age all the deciduos teeth are erupt and are in function.
As the term “deciduous” implies, teeth are shed in order to make way for their permanent successors. The process of exfoliation takes place between the sixth and twelfth years. One to two years after complete root formation resorption begins at the root apex of the deciduous teeth and continues cervical until resorption of the entire root has taken place and the crown is lost from lack of support.
The anterior deciduous teeth are replaced by the anterior permanent teeth, while the deciduous molars are replaced by the permanent premolars.
The life span of all the deciduous teeth in the oral cavity are from 6 months to 12 years of age, therefore, from 6 months to 6 years the oral cavity contains only deciduous teeth.
From 6-12 years, the oral cavity contains mixed dentition (deciduous and permanent). From 12 years on, the oral cavity contains only permanent teeth.
DECIDUOUS ANTERIOR TEETH
Maxillary central incisor
The deciduous central incisor closely resembles its permanent successor except for the following:-
- It is smaller than the permanent.
- Its crown shows greater mesiodistal width than the cervico incisal length which is the opposite for the permanent. The labiolingual dimension at the cervical third is only 1mm. less than cervicoincisally.
- The lingual surface shows well developed marginal ridges and cingulum.
- The cervical ridges of enamel are pronounced on the cervical third of the crown both labially and lingually.
- From the proximal aspect, the crown appears thick in relation to its total length.
- From the incisal aspect, the crown appears much wider mesiodistally than labiolingually.
- The root length is greater in comparison with the crown length than that of the permanent. A lingual ridge is evident on the full length of the root. On the mesal and distal surfaces of the root, there are central development depression for about the whole length of the root.
Maxillary lateral incisor
It is similar to the central incisor with some variation.
- The crown is smaller in all dimention.
- The cervico –incisal length of the crown is greater than its mesiodistal width.
- The root is similar in shape to the central incisor but it is much longer in proportion to its crown.
Mandibular central incisor
They are similar to their successors except that:
- They are much smaller.
- The crown is wide in proportion to its length in comparison with the permanent.
- The mesial and distal sides of the crown taper evenly from the contact areas.
- From the mesial aspect, the incisal ridge is centered over the root. The labial and lingaual cervical contours are quite convex, much more than those of the permanent mandibular incisors.
- The root is almost twice the crown length and evenly tapered down to a pointed apex. It is very narrow and conical in shape.
- From the incisal aspect the incisal ridge bisects the crown labiolingually unlke permanent mandibular central incisors.
Mandibular lateral incisor
The fundamental outlines of the deciduous mandibular lateral incisors and similar to thoseoyu of the deciduous mandibular central except for:-
- It is somewhat larger in all measurements except labiolingually where the two teeth are identical in measurement.
- The cingulum,marginal ridges and lingual fossa are more developed.
- The incisal ridge slopes downwards distally, and its distal margin is more rounded.
It is similar to the permanent maxillary canine except for:-
- It is small in size.
- The crown is more constricted at the cervix in relation to its mesiodistal width and more conves on its mesial distal surfaces.
- The contact areas placed at about the same level nearly at the center of the crown
- cervico – incisally.
- The cusp of the deciduous canine is much longer and shaper than the permanent. The mesial slope of the cusp is longer than the distal slope which is the opposite for the permanent.
- The tip of the cusp is more distal in relation to a line bisecting the crown mesiodistally.
- The root is about twice as long as the crown and more slender than that of its permanent successor.
It is similar to the permanent mandibular canine except for;
- It is smaller.
- The mesial slope of the cusp is shorter than the distal slope. This is true for both the permanent canines and premolars except the maxillary first premolar.
- It differs from the deciduous maxillary canine in the following:
- It is thicker at the neck of the tooth.
- The cervical ridge labially and the cingulum lingually are not quite pronounced.
- The mesial cusp slope is shorter than the distal cusp slope.
DECIDUOUS POSTERIOR TEETH
Maxillary first molar
This tooth presents four cusps mostly and three roots.The mesiolingual cusp is the largest and the distolingual cusp is the smallest which may be even absent resulting in a three cusped molar.The first molar is much smaller thatn the deciduous maxillary second molar.
- It present narrow cervical portion of crown and root than that of the same portion of the permanent molars.
- At the contact areas mesially and distally, the crown shows its widest measurements. The measurement at the cervix is less than that at the contact areas mesiodistally by about 2mm.
- The occlusal margin is slight scalloped, but with no definite cusp form.
- The buccal surface is smooth with a slight evidence of developmental grooves.
- The furcation of the roots begins almost immediately at the site of cervical line. This characteristic is not possessed by the permanent molars.
- The roots are slender and long and spread widely. All three roots are seen from this aspect. The mesial root is longer than the distal one.Each of the three roots has a single root canal.
- The buccal cervical ridge is very developed particularly mesially.
- The crown converges considerably in a lingual direction.
- The outline lingually is similar to the buccal aspect.
- The mesiolingual cusp is the longest and sharpest, while the distolingual cusp is poorly defind or even absent. The distobuccal cusp may be seen from this aspect.
- All three roots are in view and the lingual one is the longest.
- The buccolongual dimestion of the crown at the cervical third is greather than the same dimention at the occlusal third.This characteristic is true of all molar teeth,but it is more evident on the deciduous teeth (the crown is constricted at the occlusal third).
- The pronounced convexity of the buccal cervical ridge is a outstanding characteristic of this tooth.
- The mesiolingual cusp is shaper and longer in size than the mesiobuccal cusp.
- The cervical line is curved slightly toward the occlusal surface.
- The mesiobuccal and lingual roots are the only visible from this aspect.The root is long,slender and extends lingually to a marked degree then curves sharply in a buccal direction above the meddle third.
- The crown appears narrower distally than mesially.
- The distobuccal cusp is long and sharp, while the diatolingual cusp is poorly developed.
- The buccal cervical ridge seen from the mesial aspect does not continue distally.
- The cervical line may curve occlusally or may run straight.
- The distobuccal and lingual roots are seen this aspect as well as the apical part of the mesiobuccal root.
- It is nearly rectangukar in shape with the shortest sides representing the proximal sides.(mesxial and distal)
- The crown outline converges lingual and distally.
- The occlusal surface shows a sulcus with its central groove connecting a central fossa and a mesial triangular fossa.
- A distal development grove connects the central fossa and the distal triangular fossa.
- The mesial and distal triangular fossae are just inside the meaisl and distal marginal ridges with a mesial and distal pit in them.
- Supplimantal grooves radiate from the mesial and distal pits, one to abuccal, and one to a lingual directions.A third supplemental groove extends from the pit toward the marginal ridge and may extend over it.
- This tooth may show an oblique ridge connecting the mesiolingual and distobuccal cusps. This ridge may be ill defined and the central developmental groove extends from the mesila pit to the distal developmental groove.
- The distal margine ridge is thin and poorly developed in comparison with the mesial marginal ridge.
- There is a well defined buccal developmental groove dividing the mesio buccal and distobuccal cusp occlusally.
Maxillary second molar
It resembles the masillary first permanent moloar that it is smaller in size.
- This is toothe shows well defined buccal cusp separated by a buccal developmental groove.
- The crown is narrower at the cervic in comparison with its mesiodistal measurement at the contact areas.
- The roots appear slender and much longer and heavier relatively than those of the permanent maxillary first molar.
- The bifurcation of the roots is close to the cervical line.
- There is lingual convergence of the crown and root.
- It shows two well developed cusps,the mesiolingual and the distolingual cusps are separated by a short lingual development groove.
- A supplemental poorly developed to the large mesiolingual cusps and is outlined by developmental groove lingually.
- The cervical line is nearly straight.
- All three roots are visible from this aspect; the ligual root is larger and thicker than the two buccal roots.
- The outline resembles that of the permanent molars.
- The crown appears short because of its thickness buccolingually in comparison with its length.
- The mesiolingual is cusp larger than the mesiobuccal cusp.
- The lingual root extends lingually beyond the crown outline.The point of bifurcation between the mesiobuccal and lingual roots is 2-3mm. Apical to the cervical line.
- The curvature at the cervical portion is pronounced lingually,but it resembles that of the permanent maxillary first molar buccally.In this,it differs entirely from the prominent curvature found on the deciduous maxillary first molar at the cervical third buccally.
It resembles that of the permanent maxillary first molar.
- It is somewhat rhomboidal and resembles the permanent maxillary first molar except that the buccal surface is rather flat.
- The developmental grooves between the cusps are less marked than that found on the permanent molar.
Mandibular first molar
It varies much from all the teeth and appears strange and primitive. It possesses four cusps and two roots.
- It shows two cusps separated by developmental depression instead of groove.The mesiobuccal cusp is larger than the distobuccal cusp.
- The mesial outline of the crown is straight from the convex contact area to the cervix constricting the crown very little at the cevix.
- The distal outline converges toward the contact are extend distally to a marked degree.
- The distal portion of the crown is shorter than the mesial portion because of dipping of the cervical line apically over the mesial root.
- There is a cervical enamel buccally (buccal cervical ridge) which is over development mesially. This makes the cervical line dips downward in order to outline this ridge.
- The two roots are long, slender and they spread greatly at the apical third beyond the outline of the crown.The distal root is shorter than the mesial one and their bifurcation is very close to the cervical line.
- The crown and root converge lingually to a marked degree on the mesial surface, while the opposite is true distally.
- The mesiolingual cusp is long and sharp,while the distolingual cusp is rounded with alingual developmental groove separating them.
- The mesial marginal ridge is well developed to the extent that it might almost considered as another small cusp lingually.
- The crown length mesially and distally is nearly equal.
- The cervical line is nearly straight.
- It is rhomboidal in outline.
- The buccal outline shows prominent conxity representing the cervical ridge, then it flattens to the cusp tip.
- The buccal cusp is placed over the root base while the lingual outline of the crown extends out lingually beyond the confines of the root base.This design places the cusps in a favourable position for proper occlusion with the upper molars.
- The mesiobuccal cusp and the mesiolingual cusp as well as the well developed mesial marginal ridge are seen.
- The cervical line extends upward in a buccolingual direction.
- The buccal and lingual outlines of the root drop straight down from the crown approximately parallel each other for over half the root length them taper at the apical third to a square end.
- A developmental depression in usually extends almost through the full length of the root.
- The crown has an equal length buccally and lingually and the cervical line is straight.
- The distal cusps are shorter and less sharper than the mesial cusps.
- The distal marginal ridge is less developed than the mesial marginal ridge.
- There is less curvature at the cervical third (no prominent buccal cervical ridge).
- The distal root is rounder, shorter and taper more apically.
- It is rhomboidal in outline.
- All four cusps are seen, the mesiolingual cusp is the largest.
- The prominence mesiobuccally (C.R) is noticeable from this aspect.
- From a central pit, the following grooves are seen,
- A buccal developmental groove extends buccally separating the two buccal cusps. It does not extend on the buccal surface.
- A central developmental groove extends mesially ending in mesial pit in the mesial triangular fossa and extends distally ending in a distal pit in the distal triangular fossa.
- A lingual developmental groove extends lingually separating the two lingual cusps. It does not extend to the lingual surface.
- There are supplemental grooves radiating from the mesial and distal pits buccally and lingually.
Mandibular second molar
It resembles the permanent mandibular first molar except for the following.
- It is smaller insize.
- The deciduous molar present narrow mesiodistal clibration at the cervix than does the permanent molar.
- The mesiobuccal and distobuccal developmental grooves divide the buccal surface of the crown occlusally into three cuspal protions almost equal in size (mesiobuccal and distobuccal and distal cusps)
- The mesial portion of the crown seems to be little higher than the distal portion of the crown lingually which gives the impression of being tipped distally.
- There is a prominent buccal cervical ridge,then the buccal surface flattened occlusal to the ridge.
- Proximally, the crown is rhomboidal in outline.
- The mesial marginal ridge is high,while the distal marginal ridge dips down more sharply and is shorter buccolingually than the mesial marginal ridge.
- The grown is norrower buccolingually in comparison with its mesiodistal measurement than is the permanent tooth.
- The root flares out greatly mesiodistally at the middle and apical thirds.They are twice as long as the crown.Ther bifurcation starts at a point immediately below the cervical line.
- The roots are more slender than those of the permanent molars.
- The occlusal surface shows a rectangular outline that converges lingually and distally.
The major differences between the deciduous and permanent teeth
- The crowns of the deciduous teeth are lighter in color than are the permanent teeth.
- The deciduous teeth are smaller in size than the permanent.
- The crowns of the deciduous teeth are more bulbous.
- The crowns of the deciduous anterior teeth are wider mesiodistally in comparison with their crown length than are the permanent.
- The crown widths of the deciduous molars are larger in all directions in comparison with the root trunks and cervices. The crown and roots are lender at thr “neck” mesiodiswtally than are those of permanent molars.
- The buccal and lingual surfaces of deciduous molars taper occlusally above the cervical curvature much more than do the permanent molar surfaces. This results in a much narrower occlusal table of the occlusal surface buccolingually.
- The buccal cervical ridge of enamel is quite prominent on the facial aspect of the deciduous anteriors and molar teeth (especially on the first molars).
- The roots of the deciduous anterior teeth are narrower and longer in comparison with crown length, as well as tooth length and width, than are the permanent teeth roots.
- The roots of the deciduous molars are relatively longer and more slender than the roots of the permanent teeth. They are more divergent and flare more extending out beyond projected outlines of the crown. The roots thin out rapidly as the apices are approached.
- In cross section, the deciduous teeth shows the following differences:
- The enamel is relatively thin and has a consistent depth.
- The dentin thickness between the pulp chamber and the enamel is much less than in the permanent teeth.
- The pulp chambers are relatively large, and the pulp horns are high occlusally placing them much closer to enamel than the permanent teeth.