Relationships Between the Development of the Dentition and Facial Growth
A complex interplay exists between the development of the dentition and facial growth. This interplay is regulated largely by the teeth that are present. Some relevant aspects will be elaborated on with respect to the situation during infancy and during the first and second transitional periods.
The concept of the apical area and the division of it into anterior, middle, and posterior sections is described. Further, the enlargement of the apical area which occurs during growth, and the relationship between the size of the separate sections and the accommodation of the teeth therein, are discussed.
Different aspects of eruption and emergence are described. The resorption of deciduous teeth and the process of transition to the permanent dentition are discussed.
Consideration is also given to the location of the teeth and the relationship between the dentition and the facial contours.
6.2 The development of the dentition and facial growth in first years of life
The development of the teeth has a character all of its own. This is due essentially to the fact that well before a tooth emerges into the mouth the ultimate dimensions of its crown have been reached. The crown of a tooth is calcified in situ using a full-sized template. This is contrary to the process in all other organs and tissues, whose growth invariably involves a gradual change in size. With this also comes the fact that generally the enamel and the dentin, unlike most other tissues, have no capacity for repair.
The first deciduous teeth emerge at about the age of 6 months. All the deciduous teeth are normally present in the mouth in the third year of life. In the transitional phases, the deciduous teeth are successively replaced by permanent teeth. Permanent molars are added to the dental arch distally. The manner in which the amount of tooth material in the mouth alters is discontinuous in character: as deciduous teeth are exfoliated and as permanent teeth appear the total arch length varies not smoothly, but in steps. In a newborn child, the crowns of all the deciduous teeth are already entirely or to a large extent formed. The maxilla and mandible are much too small to accommodate all those teeth in their ultimate archform—side by side. In this developmental phase, the incisors and canines are situated in a sort of “overlapping fence-paling” arrangement.296
The superior margin of the ramus of the mandible in the newborn child lies a little higher than the superior border of the corpus of the mandible. The corpus and the ramus more or less make up one elongated form (Fig. 5-2D). The anterior (ventral) surface of the mandible is positioned dorsally in relation to that surface of the maxilla. The temporomandibular joints have not yet taken; their definitive form and jaw movements are uncoordinated. The tooth germs are found on the small narrow basal bone of the mandible; they are encapsulated in thin bone, buccally, lingually, and in part occlusally. The maxillary teeth are also enveloped in thin bone, except on the occlusal. The morphology of the part of the bone containing the teeth reflects the size and position of the forming teeth.
In the first six to eight months after birth, the mandible grows more to ventral than does the maxilla. Further, the maxilla and mandible display a notable increase in all dimensions of the tooth-bearing parts of the bones. Consequently, it is possible for the unerupted deciduous incisors and canines, which originally lie overlapping each other, to move medially and labially in the jaw and eventually assume good alignment before emerging. Normally, both jaws grow sufficiently to provide more than enough room for the deciduous teeth to form harmonious arches. As a rule, the development is sufficient to result in diastemata throughout the deciduous dentition.
As has been outlined in the previous chapters, the vigorous transverse development of both the jaws is possible principally because there is a suture in the median plane of the maxilla and a cartilaginous structure in the midline of the mandible of an infant. Both are capable of extensive growth. In the mandible, this potential is short-lived because the symphysis begins to ossify some six months after birth. Due to the ossification, the possibility for interstitial growth characteristic of cartilage is lost. As has been indicated in Chapter 3, bone does not have that capability. Against this, the midpalatal suture in the maxilla remains present until the development of the dentition and facial growth is concluded. The mandible and maxilla are adjusted transversely with respect to each other by the occluding dental arches once the deciduous posterior teeth have come into contact. As a result, the development in width of the maxillary arch is determined primarily by the limitations of the mandibular arch. Consequently, the growth potential of the midpalatal suture will be utilized only to a limited extent after the symphysis of the mandible has become ossified.
The mandibular central deciduous incisors are the first teeth to emerge. They are followed shortly afterwards by the remaining deciduous incisors in the mandible and maxilla.
As already indicated, occlusion in the posterior region, and the first vertical support contributed by teeth that is combined with interdigitation, occurs about the 16th month when the first deciduous molars of mandible and maxilla come into contact. These teeth seldom emerge precisely in the place where they will occlude with their antagonists without modifications in position either transversely or sagittally. In most cases, the large palatal cusp of the maxillary first deciduous molar will fall somewhere within the margins of the “crater” formed in the occlusal anatomy of the mandibular first deciduous molar. This “crater” will then function as a funnel into which the cusp of the maxillary tooth is led to establish correct occlusion.249 Any transversal adjustment in position of the teeth required to achieve this will be principally provided by the maxillary teeth, because the structure of the mandible offers fewer possibilities for that (Fig. 4-7).
At birth, the crowns of the permanent incisors and first molars are already forming in conjunction with the deciduous teeth. At about this time, the calcification of the first permanent molar begins; the incisors have already started to calcify before birth. Both the permanent incisors and the later-forming canines are located lingually to their predecessors. These latter teeth stand more or less upright in the jaws, thereby leaving room lingual to their roots for the successors to form.
6.3 Situation before transition
By the time the deciduous dentition has erupted fully, the maxilla and the corresponding part of the mandible are well and truly filled with developing tooth germs,134 203 204 which are arranged in a specific order. The available space seems to be used to the best possible advantage. Depending on the size relationships between the tooth crowns and the jaws that house them, the position of the permanent teeth can vary.
The original narrow ridge-shaped basal section of the mandible which exists at birth has, in the meantime, widened and thickened. The forces generated in biting and chewing can be withstood. Through the continued vertical growth of the jaws, the height available to accommodate the forming permanent teeth increases gradually.
Figure 6-1 (A, B, C, and D) illustrates the situation in a child of about 6 years, whose first permanent molars have emerged. The mutual relationships between the teeth and a number of other aspects are discussed.
Fig. 6-1A* A skull preparation of a 6-year-old child, in which the first permanent molars have emerged. The same preparation is also pictured in Figs. 6-1B, C, and D and 6-10.
The maxillary permanent canines (5) are located high next to the apertura piriformis. The roots of their predecessors are nearly fully formed (1). The maxillary central permanent incisors (2) lie just beneath the nasal floor. Their crowns are fully formed; the root formation has started (3). The distal angles of their crowns lie against the roots of the lateral deciduous incisors. The deciduous teeth that will be lost first—the incisors—show resorption of their roots. Also, the associated alveolar bone is already partly broken down at the cervical margin (7). The partly formed crowns of the maxillary lateral permanent incisors (4) are found lingually to the central ones and are located more occlusally. By that means more room is given to the large crowns of the central permanent incisors than would be available if all the incisors were formed at the same level. The intermaxillary suture (6) is situated between the maxillary central permanent incisors. (Van der Linden and Duterloo.294)
Fig. 6-1B Diastemata are seen between the crowns of the mandibular deciduous incisors which stand upright (5). The maxillary deciduous incisors also stand about perpendicular to the occlusal plane. The crowns of the mandibular central permanent incisors stand close to each other and are not separated by a suture as in the maxilla. The crowns of the mandibular permanent lateral incisors are lingual to and a little more caudal than those of the central incisors; they are slightly overlapped mesially by them. The roots of the mandibular permanent incisors are partly formed (1); the central incisors a little more advanced than the lateral ones. The crowns of the permanent canines are not yet complete (2). The partially formed crowns of the mandibular premolars are below and between the roots of the deciduous molars (3, 4). About half of the roots of the deciduous incisors is no longer covered with bone (6). (Van der Linden and Duterloo.294)
Fig. 6-1C The maxillary central permanent incisor is directly under the nasal floor and palatal to the root of its predecessor (1). The lateral permanent incisor lies palatally to and a little more caudal than the central one (2); the two teeth are in close contact (3). The crown of the permanent canine lies buccal to and more cranial than that of the lateral incisor (4). The mesial surface of the partly formed crown of the maxillary first premolar lies against the distal angle of the permanent canine crown. The crowns of the maxillary premolars (5, 6) are above and between the roots of their predecessors, those of the first deciduous molar already resorbing (8), while those of the second have just become completely formed (9). The mesiobuccal root of the maxillary first permanent molar is formed partially (7). (Van der Linden and Duterloo.294)
Fig. 6-1D The forming parts of the mandibular central permanent incisors are close to the labial cortical plate; their incisal edges are lingual to the roots of their predecessors. Their crowns incline lingually, the opposite to the maxillary incisors, which incline labially. The forming part of the permanent mandibular canine crown is situated directly above the cortex of the mandibular basal bone (1). The crown of the first premolar is nearly complete (2); that of the second is not yet so advanced (4). Substantial space exists between the first and second premolars (7), which is also the case between the second premolar and the mesial root of the first permanent molar (8), both roots of which are not yet completely formed (5). The crown of the second permanent molar is inclined mesially and located some distance away from the first permanent molar (6). The roots of the first deciduous molars are partly resorbed (3). Such is the case for the associated alveolar bone (10). In the maxilla, the furcations of the deciduous molars are no longer covered with bone (11). The crown of the maxillary second permanent molar is tipped distobuccally (9). (Van der Linden and Duterloo.294)
The first transitional period—in which the incisors are replaced—begins, as a rule, with the exfoliation of the mandibular central deciduous incisors.
The permanent incisors, in comparison with their predecessors, take up a more labially inclined position after emergence. Consequently, their incisal edges are situated more labially than those of their predecessors. The diastemata present initially in the deciduous dentition do not, as a rule, provide enough space entirely to accommodate the wider crowns of the permanent incisors in regular alignment. More space usually develops with an increase of width between the deciduous canines, which accompanies the exchange of the deciduous incisors for the permanent ones. In this increase in intercanine width, the relationship between the crowns of the permanent incisors and the roots of adjacent deciduous teeth, located lateral to them, plays a significant role.293 294
The three factors that jointly enable the broader crowns of the permanent incisors to be accommodated usually—the more labial inclination and position, the diastemata in the deciduous dental arches, and the increase in the intercanine width—are more pronounced in the maxilla than in the mandible. This is in conformity with the difference in total crown breadth between corresponding groups of four incisors from deciduous and permanent dentitions; the differences for the maxilla and mandible are over 7 mm and 5 mm, respectively.196 257 In Figure 6-2 (A–D) the situation is illustrated as it exists after the permanent incisors have emerged and the second transitional period has not yet begun. Several aspects are gone into specifically in the subscripts.
A notable difference between the first and second transitional periods is the variation in sequence of emergence of the permanent teeth involved. The incisors normally undergo transition always in the same sequence. The central permanent incisors first emerge, followed about a year later by the lateral ones. Because only very little growth in ventral and transverse direction occurs in the anterior region of the alveolar process after the first year, the alignment of the permanent incisors (unlike that of the deciduous incisors) cannot improve before emerging. Permanent incisors erupt from the position in which they are formed. The limited available space, especially in the maxilla, does not permit the incisors to emerge either together or soon after each other. The broad maxillary central incisor must, as indicated in Figure 6-2C, be the first to descend.
With no other tooth is there as pronounced a difference in the mesiodistal diameters of the crown compared with the root, as with the maxillary central permanent incisor. The space which is sufficient in the adult to accommodate all four roots of the maxillary permanent incisors is very tightly measured for the temporary accommodation offered the incisor crowns before their eruption. In addition, it must be noted that in that period of development the permanent canine crowns also occupy a large place in the jaws and restrict the available space more than later will be the case when the space is only required to accommodate the narrower roots. The initial convergence of the roots of the maxillary incisors present after their emergence usually does not start to alter until the permanent canines have fully erupted, providing natural correction of the so-called “ugly duckling” phase.47
Fig. 6-2A Drawing from a skull preparation of an 8-year-old child. The same preparation is also pictured in Figures 6-2B, C and D, and 6-11. The maxillary permanent canines are situated in the maxilla next to the aperture piriformis. Their crowns restrict the space available for the roots of the incisors. The roots of the laterals lie close to the permanent canine crowns. Between the roots of the maxillary central incisors there is relatively ample room (7), which is connected with the fact that the intermaxillary suture runs between those teeth. The forming parts of the central incisors (1) are closely associated with the nasal floor; those of the lateral incisor are more to the occlusal (2). The lateral incisors are less advanced in their formation than are the centrals. Between the crowns of the two central incisors is a diastema; between the crowns of the centrals and laterals there is contact (3). The eruption of the permanent incisors brings with it a local rebuilding of the cervical part of the alveolar process (5), just as is the case with all teeth for which there is a predecessor. The bone which embraces the deciduous teeth is largely resorbed as these are exfoliated. The roots of the deciduous canines and the associated cervical alveolar crest are, at this stage, already obviously resorbed (4, 6). (Van der Linden and Duterloo.294)
Fig. 6-2B The crowns of the mandibular central incisors contact each other (1). The partly formed roots of the mandibular permanent canines end close to the lower border of the mandible (4). Their crowns restrict the space available for the roots of the mandibular incisors; the latter converge. The cervical margins of the alveolar process have been rebuilt with the eruption of the mandibular incisors (2). The deciduous canines in the mandible are tipped to the buccal (3), probably as the result of their earlier displacement laterally in the process of widening the distance between the deciduous canines. The roots of the deciduous canines and the cervical margins of the associated alveolar process are already significantly resorbed (5, 6). The bone between the lower border of the mandible and the apices of the incisors is not compact, but cancellous (7). This is in contrast with the bone of the lower border itself and the bone which directly surrounds the teeth, which is compact. (Van der Linden and Duterloo.294)
Fig. 6-2C The maxillary lateral incisor, which is not yet fully erupted, could not descend until the central incisor was almost to the occlusal plane. As a rule, the former is prevented from emerging labially by the broad crown of the latter.293 The crown of the lateral is in contact with that of the central (1); but, in cases with more space available than illustrated here, contact often does not occur. The crown of the lateral incisor is also close to that of the deciduous canine (2). The mesial surface of the crown of the maxillary first premolar (3) forms in close contact with the distal angle of the permanent canine; that surface is concave. There is a septum of bone between the two maxillary premolar crowns (6). The completely formed crown of the maxillary second premolar (4) is above and between the roots of its predecessor, which are resorbing (5). A similar situation exists with the first premolar and deciduous first molar, but in a more advanced stage. Although the furcation of the roots of the latter is no longer covered with bone (8), there is still bone between the roots and the descending drown of the first premolar (9). The mesiobuccal root of the maxillary first permanent molar is four-fifths formed, with the apex still wide open (7). (Van der Linden and Duterloo.294)
Fig. 6-2D Considerably more space for the crowns of the premolars and the permanent canine exists in the mandible than in the maxilla. The forming part of the mandibular canine is close to the lower border of the mandible (1). The root formation of the first premolar crown (2) is less advanced than that of the canine, but more advanced than that of the second premolar (3), which lies inferior to a considerable layer of bone (10). The roots of the mandibular first permanent molar are four-fifths formed (4); the crown of the second molar is complete (5). The distal root of the first deciduous molar is partly resorbed (6). There are thick septa of bone between the crowns of the premolars and permanent canines in the mandible (7); this is not the case in the maxilla. There also is a good deal of space anterior to the mesial root of the mandibular first permanent molar (7), which is not so in the maxilla. The crown of the maxillary second permanent molar is tipped distobuccally (8). The bone at the alveolar margin of the maxillary first deciduous molar is resorbing and has built up at the cervical margin of the first permanent molar (9). (Van der Linden and Duterloo.294)
6.5 Second transitional period
The second transitional period, which encompasses the replacement of the deciduous canines and molars by their successors, is of shorter duration than the first. The spatial relationships within the jaws allow this to happen.
In the lower canine-premolar region, there is generally sufficient room for the permanent teeth to erupt unimpeded. That is not always so in the maxilla. Whenever the space available is limited, emergence of the maxillary first premolar must as a rule precede that of the canine. The rest of the teeth which emerge during the second transitional period in both maxilla and mandible can normally erupt without hindrance from their neighbors. All possible sequences of emergence of the permanent canines and premolars, including simultaneous emergence of all three teeth alongside each other, can be seen.155 244
The relationships between the developing dentition and the growth of the jaws, and the problems that can originate therefrom, are easier to understand if the jaws are not considered in totality, but are taken in subdivisions. Moreover, extra clarity is gained when the region in which the teeth were formed initially, and in which the roots are later located, is given prominence in such a consideration.
With that objective in view, the author introduced the concept of the “apical area” in 1979.290 He described it as follows:
The apical area† in an infant is comprised of the region that contains the forming parts of the deciduous and permanent teeth. In the deciduous dentition the apical area is constituted of the region in which the apices of the deciduous teeth can be located and the forming parts of the permanent teeth are situated. In the mixed dentition the apical area consists of the region where the roots of the deciduous and permanent teeth can be located and the forming parts of the nonerupted permanent teeth are situated. In the adult state the apical area is the region where the apices of the fully formed teeth can normally be located.297
The apical area is three-dimensional. It has not only buccolingual and mesiodistal dimensions, but also has a vertical component. The latter is of less clinical importance than the two others since there are rarely any restrictions in a vertical direction. In further discussions of the apical area, the vertical component will be included only incidentally.
On the basis of morphological characteristics and differences in growth potential, the apical area in the mandible and maxilla can be divided into three sections: anterior, middle, and posterior. This division is illustrated in Figure 6-3 and defined in the accompanying text. The clinical relevance of the apical area and the subdivision of it are discussed further in Chapter 8.
Fig. 6-3 Mesiodistal dimensions of the apical area in the mandible and maxilla, subdivided into anterior, middle, and posterior sections.
A,B In a 4-year-old child, the anterior section of the apical area is formed of the region between the mesial surfaces of the developing part of the permanent canines. This region can continue to increase in size in the maxilla thanks to the presence of the midpalatal suture; this is not the case in the mandible.
The middle section of the apical area lies between the distal border of the anterior section and the mesial surface of the developing part of the first permanent molar. This section cannot increase in length in either the mandible or maxilla since bone is incapable of interstitial growth. The posterior section of the apical area lies dorsally from the middle section and extends to include the maxillary tuberosity in the maxilla and the lingual tuberosity in the mandible.82 Through bone formation at both tuberosities, the posterior sections are enlarged gradually and in this way accommodate the molars which successively are added to the distal of the dental arches.
C,D At 10 years of age, the same principles apply to the division into anterior, middle, and posterior sections of the apical area as was outlined above for the 4-year-old. Modification is, however, necessary to allow for the vertical movement of the first permanent molars and the canines.
E,F In a 21-year-old, the borders of the sections are slightly mesial to the roots of the first molars and the canines. The latter are fully formed and in occlusion. The size of the posterior section of the apical area depends on the dorsal growth which has occurred at the maxillary and lingual tuberosities.
6.6.1 Enlargement of the apical area
The size of the apical area increases markedly in the first year of life (Figs. 4-5, 4-6). The tooth germs move within the growing jawbones. Thereafter, the increase of the apical area in transverse and ventral directions is restricted decidedly, particularly in the mandible. It is only through apposition and resorption on the surfaces that enlargement of the mandible can occur, and, in practice, that appears to happen only minimally. The anterior part of the lower border of the mandible undergoes no noticeable further change in dimensions except to increase in bone thickness. In the maxilla the midpalatal suture continues to offer a possibility for increase in width, while in the region posterior to the canine and first premolar, the maxilla can still be built outwards by apposition and resorption. The posterior section of the apical area in the maxilla and mandible is unlike the two other sections in that, from birth to the end of facial growth, it gradually increases in size and is built up dorsally (Figs. 6-4 and 6-5).
The size of the apical area does not always correspond with the space needed for the teeth. Sometimes the apical area is noticeably larger than necessary. Mostly, there is a reasonable relationship between needed and available space. However, the apical area is quite frequently too small to accommodate all the teeth adequately. Considerable variation in size is encountered in each of the three sections. They can each be classified separately as large, medium, or small. Naturally, the size of the apical area has important consequences for the position of the teeth in the jaws when they have not yet emerged, for the process of transition and for the ultimate situation after completion of the development of the dentition.
Fig. 6-4 Occlusal views of the mandible and maxilla indicating the division into anterior, middle, and posterior sections of the apical area; these views have the dental arches projected upon them.
A There are few changes in the mandible possible in the anterior and middle sections of the apical area.
B The maxillary midpalatal suture remains open until after the conclusion of the development of the dentition and facial growth. The maxillary lateral segments under the maxillary sinus, which is indicated in the drawing by shading, have the potential for apposition and resorption in a transverse direction (transformation).
Fig. 6-5 Superimposition of drawings of mandible and maxilla at ages 4, 10, and 21 years to illustrate the enlargement of the apical area, subdivided into anterior, middle, and posterior sections.
A The anterior and middle sections of the apical area in the mandible do not become larger, but the posterior section does expand dorsally at the lingual tuberosity.
B In the maxilla, the anterior section of the apical area can expand through growth at the midpalatal suture. This growth can also contribute to a lateral translation of the middle and posterior sections. The size of the middle section, however, cannot increase sagittally. The posterior section gradually expands by means of bone formation at the maxillary tuberosity.
6.6.2 Anterior section of the apical area
The picture in the anterior sections of the apical area changes considerably during development from newborn to adult. Initially, the anterior section of the apical area in both jaws is occupied completely by developing teeth. After emergence of the deciduous incisors, more space becomes available for their successors, especially as a consequence to the marked vertical development in the related regions of the jaws. With the replacement of the deciduous incisors by their successors, even more space becomes available. The large incisor crowns have emerged, the roots of the deciduous incisors are gone, and only the roots of the permanent incisors are present within the alveolar process. Subsequent to the emergence of the permanent canines, more space becomes available in the anterior sections of the apical area, thus permitting the regular alignment of the permanent incisors. Different aspects connected with the size of the anterior section of the apical area are illustrated and described in Figures 6-6 and 6-7, concerning the situation at an early age.
Fig. 6-6 Examples of large, medium, and small anterior sections of the apical area in the deciduous dentition in the mandible, in frontal and occlusal views.
A,B Large anterior section of the apical area with adequate space, in the deciduous dentition, and relatively small mesiodistal crown diameters of the permanent incisors. Their crowns have relatively much space. The permanent centrals stand apart and overlap the laterals only slightly. There is no contact between the distal surface of the permanent central incisor crowns and the roots of the adjacent deciduous lateral incisors. The same applies to the crowns of the permanent lateral incisors and the roots of the adjacent deciduous canines. There is a relatively large amount of space at the level of the incisal region of the permanent incisors (p). There is also sufficient space at the height of the necks of the permanent incisors (q). The laterals are located only slightly more lingually than the centrals at that level.
C,D Medium anterior section of the apical area with limited diastemata in the deciduous dentition and relatively large crowns for the permanent incisors. The permanent mandibular incisors are close to one another. The laterals are somewhat overlapped. At the level of the incisal region of the permanent incisors (p), the crowns of the permanent teeth and the roots of the deciduous teeth lie close together. At the height of the necks of the permanent incisors (q), the available space is obviously not greater than that needed. The lateral incisors at that level are lingual to both the central incisor and the canines.
E,F Small anterior section of the apical area, with no diastemata in the deciduous dentition. The lateral permanent incisors overlap considerably. The distal angles of the central permanent incisors contact the roots of the lateral deciduous incisors. A corresponding situation is usually applicable to the lateral permanent incisor and the deciduous canine. At the level of the incisal region of the permanent incisors (p), the permanent crowns and the/>
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