Maxillary Teeth
Central Incisors
The contact areas mesially on both central incisors are located at the incisal third of the crowns. Since the mesio-incisal third of these teeth approaches a right angle, the incisal embrasure is very slight.
Central and Lateral Incisors
The distal outline of the central incisor crown is rounded. The lateral incisor has a shorter crown and has a more rounded mesioincisal angle than the central incisor. The form of these two teeth coming into contact with each other therefore opens up an embrasure space distal to the central incisors larger than the small one mesial to the central incisors. A line bisecting the contact areas distal to the central incisor and mesial to the lateral incisor approaches the junction of the middle and incisal thirds of each crown.
Lateral Incisor and Canine
The distal contact area on the lateral incisor is approximately at the middle third. The mesial contact area on the canine is at the junction of the incisal and middle thirds. The form of these teeth creates an embrasure that is more open than the two previously described.
Canine and First Premolar
The canine has a long distal slope to its cusp, which puts the distal crest of curvature at the center of the middle third of the crown. The contact area is therefore at that point. This is an important observation to be made clinically. As mentioned, it is at this point in the dental arch that the canine, situated between the anterior and posterior segments, becomes a part of both (see Figure 5-15, B and C).
The first premolar has a long cusp form also, which puts its mesial contact area rather high up on the crown. Usually it is just cervical to the junction of the occlusal and middle thirds. The embrasure between these teeth has a wide angle.
First and Second Premolars
The contact areas of the first and second premolars are similar to those just mentioned, although usually a little cervical to the junction of the occlusal and middle thirds of the crowns. The form of these teeth creates a wide occlusal embrasure.
Note that the design of the interproximal spaces changes also with the form and dimensions of the teeth in contact.
Second Premolar and First Molar
The position of the second premolar and first molar contact areas cervico-occlusally is about the same as that found between the premolars.
First and Second and Second and Third Molars
The two contact and embrasure forms for the first and second and second and third molars may be described together, since they are similar. The distal outline of the first molar is round, a fact that puts the contact area approximately at the center of the middle third of the crown. Here again, it must be emphasized that contact levels on maxillary molars (and even on premolars to some extent) tend to be centered in the middle third of the anatomical crown.
The mesial contact area of the second molar also approaches the middle third of the crown. The occlusal embrasure is generous as a consequence, even though the cusps are not long.
The contact and embrasure design of the second and third molars is similar to that of the first and second molars. The molars become progressively shorter from the first through the third. Again, the dimensions of the tooth crowns affect the contact and embrasure design.
Mandibular Teeth
Central Incisors
The mesial contact areas on the mandibular central incisors are located at the incisal third of the crowns. At the time of the eruption of these teeth, the mesial and distal incisal angles are slightly rounded, and the mamelons are noticeable on the incisal ridges. Soon, however, incisal wear reduces the incisal ridge to a straight surface, and the mesial and distal angles approach right angles in sharpness. This is due partly to wear at the contact areas (see Figures 5-7 and 5-14). In many instances, the contact areas extend to the mesioincisal angle. Therefore a small incisal embrasure occurs mesially between the mandibular central incisors unless wear through usage obliterates it.
Central and Lateral Incisors
The distal contact areas and the incisal embrasures on the central incisors and the mesial contact areas and incisal embrasures on the lateral incisors are similar to those just described. Because the mandibular central and lateral incisors are small mesiodistally and supplement each other in function, the design of their crowns brings about similar contact and embrasure forms.
Note the slender Gothic arch-like spaces that circumscribe the interproximal spaces between the mandibular anterior teeth.
Lateral Incisor and Canine
The positions of the contact areas distally on the lateral incisor and mesially on the canine are approximately the same, cervicoincisally, as the other two just described. The teeth are in contact at the incisal third close to the incisal ridges. However, the mesioincisal angle of the canine is more rounded than the others, which form opens up a small incisal embrasure at this point.
The interproximal spacing between lateral and canine is very similar in outline to the two interproximal spaces just described.
Canine and First Premolar
The distal slope of the cusp of the mandibular canine is pronounced and long, which places the distal contact area on this tooth somewhat cervical to the junction of its incisal and middle thirds.
The first premolar has a long buccal cusp, and although its crown is shorter than that of the canine, the mesial contact area has about the same relation cervico-occlusally as that found distally on the canine and is just cervical to the junction of the occlusal and middle thirds. Thus the whole arrangement places these contact areas level with each other.
The occlusal embrasure is quite wide and pronounced because of the cusp forms of the two teeth. The interproxi-mal space has been reduced by the lowering of the contact areas cervically, comparing favorably to the design for posterior mandibular teeth.
First and Second Premolars
From the buccal aspect, the crowns of the first and second premolars are similar. The buccal cusp of the second premolar is not quite as long as that of the first premolar. The contact of these teeth is nearly level with that of the canine and first premolar. The slope of the cusps creates a large occlusal embrasure. The interproximal space is a little smaller than that between the canine and first premolar.
Second Premolar and First Molar
The contact and embrasure design for the second premolar and first molar is similar to that just described for the premo-lars. The mesiobuccal cusp of the first molar is shorter and more rounded than the cusp of the second premolar, which varies the embrasure somewhat, and since the crown of the molar is a little shorter, it reduces the interproximal space to that extent.
First and Second and Second and Third Molars
The two contact and embrasure designs of the first and second and second and third molars may be described together, since they are similar.
The proximal surfaces—that is, the distal surface of the first molar, mesial surface of the second molar, distal surface of the second molar, and mesial surface of the third molar— are quite round. The occlusal embrasures are therefore generous above the points of contact, even though the cusps are short and rounded.
Because the molars become progressively shorter from the first to the third, the centers of the contact areas also drop cervically. A line bisecting the contact areas of the second and third molars is located approximately at the center of the middle thirds of the crowns.
The interproximal spaces have been reduced considerably because of their shortened form.
Contact Areas and Labial, Buccal, and Lingual Embrasures from the Incisal and Occlusal Aspects
To study the relative positions of contact areas and the related labial, buccal, and lingual embrasures and also to get proper perspective, the eye must be directed at the incisal surfaces of anterior teeth and directly above the surface of each tooth being examined in series (Figure 5-17; see also Figures 5-8, 5-10, and 5-11). Posterior teeth are examined in the same manner. Look down on each tooth or group of teeth by facing the occlusal surfaces on a line with the long axis.
The problem at this point is to discover the relative positions of contacts in a labiolingual or buccolingual direction and to observe the embrasure form facially and lingually created by the tooth forms and their contact relations.
Figure 5-17 Contact relation of mandibular teeth labiolingually and buccolingually when surveyed from the incisal and occlusal aspects. Arrows point to embrasure spaces. A, Central incisors and lateral incisor. B, Central and lateral incisors and canine. C, Lateral incisor, canine, and first premolar. D, Canine, first premolar, and second premolar. E, First premolar, second premolar, and first molar. F, Second premolar and first, second, and third molars.
A generalization may be established in locating contact areas faciolingually. Anterior teeth will have their contacts centered labiolingually, whereas posterior teeth will have contact areas slightly buccal to the center buccolingually. This buccal inclination must be carefully studied and must not be overemphasized.
Except for the maxillary first molar, all crowns converge more lingually than facially from contact areas. The maxillary first molar is the only tooth wider lingually than buc-cally (see Figure 5-16). Its formation makes a necessary adjustment of the mesiolingual embrasure when the tooth form of maxillary posteriors changes from the maxillary premolar form to the purely rhomboidal form of maxillary second and third molars. This situation is discussed more fully later on.
The narrower measurement lingually rather than facially causes wider embrasures lingually compared with facial embrasures. Compare the two types of embrasures displayed by maxillary central and lateral incisors.
Maxillary Teeth
The contact areas of the central incisors are centered labio-lingually. The labial embrasure is a V-shaped space created by the labial form of these crowns. The lingual embrasure widens out more than the labial embrasure because of the lingual convergence of the crowns (see Figure 5-10, A). Note the centering of the labioincisal edge with respect to the crown outline of these teeth, and the narrowness of the lingual surfaces in comparison with the broad labial faces.
Central and Lateral Incisors
The contact areas of the central and lateral teeth are centered labiolingually also.
Lateral Incisor and Canine
The contact area of the lateral incisor and canine is centered labiolingually on both canine and lateral incisors. The lingual embrasure is similar to that of the central and lateral incisors, but the labial embrasure is changed somewhat by a definite convexity at the mesiolabial line angle of the canine.
Canine and First Premolar
The contact area of the canine and first premolar is centered on the distal surface of the canine but is a little buccal to the center on the mesial surface of the first premolar. The embrasure design lingually is marked by a concavity in the region of the distolingual line angle of the canine and by a developmental groove crossing the mesial marginal ridge of the first premolar.
First and Second Premolars
The contact areas of the first and second premolars are nearly centered buccolingually. The embrasures buccallym and lingually are regular in outline, although slightly different in design.
The prominence of the mesiobuccal and distobuccal line angles of the premolars is in direct contrast to the even taper of these teeth lingually, as viewed from the occlusal aspect. This form demonstrates a slight variation between buccal and lingual embrasures.
Second Premolar and First Molar
As usual, a line bisecting the contact areas of the second premolar and first molar is nearly centered on the distal surface of the second premolar. The area on the mesial surface of the first molar is located farther buccally than other contact areas on the maxillary posterior teeth. The contact areas are wider on molars because of the greater width buccolingually of the molar teeth.
The buccal embrasure between these teeth and the location of the mesial contact area of the first molar are influenced by the prominence of the mesiobuccal line angle of the maxillary first molar and the matching prominence of the distobuccal line angle of the maxillary second premolar. The lingual embrasure is kept standard for the molar area by the enlargement of the mesiolingual cusp of the first molar. Occasionally, this cusp carries a small conformation lingually as part of the change in form (fifth cusp, or cusp of Carabelli). Usually, the mesiolingual cusp of the maxillary first molar is rounded out, with no more than a developmental groove showing that an extra cusp formation may have been intended.
The mesiolingual lobe of this tooth is always large, however, causing the tooth to be wider lingually from its mesiolingual line angle to its distolingual line angle than it is from the mesiobuccal line angle to the distobuccal line angle. If it were not for this fact, the rhomboid form of the first molar in contact with the tapered form of the second premolar would open up a lingual embrasure of extremely large proportions. The large mesiolingual lobe makes up for the change in occlusal outline from premolar form to molar form, keeping the conformity of the lingual embrasures (see Figure 5-16).
First and Second and Second and Third Molars
The contact and embrasure forms of the first and second and second and third molars may be described together, since they are similar. Although the mesiobuccal line angles of the second and third molars are not as sharp as that of the first molar, they are prominent nevertheless.
The distobuccal line angles of all the maxillary molars are indistinct and rounded, so that the buccal embrasure forms are shaped and characterized mainly by the prominent mesiobuccal line angle. The mesiolingual line angles of the second and third molars are rounded and in conjunction with the rounded distolingual line angles; the lingual embrasures between first, second, and third molars present a regular and open form (see Figure 5-8, F and G).
The contact areas are broad and centered buccolingually. The embrasures are uniform. Note the generous proportions of the buccal embrasures.
Mandibular Teeth
Central Incisors and Central and Lateral Incisors
The contact areas and embrasures of the central incisors and the central and lateral incisors may be described together, since they are similar.
Although these teeth are narrow mesiodistally, their labi-olingual measurements are not much less than those of the maxillary central and lateral incisors. The mandibular central incisors come within a millimeter or so of having the same labiolingual diameter as that of the maxillary central incisors; the mandibular lateral incisors have a labiolingual diameter as great if not greater than that of the maxillary lateral incisors.
The contact areas are centered labiolingually, and the embrasures are uniform. Although the mesiodistal dimensions are less, the outline form of the incisal aspects of the mandibular central and lateral incisors is similar to that of the maxillary central and lateral incisors in that the lingual outlines have a rounded taper in comparison with broader, flattened labial faces.
Lateral Incisor and Canine
The contact areas of the lateral incisor and canine are centered, and the lingual embrasure is similar to those just described. The labial embrasure is influenced by the prominence of the mesiolabial line angle of the canine. Note that the maxillary canine presents the same characteristic.
Canine and First Premolar
The canine and first premolar contact areas are approximately centered, and the buccal embrasure is smooth and uniform in outline. The lingual embrasure is opened up somewhat by a slight concavity on the canine distolingually and by a characteristic developmental groove across the marginal ridge of the first premolar mesiolingually.
First and Second Premolars
The contact areas of the first and second premolars are nearly centered buccolingually but are broader than those found mesial to them, because the distal curvature of the first premolar describes a larger arc than the mesial curvature and the mesial contacting surface of the second premolar is relatively broad and describes a shallower curved surface than that of the distal surface of the first premolar.
Because of the lingual convergence of the first premolar and the narrow lingual cusp form, the lingual embrasure is as wide as the one mesial to it.
Second Premolar and First Molar
The second premolar and first molar contact areas are wide and almost centered. The extent of the contact areas is sometimes increased by a slight concavity in the outline of the mesial surface of the first molar below the marginal ridge. The mesial contact area of the first molar is located farther buccally than any of the other contact areas on mandibular posterior teeth. It must be remembered that the same situation holds true in the upper dental arch when the contacts of the maxillary first molars and second premolars are described.
The prominence of the first molar at the mesiobuccal line angle is readily apparent. The mesial outline of the crown tapers to the lingual, forming a generous lingual embrasure in conjunction with the smooth curvature of the second premolar distolingually.
First and Second Molar
The contact areas of the first and second molars are nearly centered buccolingually, although they are not so broad as the contact just described. This variation is brought about by the design of the first molar distally. The distal contact area of the first molar is confined to the distal cusp, which does not present the broad surface for contact with the second molar that was found mesially in contact with the second premolar. This form, along with the rounded outline at the distobuccal line angle, opens up both embrasures wider than those found immediately mesial.
The outline of the first molar crown just lingual to the distal contact area presents a straight line and an occasional concavity.
The second molar outline buccally and lingually on both sides of the mesial contact area is uniformly rounded.
Second and Third Molars
The contact areas of the second and third molars are broad, and they are nearly centered buccolingually. When the third molar is normally developed, it is similar in outline to the second molar from the occlusal aspect. The buccal and lingual embrasures between these teeth are almost alike in form and extent.
A straight line may be drawn through the contact areas of the second premolar and the three molars, and it will come very near to bisecting all of the contact areas. These four mandibular teeth are set in a line that is almost straight (see Figures 5-10, B, and 5-17, F).
