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Chapter 16: Permanent Anterior Teeth Discussion questions

Terms in this set (39)

Although the concavity of the lingual surface of all mandibular incisors I smoother than that of maxillary incisors, supragingival tooth deposits, such as dental biofilms, calculus, and stain, tend to collect in the concavity. This buildup of deposits is aided by the mandibular incisors position in the oral cavity near the duct openings of the submandibular salivary gland and sublingual salivary glands in the floor of the mouth. Saliva, with its mineral content, is released from these glands, causing the dental biofilm to mineralize quickly into calculus. With attrition, the wearing away of a tooth surface caused by tooth-to-tooth contact, the incisal edge can change on the mandibular incisors. Thus, these incisors may lose their symmetrical form, exposing the inner dentin. With severe attrition, the incisal edge also becomes a concavity lined with exposed dentin; this porous dentin becomes intrinsically stained and unattractive or can be affected by dentinal hypersensitivity. Instrumentation may be more difficult in this area because many patients overlapping mandibular incisors owing to inadequate mandibular arch size and other occlusal factors. This crowding increases with age because of normal physiological mesial drift. If the incisors tip incisally back toward the tongue, instrumentation is also extremely difficult, and use of the mouth mirror for indirect vision is essential. Prolonged hand instrumentation can narrow even further the already narrow labial and lingual root surfaces of the mandibular incisors. The crowns of the teeth can thus be placed in jeopardy during mastication because of unsupported cervical enamel. Finally, the proximal surface of the roots is difficult to explore with instruments because of the limited interproximal space and the oral root shape, and the presence of proximal root concavities may also increase the difficulty.
Permanent mandibular central incisors erupt between 6 to 7 years of age (root completion at age 9). They erupt before the maxillary central incisors. They are the smallest and simplest teeth of the permanent dentition; thus, they are smaller than the lateral incisors of the same arch. Due to its smallness, the tooth has only one antagonist in the maxillary arch. This tooth and the maxillary third molar are the only teeth that have antagonist; all others have two. However, equally different is that the two mandibular centrals usually share a mesial contact area. This tooth has a simple root which is the widest labiolingually and then mesiodistally. The root has pronounced proximal root concavities, which vary in both length and depth, and a shallow depression extends longitudinally along the midportion of root. The pulp cavity of the mandibular central is quite simple, because it has a single pulp canal and three pulp horns. The root is a narrow oval cross section. The crown is symmetrical from the labial view, having a fan shape. The imbrication lines and developmental depressions usually are not present or are extremely faint. The mesial contact with the other mandibular central is at the incisal third. The distal contact with the lateral incisor is also at the incisal third. From the labial view, both the incisal angles, mesioincisal angle and distoincisal angle, are sharp or only slightly rounded; the mesioincisal angle is slightly sharper than the distoincisal angle, which helps to distinguish the right mandibular central incisor from the left. Nevertheless, distinguishing between the right and the left central incisors is often difficult. The mesial and the distal outlines are nearly straight from the CEJ to the relatively straight incisal edge. Lingual view features: the crown of a mandibular central incisor is narrower on the lingual surface than the labial, with its outline that is the reverse of the labial view. However, it outline of the crown is the most symmetrical of the incisors, either maxillary or mandibular. Overall, the lingual surface is smooth and has a small, centered cingulum. On the lingual surface, the single lingual fossa is barely noticeable; therefore, the mesial marginal ridge and distal marginal ridge are barely noticeable as well. Because the cingulum is centered, the faint mesial and distal marginal ridges have the same length. Proximal view features; the CEJ curvature is higher incisally on the mesial than on the distal surface, which helps to distinguish the right mandibular central incisor from the left. The incisal edge is usually straight but can be rounded and is lingual to the long axis of the root. The distal view is smaller to the mesial view of the tooth, except that the CEJ curves less incisally on the distal than the mesial surface. Incisal view features; it has a nearly symmetrical crown outline on the incisal view. The incisal edge is usually at the right angle, or perpendicular, to the labiolingual axis of the crown of the tooth and overall is just lingual to the long axis of the root. The labiolingual measurement is also wider than then the mesiodistal measurement on the incisal view. Again, on the lingual surface, the faint mesial marginal ridge and distal marginal ridge are the same length.
They are incisors #23 and #26 that erupt between 7 to 8 years of age (root completion age 10). They erupt after the mandibular central incisors. It is slightly larger overall than a central; there is also more variation inform. The crown is also slightly larger than that of the central, but it resembles a central in most other ways. From both the labial and lingual views, the crown appears tilted or twisted distally in comparison with the long axis of the tooth; this gives the impression that the tooth has bent at the CEJ. The single root of a mandibular lateral is usually straight, slightly longer, and wider than that of a central. The root, like that of a mandibular central, has pronounced proximal root concavities, especially on the distal surface. These vary in length and depth. The pulp cavity for this tooth is quite simple, because it has a single pulp canal and three pulp horns. Labial view; the crown of the mandibular lateral incisor is not symmetrical as that of the central and appears tilted or twisted distally on the root from the labial view. The tooth is not symmetrical because the distal outline is slightly rounder and shorter compared with the slightly flatter and longer mesial outline. The incisal angles are different: The mesioincisal angle of the incisal edge is sharper than the distoincisal angle, which helps to distinguish the right mandibular lateral incisor from the left. The labial developmental depressions are deeper than on the central incisors. From the labial view, the mesial contact with the mandibular central incisor is in the incisor third. The distal contact with a mandibular canine is in the incisor third but is located more cervically than the mesial contact. Lingual view features; the crown of a mandibular lateral incisor lacks bilateral symmetry and appears tilted or twisted distally on the root from the lingual view, with its outline the reverse of the labial view. Overall, the lingual surface has more prominent features as compared to the lingual surface of the central incisor. The small single cingulum lies just distal to the long axis of the root. On the lingual surface, both the mesial marginal ridge and distal marginal ridge are more developed than on the central, although the mesial marginal ridge is longer than the distal marginal ridge. A single lingual fossa is also present, but a lingual pit is rarely present on the lateral, although more often than on a central. Proximal view features; the greater height of the CEJ curvature on the mesial than the distal surface helps to distinguish the right mandibular lateral incisor from the left. Also, from the mesial view, more of the lingual surface is visible because of the distal tilt or twist of the incisal edge. The distal view is similar to the mesial view of the tooth, but the CEJ is curved less on the distal than the mesial surface. Incisal view features; a rounded appearance is noted both labially and lingually from the incisal view of the mandibular lateral incisor as compared with that of a central. The entire incisal edge is not straight mesiodistally, as it is in a central; instead, the incisal edge curves toward the lingual in its distal part. Additionally the incisal angles are different: The distoincisal angle is visibly at a distinctly lingual location compared to the mesioincisal angle, and the cingulum appears displaced toward the distal. Again, on the lingual surface, the mesial marginal ridge is longer than the distal marginal ridge.