After the tooth enters into occlusion, this ridge becomes blunted and flattened, resulting in a sloping, straight outline from the proximal aspect. This flattened area is termed the incisal edge Table 4. Root: cone-shaped with a rounded blunted end, square at the cervical one-third then gradually tapered to the root apex. The labial outline is convex, while the palatal one is more convex. The crown surface is somewhat flattened with the mesial contact located in the incisal third, near the incisal margin, and is centralized labiopalatally.
It is roughly ovoid, long incisocervically and narrow labiopalatally. It is the only proximal area in the maxillary arch where mesial surface contacts mesial surface see Figure 4. Distal aspect of maxillary permanent central incisor. Cervical line: the curvature of the cervical line is less distally than mesially. Labial outline: similar to the labial outline of the mesial surface. Palatal outline: similar to the palatal outline of the mesial surface.
Incisal outline: the crown appears somewhat thicker at the incisal third. Crest of curvatures: are similar in position to their mesial counterparts. Root: the surface of the root is convex, and does not have a depression.
The distal view describes the surface of the tooth distant from the middle line of the face. This side closely resembles the mesial one. A greater part of the tooth surface is seen from this aspect compared to the mesial one as the labial surface of the crown steeped palatally, accommodating the horseshoe shape of the dental arch. Because it contacts the lateral incisor, which is a smaller tooth, the distal contact area is accordingly smaller in size.
Its shape is still ovoid, but it is more nearly round than on the mesial. It is also located farther cervically, still in the incisal third, but very near the junction of the incisal and middle thirds see Figure 5.
Incisal aspect of maxillary permanent central incisor. The incisal view of this tooth considers the portion of the tooth visible from the side where the incisal ridge is located. From this angle, only the crown of the tooth is visible, and overall, the tooth looks bilateral. The outlines are roughly triangular with the labial surface appears broad and flat, and the palatal surface tapers toward the cingulum. The distance between the mesioincisal angles to the cingulum is slightly longer than the distance between the distoincisal angles to the cingulum.
The incisal edge is centrally situated in a labiopalatal direction. The palatal fossa is seen as broad concavity between the two marginal ridges and incisal to the cingulum [ 7 , 8 ] see Figure 6. Pulp cavity for the mesiodistal, labiopalatal, midroot and cervical sections of maxillary permanent central incisor.
The mesiodistal measurement of the pulp chamber is wider compared to the labiopalatal one. The outlines of the pulp cavity follow the general shape of the tooth. If the mamelons are well developed, three definite pulp horns are found at the incisal portion of the tooth. The pulp cavity tapers gradually and evenly along its whole length until the apical constriction of the root is reached.
The apical foramen may be located slightly off center to the root tip. The pulp cavity follows the general outline of the crown and root. The pulp chamber is very narrow in the incisal region. Cervically, the pulp chamber widens to its largest labiopalatal width. Then, the root canal tapers gradually and evenly ending in a constriction at the root tip. The apical foramen may be located a little bit to the palatal or labial aspect of the root, near the very tip of the root.
At the cervical level, the pulp cavity mimics the external shape of the tooth. It is the widest in dimension compared to the other cross sections and centralized within the root dentin. In newly erupted teeth, the outline of the pulp chamber is roughly triangular in shape with the base of this triangle at the labial surface. As the amount of physiologic secondary dentin increases, the pulp cavity becomes more rounded in shape. The root and pulp canal tend to be rounder at midroot level than at the cervical level.
The anatomy at the midroot level is essentially the same as that found at the cervical level, just smaller in all dimensions [ 9 ] see Figure 7. The first socket right or left of the median line is that of the maxillary central incisor. The periphery of the socket often dips down palatally, labially, mesially and distally to accommodate the shape of the root. The central incisor socket is flattened on its mesial surface and is usually somewhat concave distally [ 10 ].
Like all upper front teeth and when the mouth is closed, the central incisors are ordinarily positioned labially to the mandibular ones. In some instances, the upper front teeth are positioned palatally to the lower ones and in such case the condition is referred as anterior crossbite.
When the teeth are biting down, the upper central incisors occlude with the lower central and lateral incisors. The contact point of the lower teeth is in the palatal fossa of the upper central incisor about 2 mm cervically from the incisal edge. The anterior open bite occurs when the upper and lower incisors do not contact even when the mouth is fully closed.
This incorrect arrangement of teeth may result from some habits, such as thumb sucking. On the other hand, the deep bite occurs when the contact of the lower incisors to the upper incisors is near or completely on the gingiva. When upper anterior teeth are located too far in front of the lower teeth, this is termed as large overjet [ 11 ]. Considered to be a common variation in Asian populations, shovel-shaped incisors derive their name from the prominent marginal ridges and the deeper palatal fossa of the teeth.
When seen from palatal view, the tooth is said to resemble a shovel. When space exists between maxillary central incisors, the condition is referred to as a diastema. One frequent cause of the space is the presence of a large labial frenum from the upper lip extending near the teeth.
The maxillary incisors are the most likely teeth to have a talon cusp, which is an extra cusp on the lingual surface. Also, the permanent maxillary incisors are the most likely teeth to have a dilacerations, which is a sharp curve on a tooth. When the root is exceptionally short, in conjunction with an abnormal contour of the crown, this anomalous condition is referred to as dwarfed root, and the lack of root support may endanger the tooth's longevity in the mouth.
In the cases affected by congenital syphilis, a notch forms on the incisal edges of all incisors. When such notch is found, the teeth are described as screwdriver-shaped and they are called Hutchinson's incisors. The alveolar bone between the roots of the two central incisors is occasionally the site of supernumerary teeth or extra teeth, known as mesiodens [ 1 ]. The general shape is similar to maxillary central incisor except that they are shorter and narrower. The mesiodistal crown dimension is the smallest of any maxillary teeth.
The mesioincisal and distoincisal angles are more rounded than the corresponding angles of maxillary central incisor. On the palatal aspect, the marginal ridges and cingulum are more prominent. It has the most cervically located contact area of any incisor. Next to third molars, maxillary lateral incisors are the teeth that show most variation in crown size, shape and form see Figure 8.
Diagram showing the labial, palatal, mesial, distal and incisal aspects of the maxillary permanent lateral incisor. The maxillary lateral incisor is the tooth located distally from both maxillary central incisors and mesially from both maxillary canines. Like all the incisors, their function is for shearing or cutting food material during mastication. It is developed from four lobes, three labially and one palatally, the palatal lobe being represented by the cingulum.
Mamelons are better seen on the central incisors as compared to the lateral incisors [ 6 ] Table 3. The mesiodistal and labiopalatal measurements for maxillary permanent lateral incisor mm are shown in Table 4. Cervical line: curves in a regular arc apically, with only slightly less depth than in the central incisor. Mesial outline: this margin resembles that of the central incisor, but usually is more convex and has a more rounded mesioincisal angle. The contact area is located farther cervically in the incisal third, quite near its junction with the middle third.
Distal outline: the distal margin is always more rounded than the distal outline of the central incisor, with a more cervically located contact area. The distoincisal angle is noticeably more rounded than its central incisor counterpart, and also more rounded than its own mesioincisal angle. Incisal outline: the incisal outline resembles the central incisor, but it is not so straight, partially because of the greater rounding of the two incisal angles.
It exhibits the greatest rounding of any incisor. The number and prominence of mamelons is variable, but two are the most common finding. Contact areas: the mesial contact at the junction between middle and incisal on-third ewhile the distal contact at the center of the middle third.
Angles: the distoincisal angle being more rounded than the mesioincisal angle. Root: the root tapers toward the pointed apex. The root apex is inclined distal to midline. It is narrow mesiodistally than that of maxillary central and usually as long as or somewhat longer than that of the central. The labial surface itself is more convex both mesiodistally and incisocervically than the maxillary central.
Labial developmental grooves, and imbrication lines are often present, similar to those of the central incisor but are less prominent. The labial height of contour is located at the cervical third see Figure 9.
Labial aspect of maxillary permanent lateral incisor. Cervical line: it curves toward the apical, but is offset to the distal.
Distal outline: is similar to its labial counterpart, and the distoincisal angle is much more rounded than the mesioincisal angle. Incisal outline: is similar to the labial aspect. Angles: are similar in position to their labial counterparts. The mesial and distal marginal ridges, as well as the cingulum, are relatively more prominent, and the palatal fossa is deeper, when compared to the same structures of the central incisor.
A palatocervical groove is a more common finding in maxillary lateral incisors than in central incisors. A palatal pit, near the center of this groove, is also more common, and when present, is a potential site for caries. The palatocervical groove usually originates in the palatal pit and extends cervically, and slightly distally, onto the cingulum. It might be helpful to think of the palatocervical fissure as running in a more or less vertical direction, while the palatocervical groove extends in a roughly horizontal direction see Figure Palatal aspect of maxillary permanent lateral incisor.
Cervical line: exhibits less depth of curvature than it does on the mesial surface of the central incisor. Crest of curvatures: the labial crest is at the cervical third near the cervical line, while the palatal one is found at the middle of the cervical one-third at the prominence of the cingulum.
Incisal outline: the incisal portion is on one line with root apex. Root: the root appears longer but narrower than that of the central. The crown is shorter, and the labiopalatal measurement of the crown is smaller. The contact area is also similar in shape to the contact of the central incisor. It is found in the incisal third very near the junction of the incisal and middle thirds, centered labiopalatally see Figure Mesial aspect of maxillary permanent lateral incisor.
Cervical line : shows less curvature incisally than on the mesial surface. Incisal outline: rounded in newly erupted teeth and flat in worn out teeth. Root: the distal surface of the root is slightly more convex than mesial. The distal surface is smaller and more convex in all dimensions than the mesial surface.
The contact area is shorter and not as incisally placed, when compared to the mesial contact. It is normally located at middle of the middle one-third and centered labiopalatally see Figure Distal aspect of maxillary permanent lateral incisor. In incisal view, this tooth resembles the central incisor to varying degrees. The tooth is narrower mesiodistally than the maxillary central incisor; however, it is nearly as thick labiopalatally.
The incisal outline is more rounded labially and palatally than the central incisor. When palatal pit is present; it is located in the depth of the palatal fossa [ 7 , 8 ] see Figure Incisal aspect of maxillary permanent lateral incisor.
The pulp cavity nearly follows the external shape of the tooth. When viewed from the labial aspect of the tooth, the pulp horns appear to be blunted. The pulp chamber and root canal taper evenly and gradually toward the root apex. In the apical portion, the root often shows a significant curvature. The anatomical feature is almost identical to that of the central incisor. Generally, the pulp cavity of the lateral incisor closely resembles the outline form of the crown and the root.
The pulp projections are usually well developed and prominent. In the incisal region, the pulp chamber is narrow, and at the cervical level of the tooth it may become very wide. When the cervical enlargement of the pulp chamber is lacking, the root canal tapers slightly to the apical constriction at the root tip. Many of the apical foramina exit on the labial or palatal aspect of the root. The cervical cross section shows the pulp chamber to be centered within the root.
The root form of this tooth shows a large variation in shape. The outline form of this tooth may be triangular, oval or round. The pulp chamber generally follows the outline form of the root, but secondary dentin may narrow the canal significantly [ 9 ] see Figure Pulp cavity for the mesiodistal, labiopalatal, midroot and cervical sections of maxillary permanent lateral incisor. The second socket from the midline is that of the lateral incisor.
It is generally conical and egg-shaped, or ovoid, with the widest portion to the labial. It is smaller on cross section, although it is often deeper than the central alveolus. Sometimes, it is curved at the upper extremity [ 10 ].
The upper lateral incisors are usually located labially to the mandibular teeth when the mouth is closed. The upper lateral incisor occludes with the distolabial half of the mandibular lateral and with the mesiolabial inclined plane of the mandibular canine [ 11 ]. Palatocervical fissure may extend all the way onto the root surface from the adjacent cingulum. Distorted crowns and unusual root curvatures are more commonly seen than with any other incisor. A diminutive peg-shaped crown form, which is relatively common, and is due to a lack of development of the mesial and distal portions of the crown.
Maxillary laterals sometimes are congenitally missing, that is, tooth buds do not form. The palatal pit of the maxillary lateral may be the entrance site where enamel and dentin have become invaginated in the tooth's pulp cavity, due to a developmental aberrancy called dens in dente [ 1 ]. The crown dimensions are the smallest of any tooth, it has bilaterally symmetrical crown, and the line angles are the sharpest of any tooth.
The proximal contact areas are at the same level. The incisal edge is lingual to labiolingual bisector. It shows the shallowest labial developmental grooves, smoothest lingual surface contour and the least developed cingulum. As the smallest tooth in the dentition, the mandibular central incisor has only one antagonist.
This tooth and the maxillary third molar are the only teeth that have one antagonist see Figure Diagram showing the labial, lingual, mesial, distal and incisal aspects of the mandibular permanent central incisor. It occupies the position adjacent to the midline in each mandibular quadrant. They share a mesial contact area with each other, while the distal contact is with the permanent lateral incisor.
These teeth function in biting, cutting, incising and shearing, just as do their maxillary counterparts. It developed from four lobes three mamelons and one cingulum. Shortly after eruption, mamelons are usually worn away by attrition and the incisal edges of all incisors are straight [ 6 ] Table 5.
The mesiodistal and labiolingual measurements for mandibular permanent central incisor mm are shown in Table 6. Cervical line: the cervical line is symmetrically curved toward the root. Mesial outline: the mesial margin normally tapers evenly toward the cervical part in a nearly straight line.
Distal outline: the outline is straight and almost exactly like the mesial outline. Incisal outline: In newly erupted teeth, three mamelons most always be seen. After incisal wear has obliterated the mamelons, the incisal outline is straight, and at right angles to the long axis of the tooth. Contact areas: mesially, the height of contour is associated with the contact area in the incisal third, very close to the incisal margin.
The height of contour is also in the incisal third and in the same level, distally. Angles: the mesioincisal angle is quite sharp with a similarly sharp distoincisal angle, normally more so than any of the incisal angles of maxillary incisors. Root: a straight single root, tapering at the apical third.
The labial surface is narrow and convex. The mesial and distal outlines are straight down to the apical portion. Its apical third ends in a pointed apex, which tends to curve distally. The root appears longer compared to the crown length. The labial surface is generally convex both mesiodistally and incisocervically, but not to the extent of the maxillary incisors, especially the maxillary lateral.
However, like the maxillary incisors, the convexities are much greater in the cervical third. In fact, in some specimens the labial surface may be quite flat incisal to the height of contour.
Developmental grooves and imbrication lines are not normally present. Occasionally, there are very faint grooves which only occur near the incisal margin of the labial surface see Figure Labial aspect of mandibular permanent central incisor.
Cervical line: curves evenly toward the root, but is located farther from the incisal ridge than the labial surface counterpart. Mesial outline: closely resembles the mesial outline of the labial aspect. Distal outline: closely resembles the distal outline of the labial aspect. Incisal outline: closely resembles the incisal outline of the labial aspect. Root: is slightly narrower on the lingual side than on the labial side. The anatomical crown of this tooth is broader buccolingually than mesiodistally usually by 1 mm.
Mesiodistal crown widths The mesiodistal dimensions of the maxillary teeth showed a higher variability than the mandibular teeth, with the first molar dimensions showing the greatest variability. The size of the maxillary central and lateral incisors also presented high variability. The most frequent congenitally missing teeth was mandibular second premolars Three-rooted molars are oddities in most modern dental practices. Molars generally have just two roots, but occasionally a third, smaller root grows.
In Europe and Africa, fewer than 3. The tooth had four roots with four root canals, two individual palatal roots mesiopalatal and distopalatal with their own separate canals. The mesiobuccal and distobuccal root had normal anatomy. Most mandibular molars have two roots one mesial and the other distal and three canals. The major variant of this tooth type is the presence of an additional third root distally or mesially or a supernumerary lingual root. This is made up of four incisors, two canines or cuspids , four premolars or bicuspids , four molars and two wisdom teeth also called third molars in each jaw.
If wisdom teeth have been removed there will be 28 teeth. The incisors are the middlemost four teeth on the upper and lower jaws. Wisdom teeth are the last adult teeth to come into the mouth erupt. Most people have four wisdom teeth at the back of the mouth — two on the top, two on the bottom.
Number of teeth A grown-up person ideally should have 32 teeth. Those with teeth would enjoy fame and respect in society. They will also be affluent.
In case you have only teeth, a mixed fate awaits you; there could be joy as well as sadness in life. Some people get one wisdom tooth, while others have two, three, four, or none at all. In this study, the prevalence of root canal bifurcation in mandibular incisors was verified in vivo and in vitro using a digital radiographic system Radiovisiography; RVG, Trophy, France.
Digital radiographs were taken in an orthoradial direction from the incisor and canine regions. The study protocol was reviewed and approved by the Institutional Review Board Protocol n. Digital radiographs were taken from the mandibular incisors in a BL direction Figure 2.
After examination, the same teeth were removed from the model and digital radiographs were taken in a MD direction Figure 3. The electronic sensor of the digital radiographic system, connected to the computer, generated images that were immediately seen on the monitor.
Then, the digital radiographs were analyzed by a single examiner for the presence of a single root canal, bifurcated root canal, or root canal with characteristics indicating bifurcation These characteristics included decreased cervical-apical radiolucency and presence of radiolucent lines longitudinally on the root. Data were submitted to statistical analysis by the chi- square test and the Yale's coefficient of association.
These characteristics corresponded to loss of cervical-apical radiolucency and longitudinal radiolucent lines found laterally in the root due to the mesiodistal flattening. Therefore, in percent values, the in vivo study indicated that Figure 4 shows images in which root canal bifurcation was observed.
Images in Figure 5 illustrate teeth with characteristics that indicated the presence of bifurcation. These images were captured during the in vivo examinations and represent loss of cervical-apical radiolucency and longitudinal radiolucent lines found laterally in the root.
Figure 6 presents images of teeth in both BL and MD directions. The chi-square test was applied to the data collected from the in vitro study for comparison between digital radiographs in both BL and MD directions. This test was able to measure the discrepancy between two mutually exclusive qualitative variables observation or not of root canal bifurcation or characteristics indicating bifurcation and verified the independence or not between these variables.
In the chi-square test, any result different from zero would indicate correlation between digital radiography in the BL and MD directions. A value of However, the chi-square test cannot determine the degree of association: therefore, the Yale's coefficient of association was employed. Figure 7A presents graphically the sample distribution of the in vitro study.
Statistical analysis was completed by observing the existence of correlation between the results from the in vivo and in vitro studies, by analysis of percentages of single and bifurcated canals Figure 7B.
The results of this in vivo study are similar to those found by Bellizzi and Hartwell 1 , who investigated teeth and found It must be emphasized that, in their study, those authors did not mention either the presence of bifurcation or the existence of characteristics suggestive of bifurcation, as mentioned in the present study.
Previous in vivo studies have reported percentages of bifurcation in mandibular incisors different from the present study 9 , In the present study, sixteen teeth exhibited a single canal in the BL direction, though presenting root canal bifurcation when evaluated by digital radiography in the MD direction. Similar finding was reported by Nattress and Martin 14 , who investigated teeth and found 17 teeth with a single canal when radiographed in the BL direction and bifurcated canals when analyzed in the MD direction.
This result shows that, even with utilization of distoradial radiography, it was not possible to observe all cases of root canal bifurcation in mandibular incisors under clinical conditions. Thus, knowledge of root canal anatomy is necessary to avoid neglecting the presence of an additional canal.
These results were expected due to overlapping of root canal images in the BL direction. This was also observed by previous authors, who found higher number of bifurcation in incisors when these teeth are radiographed in the MD direction compared to BL direction 14 , Moreover, the in vitro study revealed that teeth with a single canal 40 teeth in the BL direction also presented this characteristic in the MD direction.
In the present study, among the lateral incisors, 6 teeth presented root canal bifurcation or characteristics indicating bifurcation when analyzed in the BL direction. However, when the teeth were radiographed in the MD direction, this fact was not confirmed. In the literature, no authors that analyzed teeth in the BL and MD directions mentioned such occurrence 12 , This finding may be assigned to the fact that mandibular lateral incisors normally present root flattening in the MD direction, which can lead to appearance of a very marked longitudinal groove 8 , Root canal bifurcation in mandibular incisors plays an important role in the endodontic treatment.
In case of partial bifurcation, filling of one root canal, usually the buccal, will consequently seal the end of the other. On the other hand, this will not occur when there is total bifurcation with two apical foramina, since the lack of treatment of one canal will lead to failure of the endodontic therapy.
Some studies have reported that failure of treatment of mandibular incisors with two canals ending in a single apical foramen may occur due to poor or absent treatment of one of the canals 5 , Even though its end is sealed, the root canal may present lateral canals that can communicate with the periodontal tissues.
Clinicians, particularly endodontists, must be able to visualize all root canals of a tooth to fill them adequately 6 ,
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