Chapter 2: Surface Anatomy of Permanent Teeth PDF

# Chapter 2: Surface Anatomy of Permanent Teeth ## **INCISORS** ### **Maxillary Incisors** **General Characteristics:** - There are four maxillary incisors (two centrals and two laterals). - The two central incisors are centered in the maxilla, contact each other at the midline. - The lateral in...

# Chapter 2: Surface Anatomy of Permanent Teeth ## **INCISORS** ### **Maxillary Incisors** **General Characteristics:** - There are four maxillary incisors (two centrals and two laterals). - The two central incisors are centered in the maxilla, contact each other at the midline. - The lateral incisors are distal to the central incisors. - In some individuals the two upper central incisors are separated by a space called diastema. - The major function of the incisors is incis-ing or cutting the food. - The newly erupted incisors or none functioning have three small mamelons forming the incisal ridge. - These mamelons soon worn away with mastication changing the incisal ridge into an incisal edge. ### **Maxillary Central Incisor** - It is the widest of any of the anterior teeth. - It is the most prominent in the mouth. **Labial Aspect:** **First describe the crown:** - **Geometric outline:** trapezoidal with the shortest of the uneven sides is located cervically. - **Outline form:** - **Mesial outline:** slightly convex with the maximum convexity (representing the contact area) is in the incisal third near the mesio-incisal angle. - **Distal outline:** is more convex and the contact area is more cervically, near the junction of the incisal and middle thirds. - **Incisal outline:** newly erupted incisor shows three small mamelons. These mamelons soon undergo attrition giving a regular and straight incisal edge. The mesioincisal angle is sharp and it nearly forms a right angle. The distoincisal angle is rounded. - **Cervical outline:** convex root-wards. * **Surface anatomy:** * **Elevations:** The labial surface of the crown is smoothly convex with the maximum convexity at the cervical third (cervical ridge). In newly erupted tooth, three mamelons are prominent. * **Depressions:** There are two shallow developmental grooves, which divide the labial surface into three lobes. **Second, describe the root:** - **Number, shape and apex (position and shape):** This tooth has a single root, which is cone-shaped, with blunt centralized apex. Thus this tooth can be extracted by rotational movement. **Lingual Aspect:** **1- The crown:** - The geometric outline and outline form are similar to that of the labial aspect, but differ in crown size and surface anatomy. - The crown converges lingually to accommodate the U-shaped dental arch which has a larger size facially than lingually. - The cingulum is a well developed smooth large convexity occupies the cervical third. - The mesial and distal marginal ridges are well developed ridges that extend from the cingulum to the incisal ridge. - The lingual fossa is a large concavity lies between the marginal ridges, the cingulum, and the incisal ridge. **2- The root:** The lingual surface of the root is convex. It is narrower than the labial surface due to lingual convergence. ### **Maxillary Lateral Incisor** - The general form of the crown closelyresembles that of the upper central. - The lateral incisor is smaller in all dimensions than the central incisor except root length. - This tooth shows great variations; may show lingual pit, may be cone shaped (peg shaped) due to absence of the middle lobe (Fig. 12) or the tooth may be completely absent. **Labial Aspect:** **1- The crown:** - The geometric outline of the crown is similar to that of the central incisor. - **Mesial and distal outlines resemble that of the central incisor. The mesial contact area is near or at the junction of the incisal and middle thirds while the distal is more cervically.** - Incisal outline is rounded with distoincisal angle is more rounded than the mesioincisal angle. The mamelones are less pronounced and less common than on the central incisors. - **Cervical line is similar to that of central incisor.** **Surface Anatomy:** - The labial surface is similar to that of the upper central incisor, but is more convex. - Labial developmental grooves are less prominent. **2- The root:** The single root tapers towards a pointed distally curved apex. **Lingual Aspect:** - The marginal ridges are prominent. - Both the cingulum and the incisal ridge are well developed. - The lingual fosse is more concave. - The palatal pit, if it is found, is enclosed by the cingulum. This pit is prone to decay. **Mesial Aspect:** - The mesial aspect of the upper lateral incisor is similar to that of a small central incisor except differences in size as mentioned before. The curvature of the cervical line is well marked. **Distal Aspect:** - The curvature of the cervical line is less in depth than on the mesial side. - The distal contact area is still centralized but is located more cervically. - The distal surface of the root is slightly more convex than mesially. **Incisal Aspect:** - The incisal aspect of this tooth resembles that of central incisor except in size. - The incisal outline is more rounded labially and lingually than that of upper central incisor. - When palatal pit is present, it is located in the depth of the lingual fossa. **Pulp Cavity:** - The pulp cavity is similar but smaller than that of central incisor. It consists of a pulp chamber and a single root canal. The pulp chamber does not have three sharp pulp horns as it does in the maxillary central incisor (The mamelones are less pronounced and less common than on the central incisors). ### **Mandibular Incisors** **General characteristics:** - There are four mandibular (lower) incisors: two central and two lateral incisors. - The lower incisors function with the upper incisors in; cutting of food, speech and maintenance of a good appearance by supporting the lower lip. - The lower incisors differ from the upper incisors in the following: 1. They look alike, as their crowns labially are fan shaped (due to a wide incisal measurements and narrow cervix). 2. They are smaller; having smaller mesiodistal dimension than any of the other teeth. The central incisor is somewhat smaller than the lateral incisor, which is the reverse of the situation in the maxilla. 3. Their crowns are wider labiolingually than mesiodistally. 4. Their mamelons worn off soon after eruption. 5. Their incisal ridges are inclined lingual to the root axis. 6. Their anatomical landmarks are less prominent compared with those of upper incisors. 7. Their mesial and distal contact areas exist near the incisal ridges. 8. Their roots are flattened labiolingually and are longer in proportion to the crown. ### **Mandibular Central Incisor** - It is the smallest tooth in the permanent dentition. - The central incisor is the most symmetrical tooth in the permanent dentition **Labial Aspect:** **1- The crown:** - The geometric outline of the crown is trapezoidal with the shortest uneven sides is located cervically. - **The outline form:** - The mesial and distal outlines: are straight and taper evenly to the narrow neck giving the crown fan shaped appearance. - The mesial and distal contact areas exist in the incisal third near the incisal angles and nearly at the same level. - The incisal outline: the incisal ridge is straight and is at nearly a right angle the long axis of the tooth. Mamelons a usually present on newly erupted teeth. The mesio and distoincisal angles are sharp. - The cervical outline: convex root-wards. * **Surface anatomy:** * **Elevations:** The labial surface of the crown is smoothly convex with the maximum convexity at the cervical third (cervical ridge). In newly erupted tooth, three mamelons are prominent. **2- The root:** - The labial and lingual outlines of the root are nearly straight from the cervical line to the middle third; then tapers to the rounded apex. - The mesial surface of the root is flat with a deep developmental depression. **Distal Aspect:** - Geometric outline and outlines form are similar to that mesially except; - The curvature of the cervical line which is shallower. - The root shows a deeper developmental depression and groove at its center. **Incisal Aspect:** - The crown outline is diamond. - The crown converges lingually. - The crown thickness is larger than its width. - The labial and lingual outlines are convex. - The incisal edge is lingually situated (lingual inclination) and almost at right angles to a line bisecting the crown labiolingually, which is a characteristic feature of lower central incisor. - The lingual fossa is seen as a shallow concavity between the two marginal ridges and the cingulum. - Note, This aspect shows the mesial and distal symmetry of the lower central incisor. **Pulp Cavity:** - It is similar to that of upper incisors as it has a single root canal and three pulp horns (in newly erupted teeth). - However, the pulp chamber is narrower mesiodistally than labiolingually. ### **Mandibular Lateral Incisor** - It is very similar to the lower central incisor, but it is slightly larger than the lower central incisor. **Labial (a) and lingual (b) aspects:** **1- The crown:** - It resembles that of the lower central incisor with some differences: 1- The lateral incisor has a more fan-shaped appearance. 2- The mesial outline of the crown is often longer than the distal outline (as the incisal ridge slopes downward in a distal direction), therefore, it is not as bilaterally symmetrical as the lower central incisor. 3- The distal contact area is more cervically than the mesial contact area. 4. The distoincisal angle of the lower lateral incisor is more rounded than the sharp mesioincisal angle (both angles of the lower central incisors are relatively sharp). 5- The cingulum, incisal ridge and marginal ridges are ill developed. However, these ridges are more prominent than in the lower central incisor. 6- The cingulum shows distal deviation (it is centralized in the central incisor). **2- The root:** It is similar to that of the central incisor, but is slightly longer. **Mesial (a) and distal (b) aspects:** - There is no marked difference between mesial and distal surfaces of lower central and lateral incisors, except for the size of the tooth and the location of the contact area incisocervically. **Incisal aspect:** - The most important feature is the appearance of the crown of the lower lateral incisor to be slightly twisted distolingually on its root in order to allow the incisive ridge to follow the curve of the dental arch. This means that the incisal edge is not at a nearly right angles to a line bisecting the crown and root labiolingually, as is found in lower central incisor. **Pulp Cavity:** - The pulp cavity for this tooth is very similar to that of lower central incisor. ## **CANINES** **General characteristics:** - There are one canine in each quadraut. - Canines have longer and stronger roots than those of other teeth. - Over the labial aspect of their roots there is well developed bone ridge called the canine eminence giving the canine a very important cosmotic value since they ensure facial expression. - Canines are formed of four lobes, (3 labial and 1 lingual), the middle labial lobe is highly developed labially (forming the labial ridge), lingually (forming the lingual ridge) and incisally (forming a well developed pointed cusp). Therefore, the canines are called cuspids. - The canines are located between the incisors and premolars, so, they support the two groups in function (tearing and partial cutting). ### **Maxillary Canine** **Labial Aspect:** **First describe the crown:** - **Geometric outline:** trapezoidal with the shortest of the uneven sides is located cervically. - **Outline form:** - **Mesial outline:** from the cervical line to the contact area is convex. The contact area is nearly at the junction of the middle and incisal thirds of the crown. - **Distal outline:** from the cervical line to the contact area is concave. The contact area is more cervically than mesial (in the middle third). - **Incisal outline:** The mesial cusp slope is concave while the distal cusp slope is convex and longer than the mesial. The cusp tip is pointed and mesial to the midline (long distal slope). - **Cervical outline:** convex root-wards. * **Surface anatomy:** * **Elevations:** The labial surface of the crown is convex with the maximum convexity at the cervical third (cervical ridge). Labial ridge is prominent extending from the cusp tip to the cervical ridge. * **Depressions:** There are two shallow developmental grooves mesial and distal to the labial ridge, which divide the labial surface into three lobes. **Second, describe the root:** - **Number, shape and apex (position and shape):** This has a single root. It is long and slender. The apex is pointed and distally curved. **Lingual Aspect:** **1- The crown:** - The geometric outline and outlines form are similar to that of the labial aspect. However it differs in the crown size and surface anatomy. - The crown is narrower lingually than labially (lingual convergence). - Similar to incisors, cingulum and marginal ridges (mesial and distal) are characteristics for the lingual surfaces of anterior teeth. - Lingual ridge: a prominent vertical ridge extends from the cusp tip to the cingulum. Canines are the only teeth that have a prominent lingual ridge. - Lingual fossae: on each side of the lingual ridge a mesial and distal lingual fossae are present. **2- The root:** The lingual surface of the root is smooth and convex. It is narrower lingually than labially. **Mesial Aspect:** **First-Describe the crown:** - **Geometric outline:** triangular in shape with the base of the triangle at the cervix and the apex at the cusp tip. - **Outline form:** - **The labial outline:** is convex with the maximum convexity is at the cervical third (cervical ridge). - **The lingual outline:** is convex in the cervical third (cingulum), straight in the middle third (lingual ridge), and convex in the incisal third representing the cusp tip. - **The cervical line:** curves incisally to a marked degree. - **The cusp tip is located labially to the root axis.** - **The contact area:** It is centralized (labio-lingually) and nearly at the junction of the middle and incisal thirds of the crown (inciso-cervically). **Second-Describe the root:** - **Number, shape and apex (position and shape):** The single root is conical. Its apex is blunt and curved labially. The mesial surface is broad with a shallow longitudinal depression. **Distal Aspect:** - The geometric outline and outlines form are similar to that of the mesial aspect, except; - The cervical line has less curvature toward the cusp tip. - The contact area is still centeralized but is located more cervically. - The depression on the distal surface of the root is more pronounced than that on the mesial surface. These vertical depressions on the heavy root help to anchor the teeth in their socket bone and help to prevent rotation and displacement. **Incisal Aspect:** - For proper description of the incisal aspects of canines; Similar to that of the incisors in addition to the position of the cusp tip - The crown outline is diamond. - The crown converges lingually. - The crown thickness is larger than its width. - The labial and lingual surfaces are convex, more than either incisor. - The cusp tip is labial and mesial to the centers of the crown. - The labial ridge is very noticeable from this aspect. - The lingual ridge extends from the cusp tip to the cingulum in between the two lingual fossae. - The cingulum and marginal ridges are also seen from this aspect. **Pulp Cavity:** - **Mesiodistally:** The pulp cavity is much narrower in the mesiodistal section than in the incisors. The pulp chamber is pointed incisally with a prominent pulp horn corresponding to the cusp. The root canal is narrow along its entire length. - **Labiolingually:** Wide root canal and pulp chamber with pointed pulp horn. ### **Mandibular Canine** - It closely resembles the upper canine. - Its anatomical landmarks are less developed than those of the upper canine. **Labial Aspect:** - It resembles that of the upper canine with some differences: - Its width is narrower than the upper canine but longer. - The mesial outline is nearly straight from the cervical line to the mesial contact area. - The mesial contact area is in the incisal third while the distal is at the junction of the middle and incisal thirds, more cervically located than the mesial contact area. - Note: The crown of the lower canine appears longer than that of the upper canine. Sometimes it is longer, but the effect of greater length is emphasized by the narrowness of the crown and incisally positioned contact areas. - The cusp is less pointed than that of upper canine. - The anatomical landmarks are less developed than those of the upper canine. - The root is shorter than that of the upper canine with more pointed apex. **Lingual Aspect:** - It is similar to that of the upper canine with some differences; - The lingual ridge is restricted to the incisal third leading to presence of one lingual fossa. - The cingulum and marginal ridges are not prominent. **Mesial Aspect:** - The mesial aspect of the lower canine is similar to that of the upper canine with some differences: - The convexity of the labial outline is less prominent due to less developed anatomical landmarks. - The lingual outline in the middle third is concave due to absence of long prominent lingual ridge of the upper canine. - The cusp tip is pointed and located lingual to the root axis line (lingual inclination) or may be centered over it. - The contact area is centralized and in the incisal third. - The developmental depression on the root mesially is more pronounced than that on the upper canine root. **Distal Aspect:** - The curvature of the cervical line is less in depth than on the mesial side. - The distal contact area is still centralized but is located more cervically. - The developmental depression on the distal side of the root is deeper than the depression on the mesial side. **Incisal Aspect:** - The outline of lower canine from the incisal aspect is similar to that of the upper canine with some differences; - The cusp tip inclined lingually or centeralized. - The lingual ridge is restricted to the incisal third. **Pulp Cavity:** - The pulp cavity of lower canine resembles that of the upper canine except the possibility of presence of two separate labial and lingual root canals. **Chronology of the permanent anterior teeth** | Beginning of calcification | Crown completion | Eruption | Root Completion | |---|---|---|---| | 3-4 m. | 3 y. before eruption date | 7 y. | 3 y. after eruption date | | 10-12 m. | 6 y. | 8 y. |  | | 3-4 m. | 8 y. | 11 y. |  | | 4-5 m. | 9 y. |  |  | ## **PREMOLARS** **General characteristics:** - The premolars are so named because they are situated mesial to the permanent molars. (Fig 1 in molars). - There are two premolars in each quadrant. - They replace the deciduous molars, so they are succedaneum teeth. - They have usually two cusps, buccal and lingual, so they are called bicuspid. This term is misleading, since the lower second premolars may have three cusps. - They are developed from four lobes as anterior teeth, three buccal and one lingual except the lower second premolar (Fig. 47) - The middle buccal lobe of the premolars is highly developed. It corresponds to the middle labial lobe of the canine.. - The cusps of upper and lower first premolars are more sharp than those of the second premolars. - The premolars differ from the anterior teeth in the following: a) They have occlusal surfaces with well-developed cusps instead of incisal edges. b) Their marginal ridges are part of the occlusal surface. c) Their crowns are shorter occluso-cervically. d) The contact areas of premolars (and molars) are nearly at the same level, equal cusps levels of second premolars. e) Their cervical line is less curved proximally. f) Their crowns are broader and are more cervically than those for anterior teeth. **Function of premolars:** - They support the corners of the mouth and cheeks to keep them from sagging. - The premolars function with molars in maintaining the vertical dimension of the face. - The premolars assist the canines in tearing of food by the sharp cusps of first premolars and assist the molars in mastication of food by the nearly equal cusps levels of second premolars. ## **Maxillary First Premolar** - The maxillary first and second premolars are more alike than the mandibular premolars. - It may have two roots (80%). **Buccal Aspect:** **First describe the crown:** - **Geometric outline:** trapezoidal with the shortest of the uneven side is located cervically. **Second, describe the root:** - **Number, shape and apex (position and shape):** This tooth has a single root, which is cone-shaped, with blunt centralized apex. Thus this tooth can be extracted by rotational movement. **Lingual Aspect:** **1- The crown:** - The lingual surface is narrower than the buccal surface (lingual convergence). - The geometric outline is similar to that of the buccal aspect. - The outlines form: The mesial & distal outlines are slightly convex. **2- The roots:** it is conical in form with convex surface and pointed distally curved apex. **Mesial Aspect:** **First-Describe the crown:** - **Geometric outline:** trapezoidal with the shortest of the uneven sides is located occlusally. - **Outline form:** - **The buccal outline:** is convex with the maximum convexity is at the cervical third. - **The lingual outline:** is convex with the maximum convexity is at the middle third. - **The occlusal outline:** The buccal cusp is longer than the lingual cusp by 1 mm, the two cusp tips are sharp. The buccal cusp tip is in one line with the buccal root apex. The lingual cusp tip is in one line with the lingual border of the lingual root. - **The mesial marginal ridge lies in the middle third. ** - **The cervical line slightly curves occlusally. ** **Second-Describe the root:** - **Number, shape and apex (position and shape):** May be one or two roots but the majority is the bifurcated root at the middle third.There is deep developmental depression along the root trunk. If one root is present, the root outlines end in a blunt apex above the center of the crown. **Distal Aspect:** - Is similar to the mesial one except: - No developmental groove crossing the marginal ridge. - The distal marginal ridge is occlusal than the mesial one (the opposite of all other posterior teeth). - No developmental depression on the crown or root. - The contact area is broader and is located more occlusally (this is the opposite for all posterior teeth). **Occlusal Aspect:** **For proper description of the occlusal aspects of posterior teeth;** 1- **Geometric outline with reference to the type of convergence and the relation between width and thickness.** 2. **Surface anatomy.** - The geometric outline is roughly hexagonal (two buccal, two proximal and two lingual sides). - The crown converges lingually - The crown thickness is wider than its width. - The mesiobuccal & distobuccal sides are nearly equal in length. - The mesiolingual side is shorter than the distolingual one - The mesial side is shorter than the distal one. **Surface anatomy:** - **Elevations:** - Buccal& lingual triangular ridges over the buccal &lingual cusps. - Mesial & distal marginal ridges the distal one is well developed (this is the opposite for all posterior teeth) - **Depressions:** Mesial& distal triangular fossae with developmental pits in their bottoms. Central developmental groove extends from the two triangular fossae and pass over the mesial marginal ridge as mesial marginal developmental groove. ## **Maxillary Second Premolar** **In comparison to the upper first premolar:** - The crown is shorter. - The buccal cusp is less pointed and shorter. - The mesial slope is shorter than the distal slope. - The mesial contact area is in the occlusal third while the distal one is more cervical. - The buccal ridge is less prominent. - The single root (higher percentage) is longer and tapered to an apex that curves distally. **Lingual Aspect:** - The lingual cusp is nearly equal to the buccal cusp (to accommodate the grinding function of the second premolar rather than the tearing function found in the first premolar). - Has less lingual convergence to accommodate the shape of the dental arch at this region. **Mesial & Distal Aspects** - The buccal & lingual cusps are equal and are further apart giving wider occlusal surface búccolingual to help for grinding. **Pulp Cavity:** - The pulp chamber has buccal and lingual pulp horns then the pulp is wide until the cervix. - The upper first premolar mostly has two root canals even when it has one root, while the upper second premolar has mostly one root canal. ## **Mandibular First Premolar** - The first premolar has a large buccal cusp and a small nonfunctioning lingual cusp which sometimes resembles the cingulum found on upper canines. **Buccal Aspect:** **1- The crown:** - The geometric outline is trapezoidal with the shortest of the uneven side is located cervically. - **The outline form:** Mesial and distal outlines are slightly concave. Mesial contact area is at the junction of the middle and occlusal thirds while the distal one is slightly cervical. Occlusal outline: Mesial and distal slopes are concave, mesial slope is shorter than the distal one therefore the cusp tip is deviated mesially. Cervical outline is curved root wise. **Surface anatomy:** - **Elevations:** - Buccal ridge extends cervico- occlusally in the middle of the crown. - Cervical ridge at the cervical third. - **Depressions:** Two shallow vertical developmental grooves mesial and distal to the buccal ridge. **2- The root** is cone shape with tapered distally curved apex. **Lingual Aspect:** **1- The crown:** - The lingual surface is much narrower than the buccal surface. (highly convergence) - The lingual cusp is short and reaches 2\3 the length of the buccal cusp. - Mesiolingual developmental groove originates from the pit at the bottom of the mesial triangular fossa crosses to the mesial surface near the mesiolingual line angle and fades at the middle third. **2- The root** is similar to the buccal aspect, but is bucco- lingually converged. **Mesial Aspect:** **1- Crown:** - The geometric outline is rhomboidal in shape with constricted occlusal outline. - **The outline form:** - The buccal outline is convex and with maximal convexity at the cervical third (cervical ridge). - The lingual outline is convex with the maximal convexity at the middle third. - The occlusal outline: The lingual cusp is 2\3 the buccal one. The crown is tilted on the root lingually, so the buccal cusp tip is at one line with the root apex. while the lingual cusp tip is at one line with the lingual border of the lingual cusp. - The mesial marginal ridge severely slopes buccolingually, - The cervical line slightly curves occlusally. **Surface anatomy:** - The surface is smooth except for the mesiolingual groove. - The mesial contact area is at the junction of the middle and occusal thirds. **2- The root** is wide and has deep groove with tapered end. **Distal aspect:** - The distal aspect is identical to the mesial aspect except: - The distal marginal ridge is perpendicular on the long axis of the tooth. - The groove on the root is deeper. **Occlusal aspect:** - The geometric outline is diamond in shape - The lingual outline is much narrower than the buccal one. - The crown thickness is wider than its width. **Surface anatomy:** - **Elevations:** - The buccal triangular ridge is larger than the lingual one. - The two triangular ridges are meeting in the transverse ridge. - The mesial marginal ridge slopes more buccolingually than the distal one. - **Depressions:** There are mesial & distal rounded fossae (snake eyes) with two developmental pits. The mesiolingual developmental groove extends from the mesial pit to the mesial surface. ## **Mandibular Second Premolar** **Buccal aspect:** - In comparison to the first premolar; - Geometric oat line! square - The crown is wider but shorter with wide neck. - The buccal cusp is shorter and less pointed (due to more occlusally positioned mesial and distal contact areas). - The buccal ridge is less developed. **Lingual aspect:** - In comparison to first premolar; in 3 casp Type There their no lingual convergence - The lingual surface is wider and longer. - Geometric outline: square **Mesial aspect:** - In comparison to first premolar; - Geometric outlinelis rhomboidal - The buccal cusp tip is less pointed and slightly located buccal to line bisecting the root (less lingual inclination than first premolar). - The crown and root is wider buccolingually. - The lingual cusp may be longer than the buccal cusp. - The height of contour lingually is located at the occlusal third. **Distal aspect:** - In comparison to first premolar; - All the description is like the mesial aspect. In three cusp type, the distolingual cusp is smaller than the mesiolingual cusp. **Occlusal aspect:** - **Two-cusp type:** - no central Pit - The geometric outline is rounded and the buccal. lingual surface is slightly narrower than the buccal. - The buccal cusp triangular ridge is larger than the lingual cusp ridge and they meet at the transverse ridge. - The central groove is U or H shape grooves pattern. - **Three-cusp type:** - The geometric outline is square. - The buccal cusp is the largest cusp than the mesiolingual and the distolingual cusp is the smallest one. - The central groove is Y shape with central fossa, mesial and distal triangular fossae. **Pulp cavities of lower premolars:** - **Mesiodistally:** - The pulp chamber is pointed occlusally with one pulp horn buccally and one pulp horn lingually (two pulp horns lingually in 3 cusp type lower 5). - The root canal tapers to the apex. - **Buccolingually:** - The pulp chamber has two pulp horns, buccal & mesiolingual or distolingual - The root canal tapers to the apex **Chronology of the premolars is summarized in the following table.** | Beginning of calcification | Crown completion | Eruption | Root Completion | |---|---|---|---| | 12-13/4 y. | 10 y. | 4 | 13/4-2 y. | | 2-24 y. | 10 y. | 5 | 21/4-21/2 y. | | 11-12 y. | 3-4 y. after eruption date | |  | | 11-12 y. | 3-4 y. after eruption date | |  |