Chapter 12 Tooth Morphology

Anterior Permanent Dentition Lesson 12.1 Anterior Permanent Dentition Pronounce, define, and spell the Key Terms. Discuss the anterior permanent dentition, including: Identify the location of each anterior permanent tooth. Use the correct terminology when discussing features of the anterior permanent dentition. Describe the general and specific features of each tooth in the anterior permanent dentition. Discuss clinical considerations of each tooth in the anterior permanent dentition.

Introduction There is a certain amount of variation among individual teeth, and every tooth may not meet all criteria for identification By understanding the characteristics of each tooth, you will be able to differentiate among teeth, as well as between the left teeth and the right teeth in any particular group What does morphology mean? (Morphology means the shape of teeth.)

Clinical Uses for Tooth Morphology Mounting dental radiographs Assisting in charting a mouth with missing teeth and teeth that have “drifted” Selecting temporary crowns or orthodontic bands from a box with a variety of shapes Forming matrix bands before application Although morphology provides useful guidelines for the shape and positioning of teeth, there is always a certain amount of individual variation. Understanding the general characteristics of teeth permits identification and differentiation of an individual’s teeth.

Stainless Steel Crowns A thorough understanding of tooth morphology is useful in selecting the appropriate appliances. Stainless steel crowns are available in a variety of sizes for each tooth.

Anterior Permanent Dentition There are 12 anterior teeth in the permanent dentition, six in each dental arch The permanent anterior teeth include the central incisors, lateral incisors, and canines The central incisors are closest to the midline, the lateral incisors are the second teeth from the midline, and the canines are the third teeth from the midline All anterior teeth are succedaneous, replacing primary teeth of the same type Permanent anterior teeth tend to be the first to erupt and replace primary teeth.

Attractive Teeth Are Important People can be extremely self-conscious about the appearance of their front teeth and may take better care of a nice smile than they would of one they are not proud of. The size, shape, color, and position of the anterior teeth may affect a person’s appearance and self-esteem.

Characteristics of Permanent Anterior Teeth All anterior teeth have a cingulum, a rounded, raised area on the cervical third of the lingual surface The cingulum corresponds to the lingual developmental lobe The lingual surface on anterior teeth has rounded, raised borders on the mesial and distal surfaces called marginal ridges Some anterior teeth have a fossa, which is a wide, shallow depression on the lingual surfaces Do these lingual surfaces make a difference when the anterior teeth are being brushed? (Yes, it is important to reach all surfaces of the teeth when brushing.)

Newly Erupted Permanent Maxillary Incisor What feature do all anterior teeth have? (They all have a cingulum on the lingual surface.) Note the thin crown on the incisor, which is an adaptation for tearing food. From Bath-Balogh M, Fehrenbach MJ: Illustrated dental embryology, histology, and anatomy, ed 3, St Louis, 2011, Saunders.

Permanent Incisors There are eight permanent incisors­­: four maxillary and four mandibular The maxillary group comprises two central incisors and two lateral incisors, as does the mandibular group These teeth complement each other in form and function The central incisors erupt about a year or so before the lateral incisors do The mandibular incisors are smaller than the maxillary incisors. This means that the mandibular canine is normally mesial to the maxillary canine.

Maxillary Central Incisors The maxillary central incisors (#8 and #9) have unique anatomic features They are larger in all dimensions, especially mesiodistally, than a permanent mandibular central incisor The labial surfaces are more rounded from the incisal aspect, with the tooth tapering toward the lingual The root is short compared with the roots of other permanent maxillary teeth All lingual surface features, including the marginal ridges, lingual fossa, and cingulum, are more prominent on the maxillary central incisor than on the mandibular central incisor What is the meaning of “mesiodistally”? (It means the width of the tooth.) The maxillary central incisors are the most prominent teeth in the mouth.

Views of a Permanent Maxillary Right Central Incisor The incisors present a triangular outline. Note the virtually straight incisal edge and curve in the cervical line. From Bath-Balogh M, Fehrenbach MJ: Illustrated dental embryology, histology, and anatomy, ed 3, St Louis, 2011, Saunders.

Maxillary Central Incisors (Cont.) The incisal edges of these teeth are formed at the labioincisal line angle and do not exist until an edge has been created by wear The incisal edge is also known as the incisal surface or incisal plane When newly erupted, the central and lateral incisors have three mamelons, or rounded enamel extensions on the incisal ridge, or edge The mamelons usually undergo attrition shortly after eruption What is meant by attrition? (Mechanical wear of teeth during use) Some incisors may present with a distinctive shovel-shaped appearance on the lingual aspect.

Mamelons Mamelons are the rounded portions of the incisal edge of the lower central incisors.

Maxillary Lateral Incisors The maxillary lateral incisors (#7 and #10) are smaller than the central incisors in all dimensions except root length They usually erupt after the maxillary central incisors The crown of a maxillary lateral incisor has a single root that is relatively smooth and straight but may curve slightly to the distal Recognizing this feature is helpful in the mounting of radiographs When a lingual pit is present, caries is more likely.

Maxillary Lateral Incisors (Cont.) The lateral incisors vary in form more than any other tooth in the mouth, except the third molars, and are often congenitally missing Because of the variations in form, the permanent maxillary lateral incisors present challenges during preventive, restorative, and orthodontic procedures Unattractive open contacts (spaces between teeth), called diastema, often occur in this area because of the variations in tooth size and position in the arch Treatment for diastemas can include orthodontic treatment, crowns, or veneers.

Views of a Permanent Maxillary Right Lateral Incisor Note the narrow, cone-shaped appearance of the incisor. These teeth are among the most likely to be missing congenitally or due to heredity. From Bath-Balogh M, Fehrenbach MJ: Illustrated dental embryology, histology, and anatomy, ed 3, St Louis, 2011, Saunders.

Pegged Maxillary Lateral Incisor What are pegged laterals? (Maxillary lateral incisors with a pointed or tapered shape) Note the conical shape. The maxillary third molars differ from the other teeth considerably in terms of size, contour, and relative position. From Ibsen OC, Phelan JA: Oral pathology for the dental hygienist, ed 6, St Louis, 2014, Saunders.

Mandibular Incisors The permanent mandibular incisors are the smallest teeth of the permanent dentition and the most symmetric The central and lateral incisors of the mandibular arch resemble each other Generally the lateral incisor is larger than the central incisor, in contrast to the teeth in the maxillary arch Supragingival tooth deposits, such as plaque, calculus, and stain, tend to collect in the lingual concavity of the mandibular incisors In general the mandibular central incisor is the smallest tooth in the human mouth. Supernumerary teeth often form among the upper incisors.

Mandibular Central Incisors The mandibular central incisors (#24 and #25) are the smallest and simplest teeth and are bilaterally symmetric Each has a small centered cingulum, subtle lingual fossa, and equally subtle marginal ridges The crown of a mandibular central incisor is narrower on the lingual surface than on the labial surface The developmental horizontal lines on anterior teeth, or imbrication lines, and developmental depressions are usually not present or are very faint The mandibular central incisors present with a strong degree of bilateral symmetry.

Views of a Permanent Mandibular Right Central Incisor Note the symmetrical nature of the tooth. The lingual surface is concave, with a slight fossa and cingulum. From Bath-Balogh M, Fehrenbach MJ: Illustrated dental embryology, histology, and anatomy, ed 3, St Louis, 2011, Saunders.

Mandibular Lateral Incisors The mandibular lateral incisors (#23 and #26) are slightly larger than the mandibular central incisors but otherwise similar to them The lateral teeth usually erupt after the mandibular central incisors The lateral incisors have a small, distally placed cingulum The greater height of the cementoenamel junction (CEJ) curvature on the mesial surface than on the distal surface helps distinguish the right mandibular lateral incisor from the left incisor There is less symmetry in these teeth than in the mandibular central incisors. The mandibular lateral incisors have slightly larger roots than do the central incisors.

Views of a Permanent Mandibular Right Lateral Incisor Note the “twist” in the incisal edge. The distal surface tends to have a more pronounced curve than do the central incisors. From Bath-Balogh M, Fehrenbach MJ: Illustrated dental embryology, histology, and anatomy, ed 3, St Louis, 2011, Saunders.

Permanent Canines The permanent canines are the four anterior teeth located at the corner of each quadrant for each dental arch Their name is derived from the Latin word for dog (canis) because these teeth resemble dogs’ teeth Patients often complain of the normal slightly deeper yellow color of their canines compared with their incisor teeth “Cuspid” is an older term that has been used in place of canine. A cusp is a major elevation on a chewing surface.

Permanent Canines (Cont.) The permanent canines are the longest teeth in the dentition The root is usually the length of the crown This large root is externally manifested by the bony vertical ridge called the canine eminence Patients commonly call the canines their “eye teeth” The canines are considered the cornerstones of the dentition.

Views of Permanent Mandibular and Maxillary Canines Canines are the only teeth with one cusp. Note the single root and canine eminence. A, Labial view. B, Lingual view From Bath-Balogh M, Fehrenbach MJ: Illustrated dental embryology, histology, and anatomy, ed 3, St Louis, 2011, Saunders.

Maxillary Canines The maxillary canines (#6 and #11) usually erupt after the mandibular canines, after the maxillary incisors, and possibly after the maxillary premolars The cusp tip is sharper on a maxillary canine The mesial cusp slope is usually shorter than the distal cusp slope in both the maxillary and the mandibular canines when they first erupt The length of these cusp slopes and the cusp tip can change with attrition The maxillary canine is narrower than the central incisor.

Mandibular Canines The mandibular canines (#22 and #27) usually erupt before the maxillary canines and after most of the incisors have erupted A mandibular canine closely resembles a maxillary canine Although the entire tooth is usually as long, a mandibular canine is narrower labiolingually and mesiodistally than a maxillary canine The lingual surface of the crown of the mandibular canines is smoother than that of the maxillary canines and has a less developed cingulum and two marginal ridges Lower permanent canines on occasion have a bifurcation near the apex, resulting in two short roots.

Views of a Permanent Mandibular Right Canine Note the lack of symmetry common to all canines. From Bath-Balogh M, Fehrenbach MJ: Illustrated dental embryology, histology, and anatomy, ed 3, St Louis, 2011, Saunders.

Clinical Considerations with Canines The maxillary canines may erupt labially or lingually in relation to the surrounding teeth The maxillary canines may also fail to erupt fully and may remain impacted This occurs because the permanent maxillary canines erupt after the maxillary incisors and possibly after the premolars and their arch spaces have closed What makes the canine teeth self-cleaning? (Their location and shape) The canines are important in establishing a natural facial contour.

Posterior Permanent Dentition Lesson 12.2 Posterior Permanent Dentition Discuss the posterior permanent dentition, including: Identify the location of each posterior permanent tooth. Use the correct terminology when discussing features of the posterior permanent dentition. Describe the general and specific features of each tooth in the posterior permanent dentition. Discuss clinical considerations of each tooth in the posterior permanent dentition.

Posterior Permanent Dentition The permanent posterior teeth include the premolars and molars The crown of each posterior tooth has an occlusal surface, bordered distally and mesially by marginal ridges The occlusal surfaces have two or more cusps Imagine each cusp as a mountain with sloping areas, or cusp ridges, extending from the top of the mountain; between the ridges are sloping areas called inclined cuspal planes The posterior dentition is important in grinding and chewing food and in maintaining the shape of the face.

Occlusal Surface on a Permanent Posterior Tooth Pictured: Occlusal surface on a permanent posterior tooth and its features. The premolars are also known as bicuspids because of their two large prominences. From Bath-Balogh M, Fehrenbach MJ: Illustrated dental embryology, histology, and anatomy, ed 3, St Louis, 2011, Saunders.

Posterior Permanent Dentition (Cont.) Each shallow, wide depression on the occlusal table is a fossa One type of fossa on posterior teeth, the central fossa, is located where the cusp ridges converge in a central point, where the grooves meet Another type of fossa is the triangular fossa Sometimes located in the deepest portions of the fossa are occlusal developmental pits Each pit is a sharp pinpoint depression where two or more grooves meet How do occlusal pits relate to the fossa on the tooth? (The marginal ridges border the occlusal surface and create an inner occlusal table. Each shallow, wide depression on the occlusal table is a fossa.) How might dental sealants help the situation of having grooves, pits, and so on? (Dental sealants can prevent particles and bacteria from lodging in grooves and pits, therefore helping to prevent the formation of dental caries.)

Features of the Occlusal Table Pictured: Other features of the occlusal table on a permanent posterior tooth, including the central groove. What are developmental grooves? (The grooves are sharp, deep, V-shaped linear depressions.) Note the occlusal pit formed by the junction of grooves. Pits are more common in teeth with three cusps. From Bath-Balogh M, Fehrenbach MJ: Illustrated dental embryology, histology, and anatomy, ed 3, St Louis, 2011, Saunders.

Clinical Considerations with Posterior Teeth The occlusal surfaces on permanent posterior teeth have pit and groove patterns that make them susceptible to caries (decay) This occurs because of increased plaque retention and the thinness of the enamel forming the walls of the pits and grooves The pits and grooves need to be carefully checked for decay with an explorer and mirror and possibly a chemical caries indicator Posterior teeth with deep pit and groove patterns should have dental sealants placed shortly after erupting. Would the morphology and position of the posterior teeth make identification of caries more difficult? Why? (Yes. Morphology and position affect the ability to view the teeth.)

Permanent Premolars There are eight premolars in the permanent dentition, two in each quadrant They are located posterior to the canines and immediately anterior to the molars There are two types of premolars: First Second Premolars are always anterior to molars.

Maxillary First Premolars A maxillary first premolar (#5 and #12) is larger than a maxillary second premolar Each maxillary first premolar has two cusps (buccal and lingual) and two roots (facial and lingual) Both maxillary premolars erupt earlier than the mandibular premolars The buccal cusp is the larger of the two cusps. The lower second premolar may, at times, present with two lingual cusps.

Maxillary First Premolars (Cont.) The maxillary first premolar has a bifurcated root (two roots, one buccal and one lingual) Some first premolars have roots that are joined, or fused The roots are shorter in length and resemble the roots of the molars In contrast to the roots, the crowns of the first premolars may closely resemble those of the canines. Most upper premolars have two roots; fewer than one fifth present with a single root.

Clinical Considerations with Premolars The maxillary and mandibular premolars work with the molars in the chewing of food The first premolars help the canines in shearing or cutting bits of food The premolars also support the corners of the mouth and cheeks When people lose all of their molars, they usually can still chew if they have their premolars. Unfortunately, the fact that a person is missing one or more maxillary premolars is very noticeable when he or she smiles.

Views of a Permanent Maxillary First Premolar Note the larger buccal cusps and the well-defined occlusal groove. The concave depression near the root line is known as the canine fossa. Why might this term be misleading? (This might lead one to believe it is located on a canine tooth, rather than a premolar.) Why is the buccal cusp large and sharp? (To assist the canine with tearing) From Bath-Balogh M, Fehrenbach MJ: Illustrated dental embryology, histology, and anatomy, ed 3, St Louis, 2011, Saunders.

Maxillary Second Premolars Each maxillary second premolar (#4 and #13) has two cusps (buccal and lingual) and one root The buccal cusp is shorter, less pointed, and more rounded than the first.

Differences Between Second and First Maxillary Premolars The cusps are closer in length on the second premolar The lingual cusp is slightly shorter, but not as short as the cusp on the maxillary first premolar The mesiobuccal cusp slope is shorter than the distobuccal cusp slope on the second premolar The cusps of the secondary premolar are not as sharp as those of the maxillary first premolar The second premolar has only one root and one root canal The second premolar has a slight depression on the mesial root The second premolar is wider buccolingually than mesiodistally In most facets, second premolars are similar to but less defined than first premolars. Many features tend to be more rounded in second premolars.

Mandibular First Premolars Each mandibular first premolar (#21 and #28) has a long and well-formed buccal cusp and a small, nonfunctioning lingual cusp The lingual cusp may be no larger than the cingulum on some maxillary canines The mandibular first premolars are smaller and shorter than the mandibular second premolars The lingual cusp of this tooth is the smallest of any tooth.

Views of a Permanent Mandibular Right First Premolar Note the bilateral symmetry. Note the large buccal cusp and the diamond shape of the occlusal outline. From Bath-Balogh M, Fehrenbach MJ: Illustrated dental embryology, histology, and anatomy, ed 3, St Louis, 2011, Saunders.

Mandibular Second Premolars The permanent mandibular second premolars (#20 and #29) erupt distal to the mandibular first premolars They are the succedaneous replacements for the primary mandibular second molars There are two forms of the mandibular second premolar: Three-cusp type, or tricuspidate form Two-cusp type, or bicuspidate form Mandibular second premolars tend to be larger than the mandibular first premolars, but the buccal cusp in these teeth is less pronounced. This tooth is one of those most frequently missing as a result of heredity or congenital factors.

Views of a Permanent Mandibular Second Premolar This tooth is one of those most frequently missing as a result of heredity or congenital factors. From Bath-Balogh M, Fehrenbach MJ: Illustrated dental embryology, histology, and anatomy, ed 3, St Louis, 2011, Saunders.

Occlusal Views of a Permanent Mandibular Second A, U-type. B, H-type. C, Y-type. Note the single deep groove in the two-cusp teeth compared with the distinctive Y pattern of the three-cusp tooth. From Zeisz RD, Nuckolls J: Dental anatomy, St Louis, 1949, Mosby.

Permanent Molars There are 12 molars, three in each quadrant, in the permanent dentition The molar crowns have four or five short, blunt cusps, and each molar has two or three roots that help support the larger crown In most individuals, lower molars have two lingual cusps, whereas upper permanent molars present with two buccal cusps. Lower molars generally have two roots, whereas upper molars generally have three roots.

Permanent Molars (Cont.) The name molar comes from the Latin word for “grinding” There are three types of molars: first, second, and third The first and second molars are also called the 6-year and 12-year molars because of the approximate ages at which they erupt The permanent molars are the largest teeth in the dentition. Molar teeth are not preceded by primary teeth.

Maxillary Molars Usually the first permanent teeth to erupt into the maxillary arch Each maxillary molar usually has four major cusps, with two on the buccal portion of the occlusal table and two on the lingual Each maxillary molar has three well-separated and well-developed roots A tooth with three roots is said to be trifurcated, which means “divided into thirds” The distal of the maxillary first molar and mandibular central incisors are prone to periodontitis. The parotid gland exits near this tooth as well, so there is often supragingival calculus on the distobuccal surface.

Clinical Considerations with Maxillary Molars The roots of the maxillary molars may penetrate the maxillary sinus as a result of accidental trauma or during an extraction The permanent maxillary third molars may fail to erupt and may remain impacted within the alveolar bone If the maxillary first molar is lost, the second molar can tip and drift into the open space, causing difficulty in chewing and furthering periodontal disease The roots of the maxillary molars are close to the sinuses, causing some patients to confuse the pain caused by a sinus infection with pain related to their maxillary teeth, and vice versa. Diagnostic tests can rule out involvement of the maxillary teeth when a patient has what may be a sinus problem. Impacted third molars can irritate the surrounding tissue, leading to pain and swelling.

Maxillary First Molars The maxillary first molars (#3 and #14) are the first permanent teeth to erupt into the maxillary arch They erupt distal to the primary maxillary second molars and are therefore nonsuccedaneous (do not replace the primary teeth) The maxillary first molar is the largest tooth in the maxillary arch and also has the largest crown in the permanent dentition This molar is composed of five developmental lobes, two buccal and three lingual The fifth cusp is called the cusp of Carabelli The cusp of Carabelli is much less pronounced than the other cusps and is of little practical use. Because of the typical age at the eruption of these teeth, children and parents may need to be told that the maxillary and mandibular first molars are permanent dentition.

First Molars A, Maxillary first molar. B, Mandibular first molar. Note the three roots on the maxillary molar, compared with two on the mandibular. Note that mandibular molars tend to be wider than maxillary ones, with larger cusps. From Bath-Balogh M, Fehrenbach MJ: Illustrated dental embryology, histology, and anatomy, ed 3, St Louis, 2011, Saunders.

Views of a Permanent Maxillary Right First Molar Note that the size of the roots parallels the buccal and two lingual cusps. Note that the size of the roots tends to parallel the size of the cusps. From Bath-Balogh M, Fehrenbach MJ: Illustrated dental embryology, histology, and anatomy, ed 3, St Louis, 2011, Saunders.

Maxillary Second Molars The crown of the maxillary second molar is somewhat shorter than that of the first molar, and it usually has four cusps No fifth cusp is present There are three roots The roots of the secondary molars are smaller than those of the first molars The lingual root is still the largest and longest The buccal groove is located farther distally on the buccal surface of the second maxillary molar than on the first maxillary molar. The mesiobuccal cusp of the second maxillary molar is longer and has a more blunt cusp tip than the distobuccal cusp. Differences in cusp size are more noticeable on the maxillary second molars than on the first. The roots of the second molars are close together and sometimes fuse.

Views of a Permanent Maxillary Right Second Molar The distolingual cusp varies in size from fairly prominent to very small. Note the proximity of the three roots. From Bath-Balogh M, Fehrenbach MJ: Illustrated dental embryology, histology, and anatomy, ed 3, St Louis, 2011, Saunders.

Maxillary Third Molars The maxillary third molars (#1 and #16) differ considerably in size and contour The crown of the maxillary third molar is smaller and the roots are usually shorter The roots of the maxillary third molar tend to fuse, and the result is a single tapered root People sometimes refer to the maxillary third molars as the “wisdom” teeth because they erupt last Maxillary third molars show more variation in morphology than do other teeth. These teeth are the most likely to be missing as a result of heredity or congenital causes.

Buccal Views of Maxillary Right Molars A, First molar. B, Second molar. C, Third molar. Notice how the roots tend to be closer together when the molars are farther distally. Third molar roots are often fused. Note the pattern of increasing proximity of the roots from first to third molar. Note how cusp size and root length diminish in parallel. Modified from Brand RW, Isselhard DE: Anatomy of orofacial structures, ed 7, St Louis, 2003, Mosby.

Views of Permanent Maxillary Right Third Molars Note the closely proximate or fused roots and the less pronounced cusps compared with those of the first and second molars. From Bath-Balogh M, Fehrenbach MJ: Illustrated dental embryology, histology, and anatomy, ed 3, St Louis, 2011, Saunders.

Mandibular Molars The mandibular molars erupt 6 months to 1 year before the corresponding permanent maxillary molars The crowns of the mandibular molars have four or five major cusps, with two lingual cusps always of about the same width All mandibular molars are wider mesiodistally than buccolingually, similar to anterior teeth The lingual cusps tend to be longer and sharper than the buccal cusps.

Mandibular Molars (Cont.) Each mandibular molar has two well-developed roots, one mesial and one distal A tooth with two roots is referred to as bifurcated, which means “divided into two” A bifurcation is the area at which the two roots divide The mesial root is wider than the distal one. The two roots are generally the same length.

Clinical Considerations with Mandibular Molars The lingual inclination of the crowns of the mandibular molars can make it difficult to position the oral evacuator The lingual inclination of the molar teeth can also pose problems in oral hygiene for patients, who may miss the lingual gingiva with the toothbrush What advice would you give a patient having difficulty carrying out oral hygiene of the mandibular molars? (Answer will vary.)

Mandibular First Molars The permanent mandibular first molars (#19 and #30) erupt between 6 and 7 years of age These teeth are commonly the first permanent teeth to erupt in the oral cavity The two roots, mesial and distal, of a mandibular first molar are larger and more divergent than those of a second molar When this molar has three roots, the mesial root has both buccal and lingual branches.

Views of a Permanent Mandibular Right First Molar Note that the buccal cusps are the largest (and widest) of the cusps. In general, the distal cusp is poorly developed. In some cases, the molar may have four cusps. Rare cases present with a sixth cusp. From Bath-Balogh M, Fehrenbach MJ: Illustrated dental embryology, histology, and anatomy, ed 3, St Louis, 2011, Saunders.

Mandibular Second Molars The mandibular second molars (#18 and #31) erupt between 11 and 12 years of age These teeth erupt distal to the permanent first molars and therefore are nonsuccedaneous The crown of the mandibular second molar is slightly smaller than that of the first molar in all directions The crown has four well-developed cusps Roots on the second molars tend to be shorter than those on the first molars. A fifth cusp is seen in rare cases.

Views of a Permanent Mandibular Right Second Molar Note the prominent buccal cusps and bifurcated roots. From Bath-Balogh M, Fehrenbach MJ: Illustrated dental embryology, histology, and anatomy, ed 3, St Louis, 2011, Saunders.

Mandibular Third Molars The mandibular third molars (#17 and #32) are similar to the maxillary third molars in that they vary greatly in shape There is no typical mandibular third molar This molar is usually smaller in all dimensions than the second molar The third molar consists of four developmental lobes A mandibular third molar has two roots that are fused, irregularly curved, and shorter than those of a mandibular second molar The crown of the mandibular third molar tends to be more rounded than that of a first or second molar. Four or five cusps may be present.

Views of the Permanent Mandibular Right Third Molar Note the rounded shape of the cusps and the nearly fused appearance of the roots. From Bath-Balogh M, Fehrenbach MJ: Illustrated dental embryology, histology, and anatomy, ed 3, St Louis, 2011, Saunders.

Buccal Views of Permanent Mandibular Right Molars A, First molar. B, Second molar. C, Third molar. Note that the roots are closer together and become shorter from the first molar to the third molar. Third molar roots are often fused. Note the diminishing prominence of the cusps and increasingly rounded appearance of the crowns. Modified from Brand RW, Isselhard DE: Anatomy of orofacial structures, ed 7, St Louis, 2003, Mosby.

Lesson 12.3 Primary Dentition Discuss the primary dentition, including: Compare and contrast the features of the primary and permanent dentitions. Describe the general and specific features of the primary dentition. Discuss clinical considerations of the primary dentition.

Primary Dentition There are 20 primary teeth: 10 in the maxillary arch 10 in the mandibular arch Includes incisors, canines, and molars Numbered in the Universal Tooth Numbering System with the capital letters A through T Smaller overall and have whiter enamel than the permanent teeth do The crown of any primary tooth is short in relation to its total length The crowns are narrower at the cementoenamel junction (CEJ) The primary teeth are commonly known as “primary,” “baby,” or “milk” teeth. The primary dentition is also known clinically as the deciduous dentition.

Primary Dentition (Cont.) The pulp chambers and pulp horns in primary teeth are relatively large compared with those of the permanent teeth There is a thick layer of dentin between the pulp chambers and the enamel, especially in the primary mandibular second molar The enamel layer is relatively thin In addition to normal tooth function, the key role of the primary dentition is to maintain proper spacing for the eruption of the permanent dentition. It is for this reason, more than others, that proper care of the primary dentition is so important.

Clinical Considerations with Primary Teeth Often parents do not understand the importance of the primary teeth Primary teeth hold the eruption space for the permanent teeth Because the enamel and dentin are thinner in primary teeth, decay can travel quickly through the enamel to the pulp, possibly causing loss of the tooth Early dental health education and dental care are essential in keeping the primary dentition In the primary dentition it is particularly important to retain the second molars. If these teeth are lost, the first permanent molars are likely to drift out of position.

Primary Incisors The crowns and roots of deciduous incisors are smaller than those of their permanent successors The roots are twice as long as the crowns and taper toward the apex If a primary incisor is lost prematurely, a space maintainer is not fabricated. However, if a primary molar is lost, a space maintainer may be fabricated to prevent space loss and ensure adequate room for the adult premolars.

Primary Maxillary Central Incisors The crown of the primary maxillary central incisor (E and F) is wider mesiodistally than incisocervically It is the only tooth of either dentition with this crown dimension The primary maxillary incisors have no mamelons The cingulum and marginal ridges are more prominent than they are on the permanent successor, and the lingual fossa is deeper The incisors are the first teeth to erupt, beginning 6½ months to about 8 months after birth. The primary incisor teeth are functional for 5 to 6 years.

Views of a Primary Maxillary Right Central Incisor Note the narrow root and short crown length relative to the root length. Note the relatively large cingulum. From Bath-Balogh M, Fehrenbach MJ: Illustrated dental embryology, histology, and anatomy, ed 3, St Louis, 2011, Saunders.

Primary Maxillary Lateral Incisors The crown of the primary maxillary lateral incisor (D and G) is similar to that of the central incisor but much smaller in all dimensions The incisal angles on the lateral incisor are also more rounded than on the central incisor The lateral root is longer in proportion to its crown, and its apex is sharper How does the maxillary lateral incisor differ from a central incisor? (The maxillary lateral incisor is more rounded than a central incisor and is longer than it is wide.)

Views of a Primary Maxillary Lateral Incisor Note the similarity of the primary maxillary lateral incisor, except for size, with the central incisor. Note the sharp apex and long root. From Bath-Balogh M, Fehrenbach MJ: Illustrated dental embryology, histology, and anatomy, ed 3, St Louis, 2011, Saunders.

Primary Mandibular Central Incisors The crown of the primary mandibular incisor (O and P) resembles the primary mandibular lateral incisor more than it does its permanent central successor The mandibular central incisor is extremely symmetric It is also not as constricted at the CEJ as the primary maxillary incisor The lingual surface of the mandibular central incisors appears smooth and tapers toward the prominent cingulum The crown of the mandibular central incisor is slightly bigger than that of the permanent lateral incisor.

Views of a Primary Mandibular Central Incisor The root is slender and rather long. How would you compare the morphology of this tooth with the permanent lateral incisor? What are the similarities? (Answers will vary, but may include the observation that the permanent lateral incisor has a more ridged edge.) From Bath-Balogh M, Fehrenbach MJ: Illustrated dental embryology, histology, and anatomy, ed 3, St Louis, 2011, Saunders.

Primary Mandibular Lateral Incisors The crown of the primary lateral incisor (Q and N) is similar in form to that of the central incisor in the same arch but is wider and longer The incisal edge of the mandibular lateral incisor slopes distally, and the distoincisal angle is more rounded The root may have a distal curvature in its apical third and usually has a distal longitudinal groove.

Views of a Primary Mandibular Lateral Incisor Note that the cingulum is more noticeable and the fossa is deeper than in the central incisor. From Bath-Balogh M, Fehrenbach MJ: Illustrated dental embryology, histology, and anatomy, ed 3, St Louis, 2011, Saunders.

Primary Canines There are four primary canine teeth, two in each dental arch Differ from the outline of their permanent successors in the following ways: Maxillary canines The crown of the primary maxillary canine (C and H) has relatively longer and sharper cusp than that of its permanent successor on eruption The mesial and distal outlines of the primary maxillary canine are rounder The canines erupt between 16 and 20 months after birth. The primary canines are sometimes removed to allow other teeth to align properly.

Views of a Primary Maxillary Canine Note that the primary canines may appear to be wider than they are long. This is an optical illusion. This tooth has a well-developed cingulum and tends to have noticeable ridges on the mesial slope. From Bath-Balogh M, Fehrenbach MJ: Illustrated dental embryology, histology, and anatomy, ed 3, St Louis, 2011, Saunders.

Primary Mandibular Canines The primary mandibular canine (M and R) resembles the primary maxillary canine, but this tooth is much smaller labiolingually The distal cusp slope is much longer than the mesial cusp slope The lingual surface of the primary mandibular canine is marked by a shallow lingual fossa The primary mandibular canine (M and R) resembles the primary maxillary canine, although some dimensions are different This tooth is much smaller labiolingually Canines and incisors are considered to be anterior teeth, while premolars and molars are posterior teeth.

Views of a Primary Mandibular Canine Note the thin root and the less obvious cingulum compared with those of the maxillary canine. From Bath-Balogh M, Fehrenbach MJ: Illustrated dental embryology, histology, and anatomy, ed 3, St Louis, 2011, Saunders.

Primary Molars The primary dentition consists of a total of eight primary molars Each quadrant includes a first primary molar and a second primary molar Each molar crown is wider than it is tall The permanent premolars replace the primary molars when they are exfoliated Primary teeth are smaller than their permanent successors and have relatively larger pulp chambers. It is important that caries be treated promptly in order to prevent exposure of the pulp.

Primary Maxillary First Molars The crown of the primary maxillary first molar (B and I) does not resemble any other crown of either dentition The height of contour on the buccal surface is at the cervical third of the tooth; on the lingual side, it is at the middle third The primary maxillary molars have three roots, which are thinner and have greater flare than do those of the permanent maxillary first molar The lingual root is the longest and most divergent The crown of the first maxillary molar is the smallest found in the primary molars.

Views of a Primary Maxillary First Molar The first molars erupt between 12 and 16 months after birth. From Bath-Balogh M, Fehrenbach MJ: Illustrated dental embryology, histology, and anatomy, ed 3, St Louis, 2011, Saunders.

Primary Maxillary Second Molars The primary maxillary second molar (A and J) is larger than the primary maxillary first molar Closely resembles the permanent maxillary first molar but is smaller in all dimensions The second molar usually has a cusp of Carabelli, the minor fifth cusp How many pronounced cusps will a primary maxillary second molar have? (Four)

Views of a Primary Maxillary Second Molar The first permanent first maxillary molar may resemble the primary second molar. Primary maxillary molars have three roots, whereas mandibular molars have two. From Bath-Balogh M, Fehrenbach MJ: Illustrated dental embryology, histology, and anatomy, ed 3, St Louis, 2011, Saunders.

Primary Mandibular First Molars The crown of the primary mandibular first molar (L and S) is unlike any other tooth of either dentition The height of contour on the buccal surface is at the cervical third of the tooth; on the lingual side, it is at the middle third Has four cusps; the mesial cusps are larger Has two roots, which are positioned similarly to those of other primary and permanent mandibular molars The mesial cusps are the highest and largest on any tooth.

Views of a Primary Mandibular First Molar What makes this tooth’s morphology so unique? (The tooth has a prominent buccal cervical ridge, also on the mesial half of the buccal surface, similar to other primary molars. The height of contour on the buccal surface is seen at the cervical one third of the tooth; on the lingual side, it is noted at the middle one third.) From Bath-Balogh M, Fehrenbach MJ: Illustrated dental embryology, histology, and anatomy, ed 3, St Louis, 2011, Saunders.

Mandibular Second Molars The primary mandibular second molar (K and T) is larger than the primary mandibular first molar Most closely resembles in form the permanent mandibular first molar The three buccal cusps are nearly equal in size, however, and the primary mandibular second molar has an oval occlusal shape.

Views of a Primary Mandibular Second Molar As a practicing dental assistant, you will be surprised at how often your knowledge of tooth morphology and the other dental sciences will directly relate to patient care and your understanding of dental treatment plans. From Bath-Balogh M, Fehrenbach MJ: Illustrated dental embryology, histology, and anatomy, ed 3, St Louis, 2011, Saunders.

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