DOI: 10.5772/intechopen.79464 ProvisionalChapter chapter 2 The Permanent MaxillaryMaxillary andand MandibularMandibular PremolarPremolar Teeth IşılIşıl Çekiç NagaNagaş,ş, Ferhan EEğilmezğilmez andand BaBağdagülğdagül HelvacioHelvacioğluğlu Kivanç Additional information isis available atat thethe endend ofof thethe chapterchapter http://dx.doi.org/10.5772/intechopen.79464 Abstract The permanent premolar teeth are placed between the anterior teeth and molars. Eight premolars are found in the permanent dentition, four per arch and two in each quadrant. The main function of premolars is to assist the canines in regard to tear and pierce the food and supplement the grinding of the molars during mastication. The other functions are to support the corners of the mouth reinforce esthetics during smiling and maintain the vertical dimension. Detailed morphology of the permanent premolar teeth is narrated in a pointwise and systematic manner in this chapter. Keywords: teeth, premolars, dental anatomy 1. Introduction The premolars develop from four lobes with the exception of the mandibular second premolar which develops from five lobes. The facial surfaces of the premolars develop from three facial lobes like anterior teeth. Likewise, the lingual surfaces of most premolars develop from one lingual lobe like anterior teeth. While mandibular first premolars develop from four lobes (mesial, distal, buccal, and lingual) just like the anterior teeth and maxillary premolars, man- dibular second premolars often develop from five lobes (mesial, buccal, distal, mesiolingual, and distolingual lobes). That is why the term “bicuspid” signifies “two cusps,” widely used to describe premolars, may be inappropriate for this group of teeth since the mandibular pre- molars may show a variation in the number of cusps from one to three. In anterior teeth, the lingual lobe forms the cingulum of the incisors and canines. However, in premolar teeth, this lobe forms the lingual cusps. The lingual cusps of mandibular premolars are less prominent © 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and eproduction in any medium, provided the original work is properly cited. distribution, and reproduction in any medium, provided the original work is properly cited. 38 Dental Anatomy than the buccal cusps. There are no deciduous premolars. These teeth erupt at the position previously occupied by the deciduous molars. Timing of teeth eruption can be affected by many factors such as gender, environmental factors and genetic conditions and differs from population to population [1–3]. The agenesis of lower second premolars and maxillary lateral incisors are the most frequent and it could be radio- graphically documented if the median age of emergence of these teeth was passed [1]. On the other hand, caries in primary molar teeth or early extraction of second primary molar could accelerate the eruption time of permanent premolars [1]. The classic sequences of teeth eruption in the maxillae is as follows: first molar, central incisor, lateral incisor, first premolar, canine, second premolar and second molar whereas in the mandible, central incisor, first molar, lateral incisor, canine, first premolar, second premolar and second molar [2]. In addition, generally, in girls, the maxillary canine can be expected before the second premolar, and the mandibular second premolar can be expected before second molar; in boys both orders are reversed [3]. The detailed descriptions of morphologies of from all aspects, chronology of development, form and function, the common characteristics of the permanent premolar teeth were presented in this chapter. In addition, the major differences between these teeth were given in a pointwise and systematic manner [4–11]. 2. The permanent maxillary premolars 2.1. Permanent maxillary first premolars The maxillary first premolar is the fourth permanent tooth from the median line in the maxil- lary arch, located laterally from both the maxillary canines of the mouth but mesial from both maxillary second premolars. It is the first posterior tooth. Chronologic development of the maxillary first premolar is given in Table 1. In the universal system of notation, the right permanent maxillary first premolar is shown as “#5,” and the left one is shown as “#12.” According to the international notation, the right permanent maxillary first premolar is shown as “14,” and the left one is shown as “24.” Besides, in the Palmer notation, the right permanent maxillary first premolar is symbolized as “ ,” the left one is symbolized as “ .” The image of maxillary first premolar from all aspects is seen in Figure 1. A. Buccal, B. Lingual, C. Mesial, D. Distal, E. Occlusal. Development stage Years Initiation of calcification 1 ½–1 ¾ years Enamel completion 5–6 years Eruption 10–11 years Root completion 12–13 years Table 1. Chronologic development of the maxillary first premolar teeth. The Permanent Maxillary and Mandibular Premolar Teeth 39 http://dx.doi.org/10.5772/intechopen.79464 Figure 1. Maxillary first premolar tooth from different aspects. A. Buccal, B. Lingual, C. Mesial, D. Distal, E. Occlusal. The buccolingual dimension is higher than the mesiodistal dimension. The buccal, lingual, and distal surfaces of the crown display convexities in different degrees. 2.1.1. Buccal aspect The pentagonal or trapezoidal shape of the crown is noticeable from the facial aspect. With this form of the crown, the permanent maxillary first premolar appears to be similar to those of the maxillary canine and second premolar. While the canine has a larger size crown with a more prominent cusp tip, the second premolar has a smaller crown with a less prominent cusp tip. Additionally, the crown is smaller in the cervico-occlusal dimension than any anterior tooth, but larger than that of the second premolar or permanent molars. The greatest mesiodistal width of the crown is about 2 mm less at the cervical region. The buccal surface is convex with the exception of the developmental depressions. The well- developed middle buccal lobe forms a continuous ridge from the tip of the buccal cusp to the cervical margin. This ridge is called as “buccal ridge” and demarcates the three developmental lobes. Mesiobuccal and distobuccal developmental depressions exist on both mesial and distal sides of the buccal ridge. These depressions divide the occlusal portion of the buccal surface into vertical thirds, consisting of mesiobuccal, distobuccal, and buccal lobes. Mesiobuccal and distobuccal lobes serve to emphasize strong mesiobuccal and distobuccal line angles on the crown. The imbrication lines are in parallel and semicircular forms and also common in the cervical third of the buccal surface. 40 Dental Anatomy From this aspect, cervical line of the crown is convex. In addition, the curvature depth is less at the cervical margin of the crown than those of anterior teeth. The crest curvature of the cervical line is almost placed at the center of the root. The mesial contour of the crown presents a shallow concavity extending from the cementoenamel junction to the mesial contact area. The highest contour of mesial curvature is at the contact area and located near the junction of the occlusal and middle thirds. The mesial margin of the buccal cusp is lying from the contact area to the tip of the buccal cusp and it creates the mesio-occlusal angle. This margin is less curved and longer than the distal slope of the buccal cusp. The buccal cusp tip is placed slightly toward the distal. Therefore, unequal two portions are seen at the buccal aspect of the crown of occlusal outlines. A concavity or notch may be observed as a result of the developmental depressions passing over the occlusal margin. The distal contour of the crown presents more concave and straighter form below the cementoenamel junction than that of mesial contour. The crest curvature of the distal contact area is located slightly more occlusally. 2.1.2. Lingual aspect The tooth is narrower mesiodistally at the lingual than at the buccal. Therefore, the crown converges toward the lingual cusp. The lingual ridge is barely defined. Both the buccal and lingual cusp tips are visible from this aspect, since the lingual cusp is shorter than the buccal cusp. The lingual cusp of the maxillary first premolar is the shortest of the four maxillary premolar cusps. The lingual portion of the crown is convex and has a spheroidal form. The cervical line at this aspect is regular, with symmetrical curvature toward the root and the crest of curvature is centered on the root. The proximal outlines of the crown at the lingual aspect are convex. These outlines are convex and continuous with the mesial and distal slopes of the lingual cusp. If the tooth presents the severe mesial concavity, the mesial outline may be concave. The lingual cusp tip is situated well anterior (mesial) to the mid-buccolingual diameter of the crown, so the two cusp tips are not placed on the same axis. This cusp tip is not as sharply pointed as the buccal cusp tip. The mesio-occlusal slope of the lingual cusp is shorter than the disto-occlusal slope. The developmental depressions, grooves, or pits are normally not found on the lingual surface. 2.1.3. Mesial aspect From the proximal aspects, all maxillary posterior teeth are present in trapezoidal geometric form. The buccal cusp is longer than the lingual cusp by 1 mm or occasionally more. Well- marked mesial and distal ridges are seen in both cusps. The mesial surface of the crown displays a concavity toward the cementoenamel junction. This concavity extends cervically on the mesial surface and joins a deep developmental depression of the root area.