of premolars. the labial ridge is one that runs cervico-incisally in approximately the center of the labial surface of canines. the lingual ridge extends from the cingulum to the cusp tip on the lingual surface of most canines. the cervical ridge runs mesiodistally on the cervical third of the buccal surface of the crown. these are found on all primary teeth but only on the permanent molars. cusp ridges are ridges that radiate from cusp tips. there are two marginal ridges, mesial and distal, present on all teeth. on anterior teeth, they are located on the mesial and distal borders of the lingual surface; on posterior teeth, they are located on the mesial and distal borders of the occlusal surface. triangular ridges are those that project from the cusp tips of premolar and molars to the central groove. transverse ridges are formed by the union of two triangular ridges on posterior teeth. the joining of buccal and lingual triangular ridges is usually named as an example. the oblique ridge is found on the occlusal surfaces of maxillary molars. it is formed by the union of the distal cusp ridge of the mesiolingual cusp and the triangular ridge of the distobuccal cusp. the oblique ridges usually forms the distal boundary of the central fossa. developmental groove the teeth demonstrating the fewest developmental grooves are the mandibular central and lateral incisors. however, the canines show the most prominent developmental grooves, because they have robust anchorage to the bone. embrasures embrasures are triangularly shaped spaces located between the proximal surfaces of adjacent teeth. the borders of embrasures are formed by the interdental papilla of the gingiva, the adjacent teeth, and the contact point where the two teeth meet. there are four embrasures for every contact area: facial (also called labial or buccal), lingual (or palatal), occlusal or incisal, and cervical or interproximal space. the cervical embrasure usually is filled by the interdental papilla from the gingiva; in the absence of adequate gingival tissue a black angle, or angularis nigra is visible. embrasures have three functions. they form spillways between teeth to direct food away from the gingiva. also, they provide a mechanism for teeth to be more self cleansing. lastly, they protect the gingiva from undue frictional trauma but also providing the proper degree of stimulation to the tissues. mammelons mammelons are usually found as three small bumps on the incisal edges of anterior teeth. they are the remnants of three lobes of formation of these teeth, the fourth lobe represented by the cingulum. since this surface of the tooth is the first to wear away from attrition, mamelons may not be visible on teeth of older people. instead, the best chance to see this characteristic is soon after eruption of the tooth into the mouth. note, the presence of mamelons in adults is an indication of malocclusion. distinguishing characteristics of teeth incisor eight incisors are anterior teeth, four in the upper arch and four in the lower. their function is for shearing or cutting food during chewing. there are no cusps on the teeth. instead, the surface area of the tooth used in eating is called the incisal ridge or incisal edge. though similar, there are some minor differences between the primary and permanent incisors. maxillary central incisor a permanent maxillary central incisor main article: maxillary central incisor the maxillary central incisors are usually the most visible teeth, since they are the top center two teeth in the front of a mouth, and they are located mesial to the maxillary lateral incisor. the overall length of the deciduous maxillary central incisor is 16 mm on average, with the crown being 6 mm and the root being 10 mm. in comparison to the permanent maxillary central incisor, the ratio of the root length to the crown length is greater in the deciduous tooth. the diameter of the crown mesiodistally is greater than the length cervicoincisally, which makes the tooth appear wider rather than taller from a labial viewpoint. the permanent maxillary central incisor is the widest tooth mesiodistally in comparison to any other anterior tooth. it is larger than the neighboring lateral incisor and is usually not as convex on its labial surface. as a result, the central incisor appears to be more rectangular or square in shape. the mesial incisal angle is sharper than the distal incisal angle. when this tooth is newly erupted into the mouth, the incisal edges have three rounded features called mamelons. mammelons disappear with time as the enamel wears away by friction. maxillary lateral incisor main article: maxillary lateral incisor the maxillary lateral incisor is the tooth located distally from both maxillary central incisors of the mouth and mesially from both maxillary canines. mandibular central incisor main article: mandibular central incisor the mandibular central incisor is the tooth located on the jaw, adjacent to the midline of the face. it is mesial from both mandibular lateral incisors. mandibular lateral incisor main article: mandibular lateral incisor the mandibular lateral incisor is the tooth located distally from both mandibular central incisors of the mouth and mesially from both mandibular canines. canine (cuspid) both the maxillary and mandibular canines are called the "cornerstone" of the mouth because they are all located three teeth away from the midline, and separate the premolars from the incisors. the location of the canines reflect their dual function as they complement both the premolars and incisors during chewing. nonetheless, the most common action of the canines is tearing of food. there is a single cusp on canines, and they resemble the prehensile teeth found in carnivorous animals. though similar, there are some minor differences. maxillary canine main article: maxillary canine the maxillary canine is the tooth located laterally from both maxillary lateral incisors of the mouth but mesially from both maxillary first premolars. it is the longest tooth in total length, from root to the incisal edge, in the mouth. mandibular canine main article: mandibular canine the mandibular canine is the tooth located distally from both mandibular lateral incisors of the mouth but mesially from both mandibular first premolars. premolar (bicuspid) premolars are found distal to canines and mesial to molars. they are divided into first and second premolars. the functions of premolars vary. there are no deciduous premolars. instead, the teeth that precede the permanent premolars are the deciduous molars. maxillary first premolar main article: maxillary first premolar the maxillary first premolar is the tooth located laterally from both the maxillary canines of the mouth but mesially from both maxillary second premolars. the function of this premolar is similar to that of canines in regard to tearing being the principal action during chewing. there are two cusps on maxillary first premolars, and the buccal cusp is sharp enough to resemble the prehensile teeth found in carnivorous animals. there is a distinctive concavity on the cervical third of the crown extending onto the root. the maxillary 1st premolar is also bifurcated with two roots. maxillary second premolar main article: maxillary second premolar the maxillary second premolar is the tooth located laterally from both the maxillary first premolars of the mouth but mesially from both maxillary first molars. the function of this premolar is similar to that of first molars in regard to grinding being the principal action during chewing. there are two cusps on maxillary second premolars, but both of them are less sharp than those of the maxillary first premolars. mandibular first premolar main article: mandibular first premolar the mandibular first premolar is the tooth located laterally from both the mandibular canines of the mouth but mesially from both mandibular second premolars. the function of this premolar is similar to that of canines in regard to tearing being the principal action during mastication. mandibular first premolars have two cusps. the one large and sharp is located on the buccal side of the tooth. since the lingual cusp is small and nonfunctional, which means it is not active in chewing, the mandibular first premolar resembles a small canine. mandibular second premolar main article: mandibular second premolar the mandibular second premolar is the tooth located distally from both the mandibular first premolars of the mouth but mesially from both mandibular first molars. the function of this premolar is to assist the mandibular first molar during mastication. mandibular second premolars have three cusps. there is one large cusp on the buccal side of the tooth. the lingual cusps are well developed and functional, which means the cusps assist during chewing. therefore, whereas the mandibular first premolar resembles a small canine, the mandibular second premolar is more like the first molar. molar molars are the most posterior teeth in the mouth. their function is to grind food during chewing. the number of cusps, and thus the overall appearance, vary among the different molars and between people. there are great differences between the deciduous molars and those of the permanent molars, even though their functions are similar. permanent maxillary molars are not considered to have any teeth that precede them. despite being named "molars", the deciduous molars are followed by permanent premolars. the third molars are commonly called "wisdom teeth." maxillary first molar main article: maxillary first molar the maxillary first molar is the tooth located laterally from both the maxillary second premolars of the mouth but mesially from both maxillary second molars. there are usually four cusps on maxillary molars, two on the buccal and two palatal. most times there is also a fifth cusp, called the cusp of carabelli, located on the mesiolingual aspect of the tooth. maxillary second molar main article: maxillary second molar the maxillary second molar is the tooth located laterally from both the maxillary first molars of the mouth but mesially from both maxillary third molars. this is true only in permanent teeth. in deciduous teeth, the maxillary second molar is the last tooth in the mouth and does not have a third molar behind it. the deciduous maxillary second molar is also the most likely of the deciduous teeth to have an oblique ridge. there are usually four cusps on maxillary molars, two buccal and two palatal. maxillary third molar main article: maxillary third molar the maxillary third molar is the tooth located laterally from both the maxillary second molars of the mouth with no tooth posterior to it in permanent teeth. in deciduous teeth, there is no maxillary third molar. there are usually four cusps on maxillary molars, two buccal and two palatal. nonetheless, for this tooth, there are great variances among third molars, and a specific description of a third molar will not hold true in all cases. mandibular first molar main article: mandibular first molar the mandibular first molar is the tooth located distally from both the mandibular second premolars of the mouth but mesially from both mandibular second molars. it is located on the mandibular arch of the mouth, and generally opposes the maxillary first molars and the maxillary 2nd premolar. this arrangement is known as class i occlusion. there are usually five well-developed cusps on mandibular first molars: two on the buccal, two lingual, and one distal. mandibular second molar main article: mandibular second molar the mandibular second molar is the tooth located distally from both the mandibular first molars of the mouth but mesially from both mandibular third molars. this is true only in permanent teeth. in deciduous teeth, the mandibular second molar is the last tooth in the mouth and does not have a third molar behind it. though there is more variation between individuals to that of the first mandibular molar, there are usually four cusps on mandibular second molars: two buccal and two lingual. mandibular third molar main article: mandibular third molar the mandibular third molar is the tooth located distally from both the mandibular second molars of the mouth with no tooth posterior to it in permanent teeth. in deciduous teeth, there is no mandibular third molar. for this tooth, there are great variances among third molars, and a specific of a third molar will not hold true in all cases.