Physiology of tooth eruption


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Physiology of tooth eruption

  1. 1. Physiologic Tooth Movement: Eruption and SheddingTOOTH ERUPTION The jaws of an infant can only accommodate a few small teeth. Since teeth, once formedcannot increase in size, the larger jaws of an adult require not only more but bigger teeth. Thisaccommodation is accomplished in humans by having two dentitions. The first is known as thedeciduous teeth (primary teeth), and the second is the permanent teeth (secondary teeth). The early development of teeth develops within the tissues of the jaw thus for teeth tobecome functional, considerable movement is required to bring them into the occlusal plane.The movements teeth make are complex and may be described as: 1. Preeruptive tooth movement. Made by deciduous and permanent tooth germs within tissues of the jaw before they begin to erupt 2. Eruptive tooth movement. Made by a tooth to move from its position within the bone of the jaw to its functional position in the occlusion 3. Posteruptive tooth movement. Maintaining the osition of the erupted tooth in occlusion while the jaw continues to grow and compensate for occlusal and proximal tooth wear.TOOTH MOVEMENT I. Preeruptive Tooth Movement When the deciduous tooth germs first differentiate, they are extremely small andthere is a good deal of space for them in the developing jaw. Because they grow rapidly,however, they become crowded together. The crowding Is gradually alleviated by a lengtheningof the jaws which permits the deciduous second molar tooth germs to move backward andanterior germs to move forward. At the same time the tooth germs are moving bodily outwardand upward with the increasing length as well as width and height of the jaws. The origin of the successional permanent teeth develops on the lingual aspect oftheir deciduoud predecessors, in the same bony crypt. From this position they shift considerablyas the jaws develop. The successional anterior teeth eventually come to occupy on the lingualof the roots of their deciduous teeth and the posterior premolar tooth gers are finally positionedbetween the divergent roots of the deciduous molars.
  2. 2. The permanent molar tooth germs without predecessors develop from the backwardextension of the dental lamina. At first there is a litter room in the jaws to accommodate thesetooth germs so that in the upper jaw the molar tooth germs develop first with their oclusalsurfaces facing distally and swinginto position only when the maxilla has grown sufficiently toprovide room for such movement. It is almost the same with the permanent molars in themandible but instead of a distal inclination, there is a mesial inclination prior to the developmentof the jaw. Analysis has shown that these preeruptive movement of teeth are a combination oftwo factors: total bodily movement and growth in which one part of the tooth germ remains fixedwhile the rest continues to grow. II. Eruptive Tooth Movement During the phase of eruptive tooth movement the tooth moves from its position withinthe bone of the jaw to its functional position in occlusion, and the principal direction ofmovement is occlusal or axial.The mechanisms of eruption for deciduous and permanent teethare similar, resulting in axial or occlusal movement of the tooth from its developmental positionwithin the jaw to its final functional position in the occlusal plane. A. Eruptive Phase (Prefunctional Phase) Begins when the root starts to form and ends when the tooth reaches the occlusalplane. The PDL develops only after root formation has been initiated; once established, the PDLmust be remodeled to accommodate continued eruptive tooth movement. Tooth germundergoes intraosseous stage and supraosseous stage.During the intraosseous stage, thetooth moves out of its bony crypt to pierce the gingival. During the supraosseous stage, thetooth moves into its final occlusal plane.
  3. 3. A specialized feature associated with the erupting permanent tooth is the presenceof a gubernacular canal. This canal occurs where the roof of the alveolar crypt of the permanenttooth is not complete. The canal enables the dental follicle of the tooth germ to communicatewith, and be attached to, the overlying oral mucosa. The gubernacular canal contains thegubernacular cord, composed of a central strand of epithelium derived from dental lamina. Asthe successional tooth erupts, its gubernacular canal is widened rapidly by local osteoclasticactivity, delineating the eruptive pathway for the tooth.
  4. 4. Reduced enamel epithelium unites with the oral epithelium. It will migrate occlusallyor incisally until surface is reached, preventing the gingiva to bleed during the crown eruption.The crown breaks the double layer epithelium overlying it and enters the oral cavity. The rate of eruption depends on the phase of movement.When the erupting toothappears in the oral cavity, it is subjected to environmental factors that help determine its finalposition in the dental arch. Muscle forces from the tongue, cheeks and lips play on the tooth, asdo the forces of contact of the erupting tooth with other erupted teeth. A sustained muscular
  5. 5. force of only 4 to 5 grams is sufficient to move a tooth. The childhood habit of thumb-sucking isan obvious example of environmental destruction of tooth position. B. Functional Phase - Begins when the tooth reaches the occlusal plane and continues its functions aslong as the tooth remains in the oral cavity. As the teeth meet their antagonists, the bone isstimulated and the periodontal ligament strengthens. There is a continuous vertical eruptionmesially and occlusally but the process may decrease because it is supposed by theirantagonist teeth. - Mechanisms of Tooth Movement Currently Favored These mechanisms are still debatable and are likely to be a combination of anumber of factors. Eruptive mechanisms are not understood fully yet, and most reviews on thissubject have concluded that eruption is a multifactorial process in which cause and effect aredifficult to separate. 1. Root Formation The root growth theory supposes that the proliferating root impinges on a fixedcase, thus converting an apically directed force of the tooth into occlusal movement. Rootformation should be an obvious cause of tooth eruption because it causes an overall increase inthe length of the tooth. But it produces enough forces that lead to the resorption of the bone.
  6. 6. Rootless tooth still erupts. Some teeth erupt more than the total length of the roots. And theteeth still erupt after the complete formation of the root. Therefore root formation isaccommodated during tooth eruption and is a consequence, not a cause, of the eruptionprocess. Hammock Ligament Theory According to Sicher, a band of fibrous tissue exists below the root apex spanningfrom one side of alveolar wall to another. This fibrous tissue appears to form a network belowthe developing root and is rich in fluid droplets. The developing root forces itself against thisband of tissue, which in turn applies an oclusally directed force on tooth. 2. Bone Remodeling Bone remodeling theory supposes that selective formation and resorption ofbone brings about eruption.The bone at the base of the socket cannot act as a fixed basebecause pressure on bone results in its resorption. 3. Periodontal Ligament The ligament traction theory supposes that cells and fibers of the ligament pushthe tooth into occlusion.PDL is rich in fibroblasts that contain contractile tissue. The contractionof these PDL fibers mainly the oblique group of fibers result in axial movement of the teeth. 4. Vascular Pressure The vascular pressure theory supposes that a local increase in tissue fluidpressure in the periapical region is sufficient to move the tooth.The tissue around the developingend of the root is highly vascular. This vascular pressure is believed to cause the axialmovement of the teeth.It is known that teeth move in synchrony with the arterial pulse, so localvolume changes can produce limited tooth movement. III. Post Eruptive phase Posteruptive tooth movements are those made by the tooth after it ahs reachedits functional position in the occlusal plane. It includes three categories: (1) movements toaccommodate the growing jaws, (2) those to compensate for continued occlusal wear, (3) thoseto accommodate interproximal wear.
  7. 7. 1. Accommodation of Growth Accommodating the growth of the jaws are completed toward the end of thesecond decade, when jaw growth ceases. Readjustment of the position of the tooth socket isachieved by the formation of new bone at the alveolar crest and on the socket floor to keeppace with the increasing height of the jaws. This readjustment usually occurs between the ages14 to 18 years, when active movement of the tooth takes place. The apices of the teeth move 2to 3 mm away from the inferior dental canal. This occurs earlier in girls than in boys and isrelated to the bust of the condylar growth that separates the jaws and the teeth. 2. Compensation for Occlusal Wear This is achieved by the continued cementum deposition around the apex of thetooth; however, the deposition of cementum in this location occurs only after the tooth hasmoved. This emphasizes the role of the periodontal ligament. Axial movement that a toothmakes in most likely achieved by the same mechanism as eruptive tooth movement. 3. Accomodation for Interproximal Wear Wear also occurs at the contact points between teeth, on their proximal surfacesand its extent can be considerable (more than 7 mm in the mandible). Mesial or approximaldrifting compensates for the interproximal wear. This is important in the practice of Orthodontics because the maintenance oftooth position after treatment depends on the extent of such drift. Mesial drift is multifactorialand include: (A) anterior component of occlusal force, (B) contraction of the transseptal ligamentbetween teeth and (C) soft tissue pressure. A. Anterior component of occlusal force When teeth are brought into contact, like during clenching of the jaws, andanteriorly directed force is generated.It is the result of the mesial inclination of most teeth andthe summation of intercuspal planes.When cusps are selectively ground, the direction ofocclusal force can be enhanced or reversed When opposing teeth were removed, thereby eliminating the biting force, themesial migration of the teeth was slowed but not halted.
  8. 8. B. Contraction of the Transseptal Ligament between Teeth The Peridontal ligament plays an important role in maintaining tooth position.Transseptial fibers draw neighboring teeth together and mainten them in contact; there are alsocapable of adaptation.For example, relapse of orthodontically removed teeth is reduced if agingivectomy removing the transseptal ligament is performed.*Grinding away of proximal contacts provides room for a tooth to move, after which teeth moveto reestablish contact. C. Soft Tissue Pressures The pressures generated by the cheeks and tongue may push teeth mesially.Softtissue pressure does influence tooth position even if it does not cause tooth movement. It doesnot play a major role in creating mesial drift.CAUSES OF TOOTH ERUPTION (THEORIES) 1. Growth of Root Root formation undoubtfully causes an overall increase in the length of the tooth thatmust be accommodated by the growth of the root into the bone of the jaw, by an increase in jawheight or by the occlusal movement of the crown. Root growth produces a force that issufficient to produce bone resorption. Pressure applied to bone normally result in the removalof osteoclasts. Though root formation can produce a force, it cannot translate into eruptivetooth movement unless some structure exists at the base of the tooth capable of withstandingthis force. Since this structure does not exist, some other mechanisms must move the tooth toaccommodate root growth. The Root Growth theory supposes the proliferating root impinges on a fixed case thusconverting an apically directed force into occlusal movement. Some facts proving this statementinclude the fact that rootless teeth erupt, that some teeth erupt a greater distance than the totallength of their roots and the teeth still will erupt after the completion of root formation or whenthe tissue forming the root are removed surgically. Root growth is not required but it may accelerate tooth eruption. Depending on the rte atwhich the root elongates, the basal bone will resorb or form to maintain a proper relationshipbetween the root and bone.
  9. 9. 2. Vascular Pressure Vascular Pressure and blood vessel thrust. It is known that the teeth move in theirsockets in synchrony with the arterial pulse, so local volume changes can produce limited toothmovement. Furthermore, spontaneous changes in blood pressure have been shown to influenceeruptive behavior. Ground substance can swell from 30% to 50% by retaining additional water,so this to could create pressure. But since surgical excision of the growing root and associatedtissues eliminates the periapical vasculature without stopping eruption, this means that the localvessels are not absolutely necessary for tooth eruption. The Vascular Pressure theory supposes that a local increase of in tissue fluid pressurein the periapical region is sufficient to move the tooth. 3. Bone Remodeling (Apposition and Resorption of bone) Bone Remodeling is important to permit tooth movmement. If the tooth germ is removedand the dental follicle left intact, an eruptive pathway forms in the overlying bone. If SiliconeReplica is substituted for the tooth germ, it also erupts. But, if the dental follicle is removed, noeruptive pathway will form. The follicle provides the source for new bone-forming cells and the conduit forosteoclasts derived from monocytes through the vascular supply. Control may reside with thebone-lining cells, the osteoblasts. These cells secrete collagenase and other proteolyticenzymes to remove the osteoid layer. In so doing these cells round up and expose the newlydenuded mineralized bone surface, providing the stimulus to attract osteoclasts to the site. 4. Periodontal Ligament Traction Periodontal Ligament Traction. Eruptive force resides in the dental follicle-periodontalligament complex. Formation and renewal of the PDL has been considered a factor in tootheruption because of the traction power that fibroblasts have and because of the experimentalresults using the continuously erupting rat incisor. Periodontal Ligament Traction. Eruptive force resides in the dental follicle-periodontalligament complex. Formation and renewal of the PDL has been considered a factor in tootheruption because of the traction power that fibroblasts have and because of the experimentalresults using the continuously erupting rat incisor.
  10. 10. 5. Control of Endocrine Glands 6. Pressure from muscular action 7. Effect of Nutrition 8. Inherent tendency of teeth to eruptSEQUENCE AND CHRONOLOGY OF TOOTH ERUPTION Humans have two sets of teeth in their lifetime. The first set of teeth to be seen in themouth is the primary or deciduous dentition which will remain intact until the child is about 6years of age. At about that time the first permanent or succedaneous teeth begin to emerge intothe mouth. The emergence of these teeth begins the transition or mixed dentition period inwhich there is a mixture of deciduous and succedaneous teeth present. The transition periodlasts from about 6 to 12 years of age and ends when all deciduous teeth have been shed. Atthat time, the permanent dentition period begins. Usually at birth, no teeth are visible in the mouth; however, occasionally, infants are bornwith erupted mandibular incisors. The development of both primary and permanent teethcontinues in this period and jaw growth follows for the needed additional space for posteriorteeth. Alveolar bone height also increases, accommodating the increasing length of the teeth. Primary teeth emerge in children between the ages of 6 moths and 2 years. They play arole in “reserving” space for the permanent teeth. At about 6 months of age, the mandibularcentral incisors emerge through the alveolar gingival followed by other anterior teeth. By about13 to 16 months, all the eight primary incisors have erupted. The first primary molars emerge byabout 16 months of age. By about 19 months the primary maxillary canines erupt while theprimary mandibular canines erupt at 20 months. The primary second mandibular molar erupts ata mean of age 27 months and primary maxillary second molar follows at a mean age of 29months. The primary dentition is considered to be completed by about 30 months when thesecond primary molars are in occlusion.
  11. 11. TABLE 1.1 Chronology of Primary Teeth FIRST EVIDENCE OF CROWN ROOT ERUPTION ERUPTIONDENTITION TOOTH CALCIFICATION COMPLETED COMPLETED (MONTHS) SEQUENCE (WEEKS IN (MONTHS) (YEARS) UTERO) Primary Central 14 1.5 7.5 3 1.5 (upper) incisor Lateral Incisor 16 2.5 9 4 2 Canine 17 9 18 8 3.25 First Molar 12.5 - 15.5 6 14 6 2.5 Second Molar 12.5 - 19 11 24 10 3 Primary Central 18 2.5 6 1 1.5 (lower) incisor Lateral Incisor 18 3 7 2 1.5 Canine 20 9 16 7 3.25 First Molar 12 - 15.5 5.5 12 5 2.25 Second Molar 12.5 - 18 10 20 9 3 The transition or mixed dentition period begins with the emergence and eruption of the mandibular first permanent molar and ends with the loss of the last primary tooth which usually occurs at 11 to 12 years of age. The initial phase of transition period lasts about 2 years, during which time the permanent first molars erupt, the primary incisors are shed, and the permanent incisors emerge and erupt into position. Permanent dentition consists of 32 teeth and is completed 18 to 25 years of age. At 6 years of age, the first molars emerge in the oral cavity followed by the central incisor at 6 to 8 years of age. Mandibular lateral incisor erupts at about 1 year later or soon after the central incisors. When the child is about 10 years old, the first premolars and the mandibular canines erupt. Second premolars follow during the next year then the maxillary canines. Usually second molars come in when the individual is 12 years of age. Third molars do not come until the age of 17 or later. Considerable posterior jaw growth is required after the age of 12 to allow room for these teeth.
  12. 12. TABLE 1.2 Chronology of Permanent Teeth FIRST EVIDENCE OF CROWN ROOT ERUPTION ERUPTIONDENTITION TOOTH CALCIFICATION COMPLETED COMPLETED (YEARS) SEQUENCE (WEEKS IN (MONTHS) (YEARS) UTERO)Permanent Central incisor 3-4 4-5 7-8 5 10 (upper) Lateral Incisor 10 - 12 4-5 8-9 6 11 Canine 4-5 6-7 11 - 12 8 13 - 15 First Premolar 1.5 - 1.75 5-6 10 - 11 9 12 - 13 Second 2 - 2.25 6-7 10 - 12 11 12 - 14 Premolar First Molar At birth 2.5 - 3 6-7 3 9 - 10 Second Molar 2.5 - 3 7 -8 12 - 13 13 14 - 16 Third Molar 7-9 12 - 16 17 - 21 16 18 - 25Permanent Central incisor 3-4 4-5 6-7 1 9 (lower) Lateral Incisor 3-4 4-5 7-8 4 10 Canine 4-5 6-7 9 - 10 7 12 - 14 First Premolar 1.75 - 2 5-6 10 - 12 10 12 - 13 Second 2.25 - 2.5 6-7 11 - 12 12 13 - 14 Premolar First Molar At birth 2.5 - 3 6-7 2 9 - 10 Second Molar 2.5 - 3 7-8 11 - 13 14 14 - 15 Third Molar 8 - 10 12 - 16 17 - 21 15 18 - 25 SHEDDING OR EXFOLIATION Shedding or Exfoliation is the physiologic process resulting in the elimination of the deciduous dentition. It is the result of the gradual resorption of their roots and the consequent loss of periodontal ligament attached. Resorptions and shedding occurs to enable eruption of permanent tooth (excluding the permanent molars To understand the process of shedding or exfoliation of deciduous teeth, we must first remember that we have two sets of dentition. Mammals are described as being diphydont, with two successive sets of teeth, first the "deciduous" set and later the "permanent" set. Our deciduous teeth, or our primary teeth consist of 20 teeth, and is later replaced by our 32 permanent teeth. The fewer deciduous teeth have importance by:  Help provide nutrition
  13. 13.  Help make speech possible  Aid in the normal development of the jaw bones and facial muscles  Add to an attractive appearance  Reserve space for the permanent teeth and help guide them into position Because the jaw is smaller in younger people, the 20 deciduous teeth accommodate thespace, but as the person grows, so does the jaw, allowing for the additional 12 teeth in thepermanent set. Teeth in the permanent dentition are also larger to accommodate the larger jaw. The replacement of the deciduous teeth with its permanent successor is known asshedding or exfoliation. Shedding is the physiological process that permanent teeth influenceresorption until elimination of deciduous teeth. Resorption of the tooth is the breakdown of hardtissue and its release of its minerals. This resorption is achieved by cells with a histologicnature similar to osteoclasts called odontoclasts. Odontoclasts derive from the monocyte andmigrate from blood vessels to the resorption site, where they fuse to form the characteristicmultinucleated odontoclast with a clear attachment zone and ruffled border. Less is known about the resorption of the soft tissues of the tooth as it sheds. Althoughactive root resorption is taking place, coronal pulp appears normal and odontoblasts still line thesurface of the predentin. When root resorption is almost complete, these odontoblastsdegenerate, and mononuclear cells emerge from the pulpal vessels and migrate to thepredentin surface, where they fuse with other mononuclear cells to form odontoclast actively
  14. 14. engaged in the removal of predentin and dentin. Just before exfoliation, the resorption processstops. Tooth then sheds with pulpal tissue intact. There are at least two ways of the resorption of cells or “cell death”. Through studiesand observations show that its abrupt and yet no inflammation occurs. The two forms are asfollows: 1. Fibroblast is a type of cell that synthesizes the extracellular matrix and collagen,the structural framework (stroma) for tissues. The main function of fibroblasts is to maintain thestructural integrity of connective tissues by continuously secreting precursors of the extracellularmatrix. Fibroblasts secrete the precursors of all the components of the extracellular matrix,primarily the ground substance and a variety of fibers. But the fibroblasts are interrupted andtheir normal cellular processes such as secreting the precursors and cytotoxic alterations thateventually lead to cell death. 2. Apoptosis, form of cell death in which a programmed sequence of events leadsto the elimination of cells without releasing harmful substances into the surrounding area.Apoptosis plays a crucial role in developing and maintaining health by eliminating old cells,unnecessary cells, and unhealthy cells. Ligament fibroblasts have the same features of apopticcell death. Apoptosis produces cell fragments called apoptotic bodies that phagocytic cells areable to engulf and quickly remove.
  15. 15. With further reading, pressure can also play a factor in exfoliation. Reason maybe because if a successional tooth is missing, the normal time period for exfoliation is delayed.Some say that the force applied to a deciduous tooth can initiate resorption. Pressure from anerupting permanent tooth results in some root loss, which in turn means a loss of supportingtissue structures. So if the structures are lost, then its inevitable that the process of shedding isaccelerated.Mechanism Of Shedding A. Resorption Period In the case of Bone resorption, it is thought that the osteoblast must must first degradethe osteoid, exposing the mineralized bone to which osteoclast can attach. Osteoblast may alsoresorbs the dentin .Hard tissues resorption occurs in two phases: the extracellular during whichthe matrix fragments and dissolution begins and intracellular during which complete digestion ofthe products of resorption occurs . Resorption of intraradicular dentin takes place in someresorption of the pulp chamber, coronal dentin and sometimes enamel. Resorption of theperiodontal ligament involves apoptopic cell. This form of cell death involves shrinkage of thecells so that they can be phagocytosed be neighboring cells. Apoptotic cell death isprogrammed so that cells die at a specific tmes to permit orderly development . Occurrence ofthe apoptotic cell death together with periodontal ligament resorption and with the observationthat in monozygotic twins the eruption pattern is largely (80%) determined by genetic factorsuggest that shedding is a programmed developmental event influenced by local factors Whatever the preliminary steps in hard tissue resorption , it is clear that the odontoclastattaches to the hard tissue surface peripherally through the clear zone creating a sealed space
  16. 16. is created lined with ruffled border of the cell, that acts like a proton pump adding hydrogen ionsto the extracellular environment and acidifying it so that dissolution occurs and primarylysozymes are secreted to degrade the organic matrix . Factors that may Initiate or affect tooth resorption : 1. Pressure Pressure from erupting permanent tooth may cause some root loss that willdecrease tooth support therefoe the tooth is less able to withstand the increasing masticatoryforces thereby the process of exfoliation is accelerated. As resoption of the roots initiated bypressure of the underlying tooth occurs , there is a progressive loss of surface area forattachment of the periodontal ligament fiber bundles. This weakening of the tooth supportoccurs because it has to withstand increasingly greater occlusal forces generated by thegrowing muscles of mastication Mesial Drift is the lateral bodily movement of the teeth on both sides of the mouthtoward the midline of the arch.One condition that leads to mesial drift is when the teeth is infunction producing a rubbing of cotact areas making the transseptal fibers of the periodontalligament to maintain a tooth contact. Pressure on the periodontal ligament fibers results inresorption of bone , whereas pull on fibers results in bone apposition(formation) .As the contactareas of the crowns wear, the teeth tend to move mesially to maintain contact . The slightpressure on the mesial side of the socket results in the slow resorption of the lamina dura whilethe accompanying tension on the distal side induces appositional lamina dura bone in this area. 2. When Succesional tooth germ is missing It will delayed the shedding of deciduous teeth 3. Forces of masticatory applied to deciduous teeth As an individual grows the mastication increases in size and exert effort on toothmore than the periodontal ligament can stand that leads to trauma to the ligament and theinitiation of resoption. B. Rest Period and Repair Period Resorption of deciduous teeth is not continuous process, During rest periods, reparativetissue may be formed , leading to reattachment of the periodontal ligament. The areas of early
  17. 17. resorption are repaired by the deposition of the cementum like tissue which lay down acollagenous ns showing small foci of mineralization which helps in repair As the tooth continue to resorbs, the tooth loosens. Eventually, all the periodontalligament attachment is lost and the rootless crown of the primary tooth literally falls off the jaw If the repair process prevail over the resoption , the tooth may become anykylose to thesurrounding bone, with the loss of the periodontal ligament. Resorption occurs on the lingual aspect of the deciduous canine , and the tooth often shed with much of its lingual root intactPattern of Shedding Pressure generated by the growing and erupting permanent tooth dictates the pattern ofdeciduous tooth resorption. Because of the developmental position of the permanent incisorsand canine tooth germs their subsequent movement in an occlusal and vestibular direction ,resorption of the incisors and canines begins on their lingual surfaces and later occupy directlyapical to the primary tooth .In mandibular incisors the apical positioning of the tooth germ doesnot occur and permanent tooth erupt lingually
  18. 18. For deciduous molar, root resorption commences on the inner surfaces where thepermanent premolars initially develop . Premolars later lie beneath the roots of the deciduousmolars. However, as a result of continuous growth of the jaws and occlusal movement of thedeciduous molars, the successional tooth germs come to lie apical to the deciduous teeth. Thischange in position provides the growing bi-cuspids with adequate space for their continueddevelopment. Sequence of Shedding in the mandible follows an anterior to posterior order of the in thejaw while for the maxilla the first molar exfoliate before the canine disrupts this sequence.
  19. 19. CLINICAL CONSIDERATIONS 1. Enamel hypoplasia is caused by the disturbance in the development of the enamelduring matrix formation. This results to deficiency in the quantity of enamel. The matrix formedis defective but calcification is normal The enamel is irregular, often pitted or thin fissures orgrooves but otherwise it has normal hardness and translucency. 2. Eruption of tooth is frequently accompanied by pain and fever. This is due to traumainitiating an inflammatory response. Adding up to the inflammation is the attack of microbialinfections. 3. Retained deciduous teeth are usually caused by failure of the succedaneous tooth toform or the corresponding succedaneous tooth is impacted. Retained deciduous teeth are mostoften are the upper lateral incisor, less frequently to the second permanent premolar. If thepermanent tooth is ankylosed or impacted, its deciduous predecessor may also be retained.This is most frequently seen with the deciduous and permanent canine teeth.
  20. 20. 4. Premature loss of primary teeth can cause early eruption of its permanent successor.It can also cause a loss of arch length with a consequent tendency for crowding of thepermanent dentition. Increase chances for the adjacent teeth to mesial migrate resulting toblockage of the path of eruption of the succedaneous tooth. 5. Delayed eruption of teeth are common and may be caused by congenital, systemic,or local factors Congenital absence most commonly occurs with the permanent third molars. Systemic factors may be caused by endocrine deficiencies, nutritional deficiencies, systemic lesion, and some genetic factors. Local factors: early loss of deciduous teeth, with consequent drifting of the adjacent teeth to block the eruptive pathway, eruption cysts
  21. 21. 6. Remnants of deciduous teeth consist of dentin and cementum. They may remainembedded in the jaw for a considerable amount of time. This are most frequently foundassociated with lower second premolars. Root remnants are also may be found deep in thebone, completely surrounded by and ankylosed to the bone. 7. Submerged deciduous teeth are due to trauma resulting to the damage of eitherthe dental follicle or the developing periodontal ligament. If this happens, the eruption of thetooth ceases, and it becomes ankylosed to the bone of the jaw. Due to the continued eruption ofthe adjacent teeth and increased in height of the alveolar bone, the ankylosed tooth may beshortened or submerged in the alveolar bone it prevents eruption of their permanent successorsdue to crowding or tipping of the adjacent teeth onto the space created by missing tooth.
  22. 22. SOURCESBerkovitz, Bary K: Master Dentistry: Oral Biology . Elsevier Ltd.2011 p 113-121Melfi, Rudy C: Permar’s Oral Embroyology and Microscopic Anatomy. Lippincott Williams & Wilkins .2000 p 265-279Ten Cate A. R: Oral Histology –Development , Structure, and Function , 6th Edition , Mosby. 2008Bhaskar , S.N : Orban’s Oral Histology and Embryology , 11 edition , Mosby Inc. 1991Osborn, J.W : Advance Dental Histology p 135-140