Development of the Teeth

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A. Introduction:

1. The development of the dental structures is intimately related to the dentist's ability to properly predicate a thorough treatment plan for many patients. It is thus with total patient treatment that this overview of development is concerned.

2. Previously, when content has overlapped that of another course, present or future, the authors have elected to profile only the main points. So it is with this section on development; the salient features have been highlighted, with no effort made to reproduce the detail which the student should receive in histology, or related studies.

3. It should be pointed out that any development dates or patterns of eruption, when described as "normal" are only "average", or "most common". In reality, there is considerable variation in their range. As with other body growth patterns, if an individual is early or late in one phase of development, it is likely that other developmental phases will follow the same pattern.

B. Development of the Dental Organ:

As early as the second month of fetal life, the development of the deciduous teeth may first become evident. The transition from the earliest beginnings of the dental organ through its completion will be outlined in morphologic terms.

1. Dental lamina and Bud stage - At about six weeks of prenatal life, an epithelial thickening occurs in the region where the teeth will form. This thickening is termed the dental lamina. Shortly after the dental lamina differentiates, twenty tooth buds begin to appear on the dental lamina in the approximate location of the twenty primary teeth. The individual tooth buds are somewhat round, or ovoid, and this stage is appropriately known as the bud stage.

2. Cap stage - As further development takes place, the generally round form of the bud is altered. The basal portion invaginates, and the structure thus formed gives the appearance of a cap, and hence this phase is termed the cap stage.

3. Bell stage - As the concavity in the basal area of the cap continues to deepen, development of the tooth enters the bell stage. As this stage nears completion, the form of the tooth's crown can be recognized, and the dentinoenamel junction is identifiable. During this time, most of the crown's dentin and enamel is laid down. During the latter portion of the bell stage, the dental lamina connection with the deciduous tooth begins to break down, and eventually disintegrates. As this portion of the dental lamina disappears, the bud of the succeda-neous tooth is forming from it. D.,. .

Dental Lamina

CAP STAGE

.Oral Epithelium

Dental Lamina

BUD STAGE

BUD STAGE

CAP STAGE

BELL STAGE

4. Root development - When enamel and dentin deposition have formed the area of the cementoenamel junction, the bell stage is regarded as ending, and the root development stage begins. The enamel organ then proliferates a structure known as Hertwig's sheath, from which the root structure is formed. The dentin and cementum of the root are then deposited.

Odontoblasts Dentin

Ameloblasts Enamel

Odontoblasts Dentin

Ameloblasts Enamel c.

Enamel

Enamel

APPOSITION & CALCIFICATION

5. Chronology - The chronology of initiation of the tooth buds from the dental lamina occurs in three phases, over a total time period of about 5 1/2 years.

a. Deciduous dentition - As previously indicated, development of all deciduous teeth is initiated during the first few months of fetal life.

b. Succedaneous teeth - All the permanent successors to the deciduous teeth begin to form in a time range between five fetal months for the central incisors, to about 10 months after birth for the second premolars.

c. Non-succedaneous permanent teeth - The initiation of the permanent molars occurs in a time period between four fetal months for the first molars to approximately five years for the third molars.

Eruption:

1. Prior to the complete calcification of its root, the tooth normally originates eruption by pushing through the mucous membrane cover of the alveolar process, and into the oral cavity. The eruption process is considered complete when the tooth contacts its opponent(s) in the opposite jaw member. In reality, the term eruption involves two entities:

Dentin a. Active eruption - Active eruption is the process just described, from the ERUPTION tooth's entry into the oral cavity, to its contact with an antagonist in the opposing arch.

b. Passive eruption - Passive eruption is the continuing process of adaptation of the tooth to changing incisai and occlusal relationships, after active eruption has ended. This adjustment to attritional wear and changing locations of adjacent and opposing teeth, continues throughout the life of the tooth. In fact, many times when a tooth has been lost, the antagonist(s) will supraerupt into the space, and beyond the normal occlusal plane.

2. When the tooth erupts, a keratinous, membrane-like enamel cuticle envelopes the anatomical crown. This structure, also known as Nasmvth's membrane. is soon abraded away over most of its extent.

3. Deciduous eruption pattern - The first deciduous teeth to emerge are the mandibular central incisors at about six months after birth. They are followed shortly thereafter by the mandibular lateral and maxillary central incisors. It is interesting to note that one in every several thousand infants enters the world

. with a tooth, or teeth, most often poorly developed mandibular incisors. At approximately two years of age, the average child erupts the deciduous maxillary second molars, and thus has the function of all the deciduous teeth. This is an appropriate time to review the eruption pattern for the deciduous dentition which is presented in the first unit. D. Root completion:

As described previously, the root apex is funnel shaped shortly after eruption. Root formation is thus not complete until additional dentin deposition reduces the funnel shaped opening to a constricted foramen. At age 3, root formation has ended for all deciduous teeth. The time lag between eruption and root completion for the deciduous teeth is thus about one year, and the development tables reveal the time differential for permanent teetl

E. Position of Developing Permanent Teeth:

All the while that the child is in the deciduous dentition stage, the permanent teeth are beginning, and continuing, their growth process. At this time, the development charts for permanent teeth should be reviewed to verify the beginnings of calcification and enamel completion dates. Remember that the time when the tooth bud first differentiates from the dental lamina is always prior to the initiation of calcification. Normally the succedaneous tooth buds exhibit a consistent relationship to the roots of the deciduous teeth they are to replace. The permanent incisor and canine buds are found in a position just lingual to the roots of their deciduous predecessors, while the premolar buds are located in the root furcation of the deciduous molars. The permanent molars are not succedaneous teeth, and their buds develop from the dental lamina in the alveolar process distal to the deciduous dentition.

F. Late Deciduous Stage and Role of the Permanent First Molars:

1. By approximately five years of age, growth of the mandible and maxilla has created more space for the permanent teeth which are soon to erupt. This extra space often results in the creation of diastemas, or spaces between adjacent teeth, usually in the anterior segment of the arches. Another suggested cause for the diastemas at this stage of development is the pressure exerted from the lingual by the developing permanent anterior teeth. The greater space in the arches also allows room for the entry of the first molars distal to the deciduous dentition.

2. The mandibular first molar is normally the first permanent tooth to emerge, at about age six, thus ending the deciduous dentition stage, and initiating the mixed dentition stage. The maxillary first molars follow shortly thereafter, and the four first molars are considered to be the cornerstones in the development of occlusion of the permanent dentition. Because they erupt first, and because of their strategic location in the arches, the relationship of the maxillary and mandibular first molars to each other has a significant influence on the occlusion of the permanent dentition. In addition, they serve as a guide for the eruption of the other permanent teeth, particularly the other molars. If any of the deciduous teeth are lost prematurely, the permanent first molar in that quadrant has a tendency to tilt or "drift" mesially, thus reducing the space available for the permanent canines and premolars. This condition changes the first molar's relationship with its antagonist(s), and may result in impaction of permanent teeth, or crowding and malocclusion of the permanent dental mechanism.

ROOT COMPLETED

G. Resorption and Exfoliation:

1. Resorption:

a. Shortly after the permanent first molars appear, the permanent mandibular central incisors are scheduled to erupt. However, before this can occur, the deciduous predecessors must be shed, or exfoliated. The process by which the root of the deciduous tooth is "melted away" is termed resorption.

b. Generally, resorption begins at the apex and moves toward the cervical line. Current thought ascribes the reason for the initiation and progression of resorption to be pressure from the permanent tooth crown against the deciduous root. The actual process is due to osteoclastic activity.

c. The resorption phase normally begins at least a year prior to exfoliation. Thus, the period between the completion of the root for the second deciduous molars (about 3 years of age), and the initiation of resorption for some deciduous incisors (before age 5), is less than two years.

2. Exfoliation - When the root structure of the deciduous tooth is almost entirely resorbed, the remaining crown becomes so loosened that it is lost. This phenomenon is known as exfoliation. Exfoliation usually occurs symmetrically, with the same teeth of the right and left sides being lost at about the same time. Mandibular teeth generally precede the same maxillary teeth in exfoliation, with the exception of the second molars, where all four are lost simultaneously. The same series of events occurs for all the deciduous teeth over a range of approximately six years, when the mixed dentition period ends with the exfoliation of the deciduous second molars at about age 12.

3. Incomplete resorption - Occasionally, root resorption is only partial, and the deciduous tooth does not exfoliate. In this situation, the permanent tooth must erupt in an abnormal position, or be entirely blocked from entry. If this aberrant feature is present, it is the responsibility of the practitioner to diagnose it, and perform the customary treatment, which is extraction of the offending deciduous tooth.

4. Ankylosis - Occasionally, the root structure of the deciduous tooth becomes "fused" to the surrounding alveolar bone. When this happens, any further eruption ceases, the tooth becomes "fixed" in position, and resorption cannot progress naturally. This condition is termed ankylosis, and occurs most often with the deciduous molars. The presence of an ankylosed tooth precludes the proper eruption of the succedaneous tooth, and so the ankylosed tooth must be surgically removed as soon as it is diagnosed.

H. Permanent Eruption Pattern:

The normal eruption pattern for the permanent teeth is found in Unit # 1, and will not be reproduced here. Furthermore, the normal dates of the various stages of permanent tooth development have been previously presented in the individual tooth units, and likewise will not be duplicated here. Please review these sequences and dates.

II. Anomalies:

A. Introduction:

1. With the normal features of the teeth and their development as background, this final section is devoted to the etiology and description of some of the most common abnormalities of teeth, and tooth form. The term, anomaly, implies abnormality, as opposed to the normal range in variation of form. Even though it may be only an academic question, it is sometimes difficult to differentiate between anomalies and extreme variations in morphology.

2. In many cases, it is difficult to intelligently discuss dental anomalies without pinpointing the stage of tooth development when the abnormality was manifest. In order to more accurately discuss the stages of development, a somewhat different classifying scheme, based on physiologic processes, as compared to morphologic stages, is briefly presented. These stages show a considerable overlap in time.

a. Initiation - The initiation process includes the dental lamina and bud stages, and affects the presence or absence of tooth buds.

b. Proliferation - Proliferation occurs during the bud, cap, and bell stages, and influences the general size and proportions of the tooth.

c. Histodifferentiation - This process takes place from the advanced cap stage through the bell stage, and essentially involves the formation of potential enamel and dentin forming cells.

d. Morphodifferentiation - The shape and size of the tooth is determined during this process, which takes place during the bud, cap, and bell stages. Thus, a disturbance during morphodifferentiation may influence the size and shape of a tooth, but have no effect on the enamel and dentin forming process.

e. Apposition - This process is active during the bell stage through the completion of the root, and involves the regular laying down of the enamel and dentin.

3. The general etiology of most dental anomalies can be ascribed to hereditary and congenital factors, or to developmental and metabolic disturbances. The stage of development, along with the length of the effect, are important factors influencing the final form of the anomaly, as well as which teeth are affected.

4. The permanent dentition is much more prone to abnormality than the deciduous teeth, and this may be partially explained by the position of the permanent tooth buds on the dental lamina, when compared to the primary tooth buds.

5. It is important to recognize that all anomalies are somewhat rare occurrences. Thus, it is often difficult to describe their frequencies, and they are usually compared in relative terms. None of the anomalies is present very often, but some are relatively more common than others.

B. Abnormal numbers of teeth:

1. Introduction:

The presence of an abnormal number of teeth, either more or less than usual, is almost always the result of some type of disturbance during the initiation process (dental lamina and bud stage) of tooth development. The disturbance is most often hereditary in nature.

2. Anodontia - Although this term literally signifies a "complete lack of teeth", its meaning has come to include any missing teeth, even if but one. Maybe a preferable term is hvpodontia. which denotes agenesis of one or more teeth. Teeth which are impacted are not considered to be missing.

a. Total anodontia - This label implies a complete absence of teeth, but since that condition is extremely rare, with only a handful of reported cases, it has come to mean a large number of missing teeth. The etiology of total anodontia involves a sex-linked genetic trait which results in an ectodermal defect, and so structures such as hair, and sebaceous and sweat glands, are also abnormal. Except in the very rare cases mentioned, most or all of the primary teeth are present, while a lesser number of permanent teeth are found.

b. Partial anodontia - Generally speaking, partial anodontia involves but one, or a few, missing teeth, and is the result of hereditary factors which preclude the initiation of the tooth buds of affected teeth. It has been suggested that the dental lamina may fall below a certain threshold size for the forming of an individual tooth. The actual frequency has been shown to vary among population groups, but it can be generally stated that somewhere in the neighborhood of 5% of individuals exhibit one or more missing teeth. In order of greatest occurrence, the most commonly missing permanent teeth are the maxillary and mandibular third molars, the maxillary lateral incisor, and the mandibular second premolar. From an evolutionary standpoint, there is a trend toward less human teeth, and these most often missing teeth are considered by many to be vestigial in nature, while the least often missing teeth, the canines, are considered the most stable. Anodontia is quite rare in the deciduous dentition, but when present, almost always involves the mandibular central incisor.

PARTIAL ANODONTIA (MISSING MAXILLARY LATERAL INCISORS)

3. Supernumerary (accesssorv) teeth:

a. The term, supernumerary, indicates an excessive number of teeth which are normal in morphological respects. However, since these "extra" teeth often do not resemble any normal tooth in size or shape, many authorities prefer to use the term "accessory" rather than supernumerary. The two terms will be used interchangeably here.

SUPERNUMERARY TOOTH (PREMOLAR SHAPED)

b. Accessory teeth usually result when extra tooth buds differentiate from the dental lamina, and thus the etiology is considered to be genetic. Both deciduous and permanent dentitions may exhibit supernumerary teeth.

c. Accessory teeth have been found in various positions in the dental arches, but the vast majority of the permanent dentition specimens are found in either of two locations: between the maxillary central incisors (called mesiodens"). or in the third molar regions (distodens). The only other area of significant involvement is, as might be expected, the mandibular second premolar area. However, many of the accessory teeth found in other areas resemble premolars. With the similar etiology, it is not surprising that the areas commonly involved in supernumerary teeth are also the most frequent sites of partial anodontia. The frequency of supernumerary teeth is less than that of anodontia, and one study identified the condition in 1-2% of the general population.

C. Abnormal Size of Teeth:

1. Introduction:

Normally, an individual's teeth vary in size directly with their general face and body size. Therefore, large, or small teeth, when found in this context, are not considered to be abnormal. Furthermore, it is very rare for all of a person's teeth to be abnormal in size, since this anomaly is usually limited to a single tooth, or a few teeth of the same type. This condition is thought to be the result of a disturbance during morphodifferentiation in the bell stage, with a genetic etiology.

2. Macrodontia (Gigantism):

a. True macrodontia - In the rare case of pituitary gigantism, all the teeth are abnormally large.

b. False macrodontia - More commonly, individual teeth are excessive in size, and those most frequently involved are incisors, canines, and mandibular third molars.

MICRODONTIA

and \ MACRODONTIA \J/

NORMAL SIZE

Microdontia (Dwarfism)

a. True microdontia - Pituitary dwarfs may exhibit true microdontia, when all the teeth are abnormally small.

b. False microdontia - It is much more common to find microdontia in individual teeth, and those most frequently involved are the maxillary lateral incisors (peg lateral), and the maxillary third molars.

D. Abnormal Shape of Teeth:

1. Introduction:

The presence of abnormal crown and root shapes and contours is most often the result of disturbances during the morphodifferentiation and appositional stages of tooth development.

2. Taurodontism - This condition of premolars and molars of both dentitions is characterized by a crown which occupies a much greater proportion of the total tooth bulk than is normal. The CEJ shows no constriction, the furcation is found in the apical half of the tooth, and the floor of the pulp chamber is likewise displaced apically. Since the size of the tooth itself is normal, the increased extent of the crown and pulp chamber occur at the expense of the root and pulp canals. The condition may be unilateral or bilateral. Taurodontism is usually diagnosed by x-ray, and is clinically significant only if root canal therapy is necessary. The etiology is hereditary, often in conjunction with other syndromes.

3. Dilaceration - This abnormality reveals a distortion of the root and crown from their normally linear relationship. The cause is most often a traumatic injury, or pressure, to the area of a developing tooth, resulting in a displacement of the already formed portion of the tooth.

4. Flexion - As contrasted to dilaceration, flexion involves a distortion of the root portion only. The etiology is normally the same for both, but occurs later in the development cycle in flexion. Many teeth exhibit curvatures and deflections of their roots, but they are not considered abnormal unless the bends are sharp.

5. Gemination - Gemination is thought to be caused by the incomplete splitting of a single tooth germ. The result is a tooth which is wide mesiodistally, and which has an incisal notch if it is an anterior tooth. It normally has a single root with a common pulp cavity. The two components of the gemination may be nearly equal in size, or one portion may be rudimentary in both size and shape, when compared to the other portion. The geminated tooth is most often an incisor. The term twinning is used to identify a situation where gemination has been complete, resulting in two identical teeth, and thus an additional tooth in the dentition.

6. Fusion - This anomaly is considered to be the result of a union of two adjacent tooth buds. The exact etiology is not known, but is thought to be either hereditary or from pressure exerted when two tooth buds are in very close proximity. The two portions are always united through the enamel and dentin, and occasionally even the pulp. The fusion usually concerns only the crowns, but on occasion involves both crown and root, in which case the cementum of the two portions is also united. Fusion is also usually found in anterior teeth. Unlike

GEMINATION

gemination, there are normally two identifiable pulp cavities. It is further differentiated from gemination by an apparently greater degree of separation of the two portions. And, unlike gemination there is one less dental unit than normal in the dentition, if the fused tooth is counted as one unit. Fusion is more often found in the deciduous teeth, and may be unilateral or bilateral. Because they are sometimes difficult to differentiate clinically, the term "double tooth" has been suggested to include all geminations, twinnings, and fusions.

7. Concrescence - This entity involves the union of the root structure of two or more teeth through cementum only. The teeth involved are originally separated, but join because of excessive cementum deposition of one or both teeth. This condition is most common in the permanent molars, particularly those of the maxillary arch, and logically occurs when the roots are in close proximity. It differs from fusion, because it is not a union between two tooth germs during development, but normally occurs following eruption, and it never involves enamel and dentin. It should be obvious that concrescence would be a hazard to any extraction procedure of the teeth involved.

8. Segmented root - This anomaly is caused by some disturbance during root development, and results in two separated root segments. The specific etiology is thought to be a break in Hertwig's sheath, temporarily halting dentinogenesis, so that if the formative process continues, the two root portions are separated.

FUSION

FUSION

CONCRESCENCE

SEGMENTED ROOT

SEGMENTED ROOT

9. Dwarfed roots - This condition exists when normal sized crowns have abnormally short roots. The crowns of these teeth are also abnormal in contour, exhibiting a greater incisocervical convexity of the labial surface. Normally, dwarfed roots are found only in the anterior teeth, most commonly the maxillary central incisors. The condition is quite often bilateral. It is also thought to have a hereditary etiology. These teeth may be lost at an early age simply because of passive eruption, or periodontal disease. This anomaly should not be confused with the shortened roots and blunted apices of teeth, occasionally observed radiographically following orthodontic treatment, and caused by excessive pressures during tooth movement.

DWARFED ROOTS

10. Hvpercementosis - As its name suggests, this condition results in excessive cementum formation around the root of a tooth, and is most often associated with the roots of permanent molars. It normally is not associated with any stage of tooth development, but rather occurs after eruption. The etiology may involve one of several sources, including trauma, local or systemic metabolic disturbance, or most commonly, chronic inflammation of the pulp.

HYPERCEMENTOSIS

HYPERCEMENTOSIS

11. Accessory cusps and roots - This group constitutes the most commonly observed dental anomalies, and may be attributed to hereditary or developmental causes during the morphodifferentiation process.

a. Accessory cusps - Extra cusps, or tubercles, are most often found in molars, and third molars in particular. They also occur as an incisal extension of the cingulum in maxillary anteriors. In the maxillary incisors, this occurrence is known as talon cusp. The crown of the affected incisor may give the appearance of a Phillips screwdriver. The etiology of talon cusp is not known, but is probably hereditary, since it often occurs in conjunction with other anomalies.

b. Accessory roots - Most often, extra roots are found on teeth which un-ACCESSORY dergo root development after birth, and so the etiology is considered to be

ROOTS trauma, pressure, or metabolic disease. The third molars most often exhibit accessory roots, but they may be found on any tooth in the mouth, although rarely in the maxillary anterior teeth. Maxillary first premolars with three roots and mandibular anterior teeth with two roots are also found. As might be expected, their presence is quite often a hazard in extraction procedures.

12. Missing cusps - Cusps of permanent posterior teeth are occasionally absent. Those most often missing are the most diminutive, good examples of which are the lingual cusp of the mandibular first premolar, the distolingual cusp of maxillary molars, and the distal cusp of mandibular first molars.

13. Enamel pearls - Also known as enamelomas, or enamel drops, they are found attached to the root surfaces of teeth, in the form of small, spherical nodules of enamel surrounding a dentin core. Their specific site is usually in the furcation area of molars. Because of the root anatomy, this means their location is most likely to be the buccal and lingual of mandibular molars, and the mesial and distal of maxillary molars. They are thought to be the result of aberrant enamel deposition on the root initiated by Hertwig's sheath. The enameloma appears as a round radiopaque mass on x-rays. They may be of clinical significance in the predisposition to, or severity of, periodontal disease. This abnormality has about a 2% incidence in the general population.

14. Hutchinson's teeth - This anomaly is often classified with hypoplastic defects, because it is a type of enamel dysplasia, but we will consider it in this section of abnormal form. The condition is due to prenatal syphilis. Specifically, its etiology involves the disturbance of calcification by the treponema organism during ameloblastic morphodifferentiation. Since the incisors and first molars are the only permanent teeth at this stage of development, they exhibit the effects. Primary teeth are not normally involved. The incisor crowns exhibit a screwdriver shape, usually with a deep notch on the incisal edge. The first molars have a mulberry appearance, with gnarled enamel, and poorly developed cusps. The dental significance is primarily esthetic.

15. Dens in dente - This condition occurs when the enamel organ becomes invaginated in a specific area on the crown of the tooth, and the normally external structures of enamel and dentin become reversed inside the pulp cavity. This creates an x-ray appearance of a small tooth within a tooth, hence the name dens in dente. It is rare in the posterior teeth, and is most commonly found in the permanent maxillary lateral incisor. In these teeth, the invagination leaves a defect in the lingual surface, in the form of an opening, or lingual pit, which leads to an enamel and dentin enclosed pulp cavity. As a result, it easily becomes carious and eventually may cause pain. Normally, the condition is evident in radiographs.

HUTCHINSON'S INCISORS

HUTCHINSON'S INCISORS

DENS IN DENTE

DENS IN DENTE

ENAMEL

DENTIN

PULP

ENAMEL

DENTIN

PULP

16. Odontoma:

a. Introduction - An odontoma is really not an anomaly of shape, but rather a benign tumor. It is included in this section for lack of a better location. The odontoma is a growth of calcified dental tissues, involving structures of both ectodermal (enamel) and mesodermal (dentin, cementum, and pulp) origin. There are two basic types, both of which evidently result from developmental disturbances of the dental lamina, or follicle, by trauma or infection.

b. Complex odontoma - This growth consists of one mass of calcified dental tissues, and may be attached to a normal tooth, or located separately in the alveolar bone. It does not exhibit any definite dental form.

COMPLEX ODONTOMA (RADIOGRAPHIC VIEW)

c. Compound odontoma - This type of odontoma also consists of the calcified tissues of a tooth, but in contrast to the complex type, these tissues are arranged in the shape of a recognizable tooth form. There may be one or more of these tooth forms, sometimes with almost perfect similarity to a normal tooth, and sometimes resembling more rudimentary dental forms.

COMPOUND ODONTOMA (RADIOGRAPHIC VIEW)

E. Abnormal Calcification and Apposition:

1. Introduction:

This group of anomalies is the result of disturbances which affect enamel and dentin formation during the histodifferentiation and appositional processes. The resultant condition is dependent on the severity of the disturbance, the stage of matrix or calcification affected, as well as the length of the disturbance.

2. Enamel dysplasia:

a. Introduction - Enamel dysplasia is a catchall label, and encompasses all enamel development abnormalities. The etiologic agents may be local, systemic, or hereditary in nature. Clinically, enamel dysplasias are characterized by bands, ridges, or pitted areas of discolored enamel. The size of the affected areas is directly related to the length and severity of the etiologic disturbance. Only teeth undergoing enamel formation at the time of disturbance are affected. The two general types of enamel dysplasia include:

i. Enamel hypoplasia - This type of enamel dysplasia occurs when the disturbance in development occurs during enamel matrix formation.

ENAMEL HYPOPLASIA

COMPLEX ODONTOMA (RADIOGRAPHIC VIEW)

COMPOUND ODONTOMA (RADIOGRAPHIC VIEW)

ii. Enamel hypocalcification - The time of disturbance in hypo-calcification is later than for hypoplasia, and occurs during enamel matrix maturation.

b. Amelogenesis imperfecta - This type of enamel dysplasia has an hereditary cause. The defect may range from an almost complete absence of enamel, to enamel that was deposited, but failed to fully mature, depending on the stage at which the disturbance occurred. The crowns of teeth with this abnormality are subject to rampant caries, as well as excessive attrition. For this reason, these teeth are rarely seen as late as adult life. They are also an esthetic consideration, since the crowns exhibit a surface roughness. The incidence of this dysplasia has been reported as about one in 14,000.

c. Dental fluorosis (Mottled enamel") - The intake of excessively high levels of fluoride ion during the enamel calcification period is responsible for this type of enamel dysplasia. It is considered to be a hypocalcification problem, since sufficient enamel matrix is normally present. The clinical appearance originally reveals chalky white bands or areas, which usually become pigmented in a brown or yellow fashion. Because of the etiology, these teeth are usually quite resistant to caries, which is in contrast to the other forms of enamel dysplasia. However, they may be a severe esthetic detriment to the patient.

d. Focal hvpomaturation - This entity is similar in etiology to the other enamel dysplasias. Clinically, it appears as a chalky white and opaque area which is clearly defined, usually in a circular shape on the facial surface. The enamel is particularly susceptible to caries. If, as is normally true, it is found in the anterior teeth, it is an esthetic consideration also.

e. Turner's teeth - This condition is found in individual teeth, as a result of local etiologic factors. The most common of these specific causes involves injury to the developing permanent tooth follicle through extraction procedures of the deciduous tooth, or disturbance from periapical infection of a diseased deciduous tooth pulp. Because of the different etiology, these clinically unesthetic areas are not generally symmetrical like most of the other anomalies of this group.

AMELOGENESIS IMPERFECTA

AMELOGENESIS IMPERFECTA

DENTAL FLUOROSIS

DENTAL FLUOROSIS

FOCAL HYPOMATU RATION

FOCAL HYPOMATU RATION

TURNER'S

TEETH

TURNER'S

TEETH

3. Dentinal dysplasia:

a. Introduction - The dentin dysplasias disturb dentin matrix formation and calcification during histodifferentiation and appositional processes. They are similar in all aspects to enamel dysplasias, except that the dental tissue involved is dentin rather than enamel.

b. Tetracycline staining - It has been documented that the administration of the wide-spectrum antibiotic tetracyclines, either to the mother during certain prenatal periods, or to the infant, may impart an intrinsic color change to the dentin of teeth undergoing mineralization. Both primary and permanent teeth may be affected, and the extent and location of any individual teeth is related to the time and duration of the antibiotic therapy. The affected teeth may originally exhibit a yellowish cast but with time change to a grayish or even purplish color.

c. Dentinogenesis imperfecta - This abnormality results from the genetic disturbance of dentin formation, and is the dentinal counterpart of amelo-genesis imperfecta. The crown of the tooth exhibits an unesthetic clinical appearance of opalescence, which is bluish-brown in color, and thus the condition is also known as opalescent dentin. The pulp chamber of these teeth may be entirely obliterated during development. The enamel is normal, but fractures easily, because of the lack of sound underlying dentinal support. Therefore, these teeth are weaker, and subject to greater attrition than normal teeth.

HEREDITARY DENTINOGENESIS IMPERFECTA

F. Treatment:

Since your dental background is admittedly limited, a discussion of the normal treatment of the various anomalies has been omitted. Some of the abnormalities require no treatment at all, but many of them require very challenging, imaginative, and highly skilled treatment. However, before any treatment should be attempted, an accurate diagnosis of the abnormality, and its implications, is imperative.

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