Abnormalities of Teeth

1. Hypoplasia

2. Diffuse opacities

3. Demarcated opacities

TURNER’S HYPOPLASIA: Another frequent pattern of enamel defects seen in permanent teeth is caused by periapical inflammatory disease of the overlying deciduous tooth. The altered tooth is called a Turner’s tooth (after the clinician whose publications allowed this problem to be widely recognized). The appearance of the affected area varies according to the timing and severity of the insult. The enamel defects vary from focal areas of white, yellow, or brown discoloration to extensive hypoplasia, which can involve the entire crown. The process is noted most frequently in the permanent bicuspids because of their relationship to the overlying deciduous molars (Figs. 2-4 and 2-5). Anterior teeth are involved less frequently because crown formation is usually complete before the development of any apical inflammatory disease in the relatively caries-resistant anterior deciduous dentition. Factors that determine the degree of damage to the permanent tooth by the overlying infection include the stage of tooth development, length of time the infection remains untreated, the virulence of the infective organisms, and the host resistance to the infection.

In addition to classic Turner’s teeth, an increased prevalence of demarcated opacities has been reported in the permanent successors of carious primary teeth. In one report, if the primary tooth developed caries, the successor was twice as likely to demonstrate a circumscribed enamel defect. In addition, if the primary tooth was extracted for any reason other than trauma, then the prevalence of a demarcated enamel defect increased fivefold.

Traumatic injury to deciduous teeth also can cause significant alterations of the underlying dentition and the formation of Turner’s teeth. This is not a rare occurrence; up to 45% of all children sustain injuries to their primary teeth. In a prospective study of 114 children with 255 traumatized primary teeth, 23% of the corresponding permanent teeth demonstrated developmental disturbances. The maxillary central incisors are affected in the majority of the cases; the maxillary lateral incisors are altered less frequently (Fig. 2-6). In several large reviews, the prevalence of involvement of the posterior teeth or mandibular incisors was less than 10% of all cases.

The frequency of traumatic damage of the anterior maxillary dentition is not surprising, considering the common occurrence of trauma to the deciduous dentition of the prominent anterior maxilla and the close anatomic relationship between the developing tooth bud and the apices of the overlying primary incisors. As would be expected, the clinical appearance of the alteration varies according to the timing and severity of the damage.

Because of the position of the primary apices relative to the tooth bud, the facial surface of the maxillary incisors is the location most frequently affected. Typically, the affected area appears as a zone of white or yellowish-brown discoloration with or without an area of horizontal enamel hypoplasia. The trauma also can cause displacement of the already formed hard-tooth substance in relation to the soft tissue of the remaining developing tooth. This results in a bend of the tooth known as dilaceration and can affect either the crown or the root of a tooth (see page 97). Severe trauma early in the development of the tooth can result in such disorganization of the bud that the resultant product may resemble a complex odontoma (see page 724). Similar levels of damage late in the formative process can lead to partial or total arrest in root formation.

MOLAR INCISOR HYPOMINERALIZATION: Over the last two to three decades, a number of publications have described a unique pattern of defective enamel that has been recognized most frequently in Northern Europe, although the pathosis is not limited to that geographic region. In the past this disorder most likely went undiagnosed because of the high prevalence of caries, but with the dramatic reduction in caries, these tooth changes have become more recognized.

Patients affected with molar incisor hypomineralization have enamel defects of one or more first permanent molars. The altered enamel may be white, yellow, or brown, with a sharp demarcation between the defective and surrounding normal enamel. Often, the involved enamel is soft and porous with a resemblance to discolored chalk or old Dutch cheese (“cheese molars”). Frequently, the incisors also are affected, but the defects generally are much less severe.

The enamel of the affected molars is very fragile and can chip easily. Often, affected molars are sensitive to cold, warm, or mechanical trauma. Toothbrushing is frequently painful, with a tendency for the children to avoid brushing these teeth. As would be expected, the lack of normal enamel and absence of appropriate hygiene lead to rapid development of caries. During attempts at dental therapy, these teeth often are highly sensitive and very difficult to anesthetize.

The cause of molar incisor hypomineralization is unknown, but many investigators believe the condition arises from a systemic influence during the first years of life, coinciding with the period of mineralization of the affected dentition. A number of prevalence studies have been performed with the results ranging from 3.6% to 25%.

HYPOPLASIA CAUSED BY ANTINEOPLASTIC THERAPY: As modern medicine increases the prevalence of successful therapy against childhood cancer, it has become evident that a number of developmental alterations arise secondary to use of therapeutic radiation or chemotherapy. As would be expected, developing teeth are affected most severely, with these therapies producing clinically obvious alterations most commonly in patients younger than 12 years and most extensively in those younger than 5 years. The degree and severity of the developmental alterations are related to the patient’s age at treatment, the form of therapy, and the dose and field of radiation, if used.

Although both chemotherapeutic agents and radiation therapy can be responsible for developmental abnormalities, the most severe alterations are associated with radiation. Doses as low as 0.72 Gy are associated with mild developmental defects in both enamel and dentin. As the dose escalates, so does the effect on the developing dentition and jaws. Frequently noted alterations include hypodontia, microdontia, radicular hypoplasia, and enamel hypoplasia (Fig. 2-7). In addition, mandibular hypoplasia and a reduction of the vertical development of the lower third of the face are not rare. The mandibular hypoplasia may be the direct effect of the radiation, reduced alveolar bone growth secondary to impaired root development, or (possibly) growth failure related to altered pituitary function caused by cranial radiation. Chemotherapy alone results in much less dramatic alterations but can produce an increased number of enamel hypoplasias and discolorations, slightly smaller tooth size, and occasional radicular hypoplasia that is less severe than that secondary to radiation.

DENTAL FLUOROSIS: The ingestion of excess amounts of fluoride also can result in significant enamel defects known as dental fluorosis. In 1901, Dr. Frederick S. McKay suggested the association between this altered enamel and an agent in the Colorado Springs, Colorado, water supply during investigation of the Colorado brown stain seen in the teeth of many of his patients. In 1909, Dr. F.L. Robertson noted a similar association in many of his patients in Bauxite, Arkansas (the home of bauxite mines for aluminum). In 1930, H.V. Churchill, a chemist in Bauxite who was employed by the Aluminum Company of America, discovered high concentrations of fluoride (13.7 ppm) in the water and contacted McKay for samples of the water in affected areas of Colorado. McKay’s samples also demonstrated high levels of fluoride, and the final part of the puzzle was solved.

Although the fluoride produced an unusual and permanent dental stain, a resistance to caries also was noted. In 1931 the National Institutes of Health hired Dr. H. Trendley Dean to investigate the association between fluoride, the presence of dental fluorosis, and the prevalence of caries among children. Ultimately this led to the first water fluoridation clinical trial in Grand Rapids, Michigan. Because of the efforts of these pioneers and the simultaneous work of many others, it was discovered that fluoride in the water at 1.0 ppm reduced caries by 50% to 70%. Since 1962 fluoridation of drinking water is recommended, with the optimum range being 0.7 to 1.2 ppm. The lower concentration is recommended for warmer climates in which water consumption is thought to be higher, but this distinction has been questioned because of an evolving indoor lifestyle and the use of modern air-conditioning. In 1999 the United States Centers for Disease Control and Prevention designated fluoridation of drinking water as one of the ten great public health achievements of the twentieth century in the United States.

Initially, fluoride’s ability to reduce caries was thought to be secondary to its incorporation into developing enamel, resulting in a stronger and more acid-resistant fluorapatite crystal. A number of more recent studies have suggested that the posteruptive effects of fluoride may be of equal or even greater importance. Researchers believe that continued exposure to topical fluoride contained in products such as toothpaste or fluoridated water inhibits demineralization, enhances remineralization, and exhibits antibacterial effects. In addition, they have suggested that preeruptive fluoride is most effective against pit and fissure caries, whereas smooth surface caries is affected most significantly by posteruptive exposure.

Consumption of optimally fluoridated water has been associated with a low prevalence of altered enamel, which usually is mild in degree. However, an increased prevalence of dental fluorosis has been noted in recent years. In addition, the relative caries reduction in fluoridated communities has improved between 8% and 37%. This has been attributed to the diffusion of fluoride to nonfluoridated areas through bottling and processing of foods and beverages with fluoridated water, as well as to the widespread use of fluoride toothpaste. Adult-strength fluoride toothpastes, fluoride supplements, infant foods, soft drinks, fruit juices, and industrial environmental emissions all represent potential sources of fluoride for children in their formative years. Infant formulas also used to contain significant amounts of fluoride; however, in 1979, U.S. manufacturers voluntarily agreed to dramatically limit fluoride in infant formulas. Despite this, some investigators have noted an increased prevalence of fluorosis continuing after 1979 in individuals who consumed powdered, concentrated formula that was reconstituted with optimally fluoridated water. To minimize the chance of fluorosis, the use of ready-to-feed formula or reconstitution with low-fluoride bottled water has been recommended.

Because of this dissemination of fluoride, the need for supplements in nonfluoridated areas is declining. In patients who use fluoride toothpastes, the anticariogenic benefit of supplements is very small or nonexistent and the risk of fluorosis at the community level becomes a certainty. Several investigators have recommended strongly that children younger than 7 years of age apply only a pea-sized amount of fluoride toothpaste on the toothbrush and avoid swallowing. Because young children tend to swallow almost all toothpaste placed on their brush, parents should be warned to avoid fluoridated toothpaste in children younger than 2 years of age and perform oral hygiene with only a toothbrush and water. In addition, fluoride supplements are recommended only in nonfluoridated areas for children who are at high risk for rampant caries. Finally, an effort is under way to alter the 1962 recommendation and lower the optimum level of fluoride in the public water supply to 0.7 ppm.

Fluoride appears to create its significant enamel defects through retention of the amelogenin proteins in the enamel structure, leading to the formation of hypomineralized enamel. These alterations create a permanent hypomaturation of the enamel in which an increased surface and subsurface porosity of the enamel is observed. This enamel structure alters the light reflection and creates the appearance of white, chalky areas. Most of the problems associated with dental fluorosis are aesthetic and concern the appearance of the anterior teeth. Therefore, the critical period for clinically significant dental fluorosis is during the second and third years of life, when these teeth are forming.

The severity of dental fluorosis is dose dependent, with higher intakes of fluoride during critical periods of tooth development being associated with more severe fluorosis. The affected teeth are caries resistant, and the altered tooth structure appears as areas of lusterless white opaque enamel that may have zones of yellow to dark-brown discoloration (Figs. 2-8 and 2-9). In the past, areas of moderate-to-severe enamel fluorosis were termed mottled enamel. True enamel hypoplasia is uncommon but can occur as deep, irregular, and brownish pits. Because other factors can result in a similar pattern of enamel damage, a definitive diagnosis requires that the defects be present in a bilaterally symmetric distribution, and evidence of prior excessive fluoride intake or elevated levels of fluoride in the enamel or other tissues should be found.

Recently, an increased prevalence of dental changes similar to dental fluorosis has been linked to amoxicillin use during early infancy. Commonly affected teeth include the permanent first molars and maxillary central incisors. The number of affected teeth appears to correlate with the duration of use. Although the mechanism of this alteration is unclear, the antibiotic may reduce gene expression of selected matrix proteins or reduce the activity of proteinases that hydrolyze matrix proteins. It also should be noted that one of the etiologic theories suggested for molar incisor hypomineralization (see page 58) is prior antibiotic therapy.

SYPHILITIC HYPOPLASIA: Congenital syphilis (see page 190) results in a pattern of enamel hypoplasia that is well known but currently so rare that lengthy discussion is not warranted. Anterior teeth altered by syphilis are termed Hutchinson’s incisors and exhibit crowns that are shaped like straight-edge screwdrivers, with the greatest circumference present in the middle one third of the crown and a constricted incisal edge. The middle portion of the incisal edge often demonstrates a central hypoplastic notch. Altered posterior teeth are termed mulberry molars and demonstrate constricted occlusal tables with a disorganized surface anatomy that resembles the bumpy surface of a mulberry.

• Acid-etched composite resin restorations

• Labial veneers

• Full crowns

ATTRITION: Attrition can occur in both the deciduous and the permanent dentitions. As would be expected, the surfaces predominantly affected are those that contact the opposing dentition. Most frequently, the incisal and occlusal surfaces are involved, in addition to the lingual of the anterior maxillary teeth and the labial of the anterior mandibular teeth. Large, flat, smooth, and shiny wear facets are found in a relationship that corresponds to the pattern of occlusion. The interproximal contact points also are affected from the vertical movement of the teeth during function. Over time, this interproximal loss can result in a shortening of the arch length. Pulp exposure and dentin sensitivity are rare because of the slow loss of tooth structure and the apposition of reparative secondary dentin within the pulp chamber (Fig. 2-10).

ABRASION: Abrasion has a variety of patterns, depending on the cause. Toothbrush abrasion typically appears as horizontal cervical notches on the buccal surface of exposed radicular cementum and dentin (Fig. 2-11). The defects usually have sharply defined margins and a hard, smooth surface. If acid also is present, then the lesions will be more rounded and shallower. The degree of loss is greatest on prominent teeth (i.e., cuspids, bicuspids, teeth adjacent to edentulous areas) and occasionally is more advanced on the side of the arch opposite the dominant hand. Thread biting or the use of pipes or bobby pins usually produces rounded or V-shaped notches in the incisal edges of anterior teeth (Figs. 2-12 and 2-13). The inappropriate use of dental floss or toothpicks results in the loss of interproximal radicular cementum and dentin.

EROSION: In patients with erosion, the tooth loss does not correlate with functional wear patterns or with those typically associated with known abrasives. The predominant sites of tooth loss appear to correlate closely with those areas not protected by the serous secretions of the parotid and submandibular glands. The facial and palatal surfaces of the maxillary anterior teeth and the facial and occlusal surfaces of the mandibular posterior teeth are affected most frequently. Involvement of the lingual surfaces of the entire mandibular dentition is uncommon, possibly because of the protective buffering capacity of the submandibular serous saliva.

The classic pattern of dental erosion is the cupped lesion in which a central depression of dentin is surrounded by elevated enamel. Cupped areas are seen on the occlusal cusp tips, incisal edges, and marginal ridges (Fig. 2-14). In contrast to abrasion, erosion commonly affects the facial surfaces of the maxillary anteriors and appears as shallow spoon-shaped depressions in the cervical portion of the crown. The posterior teeth frequently exhibit extensive loss of the occlusal surface, and the edges of metallic restorations subsequently may be above the level of the tooth structure (Fig. 2-15). After a portion of the cuspal enamel has been lost, the dentin is destroyed more rapidly than the remaining enamel, often resulting in a concave depression of the dentin surrounded by an elevated rim of enamel (Fig. 2-16). The more rapid dissolution of the dentin can lead to undermined enamel that often is lost easily by chipping. Occasionally, entire buccal cusps are lost and replaced by ski slope–like depressions that extend from the lingual cusp to the buccal cementoenamel junction (Fig. 2-17). When palatal surfaces are affected, the exposed dentin has a concave surface and shows a peripheral white line of enamel (Fig. 2-18). Active erosion typically reveals a clean, unstained surface, whereas inactive sites become stained and discolored.

Focal facial tooth wear of the gingival portion has been given the nonspecific term, noncarious cervical lesions, in an attempt to emphasize the multifactorial nature of the process. These cervical defects often are seen in association with loss of occlusal tooth structure, which has features of erosion, attrition, or both.

Erosion limited to the facial surfaces of the maxillary anterior dentition often is associated with dietary sources of acid. When the tooth loss is confined to the incisal portions of the anterior dentition of both arches, an external environmental source is suggested. When erosion is located on the palatal surfaces of the maxillary anterior teeth and the occlusal surfaces of the posterior teeth of both dentitions, regurgitation of gastric secretions is a probable cause. The location of the tooth structure loss may suggest the cause of the damage but is not completely reliable.

ABFRACTION: Abfraction appears as wedge-shaped defects limited to the cervical area of the teeth and may closely resemble cervical abrasion or erosion. Clues to the diagnosis include defects that are deep, narrow, and V-shaped (which do not allow the toothbrush to contact the base of the defect) and often affect a single tooth with adjacent unaffected teeth (Fig. 2-19). In addition, occasional lesions are subgingival, a site typically protected from abrasion and erosion. The lesions predominantly affect bicuspids and molars, are seen almost exclusively on the facial surface, and exhibit a much greater prevalence in those with bruxism.

In all forms of tooth wear, the process typically proceeds at a slow rate that allows deposition of tertiary dentin and prevents pulp exposure, even when extensive loss of tooth structure is present (see Fig. 2-11). In some cases, and especially in the deciduous dentition, the tooth loss can proceed at a more accelerated rate that results in a near or frank exposure of the pulp. In a large review of 448 patients with tooth wear, 11.6% revealed near or direct pulp exposure. In addition, hypersensitivity was the presenting symptom in about one third of patients with tooth wear.

EXTRINSIC STAINS: Bacterial stains are a common cause of surface staining of exposed enamel, dentin, and cementum. Chromogenic bacteria can produce colorations that vary from green or black-brown to orange. The discoloration occurs most frequently in children and is usually seen initially on the labial surface of the maxillary anterior teeth in the gingival one third. In contrast to most plaque-related discolorations, the black-brown stains most likely are not primarily of bacterial origin but are secondary to the formation of ferric sulfide from an interaction between bacterial hydrogen sulfide and iron in the saliva or gingival crevicular fluid.

Extensive use of tobacco products, tea, or coffee often results in significant brown discoloration of the surface enamel (Fig. 2-30). The tar within the tobacco dissolves in the saliva and easily penetrates the pits and fissures of the enamel. Smokers (of tobacco or marijuana) most frequently exhibit involvement of the lingual surface of the mandibular incisors; users of smokeless tobacco often demonstrate involvement of the enamel in the area of tobacco placement. Stains from beverages also often involve the lingual surface of the anterior teeth, but the stains are usually more widespread and less intense. In addition, foods that contain abundant chlorophyll can produce a green discoloration of the enamel surface.

The green discoloration associated with chromogenic bacteria or the frequent consumption of chlorophyll-containing foods can resemble the pattern of green staining seen secondary to gingival hemorrhage. As would be expected, this pattern of discoloration occurs most frequently in patients with poor oral hygiene and erythematous, hemorrhagic, and enlarged gingiva. The color results from the breakdown of hemoglobin into green biliverdin.

A large number of medications may result in surface staining of the teeth. In the past, use of products containing high amounts of iron or iodine was associated with significant black pigmentation of the teeth. Exposure to sulfides, silver nitrate, or manganese can cause stains that vary from gray to yellow to brown to black. Copper or nickel may produce a green stain; cadmium, essential oils, and co-amoxiclav may be associated with a yellow to brown discoloration. Multiple recent reports have documented a yellow-brown staining of teeth associated with doxycycline, which can be removed by professional abrasive cleaning; the cause of this discoloration is unclear.

More recently, the most frequently reported culprits include stannous fluoride and chlorhexidine. Fluoride staining may be associated with the use of 8% stannous fluoride and is thought to be secondary to the combination of the stannous (tin) ion with bacterial sulfides. This black stain occurs predominantly in people with poor oral hygiene in areas of a tooth previously affected by early carious involvement. The labial surfaces of anterior teeth and the occlusal surfaces of posterior teeth are the most frequently affected. Chlorhexidine is associated with a yellow-brown stain that predominantly involves the interproximal surfaces near the gingival margins. The degree of staining varies with the concentration of the medication and the patient’s susceptibility. Although an increased frequency has been associated with the use of tannin-containing beverages, such as tea and wine, effective brushing and flossing or frequent gum chewing can minimize staining. Chlorhexidine is not alone in its association with tooth staining; many oral antiseptics, such as Listerine and sanguinarine, also may produce similar changes.

INTRINSIC STAINS: Congenital erythropoietic porphyria (Gönther disease) is an autosomal recessive disorder of porphyrin metabolism that results in the increased synthesis and excretion of porphyrins and their related precursors. Significant diffuse discoloration of the dentition is noted as a result of the deposition of porphyrin in the teeth (Fig. 2-31). Affected teeth demonstrate a marked red-brown coloration that exhibits a red fluorescence when exposed to a Wood’s ultraviolet (UV) light. The deciduous teeth demonstrate a more intense coloration because porphyrin is present in the enamel and the dentin; in the permanent teeth, only the dentin is affected. Excess porphyrins also are present in the urine, which may reveal a similar fluorescence when exposed to a Wood’s light.

Another autosomal recessive metabolic disorder, alkaptonuria, is associated with a blue-black discoloration termed ochronosis that occurs in connective tissue, tendons, and cartilage. On rare occasions, a blue discoloration of the dentition may be seen in patients who also are affected with Parkinson’s disease.

Bilirubin is a breakdown product of red blood cells, and excess levels can be released into the blood in a number of conditions. The increased amount of bilirubin can accumulate in the interstitial fluid, mucosa, serosa, and skin, resulting in a yellow-green discoloration known as jaundice (see page 821). During periods of hyperbilirubinemia, developing teeth also may accumulate the pigment and become stained intrinsically. In most cases the deciduous teeth are affected as a result of hyperbilirubinemia during the neonatal period. The two most common causes are erythroblastosis fetalis and biliary atresia. Other diseases that less frequently display intrinsic staining of this type include the following:

Erythroblastosis fetalis is a hemolytic anemia of newborns secondary to a blood incompatibility (usually Rh factor) between the mother and the fetus. Currently, this disorder is relatively uncommon because of the use of antiantigen gamma globulin at delivery in mothers with Rh-negative blood.

Biliary atresia is a sclerosing process of the biliary tree and is the leading cause of death from hepatic failure in children in North America. However, many affected children live after successful liver transplantation.

The extent of the dental changes correlates with the period of hyperbilirubinemia, and most patients exhibit involvement limited to the primary dentition. Occasionally, the cusps of the permanent first molars may be affected. In addition to enamel hypoplasia, the affected teeth frequently demonstrate a green discoloration (chlorodontia). The color is the result of the deposition of biliverdin (the breakdown product of bilirubin that causes jaundice) and may vary from yellow to deep shades of green (Fig. 2-32). The color of tooth structure formed after the resolution of the hyperbilirubinemia appears normal. The teeth often demonstrate a sharp dividing line, separating green portions (formed during hyperbilirubinemia) from normal-colored portions (formed after normal levels of bilirubin were restored).

Coronal discoloration is a frequent finding after trauma, especially in the deciduous dentition. Posttraumatic injuries may create pink, yellow, or dark-gray discoloration. Temporary pink discoloration that arises 1 to 3 weeks after trauma may represent localized vascular damage and often returns to normal in 1 to 3 weeks. In these instances, periapical radiographs are warranted to rule out internal resorption that may produce a similar clinical presentation. A yellow discoloration is indicative of pulpal obliteration, termed calcific metamorphosis, and is discussed more fully in Chapter 3 (see page 123). The dark-gray discoloration is long-term and occurs in teeth with significant pulpal pathosis in which blood degradation products have diffused into the dentinal tubules. Endodontic therapy initiated before or shortly after the total death of the pulp often prevents the discoloration. The pulpal necrosis may be aseptic and not associated with significant tenderness to percussion, mobility, or associated periapical inflammatory disease. A related process secondary to localized red blood cell destruction also can result in discoloration of the teeth. Occasionally, during a postmortem examination, a pink discoloration of teeth is found. The crowns and necks of the teeth are affected most frequently, and the process is thought to arise from hemoglobin breakdown within the necrotic pulp tissue in patients in whom blood has accumulated in the head.

A similar pink or red discoloration of the maxillary incisors has been reported in living patients with le-promatous leprosy (see page 198). Although controversial, some investigators believe these teeth are involved selectively because of the decreased temperature preferred by the causative organism. This process is thought to be secondary to infection-related necrosis and the rupture of numerous small blood vessels within the pulp, with a secondary release of hemoglobin into the adjacent dentinal tubules.

Dental restorative materials, especially amalgam, can result in black-gray discolorations of teeth. This most frequently arises in younger patients who presumably have more open dentinal tubules. Large Class II proximal restorations of posterior teeth can pro-duce discoloration of the overlying facial surface. In addition, deep lingual metallic restorations on anterior incisors can significantly stain underlying dentin and produce visible grayish discoloration on the labial surface. To help reduce the possibility of discoloration, the clinician should not restore endodontically treated anterior teeth with amalgam (Fig. 2-33).

Several different medications can become incorporated into the developing tooth and result in clinically evident discoloration. The severity of the alterations is dependent on the time of administration, the dose, and the duration of the drug’s use. The most infamous is tetracycline, with the affected teeth varying from bright yellow to dark brown and, in UV light, showing a bright-yellow fluorescence (Fig. 2-34). After chronic exposure to ambient light, the fluorescent yellow discoloration fades over months to years into a nonfluorescent brown discoloration. Often the facial surfaces of the anterior teeth will darken while the posterior dentition and lingual surfaces remain a fluorescent yellow. The drug and its homologues can cross the placental barrier; therefore, administration should, if possible, be avoided during pregnancy and in children up to 8 years of age. All homologues of tetracycline are associated with discoloration and include chlortetracycline (gray-brown discoloration) and demethylchlortetracycline and oxytetracycline (yellow).

One semisynthetic derivative of tetracycline, minocycline hydrochloride, has been shown to produce significant discoloration of the dentition and also may affect teeth that are fully developed. Minocycline is a widely used medication for the treatment of acne and also is occasionally prescribed to treat rheumatoid arthritis. Its prevalence of use is increasing (and, presumably, so will the number of patients affected with discolored teeth and bone).

Although the mechanism is unknown, minocycline appears to bind preferentially to certain types of collagenous tissues (e.g., dental pulp, dentin, bone, dermis). Once in these tissues, oxidation occurs and may produce the distinctive discoloration. Some investigators believe supplementation with ascorbic acid (an antioxidant) can block formation of the discoloration. No matter the cause, once the pulp tissues are stained, the coloration can be seen through the overlying translucent dentin and enamel. The staining is not universal; only 3% to 6% of long-term users become affected. In those affected, the period of time before discoloration becomes evident can range from just 1 month to several years.

In susceptible individuals, minocycline creates discoloration in the skin, oral mucosa (see page 318), nails, sclera, conjunctiva, thyroid, bone, and teeth. Coloration of the bone occasionally results in a distinctive blue-gray appearance of the palate, mandibular tori, or anterior alveolar mucosa, which represents the black bone showing through the thin, translucent oral mucosa (see page 317). Several patterns of staining are noted in the dentition. Fully erupted teeth typically reveal a blue-gray discoloration of the incisal three fourths, with the middle one third being maximally involved. The exposed roots of erupted teeth demonstrate a dark-green discoloration, although the roots of developing teeth are stained dark black.

Another antibiotic, ciprofloxacin, is given intravenously to infants for Klebsiella spp. infections. Although less notable than tetracycline, this medication also has been associated with intrinsic tooth staining, usually a greenish discoloration.

• Overlying cysts or tumors

• Trauma

• Reconstructive surgery

• Thickened overlying bone or soft tissue

• A host of systemic disorders, diseases, and syndromes

• Long-term observation

• Orthodontically assisted eruption

• Transplantation

• Surgical removal

• Crowding of dentition

• Resorption, caries, and worsening of the periodontal status of adjacent teeth (Fig. 2-37)

• Development of pathologic conditions, such as infections, cysts, and tumors

• Transient or permanent sensory loss

• Alveolitis

• Trismus

• Infection

• Fracture

• Temporomandibular joint (TMJ) injury

• Periodontal injury

• Injury to adjacent teeth

HYPODONTIA: Failure of teeth to form is one of the most common dental developmental abnormalities, with a reported prevalence of 1.6% to 9.6% in permanent teeth when absence of third molars is excluded. The prevalence increases to 20% if third molars are considered. A female predominance of approximately 1.5:1 is reported. Anodontia is rare, and most cases occur in the presence of hereditary hypohidrotic ectodermal dysplasia (see page 741). Indeed, when the number of missing teeth is high or involves the most stable teeth (i.e., maxillary central incisors, first molars), the patient should be evaluated for ectodermal dysplasia. Hypodontia is uncommon in the deciduous dentition, with a prevalence that ranges from 0.5% to 0.9% and, when present, most frequently involves the lateral incisors. Absence of a deciduous tooth is associated strongly with an increased prevalence of a missing successor. Missing teeth in the permanent dentition are not rare, with third molars being the most commonly affected. After the molars, the second premolars and lateral incisors are absent most frequently (Fig. 2-40). Hypodontia is associated positively with microdontia (see page 83), reduced alveolar development, increased freeway space, and retained primary teeth (Fig. 2-41). In whites with missing teeth, approximately 80% will demonstrate loss of only one or two teeth.

Mutation of the PAX9 gene creates an autosomal dominant pattern of oligodontia that can involve various teeth but most commonly affects most of the permanent molars. In severe cases, loss of the primary molars, second premolars, and permanent mandibular central incisors also may be seen. Mutation of the MSX1 gene also is inherited as an autosomal dominant trait. Those affected with this mutation tend to demonstrate loss of the distal tooth of each type, with more severely affected individuals also revealing anterior progression of the agenesis. In these patients the most commonly missing teeth are the second premolars and third molars. In more severe cases, often the maxillary first premolars and maxillary lateral incisors also are missing. With the MSX1 mutation, the degree of oligodontia is severe, with an average of approximately 12 missing teeth per patient. The He-Zhao deficiency arose in a large kindred from northwest China and includes a highly variable pattern of missing teeth that occurs only in the permanent dentition. The missing teeth may affect the entire dentition, but the condition most commonly involves the third molars, second premolars, and maxillary lateral incisors.

For dentists and their patients, the most critical discovery related to hypodontia revolves around the mutation of the AXIN2 gene. This pattern of oligodontia is inherited as an autosomal dominant disorder, with the most commonly missing teeth being the permanent second and third molars, second premolars, lower incisors, and maxillary lateral incisors. The maxillary central incisors always are present and usually accompanied by the canines, first premolars, and first molars. However, the number and type of missing teeth are highly variable, a typical finding of inheritable oligodontia. Although the missing teeth can produce a significant oral problem, the presence of the AXIN2 mutation in these kindreds also has been associated with development of adenomatous polyps of the colon and colorectal carcinoma. This suggests that patients with similar examples of oligodontia should be questioned closely for a family history of colon cancer, with further medical evaluation recommended for those possibly at risk.

Even in kindreds with an obviously inherited pattern of hypodontia or oligodontia, it must be stressed that, in the majority of the cases, the genes are yet to be discovered. The most common form of inherited hypodontia is an autosomal dominant pattern in which the average number of missing teeth is slightly more than two. Excluding the third molars, the most commonly missing teeth in these cases are the lower second premolars, upper second premolars, maxillary lateral incisors, and lower central incisors.

HYPERDONTIA: The prevalence of supernumerary permanent teeth in whites is between 0.1% and 3.8%, with a slightly higher rate seen in Asian populations. The frequency in the deciduous dentition is much lower and varies from 0.3% to 0.8%. Approximately 76% to 86% of cases represent single-tooth hyperdontia, with two supernumerary teeth noted in 12% to 23%, and three or more extra teeth noted in less than 1% of cases. Single-tooth hyperdontia occurs more frequently in the permanent dentition, and approximately 95% present in the maxilla, with a strong predilection for the anterior region. The most common site is the maxillary incisor region, followed by maxillary fourth molars and mandibular fourth molars, premolars, canines, and lateral incisors (Fig. 2-42). Supernumerary mandibular incisors are very rare. Although supernumerary teeth may be bilateral, most occur unilaterally (Figs. 2-43 and 2-44). In contrast to single-tooth hyperdontia, nonsyndromic multiple supernumerary teeth occur most frequently in the mandible. These multiple supernumerary teeth occur most often in the premolar region, followed by the molar and anterior regions, respectively (Fig. 2-45).

Although most supernumerary teeth occur in the jaws, examples have been reported in the gingiva, maxillary tuberosity, soft palate, maxillary sinus, sphenomaxillary fissure, nasal cavity, and between the orbit and the brain. The eruption of accessory teeth is variable and dependent on the degree of space available; 75% of supernumerary teeth in the anterior maxilla fail to erupt. Unlike hypodontia, hyperdontia is positively correlated with macrodontia (see page 83) and exhibits a 2:1 male predominance. Although examples may be identified in older adults, most supernumerary teeth develop during the first two decades of life.

Several terms have been used to describe supernumerary teeth, depending on their location. A supernumerary tooth in the maxillary anterior incisor region is termed a mesiodens (see Fig. 2-42); an accessory fourth molar is often called a distomolar or distodens. A posterior supernumerary tooth situated lingually or buccally to a molar tooth is termed a paramolar (Fig. 2-46).

Supernumerary teeth are divided into supplemental (normal size and shape) or rudimentary (abnormal shape and smaller size) types. Rudimentary supernumerary teeth are classified further into conical (small, peg-shaped), tuberculate (barrel-shaped anterior with more than one cusp), and molariform (small premolar-like or molarlike). Although odontomas are considered hamartomas and could be placed within this classification, these lesions traditionally are in-cluded in the list of odontogenic neoplasms and are discussed in Chapter 15 (page 724). The conical mesiodens represents one of the more common supernumerary teeth and can erupt spontaneously, whereas tuberculate examples are less frequent and rarely erupt.

Occasionally, normal teeth may erupt into an inappropriate position (e.g., a canine present between two premolars). This pattern of abnormal eruption is called dental transposition. Such misplaced teeth have been confused with supernumerary teeth; but in reality, patients exhibiting dental transposition have been reported to exhibit an increased prevalence of hypodontia, not hyperdontia. The teeth involved most frequently in transposition are the maxillary canines and first premolars. Crowding or malocclusion of these normal teeth may dictate reshaping, orthodontics, or extraction.

Accessory teeth may be present at or shortly after birth. Historically, teeth present in newborns have been called natal teeth; those arising within the first 30 days of life are designated neonatal teeth. This is an artificial distinction, and it appears appropriate to call all of these teeth natal teeth (Fig. 2-47). Although some authors have suggested that these teeth may represent predeciduous supernumerary teeth, most are prematurely erupted deciduous teeth (not supernumerary teeth). Approximately 85% of natal teeth are mandibular incisors, 11% are maxillary incisors, and 4% are posterior teeth.

MICRODONTIA: The term microdontia should be applied only when the teeth are physically smaller than usual. Normal-sized teeth may appear small when widely spaced within jaws that are larger than normal. This appearance has been historically termed relative microdontia, but it represents macrognathia (not microdontia). Diffuse true microdontia is uncommon but may occur as an isolated finding in Down syndrome, in pituitary dwarfism, and in association with a small number of rare hereditary disorders that exhibit multiple abnormalities of the dentition (Fig. 2-48).

Isolated microdontia within an otherwise normal dentition is not uncommon. The maxillary lateral incisor is affected most frequently and typically appears as a peg-shaped crown overlying a root that often is of normal length (Fig. 2-49). The mesiodistal diameter is reduced, and the proximal surfaces converge toward the incisal edge. The reported prevalence varies from 0.8% to 8.4% of the population, and the alteration appears to be autosomal dominant with incomplete penetrance. In addition, isolated microdontia often affects third molars. Interestingly, the maxillary lateral incisors and the third molars are among the most frequent teeth to be congenitally missing. When a peg-shaped tooth is present, the remaining perma-nent teeth often exhibit a slightly smaller mesiodistal size.

MACRODONTIA: Analogous to microdontia, the term macrodontia (megalodontia, megadontia) should be applied only when teeth are physically larger than usual and should not include normal-sized teeth crowded within a small jaw (previously termed relative macrodontia). In addition, the term macrodontia should not be used to describe teeth that have been altered by fusion or gemination. Diffuse involvement is rare, and typically only a few teeth are abnormally large. Diffuse macrodontia has been noted in association with pituitary gigantism (see page 831), otodental syndrome, XYY males, and pineal hyperplasia with hyperinsulinism. Macrodontia with unilateral premature eruption is not rare in hemifacial hyperplasia (see page 38). Authors have postulated that the unilateral bone growth resulting from this condition may also affect developing teeth on the altered side. Isolated macrodontia is reported to occur most frequently in incisors or canines but also has been seen in second premolars and third molars. In such situations, the alteration often occurs bilaterally.

GEMINATION AND FUSION: Double teeth (gemination and fusion) occur in both the primary and the permanent dentitions, with a higher frequency in the anterior and maxillary regions (Figs. 2-50 to 2-54). In the permanent dentition, the prevalence of double teeth in whites is approximately 0.3% to 0.5%, whereas the frequency in deciduous teeth is greater, with a reported prevalence from 0.5% to 2.5%. Asian populations tend to demonstrate a higher occurrence that exceeds 5% in some studies. In both dentitions, incisors and canines are the most commonly affected teeth. Involvement of posterior primary teeth, premolars, and permanent molars also can occur. Gemination is more common in the maxilla, whereas fusion tends to occur more frequently in the mandible. Bilateral cases are uncommon (Fig. 2-55).

Gemination and fusion appear similar and may be differentiated by assessing the number of teeth in the dentition. Some authors have suggested that gemination demonstrates a single root canal. Separate canals are present in fusion, but this does not hold true in all cases (Fig. 2-56). A variety of appearances are noted with both fusion and gemination. The processes may result in an otherwise anatomically correct tooth that is greatly enlarged. A bifid crown may be seen overlying two completely separated roots, or the joined crowns may blend into one enlarged root with a single canal.

CONCRESCENCE: Concrescence is two fully formed teeth, joined along the root surfaces by cementum. The process is noted more frequently in the posterior and maxillary regions. The developmental pattern often involves a second molar tooth in which its roots closely approximate the adjacent impacted third molar (Fig. 2-57). The postinflammatory pattern frequently involves carious molars in which the apices overlie the roots of horizontally or distally angulated third molars. This latter pattern most frequently arises in a carious tooth that exhibits large coronal tooth loss. The resultant large pulpal exposure often permits pulpal drainage, leading to a resolution of a portion of the intrabony pathosis. Cemental repair then occurs (Figs. 2-58 and 2-59).

CUSP OF CARABELLI: The cusp of Carabelli is an accessory cusp located on the palatal surface of the mesiolingual cusp of a maxillary molar (Fig. 2-60). The cusp may be seen in the permanent or deciduous dentitions and varies from a definite cusp to a small indented pit or fissure. When present, the cusp is most pronounced on the first molar and is increasingly less obvious on the second and third molars. When a cusp of Carabelli is present, the remaining permanent teeth often are larger than normal mesiodistally, but a similar association in deciduous tooth size is typically not noted. A significant variation exists among different populations, with the prevalence reported to be as high as 90% in whites and rare in Asians. An analogous accessory cusp is seen occasionally on the mesiobuccal cusp of a mandibular permanent or deciduous molar and is termed a protostylid.

TALON CUSP: A talon cusp is a well-delineated additional cusp that is located on the surface of an anterior tooth and extends at least half the distance from the cementoenamel junction to the incisal edge. A talon cusp is thought to represent the end of a continuum that extends from a normal cingulum, to an enlarged cingulum, to a small accessory cusp, and, finally, to a full-formed talon cusp. Investigators have muddied the literature associated with this spectrum by categorizing all enlarged cingula as talon cusps and developing a classification system for the degree of enlargement. These classification systems make prevalence data difficult to evaluate and should be discouraged.

Three fourths of all reported talon cusps are located in the permanent dentition. The cusps predominantly occur on permanent maxillary lateral (55%) or central (33%) incisors but have been seen less frequently on mandibular incisors (6%) and maxillary canines (4%) (Fig. 2-61). Their occurrence in the deciduous dentition is very rare, with the vast majority noted on maxillary central incisors. In almost all cases the accessory cusp projects from the lingual surface of the affected tooth and forms a three-pronged pattern that resembles an eagle’s talon. On rare occasions, the cusp may project from the facial surface or from both surfaces of a single tooth. A deep developmental groove may be present where the cusp fuses with the underlying surface of the affected tooth. Most, but not all, talon cusps contain a pulpal extension. Radiographically, the cusp is seen overlying the central portion of the crown and includes enamel and dentin (Fig. 2-62). Only a few cases demonstrate visible pulpal extensions on dental radiographs.

Extensive prevalence studies have not been performed, but estimates suggest the frequency of talon cusp in the population ranges from less than 1% to 8%. Variations among different population groups and inconsistent definitions of a talon cusp make a definitive calculation difficult. The process does appear to occur more frequently in Asians, Native Americans, the Inuit, and those of Arab descent. Both sexes may be affected, and the occurrence may be unilateral or bilateral. The accessory cusp has been seen in association with other dental anomalies (e.g., supernumerary teeth, odontomas, impacted teeth, peg-shaped lateral incisors, dens invaginatus, posterior dens evaginatus).

In isolated cases, genetic influences appear to have an effect, because identical talon cusps occasionally have been documented in twins. Talon cusps also have been seen in patients with Rubinstein-Taybi syndrome, Mohr syndrome, Ellis-van Creveld syndrome, incontinentia pigmenti achromians, and Sturge-Weber angiomatosis. Although the strength of association between the presence of talon cusps and these syndromes generally is not clear, Rubinstein-Taybi syndrome is strongly correlated as demonstrated by a study of 45 affected patients in which 92% demonstrated talon cusps. Other characteristic features of this syndrome include growth and mental retardation, broad thumbs and great toes, and a number of other orodental features (thin upper lip, retrognathia, micrognathia, narrow high-arched palate, submucous cleft palate, and cleft palate [rarely]).

DENS EVAGINATUS: Dens evaginatus (central tubercle, tuberculated cusp, accessory tubercle, occlusal pearl, evaginated odontome, Leong premolar, tuberculated premolar) is a cusplike elevation of enamel located in the central groove or lingual ridge of the buccal cusp of premolar or molar teeth (Fig. 2-63). Although this pattern of accessory cusps has been reported on molars, dens evaginatus typically occurs on premolar teeth, is usually bilateral, and demonstrates a marked mandibular predominance. Deciduous molars are affected infrequently. The accessory cusp normally consists of enamel and dentin, with pulp present in about half of the cases. Although the prevalence is variable, most reviews suggest a frequency between 1% and 4%. The anomaly is encountered most frequently in Asians, the Inuit, and Native Americans but is rare in whites. Researchers expect an increased prevalence of this anomaly in the United States secondary to immigration by Asians and by Hispanics of mestizo heritage (i.e., those of mixed European and Native American ancestry). Radiographically, the occlusal surface exhibits a tuberculated appearance, and often a pulpal extension is seen in the cusp (Fig. 2-64). The accessory cusp frequently creates occlusal interferences that are associated with significant clinical problems. In one large study, more than 80% of the tubercles were worn or fractured, with pulpal pathosis noted in more than 25% of patients. Pulpal necrosis is common and may occur through a direct exposure or invasion of patent, immature dentinal tubules. In addition to abnormal wear and pulpal pathosis, the accessory cusp also may result in dilaceration, displacement, tilting, or rotation of the tooth.

Frequently, dens evaginatus is seen in association with another variation of coronal anatomy, shovel-shaped incisors. This alteration also occurs predominantly in Asians, with a prevalence of approximately 15% in whites but close to 100% in Native Americans and the Inuit. Affected incisors demonstrate prominent lateral margins, creating a hollowed lingual surface that resembles the scoop of a shovel (Fig. 2-65). Typically, the thickened marginal ridges converge at the cingulum; not uncommonly, a deep pit, fissure, or dens invaginatus is found at this junction. Maxillary lateral and central incisors most frequently are affected, with mandibular incisors and canines less commonly reported.

ENAMEL PEARLS: Enamel pearls are found most frequently on the roots of maxillary molars (mandibular molars are the second most frequent site). It is uncommon for maxillary premolars and incisors to be affected. Involvement of deciduous molars is not rare. The prevalence of enamel pearls varies (1.1% to 9.7% of all patients) according to the population studied and is highest in Asians. In most cases, one pearl is found, but as many as four pearls have been documented on a single tooth. The majority occur on the roots at the furcation area or near the cementoenamel junction (Fig. 2-73). Radiographically, pearls appear as well-defined, radiopaque nodules along the root’s surface (Fig. 2-74). Mature internal enamel pearls appear as well-defined circular areas of radiodensity extending from the dentinoenamel junction into the underlying coronal dentin.

The enamel surface of pearls precludes normal periodontal attachment with connective tissue, and a hemidesmosomal junction probably exists. This junction is less resistant to breakdown; once separation occurs, rapid loss of attachment is likely. In addition, the exophytic nature of the pearl is conducive to plaque retention and inadequate cleansing.

CERVICAL ENAMEL EXTENSIONS: As mentioned previously, cervical enamel extensions are located on the buccal surface of the root overlying the bifurcation (Fig. 2-75). Mandibular molars are affected slightly more frequently than maxillary molars. In reviews of extracted teeth in the lower 48 United States, the prevalence is surprisingly high, with approximately 20% of molars being affected. Similar studies demonstrate an even greater prevalence in other locations such as Japan, China, and Alaska, with cervical enamel extensions discovered in 50% to 78% of extracted molars. Cervical enamel extensions may occur on any molar, but they are seen less frequently on third molars. Because connective tissue cannot attach to enamel, these extensions have been correlated positively with localized loss of periodontal attachment with furcation involvement. On review of a large number of dentitions with periodontal furcation involvement, a significantly higher frequency of cervical enamel extensions was found compared with dentitions without furcation involvement. In addition, the greater the degree of cervical extension, the higher the frequency of furcation involvement.

In addition to periodontal furcation involvement, cervical enamel extensions (in some cases) have been associated with the development of inflammatory cysts that are histopathologically identical to inflammatory periapical cysts. The cysts develop along the buccal surface over the bifurcation and most appropriately are called buccal bifurcation cysts (see page 698). The association between cervical enamel extensions and this unique inflammatory cyst is controversial.

HYPOPLASTIC AMELOGENESIS IMPERFECTA: In patients with hypoplastic amelogenesis imperfecta, the basic alteration centers on inadequate deposition of enamel matrix. Any matrix present is mineralized appropriately and radiographically contrasts well with the underlying dentin. In the generalized pattern, pinpoint-to-pinhead–sized pits are scattered across the surface of the teeth and do not correlate with a pattern of environmental damage (Fig. 2-84). The buccal surfaces of the teeth are affected more severely, and the pits may be arranged in rows or columns. Staining of the pits may occur. Variable expressivity is seen within groups of affected patients. The enamel between the pits is of normal thickness, hardness, and coloration.

In the localized pattern, the affected teeth demonstrate horizontal rows of pits, a linear depression, or one large area of hypoplastic enamel surrounded by a zone of hypocalcification. Typically, the altered area is located in the middle third of the buccal surfaces of the teeth. The incisal edge or occlusal surface usually is not affected. Both dentitions (or only the primary teeth) may be affected. All the teeth may be altered, or only scattered teeth may be affected. When the involvement is not diffuse, the pattern of affected teeth does not correlate with a specific time in development. The autosomal recessive type (type IC) is more severe and typically demonstrates involvement of all teeth in both dentitions.

In the autosomal dominant smooth pattern, the enamel of all teeth exhibits a smooth surface and is thin, hard, and glossy (Fig. 2-85). The absence of appropriate enamel thickness results in teeth that are shaped like crown preparations and demonstrate open contact points. The color of the teeth varies from opaque white to translucent brown. Anterior open bite is not rare. Radiographically, the teeth exhibit a thin peripheral outline of radiopaque enamel. Often, unerupted teeth exhibiting resorption are seen.

The X-linked smooth pattern has been stated to arise from an X-linked dominant mutation and is a lesson in the lyonization effect. On approximately the sixteenth day of embryonic life in all individuals with two X chromosomes, one member of the pair is inactivated in each cell. As a result of this event, females are mosaics, with a mixture of cells, some with active maternal X chromosomes and others with active paternal X chromosomes. Usually the mix is of approximately equal proportions. If one X were to direct the formation of defective enamel and the other X were to form normal enamel, then the teeth would exhibit alternating zones of normal and abnormal enamel. Aldred and Crawford have argued against subdivision of X-linked amelogenesis imperfecta into dominant and recessive variants, because both heterozygous females and hemizygous males are affected regardless of the mutation being dominant or recessive. Although the intelligence of this suggestion is less evident in an X-linked dominant pattern of amelogenesis imperfecta, the argument is quite convincing when associated with the X-linked “recessive” hypomaturation pattern of amelogenesis imperfecta (see the discussion of the X-linked pattern of hypomaturation amelogenesis imperfecta on page 103).

Males with the X-linked smooth pattern exhibit diffuse thin, smooth, and shiny enamel in both dentitions. The teeth often have the shape of crown preparations, and the contact points are open. The color varies from brown to yellow-brown. Radiographs demonstrate a peripheral outline of radiopaque enamel. Unerupted teeth may undergo resorption. On the other hand, heterozygous females exhibit vertical furrows of thin hypoplastic enamel, alternating between bands of normal thickness. The banding often is detectable with dental radiographs. An open bite is seen in almost all males and in a minority of females.

In the rough pattern, the enamel is thin, hard, and rough-surfaced. As in the smooth forms, the teeth taper toward the incisal-occlusal surface and demonstrate open contact points (Fig. 2-86). The color varies from white to yellow-white. The enamel is denser than that seen in the smooth patterns, and the teeth are less vulnerable to attrition. Radiographs exhibit a thin peripheral outline of radiodense enamel. Unerupted teeth, often undergoing resorption, may be seen. An anterior open bite is common.

As the name implies, enamel agenesis demonstrates a total lack of enamel formation. The teeth are the shape and color of the dentin, with a yellow-brown hue, open contact points, and crowns that taper toward the incisal-occlusal surface. The surface of the dentin is rough, and an anterior open bite is seen frequently. Radiographs demonstrate no peripheral enamel overlying the dentin. A lack of eruption of many teeth with significant resorption frequently occurs.

Many investigators have difficulty subdividing the diffuse hypoplastic forms of amelogenesis imperfecta into categories such as smooth, rough, and enamel agenesis. In the autosomal recessive pattern of amelogenesis imperfecta previously termed enamel agenesis, the presence of a thin band of enamel has been confirmed in many affected patients. In addition, the separation between smooth and rough forms can be highly subjective and problematic. Therefore, some investigators have suggested discontinuation of these subdivisions and combining these phenotypic patterns into one category termed generalized thin hypoplastic amelogenesis imperfecta.

HYPOMATURATION AMELOGENESIS IMPERFECTA: In a person with hypomaturation amelogenesis im-perfecta, the enamel matrix is laid down appropriately and begins to mineralize; however, there is a defect in the maturation of the enamel’s crystal structure. Affected teeth are normal in shape but exhibit a mottled, opaque white-brown-yellow discoloration. The enamel is softer than normal and tends to chip from the underlying dentin. Radiographically, the affected enamel exhibits a radiodensity that is similar to dentin.

In the pigmented pattern the surface enamel is mottled and agar-brown. The enamel often fractures from the underlying dentin and is soft enough to be punctured by a dental explorer. Anterior open bite and unerupted teeth exhibiting resorption are uncommon. Occasionally, the surface enamel may be affected severely and be similar in softness to that of hypocalcified patterns. These cases often demonstrate extensive calculus deposition.

The X-linked pattern is another lesson in lyonization; however, the lyonization is not as obvious as that seen in the X-linked hypoplastic pattern. Although the mutation has been said to be recessive, hemizygous males and heterozygous females will demonstrate clinical changes. Affected males exhibit different patterns in the deciduous and permanent dentitions. The deciduous teeth are opaque white with a translucent mottling; the permanent teeth are opaque yellow-white and may darken with age (Fig. 2-87, A). The enamel tends to chip and often can be pierced with a dental explorer point. The degree of enamel loss is more rapid than that in normal teeth but does not approach that seen in the hypocalcified forms. Focal areas of brown discoloration may develop within the white opaque enamel. Radiographically, the contrast between enamel and dentin is reduced.

Heterozygous females exhibit a similar pattern in both dentitions. The teeth demonstrate vertical bands of white opaque enamel and translucent enamel; the bands are random and asymmetric (Fig. 2-87, B). The banding can be seen under regular lighting but is more obvious with transillumination. Radiographically, the bands are not perceptible, and the contrast between enamel and dentin is within normal limits. The obvious clinical evidence of the mutation in heterozygous females strongly argues for the pathosis to be designated as simply X-linked rather than X-linked recessive.

The snow-capped patterns exhibit a zone of white opaque enamel on the incisal or occlusal one quarter to one third of the crown (Fig. 2-88). The altered areas do not exhibit a distribution that would support an environmental origin, and the surface lacks the iridescent sheen seen with mild fluorosis. The affected teeth often demonstrate an anterior-to-posterior distribution and have been compared with a denture dipped in white paint (only affected anteriors, the anteriors back to the bicuspids, or the anteriors back to the molars). Both the deciduous and the permanent dentitions are affected. Most cases demonstrate an X-linked pattern of inheritance, but an autosomal dominant form is possible.

HYPOCALCIFIED AMELOGENESIS IMPERFECTA: In this type the enamel matrix is laid down appropriately but no significant mineralization occurs. In both patterns of hypocalcified amelogenesis imperfecta, the teeth are appropriately shaped on eruption, but the enamel is very soft and easily lost. On eruption the enamel is yellow-brown or orange, but it often becomes stained brown to black and exhibits rapid calculus apposition (Fig. 2-89). With years of function much of the coronal enamel is removed, except for the cervical portion that is occasionally calcified better. Unerupted teeth and anterior open bite are not rare. Both patterns are similar, but the autosomal recessive examples are generally more severe than the autosomal dominant cases. Radiographically, the density of the enamel and dentin are similar. Before eruption the teeth are normal in shape; however, after a period of function much of the cuspal enamel is lost, with the occlusal surface becoming the most irregular.

AMELOGENESIS IMPERFECTA WITH TAURODONTISM (HYPOMATURATION/HYPOPLASTIC AMELOGENESIS IMPERFECTA): This type of amelogenesis imperfecta exhibits enamel hypoplasia in combination with hypomaturation. The deciduous and the permanent dentitions are diffusely involved. Historically, two patterns have been recognized that are similar but differentiated by the thickness of the enamel and the overall tooth size. When studying a single kindred, phenotypic variation is seen that would place members of the same family in both divisions; therefore, many believe these divisions should be joined into one phenotype termed merely amelogenesis imperfecta with taurodontism.

In the presentation known as the hypomaturation-hypoplastic pattern, the predominant defect is one of enamel hypomaturation in which the enamel appears as mottled yellow-white to yellow-brown. Pits are seen frequently on the buccal surfaces of the teeth. Radiographically, the enamel appears similar to dentin in density, and large pulp chambers may be seen in single-rooted teeth in addition to varying degrees of taurodontism.

In the hypoplastic-hypomaturation pattern, the predominant defect is one of enamel hypoplasia in which the enamel is thin but also hypomature. Except for the decrease in the thickness of the enamel, this pattern is radiographically similar to the hypomaturation-hypoplastic variant.

A pattern of teeth alteration similar to amelogenesis imperfecta with taurodontism is seen in the systemic disorder, tricho-dento-osseous syndrome. This autosomal dominant disorder is mentioned here because the diagnosis may not be readily apparent without a high index of suspicion (Fig. 2-90). In addition to the dental findings, the predominant systemic changes are present variably and include kinky hair, osteosclerosis, and brittle nails. The kinky hair is present at birth but may straighten with age. The osteosclerosis primarily affects the base of the skull and the mastoid process. The mandible often exhibits a shortened ramus and an obtuse angle.

Some authors have suggested that amelogenesis imperfecta with taurodontism may represent partial expression of the tricho-dento-osseous syndrome. Recent studies have identified distinctly different gene mutations that are responsible for tricho-dento-osseous syndrome and amelogenesis imperfecta with taurodontism. However, other investigators dispute this fact, showing evidence that some examples of this pattern of amelogenesis imperfecta appear allelic (different mutation on the same gene) to the syndrome. If only dental changes are seen in the absence of hair or bone changes, either in the individual or within the family, then the diagnosis of amelogenesis imperfecta appears appropriate.

DENTIN DYSPLASIA TYPE I: Dentin dysplasia type I (radicular dentin dysplasia), has been referred to as rootless teeth, because the loss of organization of the root dentin often leads to a shortened root length. The process exhibits an autosomal dominant pattern of inheritance and an approximate prevalence of 1:100,000. The enamel and coronal dentin are normal clinically and well formed (Fig. 2-97), but the radicular dentin loses all organization and subsequently is shortened dramatically (Fig. 2-98). Wide variation in root formation is produced because dentinal disorganization may occur during different stages of tooth development. If the dentin organization is lost early in tooth development, markedly deficient roots are formed; later disorganization results in minimal root malformation. The variability is most pronounced in permanent teeth and may vary not only from patient to patient but also from tooth to tooth in a single patient. Because of the shortened roots, the initial clinical signs are extreme tooth mobility and premature exfoliation, spontaneously or secondary to minor trauma. Less frequently, delayed eruption is the presenting symptom. The strength of the radicular dentin is reduced, with the teeth being predisposed to fracture during extractions.

Radiographically, the deciduous teeth often are affected severely, with little or no detectable pulp, and roots that are markedly short or absent. The permanent teeth vary according to the proportion of organized versus disorganized dentin (Fig. 2-99). Several years ago, a subclassification of dentin dysplasia type I was proposed and has become widely accepted (Box 2-11).

In general, the teeth without root canals are those that frequently develop periapical radiolucencies without obvious cause (see Fig. 2-98). The radiolucencies represent periapical inflammatory disease and appear secondary to caries or spontaneous coronal exposure of microscopic threads of pulpal remnants present within the defective dentin. The subclassification system has proven to be beneficial, because it assists in highlighting the mild DDId variant that often is not quickly recognized as dentin dysplasia and can be confused with dentin dysplasia type II. On occasion, reports have demonstrated patients with classic DDId-like involvement of the anteriors and bicuspids but without affected molars.

A similar but unrelated disorder is fibrous dysplasia of dentin. This autosomal dominant disorder exhibits teeth that are normal clinically. Radiographically the teeth are normal in shape but demonstrate a radiodense product filling the pulp chambers and canals. In contrast to dentinogenesis imperfecta, small foci of radiolucency can be seen in the pulp. In contrast to dentin dysplasia type I, no crescent pulp chambers and no decrease in root length are seen. The radiodense intrapulpal material consists of fibrotic dentin.

DENTIN DYSPLASIA TYPE II: Dentin dysplasia type II (coronal dentin dysplasia) is inherited as an autosomal dominant hereditary disorder that exhibits numerous features of dentinogenesis imperfecta. In contrast to dentin dysplasia type I, the root length is normal in both dentitions. The deciduous teeth closely resemble those of dentinogenesis imperfecta. Clinically, the teeth demonstrate a blue-to-amber-to-brown translucence. Radiographically, the dental changes include bulbous crowns, cervical constriction, thin roots, and early obliteration of the pulp. The permanent teeth demonstrate normal clinical coloration; however, radiographically, the pulp chambers exhibit significant enlargement and apical extension. This altered pulpal anatomy has been described as thistle tube–shaped or flame-shaped (Figs. 2-100 and 2-101). Pulp stones develop in the enlarged pulp chambers.

A similar but unrelated disorder is pulpal dysplasia. This process develops in teeth that are normal clinically. Radiographically, both dentitions exhibit thistle tube–shaped pulp chambers and multiple pulp stones.