tooth enamel is the most highly mineralized structure in the human body , with 85% of its volume occupied by hydroxyapatite crystals .
the physical properties and physiological function of enamel are directly related to the composition , orientation , disposition , and morphology of the mineral components within the tissue . during organogenesis ,
the enamel transitions from a soft and pliable tissue to its final form , which is almost entirely devoid of protein .
the final composition of enamel is a reflection of the unique molecular and cellular activities that take place during its genesis .
amelogenesis imperfecta ( ai ) encompasses a complicated group of conditions that demonstrate developmental alterations in the structure of the enamel in the absence of a systemic disorder .
the prevalence of this condition has been expected to range from 1 in 718 to 1 in 14,000 , depending on the population studied .
hypoplastic ai represents 60  73% of all cases , hypomaturation ai represents 20  40% , and hypocalcification ai represents 7% .
weinmann et al . , 1945 , subdivided amelogenesis imperfecta into hypoplastic and hypocalcified types .
several classifications have evolved since then , with at least ten subtypes , characterized by clinical features and mode of inheritance .
two x - linked phenotypic variants of amelogenesis imperfecta have been included in these classifications  a hypoplastic form and a hypomaturation form .
witkop and sauk listed the varieties of ai , divided according to whether the abnormality lay in a reduced amount of enamel ( hypoplasia ) , deficient calcification ( hypocalcification ) , or imperfect maturation of the enamel ( hypomaturation ) , and also recognized the combined defects [ table 1 ] .
classification of amelogenesis imperfecta ( witkop and sauk ) the inheritance pattern of x - linked disorders dictates that male - to - male transmission can not occur .
affected females have a 50% probability of passing on the trait to the offspring of either sex .
the most striking feature of both these conditions is that there are different manifestations between affected females and affected males . in the hypoplastic form ,
females show vertical ridging of the enamel , whereas , in males there is uniform hypoplasia . in the hypomaturation form ,
males have teeth of normal size and shape , but with irregular , pigmented mottling .
females display vertical bands of mottling , often inconspicuous under normal lighting conditions . in both types ,
this phenomenon in females represents lyonization , where alternating groups of ameloblasts are under the control of either the abnormal or the normal gene .
many authors have ascribed to haldane , the recognition of amelogenesis imperfecta as the first x - linked 
his proposition was based on one of the pedigrees presented in an earlier report by bampton on  hereditary dental pigmentation . 
the oldest reported case of vertically wrinkled dental enamel is that found in the skeletal remains of an american indian child , thought to date from ad 1100 .
the first clear descriptions of x - linked hypoplastic ai were those of schulze and lenz and schulze , who recognized the different manifestations in affected males and females .
this was confirmed and expanded upon by schulze in a monograph , detailing families from a geographically discrete area in germany .
witkop included an x - linked recessive hypomaturation form in his early classification of ai , in which the affected males showed mottling of the enamel .
he observed that clinical enamel involvement could be recognized in ( carrier ) females under specific examination conditions .
winter and brook described  x - linked recessive hypomaturation amelogenesis imperfecta ,  and reported the enamel to be of normal thickness and relatively soft , so that the surface could be penetrated with a sharp probe .
severe attrition was a feature , especially on premolars and molars and the palatal aspects of the upper anterior teeth of males .
a kindred with  x - linked recessive hypomaturation amelogenesis imperfecta  was presented by haug and ferguson .
however , the clinical description of teeth in females mentioned  vertical striations in every crown , consisting of voids and wrinkles interspersed between areas of normal enamel .
 this enamel was also softer than normal with marked abrasion , discolored , yellow to brown , with the cervical enamel of the posterior teeth less involved than the enamel of the incisors .
witkop and stewart noted that ( in the hypomaturation form ) the mottled yellow - white color of the permanent teeth could darken with absorption of stains .
in severely affected boys , the enamel of permanent teeth was slightly thinner than normal , with the cervical enamel tending to be better formed , whereas , in girls both primary and permanent teeth showed alternating bands of white opaque , and normal translucent enamel .
witkop observed that the inheritance pattern of the variant of ai referred to as snowcapped teeth was not clear .
escobar et al . , suggested that this form was x - linked in its inheritance , and in his article , witkop seemed to accept snowcapped teeth as an x - linked trait .
he also raised the possibility of an autosomal dominant form . in a pedigree with snowcapped teeth , seen by crawford and aldred , 1992 ,
histopathological examination confirms that when enamel hypoplasia is the predominant clinical finding , the enamel is reduced in thickness .
areas of homogeneous aprismatic enamel or fused indistinct prisms are seen , with  a reduction in the distance between enamel rod incremental lines ,  where any enamel rod can be identified .
, showed that the most marked defects in the enamel were seen in the outer half .
ground sections showed voids within the enamel , obliterating several rods ( prisms ) . in the deeper enamel and the surface enamel ,
( with no mention of discrete channels ) adjacent to the enamel - dentin junction in two teeth from a female with x - linked hypoplastic ai . except for the ridged hypoplasia
, from an affected male ( categorized as x - linked recessive hypoplastic ) showed marked 
demineralization  of the enamel close to the enamel - dentin junction , with channels of demineralization extending to the enamel surface .
although demineralization is a term usually applied to a posteruptive pathological change , this was not suggested to be the case here . under light microscopy ,
mclarty et al .. found irregular spaces running from the enamel - dentin junction outward in a male considered to have x - linked hypomaturation amelogenesis imperfecta .
some of these consisted of tube - like structures that ended in a peripheral expansion . although the descriptions of the enamel in the reports of mclarty et al . , and haug and ferguson are consistent with a hypomineralization defect , the additional finding of enamel wrinkling in the females indicates some degree of hypoplasia .
the observations of darling suggest that although the wrinkled surface enamel corresponding to the hypoplastic form of x - linked amelogenesis imperfecta may appear to be normally hard , there might be poorly mineralized enamel in the deeper portions .
schulze recorded that the teeth could be yellow , yellow - red , or yellow - brown .
it may be that the discoloration , evident in the enamel of some families reported as hypoplastic x - linked amelogenesis imperfecta , also indicates some degree of hypomineralization .
it is difficult otherwise to explain the abnormal color and / or lucency of this tissue .
amelogenesis imperfecta ( ai ) encompasses a complicated group of conditions that demonstrate developmental alterations in the structure of the enamel in the absence of a systemic disorder .
the prevalence of this condition has been expected to range from 1 in 718 to 1 in 14,000 , depending on the population studied .
hypoplastic ai represents 60  73% of all cases , hypomaturation ai represents 20  40% , and hypocalcification ai represents 7% .
weinmann et al . , 1945 , subdivided amelogenesis imperfecta into hypoplastic and hypocalcified types .
several classifications have evolved since then , with at least ten subtypes , characterized by clinical features and mode of inheritance .
two x - linked phenotypic variants of amelogenesis imperfecta have been included in these classifications  a hypoplastic form and a hypomaturation form .
witkop and sauk listed the varieties of ai , divided according to whether the abnormality lay in a reduced amount of enamel ( hypoplasia ) , deficient calcification ( hypocalcification ) , or imperfect maturation of the enamel ( hypomaturation ) , and also recognized the combined defects [ table 1 ] .
classification of amelogenesis imperfecta ( witkop and sauk ) the inheritance pattern of x - linked disorders dictates that male - to - male transmission can not occur .
affected females have a 50% probability of passing on the trait to the offspring of either sex .
the most striking feature of both these conditions is that there are different manifestations between affected females and affected males . in the hypoplastic form ,
females show vertical ridging of the enamel , whereas , in males there is uniform hypoplasia . in the hypomaturation form ,
males have teeth of normal size and shape , but with irregular , pigmented mottling .
in both types , this phenomenon in females represents lyonization , where alternating groups of ameloblasts are under the control of either the abnormal or the normal gene .
many authors have ascribed to haldane , the recognition of amelogenesis imperfecta as the first x - linked 
his proposition was based on one of the pedigrees presented in an earlier report by bampton on  hereditary dental pigmentation . 
the oldest reported case of vertically wrinkled dental enamel is that found in the skeletal remains of an american indian child , thought to date from ad 1100 .
the first clear descriptions of x - linked hypoplastic ai were those of schulze and lenz and schulze , who recognized the different manifestations in affected males and females .
this was confirmed and expanded upon by schulze in a monograph , detailing families from a geographically discrete area in germany .
witkop included an x - linked recessive hypomaturation form in his early classification of ai , in which the affected males showed mottling of the enamel .
he observed that clinical enamel involvement could be recognized in ( carrier ) females under specific examination conditions . winter and
brook described  x - linked recessive hypomaturation amelogenesis imperfecta ,  and reported the enamel to be of normal thickness and relatively soft , so that the surface could be penetrated with a sharp probe .
severe attrition was a feature , especially on premolars and molars and the palatal aspects of the upper anterior teeth of males .
a kindred with  x - linked recessive hypomaturation amelogenesis imperfecta  was presented by haug and ferguson .
however , the clinical description of teeth in females mentioned  vertical striations in every crown , consisting of voids and wrinkles interspersed between areas of normal enamel .
 this enamel was also softer than normal with marked abrasion , discolored , yellow to brown , with the cervical enamel of the posterior teeth less involved than the enamel of the incisors .
witkop and stewart noted that ( in the hypomaturation form ) the mottled yellow - white color of the permanent teeth could darken with absorption of stains . in severely affected boys ,
the enamel of permanent teeth was slightly thinner than normal , with the cervical enamel tending to be better formed , whereas , in girls both primary and permanent teeth showed alternating bands of white opaque , and normal translucent enamel .
witkop observed that the inheritance pattern of the variant of ai referred to as snowcapped teeth was not clear .
, suggested that this form was x - linked in its inheritance , and in his article , witkop seemed to accept snowcapped teeth as an x - linked trait .
he also raised the possibility of an autosomal dominant form . in a pedigree with snowcapped teeth , seen by crawford and aldred , 1992 ,
histopathological examination confirms that when enamel hypoplasia is the predominant clinical finding , the enamel is reduced in thickness .
areas of homogeneous aprismatic enamel or fused indistinct prisms are seen , with  a reduction in the distance between enamel rod incremental lines ,  where any enamel rod can be identified .
, showed that the most marked defects in the enamel were seen in the outer half .
 ground sections showed voids within the enamel , obliterating several rods ( prisms ) . in the deeper enamel and the surface enamel ,
( with no mention of discrete channels ) adjacent to the enamel - dentin junction in two teeth from a female with x - linked hypoplastic ai . except for the ridged hypoplasia
microradiographs of deciduous molar teeth presented by backman et al . , from an affected male ( categorized as x - linked recessive hypoplastic ) showed marked 
demineralization  of the enamel close to the enamel - dentin junction , with channels of demineralization extending to the enamel surface .
although demineralization is a term usually applied to a posteruptive pathological change , this was not suggested to be the case here . under light microscopy , mclarty et al .. found irregular spaces running from the enamel - dentin junction outward in a male considered to have x - linked hypomaturation amelogenesis imperfecta .
some of these consisted of tube - like structures that ended in a peripheral expansion . although the descriptions of the enamel in the reports of mclarty et al . ,
and haug and ferguson are consistent with a hypomineralization defect , the additional finding of enamel wrinkling in the females indicates some degree of hypoplasia .
the observations of darling suggest that although the wrinkled surface enamel corresponding to the hypoplastic form of x - linked amelogenesis imperfecta may appear to be normally hard , there might be poorly mineralized enamel in the deeper portions .
schulze recorded that the teeth could be yellow , yellow - red , or yellow - brown .
it may be that the discoloration , evident in the enamel of some families reported as hypoplastic x - linked amelogenesis imperfecta , also indicates some degree of hypomineralization .
it is difficult otherwise to explain the abnormal color and / or lucency of this tissue .
an 11-year - old girl reported to the department of pedodontics and preventive dentistry , dr . d.y .
patil dental college and hospital , pune , with the chief complaint of discolored teeth since childhood .
this little girl 's parents did not seek any treatment previously , thinking that since the condition was not resulting in any other systemic manifestations and since she had inherited the condition from her father , there was little they could really do about it and accepted it as part of her appearance .
it was only now , when they realized that the girl avoided hard food substances , they got her to a dentist .
on enquiry , it was revealed that her deciduous teeth were also similarly discolored , and her father , younger brother of eight years , and younger sister of six years , also suffered from the same condition .
pedigree chart for the case apart from this , her past medical history was noncontributory .
, she had been avoiding hard food substances ; at the same time , remaining caries free , except for a sole proximal carious lesion in 36 , involving the enamel and dentin . on intraoral examination , it was found that she had a normal complement of teeth .
the thickness of enamel was reduced on the teeth and was completely chipped off from some teeth exposing the dentin .
the teeth , in general , exhibited a yellowish brown discoloration , with diffuse pitting present on the exposed tooth surfaces , more prominent on the labial and buccal aspects .
examination of the periodontium revealed the presence of chronic , generalized , marginal , and papillary gingivitis , with calculus deposition and unsatisfactory oral hygiene [ figures 24 ] .
view of the labial surfaces of teeth maxillary occlusal view mandibular occlusal view a provisional diagnosis of hypoplastic , rough autosomal dominant ai was proposed along with a differential diagnosis of environmental enamel hypoplasia , dentinogenesis imperfecta , dentin dysplasia , regional odontodysplasia , and the tricho - dento - osseous syndrome .
radiographic investigations included an orthopantomogram ( opg ) and full mouth intraoral periapical ( iopa ) radiographs .
the opg showed the presence of all unerupted third molars , as well as a seemingly normal pattern and timing of eruption of teeth [ figure 5 ] .
examination of the iopa radiographs revealed a normal pulp chamber and root canal spaces with no signs of obliteration .
the enamel was almost half its expected thickness , but was more radiodense than the dentin .
the ground section of an over - retained deciduous molar extracted from the girl showed that the enamel was thin and was composed of laminations of irregularly arranged enamel prisms .
figure 7 shows a ground section of a normal tooth , where regularly arranged enamel prisms along with the normal thickness of enamel can be appreciated [ figure 7 ] .
ground section of affected tooth ground section of normal tooth the diagnosis of hypoplastic , rough , autosomal dominant ai was confirmed on the basis of typical , clinical , radiographic , and histopathological features .
esthetics along with functional limitations were the reason the patient 's parents brought her to the hospital for treatment .
the treatment proposed for her ranged from bonded veneer restorations to tooth preparations for the placement of a full crown .
restoration of the carious lesion in 36 would be accompanied by a full coverage restoration .
the coronal pulp in these children tends to recede faster than in normal teeth and hence crown preparations for full coverage crowns can often be done for relatively young patients .
regular brushing of the teeth using the modified bass technique was taught to the patient to be practiced twice a day ( morning and at night before going to bed ) using a soft toothbrush and a fluoridated toothpaste ( containing 1000 ppm of available fluoride ) followed by rinsing with 2% w / v of chlorhexidine gluconate for 15 days .
it usually occurs in the absence of systemic features and comprises of diverse phenotypic entities .
the predominant clinical manifestations of affected individuals are enamel hypoplasia ( enamel is seemingly correctly mineralized , but thin ) , hypomineralization ( subdivided into hypomaturation and hypocalcification ) , or a combined phenotype , which is seen in most cases . the trait of ai can be transmitted by an autosomal - dominant , autosomal - recessive , or x - linked mode of inheritance .
the distribution of ai types is known to vary among different populations . in a study in sweden ,
in contrast , in a study in the middle east , the most common prevalent type of ai was found to be autosomal - recessive .
the use of  recessive ,  in his terminology  x - linked recessive amelogenesis imperfecta ,  could be because the females were thought to be unaffected .
prompted by the presentation of a third proband , he was subsequently able to re - examine the females of one of the two initial families under adequate lighting conditions that revealed  alternating vertical bands of mottled white hypomature enamel separated by normal - appearing enamel  .
this appearance does have similarities to the cases reported by mclarty et al . and haug and ferguson , that is , an apparent hypomineralization together with vertical hypoplasia of the enamel .
weinmann et al . , subdivided ai into hypoplastic and hypocalcified types , a distinction that has persisted into most subsequent classifications .
such a differentiation may have a greater basis in clinical judgment , with its emphasis on perceived phenotype , than in the histological fact , and may account for some of the apparent discrepancies in terminology in the literature relating to x - linked amelogenesis imperfecta .
linkage studies have hitherto placed the disease on the distal short arm of the x chromosome , and further recombinant dna investigations will enable us to distinguish between an apparent simple hypoplastic form , a hypoplastic and hypomineralized form , and a pure hypomaturation form .
some of the genes encoding the specific enamel proteins have been indicated as candidate genes for ai .
the amelogenin gene is a tooth - specific gene expressed in pre - ameloblasts , ameloblasts , and in the epithelial root sheath remnants ; while a low - expression of amelogenin mrnas has been recently shown in odontoblasts . to date
the enamelin ( enam ) gene is a tooth - specific gene expressed predominantly by the enamel organ , and , at a low level , in odontoblasts .
one autosomal - inherited form of ai , namely , autosomal - dominant amelogenesis imperfecta ( adai ) , was linked to a 4 mb region on 4q21 .
the enam gene has been mapped within this locus by radiation hybrid analysis ( rha ) and fluorescent in situ hybridization ( fish ) , and was therefore considered a candidate gene for this type of ai . the work of kim et al .
further relates phenotype to genotype and identifies a mid - crown , horizontal form of genetically determined hypoplasia .
enamel phenotypes of enam mutations may be dose - dependent , with generalized hypoplastic ai segregating as a recessive trait and localized enamel pitting segregating as a dominant trait .
the ameloblastin ( ambn ) gene is expressed at high levels by ameloblasts and at low levels by odontoblasts and pre - odontoblasts , while moderate expression is also observed in hertwig 's epithelial root sheath , and in odontogenic tumors , such as in ameloblastomas .
the human ambn is localized on chromosome 4 at locus 4q21 , near other genes associated with the mineralized tissues : osteopontin , bone sialoprotein , and bone morphogenetic protein 3 .
ambn maps within the critical region for autosomal - dominant ai , and is therefore considered as a candidate gene . however , it was excluded from a causative role by mutational analyses within the families studied by mrdh - krrman c et al . the amelotin gene ( amelotin 4q13 ) has been reported by iwasaki et al . , 2005 , to play a role in the molecular interaction during amelogenesis .
however , so far no mutation of the amelotin gene has been related to ai .
the klk4 gene is located near the telomere of chromosome 19 ( 19q13.3  19q13.4 ) downstream of the klk2 gene , and is considered a member of the human tissue kallikrein gene family .
klk4 is expressed by both ameloblasts and odontoblasts . on account of the abnormal enzymic activity
, the crystallites of the enamel grow to the normal length , but not completely in thickness .
the mmp-20 gene codes for a calcium - dependent proteinase that is a member of the matrix metallopeptidases family ( mmps ) .
additionally , no other intact , physiologically normal , tissue has been demonstrated to express mmp-20 , apart from ameloblasts , pre - ameloblasts , and odontoblasts , whereas , the expression of mmp-20 in human odontogenic tumors and carcinoma cell lines originating from the tongue has recently been described .
q23 , has been described as being associated with autosomal recessive pigmented hypomaturation amelogenesis imperfecta .
the dlx3 gene is a member of the family of homeobox genes that are homologous to the distalless ( dll ) gene of drosophila , known to be expressed during development of the chondrocranium , dermatocranium , sensory organs , brain , limbs , and appendages , and in the processes of osteogenesis and hematopoiesis .
mutation within the human dlx3 gene homeodomain is associated with ai ( hypoplastic - hypomaturation type ) , with taurodontism ( aihht ) .
dong et al . , 2005 , suggest that the tricho - dento - osseous syndrome ( tdo ) and amelogenesis imperfecta hypoplastic - hypomaturation with taurodontism ( aihht ) are allelic for dlx3 .
however , amelx , ambn , enam , klk4 , and mmp-20 were excluded from a causative role in two families with autosomal - dominant hypocalcified ai , suggesting that this type of ai is caused by the mutation of a gene that is either not known or not considered to be a major contributor to enamel formation .
mutations in the amelogenin gene ( amelx ) cause x - linked amelogenesis imperfecta , while mutations in the enamelin gene ( enam ) cause autosomal - inherited forms of amelogenesis imperfecta .
recent reports involve kallikrein-4 ( klk4 ) , mmp-20 , and dlx3 genes in the etiologies of some cases . as in all genetic diseases
, the final classification will be based on genetic mutation and the resulting biochemical abnormality in each family .
several investigators have suggested a classification system based on the phenotype and pedigree , combined with a scanning electron microscopic examination , biochemical methods , and molecular genetics .
histologically , a ground section of the teeth involved showed very thin enamel , composed of laminations of irregularly arranged enamel prisms .
the sem studies of the extracted deciduous teeth , in a case of autosomal recessive rough hypoplastic amelogenesis imperfecta , showed an exposed outer enamel surface , with irregularly shaped globular protrusions . at the cervical region of the crown ,
the cementum area was clearly distinguishable from the more coronal region by its mottled and fibrillar pattern , and the tendency for the cementum to overlap the ridged coronal structure along the cervical line .
the dentinoenamel junction was sharply defined and easily identifiable because of the more homogenous appearance of the enamel matrix , as compared with that of the dentin , with its array of collagen fibrils .
the histology of autosomal dominant hypomaturation - hypoplasia type of ai with taurodontism , definitively described by winter et al . , comprised of areas of severe hypomineralization with a pore volume of between 1 and 25% .
they described a normal prismatic structure to the enamel , but with considerable post - calcification organic content and occasional bands of globular defects .
the dentin was also reported as being defective , with a decreased number of tubules , an increased amount of intertubular dentin , dilatations , and cellular inclusions .
the varying etiology of ai conjures a wide array of clinical features whose restorative management poses a challenge for dentists .
as both esthetics and function are compromised in these patients , their management usually involves complete oral rehabilitation by way of full coverage crowns , direct and indirect veneers , and bonded esthetic restorations , depending on the condition of the individual tooth and the age of the patient .
types i d , ie , ig , iia , iiia , iiib , and ivb demonstrate very thin enamel or highly defective enamel , which leads to rapid attrition .
if the treatment is delayed , a loss of usable crown length occurs . in those patients without sufficient crown lengths , full dentures ( overdentures in some cases ) ; often become the only satisfactory approach .
the other types of ai demonstrate less rapid tooth loss , and the esthetic appearance is the prime consideration . in some cases
a lack of good enamel bonding of veneers occurs and does not result in a durable restoration .
several investigators have suggested a classification system for amelogenesis imperfecta , based on the phenotype and pedigree combined with scanning electron microscopic examination , biochemical methods , and molecular genetics .
thus the dentist has to diagnose the condition as early as possible to offer early intervention and balance the decision for early intervention and long - term survival of the restorations .
dental practitioners should consider the social implications for these patients and intervene to relieve their suffering .
thus , this article is an attempt to improve the clinician 's knowledge about the clinical diagnosis as well as intervention required for such a condition .
 amelogenesis imperfecta ( ai ) is a diverse collection of inherited diseases that exhibit quantitative or qualitative tooth enamel defects in the absence of systemic manifestations . 
 also known by varied names such as hereditary enamel dysplasia , hereditary brown enamel , hereditary brown opalescent teeth , this defect is entirely ectodermal , since mesodermal components of the teeth are basically normal . 
 the ai trait can be transmitted by either autosomal dominant , autosomal recessive , or x - linked modes of inheritance . 
 genes implicated in autosomal forms are genes encoding enamel matrix proteins , namely : enamelin and ameloblastin , tuftelin , mmp-20 and kallikrein  4 . 
 this article presents a case reported to dr . 
 d. y. patil , dental college and hospital , pune , india , along with a review of this often seen clinical entity . 
INTRODUCTION
Review of Literature
CASE REPORT
DISCUSSION
CONCLUSION