第五章牙齿发有异常 Dental development anomalies 儿童口腔医学教研室 胡 讲课时间：2019年10月17日 [掌握]多生牙、个别牙缺失的临床表现、诊断方法、治疗原则：畸形中央尖、畸形活侧窝、 畸形活侧尖、过大牙、过小牙、融合牙、牙齿早萌、迟萌、第一恒磨牙异位萌出、 到牙带留的诊断及临床处理原则：釉质发育不全、四环素牙、氟牙定的形成原因及 特点。 [熟悉]外胚叶发有不全、牙瘤的临床特征及其治疗原则：结合牙、双生牙、弯曲牙、牛牙 [了解]牙齿发有异常的病因：牙本质发有不全的临床特征、遗传性乳光牙本质的遗传方式。 At the outset,we would wish to record both our personal and professional gratitude to the late Professor GB(Gerry)Winter.He always encouraged our work and was all,he was anenthusiast 1.I INTRODUCTION Both the primary and permanent dentitions may be affected by variations in the umber,size.and form of the teethas well as the structure of the dental hard tisse These variations may be excusively genetically.brought about byh ocal or systemically acting environmental factors,or possibly from a combination of both genetic and environmental factors acting together.The same interplay of nfluences may affect the primary teethas well as the eruption of permanent teeth This chapter considers a range of conditions involving abnormalities of the number.size.form.and structure of teeth and their eruption. It is important to be aware of the psycho-social aspect when meeting children and families affected by these conditions We have to often heard stories of social onof even very young childrenasaresult of their missing or teeth In the case of discoloured teeth,parents have told us that they have been 'taken to task by other adults for not looking after'their child's teeth-when the discolouration was eritd condtio it ismorant tour bohe family tree equally.Not only does this ensure that the investigation is complete.but it may also help to alleviate the sense of 'guilt'felt by an affected parent. Wherever possible,we try to avoid theuse of the word normal'care although the word will be used in this text.Clinically we would speak-when offering restorative treatment for example of making a smile 'ordinary,or 'boring.The vast
第五章 牙齿发育异常 Dental development anomalies 儿童口腔医学教研室 胡赟 讲课时间：2019 年 10 月 17 日 [掌握] 多生牙、个别牙缺失的临床表现、诊断方法、治疗原则；畸形中央尖、畸形舌侧窝、 畸形舌侧尖、过大牙、过小牙、融合牙、牙齿早萌、迟萌、第一恒磨牙异位萌出、 乳牙滞留的诊断及临床处理原则；釉质发育不全、四环素牙、氟牙症 的形成原因及 特点。 [熟悉] 外胚叶发育不全、牙瘤的临床特征及其治疗原则；结合牙、双生牙、弯曲牙、牛牙 症的临床特征；诞生牙、上皮珠、乳磨牙固连诊断及临床处理原则；釉质发育不全、 氟牙症的处理原则及其预防。 [了解] 牙齿发育异常的病因；牙本质发育不全的临床特征、遗传性乳光牙本质的遗传方式。 Dental development anomalies 1.0 ACKNOWLEDGEMENT At the outset, we would wish to record both our personal and professional gratitude to the late Professor GB (Gerry) Winter. He always encouraged our work and was generous in his comments and sharing of material. Above all, he was an enthusiast and a champion of his patients. He is missed. 1.1 INTRODUCTION Both the primary and permanent dentitions may be affected by variations in the number, size, and form of the teeth, as well as the structure of the dental hard tissues. These variations may be exclusively genetically determined, brought about by either local or systemically acting environmental factors, or possibly from a combination of both genetic and environmental factors acting together. The same interplay of influences may affect the eruption and exfoliation of primary teeth, as well as the eruption of permanent teeth. This chapter considers a range of conditions involving abnormalities of the number, size, form, and structure of teeth and their eruption. It is important to be aware of the psycho-social aspect when meeting children and families affected by these conditions. We have too often heard stories of social isolation of even very young children as a result of their missing or discoloured teeth. In the case of discoloured teeth, parents have told us that they have been 'taken to task' by other adults for 'not looking after' their child's teeth⎯when the discolouration was intrinsic and unavoidable. While investigating inherited conditions, it is important to enquire both sides of the family tree equally. Not only does this ensure that the investigation is complete, but it may also help to alleviate the sense of 'guilt' felt by an affected parent. Wherever possible, we try to avoid the use of the word 'normal' in our clinical care although the word will be used in this text. Clinically we would speak⎯when offering restorative treatment for example ⎯ of making a smile 'ordinary', or 'boring'. The vast
maiority of children with these conditions want to become 'one of the crowd'We ther the care of these children. We have been questioned repeatedly about the possibility of genetic treatment for some of these inherited conditions.We are not aware of any progress in this direction at present,outside the laboratory. 1.2 MISSING TEETH 1.2.0Introductio Hypodontia is the term most often applied toa situation where a patient has missing teeth as a result of their failure of development.Anodontia describes the total lack o teeth ofone or both dentitions.Oligodontia is aterm used to describe a situation where multiple-usually more than six-teeth are missing 1.1 Prevalence nthe primary dentition,missing more commony in the maxilla and typically the maxillary lateral incisor is the tooth involved.Various studies have shown the prevalence of missing primary teeth to be between 0.1 and 0.9%of Caucasian populations,with males and females affected equally.Developmentally nent teeth are seen in both the maxilla and mandible.In populations the the mst followed by the mandibular second premolar,the maxillary lateral incisor,and the maxillary second premolar.A female to male ratio of 4:1 has been reported.Missing third molars occur in90%of individuals If the third molars are excluded,the prevalence in the permanent varies between .%and65%according to the study Hypodontia .0.1-0.9%in the primary dentition; 3.5-6.5%in the permanent dentition Missing perm anent teeth are een n30-0%of patients who have missing primary tecth 1.2.2Aetiology The cause of an isolated missing tooth is often unclear:this may be genetic in origin or associated with some environmental insult during development.Missing teeth have been reported in association with multiple births,low birth weight,and increased matea Rubellaand thalidomide embryopathies may also be iated with missing teeth Single gene disorders have been associated with missing teeth.Multiple missing teeth as well as teeth with small crowns,may be seen in a number of syndromes including X-linked hypohidrotic ectodermal dysplasia autosomal dominant and autosomalr dysplasia and auto omal recessive chondroectodermal ysplasia (Ellis-van Creveld syndrome).Down syndrome (trisomy 21)is also associated with hypodontia. Hypodontia and microdontia involving the maxillary lateral incisor occurs in clefts involving the lip and palate
majority of children with these conditions want to become 'one of the crowd'. We have found this approach successful in our practices; our readers may choose this or one of many other approaches in order to further the care of these children. We have been questioned repeatedly about the possibility of genetic treatment for some of these inherited conditions. We are not aware of any progress in this direction at present, outside the laboratory. 1.2 MISSING TEETH 1.2.0 Introduction Hypodontia is the term most often applied to a situation where a patient has missing teeth as a result of their failure of development. Anodontia describes the total lack of teeth of one or both dentitions. Oligodontia is a term used to describe a situation where multiple⎯usually more than six⎯teeth are missing. 1.2.1 Prevalence In the primary dentition, missing teeth occur more commonly in the maxilla and typically the maxillary lateral incisor is the tooth involved. Various studies have shown the prevalence of missing primary teeth to be between 0.1 % and 0.9 % of Caucasian populations, with males and females affected equally. Developmentally missing permanent teeth are seen in both the maxilla and mandible. In Caucasian populations the third molars are the most commonly missing teeth, followed by the mandibular second premolar, the maxillary lateral incisor, and the maxillary second premolar. A female to male ratio of 4 : 1 has been reported. Missing third molars occur in 9-30% of individuals. If the third molars are excluded, the prevalence in the permanent varies between 3.5 % and 6.5 % according to the study quoted. Key Points • Hypodontia • 0.1-0.9% in the primary dentition; • 3.5-6.5% in the permanent dentition; • Missing permanent teeth are seen in 30-50% of patients who have missing primary teeth. 1.2.2 Aetiology The cause of an isolated missing tooth is often unclear; this may be genetic in origin or associated with some environmental insult during development. Missing teeth have been reported in association with multiple births, low birth weight, and increased maternal age. Rubella and thalidomide embryopathies may also be associated with missing teeth. Single gene disorders have been associated with missing teeth. Multiple missing teeth, as well as teeth with small crowns, may be seen in a number of syndromes including X-linked hypohidrotic ectodermal dysplasia autosomal dominant and autosomal recessive cases of ectodermal dysplasia and autosomal recessive chondroectodermal dysplasia (Ellis-van Creveld syndrome). Down syndrome (trisomy 21) is also associated with hypodontia. Hypodontia and microdontia involving the maxillary lateral incisor occurs in clefts involving the lip and palate
X-linked hypohidrotic ectodermal dysplasia is characterized in males by thin sparse missing teeth.These children are at risk due to their inability to cool themselves and may die in infancy if undiagnosed.This condition,while rare,is of particular importance as the dental professional be the first to come to a diagnosis,and thus to introduce families to support mechanisms.In heterozygous females the changes are stintive facial pro( retrusion of the maxilla)may be recognized.Most commony,one or both maxillary lateral incisors and/or the second premolars are missing.In some patients one maxillary lateral incisor may be of peg form.The responsible gene is the ED/gene on the X chromosome which encodes the protein ectodysplasin-A. Autosomal dominant inheritance of missing teeth is seen in families with mutations in s are the most common finding.These families may also have clefting segregating with th missing teeth.Mutations in the MSY/gene are also seen in the tooth-nail (Witkop) svndrome A pattern of autosmally dominant inheritance of missing teeth,particularly molars is ons in the on chro 14 Some patients havinga median ma illary have been found to have mutations in the sonic hedgehog (SH)gene on chromosome 7 12 3 Treatment g teeth can be comple well as genetic counselling.Missing teeth and small teeth often present together,so masking of conical or similarly distinctive teeth with composite isstrongly advised.In cases of anodontia,full dentures are required.These can be provided,albeit with likely limited suc ss、from about3 s of age,with the sibility of implan port for pros teeth can be treated by the use of partial dentures,with implants as part of the treatment protocol at a later age.Implant placement is best left until skeletal maturity Dentures will need to be replaced as the jaws grow.Progressive provision of dentures with annual replacements during the school holidays(the long vacation)mimicking the developing dentition at the childs age can dom e the stig hese be retair ned by implants,the of development of the alveolar bone may prove to be a limiting factor. 787H Fig.1.4 Hypohidrotic ectodermal dysplasia;erupted permanent teeth masked by 1.3 EXTRA TEETH Extrateeth (supernumerary teeth)have been reported to occurin2-0.% Caucasians in the primary dentition and 1.5-3%inthe permanent dentition in the same populations.There is a male to female ratio of approximately 2:1.Patients with supernumerary primary teeth have a30-50%chance of these being followed by
X-linked hypohidrotic ectodermal dysplasia is characterized in males by thin sparse hair, dry skin, absence of sweating and therefore heat intolerance, and multiple missing teeth. These children are at risk due to their inability to cool themselves and may die in infancy if undiagnosed. This condition, while rare, is of particular importance as the dental professional be the first to come to a diagnosis, and thus to introduce families to support mechanisms. In heterozygous females the changes are milder and may be restricted to the teeth, although a distinctive facial profile (slight retrusion of the maxilla) may be recognized. Most commonly, one or both maxillary lateral incisors and/or the second premolars are missing. In some patients one maxillary lateral incisor may be of peg form. The responsible gene is the ED1 gene on the X chromosome which encodes the protein ectodysplasin-A. Autosomal dominant inheritance of missing teeth is seen in families with mutations in the MSX1 gene on chromosome 4. Missing third molars and second premolars are the most common finding. These families may also have clefting segregating with the missing teeth. Mutations in the MSX1 gene are also seen in the tooth-nail (Witkop) syndrome. A pattern of autosomally dominant inheritance of missing teeth, particularly molars, is seen as a result of mutations in the PAX9 gene on chromosome 14. Some patients having a solitary median maxillary central incisor have been found to have mutations in the sonic hedgehog (SHH) gene on chromosome 7 1.2.3 Treatment The care of children with multiple missing teeth can be complex and ideally requires multidisciplinary input from paediatric dentists, orthodontists, and prosthodontists as well as genetic counselling. Missing teeth and small teeth often present together, so masking of conical or similarly distinctive teeth with composite is strongly advised. In cases of anodontia, full dentures are required. These can be provided, albeit with likely limited success, from about 3 years of age, with the possibility of implant support for prostheses provided in adulthood. Multiple missing teeth can be treated by the use of partial dentures, with implants as part of the treatment protocol at a later age. Implant placement is best left until skeletal maturity. Dentures will need to be replaced as the jaws grow. Progressive provision of dentures with annual replacements during the school holidays ('the long vacation'), mimicking the developing dentition at the child's age, can do much to minimize the stigma of these conditions. Although, ultimately, dentures can be retained by implants, the lack of development of the alveolar bone may prove to be a limiting factor. 787H Fig. 1.4 Hypohidrotic ectodermal dysplasia; erupted permanent teeth masked by 'porthole' denture with canine retractors during eruption. 1.3 EXTRA TEETH Extra teeth (supernumerary teeth) have been reported to occur in 0.2-0.8% of Caucasians in the primary dentition and 1.5-3% in the permanent dentition in the same populations. There is a male to female ratio of approximately 2 : 1. Patients with supernumerary primary teeth have a 30-50% chance of these being followed by
supernumerary permanent teeth.Teeth which resemble those of the normal series are supplemental teeth hile those of typical,ofen reduced supernumerary teeth Supernumerary teeth are most often located in the anterior maxilla in the midline.or immediately adjacent to the midline,and are then referred to as a mesiodens. molars respectively In some cases the supernumerary teeth may be an odontom Supernumerary teeth are more common in the maxilla than the mandible,with a ratio of about 5:1.Apart from those in the midline,they may be present bilaterally and symmetrically,hence the presence of a supernumerary in one part of the jaws should within the jaw.This commonly occurs in the case ofa mesiodens There is a significant association between supernumerary teeth and invaginated teeth There is also an association with palatal clefts.with approximately 40of patients with a the anterior palate having supernu merar Multiple supernumerary teeth are seen in cleidocranial dysplasia as well as in other syndromes such as oral-facial-digital syndrome type 1 and Gardner syndrome.The management of supernumerary teeth is discussed in 791HChapter 14. Key Points 1.5-3.5%of the permanent dentition. 2:I male to female ratio: 5:1 maxilla to mandible ratio 702H 1.4 ABNORMALITY OF TOOTH SIZE 1.4.1 Crown size There is a degree of subiectivity regarding what constitutes normal (ordinary")tooth size (and shape).Teeth which are obviously larger than normal are referred to as megadont or macrodont whereas teeth which are smaller than normal are termed microdont Crown size is ofe related large often have large(broad)roots,teeth with small crowns tend to have small(slender)roots Microdontia can be associated with hypodontia as in the example of X-linked hypohidrotic ectodermal dysplasia,where a heterozygous female might have one missing lateral incisor and a peg-shaped crown of the contralateral maxillary lateral Megadont teeth Megadont maxillary incisors can occurs as a result of fusion of adjacent tooth germs or as a result of an attempt at separation of a single tooth germ to form two separate teeth.It is important in these circumstances to count the number of teeth to determine
supernumerary permanent teeth. Teeth which resemble those of the normal series are referred to as supplemental teeth while those of less typical, often reduced, form-sometimes further described as tuberculate or conical-can be termed accessory supernumerary teeth. Supernumerary teeth are most often located in the anterior maxilla in the midline, or immediately adjacent to the midline, and are then referred to as a mesiodens. Supernumerary teeth in the molar regions adjacent or distal to the normal sequence of teeth are referred to as paramolars or distomolars respectively. In some cases the supernumerary teeth may be an odontome. Supernumerary teeth are more common in the maxilla than the mandible, with a ratio of about 5 : 1. Apart from those in the midline, they may be present bilaterally and symmetrically, hence the presence of a supernumerary in one part of the jaws should lead to consideration of further supernumeraries elsewhere. Supernumerary teeth may fail to erupt and may delay eruption of a permanent tooth which is developing deeper within the jaw. This commonly occurs in the case of a mesiodens. There is a significant association between supernumerary teeth and invaginated teeth. There is also an association with palatal clefts, with approximately 40 % of patients with a cleft of the anterior palate having supernumerary teeth. Multiple supernumerary teeth are seen in cleidocranial dysplasia as well as in other syndromes such as oral-facial-digital syndrome type 1 and Gardner syndrome. The management of supernumerary teeth is discussed in 791HChapter 14. Key Points Supernumerary teeth • 0.2-0.8% of the primary dentition; • 1.5-3.5% of the permanent dentition; • 2 : 1 male to female ratio; • 5 : 1 maxilla to mandible ratio. 792H 1.4 ABNORMALITY OF TOOTH SIZE 1.4.1 Crown size There is a degree of subjectivity regarding what constitutes normal ('ordinary') tooth size (and shape). Teeth which are obviously larger than normal are referred to as megadont or macrodont whereas teeth which are smaller than normal are termed microdont. Crown size is often related to root size, so teeth with large crowns often have large (broad) roots, teeth with small crowns tend to have small (slender) roots. Microdontia can be associated with hypodontia as in the example of X-linked hypohidrotic ectodermal dysplasia, where a heterozygous female might have one missing lateral incisor and a peg-shaped crown of the contralateral maxillary lateral incisor Megadont teeth Megadont maxillary incisors can occurs as a result of fusion of adjacent tooth germs or as a result of an attempt at separation of a single tooth germ to form two separate teeth. It is important in these circumstances to count the number of teeth to determine
which of these possibilities has occurred,as this will influence treatment planning. by the mandibular second premolars.Isolated megadontia has been estimated tooccur in approximately 1%of patients in the permanent dentition.The condition may be symmetrical.Generalized megadontia has been reported in association with pituitary gigantism.in unilateral facial hyperplasia and in hereditary gingival fibromatosis Microdontia Microdont primary teeth are uncom with a reported prevalence f%In the permanent dentition the prevalence is approximately 2.5%for individual teeth, with generalized microdontia occurring in approximately 0.%of individuals. Females are more often affected than males.with the maxillary lateral incisor being most commonly affected,having a peg-shaped or conical crown.As noted hypodontia. 797H 1.4.2 Root size nghappabe c to som rcia vartion ckground and larger roots in patients of Afri can origi Large root re Larger than normal roots are most typically seen affecting the permanent maxillary central incisors,with a population prevalence in one Swedish study of 2.3%.Males were four times more likely to be affected than females. Small root size Short-oohinthe maybe abnormalities.Short roots may also be seen in a number of conditions affecting the dentine and/or pulp.These will be considered in a later section Short roots may be seen affecting the permanent maxillary central incisors.The shortening affects appr ximately 2 5%of children and so me 15%ofthese may have er teeth,most often premolar canines.The cause is often unkno wn.though this as a result of In regional odontodysplasia 8there is typically abnormal root formation as well as abnormalities of the crowns of the teeth. Irradiation of the jawsor chemotherapy.during the period of root formation may lead to truncation of the r oots of teeth who edeveloping t the e time of 14.3 Treatment As with hypodontia the active cooperation of paediatric dentist.orthodontist.and restorative dentist should be encou ged planning for youn people afected by A megadont maxillary central incisor can be cosmetically unaesthetic and treatment decisions may need to be considered soon after (or.in some cases.before)eruption of the tooth.The options include acceptance.remodelling of the tooth,extraction of the tooth with orthodontic treatment if necessary.and subsequent masking of the space
which of these possibilities has occurred, as this will influence treatment planning. The permanent maxillary central incisors are most often affected followed by the mandibular second premolars. Isolated megadontia has been estimated to occur in approximately 1% of patients in the permanent dentition. The condition may be symmetrical. Generalized megadontia has been reported in association with pituitary gigantism, in unilateral facial hyperplasia and in hereditary gingival fibromatosis. Microdontia Microdont primary teeth are uncommon, with a reported prevalence of 0.2-0.5%. In the permanent dentition the prevalence is approximately 2.5% for individual teeth, with generalized microdontia occurring in approximately 0.2% of individuals. Females are more often affected than males, with the maxillary lateral incisor being most commonly affected, having a peg-shaped or conical crown. As noted in the previous section (1.2), there is an association between microdontia and hypodontia. 797H 1.4.2 Root size Root length appears to be subject to some racial variation, with shorter roots being seen in people of Oriental background and larger roots in patients of African origin. Large root size Larger than normal roots are most typically seen affecting the permanent maxillary central incisors, with a population prevalence in one Swedish study of 2.3%. Males were four times more likely to be affected than females. Small root size Short-rooted teeth in the primary dentition may be associated with other dental abnormalities. Short roots may also be seen in a number of conditions affecting the dentine and/or pulp. These will be considered in a later section. Short roots may be seen affecting the permanent maxillary central incisors. The shortening affects approximately 2.5% of children and some 15% of these may have shortened roots on other teeth, most often premolars and/or canines. The cause is often unknown, though this can occur as a result of orthodontic treatment. In regional odontodysplasia 8there is typically abnormal root formation as well as abnormalities of the crowns of the teeth. Irradiation of the jaws, or chemotherapy, during the period of root formation may lead to truncation of the roots of teeth whose roots were developing at the time of treatment . 802H 1.4.3 Treatment As with hypodontia, the active cooperation of paediatric dentist, orthodontist, and restorative dentist should be encouraged to optimize treatment planning for young people affected by these conditions from an early age. A megadont maxillary central incisor can be cosmetically unaesthetic and treatment decisions may need to be considered soon after (or, in some cases, before) eruption of the tooth. The options include acceptance, remodelling of the tooth, extraction of the tooth with orthodontic treatment if necessary, and subsequent masking of the space
with a bridge,denture,or implant. miconh pricarlysthelryrncsme typical contours of the crown.In adult life,porcelain veneers may also be used or the tooth can be crowned 805H 1.5 ABNORMALITY OF TOOTH FORM 1.5.1Ab rmality of crown form Fusion and gemination Some cases of megadont crowns are as a result of fusion of adjacent tooth germs (fusion),or attempts at developmental separation of a single tooth germ to produce two separate teeth (gemination)and a variety of terms have been used for such ns It is radiographs to determine whether fusion or gemination is more likely to have occurred.The prevalence of such abnormalities ranges from5%to16%of Caucasian populations studied in the primary dentition.The permanent dentition is ess commonly affected (prevalence1%).Malesand females are affected ually. etic basis has been su The clinical manifestation may vary from aminor notch on the incisal edge of an abnormally wide incisor crown to two separate crowns with a single root.The crowns and root may be in continuity along their entire length or may be almost separate: n intercommunication is often present e most typical areas affected are ents of the arches i commonly affected than the maxilla.There may be an association with hypodontia.so that a larger than normal tooth of the primary series ogether with a missing tooth in that series may represent an intermediate stage between the presence or absence of a tooth. rption ofprimary fused or geminated teth may be delayed and this may lead to delayed eruption of the Treatment When this condition affects the primary dentition no treatment perse is required.It is important.however.to consider the possibility of abnormalities of the number and/or form of the permanent dentition in the area.One problem which can occur is that caries can develop at the interface between the tw own segm ents This can be prevented by an etch-retained restoration to fill in the defect,which will also improve the cosmetic appearance.In the permanent dentition.the final decision on whether to retain,extract,surgically divide or otherwise treat such teeth will depend on many factors including space available within the arch,the morphology of the pulp wo parts of the Key Points Double teeth 0.1-1.6%in the primary dentition
with a bridge, denture, or implant. A microdont tooth, particularly if this affects the maxillary lateral incisors, may be modified by acid-etch composite material being added to the tooth to reproduce the typical contours of the crown. In adult life, porcelain veneers may also be used or the tooth can be crowned. 805H 1.5 ABNORMALITY OF TOOTH FORM 1.5.1 Abnormality of crown form Fusion and gemination Some cases of megadont crowns are as a result of fusion of adjacent tooth germs (fusion), or attempts at developmental separation of a single tooth germ to produce two separate teeth (gemination) and a variety of terms have been used for such situations. The term 'double teeth' has been applied to cover both situations. It is important to count the number of teeth present clinically and, with the aid of radiographs to determine whether fusion or gemination is more likely to have occurred. The prevalence of such abnormalities ranges from 0.5% to 1.6% of Caucasian populations studied in the primary dentition. The permanent dentition is less commonly affected (prevalence 0.1-0.2%). Males and females are affected equally. A genetic basis has been suggested but not confirmed. The clinical manifestation may vary from a minor notch on the incisal edge of an abnormally wide incisor crown to two separate crowns with a single root. The crowns and root may be in continuity along their entire length or may be almost separate; some pulp intercommunication is often present. The most typical areas affected are the anterior segments of the arches in the primary dentition, with the mandible more commonly affected than the maxilla. There may be an association with hypodontia, so that a larger than normal tooth of the primary series together with a missing tooth in that series may represent an intermediate stage between the presence or absence of a tooth. Physiological root resorption of primary fused or geminated teeth may be delayed and this may lead to delayed eruption of the permanent successors. Treatment When this condition affects the primary dentition no treatment per se is required. It is important, however, to consider the possibility of abnormalities of the number and/or form of the permanent dentition in the area. One problem which can occur is that caries can develop at the interface between the two crown segments. This can be prevented by an etch-retained restoration to fill in the defect, which will also improve the cosmetic appearance. In the permanent dentition, the final decision on whether to retain, extract, surgically divide or otherwise treat such teeth will depend on many factors including space available within the arch, the morphology of the pulp chambers and/or root canals and the degree of attachment between the two parts of the tooth or teeth. Key Points Double teeth • 0.1-1.6% in the primary dentition;
0.1-0.2%in the permanent dentition No sex predilection 1.5.2 Accessory cusps Extra cusps are not uncommon in the human dentition and may occur in both the primary dentition the most common accessory cusps are seen either on the mesiobuccal aspects of the maxillary first molar or the mesiopalatal aspect of the maxillary second molar.the latter being similar to the cusp of Carabelli seen on the first permanent molar.The latter is a relatively frequent finding on the mesiopalatal aspect of the crown of the maxillary first molars is typically bilateral and may be in 10-60%of vario cusp arising from the lingual cingulum,often referred to as a'talon cusp'This affects the maxillary central incisor most commonly.Talon cusps may interfere with the occlusion and may be aesthetically unpleasing.As with double teeth,caries may occur in the groove between the cusp and palatal surface of ive been anent canines may a have prominentin up,perhapsindit inci vaginations reporte tendency towards a premolar tooth form.Additional cusps may uncommonly be seen on premolars. Treatment sons.Selecti od ofmthe eih ofhepnd require action for both aesthetic and occlusa rea deposition of reactionary dentine on the pulpal surface of the dentine.Single visi sectioning of the cusp from the tooth followed by elective pulpotomy can also be considered. 只1日 1.5.3 Invaginated teeth This term refers to the presence of an invagination in the crown of the tooth forming an infolding lined by enamel within the crown of the tooth,sometimes extending into the root.An invagination of enamel epithelium into the dental papilla during development leads to the formation of the abnormality.The terms invaginated tooth or dens invaginatus c ed othe moy app lied (but not ne odontome The maxillary lateral incisor is the most commonly affected tooth.The maxillary central incisors are less commonly affected and.occasionally.the cnines are affected.In itsmildestform an tooth is typically a maxilary pect of the crown.In its mor extreme form the invagination is associated with a grossly abnormal crown form and root form.In these gross examples the crown is tuberculate with the invagination appearing on the cusp of the abnormal tooth.Radiographs show the extent of the invagination chamber.Enamel.which may be extremely thin and mav
• 0.1-0.2% in the permanent dentition; • No sex predilection; • Permanent anomalies in 30-50 % of primary cases. 809H 1.5.2 Accessory cusps Extra cusps are not uncommon in the human dentition and may occur in both the primary and permanent dentition, most commonly affecting molar teeth. In the primary dentition the most common accessory cusps are seen either on the mesiobuccal aspects of the maxillary first molar or the mesiopalatal aspect of the maxillary second molar, the latter being similar to the cusp of Carabelli seen on the first permanent molar. The latter is a relatively frequent finding on the mesiopalatal aspect of the crown of the maxillary first molars, is typically bilateral and may be seen in 10-60% of various populations. Permanent incisor teeth may have an additional cusp arising from the lingual cingulum, often referred to as a 'talon cusp'. This affects the maxillary central incisor most commonly. Talon cusps may interfere with the occlusion and may be aesthetically unpleasing. As with double teeth, caries may occur in the groove between the cusp and palatal surface of the incisor. Other incisor evaginations have been reported. Permanent canines may also have a prominent lingual cusp, perhaps indicating a tendency towards a premolar tooth form. Additional cusps may uncommonly be seen on premolars. Treatment The talon cusp may require action for both aesthetic and occlusal reasons. Selective grinding, repeated over a period of time, will reduce the height of the cusp and allow deposition of reactionary dentine on the pulpal surface of the dentine. Single visit sectioning of the cusp from the tooth followed by elective pulpotomy can also be considered. 81H 1.5.3 Invaginated teeth This term refers to the presence of an invagination in the crown of the tooth, forming an infolding lined by enamel within the crown of the tooth, sometimes extending into the root. An invagination of enamel epithelium into the dental papilla during development leads to the formation of the abnormality. The terms invaginated tooth or dens invaginatus can be used; other terms commonly applied (but not necessarily correctly) are dens in dente, gestant composite odontome, and dilated composite odontome. The maxillary lateral incisor is the most commonly affected tooth. The maxillary central incisors are less commonly affected and, occasionally, the canines are affected. In its mildest form an invaginated tooth is typically a maxillary lateral incisor with a deep cingulum pit on the palatal aspect of the crown. In its more extreme form the invagination is associated with a grossly abnormal crown form and root form. In these gross examples the crown is tuberculate with the invagination appearing on the cusp of the abnormal tooth. Radiographs show the extent of the invagination chamber. Enamel, which may be extremely thin and may
even be absent,can be seen lining this chamber.The pulp may be displaced and expandec Invagination of primary teeth is uncommon but in the permanent dentition has been estimated to affect between 1%and 5%of different groups.Males are more commonly affected than females,with aratio of:1.Invaginations may as differ in commonly affected Invaginated teeth may cause problems because of the development of caries and pulpal pathology.This can occur soon after tooth eruption,with the child presenting an acute abscess or facial cellulitis In such cases the radiograph will invariably riapica rarefaction The presence ofone invaginated tooth should ead to consideration of the contralateral tooth and/or adjacent teeth being affected.Invaginations are often bilateral,though not necessarily symmetrical.Some patients with invaginated teeth may also have supernumerary teeth and therefore full radiographic examination is warranted Treatment If invaginations are identified at an early stage after eruption of the tooth then etchretained resin sealants can be placed to prevent bacteria entering the invagination and subsequent development of caries.Acute infective episodes,particularly when associated with cellulitis.should be treated with ap opriate antibiotic therany as well as incision and dra any pointin abs ed,or extracted if the long-term prognosis is poor.This tends to be the case with the more gross examples where the crown and root form are abnormal.In less extreme forms endodontic treatment,firstly involving apexification,can be considered. 818H 1.5.4 Evaginated teeth Permanent molar teeth may also be affected.Typically there is a small tuberculeon the occlusal surface of the premolar in the central part of the fissure pattern.The condition is more common in patients of Chinese descent and has been estimated to occur in 1-4%of the group.The evaginations are typically fractured off or worn down leading to pulpal exposure pulpal pathology,and periapica involvement Treatment Careful radiographic evaluation is necessary to determine the extent of any pulpal extension into the evagination.Restricted and repeated grinding of the tubercule can be undertakento promote on the pulpal aspect of the cases and,more commonly,removal of the tubercule and a limited pulpotomy are required. 1.6 ABNORMALITY OF ROOT FORM
even be absent, can be seen lining this chamber. The pulp may be displaced and surround the invagination cavity, appearing radiographically as narrow slits around the dentine forming the wall of the invagination. Sometimes the root is significantly expanded. Invagination of primary teeth is uncommon but in the permanent dentition has been estimated to affect between 1% and 5% of different groups. Males are more commonly affected than females, with a ratio of 2 : 1. Invaginations may also differ in different racial groups, with people of Chinese ethnicity being reportedly more commonly affected. Invaginated teeth may cause problems because of the development of caries and pulpal pathology. This can occur soon after tooth eruption, with the child presenting an acute abscess or facial cellulitis. In such cases the radiograph will invariably demonstrate incomplete root formation as well as periapical rarefaction . The presence of one invaginated tooth should lead to consideration of the contralateral tooth and/or adjacent teeth being affected. Invaginations are often bilateral, though not necessarily symmetrical. Some patients with invaginated teeth may also have supernumerary teeth and therefore full radiographic examination is warranted. Treatment If invaginations are identified at an early stage after eruption of the tooth then etchretained resin sealants can be placed to prevent bacteria entering the invagination and subsequent development of caries. Acute infective episodes, particularly when associated with cellulitis, should be treated with appropriate antibiotic therapy as well as incision and drainage of any pointing abscess. The tooth should be opened, or extracted if the long-term prognosis is poor. This tends to be the case with the more gross examples where the crown and root form are abnormal. In less extreme forms endodontic treatment, firstly involving apexification, can be considered. 818H 1.5.4 Evaginated teeth Evaginated teeth, or dens evaginatus, most commonly affect the premolar teeth. Permanent molar teeth may also be affected. Typically there is a small tubercule on the occlusal surface of the premolar in the central part of the fissure pattern. The condition is more common in patients of Chinese descent and has been estimated to occur in 1-4% of the group. The evaginations are typically fractured off or worn down by virtue of normal wear, leading to pulpal exposure, pulpal pathology, and periapical involvement. Treatment Careful radiographic evaluation is necessary to determine the extent of any pulpal extension into the evagination. Restricted and repeated grinding of the tubercule can be undertaken to promote reactionary dentine deposition on the pulpal aspect of the evagination. However, this approach may only be applicable in a small number of cases and, more commonly, removal of the tubercule and a limited pulpotomy are required. 1.6 ABNORMALITY OF ROOT FORM
1.6.1 Taurodontism The termtaurodontism(trally-bull-iketeethresembingabull's neck)isused to describe molar teeth in which the body of the tooth is enlarged vertically at the expense of the roots.The normal constriction of a tooth at the level of the amelocemental junction is frequently reduced or absent in affected teeth.The mechanism leading to taurodontism is the late invagination(or failure)of Hertwig's apically.Varying degrees of taurodontism are seen,with the mos extreme exampl being when only a single root is present rather than separate roots.Taurodont teeth may also be described as pyramidal,cuneiform,or fused.The root canal morphology may have implications when endodontic treatment or extraction is required. Taurodontism is most commonly recognized in the permanent dentition.Although the term is traditionally applied ony tomolar patients with taurodo ntism of the molar teeth the pulps of single-rooted teeth may be larger than normal prevalence of taurodontism varies according to the criteria used.In British schoolchildren a prevalence of6%for mandibular first permanent molars has been reported.Higher prevalences have racial groups such as the Bantu in South Africa.In ome familis ms to foll w an aut atavistic trait.It is found in association with amelogenesis imperfecta,the trichodento osseous syndrome,ectodermal dysplasias,and a number of other syndromes. Taurodontism is also more common in X-chromosomal aneudoploidy. 1.6.2Accessory roots ts inamost any tooth.In the primary dentition this mos commonly affects the molars but the primary canines and maxillary incisors can also be affected.In the permanent dentition.accessory roots are occasionally seen in maxillary incisors,mandibular canines,premolars,and molars.These accessory roots ect of the tooth vary in shape, and may radiograp ts ha ve been rep ted to %of the primary dentition and from %to45%of the permanent dentition There is an association between accessory roots and large cusps of Carabelli on the maxillary first permanent molar and with accessory cusps on maxillary second and third molars.In some cases the presence of accessory rootsreflects macrodontia. 1.7ABNORMALITY OF TOOTH STRUCTURE 1.7.1All tissues Arrested development of tooth-germs Arrested development of tooth-germ formation may occur following such external influences as trauma ionizing radiation.osteomvelitis or chemotherapy.The teeth affected and the affected will be the nature and developing.thismay defects and corresponding dentine defects may be seen on microscopic sections should the tooth ultimately be extracted.If roots are developing at the time of the insult these may appear stunted Locally,one or more permanent tooth-germs may be affected by infection from an
1.6.1 Taurodontism The term taurodontism (literally⎯bull-like teeth, resembling a bull's neck) is used to describe molar teeth in which the body of the tooth is enlarged vertically at the expense of the roots. The normal constriction of a tooth at the level of the amelocemental junction is frequently reduced or absent in affected teeth. The mechanism leading to taurodontism is the late invagination (or failure) of Hertwig's root sheath, which maps out the shape of root formation. The furcation is displaced apically. Varying degrees of taurodontism are seen, with the most extreme example being when only a single root is present rather than separate roots. Taurodont teeth may also be described as pyramidal, cuneiform, or fused. The root canal morphology may have implications when endodontic treatment or extraction is required. Taurodontism is most commonly recognized in the permanent dentition. Although the term is traditionally applied only to molars, in some patients with taurodontism of the molar teeth the pulps of single-rooted teeth may be larger than normal. The prevalence of taurodontism varies according to the criteria used. In British schoolchildren a prevalence of 6% for mandibular first permanent molars has been reported. Higher prevalences have been recorded in certain racial groups such as the Bantu in South Africa. In some families taurodontism seems to follow an autosomal dominant pattern of inheritance. Taurodontism has also been considered to be an atavistic trait. It is found in association with amelogenesis imperfecta, the trichodentoosseous syndrome, ectodermal dysplasias, and a number of other syndromes. Taurodontism is also more common in X-chromosomal aneudoploidy. 1.6.2 Accessory roots Accessory roots may occur in almost any tooth. In the primary dentition this most commonly affects the molars but the primary canines and maxillary incisors can also be affected. In the permanent dentition, accessory roots are occasionally seen in maxillary incisors, mandibular canines, premolars, and molars. These accessory roots are often situated on the distolingual aspect of the tooth, may vary in shape, and may be difficult to identify radiographically. Accessory roots have been reported to occur in 1-9% of the primary dentition and from 1% to 45% of the permanent dentition. There is an association between accessory roots and large cusps of Carabelli on the maxillary first permanent molar and with accessory cusps on maxillary second and third molars. In some cases the presence of accessory roots reflects macrodontia. 1.7 ABNORMALITY OF TOOTH STRUCTURE 1.7.1 All tissues Arrested development of tooth-germs Arrested development of tooth-germ formation may occur following such external influences as trauma, ionizing radiation, osteomyelitis, or chemotherapy. The teeth affected and the particular tissues affected will be dependent upon the nature and timing of the insult. In teeth whose crowns are developing, this may result in enamel defects and corresponding dentine defects may be seen on microscopic sections should the tooth ultimately be extracted. If roots are developing at the time of the insult these may appear stunted. Locally, one or more permanent tooth-germs may be affected by infection from an
overlying primary predecessor.Such teeth are termed Turner teeth and typically have premo ars are most commonly affected. Regional odontodysplasia This is an uncommon developmental anomaly.typically affecting the primary teeth and corresponding permanent successors within a segment of the dentition.The anterior tecth are m .The term'ghos radiographic appearance seen.Affected patients may present with abscesses prior to the eruption of the teeth.The abnormal teeth have poorly developed crowns with enamel and dentine changes,large pulp chambers,and open apices.The permanent teeth may be less severely affected than the primary predecessors The removal of teeth affected by regional odontodysplasia isoften necessary.As this is often the case in the primary dentition,consideration then needs to be given to management of the affected permanent successors.While there are reports of the effective use of etch-retained restorations in these cases.the teeth are often slow to phology is such that infectionisaficguetouicome.Rool estoratively useful.A case-by-case approach to treatment planning is required.Block removal of unerupted teeth with surrounding bone is not required. 823H 1.7.2 Enamel defects Enamel defects may be caused by factors. combination.Where less enamel matrix than normal is produced the resulting ename will be thinner(hypoplasia).If there is a defect in mineralization of the enamel matrix proteins then the result will be poorly mineralized enamel (subdivided into hypocalcification for more severe defects and hypomaturation for milder changes).In cases there will be of both hypoplasi and hypominera ough sometimes the defect will be perceived clinically as predominantly one or the other.When enamel hypoplasia is seen the enamel may be uniformly thin,or grooved or pitted.In hypomineralization the enamel will typically be discoloured.usually a yellow-brown colour.This is particularly sowhere the defect is severe(hypocalcification)whereas in a lesss ere pres n( yp nay be almosr t normal b appear mottledor even ony slightly opaque rather than translucent Key Points Enamel defects Hypoplasia-deficient matrix: Amelogenesis imperfecta Amelogenesis imperfecta is the term applied to generalized enamel defects affecting all (or predominantly all)of the teeth of both the primary and permanent dentitions.It is of genomic origin and thus there may be a family history of similar defects in other
overlying primary predecessor. Such teeth are termed Turner teeth and typically have areas of enamel hypoplasia and/or enamel hypomineralization. The mandibular premolars are most commonly affected. Regional odontodysplasia This is an uncommon developmental anomaly, typically affecting the primary teeth and corresponding permanent successors within a segment of the dentition. The anterior teeth are more commonly affected than the posterior teeth and the defect may cross the midline. The term 'ghost teeth' is sometimes applied to reflect the radiographic appearance seen. Affected patients may present with abscesses prior to the eruption of the teeth. The abnormal teeth have poorly developed crowns with enamel and dentine changes, large pulp chambers, and open apices. The permanent teeth may be less severely affected than the primary predecessors Treatment The removal of teeth affected by regional odontodysplasia is often necessary. As this is often the case in the primary dentition, consideration then needs to be given to management of the affected permanent successors. While there are reports of the effective use of etch-retained restorations in these cases, the teeth are often slow to erupt, with a distinctive local gingivitis, and the pulpal morphology is such that infection is a frequent outcome. Root development may be slow but restoratively useful. A case-by-case approach to treatment planning is required. Block removal of unerupted teeth with surrounding bone is not required. 823H 1.7.2 Enamel defects Enamel defects may be caused by genetic or environmental factors, acting alone or in combination. Where less enamel matrix than normal is produced the resulting enamel will be thinner (hypoplasia). If there is a defect in mineralization of the enamel matrix proteins then the result will be poorly mineralized enamel (hypomineralization⎯sometimes subdivided into hypocalcification for more severe defects and hypomaturation for milder changes). In many cases there will be a combination of both hypoplasia and hypomineralization, although sometimes the defect will be perceived clinically as predominantly one or the other. When enamel hypoplasia is seen the enamel may be uniformly thin, or grooved or pitted. In hypomineralization the enamel will typically be discoloured, usually a yellow-brown colour. This is particularly so where the defect is severe (hypocalcification) whereas in a less severe presentation (hypomaturation) the enamel may be almost normal but appear mottled or even only slightly opaque rather than translucent. Key Points • Enamel defects; • Hypoplasia⎯deficient matrix; • Hypomineralisation⎯poor mineralisation. Amelogenesis imperfecta Amelogenesis imperfecta is the term applied to generalized enamel defects affecting all (or predominantly all) of the teeth of both the primary and permanent dentitions. It is of genomic origin and thus there may be a family history of similar defects in other