Root lengths in the permanent teeth of Klinefelter (47,XXY) men

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t tDepartment of Oral Development and Orthodontics, Institute of Dentistry, University of Oulu and University Hospital of Oulu, Finlanda r ch i v e s o f o r a l b i o l o g y 5 2 ( 2 0 0 7 ) 8 2 2 8 2 7avai lable at www.sc iencedi rec t .comls1. IntroductionMen with Klinefelter syndrome have two X chromosomes inaddition to one Y chromosome (47,XXY), or in rare cases threeor four X chromosomes. This is in fact the most common sexchromosome abnormality, with an incidence of 1 in 576newborn boys,1 and 1 in 769 has also been suggested.2 Theincidence of 47,XXY boys increases with maternal age findingan explanation in maternal meiosis. Prenatal testosteronelevel of 47,XXY boys does not differ significantly from normalmen. Later the production of testosterone is insufficient andneeds to be substituted already from the age of 11 until 50years of age. The head circumference, body weight and lengthhave been found to be relatively reduced among 47,XXY boysat birth.3 They show somewhat greater height growthacceleration than normal boys between 5 and 8 years of ageowing to relatively greater leg growth. The magnitude andtiming of the pubertal growth spurt is like in normal boys.47,XXY men grow taller than normal men, with a mean adultheight of 186 and 180 cm correspondingly, but remain 810 cmshorter than 47,XYY men or males with an extra Y chromo-some.2 In a Finnish study the final height in 47,XXY men was182 cm.4 The somewhat greater growth acceleration in adultheight is due to relatively increased leg length and thea r t i c l e i n f oArticle history:Accepted 5 February 2007Keywords:Klinefelter manX chromosomeY chromosomeHumansAneuploidyTooth rootGrowth and developmenta b s t r a c tEarlier studies on human teeth have provided proof of an expression of the X and Ychromosome genes in tooth crown growth. The Y chromosome promotes the growth ofpermanent tooth crown enamel and dentin, whereas the effect of the X chromosome seemsto be restricted mainly on enamel formation. Also, there are evidences that both of the sexchromosomes are expressed in tooth root growth. The permanent tooth crowns in 47,XXYmales or individuals with an extra X or Y chromosome show increased size compared tonormal men, which is mainly due to increased enamel thickness, the dentin thickness issomewhat reduced. There is some evidence of increased mesio-distal tooth crown size alsoin their primary dentition. The aim of the present study was to determine their completepermanent tooth root lengths. The study groups consisted of 49 47,XXY males, 22 relativemales, 8 relative females, 35 population control males and 46 population control femalesfrom the Kvantti research project. Root length measurements were made from panoramicradiographs on both sides of the jaw using a digital sliding calliper. The results showedgrowth increase in the final tooth root sizes in 47,XXY males which conceivably becomeevident beginning 8 years after birth up to the age of 14 years, at least. The present resultsand earlier ones on 45,X and 45,X/46,XX females, normal females and males indicate thatthe promoting effect of the Y chromosome on tooth root growth is greater than that of the Xchromosome. These differential effects are conceivably causative factors in the develop-ment of the sexual dimorphism in tooth root size.# 2007 Elsevier Ltd. All rights reserved.* Corresponding author. Tel.: +358 8 3153934; fax: +358 8 5375560.E-mail address: raija.lahdesmaki@oulu.fi (R. Lahdesmaki).00039969/$ see front matter # 2007 Elsevier Ltd. All rights reserved.doi:10.1016/j.archoralbio.2007.02.002Root lengths in the permanenmenRaija Lahdesmaki *, Lassi Alvesalojourna l homepage: www. int l .eeeth of Klinefelter (47,XXY)evierhea l th .com/ journals /arobdental organ around the growing dental papilla to initiate thedifferentiation of root odontoblasts. The formation of primarypossible. The other criteria were age, generation and thenumber of the teeth available. The Institutional Review Boardof the Medical Faculty, University of Turku, Finland, hadreviewedand approved the protocol, ofwhich the patients andtheir relatives were informed. All examinations were carriedout with the individuals consent, and the subjects were not atrisk in any way.2.2. MeasurementsPermanent tooth root lengths in maxilla and mandible weremeasured from dental panoramic radiographs and crownheights were measured at the same time for further study. Allthe radiographs had been taken by the same person at theInstitute of Dentistry, University of Turku, following astandardized procedure and with the same machine, anOrthopantomograph 3, Palomex Corporation, Helsinki, Fin-land. Themagnificationwas in the range 1.281.31 throughoutthe image layer of the panoramic radiograph. A magnifyinglens (2) was used to determine the outlines of the tooth froma r c h i v e s o f o r a l b i o l o g y 5 2 ( 2 0 0 7 ) 8 2 2 8 2 7 823physiological dentin continues until the external root form iscompleted.14 Excluding third molars, in terms of populationdevelopmental standards, permanent tooth roots completetheir growth on average between the ages of 8 and 14 years.In the present study, complete permanent tooth rootlengths in Klinefelter men (47,XXY males) or individuals withextra X or Y chromosome are determined to gain additionalinformation about their dental growth and the role of the Xand Y chromosomes in this process. It has been suggestedearlier that the genes on the X and Y chromosome that affecttooth crown growth are also expressed in the following rootgrowth.152. Subjects and methods2.1. SubjectsThe patients, their relatives and population controls were allparticipants in Alvesalos Kvantti dental research project onindividuals with sex chromosome abnormalities. The subjectswere from different parts of Finland and consisted of 4947,XXY males (mean age 30.7 years, S.D. 11.71, minimum10.16, maximum 57.61), 22 relative men (16 fathers and 6brothers) (mean age 41.0 years, S.D. 15.53, minimum 13.52,maximum 67.50), 8 relative women (mothers) (mean age 39.7years, S.D. 5.64, minimum 31.17, maximum 50.55), 35 popula-tion control men (mean age 25.5 years, S.D. 12.41, minimum11.60, maximum 45.64) and 46 population control women(mean age 27.6 years, S.D. 10.66, minimum 9.74, maximum55.63), who were relatives of patients other than 47,XXY menin the Kvantti research project. The diagnoses of the patientswere based on clinical and karyotypic evidence. All theircytogenetic diagnosis had been carried out for medicalreasons. For comparisons the relatives were chosen on afeminine trunk proportions in 47,XXY males are caused by adecrease in shoulder width, possibly affected by the doubledose of X chromosomes. Their adult head circumference isunder normal men, but above normal women,4 also, theirfacial dimensions are smaller than those in normal men.4,5Interestingly enough, 47,XXX females or femaleswith an extraX chromosome also show reduced head and skull size,6 andthey are tall because of relatively increased leg length.The total permanent tooth crown size increase in 47,XXYmales is caused by thicker enamel layer relative to normalmen or women, the dentin thickness is less than in men, butabove that of women.7 Larger tooth crown size in normal menrelative to women is due to the thicker dentin layer inmen,810and men also show longer roots than women.11,12 A casereport of increased mesio-distal tooth crown size in theprimary dentition13 of a 47,XXY male is parallel with theresults of the permanent dentition.7 After the crown growth iscompleted the epithelial cells in the tooth root sheathdetermine the size, shape and number of the roots.14 Rootdentin is formed later than crown dentin and requires aproliferation of epithelial cells from the cervical loop of thepaired basis, one relative of the same phenotypic sex for eachpatient and comparisons were also extended to opposite sex ifthe radiograph on a light table, after which the outlines weremarked with a special pencil for plaster (Schwan All Stabilo8008, Schwanhauber GmbH & CO, KG Heroldsberg, Germany)and the measurements made in the same manner with asliding digital calliper (Mitutoyo, digimatic 500-123U, CD-15B,Andover, England) to an accuracy of 0.01 mm. The outlines ofthe roots were hard to determine in places and the drawingshad to be made straight on the radiograph. All the drawingsand measurements were made by one of the authors (RL)(Fig. 1a). The measurements of root lengths were madeperpendicular to two parallel lines, one touching the outer-most part of the root and the other joining the mesial anddistal cervical margins of the enamel (Fig. 1b). Root lengthrefers to the longest root on the radiograph in the case ofpremolars and the longest mesial root in the case of molars.The aim was to measure all the teeth with complete rootformation on both sides of the jaws except for the thirdmolars. Teeth that were partly outside the plane-in-focus inFig. 1 Root lengths were measured by reference to linesmarked on the tomographic radiographs (a) as describedin the text and shown in the picture (b).show numerically larger values in root length in 22 measure-on dentin, can explain the expression of somatic sexuala r c h i v e s o f o r a l b i o l o g y 5 2 ( 2 0 0 7 ) 8 2 2 8 2 7824the panoramic radiograph or showed obvious distortionbecause of being on the inner or outer surface of the imagelayer16 were excluded. Teeth with root resorption or incom-plete root formation were also excluded, but teeth with largerestorations or large caries lesions with pronounced loss ofcrown structure were measured whenever possible. Dilacer-ated or crooked roots were measured in terms of perpendi-cular length as explained above. Some impacted canine teethwith a closed apex were measured. Acellular cementum isformed on the root surface until the tooth reaches theocclusion, at which time the proliferation of the epithelialroot sheath is reduced and it may become entrapped withinthe forming matrix of cellular cementum.17 Cellular cemen-tum formation continues after the root form is complete. Theline between apical cementum and dentin was evaluatedwhile marking the outlines of the roots and the apicalcementum layer was excluded from the present root lengthdeterminations.Permanent tooth root lengths may be affected by severalexternal factors, which could bias the results. Orthodontictreatment, especially with fixed appliances, may cause rootresorption, as also can traumatic occlusion, bruxism, nail-biting, trauma, apical infection or root treatment, for instance.According to anamnestic information, the patients or theirrelatives had not had any orthodontic treatment, at least withfixed appliances, before the examination procedures. Simi-larly, anamnestic information on the population controlssuggested that they had not undergone orthodontic therapy.This is supported by the fact that at the time in question therewere only very few dental offices in Finland where fixedappliance orthodontics, or orthodontics in general, werecarried out. Regarding the possible effects of other externalfactors, an assumption was made of an even distributionbetween the groups.The reliability of the measurements was examined byperforming double determinations on a total of 45 dentalradiographs from the Kvantti research material representingadult 45,X females and their relativemen and women, with 15persons in each group. The measurements were made by thesame person (RL) at an interval of 2 weeks, the line joining themesial and distal cervical margins of the enamel marked oneach tooth being rubbed out after the first measurement anddetermined again and re-drawn for the second. The reprodu-cibility of the double determinations of root length wasexpressed with the method error statistic (S) (x1 = originalmeasurement value, x2 = repeated measurement value,n = number of patients) S P x1 x22=2nq.18The absolute error values for the root length measure-ments ranged from 0.35 to 0.75 mm, the correspondingpercentages being 1.95 and 5.11. The largest differences inthe double determinations of root lengths were in the uppersecond premolars and molars and mandibular incisors andcanines. The values were considered acceptable for furthermeasurements.2.3. Statistical analysisThe Statistical Package for the Social Sciences 10.0 (SPSS, CA,USA)was used for the statistical analysis. Mean values for rootdimorphism in the crown size, shape, maturation and in thenumber of the teeth, e.g. supernumerary permanent teeth areapproximately twice as common in normal men than inwomen, and ordinary teeth are more frequently missing inwomen than in men.20,22,23 Also, assuming genetic pleiotropy,sexual dimorphism in root size,12 in the expression of torusments out of 28 (Table 2), and the roots of relative men aregenerally longer than those of relative women. It is notablethat the differences of root lengths between 47,XXYmales andcontrol women are larger with one exception than thosebetween 47,XXY males and control men. Visual inspection ofthe root morphology on the radiographs of 47,XXY males didnot reveal any major deviations from normality. However,minor deviation in the form of taurodontic teeth was presentin mild expression in 30% of the cases. Taurodontism is anextension of the pulp chamber in which the furcation of theroots takes place more apically in multirooted teeth. The factthat themean root lengths of antimeric teeth differed to someextentmay be due to the sample sizes, the varying numbers ofmeasurements available and general technical reasons.Certainly, the measurements of natural tooth roots also showdifferences between the mean lengths for antimeric teeth.114. DiscussionStudies on families19,20 and individuals with sex chromosomeabnormalities,8,2123 and molecular research,2426 have pro-vided proof of an expression of the X andY chromosomegenesin tooth crown growth. The Y chromosome promotes growthof permanent tooth crown enamel and dentin, whereas theeffect of the X chromosome in tooth crown growth seems to berestricted mainly on enamel formation.22,23 Enamel growth isdecisively influenced by cell secretory function and that ofdentin by cell proliferations.27 The promoting effect of the Ychromosome genes on tooth crown development, particularlylength were calculated and compared between the 47,XXYmales, relative men (47,XXY male versus father or brother),population control men and women using the t-test forequality of means to indicate the significance of differencesbetween the groups. Results were considered statisticallysignificant when p was 0.05 or less.3. ResultsThe results show that mean permanent tooth root lengths in47,XXY males are generally longer than those in normalcontrol men (Table 1). In the mandible, the differences aresignificant in 12 out of 14 comparisons and in the maxilla inpremolars and molars. The root lengths of lower and uppercanines in 47,XXYmales are close to the corresponding valuesof control men. Relative to control women, the 47,XXY maleshave significantly longer roots except in maxillary canines(Table 1), and control men also show longer roots than controlwomen. Comparisonwith their relativemen the 47,XXYmalesmandibularis, the timing of skeletal maturation, staturalgrowth and sex ratio (the ratio of the number of boys to thatropumma r c h i v e s o f o r a l b i o l o g y 5 2 ( 2 0 0 7 ) 8 2 2 8 2 7 825Table 1 Mean maxillary and mandibular permanent toothwomenTooth 47,XXY males PoMean (mm) S.D. N Mean (MaxillaryRight central incisor 21.0 2.4 33 20.1Lateral incisor 19.8 1.9 28 19.3Canine 23.3 2.9 30 23.8First premolar 19.9 2.2 29 18.1Second premolar 19.5 2.6 18 16.8First molar 17.4 1.8 23 14.8Second molar 17.1 2.2 24 15.0MaxillaryLeft central incisor 21.1 2.4 32 20.1Lateral incisor 20.0 2.0 28 19.2Canine 23.4 2.7 25 24.1First premolar 19.9 1.9 24 17.8of girls) at birth and in the earlier stages of development can beexplained by this effect.22,23 It has been suggested that the locifor the tooth growth promoting genes are on the proximalportion of the long arm of the Y chromosome,28 and on theshort arm of the X chromosome.29 Molecular studies haveindicated that loci for human amelogenin, the main proteincomponent of the enamel organic matrix, are to be found onthe distal short arm of the X chromosome and possibly on theproximal long arm of the Y chromosome, although the shortarm of the Y chromosome has also been suggested.2426 Thetranscriptional products of the X and Y amelogenin genesseem to be both quantitatively and qualitatively different. TheY chromosome locus encodes a functional protein, and itslevel of expression is only 10% of that on the X chromosome.26Earlier studies on permanent tooth root growth inindividuals with sex chromosome abnormalities have shownincreased root lengths in 47,XYYmales or males with an extraY chromosome.12 Their tooth crown size is also increasedSecond premolar 19.7 2.4 24 16.9First molar 16.8 1.7 21 14.4Second molar 17.4 2.4 27 14.5MandibularRight central incisor 17.6 1.8 41 15.3Lateral incisor 18.6 1.9 41 17.2Canine 22.6 2.2 39 21.3First premolar 19.9 2.0 39 18.5Second premolar 20.7 2.3 22 18.9First molar 19.7 1.7 24 18.7Second molar 18.5 2.0 22 16.9MandibularLeft central incisor 17.9 1.9 41 15.7Lateral incisor 18.7 2.0 43 17.2Canine 22.5 2.7 42 22.5First premolar 19.4 1.9 37 19.0Second premolar 21.1 2.1 20 19.2First molar 20.3 1.6 19 18.8Second molar 18.9 2.0 22 17.5Statistical testing by two-tailed t-test.47,XXY males vs. population control men ( pa), 47,XXY males vs. populatns = not significant.* p < 0.05.** p < 0.01.*** p < 0.001.$ p < 0.1.ot lengths in 47,XXY males, population control men andlation control men Population control women) S.D. N pa Mean (mm) S.D. N pb2.2 31 ns 18.8 1.5 39 ***2.0 26 ns 18.1 1.6 36 ***2.2 27 ns 21.5 2.2 39 *1.8 22 ** 17.3 1.9 33 ***1.9 29 *** 17.1 1.4 32 ***1.6 26 *** 14.5 1.8 32 ***1.8 29 *** 14.3 1.9 37 ***2.1 31 $ 19.0 1.2 39 ***2.1 31 ns 18.2 1.7 36 ***1.7 29 ns 21.7 1.9 38 *1.9 23 *** 17.0 1.8 36 ***which is due to the increase in dentin and enamel thickness.22The results for 46,XY females or females with male sexchromosome complement and complete form of androgeninsensitivity syndrome have also shown increase in toothroot30 and crown sizes, which are close to those in normalmen. Their crown size increase relative to normal women isdue to the dentin layer.22 The root dentin growth in 45,Xfemales or females with one X chromosome and 45,X/46,XXfemales or females with normal XX and one X cell lines, isreduced.15,31 Crown size reduction in both groups is mainlydue to the thin enamel layer, the dentin layer is close to that ofnormal women.8,9,22 It has been suggested that tooth rootgrowth increase is caused by the X and Y chromosome geneswhich promote crown dentin and enamel growth.15The present results in Klinefelter (47,XXY) men showincrease in their completed permanent tooth root lengths;growth increasehas already appeared in their tooth crown size.In terms of population dental developmental standards, the2.3 27 *** 17.0 1.7 34 ***1.8 25 *** 14.3 1.7 34 ***2.3 26 *** 14.1 1.8 33 ***2.3 34 *** 14.7 1.9 46 ***2.4 32 ** 15.9 1.8 45 ***2.8 32 * 19.9 2.3 42 ***2.1 34 ** 17.6 1.9 40 ***2.4 29 ** 18.5 1.7 36 ***1.3 26 * 17.9 1.4 30 ***1.4 20 ** 17.3 1.6 31 **2.1 35 *** 14.7 1.9 43 ***2.0 35 ** 16.1 1.9 44 ***2.2 33 ns 19.7 2.1 40 ***2.2 34 ns 17.9 1.9 40 ***2.4 28 ** 18.9 1.8 38 ***2.1 25 * 18.0 1.4 29 ***1.5 20 * 17.3 1.8 34 **ion control women ( pb).d m11111111a r c h i v e s o f o r a l b i o l o g y 5 2 ( 2 0 0 7 ) 8 2 2 8 2 7826Table 2 Mean permanent tooth root lengths in maxilla anTooth 47,XXY malesMean (mm) S.D.MaxillaryRight central incisor 21.1 2.9Lateral incisor 20.2 2.3Canine 22.8 3.6First premolar 20.6 1.6Second premolar 18.3 2.7First molar 17.5 1.7Second molar 17.4 2.9MaxillaryLeft central incisor 21.5 2.8Lateral incisor 20.0 2.6Canine 23.9 3.2First premolar 19.5 2.0Second premolar 18.6 2.3First molar 17.0 1.6Second molar 17.8 1.5Mandibularresults indicate that root size increases in these men becomeevident infinal formbeginning8yearsafterbirthuptotheageof14 years, at least and expressing likely a continuous geneticinfluence due to an extra X or Y chromosome. It is obvious thatthe addition of the Y chromosome to XX complement hasgreater influence on root growth than the addition of the Xchromosome to XY complement. Results on tooth root lengthsin normal men, women, 45,X and 45,X/46,XX females, togetherwith the present results in 47,XXY men indicate that thepromotingeffectof theYchromosomeonthegrowthof the rootlength is greater than that of the X chromosome. Thesedifferential effects are conceivably causative factors in thedevelopment of the sexual dimorphism in tooth root size.AcknowledgementsThe Kvantti research project was supported by the EmilAaltonen Foundation, the University of Turku Foundation andthe Academy of Finland. Professor Erkki Tammisalo con-tributed to the performing of the radiographic examinations.Right central incisor 17.3 1.2 1Lateral incisor 18.0 1.4 1Canine 22.2 1.8 1First premolar 20.4 1.7 1Second premolar 20.8 2.3First molar 21.0 1.7Second molar 18.7 2.3MandibularLeft central incisor 17.3 1.7 1Lateral incisor 18.5 2.1 1Canine 22.2 2.9 1First premolar 19.5 1.7 1Second premolar 20.5 3.2First molar 20.8 2.1Second molar 19.1 2.1Statistical testing by two-tailed t-test. 47,XXY males vs. relative males.ns = not significant.* p < 0.05.$ p < 0.1.andible of 47,XXY males and relative malesRelative malesN p Mean (mm) S.D. N5 ns 20.9 2.4 151 ns 20.0 2.6 111 $ 24.5 2.6 110 ns 19.0 2.7 105 ns 19.8 3.3 50 $ 16.2 2.1 108 ns 15.9 2.1 83 ns 21.0 2.5 132 ns 20.0 1.4 128 ns 24.3 2.1 80 ns 18.6 1.7 108 ns 17.9 1.7 89 ns 16.5 2.0 99 * 15.2 2.5 9r e f e r e n c e s1. Nielsen J, Wohlert M. Sex chromosome abnormalities foundamong 34 910 newborn children: results from a 13-yearincidence study in Arhus, Denmark. Hum Genet 1991;87:813.2. Ratcliffe S. Long term outcome in children of sexchromosome abnormalities. Arch Dis Child 1999;80:1925.3. Ratcliffe S, Masera N, Pan H, McKie M. Head circumferenceand IQ of children with sex chromosome abnormalities. DevMed Child Neurol 1994;36:53344.4. Varrela J. Effects of X chromosome on size and shape ofbody: an anthropometric investigation in 47,XXY males. AmJ Phys Anthropol 1984;64:23342.5. Brown T, Alvesalo L, Townsend GC. Craniofacial patterningin Klinefelter (47,XXY) adults. Eur J Orthod 1993;15:18594.6. Krusinskiene V, Alvesalo L, Sidlauskas A. The craniofacialcomplex in 47,XXX females. Eur J Orthod 2005;27:396401.7. Alvesalo L, Tammisalo E, Townsend G. Upper central incisorand canine tooth crown size in 47,XXY males. J Dent Res1991;70:105760.8. Alvesalo L, Tammisalo E. Enamel thickness in 45,X femalespermanent teeth. Am J Hum Genet 1981;33:4649.6 ns 16.3 1.5 168 ns 17.7 2.0 185 ns 22.3 2.6 156 ns 19.2 3.1 168 ns 19.8 3.8 86 ns 19.2 2.8 67 ns 17.3 3.9 73 ns 17.2 2.1 138 ns 17.8 2.0 188 ns 22.4 2.6 183 ns 18.9 3.3 137 ns 19.3 2.8 78 ns 19.5 2.3 87 ns 17.7 3.2 79. Zilberman U, Smith P, Alvesalo L. Crown components ofmandibular molar teeth in 45,X females (Turner syndrome).Arch Oral Biol 2000;45:21725.10. Harris EF, Hicks JD. A radiographic assessment of enamelthickness in human maxillary incisors. Arch Oral Biol1998;43:82531.11. Selmer-Olsen R. An odontometrical study on the NorwegianLapps. Thesis. University of Oslo: Anatomical Institute,Anthropological Department; 1949.12. Lahdesmaki R, Alvesalo L. Root lengths in 47,XYY malespermanent teeth. J Dent Res 2004;83:7715.13. Hunter ML, Collard MM, Razavi T, Hunter B. Increasedprimary tooth size in a 47,XXY male: a first case report. Int JPaediatr Dent 2003;13(4):2713.14. Ten Cate AR. The role of epithelium in the development,structure and function of the tissue of tooth support. OralDis 1996;2:5562.15. Lahdesmaki R, Alvesalo L. Root growth in the permanentteeth of 45,X/46,XX females. Eur J Orthod 2006;28:33944.16. Tammisalo EH. The dimensional reproduction of the imagelayer in orthopantomography. Proc Finn Dent Soc (SuomenHammaslaakariseuran Toimituksia) 1964;60:212.17. Thomas HF. Root formation. Int J Dev Biol 1995;39:2317.18. Dahlberg G. Statistical methods for medical and biologicalstudents. 2nd ed. George Allen and Unvin Ltd.; 1948.19. Garn S, Lewis A, Kerewsky R. X-linked inheritance of toothsize. J Dent Res 1965;44:43940.20. Alvesalo L. The Influence of sex-chromosome genes ontooth size in man. Ph.D. thesis. Proc Finn Dent Soc (SuomenHammaslaakariseuran Toimituksia) 1971;67:354.21. Filipsson R, Lindsten J, Almqvist S. Time of eruption of thepermanent teeth, cephalometric and tooth measurementand sulphation factor activity in 45 patients with Turnerssyndrome with different types of X chromosomeaberrations. Acta Endocrinol 1965;48:91113.22. Alvesalo L. In: Sandberg AA, editor. The Y Chromosome. PartB. Clinical aspects of Y chromosome abnormalities: dentalgrowth in 47,XYY males and in conditions with other sex-chromosome anomalies. New York, USA: Alan R. Liss, Inc.;1985. p. 277300.23. Alvesalo L. Sex chromosomes and human growth: a dentalapproach. Hum Genet 1997;101:15.24. Lau E, Mohandas T, Shapiro L, Slavkin H, Snead M. Humanand mouse amelogenin gene loci are on the sexchromosomes. Genomics 1989;4:1628.25. Nakahori Y, Takenaka O, Nakagome Y. A human X-Yhomologous region encodes amelogenin. Genomics1991;9:2649.26. Salido E, Yen P, Koprivnikar K, Yu L, Shapiro L.The human enamel protein gene amelogenin is expressedfrom both the X and Y chromosomes. Am J Hum Genet1992;50:30316.27. Kraus BS, Jordan RE. The human dentition before birth.Philadelphia, USA: Lea and Febiger; 1965. p. 119144.28. Alvesalo L, de la Chapelle A. Tooth sizes in two males withdeletions of the long arm of the Y chromosome. Ann HumGenet 1981;45:4954.29. Mayhall JT, Alvesalo L, Townsend G. Tooth crown size in46,Xi(Xq) human females. Arch Oral Biol 1991;36:4114.30. Lahdesmaki R, Alvesalo L. Root growth in the teeth of 46,XYfemales. Arch Oral Biol 2005;50:94752.31. Midtb M, Halse A. Root length, crown height and rootmorphology in Turner syndrome. Acta Odontol Scand1994;52:30314.a r c h i v e s o f o r a l b i o l o g y 5 2 ( 2 0 0 7 ) 8 2 2 8 2 7 827Root lengths in the permanent teeth of Klinefelter (47,XXY) menIntroductionSubjects and methodsSubjectsMeasurementsStatistical analysisResultsDiscussionAcknowledgementsReferences

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