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1、下颌骨的生长发育,口腔正畸学教研室 刘月华,The Growth and Development of Mandible,Department of OrthodonticsLiu Yuehua, DDS, PhD, M.Orth.RCS(Edin),下颌骨的发生（Sperber，GH，1989） 图示下颌骨副软骨的发生部位,At birth:Body is still defined.Alveolar process scarcely present.Rami are proportionally short.Condyles are poorly defined.Symphyseal gr
2、owth still occurs increasing widthMandible symphysis closes 1-2 years.,Three major parts: body, rami, alveolar process,下颌骨的三向生长,生长方式：髁突软骨成骨骨膜下的骨表面增生,The mandible is a composite bone with endochondral growth at the condyle and intramembranous bone formation.,长度的增长宽度的增长高度的增长,下颌骨的三向生长,下颌骨各部分的生长方向 （Enlo
3、w，DH，1990）,下颌骨长度增长,下颌升支前缘吸收陈骨、后缘及外侧增生新骨；下颌骨外侧增生新骨、内侧吸收陈骨；下颌骨的增长，以磨牙区为最多，由第二乳磨牙至下颌角的距离，在新生儿约为10mm，岁时约20mm，成人约45-50mm。, Posterior border of ramus- intramembranous bone formation by periosteal tissues. Simultaneous resorption of bone on the anterior border of ramus. Surface deposition and reposition on
4、 complete surface of mandibular- remodelling. Mandibular lingual tuberosity (intramembranous)-appositional growth for horizontal elongation of the mandibular body on the lingual surface(between most posterior molar and mandibular foramen),The mandible appears to “grow” in a downward and forward mann
5、er when visualized on superimposed serial cephalometric tracing registered on cranial base.A: Simultaneous displacement occurs in the opposite direction, displacing the chin anteriorly and inferiorly.B: Actual growth takes place in a wide variety of regional direction with the predominent growth tre
6、nd posteriorly and superiorly.,下颌骨宽度的增长,下颌骨外侧面增生新骨，内侧面吸收陈骨；髁突随颞凹向两侧生长，使升支宽度增加；下颌骨前部在乳牙萌出后，宽度较少增加，下颌尖牙间宽度在岁以后几无增加。,下颌骨高度的增长,下颌升支高度的生长主要靠下颌髁突新骨的生长；喙突的同时生长；下颌体的生长，主要是靠下颌牙齿萌出时牙槽突的增高及下颌骨下缘少量增生新骨。, The mandibular condyle-Endochondral growth by interstitual and appositional proliferation of cartilage Surfa
7、ce deposition and resorption on complete surface of mandibular-remodelling inferior border of mandible coronoid process become fully differentiated Alveolar process(intramembranous) -Grows when teeth begin to erupt -resorbs when teeth are lost,The combination of condylar and ramus growth brings abou
8、t:, A backward transposition of the ramus, thereby permitting elongation of the body of the mandible. A displacement of the body (and dentition) in an anterior direction. A vertical lengthening of the ramus, providing displacement of the mandible inferiorly and vertical dimension for alveolar growth
9、. A moveable articulation during various growth changes.,下颌支的骨改建机制(remodelling),下颌升支肌肉附着处的横断面（Enlow，D.H.1990）,Vertical section through the ramus and the coronoid process showing the charateristic pattern of resorption,下颌支向侧方扩大，“”字形原理,The remodelling mechanism involved in this superior and lateral re
10、location is basically the expanding “V” principle. As the coronoid termini become higher, they grow apart at their apicies.,关节部的生长与改建,髁突向后上方生长，形成头大颈小的形态；髁突的位置根据字形原理，向字开阔的侧方生长。,髁状突的生长 （Goose，DH，1982）,髁状突软骨的作用,Severe mandibular deficiency from TMJ infection.,颏部的生长,灵长类中只有人类具有颏的特征；颏部是骨改建的结果；颏部对侧面外形具有重要意
11、义。,四、牙列与合的发育,（一）合的建立,婴儿在无牙齿萌出时，无合关系；婴儿第个月乳牙萌出时开始建合；成人第三磨牙萌出时才完成建合。,向前的动力向后的动力内外的动力平衡垂直向的动力平衡,（二）建合的动力平衡（肌肉）,萌牙前期的颌间关系乳牙合替牙合恒牙合,（三）合的发育阶段,乳牙合期,第-个月时下颌乳中切牙萌出，在-岁时上颌第二乳磨牙萌出，到岁半时，乳牙牙根形成。一般萌出顺序为： I II IV III VSequence of eruption of primary teeth:Central & lateral incisors 6-9 months, first molars, canin
12、es 12-18 months, second molars 20-24 months.Mandibular teeth usually precede maxillary teeth by 1-4 months.,乳牙列间隙变化,生长间隙：-岁，前牙部分；灵长间隙(primate space):上颌乳尖牙近中或远中。,In the maxillary arch, the primate space is mesial to the canines. In the mandibular arch, the primate space is distal to the canine.,Spaci
13、ng in the primary incisor region is normally distributed among all the incisors, not just in the “primate space” locations where permanent spaces exist in most mammalian species.,终末平面的类型,垂直型(flush terminal plane)近中型(mesial step)远中型(distal step),2-4岁 无间隙、无磨耗、E远中呈直线4-6岁 有间隙、有磨耗、E 近中移动,正常乳牙合的特征,正常乳牙合的特
14、征,前牙合关系：覆盖很浅，覆合较深；前牙部分具有生长间隙及灵长间隙；终末平面以垂直型及近中型较多，对恒牙合的建立意义较大；上颌乳尖牙的近中舌侧面与下颌乳尖牙的远中唇侧面相接触。,（二）替牙合期,-岁，“丑小鸭”阶段,Period when both primary and permanent teeth are present in the mouth.,恒牙萌出时间及顺序,上：6-1-2 -4-5-3-7 -8 下：6-1-2 -3-4-5-7 -8,Most common eruption sequence:,5-8.5 yrs.early mixed dentition,9-13 yrs
15、.late mixed dentition,18-25yrs,或为：上：6-1-2 -4-3-5-7 -8下：6-1-2 -4-3-5-7 -8,Another sequence of eruption fairly common in the mandibular arch is:,The sequence of eruption of the permanent teeth is more important than the exact time of eruption.,Eruption of the first permanent molars,Gives the key to th
16、e occlusion,Three ways a Class I molar relationship can develop:,Mesial step terminal plane: permanent molars erupt directly into a Class I relationship.Straight(Flush) terminal plane: erupting lower first permanent molars may give mesial force moving lower second primary molars forward to allow a C
17、lass I molar relation.(iii) Late mesial shift of a straight terminal plane.-most common way that a Class I molar relation results.-permanent molars erupt end-to-end.-because of dimensional differences between the primary and permanent 3,4 and 5(Leeway space of Nance), after exfoliation of the primar
18、y teeth the lower first permanent molars move mesially into a Class I occlusions.,替牙间隙（Leewayspace) =（C+D+E）（3+4+5） 上颌单侧约0.9mm 下颌单侧约1.7mm,替牙间隙（Leewayspace),On the average, the combined width of the mandibular deciduous canine and first and second deciduous molars is 1.7 mm greater than the permanent
19、 successors. The deciduous versus permanent tooth dimension for the comparable maxillary arch segment is only 0.9mm. Mesial drift is consequently greater in the mandibular arch, often compensating for a flush terminal plane.,“Leeway space” in maxillary and mandibular arches, as described by Nance.,I
20、f a child has a flush terminal plane molar relationship early in the mixed dentition, about 3.5 mm of movement of the lower molar forward relative to the upper molar is required for a smooth transition to a Class I molar relationship in the permanent dentition. About half of this distance must be su
21、pplied by differential growth of the lower jaw, carrying the lower molar with it. the other half can be obtained from the leeway space, which allows greater mesial movement of the mandibular than the maxillary molar.,Eruption of the permanent teeth,First molars followed almost immediately by lower c
22、entral incisors and thenlateral incisors.Mandibular incisors development lingual to the resorbing roots ot the primary incisors, the primary incisors being moved labially as they exfoliate.(iii) the permanent incisors find their correct positions by influence of their eruptive pathways and functiona
23、l forces.(iv) If primary incisors are not resorbing properly, both teeth may be present at the same time. The primary tooth should be removed to alloew the lingually placed permanent incisor to assume its proper position.(v) The eruption of the mandibular lateral incisor pushes the primary cuspid di
24、stally and labially so that the primate space is lessenes or closed.,Incisor eruption-mandible,Lower permanent incisors erupt without crowding and attain good alignment. Small amounts of crowding may be present during eruption of the lower latral incisors but this may be relieved by significant incr
25、eases in arch length and width in this region during their eruption.(ii) Intercanine width increases up to the eruption of the lateral incisors. No great relief of crowding in the incisor segment can be expected after the complete eruption if lateral incisors”.,(b) When normal spacing is present,( c
26、 ) if lack of spacing is present,(i) Permanent incisors will be crowded upon eruption. Laterals in lingulversion(ii) Laterals may erupt rotated and not diplace primary cuspids into primate space.(iii) Resorption of roots of primary canine may result in premature exfoliation of the canine. When this
27、happens the permanent incisors may be tipped lingually by lip muscles. The permanent canine may then be displaced by the root of the lateral and erupt in severe labioversion.(v) If primary canine ar deflected into traumatic occlusion with maxillary canines, the mandible may be retruded to a wide por
28、tion of the maxilla, producing a functional Class II relationship(relieve by grinding crowns out of traumatic occlusion).,(d) Maxillary incisor eruption,Maxillary central incisors:Erupt slightly labial to primary centralsHave slight distal inclinationUsually space(diastema) between the centrals.Maxi
29、llary lateral incisors:Erupt slightly lingual to permanent centrals.With distal inclination.,(e) The “ugly duckling” stage of development,(i) Pattern formed by the 4 maxillary incisors.(ii) As the laterals erupt, the canines higher up are also erupting, being guided down by the roots of the lateral
30、incisors.(iii)This canin position tends to move the roots of the lateral mesially and the crowns flare distally.(iv) As the canines erupt, the laterals upright and the spacs between the incisors close.(v) Orthodontic movement of lateral incisors before th canines come close to eruption is dangerous
31、because the apices of the lateral incisors may be damaged or the permanent canines may be deflected.,(f) Mandibular canine and premolar eruption,(i) Favorable sequenc: 3, 4, 5(ii) As should precede the second molar.(iii)Canine eruption should be first to: Maintain proper arch length. Prevent lingual
32、 tipping of lower incisors(iv) First premolar eruption is uneventful.(v) second premolar is tooth most susceptible to malposition or impaction in the mandibular arch. It suffers the problems of inadequate space since it is the last tooth to be fitted in .,(f) Mandibular canine and premolar eruption,
33、If the second molar erupts before it, the first permanent molar may move mesially and block out the second premolar.If the second primary molar is lost prematurely, the first permanent molar moves mesially blocking out the second premolar.If leeway space is small, the first permanent molar should no
34、t be allowed to move mesially until the second premolar in in occlusion.Second premolars are often congenitally absent. Be careful!,(g) Maxillary canine and premolar eruption,(i) Favorable sequenc: 4, 5, 3(ii) Maxillary incisor segment is supported by the lower anterios thus is not prone to lingual
35、collapse.,(h) First premolar erupts uneventually,(i) Second premolar,Usually erupts easily duo to larger size of primary second molarBeware of early loss of maxillary second primary molarsthe permanent molars will move mesially, blocking out the second premolars,(j) canine eruption is the most criti
36、cal situation in the maxillary arch.,Situation necessary for good canine position:(i) Excessive space when the second premolar erupts.(ii) Canine eruption immediately after second premolar eruption.(iii) No mesial tipping of first permanent molar.(iv) Second permanet molar should not erupt before th
37、e second peremolar and the canine.(v) Eruption of maxillary canine closes spaces between the incisors. If maxillary arch length is deficient and sequence is normal, the canine will erupt malposed (most often to labial).,(k) Second molar eruption,(i) Lower should erupt before upper molar to prevent o
38、ver-eruption of the upper molar.(ii) Second molars should erupt after all teeth mesial to them.,替牙过程中的间隙补偿机制,乳牙间适当的间隙恒切牙偏唇侧萌出尖牙间牙弓宽度增加双尖牙偏颊侧萌出乳恒牙大小比例协调替牙间隙的调节作用, Proper space among deciduous teeth. Slight labial positioning of central and lateral incisors. A Slight increase in arch width across the
39、canines. Slight buccal positioning of premolars. Proportional permanent teeth. “Leeway space” adjustment of occlusal relationship.,上颌中切牙萌出早期，出现间隙；上颌侧切牙初萌时，牙冠向远中倾斜； 恒切牙萌出时，轻度拥挤；上下第一恒磨牙建合初期，可能为尖对尖关系；上下恒切牙萌出早期，出现前牙暂时性深覆合。,暂时性错合的表现, The maxillary incisors flare laterally and are spaced when they first e
40、rupt. The spaced incisors teed to improve when the permanent canines erupt. Mild irregularity of the mandibular incisors is normal at age 7 to 8, when the permanent incisors and first molars have erupted but the primary canines and molars are retained. The flush terminal plane relationship , which p
41、roduces an end-to-end relationship of th permanent molars when they first erupt, can change to Class I in the permanent dentition.,(三) 恒牙合的特征,前牙覆合、覆盖,尖牙、磨牙关系,牙弓大小的变化,牙弓长度和周长从青春期晚期到青年期显著减小，牙弓宽度略有增加。 -岁，下颌周长减少5mm(Fisk)。 -岁，下颌周长减少3mm(Knot)。上下颌的牙弓宽度增加1-2mm。,牙龄与骨龄,Hellman牙齿发育进度,I 乳牙合完成前期IIA 乳牙合完成期IIC 第一恒磨牙开始萌出期IIIA 第一恒磨牙及前牙萌出完成期IIIB 乳磨牙脱落、后继前磨牙开始萌出期IIIC 第二恒磨牙开始萌出期IVA 第二恒磨牙萌出完成期IVC 第三恒磨牙开始萌出期VA 第三恒磨牙萌出完成期,提问与解答互动时间,
