2a) Basic principles of growth.ppt
- 1. الرحيم الرحمن هللا بسم َلَخ ِيذَّال َكِب َر ِمْساِب ْأ َرْقا َق قَلَع ْنِم َانَسنِ ْ اْل َقَلَخ م َرْكَ ْ اْل َُّكب َر َو ْأ َرْقا ِمَلَقْالِب َمَّلَع ِيذَّال ْمَلْعَي ْمَل اَم َانَسنِ ْ اْل َمَّلَع 1
- 2. DR. GHULAM RASOOL Associate Professor/ Head dept of orthodontics KCD. Basic Principles of Growth 2
- 3. Bone Formation Embryogenesis of craniofacial skeletal tissue: Chondrogenesis Endochondral bone formation Intramembranous bone formation 3
- 4. BONE FORMATION: Inductive Signals from Epithelial and Neural Tissues Mesenchymal Precursor Cells Condense Chondrocytes Osteoblasts (Flat Bones) 4
- 5. Chondrogenesis Formation of cartilage: Chondroblasts produce intercellular matrix Cells become encased in matrix and become chondrocytes Chondrocytes enlarge, divide and produce matrix (interstitial growth) New chondrocytes differentiate from surface membrane (appositional growth) Matrix remains uncalcified 5
- 6. Endochondral Bone Formation Cartilage is converted into bone: Begins 9th week IUL Hypertrophy and death of chondrocytes Cartilage matrix begins to calcify Invasion of blood vessels and CT cells Osteoblasts differentiate to form osteoid matrix and bone collar Osteoid tissue calcifies Membrane covers the bone and is essential Secondary Proliferation of Chondrocytes along peripheries 6
- 7. Intramembranous Bone Formation Bone formation from undifferentiated mesenchymal tissue Process begins in 8th week IUL Osteoblasts from ectomesenchyme produce osteoid tissue Cells become encased in matrix and become osteocytes Blood vessels retained within spaces and develop haversian system Osteocytes lose capacity to produce osteoid Periosteum produces more osteoid tissue (appositional growth) Osteoid calcifies Essential membrane covers bone 7
- 8. Intramembranous Bone Formation Blue arrow: surface layer of osetoblasts Red arrow: bone marrow cells Green arrow: osteocytes entrapped in bone 8
- 9. Bones formed by Endochondral Ossification Mostly forms bones of the cranial base (THOMES) Sphenoid bone Parts of Occipital bone Ehtmoid bone Temporal bone Malleus, Incus, Stapes Hyoid bone Clinical Significance: WHY is endochondral bone formation so necessary at the cranial base? 9
- 10. Answer: Cranial base is a region where PRESSURE forces exist Cartilage is pressure tolerant Results in increase in cranial base length against existing pressure (synchondroses) 10
- 11. Bones formed by Intramembranous Ossification Mostly forms bones of the calvaria and facial regions Frontal bone, Parietal bone, Parts of occipital bone (interparietal) Parts of sphenoid (greater wing, pterygoid plates) Parts of temporal bone (squamous and tympanic) Maxilla, Zygoma, Lacrimal bone Nasal bone, Vomer Mandible Occurs mostly where mild tension forces are present 11
- 12. Bone formation In the mature craniofacial skeleton, there are no qualitative differences between bone derived from endochondral or intramembranous mechanisms 12
- 13. Terminology related to Growth Growth field Growth site Growth center Remodelling Cortical drift Displacement 13
- 14. Growth Field Both inner and outer surfaces of bone are covered by an irregular pattern of “growth fields” comprised of various soft-tissue osteogenic membranes or cartilages The bone’s investing soft-tissue induces bone growth, and may be in the form of: Muscles Mucosa Blood vessels Nerves Connective tissue 14
- 15. Growth Field Bone has depository + resorptive fields over its surfaces (50-50) The varying activities and rates of growth of these fields are the basis for the differential growth processes that produce bones of irregular shapes The irregularity arises due to varied functions imposed on the bone by articulation of sutures, muscle attachments, insertions of teeth etc 15
- 16. Growth Site Growth fields having special roles in the growth of certain particular bones are called growth sites These include: Mandibular condyle Maxillary tuberosity Sutures Alveolar processes 16
- 17. Growth Center Special growth sites that control the overall growth of a particular bone are termed as growth centers The term “growth center” also implies that the “force” or “energy” for a bone resides primarily or solely within its growth center These are genetically predisposed areas Examples: Epiphyseal plates of long bones Synchondroses of the cranial base 17
- 18. Remodeling The differential growth activity involving simultaneous deposition and resorption on all the inner and outer surfaces of the bone Facial bones do not get bigger as a balloon enlarges Growth activity requires bone shaping 18
- 19. 19
- 20. Remodeling This shape change is brought about by remodeling Remodeling: Basic growth process Provides regional changes in shape, dimensions and proportions Produces regional adjustments that allow the bone to adapt to developing functions Basically is a process of reshaping and resizing of bone 20
- 21. Remodeling Types: Biochemical remodeling: continuous removal and deposition of ions to maintain mineral homeostasis Growth remodeling: the constant replacement of bone during childhood Haversian remodeling: secondary process of cortical reconstruction as primary vascular bone is replaced Healing: the regeneration and reconstruction of bone following pathology or trauma 21
- 22. Growth Movements: 1. Cortical Drift/Relocation Movement of a bone as a result of remodeling Growth by selective deposition and resorption Growth movements of the enlarging portion of the bone towards the depository surface Remodeling (deposition + resorption) Depository surface = increase in size of bone = enlarging portion Apparent growth towards that side as: ¬ deposition of bone on one side of cortical plate ¬ resorption of bone on other side 22
- 24. + + + + + + + + + - - - - - - - - - - Inferior Relocation of Palate 24
- 25. + + + + + + + + + + + - - - - - - - - - Posterior Relocation of Ramus As a result of cortical drift 25
- 26. Movement of the whole bone as a unit As a bone is carried away from its articulation with other bones, growth remodeling simultaneously maintains relationships of the bones to each other Growth Movements: 2. Displacement 26
- 27. Displacement 27
- 28. Types of displacement; Primary displacement: Secondary displacement: 28
- 29. Primary displacement: displacement associated with the bone’s own enlargment, e.g. Mandibular growth 29
- 30. Displacement 1st!!!! Adaptive 2nd!!!! Primary Displacement of Mandible 30
- 31. Secondary displacement Movement of a bone related to enlargement of other bones, e.g. Cranial base development resulting in secondary displacement of the maxilla 31
- 32. + + + + + ++ + + + + + + + + + + + + + + + Secondary Displacement of Maxilla 32
- 33. Combinations of Drift & Displacement 33
- 34. Growth Hypotheses 1930's: Remodeling Theory (James Couper Brash) 1940's: The Sutural Dominance Theory (Weinmann and Sicher) 1950's: The Nasal Septum/Cartilaginous Theory (James Scott) 1960’s: Functional Matrix Theory (Melvin Moss) 1970’s: Servo-system Theory (Alexandre Petrovic) 2000: Growth Relativity (Voudouris) 2004: Environmental Modulation of Genetic Inheritence (Mao & Nah) 34
- 35. THEORIES OF GROWTH THE GENETIC THEORY SICHER HYPOTHESIS (SUTURAL DOMINANCE) SCOTT’S HYPOTHESIS (NASAL SEPTUM) MOSS HYPOTHESIS (FUNCTIONAL MATRIX) PETROVIC HYPOTHESIS (SERVOSYSTEM) 35
- 36. THE GENETIC THEORY Genes are blamed for normal & abnormal growth Genetic mapping / engineering e.g. cleido-cranial dysplasia is caused by autosomal dominant genes (chromosome 8, at locus 8q 22) 36
- 37. SICHER SUTURAL THEORY Connective tissue between two bones (sutures) is responsible for growth by forcing them apart Tissue apart force makes space to be filled by appositional growth to occur at the borders of bones He assumed sutures, cartilage & periosteum responsible for growth but made sutures more responsible Sutures in naso-maxillary complex & vault produce force as in the base of skull by synchondrosis or epiphyseal plate in the long bones Sicher said about mandible that it grows like cartilage by “interstitial growth” & like epiphyseal plate by appositional growth under periosteum 37
- 38. SICHER SUTURAL THEORY DRAWBACKS: In untreated clefts of palate, though suture is not present, growth still occurs Translatory growth continues normally even in the absence or extirpation of sutures in experimental animals 38
- 39. SCOTT’S NASAL SEPTUM/Cartilaginous THEORY Scott found the importance of the cartilaginous portions of the head, nasal capsule, mandible & cranial base, felt that development of these is under intrinsic genetic control that continue postnatally Specifically he found nasal septum (cartilage) responsible for maxillary growth Nasal Septum Cartilage ---- Downward and Forward displacement of Maxilla Synchondroses ---- Elongating Cranial Base Condylar Cartilage ---- Downward and Forward displacement of Mandible Latham elaborated his hypothesis & found septum & septo-premaxillary ligament responsible for naso-maxillary growth 39
- 40. MOSS FUNCTIONAL MATRIX THEORY Moss felt that bone & cartilage lack growth determination & grow in response to intrinsic growth of associated tissues Genetic coding for craniofacial growth is outside the “bony skeleton” (functional matrices) All functions like respiration, mastication, speech etc. is associated with bony growth 40
- 41. MOSS FUNCTIONAL MATRIX THEORY ONE FUNCTION FUNCTIONAL CRANIAL COMPONENT FUNCTIONAL MATRIX SKELETAL UNIT PERIOSTEAL MATRIX MICROSKELETAL CAPSULAR MATRIX MACROSKELETAL MASSES FUNCTIONAL SPACES 41
- 42. MOSS FUNCTIONAL MATRIX THEORY There is no direct genetic influence on the size, shape, or position of skeletal tissues, only the initiation of ossification. All genetic skeletogenic activity primarily depends upon the embryonic functional matrices The “periosteal matrix” includes, muscles that are attached to periosteum for their action on “micro-skeletal units” The “tooth socket / alveolar bone” resorbs when a “tooth” is extracted “Capsular” matrix that affect “macroskeletal units”, like brain (capsule) effects the overlying cranium 42
- 43. PETROVIC THEORY Using the idea of cybernetics Petrovic reasoned that it is the interaction of a series of casual change & feedback mechanisms which determines the growth of various craniofacial regions Cybernetics is the science of communication & control theory that is concerned especially with the comparative study of autonomic control systems. E.g. ANS & brain According to Petrovic no genetically predetermined final length of mandible was found, rather, the direction & magnitude of condylar growth variation are perceived as quantitative responses to the lengthening of maxilla 43
- 44. Growth Relativity (Voudouris 2000) It was previously thought that increased activity in the postural masticatory muscles was the key to promoting condyle – glenoid fossa growth. (Petrovic et al) Non Muscular Hypothesis: Growth modification is associated with decreased activity. This premise has its foundation on 3 key specific findings Displacement Viscoelastic Forces Transduction 44
- 45. Environmental Modulation (Mao and Nah 2004) Previous synthetic accounts of craniofacial growth and development have used a “top- down” approach - examining changes in the length of the mandible over time and attributing addition or subtraction of length at different locations to bone formation or resorption. This approach is not sufficient and might benefit from a complementary “bottom-up" approach to examine how cellular growth contributes to addition and subtraction of, for instance, the increase in mandibular length under the influence of genes and environmental cues. Growth and development can only be understood correctly and comprehensively by a combination of both approaches. 45
- 46. Questions? 46