Orthodontic Tooth Movement - Histology and Biomechanics PDF

Orthodontic Tooth Movement: Histology and Biomechanics D r. Ö ğ r. Ü y e s i B e g ü m A S L A N  O r t h o d o n t i c To o t h M o v e m e n t  O r t h o d o n t i c t re a t m e n t re l i e s o n a p p l y i n g p ro l o n g e d p re s s u re t o teeth, leading to...

Orthodontic Tooth Movement: Histology and Biomechanics D r. Ö ğ r. Ü y e s i B e g ü m A S L A N  O r t h o d o n t i c To o t h M o v e m e n t  O r t h o d o n t i c t re a t m e n t re l i e s o n a p p l y i n g p ro l o n g e d p re s s u re t o teeth, leading to tooth m o v e m e n t a s t h e s u rro u n d i n g b o n e re m o d e l s.  O r t h o d o n t i c To o t h M o v e m e n t  T h i s i n v o l v e s s e l e c t i v e re m o v a l and addition of bone, causing t h e t o o t h t o c a rr y i t s a t t a c h m e n t a p p a r a t u s w h i l e t h e t o o t h s o c ke t migrates.  Orthodontic Tooth Movement  To o t h movement is primarily a ‘periodontal ligament’ phenomenon. Periodontium (Tooth supporting structures)  Gingiva  Cementum  Pe r i o d o n t a l L i g a m e n t  Alveolar bone  Gingiva C o n n e c t i v e t i s s u e c o n s i s t i n g o f:  C o l l a g e n fi b e r s : 6 0 %  Fibroblasts: %5  Extracellular matrix, nerves and vessels: 35%  Gingival Fibers Pro v i d e s re s i s t a n c e t o m a i n t a i n t h e f o rm a n d integrity of the dentogingival attachment.  Gingival Fibers  C i r c u m f e r e n t i a l fi b r e s  Surrounds the tooth and extends into the gingival margin  D e n t o g i n g i v a l fi b r e s  Extends from supraalveolar part of cementum into the gingival margin  Gingival Fibers  D e n t o p e r i o s t e a l fi b r e s  Extends from cementum to attached gingiva  Tr a n s e p t a l fi b r e s  Extends above the interdental bone and inserts to cementum of adjacent tooth  Cementum  The non-vascularized, non- i n n e r v a t e d l ay e r t h a t c o v e r s the root surface.  Cementum  During root formation, the initial cementum that forms is acellular (primary) cementum.  Fo l l o w i n g t o o t h e r u p t i o n , Celllular cementum c e l l u l a r ( c e l l u l a r- s e c o n d a r y ) Acelllular cementum develops in cementum response to the functional needs of the tooth.  Periodontal Ligament  The periodontal ligament is a soft, vascular, and cellular connective tissue that surrounds tooth roots and links the root cementum with the lamina dura.  Periodontal Ligament Nutritional requirements :  Ve s s e l s e x t e n d i n g f r o m t h e alveolar bone to the periodontal ligament (PDL) space,  Va s c u l a r i z a t i o n i n t h e a p i c a l a n d gingival regions.  Periodontal Ligament Cellular elements: U n d i ff e r e n t i a t e d m e s e n c h y m a l c e l l s , fi b r o b l a s t s a n d o s t e o b l a s t s. Ground substance : Proteoglycan, Glucoseaminoglycans and other proteins  Periodontal Ligament  T h e m a i n fi b e r o f t h e P D L :  Alveolar crest  Oblique  Horizontal  Apical  I n t e r r a d i c u l a r fi b r e s  Periodontal Ligament  The diagonal arrangement of the s u p p o r t i n g fi b e r s r e s i s t s t h e displacement of the tooth expected during normal function  PDL Response to Normal Fu n c t i o n  During mastication, the teeth and periodontal structures are subjected to intermittent heavy forces which last for 1 seconds or less.  D u e t o i n c o m p r e s s i b l e t i s s u e fl u i d o f PDL, the force is transmitted to the alveolar bone, which bends in response.  PDL Response to Normal Fu n c t i o n  Bone bending in response to normal function generates piezo-electric currents that appear to be an i m p o r t a n t s t i m u l u s t o s ke l e t a l r e g e n e r a t i o n a n d r e p a i r.  This is the mechanism by which bony architecture is adapted to functional demands.  PDL Response to Normal Fu n c t i o n  If pressure against a tooth is m a i n t a i n e d , h o w e v e r , t h e fl u i d is rapidly expressed and the tooth displaces within the PDL space, compressing the ligament itself against adjacent bone and pain is felt.  Alveolar Bone  Surrounds the tooth 1 mm apical to cementoenamel junction.  Alveolar Bone  The portion of the alveolar bone into which principal fi b e r s o f P D L a r e e m b e d d e d i s called the bundle bone.  Alveolar Bone  Osteoclasts and osteoblasts are responsible for alveolar bone remodeling.  P h y s i o l o g i c a l To o t h M o v e m e n t  Eruption of teeth  Mesial/Distal migration of teeth  P h y s i o l o g i c a l To o t h M o v e m e n t  Any alteration in occlusal f o rc e s c a n l e a d t o movement of the tooth. (e.g. loss of neigbour/ antagonist teeth)  During the tooth migration, the periodontal ligament (PDL) and alveolar b o n e u n d e rg o re m o d e l i n g.  The t u rn o v e r r a t e o f t h e P D L i s n o t u n i f o rm along the ligament. Cells on the bony side a re m o re a c t i v e t h a n t h o s e o n t h e ro o t side.  T h e re f o re , re m o d e l i n g p r i m a r i l y o c c u r s o n the bony side.  Ac e l l u l a r cementum p ro t e c t s t h e ro o t s u r f a c e f ro m g e t t i n g re s o r b e d d u r i n g t h e physiological migration. O r t h o d o n t i c To o t h M o v e m e n t  O r t h o d o n t i c To o t h M o v e m e n t  W h e n a f o rc e i s a p p l i e d t o a tooth over a certain period, tooth movement occurs as a re s u l t o f d y n a m i c c h a n g e s in the shape and composition of the s u rro u n d i n g b o n e a n d s o ft tissues.  O r t h o d o n t i c To o t h M o v e m e n t  T h e a p p l i e d f o rc e re s u l t s i n l o c a l pressure and tension fi e l d s i n t h e a d j a c e n t tissues of the tooth, mediating bone re s h a p i n g.  O r t h o d o n t i c To o t h M o v e m e n t  During this re m o d e l i n g p ro c e s s , s o m e a re a s o f t h e Bone Bone b o n e ex p e r i e n c e aposition resorption resorption, while in o t h e r a re a s , b o n e aposition occurs.  ’Orthodontic f o rc e s a re h e a v i e r t h a n n a t u r a l f o rc e s t h a t re s u l t s i n p h y s i o l o g i c a l t o o t h migration’ B i o l o g i c C o n t r o l o f To o t h Movement  Biological control mechanisms from the time of sustained force application to orthodontic tooth movement Theories of Orthodontic Tooth Movement Piezoelectricity Pressure- Tension Theory Theory Changes in bone Cellular changes produced metabolism controlled by by c h e m i c a l the e l e c t r i c s i g n a l s messengers, that are produced when traditionally thought to be a l v e o l a r b o n e fl e xe s a n d generated by alterations bends. i n b l o o d fl o w t h r o u g h  Piezoelectricity Theory  Deformation of the crystalline structures (e.g: hydroxyapatite and c o l l a g e n ) r e s u l t s i n a fl o w o f e l e c t r i c current as electrons are displaced from one part of the crystal lattice to a n o t h e r.  This phenomenon occurring in numerous crystalline materials is called ‘p i e z o e l e c t r i c i t y ’  Piezoelectricity Theory  When force is applied to the t o o t h , t h e fi b e r s o f t h e P D L g e t stretched, transmitting the forces to the alveolar bone.  In response, the alveolar bone fl e xe s. T h e b e n d i n g i n t h e b o n e gives rise to piezoelectric currents.  Piezoelectricity Theory Bending of the alveolar bone during mastication Piezoelectric Signals Maintains the width of PDL space  Pressure- Tension Theory  Re l i e s o n t h e c h e m i c a l r a t h e r than electric signals are involved in tooth movement.  Pressure- Tension Theory  Sustained pressure causes tooth to shift in PDL space.  Ligaments are compressed in one area while stretched in the other parts.  C o m p r e s s i o n a r e a  b l o o d fl o w i s decreased  Te n s i o n a r e a  b l o o d fl o w i s i n c r e a s e d or maintaned  Pressure- Tension Theory To o t h m o v e m e n t o c c u r s i n 3 s t a g e s :  1) Pressure in the PDL causes a l t e r a t i o n o f b l o o d fl o w  2 ) C h e m i c a l a g e n t s ( c A M P, c G M P, i n t e r l e u k i n s ) a r e f o r m e d and/or released  3) Cellular activation  The heavier the sustained pressure, the greater should be t h e r e d u c t i o n i n b l o o d fl o w through compressed areas of the PDL, up to the point that the vessels are totally collapsed and n o f u r t h e r b l o o d fl o w s  Fro m a contemporary perspective, it appears that both mechanisms may play a part in the biologic c o n t ro l o f t o o t h m o v e m e n t E ff e c t o f F o r c e M a g n i t u d e o n To o t h M o v e m e n t  Eff ects of Force Magnitude Sustained Heavy Light Forces Forces  When light but prolonged  Heavier the sustained force is applied to a tooth, pressure, the greater should b l o o d fl o w t h r o u g h t h e p a r t i a l l y b e t h e r e d u c t i o n i n b l o o d fl o w compressed PDL decreases as through compressed areas of s o o n a s fl u i d s a r e e x p r e s s e d the PDL, up to the point that from the PDL space and the the vessels are totally to o th m o v e s in its s o c ke t (i.e. , in a few seconds) collapsed and no further blood Response to Light Orthodontic Forces Direct (Frontal) Bone Resorption  Direct (Frontal) Bone Resorption  Occurs via the osteoclasts located on the alveolar bone surface facing the PDL.  U n d i ff e r e n t i a t e d m e s e n c h y m a l c e l l s a r e t r a n s f o r m e d t o osteoclasts  Light, continuous and optimal forces are required.  Blood vessels are not occluded.  Osteoclasts appear within 30-40 hours and orthodontic tooth movement is iniated.  Normal appearance of vessels under no pressure. Notice the b l o o d fl o w  Constriction of the blood vessels under light pressure in the compression area. Vessels are constricted but not occluded. Response to Sustained Heavy Pressure Indirect (Undermining) Bone Resorption  Indirect (Undermining) Bone Resorption  U n d e rm i n i n g re s o r p t i o n t a ke s p l a c e u n d e r heavy pressure  B l o o d v e s s e l s a re o c c l u d e d a n d b l o o d s u p p l y i s c u t o ff.  H y a l i n i z e d t i s s u e , which is acellular, a v a s c u l a r t i s s u e w i t h g l a s s - l i ke a p p e a r a n c e , i s f o rm e d i n t h e P D L.  Indirect (Undermining) Bone Resorption  Af t e r a d e l ay o f s e v e r a l d ay s , c e l l u l a r e l e m e n t s begin to invade the necrotic (hyalinized) area.  Osteoclasts appear within the adjacent bone marrow spaces and begin an attack on the under side of the bone immediately adjacent to the necrotic PDL area.  This process is appropriately described as undermining resorption, since the attack is from the underside of the lamina dura.  Indirect (Undermining) Bone Resorption  I t t a ke s 7 - 1 4 d a y s f o r o s t e o c l a s t s t o m i g r a t e t o the area and tooth movement to get started. T h e d e l ay w i t h h y a l i n i z a t i o n a n d u n d e r m i n i n g resorption tooth movement is due to;  t h e d e l a y i n s t i m u l a t i n g d i ff e re n t i a t i o n o f c e l l s w i t h i n t h e m a rro w s p a c e s ,  the considerable thickness of bone that needs to be re m o v e d f ro m t h e u n d e r s i d e b e f o re a n y t o o t h m o v e m e n t c a n t a ke p l a c e. C o m p l e t e l y c u t - o ff b l o o d fl o w i n t h e a r e a o f c o m p r e s s i o n  With frontal resorption ( light force ) ,a steady attack on the outer surface of the lamina dura results in smooth continuous tooth movement.  With undermining resorption (heavy force), there is a delay until the bone adjacent to the tooth can be removed. At that point, the tooth "jumps" to a new position, and if heavy force is maintained, there will again be a delay until a second round of u n d e r m i n i n g r e s o r p t i o n c a n o c c u r. Factors that enhance the formation of hyalinized tissue:  Heavy force magnitudes  Fo r c e s c o n c e n t r a t i n g o n n a r r o w a r e a s ( To o t h movement type, i.e. intrusion)  Sudden or continuous type of force ( Force type )  Anatomy of the alveolar bone (Increased in cortical bone)  Anatomy of the root form  E ffi c i e n t t o o t h m o v e m e n t a n d r e d u c e d p a i n a r e associated with avoiding areas of periodontal ligament (PDL) necrosis. However, even with light forces, avascular areas may develop in the PDL, causing a delay in tooth movement until these areas can be removed through undermining resorption.  The ideal smooth progression of tooth movement with light force is challenging in clinical practice, often resulting in a more stepwise fashion due to inevitable areas of undermining resorption.  In orthodontic practice, the objective is to p ro d u c e t o o t h m o v e m e n t a s m u c h a s p o s s i b l e b y f ro n t a l re s o r p t i o n , re c o g n i z i n g t h a t s o m e a re a s o f P D L n e c ro s i s a n d u n d e rm i n i n g re s o r p t i o n w i l l p ro b a b l y o c c u r d e s p i t e e ff o r t s t o p re v e n t t h i s. Thank you for your attention…