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Modus operandi of functional appliances

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Modus operandi of functional appliances

  1. 1. www.indiandentalacademy.com
  2. 2. • Introduction. • History. • Premise on which modus operandi of functional appliance was built. • Modus operandi of functional appliance – schools of thought. • Research findings. - Cellular and bio molecular findings. - Jaw muscle activity and and muscle fiber recruitment. - Skeletal and dental changes. • Conclusion. Contents www.indiandentalacademy.com
  3. 3. “Working with growth” has had been a term which has been in for quite sometime now. Its presence has not only given orthodontics a huge credit but also promised a greater working range for orthodontist. This seminar would present claims and counter claims on the working principles of functional appliance and at present what to expect out of it. Introduction www.indiandentalacademy.com
  4. 4. History www.indiandentalacademy.com
  5. 5. • European orthodontists have long been aware of the role of peri-oral musculature in orthodontic problems. They also recognized the potential use of deforming forces to eliminate these problems. These ideas have been borrowed latter by the Americans. www.indiandentalacademy.com
  6. 6. 1912 • The spark arose by Lischer’s theory, which states that if compensatory, adaptive lip and tongue function could exacerbate excessive overjet in class-II type of malocclusion and if abnormal swallowing and prolonged finger sucking habits could create anterior open bite and narrow arches, could not the same muscles be used to correct these and other problems. www.indiandentalacademy.com
  7. 7. 1936 : Andresen: working hypothesis • Though Andresen working hypothesis was not intended for “guiding growth" at that time ,but only to eliminate the adverse effects of abnormal function. • Andresen was surprised to see that night time wearing of the appliance not only had eliminated the abnormal neuro-muscular compensation but also produced a complete saggital correction and significantly improved the facial profile. www.indiandentalacademy.com
  8. 8. 1967 • Findings concerning the biological peculiarities of mammalian condyle cartilage, role of respiration on craniofacial morphology and popular theories on functional matrix hypothesis and epigenitics at that time have helped fuel this understanding • Petrovic and coworkers produced the first rigorous demonstrations that the condylar cartilage’s growth rate and amount can be modified using appropriate functional and orthopedic appliances. • Since then, many other clinicians and researchers have inquired about possibility of modifying the condylar cartilage’s growth ratewww.indiandentalacademy.com
  9. 9. Premise on which modus operandi of functional appliances was built www.indiandentalacademy.com
  10. 10. Peculiarity of condylar cartilage: • Unlike the primary cartilage found at other growth sites, i.e. Epiphysis of long bones, Speno-occipital syncondrosis, which are embryonic in origin, the condylar cartilage originates separately during the development and further more Stutzmann 1967 emphasized that in primary cartilage the dividing cells, differentiated condroblasts, are surrounded by cartilaginous matrix that isolates them from local factors able to restrain or stimulate cartilage growth whereas the secondary cartilage ;the dividing cells, precondroblasts, are not surrounded by a cartilaginous matrix and thus are not isolated from local factor influence. www.indiandentalacademy.com
  11. 11. Fig primary vs secondry www.indiandentalacademy.com
  12. 12. Popularity of epigenetic theory • The genome as providing a set of formal, prior, intrinsic, and necessary causal factors which, when combined with efficient, proximate, extrinsic, and necessary casual factors, together are sufficient to account for the regulation of development. • The genetic theory views that the diploid genome, at the moment of fertilization, contains all the information necessary, “a blue print,” to regulate skeletal size, Shape, and location – a blue print, moreover, that merely requires a permissive environment in which to express itself.www.indiandentalacademy.com
  13. 13. Various hypothesis on the modus operandi of functional appliances www.indiandentalacademy.com
  14. 14. • Five hypotheses based on neuromuscular mechanisms have evolved to account for the skeletal changes associated with functional appliance therapy. • In three of these concepts an increase in postural and functional muscle activity is fundamental to the proposed mode of action of the appliances and thereby their design and the degree of vertical opening used in the bite registration. This increased activity is thought to result from either an enhanced stretch (myotonic) reflex of the masticatory muscle, www.indiandentalacademy.com
  15. 15. or from "conditioning" of the patient that produces an enhanced higher-brain-center drive of the motor neurons supplying the muscles, even during sleep (Myodynamic). • Fourth view proposes that increased lip strength is the prime force in alveolar bone remodeling during functional appliance therapy. • Fifth emphasizes the importance of viscoelastic elements in the stretched masticatory muscles and other orofacial tissue; these elements produce an increase in "passive" muscle tension, which provides the major force elicited by the appliance. www.indiandentalacademy.com
  16. 16. Modus operandi of functional appliances • Melvin Moss school of thought (1962) • Petrovic school of thought. (1972) • Voudoris school of thought.(2000) www.indiandentalacademy.com
  17. 17. Functional matrix hypothesis • Claims that the origin, growth (i.e., changes in size, shape, and location), and maintenance in being of all skeletal tissues and organs (i.e., skeletal units) are always secondary, compensatory, mechanically obligatory responses to temporally and operationally prior events or processes occurring in specifically related non skeletal tissues, organs, or functioning spaces (i.e., in functional matrices, either capsular or periosteal). www.indiandentalacademy.com
  18. 18. Functional cranial component Skeletal unit Functional matrices Micro- skeletal unit Macro Skeletal unit Periosteal matrices Capsular matrices www.indiandentalacademy.com
  19. 19. • Moss stresses the dominance of non osseous structures of the Cranio-facial complex over the bony parts. He claims that the growth of the skeletal components ,whether endocondrial or intra membranous in origin is largely dependent on the growth of functional matrices www.indiandentalacademy.com
  20. 20. Petrovic school of thought • Role of lateral pterigoid muscle (LMP) to regulate in the control of the condylar cartilage growth as shown by Petrovic, Stutzmann in 1972,1974,1975 was further confirmed by McNamara in 1980’s • Stutzmann et al in 1976 discovered that the reterodiscal pad apparently has a mediator role in the efforts of the LPM to control condylar growth www.indiandentalacademy.com
  21. 21. Functional appliances Increased contractile activity of lateral pterygoid Intensification in reterodiscal pad iterative activity Supplementation in growth stimulating factors Enhancement of local mediators Reduction of local regulators Additional growth of the condylar cartilage Additional subperiosteal ossification Supplementary lengthening of the mandible www.indiandentalacademy.com
  22. 22. Cybernetic model • It is based on communication and information theory. • Petrovic 1977 was the first to promulgate a cybernetic model to account for physiological phenomenon involved in facial growth and the method of operation of orthodontic and functional appliance. • Claims that the upper arch is the constantly changing reference input and the lower arch is the controlled variable. Servosystem theory www.indiandentalacademy.com
  23. 23. • STH or Testosterone blood level increases, the supplementary lengthening of the mandible is greater than that of the maxilla. STH or Testosterone Optimum occlusion Suboptimum occlusion. No positional change Growth or growth represented Servo system Servo system www.indiandentalacademy.com
  24. 24. Condylar growth with STH , HP www.indiandentalacademy.com
  25. 25. RDP LPM Septal cartilage Mandible Maxilla Growth hormones Functional appliances Peripheral comparator CO Central comparator Deviation signal Detectors PDL CNS www.indiandentalacademy.com
  26. 26. Working hypothesis of different functional appliance. www.indiandentalacademy.com
  27. 27. • Functional appliances that position the mandible forward increase the condylar growth rate and amount • Wearing the postural hyperpropulsor everything occurs as if the upper dental arch were in a more anterior position than normal. • The “operation of confrontation” of the two dental arches then gives a deviation signal. • During the growth period the saggital deviation produced by the postural hyperpropulsor decreases through the supplementary forward growth of the mandible. Postural hyperpropulsor (Herbst, Frankle) www.indiandentalacademy.com
  28. 28. • Periodic increase in thickness of the postural hyperpropulsor produce increase in LPM activity and in the activity of the retrodiscal pad as recorded electromyographically; these, consequently, bring about increase in the rate and amount of condylar cartilage growth. • If the appliance is removed after the growth is completed, little or no relapse is observed. If the appliance is removed before the growth is completed, no significant relapse is detected if good inter- cuspation is maintained however if good intercuspation is not achieved, the comparator of the servosystem imposes an increase or decrease condylar growth rate until a state of intercuspal stability is established. • Functional maxipropulsion involving periodic forward repositioning appears to be the best procedure for eliciting a supplementary lengthening of mandible. www.indiandentalacademy.com
  29. 29. Frankel • Fränkel's functional regulator is worn primarily in the lingual and dental regions, and uses the vestibule as the operational base in contrast to other functional appliances. It is claimed that the system of labial, lingual, and buccal pads and shields directly affects the level of postural activity in the facial and masticatory muscles by means of a training effect. The buccal and labial shields placed highly in the vestibule would also indirectly put traction onto the periosteum. This traction would stimulate bone growth in the apical subperiosteal areas and provide a guidance of eruption for the teeth. www.indiandentalacademy.com
  30. 30. • The basic components are - Equilibrium theory. - Bone deposition secondary to periosteal pull. - Training of muscles (hypotonic or hypertonic) www.indiandentalacademy.com
  31. 31. Class II elastics • Intermaxillary intra-oral elastics, placed bilaterally for 14 hours daily, in rats between upper first molar and lower third molar, are not only orthodontic devices but also functional appliances capable of stimulating the growth rate and amount of the condylar cartilage • Class II elastics don’t increase the contractile activity of LPM as the hyperpropulsor .The stimulating effect of class II elastics is primarily mediated through the retrodiscal pad (metabolic pump) www.indiandentalacademy.com
  32. 32. Herren (L.S.U.) Ativator • The Herren activator, or the Louisiana state university modification of it,is different form of postural hyperpropulsor; it opens the construction bite well beyond the postural rest position, similar to that achieved by the Harvold – Woodside activator. • Such construction bite do not bring about any increase activity of the LPM. instead it has a two step effect. when the appliance is worn ,it creates a new sensory engram which stimulates reterodiscal pad. But the most important action of this appliances is seen when the appliance is not worn. This happen due to decreased length of LPM which stimulates the condyle when the appliance is not wornwww.indiandentalacademy.com
  33. 33. • Amidst the claims on the working hypothesis of functional appliances as put forward by Petrovec et al, John Voudouris in 2000 proposed the concept of growth relativity. • He attributes the failure of earlier research on the working hypothesis of functional appliances due to earlier EMG methods, which were transcutaneous, short term and removable as described in 2003. www.indiandentalacademy.com
  34. 34. Voudouris school of thought • The theory of relatively essentially states that bone growth modification occurs relative to 2 elements: 1. The reterodiscal tissues are stretched reciprocally, similar to a large elastic band, between the fossa and the displaced condyle during the expansion of the growing facial complexwww.indiandentalacademy.com
  35. 35. www.indiandentalacademy.com
  36. 36. 2.This is followed by the stretch of nonmuscular viscoelastic tissues. 3.The transduction of these nonmuscular forces has been shown to be effective at a significant distance from the actual physical soft tissue www.indiandentalacademy.com
  37. 37. www.indiandentalacademy.com
  38. 38. • The growth relativity concept describes a specific set of reciprocal soft tissue forces that operate during herbst treatment, when muscle hyperactivity does not appear to to be the primary cause of skeletal change. The displaced condyle modifies in a radiating manner relative to the fossa, and the fossa grows in a radiating fashion relative to the condyle. The reterodiskal streached between the displaced condyle and the fossa contributes to the the formation of new bone in each region. Further more, force referral or transduction from the posterior retero discal attachment to the condyle radiating along condylar fibrocartilage has been implicated in causing growth modification. www.indiandentalacademy.com
  39. 39. Fixed vs. Removable functional appliance • There are innumerable number of advantages of fixed functional or full time wear appliance over removable appliances . • Previous EMG studies on removable functional appliances by petrovic et al has been discredited because of the decrease in EMG activity after appliance wear. • Where as fixed functional appliances The mode of action of functional appliance therapy has been linked to neuromuscular and skeletal adaptations to altered function in the orofacial region. The EMG studies as shown by Pancherz ,kharbanda showed that though there was decrease in the EMG activity during the initial phase of the treatment because the muscles were in the stage of adaptation and from 3 months to 6 months there has been a continuous increase in EMG activity due the continuous forward posturing unlike removable functional appliances which do not allow the muscles to stabilize and adapt. www.indiandentalacademy.com
  40. 40. • 1987 Linden et al. • During the first phase of functional treatment, reflexes in jaw muscles are transiently brought into a state of imbalance. This phase of imbalance could act as a trigger for the mandible to attain a new functional position, which subsequently leads to morphologic changes. www.indiandentalacademy.com
  41. 41. • Full-time wearing of the appliance is of importance in this respect since a continuous anterior functioning might elicit the muscle response more rapidly than a discontinuous one. In view of these considerations, functional appliances that are worn full-time (Herbst appliance) or nearly full-time (eg, Fränkel's functional regulator, Bionator) could be expected to have a greater net result than those worn only part-time (eg, activator) www.indiandentalacademy.com
  42. 42. Behind the Screen www.indiandentalacademy.com
  43. 43. • The mechanism of action of functional appliance in growth modification has been basically targeted toward the changes at the condyle and the gleniod fossa but there are other effects . It wouldn't be justified and the M.O.A would be in complete without bringing them to light www.indiandentalacademy.com
  44. 44. • Effect on palatal plane • Restraining effect on the maxilla Vargervik and Harvold found that the activator inhibited the horizontal growth of the maxilla by 2 mm; Pancherz found it was restricted by 1.7 mm. • Relative intrusion of the dentoalveolar segment Do you know how much teeth erupt from age of 8 years to 15 years of age? www.indiandentalacademy.com
  45. 45. • Maxillary teeth at the molars erupt by 6.3 mm and incisors erupt 6mm Mandibular incisors erupt by 5 mm and molar erupts by 5.7 mm in boys and 3.7 mm and 4.4 mm in girls. • If u can relatively intrude or hold on the teeth vertically and prevent eruption by 5 mm the mandible will auto rotate by 12 degrees and net A-P gain would be helpful in converting a borderline vertical malocclusion case with in the domain of orthodontics www.indiandentalacademy.com
  46. 46. Petrovic vs. Voudoris • Petr : EMG studies showed hyperactivity of LPM • Voud : EMG studies were short term and transcutaneous • Voud : Most of the EMGs on a long term showed in contrary reduced activity of LPM • . www.indiandentalacademy.com
  47. 47. • Petr : It was believed that upper lateral pterygoid muscle was attached to the articular disk and the condyle • Voud : It has been shown that only few fibers from the upper lateral pterygoid are attached to the fibrocarilage of the condyle through lateral pterygoid tendon • Petr : Condylar cartilage cell failed to proliferate in homoautotransplant due to absence of LPM activation • Voud : It was thought that resection of LPM compromised the blood supply and there fore cell proliferation www.indiandentalacademy.com
  48. 48. Research findings www.indiandentalacademy.com
  49. 49. Cell and molecular biological findings www.indiandentalacademy.com
  50. 50. • Electromyography of the condylar cartilage show that cell to cell cytoplasmic junctions between skeletoblasts become quantitatively reduced. Consequently, possibilities of inhibitory inter cellular communications are cut down; i.e., the cell division rate increases. Simultaneously, the rate of differentiation of the skeletoblasts into precondroblasts also increases Petrovic (1982). www.indiandentalacademy.com
  51. 51. • Characteristic and consistent transmembrane ion flux variations can be detected : intra cellular Na++ concentration is raised, intracellular K+ concentration is very slightly lowered, and discharge of H+ from both skeletoblast and precondroblast is increased, leading to a rise of intracytoplasmic PH. Intracytoplasmic Ca++ concentration decreases. • Calmodulin as well as [Ca++ ,Mg++ ] – ATPase and [H] – ATPase activities are promoted,where as cAMP, fibronectin, [Na/K] – ATPase activity,cell trans glutaminase are reduced. The cell division process is initiated through the momentry surge of cytoplasmic Ca++ and endogenous cAMP www.indiandentalacademy.com
  52. 52. • The local coupling mechanism include: a) An open loop part of the control system having a stimulating effect on the cell multiplication and comprised of growth hormone ,testosterone, estrogen, insulin,, glucagon, parathormone, calcitonin, prostaglandin F2, as well as other mitogenic peptides that corresponds to, operationally, to fibroblast growth factor which convert the cell from quiescent to a new cycle stage b) A feed back part of the control system having an inhibiting effect on the cell multiplication and comprising regulators of local origin: a skeletoblast or precondroblast- multiplication restraining signal of un known nature. • The intensification in meniscotemporocondylar ligament activity is associated with an increase in blood and lymph flow and decrease in cell catabolite concentration and in negative feed back factors.www.indiandentalacademy.com
  53. 53. Proliferative cells SOX 9 Differentiation Condroblasts Cartilage matrix/ condrocytes SOX 9Regulates type II collagen synthesis Hypertrophic cartilage Precedes on set of EO Secretes Type x collagen express VEGF New blood vesselsRecruits Osteoprogenator Mesenchymal cells Osteoblasts osteocytes Endocondrial ossification Condylar growth Differentiation osteogenisis www.indiandentalacademy.com
  54. 54. Effect of hyperpropulsor on the precondroblastic cells count • The following data are from the study of periodic forward repositioning of the mandible (12 male rats in each experimental group, sacrificed at day 48 ) • Number of H- methyl-thymidine- labelled cells in condylar cartilage for various thickness of postural hyperpropulsor. • Group 1 (control) at 0 mm thickness - 876 cells – 13.5 mm • Group 2 at 0.5 mm thickness - 1049 cells – 14.9 mm • Group 3 at 1.0 mm thickness - 1316 cells - 15.2 mm • Group 4 at 2.0 mm thickness - 1499 cells - 15.4 mm • Group 5 at 3.0 mm thickness - 818 cells - 13.5 mm www.indiandentalacademy.com
  55. 55. Effect of various functional appliances on the growth of the rat mandible • H- methyl-thymidine- labeled cells in condylar cartilage for various appliances • Bionator and frankel • No appliance – 859 cells – 14.2 mm • Bionator (end to end) – 988 cells – 14.6 mm • Bionator (1mm) - 1199 cells – 15.2 mm • Frankel (lip pad) - 1236 cells – 15.2 mm • Postural hyperpropulsor and intra oral elastics • No appliance - 878 cells – 13.9 mm • P H (0.5 mm) - 1049 cells – 14.8 mm • PH (1mm) - 1316 cells – 15.25 mm • Elastics - 1336 cells – 15.26 mmwww.indiandentalacademy.com
  56. 56. Study to identify and quantify the temporal Sequence of, replicating mesenchymal cells during natural growth and mandibular advancement in the condyle and the glenoidfossa . Rabie et.al., (Ajo 2003.) www.indiandentalacademy.com
  57. 57. • The number of mesenchymal cells in anyone is genetically controlled. Heritable influences were found to contribute up to 90%. Nongenetic factors were still appreciable and account for approximately 3.6%. • A most interesting finding in the present study is that resident mesenchymal cells in the condyle contributed to bone formation in response to forward mandibular positioning, whereas resident mesenchymal cells in the glenoid fossa contributed less to growth modification. www.indiandentalacademy.com
  58. 58. •Human mesenchymal cells can be harvested, purified, and grown in vitro to increase their numbers and, when reimplanted, they can still differentiate into bone-making cells and lead to a significant increase in bone formation — a principle that should be seriously considered for managing patients with hemifacial microsomia and other craniofacial anomalies requiring growth modification. •The number of replicating mesenchymal cells, which is genetically controlled, influences the growth potential of the condyle and the glenoid fossa. Mandibular protrusion leads to an increase in the number of replicating cells in the temporomandibular joint. Individual variations in the response to growth modification therapy could be a result of the close correlation between mesenchymal cell numbers and growth. www.indiandentalacademy.com
  59. 59. • BMP-2 is characterized by an ability to induce ectopic cartilage and bone in soft tissues. • A recent report showed that the lack of expression of Sox 9 leads to campomelic displasia in humans, a disease affecting all cartilage-derived skeletal structures, resulting in bowing and angulation of long bones, vertebral abnormalities, small thoracic cages, craniofacial defects with macrocephaly, micrognathism, and cleft palate. Rabie, Urban Hagg (Am J Orthod Dentofacial Orthop 2003;123:40-8) www.indiandentalacademy.com
  60. 60. Photomicrograph showing positive immunostaining of VEGF expression (®) in the posterior (P) and middle (M) regions of the mandibular condyle with forward mandibular positioning on Day 14. During normal growth on Day 14. Photomicrograph showing positive PAS staining of new bone formation (B) in the posterior region of the mandibular condyle during forward mandibular positioning on Day 30..www.indiandentalacademy.com
  61. 61. Mechanical stimuli (static or dynamic) Deform EM & bone cell Reception Transduction Transmission Ionic Mechanical Multicellular Bone cell response CCN MMCCytoskeleton (connectin) (actin) Nuclear membraneOsteocytic genome Ca++ Frankel www.indiandentalacademy.com
  62. 62. Effect of functional appliances on the jaw muscle activity and type of muscle fibers recruited www.indiandentalacademy.com
  63. 63. Muscle fibers • Muscle fibers can be characterized by type according to the amount of myoglobin; fibers with higher concentration of myoglobin are deep red in color and capable of slow but sustained contraction. They have well developed aerobic metabolism and there fore resistant to fatigue • Fibers with low concentration of myoglobin are whiter and are called fast muscle fibers; they have fewer mitochondria and relay more on anaerobic activity for function. Fast fibers are capable of quick contraction but fatigue more rapidly • Type I and Type IIa are slow twitch fibers. • Type II b is fast twitch fibers www.indiandentalacademy.com
  64. 64. www.indiandentalacademy.com
  65. 65. Functional appliance Muscle fatigue Excessive muscle function Lateral pterygoid Type IIb Type I & IIa Accumulation Of Lactic acid Lateral pterygoid Type I & IIa Type IIb Excessive muscle function Accumulation Of Lactic acid S A D Continuous Muscle activity www.indiandentalacademy.com
  66. 66. • Adaptations of masticatory muscles to a hyperpropulsive appliance in the rat by Reggiani 1996 • The plasticity of masticatory muscles, i.e., their ability to change their properties in relation to loading conditions, represents a potentially important determinant of structure and function of the mouth and the teeth. The effects of changes of the masticatory loading conditions have been described by Kiliaridis by comparing two groups of rats fed with a hard diet and with a soft diet. In the two muscles examined (deep masseter and anterior belly of digastric), the soft diet was associated with a higher proportion of fast and easily fatiguable IIB fibers. www.indiandentalacademy.com
  67. 67. • A series of studies was carried out by Petrovic and by other workers to test the hypothesis that protrusion muscles, and particularly lateral pterygoid, can influence the growth of condylar cartilage. Interestingly wearing a protrusive appliance induced fiber transformation in pterygoideus lateralis and superficial masseter. The proportions of slow fibers and of fatigue- resistant type I & IIA fibers increased in pterygoideus lateralis, whereas only an increase in IIA fibers occurred in the superficial masseter muscle. www.indiandentalacademy.com
  68. 68. • Adaptation of the lateral pterygoid and superficial masseter muscles to mandibular protrusion in the rat - Easton and Carlson 1990 • The experimental rats wore bonded protrusive-type appliances for 2 weeks. Histochemically, the lateral pterygoid muscle in the experimental group exhibited a significantly greater area occupied by type I fibers at the expense of type llb fibers. The superficial masseter muscle exhibited a significantly greater percentage of areas for both type lla and type llb fibers in the experimental group. Contraction time (TPT) increased in both muscles; that is, the muscles became slower. The histochemical and contractile-properties data indicate that the protrusive appliance caused the lateral pterygoid muscle to become more active with respect to tonic (postural) activity, whereas the superficial masseter muscle became more active phasically. www.indiandentalacademy.com
  69. 69. • 1990 Woodside et. al. • Effect of functional appliances on jaw muscle activity - The electromyographic (EMG) activity of masticatory muscles was monitored longitudinally with chronically implanted EMG electrodes to determine whether functional appliances produce a change in postural EMG activity of the muscles. Preappliance and postappliance EMG levels in four experimentals that had been fitted with functional appliances were compared against the background of EMG levels in controls without appliances. The insertion of two types of functional appliance to induce mandibular protrusion was associated with a decrease in postural EMG activity of the superior and inferior heads of the lateral pterygoid, superficial masseter, and anterior digastric muscles; the decrease in the first three muscles was statistically significant. This decreased postural EMG activity persisted for approximately 6 weeks, with a gradual return toward preappliance levels during a subsequent 6-week period of observation. Progressive mandibular advancement of 1.5 to 2 mm every 10 to 15 days did not .prevent the decrease in postural EMG activity. www.indiandentalacademy.com
  70. 70. • The action of the types of functional appliances on the activity of the masticatory muscles Camilo Yamin- ajo 1997 • Three commonly used functional appliances; namely, the Herbst, Frankel, and a simulation of the Clark twin block appliances were used to test the lateral pterygoid muscle hypothesis. The electromyographic (EMG) activity of the masseter, digastric, superior, and inferior heads of the lateral pterygoid muscles was monitored with chronically inserted EMG electrodes, in nonhuman primates. The insertion of these three appliances was associated with a decrease in functional EMG activity of the four muscles. This decrease was statistically significant in all muscles 3 and 6 weeks after appliance insertion. In view of the fact that the animals showed large skeletal changes in the temporomandibular facial area, this study could not support the lateral pterygoid muscle hypothesis. www.indiandentalacademy.com
  71. 71. • An electromyographic study was performed on 10 young growing girls in the age group of 9 to 12 years with Class II Division 1 malocclusion and retruded mandible, who were under treatment with Twin-block appliances. Bilateral EMG activity of elevator muscles of the mandible (ie, anterior temporalis and masseter) was monitored longitudinally with bipolar surface electrodes to determine changes in postural, swallowing, and maximal voluntary clenching activity during an observation period of 6 months. www.indiandentalacademy.com
  72. 72. • The changes were noted at the start of treatment (0 month), within 1 month of Twin-block insertion, at the end of 3 months, and at the end of 6 months. The results revealed a significant increase in postural and maximal clenching EMG activity in masseter and a numeric increase in anterior temporalis activity during the 6 month period of treatment. The increased electromyographic activity can be attributed to an enhanced stretch (myotatic) reflex of the elevator muscles, contributing to isometric contractions. The main force for Twin-block treatment appears to be provided through increased active tension in the stretched muscles (motor unit stimulation) and from initiation of myotatic reflex activity and not through passive tension (viscoelastic properties) of jaw muscles. The results of this study reaffirm the importance of full-time wear for functional appliances to exert their maximum therapeutic effect by way of neuromuscular adaptation. Ajo 1999 Preeti Aggarwal, . Kharbanda,, www.indiandentalacademy.com
  73. 73. Skeletal and dental effects of functional appliances www.indiandentalacademy.com
  74. 74. • Kevin O Brien et al conducted a multicentric, randomized, controlled trial evaluated the effectiveness of early orthodontic treatment with the twin block appliance for class II division 1 malocclusion www.indiandentalacademy.com
  75. 75. Over jet correction 6.93 mm 100% Dental 5.05mm 73% Skeletal 1.88mm 27% MAX 3.03 mm 44% MAND 1.00mm 14% MAND 2.03mm 29% MAX 0.88mm 13% www.indiandentalacademy.com
  76. 76. Molar correction 4.59 mm 100% Dental 2.71mm 59% Skeletal 1.88mm 41% MAX 1.19 mm 26% MAND 1.00mm 22% MAND 1.52mm 33% MAX 0.88mm 19% Kevin O’ Brien et al ajo-2003 www.indiandentalacademy.com
  77. 77. • Most of the studies on the functional appliances claim that the small changes that occur in the skeletal relation ship might not be considered clinically significant or functional appliances accelerates growth ahead of time. Hence may be effective in reducing the skeletal dysplasia earlier and interception of exacerbation of malocclusion and has psychological benefit. www.indiandentalacademy.com
  78. 78. Conclusion • Functional appliances or rather Dentofacial orthopedics has been a lurking mirage in orthodontic literature and has had enough victims, disappointments and limited long term success, but no wonder the quest is still on, hoping that there are still ways to communicate with various cell populations of the condylar cartilage with mechanical stimuli which remain to be learned. The answer to whether mandible can be grown in excess beyond the whelms of genetics or it’s a barren field, lies with time. www.indiandentalacademy.com
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The Indian Dental Academy is the Leader in continuing dental education , training dentists in all aspects of dentistry and offering a wide range of dental certified courses in different formats.for more details please visit www.indiandentalacademy.com

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