Third molars& its significance in orthodontic treatment & relapse /certified fixed orthodontic courses by Indian dental academy


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Third molars& its significance in orthodontic treatment & relapse /certified fixed orthodontic courses by Indian dental academy

  1. 1. INDIAN DENTAL ACADEMY Leader in continuing dental education
  3. 3. INTRODUCTION • Third molars are the teeth which are most often missing, impacted and with altered morphology. • Advances in dental anthropology states that there is a reduction in the number of teeth and size of jaws on evolutionary basis for the past 1,00,000 years. • Third incisors ,third premolars and fourth molars have disappeared already.
  4. 4. • At present human third molars often fail to develop, which indicate that these teeth may be on their way out. • Although there are some who advice the early removal of the third molars , many strongly believe that the retention of asymptomatic third molars may be useful in later years as a substitute for badly decayed teeth or may even be useful as a transplant.
  5. 5. DEVELOPMENT AND ERUPTION • There is great variation in the timing of • • • development, calcification, and eruption of third molars. Development may begin as early as 5 years or as late as 16 years, with the peak formation period at 8 or 9 years. Calcification can start at age 7 years in some children and as late as age 16 years in others. Enamel formation is normally complete between 12 and 18 years and root formation is normally completed between 18 and 25 years.
  6. 6. • Hellman reported that the average age of eruption was 20.5 years. • In 1962,Fanning reported average ages of eruption of 19.8 years for females and 20.4 years for males. • Early formation of third molars is generally regarded as predictive of early maturation but not always of early eruption. • Most surveys report that more than 17% of lower third molars become impacted.
  7. 7. • Lower third molars normally have their occlusal surfaces tilted slightly forwards and lingually during early calcification. • As the mandible increases in length, with bone resorption at the inner angulation between the body and the ascending ramus of the mandible, the third molars become more upright.
  8. 8. • In contrast, upper third molars erupt downwards, backwards, and often outwards. • There is, therefore, a possibility of crossbite, but tongue pressure on lower crowns and buccinator pressure on upper crowns will often correct this. If there is a lack of space, then normal eruptive paths cannot be followed, and crossbites can result.
  9. 9. ERUPTIVE PATHWAYS OF THIRD MOLARS • Richardson investigated the development of lower third molars between ages 10 and 15 years,using models and four cephalometric radiographs (90 degree left lateral, straight posteroanterior and 60 degree left and right lateral views). • She found that the angle of the occlusal surface of the lower third molars to the mandibular plane was 41 degree On average she found this decreased by 11 degree by age 15.
  10. 10. • Successful eruption of the lower third molar occurs by the tooth continuing to decrease its angle to the mandibular plane and moving occlusally into sufficient space.
  11. 11. • J.B.Fayad et al in AJO 2004 determined the • • relationship between the maxillary molar’s sagittal inclination and the eruption of third molars using CT scans. In their study the sagittal inclination of maxillary first and second molars were greater in the subjects with erupted maxillary third molars than in those with impacted third molars and particularly in the younger subjects. They concluded that the vertical position of the first maxillary molar in the sagittal plane is a predictor of the eruption of the adjacent third molar; and that the sagittal inclination of the maxillary molars increases with age which could be the effect of a mesial drift.
  12. 12. • Kahl et al evaluated orthopantomograms of 58 orthodontically treated patients with asymptomatic impacted third molars. • In a 15 year follow up ,they observed that some of the maxillary and mandibular molars have rotated to a more upright position while others had an increase in the mesio or disto-angulation. • They found that age, period of impaction, extent of space deficiency, developmental stage, level of eruption and bone conditions had no predictive values.
  13. 13. ASSESSMENT OF SPACE FOR THIRD MOLARS • Shortage of space between the second molar and the ramus has long been identified as a major factor in the etiology of lower third molar impaction. • Henry and Morant suggested a technique for predicting impaction of lower third molar using their third molar space index; obtained by expressing the mesiodistal width of the third molar as a percentage of the space available measured on bimolar radiographs.
  14. 14. • If this index, exceeded a value of 120 for a person at maturity, impaction could be predicted. • This index decreases as the growth continues and the space available increases. • Ledyard, studying lateral jaw radiographs, found that less than a 2 mm increase in space between the lower second molar and the ramus could be expected after the age of 14 years and a negligible increase after 16 years
  15. 15. • Ricketts claimed that if 50% of the third molar crown lies ahead of the external oblique ridge at maturity, there is a 50% chance of eruption. • Schulhof in 1976 claimed that growth prediction can estimate the adult dimension from Xi point to the mandibular second molar on a lateral cephalogram taken at the age of 9 years, with a standard error of 2.8 mm Schulhof suggested that lower third molars could not be classified as likely to erupt to good occlusion if the Xi point to lower second molar was measured less than 25mm
  16. 16. • Richard Olive et al in AJO 81 in a study on dried human skulls, examined the reproducibility of estimates of a space width ratio (space available between lower second molar and the ramus divided by mesiodistal width of mandibular third molar) on the lateral cephalogram, rotational tomograms(OPG), intraoral bitewings and 60 degree cephalograms.
  17. 17. • A template of cellulose acetate was prepared with • a right angle T drawn in line through the tips of the most superior, anterior and posterior cusps of the first premolar to second molar section of buccal segment. The template was placed over the radiograph with the horizontal part of the T on the occlusal plane and the vertical part touching the most distal part of second molar crown.
  18. 18. • The space available (AB),the mesiodistal width of the lower third molar(CD) and space width ratio (AB/CD) were computed from the digitized data. • A ratio of less than 120% will indicate a high probability of impaction. • The rotational tomogram, intraoral bitewing and 60 degree rotated cephalogram were superior to the lateral cephalogram on the basis of reliability of results and reproducibility of radiograph technique for estimating the space width ratio.
  19. 19. • The results suggested the difficulties in landmark location on lateral cephalogram. Locating anterior border of the ramus on lateral cephalogram is often difficult, which militates against good reproducibility of results. • It was shown that the reliability for the lateral cephalogram technique alone was not as good as for the other techniques. • The rotational tomograms yielded the most accurate estimates of space width ratio. • Intraoral bitewings yielded the next best estimates.
  20. 20. IMPACTIONS • Archer defined an impacted third molar as ‘One • • which was completely or partly erupted and positioned against another tooth,bone or soft tissue, so that its further eruption was unlikely. Dachi and Howell in their study found that the incidence of patients with atleast one impacted tooth was 16.7%. Teeth most often impacted in order of frequency were the maxillary third molars,mandibular third molars,maxillary canines and mandibular premolars.No sex differences were noted.
  21. 21. • Bjork and colleagues identified 3 skeletal factors that are separately influencing third molar impaction – Reduced mandibular length,measured as the distance from the chin point to the condylar head. – Vertical direction of condylar growth as indicated by the mandibular base angle. – Backward directed eruption of mandibular dentition determined by the degree of alveolar prognathism of lower jaw.
  22. 22. • Capelli in a 1991 study evaluated 60 patients who had four first premolar extractions. • The findings from pretreatment and posttreatment cephalograms suggested that third molar impactions were more likely to occur in patients with pretreatment vertical mandibular growth. • A long ascending ramus, short mandibular length, and greater mesial crown inclinations of third molars, seem to be indicative of third molar impaction.
  23. 23. TYPES OF IMPACTION Richardson suggested five categories of impaction • Type A : The tooth can follow the pattern of an ideally developing third molar, by decreasing its angle to the mandibular plane and becoming more upright, but the uprighting may not be enough to allow full eruption.
  24. 24. • Type B : The angular developmental position relative to the mandibular plane may remain unchanged • Type C : The tooth can increase its angulation to the mandibular plane ,and become more mesially inclined .There is at present no reliable way of predicting which teeth will follow this unfavourable pattern,which sometimes occurs unilaterally and leads to horizontal impaction
  25. 25. • Type D :The tooth can be seen to make favourable changes in angulation ,but fail to erupt owing to lack of space.These are so called vertical impactions. • Type E :The tooth can continue to change its angulation beyond the ideal occlusal position,and show disto angular impaction
  26. 26. MECHANISM FOR ERUPTION AND IMPACTION • Differential root elongation might explain differences in eruptive behaviour among lower third molars. • Richardson offered a theoretical explanation for favorable or unfavorable rotational movement.
  27. 27. • Favorable change in angulation ,to a more upright position ,seemed to occur in teeth where the mesial root developed ahead of the distal crown surface and root. • The typical root configuration showed a mesial root which was curved in a distal direction and was slightly longer than the distal root.
  28. 28. • Unfavorable mesial tipping, leading to horizontal • impaction, seemed to occur when the distal root became the same length, and then longer than the mesial root. The distal root on such teeth was seen to appear to have a mesial curvature.
  29. 29. FACTORS INFLUENCING AVAILABILITY OF SPACE • GROWTH Bjork et al measured the distance from the anterior border of the ramus to the second molar,and concluded that the bigger the space,the better the chance of eruption.Richardson measured an average of 11.4 mm of growth between the age of 10 and 15 years.
  30. 30. • BONE RESORPTION In 1987 Richardson examined the creation of space for third molars in 51 subjects. She found that increased space was obtained from both the mesial movement of the dentition and bone remodeling along the anterior border of the ramus. On average 2 mm of posterior space was created by bone remodeling
  31. 31. SPACE RELEASED BY ATTRITION In so-called primitive dentitions, where considerable attrition takes place, the third molars erupt to take up the space released. Begg felt that lack of this attrition,due to highly refined diets,was a mojor cause of third molar impaction. Other authors,such as Profitt,have questioned this hypothesis. Early and extensive interproximal caries could also reduce the size of erupted teeth, owing to disappearance of proximal contacts.
  32. 32. SECOND MOLAR EXTRACTION • Richardson and Richardson in AJO 93 investigated 63 patients after extraction of lower second molars and found that all the lower third molars erupted more or less successfully after an average observation period of 5.8 years. • There was considerable variation in the time taken for eruption, ranging from 3 to 10 years and Richardson noted that it is not possible to predict how long eruption will take.
  33. 33. • Bonham Magness in JCO 86 suggests that upper third molars has a much more predictable eruption pattern than lower third molars. • He suggested the extraction of upper second molars in some cases to assist first molar positioning and increase space for upper third molars.
  34. 34. • Tae-Woo Kim et al in AJO 2003 confirmed the findings of Faubion and Kaplan that impaction of mandibular third molars occurs about twice as often in non-extraction patients than in extraction patients. • The mechanism may be that premolar extraction therapy is associated with an increase in the amount of mesial movement of the maxillary and mandibular molars and an increase in the eruption space for the third molars.
  35. 35. • Cephalometric growth studies suggest 2 important mechanisms for development of the retromolar space in the mandible; Resorption at the anterior border of the ascending ramus and the anterior migration of the posterior teeth during the functional phase of tooth eruption. • More than 60% of the patients in the study, with a distance of 23 mm or less from the distal of the mandibular second molar to the Ricketts’ Xi point at the end of the active treatment experienced eruption of mandibular third molars.
  36. 36. • The retromolar space can increase about 2 mm from age 15 to adulthood. • They also showed that as many as 60% of the subjects with a distance from the anterior border of the ramus to the distal of second molar of 5 mm or less experienced eruption. • These suggest that the size of third molar eruption space associated with a high risk of impaction might be smaller than previously suggested
  37. 37. UPRIGHTING IMPACTED MOLARS • Third molar retention may be beneficial in many situations. • Some investigators maintain that third molars could be used at a later date as replacements or for prosthetic abutments in case of loss of first and second molars. • Third molars could also be used as transplants
  38. 38. • In shallow mesio-angular impactions Richardson • used a one stage method. A second molar tube can normally be bonded onto the buccal aspect of a partly erupted lower third molar, if enough enamel is visible. • It is then possible to include the tooth in full • treatment ,if other teeth are already bonded and bracketed. If the case is not fully banded, then lower second or first molars alone can be used, with a lingual arch for support
  39. 39. • In deep mesio-angular impactions,a two-stage • • method is used. If it is not possible to bond onto the buccal surface,a different technique is used which can be delayed until 18 –19 years of age, to allow time for the tooth to improve its position. The first stage involves bonding a second molar tube onto the occusal surface of the lower third molar.
  40. 40. • The hook is removed from the tube, before bonding. • Lower first or second molars are banded with a • • lingual arch, using first molar bands and brackets. A small sectional archwire, with a compressed coil spring, is used to provide a distalizing and uprighting force to the crown of the impacted molars. After some uprighting using this method, it is normally possible to bond a tube buccally for the second stage.
  41. 41. • Ike Slodov et al in AJO 89 describes an orthodontic uprighting technique similar to ‘Sling shot’ appliance described by Moyers and by Profitt. • Modified impaction related surgical procedures provide easy application of techniques to facilitate exposure of unerupted and partially erupted third molars and allow orthodontic manipulation
  42. 42. • After surgical exposure a cleat is bonded in center • • • of mesial marginal ridge. The wire portion of the appliance is fabricated from 0.032 inch stainless steel wire and adapted closely to the mucosa. The mesial hook is placed 3 mm distal to the distal portion of the third molar. Standard soldering techniques are used to attach the wire to the buccal (or lingual) surface of the band. Appliance is cemented in place and is activated with elastic modules
  43. 43. • By manipulation of the distal arm of the appliance either buccally or lingually ,depending on the desired movement,teeth can be directed or rotated with some effectiveness. Variation can also be accomplished by alteration of the bond position of the cleat. • Following activation,rapid uprighting and distalisation will occur in 3 to 6 months in most cases.Grinding of occlusal surface is not necessary. When the third molars are upright, the appliances are removed and the third molars are banded, leveled and aligned with the rest of the teeth.
  44. 44. • This procedure is contraindicated when the molar to be uprighted has no antagonist; is severely malformed or is abnormally large or small, and it should be done carefully when there is a tendency for open bite. Advantages are: 1. Ease of fabrication and manipulation 2. Rapid treatment 3. Little discomfort 4. No demands for patient cooperation
  45. 45. • Orton and Jones in JCO 87 described a simple • • • • whip spring that is unobtrusive and fairly fast acting with a treatment time of 4 to 12 months. It is used for disimpacting , mild to severe mesially impacted lower terminal molars (LTM). LTM crown must be accessible for an edgewise tube, preferably on a band. Partial seating of the band on the mesial surface is acceptable at first, which can be fully seated as correction proceeds. If the impacted molar has not sufficiently erupted then surgically expose distobuccal surface and bond an attachment.
  46. 46. • The whip spring is fabricated with 0.018X 0.025 wire for 0.022 slot and 0.017X0.022 wire for 0.018 slot. • A circular loop is placed mesial to the tube to prevent posterior displacement of the wire and to provide attachment of an elastic module that anchors the wire in the tube.
  47. 47. • Wire extends mesially from the loop. A vertical bend • • is placed occlusally next to the midbuccal fissure of the anchor molar. The wire is curved lingually to pass through the midbuccal groove onto the occlusal surface. It is then contoured distally to run along the occlusal surface. Moving the whip to the occlusal surface of the anchor molar activates the appliance.
  48. 48. • The whip spring can be reactivated in the mouth by lifting the wire away from occlusal surface and gently squeezing the arm of the spring between loop and vertical bend with Tweeds loop forming plier. • After initial adjustment at 3 to 4 weeks, adjustments every 6 week seen to be adequate. Overcorrection is advised.
  49. 49. • The force of the whip tends to extrude the impacted • • molar and intrude the anchor molar. If there is too much intrusion of anchor molar, a new whip can be made that extends to another anchor tooth. The couple tends to disimpact the LTM by a combination of distal crown tipping and mesial root movement, resulting in root paralleling of the molars.
  50. 50. • If the vertical development of the LTM is impeded by an upper molar, then the overerupted upper molar must be intruded by a removable appliance with an intrusive arm
  51. 51. REPLACEMENT OF THIRD MOLARS FOR SECOND MOLARS • During growth of maxilla ,space to accomodate • • the erupting first, second, and third molars must be created by growth in the posterior region of the tuberosity. The maxillary growth in this area must normally be downward and forward to create room for the eruption of each succeeding molar. If growth in this region is insufficient, abnormal eruption or lack of eruption will be the result.
  52. 52. • According to Malcolm.R.Chipman in AJO 1961 • the third molars can be substituted for the second molars in certain situations and solve some of the problems of maxillary tuberosity area. The indications for eliminating maxillary second molar and replacing it with third molars are 1.Maxillary third molars of fair size and shape with the possibility of good root development 2.Small,restricted maxillary tuberosities and the possibility of interference with distal movement in maxillary posterior region. 3.Second molars erupted buccally.
  53. 53. 4.Second molars decayed ,badly decalcified or having large restorations. 5.Maxillary third molars in favourable position and angulation relative to second molars and maxillary tuberosity. 6.Maxillary third molars in favourable relation to mandibular second molars. 7.Desirability of relieving the anchorage units of an overload. • The replacement of maxillary second molar will be considered in both Class I and Class II malocclusions
  54. 54. • The contraindications for substitutions are 1.Maxillary third molars too high in the tuberosity. 2.Maxillary third molars too low in relation to the second molars 3.Poor angulation in relation to second molar and the tuberosity. 4.The possibility of third molars involving maxillary sinus. 5.Small,odd shaped third molars or an indication of the formation of small roots.
  55. 55. • There is a great variation in the time of • development of third molars, and this together with the amount of development in the tuberosity region, has a bearing on the decisions to be made in the event of a needed maxillary distal movement and a possible replacement of the second molar by third molar. For this reason the dental age as evidenced by the development of dental components, must be given as much considerations as chronological age.
  56. 56. • The shape of third molar crowns is also considered. • Small crowns with narrow width at the cervical margin do not lend themselves to development of normal sized roots. • Many third molars have odd shaped crowns with irregular cusp formations ,and, while occlusal grinding frequently is needed, there is a limit to its use and these teeth cannot be recommended.
  57. 57. • During its eruption following a second molar • • • extraction ,the third molar rotates or tip mesially as it descends; the amount of rotation being directly associated with the degree of angulation. The greater the degree of angulation the greater is the amount of rotation, with the center of rotation being based on root apex. This rotation together with the downward and forward path of eruption ,is a major factor in determining when the second molar extraction may be planned. The ideal condition calls for the descending third molar to come into contact with the maxillary first molar and into occlusion with the mandibular second molar at the same time.
  58. 58. • In a Class I malocclusion,the third molar should • • • have descended to the extent that the occlusal surface is approximately level with the vertical midline of second molar root and the mesial surface of unerupted third molar is fairly in line horizontally with the distal surface of mandibular second molar. Following extraction of second molar, the third molar will then descend in a downward and forward arc, rotating into contact and occlusion at the same time. If third molar is at a much higher point there is a possibility of impaction or premature contact. before occlusion is attained. If it is at a lower level in relation to second molars, it is likely to erupt into occlusion before contact is established with first molar, resulting in open contacts and poor interproximal situations.
  59. 59. • In Class II malocclusions,the crown of maxillary • • • third molar is horizontally advanced in relation to the mandibular second molar. In Class II cases in which second molar is to be extracted,the most ideal location of third molar is approximately at the junction of crown and root of second molar. The angulation of maxillary third molars to the plane of occlusion and their relation to the tuberosity must be carefully considered. The usable angulation will range from 0 to +30 degree.(distal tip) to occlusal plane.
  60. 60. • Orton-Gibbs et al in AJO 2001 described the • • eruptive path of maxillary and mandibular third molars after extraction of second molars with the use of radiograph and assessed the final position from study models. They showed that the angulation of the mandibular third molar crown long axis showed progressive uprighting from a mean of 55 to the occlusal plane at the start of active treatment (SAT). Uprighting of mandibular third molars from SAT to end of active treatment (EAT) was limited (mean 6 ). However the third molars continued to upright thereafter on average a further 13 .
  61. 61. • Clinically it is important to note that EAT • • • radiographs will not give a true picture of the likely final mandibular third molar angulation. Approximately 50% of the space closure occurs by EAT. Interestingly space closure is not a result of mesial tipping but is due to significant horizontal translation. The relationship of the first and the third molar crown should be the most important indicator of successful outcome, not angulation of the whole tooth. The results confirm findings by Dacre, and Richardson and Richardson that the original angulation of the third molar is not a reliable predictor of outcome for third molar position.
  62. 62. • In contrast to the mandibular third molars, the maxillary third molars upright rapidly by 14 degree on average from SAT to EAT. • Angular changes is minimal as the maxillary molars settle into occlusion. • The rate of vertical change is rapid, with almost 7 mm of eruption occurring by the completion of active treatment and a further 6 mm after active treatment
  63. 63. • The third molars in the study were invariably in a • • • position that maintains a good functional occlusion. The periodontal health of the sample was excellent. There was no correlation between third molar position and the presence of gingivitis or periodontitis. The results showed that relief of crowding by removal of second molar is a realistic option in appropriate cases with mild to moderate crowding, particularly in patients in whom third molar impaction is predicted and in reducing the likelihood of increasing crowding through the teenage years
  64. 64. AUTOTRANSPLANTATION OF THIRD MOLARS • Autotransplantation of teeth has become an accepted and reliable treatment modality in patients with early loss of teeth or aplasia. • According to William Northway in AJO 80 autogenic tooth transplantation can give the concept of space management a much broader horizon. • Third molars have been frequently used for transplantation. These teeth, which are often extracted have served well as replacements, for cariously destroyed first molars. • Their root development which continues into the late teens and twenties makes these teeth suitable for use into adulthood. • The last tooth in the arch may offer better access for removal, and it is essential that the root not be damaged in any way during its relocation
  65. 65. • The prognosis for successful transplantation is • • • • diminished as the root apex nears closure. Revascularisation must take place. While post operative resorption is rarely reported, the effective reduction in root length is minimized by allowing adequate development prior to transplantation. Hale believed that the most favourable time for transplanting was at 3 to 5 mm of root formation. Apfel stressed the need for delaying transplantation until after furcation formation. Andreasen,Baum,Peskin and Guralnick have contented that the results will be maximized if the operations are performed sometime between one third and three fourth of completion of root formation.
  66. 66. • Proper alveolar architecture is essential for • • • housing the transplant. The recipient site should be covered with adequate attached, keratinised tissue to allow proper coverage or approximation to the transplant and it should be free of chronic inflammation. Mesiodistal space deficiencies be eliminated prior to the surgical procedure,either by orthodontic means or by slicing of adjacent teeth. Also there should be adequate labiolingual width on the ridge to accommodate alveolar plates on both surfaces
  67. 67. SURGICAL PROCEDURE • A full thickness mucoperiosteal flap should be employed,allowing adequate exposure for atraumatic preparation of the recipient site. • A very gentle handling of the soft tissue is ensured. The socket is prepared with bone burs and rongeurs. • Once the socket is judged to be of adequate depth and circumference, a trial insertion of presterilised dummy tooth can be made. • Ideally, the preparation of the recipient site will allow insertion deep enough that the cusp tips will be at or apical to the alveolar crest height. This allows eruption and hence root formation postoperatively.
  68. 68. • Now the transplant can be removed. Again, adequate flaps allow exposure and a minimum of trauma. • With gentle manipulation of surgical instruments the dental follicle is removed from around the crown. • The tooth is removed and transferred immediately to the previously prepared crypt. • It is preferable that the tooth be manipulated only by its crown. In the event that buccolingual width does not allow proper placement, it can be inserted in a rotated position.
  69. 69. • This will allow preservation of • • alveolar crest and the tooth can later be repositioned orthodontically as desired. Mucoperiosteal flap is repositioned and sutures are placed over the crown to hold the tissues together and tooth in its crypt. After a week or 10 days sutures are removed and direct bonded stabilization can be employed for upto 6 weeks
  70. 70. • Oskar Bauss et al in AJO 2004 in their study determined the influence of orthodontic tooth movements on pulpal and periodontal conditions in transplanted immature third molars. • The indication for transplantation was aplasia of premolars or early loss of molars.
  71. 71. • In patients with horizontal atrophy of alveolar • • • • process, with narrow alveolar ridges and unfavourable root morphology, transplants were placed in 45 to 90 degrees distally rotated positions. Derotation to a correct position in the dental arch was performed with a couple of forces. The initial rotational force varied between 200 to 300 grams/mm. Mean rotation time was 12 weeks. After complete derotation, all transplants were integrated into a fixed appliance for leveling and approximal space closure. Average Orthodontic treatment time was 15.2 months.
  72. 72. • In vertically atrophied jaw sections,transplants • • • • were fixed in distinct infraocclusion (average 5.1 mm) Transplants were leveled to the occlusal plane before closing the approximal spaces. Mean orthodontic treatment time was for 14.4 months. For determining pulpal and periodontal conditions,clinical and radiologic examinations were carried out. Autotransplanted third molars without subsequent orthodontic treatment had the best pulpal and periodontal results. All transplants were at the developmental stage with their open apices providing a high chance of pulp revascularization.
  73. 73. • The results suggest that orthodontic extrusion • • • and minor lateral tooth movement have no harmful effects on the pulpal and periodontal condition of autotransplanted immature third molars. Atrophy of the alveolar process did not affect pulpal and periodontal healing of the transplants in the extrusion group. A certain amount of spontaneous eruption had occurred in most patients by the time orthodontic treatment began. The formation of new alveolar processes was observed during subsequent orthodontic treatment.
  74. 74. • Revascularisation started on the fourth • • postoperative day with an ingrowth of new vessels and was usually completed after 30 days, with the entire pulp containing new vessels.In contrast to pulpal revascularization ,first signs of pulpal reinnervation cannot be demonstrated until at least a month after transplantation and are limited to the apical part of the pulp. Even after 2 years, the restored pulpal nerves are described as sparse, and the new axons are small in diameter. By postponing the onset of orthodontic treatment to the third to sixth month after transplantation and slower derotation of multirooted transplants might increase the success rate.
  75. 75. THIRD MOLARS AND CROWDING • Lower arch crowding after establishment of the • • • permanent dentition during teenage period (post adolescent crowding) is a common orthodontic problem. This late lower arch crowding is caused by pressure from the back of the arch. Whether this pressure results from a developing third molar, physiologic mesial drift or the anterior component of force derived from the forces of occlusion on mesially inclined teeth is not clear. There is also a school of thought holding the view that in the absence of third molar, the dentition has room to settle distally under anterior pressures caused by late growth or soft tissue changes. Thus the third molar plays, at the very least, a passive role in the development of late lower arch crowding
  76. 76. • Bishara et al evaluated the changes in the lower incisors between 12 and 25 years of age and then re-evaluated the same subjects at 45 years of age. • Their findings indicated that there was an increase in the tooth size-arch length discrepancy with age. • The average changes amounted to 2.7 mm in males and 3.5 mm in females. • These changes were attributed to a consistent decrease in arch length that occurred with age.
  77. 77. • Margaret Richardson in AJO 92 examined changes in the lower arch crowding in young adults and showed that between the ages of 18 and 21 years, the lower arch is stable in terms of tooth alignment and mesial drift, regardless of third molar status or continuing mandibular growth.
  78. 78. STUDIES RELATING THIRD MOLAR TO CROWDING • Bergstrom and Jensen in 1961 examined • • sixty dental students, of whom thirty had unilateral agenesis of the upper third molars, twenty-seven had agenesis of the lower third molar and three had one third molar absent or lost. They found that there was more crowding in the quadrant with a third molar present than in the quadrant with a third molar missing. There was a mesial displacement of the lateral dental segments on the side with the third molar in the mandibular arch, but not in the maxilla.
  79. 79. • They found no evidence of a correlation between age and the degree of crowding or mesial tooth displacement. • Bergstrom and Jenson concluded that the presence of a third molar appeared to exert some influence on the development of the dental arch but not to the extent that would justify either the removal of tooth germ or the extraction of third molar.
  80. 80. • Vego in another study examined forty patients with • • • • lower third molar present and 25 patients with third molar congenitally absent. Each individual arch was measured first after the eruption of second molar at an average age of 13 years and second at an average age of 19 years. Crowding was defined as loss of arch perimeter, manifested as closure of space or by slipping of contacts resulting in rotation or adverse movement of teeth. Vego found that all cases showed a decrease in arch perimeter. The decrease was less noticeable in persons without lower third molars. Vego also indicated that there are multiple factors involved in the crowding of the arch.
  81. 81. • According to Richardson in AJO 89 the Belfast • • third molar study produced further evidence in support of the ‘pressure from behind’ theory. A group of 51 subjects with intact lower arches and bilateral third molars present were examined at ages 13 to 18 years. On average these cases had an increase in lower arch crowding of slightly more than 1mm on each side during the five-year observation period. In some quadrants the crowding increased by as much as 4mm.
  82. 82. • Molar space measured along the maxillary • • horizontal as the distance between the distal contact point of the first molar and the junction of the ramus with the body of the mandible was also examined. The changes in molar space condition were calculated by subtracting the size of second and third molars from the measurement of molar space. A significant correlation between increase in anterior crowding and initial degree of molar crowding was found suggesting that a person who lacks adequate space in the molar region in early permanent dentition is likely to show an increase in crowding anterior to first molar in subsequent years.
  83. 83. • They also showed that conditions in the molar region were only partly responsible for increased crowding. • Mesial inclination of lower canine usually is considered to be a sign that the buccal segment has moved forward. • Richardson also investigated the effect of second molar extraction on the development of late lower arch crowding ands found that there was a slight decrease in crowding (-1.5mm) and a slight distal movement of first molar (-1.3mm).
  84. 84. STUDIES INDICATING LACK OF CORRELATION BETWEEN THIRD MOLAR AND CROWDING • Kaplan in 1974 compared pre-treatment, posttreatment and 10year post-treatment study models and lateral cephalograms of 75 orthodontically treated patients. • Three groups with third molars erupted, impacted and congenitally missing were compared. Kaplan showed that some degree of lower anterior crowding relapse occurred in majority of cases. • He concluded that the presence of third molars does not produce a great degree of lower anterior crowding or rotational relapse after cessation of retention. • According to Kaplan the theory that third molars exert pressure on the teeth mesial to them could not be substantiated.
  85. 85. • Ades et al in AJO 1990 studied pretreatment, posttreatment and postretention study models and lateral cephalometric radiographs of 97 patients. The subjects were divided into those with lower third molar erupted, impacted, agenesis and extracted at least 10 years before. The study showed that: a. With time, mandibular incisor irregularity usually increases whereas arch length and intercanine width typically decreases b. The persons with third molars erupted into satisfactory function was not having a different mandibular growth pattern than those with third molars impacted or congenitally missing • In majority of cases some degree of mandibular incisor crowding took place after retention, suggesting that the recommendation for mandibular third molar removal with the objective of alleviating or preventing long term mandibular incisor irregularity may not be justified.
  86. 86. • Lifshitz in 1982 evaluated the effect of lower • premolar extraction versus non extraction as well as the presence or absence of lower third molars on mandibular incisor crowding. He concluded that in all groups evaluated, there was a significant increase in crowding, but there were no significant difference between the groups that did or did not have premolar extractions or whether third molars were present or missing.
  87. 87. • In 1981 Little et al observed that 90% of the extraction cases that were well treated orthodontically ended up with an unacceptable amount of lower incisor crowding. • These studies indicate that incidence of mandibular incisor crowding increased during adolescence and adulthood in untreated as well as orthodontically treated patients after retention is discontinued.
  88. 88. EXTRACTION OF THIRD MOLARS The third molars need to be considered as part of overall treatment planning, and this may include a recommendation for extraction. The timing of extractions requires an understanding of the various techniques available.
  89. 89. EXTRACTION BEFORE TREATMENT • It is not common practice for third molar teeth to be enucleated before orthodontic treatment of adolescents. • Orthodontists are normally reluctant to make surgical extractions a prerequisite of providing treatment. • They may feel that ramus growth and lower third molar eruptive pattern cannot be predicted, and take the view that the third molars may erupt eventually.
  90. 90. • Those in favour of enucleation believe that many • • • young adults between the age of 18 and 22 years experience problems with their third molars and that at later ages, pathologic changes often occur. Ricketts et al indicated that removal of the third molar bud at the age of 7 to 10 years is surprisingly simple and relatively atraumatic. Schulhof recommended that enucleation should be considered for any lower third molars which, after careful diagnosis, had a greater than 50% chance of impaction. Enucleation is not, however, a generally accepted procedure. Later caries experience, space conditiond, and the effect of orthodontic treatment are unknown at this early age.
  91. 91. LATERAL TREPANATION • At about age 12 years ,the need for third molar extraction may be more obvious. • Conventional surgical removal of the calcified crowns, at this age is difficult. • The tooth rolls in its crypt with considerable trauma to the adjacent tissues. • There is also a risk of gingival damage,with a pocket formation to the distal of the lower second molars due to the U shaped incision involved.
  92. 92. • Henry recommended a deep lateral approach ,calling it ‘Lateral trepanation’ for third molars in an early stage of partial development. • Burgess et al and Henry recommended lateral trepanation as an easier technique, with less complications and more rapid healing.
  93. 93. EXTRACTION DURING TREATMENT • If orthodontic treatment includes orthognathic surgery to one or both jaws, and third molars also require extractions, surgeons prefer to do it at the same operation. • However, some prefer to remove lower third molars 6 months before orthognathic surgery,so that bone healing can occur in the surgical site.
  94. 94. EXTRACTION AFTER ORTHODONTIC TREATMENT • Extraction of third molar after orthodontic treatment with a view to prevention of relapse should seldom be necessary. • Lindquist and Thilander in 1982 attempted to determine the effect of the prophylactic removal of mandibular third molars on the lower incisors. • They extracted a third molar on one side at an average age of 15.5 years and left the third molar on the other side as a control. • They measured study casts and cephalograms on these patients 3 years postoperatively. • They evaluated numerous parameters but were unable to predict which patient would benefit from such a procedure as both sides essentially had similar changes.
  95. 95. • Southard et al in 1991 measured proximal contact tightness between the mandibular teeth in cases with bilateral unerupted third molars. • The measurements were taken before and after the unilateral removal of one third molar. • They found that surgical removal of third molar did not have a significant effect on contact tightness.
  96. 96. • Pirttiniemi et al in 1994 evaluated the effect of removal of impacted third molars on 24 individuals in their third decade of life. • Dental casts were evaluated before and after one year after extractions. • They found that the extractions allowed for slight distal drift of the second molar but had no significant change in the lower anterior area. • From the available data it can be concluded that third molars do not play a significant, quantifiable role in mandibular anterior crowding.
  97. 97. • Two consensus conferences were dedicated to the 1. management of third molars ,one sponsored by the National institute of Dental Research in 1979 and the other by the American Association of Oral and Maxillofacial Surgery in 1993. Points of the concensus which were important to Orthodontics were: Crowding of the lower incisors is a multifactorial phenomenon that involves a decrease in arch length, tooth size, shape and relationship, narrowing of the intercanine dimension, retrusion of the incisors, and growth changes occurring in adolescence. Therefore, it was agreed that there is little rationale based on the available evidence for the extraction of third molars solely to minimize present or future crowding of the lower anterior teeth. If adequate room is available for third molar eruption, every effort should be made to bring these teeth into functional occlusion.
  98. 98. 2. Orthodontic therapy, in both maxillary and mandibular arches, may require posterior movement of both first and second molars by either tipping or translation, which can result in the impaction of third molars. To avoid impacting third molars and to facilitate retraction, it may be deemed advisable in some cases to remove third molars before starting retraction procedures. 3. There is no evidence to suggest that a third molar is needed for the development of the basal skeletal components of the maxilla and mandible.
  99. 99. 4.There was agreement that postoperative pain, swelling, infection, and other possible consequences of surgery are minimized when surgery is performed in patients who are dentally young, as judged by the third molar roots being about two thirds developed. • As a result, it is important to instruct the clinician in recognizing the benefit of early removal of third molars in those cases in which extraction is definitely indicated. 5. Although there are orthodontic reasons for the early removal of third molars, the consensus was that enucleation of third molar buds based on measurements obtained at age 7 to 9 years is not acceptable. This is because the present predictive techniques for third molar eruption or impaction are not highly reliable and should be used with caution.
  100. 100. 6.Patients should be informed of potential surgical risks including any permanent condition that has an incidence greater than 0.5% or any transitory condition that occurs with an incidence of 5% or more. On this basis, patients should be informed about hemorrhage, pain, swelling, alveolar osteitis, trismus, and nerve injury.
  101. 101. • Bonding techniques allow placement of fixed lower • • • retainer which allows stabilization of lower incisors, while awaiting further development of third molars. Bonding techniques also allow uprighting of some third molars. Thus the case for ‘wait and see’ with third molars is stronger than it was, and the case for extractions has become weaker. Kahl et al who carried out a long term radiographic follow up of asymptomatic impacted third molars recommend every 2 year radiographic review of former orthodontic patients.
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