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Role of third molars in orthodontics /certified fixed orthodontic courses by Indian dental academy


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Role of third molars in orthodontics /certified fixed orthodontic courses by Indian dental academy

  1. 1. ROLE OF THIRD MOLARS IN ORTHODONTICS INDIAN DENTAL ACADEMY Leader in continuing dental education
  2. 2. DEVELOPMENT AND ERUPTION • There is a 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 yrs. • Calcification can start at age 7 years and as later as age 16 years. • Enamel formation is normally complete between 12 and 18 yrs and root formation is normally completed between 18 and 25 yrs.
  3. 3. • In 1992 fanning reported average ages of eruption of 19.8 yrs for females and 20.4 yrs for males. • Lower 3rd molars normally have their occlusal surface tilted slightly forwards and lingual during early clarification. As the mandible increases in length with bone resorbtion at the inner angulation between the body and the ascending ramus of the mandible the third molars become more upright.
  4. 4. • In contrast, upper 3rd molar erupt down word back ward and often outwards. There is therefore a possibility of cross bite but tongue pressure on lower crowns and buccinator pressure on upper crowns will often correct this. • If there is lack of space, then normal eruptive paths cannot be followed, and cross bite can results.
  5. 5. Predication of crown size by factor and multiple regression analysis (AJO 1996: 109: 79-85) • Abe et al showed that it is possible to predict the size of unerupted third molars, based on measurement of erupted teeth. They found an accuracy of approximately 0.5 mm in the maxillary arch and 0.4 mm in the mandibular arch. The accuracy was highest when the maxillary dentition measurements were based on the sie of the lateral incisor, the second bicuspid, and the second molar. In the mandibular arch the accuracy was highest when the prediction was based on the size of the central incisor, the first bicuspid, and the second molar.
  6. 6. BRACKET SPECIFICATIONS Second molar tubes can used for erupted third molars, with 0° tip, - 14° torque, and 10° rotation in the upper and 0° tip and -10° torque in the lower. 3rd molar seldom required to move unless high percentage of adult treatment or 2nd molar extractions.
  7. 7. Eruptive pathways of lower 3rd molars (AJO 1992: 102, 322-327 • Richardson investigated the development of lower 3rd molars between ages 10 and 15 years. • In a group of 46 children of average age 10 yrs, she found that the angle of the occlusal surface of the lower 3rd molars to the mandibular plane was 41° she found this decreased by 11° by age 15. But 10% of her sample increased their angulation, worsening their eruptive position.
  8. 8. Full eruption of 3rd molars • Successful eruption of the lower third molars occurs by the tooth continuing to decrease it angle to the mandibular plane and moving occlusally into sufficient space.
  9. 9. Type of impaction • Impaction of 3rd molar occur due to lack of space or to unfavourable changes in angulation or a combination of these two problems. 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 fully eruption.
  10. 10. 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. However, if the mesial root develops ahead of the distal root this may be a favourable indication.
  11. 11. 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 distoangular impaction.
  12. 12. Changes in lower third molar position in the young adult. (AJO 1992; 102: 320-7). • Richardson investigated the later development and mesio-angular impaction of lower third molars. • For this study she defined an impacted lower third molar as one which was prevented from eruption because of its mesio-angular relationship with the second molar. • From her study stated 46% became more upright, but failed to erupt, 13% showed the same angulation, and 41% became more mesially inclined, the change varying
  13. 13. Changes at 18 year and later In a 1992 investigation, reported on a group of 41 dental students with intact (no missing teeth) lower arches. At age 18 years only 31 per cent of lower third molars present had erupted. Between the ages of 18 and 21 the unerupted third molars were observed to show changes in position ranging from +39° to -46° in the mesio-distal dimension and from +24° to -24° in the bucco-lingual dimension. Only 20 per cent did not change their mesio-distal angulation. He noted that, in spite of these positional changes, because of lack of space, only four teeth successfully erupted in the observation period.
  14. 14. Positional changes in mesio-angular impacted 3rd molars during a year (JADA 1989 (99) 460-4). • Shiller stated that positional changes in the mesioangular inclination of third molars continues well into mid-20s, and he noted that after second molar extractions the third molars did not initially erupt into optimal positions. However, considerable improvement in angulation, space closure, and occlusion commonly occurred after eruption.
  15. 15. Mechanism for lower third molar eruption and impaction Favourable change in angulation, to a more upright position, seemed to occur in teeth where the mesial crown surface and the mesial root developed ahead of the distal crown surface and root.
  16. 16. •Unfavourable 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.
  17. 17. Factors influencing the space available for lower 3rd molars (Angle Orthod. 1987; 57; 155-61). 1. 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 chance of eruption. But after 16 years of age there was negligible growth of the refromolar area.
  18. 18. 2. Bone resorbtion: • Increased space was obtained from both the mesial movement of the dentition and bone remodelling along the anterior border of the ramus. On average 2mm of posterior space was created by bone remodelling (range 0-6mm). • The largest increase in 3rd molar space resulted from a large amount of overall mandibular growth and forward eruption of the mandibular dentition.
  19. 19. 3. Space released by attrition: • In primitive dentitions, where considerable attrition takes place, the 3rd molars erupt to take up the space released. • Begg felt that lack of this attraction, due to highly refined diets, was a major cause of 3rd molar impaction. • In high caries situations mesial and distal lesions could possibly also increase space.
  20. 20. 4. Space can be increased by 2nd molar extraction 5. Reduction of Space: • Silling showed that orthodontic therapy in non extraction cases can increase the probability of 3rd molar impaction by holding back or distally tipping lower 1st and 2nd molars. • Distal movement of upper 1st molars with head gear can reduce the space for upper 3rd molars. • Magness and Graber have suggested the extraction of upper second molar in some cases to assist 1st molar positioning and increase space for upper 3rd molars. 6. Eruption into space released by bicuspid extraction: • Bicuspid or other extractions increase the chance of 3red molar eruption.
  21. 21. The effect of bicuspid extractions on 3rd molar eruption: • Bjork et al observed that extraction of a tooth in a quadrant considerably lowers the prevalence of 3rd molar impaction. • Fanning found that 75% of 3rd molar erupted in a growth with bicuspid extractions but only 57% erupted in a non-extraction group. • Faubion compared 40 treated orthodontic patients, 20 of whom were non extraction and 20 who had four 1st bicuspid extraction. He found four times as many erupted extraction group. He concluded that removal of 1st bicuspid for patients with arch length discrepancy helps to provide space for the eruption of mandibular 3rd molars.
  22. 22. • Kaplan concluded, where bicuspids have been extracted as part of orthodontic therapy, there is an increased probability of 3rd molar eruption. • Richardson stated that, extraction of a bicuspid has the effect of reducing the frequency of 3rd molar impaction, and the extraction of a 2nd molar virtually eliminates it. And also stated that 2nd bicuspid extraction may be more favourable than 1st bicuspid extraction, in releasing space for lower 3rd molar eruption. • In a class III case, with class III elastics, the lower labial segment would be retracted into the space released by bicuspid extractions. However, in a class II uncrowded case, with class II elastics, an optimal release of space for lower 3rd molar could be predicted.
  23. 23. In a case with mild crowding, bicuspid extraction could be expected to icnreased space for 3rd molars. However in a bimaxillary protrusion case, the 7mm of space gained on each side would be used for retraction of anterior teeth and minimal improvement could be predicted for 3rd molars.
  24. 24. Accelerated eruption of third molars after extractions: • Fannng, Richardson have reported accelerated eruption of 3rd molar following extraction of teeth further forward in the arch; with Richardson noting that molar extractions produced the greatest acceleration. • Haavikko et al., felt that bicuspid extractions merely accelerate, but do not promote, eruption of third molars. • Huggins, in a review of six cases, believed that extraction stimulated 3rd molars to early eruption and noted that some erupted as much as seven years earlier than average. • Accelerated eruption can also occur in association with missing teeth in the anterior region.
  25. 25. • Silling sampled 100 non-extraction orthodontic patients and found 67 per cent males and 69 per cent females developed impacted 3rd molars. • Ricketts claimed that more than 50 per cent of orthodontic patients required extraction of lower 3rd molars. • Richardson found 55 per cent of lower 3rd molars were impacted in the Belfast group of patients, who had had no lower arch extractions. • The incidence of impaction of lower 3rd molars is probably 25 per cent or higher in many populations. It is also probable that between 30 and 70 per cent of so called non extraction treatments will have impaction of lower third molars.
  26. 26. Etiology of lower 3rd molar impaction:  Poor mandibular bone growth  3rd molar who had lighter in weight and had smaller cranial dimensions.  Vertical grower with short mandibular lengths.  Retarded facial development  Retarded 3rd molar development  Late mineralization of the lower 3rd molar crowns.  Less space b/w second molar to the anterior border of the ramus.
  27. 27. Width of the mandible: (Transverse dento-skeletal relationships and 3rd molar impaction. – Angle orthod 1981; 51: 41-7). Olive and Basford showed a relationship b/w lower 3rd molar impaction and ratio b/w bilateral molar and ramus widths. They stated that low ramus/ molar ratio leads to impaction.
  28. 28. The development of 3rd molar impaction and its prevention. AJO 1981; 122-130 Richardson showed that 12% of all lower 3rd molars became more mesially angulated and also concluded that radiographic measurement at age 10 or 11 years could not be used to predict impaction accurately.
  29. 29. 3rd molars and lower incisor crowding Facial growth Bjork’s implant studies showed a distal migration of the lower teeth near the end of the mandibular growth spurt. This facial growth has been suggested as a possible reason for lower incisor crowding. Impacted 3rd molars may, in theory, impede this distal migration, and contribute to incisor crowding.
  30. 30. Pressure from behind theory • Vego found more crowding in a group with erupting 3rd molars than in a group with developmentally absent lower 3rd molar. • Lindquist and Thilander extracted lower 3rd molars on one side only in a group, and found less crowding on the extraction sides than on the non-extraction side. • Bergstrom and Jensen studied 60 dental students and concluded that 3rd molars exerted some influence on the development of lower arch crowding. but not enough to recommend extraction or enucleation of 3rd molars except in exceptional circumstances
  31. 31. • Schwarze reported that 56 orthodontically treated patients for whom lower 3rd molars had been enucleated were more resistant to late lower incisor crowding than a group with lower 3rd molars. • Bergstrom and Jensen examined 30 dental students with unilateral agenesis of lower 3rd molars and found more crowding on the side with the 3rd molar present compared with the side where it was absent. • Richardson's Belfast 3rd molar study has produced further evidence to support the 'pressure from behind' theory. A group of 51 subjects with intact lower arches and both lower 3rd molars present were examined at ages 13 and 18 years. Only 16% showed no increase in crowding. The average increase in crowding was slightly more than 1mm on each side over 5 years. In some quadrants the crowding increased by 4 mm.
  32. 32. • More recently, Richardson found that later on (between ages 18 and 21 years) the lower arch is stable in terms of tooth alignment and mesial drift, regardless of continuing mandibuiar growth and 3rd molar status. • It should also be noted that Richardson's observation that there is greater lower incisor stability after extraction of 2nd molar, supportive of the pressure from behind theory is
  33. 33. No pressure from behind theory •Kaplan studied 75 orthodontically treated patients on average 9.3 years after treatment. The mean age of Kaplan's sample was 26.6 years; it included extraction and non-extraction cases, which introduced another variable. During the post-retention period he found that no more lower crowding and rotational relapse occurred in cases with 3rd molars than in those with agenesis of 3rd molars. •Sampson, Richards, and Leighton studied 54 nonorthodontically treated Caucasians and found no significant difference in the crowding among groups with erupted, impacted, or missing 3rd molars. They concluded that it did not seem to be important whether the mandibular 3rd molar erupted vertically, remained mesio-angularly impacted, or was absent.
  34. 34. • Southard reported in 1992 on the tightness of contact points in the mandibuiar arch after unilateral extraction of one lower 3rd molar. The presence of a 3rd molar was not found to affect contact point tightness. • This suggests that the pressure from a lower 3rd molar is not continuous and may occur only when the tooth is trying to erupt, slopping after the tooth becomes impacted. He concluded that extraction of 3rd prevent incisor molars did not help to crowding. • He noted that the general tendency for lower incisors to crowd with age occurs well into adulthood, with or without the presence of 3rd molars, and past the time when unerupted 3rd molars would exert any influence.
  35. 35. Techniques for uprighting lower 3rd molars • Uprighting and detail positioning of 3rd molars is likely to be needed for some patients if 2nd molars have been extracted. • It may also be required for routine orthodontic patients where 3rd molars have erupted in a less than ideal position after four bicuspids have previously been extracted, to avoid leaving the patient with only 24 teeth.
  36. 36. Shallow mesio-angular impaction: • A one-stage method is used. A 2nd molar tube can normally be bonded onto the buccal aspect of a partly erupted lower 3rd 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, the lower 2nd or 1st molars alone can be used with a lingual arch for support.
  37. 37. Decp mesico-angular impactions • A two-stage method is used. If it is not possible to bond onto the buccal surface of an impacted lower 3rd molar owing to the level of the gingival tissue, then a different technique should be considered. This can be delayed until 18-19 years of age, to allow lime for the tooth to improve its position spontaneously as sometimes occurs. • The 1st stage involves bonding a 2nd molar lube on to the occlusal surface of the lower 3rd molar. The hook is removed from the tube, before bonding. Lower 1st or 2nd molars are banded, with a lingual arch, using 1st molar bands and brackets. Capping is removed from the molar brackets.
  38. 38. • A small sectional archwire- with a compressed coil spring, is used to provide a disializing and uprighting force to the crown of the impacted molar. After some uprighting using this method, it is normally possible to bond a tube buccally for the 2nd stage.
  39. 39. The Extraction of 3rd molars Extraction before treatment • Henry described enucleation as a simple, rapid technique, with minimal trauma, removing the lower 3rd molar tooth germ when it is a mere uncalcified sac between ages 7 and 10 years. • Schulhof recommended that enucleation should be considered for any lower 3rd molars which, after careful diagnosis, had a greater than 50% chance of impaction. • Liddle" reported early success with enucleation, but noted one case of interference with the posterior facial nerve. He mentioned this possibility, and the chance of damage to the developing lower 2nd molars, as contraindications
  40. 40. Lateral trepanation: • Henry recommended a deep lateral approach, calling it lateral trepanation' for tower 3rd molars in an early stage of partial development. This was in contrast to the conventional approach downwards through the external oblique ridge. • He recommended lateral trepanation as an easier technique, with less complications and more rapid healing. The technique of lateral trepanation, with its possible importance to orthodontics, was also described by Burgess et al. Nevertheless, it can be a traumatic procedure. • In 1973, Schwarze reported positively on 56 percent who had had early removal of 3rd molars, describing the technique as 'germectomy'. He compared them with 49 patients who did not have extraction, and concluded that upper and lower 1st molars subsequently drifted less mesially in the extraction group.
  41. 41. Extraction during treatment: • If orthodontic treatment includes orthognathic surgery to one or both jaws, and 3rd molars also require extraction, some surgeons prefer to do all the necessary surgery, including any 3rd molar extractions, at the same operation. • However, other surgeons prefer to remove lower 3rd molars 6 months before orthognathic surgery, so that bone healing can occur in the surgical site.
  42. 42. Extraction after orthodontic treatment: • Extraction of 3rd molars after orthodontic treatment with a view to prevention of relapse should seldom be necessary. If their impaction causes problems they can be removed by the conventional approach. • Richardson has warned that a final prediction of mesioangular impaction should not be made before age 18 years, because lower 3rd molars continue to show rotational change up to and beyond this time. • The lower 3rd molars are just one of many factors which may contribute to late lower incisor crowding, and there has been a tendency to favor extraction soon after placing retainers, instead of waiting to give them a chance to erupt. This tendency should Schwarze reported that lower 1 st drifted less be resisted. molars
  43. 43. Conclusions: . The influence of the 3rd molars on the alignment of the anterior dentition maybe controversial, but there is no even the major etiologic factor in the post treatment changes in incisor alignment. The evidence suggests that the only relationship between these two phenomena is that they occur at approximately the same stage of development. ie., in adolescence and early adulthood. But this is not a cause and effect relationship. . The clinician has to have a justifiable reason to recommend the extraction of any tooth. . . The clinician has to consider the impact of the extraction decision on any future treatment plan from an orthodontic, surgical, periodontic, or prosthodontic aspect. If extraction is indicated, 3rd molars should be removed in young adulthood rather than at an older age.
  44. 44. Thank “U”