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  • Six months was a familiar landmark time period for most orthodontists, and it was likely that most patients will still be complying with their retainer wear and so it was chosen.
  • It was calculated that a total sample size of 388 subjects would give a power of 80% with a 5% significance level to detect a true difference in contactpoint displacement of greater than 0.2 mm.
    at least 400 patients (200 in each group) would be recruited to allow for dropouts and loss to follow-up
  • was chosen, based on equal numbers of both types of
    and were blind to the fact that they were making retainers for patients included in the trial.
  • It was found that the VFRs were significantly better at retaining the labial segments than the Hawley retainers.
  • retiner hawleys

    1. 1. The effectiveness of Hawley and vacuum formed retainers: a single center randomized controlled trial INDIAN DENTAL ACADEMY Leader in continuing dental education
    2. 2.  Post fixed appliance therapy , retainers routinely fitted by the orthodontists are worn by the patient for 6 to 12 months while the soft and hard tissues remodel around the teeth.  In the long term retention might be necessary until growth is complete or indefinitely, if teeth are in unstable positions.  Hawley retainers and vacuum formed retainers are the 2 most commonly prescribed retainers in the UK NHS.
    3. 3.  This is probably due to their improved esthetics, ease of fabrication and lower costs.  There is no evidence to support the use of VFR’s over Hawley’s retainers .  But evidence suggests that the Hawley's might be the retainer of choice when a lateral open bite is present before debond.
    4. 4.  Although studies have mentioned that there is little to choose between Hawley and VFR, except in open bite patients ,the evidence is weak because of the small sample sizes.  However ,the potential cost savings in a health care system with the routine use of VFR’s rather than Hawley's are significant which alone justifies more research and greater statistical power to enable valid clinical and economic considerations to be reached.
    5. 5.  The aim of this randomized clinical trial was to compare the clinical effectiveness of Hawley and VFR’s over a 6-month period after debonding , in terms of Little’s index of irregularity (LII), tooth rotation, intercanine width (ICW), intermolar width (IMW), over jet, and overbite . Aim
    6. 6. Material and methods  Clinical trial was conducted in an orthodontic practice with a large sample treated by an orthodontist approved by local research and ethics committee at united Bristol health care trust .
    7. 7.  Inclusion criteria:  Patients who were due to have their fixed orthodontic appliances removed.  Treated under the NHS by the same orthodontist.  fixed appliance treatment involving both arches.  preadjusted edgewise appliances.  pretreatment records.  treatment plan.  study models available.  willingness to wear maxillary and mandibular retainers.
    8. 8.  Exclusion criteria:  Single-arch or sectional fixed appliance treatment.  Hypodontia requiring tooth replacement on the retainer as a temporary measure.  Rapid maxillary expansion.  Bonded retainers.  Poor periodontal status.  Early debonding.  Transfer patients.  Learning difficulties.  Cleft lip or palate.
    9. 9.  Potential participants were identified before debonding, and the study’s purpose was explained to the patients and their parents or legal guardians.  Written information about the study was given to all potential participants, and written consent was obtained before the debond appointment.  For patients under 16 years, written consent was also obtained from the parent or legal guardian.  Gillick competence was applied when necessary
    10. 10.  Enrolment started in March 2003 and was completed by December 2004.  The orthodontist assessed 531 subjects for eligibility.  55 did not meet the inclusion criteria.  79 refused to participate,  recruitment rate was 75%.  Three hundred ninety-seven subjects agreed to take part in the study.
    11. 11.  At the debond appointment after appliance removal (T1), the orthodontist recorded over jet and overbite.  One set of maxillary and mandibular alginate impressions were made, and study models and working models were cast on which the retainers were to be made.  All subjects were randomized by the research team to receive either maxillary and mandibular Hawley retainers or VFR’s.
    12. 12.  A blocked randomization method and retainers were allocated per block of 20 patients.  randomization was undertaken after obtaining patient consent to ensure concealment of allocation  196 patients were randomized to Hawley retainers and 201 to VFRs.  Two fully qualified, blinded lab. technicians fabricated the retainers to standardized designs.
    13. 13.
    14. 14.
    15. 15.
    16. 16.  The Hawley retainer  acrylic base plate  Adams clasps of 0.7- mm s.s wire on the molars.  A Hawley bow (open looped short labial bow) from 0.7-mm s.s wire extending from canine to canine.  The Hawley bow was then contoured with acrylic resin to contact the labial surfaces of the incisors
    17. 17.  Vacuum formed retainers  Erkodur blank (Erkodent, Erich Kopp, GmbH, Pfalzgrafenweiler, Germany) 1.5 mm in thickness was used.  The retainer was trimmed to provide 1 to 2 mm buccal and 3 to 4 mm lingual extensions past the gingival margin.  All occlusal surfaces were covered up to and including the most distal tooth
    18. 18.  The retainers were fitted within 1 week after debond.  The duration of retainer wear was standardized based on the standard protocol for retainer wear.  Hawley retainers were to be worn 24 hours a day for 3 mths, including while eating, but to remove them when brushing their teeth. After 3 mths, wear time was reduced to 12 hours a day.  the VFRs were to be worn 24 hours a day for the 1st week except while eating and brushing teeth. After the 1st week, wear time was reduced to 12 hours a day.
    19. 19.  The subjects were reviewed by a member of the research team at 2 intervals; 3 months and 6 months after debond (T2).  At the 6-month review appointment, over jet and overbite were recorded, and alginate impressions for end-of-trial study models were taken.  The subjects were asked to remove their retainers before their appointments so that the research team would be blind to the type of retainers that they were wearing.
    20. 20.  Orthodontic study models collected at T1 and T2. were examined by 1blind researcher . Casts of poor quality were excluded from the analysis .  The number of models excluded and the reasons for exclusion were documented.  The method used to measure changes in the study models between debond and 6 months was based on the study of Tran et al, in which the LII was measured on 2-dimensional scanned and printed images of study models.
    21. 21. Methodology for the analysis of the study models  The heels of the maxillary and mandibular models were trimmed so that all occlusal surfaces of the teeth contacted the glass bed of the scanner.  The mesiopalatal/mesiolingual cusp of the molars, the buccal and mesiopalatal/mesiolingual cusps of the premolars, and the canine cusp tips were marked with a pencil.  The models were then placed on the glass of the flatbed scanner (Agfa SnapScan 1236 flatbed scanner; Agfa-Gevaert N.V., Mortsel, Belgium), with their occlusal surfaces facing down and in contact with the glass. Each was scanned at a resolution of 600 dpi, and the resulting image was saved to a PC as a JPEG
    22. 22.  The JPEG image was enlarged to 200% by using Paint Shop Pro 9 software (Corel UK Limited, Maidenhead, Berkshire, United Kingdom) to make point identification easier during subsequent digitizing.  The image was then printed in color with a laser printer . A total of 34 points were digitized in sequence from point 1 to point 34 by using a GTC digitizer (GTCO Cal Comp, Columbia, Md) on each printed image of a study model  A computer program, written specifically for the study, automatically calculated the following outcomes in both arches for each digitized image.
    23. 23.
    24. 24. Tooth rotations mesial to the first permanent molars.  The rotations of the incisors and canines was determined by constructing a line that bisected 2 points per tooth that best marked its rotational angulation .  The angle formed by the intersection of this line with the line forming arch depth gave the measurement of rotation of the tooth.  Arch depth was defined as the length of a line perpendicular to the intermolar width that passed through the midpoint of the contact points of the central incisors.
    25. 25.  The LII was defined as the sum of the displacements of the 5 contact points of the incisors.  The method described by Little used the true anatomic contact point to assess tooth displacements.  However, with a printed 2-dimensional image, it was almost impossible to determine the true anatomic contact point.  The LII was therefore redefined for this study as the displacement between the midpoint of the incisor edges.
    26. 26.  ICW was the distance between canine cusp tips  IMW was the distance between the mesiopalatal/ mesiolingual cusps of the first molars
    27. 27. The measurement of rotation for the premolars  was calculated by constructing a line that bisected the buccal and the palatal/lingual cusp tips .  In premolars with 2 lingual/palatal cusps, the mesiopalatal / mesiolingual cusp was bisected to form the line.  The angle formed by the intersection of this line with the line forming arch depth gave the rotation of the tooth.
    28. 28.  The digitization of 1 model resulted in creation of a “comma-separated-variable-string” file that enabled the data to be exported electronically into a database (version 13.0; SPSS, Chicago, Ill) for statistical analysis.  To record the reproducibility of the method, 1 examiner (H.R.) made all measurements on 30 models on 2 occasions ,a week apart. Intra observer reliability coefficients were then calculated.
    29. 29.  An intention-to-treat analysis was used wherever data were available so that the data from all patients who were successfully randomized and for whom baseline and final records were available were included in the analysis.  Relapse amounts for LII, ICW, IMW, tooth rotation, and over jet were determined by comparing the difference between the measurements at T1 and T2. Absolute values for these outcome measures were calculated because any change in either a positive or a negative direction could be considered relapse. The absolute difference was calculated so that positive and negative changes did not cancel each other.
    30. 30.  Visual inspection of the histograms showed that the data were considerably skewed and did not follow a normal distribution.  The median and the interquartile range were therefore calculated for each outcome at T1 and T2. Mann-Whitney tests were used to compare the Hawley and the VFR groups in terms of the changes between T1 and T2.
    31. 31.  Relapse of overbite between T1 and T2 was calculated by first determining the numbers of subjects who stayed the same and whose overbite changed in each group. The differences between the overbite change for both groups were assessed by using the Fisher exact test.  Because of the number of tests performed, a P value of .01 was taken to be statistically significant.
    32. 32.  355 subjects (172 Hawley, 183 VFR) attended the 6- month review, giving a completion rate of 89%. 155 models were analyzed in the Hawley group and 155 in the VFR group.  Both groups had a median change in over jet between T1 and T2 of 0.5 mm . In 54 subjects (32%) in the Hawley group and 49 subjects (27%) in the VFR group, a change in overbite was observed at T2 . Overall, there was no statistically significant difference in overbite between the 2 retainers.
    33. 33.
    34. 34.  The intraobserver reliability coefficients ranged from 0.96 to 1.0 for linear measurements and from 0.93 to 1.0 for angular measurements, demonstrating that the method had good reliability.
    35. 35. RESULTS
    36. 36. DISCUSSION  Conducting this study in a practice setting enabled the research team to recruit and randomize 397 patients treated by 1 operator over a relatively short time period (18 months). To date, this is the largest such clinical trial on the effectiveness of the Hawley and the VFR.  In this study, the retainer groups matched favorably for baseline characteristics, and it is therefore likely that the 2 groups were equally matched and that the randomization process worked well.
    37. 37.  No statistically significant differences were found in the effectiveness of the Hawley and the VFR to retain tooth rotations, ICW, and IMW in both arches.  Anecdotal concerns that VFRs lack rigidity and might not support transarch stability were not upheld in this study.  However, a statistically significant difference was found between the retainers in the maintenance of incisor irregularity, because the Hawley group had double the change in irregularity over 6 months compared with the VFR group. These differences were 0.56 mm in the mandibular arch and 0.25 mm in the maxillary arch.
    38. 38.  Although this difference is unlikely to be clinically significant in the maxillary arch, it might be considered clinically significant in the mandibular arch, particularly if the relapse was located to a single tooth displacement.  The results contrast with those of the previous studies comparing the Hawley and the VFR. The differences in results from the previous trials might in part be explained by the much larger sample and its considerably greater statistical power.
    39. 39.  Greater irregularity was seen in the mand.labial segment compared to the max. labial segment which follows the trend that irregularity is most marked in the mandibular labial segment.  This study can perhaps be criticized for using 2 retainer wear regimens. However, the protocols were chosen to match the wear regimens already in place at the practice.  An advantage of conducting a trial in this manner was that the findings should be more representative of what occurs in everyday clinical practice, measuring effectiveness rather than efficacy.
    40. 40.  Although the Hawley retainers were worn full time for a longer period than the VFRs in this study, the latter were still more effective in maintaining incisor alignment, particularly in the mandibular arch.  It could perhaps be argued that if relapse of incisor position is truly to be minimized, then consideration should be given to the use of a bonded retainer.  However, a recent Cochrane review examining a number of aspects of retention, including removable vs fixed retention, found the quality of the studies to be poor, and there is as yet no reliable evidence that fixed retainers are more effective than VFRs.
    41. 41.  If there is little difference in the clinical effectiveness between the 2, questions could arise as to whether any other factors might influence the choice of retainer, including cost, ease of fabrication, risk of breakage, patient compliance, and patient preference or satisfaction.  The answers to these questions will be addressed in a parallel study. Each patient should, however, be assessed individually because Hawley retainers still offer the additional benefit of allowing superior vertical settling compared with VFRs.
    42. 42. CONCLUSIONS  The results of this study suggest that VFR’s are more effective than Hawley retainers at holding corrections in irregularity in the mand. labial segment compared with the max.labial segment.  With regard to long-term occlusal changes, this follows the trend that irregularity is most marked in the maxillary and mandibular labial segments.  This is likely to be clinically significant only in the mandibular arch if located to a single tooth displacement. In addition, this trial supports the need for further research in primary care.
    43. 43. Comparison of occlusal contacts with use of Hawley and clear overlay retainers Earl Sauget, David A. Covell, Roger P. Boero, William S. Lieber. Angle Orthodontist, 1997, No. 3, 223 - 230
    44. 44.  After orthodontic repositioning of teeth, retention devices are used to maintain arch form and minimize the tendency of teeth to shift.  undesirable changes - “relapse,”  desirable changes - “settling.”  With settling, the number of occlusal contacts increases, improving the fit of the teeth. The best retention device would be one that allows settling but prevents relapse.
    45. 45.  Commonly prescribed retainers include the Hawley, wrap, fixed, clear overlay, and tooth positioners.  The designs of these retainers differ, particularly the extent of the retainer-tooth contacts.  Due to these contrasts in retainer design, characteristic differences in tooth position following their use would be anticipated
    46. 46.  The design of the Hawley retainer has remained unchanged.  The original method of fabrication used lingual and palatal plates made of vulcanized rubber that were accurately adapted to the lingual surfaces of the teeth, and a labial wire with adjustment loops at the canines. Today, acrylic has replaced the rubber.  The clear overlay retainer, by Ponitz in 1971, is made of thin (0.025 inch), vacuum-formed thermoplastic material that adapts closely to the lingual, facial, and occlusal surfaces of the teeth.
    47. 47.  Tibbetts compared Hawley retainers, clear overlay retainers, and tooth positioners by analyzing dental casts at debonding and after a 6-month retention period.  The results showed no statistically significant differences in Angle’s molar classification, overbite, over jet, maxillary or mandibular intercanine width, intermolar width, or arch length.
    48. 48.  Aim of this study was to use changes in occlusal contacts for comparing the retention characteristics of the Hawley and clear overlay retainers.  Occlusal contacts between the maxillary and mandibular teeth were statistically compared at debanding, when retainers were delivered, and after 3 months of retention. Aim
    49. 49. Materials and methods  Sample characteristics  30 patients from the Orthodontic Clinic at the University of the Pacific School of Dentistry were prescribed alternately, Hawley retainers or clear overlay retainers .  13 patients ( 8 females, 5 males) received maxillary and mandibular Hawley retainers.  2 patients (both female) received maxillary Hawley retainers with mandibular fixed lingual retainers.
    50. 50.  15 patients (9 females, 6 males) received maxillary and mandibular clear overlay retainers.  All patients had been in orthodontic treatment for at least 18 months.  The Hawley retainer sample contained  5 patients - premolar extractions,  8 patients – non extraction,  2 patients - congenitally missing maxillary lateral incisors.
    51. 51.  mean age - 18 yrs 8 mths (range: 13 yrs 11 mths to 35 yrs 10 mths).  The clear overlay retainer sample included  6 patients - premolar extractions,  8 - non extraction,  1 - missing maxillary lateral incisors.  The mean age was 19 years 6 months (range: 13 years 9 months to 42 years 2 months).
    52. 52.  Retainers  Immediately following removal of the fixed appliances, models of the maxillary and mandibular arches were made .  the retainers were delivered 1week later and the Hawley appliances were adjusted so the labial bow made uniform, passive contact with each anterior tooth.  The mandibular incisors were in light contact with the acrylic, lingual to the maxillary incisors, when the posterior teeth were in maximum intercuspation.
    53. 53.  The clear overlay retainers were fabricated from 0.025 inch thermoplastic (Tru – Tain; Rochester, Minn) vacuum-heat adapted to dry models.  The facial surfaces of the retainers were trimmed to cover the incisal 1/3rd of the incisors and to extend 3 mm beyond the gingival margin posteriorly.  Occlusal coverage extended distally to cover approx the mesial half of the maxillary and mandibular second molars.
    54. 54.  Patients receiving Hawley retainers were instructed to wear them full-time, except during meals.  Those prescribed clear overlay retainers were instructed to wear their retainers full-time for the first three days (except during meals), and nightly thereafter.
    55. 55.  Bite registrations  Vinyl polysiloxane impression material (Regisil PB; Caulk– Dentsply, Milford, Del) was used to record the occlusal contacts.  Patients were seated upright in a dental chair and the registration material was applied over the occlusal surfaces of the mandibular teeth. The patient was told to bite firmly in maximum intercuspation .  A second bite registration was made within 15 minutes to test the reproducibility.
    56. 56.  The two bite registrations were examined on a light box and contacts appearing as transparencies in the material, were compared.  If a subjective difference in the pattern of contacts was observed, another registration was made. In no case was a fourth registration needed.  To objectively analyze the bite registrations, each was labelled with a randomized identification code and the registrations intermixed.
    57. 57.  For analysis of the occlusal contacts, individual registrations accumulated from multiple patients were selected at random.  Occlusal contacts were evaluated and classified as either true or near contacts.  True contacts perforated the impression material; near contacts appeared as thin translucencies and were counted only if they were 0.20 mm or less as measured with an Iwanson caliper.
    58. 58.  Observing from the maxillary side, the locations of the contacts were assigned by tooth and then grouped as either anterior (incisors and canines) or posterior (premolars, first molars, and second molars).  All registrations were evaluated and measured by the same individual.
    59. 59.  Error of method  The registrations were made within 30 minutes of debanding (T1), at the time of retainer delivery (T2), and three months later (T3).  All registrations were made in the afternoon by the same clinician. To test the measurement accuracy, 10 bite registrations were selected at random and the near contacts measured. The same registrations were remeasured on a different day.  The standard measurement error (Sx) was calculated using Dahlberg’s formula, Sx = sq.root of D2 /2N where D is the difference between duplicated measurements and n is the number of double measurements .
    60. 60. Results  Method error  The standard measurement error (Sx) from repeated thickness measurements of the same bite registration was 0.014 mm.  Comparison of measurements between paired records made on the same day showed an error of 0.018 mm.  Thus the variation found in repeated registrations approximated the limits of the measurement technique.
    61. 61.  Occlusal contacts at debanding (T1)  a wide variation was seen between individuals of both retainer groups with regard to the number of total occlusal contacts.  The Hawley retainers had a mean of 34.3 occlusal contacts (± 10.45 standard deviation) and the clear overlay retainers had a mean of 31.8 .  Comparing the Hawley and clear overlay retainer groups at debanding, there were no statistically significant differences between the mean number of total contacts, true contacts, near contacts, or anterior/posterior contacts
    62. 62.  Occlusal contacts at retainer delivery T2  At the time of retainer delivery, T2, there were no significant differences between the two retainer groups in the average number of each classification of occlusal contacts  Within each retainer group there were no significant changes between T1 and T2 except for an increase in posterior true contacts in the Hawley group (T1: 10.9 ± 4.0; T2: 14.1 ± 4.0, P<0.05).
    63. 63.  Occlusal contacts after 3 months retention (T3)  At T3 The mean number of posterior true contacts (Hawley: 16.4; clear overlay: 11.9) and the mean number of total true contacts (Hawley: 20.2; clear overlay: 15.1) were significantly different between the retainer groups  Neither sample showed a significant within–group change between T2 and T3.
    64. 64.  In the Hawley group, between T1 and T3, significant increases were found in the average number of total contacts, the mean number of total true contacts, near contacts, posterior contacts, and posterior true contacts  The average number of posterior near contacts approached statistical significance (P=0.06). There were no differences in anterior contacts.  The clear overlay group displayed no significant differences in any category between T1 and T3
    65. 65.
    66. 66.
    67. 67.  Comparison of changes between groups  No significant changes occurred between the two retainer groups from T1 to T2 in any of the occlusal contact categories  From T2 to T3 the number of total contacts and posterior contacts increased significantly more in the Hawley group than the clear overlay group
    68. 68.  There was a small reduction in the number of true posterior contacts with the clear overlay retainers. Most of the decrease occurred at the first molars and to a lesser extent at the first premolars. The mean changes in anterior contacts were not significant  From T1 to T3, the occlusal contact changes in the Hawley group compared with the clear overlay group showed a similar pattern to that found from T2 to T3
    69. 69.
    70. 70.
    71. 71. Discussion  Results from this study show statistically significant differences in the number of occlusal contacts between Hawley and clear overlay retainers.  After 3 months of retention with the Hawley retainers, there was a statistically significant increase in the number of total contacts.  In contrast, over the same time period with the clear overlay retainers, there was no change in the number of occlusal contacts.
    72. 72.  We believe these results are reliable due to minimal number of confounders.  The two samples matched favorably for size, age, gender, and numbers of cases with teeth extracted or missing.  With regard to the methods, the bite technique for recording occlusal contacts was highly reproducible. In addition, the method has been validated in several previous investigations.  Finally, because diurnal variation in occlusal contacts has been reported, the bite registrations were made only during the afternoon.
    73. 73.  The number of occlusal contacts at debonding in both retainer samples was similar to that reported by Radolsky and Sadowsky.  The mean number of total contacts in their study was 36.6 (17.1 near contacts, 19.1 actual contacts), while this study recorded 34.3 ± 10.5 total contacts (18.7 ± 7.0 near contacts, 15.6 ± 5.8 true contacts) for the Hawley retainer group and 31.8 ± 11.8 total contacts (14.0 ± 6.5 near, 17.8 ± 7.5 true) in the clear overlay retainer group.
    74. 74.  The increase in contacts observed in the Hawley retainer group agrees with the findings of Durbin and Sadowsky, who compared Hawley retainers with tooth positioners.  With the Hawley retainer they found the total number of contacts increased significantly during the first 3 months of retention, with most of the increase associated with posterior contacts.  From these results it is apparent that with a Hawley retainer, the posterior teeth settle after the bands are removed.  Razdolsky and Sadowsky described minimal migration of the contacts toward the central groove. No attempt was made in this study to characterize the location, or alteration of location, of contacts on individual teeth.
    75. 75.  From appliance removal to retainer delivery, any alteration in occlusal contacts in both samples should be similar.  Both showed a small increase in the number of posterior contacts from T1 to T2, with a greater increase in the Hawley retainer group  Several possibilities can be proposed to account for the differences between retainer groups from T1 to T3.  First, no attempt was made to adjust the overlay retainers to optimal occlusal contact.
    76. 76.  With up to 0.05 inches of retainer material between the teeth, initial contact at closure was between the more posterior teeth.  This contact may have loaded the molars more than the anterior teeth and have prevented further eruption or settling, or possibly intruded the molars.  However, the differential occlusal loading when the retainers were worn at night would have been counteracted during the day when the retainers were not worn
    77. 77.  Alternately, if the mandibular condyles had been distracted to produce a more uniform distribution of occlusal contact with the retainers in place, there should have been an increase in posterior contacts when the overlay retainers were removed and the condyle assumed its normal position.  The data shows the opposite occurred. Because the second molars were only partially covered by the overlay retainers, they may have erupted more relative to the more mesial teeth. The second molars would then become an occlusal stop when the retainers were removed. However, this explanation is unlikely because the second molars did not show an increase in occlusal contacts.
    78. 78.  It is most likely that the overlay retainers reverse the settling occurring between T1 and T2 because the retainers are fabricated on casts taken at T1.  This hypothesis is consistent with data from the clear overlay group showing a slight reduction in posterior contacts from T2 to T3, but no difference in the number of contacts at T3 compared to T1.  The Hawley retainer, on the other hand, may encourage posterior tooth eruption. Since the Hawley retainers were worn full time, the anterior bite plane and labial wire may have held the anterior teeth, allowing the posterior teeth to extrude.  This suggestion is supported by data showing no change in the anterior contacts in the Hawley group, while the posterior contacts increased.
    79. 79.  Assuming some tooth settling had occurred during the day in the clear overlay retainer patients, it is likely that had the bite registrations been made in the morning, differences between the two retainer groups would have been even greater.  Based on previous studies, additional increases in occlusal contacts during retention should be expected over time, particularly as daily retainer wear is reduced.
    80. 80.  In the present study, greater increases would be anticipated in the clear overlay patient group if retainer use were to be discontinued.  Areas for future investigation include comparisons of changes in occlusal contacts with other types of removable as well as fixed retainers, and long-term follow-up on changes occurring over an extended retention period. Ultimately, it would be of interest to establish whether the differences in occlusal contact patterns after 3 months retention will result in differing tendencies toward settling or relapse at extended retention and post retention intervals.
    81. 81. Conclusion  This study demonstrates that significantly more occlusal contacts appear during the first 3 months of retention with use of the Hawley retainer, whereas little change is found with the clear overlay retainer.  These findings suggest that Hawley retainers should be prescribed if one of the objectives of retention is to allow for relative vertical tooth eruption (tooth settling), particularly of posterior teeth.  Conversely, if the desired occlusion is established before retainer fabrication, for example with a positioner, the clear overlay retainers should function well to maintain the occlusal contact pattern.
    82. 82. Comparison of Essix and Hawley Retainers STEVEN J. LINDAUER, ROBERT C. SHOFF, JCO 2003 ,VOL 35 ,1998
    83. 83.  Essix retainers were introduced in 1993, as an esthetic, comfortable, and inexpensive alternative to traditional fixed and removable orthodontic retainers.  They are thermoformed from plastic, copolyester Essix sheet material and trimmed to fit over the anterior teeth from canine to canine. Patients are instructed to wear them only at night after a short period of nearly full-time wear.
    84. 84. Materials & Methods  Patients completing full orthodontic treatment at the Medical College of Virginia clinic were alternately assigned to Essix and Hawley retention groups.  Those who had posterior cross bites or anterior open bites before treatment were excluded from the study.  Twenty-eight patients were assigned to each group for observation during the first six months of active retention.
    85. 85.  The Essix retainers were thermoformed from .030" sheets according to the manufacturer's instructions.  The patients were instructed to wear their mandibular retainers full-time and their maxillary retainers half- time for the first four weeks, and both retainers only at night thereafter.  Patients were given two retainers per arch, with one serving as a replacement in case the other was lost or broken.
    86. 86.  Patients wore the retainers full -time for the first 3 mths and only at night for the next 3 mths.  Occlusal measurements were taken from study casts made before treatment, after treatment, and after six months of retention.  Anterior crowding was evaluated with Little's Irregularity Index, and overbite and over jet were measured as usual.  The differences between groups were tested with multivariate analysis of variance.
    87. 87. Results  16 of the 56 patients were eventually eliminated from the study.  7 patients--5 in the Essix group and 2 in the Hawley group--lost their retainers and did not wear them for more than a week.  The difference in loss rates was not statistically significant. Four patients from each group moved out of the area or did not show up for their 6 month retention appointments.  One Hawley patient requested that a fixed retainer be placed instead of the removable appliance.  This left 19 patients in the Essix group and 21 in the Hawley group.
    88. 88.  The Hawley patients showed slightly more incisor irregularity in both arches than the Essix group did but the difference was significant only for the maxillary arch .  There were no significant differences between groups in the change in irregularity recorded for either arch over the six-month retention period.  Likewise, there were no significant differences between groups in the amount of change in overbite or over jet .  Two Essix patients and three Hawley patients showed small decreases in over bite of about .5mm each. No patient in either group developed anterior open bite.
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    92. 92. Discussion  Various clinicians have reported individual cases of anterior open bite in patients wearing Essix retainers, probably because of the posterior disclusion caused by the anterior contact of the Essix material .  In the present study, with patients wearing the appliances only at night after the first four weeks, there were no such cases.  The number of patients with minor decreases in overbite during retention was similar to that of the Hawley group.  It has also been claimed that Essix retainers are more easily lost than traditional appliances because they are transparent.
    93. 93.  In this study, the number of Essix patients who lost their retainers was not significantly greater than Hawley patients.  One method to reduce the loss of Essix retainer is to add a color stripe along the lingual edge of the appliance making it more visible when out of the mouth.  Another disadv is that Essix retainers may wear out and will have to be replaced annually. No remake was done during this study but several became perforated or cracked after 6 to 12 mths. manufacturer claims the durability of the material has been recently improved.
    94. 94. Conclusion  When Essix retainers are used as recommended, they do not appear to be any less effective than Hawley retainers in maintaining orthodontic corrections.  The Essix patients in this study did not show any increased tendency to develop anterior open bites.  Essix retainers were somewhat more likely than Hawley retainers to be lost, but this finding was not statistically significant.  If patients and clinicians keep in mind that replacements may be needed as Essix retainers age, these appliances can serve effectively as alternatives to traditional Hawley retainers.
    95. 95. For more details please visit