Periodontal implications of bonded versus removable retainers

Evi E. Heier, DDS, a Aimd A. De Smit, DDS, PhD, a Ingrid A. Wijgaerts, DDS, b and Patrick A. Adriaens, DDS, DMD, MScD, PhD b Brussels, Belgium

Removable retainers have been used by clinicians since the early years of orthodontic practice. During the last decades, an increasing number of cases are retained with bonded lingual retainers. The current study was performed to evaluate whether significant differences in gingival conditions exist between patients who wear removable or fixed retainers. Differences in build-up of plaque and calculus were also investigated. Maxillary and mandibular measurements were taken at baseline (just before debonding) and 1, 3, and 6 months later, from canine to canine on 36 patients. Among these patients, 22 had fixed retainers, and 14 wore removable retainers. The gingival condition was scored according to three parameters: Modified Gingival Index, bleeding on probing, and gingival crevicular fluid flow. After staining with Diaplac, the Plaque Index was registered. The amount of calculus was measured with a calibrated periodontal probe. Gingival inflammation decreased from baseline throughout the entire period of retention. A comparable limited gingival inflammation was found in the presence of both types of retainers. Slightly more plaque and calculus were present on the lingual surfaces in the fixed retainer group. This did not result in more pronounced gingival inflammation than in the removable retainer group, within the evaluated period. (Am J Orthod Dentofac Orthop 1997;112:607-16.)

W h en removable retainers are used, cli- nicians have to rely on patients' discipline and long-term compliance. Oral hygiene, however, will not be complicated by this kind of appliance. The introduction of bonding techniques enabled the construction of permanent interdental wire connec- tions as retention device. 16 As these retainers are placed "invisibly" on the lingual tooth surfaces, patients' acceptance is evident and compliance with the orthodontic retention therapy is high. The con- tinuing presence of the retention wires, however, creates areas that are difficult to keep clean, thus favoring plaque formation and food impaction. This situation may lead to the development of carious lesions, TM favor the formation of calculus, and in- duce gingival inflammation and periodontal dis- ease. 9

Zacchrisson, 1° one of the pioneers in the field of

From the Faculty of Dentistry, Free University of Brussels. aAssistant Professor, Department of Orthodontics. aProfessor and Chairman, Department of Orthodontics, School of Den- tistry. bAssistant Professor, Department of Periodontology. bProfessor and Chairman, Department of Periodontology, School of Dentistry. Reprint requests to: Dr. Aim~ A. De Smit, Department of Orthodontics, School of Dentistry, Free University of Brussels, Laarbeeklaan 103, 1090 Brussels, Belgium. Copyright © 1997 by the American Association of Orthodontists. 0889-5406/97/$5.00 + 0 8/1/79813

bonded lingual retainers, stressed the importance of daily interproximal cleaning with dental floss. De- spite optimal oral hygiene instructions, calculus formed to a greater extent on the lingual surfaces of the incisors with bonded retainers, compared with incisors without retainers. These findings were con- firmed on a long-term basis by Dahl and Zacchris- son. 11 They found more plaque and calculus around mandibular retainers, compared with the maxilla. The long-term use of different types of bonded

12 lingual retainers was analyzed by Artun. Plaque and calculus were only occasionally registered. Car- ious lesions or periodontal reactions in the region surrounding the bonded wires were absent. To our knowledge, only ~&~rtun et al. 13 have reported on the differences between the use of bonded and remov- able retainers. Four months after debonding, no differences in gingival inflammation and accumula- tion of plaque and calculus could be detected in the lower incisor region.

Compared with the widespread and still increas- ing use of bonded lingual retainers, research reports on the influence of retainers on dental and peri- odontal tissues are scarce. In clinical observation, our attention was drawn to rather obvious calculus deposits around bonded lingual retainers in some of our patients. As we had never had this impression in the formerly, more often used removable retainers, the current investigation was designed and initiated

607

608 Heier et aL American Journal of Orthodontics and Dentofacial Orthopedics December 1997

Fig. 1. Fixed lingual retainer bonded in Dentaflex 0 0.0175 arch from canine to canine.

to evaluate the differences in gingival conditions in patients who wear bonded or removable retainers. Moreover , differences in p laque and calculus accu- mulat ion were analyzed.

MATERIAL AND METHODS

Thirty-six orthodontic patients, between the ages of 12.8 and 21.1 years, (mean 16.3 years) were treated with fixed Begg appliances in the upper and lower arches. Some of them were recruited in a private orthodontic practice, others in the dental clinic at the Free University of Brussels. A majority of patients wore retainers in both arches. The decision whether a removable or bonded lingual retainer would be used after active treatment was made at treatment planning. Patients with pretreatment spacing or extensive incisor rotations were given perma- nent bonded retainers. The others received removable retainers. The level of oral hygiene was not taken into account in the choice of retention device. Thus two experimental groups were created: the fixed retainer group (FRG) with 22 patients and the removable retainer group (RRG) containing 14 patients.

At the end of active orthodontic treatment, standard procedures for adhesive removal, polishing, and prophy- laxis were performed. The fixed retainers were bent in flexible spiral wire (Dentaflex 0.0175, Dentaurum) and bonded to each lingual tooth surface from canine to canine (Fig. 1). Care was taken not to leave any bonding substance (Super C Ortho, Amco) in contact with gingival tissues. All removable retainers had a labial arch and several retention clasps embedded in an acrylic plate. At the time of retainer insertion, oral hygiene instructions were given. The patients were instructed to brush three times a day. In order not to influence measurements, disinfecting or fluoride containing mouthrinsing solutions could not be applied. The daily use of wooden toothpicks for interdental hygiene was expected from patients with fixed retainers, whereas patients wearing removable re- tainers used dental floss.

All measurements were taken in the maxilla and mandible from canine to canine just before debonding (baseline) and 1, 3, and 6 months later. The same clinician scored the lingual, interdental, and buccal tooth sites.

Modified Gingival Index (MGI)

The MG114'I5 permits a noninvasive evaluation of early and subtle visual changes in the severity and extent of gingival inflammation. It is scored as follows: absence of inflammation (0), part of gingival unit mild inflamma- tion (1), complete gingival unit mild inflammation (2), moderate inflammation (3), and severe inflammation (4).

Bleeding On Probing (BOP)

The BOP 16 is widely used in diagnosis of gingival inflammation. To obtain a standardized pressure of 25 gm, 17'18 a Florida probe 19 with a Michigan O probe tip was inserted into the gingival crevice. This way the probing force was standardized and could not be influenced by the clinician. Bleeding was registered after 15 seconds2°: no bleeding (0), point-bleeding (1), and profuse bleeding (2).

Gingival Crevicular Fluid Flow (GCFF)

The examined teeth were isolated with cotton rolls and cheek retractors and gently dried with the air syringe. The tip of a Periopaper strip (Pro Flow Inc.) was placed at the entrance of the gingival sulcus for 30 seconds. The amount of gingival crevicular fluid absorbed into the Periopaper is proportional to the digital reading on the Periotron 600021-23 (Pro Flow Inc.). Values higher than 30 are considered as pointing to gingival inflammation. The Periotron registrations were limited to the following sites: the mesial and buccal surfaces of the upper right central incisor, the distal and lingual surfaces of the upper left canine, the distal and lingual surfaces of the lower left central incisor, and the mesial and buccal surfaces of the lower right canine.

Plaque Index (PI)

Plaque was disclosed with Diaplac (OY Mdlnlycke Ab). The modified plaque index, according to Quigley and Hein (modification according to Turesky), 24 was regis- tered for the buccal and lingual tooth surfaces according to the following scale: no plaque (0), spots of plaque at the cervical margin (1), thin continuous band of plaque at the cervical margin (2), gingival third of tooth surface covered with plaque (3), two thirds of tooth surface covered with plaque (4), and more than two thirds of tooth surface covered with plaque (5).

Dental Calculus Index (DCI)

To measure the amount of dental calculus, the assess- ment according to Volpe et alY was used. A calibrated periodontal probe was applied at three locations of the buccal and lingual sides of each lower incisor and canine: a mesial location, at the tooth center, and a distal location.

American Journal of Orthodontics and Dentofacial Orthopedics H e i e r e t al. 6 0 9 Volume 11.2, No. 6

Table I. M e a n s of five o u t c o m e m e a s u r e s o n d i f fe ren t l oca t ions by t r e a t m e n t g r o u p a n d t ime of fo l low-up

Baseline measure

Index Site FR RR

1-month follow-up 3-month follow-up

FR RR

6-month follow-up

FR RR FR RR

MGI B 0.71 0.74 0.44 0.68 0.21 0.68 0.24 0,89 IB 1.71 1.40 1.01 1.02 0.56 1.23 0.66 1,40 IL 1.42 1.26 1.03 0.87 0.86 0.99 0.94 1,23 L 0.79 0.80 1.12 0.49 0.30 0.63 0.40 0,74

BOP B 0.25 0.40 0.18 0.30 0.19 0.34 0.22 0,41 IB 0.36 0.57 0,23 0.46 0.23 0.35 0.30 0.47 IL 0.50 0.70 0.37 0.43 0.32 0.45 0.30 0.40 L 0.32 0.34 0.56 0.23 0.18 0.18 0.23 0.22

GCFF B 24.57 25.56 11.I1 12.04 11.04 12.32 22.29 16.88 ID 46.91 55.27 28.31 21.71 20.07 28.98 25.46 35.18 L 15.29 15.70 16.25 4.56 8.86 10.83 8.04 11.00

PI B 2.86 2.56 1,12 1.18 1,38 1.59 1.02 1.24 L 2.78 2.78 3.34 2.50 2.82 2.43 3.03 2.52

DCI B 0.01 0.01 0.00 0.00 0.00 0.00 0.00 0.00 L 0.20 0,05 0.13 0.01 0.19 0.01 0.20 0.06

MGI: Modified Gingival Index; BOP." Bleeding On Probing; GCFF: Gingival Crevicular Fluid Flow; Ph Plaque Index; DCI: Dental Calculus Index. B: Buccal; IB: Interdental Buccal; IL: Interdental Lingual; L: Lingual; ID: Interdental. FR: Fixed Retainer; RR: Removable Retainer.

Statistical Analysis

A univariate repeated measurement analysis of vari- ance (ANOVA) model was used, containing one repeated factor (time) and one between factor (code:distinguishing the removable versus the fixed retainer group). Each analysis resulted in three P values, one for each factor and one as interaction term. Subsequently, a Scheff6 post hoc analysis calculated the significance levels of the differ- ences between pairs. Throughout the entire statistical analysis, a significance level ofp <- 0.05 was maintained.

RESULTS

For each of the two study groups (fixed or removable retainer), mean values at baseline, at 1-month, 3-month, and 6-month follow-up examina- tions are presented in Table I. The changes through time are visualized in Figs. 2 through 6. Table II shows the changes from baseline to 1-month follow- up, from 1- to 3-month follow-up, and from 1- to 6-month follow-up. The differences for the five outcome measures between the group wearing fixed retainers (FR) and the group with removable retain- ers (RR) can be seen in Table III.

At baseline, the mean MGI (Fig. 2) of both retainer groups was below score 1 for the buccal and lingual sites. The mean interdental values (Table I) were slightly higher in the FR than in the RR group (at the lingual aspect FRIL:l.42; RRIL:1.26 and at the buccal aspect FRIB:I.71; RRIB:I.40). These differences were only significant for the interdental buccal region (p = 0.0163). The mean MGI after wearing retainers for 1 month showed a tendency to be lower than at baseline for all sites and for both

retainer types. The changes were not significant at the lingual sites for both retainer types and at the buccal sites for the removable retainers (Table II).

After the first month, however, the mean MGI tended to increase in the group with removable retainers, but generally these increases were not significant (Table II). At the 6-month follow-up, the mean values remained below score 1 at the buccal and lingual sites. At 6 months, the lingual sites showed a mean MGI of 1.23 and the buccal sites showed a mean MGI of 1.40 (Table I). In the group with fixed retainers, a reduction in MGI values was found between months 1 and 3, followed by a small increase between the months 3 and 6 (Table II). At the 6-month evaluation, the mean MGI values at all sites were lower in the group with fixed retainers than in the removable retainer group (Table I). The mean MGI after wearing retainers for 6 months remained below score 1 for both retainer types at the buccal and lingual sites. The highest mean MGI after 6 months (1.40) was seen for removable retain- ers at the interdental buccal sites. In contrast, for the fixed retainer group, the lowest mean MGI (0.66) was registered at these interdental buccal sites (Ta- ble I).

The mean BOP index (Fig. 3) of both retainer groups stayed below score i at all sites from baseline to 6-month follow-up (Table I). In all instances, the mean BOP index at baseline was lower in the fixed retainer group than in the group that would receive a removable retainer (Table I). Statistical analysis showed that these differences were only significant

6 1 0 Heier et al. American Journal of Ot¢hodontics and Dentofacial Orthopedics December 1997

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for the interdental sites (Table III). At the lingual sites, the mean BOP increased to 0.56 after 1 month with fixed retainers (Table I). This change was not significant (Table III).

At the other sites, a nonsignificant downward evolution of the mean BOP was noticed at i-month follow-up for both retainer groups. With both kinds of retainers, the changes in the mean BOP toward 6 months were very small (Table II). A slight reduc- tion was observed toward the 6-month follow-up for the lingual and lingual interdental sites. A tendency toward an increased BOP was found for the buccal and interdental buccal sites (Table II). The maxi- mum mean BOP at 6 months was found at the interdental buccal sites. However, it remained lim- ited to 0.47 (Table I). At that time, the mean BOP values were slightly, but not significantly, lower in the group with fixed retainers compared with the removable retainer group. The values at the lingual

sites were nearly identical for both retainer types (Table I).

The lowest mean values for the gingival crevic- ular fluid (Fig. 4) at baseline were found on the lingual surfaces for both groups (15 periotron units). For the buccal sites, level 25 was reached; the interdental sites reached up to 47 in the fixed retainer group and to 55 in the group that would get removable retainers (Table I). None of the differ- ences between RR and FR proved to be statistically significant (Table III). One month later, the peri- otron score had dropped for all, but one measure that remained practically unchanged, i.e., the lingual sites in the fixed retainer group. Toward the 6- month follow-up, this downward trend was stopped or reversed (Table II). The values for the fixed retainer group were not significantly different from those in the removable retainer group (Table III). The highest GCFF values after 6 months were found

American Journal of Orthodontics and Dentofacial Orthopedics Heier et al. 611 Volume 112, No. 6

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for the interdental sites: 35 in the removable re- tainer group and 25 with fixed retainers. The lowest GCFF values were situated at the lingual sites: 11 in the RR group, and 8 in the FR group.

Before debonding, comparable mean plaque in- dexes near 2.8 were found in the two groups on the buccal and lingual surfaces (Fig. 5). The buccal value had dropped significantly to about 1.2 on the buccal surfaces at 1-month follow-up (Table I). It remained at approximately the same level at 6 months, after a small but nonsignificant increase at the 3-month follow-up (Table II). The mean lingual PI in the removable retainer group was reduced to 2.5 after 1 month, 2.4 at month 3, and 2.5 at the 6-month follow-up. In the fixed retainer group, the mean PI at the lingual sites climbed to 3.3 at 1-month, to end at 3.0 at 6 months (Table I). This score was significantly higher than the score in the removable retainer group (Table III).

On the buccal surfaces, the mean DCI (Fig. 6)

remained near zero throughout the evaluation pe- riod. The mean DCI on the lingual surface at baseline was slightly above zero (0.2 ram) in the group receiving a fixed retainer, whereas calculus was almost absent (0.05 ram) in the other group. One month 'later, the mean calculus level was brought down further to 0.1 mm for the FR group and to 0.01 mm for the RR group. At 6 months, the mean lingual measurements had gone up to the original values (Table I).

DISCUSSION

At the end of the presence of fixed orthodontic appliances on the buccal tooth surfaces, the record- ings of MGI, BOP, and GCFF for the buccal and lingual gingival units indicate that generally only limited parts of these gingival units showed mild inflammation, very few bleeding points were present, and a normal gingival crevicular fluid flow existed. For the interdental areas, the MGI pointed

6"12 Heier et al. American Journal of Orthodontics and Dentofaciat Orthopedics December 1997

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to more complete gingival units with mild gingival inflammation, the BOP test showed the existence of more point bleedings, and the GCFF was found to correspond with the presence of mild gingival in- flammation. The differences between the fixed and removable retainer groups being very small, this suggests that the oral hygiene at the end of the active orthodontic treatment had been acceptable for the buccal and lingual tooth surfaces in both groups, but some inflammation was present in the approximal area. Somewhat more calculus was present at the lingual sites of the FR group.

The 1-month, 3-month, and 6-month follow-up recordings have been gathered in two different situations, as far as access for oral hygiene was concerned. In one group, wires bonded to the lingual surfaces of incisors and canines were cross- ing the interdental spaces. The use of wooden toothpicks for plaque removal in the interproximal areas had been explained and required in this group.

The other group had the opportunity to perform completely normal oral hygiene procedures as the removable retainers were used only at nighttime. Considering the change from fixed orthodontic ap- pliances present on the buccal tooth surfaces at baseline, to naked buccal tooth surfaces 1 month later, we were not surprised to find that the three indices concerning gingival inflammation tended to be lower at 1-month follow-up. The buccal tooth surfaces, being easier to clean, could be considered as healthy. This also applied for the lingual surfaces in the removable retainer group, but not for the lingual aspect with fixed retainers. There, the indices scored somewhat higher, suggesting a little less favorable gingival health. In the interdental regions, all indices showed lower mean values at 1-month than at baseline, especially the GCFF dropped below 30 periotron units, taking it below the inflam- mation limit. At all tooth surfaces, the gingival condition could be considered as healthy for both

American Journal of Orthodontics and Dentofacial Orthopedics He ier et al. 61:3 Volume 112, No. 6

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kinds of retainers. Some of the mean indices were a little lower in the fixed retainer group, some a little higher than in the removable retainer group, but these small differences were not statistically signifi- cant. On this basis, it can be concluded that, in the scored patient groups who wore fixed lingual retain- ers during a 1-month period, this did not lead to a gingival condition, which was more unfavorable than that in the group wearing removable appliances.

Our assessments of MGI, BOP, and GCFF at 3-month recall appeared to bring all mean values of the group with fixed retainers at a lower level than those with the removable retainers worn only during the night. As the differences were seldom statisti- cally significant, we cannot state that oral hygiene conditions were more favorable in the group with fixed retainers. Moreover, there is even less reason to accept that they had worse gingival conditions.

Going to 6-month recall, a tendency toward higher indices was noticed in both groups. How-

ever, these increases were not statistically signifi- cant. In general, the mean MGI, BOP, and GCFF in the fixed retainer group remained below the indices for the removable retainer group. A strik- ing difference between the two groups concerning gingival health could not be observed. The t rend toward increased values at 6 months for both groups could be in terpre ted as an indication for the need for repea ted motivation and oral hygiene instructions at least on a 6-month interval basis. Fur ther investigation could test the validity of this interval on a long-term basis.

In both groups, the mean buccal PI before debonding was found to be very close to the lingual values. The mean value near 2.8 shows that, at the end of the orthodontic treatment, the patients did not succeed in reaching a high standard of oral hygiene. The mean MGI, BOP, and GCFF values discussed previously suggest that, in those regions with a buccal and lingual presence of at least a

614 Heier et aL American Journal of Orthodontics and Dentofacial Orthopedics December 1997

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continuous band of plaque at the cervical margins, a rather mild gingival inflammation existed.

After removal of the buccal fixed appliances, an improvement in plaque condition was seen on the buccal surfaces in both retainer groups. Continuous bands of plaque were rarely recorded. Rather com- monly, spots of plaque have been noticed at the cervical margin. This nonideal situation of oral hygiene remained until the 6-month follow-up. It could be considered acceptable because the local gingival condition showed no real inflammation.

The lingual plaque condition in both groups did not improve after debonding. This could be explained by the remaining lack of direct view on those surfaces, which makes oral hygiene more difficult and seemingly less necessary. The pres- ence of the fixed wires was accompanied by a

rather small, but nonsignificant increase in plaque accumulation on the lingual surfaces. Until the 6-month follow-up, the measured plaque levels had not caused any significant gingival inflamma- tion. This confirms and extends the results of Artun et al. 13 of finding no significant differences in gingival inflammation nor accumulation of plaque and calculus after 4 months with fixed or removable retainers.

The deposit of calculus was nearly nonexistent on the buccal tooth surfaces. For the lingual sites, this applied for both kinds of retainers.

C O N C L U S I O N

A comparable limited gingival inflammation was found in the presence of both types of retainers. The clinical observation of an increased tendency of calculus

American Journal of Orthodontics and Dentofacial Orthopedics Heier et al. 615 Volume 112, No. 6

T a b l e II. Mean differences a n d p levels from baseline to 1 month follow-up, from 1 to 3 month follow-up, and from 1 to 6 month follow-up, for five outcome measures on different locations by treatment groups

Baseline to 1-month follow-up

FR RR

Index Site X P X J P

MGI B -0.27 0.0540* -0.06 0.9519 IB -0.70 0.0000" -0.38 0.0013" IL -0.39 0.0004* -0.39 0.0005* L +0.33 0.9436 -0.31 0.9567

BOP B -0.07 0.8420 -0.10 0.6177 IB -0.13 0.2364 -0.11 0.3140 IL -0.13 0.1980 -0.27 0.0006* L +0.24 0.8963 -0.11 0.9896

GCFF B -13.46 0 .1933 -13.52 0.2350 ID -18.60 0 .1398 -33.56 0.0021" L +0.96 0 .9994 -11.14 0.5851

P I B - 1,74 0.0000" - 1.38 0.0000" L +0.56 0.0009* -0.28 0.2553

DCI B -0.01 0.2472 -0.01 0.9854 L -0.07 0.1272 -0.04 0.7354

1- to 3-month follow-up 1- to 6-month follow-up

FR RR FR RR

X P X J P X P X P

-0.23 0.1474 0.00 0.9999 -0.20 0,2717 +0.21 0.2420 -0.45 0.0000" + 0 . 2 1 0.1832 -0.35 0.0027* +0.38 0.0016" -0.17 0.3137 +0.12 0.6343 -0.09 0.8064 +0.36 0.0015" -0.82 0.4913 +0.14 0.9954 -0.72 0.6077 +0.25 0.9748 +0.01 0.9999 +0.04 0.9594 +0.04 0.9763 +0.11 0.5257

0.00 1.0000 -0.11 0.3621 +0.07 0.7124 +0.01 0.9963 -0.05 0,8996 +0.02 0.9944 -0.07 0.7370 -0,03 0.9815" -0.38 0.6653 -0.05 0.9990 -0.33 0.7662 -0.01 0.9999 -0.07 1.0000 +0.28 0.9999 +11 . 18 0.3518 +4.84 0.9073 -8.24 0.7808 +7.27 0.8724 -2.85 0 .9880 + 1 3 . 4 7 0.4921 -7.39 0.7904 +6.27 0.8927 -8.21 0.7318 +6.44 0.8846 +0.26 0.3915 +0.41 0.0814 0.10 0.9209 +0.06 0.9858* -0.52 0.0023* -0.07 0.9684 -0.31 0.1590 +0.02 0.9995

0.00 0.1102 0.00 0.9999 0.00 0.1253 0.00 0.9999 +0.06 0.1903 0.00 1.0000 +0.07 0.1976 +0.05 0.5194

MGI: Modified Gingival Index; BOP: Bleeding On Probing; GCFF: Gingival Crevicular Fluid Flow; PI: Plaque Index; DCI: Dental Calculus B: Buccal; IB: Interdental Buccal; IL: Interdental Lingual; L: Lingual; ID: Interdental. FR: Fixed Retainer; RR: Removable Retainer. *Significant atp -< 0.05.

Index.

T a b l e I l l . Mean differences and p levels between wearing fixed and removable retainers for five outcome measures on different locations by time of follow-up

Baseline 1-month 3-month 6-month

I I Index Site X P X I P X P X I P

MGI B -0.03 0.9950 -0.24 0.1261 -0.47 0.0000" -0.65 0.0000" IB 0.31 0,0163" -0.01 0.9999 -0.67 0.0000" -0.74 0.0000" IL 0.16 0.4032 0.16 0.3597 -0.13 0.5858 -0.29 0.0185" L -0.01 1.0000 0.63 0.7108 -0.33 0.9436 -0.34 0.9403

BOP B -0.15 0.2615 -0.12 0.5010 -0.15 0.2525 -0.19 0.0789 IB -0.21 0.0051" -0.23 0.0035* -0.12 0.3196 -0.17 0.0517 IL -0.20 0.0242* -0.06 0.8250 -0.13 0.2679 -0.10 0.4466 L -0.02 0.9999 0.33 0.7708 0.00 0.9999 0.01 0.9999

GCFF B -0.99 0.9990 -0.93 0.9991 - 1,28 0.9978 5.41 0.8667 ID -8.36 0.7977 6.60 0.8887 -8.91 0.7648 -9.72 0,7126 L -0.41 0.9999 11.69 0.5042 - 1.97 0.9955 -2.96 0.9850

PI B 0.30 0.2762 -0.06 0.9830 -0.21 0.6134 -0.22 0,5321 L 0.00 0.9999 0.84 0.0000* 0.39 0.0533* 0.51 0.0040*

DCI B 0.00 0.8592 0.00 0.0214" 0.00 0.8582 0.00 0.9900 L 0.15 0.0012" 0.12 0.0242* 0.18 0.0000* 0.14 0.0101"

MGI: Modified Gingival Index; BOP." Bleeding On Probing; GCFF: Gingival Crevicular Fluid Flow; PI: Plaque Index; DCI: Dental Calculus Index. B: Buccal; IB: Interdental Buccal; IL: Interdental Lingual; L: Lingual; [19: Interdental. FR: Fixed Retainer; RR." Removable Retainer. *Significant atp -< 0.05.

f o r m a t i o n a r o u n d fixed re ta ine rs was conf i rmed. H o w -

ever, this difference was al ready p r e s e n t be fo re the place-

m e n t of the fixed re ta iner , I f a p ro fess iona l p l aque and

calculus r emova l a c c o m p a n i e d by a sess ion on mot iva t ion

and oral hygiene ins t ruc t ion is r e p e a t e d every 6 m on ths , it

is likely tha t the p e r i o d o n t a l hea l th shou ld no t be com-

p r o m i s e d by the p r e sence of b o n d e d l ingual wires.

W e express ou r thanks to Ka thy Goeffers , D D S ,

Ass i s t an t Professor , D e p a r t m e n t of Or thodon t i c s , F r e e

Univers i ty of Brussels , for al lowing us to take m e a s u r e -

m e n t s f r o m s o m e of h e r pa t i en t s and to G i n o Verleye,

Ass i s t an t P r o f e s s o r in App l i ed Statistics, D e p a r t m e n t of

Statistics, F r e e Univers i ty of Brussels , for his ass is tance

wi th the statistical analysis.

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