European Journal of Orthodontics 13 (1991) 264-270
i 1991 European Orthodontic Society
Surface resorption following two forms of rapid maxillary expansion Lars Odenrick*, DDS, Odont Dr, Eva Lilja Karlander**, DDS, Odont Dr, Angela Pierce***, MDS (Adel), Odont Dr, FRACDS, and Uwe Kretschmar*, DDS 'Department of Orthodontics, Faculty of Odontology, Karolinska Institutet, Stockholm, "Orthodontic Clinic, Motala Hospital, Motala, Sweden, and "'Department of Dentistry, University of Adelaide, Adelaide, Australia
Introduction
Rapid maxillary expansion (RME) is a useful method in orthodontic treatment aimed at the correction of posterior cross-bite. However, various iatrogenic effects associated with this form of treatment have been reported, such as impairment of the median suture (Melsen, 1972), and root resorption (Timms and Moss, 1971; Barber and Sims, 1981). Barber and Sims used an all-wire framework RME appliance and reported root resorption of the premolars serving as anchor teeth, whereas unattached premolars carried laterally with the expansion device showed no evidence of root resorption. Their study also indicated that the longer the anchor teeth were held in an over-corrected position during retention, the more extensive
the resorption, which they attributed to relapse forces. Odenrick et al. (1982) examined root resorption following RME, and showed that resorption lacunae extended into dentine. Numerous resorbing cells could be observed on the surface of the lacunae, indicating progressive activity. These authors also examined the possibility of reducing iatrogenic tissue damage by using weak expansion forces in the early mixed dentition, and concluded that weak expansion forces produced fewer resorption lacunae, which were of a reparative type (Lilja and Odenrick, 1982). However, less opening of the median suture was observed. These findings are, therefore, somewhat conflicting with respect to choice of therapy. We hypothesized that to both benefit from
Downloaded from by guest on June 23, 2015
SUMMARY Rapid maxillary expansion (RME) is a useful orthodontic technique for correction of posterior cross-bite of skeletal origin. The aim of the present study was to compare the frequency and nature of root resorption in premolars subjected to RME by means of either a tissue-borne, fixed split acrylic (Haas) palatal expansion appliance, or an all-wire framework appliance. Another factor examined was the relationship between the pattern of resorption and the duration of the retention period. RME was performed on five patients using the fixed split acrylic appliance and on four patients with the all-wire framework appliance. Following the transverse expansion, two upper and two lower premolars were extracted and processed for histological examination. Root resorption was found mainly on the buccal surfaces of all maxillary premolars. The resorption lacunae covered more of the root surface in premolars treated with an all-wire framework appliance compared to premolars treated with the acrylic expansion plate. The largest resorption areas were found on teeth extracted shortly after the expansion period and the smallest on premolars retained for a relatively longer period. Mandibular premolars showed neither buccal nor lingual resorptions. It was concluded that maximum anchorage of the expansion device, using the tissue-borne acrylic appliance, seems preferable in order to minimize the incidence of buccal surface root resorption. A longer post-treatment observation time is needed in order to draw more specific conclusions regarding the healing process of the damaged root surface.
RESORPTION AND RAPID MAXILLARY EXPANSION
265
The study consisted of nine patients, five girls and four boys between the ages of 10 and 13, presenting with posterior cross-bite of skeletal origin and bimaxillary crowding. The treatment plan aimed at elimination of the cross-bite and crowding by means of RME, extraction of four first or second premolars, and final alignment of the dental arches. The RME technique was performed on five patients (three girls, two boys) by means of a tissue-borne fixed split acrylic appliance, and in four patients (two girls, two boys) with an all-wire framework appliance
Figure 2 All-wire framework RME appliance used in four patients.
Figure 1 Tissue-borne split acrylic RME appliance (ad modum Haas) used in five patients.
RME therapy and minimize iatrogenic effects, the rapid palatal expansion device ad modum Haas (1980) through its maximum anchorage construction would cause less root resorption than an RME device attached to only some teeth. Afixedacrylic plate split along the median plane with an expansion screw close to the palatal vault would transfer the expansion forces not only to the four anchor teeth, but to all of the teeth of the two lateral segments connected to the appliance, as well as to the supporting tissues of the acrylic plate. Hence, the teeth would be encouraged to move with, rather than through, the alveolar bone (Fig. 1). The aim of the present study was to compare the occurrence and nature of root resorption in premolars subjected to RME by either a fixed split acrylic palatal expansion appliance or an all-wire framework expansion device. In addition, the nature of root resorption in relation to the length of the retention period was analysed.
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Subjects and methods
(Figs 1 and 2). The appliances were anchored to the first premolars and molars, respectively. In all patients, the activation rate was prescribed to be one-quarter of a turn twice a day, corresponding to 0.5 mm per day. The expansion screw allowed a maximum expansion of 7 mm which was the objective in all patients. The median suture and the premolars were examined radiographically using an intra-oral technique by standardized projection. Radiographic examination of the premolars was performed before the start of treatment and at the end of the transverse expansion period. The median suture was examined radiographically before treatment and after 2 weeks of treatment. Following the transverse expansion, two upper and two lower first or second premolars were extracted after varying retention periods. A total of 14 maxillary first premolars, four maxillary second premolars, and eight randomly selected mandibular premolars serving as controls, were processed for routine histologic examination. All teeth had erupted at the start of treatment. The teeth were step-serially sectioned in a bucco-lingual direction parallel to their long axes. Sections from the middle third of the teeth were selected for histological examination. To describe the location of the resorption lacunae, both the buccal and lingual root surfaces were divided into three parts, in a cervicoapical direction, and designated as the marginal, middle, and apical parts, giving a total of six areas. The length and depth of each resorption lacuna was measured using a Leitz Orthoplan® microscope with a micrometer fitted into the eyepiece. The micrometer was calibrated for each magnification against a Zeiss microscale with a 0.1 mm division. Only resorption cavities involving both cementum and dentine were recorded. The resorption lacunae were classified
266
Results Clinical investigation The skeletal posterior cross-bites in the nine patients were eliminated either by means of a tissue-borne fixed split acrylic appliance (in five patients) or by an all-wire framework appliance (in four patients). In all cases, the rapid expansion treatment was discontinued when maximum expansion of the screw, i.e. 7 mm, was achieved. The active treatment period varied between 15 and 21 days indicating that the patients had turned the screw once or twice per 24 hours. The retention period varied between 3 and 267 days. At the end of the retention period, two upper and two lower premolars were extracted. Radiographic examination The median suture was found to have opened in all cases, and was estimated to have been relatively more in those cases treated with the Haas appliance. The maxillary premolars showed a widening of the periodontal space, but there were no radiographic signs of root resorption. Histological investigation All of the 18 maxillary premolars investigated showed root resorption. There was no difference
with respect to nature and frequency of resorption between the right and left side premolars within each patient. Apart from minor root resorptions found apically on all maxillary premolars, the dominant resorption site was the buccal surface of premolars. However, two premolars treated with the acrylic palatal expansion devices showed resorption lacunae on their palatal surfaces as well (Table 1). The most coronally positioned edge of the buccal resorption lacunae was located an average of 1.2 mm from the cemento-enamel junction (CEJ). In this respect, there was no difference between the two forms of appliance used. The size of the resorption lacunae increased with proximity to the CEJ. The largest resorption areas were found on premolars extracted shortly after the end of the expansion period and the smallest were found on premolars retained for a relatively longer period (Table 1). The lengths of the resorption lacunae varied between 2.95 mm, found in a premolar without any retention period, and 0.2 mm, in a premolar left for a retention period of 224 days (Table 1). The depths of the lacunae varied between 0.09 and 0.47 mm. The dimensions of buccally located resorption lacunae were relatively larger in premolars treated with an all-wire framework appliance than in premolars treated with the Haas-type appliance. Premolars serving as anchor teeth exhibited more resorption lacunae than non-anchored second premolars. Active surface resorption was demonstrated in cases with short retention periods whereas reparative resorption dominated in cases with longer retention periods (Table 1, Figs 3a,b, and 4a,b). With respect to age, the smallest resorption areas were found in the youngest patient, a 10-year-old girl treated with a Haas appliance (patient no.3, Table 1). The control premolars taken from the mandible showed no buccal or lingual resorption lacunae. However, slight apical root resorptions were found in all teeth. Denticles were frequently found in the pulps of maxillary premolars. Polarized light was used to analyse the fibres extending from the cementum. No new fibres were found in areas of healing, even up to 267 days of retention when the repair of surface resorptions was almost complete (Table 1, Fig. 3b). In contrast, all premolars serving as
Downloaded from by guest on June 23, 2015
into the following three groups (Andreasen, 1975). 1. Active surface resorption: resorption cavities present on the root surface. The resorption process is in progress, involving uni- or multinucleated cells. 2. Arrested surface resorption: resorption cavities present on the root surface. No resorbing cells can be seen within the lacunae and the resorption process has ceased. 3. Repaired surface resorption: resorption cavities present on the root surface. The cavities have undergone repair with cellular cementum-like material. In addition, lacunae which were completely filled with reparative cementum-like material were designated as totally repaired surface resorption. Periodontal reattachment was assessed by using polarized light to visualize birefringent collagen fibres in reparative cementum extending into the adjacent periodontal connective tissue (Picken, 1940; Tonna, 1979).
L. ODENRICK ET AL.
267
RESORPTION AND RAPID MAXILLARY EXPANSION
Table 1 Rapid maxillary expansion (RME) in nine patients. For each patient, the type of appliance, activation time, retention time, main location of resorption areas, resorption classification, and reattachment of periodontal fibres are described for maxillary premolar teeth. Left and right premolar of patient no., sex, age in years
Activation time (days)
Acrylic palatal expansion 1.? 12.5 21
Retention time (days)
3
Location of root resorption
Type of resorption
Periodontal reattachment
Buccal side, marginal, middle part Entire buccal, part lingual middle Buccal side middle part Entire buccal side Buccal side marginal, lingual side apical
Active
None
Active
None
Arrested Repaired Repaired and totally repaired
None None None
Active Active and repaired Repaired and totally repaired Repaired and totally repaired
None None
2. $ 11.9
15
21
3. ? 10.0 4. (J 13.1 5. c? 13.3
15 18 21
40 53 224
All-wire framework 6. 9 10.9 21 15 7 . 9 11.2
3 90
Entire buccal side Entire buccal side
21
194
Entire buccal side
9. tJ 13.1
15
267
Entire buccal side
controls showed collagen fibres extending from the cementum buccally and lingually. Discussion In the present study, both the frequency and the nature of root resorption in premolars subjected to RME were histologically analysed, and the findings related to the type of RME appliance and the retention time. Ten premolars were subjected to an RME appliance admodum Haas, and eight to an all-wire framework appliance. It was hypothesized that the Haas appliance with its acrylic plate and expansion screw close to the palatal vault would distribute the expansion forces more evenly, not only to anchor teeth, but to other tissues involved, and thus cause less root resorption. All of the test premolars exhibited buccallylocated resorption lacunae whereas no such findings were observed on the control mandibular premolars. The observed buccal lacunae became larger with increasing proximity to the CEJ and the average distance from the CEJ of the most coronally positioned lacunae was 1.2 mm. This may be an indication that the transverse movement of the teeth was not totally parallel, but included a slight tipping movement.
None None
The difference in form of the resorption lacunae could also be due to a difference in bone morphology, the marginal bone being more dense. All maxillary premolars showed resorption lacunae, but there were fewer second premolars not serving as anchor teeth. Barber and Sims (1981) reported that resorption lacunae were not detected in non-anchored premolars using an all-wire framework device for RME. In the present study, both expansion appliances had initial palatal contacts with the second premolars. Denticles were found frequently in maxillary premolars, not in controls and might be considered as evidence of degenerative changes in the pulp. These findings had earlier been pointed out by Timms and Moss (1971). Comparing the two types of appliance with respect to the type of resorption lacunae, it was found that smaller and more shallow lacunae were evident on premolars subjected to the Haas appliance indicating that, in these cases, less force was transmitted exclusively to the teeth (Rygh, 1977; Lilja, 1983). However, lingual resorption was found in two cases where the Haas type of appliance was used. It could be interpreted as an effect due to pressure of the acrylic part of the appliance moving the alveolar
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8. (J 12.4
268
L. ODENRICK ET AL.
(a)f/
(b
Figure 3 (a) The buccal root surface of a maxillary first premolar serving as an anchor tooth for an all-wire framework appliance. The tooth was extracted immediately after the expansion period. The resorption lacuna is bordered by dentinoclasts (arrows), indicating active surface resorption. P = periodontal membrane, D = dentine. (Bar = 100 fim.) (b) Repaired resorption lacuna on the buccal marginal surface of a maxillary first premolar subjected to RME with a fixed split acrylic appliance followed by a retention period of 53 days. R = reparative cementum, C = connective tissue, D = dentine. (Bar = 50|im.)
bone against the root. Hence, the extension of the acrylic plate should be modified somewhat. The size of the resorption lacunae was found to decrease with increasing retention period due to repair. The smallest area was on a premolar retained for the maximum period of 224 days. The nature of resorption was also related to the retention period in a sense that a change from active towards arrested and reparative forms of root resorption became apparent on premolars retained for longer periods. Thesefindingsindicate that a transition to a healing phase occurs, although few completely healed lacunae were observed. Furthermore, these results differ from those of Barber and Sims (1981) who reported an increase in resorption areas during the retention period. This discrepancy could be due to differences in both the degree of lateral expan-
sion and the ages of the patients, both of which could be responsible for generating different relapse forces. Although it appears that deposition of hard tissue within resorption lacunae indicates a healing process, in this study polarized light failed to reveal the presence of fibres linking the new hard tissue to the periodontal membrane. Hence, we can not conclude that the reparative cementum lining the lacunae is attached to the periodontal membrane, nor that periodontal attachment is re-established in these damaged areas. This observation agrees with the findings of Barber and Sims (1981). The smallest resorption lacunae at the largest distance (3.5 mm) from the CEJ was observed in the 10-year-old girl treated with the Haas appliance. The widest opening of the mid-pal-
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V
269
RESORPTION AND RAPID MAXILLARY EXPANSION
'1l D
\
L
•i
Figure 4 (a) Repaired resorption lacuna on the buccal surface of a maxillary first premolar subjected to RME with an all-wire framework device, followed by a retention period of 194 days. L = resorption lacunae containing reparative cementum, P = periodontal membrane, D = dentine. (Bar=50/un.) (b) Polarized light micrograph of reparative cementum in Fig. 4a. No birefringent fibres can be seen extending from the cementum into the superficial layer (arrows) of the periodontal membrane. P = periodontal membrane, D = dentine. (Bar=50^m.)
atal suture was also observed in this patient. These findings may be interpreted to indicate that the mid-palatal suture generates less resistance to expansion forces in children of a relatively younger age, thus relieving the dentoalveolar region of large expansion forces. Comparing the findings from the two treatment methods, it can be said that the acrylic Haas appliance with its maximum anchorage causes less root resorption than the all-wire device anchored only to a number of teeth. However, this conclusion must be viewed with some caution. In order to minimize iatrogenic damages, further studies in which RME forces are related to age and appliance design seem indicated. Address for correspondence
Dr Lars Odenrick Department of Orthodontics
Karolinska Institutet Box 4064 S-14104 Huddinge Sweden References Andreasen J O 1975 The effect of splinting upon periodontal healing after replantation of permanent incisors in monkeys. Acta Odontologica Scandinavica 33: 313-323 Barber A E, Sims MR 1981 Rapid maxillary expansion and external root resorption in man: a scanning electron microscopic study. American Journal of Orthodontics 79: 630-652 Haas A J 1980 Long-term post treatment evaluation of rapid palatal expansion. Angle Orthodontist 50: 189-217 Lilja E 1983 Tissue reactions following different orthodontic forces in rat and in man. PhD thesis, Karolinska Institutet, Stockholm Lilja E, Odenrick L 1982 Root resorption following slow maxillary expansion. Swedish Dental Journal (Supplement) 15: 123-129
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(a)
270 Melson B 1972 A histological study of the influence of sutural morphology and skeletal maturation on rapid palatal expansion in children. Transactions of the European Orthodontic Society 499-507 Odenrick L, Lilja E, Lindback K E 1982 Root surface resorption in two cases of rapid maxillary expansion. British Journal of Orthodontics 9: 37-40 Picken L E R 1940 Thefinestructures of biological systems. Biological Reviews of the Cambridge Philosophy Society 15: 133-167
L. ODENRICK ET AL. RyghP 1977 Orthodontic root resorption studied by electron microscopy. Scandinavian Journal of Dental Research 47: 1-15 Timms DJ, Moss J P 1971 An histological investigation into the effects of rapid maxillary expansion on the teeth and their supporting tissues. Transactions of the European Orthodontic Society 263-271 Tonna E A 1979 Bone tracers: cell and tissue level technique. In: Simmons D J, Kunin A S (eds) Skeletal research— an experimental approach. Academic Press, New York, 487-556
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i 1991 European Orthodontic Society
Surface resorption following two forms of rapid maxillary expansion Lars Odenrick*, DDS, Odont Dr, Eva Lilja Karlander**, DDS, Odont Dr, Angela Pierce***, MDS (Adel), Odont Dr, FRACDS, and Uwe Kretschmar*, DDS 'Department of Orthodontics, Faculty of Odontology, Karolinska Institutet, Stockholm, "Orthodontic Clinic, Motala Hospital, Motala, Sweden, and "'Department of Dentistry, University of Adelaide, Adelaide, Australia
Introduction
Rapid maxillary expansion (RME) is a useful method in orthodontic treatment aimed at the correction of posterior cross-bite. However, various iatrogenic effects associated with this form of treatment have been reported, such as impairment of the median suture (Melsen, 1972), and root resorption (Timms and Moss, 1971; Barber and Sims, 1981). Barber and Sims used an all-wire framework RME appliance and reported root resorption of the premolars serving as anchor teeth, whereas unattached premolars carried laterally with the expansion device showed no evidence of root resorption. Their study also indicated that the longer the anchor teeth were held in an over-corrected position during retention, the more extensive
the resorption, which they attributed to relapse forces. Odenrick et al. (1982) examined root resorption following RME, and showed that resorption lacunae extended into dentine. Numerous resorbing cells could be observed on the surface of the lacunae, indicating progressive activity. These authors also examined the possibility of reducing iatrogenic tissue damage by using weak expansion forces in the early mixed dentition, and concluded that weak expansion forces produced fewer resorption lacunae, which were of a reparative type (Lilja and Odenrick, 1982). However, less opening of the median suture was observed. These findings are, therefore, somewhat conflicting with respect to choice of therapy. We hypothesized that to both benefit from
Downloaded from by guest on June 23, 2015
SUMMARY Rapid maxillary expansion (RME) is a useful orthodontic technique for correction of posterior cross-bite of skeletal origin. The aim of the present study was to compare the frequency and nature of root resorption in premolars subjected to RME by means of either a tissue-borne, fixed split acrylic (Haas) palatal expansion appliance, or an all-wire framework appliance. Another factor examined was the relationship between the pattern of resorption and the duration of the retention period. RME was performed on five patients using the fixed split acrylic appliance and on four patients with the all-wire framework appliance. Following the transverse expansion, two upper and two lower premolars were extracted and processed for histological examination. Root resorption was found mainly on the buccal surfaces of all maxillary premolars. The resorption lacunae covered more of the root surface in premolars treated with an all-wire framework appliance compared to premolars treated with the acrylic expansion plate. The largest resorption areas were found on teeth extracted shortly after the expansion period and the smallest on premolars retained for a relatively longer period. Mandibular premolars showed neither buccal nor lingual resorptions. It was concluded that maximum anchorage of the expansion device, using the tissue-borne acrylic appliance, seems preferable in order to minimize the incidence of buccal surface root resorption. A longer post-treatment observation time is needed in order to draw more specific conclusions regarding the healing process of the damaged root surface.
RESORPTION AND RAPID MAXILLARY EXPANSION
265
The study consisted of nine patients, five girls and four boys between the ages of 10 and 13, presenting with posterior cross-bite of skeletal origin and bimaxillary crowding. The treatment plan aimed at elimination of the cross-bite and crowding by means of RME, extraction of four first or second premolars, and final alignment of the dental arches. The RME technique was performed on five patients (three girls, two boys) by means of a tissue-borne fixed split acrylic appliance, and in four patients (two girls, two boys) with an all-wire framework appliance
Figure 2 All-wire framework RME appliance used in four patients.
Figure 1 Tissue-borne split acrylic RME appliance (ad modum Haas) used in five patients.
RME therapy and minimize iatrogenic effects, the rapid palatal expansion device ad modum Haas (1980) through its maximum anchorage construction would cause less root resorption than an RME device attached to only some teeth. Afixedacrylic plate split along the median plane with an expansion screw close to the palatal vault would transfer the expansion forces not only to the four anchor teeth, but to all of the teeth of the two lateral segments connected to the appliance, as well as to the supporting tissues of the acrylic plate. Hence, the teeth would be encouraged to move with, rather than through, the alveolar bone (Fig. 1). The aim of the present study was to compare the occurrence and nature of root resorption in premolars subjected to RME by either a fixed split acrylic palatal expansion appliance or an all-wire framework expansion device. In addition, the nature of root resorption in relation to the length of the retention period was analysed.
Downloaded from by guest on June 23, 2015
Subjects and methods
(Figs 1 and 2). The appliances were anchored to the first premolars and molars, respectively. In all patients, the activation rate was prescribed to be one-quarter of a turn twice a day, corresponding to 0.5 mm per day. The expansion screw allowed a maximum expansion of 7 mm which was the objective in all patients. The median suture and the premolars were examined radiographically using an intra-oral technique by standardized projection. Radiographic examination of the premolars was performed before the start of treatment and at the end of the transverse expansion period. The median suture was examined radiographically before treatment and after 2 weeks of treatment. Following the transverse expansion, two upper and two lower first or second premolars were extracted after varying retention periods. A total of 14 maxillary first premolars, four maxillary second premolars, and eight randomly selected mandibular premolars serving as controls, were processed for routine histologic examination. All teeth had erupted at the start of treatment. The teeth were step-serially sectioned in a bucco-lingual direction parallel to their long axes. Sections from the middle third of the teeth were selected for histological examination. To describe the location of the resorption lacunae, both the buccal and lingual root surfaces were divided into three parts, in a cervicoapical direction, and designated as the marginal, middle, and apical parts, giving a total of six areas. The length and depth of each resorption lacuna was measured using a Leitz Orthoplan® microscope with a micrometer fitted into the eyepiece. The micrometer was calibrated for each magnification against a Zeiss microscale with a 0.1 mm division. Only resorption cavities involving both cementum and dentine were recorded. The resorption lacunae were classified
266
Results Clinical investigation The skeletal posterior cross-bites in the nine patients were eliminated either by means of a tissue-borne fixed split acrylic appliance (in five patients) or by an all-wire framework appliance (in four patients). In all cases, the rapid expansion treatment was discontinued when maximum expansion of the screw, i.e. 7 mm, was achieved. The active treatment period varied between 15 and 21 days indicating that the patients had turned the screw once or twice per 24 hours. The retention period varied between 3 and 267 days. At the end of the retention period, two upper and two lower premolars were extracted. Radiographic examination The median suture was found to have opened in all cases, and was estimated to have been relatively more in those cases treated with the Haas appliance. The maxillary premolars showed a widening of the periodontal space, but there were no radiographic signs of root resorption. Histological investigation All of the 18 maxillary premolars investigated showed root resorption. There was no difference
with respect to nature and frequency of resorption between the right and left side premolars within each patient. Apart from minor root resorptions found apically on all maxillary premolars, the dominant resorption site was the buccal surface of premolars. However, two premolars treated with the acrylic palatal expansion devices showed resorption lacunae on their palatal surfaces as well (Table 1). The most coronally positioned edge of the buccal resorption lacunae was located an average of 1.2 mm from the cemento-enamel junction (CEJ). In this respect, there was no difference between the two forms of appliance used. The size of the resorption lacunae increased with proximity to the CEJ. The largest resorption areas were found on premolars extracted shortly after the end of the expansion period and the smallest were found on premolars retained for a relatively longer period (Table 1). The lengths of the resorption lacunae varied between 2.95 mm, found in a premolar without any retention period, and 0.2 mm, in a premolar left for a retention period of 224 days (Table 1). The depths of the lacunae varied between 0.09 and 0.47 mm. The dimensions of buccally located resorption lacunae were relatively larger in premolars treated with an all-wire framework appliance than in premolars treated with the Haas-type appliance. Premolars serving as anchor teeth exhibited more resorption lacunae than non-anchored second premolars. Active surface resorption was demonstrated in cases with short retention periods whereas reparative resorption dominated in cases with longer retention periods (Table 1, Figs 3a,b, and 4a,b). With respect to age, the smallest resorption areas were found in the youngest patient, a 10-year-old girl treated with a Haas appliance (patient no.3, Table 1). The control premolars taken from the mandible showed no buccal or lingual resorption lacunae. However, slight apical root resorptions were found in all teeth. Denticles were frequently found in the pulps of maxillary premolars. Polarized light was used to analyse the fibres extending from the cementum. No new fibres were found in areas of healing, even up to 267 days of retention when the repair of surface resorptions was almost complete (Table 1, Fig. 3b). In contrast, all premolars serving as
Downloaded from by guest on June 23, 2015
into the following three groups (Andreasen, 1975). 1. Active surface resorption: resorption cavities present on the root surface. The resorption process is in progress, involving uni- or multinucleated cells. 2. Arrested surface resorption: resorption cavities present on the root surface. No resorbing cells can be seen within the lacunae and the resorption process has ceased. 3. Repaired surface resorption: resorption cavities present on the root surface. The cavities have undergone repair with cellular cementum-like material. In addition, lacunae which were completely filled with reparative cementum-like material were designated as totally repaired surface resorption. Periodontal reattachment was assessed by using polarized light to visualize birefringent collagen fibres in reparative cementum extending into the adjacent periodontal connective tissue (Picken, 1940; Tonna, 1979).
L. ODENRICK ET AL.
267
RESORPTION AND RAPID MAXILLARY EXPANSION
Table 1 Rapid maxillary expansion (RME) in nine patients. For each patient, the type of appliance, activation time, retention time, main location of resorption areas, resorption classification, and reattachment of periodontal fibres are described for maxillary premolar teeth. Left and right premolar of patient no., sex, age in years
Activation time (days)
Acrylic palatal expansion 1.? 12.5 21
Retention time (days)
3
Location of root resorption
Type of resorption
Periodontal reattachment
Buccal side, marginal, middle part Entire buccal, part lingual middle Buccal side middle part Entire buccal side Buccal side marginal, lingual side apical
Active
None
Active
None
Arrested Repaired Repaired and totally repaired
None None None
Active Active and repaired Repaired and totally repaired Repaired and totally repaired
None None
2. $ 11.9
15
21
3. ? 10.0 4. (J 13.1 5. c? 13.3
15 18 21
40 53 224
All-wire framework 6. 9 10.9 21 15 7 . 9 11.2
3 90
Entire buccal side Entire buccal side
21
194
Entire buccal side
9. tJ 13.1
15
267
Entire buccal side
controls showed collagen fibres extending from the cementum buccally and lingually. Discussion In the present study, both the frequency and the nature of root resorption in premolars subjected to RME were histologically analysed, and the findings related to the type of RME appliance and the retention time. Ten premolars were subjected to an RME appliance admodum Haas, and eight to an all-wire framework appliance. It was hypothesized that the Haas appliance with its acrylic plate and expansion screw close to the palatal vault would distribute the expansion forces more evenly, not only to anchor teeth, but to other tissues involved, and thus cause less root resorption. All of the test premolars exhibited buccallylocated resorption lacunae whereas no such findings were observed on the control mandibular premolars. The observed buccal lacunae became larger with increasing proximity to the CEJ and the average distance from the CEJ of the most coronally positioned lacunae was 1.2 mm. This may be an indication that the transverse movement of the teeth was not totally parallel, but included a slight tipping movement.
None None
The difference in form of the resorption lacunae could also be due to a difference in bone morphology, the marginal bone being more dense. All maxillary premolars showed resorption lacunae, but there were fewer second premolars not serving as anchor teeth. Barber and Sims (1981) reported that resorption lacunae were not detected in non-anchored premolars using an all-wire framework device for RME. In the present study, both expansion appliances had initial palatal contacts with the second premolars. Denticles were found frequently in maxillary premolars, not in controls and might be considered as evidence of degenerative changes in the pulp. These findings had earlier been pointed out by Timms and Moss (1971). Comparing the two types of appliance with respect to the type of resorption lacunae, it was found that smaller and more shallow lacunae were evident on premolars subjected to the Haas appliance indicating that, in these cases, less force was transmitted exclusively to the teeth (Rygh, 1977; Lilja, 1983). However, lingual resorption was found in two cases where the Haas type of appliance was used. It could be interpreted as an effect due to pressure of the acrylic part of the appliance moving the alveolar
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(a)f/
(b
Figure 3 (a) The buccal root surface of a maxillary first premolar serving as an anchor tooth for an all-wire framework appliance. The tooth was extracted immediately after the expansion period. The resorption lacuna is bordered by dentinoclasts (arrows), indicating active surface resorption. P = periodontal membrane, D = dentine. (Bar = 100 fim.) (b) Repaired resorption lacuna on the buccal marginal surface of a maxillary first premolar subjected to RME with a fixed split acrylic appliance followed by a retention period of 53 days. R = reparative cementum, C = connective tissue, D = dentine. (Bar = 50|im.)
bone against the root. Hence, the extension of the acrylic plate should be modified somewhat. The size of the resorption lacunae was found to decrease with increasing retention period due to repair. The smallest area was on a premolar retained for the maximum period of 224 days. The nature of resorption was also related to the retention period in a sense that a change from active towards arrested and reparative forms of root resorption became apparent on premolars retained for longer periods. Thesefindingsindicate that a transition to a healing phase occurs, although few completely healed lacunae were observed. Furthermore, these results differ from those of Barber and Sims (1981) who reported an increase in resorption areas during the retention period. This discrepancy could be due to differences in both the degree of lateral expan-
sion and the ages of the patients, both of which could be responsible for generating different relapse forces. Although it appears that deposition of hard tissue within resorption lacunae indicates a healing process, in this study polarized light failed to reveal the presence of fibres linking the new hard tissue to the periodontal membrane. Hence, we can not conclude that the reparative cementum lining the lacunae is attached to the periodontal membrane, nor that periodontal attachment is re-established in these damaged areas. This observation agrees with the findings of Barber and Sims (1981). The smallest resorption lacunae at the largest distance (3.5 mm) from the CEJ was observed in the 10-year-old girl treated with the Haas appliance. The widest opening of the mid-pal-
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RESORPTION AND RAPID MAXILLARY EXPANSION
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Figure 4 (a) Repaired resorption lacuna on the buccal surface of a maxillary first premolar subjected to RME with an all-wire framework device, followed by a retention period of 194 days. L = resorption lacunae containing reparative cementum, P = periodontal membrane, D = dentine. (Bar=50/un.) (b) Polarized light micrograph of reparative cementum in Fig. 4a. No birefringent fibres can be seen extending from the cementum into the superficial layer (arrows) of the periodontal membrane. P = periodontal membrane, D = dentine. (Bar=50^m.)
atal suture was also observed in this patient. These findings may be interpreted to indicate that the mid-palatal suture generates less resistance to expansion forces in children of a relatively younger age, thus relieving the dentoalveolar region of large expansion forces. Comparing the findings from the two treatment methods, it can be said that the acrylic Haas appliance with its maximum anchorage causes less root resorption than the all-wire device anchored only to a number of teeth. However, this conclusion must be viewed with some caution. In order to minimize iatrogenic damages, further studies in which RME forces are related to age and appliance design seem indicated. Address for correspondence
Dr Lars Odenrick Department of Orthodontics
Karolinska Institutet Box 4064 S-14104 Huddinge Sweden References Andreasen J O 1975 The effect of splinting upon periodontal healing after replantation of permanent incisors in monkeys. Acta Odontologica Scandinavica 33: 313-323 Barber A E, Sims MR 1981 Rapid maxillary expansion and external root resorption in man: a scanning electron microscopic study. American Journal of Orthodontics 79: 630-652 Haas A J 1980 Long-term post treatment evaluation of rapid palatal expansion. Angle Orthodontist 50: 189-217 Lilja E 1983 Tissue reactions following different orthodontic forces in rat and in man. PhD thesis, Karolinska Institutet, Stockholm Lilja E, Odenrick L 1982 Root resorption following slow maxillary expansion. Swedish Dental Journal (Supplement) 15: 123-129
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270 Melson B 1972 A histological study of the influence of sutural morphology and skeletal maturation on rapid palatal expansion in children. Transactions of the European Orthodontic Society 499-507 Odenrick L, Lilja E, Lindback K E 1982 Root surface resorption in two cases of rapid maxillary expansion. British Journal of Orthodontics 9: 37-40 Picken L E R 1940 Thefinestructures of biological systems. Biological Reviews of the Cambridge Philosophy Society 15: 133-167
L. ODENRICK ET AL. RyghP 1977 Orthodontic root resorption studied by electron microscopy. Scandinavian Journal of Dental Research 47: 1-15 Timms DJ, Moss J P 1971 An histological investigation into the effects of rapid maxillary expansion on the teeth and their supporting tissues. Transactions of the European Orthodontic Society 263-271 Tonna E A 1979 Bone tracers: cell and tissue level technique. In: Simmons D J, Kunin A S (eds) Skeletal research— an experimental approach. Academic Press, New York, 487-556
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