A new protocol for maxillary protraction in cleft patients: repetitive weekly protocol of alternate rapid maxillary expansions and constrictions.

OBJECTIVE: It was hypothesized that, through a repetitive weekly protocol of Alternate Rapid Maxillary Expansions and Constrictions (Alt-RAMEC), the maxilla in cleft patients could be protracted more effectively than with a single course of rapid maxillary expansion (RME). METHODS: Twenty-six consecutive unilateral cleft lip and palate patients at the age of mixed dentition were included in this prospective clinical study. The rapid maxillary expansion group included the first 16 consecutive patients undergoing 1 week of rapid maxillary expansion (1 mm/day) followed by 5 months, 3 weeks of maxillary protraction. The Alternate Rapid Maxillary Expansions and Constrictions group included the next 10 consecutive patients undergoing 9 weeks of Alternate Rapid Maxillary Expansions and Constrictions followed by 3 months, 3 weeks of maxillary protraction. Daily activation of the weekly expansion or constriction was 1.0 mm. Two-hinged expanders and intraoral maxillary protraction springs were used in both groups. Treatment results were evaluated cephalometrically. RESULTS: The amount of maxillary anterior displacement by the 2-hinged expander in the Alternate Rapid Maxillary Expansions and Constrictions group was 3.0 +/- 0.9 mm at A point, significantly greater than the 1.6 +/- 1.0 mm in the rapid maxillary expansion group. The amount of maxillary advancement with intraoral protraction springs in the Alternate Rapid Maxillary Expansions and Constrictions group was 2.9 +/- 1.9 mm at A point, significantly greater than the 0.9 +/- 1.1 mm in the rapid maxillary expansion group. The overall amount of maxillary advancement in the Alternate Rapid Maxillary Expansions and Constrictions group was 5.8 +/- 2.3 mm at A point. This result remained stable, without significant relapse after 2 years. CONCLUSIONS: Maxillary protraction using the 2-hinged expander, a repetitive weekly protocol of Alternate Rapid Maxillary Expansions and Constrictions, and intraoral protraction springs is most effective, with stable results at 2-year follow-up.     

成人RME矫治后长期稳定性的初步探讨

目的　通过对 2 1例成人经上颌快速扩大 (RME)矫治后的牙关系进行了随访观察 ,旨在对成人RME矫治后的长期稳定性进行初步探讨。材料　本研究对象由 2 1例经RME矫治的成人所构成。均经Hass型扩弓器扩弓和方丝弓矫治器联合矫治。在矫治前 (T1 )和矫治结束时 (T2 )分别制取牙石膏模型 ,并戴用Hawley式保持器进行保持。保持器戴用时间最短 1年 ,最长 5年。在停止戴用保持器后至少 1年 (大部分 5年 ) ,制取随访模 (T3)。方法　对 2 1例保持前后 (T2 ,T3)的模型进行以下测量 :1 上颌第一磨牙间宽度 ;2 上颌第二前磨牙间宽度 ;3 上颌第一前磨牙间宽度 ;4 上颌尖牙间宽度 ;5 第一磨牙颊侧牙槽间宽度。对所测量数据用Sigmastate统计软件进行配对t检验。结果　观察所有样本保持前后的模型 ,未见有样本在保持后 ,其后牙咬合关系为反关系。但测量数据的统计结果显示 :除第一磨牙间宽度外其余指标的变化均有统计学意义。结论　成人经RME矫治保持后 ,虽有轻度复发 ,但未见有复发至后牙反的状况 ,故总体疗效是基本稳定的     

A comparison of dentoalveolar inclination treated by two palatal expanders

The objective of the present study was to evaluate buccal dentoalveolar inclinations in subjects treated with a Hyrax (tooth-borne) or acrylic-bonded (tooth-tissue borne) palatal expander. The sample comprised 39 patients (10 males and 29 females) aged between 11 and 16 years randomly assigned to two groups. Rapid maxillary expansion (RME) was carried out with a Hyrax appliance in one group (n = 21) and with an acrylic-bonded appliance in the other (n = 18). Their mean ages were 13 years 9 months and 13 years 6 months, respectively. Orthodontic study models were obtained before RME (T1) and approximately 1 week after completion of maxillary expansion (T2). A line of barium sulphate solution was drawn between the upper first molars on the models, and radiographs were taken. The radiographic images of the models were transferred to digital medium, and buccal tipping of the molar crowns and alveolar processes were evaluated by means of a software program. The data were analysed by paired and Student's t-tests. Both RME appliances produced significant (P < 0.001) dentoalveolar tipping during RME, but this was greater in the Hyrax group (P < 0.05).     

Buccal alveolar bone changes following rapid maxillary expansion and fixed appliance therapy

ObjectivesTo assess factors that may be associated with buccal bone changes adjacent to maxillary first molars after rapid maxillary expansion (RME) and fixed appliance therapy.Materials and MethodsPretreatment (T1) and posttreatment (T2) cone-beam computed tomography scans were obtained from 45 patients treated with RME and preadjusted edgewise appliances. Buccal alveolar bone thickness was measured adjacent to the mesiobuccal root of the maxillary first molar 4 mm, 6 mm, and 8 mm apical to the cementoenamel junction, and anatomic defects were recorded. Paired and unpaired t-tests were used to compare alveolar bone thickness at T1 and T2 and to determine whether teeth with posttreatment anatomic defects had thinner initial bone. Correlation analyses were used to examine relationships between buccal alveolar bone thickness changes and amount of expansion, initial bone thickness, age at T1, postexpansion retention time, and treatment time.ResultsThere was a statistically significant reduction in buccal alveolar bone thickness from T1 to T2. Approximately half (47.7%) of the teeth developed anatomic defects from T1 to T2. These teeth had significantly thinner buccal bone at T1. Reduction in alveolar bone thickness was correlated with only one tested variable: initial bone thickness.ConclusionsRME and fixed-appliance therapy can be associated with significant reduction in buccal alveolar bone thickness and an increase in anatomic defects adjacent to the expander anchor teeth. Anchor teeth with greater initial buccal bone thickness have less reduction in buccal bone thickness and are less likely to develop posttreatment anatomic defects of buccal bone.     

Arch width changes with a rapid maxillary expansion appliance anchored to the primary teeth

OBJECTIVE: To examine the dimensional changes after rapid maxillary expansion (RME) carried out in the transitional dentition with the primary teeth as anchorage. MATERIALS AND METHODS: Group A was composed of 31 consecutive transitional dentition patients with posterior quadrant crossbites treated with a Haas-type RME appliance anchored on the maxillary primary molars and canines. No treatment was administered after palatal expansion. Study models were made before RME (T1), at appliance removal (T2), and at least 1 year after appliance removal (T3). A control sample of 60 individuals with posterior quadrant crossbites who had had no orthodontic treatment was categorized into group B (30 individuals with an average age comparable with the treated patients at T2) and group C (30 individuals with an average age comparable with the treated patients at T3). RESULTS: Permanent molar crossbites were corrected at T2, and this correction was maintained at T3 in all patients. The mean permanent maxillary intermolar width was 42.6 +/- 2.3 mm at T1, 46.7 +/- 1.9 mm at T2 (P < .01), and 46.3 +/- 1.8 mm at T3 (P < .01) in group A; 42.9 +/- 2.7 mm (P < .01) in group B; and 44.4 +/- 3.0 (P < .01) in group C. Premolar and canine widths were slightly wider than the control at T3. CONCLUSION: To avoid undesirable treatment-induced effects on maxillary permanent molars, a stable transverse correction could be achieved with the RME appliance anchored on the primary teeth.     

Assessment of the relationship between the upper and lower arch changes with the opening of the expanding screw after the rapid maxillary expansion

Objective: The purpose of this study is to assess the relationship of the upper and lower arch dimension changes after the rapid maxillary expansion (RME) with the screw opening of the modified Hyrax type appliance. Materials and methods: Initial (T1) and final (T2) models of study of 63 children between 7 years and 6 months and 16 years and 5 months were performed. From these, 21 showed maxillary atresia and/ or posterior crossbite and were submitted to expansion and 42 children formed the control group .The appliance used in this work was the modified Hyrax appliance using the 7mm expanding screws "Dentarum". The measures of the upper intercanine and the upper and lower intermolar distances were performed in plaster models with the help of a "Digital Paquimeter". The opening of the appliance's screw was also assessed. Results: the RME provoked a statistically significant increase in the upper interdental distances and no statistic significance in the lower interdental distances, i.e. the change in the 16 - 26, 13 - 23 e 36 - 46 distance was of 5,85 mm, 5,31 and 0,34 mm respectively. The average opening of the expander screw, which was of 6,27 mm. Conclusion: the appliance's opening is related to the interdental distance changes, i.e. for each appliance's opening mm, a 0,94 variation in the upper intermolar distance, a 0,87 in the upper intercanine distance and 0,054 in the lower intermolar distance are provoked. KEY WORDS: Rapid maxillary expansion, posterior crossbite, transverse maxillary deficiency, dental arch.     

Rapid Maxillary Expansion with Palatal Anchorage of the Hyrax Expansion Screw—Pilot Study with Case Presentation

Abstract. Background: Rapid maxillary expansion (RME) with the appliance fixed at the crowns of the first premolars and molars leads not only to transversal expansion but also to tipping of the anchorage teeth and a risk of increased tooth mobility as well as of root and bone resorptions. These disadvantages were to be avoided by fixing the transversal screw directly to the hard palate. Material and Method: Following preliminary experimental work to determine the extent to which the hard palate could be loaded with orthodontic implants, two female patients were treated for extreme transverse maxillary deficiency using a Hyrax expansion screw fixed on one side with an implant with the following dimensions: length 4.0 mm, diameter 3.5 mm, abutment diameter 5.00 mm (EO implant, Straumann, Freiburg i. Br., Germany), and on the other side with a bone screw between the roots of the second premolars and the first molars. Presurgical osteotomy according to Glassmann was followed immediately by loading, i. e. by expansion through activation of the screw several times per day. Additional anterior guidance of the right and left maxilla was provided by crossed segmented archwires and a tension coil spring for space opening in the incisor region. After adequate expansion by 8.0 mm and correction of the position of the buccal teeth, the Hyrax expansion screw and the osteosynthesis screw were removed. The implant served as orthodontic anchorage for a molar-to-molar transpalatal bar aimed at preventing relapse. Results and Conclusions: The tooth axis inclination measured on cut sections of the plaster casts made at the beginning and end of treatment was largely without transversal discrepancies. Direct fixing of the transversal screw in the palatal arch prevents buccal tipping of the posterior teeth, especially in patients with a small apical base. Compared with other direct procedures involving osteosynthesis plates, this technique offers adequate guiding stability and is minimally invasive.     

Does rapid maxillary expansion affect the eruption of upper third molars?

OBJECTIVE: To test the hypothesis that there is no difference in the movement of the upper third molars between rapid maxillary expansion (RME) and non-RME patients. MATERIALS AND METHODS: This study was performed on 30 patients divided into two groups. The study group included 20 patients who had maxillary narrowness and bilateral maxillary third molars and who had undergone RME application. The control group of 10 patients had a bilateral crossbite, had bilateral maxillary third molars, and did not receive orthodontic treatment. The records included lateral and frontal cephalometric films and maxillary plaster models. In the study group, records were taken before expansion (T1), after expansion (T2), and at the retention period (T3). T2 records were not taken in the control group because this period was too short to observe any changes. Friedman tests were used to observe within groups, and the Mann-Whitney U-test was used to see the differences between groups on films and casts. RESULTS: Frontal films showed that vertical eruption occurred after the retention period in the RME cases. Cephalometric films revealed that the angular eruption occurred immediately after expansion. However, the results were not significant with respect to the control group. CONCLUSION: The hypothesis was rejected. Rapid maxillary expansion affects maxillary third molar movement during and after the RME procedure. RME may indicate upper third molar eruption, but the final position of third molar was not different compared to the normal growth pattern.     

A photogrammetric technique for the analysis of palatal three-dimensional changes during rapid maxillary expansion

The aim of this study was to assess, by a digital photogrammetric technique, the relative dimensional changes before and after rapid maxillary expansion (RME). The transverse diameters and volumetric variations of the palate were measured by photogrammetry on study casts taken at three different phases of therapy: at the beginning of treatment (T1), on removal of the rapid expander, after expansion and retention for three months (T2), and six months after appliance removal (T3). The sample consisted of 30 children, (age range 7-8 years), all with a crossbite; 15 were angle Class I, six Class II and nine Class III. They were treated with an acrylic splint expander with two turns per day until the maxillary molar palatal cusps were in contact with the mandibular molar buccal cusps. The RME device was used as a passive retainer for three months, after which it was removed. During the following six months, no retention was used and no orthodontic treatment was undertaken. The findings demonstrated a significant relapse (P < 0.001) in the dental transverse diameter in all patients six months after appliance removal, although the palatal volume remained stable.     

Rapid maxillary expansion--tooth tissue-borne versus tooth-borne expanders: a computed tomography evaluation of dentoskeletal effects

This study evaluated rapid maxillary expansion (RME) dentoskeletal effects by means of computed tomography (CT), comparing tooth tissue-borne and tooth-borne expanders. The sample comprised eight girls aged 11 to 14 years presenting Class I or II malocclusions with posterior unilateral or bilateral crossbite that were randomly divided into two treatment groups, palatal acrylic (Haas-type) and hygienic (Hyrax) expanders. All appliances were activated up to the full seven mm capacity of the expansion screw. The patients were subjected to a spiral CT scan before expansion and after a three-month retention period when the expander was removed. One-millimeter-thick axial sections were scanned parallel to the palatal plane, comprising the dentoalveolar area and the base of the maxilla up to the inferior third of the nasal cavity. Multiplanar reconstruction was used to measure maxillary transverse dimensions and posterior teeth inclination by means of a computerized method. The results showed that RME produced a significant increase in all measured transverse linear dimensions, decreasing in magnitude from dental arch to basal bone. The transverse increase at the level of the nasal floor corresponded to one-third of the amount of screw activation. Tooth-borne (Hyrax) and tooth tissue-borne (Haas-type) expanders tended to produce similar orthopedic effects. In both methods, RME led to buccal movement of the maxillary posterior teeth, by tipping and bodily translation. The second premolars displayed more buccal tipping than the appliance-supporting teeth. The tooth tissue-borne expander produced a greater change in the axial inclination of appliance-supporting teeth, especially first premolars, compared with the tooth-borne expander.     

A prospective study of the short-term treatment effects of the acrylic-splint rapid maxillary expander combined with the lower Schwarz appliance

This prospective clinical study evaluated the short-term treatment effects of acrylic-splint rapid maxillary expander in conjunction with lower Schwarz appliance (RME-Sz) therapy to the acrylic-splint rapid maxillary expansion alone (RME-only group). Pretreatment and posttreatment lateral cephalograms were analyzed for 25 RME patients and 19 RME-Sz patients. The average time between films ranged between nine and 12 months. Statistical comparisons of the treatment changes in the RME-only and RME-Sz groups were performed by means of independent sample t-tests (P < .05). The largest difference between the two groups was in lower anterior facial height (LAFH). The normally occurring increase in LAFH was not observed in the RME-only group during the treatment period, indicating that the acrylic-splint expander had a posterior "bite block effect" on the developing craniofacial complex. LAFH increased by 1.7 mm in the RME-Sz group, a value similar to that observed in untreated individuals. Slight forward displacement of the maxilla was observed when RME was used alone, and the sagittal position of the maxilla remained unchanged in the RME-Sz group. A significant amount of intrusion of the maxillary molars (-0.8 mm) was noted in the RME-only group, whereas the maxillary molars were prevented from erupting in the RME-Sz group. The lower dentition showed a significantly greater amount of extrusion in the RME-Sz group than in the RME-only group. Finally, the Sz appliance prevented the mesial movement of the lower molars during the treatment period.     

Changes in clinical crown height as a result of transverse expansion of the maxilla in adults

The risk of developing bony dehiscence and gingival recession may lead clinicians to prefer extraction to expansion in borderline cases. The purpose of this research was to compare changes in clinical crown height that occur at the buccal aspect of the maxillary lateral teeth of adult patients in which the transverse dimension was increased with those occurring if no expansion had been performed. Secondly it was the intention to identify factors increasing the risk of development of gingival recessions.The material comprised the pre- and post-treatment study casts from two groups of 50 adult patients. In one group an average transverse expansion of 3 mm was performed while in the other no change in the arch width was generated during treatment. Clinical crown heights of the two groups before and after treatment were compared with a Student's t-test and correlation analysis was used to determine whether any demographic or treatment-related parameters could be applied to predict an increase in clinical crown height.The increase in transarch width was greater in males (2.4-3.4 mm) than in females (1.8-2.5 mm), and greater at the level of the premolars than at the molars. No significant increase in buccal crown height could be identified. The increase in width was, however, related to buccal tipping as a positive correlation was found between the amount of expansion and tipping (P < 0.01). No detrimental effect of slow maxillary expansion could be demonstrated.     

A clinical comparison of the quadhelix appliance and the nickel titanium (tandem loop) palatal expander: a preliminary, prospective investigation

Maxillary expansion using either a quadhelix appliance (Qx) or a nickel titanium palatal expander (Nt) was prospectively compared in 28 consecutive new patients (19 female, nine male) presenting with posterior buccal segment crossbites. Study models taken at each activation were measured to determine the mean maxillary expansion efficacy (Emax) and the mean expansion rate (m(max)) across the first molars and first premolars. Patient discomfort was assessed using visual analogue scores, and cost-effectiveness was also considered. Neither Emax nor m(max) differed significantly between Qx and Nt across either the first molars or the first premolars. However, both Emax and m(max) were significantly greater across the first molars than across the first premolars only with Qx (Emax: 8.4 +/- 0.7 mm versus 5.1 +/- 0.6 mm, P = 0.001; m(max): 0.09 +/- 0.005 mm/day versus 0.05 +/- 0.006 mm/day, P = 0.0001). In addition, greater variance was apparent in m(max) with Nt than with Qx across both the first molars and the first premolars. Overall, Qx and Nt elicited similar discomfort. However, significantly less was reported with Nt on days 6 (P = 0.04) and 7 (P= 0.03) following the second 'activation'. These preliminary results suggest that Qx and Nt are equally efficacious maxillary expanders. However, Qx expansion appeared significantly more controlled, as well as more individually predictable in expansion rate. Overall, Qx and Nt probably elicit similar discomfort, but significantly less discomfort may be seen with Nt following the second activation. Finally, because more than one appliance is invariably required with Nt, Qx expansion is potentially less costly.     

Clinical Profile of Rapid Maxillary Expansion—Outcome of a National Inquiry

BACKGROUND: Rapid maxillary expansion (RME) is a therapeutic orthodontic option with a long history, and there are many reports in the literature reporting widely divergent results concerning the appliance efficacy and many different treatment protocols. We aimed to evaluate the treatment protocols and clinical experiences with RME via a national inquiry of orthodontists to identify the status quo of RME in clinical daily routine. METHOD: Within the framework of an anonymous questionnaire, 2003 orthodontists and members of the German Orthodontic Society (DGKFO) were asked to report on their clinical experiences with RME. The standardized questionnaire covered clinical indications, dentition period at the time of insertion, mode of activation, retention time, observed side effects, and the reasons for requiring surgical assistance. RESULTS: The data from 487 questionnaires could be evaluated. The only indication for RME named by a large majority of responders was transversal maxillary deficiency. The average extent of the transversal deficiency amounted to 5.29 +/- 2.25 mm (median 5 mm). Most orthodontists (87.7%) employed RME in the permanent dentition of adolescents; it was significantly less frequently applied in the primary dentition or adults. Answers regarding the mode of activation varied greatly. The most frequent mode of activation was "1-2 activations a day" independent of the dentition period. 64.5% of the orthodontists reported buccal tipping of the anchorage teeth. No correlation was detected between mode of activation, time of insertion and observed side effects. 60% of the orthodontists reported a retention period of between 3 and 6 months (median 4.5 months). With an average age of 19.28 years, 79.3% assessed chronological age as a limiting factor for conventional RME. It was not possible to identify a homogeneous diagnostic procedure for the indication of surgical assistance. CONCLUSIONS: Although RME has a long clinical history, no standardized treatment protocols exist. Randomized clinical trials are necessary to make clear-cut clinical recommendations on the use of RME, as required by the tenets of evidence-based medicine and quality assurance.     

上颌快速扩弓的生物力学研究进展

上颌快速扩弓是临床上常用的治疗方法。上颌骨邻近组织结构复杂,而快速扩弓的矫治力作用于牙和腭部再通过骨和软组织的传导分散到整个上颌骨及其周围组织,因此其生物力学作用机制亦十分复杂。下面就其生物力学原理的国内外研究进展进行综述,以期对临床医师应用该法有所帮助。     

成人上颌快速扩弓后牙龈退缩状况的研究

目的　探讨上颌快速扩弓对成人牙龈退缩的影响。方法　测量成人上颌快速扩弓组 (RME组 )和非上颌快速扩弓矫治病例组 (对照组 ,C组 )治疗前后牙牙合石膏模型临床牙冠高度的变化。结果　矫治前后第一磨牙、第二前磨牙、第一前磨牙临床牙冠高度的差值与C组矫治前后同名牙临床牙冠高度的差值比较 ,男性RME组无统计学意义 ,女性RME组第二前磨牙无统计学意义 ,第一磨牙和第一前磨牙的差值有统计学意义。结论　成人上颌快速扩弓不会加速和 (或 )导致成人牙龈退缩。     

Cephalometric evaluation of rapid and slow maxillary expansion in patients with BCLP: Secondary data analysis from a randomized clinical trial

Objective:To compare the dentoskeletal effects of rapid (RME) and slow (SME) maxillary expansion in patients with bilateral complete cleft lip and palate (BCLP).Materials and Methods:This was a secondary analysis of a previous randomized controlled trial (RCT). Forty-six patients (34 male, 12 female) with BCLP and posterior crossbite (mean age of 9.2 years) were randomly assigned to two study groups. Group RME comprised subjects treated with Haas/Hyrax expander. Group SME included patients treated with quad-helix appliance. Cone-beam computed tomography (CBCT) was performed before expansion (T1) and after appliance removal at the end of a 6-month retention period (T2) for a previous RCT that compared the transverse skeletal effects of RME and SME. CBCT-derived cephalometric images were generated and cephalometric analysis was performed using Dolphin Imaging Software (Chatsworth, Calif). Intergroup comparisons were performed using t tests (P < .05).Results:Baseline forms were similar between groups. No significant differences between RME and SME groups were found.Conclusions:Rapid and slow maxillary expansion produced similar sagittal and vertical changes in patients with BCLP. Both Haas/Hyrax and quad-helix appliances can be used in patients with vertical facial pattern. Clinical relevance: RME and SME can be equally indicated in the treatment of maxillary arch constriction in patients with BCLP.     

Skeletally-anchored Rapid Maxillary Expansion using the Dresden Distractor

INTRODUCTION: It was the aim of this study to carry out a 3-D analysis of the teeth, alveolar and skeletal structures during bone-borne, surgically-assisted rapid maxillary expansion (RME) with the Dresden Distractor (DD). We aimed to determine whether a translatory and skeletal movement of the segments would be possible while reducing the dento-alveolar side effects associated with tooth-borne RME. MATERIALS AND METHODS: Standardized axial computed tomography (CT) was performed on twelve patients averaging 25.3 years of age prior to and after RME with the DD. Reference planes and the triple-0-ELSA were defined bilaterally referring to the following anatomic points: the foramina spinosa, external auditory meati and the anterior margin of the foramen magnum. We measured the amount of movement that occurred before and after RME with the DD against ELSA. RESULTS: A screw activation of 6.0 mm led to a transverse expansion of 5.55 mm in the alveolar process in the premolar region, and of 4.87 mm in the molar region, with 8 degrees to 9.8 degrees of buccal tipping and an increase in width of 6.07 mm and 5.71 mm, respectively, occurred in conjunction with only slight buccal tipping of the premolars (3.1 degrees -4.6 degrees ) and molars (1,1 degrees -2.6 degrees ). These data signify, beyond the considerable skeletal efficacy, an uprighting of the teeth due to the multibracket appliance's torque effect, and a direct transfer of the expansion forces onto the bone. Autorotation of the mandible in forward and upward directions was possible due to the considerably less dental tipping resulting from RME with the DD in comparison to tooth-borne RME. This fact demonstrated that the DD is also well-suited for patients with vertical growth pattern. CONCLUSION: The bone-borne DD is an effective therapeutic method that spares the patient the negative side effects associated with tooth-borne RME such as root resorption, bone dehiscence, bite opening and excessive buccal tipping of the teeth. The prerequisites for stable occlusion are brought about by the fact that the expansion is skeletal in nature, with minimal dental tipping.     

Hyrax快速与慢速扩弓矫治替牙晚期上颌狭窄疗效对比研究

目的 比较Hyrax快速与慢速扩弓矫治替牙晚期上颌狭窄的疗效。 方法 选取2011年1月至2012年12月来大连市口腔医院正畸科就诊的替牙晚期上颌基骨狭窄患者60例,随机分成2组,分别采用Hyrax快速扩弓与Hyrax慢速扩弓进行矫治,扩弓前后拍摄锥形束CT（cone beam computerized tomography ,CBCT）,通过Invivo5牙科软件三维重建,分别测量扩弓前后上颌第一磨牙、第一前磨牙冠状位硬腭水平基骨宽度、颊侧牙弓宽度、双侧牙槽骨倾斜角度的交角、双侧牙齿倾斜角度的交角,轴位颊、舌侧骨质厚度。扩弓前后数据采用SPSS 17.0统计软件进行分析。结果 冠状位：Hyrax快速扩弓与Hyrax慢速扩弓在骨性开展和牙弓总宽度变化上无差别,扩弓后牙弓总宽度增加,第一前磨牙平面的骨开展量大于第一磨牙平面,牙齿和牙槽嵴颊向倾斜,牙槽嵴倾斜的角度慢速扩弓组大于快速扩弓组,牙齿倾斜的角度快速扩弓组大于慢速扩弓组;轴位：颊侧骨质厚度减少,舌侧骨质厚度增加,但Hyrax慢速扩弓组颊侧的减少量小于Hyrax快速扩弓组,两组差异有统计学意义（P＜0.05）。结论 对于替牙晚期患者,与Hyrax快速扩弓相比,Hyrax慢速扩弓慢速轻力的特点更符合生理特性,并且对颊侧的骨质厚度影响小,是一种有效的扩弓方式。