Correlating Frictional Forces Generated by Different Bracket Types during Sliding and Surface Topography Using Scanning Electron Microscopy and Optical Profilometer.

AIM: The study aims to correlate the frictional forces (FF) of four different types of commercially available ceramic brackets to their surface topography. MATERIALS AND METHODS: Two monocrystalline (MC) brackets (CLEAR™, Adanta, Germany; Inspire ICE™, Ormco, USA), one polycrystalline (PC) bracket (Symetri Clear™, Ormco, USA), one clear hybrid esthetic bracket (DISCREET™, Adanta, Germany), and a stainless-steel (SS) bracket (Victory™, 3M Unitek, USA) served as control. Both static friction (SF) and kinetic friction (KF) were recorded during sliding using an Instron universal machine in dry settings. The bracket slot surface topography was evaluated. A scanning electron microscope (SEM) and a profilometer machine were used for assessment before and after sliding. RESULTS: Frictional forces values during sliding were as follows in descending order; Inspire ICE™, CLEAR™, DISCREET™, Symetri Clear™, and, lastly, Victory™. Also, DISCREET™ scored the highest in surface roughness (Sa) values followed by Symetri Clear™. None of the correlations were statistically significant. CONCLUSION: Frictional forces produced during sliding were not always directly related to surface roughness. Monocrystalline ceramic brackets appeared to have the greatest FF and a low surface roughness. Furthermore, DISCREET™ scored a very low frictional value comparable to metal brackets yet showed the highest surface roughness. Metal brackets exhibited the greatest surface smoothness before sliding and the least SF. CLINICAL SIGNIFICANCE: Predicting the FFs produced during sliding mechanics would help the practitioner while choosing the bracket system to be used, and while planning the treatment mechanics, how much force to deliver, and how much tooth movement to expect. How to cite this article: AlBadr AH, Talic NF. Correlating Frictional Forces Generated by Different Bracket Types during Sliding and Surface Topography Using Scanning Electron Microscopy and Optical Profilometer. J Contemp Dent Pract 2024;25(1):41-51.

Testing the tensile fracture strength tie-wings of different orthodontic ceramic bracket using an Instron machine.

Introduction: Newly released products should address the shortcomings of the older ones. Frequent breakages have always been a major drawback when using ceramic brackets. This study assessed the difference in tensile fracture strength at maximum load of tie-wings of different orthodontic ceramic brackets recently available for clinical use. Materials and Methods: In this in-vitro study, four ceramic brackets were examined. Two monocrystalline brackets (CLEAR™, Adanta®, Germany; Inspire ICE™, Ormco®, USA), one polycrystalline bracket (Symtri Clear™, Ormco®, USA), and one clear hybrid bracket (DISCREET™, Adanta®, Germany). A steel ligature wire was placed around the tie-wing and on the Instron machine to apply tension. The mean maximum load (MxL) and fracture strength (FS) was evaluated and recorded. The significance level was set at p ≤ 0.05. Results: Statistical difference in fracture strength of the tie-wing fracture was noted among all four groups. Inspire ICE™ showed the highest maximum load and fracture strength with (202.78 N and 107.3 MPa), followed by Symtri Clear™ (111.99 N and 59.25 MPa). In contrast, CLEAR™ and DISCREET™ showed lower MxL values (79.63 N and 47.01 N). The monocrystalline Inspire ICE™ brackets showed the greatest tie-wing fracture resistance and the hybrid clear ceramic bracket DISCREET™ exposed the least resistance to fracture. Conclusion: Brand (manufacturing specifications) as well the bracket crystalline structure seems to have a direct effect on its tie-wing strength.

Comparison of static friction and surface topography of low friction and conventional TMA orthodontic arch wires: An in-vitro study.

BACKGROUND: Arch wire surface characteristics, especially surface roughness and topography, influence the coefficient of friction during sliding. The clinician should be familiar with the properties of orthodontic appliances and materials that could result in high friction to maximize the efficiency of treatment. This study aimed to compare the static friction of orthodontic arch wire materials, including a newly introduced low-friction TMA, conventional TMA, and stainless steel arch wires, using an Instron universal testing machine and to evaluate their surface topographical features using a noncontact optical profilometer. METHODS: A total of 30 arch wire specimens were used, including 10 low-friction TMA (TMA-Low), 10 conventional TMA (TMA-C), and 10 stainless steel (SS), (Ormco, Orange, CA, USA) measuring 0.016 × 0.022 in. The static frictional force of each arch wire material was measured using the universal Instron machine. The surface topography was evaluated using a noncontact profilometer machine. RESULTS: The static frictional resistance forces were highest in the TMA-C alloy group, and the value was statistically significant in comparison to the SS arch wire but not to the TMA-Low arch wire. The mean value of the static friction of the TMA-Low group was intermediate between the TMA-C and SS arch wires. However, this difference was statistically insignificant compared to the other two alloys. A surface roughness evaluation using a profilometer machine revealed that the highest mean of all three roughness parameters was found in the TMA-C group, followed by the TMA-Low and SS arch wires in descending order. CONCLUSION: The static friction resistance forces and surface roughness values of the TMA-Low arch wire are comparable to those of TMA-C but are still considered inferior to those of the SS arch wire.

Comparison of surface topography of low-friction and conventional TMA orthodontic arch wires using atomic force microscopy.

OBJECTIVE: To evaluate the surface topography and roughness of orthodontic arch wire materials, including low-friction titanium molybdenum alloy (TMA), conventional TMA, and stainless-steel arch wires. MATERIALS AND METHODS: The surface topography was evaluated using atomic force microscopy (AFM). A total of 24 wire specimens were used for the AFM scans {8 low-friction TMA (TMA-Low), 8 conventional TMA (TMA-C), and 8 stainless steel (SS)} (Ormco, Orange, CA, USA), measuring 0.016 × 0.022 inches. The conventional and low-friction TMA arch wires served as the test groups, while the stainless-steel arch wire served as the control group. RESULTS: Surface roughness evaluation using AFM revealed that the highest mean of all three roughness parameters was found in the TMA-C group followed by the TMA-Low and SS arch wires in descending order. Pairwise comparison of the mean values showed that the mean value of the SS arch wire material is statistically significantly lower than the mean values of the other two arch wire materials (TMA-C and TMA-Low). However, there was no statistically significant difference in the mean values of TMA-C and TMA-Low arch wires. CONCLUSION: The SS arch wire showed the smoothest surface topography among the alloys and had statistically significantly lower roughness values than the TMA-C and TMA-Low groups. Low-friction TMA arch wire is still considered to be inferior to stainless steel arch wire.

Comparison of force loss during sliding of low friction and conventional TMA orthodontic archwires : An in vitro study.

OBJECTIVE: The goal was to measure and compare the amount of force loss during tooth movement guided by archwires, including a newly introduced low-friction titanium molybdenum alloy (TMA), conventional TMA, and stainless steel archwires. METHODS: The force loss was measured using a specialized biomechanical set-up, the orthodontic measurement and simulation system (OMSS). A total of 30 specimen were used (10 low-friction TMA (TMA-Low), 10 conventional TMA (TMA-C), and 10 stainless steel (SS) archwires, each having a dimension of 0.016â€¯× 0.022 inches). The conventional and low friction TMA archwires served as test groups, while the SS archwires served as the control group. RESULTS: The mean values of force loss between the three types of wires (TMA­C, TMA-Low, and SS) were significantly different (p < 0.0001). The highest mean force loss during sliding movement was found in the conventional TMA group (72.1%), followed by low friction TMA (48.8%) and stainless steel wires (33.7%) in a descending order. CONCLUSION: The friction property of the low friction TMA archwire was superior to the conventional TMA archwire but was still inferior to the stainless steel archwire.

Failure Rates of Orthodontic Fixed Lingual Retainers bonded with Two Flowable Light-cured Adhesives: A Comparative Prospective Clinical Trial.

INTRODUCTION: This comparative prospective randomized clinical trial examined the in vivo failure rates of fixed mandibular and maxillary lingual retainers bonded with two light-cured flowable composites over 6 months. MATERIALS AND METHODS: Consecutive patients were divided into two groups on a 1:1 basis. Two hundred fixed lingual retainers were included, and their failures were followed for 6 months. One group (n = 50) received retainers bonded with a nano-hybrid composite based on nano-optimized technology (Tetric-N-Flow, Ivoclar Vivadent). Another group (n = 50) received retainers bonded with a low viscosity (LV) composite (Transbond Supreme LV, 3M Unitek). RESULTS: There was no significant difference between the overall failure rates of mandibular retainers bonded with Transbond (8%) and those bonded with Tetric-N-Flow (18%). However, the odds ratio for failure using Tetric-N-flow was 2.52-fold greater than that of Transbond. The failure rate of maxillary retainers bonded with Transbond was higher (14%), but not significantly different, than that of maxillary retainers bonded with Tetric-N-flow (10%). There was no significant difference in the estimated mean survival times of the maxillary and mandibular retainers bonded with the two composites. CONCLUSION: Both types of composites tested in the current study can be used to bond fixed maxillary and mandibular lingual retainers, with low failure rates.

Study of force loss due to friction comparing two ceramic brackets during sliding tooth movement.

OBJECTIVE: To compare the percentage of force loss generated during canine sliding movements in newly introduced ceramic brackets with metal brackets. MATERIALS AND METHODS: Two types of ceramic brackets, namely polycrystalline alumina (PCA) ceramic brackets (Clarity Advanced) and monocrystalline alumina (MCA) ceramic brackets (Inspire Ice) were compared with stainless steel (SS) brackets (Victory Series). All bracket groups (n = 5 each) were for the maxillary canines and had a 0.018-inch slot size. The brackets were mounted on an Orthodontic Measurement and Simulation System (OMSS) to simulate the canine retraction movement into the first premolar extraction space. Using elastic ligatures, 0.016 × 0.022″ (0.40 × 0.56 mm) stainless steel archwires were ligated onto the brackets. Retraction force was applied via a nickel-titanium coil spring with a nearly constant force of approximately 1 N. The OMSS measured the percentage of force loss over the retraction path by referring to the difference between the applied retraction force and actual force acting on each bracket. Between group comparisons were done with one-way analysis of variance. RESULTS: The metal brackets revealed the lowest percentage of force loss due to friction, followed by the PCA and MCA ceramic bracket groups (67 ± 4, 68 ± 7, and 76 ± 3 %, respectively). There was no significant difference between SS and PCA brackets (p = 0.97), but we did observe significant differences between metal and MCA brackets (p = 0.03) and between PCA and MCA ceramic brackets (p = 0.04). CONCLUSION: PCA ceramic brackets, whose slot surface is covered with an yttria-stabilized zirconia-based coating exhibited frictional properties similar to those of metal brackets. Frictional resistance resulted in an over 60 % loss of the applied force due to the use of elastic ligatures.

The effect of dietary pigmentation on the esthetic appearance of clear orthodontic elastomeric modules.

OBJECTIVE: To compare the stain resistance of three types of clear elastomeric modules exposed to several common dietary substances through the assessment of the perception of a group of dentists to discoloration using visual analog scale (VAS). MATERIALS AND METHODS: Elastomeric modules from Unitek (AU), Ormco (OR), and dentaurum (DE) were immersed in the following food substances: Coffee, black tea, chocolate, energy drink, ketchup, and Coca-Cola for 72 h. VAS was used to reflect the module staining severity. RESULTS: Significant difference was found among the three types of modules examined in this study. OR modules showed the least mean staining ratings by the examiners. There was no statistical difference in the staining properties between AU and DE modules. Coffee and tea showed higher staining potential as compared to all staining media. Furthermore, there was no difference in the staining characteristics of coffee and black tea. CONCLUSIONS: Coffee and tea are strong staining media that should be avoided by patients who opted to have esthetic appliances for their orthodontic treatment. Elastomeric modules manufactured by AU showed higher staining optical properties as compared to the other two companies, which could be related to the manufacturing processing of these modules.

Factors Affecting the Shear Bond Strength of Orthodontic Brackets - a Review of In Vitro Studies.

The adhesive material used to bond orthodontic brackets to teeth should neither fail during the treatment period, resulting in treatment delays, untoward expenses or patient inconvenience nor should it damage the enamel on debonding at the end of the treatment. Although the effectiveness of a bonding system and any unfavorable effects on the enamel may be studied by conducting in-vivo studies, it is nearly impossible to independently analyze different variables that influence a specific bonding system in the oral environment. In-vitro studies, on the other hand, may utilize more standardized protocols for testing different bonding systems and materials available. Thus, the present review focused attention on in-vitro studies and made an attempt to discuss material-related, teeth-related (fluorotic vs non-fluorotic teeth) and other miscellaneous factors that influences the shear bond strength of orthodontic brackets. Within the limitations of this review, using conventional acid-etch technique, ceramic brackets and bonding to non-fluorotic teeth was reported to have a positive influence on the shear bond strength of orthodontic brackets, but higher shear bond strength found on using ceramic brackets can be dangerous for the enamel.

Bond strength and micro-computed tomographic evaluation of pre-coated brackets.

OBJECTIVES: The aim of the present study was to assess and compare the shear bond strength (SBS) of metal pre-coated orthodontic brackets bonded to fluorotic and non-fluorotic teeth treated with three different etching techniques. A second aim was to determine the volume of adhesive remaining on the tooth at debond using micro-computed tomography (µCT). METHODS: Ninety extracted premolars were selected to include 45 fluorotic (test group) and 45 non-fluorotic (control group) teeth. Each group was divided into three subgroups of 15 each, which were treated as follows: 1) micro-etched; 2) acid-etched; and 3) both micro-etched and acid-etched. A bonding agent was applied to the prepared surfaces; pre-coated and light-cured brackets were attached to all teeth. An Instron universal testing machine was used to record the debonding force. Specimens were then scanned using a microCT to evaluate the amount of adhesive remaining on the teeth. The significance of the statistical tests was pre-determined at p < 0.05. RESULTS: Two-way ANOVA showed that fluorosis of teeth had no influence on the SBS (p = 0.165) whereas the volume of adhesive remnants was significantly higher in the control group compared with the test group (p < 0.001). CONCLUSIONS: Fluorosis had no influence on the SBS of brackets, whereas it had a negative influence on retaining adhesives onto the tooth surfaces.

Nickel and chromium levels in the saliva of a Saudi sample treated with fixed orthodontic appliances.

AIM: The aim of this study was to measure the amount of nickel (Ni) and chromium (Cr) released into the saliva of Saudi patients treated with fixed orthodontic appliances. MATERIALS AND METHODS: Ninety salivary samples were collected in a cross-sectional manner. Forty samples were collected from patients (17 males, 23 females) with fixed orthodontic appliances after different periods of orthodontic treatment ranging from the first month and up to 32 months into treatment. The fixed orthodontic appliance consisted of 4 bands, 20 stainless steel brackets, and upper and lower nickel titanium or stainless-steel arch wires. The other 50 samples were collected from people without appliances (24 males, 26 females). Samples were analyzed using Inductive Coupled Plasma/Mass Spectrometry and Inductively Coupled Plasma Optical Emission Spectroscopy to measure Ni and Cr levels, respectively. Student's t-test was used to compare Ni and Cr levels in the treated and untreated control groups. RESULTS: The mean Ni level was 4.197 µg/L in the experimental group and 2.3 µg/L in the control group (p < 0.05). The mean Cr level was 2.9 µg/L in the experimental group and 3.3 µg/L in the control group (p < 0.05). CONCLUSION: Fixed orthodontic appliances resulted in a non-toxic increase in salivary levels of Ni, but no change in Cr levels. Duration of orthodontic treatment did not affect Ni and Cr levels in the saliva.

Perception of Saudi dentists and lay people to altered smile esthetics.

AIM: To evaluate and compare the perceptions of Saudi dentists and lay people to altered smile features. METHODS: Thirty-six digital smile photographs with altered features were used. Altered features included the following: crown length, width, gingival level of the lateral incisors, gingival display, midline diastema, and upper midline shift. The photographs were presented to a sample of 30 dentists and 30 lay people with equal gender distribution. Each participant rated each picture with a visual analogue scale, which ranged from 0 (very unattractive) to 100 (very attractive). RESULTS: Dentists were more critical than lay people when evaluating symmetrical crown length discrepancies. Compared to lay people, Saudi dentists gave lower ratings to a crown length discrepancy of >2 mm (P < 0.001), crown width discrepancy of ⩾2 mm (P < 0.05), change in gingiva to lip distance of ⩾2 mm (P < 0.01), and midline deviation of >1 mm (P < 0.01). There was no significant difference between dentists and lay people towards alterations in the gingival level of the lateral incisors or towards a space between the central incisors. No significant sex difference was seen across the groups. CONCLUSION: In this sample, Saudi dentists gave significantly lower attractiveness scores to crown length and crown width discrepancies, midline deviations, and changes in gingiva to lip distance compared to Saudi lay people.

Immunolocalization of lubricin in the rat periodontal ligament during experimental tooth movement.

Lubricin is a protein which contributes to the boundary lubrication, facilitating low friction levels at the interfacing surfaces of joints. In tendons and ligaments it facilitates the relative movement of collagen bundles. Its expression is affected by mechanical signals and cytokines. During application of orthodontic forces to teeth, there is a transduction of mechanical forces to the cells of the periodontal ligament (PDL), which triggers several biological reactions causing the synthesis of prostaglandins, cytokines and growth factors. The aim of the present study was to examine the immunolocalization of lubricin and to evaluate if it is time-dependently and differentially detected within the PDL following the application of orthodontic forces to create areas of compression and tension. This was achieved by placing elastic bands between the maxillary first and second molars of 16 male Sprague-Dawley rats (each weighing 120-200g) for 12 and 24h. The molar-bearing segments were dissected and processed for histological and immunohistochemical examination. Binding of a monoclonal antibody was used to evaluate lubricin localization using an indirect streptavidin/biotin immunperoxidase technique. Lubricin, was constitutively expressed in the PDL of rat molars. After the experimental force was applied to the tooth, lubricin was down-regulated, on both sides (compression and tension) of the PDL, in a time-dependent fashion, although to a different extent, being at any time more expressed on the tension side. Furthermore, in every sample, almost all PDL cells in the adjacent tooth cementum and alveolar bone, were more heavily immunolabeled by lubricin antibody, contrary to those located in the central portion of the PDL. Lubricin expression therefore seems related to PDL remodeling and tooth displacement following the application of an orthodontic force, and it appears that lubricin may play an important role during tooth movement.

Effect of fluoridated paste on the failure rate of precoated brackets bonded with self-etching primer: a prospective split-mouth study.

INTRODUCTION: The aim of this prospective randomized clinical trial was to determine the effect of using fluoridated paste (Dentsply, York, Pa) compared with plain pumice (Ortho Technology, Tampa, Fla) on the clinical bond failure rates of precoated brackets bonded with self-etching primer. METHODS: A split-mouth technique was used. The teeth in the maxillary right and mandibular left quadrants were prepared with a fluoridated paste only, and the teeth in the maxillary left and mandibular right quadrants were prepared with plain pumice before bonding the precoated brackets. A total of 627 brackets in 34 orthodontic patients (20 female, 14 male) were included in this study; 315 brackets were bonded after pumice treatment, and 312 were bonded after paste treatment. The patients were followed for 6 months to determine the rates of bracket failure. RESULTS: The overall failure rate was 8%. The failure rates for pumice and paste were 4.8% and 11.2%, respectively. The McNemar test showed a statistically significant difference between the 2 groups. Based on tooth type, the failure rate of the maxillary canine and the mandibular central incisor brackets were significantly different for paste and pumice. There was also a difference in the survival rates of the brackets in both groups. CONCLUSIONS: Preparation of the enamel surface with fluoridated paste before bonding with self-etching primer is not recommended. However, the use of plain pumice is recommended, even if it is time-consuming.

Adverse effects of orthodontic treatment: A clinical perspective.

Orthodontic treatment is associated with a number of adverse effects, such as root resorption, pain, pulpal changes, periodontal disease, and temporomandibular dysfunction (TMD). Orthodontists should be aware of these effects and associated risk factors. Risk factors linked to root resorption include the duration of treatment, length, and shape of the root, trauma history, habits, and genetic predisposition.

MMP-13 (collagenase 3) immunolocalisation during initial orthodontic tooth movement in rats.

Matrix metalloproteinases (MMPs) are enzymes that play a central role in periodontal ligament (PDL) space remodelling during orthodontic tooth movement. It has previously been shown that messenger RNA levels of MMP-13 increase significantly following the application of orthodontic forces. The aim of the present study was to examine immunolocalisation of MMP-13 and to evaluate if this collagenase is time-dependently and differentially detected within the PDL following the application of orthodontic forces to create areas of compression and tension. This was achieved by placing elastic bands between the maxillary first and second molars of 16 male Sprague-Dawley rats (each weighing 120-200g) for 12 and 24h. The molar-bearing segments were dissected and processed for histological and immunohistochemical examination. Binding of a monoclonal antibody was used to evaluate MMP-13 localization using an indirect streptavidin/biotin immunperoxidase technique. MMP-13 was found to be inducible at the protein level by the application of forces. The PDL and osteoblast-lineage cells showed a time-dependent increase in immunolabelling of MMP-13. Immunolabelling of MMP-13 was detected initially on the compression side, and then on both the compression and the tension sides. Since this increase in MMP-13 immunolabelling occurred very early following the application of an orthodontic force in both PDL and alveolar bone, this would indicate that MMP-13 might play an important role during tooth movement.

Inhibition of orthodontically induced root resorption with echistatin, an RGD-containing peptide.

INTRODUCTION: Induced dental root resorption is a common side effect of orthodontic treatment. It is an unpredictable phenomenon, and its etiology is unknown. Odontoclasts responsible for the resorption of the dental tissues--ie, cementum and dentin--share many cytochemical and morphological characteristics with osteoclasts, which are responsible for bone resorption. The aim of this study was to explore cellular mechanisms that decrease induced root resorption in orthodontically treated teeth. METHODS: The effects of targeting the alphavbeta3 integrin receptor, expressed by odontoclasts, on induced root resorption surface areas and the number of root resorption lacunae were investigated by using an RGD-containing peptide, echistatin. The effect of echistatin on the number of clast cells in the periodontium was also examined. Tooth movement was achieved in 14 Sprague-Dawley rats by placing elastic bands between the right maxillary first and second molars for 24 hours. The animals were equally divided into 2 groups; the experimental animals received echistatin intravenously for 8 hours (0.8 microg/kg/min), and the controls received sterile water. The specimens obtained were processed for light microscopy. The surface area and the number of root resorption lacunae were measured histomorphometrically by using digital photomicrographs. Echistatin labeled with a fluorescent marker was used to confirm its presence in clast cells with fluorescent microscopy. Cytochemically, tartrate-resistant acid phosphatase was used to quantify mature and committed clast cells. Echistatin was localized in targeted cells in the periodontium. RESULTS: Echistatin significantly decreased root resorption surface areas (P < .01) and reduced the number of root resorption lacunae (P < .01). There was no statistically significant difference in clast cell numbers. CONCLUSIONS: Targeting alphavbeta3 integrin receptor expressed by odontoclasts can be effective in reducing root resorption during tooth movement. Further studies are needed to elucidate the mechanism of this inhibition.

Immunohistochemical localization of alphavbeta3 integrin receptor during experimental tooth movement.

During orthodontic treatment, multinucleated clast cells carry out the resorption of mineralized tissues. Adhesion of clast cells to the mineralized tissues is mediated by transmembrane cell-surface glycoproteins called integrins, specifically by the alphavbeta3 integrin, which plays an important role in the process of bone resorption. The role of the alphavbeta3 integrin in bone resorption leading to osteoporosis has been demonstrated, but its role in alveolar bone and root resorption during orthodontic tooth movement is unknown. This study examined the expression of the alphavbeta3 integrin during experimental tooth movement. Tooth movement was achieved in 16 male Sprague-Dawley rats (each weighing 120-200 g) with elastic bands between their maxillary first and second molars. The molar-bearing segments were dissected and processed for histologic and immunohistochemical examination. The expression of alphavbeta3 integrin was examined with 2 primary antibodies: a polyclonal anti-alphav integrin subunit antibody and a polyclonal anti-beta3 integrin subunit antibody. Negative controls were similarly processed but without incubation with primary antibodies. The alphavbeta3 integrin was expressed both by osteoclasts associated with alveolar bone resorption and by odontoclasts associated with root resorption during experimental tooth movement. Furthermore, the beta3 integrin subunit was expressed by the epithelial rests of Malassez in the periodontal ligament. Negative controls did not show immunolabeling. The alphavbeta3 integrin adhesion receptor is expressed during experimental tooth movement and might be involved in the process of mineralized tissue resorption and the functions of the epithelial rests of Malassez.

Proliferation of epithelial rests of Malassez during experimental tooth movement.

The epithelial rests of Malassez (ERM), remnants of Hertwig's epithelial root sheath, are found near the root surface in the periodontal ligament. The functional significance of the ERM is still unknown. The purpose of this study was to examine the behavior of the ERM during experimental tooth movement. Tooth movement was achieved in 12 male Sprague-Dawley rats (each, 120-200 g) by placing elastic bands between the maxillary right first and second molars. The left molars served as controls. The rats were killed after 6, 12, 18, 24, 60, and 72 hours. The mitotic activity of the ERM was assessed by injecting the animals with 5-bromo-2'-deoxyuridine (BrdU) 2 to 3 hours before killing by intracardial perfusion with 4% paraformaldehyde. The molar-bearing segments were dissected and processed for histological examination. The incorporated BrdU was detected by immunohistochemistry. The number of cells in each ERM cluster was counted in all groups. In the 18-, 24-, 60-, and 72-hour experimental groups, the cell numbers were significantly higher than in the controls. The surface areas of the ERM clusters were also measured in all groups, but only in the 18-, 24-, 60-, and 72-hour specimens were the areas significantly higher in the experimental than in the control groups. The ERM cells in the experimental specimens were labeled with anti-BrdU, while those in the controls were not. It was concluded that experimental tooth movement stimulates ERM cells to proliferate and increase in size. These increased activities of the ERM are consistent with a putative role for these cells in collagen turnover in the periodontal ligament that is accelerated during tooth movement.