Gingival blood flow before, during, and after clenching, measured by laser Doppler blood flowmeter: A pilot study.

INTRODUCTION: This study aimed to investigate the effects of the strong occlusal force on the hemodynamics of gingival microcirculation. METHODS: Eleven adult volunteers with healthy periodontium and normal occlusion participated in this study. Using a noncontact laser Doppler flowmeter placed at the attached gingiva and the interdental papilla of the maxillary first premolar, changes in gingival blood flow (GBF) were examined during and after clenching. RESULTS: When the strong occlusal pressure was applied on the maxillary first premolar by clenching, GBF in the attached gingiva on the buccal side decreased significantly compared with the resting GBF, with medians of 2.3 mL/min/100 g and 5.4 mL/min/100 g, respectively (P <0.05). After the release of the maximum clenching, GBF recovered immediately and transiently increased to a median of 2.4 mL/min/100 g, showing a significant difference to the resting GBF (P <0.05). In contrast, in the interdental papilla, no significant change in GBF was found by clenching. CONCLUSIONS: Ischemia of the buccal attached gingiva associated with strong clenching may be due to compression of the vascular network of the periodontal membrane. Through reactive hyperemia resulting from the release of clenching, it is possible not only that blood flow will be restored to the tissue but that the tissue itself may be damaged by the reperfusion. During active orthodontic treatment, it is suggested that occlusal management to prevent occlusal trauma is important to avoid detrimental effects on periodontal tissues.

Change in clinical crown height in adult patients treated by means of the multi-bracket appliance with extraction of four first premolars.

OBJECTIVE: To evaluate the gingival condition due to adult orthodontic treatment using the clinical crown height (CCH) as an index. DESIGN: Retrospective study. SETTING: Department of Orthodontics at a university. PARTICIPANTS: A total of 21 adult female patients with healthy periodontal tissue were treated by means of the multi-bracket appliance with extraction of four first premolars. METHODS: Three-dimensional (3D) digital dental models were reconstructed to assess the vertical movement of the free gingival margin caused by adult orthodontic treatment. Pre- and post-treatment CCH were measured, and changes in CCH due to treatment were examined. RESULTS: The change in CCH by orthodontic treatment was able to be assessed objectively using 3D digital models of the dental casts. In the upper dentition, a significant reduction in CCH was found on the labial and lingual sides of the central incisor, with a mean of -0.28 mm and -0.34 mm, respectively (P < 0.001). In contrast, a significant increase in CCH was found on the labial side of the lateral incisor with a mean of 0.75 mm (P < 0.001). In the lower dentition, CCH on the lingual side of the canine, the second premolar and the first molar increased significantly (P < 0.001), with a mean of 0.41 mm, 0.45 mm and 0.50 mm, respectively. For the buccal side, the second premolar showed a significant increase in CCH with a mean of 0.61 mm (P < 0.001). CONCLUSION: By using the CCH as an index, it was possible to assess the gingival condition after active orthodontic treatment.

Innovative design of closing loops producing an optimal force system applicable in the 0.022-in bracket slot system.

INTRODUCTION: Most closing loops designed for producing higher moment-to-force (M/F) ratios require complex wire bending and are likely to cause hygiene problems and discomfort because of their complicated configurations. We aimed to develop a simple loop design that can produce optimal force and M/F ratio. METHODS: A loop design that can generate a high M/F ratio and the ideal force level was investigated by varying the portion and length of the cross-sectional reduction of a teardrop loop and the loop position. The forces and moments acting on closing loops were calculated using structural analysis based on the tangent stiffness method. RESULTS: An M/F ratio of 9.3 (high enough to achieve controlled movement of the anterior teeth) and an optimal force level of approximately 250 g of force can be generated by activation of a 10-mm-high teardrop loop whose cross-section of 0.019 × 0.025 or 0.021 × 0.025 in was reduced in thickness by 50% for a distance of 3 mm from the apex, located between a quarter and a third of the interbracket distance from the canine bracket. CONCLUSIONS: The simple loop design that we developed delivers an optimal force and an M/F ratio for the retraction of anterior teeth, and is applicable in a 0.022-in slot system.

Effect of bracket slot and archwire dimensions on anterior tooth movement during space closure in sliding mechanics: a 3-dimensional finite element study.

INTRODUCTION: It has been found that controlled movement of the anterior teeth can be obtained by attaching a certain length of power arm onto an archwire in sliding mechanics. However, the impact of the archwire/bracket play on anterior tooth movement has not been clarified. The purpose of this study was to compare the effect of the power arm on anterior tooth movements with different dimensions of bracket slots and archwires. METHODS: A 3-dimensional finite element method was used to simulate en-masse anterior tooth retraction in sliding mechanics. Displacements of the maxillary central incisor and the archwire deformation were calculated when applying retraction forces from different lengths of power arms. RESULTS: When a 0.017 × 0.022-in archwire was engaged into the 0.018-in slot bracket, bodily movement of the incisor was obtained with 9.1-mm length of the power arm. When a 0.022-in slot system was coupled with a 0.019 × 0.025-in archwire, bodily movement was observed with a power arm length of 11.6 mm. CONCLUSIONS: Archwire/bracket play has a remarkable impact on anterior tooth movement. An effective torque application to the anterior teeth becomes clinically difficult in sliding mechanics combined with power arms when the archwire/bracket play is large.

Stress Analysis of Periodontal Tissue in en Masse Retraction With Integration of Maxillary Anterior Teeth: A Three-Dimensional Finite Element Method Study.

OBJECTIVE: To simulate the en masse traction technique with the integration (EMTI) of six maxillary anterior teeth using a finite element model (FEM) and explore various protocols for maxillary protrusion. The study aimed to investigate root displacement and stress distribution in the periodontal ligament (PDL) by varying the retraction position and direction of EMTI applied to the maxillary anterior teeth. No actual participants were involved. MATERIALS AND METHODS: The FEM model included six teeth (central and lateral incisors and canines) with a PDL thickness of 0.3 mm. The model encompassing the alveolar bone (ALB) and EMTI had 180,528 elements and 47,836 nodes. The EMTI integrated six anterior teeth via a 0.9-mm-diameter stainless steel lingual wire, equipped with three moment arms extending toward the root apex: one midline (central arm) and two distal to the canines (lateral arms). The position and direction of the traction force applied to the three moment arms of the EMTI were varied to assess crown and apex displacement, as well as PDL stress. RESULTS: Lingual tipping was consistent across all protocols, emphasizing controlled incisor tipping. The application of horizontal traction at 10 mm and traction at 7 mm from the central and lateral arms of the EMTI, respectively, demonstrated the most uniform stress distribution across the PDL of all six anterior teeth. CONCLUSIONS AND CLINICAL SIGNIFICANCE: The FEM analysis results suggest that the new EMTI method, which retracts the maxillary anterior teeth as a unit, is effective for tooth movement and PDL stress distribution. The EMTI technique, with its specific traction protocols and emphasis on controlled tipping, appears to be a promising approach for addressing maxillary protrusions.

Physiological positioning strategy alters condylar position after mandibular ramus sagittal split osteotomies for mandibular prognathism.

OBJECTIVE: The aim of this study was to elucidate the physiological position of the proximal segment for postoperative jaw movement in patients with mandibular prognathism. METHODS: Twenty-two patients with mandibular prognathism were treated by orthognathic surgery using bilateral mandibular sagittal split ramus osteotomies (SSRO) with a physiological positioning strategy. The skeletal stability was assessed, and the movement of the proximal segment was evaluated by cephalography and computed tomography performed preoperatively, immediately postoperatively, and one year postoperatively. RESULTS: The patients were divided into two groups: the stable group (SNB relapse <1.5°) and the relapse group (SNB relapse ≥1.5°). In the stable group at one year postoperatively, the average SNB relapse was only 0.29° (7%), the condylar head had moved posteriorly by 0.75 mm, and the proximal segment had rotated counterclockwise by 1.2°. CONCLUSION: This new physiological positioning strategy improves the position of the condyle compared with the preoperative position in patients with mandibular prognathism.

Biomechanical aspects of segmented arch mechanics combined with power arm for controlled anterior tooth movement: A three-dimensional finite element study.

The porpose of this study was to determine the optimal length of power arms for achieving controlled anterior tooth movement in segmented arch mechanics combined with power arm. A three-dimensional finite element method was applied for the simulation of en masse anterior tooth retraction in segmented power arm mechanics. The type of tooth movement, namely, the location of center of rotation of the maxillary central incisor in association with power arm length, was calculated after the retraction force was applied. When a 0.017 × 0.022-in archwire was inserted into the 0.018-in slot bracket, bodily movement was obtained at 9.1 mm length of power arm, namely, at the level of 1.8 mm above the center of resistance. In case a 0.018 × 0.025-in full-size archwire was used, bodily movement of the tooth was produced at the power arm length of 7.0 mm, namely, at the level of 0.3 mm below the center of resistance. Segmented arch mechanics required shorter length of power arms for achieving any type of controlled anterior tooth movement as compared to sliding mechanics. Therefore, this space closing mechanics could be widely applied even for the patients whose gingivobuccal fold is shallow. The segmented arch mechanics combined with power arm could provide higher amount of moment-to-force ratio sufficient for controlled anterior tooth movement without generating friction, and vertical forces when applying retraction force parallel to the occlusal plane. It is, therefore, considered that the segmented power arm mechanics has a simple appliance design and allows more efficient and controllable tooth movement.

Effect of play between bracket and archwire on anterior tooth movement in sliding mechanics: A three-dimensional finite element study.

OBJECTIVES: The aim of this study was to clarify the effect of the play between the bracket and the archwire on anterior tooth movement subjected to the retraction force from various lengths of power arms in sliding mechanics. MATERIALS AND METHODS: A three-dimensional finite element method was used to simulate en masse anterior tooth retraction in sliding mechanics. The displacements of the maxillary incisor and the archwire deformation were calculated when the retraction force was applied. RESULTS: When a play did not exist, bodily movement was obtained at 5.0 mm length of power arm. In case a play existed, bodily movement was observed at the power arm length of 11.0 mm. CONCLUSIONS: In the actual clinical situation, a bracket/archwire play and the torsion of the archwire within the bracket slot should be taken into consideration to prescribe an optimal power arm length and to achieve effective anterior tooth movement.