Maxillary protraction with and without maxillary expansion: a finite element analysis of sutural stresses.

INTRODUCTION: In this finite element study, we compared the stress patterns along the various craniofacial sutures with maxillary protraction with and without expansion. METHODS: Two 3-dimensional analytic models were developed, 1 simulating maxillary protraction and the other simulating maxillary protraction with expansion. The model consisted of 108799 10 node solid 92 elements (tetrahedron), 193633 nodes, and 580899 degrees of freedom. RESULTS: The overall stresses after maxillary protraction with maxillary expansion were significantly higher than with a facemask alone. The magnitude of stress on the craniofacial sutures with maxillary protraction alone was in the range of a few millinewtons per square millimeter, whereas, with maxillary protraction with maxillary expansion, the stresses ranged from a few newtons per square millimeter to a few hundred newtons per square millimeter. The pattern of stress distribution also differed with the 2 treatment modalities as did the sutures experiencing maximum and minimum stresses. CONCLUSIONS: The osteogenic potential of such low stresses after maxillary protraction can be questioned. High stresses generated in various craniofacial sutures after maxillary protraction with expansion are responsible for disrupting the circummaxillary sutural system and presumably facilitating the orthopedic effect of the facemask.

Skeletal response to maxillary protraction with and without maxillary expansion: a finite element study.

INTRODUCTION: The purpose of this finite element study was to evaluate biomechanically 2 treatment modalities-maxillary protraction alone and in combination with maxillary expansion-by comparing the displacement of various craniofacial structures. METHODS: Two 3-dimensional analytical models were developed from sequential computed tomography scan images taken at 2.5-mm intervals of a dry young skull. AutoCAD software (2004 version, Autodesk, San Rafael, Calif) and ANSYS software (version 10, Belcan Engineering Group, Cincinnati, Ohio) were used. The model consisted of 108,799 solid 10 node 92 elements, 193,633 nodes, and 580,899 degrees of freedom. In the first model, maxillary protraction forces were simulated by applying 1 kg of anterior force 30 degrees downward to the palatal plane. In the second model, a 4-mm midpalatal suture opening and maxillary protraction were simulated. RESULTS: Forward displacement of the nasomaxillary complex with upward and forward rotation was observed with maxillary protraction alone. No rotational tendency was noted when protraction was carried out with 4 mm of transverse expansion. A tendency for anterior maxillary constriction after maxillary protraction was evident. The amounts of displacement in the frontal, vertical, and lateral directions with midpalatal suture opening were greater compared with no opening of the midpalatal suture. The forward and downward displacements of the nasomaxillary complex with maxillary protraction and maxillary expansion more closely approximated the natural growth direction of the maxilla. CONCLUSIONS: Displacements of craniofacial structures were more favorable for the treatment of skeletal Class III maxillary retrognathia when maxillary protraction was used with maxillary expansion. Hence, biomechanically, maxillary protraction combined with maxillary expansion appears to be a superior treatment modality for the treatment of maxillary retrognathia than maxillary protraction alone.

A comparison of stress distribution and flexion among various designs of bar attachments for implant overdentures: a three dimensional finite element analysis.

CONTEXT: Bar overdentures are popular choices among clinicians worldwide but configurations that provide an optimal biomechanical distribution of stress are still debatable. AIMS: To compare the stresses and elastic flexion between implant supported bar overdentures in various configurations using finite element analysis. SETTINGS AND DESIGN: A CAT scan of a human mandible was used to generate an anatomically accurate mechanical model. MATERIALS AND METHODS: Three models with bars and clips in three different configurations were constructed. Model 1 had a single bar connecting two implants, Model 2 had three bars connecting all the four implants, and Model 3 had two bars connecting the medial and distal implants on the sides only. The models were loaded under static conditions with 100N load distributed at the approximate position of the clip. The mandibular boundary conditions were modeled considering the real geometry of its muscle supporting system. Maximum von Mises stress at the level of the bar and at the bone implant interface were compared in all three models. The flexion of mandible and the bar was also compared qualitatively. STATISTICAL ANALYSIS USED: The analyses were accomplished using the ANSYS software program and were processed by a personal computer. Stress on these models was analyzed after loading conditions. RESULTS: Qualitative comparisons showed that stress at the level of the bar and at the bone implant interface were in the following order: Model 1> Model 3> Model 2. The flexion of the mandible and the bar were in the following order: Model 2 > Model 1 > Model 3. CONCLUSIONS: Four implant bar systems connected by bars on the sides only is a better choice than two implant bar systems and four implant bar systems with bars connecting all four implants.

Craniofacial displacement in response to varying headgear forces evaluated biomechanically with finite element analysis.

INTRODUCTION: The aim of this study was to evaluate biomechanically the displacement patterns of the facial bones in response to different headgear loading by using a higher-resolution finite element method model than used in previous studies. METHODS: An analytical model was developed from sequential computed tomography scan images taken at 2.5-mm intervals of a dry skull of a 7-year-old. Different headgear forces were simulated by applying 1 kg of posteriorly directed force in the first molar region to simulate cervical-pull, straight-pull, and high-pull headgear. Displacements (in mm) of various craniofacial structures were evaluated along the x, y, and z coordinates with different headgear loading. RESULTS: All 3 headgears demonstrated posterior displacement of the maxilla with clockwise rotation of the palatal plane. The distal displacement of the maxilla was the greatest with the straight-pull headgear followed by the cervical-pull headgear. The high-pull headgear had better control in the vertical dimensions. The midpalatal suture opening was evident and was more pronounced in the anterior region. The articular fossa and the articular eminence were displaced laterally and postero-superiorly with each headgear type. CONCLUSIONS: The high-pull headgear was most effective in restricting the antero-inferior maxillary growth vector. Midpalatal suture opening similar to rapid maxillary expansion was observed with all 3 headgear types. The center of rotation varied with the direction of headgear forces for both the maxilla and the zygomatic complex. A potential for chondrogenic and osteogenic modeling exists for the articular fossa and the articular eminence with headgear loading.

Stress and displacement patterns in the craniofacial skeleton with rapid maxillary expansion: a finite element method study.

INTRODUCTION: The purpose of this finite element study was to evaluate stress distribution along craniofacial sutures and displacement of various craniofacial structures with rapid maxillary expansion (RME) therapy. METHODS: The analytic model for this study was developed from sequential computed tomography scan images taken at 2.5-mm intervals of a dry young human skull. Subsequently, a finite element method model was developed from computed tomography images by using AutoCAD software (2004 version, Autodesk, Inc, San Rafael, Calif) and ANSYS software (version 10, Belcan Engineering Group, Downers Grove, Ill). RESULTS: The maxilla moved anteriorly and downward and rotated clockwise in response to RME. The pterygoid plates were displaced laterally. The distant structures of the craniofacial skeleton--zygomatic bone, temporal bone, and frontal bone--were also affected by transverse orthopedic forces. The center of rotation of the maxilla in the X direction was somewhere between the lateral and the medial pterygoid plates. In the frontal plane, the center of rotation of the maxilla was approximately at the superior orbital fissure. The maximum von Mises stresses were found along the frontomaxillary, nasomaxillary, and frontonasal sutures. Both tensile and compressive stresses could be demonstrated along the same suture. CONCLUSIONS: RME facilitates expansion of the maxilla in both the molar and the canine regions. It also causes downward and forward displacement of the maxilla and thus can contribute to the correction of mild Class III malocclusion. The downward displacement and backward rotation of the maxilla could be a concern in patients with excessive lower anterior facial height. High stresses along the deep structures and the various sutures of the craniofacial skeleton signify the role of the circummaxillary sutural system in downward and forward displacement of the maxilla after RME.