Stresses and Strains Analysis Using Different Palatal Expander Appliances in Upper Jaw and Midpalatal Suture

Analysis of Stress Distribution and Displacement Based on the Miniscrew Positions of the Palatal Slope Bone-borne Expander: A Finite Element Study

OBJECTIVES

 This study aimed to investigate the stress distribution pattern of the palatal slope bone-borne expander on the maxillary area according to a different anteroposterior position of anchored miniscrews using finite element analysis.

MATERIALS AND METHODS

 Nasomaxillary stereolithography files with three different anteroposterior anchored miniscrew positions of the palatal slope bone-borne expander were determined as model A, B, and C. Each model consists of four supported miniscrews. Model A: two anterior miniscrews were located between the maxillary canine and the first premolar, and two posteriors between the second premolar and the first molar. Model B: two anteriors were between the lateral incisor and the canine, and two posteriors were the same as in model A. Model C: two anteriors were the same as in model A, and two posteriors were distal to the first molar. One turn of expander screws was applied. Maximum principal stress, equivalent elastic strain, equivalent von Mises stress, and transverse displacement were evaluated.

RESULTS

 The maximum principal stress was mostly found at the bone-miniscrew interface. Model A exhibited an intersecting area of stress between the supported miniscrews. The highest value of principal stress was in model B, while model C showed a uniform distribution pattern. The elastic strain pattern was similar to the principal stress in all models. The highest value of equivalent von Mises stress was located on the expander screw. The largest amount of transverse displacement of teeth was in model A, while model C exhibited a more consistent transverse displacement than other models. Vertical displacement of posterior teeth was also noticed.

CONCLUSION

 Based on the result, it revealed that the various anteroposterior miniscrew placements of the palatal slope bone-borne expander had various patterns of stress distribution and resulted in various outcomes. It may be inferred that model A's miniscrew location was advantageous for obtaining expansion quantities, but model C's miniscrew position was advantageous for maintaining consistent biomechanics.

Finite element analysis of the influence of interdigitation pattern and collagen fibers on the mechanical behavior of the midpalatal suture

The midpalatal suture (MPS) corresponds to the tissue that joins the two maxillary bones. Understanding the mechanical behavior of this tissue is of particular interest to those patients who require orthodontic treatments such as Rapid Maxillary Expansion (RME). The objective of this research was to observe the influence of interdigitation and collagen fibers on the mechanical response of MPS. To this end, a finite element analysis in two-dimensional models of the bone-suture-bone interface was performed considering the characteristics of the MPS. The geometry of the suture was modeled with 4 different levels of interdigitation: null, moderate, scalloped and fractal. The influence of collagen fibers, aligned transversely along the suture, was considered by incorporating linked structures of the bone fronts. According to the results, the factor that has the greatest impact on the magnitude and distribution of stresses is the interdigitation degree. A higher level of interdigitation produces an increase in tissue stiffness and a lower influence of collagen fibers on the mechanical response of the tissue. Therefore, this research contributes to the understanding of the MPS biomechanics by providing information that may be useful to health staff when evaluating the feasibility of procedures such as RME.

Evaluation of dental and skeletal effects of the asymmetric rapid maxillary expansion appliance: A three-dimensional finite element study

BACKGROUND

Transverse maxillary deficiency is one of the most common skeletal anomalies. The incidence of posterior crossbite caused by maxillary deficiency is between 2.7% and 23.3%. Unilateral posterior crossbite is more common than bilateral crossbite. The most common treatment for skeletal posterior crossbite is rapid maxillary expansion (RME), in which the base of the maxillary bone is expanded by separating the midpalatal suture.

OBJECTIVE

This study compares the biomechanical effects of three different RME appliances, especially the effects on the midline, and evaluates the usability of the modified asymmetric RME (ARME) appliance for treating unilateral crossbites.

METHODS

Three scenarios were created with skull models using three different appliances: (1) conventional-bonded RME appliance; (2) full-cap splint RME appliance, with all teeth covered with acrylic; and (3) ARME, with all teeth on the right side and premolars and molars on the left side covered with acrylic. The finite element method was used to assess stress levels and displacements in all models after applying a 5-mm horizontal displacement to the RME screw.

RESULTS

The lateral transverse movement of the first molars was greater with the conventional RME appliance than with the full-cap splint RME appliance. The lateral transverse movement of the first molar was greater on the left than on the right side with the ARME. The lateral transverse movement of the central incisors was greater with the full-cap splint RME appliance than with the conventional RME appliance. The lateral transverse movement of the central incisor was greater on the right than on the left side with the ARME.

CONCLUSION

Asymmetrical RME appliance increases unilateral expansion compared to other appliances. Therefore, it should be used in cases of unilateral posterior crossbite. This appliance can also successfully treat posterior crossbite with upper midline deviation, since it corrects the shifted midline.

Skeletal and dentoalveolar effects of slow vs rapid activation protocols of miniscrew-supported maxillary expanders in adolescents: A randomized clinical trial

OBJECTIVES

To compare between skeletal and dentoalveolar effects of slow and rapid activation of miniscrew-supported expanders.

MATERIALS AND METHODS

A total of 30 patients were randomly allocated to two groups using block randomization and the allocation ratio 1:1. Both groups received maxillary expanders anchored using four miniscrews. Activation protocol was once every other day in the slow expansion (SME) group and twice daily in the rapid expansion (RME) group. Cone-beam computed tomography (CBCT) scans were obtained before expansion and after removal of the expanders. Transverse skeletal and dentoalveolar changes were measured using CBCT.

RESULTS

A total of 12 patients in the SME group (mean age, 14.30 ± 1.37 years) and 12 patients in the RME group (mean age, 15.07 ± 1.59 years) were analyzed. RME showed significantly greater widening of the mid-palatal suture at the level of first molars (mean difference [SME - RME] = -0.61 mm), and a greater increase in right and left molar buccal inclination (mean difference= -3.83° and -2.03°, respectively). Percentage of skeletal expansion relative to the jackscrew opening was not significantly different between the groups. Palatal inflammation was evident following appliance removal. Miniscrew mobility and bending were observed with RME.

CONCLUSIONS

Both SME and RME were effective in correcting skeletal transverse maxillary deficiency. However, RME resulted in more buccal tipping of maxillary molars and in miniscrew failures and bending.

Biomechanical behavior of an alveolar graft under maxillary therapies

Cleft lip and palate is a congenital defect that affects the oral cavity. Depending on its severity, alveolar graft surgery and maxillary orthopedic therapies must be carried out as a part of the treatment. It is widely accepted that the therapies should be performed before grafting. Nevertheless, some authors have suggested that mechanical stimuli such as those from the maxillary therapies could improve the success rate of the graft. The aim of this study is to computationally determine the effect of maxillary therapies loads on the biomechanical response of an alveolar graft with different degrees of ossification. We also explore how the transverse width of the cleft affects the graft behavior and compare results with a non-cleft skull. Results suggest that stresses increase within the graft as it ossifies and are greater if maxillary expansion therapy is applied. This has consequences in the bone remodeling processes that are necessary for the graft osseointegration. Maxillary orthopedic therapies after graft surgery could be considered as a part of the treatment since they seem to act as a positive extra stimulus that can benefit the graft.

Influence of interdigitation and expander type in the mechanical response of the midpalatal suture during maxillary expansion

BACKGROUND AND OBJECTIVE

The orthopedic Maxillary Expansion (ME) procedure is used for treating the transverse maxillary deficiency. This pathology consists in a smaller transverse dimension in the maxilla and leads to malocclusion. The treatment takes advantage of the existence of the midpalatal suture (MPS), which corresponds to the junction at the palatine bones of its horizontal portions. The technique employs a device, conventionally a palatal expander attached to the posterior teeth, to separate the two maxillary bones in the MPS. The objective of this study was to analyze, using the Finite Element Method, the biomechanical behavior of the MPS when an expansion is applied.

METHODS

A Computer Tomography image of the maxilla was reconstructed, the suture geometry was modeled with different interdigitation levels and types of hyrax devices. A total of 12 geometric models (three levels for interdigitation and four types of hyrax devices) were prepared and analyzed taking into account the chewing forces and the expansion displacement. For each case, maximum principal stresses on the maxilla (bone), and equivalent stresses on the expander device (stainless steel) were observed. In the MPS, maximum principal stresses and directional displacement were evaluated.

RESULTS

The results showed that the interdigitation does not have an important influence on the deformation behavior of the maxilla but it affects the stress distribution. In addition, the type of expander device and anchorage have a direct relationship with the treatment effectiveness; larger deformation in the expansion direction was obtained with skeletal when compared to dental anchorage.

CONCLUSIONS

A study that allows a better understanding of the oral biomechanics during the application of ME was presented. To our knowledge, it is the first study based on computational simulations that takes into account bone structures, like maxilla and part of the skull, to analyze the interdigitation influence on the MPS behavior when exposed to a ME.

A comparative finite element analysis of maxillary expansion with and without midpalatal suture viscoelasticity using a representative skeletal geometry

The goal of this investigation was to adapt and incorporate a nonlinear viscoelastic material model representative of the midpalatal suture’s viscoelastic nature into finite element analysis simulations of maxillary expansion treatment. Step-wise displacements were applied to a partial skull geometry to simulate treatment using an expansion screw appliance. Four simulation cases were considered for the midpalatal and intermaxillary sutures: 1. Neglecting suture tissue; 2. Linear elastic properties; 3. Viscoelastic properties; 4. A fused intermaxillary and viscoelastic midpalatal suture. Results from simulations indicated that removal of suture tissue and inclusion of viscoelastic properties resulted in the same maxillary displacement following 29 activations of 0.125 mm applied directly to the maxilla; however, assuming a fused intermaxillary suture significantly changed maxillary displacement patterns. Initial stress results within the suture complex were significantly influenced by the inclusion of suture viscoelasticity as compared to linear elastic properties. The presented study demonstrates successful incorporation of suture viscoelasticity into finite element analysis simulations of maxillary expansion treatment, and elucidates the appropriateness of various suture material property assumptions depending desired research outcomes.

Bone-borne accelerated sutural expansion: A microcomputed tomography study in rabbits

INTRODUCTION

In this study, we evaluated the effect of bone-borne accelerated expansion protocols on sutural separation and sutural bone modeling using a microcomputed tomography system. We also determined the optimum instant sutural expansion possible without disruption of bone modeling.

METHODS

Sixteen New Zealand white rabbits, 20 to 24 weeks old, were randomly divided into 4 experimental groups. Modified hyrax expanders were placed across their interfrontal sutures and secured with miniscrew implants located bilaterally in the frontal bone. The hyrax appliances were activated as follows: group 1 (control), 0.5-mm per day expansion for 12 days; group 2, 1-mm instant expansion followed by 0.5 mm per day for 10 days; group 3, 2.5-mm instant expansion followed by 0.5 mm per day for 7 days, and group 4, 4-mm instant expansion followed by 0.5 mm per day for 4 days. After 6 weeks of retention, sutural separation and sutural bone modeling were assessed by microcomputed tomography and quantified. Statistical analysis was performed using Kruskal Wallis and Mann-Whitney U tests and the Spearman rho correlation (P <0.05).

RESULTS

Median amounts of sutural separation ranged from 2.84 to 4.41 mm for groups 1 and 4, respectively. Median bone volume fraction ranged from 59.96% to 69.15% for groups 4 and 3, respectively. A significant correlation (r = 0.970; P <0.01) was observed between the amounts of instant expansion and sutural separation.

CONCLUSIONS

Pending histologic verifications, our findings suggest that the protocol involving 2.5 mm of instant expansion followed by 0.5 mm per day for 7 days is optimal for accelerated sutural expansion. When 4 mm of instant expansion was used, the sutural bone volume fraction was decreased.

Artificial Organs 2017: A Year in Review

In this Editor's Review, articles published in 2017 are organized by category and summarized. We provide a brief reflection of the research and progress in artificial organs intended to advance and better human life while providing insight for continued application of these technologies and methods. Artificial Organs continues in the original mission of its founders "to foster communications in the field of artificial organs on an international level." Artificial Organs continues to publish developments and clinical applications of artificial organ technologies in this broad and expanding field of organ Replacement, Recovery, and Regeneration from all over the world. Peer-reviewed Special Issues this year included contributions from the 12th International Conference on Pediatric Mechanical Circulatory Support Systems and Pediatric Cardiopulmonary Perfusion edited by Dr. Akif Undar, Artificial Oxygen Carriers edited by Drs. Akira Kawaguchi and Jan Simoni, the 24th Congress of the International Society for Mechanical Circulatory Support edited by Dr. Toru Masuzawa, Challenges in the Field of Biomedical Devices: A Multidisciplinary Perspective edited by Dr. Vincenzo Piemonte and colleagues and Functional Electrical Stimulation edited by Dr. Winfried Mayr and colleagues. We take this time also to express our gratitude to our authors for offering their work to this journal. We offer our very special thanks to our reviewers who give so generously of time and expertise to review, critique, and especially provide meaningful suggestions to the author's work whether eventually accepted or rejected. Without these excellent and dedicated reviewers the quality expected from such a journal could not be possible. We also express our special thanks to our Publisher, John Wiley & Sons for their expert attention and support in the production and marketing of Artificial Organs. We look forward to reporting further advances in the coming years.

Evaluation of the effects of miniscrew incorporation in palatal expanders for young adults using finite element analysis

Objective

The aim of this study was to evaluate the stress distribution and displacement of various craniofacial structures after nonsurgical rapid palatal expansion (RPE) with conventional (C-RPE), bone-borne (B-RPE), and miniscrew-assisted (MARPE) expanders for young adults using three-dimensional finite element analysis (3D FEA).

Methods

Conventional, bone-borne, and miniscrew-assisted palatal expanders were designed to simulate expansion in a 3D FE model created from a 20-year-old human dry skull. Stress distribution and the displacement pattern for each circumaxillary suture and anchor tooth were calculated.

Results

The results showed that C-RPE induced the greatest stress along the frontal process of the maxilla and around the anchor teeth, followed by the suture area, whereas B-RPE generated the greatest stress around the miniscrew, although the area was limited within the suture. Compared with the other appliances, MARPE caused relatively even stress distribution, decreased the stress on the buccal plate of the anchor teeth, and reduced tipping of the anchor teeth.

Conclusions

The findings of this study suggest that the incorporation of miniscrews in RPE devices may contribute to force delivery to the sutures and a decrease in excessive stress on the buccal plate. Thus, MARPE may serve as an effective modality for the nonsurgical treatment of transverse maxillary deficiency in young adults.