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

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.

Three-dimensional morphometric analysis of cranial sutures - A novel approach to quantitative analysis

Objective

Differences in complexity of cranial suture forms on the endocranial (i.e., deep) and ectocranial (i.e., superficial) skull surfaces have been noted in the literature, indicating through thickness three-dimensional (3D) suture variability depending on the chosen section and necessity for considering the complete 3D structure in many cases. This study aims to evaluate the variability of suture morphology through the skull thickness using a rat model, and to provide more robust metrics and methodologies to analyze suture morphology.

Design

X-ray micro-computed tomographic (μCT) imaging methods were utilized in order to provide internal structure information. Methods were developed to isolate and analyze sutures widths and linear interdigitation index (LII) values on each adjacent offset transverse plane of the μCT datasets. LII was defined as the curved path length of the suture divided by the linear length between the ends of the region of interest. Scans were obtained on 15 female rats at ages of 16, 20, and 24 weeks (n = 5/age). Samples were imaged at 18 μm resolutions with 90 kV source voltage, 278 μA source amperage, and 0.7° increments. Suture widths and LII values were compared using a Kruskal-Wallis test.

Results

3D variability in local suture widths within individuals, as well as through thickness variabilities in planar widths and LII was observed. Kruskal-Wallis tests for bulk through thickness averaged suture widths and LII were found to be statistically insignificant, despite clear geometric differences through suture thicknesses.

Conclusion

Although the bulk morphometric variability between age groups was found to be statistically insignificant, the 3D variability within individuals point to the importance of analyzing suture form using 3D metrics when studying suture development, response to functional activity, or morphometry in general.

Midpalatal Suture: Single-Cell RNA-Seq Reveals Intramembrane Ossification and Piezo2 Chondrogenic Mesenchymal Cell Involvement

The midpalatal suture is mainly responsible for the growth and development of the maxillary and resistance to rapid maxillary expansion (RME). It is essential for clinical researchers to explore the intramembrane ossification and to elucidate the underlying mechanism of the maturation and ossification process of the midpalatal suture to help identify the optimum time and force of RME. However, mechanistic studies associated with the midpalatal suture are rare. The aim of this present study is to create an intramembrane osteogenesis model for the midpalatal suture region of mice. Interestingly, we discovered a type of chondrogenic mesenchymal cell expressing Piezo2, which might be related to the detection of mechanical and external stimuli. This result provides a potential molecular and cellular mechanism that explains why the midpalatal suture is not closed until adulthood. We depict a landscape of mesenchymal cells that might play an important role in the intramembrane osteogenesis of the midpalatal suture and provide new perspectives on midpalate suture maturation and ossification, which might lead to further possibilities for clinical operations.

Cranial suture morphometry and mechanical response to loading: 2D vs. 3D assumptions and characterization

Cranial sutures are complex soft tissue structures whose mechanics are often studied due to their link with bone growth in the skull. Researchers will often use a cross-sectional two-dimensional slice to define suture geometry when studying morphometry and/or mechanical response to loading. However, using a single cross section neglects the full suture complexity and may introduce significant errors when defining their form. This study aims to determine trends in suture path variability through skull thickness in a swine model and the implications of using a 'representative' cross section on mechanical modeling. To explore these questions, a mixture of quantitative analysis of computed tomography images and finite element models was used. The linear interdigitation and width of coronal and sagittal sutures were analyzed on offset transverse planes through the skull thickness. It was found that sagittal suture width and interdigitation were largely consistent through the skull thickness, whereas the coronal suture showed significant variation in both. The finite element study found that average values of displacement and strain were similar between the two-dimensionally variable and three-dimensionally variable models. Larger ranges and more complex distributions of strain were found in the three-dimensionally variable model. Outcomes of this study indicate that the appropriateness of using a representative cross section to describe suture morphometry and predict mechanical response should depend on specific research questions and goals. Two-dimensional approximations can be sufficient for less-interdigitated sutures and when bulk site mechanics are of interest, while taking the true three-dimensional geometry into account is necessary when considering spatial variability and local mechanical response.

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.

Radiological evaluation of the bone and soft tissue thicknesses of the palate for using a miniscrew-supported maxillary skeletal expander

PURPOSE

The purpose of this study was to determine the palatal bone and soft tissue thicknesses using a miniscrew-supported maxillary skeletal expander (MSE) in Class III malocclusion.

METHODS

The thicknesses of the palatal bone and soft tissue were measured in cone-beam computed tomography images obtained from 58 patients. All 20 points were crossing points between five levels, which were defined at 3 mm intervals relative to the line connecting the central fossae of the first molar (Level 0), and 2 mm and 4 mm lateral to the anteroposterior reference line (AP line).

RESULTS

The palatal bone was significantly thicker in males than females in the anterior palate up to Level 0, while there was no significant sex-related difference in the posterior palate. There was a tendency for the thickness to decrease in the posterior direction, except in females at 2 mm lateral to the AP line. The palatal soft tissue was significantly thicker in males than females in all positions. At 2 mm lateral to the AP line, the palatal soft tissue thickness decreased in the posterior direction. A 4 mm lateral to the AP line, it initially decreased in the posterior direction, and then increasing again at Level - 6 (6 mm posterior of Level 0). As the lateral distance from the AP line increased, the palatal bone thickness decreased while the palatal soft tissue thickness increased.

CONCLUSIONS

These findings provide quantitative data on the palatal bone and soft tissue thicknesses for the miniscrew-supported MSE in the posterior palate.