Influence of cortical bone thickness on miniscrew microcrack formation

Jaw osteoporosis: Challenges to oral health and emerging perspectives of treatment

Osteoporosis is a prevalent bone metabolic disease that poses a significant challenge to global human health. Jaw osteoporosis, characterized by microstructural damage of the jaw resulting from various factors, is one of the common manifestations of this condition. Recent studies have demonstrated that jaw osteoporosis has multifaceted effects on oral health and can negatively impact conditions such as periodontitis, oral implantation, orthodontic treatment, and wound healing. However, there are still some limitations in the conventional treatment of osteoporosis. For instance, while bisphosphonates can enhance bone quality, they may also lead to osteonecrosis of the jaw, which poses a potential safety hazard in oral diagnosis and treatment. In recent years, considerable attention has been focused on improving the pathological condition of jaw osteoporosis. Treatment strategies such as gut microbial regulation, extracellular vesicles, molecular targeted therapy, herbal medicine, mechanical stimulation are expected to enhance efficacy and minimize adverse reactions. Therefore, understanding these effects and exploring novel treatments for jaw osteoporosis may provide new insights for oral health maintenance and disease treatment. This article reviews the impact of jaw osteoporosis on oral health and describes the limitations associated with current methods. It also discusses emerging perspectives on treatment, offering a comprehensive overview of the challenges and future directions in managing jaw osteoporosis.

Minimum required length of orthodontic microimplant: a numerical simulation and clinical validation

INTRODUCTION

This study aimed to determine the minimum required length of microimplants (MIs) to prevent excessive micromotion during MI healing that can lead to MI failure.

METHODS

Hypothesizing that the implantation depth of MI in cancellous bone (ID_cancel) is the key to the control of micromotion during MI healing, we numerically investigated the minimum ID_cancel required to maintain MI micromotion to below the threshold (30 μm) that would threaten MI survival. Twenty MI and bone models were built using MIs of 4 lengths and bone specimens with 5 different cortical bone thicknesses to create ID_cancel in the 0.5-5.5 mm. Then, applying a horizontal force of 1.5 N on the MI head, we calculated the micromotion (peak and average MI micromotions) and determined the minimum ID_cancel. A clinical test was performed to verify the numerical result by placing 160 MIs in the posterior maxilla and mandible.

RESULTS

A strong correlation (r²= 0.694) was found to exist between ID_cancel and MI micromotion. A minimum of 2.5 mm of ID_cancel was needed to maintain the level of MI micromotion (peak micromotion) <30 μm threshold. The 6-month survival rate of MI was strongly correlated with ID_cancel (r²= 0.744) and decreased sharply when ID_cancel was ≤2 mm.

CONCLUSIONS

The minimum lengths of MIs to provide the minimum ID_cancel of 2.5 mm required to promote successful MI healing in the posterior maxilla and mandible are 5.2 and 6.5 mm, respectively.

Revisiting the Complications of Orthodontic Miniscrew

Miniscrew has been used widely as an effective orthodontic anchorage with reliable stationary quality, ease of insertion and removal techniques, immediate or early loading, flexibility in site insertion, less trauma, minimal patient cooperation, and lower price. Nonetheless, it is not free of complications, and they could impact not only the miniscrew success rate but also patients’ oral health. In this article, literature was searched and reviewed electronically as well as manually to evaluate the complications of orthodontic miniscrew. The selected articles are analyzed and subcategorized into complications during and after insertion, under loading, and during and after removal along with treatment if needed according to the time. In addition, the noteworthy associated factors such as the insertion and removal procedures, characteristics of both regional and local anatomic structures, and features of the miniscrew itself that play a significant role in the performance of miniscrews are also discussed based on literature evidence. Clinicians should notice these complications and their related factors to make a proper treatment plan with better outcomes.

The effects of cortical bone thickness and miniscrew implant root proximity on the success rate of miniscrew implant: A retrospective study

OBJECTIVE

To investigate the effects of cortical bone thickness (CBT), miniscrew implant root proximity (MRP) and other related factors on the success rate of miniscrew implant (MSI).

MATERIALS AND METHODS

Four hundred and five MSIs placed in 171 patients were analysed in this retrospective study. The primary predictor variables were CBT and MRP at MSI insertion sites. The predictor variables also included patient, location, MSI design and procedure related factors. The outcome variable was the survival of MSI. The differences in measurement data between success group and failed group were evaluated by the analysis of variance and independent samples t tests. Patient, location, MSI design and procedure related factors associated with the MSI prognosis were analysed by survival analysis with Cox proportional hazard regression model. The P value was set at .05. And the survival curves of independent factors were plotted.

RESULTS

The overall success rate of MSI was 82.7%. The age of MSI host, CBT, interdental root distance (IRD) and MRP at MSI sites showed no significant differences between failed group and success group. CBT and insertion jaws were independent prognosis factors screened out by Cox proportional hazard regression model. Failure risk (hazard ratio) of MSI with CBT <1 mm was 4.72. The failure risk in the mandible was 3.80 times as high as that in the maxilla.

CONCLUSION

Inadequate CBT (<1 mm) contributed to the failure of MSI. MSI placed in the maxilla showed better prognosis compared to the mandible. MRP had no significant effect on the prognosis.

Evaluation of Cortical Bone Microdamage and Primary Stability of Orthodontic Miniscrew Using a Human Bone Analogue

Orthodontic miniscrews have gained popularity; however, they have some drawbacks, including screw loosening that results from bone resorption caused by excess microdamage created during screw insertion. Pilot hole preparation through the cortical bone is considered beneficial to avoid such microdamage, while an overly large pilot hole impairs primary stability. Hence, we used a human bone analogue to evaluate the microdamage and primary stability to estimate the optimal pilot hole size that would minimize the screw loosening risk. Ti6Al4V orthodontic miniscrews and 1.0-mm-thick synthetic cortical bone pieces were prepared. Various compressive loads were applied in indentation tests to test pieces' surfaces, and the microdamaged areas were confirmed as stress-whitening zones. Screw insertion tests were performed in which a miniscrew was inserted into the test pieces' pilot hole with a diameter of 0.7-1.2 mm in 0.1-mm intervals, and the stress-whitening area was measured. The insertion and removal torque were also measured to evaluate primary stability. The stress-whitening areas of the 1.0-1.2 mm pilot hole diameter groups were significantly smaller than those of the other groups (p < 0.05), whereas the 0.9 and 1.0 mm pilot hole diameter groups showed higher primary stability than other groups. In conclusion, the bone analogue could be utilized to evaluate microdamage in cortical bones and the primary stability of miniscrews.

Biomechanical analysis of occlusal modes on the periodontal ligament while orthodontic force applied

OBJECTIVE

The study objective was to investigate four common occlusal modes by using the finite element (FE) method and to conduct a biomechanical analysis of the periodontal ligament (PDL) and surrounding bone when orthodontic force is applied.

MATERIALS AND METHODS

A complete mandibular FE model including teeth and the PDL was established on the basis of cone-beam computed tomography images of an artificial mandible. In the FE model, the left and right mandibular first premolars were not modeled because both canines required distal movement. In addition, four occlusal modes were simulated: incisal clench (INC), intercuspal position (ICP), right unilateral molar clench (RMOL), and right group function (RGF). The effects of these four occlusal modes on the von Mises stress and strain of the canine PDLs and bone were analyzed.

RESULTS

Occlusal mode strongly influenced the distribution and value of von Mises strain in the canine PDLs. The maximum von Mises strain values on the canine PDLs were 0.396, 1.811, 0.398, and 1.121 for INC, ICP, RMOL, and RGF, respectively. The four occlusal modes had smaller effects on strain distribution in the cortical bone, cancellous bone, and miniscrews.

CONCLUSION

Occlusal mode strongly influenced von Mises strain on the canine PDLs when orthodontic force was applied.

CLINICAL RELEVANCE

When an FE model is used to analyze the biomechanical behavior of orthodontic treatments, the effect of muscle forces caused by occlusion must be considered.

Drilling Capability of Orthodontic Miniscrews: In Vitro Study

The aims of this study were to assess the values and mechanical properties of insertion torque (IT) of steel miniscrews inserted in artificial bone blocks (Sawbones, Pacific Research Laboratories, Vashon, WA, USA) with different bone densities and to detect any scratches on the surface of the miniscrews after insertion. Forty self-drilling miniscrews (Leone S.p.A. ø 1.75 mm, L 8 mm) have been inserted into bone blocks that mimic different stability conditions (density: 20 PCF-pounds per cubic foot, 40 PCF, and 30 + 50 PCF with 2 mm and 4 mm of cortical bone). Before insertion and after removal, all miniscrews were inspected with a stereomicroscope 5x and a SEM to detect potential microscopic cracks. Using an electronic surgical motor (W&H Dentalwerk Bürmoos GmbH, Werner Bader Str. 1, 5111 Bürmoos, Austria), the maximum insertion torque value was registered. Stereomicroscope and SEM examination did not indicate any morphological and surface structural changes to the miniscrews, irrespective of the bone density they were inserted into. The findings showed that IT increased significantly with increasing bone density. In each artificial bone block, morphostructural analysis demonstrated the adequate mechanical properties of the self-drilling miniscrews. IT measurements indicated torque values between 6 and 10 Ncm for blocks with a density of 30 + 50 PCF, whereas the suggested values are between 5 and 10 Ncm.

Mechanical Evaluation of the Stability of One or Two Miniscrews under Loading on Synthetic Bone

The aim of the present study was to evaluate the primary stability of a two-miniscrew system inserted into a synthetic bone and to compare the system with the traditional one. Forty-five bi-layered polyurethane blocks were used to simulate maxillary cancellous and cortical bone densities. Samples were randomly assigned to three groups—one-miniscrew system (Group A, N = 23), two-miniscrew system (Group B, N = 22) and archwire-only (Group C, N = 10). A total of 67 new miniscrews were subdivided into Group A (23 singles) and Group B (22 couples). 30 mm of 19″ × 25″ archwires were tied to the miniscrew. The load was applied perpendicularly to the archwire. Maximum Load Value (MLV), Yield Load (YL) and Loosening Load (LL) were recorded for each group. The YL of Group B and C had a mean value respectively of 4.189 ± 0.390 N and 3.652 ± 0.064 N. The MLV of Group A, B and C had a mean value respectively of 1.871 ± 0.318N, of 4.843 ± 0.515 N and 4.150 ± 0.086 N. The LL of Group A and B had a mean value respectively of 1.871 ± 0.318 N and of 2.294 ± 0.333 N. A two- temporary anchorage device (TAD) system is on average stiffer than a one-TAD system under orthodontic loading.

Migration and differentiation of osteoclast precursors under gradient fluid shear stress

The skeleton can adapt to mechanical loading through bone remodeling, and osteoclasts close to microdamages are believed to initiate bone resorption. However, whether local mechanical loading, such as fluid flow, regulates recruitment and differentiation of osteoclast precursors at the site of bone resorption has yet to be investigated. In the present study, finite element analysis first revealed the existence of a low-fluid shear stress (FSS) field inside microdamage. Based on a custom-made device of cone-and-plate fluid chamber, finite element analysis and particle image velocimetry measurement were performed to verify the formation of gradient FSS flow field. Furthermore, the effects of gradient FSS on the migration, aggregation, and fusion of osteoclast precursors were observed. Osteoclast precursor RAW264.7 cells migrated along a radial direction toward the region with decreased FSS during exposure to gradient FSS stimulation for 40 min, thereby deviating from the direction of actual fluid flow indicated by fluorescent particles. When calcium signaling pathway was inhibited by gadolinium and thapsigargin, cell migration toward a low-FSS region was significantly reduced. For the other cell lines MC3T3-E1, PDLF, rat mesenchymal stem cells, and Madin-Darby canine kidney epithelial cells, gradient FSS stimulation did not lead to low-FSS inclined migration. After being cultured under gradient FSS stimulation for 6 days, RAW264.7 cells showed significantly higher density and ratio of TRAP-positive multinucleated osteoclasts in the low-FSS region to those in the high-FSS region. Therefore, osteoclast precursor cells may exhibit the special ability to sense FSS gradient and tend to actively migrate toward low-FSS regions, which are regulated by calcium signaling pathway.

Assessment of cortical bone microdamage following insertion of microimplants using optical coherence tomography: a preliminary study

OBJECTIVES

The study was done to evaluate the efficacy of optical coherence tomography (OCT), to detect and analyze the microdamage occurring around the microimplant immediately following its placement, and to compare the findings with micro-computed tomography (μCT) images of the samples to validate the result of the present study.

METHODS

Microimplants were inserted into bovine bone samples. Images of the samples were obtained using OCT and μCT. Visual comparisons of the images were made to evaluate whether anatomical details and microdamage induced by microimplant insertion were accurately revealed by OCT.

RESULTS

The surface of the cortical bone with its anatomical variations is visualized on the OCT images. Microdamage occurring on the surface of the cortical bone around the microimplant can be appreciated in OCT images. The resulting OCT images were compared with the μCT images. A high correlation regarding the visualization of individual microcracks was observed. The depth penetration of OCT is limited when compared to μCT.

CONCLUSIONS

OCT in the present study was able to generate high-resolution images of the microdamage occurring around the microimplant. Image quality at the surface of the cortical bone is above par when compared with μCT imaging, because of the inherent high contrast and high-resolution quality of OCT systems. Improvements in the imaging depth and development of intraoral sensors are vital for developing a real-time imaging system and integrating the system into orthodontic practice.

Effect of loaded orthodontic miniscrew implant on compressive stresses in adjacent periodontal ligament

OBJECTIVES

To describe the relationship between the proximity of miniscrew implants (MSIs) to the periodontal ligament (PDL) and stress in the PDL under different load magnitudes and different bone properties.

MATERIALS AND METHODS

Sixteen subject-specific finite element models of the region of the maxillary first molar and second premolar were developed using computed tomography images of four patients. For each patient, an MSI surface model derived from micro-computed tomography was placed at four different distances from the premolar PDL. Finite element analysis was conducted with mesial load on the MSI, increasing from 1 N to 4 N. Peak absolute compression stress (CS) was calculated at each 1 N step. Stepwise multiple regression modeling was conducted to explain compressive stress by proximity, load magnitude, and bone properties.

RESULTS

The multiple regression model explained 83.47% of the variation of CS and included all three factors: proximity, load magnitude, and bone properties. The model expected significant interaction between the bone properties and load magnitude, implying that strong bone properties could be associated with significant increases in CS at small increases in load.

CONCLUSIONS

To ensure the safety of adjacent roots, MSIs should be placed at least 1 mm from the roots. Assessment of alveolar bone properties is recommended when the use of MSI is intended, as some patients may present with strong bone properties and thereby a high risk of MSI-induced root resorption.