Microsphere controlled drug delivery for local control of tooth movement

Engineering approaches to manipulate osteoclast behavior for bone regeneration

Extensive research has delved into the multifaceted roles of osteoclasts beyond their traditional function in bone resorption in recent years, uncovering their significant influence on bone formation. This shift in understanding has spurred investigations into engineering strategies aimed at leveraging osteoclasts to not only inhibit bone resorption but also facilitate bone regeneration. This review seeks to comprehensively examine the mechanisms by which osteoclasts impact bone metabolism. Additionally, it explores various engineering methodologies, including the modification of bioactive material properties, localized drug delivery, and the introduction of exogenous cells, assessing their potential and mechanisms in aiding bone repair by targeting osteoclasts. Finally, the review proposes current limitations and future routes for manipulating osteoclasts through biological and material cues to facilitate bone repair.

Connecting the dots towards precision orthodontics

Precision orthodontics entails the use of personalized clinical, biological, social and environmental knowledge of each patient for deep individualized clinical phenotyping and diagnosis combined with the delivery of care using advanced customized devices, technologies and biologics. From its historical origins as a mechanotherapy and materials driven profession, the most recent advances in orthodontics in the past three decades have been propelled by technological innovations including volumetric and surface 3D imaging and printing, advances in software that facilitate the derivation of diagnostic details, enhanced personalization of treatment plans and fabrication of custom appliances. Still, the use of these diagnostic and therapeutic technologies is largely phenotype driven, focusing mainly on facial/skeletal morphology and tooth positions. Future advances in orthodontics will involve comprehensive understanding of an individual's biology through omics, a field of biology that involves large-scale rapid analyses of DNA, mRNA, proteins and other biological regulators from a cell, tissue or organism. Such understanding will define individual biological attributes that will impact diagnosis, treatment decisions, risk assessment and prognostics of therapy. Equally important are the advances in artificial intelligence (AI) and machine learning, and its applications in orthodontics. AI is already being used to perform validation of approaches for diagnostic purposes such as landmark identification, cephalometric tracings, diagnosis of pathologies and facial phenotyping from radiographs and/or photographs. Other areas for future discoveries and utilization of AI will include clinical decision support, precision orthodontics, payer decisions and risk prediction. The synergies between deep 3D phenotyping and advances in materials, omics and AI will propel the technological and omics era towards achieving the goal of delivering optimized and predictable precision orthodontics.

Comparative Efficacy of Traditional Corticotomy and Flapless Piezotomy in Facilitating Orthodontic Tooth Movement: A Systematic Review and Meta-Analysis

Background and Objectives: This study aimed to perform a meta-analysis comparing the effects of corticotomy and flapless piezocision on accelerated tooth movement. Materials and Methods: A comprehensive search using a combination of controlled vocabulary (MeSH) and free-text terms was undertaken by two reviewers to identify published systematic reviews. Three major electronic databases (Medline via PubMed, Cochrane Database, and Embase) were searched up to 2 June 2023. Results: The results of the meta-analysis showed that the pooled standardized mean difference values of accumulative movement distances for flapless piezocision were 1.43 (95% CI, 0.38 to 2.48; p < 0.01), 1.09 (95% CI, -0.08 to 2.26; p = 0.07), and 0.73 (95% CI, -0.58 to 4.02; p = 0.14). The results of the meta-analysis demonstrated that the pooled SMD values of accumulative movement distances for the corticotomy were 2.76 (95% CI, 0.18 to 5.34; p = 0.04), 1.43 (95% CI, -1.10 to 3.96; p = 0.27), and 4.78 (95% CI, -4.54 to 14.10; p = 0.32). Although the test for overall effectiveness was significant for piezocision and corticotomy, there were no significant differences between piezocision and corticotomy. Conclusions: The study determined that both conventional corticotomy and flapless piezosurgery are effective as adjuncts to orthodontic treatment. Moreover, no significant difference was observed in the short-term effectiveness of canine retraction acceleration between conventional corticotomy and flapless piezocision. While piezocision may be a favorable option for orthodontic treatment, corticotomy can be considered in cases requiring additional procedures such as bone grafting.

Functional Biomaterials for Local Control of Orthodontic Tooth Movement

Orthodontic tooth movement (OTM) occurs with the application of a controlled mechanical force and results in coordinated tissue resorption and formation in the surrounding bone and periodontal ligament. The turnover processes of the periodontal and bone tissue are associated with specific signaling factors, such as Receptor Activator of Nuclear factor Kappa-β Ligand (RANKL), osteoprotegerin, runt-related transcription factor 2 (RUNX2), etc., which can be regulated by different biomaterials, promoting or inhibiting bone remodeling during OTM. Different bone substitutes or bone regeneration materials have also been applied to repair alveolar bone defects followed by orthodontic treatment. Those bioengineered bone graft materials also change the local environment that may or may not affect OTM. This article aims to review functional biomaterials that were applied locally to accelerate OTM for a shorter duration of orthodontic treatment or impede OTM for retention purposes, as well as various alveolar bone graft materials which may affect OTM. This review article summarizes various types of biomaterials that can be locally applied to affect the process of OTM, along with their potential mechanisms of action and side effects. The functionalization of biomaterials can improve the solubility or intake of biomolecules, leading to better outcomes in terms of increasing or decreasing the speed of OTM. The ideal timing for initiating OTM is generally considered to be 8 weeks post-grafting. However, more evidence is needed from human studies to fully understand the effects of these biomaterials, including any potential adverse effects.

A Comprehensive Review on Drug Therapies and Nanomaterials used in Orthodontic Treatment

Orthodontic treatment typically requires an extended duration of 1-2 years to complete the treatment. Accelerating the rate of tooth movement during orthodontic treatment is essential for shortening the overall treatment duration. After the completion of orthodontic treatment, a prominent concern arises in the form of orthodontic relapse, where the teeth tend to revert to their original positions. This issue affects approximately 60% of the global population, underscoring the importance of implementing effective measures to address orthodontic relapse. An approach in this regard involves the targeted administration of herbal and synthetic drugs applied directly to the specific area of interest to facilitate tooth movement and prevent orthodontic relapse. Apart from this, researchers are investigating the feasibility of utilizing different types of nanoparticles to improve the process of orthodontic tooth movement. In recent years, there has been a noticeable increase in the number of studies examining the effects of various drugs on orthodontics. However, the currently available literature does not provide significant evidence relating to orthodontic tooth movement. In this review, the authors provide valuable information about the drugs and nanomaterials that are capable of further enhancing the rate of orthodontic tooth movement and reducing the risk of orthodontic relapse. However, a notable hurdle remains, i.e., there is no marketed formulation available that can enhance orthodontic tooth movement and reduce treatment time. Therefore, researchers should try herbal-synthetic approaches to achieve a synergistic effect that can enhance orthodontic tooth movement. In this nutshell, there is an urgent need to develop a non-invasive, patient-compliant, and cost-effective formulation that will provide quality treatment and ultimately reduce the treatment time. Another critical issue is orthodontic relapse, which can be addressed by employing drugs that slow down osteoclastogenesis, thereby preventing tooth movement after treatment. Nevertheless, extensive research is still required to overcome this challenge in the future.

Control of Orthodontic Tooth Movement by Nitric Oxide Releasing Nanoparticles in Sprague-Dawley Rats

Orthodontic treatment commonly requires the need to prevent movement of some teeth while maximizing movement of other teeth. This study aimed to investigate the influence of locally injected nitric oxide (NO) releasing nanoparticles on orthodontic tooth movement in rats.

MATERIALS AND METHODS

Experimental tooth movement was achieved with nickel-titanium alloy springs ligated between the maxillary first molar and ipsilateral incisor. 2.2 mg/kg of silica nanoparticles containing S-nitrosothiol groups were injected into the mucosa just mesial to 1^st molar teeth immediately prior to orthodontic appliance activation. NO release from nanoparticles was measured in vitro by chemiluminescence. Tooth movement was measured using polyvinyl siloxane impressions. Bones were analyzed by microcomputed tomography. Local tissue was assessed by histomorphometry.

RESULTS

Nanoparticles released a burst of NO within the first hours at approximately 10 ppb/mg particles that diminished by 10 × to approximately 1 ppb/mg particles over the next 1-4 days, and then diminished again by tenfold from day 4 to day 7, at which point it was no longer measurable. Molar but not incisor tooth movement was inhibited over 50% by injection of the NO releasing nanoparticles. Inhibition of molar tooth movement occurred only during active NO release from nanoparticles, which lasted for approximately 1 week. Molar tooth movement returned to control levels of tooth movement after end of NO release. Alveolar and long bones were not impacted by injection of the NO releasing nanoparticles, and serum cyclic guanosine monophosphate (cGMP) levels were not increased in animals that received the NO releasing nanoparticles. Root resorption was decreased and periodontal blood vessel numbers were increased in animals with appliances that were injected with the NO releasing nanoparticles as compared to animals with appliances that did not receive injections with the nanoparticles.

CONCLUSION

Nitric oxide (NO) release from S-nitrosothiol containing nanoparticles inhibits movement of teeth adjacent to the site of nanoparticle injection for 1 week. Additional studies are needed to establish biologic mechanisms, optimize efficacy and increase longevity of this orthodontic anchorage effect.

Effect of locally delivered protein complex-loaded nanoparticles on bone remodelling of atrophic alveolar ridge in beagles

OBJECTIVE

To investigate the effect of local injection of mineralized hybrid nanoparticles loading dentin matrix protein-1 (DMP-1) and matrix metalloproteinase-13 (MMP-13) complex (P-NPs) on the bone remodelling on atrophic alveolar ridges (AAR) ahead of orthodontic tooth movement (OTM).

SETTINGS AND SAMPLE POPULATION

Four beagles were randomly allocated into Group C (OTM only) and Group NP (OTM with P-NPs injection). Experimental model of AAR was prepared in 8 mandibular quadrants after extraction of the third premolars (n = 4 per Group).

MATERIALS AND METHODS

Reciprocal traction of the second and fourth premolars was performed towards AAR for 8 weeks. P-NPs were prepared by loading recombinant DMP-1 and MMP-13 complex into calcium carbonate (CaCO3 )-mineralized hybrid nanoparticles and injected at 0, 3 and 6 weeks. The rate of OTM and the bone remodelling characteristics were compared between Groups using fluorescent microscopic analysis and microstructural histomorphometric analysis.

RESULTS

Group NP revealed higher bone volume fraction and higher trabecular ratio with lower bone mineral density than Group C on AAR area. Meanwhile, the root movement towards AAR was facilitated in Group NP representing more bodily movement than Group C.

CONCLUSION

Non-invasive intervention of P-NPs injection suggested a clinical potential to facilitate translational movement into the AAR with sustaining woven bone-like microstructural environment.

Immune Changes Induced by Orthodontic Forces: A Critical Review

Orthodontic tooth movement (OTM) is generated by a mechanical force that induces an aseptic inflammatory response in the periodontal tissues and a subsequent coordinated process of bone resorption and apposition. In this review, we critically summarize the current knowledge on the immune processes involved in OTM inflammation and provide a novel insight into the relationship between classical inflammation and clinical OTM phases. We found that most studies focused on the acute inflammatory process, which ignites the initial alveolar bone resorption. However, the exact mechanisms and the immune reactions involved in the following OTM phases remain obscure. Recent studies highlight the existence of a typical innate response of resident and extravasated immune cells, including granulocytes and natural killer (NK), dendritic, and γδT cells. Based on few available studies, we shed light on an active, albeit incomplete, process of resolution in the lag phase, supported by continuously elevated ratios of M1/M2 macrophage and receptor activator of nuclear factor κB ligand/osteoprotegerin ratio. This partial resolution enables tissue formation and creates the appropriate environment for a transition between the innate and adaptive arms of the immune system, essential for the tissue's return to homeostasis. Nevertheless, as the mechanical trigger persists, the resolution turns into a low-grade chronic inflammation, which underlies the next, acceleration/linear OTM phase. In this stage, the acute inflammation dampens, and a simultaneous process of bone resorption and formation occurs, driven by B and T cells of the adaptive immune arm. Excessive orthodontic forces or tooth movement in periodontally affected inflamed tissues may hamper resolution, leading to "maladaptive homeostasis" and tissue loss due to uncoupled bone resorption and formation. The review ends with a brief description of the translational studies on OTM immunomodulation. Future studies are necessary for further uncovering cellular and molecular immune targets and developing novel strategies for controlling OTM by local and sustained tuning of the inflammatory process.

Does local injection of reveromycin A inhibit tooth movement without causing systemic side effects?

OBJECTIVE

To determine the feasibility of local inhibition of osteoclast activity and control of tooth movement with local intraoral reveromycin A (RMA) injection in model mice for experimental tooth movement.

MATERIALS AND METHODS

Eight-week-old wild-type mice (n = 6 per group) were divided into four groups consisting of two non-RMA groups that received normal saline for 14 (14-day non-RMA group) or 21 consecutive days (21-day non-RMA group) and 2 RMA groups that received RMA (1.0 mg/kg of weight) for 14 (14-day RMA group) or 21 consecutive days (21-day RMA group). RMA was injected locally into the buccal mucosa of the left first maxillary molar twice daily starting 3 days before placement of the 10-gf Ni-Ti closed coil spring. Tooth movement distance was analysed using micro-computed tomography. The effects on surrounding alveolar bone were evaluated by measuring the ratio of bone surface area to tissue surface area with haematoxylin-eosin-stained sections and counting the number of osteoclasts in periodontal tissue with TRAP-stained sections. Blood tests were performed and bone volume and trabecular separation at the tibial neck were measured to analyse systemic side effects.

RESULTS

Local RMA injection inhibited tooth movement by 40.6 per cent, promoted alveolar bone volume maintenance by 37.4 per cent, and inhibited osteoclast activity around the tooth root at 21 days by 40.8 per cent. Systemic effects on osteoclasts or osteoblasts were not observed.

CONCLUSION

Local injection of RMA enabled control of tooth movement without systemic side effects in a mouse model.

Injectable RANKL sustained release formulations to accelerate orthodontic tooth movement

BACKGROUND

Accelerating orthodontic tooth movement (OTM) through biologically effective methods, such as increasing osteoclast-mediated alveolar resorption, could effectively shorten treatment time.

OBJECTIVE

To evaluate an injectable formulation containing receptor activator of nuclear factor kappa-B ligand (RANKL) on the OTM.

MATERIALS AND METHODS

We fabricated a RANKL formulation from 100 µl of 100 µg/ml RANKL adsorbed on 10 mg of poly(lactic acid-co-glycolic acid) microspheres embedded in a 10 wt% aqueous hydroxyethyl cellulose carrier gel. We characterized these formulations for the rate of RANKL release, and then tested for bioactivity using in vitro cell culture. In vivo OTM studies were conducted using 15 week old male Wistar rats for 14 days. We injected the RANKL formulations palatal to the left maxillary first molar and accomplished OTM with a nickel-titanium (NiTi) coil spring applying 5-8 g force. Control groups involved the application of NiTi coil spring with and without placebo formulation. The outcome measure included the distance of tooth movement, bone volume fraction, tissue density, and root volume determined with micro-computed tomography. We determined the amount of osteoclast activity using tartrate-resistant acid phosphatase (TRAP) staining.

RESULTS

These formulations were able to sustain the release of RANKL for more than 30 days, and the released RANKL showed a positive effect on mice osteoclast precursor cells (RAW 264.7). Reported injectable RANKL formulations were effective in accelerating OTM compared with other control groups, with 129.2 per cent more tooth movement than no formulation and 71.8 per cent more than placebo formulation, corresponding with a significant increase in the amount of TRAP activity. We did not observe any significant differences in root resorption between the groups.

CONCLUSION

Our study shows a significant increase in OTM with injectable formulations containing RANKL.

Impact of pharmacologic inhibition of tooth movement on periodontal and tooth root tissues during orthodontic force application

OBJECTIVE

The goal of this study was to investigate potential negative sequelae of orthodontic force application ±delivery of an osteoclast inhibitor, recombinant osteoprotegerin protein (OPG-Fc), on periodontal tissues.

SETTING AND SAMPLE POPULATION

Sprague Dawley rats from a commercial supplier were investigated in a laboratory setting.

MATERIALS AND METHODS

Rats were randomly divided into four groups (n = 7 each): one group with no orthodontic appliances and injected once prior to the experimental period with empty polymer microspheres, one group with orthodontic appliances and injected once with empty microspheres, one group with orthodontic appliances and injected once with polymer microspheres containing 1 mg/kg of OPG-Fc, and one group with orthodontic appliances and injected with non-encapsulated 5 mg/kg of OPG-Fc every 3 days during the experimental period. The animals were euthanized after 28 days of tooth movement for histomorphometric analyses.

RESULTS

Root resorption, PDL area and widths were similar in animals without appliances and animals with appliances plus high-dose OPG-Fc. PDL blood vessels were compressed and decreased in number in all animals that received orthodontic appliances, regardless of OPG-Fc. Hyalinization was significantly increased only in animals with orthodontic appliances plus multiple injections of 5 mg/kg non-encapsulated OPG-Fc when compared to animals without appliances.

CONCLUSIONS

Results of this study indicate that while pharmacological modulation of tooth movement through osteoclast inhibition is feasible when delivered in a locally controlled low-dose manner, high-dose levels that completely prevent tooth movement through bone may decrease local blood flow and increase the incidence of hyalinization.