Process Of Tooth Movement Research Articles

Increased TGF-β1 level after cocoa administration during orthodontics tooth movement in Cavia cobaya

Background: Orthodontic tooth movement (OTM) is a process of tooth movement in the alveolar socket through a bone remodeling process. Cocoa contains caffeine as a bioactive component. The number of studies on the effects of caffeine on orthodontic tooth movement is rising. Purpose: This study aimed to determine the effect of caffeine in cocoa administration on TGF-β1 levels in the pressure side during orthodontic tooth movement. Methods: Twelve Cavia cobaya were divided into 4 groups: control group (ONC), treatment group with 2.3 mg caffeine in cocoa (OWC1), 3.45 mg dose (OWC2) and 4.6 mg dose (OWC3) (n=3). A NiTi open coil spring with light force was applied to two lower incisors tooth of Cavia cobaya. TGF-β1 level in GCF of the pressure side was analyzed using ELISA on days 0, 1, 7, and 14. Data were analyzed using the Two-way ANOVA test (p<0.05) and the LSD Post-Hoc test. Results: Research indicated improvement of TGF-β1 level from the control group with the least average followed group caffeine in cocoa 2.3 mg (OWC1), 3.45 mg (OWC2), and 4.6 mg (OWC3) (p<0.05). Conclusion: This study confirmed that caffeine in cocoa administration increase TGF-β1 level during orthodontics tooth movement on Cavia cobaya in the pressure side.

Perbedaan Jumlah Hitung Osteoblas pada Pergerakan Ortodontik Gigi Setelah Pemberian Jintan Hitam

Osteoblasts are important for orthodontic tooth movement because they influence the activity of bone formation on the tension area. The administration of natural ingredients such as black cumin is proven to increase the number of osteoblasts because it contains thymoquinone as antioxidants to accelerate the process of tooth movement. The study aims to determine the differences in osteoblast count and their effect on the orthodontic movement of teeth after oral administration of black cumin. The method used in this research is experimental laboratory in vivo with a randomized post-test only control group design using 16 male Sprague-Dawley rat samples that were devided into four groups: the control group (K) with distilled water for 7 and 14 days, also the treatment group (P) with black cumin (Nigella sativa) for 7 and 14 days Elastomeric separators were placed on the upper jaw central incisors (right central incisor) using a separator applier to provide orthodontic mechanical force conditions. Alveolar bone tissue samples were taken after treatment then the number of osteoblasts was calculated histologically. Data were anaylzed using One Way Anova Test and LSD (p<0.05). Result of this research indicated that there was an increase in the number of osteoblasts in orthodontic movement after oral administration of black cumin.

Difference in apical resorption activity during rat molar root formation in response to mechanical force.

To investigate whether there is a difference in apical resorption activity during the development of roots in response to mechanical force in vivo. Maxillary first molars (M1) from postnatal day (PN) 21 and PN35 male rats were selected as representatives of the root-developing and root-completing groups, respectively. A mechanical force of 3 cN was applied to M1 on PN21 and PN35, and the maxilla was collected on PN28 and PN42. Odontoclastogenesis and root morphology were investigated using micro-focus X-ray computed tomography, followed by immunohistochemistry and quantitative real-time polymerase chain reaction to clarify root resorption activity. Development of the mesiobuccal root (MBR) preceded the mesial root (MR). In the PN28 force application (FA) group, the dentine was bent, but the histology, including Hertwig's epithelial root sheath (HERS), was intact. No odontoclasts and resorption lacunae were found in the apical area of the MRs, and only lateral root resorption was observed. External apical root resorption (EARR) was observed in the MR of PN42 (FA) and in the MBR of both PN28 (FA) and PN42 (FA). The expression of osteopontin changed accordingly. No significant change occurred in osteoprotegerin or receptor activator of nuclear factor-κB ligand expression in the MRs of the PN28 (FA) group. Our animal model did not adequately simulate the clinical process of tooth movement in humans. Force application delayed HERS dissociation on the compression side of the developing roots, leading to inhibitory effects on cementogenesis, which resulted in decreased odontoclast differentiation and prevention of EARR.

Effect of oral environment on contemporary orthodontic materials and its clinical implications.

Contemporary orthodontics entails using advanced materials and devices, simplifying the process of tooth movement. It is well documented that orthodontic materials are subjected to various fluctuations and stresses in the oral environment, such as salivary pH, dietary habits, temperature changes, and masticatory loads. These changes reduce bonding materials' longevity, plasticize resin polymers, and reduce elastic properties. In addition, the corrosion of orthodontic appliances in the oral environment has concerned clinicians for some time. This is focused on two principal issues: whether corrosion products are absorbed into the body and cause either localized or systemic effects, and the results of corrosion on the physical properties and the clinical performance of orthodontic appliances. Recently, another major concern is the potential release of bisphenol-A from materials containing polymers such as thermoplastic aligners and resins, which is known to induce xenoestrogenicity and cytotoxicity when the tissue level exceeds the daily recommended intake. However, most of these findings are based on in vitro studies that suffer from serious drawbacks such as failure to replicate the exact oral environment and process during orthodontic treatment. Therefore, developing clinically relevant methods should be the goal of future research related to the aging of orthodontic materials. The purpose of this review is to outline the impact of the oral environment on contemporary orthodontic materials.

Effects of Hederin (Hed) on Alveolar Bone Microstructure During Tooth Movement in Rats

Purpose: To discuss effects of Hederin (Hed) to tooth movement process in rats. Materials and methods: 54 rats were divided into Model and Hed groups at 7 d, 14 d and 21 d, establishment of rat tooth movement model, the Hed and Model group injected Hed [5 mg/(kg· d)] and equal volume normal saline intraperitoneally respectively, Take the medicine regularly every night. After 14 days, 9 rats in each group were killed, BV/TV, Tb. SP and trabecular number (Tb. N) were measured by Mirco CT. Using TRAP staining and HE staining to observe osteoclasts number and pathology change. The relative protein expressions were measured by SP staining. Results: Compared with Model group, BV/TV and Tb.N were significantly down-regulation and Tb.Sp was significantly up-regulation in Hed group (P < 0.05, respectively); meanwhile, tooth movement and osteoclast number were significantly improved in Hed groups at 7 d, 14 d and 21 d (P <0.05, respectively). By SP staining, compared with Model group, ADRB2 and RANKL proteins expression were significantly enhanced at 7 d, 14 d and 21 d (P <0.05, respectively). Conclusion: Hed could promote alveolar bone resorption and increase the expression of ADRB2 and RANKL during orthodontic tooth movement.

Compressive force regulates GSK-3β in osteoclasts contributing to alveolar bone resorption during orthodontic tooth movement in vivo

BackgroundOrthodontic tooth movement mainly depends on biological and mechanical reactions in the periodontium, such as the indispensable reconstruction process of the periodontal ligament and alveolar bone. To explore whether orthodontic compressive force can induce bone resorption during orthodontic tooth movement by regulating the GSK-3β/β-catenin pathway. MethodsWe established orthodontic tooth movement models in Sprague-Dawley rats. In addition, compressive force-induced bone resorption that occurred during orthodontic tooth movement was analyzed by HE staining and micro-CT. The number and distribution of osteoclasts were observed by TRAP staining. Furthermore, pressure-induced bone resorption mediated by the GSK-3β/β-catenin signaling pathway was analyzed by immunohistochemistry. ResultsAs shown by the micro-CT results, bone parameters, such as bone mineral density (BMD), the bone volume fraction (BV/TV), and trabecular thickness (Tb. Th), were significantly decreased under orthodontic compressive force stimulation, in contrast with the dramatically increased trabecular spacing (Tb. Sp). During the process of tooth movement, the compressive force can induce bone resorption on the side with the force, which increases the expression of phosphorylated Ser-GSK-3β and activation of the β-catenin signaling pathway. Additionally, downregulation of the GSK-3β activity further caused the downregulation of bone parameters, leading to bone loss. The TRAP staining and immunohistochemistry staining results indicated that orthodontic compressive force influenced osteoclast formation and the secretion of osteoclast-related cytokines, matrix metallopeptidase 9 (MMP-9) and receptor activator of nuclear factor-κB ligands (RANKLs), which is also related to the duration of orthodontic force. ConclusionsThese results indicated that the GSK-3β inhibitor can promote osteoclast formation on the side with orthodontic compressive force. In addition, the activation of the GSK-3β/β-catenin signaling pathway contributes to bone reconstruction caused by orthodontic compressive force. Therefore, the GSK-3β/β-catenin signaling pathway can be a potential target for further clinical applications.

Force-Induced Autophagy in Periodontal Ligament Stem Cells Modulates M1 Macrophage Polarization via AKT Signaling.

Autophagy, a lysosomal degradation pathway, serves as a protective cellular mechanism in maintaining cell and tissue homeostasis under mechanical stimulation. As the mechanosensitive cells, periodontal ligament stem cells (PDLSCs) play an important role in the force-induced inflammatory bone remodeling and tooth movement process. However, whether and how autophagy in PDLSCs influences the inflammatory bone remodeling process under mechanical force stimuli is still unknown. In this study, we found that mechanical force stimuli increased the expression of the autophagy protein LC3, the number of M1 macrophages and osteoclasts, as well as the ratio of M1/M2 macrophages in the compression side of the periodontal ligament in vivo. These biological changes induced by mechanical force were repressed by the application of an autophagy inhibitor 3-methyladenine. Moreover, autophagy was activated in the force-loaded PDLSCs, and force-stimulated PDLSC autophagy further induced M1 macrophage polarization in vitro. The macrophage polarization could be partially blocked by the administration of autophagy inhibitor 3-methyladenine or enhanced by the administration of autophagy activator rapamycin in PDLSCs. Mechanistically, force-induced PDLSC autophagy promoted M1 macrophage polarization via the inhibition of the AKT signaling pathway. These data suggest a novel mechanism that force-stimulated PDLSC autophagy steers macrophages into the M1 phenotype via the AKT signaling pathway, which contributes to the inflammatory bone remodeling and tooth movement process.

Analysis of lncRNAs-miRNAs-mRNAs networks in periodontal ligament stem cells under mechanical force.

Our study aims to analyze the expression profiles of long non-coding RNAs (lncRNAs) and investigate the potential regulatory networks among lncRNAs, microRNAs (miRNAs), and mRNAs in periodontal ligament stem cells (PDLSCs) under mechanical force (MF). PDLSCs were isolated from human periodontal ligament tissues and identified by flow cytometry analysis. Multidirectional differentiation potential of PDLSCs was obtained by osteogenic and adipogenic induction. High-throughput RNA sequencing was used to identify the expression patterns of lncRNAs and mRNAs in PDLSCs under MF. MF-responsive miRNAs were obtained from the previous microarray data. LncRNAs-miRNAs-mRNAs networks were constructed by Cytoscape. PDLSCs cultured from the periodontal ligament tissues were positive for STRO-1, CD146 and negative for CD45, CD34. Alizarin red staining and Oil Red O staining showed that PDLSCs had the ability of osteogenic and adipogenic differentiation. Then, a total of 1,339 and 1,426 differentially expressed lncRNAs and mRNAs were identified, respectively, in PDLSCs under MF. Based on the previous miRNA microarray analysis, the potential interaction networks of lncRNAs-miRNAs-mRNAs were constructed. It was found that lncRNAs and mRNAs could competitively interact with the same miRNA. LncRNAs-miRNAs-mRNAs networks were involved in PDLSCs under MF, which might provide a novel mechanism in the regulation of clinical orthodontic tooth movement process.

Mechanical load-induced H2S production by periodontal ligament stem cells activates M1 macrophages to promote bone remodeling and tooth movement via STAT1

BackgroundTooth movement is a unique bone remodeling process induced by mechanical stimulation. Macrophages are important in mediating inflammatory processes during mechanical load-induced tooth movement. However, how macrophages are regulated under mechanical stimulation remains unclear. Mesenchymal stem cells (MSCs) can modulate macrophage polarization during bone remodeling. Hydrogen sulfide (H2S) can be produced by MSCs and have been linked to bone homeostasis. Therefore, this study aimed to investigate whether H2S contributed to periodontal ligament stem cell (PDLSC)-regulated macrophage polarization and bone remodeling under mechanical stimulation.MethodsAn experimental mechanical load-induced tooth movement animal model was established. Changes in cystathionine-β-synthase (CBS), markers of M1/M2 macrophages, tooth movement distance, and the number of osteoclasts were examined. The conditioned medium of PDLSCs with or without mechanical loading was utilized to treat THP-1 derived macrophages for 24 h to further investigate the effect of PDLSCs on macrophage polarization. Different treatments with H2S donor, CBS inhibitor, or the inhibitor of STAT1 were used to investigate the related mechanism. Markers of M1/M2 polarization and STAT1 pathway expression were evaluated in macrophages.ResultsMechanical load promoted tooth movement and increased the number of M1-like macrophages, M1-associated pro-inflammatory cytokines, and the expression of CBS on the compression side of the periodontal ligament. The injection of CBS inhibitor or H2S donor could further repress or increase the number of M1-like macrophages, tartrate-resistant acid phosphatase-positive osteoclasts and the distance of tooth movement. Mechanistically, load-induced PDLSCs enhanced H2S production, which increased the expression of M1-associated cytokines in macrophages. These effects could be blocked by the administration of CBS inhibitor. Moreover, load-induced H2S steered M1 macrophage polarization via the STAT1 signaling pathway.ConclusionsThese data suggest a novel mechanism indicating that mechanical load-stimulated PDLSCs produce H2S to polarize macrophages toward the M1 phenotype via the STAT1 signaling pathway, which contributes to bone remodeling and tooth movement process. These results provide new insights into the role of PDLSCs in regulating macrophage polarization and mediating bone remodeling under mechanical stimulation, and indicate that appropriate H2S supplementation may accelerate tooth movement.

THE REVOLUTION OF CLEAR ALIGNERS IN MODERN ORTHODONTICS

The evolution of clear aligners has significantly transformed orthodontics, providing an aesthetic and comfortable alternative to traditional fixed braces. Since the introduction of these devices in the 1990s, continuous technological advancements have expanded aligners' ability to address an increasing variety of orthodontic cases. Initially, aligners were limited to minor dental corrections due to restricted biomechanical control. However, advances in 3D modeling, 3D printing, intraoral scanning, and artificial intelligence have enabled greater personalization, enhancing the precision and effectiveness of treatments. Recent algorithm developments allow orthodontists to simulate the entire tooth movement process, adjusting each treatment stage. This increases control and reduces the overall treatment time. Flexible and durable materials have also improved aligners' ability to perform complex movements, which previously required fixed braces. Additionally, technologies like augmented reality provide patients with a preview of the final result, fostering greater adherence to treatment. The growing popularity of clear aligners requires orthodontists to acquire skills in digital tools and detailed planning. This new digital approach transforms clinical practice and makes treatment more accessible, driving acceptance of these devices among adults seeking less invasive options. Although challenges remain in expanding the predictability of certain movements, ongoing technological progress continues to broaden aligners' applicability, benefiting both patients and professionals and setting a new standard for personalization and efficiency in orthodontics.

Effect of Vitamin C on Tooth Movement in Terms of Periodontal Ligament Space in Guinea Pigs

Periodontal ligaments are one of the supporting tissues of teeth that undergo remodeling during the tooth movement process. Vitamin C deficiency inhibits the regeneration of collagen fibers, which are important in tissue remodeling that affects the widening of the periodontal ligament space during the process of tooth movement. The widening of periodontal ligament space can be seen by taking radiographic photos. The purpose of this study was to determine the width of the periodontal ligament space of guinea pigs by administering vitamin C, without vitamin C, and the differences between the two groups. Those samples were grouped into four groups with observation times of 1, 4, 7, and 10 days, and each group consisted of the control group and vitamin C group. Those samples were paired with orthodontic separator rubber. After the specified time was completed, periapical radiographs were taken, and the width of the periodontal ligament space was measured by using Image J software. The mean width of the periodontal ligament space in the vitamin C group was smaller than the control group. Based on this study, it can be concluded that vitamin C has an effect on reducing periodontal ligament space in the process of tooth movement.
 
 Key words: periodontal ligament space, vitamin C, tooth movement, remodeling

The Effects of Drug Intake by Patients on Orthodontic Tooth Movement

Paradental tissue remodeling forms the central theme of orthodontic tooth movement, and optimal responses are achieved with judicious force application. In some patients, the use of medications for various ailments may alter paradental tissue remodeling, either augmenting or decelerating the pace of tooth movement. Most of the reviews carried out have concentrated on nonsteroidal anti-inflammatory drugs and their effect on reducing the velocity of tooth movement. This article reviews data on the effects of systemic diseases on the tooth movement process, with a special emphasis on specific medications used by patients. It is intended to provide a database for referral by orthodontists and other medical specialists, to provide information to control the main and side effects of the drugs on tooth movement. It also emphasizes the importance for orthodontists to obtain a complete list of all the medications being taken by every patient, both before and during the course of orthodontic treatment. Paradental tissue remodeling forms the central theme of orthodontic tooth movement, and optimal responses are achieved with judicious force application. In some patients, the use of medications for various ailments may alter paradental tissue remodeling, either augmenting or decelerating the pace of tooth movement. Most of the reviews carried out have concentrated on nonsteroidal anti-inflammatory drugs and their effect on reducing the velocity of tooth movement. This article reviews data on the effects of systemic diseases on the tooth movement process, with a special emphasis on specific medications used by patients. It is intended to provide a database for referral by orthodontists and other medical specialists, to provide information to control the main and side effects of the drugs on tooth movement. It also emphasizes the importance for orthodontists to obtain a complete list of all the medications being taken by every patient, both before and during the course of orthodontic treatment.

The use of gene therapy vs. corticotomy surgery in accelerating orthodontic tooth movement

Alveolar corticotomy surgery is an adjunctive therapy for reducing orthodontic treatment duration. The activation pathways of bone resorption involved in the tooth movement (TM) process are directly linked to the receptor activator of the nuclear factor-kB ligand (RANKL). Whether similar molecular pathways through RANKL, are shared by the acceleratory TM process (corticotomy-induced or not), sustained acceleration would therefore be expected with transgenic overexpression of this factor. We hypothesize that maintaining transgenic overexpression of RANKL will accelerate TM under force over time rather than at the beginning of therapy only; this contrasts with the corticotomy procedure. We transfected the pcDNA3.1(+)-mRANKL transgene in vitro into NIH3T3 cells, then evaluated by PCR, Western blot and ex vivo resorption assay. Quantification of RANKL immunofluorescence, fluorescence-based tartrate-resistant acid phosphatase+ (TRAP+) osteoclast counts and histological analyses of the bone resorption area were performed and clinically correlated after a 32-day in vivo experiment comparing corticotomy and gene therapy. In vitro experiments resulted in increased level of RANKL protein (46%, p<0.05) and greater mineral resorption (39%, p<0.05) compared to the controls. In vivo results showed increased RANKL immunoexpression for both corticotomy (twofold) and transfection groups (threefold) after 10 days. After 32 days, a similar result was obtained for the transfected group but not for the surgery group. These data correlate with the clinical effect of decelerating TM in the surgery group. Selective gene therapy with RANKL has been experimentally tested as an alternative method to corticotomy surgery, showing higher effectiveness than surgical methods used for acceleratory purposes in orthodontics.

The effect of drugs on orthodontic tooth movement

Molecules produced in various diseased tissues, or drugs and nutrients consumed regularly by patients, can reach the mechanically stressed paradental tissues through the circulation, and interact with local target cells. The combined effect of mechanical forces and one or more of these agents may be inhibitory, additive or synergistic. The objective of this review is to outline the mechanisms of action and effects of some commonly used drugs on tissue remodeling and orthodontic tooth movement. All the existing published literature on the effects of various drugs that are prescribed by orthodontists, which are consumed by patients for systemic diseases and those that are known to promote and retard the tooth movement process was obtained and subjected to thorough review process. All the drugs reviewed have therapeutic effects, as well as side effects, that may influence the cells targeted by orthodontic forces. Therefore, it is imperative that the orthodontist pays close attention to the drug consumption history of each and every patient, before and during the course of orthodontic treatment. When the use of drugs is revealed, their effects and side effects on tissue systems should be explored, to determine their potential influence on the outcome of mechanotherapy. Drug-consumption history must be an integral part of every orthodontic diagnosis and treatment plan.

The effect of functional occlusal forces on orthodontic tooth movement and tissue recovery in rats

The influence of physiologic occlusal forces on tissue response to orthodontic tooth movement and its subsequent recovery was investigated in rats. The mandibular incisors were subjected to tipping and intrusive loads for 2 weeks. In 27 animals, the teeth remained in occlusion, while the incisors were shortened out of occlusion in 29. In each group, some rats were killed at the end of the tooth movement process, and the rest were kept alive for a 13-week recovery period. The subgroups were matched with corresponding controls. Tooth intrusion and eruption were monitored throughout the experiment; then histomorphometric and histopathologic evaluations were performed on the incisors and their periodontal tissues. Tooth movement was barely affected by the functional forces. However, immediately upon 2-week load application, damage to the pulp was more extensive in the occluding teeth; this might be due to the combined intrusive vectors of functional and mechanical loads. The effect of the physiologic function was expressed primarily during the recovery period, in which the eruptive function and distorted periodontal ligament space returned to normal significantly faster in the occluding teeth. This was also true for the healing of dental and periodontal lesions. The incidence of tooth resorption was also reduced. Normal occlusal function is imperative for rapid reconstitution of the damage caused by orthodontic forces. (Am J Orthod Dentofacial Orthop 2002;121:620-8)

A comparison between friction and frictionless mechanics with a new typodont simulation system

This study was designed to explore the differences between friction and frictionless mechanics for maxillary canine retraction with the use of a new typodont simulation system, the Calorific machine system. The unit was designed to observe the whole process of tooth movement and is composed of 3 parts: a temperature regulating system, electrothermodynamic teeth, and an artificial alveolar bone component. The efficiency of maxillary canine retraction was compared with the sliding mechanics (along a.016 ×.022-in stainless steel labial arch and nickel-titanium closed coil spring) and a canine retraction spring. The patterns of tooth movement obtained with both of these mechanics were measured 5 times each. Friction mechanics were superior to frictionless mechanics in terms of rotational control and dimensional maintenance of the arch (P <.0001); frictionless mechanics were shown to be more effective at reducing tipping and extrusion (P <.0001). However, the observed differences between the 2 methods were relatively small in terms of their clinical significance, and no differences were found in anchorage control (P =.2078). In conclusion, this study indicated that friction and frictionless mechanics perform similarly. (Am J Orthod Dentofacial Orthop 2001;119:292-9)

NSAID impairment of orthodontic tooth movement.

To evaluate the impairment of orthodontic tooth movement caused by nonsteroidal antiinflammatory drugs (NSAIDs). Biomedical literature accessed through MEDLINE (1966-January 2000), EMBASE (1980-January 2000), and International Pharmaceutical Abstracts (1970-January 2000). Key search terms included NSAIDs, orthodontics, and tooth movement. Orthodontic dentistry applies mechanical force to generate tooth movement. Since prostaglandins are mediators of tooth movement, it is reasonable to expect that prostaglandin inhibitors, such as NSAIDs, inhibit or delay tooth movement. An evaluation of studies measuring the extent of NSAID impairment on tooth movement was undertaken. Results from animal studies have shown that NSAIDs can impair the tooth movement process. Until long-term human data are obtained, acetaminophen remains an appropriate alternative to NSAIDs for treating orthodontic-associated pain.

Comparative histologic study of heavy intermittent and light continuous forces

The influence of physiologic occlusal forces on tissue response to orthodontic tooth movement and its subsequent recovery was investigated in rats. The mandibular incisors were subjected to tipping and intrusive loads for 2 weeks. In 27 animals, the teeth remained in occlusion, while the incisors were shortened out of occlusion in 29. In each group, some rats were killed at the end of the tooth movement process, and the rest were kept alive for a 13-week recovery period. The subgroups were matched with corresponding controls. Tooth intrusion and eruption were monitored throughout the experiment; then histomorphometric and histopathologic evaluations were performed on the incisors and their periodontal tissues. Tooth movement was barely affected by the functional forces. However, immediately upon 2-week load application, damage to the pulp was more extensive in the occluding teeth; this might be due to the combined intrusive vectors of functional and mechanical loads. The effect of the physiologic function was expressed primarily during the recovery period, in which the eruptive function and distorted periodontal ligament space returned to normal significantly faster in the occluding teeth. This was also true for the healing of dental and periodontal lesions. The incidence of tooth resorption was also reduced. Normal occlusal function is imperative for rapid reconstitution of the damage caused by orthodontic forces. (Am J Orthod Dentofacial Orthop 2002;121:620-8)

Certain limitations in the use of appliances in orthodontia

I N the following paper and clinic it is purposed to consider ort.horlont ic appliances,-not in any exhaustive way, but rather from the viewpoint of some of the limitations which ought to be borne in mind in daily clinical practice. In discussing the bad features and limitations of appliances, onc must ]'C'member that appliances are mechanical devices for exerting pressure on 111<)1posed teeth, thereby influencing cell metabolism with a view of causing the teeth to assume their correct functional relationship. Dr. John V. Mershon defines functional relationship in this wav. 'While we are moving the teeth from their positions of malocclusion to normal fl11J('tional relations, the tissues surrounding and supporting the teeth will so adapt and adjust themsel ves through an interaction of forces, that the proper equil ihrium between teeth and tissues is maintained during the whole process of tooth movement. Going further, he says: Appliances are effective in proportion as they apply force in the direction of normal growth, and in so rlointr, do not interfere with the function of any of the tissues associated with the teeth. or with the teeth themselves collectively or individually; each tooth lwing free to functionate normally. An appliance in conformity with absolute harmony between normal grO\vth and the stimulation of the supporting tissues would be ideal; but as yet, there is no ideal appliance. All types of appliances thus far devizcd have some admittedly bad features, and successful orthodontia is not altogether due to the appliances employed. Orthodontia depending entirely on the appliances often comes to grief in its ultimate results. In the past orthodontia consisted in aligning irregular teeth. Now, we believe we are treating oral deformities, partially or wholly interfering with normal function. In the past, the object in view was to push or pull teeth into position in the quickest wa~-,-l'cgal'Cliess of the results. Now, we understand that no mechanical device can make an absolutely perfect normal occlusion. The individual size and shape of the teeth and the gradual growth of the associated oral structures plav all important part. No appliance working alone can accomplish the ultimate good sought. , proper appliance should be only a stimulus to supporting tissues of the tooth by pressure applied to it. It should work in conjunction with, and at the same time in opposition to the natural stimulus of growth going' on in these tissues, The dental arch as a part of the individual grows with the individual,