Maxillary fixed expansion appliance

Abstract

The application belongs to the technical field of oral medicine, and specifically relates to a maxillary fixed expansion appliance, which comprises a spiral expander, a plastic base, a connecting rod, a retaining device and a dental retraction hook. The spiral expander is located in the center of the appliance, the plastic base is divided into two parts in the center and covers the hard palate of the maxilla, the retaining device is composed of a continuous band ring casted by the lower molar or premolar and a single band ring casted by the first molar, and the dental retraction hook is located in the plastic base and used for retracting and lowering the maxillary first molar with buccal inclination after expansion. The appliance has a wide clinical application range and is suitable for patients with mild to moderate transverse maxillary hypoplasia and maxillary posterior tooth buccal inclination compensation. The appliance can achieve good skeletal expansion effect for patients in the mixed dentition period or early permanent dentition period and reduce excessive tooth buccal inclination and movement in the maxillary rapid expansion patients.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of oral medicine, and particularly relates to a maxillary fixed expansion appliance. BACKGROUND

[0002] Malocclusion is one of the common oral diseases in adolescents, and its etiology involves the complex interaction of genetic and environmental factors. In particular, during the mixed dentition stage, children are at the peak of growth and development, and the replacement of deciduous and permanent teeth makes the oral environment more complex, and the incidence of various malocclusions is as high as 79.4%. Among the three-dimensional morphological abnormalities of malocclusion, maxillary transverse deficiency (MTD) is of great concern due to its high incidence and potential harm. Shen et al. used the revised Andrews Element III analysis method to investigate and found that the prevalence of MTD in Chinese children and adolescents was 31.1%, and the clinical manifestations were complex, with narrow maxillary arch and / or wide mandibular arch, which could manifest as posterior crossbite, maxillary arch crowding, wide buccal corridor, excessive buccal inclination of maxillary molars, and excessive lingual inclination of mandibular molars, etc. See reference: Shen, J. et al. Transverse dentoalveolar development in Chinese children and adolescents: A cross-sectional study using revised Andrews’ Element III analysis. American Journal of Orthodontics and Dentofacial Orthopedics 167, 144-153 (2025). Insufficient dental arch width not only affects masticatory efficiency and occlusal stability, but also may cause temporomandibular joint disorder due to compensatory tongue protrusion, affecting craniofacial development and facial aesthetics, and even causing sleep-disordered breathing by limiting the upper airway space, endangering the development and physical and mental health of children. Therefore, early intervention for insufficient dental arch width in adolescents has significant clinical significance.

[0003] Rapid maxillary expansion (RME) is the main clinical strategy for treating transverse maxillary deficiency. It can achieve physiological expansion of the dental arch width through mechanical force or functional stimulation. According to the mechanism and biological effect, RME can be divided into three types: orthodontic expansion, orthopedic expansion and passive expansion. Orthodontic expansion is mainly through the orthodontic appliance to exert force on the teeth, so that the teeth move in the alveolar bone, and the teeth move buccally to compensate for the increase in dental arch width. Orthopedic expansion is to achieve the reconstruction of the basal bone structure through the expansion of the midpalatal suture. Passive expansion refers to the phenomenon of passive widening of the dental arch after the use of functional appliances to reshape the strength of the oral muscles. For children before the peak of growth and development, rapid maxillary expansion (RME) can produce more bone expansion effect, which is beneficial to the overall movement of the posterior teeth. Slow expansion is suitable for patients who have passed the peak of growth and development, with less damage to the palate and less recurrence, which is conducive to the stability after treatment. The existing rapid maxillary expansion commonly uses Haas appliance and Hyrax appliance. Clinical practice has proved that both of these two appliances can effectively open the midpalatal suture, promote the deposition of new bone in the suture, cause the reconstruction of the palatal bone tissue, promote the reconstruction of the palatal alveolar bone, and promote the buccal movement of the maxillary posterior teeth, thereby effectively expanding the maxillary dental arch, and the clinical effect can be kept stable for a long time. However, Haas appliance and Hyrax appliance still have the following shortcomings. Table 1 summarizes the advantages and disadvantages, indications and complications of the two appliances.

[0004] (1) Maxillary expansion treatment aggravates the compensatory buccal inclination of molars: The rigid support of the expansion appliance inevitably exerts buccal push force on the maxillary posterior teeth while expanding the midpalatal suture, leading to an increase in the buccal inclination of the molars. This iatrogenic stimulus not only aggravates the original dental compensation of the maxillary arch width deficiency, but also easily causes posterior locking, tooth wear, occlusal disorder, etc., affecting the coordination of patients' maxillofacial development and function;

[0005] (2) The bone expansion effect of maxillary expansion treatment is not ideal: The compensatory excessive buccal inclination or movement of the maxillary anchorage teeth, or even the appearance of positive lock, leads to a higher proportion of dental effect in the total expansion, and the bone expansion does not reach the expected value, increasing the difficulty of subsequent treatment;

[0006] (3) The vertical control of rapid maxillary expansion treatment is not good: Traditional fixed rapid maxillary expansion appliances (such as Hyrax and Haas) may cause excessive elongation of posterior teeth during expansion, affecting the treatment effect and facial appearance.

[0007] Table 1 Clinical application analysis of Haas appliance and Hyrax appliance

[0008] SUMMARY

[0009] In view of the above-mentioned defects of the prior art, the purpose of the present application is to provide a maxillary fixed expansion appliance, which overcomes the defects of the prior art, improves the expansion efficiency, increases the proportion of bone expansion effect, reduces adverse complications, and prevents interference caused by excessive buccal inclination and elongation of maxillary permanent molar.

[0010] To achieve the above-mentioned purposes of the application, the technical solutions of the present application are as follows:

[0011] A maxillary fixed expansion appliance, comprising a spiral expander 1, a plastic base, a connecting rod, a retention device, and a dental retraction hook 6.

[0012] The appliance is symmetrical about the midline of the hard palate, which is the median palatine suture, to ensure that the expansion force is evenly distributed to the left and right sides.

[0013] The spiral expander 1 is placed in the center of the appliance, spanning the median palatine suture. The structure of the spiral expander 1 includes a screw rod 9, a support rod 11, and a metal bracket 12. The screw rod 9 spans the median palatine suture transversely and has reverse threads at both ends. The support rod 11 has two parallel rods at the mesial and distal ends of the screw rod 9 to enhance the structural rigidity. The metal bracket 12 is symmetrically fixed on both sides of the median palatine suture to support and fix the screw rod 9 and the support rod 11. When the screw rod 9 is rotated, its two ends drive the metal bracket 12 and the plastic base on both sides to separate, widening the ends of the appliance. The spiral expander 1 is used to expand the median palatine suture and increase the width of the maxilla.

[0014] The plastic base is a completely symmetrical two-part structure, divided into a left base 2a and a right base 2b by the median palatine suture. The two parts are not physically connected at the median palatine suture, but are mechanically linked only through the metal bracket 12 of the spiral expander 1 and the connecting rod. The plastic base is used to uniformly transmit the correction force generated by the spiral expander to the palatal part of the maxilla, while maintaining the overall stability of the appliance.

[0015] The left base 2a and the right base 2b are mirror-symmetric about the median palatine suture, and their shapes match the anatomical shape of the hard palate of the maxilla. The posterior edge ends in front of the junction of the hard palate and the soft palate, and does not extend to the soft palate area. The plastic base forms a rigid connection by embedding the metal bracket 12 of the spiral expander 1 and the connecting rod.

[0016] The connecting rods are three, divided into two categories: two first category connecting rods, first category connecting rod A 8a and first category connecting rod B 8b, one end of which is fixed to the middle of the lingual side of the continuous band ring 3, and the other end extends into the plastic base and is completely embedded and fixed; the second category connecting rod 8c is one, one end of which is fixed to the middle of the lingual side of the first permanent molar separate band ring 4, and the other end is fixed with the support rod 11 of the helical expander 1, and the main part is embedded in the plastic base; the connecting rod connects the appliance as a whole through the above structure, and transmits the correction force generated by the helical expander 1 to the continuous band ring 3, the first permanent molar separate band ring 4 and the anchorage tooth;

[0017] The retention device is composed of a continuous band ring 3 and a first permanent molar separate band ring 4, which are independent of each other and are used to fix the appliance in the patient's mouth and disperse the correction force:

[0018] The continuous band ring 3 surrounds and adheres to the mesial surface, distal surface, buccal surface and lingual surface of the deciduous molar or premolar; a buccal tube 7 is horizontally welded at the clinical crown midpoint of the buccal surface of the first deciduous molar or premolar, and the tube cavity axis is parallel to the occlusal plane, which is used for subsequent fixation of orthodontic arch wire during fixation during orthodontic treatment;

[0019] The first permanent molar separate band ring 4 adopts a three-surface or four-surface design with a missing mesial surface, which wraps around the corresponding tooth surface of the first permanent molar; a lingual buckle 5 is welded at the clinical crown midpoint of the lingual side to connect the elastic device and apply lingual and apical forces to retract and lower the molar;

[0020] The dental retraction traction hook 6 is symmetrically arranged on both sides of the median palatine suture, and each side includes a welding part 14, a horizontal crossbar part 15, a hook part 16, a terminal back bend 17, and a rubber chain or elastic wire 18; the main body of the dental retraction traction hook 6, the welding part 14, the horizontal crossbar part 15 and the terminal back bend 17 are wrapped in the plastic base, wherein the welding part 14 is welded and fixed with the connecting rod connecting the first permanent molar separate band ring 4; the horizontal crossbar part 15 extends from the welding part in the mesial-distal direction, parallel to the median palatine suture; the terminal back bend 17 is horizontally bent 90° to the buccal side at the end of the horizontal crossbar part, and is embedded in the plastic base to form an anti-rotation anchor point; the hook part 16 is exposed in the mouth and points to the median palatine line, and pulls the rubber chain or elastic wire 18 between the lingual buckle 5 of the same side permanent molar; the rubber chain or elastic wire 18 is used to connect the same side hook part 16 and the molar lingual buckle 5, generating a complex vector of lingual component force retraction and apical component force lowering, to correct the molar which is expanded and proclined after expansion.

[0021] As a preferred mode, the structure of the helical expander 1 further includes an adjustment hole 10 and an expansion key 13; the adjustment hole 10 is located in the center of the screw rod 9, and the expansion key 13 is inserted to rotate the screw rod 9, push the metal bracket 12 and the plastic base apart to the two sides, and expand the two ends of the appliance.

[0022] As a preferred mode, the plastic base rear edge terminates at 2-3 mm in front of the junction of the hard palate and the soft palate, is made of medical grade acrylic resin, and has a vertical thickness of 2.0-2.5 mm, which is tightly attached to the palatal mucosa.

[0023] As a preferred mode, the retention device is made of stainless steel casting.

[0024] As a preferred mode, the connecting rod is made of stainless steel bending, wherein one end of the first connecting rod A and the first connecting rod B is welded to the lingual side of the corresponding anchorage tooth of the continuous band 3, and the other end extends into the plastic base and is completely embedded and fixed; one end of the second connecting rod 8c is fixed to the lingual side of the first molar single band 4, and the other end is welded to the support rod of the spiral expander and embedded in the plastic base, ensuring that the force generated by the spiral expander is transmitted to the band through the connecting rod and acts on the tooth and the jaw. At the same time, the second connecting rod 8c is sawn off during the tooth retraction stage, and the stability of the overall rigid support of the appliance can still be maintained.

[0025] As a preferred mode, the tooth retraction traction hook 6 is made of stainless steel bending, and the lingual buckle 5 is welded at the clinical crown midpoint of the lingual side of the first molar single band 4, and the tooth retraction traction hook 6 is fixed with the second connecting rod 8c through welding, and the main body is wrapped in the plastic base, and the terminal hook part 16 penetrates out of the plastic base, forming a hook-shaped structure horizontally to the midline.

[0026] As a preferred mode, the spiral expander 1 uses the expansion key 13 to insert the adjusting hole 10 and rotate 90° each time, and the screw rod 9 pushes the widened distance between the two metal supports 12 and the plastic base by 0.2-0.25 mm.

[0027] The working principle of the present application is as follows:

[0028] During the bone expansion stage, the continuous band and the first molar single band are adhesively fixed on the corresponding anchorage tooth, the spiral expander is placed on the palatine raphe line near the top of the palatine vault, the plastic base is close to the hard palate tissue, the central screw of the spiral spring is rotated by the special expansion key, and the palatine raphe is opened. At the same time, the orthopedic force is transmitted and dispersed to the hard palate by the plastic base, promoting the palatal bone remodeling. Through the connecting rod, the cast continuous band and the first molar single band of the deciduous molar or premolar can be used as an important anchorage site for orthopedic force transmission in the early stage of expansion, promoting the alveolar bone remodeling and the buccal inclination and displacement of the anchorage tooth, effectively expanding the dental arch width.

[0029] In the late expansion or maintenance phase, i.e., the tooth retraction phase, the second-class connecting rod connected to the first permanent molar is sawed off, the stress transmission is interrupted, and a rubber chain or elastic cord is used between the lingual buckle and the tooth retraction hook for elastic traction, applying lingual and root traction to the maxillary first permanent molar, so that the excessively buccal first permanent molar with excessive tilt is repositioned buccolingually and the molar is depressed. The rubber chain or elastic cord is replaced regularly to establish an ideal molar relationship in three dimensions. However, the orthopedic force can still be transmitted to the deciduous molar or premolar area along the spiral expander, connecting rod, and band, achieving effective widening of the middle section of the dental arch, providing space for tooth replacement, and maintaining the bony effect of maxillary expansion.

[0030] The beneficial effects of the present invention are as follows:

[0031] (1) The appliance of the present invention can achieve the ideal arch expansion method of "bone expansion and tooth contraction": the present invention is a bidirectional arch expansion appliance. During the treatment process of bony widening of the palatal suture, the bidirectional arch expansion appliance can sequentially regulate the bony arch expansion effect of the middle and posterior segments of the dental arch, and balance the proportion of dental arch expansion and bony arch expansion; through the split bracket design, while maintaining the traditional Haas appliance's ability to efficiently open the palatal suture, it innovatively applies lingual and root traction to the maxillary first permanent molar during arch expansion treatment, thereby achieving the ideal arch expansion method of "bone expansion and tooth contraction".

[0032] (2) The appliance of the present invention can optimize the efficiency of early arch expansion and control side effects: during the process of maxillary horizontal arch expansion, the buccal and lingual inclination and vertical control of the posterior teeth are better, and the physiological occlusal contact of the posterior teeth can be maintained after treatment. The risk of unexpected buccal movement of the anchor teeth can be significantly reduced, providing a safer and more efficient solution for the transverse coordination of the jaws of adolescents.

[0033] (3) The appliance of the present invention can solve the vertical control problem in maxillary arch expansion treatment: the bidirectional arch expansion technology is expected to effectively correct the vertical control problem of traditional arch expanders through the unique mechanism of retracting and lowering the posterior teeth, and provide more ideal vertical control. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Attachment Figure 1 It is a schematic diagram of the overall structure of the BD appliance of the present invention from a horizontal perspective.

[0035] Attachment Figure 2 This is a schematic diagram of the overall structure of the BD appliance of the present invention at a 45° viewing angle on the coronal plane.

[0036] Attachment Figure 3 It is a structural schematic diagram of the spiral expander of the present invention from a horizontal perspective.

[0037] Attachment Figure 4 This is a schematic structural diagram of the tooth retraction hook of the present invention from a horizontal perspective during bony arch expansion.

[0038] Figure 2 is a schematic view of the structure of the tooth retraction hook of the present application in the sagittal plane during tooth retraction. Figure 5 Figure 2 is a schematic view of the structure of the tooth retraction hook of the present application in the sagittal plane during tooth retraction.

[0039] wherein 1 is a screw expander, 2a is a left base plate, 2b is a right base plate, 3 is a continuous band, 4 is a first molar individual band, 5 is a lingual clasp, 6 is a tooth retraction hook, 7 is a buccal tube, 8a is a first type of connecting rod A, 8b is a first type of connecting rod B, 8c is a second type of connecting rod, 9 is a screw rod, 10 is an adjusting hole, 11 is a support rod, 12 is a metal bracket, 13 is an expansion key, 14 is a welding part, 15 is a horizontal crossbar part, 16 is a hook part, 17 is a terminal bend, and 18 is a rubber chain or elastic wire. DETAILED DESCRIPTION

[0040] Other advantages and effects of the present application can be easily understood by those skilled in the art from the disclosure of the present specification. The present application can also be implemented or applied by means of other different specific embodiments, and various modifications or changes can be made to the details in the present specification based on different viewpoints and applications without departing from the spirit of the present application.

[0041] Comparative Example

[0042] The structure of the Haas expander in the prior art is: screw expander, plastic base plate, cast continuous band, buccal tube and connecting rod.

[0043] The screw expander is placed in the center of the appliance, spanning the median palatal suture, and the specific structure includes: a screw rod, a support rod, and a metal bracket. The screw rod spans the median palatal suture transversely, with reverse threads at both ends. The support rod is parallel to the mesial and distal ends of the screw rod, serving to enhance structural rigidity. The metal bracket is symmetrically fixed on both sides of the median palatal suture, supporting and fixing the screw rod and the support rod. When the screw rod is rotated, its two ends drive the metal bracket and the plastic base plate on both sides apart through the threads, expanding the two ends of the appliance. The screw expander is used to expand the median palatal suture and increase the width of the upper jaw.

[0044] The plastic base plate is a two-part independent structure that is mirror-symmetric to the median palatal suture, with no physical connection at the median palatal suture. The shape matches the anatomical shape of the hard palate of the upper jaw, and the posterior edge terminates 2-3 mm in front of the junction between the hard and soft palates. The plastic base plate embeds and fixes the metal bracket and the connecting rod of the screw expander, forming a rigid connection. The plastic base plate is used to uniformly transmit the orthodontic force generated by the screw expander to the upper palatal region, while maintaining the overall stability of the appliance.

[0045] The casting continuous band ring and the connecting rod are integrated casting structure, the band ring body wraps the mesial surface, distal surface, buccal surface and lingual surface of the bilateral first primary molar / premolar and first permanent molar, and integrally extends from the lingual mucosa turning part of the band ring to form the connecting rod, the distal end is curved to the palatal side, and is completely embedded and fixed in the plastic base.

[0046] The buccal tube is welded in the clinical crown midpoint of the first primary molar / premolar buccal surface, and the tube cavity axis is parallel to the occlusal plane, which is used for fixing the subsequent fixed orthodontic arch wire during the fixed orthodontic period.

[0047] The difference between the structure of the comparative example (prior art) and the structure of the present application is that in the comparative example, the casting continuous band ring and the connecting rod are integrated casting structure, the band ring body wraps the mesial surface, distal surface, buccal surface and lingual surface of the bilateral first primary molar / premolar and first permanent molar, and integrally extends from the lingual mucosa turning part of the band ring to form the connecting rod, the distal end is curved to the palatal side, and is completely embedded and fixed in the plastic base; there is no first permanent molar separate band ring.

[0048] There is no tooth retraction hook and lingual buckle in the plastic base of the Haas expander, and the buccal-lingual and vertical control of the molar is not good.

[0049] The main defects of the Haas expander are:

[0050] (1) Maxillary expansion treatment aggravates the compensatory buccal inclination and movement of the molar, which easily causes posterior teeth locking, tooth wear, occlusion disorder, etc., affecting the development of the patient's jaw and functional coordination;

[0051] (2) The bone expansion effect of maxillary expansion treatment is not ideal: the compensatory excessive buccal inclination or movement of the maxillary anchorage tooth, the early appearance of locking, and the loss of occlusion release, at this time the bone expansion has not reached the expected value, increasing the proportion of secondary expansion treatment;

[0052] (3) The vertical control of the maxillary molar in the Haas rapid expansion treatment is not good, which can cause excessive elongation of the posterior teeth, affecting the treatment effect and face shape.

[0053] Table 2

[0054]

[0055] Two patients with insufficient transverse development of the maxilla in the mixed dentition were respectively fitted with the BD appliance of Example 1 of the present application and the traditional Haas appliance, and the expander was opened by 6mm, and the treatment effect was evaluated after the expansion was completed and kept for 6 months. The evaluation indexes include transverse and vertical indexes, which are measured at T0 (before treatment) and T1 (after expansion is completed and kept for 6 months).

[0056] 1. Transverse index

[0057] (1) Actual expansion amount: after the expansion is completed and maintained for 6 months, the expander is removed, and the distance between the expanders (T1) is measured using an electronic digital caliper, and the actual expansion amount = distance between expanders (T1) - initial distance between expanders (T0);

[0058] (2) Skeletal expansion amount: the maxillary basal bone width (MBBW) is measured using CBCT;

[0059] (3) Dental expansion amount: the intermaxillary width (IMW) of the maxillary first permanent molar is measured using a digital dental model;

[0060] (4) Molar buccal inclination: the maxillary first molar inclination (TI-M1) is measured using CBCT, that is, the angle between the CBCT coronal axis and the palate plane.

[0061] 2. Vertical index:

[0062] (1) The mandibular plane angle (MP-SN) is measured using a lateral film.

[0063] 3. The score result statistics are shown in Table 2, and it can be seen that for the treatment of such patients, the maxillary expander described in the application is significantly better than the traditional Haas expander in terms of bone expansion effect, dental retraction efficiency and vertical control.

[0064] The preferred examples of the application will be described in detail below, Figure 1 ,so that the advantages and features of the application can be more easily understood by those skilled in the art, and the scope of protection of the application can be more clearly defined. 2 Example 1

[0065] As shown in

[0066] , a maxillary fixed expander, comprising a spiral expander 1, a plastic base, a connecting rod, a retention device and a dental retraction hook 6; Figure 1 Figure 2 The expander is symmetrical left and right with the midline of the hard palate as the center; and ensures that the expansion force is uniformly distributed to the left and right sides;

[0067] The expander is symmetrical left and right with the midline of the hard palate as the center; and ensures that the expansion force is uniformly distributed to the left and right sides;

[0068] As shown in Figure 3As shown, the screw expander 1 is placed in the center of the appliance, across the median palatal suture, and the structure of the screw expander 1 includes: a screw rod 9, a support rod 11, a metal bracket 12, the screw rod 9 is transversely across the median palatal suture, and both ends are provided with reverse threads, the support rod 11 is two, which are respectively arranged on the mesial end and the distal end of the screw rod 9 in parallel, for enhancing the structural rigidity; the metal bracket 12 is symmetrically fixed on both sides of the median palatal suture, supporting and fixing the screw rod 9 and the support rod 11; when the screw rod 9 is rotated, its both ends drive the metal bracket 12 and the plastic base through the threads to separate to both sides, widen the both ends of the appliance; the screw expander 1 is used for expanding the median palatal suture and increasing the width of the upper jaw;

[0069] The plastic base is a completely symmetrical two-part structure, which is divided into a left base 2a and a right base 2b by the median palatal suture, and the two parts are not physically connected at the median palatal suture, but are mechanically linked only through the metal bracket 12 and the connecting rod of the screw expander 1; the plastic base is used for uniformly transmitting the orthodontic force generated by the screw expander to the upper palatal part, while maintaining the overall stability of the appliance;

[0070] The left base 2a and the right base 2b are mirror-symmetric about the median palatal suture, and the shape thereof matches the anatomical shape of the hard palate of the upper jaw, and the posterior edge terminates in front of the junction of the hard palate and the soft palate, and does not extend to the soft palate area; the plastic base fixes the metal bracket 12 and the connecting rod of the screw expander 1 by embedding, forming a rigid connection;

[0071] The connecting rod is three, which is divided into two categories: the first type of connecting rod is two, which is a first type of connecting rod A 8a and a first type of connecting rod B 8b, one end of which is fixed on the median lingual side of the continuous band 3, and the other end extends into the plastic base and is completely embedded and fixed; the second type of connecting rod 8c is one, one end of which is fixed on the median lingual side of the first molar single band 4, and the other end is fixed with the support rod 11 of the screw expander 1, and the main part is embedded in the plastic base; the connecting rod connects the appliance as a whole through the above structure, and transmits the orthodontic force generated by the screw expander 1 to the continuous band 3, the first molar single band 4 and the anchorage tooth;

[0072] The retaining device is composed of the continuous band 3 and the first molar single band 4, which are independent of each other and are used for fixing the appliance in the patient's mouth and dispersing the orthodontic force:

[0073] The continuous band 3 surrounds and fits the mesial surface, distal surface, buccal surface and lingual surface of the deciduous molar or premolar; at the clinical crown midpoint of the buccal surface of the first deciduous molar or premolar, a buccal tube 7 is horizontally welded, and the tube cavity axis is parallel to the occlusal plane, which is used for subsequent fixation of the orthodontic arch wire during the fixation period;

[0074] The first constant molar single ring 4 adopts a three-surface or four-surface design without a mesial surface, and wraps around the corresponding tooth surface of the first constant molar; a lingual buckle 5 is welded at the clinical crown midpoint on the lingual side to connect the elastic device and exert lingual and apical forces to retract and depress the molar;

[0075] As shown in Figure 4 , Figure 5 The dental retraction traction hook 6 is symmetrically arranged on both sides of the median palatine suture and includes, on each side, a welding portion 14, a horizontal crossbar portion 15, a hook portion 16, a terminal back bend 17, and a rubber chain or elastic wire 18; the main body welding portion 14, the horizontal crossbar portion 15, and the terminal back bend 17 of the dental retraction traction hook 6 are wrapped in the plastic base, wherein the welding portion 14 is fixedly welded with the connecting rod of the first constant molar single ring 4; the horizontal crossbar portion 15 extends from the welding portion in the mesiodistal direction and is parallel to the median palatine suture; the terminal back bend 17 is horizontally bent 90° toward the buccal side at the end of the horizontal crossbar portion and is embedded in the plastic base to form an anti-rotation anchor point; the hook portion 16 is exposed in the mouth and points to the median palatine line and is connected with the lingual buckle 5 of the constant molar on the same side by the rubber chain or elastic wire 18; the rubber chain or elastic wire 18 is used to connect the hook portion 16 on the same side and the lingual buckle 5 of the molar to generate a composite vector of the lingual component force retraction and the apical component force depression, thereby correcting the molar that is expanded, buccally inclined, and elongated.

[0076] As a preferred mode, the structure of the screw expander 1 further includes an adjusting hole 10 and an arch expander key 13; the adjusting hole 10 is located in the center of the screw rod 9 and is inserted with the arch expander key 13 to rotate the screw rod 9, push the metal support 12 and the plastic base apart to the two sides, and expand the two ends of the appliance.

[0077] As a preferred mode, the rear edge of the plastic base ends 2-3 mm in front of the junction of the hard palate and the soft palate and is made of medical-grade acrylic resin, with a vertical thickness of 2.0-2.5 mm, which is tightly fitted with the mucosa of the palate.

[0078] As a preferred mode, the retention device is made of stainless steel casting and is composed of the continuous ring 3 and the first constant molar single ring 4, which are independent of each other and are not connected.

[0079] As shown in Figure 5 , the connecting rod is made of stainless steel bending, wherein one end of the first type of connecting rod A and the first type of connecting rod B is welded to the lingual middle of the corresponding anchorage tooth of the continuous ring 3, and the other end extends into the plastic base and is completely embedded and fixed; one end of the second type of connecting rod 8c is fixed to the lingual middle of the first constant molar single ring 4, and the other end is welded with the support rod of the screw expander and is embedded in the plastic base, thereby ensuring that the force generated by the screw expander is transmitted to the ring through the connecting rod and acts on the teeth and the jaw, and at the same time, the second type of connecting rod 8c is sawn off at the dental retraction stage, which can still maintain the stability of the overall rigid support of the appliance.

[0080] As a preferred mode, the dental retraction hook 6 is made of stainless steel, the lingual buckle 5 is welded on the clinical crown midpoint of the lingual side of the single band of the maxillary first permanent molar, the dental retraction hook 6 is fixed with the second connecting rod 8c by welding, the main body is wrapped in the plastic base, and the hook part 16 is exposed to the mouth and horizontally points to the midline.

[0081] As a preferred mode, the screw expander 1 is forced each time, the expansion key 13 is inserted into the adjusting hole 10 to rotate 90°, and the screw rod 9 pushes the widened distance between the metal support 12 and the plastic base to be 0.2-0.25 mm.

[0082] As a preferred mode, the hook part 16 of the dental retraction hook 6 is exposed to the mouth and horizontally points to the midline, in the late expansion or retention stage, the second connecting rod 8c connected with the single cast band of the maxillary bilateral first permanent molar is sawn off, the rubber chain or elastic wire 18 is used to connect the hook part 16 and the molar lingual buckle 5 on the same side to generate a composite vector of the lingual force (retraction) and the root force (depression), thereby correcting the molar which is expanded and buckled on the buccal side.

[0083] The working principle of the present application is as follows:

[0084] In the bone expansion stage, the continuous band and the single band of the first permanent molar are fixed on the corresponding anchorage tooth by bonding, the screw expander is placed on the palatal suture near the top of the palatal vault, the plastic base is close to the hard palate tissue, the central screw of the screw spring is rotated by the special expansion key to open the palatal suture. At the same time, the orthopedic force is transmitted and dispersed to the hard palate by the plastic base to promote the palatal bone remodeling. Through the connecting rod, the cast continuous band of the deciduous molar or premolar and the single band of the first permanent molar can be used as an important anchorage part for transmitting the orthopedic force in the early expansion stage to promote the alveolar bone remodeling and the buccal inclination and displacement of the anchorage tooth, thereby effectively expanding the dental arch width.

[0085] In the late expansion or retention stage, that is, the dental retraction stage, the second connecting rod 8c connected with the first permanent molar is sawn off, the stress transmission is interrupted, the rubber chain or elastic wire is used for elastic traction between the lingual buckle and the dental retraction hook to exert the traction force to the lingual side and the root side of the maxillary first permanent molar, so that the maxillary first permanent molar which is excessively inclined on the buccal side is reset and appropriately depressed in the buccal-lingual direction, and the rubber chain or elastic wire is regularly replaced to establish the ideal molar relationship in the three-dimensional direction. While the orthopedic force can still be transmitted along the screw expander, the connecting rod and the band to the deciduous molar or premolar area to effectively expand the width of the middle segment of the dental arch, provide space for the replacement of the dentition, and maintain the bone effect of the maxillary expansion.

[0086] When installing this device, glass ionomer cement is coated on the inner sides of the cast continuous bands 3 for primary molars or premolars and the single bands 4 for the first permanent molars, and then it is seated on the corresponding anchorage teeth for curing. At this time, the resin base closely adheres to the palatal mucosa in the primary molar area or premolar area.

[0087] At 12 weeks of palatal expansion, a high-speed dental handpiece is used to saw off the second-type connecting rod 8c connecting the single band 4 of the first permanent molar and the screw expander 1. An elastic chain or elastic thread 18 is placed between the lingual button 5 and the dental retraction traction hook 6 on the resin base and replaced regularly, applying a traction force to the lingual side and root direction to the first permanent molar in the maxilla, and performing lingual repositioning and appropriate intrusion on the buccally inclined and elongated molars.

[0088] This appliance maintains the high efficiency of the traditional Haas appliance in opening the palatal mid-suture, has better control over the buccolingual inclination and vertical direction of the posterior teeth, can maintain physiological posterior tooth occlusal contact after treatment, realizes the ideal palatal expansion method of "bone expansion and tooth contraction", optimizes the early palatal expansion efficiency, reduces the risk of unexpected movement of the anchorage teeth, and solves the problem of vertical control in maxillary palatal expansion treatment.

[0089] The above embodiments are only illustrative of the principles and effects of the present invention, rather than limiting the present invention. Any person familiar with this technology can modify or change the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes made by those with ordinary knowledge in the technical field without departing from the spirit and technical idea disclosed by the present invention should still be covered by the claims of the present invention.

[0090] "Occlusion" in this article is a professional term in stomatology, and its English is occlusion. The character "牙合" is composed of the left and right parts of a single character.

[0091] This character cannot be found in the common font library, so it is written separately as "牙合".

[0092] The above embodiments are only illustrative of the principles and effects of the present invention, rather than limiting the present invention. Any person familiar with this technology can modify or change the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes made by those with ordinary knowledge in the technical field without departing from the spirit and technical idea disclosed by the present invention should still be covered by the claims of the present invention.

Claims

1. A maxillary fixed arch expansion appliance, characterized by: The screw expander (1), plastic base, connecting rod, retaining device and dental retraction hook (6) are included. The appliance is symmetrical left and right with the median palatal suture as the center line; and ensures that the expansion force is evenly distributed to the left and right sides. The screw expander (1) is placed in the center of the appliance, across the median palatal suture, and the structure of the screw expander (1) includes a screw rod (9), a support rod (11), and a metal bracket (12). The screw rod (9) is transversely across the median palatal suture, and both ends are provided with reverse threads. The support rod (11) is parallel to the mesial end and the distal end of the screw rod (9), respectively, for enhancing the structural rigidity. The metal bracket (12) is symmetrically fixed on both sides of the median palatal suture, supporting and fixing the screw rod (9) and the support rod (11). When the screw rod (9) is rotated, its both ends drive the metal bracket (12) and the plastic base on both sides through the threads, and separate the plastic base on both sides, expanding the ends of the appliance; the screw expander (1) is used to expand the median palatal suture and increase the width of the upper jaw. The retaining device is composed of a continuous band ring (3) and a first permanent molar individual band ring (4), which are independent of each other without connection, and is used to fix the appliance in the patient's mouth and disperse the orthodontic force: The continuous band ring (3) surrounds and fits the mesial surface, distal surface, buccal surface and lingual surface of the deciduous molar or premolar; a buccal tube (7) is horizontally welded at the clinical crown midpoint of the buccal surface of the first deciduous molar or premolar, and the tube cavity axis is parallel to the occlusal plane, which is used for fixing the orthodontic arch wire during subsequent fixation; The first permanent molar individual band ring (4) adopts a three-surface or four-surface design without mesial surface, which wraps around the corresponding tooth surface of the first permanent molar; a lingual buckle (5) is welded at the clinical crown midpoint of the lingual side, which connects the elastic device and applies lingual and apical force to retract and lower the molar; The connecting rod is 3 in total, which is divided into two categories: the first category of connecting rod is two, which is the first category of connecting rod A (8a) and the first category of connecting rod B (8b), one end of which is fixed to the middle of the lingual side of the continuous band ring (3), and the other end extends into the plastic base and is completely embedded and fixed; the second category of connecting rod (8c) is one, one end of which is fixed to the middle of the lingual side of the first permanent molar individual band ring (4), and the other end is fixed with the support rod (11) of the screw expander (1), and the main part is embedded in the plastic base; the connecting rod connects the appliance as a whole through the above structure, and transmits the orthodontic force generated by the screw expander (1) to the continuous band ring (3), the first permanent molar individual band ring (4) and the anchorage tooth; The plastic base is a completely symmetrical and separated two-part structure, which is divided into left base (2a) and right base (2b) by the median palatal suture, and the two parts are not physically connected at the median palatal suture, but are connected only through the metal bracket (12) of the screw expander (1) and the connecting rod for mechanical linkage; the plastic base is used to uniformly transmit the orthodontic force generated by the screw expander to the upper palatal part, while maintaining the overall stability of the appliance; The left base (2a) and the right base (2b) are mirror-symmetric about the median palatal suture, and the shape thereof matches the anatomical shape of the hard palate of the upper jaw, and the posterior edge ends in front of the junction of the hard palate and the soft palate, and does not extend to the soft palate region; the plastic base is fixed to the metal support (12) and the connecting rod of the screw expander (1) by embedding, so as to form a rigid connection; The dental retraction traction hook (6) is symmetrically arranged on both sides of the median palatal suture, and each side comprises a welding portion (14), a horizontal crossbar portion (15), a hook portion (16), and a terminal bend (17), and further comprises a rubber chain or an elastic wire (18); the welding portion (14), the horizontal crossbar portion (15), and the terminal bend (17) of the dental retraction traction hook (6) are wrapped in the plastic base, wherein the welding portion (14) is welded and fixed with the connecting rod connecting the first permanent molar single ring (4); the horizontal crossbar portion (15) extends from the welding portion in the mesial-distal direction and is parallel to the median palatal suture; the terminal bend (17) is horizontally bent by 90° towards the buccal side at the end of the horizontal crossbar portion and is embedded in the plastic base to form an anti-rotation anchor point; the hook portion (16) is exposed in the mouth and points to the median palatal line and pulls the rubber chain or the elastic wire (18) between the hook portion (16) and the lingual buckle (5) of the same side molar; the rubber chain or the elastic wire (18) is used to connect the hook portion (16) and the lingual buckle (5) of the same side molar, so as to generate a composite vector of the lingual retraction force and the root pressure force, thereby correcting the molar which is expanded, buckled, and elongated.

2. The maxillary fixed arch expansion appliance of claim 1, wherein: The structure of the screw expander (1) further comprises an adjusting hole (10) and an expansion key (13); the adjusting hole (10) is located in the center of the screw rod (9) and is inserted into the expansion key (13) to rotate the screw rod (9), so as to push the metal support (12) and the plastic base apart to the two sides and expand the two ends of the expander.

3. The maxillary fixed arch expansion appliance of claim 1, wherein: The plastic base has a posterior edge which ends in front of the junction of the hard palate and the soft palate by 2-3 mm, is made of medical-grade acrylic resin, and has a vertical thickness of 2.0-2.5 mm, so as to be closely attached to the palatal mucosa.

4. The maxillary fixed arch expansion appliance of claim 1, wherein: The dental retraction traction hook (6) is made of stainless steel and is welded to the clinical crown midpoint of the lingual side of the first permanent molar single ring (4) of the upper jaw, and the dental retraction traction hook (6) is fixed with the second type of connecting rod (8c) by welding, the main body is wrapped in the plastic base, and the terminal hook portion (16) penetrates through the plastic base to form a hook-shaped structure which is horizontal to the median line.

5. The maxillary fixed arch expansion appliance of claim 2, wherein: The screw expander (1) is used to expand the distance between the two metal supports (12) and the plastic base by 0.2-0.25 mm each time.

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