Retention period: stabilization of results
After active tooth movement is completed, a critical stage begins—the retention period. During this time, functional and morphological changes occur in the tissues to stabilize the dental arch:
- Cellular remodeling: osteoblasts actively arrange themselves along the alveolar bone tissue, forming new bone.
- Periodontal transformation: the periodontal space gradually evens out, eliminating areas of compression and tension.
- Ligamentous apparatus: terminal sections of collagen fibers strengthen, adapting to the new tooth position.
The clinical outcome of these processes is the complete preservation of the periodontal fixation capacity. To prevent teeth from returning to their original position, a fixed retainer is installed—a special wire arch that is securely fixed to the oral (lingual/palatal) surface of the teeth.
Classification of therapeutic appliances
Orthodontic devices are classified according to several key criteria. Based on their location (site of action), two large groups are distinguished:
- Extraoral appliances: cervical, maxillo-facial (anchored to the frontal bone and chin), and headgear.
- Intraoral appliances: palatal, vestibular, dental, and lingual.
Based on the method of fixation in the oral cavity, appliances are divided into removable and fixed.
Removable orthodontic appliances
These include plate devices, block appliances (massive plastic base with metallic arches and clasps), framework devices (two-jaw appliances with a rigid metal framework and plastic shields), elastic devices, and clear aligners (thin-walled transparent aligners made of biocompatible polymer that replicate crown topography).
| Advantages of removable appliances | Disadvantages of removable appliances |
|---|---|
| Wide choice of anchorage area (teeth, palate, alveolar process) | Risk of oral mucosa irritation |
| Satisfactory level of hygiene | Highly dependent on patient compliance |
| High level of aesthetics (especially for aligners) | Inaccuracy in correcting the 3D spatial position of a tooth |
Principles of force application
Depending on the source of force for tooth movement, appliances are divided into passive and active.
Passive (functional) appliances Include functionally guiding and functionally acting designs.
- Source of force: natural contraction of the maxillofacial muscles.
- Mechanism: muscular force is transmitted to structural elements (shields, inclined planes), which redirect this pressure onto the dentition for its correction.
Active (mechanical) appliances
- Source of force: embedded in the material of the design itself (elastic deformation of the wire arch, tension of the elastic) or in the integrated active element (orthodontic screw).
- Structure: a classic mechanical appliance consists of a base, vestibular arch, screw, and retaining clasps.
Fixed appliances: bracket systems
Fixed appliances (arch and plate) solve the most complex clinical problems. The main example is the bracket system. Unlike removable plates, braces guarantee high precision of tooth movement, handle large-scale corrections, and are minimally dependent on patient compliance. However, they complicate oral hygiene, have questionable aesthetics, and require highly specialized skills from the orthodontist.
Classification of braces:
- By fixation site: vestibular (external) and lingual (internal/palatal).
- By ligation method: requiring classic ligation and self-ligating.
Key elements of the bracket system:
- Brackets: control the position of the tooth (strictly individual for each tooth, except for teeth 18, 28, 38, 48).
- Archwire: the main active power element.
- Ligatures: metal or elastic — fix the archwire in the bracket slot. The "figure-eight" tie is needed for dental arch consolidation and creating reliable anchorage.
- Springs: opening or closing (used for working with interdental spaces).
- Elastic traction: closes spaces strictly within a single dental arch.
A distinct approach is bioprogressive therapy, in which the final correct tooth position is determined by a specific bend that the practitioner forms in a stainless steel wire.
Class and exam questions
What is the main difference between functional and mechanical appliances?
Functional appliances are passive and use the natural forces of the maxillofacial muscles to move teeth. Mechanical appliances are active: the force is generated by the appliance itself (by activating a screw or through the elasticity of the arch wire).
Which teeth do not require strictly individual brackets?
An exception to the rule of strict bracket individuality is third molars (wisdom teeth) — teeth 18, 28, 38, and 48.
Why is a figure-eight ligature tie needed?
This type of metal ligature is used to consolidate several teeth into a single block, creating stable anchorage for subsequent orthodontic movement.
What else to study on this topic
- Morphological changes in the periodontal ligament during retention
- Comparative analysis of labial and lingual bracket systems
- Bioprogressive technique: mechanics of steel wires
- Indications for extraoral appliances
- Complications associated with removable aligner appliances
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Other topics in "Chapter 11. Introduction to Orthodontics"
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