Orthodontic Aligners: A Modern Therapeutic Tool

Introduction

Orthodontic patients, especially adults, increasingly seek quick and aesthetically pleasing treatments. Traditional multi-bracket systems are often rejected due to their visibility, leading to the development of alternatives like ceramic brackets, lingual orthodontics, and, more recently, clear aligners. These transparent, removable devices, such as Invisalign® by Align Technology®, allow tooth movement through a series of custom-made trays. The ClinCheck® software enables 3D visualization of treatment stages, ensuring precise planning. Successful aligner therapy relies on patient compliance and the practitioner’s ability to select appropriate cases and manage biomechanical aspects. Future advancements may make this technology more accessible in dental practices.

1. Understanding Aligners

Aligners are transparent, removable trays made from thermoformable polymers, designed to apply gentle, controlled forces for tooth movement. This thesis focuses on Invisalign®, the most widely used system, due to its extensive research and documentation, without endorsing any specific brand.

1.1 Factors Influencing Aligner Forces

Several factors affect the forces delivered by aligners:

• Material Thickness: Thicker aligners exert stronger forces, regardless of the polymer used.
• Polymer Type: The polymer’s physical and chemical properties, such as flexibility, non-toxicity, and resistance to saliva and cleaning agents, influence force delivery, especially at low activation levels (0.15–0.30 mm).
• Thermoforming Method: Vacuum or pressure-based thermoforming affects the aligner’s fit and force precision. Vacuum systems pull the material over a model, while pressure systems press it down, with accuracy critical for larger movements (0.5 mm).
• Tooth Morphology: Complex dental anatomies lead to variable forces. Attachments enhance retention and reduce variability by improving aligner fit.
• Activation Duration: Forces diminish over time due to material relaxation. Repeated insertion/removal cycles further reduce force output, though standard two-week wear periods have minimal impact on polymer properties.

1.2 Challenges in Aligner Biomechanics

Studying aligner biomechanics is complex because forces are distributed across the entire tooth crown, not a single point, and change dynamically as teeth move. Unlike fixed appliances, aligners are removable, leading to intricate interactions during sliding movements. Misalignment during treatment can cause unintended forces, complicating outcomes.

2. Diagnosis, Objectives, and Treatment Planning

Aligner therapy requires a thorough orthodontic diagnosis, including:

• Medical History: Assessing genetic or environmental factors, patient motivation, health conditions, medications, habits, and past dental care.
• Extra-Oral Examination: Analyzing facial symmetry, proportions, lip position, and smile aesthetics through photographs.
• Intra-Oral Examination: Evaluating periodontal health (inflammation, plaque, mobility), dental condition (missing or treated teeth), and arch relationships (occlusion, crowding, diastemas).
• Functional Assessment: Checking swallowing, breathing, speech, mastication, and temporomandibular joint function, noting any habits like thumb-sucking.
• Study Models: Physical or digital models help measure crowding and arch shapes.
• Radiographic Exams: Panoramic and cephalometric radiographs assess tooth roots, bone structure, and growth patterns, with additional imaging (e.g., cone beam) if needed.

2.2 Diagnostic Summary and Goals

The practitioner synthesizes clinical and radiographic findings to diagnose aesthetic, functional, dental, periodontal, alveolar, and skeletal issues in three dimensions (transversal, vertical, sagittal). Treatment goals are set based on these findings and the patient’s consultation reason.

2.3 Treatment Plan

The plan outlines the chosen orthodontic approach, considering aligners or combined therapies (e.g., multi-brackets, surgical options). Patient-specific risks, such as psychological factors, are evaluated. Treatment involves scheduling, appliance placement, monitoring, and long-term retention to prevent relapse. Clinicians must actively guide the process, avoiding over-reliance on software or technicians. Auxiliaries like elastics or mini-screws may enhance outcomes.

3. Relevance of Aligners

3.1 Indications, Contraindications, and Limitations

Aligners are suitable for:

• Mild to moderate crowding or spacing (1–5 mm).
• Minor anteroposterior discrepancies (<4 mm).
• Limited expansion (2–4 mm) or correction of mild crossbites.
  More complex cases, like severe crowding requiring extractions or large anteroposterior corrections (>5 mm), are challenging without auxiliary devices.

3.2 Advantages and Disadvantages

Advantages:

• Aesthetic appeal due to transparency.
• Removability for eating and hygiene.
• Reduced discomfort compared to brackets.
• Predictable 3D planning with ClinCheck®.
  Disadvantages:
• Dependence on patient compliance (22 hours/day wear).
• Limited efficacy for complex movements.
• Higher cost than traditional systems.

3.3 Comparison with Multi-Bracket Systems

• Force Transmission: Aligners distribute forces across the crown, unlike brackets’ localized application, affecting movement precision.
• Alignment and Friction: Aligners reduce friction, aiding leveling, but may struggle with severe rotations.
• Treatment Efficiency: Aligners are effective for mild cases but less so for complex malocclusions.
• Periodontal Health: Aligners allow better hygiene, reducing gingival inflammation risks.
• Dental Health: Less risk of caries or white spots compared to brackets.
• Quality of Life: Aligners improve comfort and aesthetics, enhancing patient satisfaction.
• Appointment Efficiency: Fewer and shorter visits due to pre-planned aligner changes.

4. The Invisalign® System

4.1 Overview

Invisalign® aligners are custom-made using digital scans and ClinCheck® software to plan tooth movements. Patients wear a series of aligners, each for 1–2 weeks, to achieve the desired outcome.

4.2 Variants

• Invisalign Go®: Simplified system for minor corrections.
• Invisalign Teen®: Designed for adolescents, accommodating erupting teeth.

4.3 Virtual Tools

The Invisalign Doctor Site (IDS) and Virtual Invisalign Practitioner (VIP) platforms allow clinicians to manage cases online, submitting digital impressions and treatment plans. Clinical records include scans, photos, and radiographs.

4.4 ClinCheck® Strategy

ClinCheck® enables:

• Sequencing: Planning the order of tooth movements.
• Movement Control: Monitoring rotations, translations, and torque.
• Space Management: Ensuring adequate space for movements.
• Anchorage Control: Preventing unwanted tooth shifts.

5. Attachments: Materials and Biomechanics

5.1 Attachments

Attachments are composite resin shapes bonded to teeth to enhance aligner retention and control specific movements (e.g., extrusion, intrusion, rotation, translation, torque, root parallelism).

5.2 Biomechanics

Attachments improve force application for:

• Extrusion/Intrusion: Vertical tooth movement.
• Rotation: Correcting tooth alignment.
• Translation: Horizontal shifts.
• Torque and Root Control: Adjusting angulation and root positioning.

6. Retention

Post-treatment retention is critical to prevent relapse, typically using fixed retainers or removable aligners worn at night.

7. Future Perspectives

7.1 In-Office Aligner Thermoforming

Producing aligners directly in dental practices using 3D-printed models could:

• Advantages: Reduce costs, speed up production, and allow immediate adjustments.
• Disadvantages: Requires investment in equipment and training, with potential inconsistencies in quality.

7.2 Computer-Aided Design and Manufacturing

Advanced software could enable direct aligner fabrication from digital simulations, improving precision and customization.