Application Case of SLA Technology in 3D Printing: Fabrication of Dental Orthodontic Invisible Aligners-Case Studies

Dental orthodontic invisible aligners have gradually replaced traditional metal brackets as the mainstream orthodontic tool due to their advantages of aesthetics, comfort, and removability. Their core requirements are to fit the patient's tooth morphology accurately, achieve progressive tooth movement, and possess good biocompatibility and mechanical stability. The traditional manual fabrication process relies on the technician's experience, featuring a long cycle and low precision, which is difficult to meet the demand for personalized orthodontics. SLA (Stereolithography) technology cures liquid photosensitive resin with ultraviolet light, enabling rapid prototyping of complex curved structures with a precision of 0.02mm, perfectly adapting to the customized production of invisible aligners. Taking adult maxillary invisible aligners as the processing object, this article elaborates on the application process, technical key points, and process value of SLA technology, providing a reference for the production of similar medical personalized products.

I. Product Characteristics and Core Technical Requirements

The maxillary invisible aligner fabricated in this case is a single orthodontic stage component, featuring an overall arc-shaped shell structure that fits 14 maxillary teeth of the patient. Its inner wall adheres to the occlusal and lateral surfaces of the teeth, with an edge thickness of 1.2-1.5mm and a 0.3mm reserved space on the occlusal surface for tooth movement. It must withstand an orthodontic force of 3-5N without deformation or cracking. The product must comply with the YY/T 0270-2011 standard for dental orthodontic products, achieve biocompatibility requirements specified in ISO 10993, be non-cytotoxic and non-irritating to the oral cavity, and have a smooth, burr-free surface to avoid damaging oral mucosa.

Core technical indicators are strictly controlled: the fitting gap between the aligner and the tooth model ≤0.05mm, dimensional accuracy ±0.03mm, surface roughness Ra≤0.2μm, resin hardness after curing ≥85D, tensile strength ≥35MPa. It also has a certain toughness to adapt to slight deformation during oral chewing movements.

II. Selection of SLA Printing Materials and Equipment

Medical-grade transparent photosensitive resin (model: Formlabs Dental LT Clear) is selected as the raw material, specifically designed for the oral medical field. It possesses excellent biocompatibility, light transmittance, and mechanical stability, with no odor or yellowing after curing, and can resist corrosion by oral saliva. With a viscosity of 500mPa·s (25℃), it meets the liquid forming requirements of SLA printing. Before use, the raw material shall be left standing at room temperature (23±2℃) for 2 hours to eliminate internal bubbles, and the resin level shall meet the printer requirements to avoid printing interruption.

A Formlabs Form 3+ SLA 3D printer is selected, equipped with a 405nm ultraviolet laser emitter, with a laser spot diameter of 0.05mm, an adjustable printing layer thickness range of 0.025-0.2mm, and a forming size of 145mm×145mm×185mm. It supports automatic calibration and constant resin temperature control, which can accurately match the small-size and high-precision printing needs of aligners. Auxiliary equipment includes: isopropanol cleaning machine (for cleaning residual resin after printing), ultraviolet curing oven (secondary curing to improve mechanical properties), 3D scanning equipment (for collecting oral tooth data), and professional dental design software (Exocad DentalCAD).

III. Full Process and Key Points of Aligner Fabrication via SLA Technology

(I) Oral Data Collection and Model Design

First, 3D data of the patient's maxillary teeth is collected using an intraoral scanner (iTero Element 5D) with a scanning accuracy of 0.01mm. After generating point cloud data, it is imported into Exocad DentalCAD software for model reconstruction and aligner design. Based on the orthodontist's treatment plan, the designer adjusts the fit, edge thickness, and occlusal gap of the aligner, optimizes the structure to avoid stress concentration, and designs support structures (tree-shaped supports with a diameter of 0.5mm and a connection area with the aligner ≤0.3mm²) to prevent deformation during printing. After design completion, the model is exported in STL format and imported into the printer control software for slicing.

(II) Slicing Parameter Setting and SLA Printing Forming

Slicing parameters directly affect printing accuracy and efficiency. Combined with the characteristics of the aligner, the parameters are set as follows: printing layer thickness 0.05mm, laser power 80%, scanning speed 1500mm/s, exposure time per layer 8-10s, and resin temperature controlled at 25℃ (a constant temperature environment reduces resin viscosity fluctuation). The angle between the support structure and the printing platform is 30° to ensure the support is stable and easy to remove later. Before printing, the equipment is calibrated, including laser focus and printing platform levelness, with calibration error controlled within 0.01mm.

During printing, the ultraviolet laser cures the liquid photosensitive resin point by point along the slicing path, forming the product through layer-by-layer superposition. The printing status is monitored in real-time to avoid printing defects caused by low resin level, laser deviation, and other issues. The printing time for a single aligner is about 4 hours. After printing, the printer automatically lifts the printing platform, and the aligner blank with supports is taken out.

(III) Post-Processing and Precision Optimization

Cleaning process: The blank is placed in an isopropanol cleaning machine, soaked in 99% concentration isopropanol for 10 minutes, and ultrasonic vibration (power 300W) is turned on to remove residual surface resin. Then, the surface is gently wiped with a lint-free cloth and rinsed in clean water for 5 minutes to avoid oral irritation caused by residual isopropanol. After cleaning, the aligner surface is inspected to ensure no residual resin agglomeration.

Curing process: The cleaned aligner is placed in an ultraviolet curing oven with the following parameters: ultraviolet wavelength 405nm, power 60W, curing time 20 minutes. During curing, the aligner is turned over regularly to ensure uniform overall curing and improve mechanical properties and hardness. After curing, the support structures are removed, the connection points are gently polished with a diamond grinding head to achieve a smooth, burr-free edge, and secondary precision cleaning is performed to remove polishing dust.

IV. Quality Inspection and Process Advantage Summary

Finished product inspection adopts the mode of "100% precision inspection + sampling performance inspection": Dimensional accuracy is tested by a coordinate measuring machine, with 10 feature points (key tooth-fitting positions) selected, and all deviations are controlled within ±0.03mm, with a fitting gap ≤0.04mm. Surface quality is inspected by a roughness meter, with Ra value ≤0.18μm, no scratches, bubbles, or depressions. For biocompatibility sampling, 3 finished products are selected per batch, and both cytotoxicity test and oral mucosal irritation test comply with ISO 10993 standards. Mechanical performance tests show that the cured aligner has a hardness of 88D and a tensile strength of 38MPa, meeting the requirements of bearing orthodontic force.

Compared with traditional manual fabrication processes, SLA technology shows significant advantages: the production cycle is shortened from 7 days to 1.5 days, with efficiency improved by more than 75%; personalized fitting accuracy is greatly enhanced, and the scrap rate is controlled below 0.5%; it is not dependent on technician experience, with a high degree of process standardization to ensure consistent quality of each aligner; design adjustments can be quickly made according to treatment plans to realize batch customized production of progressive orthodontic stage components, reducing unit production costs.

Conclusion

With core advantages of high precision, high efficiency, and personalization, SLA technology has become the core technology for customized production of dental orthodontic invisible aligners. Through scientific material selection, parameter setting, and post-processing processes, this application case successfully realizes the fabrication of invisible aligners that meet medical standards, effectively solving the pain points of traditional processes such as low precision, long cycle, and poor consistency. With the iteration of SLA technology and the upgrading of medical photosensitive resin materials, its application in the oral medical field will be further expanded to cover more products such as crowns, surgical guides, and orthodontic retainers, providing strong technical support for precision medicine and personalized treatment.