Carbon Printers KeyPrint KeySplint Soft™ Clear is a dual-cure photopolymer resin within the KeyPrint portfolio supplied for the Carbon Digital Light Synthesis (DLS) platform. The material is indicated for the fabrication of clear, flexible occlusal splints, bite guards, and removable dental appliances. The product is packaged in a sealed resin cassette that carries radio-frequency identification data and binds the printer to a validated resin profile. In the cured state, KeySplint Soft™ Clear belongs to the elastomeric segment of the KeySplint family and is specified as a Shore A flexible material rather than the rigid Shore D classification of KeySplint Hard. Representative published hardness data place the cured material in the Shore A 80 range. Biological evaluation testing includes ISO 10993-5:2009 for cytotoxicity and ISO 10993-10:2010 for sensitization and irritation. The resin is manufactured under a quality management system aligned with ISO 13485:2016, and finished devices are controlled under 21 CFR Part 820 when distributed in the United States.

What Limits the Mechanical Performance of KeySplint Soft™ Clear in Occlusal Splint Service?

The mechanical response of the cured resin is determined by a two-stage cure sequence. In the first stage, continuous liquid interface photopolymerization occurs through an oxygen-permeable window. The oxygen inhibition zone at the window maintains a liquid dead zone that permits the build platform to move continuously while photopolymerization proceeds above the dead zone. In the second stage, thermal post-cure drives conversion of residual methacrylate and acrylate groups, raises crosslink density, and reduces the unreacted monomer fraction that would otherwise migrate from the appliance surface. The distinction between the flexible and hard grades is primarily a function of the oligomer backbone and crosslinker concentration. KeySplint Soft™ Clear uses a lower crosslink density network that yields higher elongation and lower flexural modulus than KeySplint Hard.

For selection purposes, the flexible grade is substantiated by Shore hardness testing under ISO 7619-1:2010 and flexural property testing under ISO 178:2019. Because the material is an elastomer, tensile data under ASTM D638-14 are reported for elongation at break and tensile strength. The manufacturer’s technical data sheet lists property values that are batch-controlled through the printed resin cassette. When the thermal post-cure step is shortened or performed in an oxygen-rich chamber, the surface of the appliance can remain tacky and the measured Shore A value can fall below the lower acceptance limit. Operators should therefore treat the post-cure profile as a critical process parameter rather than a generic drying step. Service performance under bruxism is influenced not only by the resin but also by minimum wall thickness and occlusal contact area; thin regions below the design guideline can tear even though the bulk material is flexible.

On the production floor the resin cassette is loaded into a Carbon DLS printer and the RFID tag instructs the software to apply a resin-locked build profile. The profile defines exposure energy, build temperature, layer height, and support strategy. The validated layer height for KeySplint Soft™ Clear falls within the Carbon DLS capability range of 25 µm to 100 µm; production builds normally use the upper end of this range to reduce print time while maintaining occlusal surface detail. Parts are oriented in the build preparation software so that the occlusal surface is angled away from the build window, which reduces the number of support contact points on functional cusps. After the build, the platform is removed and the parts are transferred to a two-stage solvent wash. A first wash with isopropyl alcohol or an approved solvent removes gross liquid resin, and a second clean-solvent wash reduces residual monomer on internal and external surfaces. The Carbon Smart Part Washer provides consistent agitation and solvent exposure; manual washing in a static bath is not recommended because it may not remove resin from occlusal grooves and retention undercuts.

After washing, the parts are dried in a low-temperature air stream and placed in the Carbon Cure Box for thermal post-cure. The cure profile for KeySplint Soft™ Clear is resin-specific and is not interchangeable with KeySplint Hard or other KeyPrint resins. Inert or controlled ventilation in the cure chamber limits surface oxygen inhibition during the thermal stage. Batch records should include the cassette lot number, wash solvent batch, wash duration, dry time, and post-cure cycle identification. These records form part of the device master record under 21 CFR Part 820 and support traceability for each appliance. Because the liquid resin is hygroscopic in the cassette, the cassette must remain sealed when not in use; exposure to high humidity can introduce water into the polymerization zone and reduce green-part strength.

The optical clarity of KeySplint Soft™ Clear after post-cure is sufficient for a transparent occlusal appliance, but final clarity depends on post-processing as much as on the resin itself. Support removal should be performed with a sharp instrument or rotary tool before post-cure; removing supports after the thermal cure step becomes more difficult because the elastomer gains toughness and support nibs may tear the surface. Splints are typically finished with a series of decreasing grits and then polished with a clear acrylic or silicone polish. Aggressive polishing can generate frictional heating that softens the elastomer and creates burnished marks; low-speed polishing with intermittent contact is therefore used. The material is not supplied with a separate clear coat, and the application of a light-cured glaze is not covered by the manufacturer’s process validation unless specifically stated in the current instructions for use.

For optical inspection, the part should be examined under a light source for haze, trapped solvent, or white stress zones near supports. Haze can indicate retained solvent or incomplete washing; white zones can indicate polymer-water interaction or rapid stress application during support removal. The production unit should reject parts with visible surface defects on the occlusal contact area because such defects can act as stress concentrators under cyclic bruxism loading. Dimensional verification is performed on a printed or stone model, and the marginal fit should be evaluated at the buccal and lingual flanges before the appliance is delivered.

When KeySplint Soft™ Clear Replaces Thermoformed PMMA in a Digital Splint Workflow

In a conventional splint workflow, a stone model is duplicated from a dental impression, and a poly(methyl methacrylate) sheet is pressure-formed over the model, trimmed, and polished. When KeySplint Soft™ Clear is used, an intraoral scan or digitized cast is converted into a splint design with variable occlusal thickness, buccal wrap, and retention features. The design file is nested in the Carbon build preparation software, supports are generated, and the part is printed directly on the DLS platform. The printed appliance is then washed, post-cured, and polished. This route eliminates the stone model and thermoforming sheet but introduces a different set of process controls: build orientation, support placement, wash completeness, and post-cure uniformity become primary determinants of final fit and mechanical behavior.

The flexible grade is indicated for patients requiring a soft occlusal surface, including temporary joint decompression and nocturnal bruxism management. The rigid KeySplint Hard grade remains appropriate for splints that must resist high occlusal load with minimal deformation. Direct substitution of one grade for the other without design review can produce clinical failure: a hard splint geometry with thin posterior extensions may become overly flexible in the soft grade, while a soft splint geometry remade in the hard grade may create high stress concentration at the anterior contact point. Material selection should therefore be paired with appliance design verification under the relevant dental device standards, including ISO 20795-2:2013 for orthodontic base polymers where applicable.

Printer compatibility extends to Carbon DLS systems that accept the KeyPrint cassette form factor. The Carbon M2 production printer, for example, provides a build volume of 189 mm × 118 mm × 326 mm, allowing multiple splints to be nested in a single build. The cassette RFID data set instructs the printer to apply the resin-locked profile; if the printer is not recognized or the software version does not support the resin, the build is blocked. This hardware-software lock prevents the use of KeySplint Soft™ Clear on unvalidated third-party printers. Laboratories operating multiple Carbon printer models should verify the first build from each machine separately because build light intensity calibration and part orientation constraints can produce slight differences in support contact location and surface finish.

Assessing Batch-to-Batch Variance in Flexible Splint Production

Batch-to-batch variance in dual-cure resins is controlled through resin lot release testing before cassette filling. The manufacturer releases each lot for viscosity, cure speed, and mechanical properties after standard post-cure. On the printing side, cassette RFID data allow the printer software to compensate for minor lot-specific exposure requirements so that the operator does not manually adjust exposure energy. Despite this compensation, production-scale failure modes remain possible when the wash solvent is saturated with dissolved resin, when the post-cure oven is loaded beyond its validated part density, or when parts are stacked in the Cure Box such that shadowing prevents uniform heat and light exposure. These failures typically appear as tacky surfaces, reduced Shore A hardness, or increased water sorption rather than as catastrophic build collapse. Therefore, the first build after a new cassette lot or after a wash-solvent change should be inspected with a durometer and visually checked for surface haze or residual tack before the remaining appliances are processed.

The continuous liquid interface process itself reduces the discrete layer lines observed in conventional digital light processing, but anisotropy is not fully eliminated. Support contact points and abrupt changes in cross-section can still generate local differences in conversion and surface roughness. When occlusal contact surfaces are placed facing the build window without sufficient support, the green part may deflect during continuous separation and produce dimensional error. Nesting software compensates for some of this deflection, but the operator should confirm that the first printed splint from each new design file fits the printed model or digital cast with an even marginal gap. Published data for specific wear rates of this flexible material under continuous bruxism are limited; bench-top abrasion data cannot be directly extrapolated to long-term clinical wear.

KeySplint Soft™ Clear Versus KeySplint Hard and Third-Party Flexible Splint Resins

The following table summarizes the principal differences relevant to material selection and process routing. The table is qualitative because batch-specific quantitative values are controlled by the manufacturer’s technical data sheet and certificate of analysis.

KeySplint Soft™ Clear is indicated only for removable dental appliances and is not intended for permanent implantation, orthodontic tooth movement, or long-term continuous wear beyond the prescribed treatment period. The resin cassette must be stored under the ambient temperature and light-exclusion conditions printed on the cassette label; prolonged exposure to UV or sunlight can initiate premature photopolymerization in the cassette. The liquid resin should not be mixed with other KeyPrint resins or third-party resins because the resin-locked exposure and post-cure profiles are formulation-specific. In the washed and cured state, the appliance should be cleaned with neutral pH detergents; strongly alkaline or amine-containing disinfectants may attack the ester linkages in the cured network and reduce tear resistance. Autoclave sterilization is contraindicated because the elastomer may soften and distort at the temperatures used in steam sterilization. If disinfection is required, the manufacturer’s approved chemical protocol should be used, and the appliance should be inspected for dimensional change after repeated cycles.

Solvent exposure is another operational boundary. Parts left in isopropyl alcohol beyond the validated wash duration can swell, absorb solvent, and exhibit a temporary reduction in Shore A hardness that may not recover after post-cure. Parts that are washed but not sufficiently dried before post-cure can develop surface haze and lower optical clarity. The production unit should therefore maintain written work instructions for wash time, dry time, and post-cure loading density. When a new operator or a new cassette lot is introduced, a first-article inspection should record surface appearance, hardness, and fit on a verification cast. If any of these records fall outside the acceptance limits, the batch should be quarantined pending root-cause review rather than released on the basis of visual transparency alone.