3D printed occlusal splint: modelling in MeshMixer

The occlusal splint presents the most favourable ratio between modelling complexity and clinical applicability. Its dimensional tolerances permit it to be approached as the first case of the digital workflow without compromising the therapeutic outcome.

Rationale as an initial case

The tolerances associated with this appliance are considerably wider than those demanded by an indirect restoration. A discrepancy of some hundreds of micrometres that would render a crown unserviceable is resolved in the splint by adjustment with rotary instruments.

This permits the complete workflow — scanning, modelling, slicing, printing and post-curing — to be traversed in a case that admits correction, acquiring technical competence without risk to the treatment.

Starting material

• STL file of the receiving arch.
• STL file of the antagonist.
• Interocclusal record or models previously articulated in the established therapeutic relationship.

Where models are presented unarticulated, positioning with Transform (T) and Align (N) must precede any modelling procedure.

Stage 1 — Model cleaning

The Inspector (I) is run and discontinuities corrected. Irrelevant elements are then removed: excess gingival tissue, artefacts corresponding to tongue and buccal mucosa, and noise at the scan margins. Selection is performed with S and removal with X.

Stage 2 — Delimitation of the coverage area

Using Select Faces (S), the surface to be covered by the appliance is delimited: occlusal, buccal and palatal or lingual aspects up to the established height. Extent responds to the indicated therapeutic design and constitutes a clinical decision.

The boundary is regularised with < and > until a uniform line is obtained. Irregularities in the digital boundary are reproduced in full in the printed appliance.

Stage 3 — Shell generation

With the area delimited, Extract (Shift+D) is employed to generate a shell offset from the dental surface. This displacement fulfils two functions concurrently: it confers structural thickness and establishes the relief necessary for seating.

Alternatively, the sequence Offset (Ctrl+D) followed by Extrude (D) affords greater control over the direction of thickness.

Insufficient thickness predisposes to fracture in function; excessive thickness compromises comfort and alters vertical dimension beyond that planned. The appropriate value depends on the resin and the design and should be calibrated in the initial cases.

Stage 4 — Contact surface

This stage distinguishes a therapeutically effective appliance from mere occlusal coverage.

A surface reproducing the anatomy of the antagonist establishes an interdigitation restricting mandibular movement. For most therapeutic objectives the contrary effect is sought: a regular surface, with distributed contacts, permitting excursive gliding.

• The Volume Brush (3) is employed to regularise the occlusal aspect, eliminating the deep imprints of the opposing cusps.
• A brush of wide diameter and low intensity is recommended, adjustable with [ and ]. Broad movements produce uniform surfaces; short, intense movements generate irregularities.
• Incorporating the antagonist permits verification of contact distribution, avoiding concentration of load at isolated points.

The specific design — flat, with canine guidance, with an anterior ramp — responds to the diagnosis and to the therapeutic indication established by the practitioner.

Stage 5 — Consolidation and validation

1. Make Solid for conversion into a closed solid.
2. Separate Shells (Shift+Y), retaining only the appliance.
3. Inspector (I) to confirm a closed mesh and single component.
4. Sectional inspection to verify the absence of regions of critical thickness, particularly at the margins and over deep cusps.

Printing considerations

• Inclined orientation. In the horizontal position the cross-sectional area per layer reaches its maximum and the peel force may deform the piece or detach it from the platform.
• Supports away from the contact surface. Scarring on the occlusal aspect generates irregularities against the opposing tooth and demands manual adjustment.
• Appropriate resin. Formulations specific to occlusal appliances exist, with mechanical properties and regulatory status appropriate to intraoral use. Model resins are not substitutes.