If you have a drawn curve (generated in dental software) import it in Fusion360 and go to Next Step
In this section we will go through the process of drawing a trim line for the aligner. Before we proceed we need to make sure that the previous step of preparing the mesh has been completed.
Select the reduced (Dental mesh body)
Check that you are in Design environment in Fusion360. You may want to hide all unnecessary geometries so it does not interfere with you line placement.
Press S key on your keyboard to bring up design shortcuts and type fit point spline. Now we can draw a curve onto your mesh by selecting mesh points.
Select the dental body again (wait as this may take a moment to process)
If you are having trouble selecting, at the bottom of Fusion software is view preferences, select the (grid) icon, enable (Snap to Grid)
Within the sketch pallet toolbar make sure (show points) + (snap) is enabled.
When selecting points on the mesh for the curve, you will notice that the mesh face you hover over turns blue and white points appear at its vertexes. Make sure that the curve points you are placing are snapping to these vertexes.
Vertex points diagram
Around the edge of each poly-triangle you may notice white shape indicators.
Your mouse should automatically snap to points on the surface:
Always be sure that your curve is attaching to these points/surfaces.
When placing the curve it will react and stretch and appear misshapen, only after connecting it fully it will assume its complete shape, finish the curve completely.
If it breaks, it is better to start again. If it sticks to itself and appears misshapen, do not worry this can be fixed afterward.
The first curve may seem difficult and may not work, persevere and spend some time on it in the beginning, get to grips with this, because once you understand how the curve reacts, placing the curve will be successful every time with minimum error.
The optimal way we have formulated how to place a curve along an STL mesh.
Place less points at the beginning, limiting to no more than 3 points per smaller tooth and 4 for a larger tooth. This will significantly reduce any complexity of error and allow a more natural flowing curve.
As the curve wraps around the back of the mesh you want to place more curves to compensate for height and flowing angle changes.
Avoid placing points on sharp points (No steep cliff edges). Do not break the Curve (Complete in one full piece). Do not worry about errors, carry on. You can amend this after.
Use the (View Cube) as much as possible.
Rotating using keyboard shortcuts may result in breaking the curve forcing you to start over again.
Rear Molars and inner curve
- When reaching the back of the molars, place more points on flatter faces to compensate for the acute change in height I usually add around 8 points around the rear molar to achieve the smoothest curve
- Use View Cube for rotation here
- As you begin to reach the inner front of the dental mesh, the surface geometry becomes very uneven, do your best to add points that allow shallowest curves and inclinations, more acute angles will cause the tool to lead out, as it will deem it not safe to proceed.
- Once you have completed the curve and connected the points press “enter” this will complete the curve your curve will then assume its final shape.
- Hide the Dental body and change to “top” view and inspect your curve for errors.
- If the Curve has snapped to another line, Do Not Worry. Add points on either side of the issue, then delete the point thus breaking the link.
Editing Trimming Line (Adding and Moving Points)
You can add new points by right-clicking on the curve and selecting (Insert Spline to point)
Delete points causing the curve to rest between existing points, insert a point between them.
Select a new point then press “M” key contained in the move/copy toolbar under “move type select (Point to point) (Origin point = Select the point) (Target point = Chosen vertex point) This will then snap to the vertex amending the curve.
Repeat this process for any errors/sharp curves.
Make the dental mesh visible/Change the appearance/ctrl+4. Hiding the wireframe and making the curve visible.
Follow the curve and look for areas that intersect deep into the mesh
(Repeat adding points moving by point to point process)
If the line is shallow do not worry, make sure that all points are connected to the vertex.
Remember that the vacuum form will add a “>mm” onto your overall stock size so any minor gaps in the curve will be trimmed.
Building the Guide wall
When creating a trimming toolpath, Fusion360 needs two things: a line to follow and geometry to orient the tool. If we were to use dental mesh that we have for our geometry the change in surface orientation of the mesh along the trim line would result in drastic and unpredictable tool behaviour that would result in collisions. To avoid this we have developed a technique that maintains constant tool inclination along the whole of trim line by use of a guide wall geometry.
Follow these steps to build a guide wall.
Hide the Dental mesh>Select the curve>copy/paste>Within Move/Copy toolbar select select Pivot>Select the (Center point) of your (working origin plane)>select the Tick icon>change the Z distance to +3 and select OK
A Loft connects two curves together to form a body.
Follow these steps to loft the two curves together.
>Select both curves>select surface>create>loft>ok. (This will loft the two curves and create a body from them)
Thickening the body will add edges to the body. When selected in CAM (Manufacture) acts as the boundary plane. Meaning the tool will only try to stay perpendicular to the outside face.
Select the body>Surface>create>Thicken (This will automatically add thickness to the wall) be sure that Thickness is added inside of the curve around 1mm
Rename this Guide wall > delete the copied sketch curve above>delete the previous guide body.
Move the guide wall -2mm Z distance (Remember set pivot centre origin before moving)
Below is a drop-down diagram of the whole process.
Go to Next Step to prepare toolpath.