We would like to develop a mechanical testing technique to investigate the factual resistant and behavior of minimally invasive restorations or any fixed dental restoration cemented to tooth analog materials rather than the use of natural teeth and the use of general standard test, such as uniaxial and biaxial bending test. The one millimeter thick occlusal veneers milled from CAD/CAM in nano ceramic with lower effectual strain have superior factual resistant than conventional lithium disilicate. Still, both demonstrated adequate factual strain, again, voluntary and involuntary, maximum bite force and are promising materials for restoring posterior teeth under a minimally invasive scheme.
This is a simple and repeatable method for new dental researcher interested in testing novelty developed restorative materials. To begin, use coarse and find diamond burrs to anatomically reduce the occlusal surface of the typodont mandibular first by one millimeter and bevel the margin. Next, scan the prepared typodont using a dental laboratory scanner.
Open the scan file with OrthoAnalyzer in the CAD software. In the sculpt toolkit window, select the wax knife tool, then set the diameter to 2.6 millimeters and level to 63 micrometers. Gradually pull each root surface toward each other to merge the bifurcated roots into a single root to facilitate the milling process.
Next, mill the tooth analog dyes from high pressure fiberglass laminate material using a five axis milling machine. In the Autodesk Inventor Professional 2025, design a jig to fit the root section of the model tooth and align it with the space inside the polyvinyl chloride end caps. Next, print one jig per test tooth in polymethylmethacrylate or a material with a similar modulus using a 3D printer.
Combine the root parts and dyes with the polyvinyl chloride end cap. Mix the cold curing low viscosity epoxy resin and pour it up to the cemento-enamel junction region of the model teeth, taking care to avoid contamination of the occlusal surface. Leave the epoxy resin to set fully at room temperature for at least 24 hours.
Import the scan file of the tooth analog into the CAD software. In the Directions menu, determine the insertion direction for the occlusal veneer. Under Interfaces, select margin line and mark the margin line of the scan tooth analog.
Then, select dye interface. And from the Advanced Settings, adjust the cement gap to 0.025 millimeters and the extra cement gap to 0.050 millimeters. Next, under Anatomy Design, create a one millimeter thick occlusal veneer using a template from the Smile Library.
Adjust the veneer as needed using tools and sculpt. To begin, place the restoration onto the prepared master dyes by loading it under a silicone filled compression head in the universal testing machine at a 40 Newton load. Cure the restoration using a light-emitting diode at a light intensity of 1, 000 to 1, 200 milliwatts per square centimeter in normal mode for one to two seconds.
Remove any excess cement and continue curing each surface for 20 seconds. After curing, remove the restoration from the universal testing machine and place it in distilled water at 37 degrees Celsius for 48 hours to allow the cement to fully cure. Before testing, use fine permanent markers to draw three medial lateral reference lines and three anterior posterior reference lines in different colors on restorations.
Position the test specimen in the center of the lower platen of a mechanical testing machine equipped with a five kilonewton load cell configured for compression testing. Then, place a 5.5 millimeter diameter stainless steel ball in the central fossa of the restoration, aligning it at the intersection of the central reference lines. Place a protective acrylic ring around the specimen and a debris shield in front of the testing machine to contain any potential flying debris.
Lower the crosshead until it is nearly in contact with the steel ball. Then, set both load and displacement to zero. Next, apply compression at a rate of one millimeter per minute until the restoration fractures signaled by a sudden drop in load.
Record the fracture load. After the fracture, remove the debris shield and acrylic ring. Carefully collect the test specimen and its fragments.
Mount eyepiece camera on the stereo microscope. Using stereo microscopy software capture aerial and side view images of the samples at 20x magnification. For scanning electron microscopy, cut the specimen at the cemento-enamel junction and place it in an acetone bath in an ultrasonic cleaner.
After air drying the specimen, apply a gold coating to the surface. Capture images of the aerial and side views at 250 to 300x magnification. Stereo microscope images of fractured occlusal veneers from LD and RNC showed a surface ring shaped crack at the intersection of central reference lines at the central fossa.
This crack, part of the Hertzian cone crack system extended into the deeper restoration layers. Fractographic analysis revealed that both LD and RNC consistently fractured at the distal lingual aspect except for one RNC sample with a buccolingual fracture. Scanning electron microscope images showed that the fracture surfaces of RNC appeared rough and fibrous due to nano ceramic filler impregnation indicating plastic deformation.
In contrast, LD fractures propagated straightforwardly, forming multiple distinct fracture pieces.
