in vitro part :
All selected primary molars should fulfill the following criteria:
Freshly extracted molars with at least three sound walls.
Retain at least one third of their roots Teeth preparation All soft tissue debris
will be removed with a hand scaler and teeth will be disinfected, and then stored in
distilled water at 4 degrees Celsius until the start of the study.
Pulpotomy procedures will be performed to the extracted molars and the molars will be
filled. Then, they will be randomly allocated into two groups.
Group 1: Will receive 3D-printed crowns Group 2: Will receive prefabricated zirconia
crowns The specimens will be embedded perpendicularly in Polyvinyl chloride (PVC) cubes
with the occlusal surface parallel to the ground using acrylic resin extending 2mm below
the cementoenamel junction.
Evaluations: teeth in both groups will be evaluated for the following:
Marginal gap:
Precementation measurements of the cervical vertical marginal discrepancies will be
performed before cementation., Four optical images for each specimen will be
captured using a stereomicroscope (Wild 400, Switzerland) at a 32× magnification.
Images will then be transferred to the computer software for image analysis.
Fracture Resistance:
An axial loading condition through the functional cusp will be defined in the mechanical
failure description. Failure-to-fracture strength will be tested with a universal testing
machine (LLOYD machine) at a 0.5 mm/sec crosshead speed. Application of a round-end
vertical loading tip on the occlusal third of a specimen fixed into a loading apparatus
as functional loading simulation.
in vivo part : Teeth will be polished using a polishing paste and brush, and dried before
being examined.
A dental mirror will be used for clinical examination under light emitting diode (LED)
illumination to confirm the fulfillment of the inclusion criteria of the patient's
selection.
The molars will be randomly allocated into two equal treatment groups 23/each):
Group 1: 3D-printed crowns
Group 2: prefabricated zirconia crowns
Pulpotomy procedure for both groups:
Local anesthesia will be administered.
Teeth will undergo pulpotomy procedure' as follows:
Caries removal will be done using a large size 4 round bur, mounted onto a
high-speed hand piece with constant coolant.
All access cavity walls will be flared to allow complete exposure of the pulp
chamber, and easy undisturbed access to the canals, followed by removal of all the
soft pulpal tissue tags by a sharp spoon shaped excavator.
Bleeding control will be done using moist cotton pellet with gentle pressure.
Formocresol will be applied using a cotton pellet for 3-5 mins, for fixation.
The pulp chamber will be filled with re-inforced zinc oxide and eugenol that will be
mixed according to manufacturer's instructions.
Analgesics will be prescribed to the patient to be taken when needed.
Intervention Group 1:
Crown reduction: The teeth will be prepared using taper diamond bur with round end
for buccal, lingual, mesial, and distal wall for 0.8- 1 mm, producing a chamfer
margin circumferentially, and then, reduction of the occlusal surface will be done
using a round wheel to produce occlusal clearance of 1.5 mm.
Impression for the preparation will be taken using putty and light poly vinyl
siloxane material.
The impression will be sent to the lab and the patient will be dismissed.
The preparation will be optically scanned in the lab and the crown will be digitally
designed using computer designing software.
The crown will be printed using 3D printer.
The 3D printed crown will be cemented in the 2nd visit.
Control: Group 2:
Crown reduction:
In order to compensate for the thickness of zirconia crown, reduction will be
performed on the mesial, distal, buccal and lingual surfaces of the tooth for
0.7-1.75mm. Reduction will be performed using fine needle stone in the
beginning to free the contact from the adjacent teeth then followed by
reduction of the other surfaces using a diamond stone.
Reduction of the occlusal surface will be performed using a flame stone or
wheel stone to produce occlusal clearance of 1.5- 2 mm.
All line angles will be checked to remove any sharp line angles.
Selection of the matching size from zirconia crowns will be made taking into
consideration that the preparation must be free from any undercuts to avoid crown
fracture.
After checking the selected size of the crowns, it will be removed, dried and
cemented to the tooth using resin cement.
Method of evaluation:
After cementation , at baseline ,3rd ,6th and 12th months evaluation of the crowns will
be performed clinically using the modified U.S. Public Health Service criteria for
retention, marginal integrity and gingival health for both groups. Also, parental
satisfaction will be evaluated at end of the study using 5-point likert scale.