3D-printed Crowns Versus Zirconia Crowns for Primary Molars

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:

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• 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.

Inclusion criteria

• Children included in the study should stratify to the following criteria:

• Age range of children from 4 -7 years.
• Having at least one vital primary molar with deep carious lesion indicated for pulpotomy or pulpectomy.
• The expected exfoliation date of the selected primary teeth must be more than 12 months from the start date of the study.

Exclusion criteria

• a) Uncooperative children who needs sedation or general anesthesia. b) Children with physical, intellectual disability or medical conditions that may complicate treatment.

c) Teeth with poor prognosis due to the presence of an abscess or a sinus, mobility or advanced bone resorption.

d) Presence of internal or external root resorption.