الفهرس 
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Abstract
Crowns are an alternative treatment option to restore the natural appearance of a multi-surfaces badly decayed teeth of children. One of the most available esthetic pediatric dental crowns in the market today are the ready-made zirconia crowns. Nowadays, CAD/CAM technology is available in dental clinics and it is capable, via its software, of fabricating customized crowns for dentition at one appointment.
The aim of the current study was to compare hybrid ceramic CAD/CAM and prefabricated zirconia crowns restoring primary molars through: an in-vivo evaluation of the clinical performance of the two types of crowns. Moreover, an in-vitro assessment of the marginal adaptation of the both types of crowns.
Subjects and methods: for in vivo study, caries was removed and pulpotomy was performed when indicated. Tooth was prepared; occlusal reduction followed the anatomical contour, circumferential axial walls reduction up to warranty a passive fit of the restorations. The preparation margin was carefully extended to a smooth feather-edge beyond the CEJ.
For group “A” CAD/CAM VE crown, an optical impression was obtained through scanning each prepared tooth using intraoral scanner. In a full intercuspation between maxillary and mandibular arches, the preparation and gingival margins were defined automatically and manually designed. The crown path of insertion, the occlusal and interproximal contacts were determined automatically. A biogeneric design technique was used to set the crown design to the mandibular first permanent molar.
After suitable tooth shade selection, VE block was milled using a milling machine following the milling parameters. According to the manufacture protocol, the crown was polished and subsequently characterized with surface stain.
Following the manufacturer’s instructions, dual-cured, self-adhesive resin cement was applied to the prepared tooth walls. The restoration was gently set in place then cured with LED light cure. Excess cement was removed. Occlusion was re-checked for premature spots with an articulating paper.
For group “B”, a suitable prefabricated zirconia crown size (NuSmile) was identified. Cementation was performed as prescribed for the intervention group.
Children were recalled at 3 intervals (3, 6, 12 months). To assess the clinical performance; it was evaluated in terms of: crown retention, marginal adaptation, color match, proximal contact, and gingival health. Radiographic evaluation adopting the modified United States Public Health Service (USPHS) criteria. Parental satisfaction (via questionnaire) and overall satisfaction was recorded. Two pediatric dentists evaluated the two restorations independently at different follow-up periods.
In the in-vitro study; on a dental study model for primary dentition set, a second mandibular primary molar acrylic master tooth was selected. To standardize crown preparation, a single pediatric dentist was responsible for teeth preparation according to the technical guide instructions previously mentioned.
Twenty-five impressions were taken to the prepared tooth. The impressions were poured with an epoxy resin, 25 paired negative replicas were fabricated and allowed to set. A dowel pin was placed at the bottom of the die to provide an easy path of insertion and removal. group “A ”epoxy dies were restored with custom made CAD/CAM VE crowns and group “B” were restored with prefabricated PZCs (twenty-five epoxy resin dies per group).
Optical impressions of the 25 epoxy resin dies for group “A” were acquired. The milling procedure was done as previously mentioned.
After retrieving the crown out of its block, the restoration was hand polished. The inner surface of the crown was sandblasted with Al2O3. Then was salinized with a Vitasil and Vita Enamic Glaze was applied. It was polymerized with light-curing device. While the luting cement was set an axial load was applied with a loading apparatus. The excess cement was removed. Then, thermocycling process of specimens was done at a temperature between 5° to 55°C for 5000 cycles with a 20-25 seconds dwell time.
As for group “B”, a suitable E2 PZC size was placed for all specimens. Finally, the PZC was cemented using the similar luting cement that had been adopted in group “A”. Similarly, specimens’ storage and thermocycling were performed as prescribed in the CAD/CAM crown.
External marginal gap was measured by stereomicroscope for specimens; at magnification ×20. The digital images were captured with a digital HD camera and measurements were done using IMAGE J software. Furthermore, all the specimens were cut axially in two directions (mesiodistally and buccolingually) with a saw microtome and analyzed with SEM at magnification ×500.
Results : In-vivo results showed that the CAD/CAM VE crowns group “A” had better success rates than PZCs group “B” with no statistically significant difference at different follow-up periods ( p >0.05) for all clinical parameters (crown retention, marginal adaptation, color match, proximal contact, gingival health, radiographic evaluation and overall satisfaction) except for parental satisfaction for color and size of CAD/CAM VE crowns; they revealed higher satisfaction scores, which was statistically significant.
In-vitro results revealed that the mean external and internal marginal gap values of CAD/CAM VE crowns group “A” were significantly lower than that of PZCs group “B”.
CONCLUSIONS
Within the limitations of the current study, it can be concluded that:
1. Custom-made CAD/CAM VITA ENAMIC crown is a promising material for the restoration of primary molars.
2. Custom-made CAD/CAM VITA ENAMIC crown can be considered as an esthetic alternative to PZCs in primary molars.
3. CAD/CAM VE crowns showed a comparable superior clinical performance compared to PZCs after 12 months of follow-up.
4. Both CAD/CAM VE and PZCs crowns showed high parental satisfaction, parents were more satisfied with the color and size of CAD/CAM VE crowns compared to PZCs after 12 months of follow-up period.
5. CAD/CAM hybrid ceramics provide a remarkable marginal external and internal fitness and adaptation over the PZC in the restoration of primary teeth.
RECOMMENDATIONS
1. Clinical investigations should be conducted in order to define the clinically acceptable parameters for prefabricated crowns in terms of marginal and internal fit of primary molars.
2. Further experimental studies with larger sample size and different functional loads application are required to simulate the oral environment.
3. Investigations can also include 3D-printed crowns and CAD/CAM crowns using other ceramic material variety for restoring primary molars.
4. Researches using microcomputed tomography is important to evaluate the marginal adaptation of crowns for primary teeth.
5. Further studies with longer follow-up period is essential to evaluate clinical performance and success of CAD/CAM crowns for primary teeth.