Sample size calculation: G*Power 184.108.40.206 software (Franz Faul, Universität Kiel, Germany, 2014) performed for power analysis, indicated that we needed a total 120 teeth (corresponding to around 30 children to achieve 80% power with 95% confidence assuming medium effect size in the mean change in gingival health 6 months after crown application in the zirconia and composite groups with the assumption of non-normal distribution. The number of crowns in each arm will be 60.
Sample selection: A sample of 120 primary upper anterior incisors was treated in the Pediatric Dental Clinics, King Abdulaziz University, Faculty of Dentistry (KAUFD), at Jeddah, Saudi Arabia. (32 patients, 28 of them restorations were obtained to upper 4 anterior teeth and 4 of them restorations were done to upper tow central anterior teeth). All children visiting the clinics between November 1, 2015 to January 31, 2016 with the following criteria were included in the study:
- Healthy four to six years old children.
- Those having opposed anterior teeth.
- No history of systemic illness or dental developmental anomalies which can affect dietary patterns, caries susceptibility or the selection of restorative materials to the best of current knowledge.
- Minimal of two surfaces of caries in the targeted teeth.
- Patient with Early Childhood Caries as defined by AAPD, 2016.
- Cooperative patients who had behavioral rating “positive” or “definitely positive” followed the Frankl behavior classification scale (10).
Written consents were obtained from the parents/guardians after explaining the full details of the treatment procedure and its possible outcomes, discomfort, risks, and benefits.
No patient was excluded based on gender, race, social or economic background. Oral hygiene instructions were given and reinforced in each follow up visit.
Exclusion Criteria: Children having the following criteria were excluded from this research:
- Teeth with proximity to exfoliation and resorption of the root passed its half.
- Presence of single surface caries not involving the proximal surfaces.
- Teeth that have been subjected to trauma.
- Anxiety and lack of cooperation which required treatment under general anesthesia.
- Special health needs.
- Presences of teeth wear on the opposing teeth, or absence of opposing.
Study design: The present study was a randomized controlled clinical trial that followed the guidelines published by Consolidated Standards of Reporting Trials (CONSORT) (11). This research has been ethically accepted by the Committee of Research Scientific Unit at King Abdulaziz University with reference no. 076-16. Before enrolment, every patient’s parent/ guardian signed an informed consent sheet. The parameters that were evaluated in this study are listed in Table 1. Also, the presented research was registered at ClinicalTrials.gov under registration number NCT03184012.
Randomization: Concealment was applied for randomization of children in each group to either resin composite strip crown or zirconia crowns. Randomization was done using SPSS software version 20.0 (IBM Corp., Armonk, NY) Allocation concealment was assured by handling sequentially numbered opaque sealed envelopes to the attending candidate. At the time of crown application, an envelope was opened and allocate the child to the written restoration material inside that envelop.
Examiner calibration: The same examiner was responsible of preparation and evaluation. To test the reliability of the examiner and evaluate the restoration performance, sixteen teeth were treated by full coronal restorations then examined. The examiner evaluated those teeth based on the standard evaluation criteria of the study. The results produced by the examiner were analyzed using Cohen’s kappa to test intra-examiner reliability.
Procedure: All treatments were done under nitrous oxide sedation and physical restrains to manage the children behavior, topical anesthesia as well as local infiltration was administered. The following clinical procedures were done in each group:
A) Zirconia crowns: The crowns were selected previously based on the mesio-distal measurement of the tooth. Each tooth was prepared for “passive fit” as the zirconia crowns are not flexible. According to the manufacturer instructions, incisal edge was reduced to obtain a 2 mm clearance. For the labial surface: the 2-plane reduction was made close to natural tooth and for proximal surface the distance to the adjacent teeth was considered and parallel mesial and distal walls were created extending 1-2 mm subgingivally. Enough reduction of cingulum was done on the palatal surface. Feather-edge margins were provided about 1-2 mm subgingivally. After evaluation made for marginal fit, the zirconia crowns were cemented with light cure resin cement (NuSmile BioCem®) and firm consistent pressure at proper position was applied on the tooth till the initial set (Figure1).
B) Strip crowns: Prior to treatment appointments, strip crowns were prepared and adjusted. Escape venting holes were prepared by piercing the mesial or distal incisal angles of the crowns, this was achieved using sharp explorers (this hole formed a core vent to allow extra air bubbles trapped inside the crown to go out easily). Strip crowns were seated and fitted after applying a coating of resin-modified glass ionomer base to protect dentinal tissues. Each crown was cured individually after filling with composite resin as the adjacent strip crowns placed (unfilled) on their respective teeth to make sure that appropriate spacing between crowns preserved. A cleoid/discoid carver or scalpel was used to peel off the strip crown shell from the lingual side then ooclusion is checked and adjusted if needed (Figure 2).
Statistical Analysis: This study was analyzed using IBM SPSS version 23 (IBM Corp., Armonk, NY). Simple descriptive statistics were applied to characterize the variables of the study via tally and percentages for the definitive and nominal variables, whereas mean and standard deviations were used to represent the constant variable. In comparing the distributions of two variables, a chi-square test were used. These tests were assumed to be observing normal distribution. Friedman analysis was used to check the difference of Gingival Health, Plaque index, Recurrent caries, Restoration failure, Tooth wear of opposing relative to multiple time points and separated by crown types. These tests were done with the assumption of normal distribution.