A Comparison of Anterior Pediatric Zirconia Crowns and Bonded Composite Resin Strip Crowns: A One-year Feasibility Study
Phase: NA
Conditions: Caries, Dental
Sponsor: The Hospital for Sick Children

Study Title: A comparison of anterior pediatric zirconia crowns and bonded 
composite resin strip crowns: one-year feasibility study 
 
Principal Investigator: 
Michael Casas, DDS, MSc, FRCDC 
Dentist-in-Chief, Department of Dentistry 
Project Investigator, Child Health Evaluative Sciences, Research Institute 
The Hospital for Sick Children 
Associate Professor, University of Toronto 
 
Co- Investigators: 
Stéphanie Labbé, DMD 
Pediatric Dentistry Graduate Student, University of Toronto, 
Department of Dentistry, The Hospital for Sick Children 
 
Gabriella Garisto, DDS, MSc, FRCDC 
Director, Dental Education, Department of Dentistry 
The Hospital for Sick Children 
Associate Professor, University of Toronto 
 
Edward Barrett, BSc, DDS, MSc, FRCDC 
Director, Paediatric Dentistry, Department of Dentistry 
The Hospital for Sick Children 
Assistant Professor, University of Toronto 
 
 
 
 
 
 
 
 
 
 
 
 
 
Date of Document: March 1, 2019 

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Background 
 
Bonded composite resin strip crowns (strip crowns) are routinely used by pediatric 
dentists to restore carious primary incisors.7 Advantages of strip crowns include: good esthetics, 
ease of repair, ability to restore crowded incisors, and the availability of various shades.5, 6 
Unfortunately, strip crowns are technique sensitive and intolerant to moisture contamination 
from saliva or blood during placement.5, 6 Furthermore, shade mismatch, unaesthetic crown 
contours, loss of composite resin, marginal defects and marginal gingivitis have been reported at 
follow-up. 9 Parents reported overall good satisfaction for strip crowns, regardless of their 
dissatisfaction for color, shape and appearance, but reported overall poor satisfaction when their 
child’s strip crown was lost. 8 Retention rates of 49% at 6 months 1, 70% at 6 to 27 months 2, 
78% at more than 3 years 9, 85% at 6 to 24 months 4 and 88% at an average follow-up of 18 
months were reported in the literature.  However, retention was not consistently defined in those 
studies. Times to failure were also incorrectly depicted due to the unclear follow-up protocols in 
those studies. 
 
In 2008, zirconia crowns were introduced to pediatric dentistry as an alternative restorative 
option.7 Purported advantages of the pediatric zirconia crowns included: excellent esthetics, 
resistance to fracture, biocompatibility, reduced plaque accumulation, color stability, and 
potentially less technique sensitivity. 5, 7, 10, 12, 13 Excellent esthetics were reported by clinicians 
and parents. 10 Resistance to fracture was measured in vitro, using an inappropriate model that 
did not represent physiologic forces applied to teeth. 12, 13 Biocompatibility and reduced plaque 
accumulation were found to be due to the polished surface of zirconia crowns leading to less 
gingival inflammation, when compared to veneered stainless-steel crowns. 10, 15 Color stability 

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was reported but not measured, being visually compared to natural adjacent teeth. 10 The 
statement of decreased technique sensitivity was questionable, as zirconia crowns need to be 
cemented with glass ionomer cements, which are sensitive to moisture contamination.  Those 
conjectured advantages of zirconia crowns were supported by studies with little validity due to 
extensive exclusion criteria, unsatisfactory sample sizes, unreproducible protocols or unclear 
data collection criteria.  
 
One of the demonstrated disadvantages of the zirconia crowns compared to strip crowns was 
increased tooth reduction necessary, due to its inflexibility and thickness, in order to fit the 
zirconia crown to the tooth.7 The amount of tooth reduction required for zirconia crowns was 
demonstrated in vitro using typodont teeth, weighted before and after tooth reduction. Anterior 
zirconia crowns required more than double the amount of tooth structure reduction, when 
compared to anterior stainless steel crowns. 7 Furthermore, limited shade selection, limited 
potential to alter the shape of the crown, and the cost per crown represented additional potential 
disadvantages of zirconia crowns. 5, 7, 10  
 
Pediatric zirconia crowns have a reported survival outcome ranging from 80.2% to 100% at 6 to 
30 months. 10, 11, 14, 15, 16 Literature on primary zirconia crowns is limited to retrospective studies, 
case reports, one prospective study and one randomized control trial. The lowest survival rate 
(80.2%) was found at 24 months in a prospective study using an unconventional restorative 
method. In that study, one operator restored maxillary primary incisors that were deemed non-
restorable with conventional techniques.14 No details were given in regard to the definition of 
“conventional techniques”. Severely degraded primary maxillary incisors were included in the 

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study after parents requested treatment rather than extraction. The incisors were treated with a 
method using glass ionomer (Fuji IX) post and core following pulpectomy, and then restored 
with zirconia crowns. This same study revealed a survival rate of 95.3% at 12 months.14 Survival 
was defined as presence of the zirconia crown. As this method does not mimic clinical reality, 
zirconia crowns potentially present a retention rate of 96 to 100% at 6 to 30 months, according to 
the current literature representative of clinical practice. 10, 11, 12, 15, 16 With always only one time 
point included during the follow-up of the investigations, these studies provide an incomplete 
picture of time to failure. Once again, retention was not consistently defined in studies.  
 
To date, only one randomised controlled trial comparing full coronal coverage restorations for 
primary maxillary incisors (pre-veneered stainless steel crowns, bonded resin composite strip 
crowns and zirconia crowns) has ever been performed. In this randomized controlled trial, 39 
healthy patients underwent dental treatment done by 3 trainees of unspecified level, using local 
anesthetic and physical restraint only. Teeth requiring pulp therapy secondary to carious 
exposure or trauma were excluded from the clinical trial, as were teeth in children requiring 
sedation, special needs patients, patients with a deep bite, bruxism or presenting signs of attrition 
on lower incisors. The results showed a retention rate of 100% for zirconia crowns at 6 months, 
followed by 95% for pre-veneered stainless-steel crowns and 78% for bonded resin composite 
strip crowns.15 The strict exclusion criteria limited the validity of the study, as it may not 
represent clinical practice.  
 
Despite the apparent increase in popularity of the zirconia crowns in the practice of pediatric 
dentistry, studies examining their clinical outcomes are extremely variable as they are based on 

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expert opinions, case reports, retrospective studies and one randomised controlled trial of 
questionable design. This indicates the lack of good scientific evidence to justify the clinical use 
of zirconia crowns. To assess the clinical outcome of pediatric zirconia crowns and to provide 
evidence-based treatment, a prospective, well controlled study would be beneficial. Due to a lack 
of existing outcome data for bonded resin strip crowns and zirconia crowns, a feasibility study is 
indicated to establish the basis for randomized controlled trial design.  The goal of this feasibility 
study is to compare the clinical outcomes of the zirconia crowns and bonded composite resin 
strip crowns in primary maxillary incisors.  
 
Aims 
1. To statistically compare the one-year survival of resin composite strip crowns and 
zirconia crowns in primary maxillary incisors. 
 
2. To statistically compare the frequency of pulp therapy required for placement of zirconia 
crowns and resin composite strip crowns in primary maxillary incisors.  
 
3. To measure the frequency at which teeth randomized to zirconia crowns are deemed 
restorable with strip crowns only, and not zirconia crowns.  
 
Null hypotheses  
 
1. There is a statistically significant difference between the one-year survival of resin 
composite strip crowns and zirconia crowns in primary maxillary incisors. 

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2. There is no statistically significant difference between the frequency of pulp therapy 
required for placement of zirconia crowns and resin composite strip crowns in primary 
maxillary incisors. 
3. The frequency at which teeth randomized to zirconia crowns are deemed restorable with 
strip crowns only, and not zirconia crowns, is 0. 
 
Alternative hypotheses  
 
1. There is no statistically significant difference between the one-year survival of resin 
composite strip crowns and zirconia crowns in primary maxillary incisors.  
2. There is a statistically significant difference between the frequency of pulp therapy 
required for placement of zirconia crowns and resin composite strip crowns in primary 
maxillary incisors. 
3. The frequency at which teeth randomized to zirconia crowns are deemed restorable with 
strip crowns only, and not zirconia crowns, is greater than 0. 
 
Materials and methods 
 
Eligible children will meet the following inclusion criteria: i) 18 to 48 months of age, ii) 
ASA I and ASA II who will receive treatment under general anesthesia at The Hospital for Sick 
Children, and iii) one or more carious or fractured primary maxillary incisors that require full 
coverage restoration based on clinical judgement and criteria listed below.  
 

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Inclusion criteria for zirconia crowns and strip crowns are the same: 16  
1. Incisors with large carious lesions not restorable with intra-coronal restorations 
2. Incisors that have received pulp therapy 
3. Incisors that have been fractured and have lost an appreciable amount of tooth 
structure 
4. Incisors with multiple hypoplastic defects or developmental disturbances 
5. Incisors with small interproximal lesions with large areas of cervical 
decalcification 
 
Incisors will be ineligible if  i) patient is ASA III or higher, ii) associated with signs and 
symptoms of irreversible pulpitis and/or clinical evidence of an odontogenic infection, iii) there 
is radiographic evidence of pathological root resorption, root fracture secondary to trauma or 
periapical radiolucency, iv) lacking adequate dental coronal structure to allow restoration with 
full coverage restoration, and v) patient has non-English speaking parents.  
 
 
Prior to commencement of the project, one of the investigators (SL) will review screening and 
eligibility criteria with the Department of Dentistry at The Hospital for Sick Children. Clinical 
staff in the Department of Dentistry will identify potentially eligible patients during regular 
ambulatory clinic scheduling of patients for oral care in the OR. 
 
The department research coordinator will obtain consent from prospective patients to participate 
in the research project. The treating pediatric dentists (EJB, MJC, GG) will confirm continuing 
consent on the day of the treatment under general anesthesia.  

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After induction of general anesthesia, following the confirmation of incisor restorability by the 
treating dentist, each study participant will be randomly allocated to either the strip crown or the 
zirconia crown group. The assignment will be done using a computer-generated simple random 
number sequence with a one to one allocation ratio in a Research Electronic Data Capture 
(REDcap) database . The treatment will be consistent for each patient for all eligible teeth, 
although the experimental unit is the incisor. If one of the incisors in one patient is deemed non-
restorable, this incisor will no longer be eligible for the study. If all of the incisors in one patient 
are deemed non-restorable, the patient will no longer be eligible for the study. 
 
The treating dentists are staff pediatric dentists at The Hospital for Sick Children. Training in 
zirconia crown technique will be provided by the manufacturer of the crowns used in this study.  
As the strip crowns are the current standard full coverage restoration provided for primary 
incisors, and the treating dentists all have similar education and experience, additional training 
for strip crowns will not be required.  
 
The restorative techniques will be carried out under general anesthesia, in the usual fashion for 
the strip crowns (Appendix 1), and following the manufacturer’s protocol for the zirconia crowns 
(Appendix 2).   
 
Commonly, four maxillary incisor teeth are affected by severe early childhood caries. Due to the 
nature of this study sample, i.e. pre-cooperative children with severe early childhood caries, 
tentative treatment plans are made prior to treatment in the operating room (OR). Radiographic 

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and clinical examinations are completed in the OR while the patient is anesthetized, and the 
treatment plan is finalized at that time. Therefore, on occasion, teeth that were planned to be 
restored with crowns at the ambulatory consultation, may be deemed non-restorable in the 
operating room regardless of the treatment group that they were randomized into. These teeth 
would be withdrawn as they will not receive crowns of either type.   
When a tooth is restorable with a crown, it may also require pulp (nerve) treatment if dental 
caries extends to the dental pulp. Pulp outcomes are largely independent of the restoration placed 
on the incisor. If the pulp treatment fails during the follow-up period (a small risk), the 
consequence would be odontogenic infection and extraction of the affected tooth is indicated, 
even if the restoration is intact.  Any remaining crowned incisors that are enrolled will continued 
to be followed in a child who loses a tooth to pulp therapy failure.  
Failure of a crown (fracture of the crown, dislodgement of the crown, etc.) will be documented 
as a treatment failure. The family will be offered replacement of the crown and not withdrawn 
from the investigation. The remaining crowned incisors will be followed for the study duration.  
All crowned incisors will be kept in the study and followed for outcomes unless the patient 
chooses to withdraw.  
Each research participant will be reassessed clinically at 6 and 12 months after treatment. 
Follow-up appointments will be scheduled by the department of Dentistry. Clinical reassessment 
will be conducted by one investigator (SL). Intra-oral photographs will be acquired at 6 months 
and at 12 months. All photographs will be taken by the same investigator (SL), using a 
standardized imaging format. Two photographs per patient will be acquired: one extra-oral 
photograph, limited to the maxillary right cuspid (tooth 53) to left cuspid (tooth 63); and one 
extra-oral maxillary occlusal photograph, limited to the maxillary right cuspid (tooth 53) to left 

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cuspid (tooth 63) (Appendix 3). Photographs will be taken with a Canon Rebel XSi and a Canon 
ring flash Macro Ring Lite MR-14EX II, using the following settings: shutter speed 1/200, ISO 
200 and aperture f25. Photographs will be stored in the Hospital for Sick Children’s online 
photograph database (Apollo).  
 
Parents will also take 2 photographs of their child’s using their own camera or phone. They will 
be provided with an example of those photographs (Appendix 4). Photographs found in appendix 
4 were taken with an iPhone X. They will send the photographs to the investigators via a secured 
Sickkids e-mail. Only the research investigators and the research coordinator will have access to 
the secured e-mail. Pictures sent by the parents will be stored on Appollo. A reminder to take the 
pictures at 6 and 12 months after the surgery will be sent using the secured e-mail.  Photographs 
taken by the parents will be used for the photographic assessment if clinical photographs are 
unsuccessful at the follow-ups and if they are of sufficient quality for assessment based on the 
investigators’ judgment.  
 
If the parents and the investigators cannot obtain photographs of a participant, the participant 
will no longer be eligible for the survival assessment.  
 
Clinical assessment, photographic assessment and data collection 
 
 
Treated incisors will be assessed for survival and clinical outcomes on a number of 
clinical criteria. The outcomes are as follows:  
 

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1) Survival outcome 
Clinical assessment  
Clinical assessment will be conducted by one investigator (SL), at the time of the 
follow-up appointments. The investigator will be a pediatric dental resident. She will 
clinically assess the incisors for restoration survival. The survival outcome measures 
will be statistically compared. The assessed criteria are: presence of the tooth (teeth 
lost prior to general anesthesia or during general anesthesia will be excluded from 
statistical analysis), presence of the restoration, integrity of the restoration, recurrent 
decay and discoloration. Each incisor will be classified as follows (Appendix 5): 
I: Intact 
D: Damaged; restoration present but not intact, clinically acceptable 
(minor chip of material, discoloration due to leakage); no immediate 
treatment recommended  
TR: Treatment required; restoration absent or restoration present with 
major failure or presence of recurrent decay on restored incisor; re-
treatment or extraction required 
 
Photographic assessment 
Photographic analysis will be conducted by two blinded disinterested expert raters. 
They will be two staff pediatric dentists. They will assess the photographs for 
restoration survival. Expert raters will be subjected to measures of intra-rater and 
inter-rater reliability. The survival outcome measures will be statistically compared. 
The assessed criteria are: presence of the tooth (teeth lost prior to general anesthesia 

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or during general anesthesia will be excluded from statistical analysis), presence of 
the restoration, integrity of the restoration, recurrent decay and discoloration. Each 
incisor will be classified as follows (Appendix 6):  
I: Intact 
D: Damaged; restoration present but not intact, clinically acceptable 
(minor chip of material, discoloration due to leakage); no immediate 
treatment recommended  
TR: Treatment required; restoration absent or restoration present with 
major failure or presence of recurrent decay on restored incisor; re-
treatment or extraction required 
 
2) Frequency of pulp therapy 
On the day of treatment under general anesthesia, the treating dentist, the dental 
assistant or the nurse will fill out the pulpotomy data collection form. Each treated 
tooth will be marked as having received a pulpotomy (P), or not having receveived a 
pulpotomy (X) (Appendix 7).  
 
3) Treatment plan alteration 
On the day of treatment under general anesthesia, the treating dentist, the dental 
assistant or the nurse will fill out the restorative treatment data collection form. Each 
form will be filled with the randomly assigned treatment and the completed treatment: 
zirconia crowns (ZC) or composite resin strip crowns (CRSC). The following 
questions will also be answered on the form (Appendix 7):  
 Did the patient receive the restorative treatment originally assigned?  

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o Yes 
o No 
 Deviated from randomly selected treatment because:  
o Severe attrition (bruxism) 
o Deep bite 
o Crowding 
o Other 
 
Storage of patient information 
 
Participants will be assigned to a unique study identification number. A password-
protected code-breaking file that corresponds to each unique identification number with patient’s 
identity name, DOB and MRN will be created. This file will be only accessible by the research 
investigators and the research coordinator. It will be stored separately from the study database. 
All study participants paper data collection forms and consent forms will be stored in individual 
participant research study charts, separate from the clinical charts. The charts will be kept in a 
locked filing cabinet in a locked office. Each participant’s chart will be labeled by the individual 
study identification number and have no patient identifiers. All collected data will be entered and 
stored in a REDcap database, on a password-protected computer, in a locked office. The data 
entered in the database will be de-identified by using only the unique study identification number 
to enter each patient’s data. The REDcap database will only be accessible to the research 
investigators and the research coordinator. The collected patient data entered into the REDCap 
database will include: 

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1. Date of initial examination 
2. Participant demographics: age and sex 
3. Number of carious maxillary incisors included in study 
4. Date of general anesthesia 
5. OR pulp data collection 
6. OR treatment data collection 
7. Date of first and second recall 
8. Photographic data collection 
9. Date of extraction of incisor and reason, if applicable 
 
Upon the conclusion of data collection, the data will be exported into an Excel spreadsheet for 
statistical analysis.  
 
Statisical Analysis 
 
Statistical analyses will be performed using SPSS. All treated teeth will be included in 
statistical analyses. A general estimating equation will be used to compensate for the lack of 
independence.  The two groups will be statistically compared for sex distribution with a chi-
square test and for age at the time of treatment with a sample t test. Logistic regressions will be 
corrected for age, sex, tooth and provider, and their effect will be compared with chi-square tests. 
A sample size calculation will be done to assess feasibility of a future randomized controlled 
trial.  
 
Outcomes analyses: 

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1. Survival outcome 
Expert raters will be subjected to measures of intra-rater and inter-rater reliability, using 
Cohen’s kappa test. The outcome measures will be statistically compared. Chi-square 
tests will be used to compare I, D and TR outcomes for strip crowns and zirconia crowns. 
Difference in survival of strip crowns and zirconia crowns will be calculated with log-
rank tests. Kaplan-Meier survival curves will be derived for strip crowns and zirconia 
crowns.  
 
2. Frequency of pulp therapy 
Frequency of pulp therapy for strip crowns and zirconia crowns will be compared using a 
chi-square test.  
 
3. Frequency of treatment plan alteration 
Frequency of treatment plan alteration will be demonstrated using a chi-square test. 
 
 
 
 
 
 
 
 
 

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