Removable Partial Denture Abutments Restored With Monolithic Zirconia Crowns: A Randomized Controlled Trial
Phase: NA
Conditions: Crowns, Denture
Sponsor: Hiroko Nagaoka

 
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Study Title: Removable Partial Denture Abutments Restored with Monolithic Zirconia Crowns 
 
Institution/Site: 
University of Kentucky
Document (Approval/Update) Date:
02/09/16
NCT Number:
NCT03283709
IRB Number
17-0511-F1V
Coversheet created:
02/25/20
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

 
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Removable Partial Denture Abutments Restored with Monolithic Zirconia 
Crowns: A Randomized Controlled Trial 
 
 
This study will investigate the use of highly esthetic, second and third generation multi-layer zirconia crown 
materials to restore removable partial denture abutment teeth. All performed treatment will be the standard of 
care and to the usual and customary standards used in United states dental clinics for crown and RPD 
procedures. Treatment subjects will have RPD abutment teeth restored with either Noritake Katana STML 
(anterior teeth) or HTML (premolars and molars) zirconia crowns, and periodically evaluated for 60 months 
following RPD delivery. Outcomes will be compared to a similarly treated control group restored with metal, 
metal-ceramic, or a combination of metal and metal-ceramic crowns. 
 
Following informed consent, subjects will be randomly assigned using an internet program 
(https://www.randomizer.org/) to either a treatment (zirconia abutment tooth crown) or control (metal or metal-
ceramic abutment tooth crown) group. Using information from the oral examination, articulated diagnostic casts 
will be evaluated , the RPD design confirmed, and the need for a crown on one or more abutment teeth verified. 
Enrolled subjects will be given oral hygiene instruction at the beginning of the study. They will also be instructed 
to brush their teeth twice daily using an OTC fluoride dentifrice of their choice. They will also be asked to use a 
0.05% NaF oral rinse for 1 minute daily. 
 
Abutment teeth must be in function with the opposing arch and vital at the beginning of the study. Vitality will be 
be determined using a synthesis of history, percussion, palpation and pulp testing. Pulp tests will be conducted 
using cold and an EPT, and the facial, lingual and occlusal (incisal) surfaces of all abutment teeth will be tested 
for responsiveness. If abutment tooth vitality is confirmed, teeth requiring surveyed crowns will be prepared and 
restored using standardized clinical and laboratory guidelines. 
 
Abutment teeth restored with metal and zirconia crowns will be prepared and restored using the following clinical 
and laboratory guidelines. The margin will be a circumferential chamfer prepared to a depth of 0.5 mm with a 
rounded internal line angle and a 90° cavosurface exit angle. Margin height will be at or slightly coronal to the 
free gingival margin where possible. Axial surfaces will be prepared with a total occlusal convergence of >6° but 
not to exceed 20°. Incisal and facial surfaces will be reduced 0.7-1.0 mm. Functional surfaces will be reduced to 
1.0 mm of opposing tooth clearance with the exception of under rest seats, where opposing tooth clearance will 
be 2.0 mm. At completion, the prepared tooth should have a height to base ratio of 0.4. If inadequate retention 
and resistance form is identified following preparation of axial walls, supplementary grooves will be added, the 
number and location of which are at the discretion of the investigator. Final impressions will be made using PVS 
in a custom tray (Extrude) and poured in type V dental stone (Jadestone). Following fabrication, the working cast 
will be articulated, tripoded, and the die(s) sectioned, trimmed and scanned (3Shape D2000 laboratory scanner 
or equivalent). The crown(s) will be waxed to full contour. Rest seats, undercuts and guide planes will then be 
developed in wax. Once the waxup has been surveyed and finalized, it will be secured to the scanning platform 
and a new scan performed with the waxup in place. The data file with the die scan will be merged with the file 
that contains the waxup. The merged file will then be transmitted to a designated production facility where the 
zirconia crown(s) will be milled. Canines will be milled using Noritake Katana STML zirconia and premolars and 
molars will be milled using Noritake Katana HTML zirconia. Once the crown(s) are returned and the margins, 
contacts, occlusion and contours clinically verified, they will be luted using a self-adhesive resin-based cement 
(RelyX Unicem 2). 
 
Porcelain-fused-to-metal (PFM) crowns will be prepared and restored using a standard protocol utilizing the 
following guidelines. Posterior crowns will have metal occlusal surfaces with the porcelain-metal junction on the 
occlusal surface at half the distance between the central groove and the buccal cusp tip. Mesial, distal and 
lingual surfaces will be in metal, and the crown will have a disappearing metal margin on the facial surface. The 
facial preparation from mesiofacial to distofacial line angles will be a heavy chamfer or modified shoulder 1.0-1.2 
mm in depth with a rounded internal line angle and a 90° cavosurface exit angle. Mesial, distal and lingual 
chamfer margins will be prepared to a horizontal depth of 0.5 mm. Facial margin height will be at or slightly 
apical to the free gingival margin. Mesial, distal and lingual margin height will be at or slightly coronal to the free 
gingival margin if possible. Functional surfaces will be prepared with opposing tooth clearance of 1.5 mm with 
the exception of under rest seats where opposing tooth clearance will be 2.0 mm. Nonfunctional cusp reduction 
will be 1.0 mm. Final impressions will be made using PVS (Extrude) in a custom tray and poured in type V dental 

 
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stone (Jadestone). Following working cast fabrication it will be articulated, tripoded, and the die(s) prepared for 
conventional laboratory crown fabrication. Conventional (all-metal and PFM) surveyed crowns will be fabricated 
using noble and high-noble casting alloys and PFM crowns will use feldspathic porcelain as a veneering ceramic. 
Once the crown(s) are returned and the margins, contacts, occlusion and contours clinically verified, they will be 
luted using a self-adhesive resin-based cement (RelyX Unicem 2). 
 
Qualifying RPD designs may be Kennedy class I-IV with up to two modification spaces, and will be designed 
using a standardized protocol. Maxillary major connectors may consist of a complete palatal plate, modified 
palatal plate, anterior-posterior palatal strap or palatal strap. Mandibular major connectors will consist of either a 
lingual plate or a lingual bar. Frameworks will be fabricated from nickel-chrome alloy (Ticonium), the denture 
bases acrylic resin (Lucitone 199), and artificial teeth will be DENTSPLY Trubyte IPN Portrait. To meet the 
definition of an RPD abutment tooth it must host a direct retainer consisting of an occlusal or cingulum rest, a 
proximal plate and a retentive clasp. Reciprocation must be provided in the form of a plate, reciprocating clasp or 
minor connector and rest. The plan for occlusion will be based upon the number and distribution of remaining 
natural teeth. If an arch opposing the RPD is edentulous and restored by a removable complete denture, then 
natural and artificial teeth will be arranged in bilateral balance. If anterior guidance is present on natural teeth in 
both arches it will be preserved so that artificial RPD teeth contact opposing teeth in maximum intercuspation 
only. 
 
Clinical assessments, procedures and annual examinations will be performed in the University of Kentucky 
College of Dentistry second, third, and fourth floor student clinics. Clinical procedures will be performed by third 
and fourth year dental students, and clinical supervision for these procedures will be provided by licensed, 
calibrated investigators.   
 
 
 
ELIGIBILITY CRITERIA 
 
Study participants must be between the ages of 25-70 when they enroll in the study and be available for follow- 
up for five years following the conclusion of their treatment. Patients must be able to speak and read English, 
understand the study and informed consent documents, and be eligible for care in the UKCOD student clinics. 
You will be excluded from the study if you have any chronic or degenerative condition which impairs your consent 
capability including: 
 
 
traumatic brain injury 
 
severe depression or bipolar disorders 
 
 
schizophrenia or other mental disturbance with an associated cognitive impairment 
 
stroke 
 
degenerative dementia or Alzheimer’s disease 
 
CNS cancer or cancer with CNS involvement 
 
Parkinson’s Disease 
 
persistent substance dependence 
 
chronic pain 
 
any disorder with secondary drug effects which may result in fluctuations in consent capacity 

 
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Participants must also be healthy enough to tolerate planned dental procedures. Patients may be excluded if they 
require antibiotic premedication before dental treatments, and if they have been diagnosed with any of the 
following: 
 
 
severe anxiety 
 
unstable diabetes or asthma 
 
unstable hypertension 
 
COPD 
 
ischemic heart disease 
 
HIV/AIDS 
 
renal insufficiency 
 
autoimmune or inflammatory disorders 
 
Participants must also be capable of continuous participation and follow-up in the study once they enroll, so may 
be excluded for the following: 
 
 
pregnancy 
 
planned extensive leave such as 
o 
sabbatical 
o 
overseas military assignments 
o 
permanent relocation outside of the University of Kentucky treatment corridor 
 
Finally, subjects must be stable with respect to caries (decay) and periodontal (gum) disease, they must 
demonstrate proper care for remaining teeth, and be willing to use an oral rinse as directed. 
 
Patients participating in the study must have the following treatment requirements and conditions: 
 
 
patients must have been treatment planned for a removable partial denture (RPD) in one or both jaws 
 
patients must require at least one crown on an RPD abutment tooth 
 
abutment teeth requiring crowns must be in contact with opposing teeth (or dentures) 
 
abutment teeth must be healthy and not in need of root canal therapy at the time of their enrollment 
 
LOCATION 
 
The clinical procedures for this study will be conducted at the University of Kentucky College of Dentistry student 
clinics on the second, third and fourth floors of the UK Chandler Hospital in Lexington, Kentucky. You will need to 
come to these clinical facilities approximately 15-25 times over the course of 9-12 months to complete planned 
treatment. Each of those visits will take about 3 hours. Following treatment completion investigators will want to 
evaluate you every 6-12 months for 5 years. The total amount of time you will be asked to volunteer for this study 
is approximately 70 hours over the next 5 years. 
 
 
WHAT WILL PATIENTS BE ASKED TO DO? 
 
Participants will have a dental examination, study documents will be reviewed, and informed consent obtained. 
You will be given oral hygiene instruction by your student dentist, and asked to brush remaining teeth twice daily, 
floss once daily, and rinse for 1 minute daily with ACT®, an over the counter 0.05% sodium fluoride oral rinse. 

 
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Investigators then ask that you complete your restorative dental treatment as planned, and care for your teeth as 
instructed. If you decide to participate in this study, we ask that you not enroll as a subject in any other research 
until this investigation has concluded. 
 
A dental treatment plan that includes a removable partial denture and one or more crowns typically requires 15-25 
visits. These visits usually consist of 1-3 mornings or afternoons a month for 9-12 months until treatment is 
complete. The timeline for treatment is similar whether you are treated in a private office or in a student clinic. The 
difference is that students who provide care for patients require professional supervision, so each appointment is 
typically for an entire morning or afternoon, rather than an hour or two as would be the case in a private practice. 
 
Crown procedures are routine dental treatment, and typically require 2-4 visits to complete. Removable partial 
denture procedures typically require 3-5 visits to complete. Removable partial dentures must be started after any 
necessary crowns are completed. For this reason, the removable partial denture is usually the last part of your 
treatment plan to be finished. 
 
The part of your treatment that is the focus of this investigation is the crown material that will be used for 
the tooth or teeth that will be clasped by your removable partial denture. The treatment group will have teeth 
restored with zirconia. Zirconia is a new type of all-ceramic crown material that is already widely used in dentistry 
to make crowns for natural teeth and implants. This material is of interest because it is tooth colored, 
exceptionally strong, and requires less tooth structure removal than alternative materials. We are investigating 
whether zirconia crowns will last as long as conventional crowns when used with a removable partial 
denture. There are very few scientific reports on how well this material lasts when used in this manner. 
 
Participants who will have their crowns made from zirconia will be followed for 5 years, and their oral health will be 
compared to another group of patients restored with all-metal or PFM crown materials. If there are significant 
differences between the outcomes of the two groups, investigators can use this information to make treatment 
recommendations to future patients. Since this is a randomized controlled study, you will be randomly assigned to 
the PFM or monolithic zirconia crown group. This means that you do not get to choose which material 
investigators use to make your crown. 
 
The following chart provides a general timeline for a patient needing one crown, and a removable partial denture 
to restore missing teeth in one of your jaws. This represents the simplest sequence of procedures that a qualifying 
subject will need to complete. All appointments in the student clinics are 3 hours in length. 
 
Appointment Number
Timeline
Procedure
1
Day 1
Examination, preliminary impressions, x-rays, faculty consultation 
2 
Week 2 
Records, complete any unfinished examination or x-ray procedures, 
introduction to clinical study and review of consent documents 
3 
Week 3 
Treatment planning. Financial arrangements. Meet with investigator. 
Review clinical study and informed consent documents 
4 
Week 4 
Finalize treatment plan, review study documents, and clarify any 
questions patients have regarding treatment. If they agree to 
participate in the study the informed consent document must be 
signed by this time and random assignment will be made. 
Whether a patient participates in the study or not, diagnosis, treatment planning and financial arrangements
take at least 3 and commonly 4 appointments before clinical treatment is started in UK student clinics. 
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Week 5 
Replace any old fillings in abutment tooth and prepare it for a PFM 
or zirconia crown (anesthesia required). Make temporary crown. 
6 
Week 7 
Finish preparation (anesthesia required). Final impression. 
Recement temporary crown. 
7 
Week 8 
Bite record of how the upper and lower teeth contact. Shade 
8 
Week 12 
Cement crown (anesthesia sometimes required). Preliminary 
impression for removable partial denture. 
9
Week 13
Removable partial denture framework impression using custom tray 
10 
Week 16 
Secondary impression to accurately record the area missing the 
teeth (called an “altered cast” impression) 
11 
Week 18 
Bite records including face-bow. Selection of shade, shape and size 
of artificial teeth. 
12
Week 20
Try-in of artificial teeth to evaluate their color, shape and position 

 
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13
Week 23
Delivery, bite adjustment and take-home instructions 
14
1-2 days later: Week 23
Follow-up for adjustments 
15
Week 24
Follow-up for adjustments 
16
Week 26
Follow-up for adjustments 
 
 
The appointments listed in the table above are considered the standard of care, and are necessary for 
treatment whether you participate in this investigation or not. If you decide to participate in the study, the 
following additional appointments are considered research, and will be needed for investigators to collect 
outcome information. You will not be charged for services provided in the following appointments 
17 
6 months after appointment 
#13 
2 hour follow-up examination with investigators (includes 
questionnaire) 
18 
1 year after appointment #13 
2 hour follow-up examination with investigators (includes 
questionnaire and x-ray of abutment teeth) 
19 
2 years after appointment #13 
2 hour follow-up examination with investigators (includes 
questionnaire and x-ray of abutment teeth) 
20 
3 years after appointment #13 
2 hour follow-up examination with investigators (includes 
questionnaire and x-ray of abutment teeth) 
21 
4 years after appointment #13 
2 hour follow-up examination with investigators (includes 
questionnaire and x-ray of abutment teeth) 
22 
5 years after appointment #13 
2 hour follow-up examination with investigators (includes 
questionnaire and x-ray of abutment teeth) 
 
Participants will be randomly assigned to either an experimental group (monolithic zirconia) or a control group 
(PFM). Random assignment means that your group assignment is by chance, similar to a coin toss. An internet- 
based, random number generator will be used to make group assignments. Since there are only two treatment 
groups, the chance of being assigned to either group is 50%. 
 
POSSIBLE RISKS  
 
Risks specific to this study include the following for zirconia crown recipients: ceramic fracture, caries (decay along 
the border of a crown), faster wear of the ceramic material relative to conventional metals, faster wear of the 
removable partial denture framework due to contact with the ceramic, possible abscess of abutment tooth, and 
fracture or loss of an abutment tooth 
 
Caries (decay along the border of a crown) is expected to occur occasionally in a five year follow-up period. Caries 
is the most common reason conventional metal and PFM crowns need to be replaced, and this may also be the 
case with all-ceramic crowns. 
 
Ceramic fracture is also expected to occasionally occur in a five-year follow-up period. Ceramic fracture can be 
avoided if crowns are made entirely of metal. However this would be unsightly for teeth in the front of the mouth. 
Ceramic fractures have been reported for both PFM and all-ceramic crowns, largely with the veneering ceramic. 
Although the zirconia crowns used in this study are monolithic and do not have a veneering layer of weaker 
ceramic, it is possible that more fractures occur with this group compared to PFM crowns. 
 
Wear of ceramic or removable partial denture framework material is expected to be rare, because there have 
been very few reported incidences of this in the scientific literature with conventional materials. 
 
Radiographs (x-rays) will be taken before, during and after treatment. The radiation dose from a typical dental x-ray 
is about 1/80th of the typical background dose that we all receive every year. It is also about 1/7th of the annual safe 
dose limit dose (not including medical exposures) for members of the public and well below the levels that are 
considered to be a significant risk of any harmful effects. The ALARA radiation safety principle (as low as 
reasonably achievable) to minimize patient x-ray exposure will be followed by students and researchers at all times. 

 
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Possible abscess of abutment tooth is expected to be a rare-occasional occurrence in a five year follow- up period, 
consistent with historical norms for any teeth requiring conventional crowns. 
 
Abutment tooth fracture within a five year period is expected to be a rare occurrence in either group. This is a more 
likely occurrence with teeth that are structurally weakened to begin with. Since participants must have vital, 
periodontally sound, caries (decay) free abutment teeth for study participation, abutment tooth fracture would be a 
highly unexpected occurrence. 
 
Risks for permanent side effects from dental treatment in this study are identical to those receiving dental care 
outside of this study: permanent numbness to the lip or cheek following anesthesia, aspiration of loose foreign 
objects that are inadvertently dropped down patient’s throats, and allergic reaction to a material or medication. 
 
Permanent numbness of the lip or cheek can make speech, eating and facial expressions difficult, similar to people 
who experience a stroke. 
 
Foreign body aspiration may block the airway and make breathing difficult, requiring surgical retrieval. Difficulty in 
breathing can range from mild to severe. Complete airway blockage can result in death. 
 
Allergic reactions can also range from mild to severe. Severe reactions can result in death. Other allergic reactions 
may require administration of a medication to manage its severity. Allergies commonly go away with removal of the 
product or material that is causing the allergy. 
If a subject becomes pregnant while receiving treatment, further radiographs and restorative care may be 
postponed until after childbirth. If a study subject is unknowingly pregnant at any time during the study, the risks to 
the embryo or fetus are minimal, and identical to those of a patient who chooses not to participate in the study. 
Local anesthesia will be administered before crown procedures. Risks associated with this procedure include 
soreness, bruising, pain, infection, fainting, bleeding, allergic reaction, and permanent numbness associated with 
the nerves which are blocked. 
 
 
 
Possible
Risk/Side Effect 
How often has it
occurred? 
How serious is it?
Can it be corrected?
Bruising 
It may occur just after 
drug administration 
Usually of short 
duration, 2-5 days 
Yes. It will go away with time 
Pain and soreness 
Commonly occurs with 
anesthesia 
Usually minor and of 
short duration 
It will go away with time 
Infection 
It is extremely 
uncommon 
Very serious 
Yes, but may require 
antibiotics 
Permanent 
numbness 
It is extremely 
uncommon 
The damage is 
permanent and can 
affect the rest of your 
health 
No 
Allergic reaction 
Rare 
Can be very serious 
Yes, but may require 
administration of medications
Fainting 
Rare 
Usually minor and of 
short duration 
Yes 
 
 

 
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STATISTICAL ANALYSIS 
 
Power analysis indicates that approximately 80 participants will need to be enrolled (40 per group) to obtain long-
term (60 month) oral health data. Participants who will have their crowns made from zirconia will be followed for 5 
years, and their oral health will be compared to another group of patients restored with all-metal or PFM crown 
materials. Failure and complication rates of each material will be analyzed using random-effects Poisson’s 
regression models to obtain summary estimates. Multivariate analyses will be used to determine significance for 
outcomes with overlapping dependent variables.