Novel Use of 2-unit Cantilever Resin-bonded Bridges for Replacing Missing Molar Teeth - a Randomized Clinical Trial

Tooth replacement is a significant issue in the World and while dental implants and conventional bridges have been used to replace missing teeth, dental implants are too expensive for many and conventional dental bridges are destructive to supporting tooth tissue.

Resin-bonded bridges (RBBs) are a conservative and cost effective replacement option that involves minimal tooth preparation, leaving the majority of the tooth intact. They are secured in place with an adhesive cement, which is bonded to the outer enamel layer. Clinical audit of these prostheses at the University of Hong Kong shows two-unit RBBs to have some of the highest success rates in the dental literature for the replacement of missing premolar and incisor teeth. However, for the replacement of molar teeth, two-unit RBBs are not performed, as established protocol and recognised texts contraindicate their use due to concerns with tipping or drifting of supporting teeth. Replacement of a single missing molar tooth can be with a three-unit, fixed-fixed (single-piece casting) or three-unit, fixed-movable (two-part casting). However, the fixed-fixed option has a higher debond failure rate than two-unit RBBs and therefore, at this centre, a modified, 3-unit fixed-movable design is used. This two-part casting allows for minor, independent movements of the supporting teeth and thereby aims to reduce stresses between them and, similarly, reduce de-bonding forces. This has the potential for greater longevity and easier long-term maintenance as if the major part of the bridge debonds it can be recemented.

The aim of this unique study is to compare 2-unit and 3-unit RBBs for the replacement of single missing molar tooth in a randomized clinical trial. These two designs will be clinically evaluated at 6 months , 1 year, 2 years and 3 years to observe the outcome measures. The primary outcome will examine the success of the dental prostheses with respects to the need of any clinical intervention to repair or remediate the RBB or supporting tooth. Minor outcome measures will examine fatigue or damage to the prosthesis, changes in bone support, pulpal or periodontal health or tooth mobility. Patient satisfaction and quality of life evaluation of the dental prostheses will also be examined. Will 2-unit RBBs offer patients a simpler, cheaper, and successful option over current designs? This has not been previously reported.


Eligibility Criteria:
Inclusion Criteria:

1. A missing molar tooth that ranges in length from 8-10 mm as judged by the pre-treatment study model. (No more than one per quadrant, if more than one, then different designs will be used in the same mouth.)
2. The patient has been informed of the various treatment options (dental implants, partial dentures, conventional fixed prosthodontics and no treatment) and if the patient has chosen the RBB as their preferred treatment option, they will be invited to participate in the study
3. The patient is available to attend for clinical examination at 6 monthly interviews for a period up to 36 months from the start of the study
4. The patient will have a minimum of 12 occluding pairs of teeth (24 teeth in total)
5. have a natural dentition opposing the planned RBB
6. More than 30% bone support on the tooth abutment(s)
7. Patients will agree to being randomly assigned to one of the two treatment groups, a 2-unit bridge or 3-unit fixed movable bridge
8. The patient will have been informed on the nature of the study and be required to sign a consent form agreeing to undertake treatment in the study
9. The patient is over 18 years old
10. The patient is in sound dental health, ie no active caries and controlled periodontal disease

Exclusion Criteria:

1. Patients with active tooth decay
2. Patients with uncontrolled periodontal disease. RBB abutment with a probing depth greater than 5mm and bleeding on probing
3. Patients with teeth missing opposite to the planned RBB
4. Abutment tooth mobility of 2 or greater (Millers classification)
5. Patients with a known allergy to the dental alloy used to make the RBB, ie. Ni/Cr
6. Patients with debilitating illnesses or complicating medical conditions
7. Non-vital or root treated abutment teeth