DR. DENNIS HARTLIEB

Zirconia Bridge Technique: Conservative Esthetic Tooth Replacement

Discover how to use resin cement to secure Zirconia Bonded Bridges and create minimally invasive, esthetic tooth replacement. 

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(Read time 7-9 minutes)

It’s Not Your Dad’s Maryland Bridge

The need for conservative dental treatment to replace a missing anterior tooth – i.e. dentistry that doesn’t destroy the neighboring teeth with preparations for traditional crown and bridge treatment has been a concern for dentists for decades.
The movement towards minimally invasive dentistry has been advanced with the improvement of adhesive and restorative materials, and the bonding techniques to ensure restorative success. With proper adhesive protocols, utilizing minimal tooth preparation techniques, tooth replacement restorations can be created that are both esthetic and functional. Minimizing tooth reduction for the restoration (less drilling) should improve the long-term survivability of the patient’s teeth.
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Three Reasons why the Replacement of Anterior Teeth Might be Necessary:

  • There is an estimated 2% of people born with congenitally missing maxillary lateral incisors1 that need tooth replacement options during their adolescent years. 

  • Teeth that have been lost due to trauma, such as cases where the tooth has been completely avulsed, or ‘knocked out.’ 

  • A tooth that has been lost secondary to previous trauma.

These traumatized teeth can manifest with resorptive lesions or peri-radicular breakdown secondary to root fracture.

The replacement of these missing anterior teeth must be completed in an esthetic manner, with an understanding that both the tooth structure and soft tissues (gum tissue and mucosa) may need to be replaced or enhanced. 

Also, paramount to restorative success is an understanding of the functional and parafunctional tooth contacts as patients use their teeth in their day-to-day living.
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Removable Treatment Options to Replace the Missing Anterior Tooth

There is a myriad of prosthetic options to replace the missing anterior tooth in today’s dental world. There are several removable treatment options to replace missing teeth, including the use of a removable partial denture (a metal-based prosthesis that “clasps”, or grabs onto other teeth in the dental arch with a denture tooth, or teeth, to replace the missing teeth).

1. Dental Flipper

A dental ‘flipper’ which has an acrylic, or plastic base that supports a denture tooth – is a commonly used prosthesis for adolescents that are missing their teeth for temporary tooth replacement.

2. Utilizing a Patient's Invisalign Tray

Another common technique currently used for short term tooth replacement is to utilize a patient’s Invisalign tray, or a similar clear plastic retainer, with a tooth colored resin or acrylic inside the clear shell to make it appear that the patient has a tooth in place while wearing the retainer.

While all of these options have the advantage of minimizing dental treatment to the surrounding teeth, and the financial investment may be minimized, many patients are unhappy with the challenges of wearing a removable appliance.

Six Potential Challenges Presented by the Removable Prosthesis

  1.  Eating with the appliance can be difficult as the appliance can ‘move’ during chewing

  2. Speech may be affected due to the necessary thickness of the base material necessary to support the denture tooth (teeth)

  3. Esthetic Limitations - There are esthetic limitations of the replacement teeth

  4. The ‘losability’ of the appliance – it is not uncommon to hear that a flipper or temporary removable retainer was accidently thrown out or lost when a patient had left the appliance out of their mouth

  5. Uncomfortable - Many patients will find the appliance uncomfortable and will wear only socially

  6. Social Limitations - There can be social issues related to having a missing front tooth. In my 30+ years of dental practice, I have yet to have an adolescent, or an adult, excited to have a removable prosthetic option for their missing front tooth.

"Fixed" Treatment Options to Replace the Missing Anterior Tooth

The alternative to a removable prosthesis is what is referred to as a ‘fixed’ dental restoration. The term ‘fixed’ implies that the restoration, or prosthesis, is not removable by the patient. The prosthesis could be cemented (glued), bonded (chemical adhesion), or screw-retained (yep, exactly as it sounds – a screw – or screws – are used to hold the prosthesis to dental implants)

For the missing anterior tooth, there are several fixed, or non-removable, options used commonly today.

1. Traditional, or Conventional Bridge

With a traditional, or conventional bridge, the teeth adjacent to the missing tooth space are prepared for crowns, and a dental bridge is fabricated by a dental laboratory. The bridge, or ‘fixed partial denture’ is cemented to the neighboring teeth. These bridges can be made from a variety of materials, including the use of a metal base with porcelain baked onto the surface of the metal to create an esthetic tooth replacement. More currently, Zirconia, a tooth colored dental restorative material, can be used to create the bridge for the missing tooth maximizing the esthetics. 
Dental bridges are still commonly used in dentistry, and can be used when working on natural teeth, or dental implants. The disadvantage of dental bridges is the inherent drilling necessary to the ‘abutment’ teeth that support the bridge. The teeth that are drilled become more compromised due to the treatment, and are more prone to nerve damage issues along with other potential problems. There are, however, still many indications for traditional bridges where other treatment options are not reliable, predictable or practical. 

2. Cantilevered Bridge

A cantilevered bridge is also an option for replacing a missing anterior tooth. If the abutment tooth that is supporting the cantilevered pontic is healthy with appropriate preparation height, root length and stability, it may not be necessary to include both teeth on either side of the pontic space in the restorative treatment. I have used both a maxillary central incisor as single abutments:
and canines as single retainers with cantilevered lateral incisor pontics with long-term success with multiple patients.

Dental implants have evolved as a tremendous opportunity to replace missing teeth with an estimated 450,000 dental implants placed annually around the world.2

Dental implants have the advantage of providing the patient with a tooth without any additional treatment to the neighboring teeth.

Limitations of Dental Implants

There are some limitations to dental implants however – there must be adequate space between the neighboring teeth and there must be sufficient bone and gum tissue to support the implant.

1. Placement

It is critical that the implant is placed in the appropriate 3-dimensional space by the surgeon and that care is taken by the restorative dentist when fabricating and placing the crown onto the implant.

2. Patients that are Still Growing

Dental implants should not be placed on individuals that are still exhibiting facial growth. An implant will maintain its position in the patient’s facial bone, and if there is facial growth, the teeth will move downward, and forward, as the face grows. The clinical significance of placing an implant too early is that the implant will not move and emerge with the teeth, creating a discrepancy in the positioning of the implant tooth relative to the natural teeth.

The implant tooth will appear shorter at the incisal edges, relative to the other teeth in the smile as the teeth move downward and forward with the facial growth. As a result, the gum line of the dental implant will be more apical, creating an imbalance at the soft tissue level.

3. Age

Recent evidence suggests that dental implants should not be placed in the esthetic zone until a person is in their 20’s, perhaps even into their 30’s because of latent facial growth3.

This is of course a real concern for adolescents and the young adult population that have congenitally missing teeth or for those that have had teeth lost due to trauma.

How the Rochette Bridge Became the Maryland Bridge

Prior to the development of dental implants, an option for conservative tooth replacement was presented in 1973, by Dr. Alain Rochette4.

The restorative solution, described as a ‘Rochette Bridge”, was a two-winged metal-based bridge that utilized pin holes and retentive preparation designs on the lingual or palatal surfaces of the abutment teeth to support a cemented bridge.

These metal-based tooth replacements where the first step in conservative based dentistry to replace a missing front tooth.
With the advent of adhesive dentistry, the Rochette Bridge was transformed and later became better known as the “Maryland Bridge”.

The Maryland Bridge was the first ‘Resin Bonded Bridge’ (RBB) and was developed by Drs. Livaditis and Thompson, from the University of Maryland College of Dental Surgery.

The Maryland bridge design and technique were dependent on utilizing a specific metal etching technique which made the retentive holes, slots, or other preparation features found in the Rochette Bridge unnecessary.

However, there were challenges with the Maryland bridges, including, the shine thru of the metal through the teeth which could make the neighboring teeth look dark, or create a grey, unaesthetic cast to the teeth.
Also, despite the advances in adhesion in dentistry in the 1980’s, it was not uncommon for one, or both of the metal retainers to debond from the neighboring teeth.

Potential Complications from the Maryland Bridge

One Debonded Wing

The most severe complication with the Maryland Bridge would be when one wing remained bonded to its tooth, while the other wing debonded. The debonded tooth would invariably suffer from dental caries as bacteria would be trapped under the ‘loose’ wing with the patient unable to clean the area.

Improper Preparation

These debondings could occur from improper treatment of the metal by the lab technician or by poor preparation design or adhesion protocols employed by the dentist.

Occlusal Forces

However, unilateral debondings could also occur from the occlusal forces from the patient, even if there was strict attention to proper protocols by the dentist and lab technician. These debondings could occur secondary to occlusal pressures from chewing and other occlusal forces on the teeth.

Considering the replacement of a maxillary lateral incisor, during normal function, we would expect occlusal forces to ‘push’ the central incisor abutment tooth in a facial direction. However, in a normal Class I occlusion, the forces on the canine would be more in a lateral direction.

These occlusal forces, being in opposite directions, create tension in the adhesive interface and commonly, with one of the wings debonding from the abutment tooth.

How long do Zirconia Bridges Last?

Multiple clinical studies have compared unilateral, or single-winged Zirconia Resin Bonded Bridges’ survival rate with the two-winged RBB’s.
Matthias Kern reported a 92% 5-year success of single-wing RBB’s compared to a 67% survival rate for two-winged RBB’s.

Kern’s 10-year study showed a 91% survival rate demonstrating that these single-winged bonded restorations can be a reliable conservative tooth replacement option for the missing anterior tooth.

In his book, “RBFPD’s – Resin-Bonded Fixed Dental Prostheses, Kern states that the sole reason for failure of the bridges in their study was due to fracture of the restorative material. The restorative material utilized for the RBB’s at the time of his studies Alumina Oxide, more commonly recognized as InCeram.

While InCeram was an improvement in the strength of tooth colored, non-metal restorative materials, its strength falls significantly short of the zirconia materials available in dentistry today.

Kern noted that none of the bridge failures were related to adhesive failures. Given that our materials and understanding of adhesive bonding is significantly advanced over the last several decades, we should conclude that a single-winged bridge made of a stronger material (zirconia) with improved adhesive techniques should match, or exceed, performances previously recorded. 

Overall, there are several reasons for treatment planning single winged ZRBB’s including higher long-term success rates, improved hygiene with the ability to floss in between the non-restored contact and slide the floss under the pontic, and reduction in preparation complexity with only one abutment.

While single winged bonded restorations may be advantageous in many single tooth replacement situations, two-winged zirconia bonded bridges still may be appropriate when more than one tooth is being replaced, or for treatment considerations when additional restorative treatment is needed on anchoring teeth.

How Thick Should a Zirconia Bond be for Maximum Bondability?

There is no universal agreement on the wing design for the Zirconia RBB.

Sillam et al reported in their paper “Influence of the amount of tooth surface preparation on the shear bond strength of zirconia cantilever single-retainer resin -bonded fixed partial denture”5

that the key determinate for survival of the single-wing, or cantilevered RBB is the connector site being 4mm x 3mm, or 12 mm2.

The shear bond strength to dislodge a 7 mm wide wing had no statistically significant difference compared to a 3.5 mm wide wing. Failures of all the bridges tested were adhesive in nature, with no failure of restorative material reported.

Additional information on zirconia research has demonstrated that the minimal thickness of the zirconia material should be 1.0 mm6. Based on this information, it can be concluded that a retainer wing should be 1.0 mm thick, 3.5 mm from proximal to the cingulum, and about 4.0 mm tall.
Critically, the proximal box must be 12.0 mm2 for sufficient zirconia bulk at the connector site (the area where the pontic joins the wing).
I have found from clinical practice that the seating and delivery of the single-winged cantilevered restoration can be more predictable with a larger wing. With a small wing, there can be reduced stability of the prosthesis during bonding of the zirconia RBB.

APC Protocol for Securing Zirconia Resin Bonded Bridges

Dedication to precise protocol during bonding of the bridge is critical for predictable adhesion. The ‘APC’ concept promoted by Dr. Marcus Blatz is generally considered to be the standard for zirconia bonding technique7. 

The ‘A’ of the ‘APC’ concept stands for air abrasion – the zirconia should be lightly air abraded with 25-50 micron aluminum oxide. I also air abrade the tooth restorative surface to clean the preparation and maximize bond strength prior to cementation.
The ‘P’ refers to the need to prime the zirconia surface. Primers that contain the 10-MDP monomer (methacryloyloxydecyl dihydrogen phosphate) are critical for zirconia bonding.
10-MDP is found in many of the Universal resin cements currently used in dentistry, including Panavia V (Kurrary), Rely X Unicem (3M) and SpeedCem Plus (Ivoclar).

The third step, or the ‘C’ in the zirconia bonding concept, is that an adhesive composite resin is utilized for the cementation.

How I Use Resin Cement to Secure Zirconia Bonded Bridges

Step 1. 

The resin cements used for zirconia bonding should be dual-cured, as the zirconia may be too opaque for complete light curing options.

Research has found that the though the dual-cure cements can be cured with only the chemical initiation, light activation has proven to create a stronger resin cement.

Step 2. 

After isolation, the tooth should be etched and appropriate adhesion protocol followed. The restoration should be properly positioned and excess cement removed with artist’s brushes, microbrushes, and floss prior to light curing.

After light polymerization, excess cement can be removed with scalers, surgical blades and rotary instrumentation.

Step 3. 

The patient’s occlusion is checked to minimize excursive forces on the pontic and the connector site.

It is critical that the connector area is not thinned from adjusting – if necessary, the opposing tooth contact(s) should be adjusted to maintain the 12.0 mm squared thickness of material.

Step 4. 

Final polishing of the resin cement and the zirconia surfaces is critical for the long-term success of the restoration.

The Zirconia Resin Bonded Bridge Technique:

A Restorative Treatment Option for Patients Missing Anterior Teeth

The Zirconia RBB has proven to be an important restorative treatment option for my dental practice. The treatment of adolescents and young adults that either have congenitally missing anterior teeth, or have lost teeth due to trauma, require conservative tooth replacement restorative solutions.

The restorative replacement of the missing tooth should have minimal tooth preparation and must be esthetic and long lasting. Special attention to preparation design and cementation protocol is critical to the long-term success of the zirconia resin bonded bridge.

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Citations

1) Agenesis of the permanent lateral incisor: distribution, number and sites. Stamatiou J., Symons A.L. J. Clin. Pediatr. Dent. 1991;15(4):244–246

2) Current trends in dental implants, Laura Gaviria, John Paul Salcido, Teja Guda, and Joo L. Ong , J Korean Assoc Oral Maxillofac Surg. 2014 Apr; 40(2): 50–60.

3) Effect of age on single implant submersion rate in the central maxillary incisor region: a long-term retrospective study, Devorah Schwartz-Arad, Nitzan Bichacho, Clin Implant Dent Relat Res 2015 Jun;17(3):509-14

4) RBFPD; Resin-Bonded Fixed Dental Prostheses: Minimally invasive - esthetic – reliable, Kern, M, October 2017, Edition: 1, Quintessence

5) Influence of the amount of tooth surface preparation on the shear bond strength of zirconia cantilever single-retainer resin-bonded fixed partial denture. Charles-Ellie Sillam 1, Sibel Cetik 1 2, Thai Hoang Ha 1, Ramin Atash 1. J Adv Prosthodont. 2018 Aug;10(4):286-290.

6) Load-bearing capacity and the recommended thickness of dental monolithic zirconia single crowns, Sun, T et al, J Mech Behav Biomed Mater. 2014 Jul;35:93-101.

7) How to Bond Zirconia: The APC Concept, Blatz, M et al. Compend Contin Educ Dent. 2016 Oct;37(9):611-617



Dennis Hartlieb, DDS, AAACD

DOT Founder

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