Dental Health Library Article
Dental Bridge: Cemented versus Screw Retained
Cantilevers: Most Teeth - Fewest Implants
A dental bridge is a prosthetic device that can be used to replace the span of 1 tooth or up to an entire arch of teeth.
|Maryland Bridge - lingual mount
One of the most common types in the form of a removable bridge is a denture product. Implant supported (mini implants) and implant retained (traditional implants) are popularly used to keep dentures secure and highly serviceable in terms of biting, chewing, speaking clearly, etc., and are usually removed daily.
|Click picture to see multiple anchor cementation
A fixed bridge is a product (short span or long) that is designed to remain permanently attached. The most popular bridge is a product that has a short span and uses at least two healthy teeth (typically at each end) to provide anchoring. The existing teeth are modified to be integrated into the bridge, with special cements applied to the anchor points.
Cosmetic Outcome versus Long Term Function
Depending upon the span of teeth to be replaced, location of the bridge within the occlusal plane and the cosmetic goals of the patient, the infrastructure, or framework, can be fabricated from common metals, titanium, porcelain and zirconia.
|Porcelain on Zirconia Frame
Premium grades of porcelain have qualities of translucency which enable the dentist and his/her dental lab to design teeth that mimic Mother Nature. Despite the thicknesses of porcelain that are layered onto the frame, some "bleed through" can occur.
Dentists almost routinely recommend the use of an all metal framework for posterior locations in the jaw because of extreme biting forces. The bleed through effect, if it occurs, won't be as critical or apparent.
Not so with front or anterior teeth. Variations of lighting can cause a "metallic tinge" to appear on some metallic bridges. Porcelain, zirconia or gold alloy fixed bridge frames eliminate this cosmetic problem and is typically the best choice of infrastructure composition.
(Although metallic frameworks typically have a specialized coating of color blocking agents, technical errors do occur whereby the metallic tinge is evident.)
|All Zirconia Frame
Fixed bridges that are attached via dental cements are the most popular method of multiple tooth replacements. They are very affordable and are a qualifying treatment with most insurance carriers.
A cemented bridge attached to modified anchor teeth probably provides the best enduring function for most patients where occlusal forces are low and the chances for "lateral forces" are at a minimum.
Leakage and decay, a common issue with dental crowns, similarly affects the cemented bridges mounted to natural anchor teeth that have been modified. Of special importance is the possibility of lateral forces that can result from poor occlusion or the flexing of a bridge.
Lateral forces can cause a cement joint to flex and eventually cause a leakage problem. Bacteria slowly seeps into the interface area and causes the underlying tooth structure to start decaying rapidly. Typically, teeth modified into anchor teeth no longer have the protective dental enamel they once had.
Left untreated, a leaking anchor tooth will eventually cause the entire bridge to fail. As the first anchor tooth fails, miniscule movements and lateral forces will telegraph through the bridge and affect other anchor teeth.
Bridge Failure ASAP Response
In general terms, a long span cemented bridge has a higher probability of failure than a short span bridge. The number of anchor teeth being used also influences failure rates.
Leakage caused by poor oral health habits, faulty occlusion or poorly monitored eating habits usually initiates the decay problems quickly. Unfortunately, for many patients, the damage isn't obvious until it is too late.
At the hint of a possible problem (e.g., bridge feels like it is flexing or moving) it is critical that an evaluation be obtained quickly to address a possible leakage problem.
As can be seen in the adjacent photos of bad bridgework, the devastation to remaining tooth structures that were used to mount the cemented bridge is total. Both of these patients underwent bone grafting and implant surgery to recreate what was lost (at unnecessary expense, theoretically).
Implant Supported Bridges - Premium Tooth Replacement
Dental bridgework that is installed into a configuration of implants, whether for short span or long span is the treatment of choice for replacing teeth and maintaining healthy jaw bone mass and quality.
Dental implants, because of their ability to stimulate bone tissue in essentially the same way natural teeth do, have become popularly regarded as the Gold Standard of Tooth Replacement.
Implant abutments permit dentists to adapt each implant for mounting a single tooth, denture locator attachments, a cementable bridge or a screw retained bridge.
Implant Bridge Mounting Choices: Cemented vs Screw Mount
Dental implants can be prepared with special abutments that allow a fixed bridge to be cemented in place. As can be seen in the adjacent photo, the surface area for cement is considerable, assuring a good cementation result.
A picture of the underside of the cementable bridge that corresponds with the preceding photo is presented to show how the implant abutments match perfectly with the milled framework of the new porcelain bridgework.
Can Cemented Implant Bridges Fail?
Unfortunately, bridgework that is cemented to implants can fail in some of the same ways a non implant supported bridge does. Implant bridges typically don't have the leakage and decay problems associated with anchor teeth cementations since natural teeth are not involved.
Bacteria however can accumulate around the implant devices if proper oral health habits are not maintained. In extreme cases where negligence is overwhelming, the bacteria can seep into the implant site and cause infection and decay within the implant site, causing bone loss and future loosening of the implant.
In some cases, improperly prepared implant sites and poorly contoured gingiva that is not snug against the implant abutment have been reported to promote decay.
The principal of lateral forces can cause an implant to fail. As the implant device loses its tight osseointegration with bone tissue, bacteria can seep into the area, initiating a decay process of bone in the immediate area.
These lateral forces can be caused by other events, such as changing occlusion, bruxism, broken teeth elsewhere in the occlusal plane that go untreated, inappropriate biting and chewing habits, food preferences and trauma.
On a short span implant bridge, in particular, a failed cementation on one end of the bridge can cause flexing and movement of the bridge in the same fashion as a non implant supported bridge.
The risk of bone loss can be significant since any movement of a bridge will affect all implants in the bridge. The telegraphing effect can cause bone loss throughout all implant sites. Implants that were once rock solid via complete osseointegration become, through even miniscule lateral motion, agents of destruction.
Implant Bridge Failure ASAP - If not sooner
ANY hint of failure of an implant bridge should be addressed immediately. Replacing implants and undergoing additional bone graft surgery (if still possible) is a lengthy and costly process. Dental implants have the ironic characteristics of being the best in tooth replacement and bone preservation while also being capable of destroying precious bone quantity and quality.
Screw Retained Fixed Bridges
In general terms, dental practices that focus primarily on implant or reconstructive dentistry will typically have more access to implant technologies that can address nearly any dental need or problem imaginable. In short, they will have the best treatment method for possible for solving the functional and/or cosmetic interests of an implant patient.
Many reconstructive dentists will insist upon the use of screw retained fixed bridges, thereby promoting the maximum ranges of servicability, cosmetic result and maintenance of optimized bite possible.
Teeth In An Hour, a fixed bridge solution for replacing entire upper and/or lower arch's of teeth are entirely screw retained. Employing principles of CAD/CAM design and catscan diagnostics, the All-On-Four immediate function treatment hybrid boasts levels of accuracy and fit that are becoming well known.
The Marius Bridge, a unique use of implant technology and custom titanium bridge and prosthetic mounting interfaces, also is a screw retained prosthesis.
Dentists who fully support screw retained prosthetics usually have access to specialized implant abutments that are designed to be adjustable, thereby moving closest to the goal of the perfect tooth replacement option (cemented implant abutments are not adjustable).
On - Off - On - Off: Removal at Will
The Marius Bridge was designed on the principle that a patient could remove and reinstall their fixed bridge at will.... at any time... with any frequency desired.
|Screw Mount - Nobel Biocare
Patients are not required to schedule an office visit to remove the bridge for cleaning and inspection.
It also promotes the use of having a "back-up" prosthetic. Two fixed bridges instead of one (cost of an extra bridge is negligible).
Other screw retained fixed bridges are designed to permit the dentist to remove the fixed bridge for oral health maintenance and inspection of underlying tissues.
This type of routine maintenance theoretically overcomes nearly all of the factors that are popular or common causes of implant bridge failure.
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