Noreen Mohammed Naguib Mosaad

5212322

G.11

Connectors in fixed prosthodontics

To stress-break or not to stress-break, that is the

question!!

Maxillary FPD

Anterior : fixed

Posterior : fixed-free

Mandibular FPD

Anterior : Fixed

Posterior : Fixed-free i.e. Fixed at the posterior

connector and stress broken at the anterior connector.

Now, it is becoming more common to stress break

ALL POSTERIOR BRIDGE

The occlusal forces applied to a fixed partial denture (FPD) are

transmitted to the supporting structures through the pontic, the

connectors, and the retainers.

Variables that may influence the longevity of a bridge and its

abutments include the occlusion, span length, bone loss, and

the quality of periodontium.

The excessive flexing of the long-span FPD, which varies with the

length of the span cubed, can lead to material failure of the prosthesis

or to an unfavorable tissue/bone response.

Biomechanical factors such as occlusal overload, leverage,

torque, and flexing, induce abnormal stress concentration in an

FPD.

This stress concentration is found in the connectors of the bridge

and in the cervical dentin area near the edentulous ridge. This factor

plays an important role in the potential for failure, particularly in

long-span bridge.

Remember that connectors are that portion of the bridge that unites the

retainers and the pontics. They are of two types, rigid connectors and

non-rigid connectors (NRCs).

Rigid connector could be made by casting, soldering, and welding. The

cast connectors should be properly shaped in wax patterns. The

soldered connectors are made by fusion of an intermediate metal alloy

to the previously made castings. These days, the one piece casting goes

a long way towards overcoming rigid connector failure in bridgework.

The connector that permits limited movement between the otherwise

rigid members of the FPDs, is the Non- Rigid Connector or NCR.

The NRC could be made by an incorporation of prefabricated

precision inserts, by use of a custom-milling machine or by use of the

prefabricated plastic patterns.

Ref. Pissiotis AL, Michalakis KX. An esthetic and hygienic approach to the use of

intracoronal attachments as interlocks in fixed prosthodontics. J Prosthet Dent

Non-rigid conncetors

The indications for the use of the NRC in fixed prosthodontics are:

1 .The existence of a Pier abutment , which promotes a fulcrum-like

situation that can cause the weakest of the terminal abutments to fail

and may also cause intrusion of the pier abutment. But should Pier

Abutments be used at all considering their high failure rate ??? (Ziada

et al. 1998).

2 .The existence of a malaligned abutment , where parallelling

preparations might result in excessive tooth preparation and

devitalisation. Such situations can be solved through the use of

intracoronal attachments as connectors.

3 .The presence of mobile teeth , which need to be splinted together

with the fixed prosthesis. In such situations, it is not practical to

cement a splinting type restoration with numerous teeth involved.

Through the use of interlocks, smaller segments can be cemented with

the splinting effect provided by the interlocks

4 .Long span FPDs: which can distort due to shrinkage and pull of

porcelain on thin sections of framework and thus affect the fitting

of the prosthesis on the teeth. Again, should long span bridges be

favored considering their failure rate and considering the success

rate of implants???

5 .In situations where a questionable distal abutment exists and

fabrication of the fixed partial denture is considered to be the best

interim treatment, the use of the NRC may solve the problem of not

having to repeat the restoration of the remaining abutment(s) after

final failure of the questionable abutment.

6 .It could also be used with osseointegrated implants.

So, the NRCs are mainly used to reduce stress on the

abutment and to accommodate malaligned FPD

abutments.

The four types of NRCs are the

1 .Dovetail (key-keyway) or (Tenon-Mortise) connectors.

2 .Loop connectors.

3 .Split connectors.

4 .Cross pin and wing connectors.

Align the path of the keyway to that of the mesial abutment. A

deep wax box is carved into the distal of the wax pattern for the

incorporation of a keyway, which in turn requires an intracoronal

preparation of adequate depth and a parallel path of insertion.

Ref: Badwalk PV, Pakhan AJ. Non-rigid connectors in Fixed

Prosthodontics: current concepts. J Indian Dent Assoc. 2005;5:2,99-102

Banjaree S. et al Non-rigid connectors- the wand to reduce stresses on the

abutment teeth. Contemp Clin Dent 2011,2:351.

Sutherland et al. (1980) suggested that a rigid bridge

resolves more of its stress internally before the

remaining stress can reach the bone, and it has been

found that the greatest stress concentrations in a rigid

bridge occur in the connectors.With a non-rigid

design, the stress may be directed through the

abutment teeth to the supporting bone rather than

being concentrated in the connector itself.

_This means that the prosthetic material and the luting

cement in a rigid design must withstand much greater

stress than in the non-rigid design.

Another problem that exists in the posterior mouth is the

inequality of the abutment tooth size.

_In a bridge replacing a first molar for example, the smaller

abutment (second premolar) may develop a thicker pericemental

cushion following frequent stress, as a compensating measure for

this stress. As a result, weaker abutments may move more than

the larger sturdier abutment. This results in large lever strains on

the weaker abutment which tends to shear the luting bond.

_However, when a stress-breaker is used on the smaller abutment,

it will tend to dissipate much of the leverage force.

_Stress-breakers can also be required in long-span bridges as

satisfactory tooth alignment becomes more difficult to achieve.

_Even in short-span bridges with divergent abutment teeth,

abutment preparations do not have to be parallel to each other.

Each preparations can be designed to MAXIMIZE individual

retention, independent of a common path of insertion.

The use of stress-breakers also tends to break up bridge length to more

manageable portions and makes subsequent repair/replacement easier.

Fixed-fixed

Rigid connectors