|
Stainless
Steel Reinforced Resin Retained Bridges
By Daniel E. Purvis, DDS
Provisional restorations are an important and desirable
restoration in today’s practice. The advent of implant dentistry, total
mouth cosmetic restorations, increased tooth life due to periodontal therapy
advances, and the public’s demand for cost-effective restorative alternatives
all place the provisional prosthesis in the forefront of the modern dental
practice.
Every practitioner has faced the situation where an
effective provisional prosthesis would make the difference in the long-term
scheme of treatment. In addition, certain patients, such as the medically
compromised or those with financial concerns, may require an alternative treatment
to conventional fixed bridges or implant-retained restorations. The design
of a provisional prosthesis must consider the following requirements:
(1) Minimal invasiveness. Any provisional restoration must be capable
of change or modification. The treatment plan is ongoing, and change is often
indicated in the long term. Minimal invasiveness allows this to take place
with relative ease.
(2) Durability and serviceability. Any provisional restoration must
be durable enough to with stand the functional forces of the dentition being
treated. It must also be easily repairable, especially when long-term applications
are considered.
(3) Aesthetics. With reasonable aesthetics, patient acceptance and
compliance are assured.
These factors, coupled with a prefabricated universal
design can give the practitioner a distinct advantage in executing long-term
treatment plans and treating medically compromised or financially challenged
patients.
Stainless steel reinforced resin retained fixed bridge techniques
take advantage of several physical and biological principles to provide a
lasting fixed provisional prosthesis. To understand the use of this technique
one must understand the histological and physical principles at work in the
contact areas of teeth. The density per unit area of enamel rods is largest
in the contact areas.[1] The dentin-enamel interfaces
in these areas also show a convergence angle of less than 45º. This convergence
angle provides a greater resistance to compression mathematically than convergence
angles of higher values.[2] These two histological factors
give the areas approximating the contact point the strongest dentin-enamel
etched bond.
The mechanical design of the reinforcing steel is
the second factor in the success of the steel reinforced bonded bridge (Figures
1 and 2). A double axis of rotation provides a better resistance than a single
axis of rotation. Components designed with a double axis of rotation not only
have greater resistance to rotation and dislodgment, but also have greater
surface area for bond adhesion. Studies show that this system has a resistance
of 1,200 psi.3 Load testing of “split wing” or double axis metal
components demonstrating failure at the pontic facing, but not at the attachment
point. This demonstrates the strength of the attachment bond.
The preparations are standard class III preparations. Their placement
is in the zone of attachment.4 The zone of attachment is described in Figure
3. It is determined by statistical analysis of surveyed patient models. The
preps should be placed as close to the axial height of contour of the tooth
as possible. Their width should be at least 2mm and deep enough to incorporate
the steel component. Survey studies reveal that the difference between the
axial height of contours of anterior teeth is 2mm. This measurement is what
is used to determine the width of the double axis retention wing. Furthermore,
stainless steel when freshly micro-etched increases bond adhesion. This further
adds to the strength of the total restoration.
THE DIRECT EASTFLEX
BRIDGE TECHNIQUE
The technique for fabricating a stainless steel reinforced
resin bridge utilizes Eastflex bridge components. These components allow the
fabrication and placement of single pontic bridges without the need for laboratory
support. When the procedure is followed, a durable fixed prosthesis can be
fabricated that can withstand a minimum of 1,200 psi. armamentarium consists
of the Eastflex bridge component selected to fit the space; appropriate handpiece(s)
and bur(s) for tooth preparation; 35% phosphoric acid etchant gel; bonding
agent and composite resin; curing light if light-cured resin is used; and
suitable plastiform crown contoured to fit the space.
The technique consists of the following steps:
(1) Examine the patient’s dentition and prepare
the teeth to accept the Eastflex component (Figures 4 and 5).
(2) Contour and fit the component into the prepared
space (Figure 6).
(3) Prepare the plastiform crown (Figures 7 and 8).
(4) Bond the component into the teeth preparations.
Remove excess resin from the component that will interfere with the investment
of the crown form to the component.
Invest the crown form and place it onto the space, making sure it is also
completely invested to the supporting component (Figures 9 and 10).
(5) Finish with appropriate composite finishing equipment
(Figure 11).
CLINICAL RESULTS
The author and Dr. Maris J. Lans (a practitioner in Lanham, MD)
have placed 150 stainless steel reinforced resin bridges and followed them
from 3 months to 5 years.5 They produced the following data: 28 posterior
bridges; 57 premolar bridges; and 65 anterior bridges. The total repair rate
was 8%. The breakdown was: 2 posterior repairs; 4 postmolar repairs; and 6
anterior repairs.
Stress studies performed on these bridges gave the
following results6: the anterior bridges can with stand over 1,000 psi before
breaking. The posterior bridges can with stand over 1,200 psi before breaking.
Breakage occurred at the resin portion of the pontic. The metal component
remained intact. These results are well within the average masticatory forces,
which are 600 psi and 1,200 psi, respectively.[7]
CONCLUSION
Properly designed stainless steel micro-etched components
can provide a reinforcement to resin retained bridges that rivals conventional
single tooth bridge procedures. This technique is less invasive than conventional
cast bridges. It is also more cost-effective than conventional bridgework
and requires minimal lab work. This is a viable treatment option that the
dentist can do in his/her office.
This technique will provide a tooth replacement for
many patients who otherwise cannot afford a fixed procedure, or a provisional
restoration during long-term treatment.
____________
REFERENCES
[1] Leeson,
DF. History of the Oral structures. St. Louis, Mo: Mosby; 1987-326-328.
[2]. Travis
DF, Glimacher MJ. Structure and relationship of bovine enamel to dentine.
J of Cell Biol. 1964; 23:447.
[3]
Lab Report No. a68347, 1999, Ramble Test Labs Inc., Cinnaminson, NJ
[4]
Eastflex Scientific Report 1997, Eastflex Inc., Indianapolis, Ind.
[5]
Eastflex Case Files 1994-1999, Indianapolis, Ind.
[6]
Lab report No. A68347, Ramble Test Labs Inc., Cinnaminson,
NJ
[7] RG
Craig Restorative Dental Materials, 7th ed. St. Louis, Mo: Mosby; 1985:61. |
|
|
