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Resin Bonded Retainers
By
Dr. Manal Rafie Hassan
Lecturer, Fixed Prosthodontics Department
Faculty of Dentistry
Minia University
بسم هللا الرحمن الرحيم
Definition: It is a restoration of one or two
pontics supported by thin metal ( wing
retainers ) or ceramic retainers , placed
lingual and proximally on the minimally
prepared abutment teeth and depends
largely in their retention on adhesive
bonding between etched enamel and the
metal or ceramic surface of the retainers.
Resin Retained Bridges
retainers
pontic
CONCEPTS OF ADHESION
Definitions:
•Adhesion: is the surface attachment that
involves some types of intermolecular
attraction between adhesive and adherend.
•Adhesive: the material or film added to
produce adhesion.
•Adherend: the substrate to which the
material adhered e.g., enamel.
Adhesion mechanisms:
a) Mechanical adhesion:
•It is based on the old mechanical retention concept.
•It occurs when the solidified adhesive interlocks
micro-mechanically with the roughness and
irregularities of the surface of the adherend
(substrate).
b) Chemical or true adhesion:
It refers to the forces or energies between
atoms or molecules at an interface that
holds two phases together.
c) Electrostatic adhesion:
It occurs when an electrical double layer
forms at the interface between a metal
and a polymer.
Factors affecting adhesive system:
1- Wet ability of substrate surfaces by the restorative
materials.0º & 180º contact angle indicating max.
wet ability.
2- Stability of the adhesive.( the oral cavity is liable to
thermo cycling leading to failure in the adhesion )
3- Bonding strength.
4- Free of voids.
5- Bio-compatibility.
6-Low surface tension.
Rochette in 1973 suggested minimal removal of tooth structure then bonding a metal framework to the lingual surface of the abutments.
The metal is perforated into 4 or 5 holes then a resin cement is applied to the etched enamel surface.
The disadvantages of this technique are:1-bulky restoration , the bond is confined to the area of perforations.2- exposure of cement to the oral fluids & biting on it caused wear of cement
and finally debonding of the restoration.
Types of R.B.R.:
1- Direct bridge: bonding a natural extracted tooth directly to the proximal surface of the abutments. or using denture teeth.
2- Indirect Bridge:
a) Macro mechanical retention e.g. Rochette bridge.
Labial view of
the bridge
Lingual view of
the bridge
Advantages Minimal tooth structure is removed. The preparation is confined
to enamel only.
No pulpal trauma is expected.
No anesthesia is needed.
No periodontal injury as the finish line is kept supragingivaly.
Time of preparation is reduced and impression taking is simplified.
It is considered as intermediate bridge , we can always move to the conventional bridge if debonding occurs frequently due to one or other factor.
Cost is reduced.
Durability.
Resin bonded retainers show excellent biological,
chemical and mechanical properties.
The preparation is confined to enamel.
Frequently do not require anesthesia.
Disadvantages
The main disadvantages related mostly to the
debonding that occurs after cementation , or
the sensitive technique of construction , failure
may occurs due to bad design or bad selection
of the cement used ,or due to bad selection of
the patient.
Strict and limited indications.
Indications The presence of healthy abutments ,restoration free or
with minimal restoration which will be included in the preparation.
Adequate crown size to improve retention & resistance form.
Resin B.R. is considered in young patients with large pulp, in which pulp exposure is expected if complete coverage is constructed.
It can be used as splint for periodontally compromised teeth .
It can be used anterior and in pre molar region & in few selected cases in molar area (in young patients with under developed muscles)
Contraindications
Lack of sufficient enamel bonding. Bonding to dentine is not as good as enamel & can’t retain the bridge.
Abutments with large restorations or broken teeth (no enamel for bonding, no retention).
Very thin or translucent anterior teeth due to impairment of esthetics.
Abutments with enamel defects e.g. Hypoplastic enamel, mottled, tetracycline stained teeth.
Patients with abnormal forces of occlusion.
Normal alignment abutments with no mobility.
In long span bridge.
FABRICATION
THREE FASES ARE CONSIDERED:
Preparation of the abutments.
Framework design.
Bonding of the restoration to the abutments.
Whether the abutments are anterior or posterior,
the common principles are:1- distinct path of
insertion .2-proximal under cut must be
removed to provide (PLANES OF
METAL) on the proximal and the
lingual surfaces . 3-occlusal rest seat &
proximal grooves or slots must provide
the resistance form. 4-definite gingival
margin ,supragingival in most cases.
Distinct path of insertion , under cut
removal to provide a plane of metal on
proximal & lingual surface ,occlusal rest
seat and or proximal grooves (resistance
,retention ) & supragingival margin (F.L.)
Different Anterior
Designs
Supragingival gingival
margins
Interproximal
wrap around
The general preparation
features :prepare the
largest enamel area that
will not impair esthetics
(the tooth should be free
of contact in all excursive
movements ,if a must
recontouring of the
opposite tooth is done.
*the retentive retainers,
wings, should be one
distal & mesial to the
pontic, in replacing two
teeth ,two retainers are
used.
*one or two retentive
grooves are parallel to the
path of insertion and to
the long axis.
*distinct gingival margin
with chamfer f.l.
N.B. :Leave about 1mm from the incisal margin and 1mm from gingival margin, this will help in seating of the retainer, in addition lingual ledge resists gingival displacement under biting forces.
Abutments should have parallel proximal surfaces, an optional slot may added lingual to the labial end of the proximal preparation.
A distinct rest seat is placed on the cingulum to resist gingival displacement.
IN mandibular teeth, enamel is thinner than in maxilla so more conservative (o.3mm)reduction is performed.
Posterior preparation
The General Features
The occlusal spoon shape rest seat is prepared on the marginal ridge area of the abutment near the pontic , additional seat may be added on the opposite side if needed.
Retentive surfaces: proximal and lingual axial walls are prepared (1mm) reducing the height of contour & ends 1mmbefore the gingiva.the bonding area may be increased by extending to the occlusal surface.
Proximal wrap around : the framework should engage 180 degree of the tooth circumference to resist tie lingual & lateral displacing forces.
The difference between mandibular & maxillary molars is that the preparation in the lingual s. of lower teeth is performed in one plane while in the upper , we must accommodate the secondary plane of the functional cusp.
Different posterior designs
Extension of the preparation on
the occlusal surface.
Simpler design.
Resin bonded bridge used as a splint for lower teeth
TECHNIQUES USED FOR ALLOYS
OF R.B.R. TO IMPROVE BONDING
WITH TOOTH STRUCTURE
Metal surface treatment
Mechanical Chemical
Macromechanical Micromechanical Interfacial Adhesive
1)Cast perforated resin
reinforced bridge
2) Water soluble salt
crystals.eg. Virginia
bridge.
3)Cast mesh pattern
4) retention acrylic
beads.
1) Electrolytic
etching
2) Chemical
etching
3)Porous metal
coating
4)Sandblasting
1) Tin plating
2)Silicoater tech.
3) Rocatec
system
4)Application of
liquid Ga-Sn alloy.
5) Ion coating
surface traet. Of
alloy
1) Heating of
alloy
2)Immersion in
an oxidizing
soln
3)Immersion
in concentration
nitric acid
Mechanical Techniques : *Macro mechanical
techniques , in these techniques ,no. of pores are
performed on the lingual surface e.g. Rochett
bridge OR the use of mesh work muslin adapted
on the lingual surface of the wax pattern , after
burning out of the wax and casting, the metal
framework of the resulted lingual surface will
have the irregularities of the mesh work muslin
e.g. Duralingual bridge
a) Macro mechanical retention e.g. Rochette
b) medium mechanical retention e.g. Duralingual system
( mesh work muslin ).
Micro-mechanical as electrolytic etching , & chemical etching (mixture of nitric , HCl & HF acids in gel form for 20 min. then rinsed with distilled water &air dried for 30 min.) .
The electrolytic etching is a sensitive technique in which the metal is cleaned with 50µ Al2O3 FOR 30 sec. then mounted on an electrode (+ve pole ) ( anode) then the metal is immersed in electrolyte solution opposite to st.st. cathode( –ve pole). ( the framework is a part of an electric circuit )
A specific current density is used for predetermine time.
Maryland bridge is the famous name for this technique.
C) MicroMechnical retention e.g. Maryland bridge by
either: electrolytic etching or chemical etching by
hydrofluoric acid ,HCl , Nitric acid gel.
The disadvantages of this technique are:
Extremely sensitive technique.
Limited to the base metal alloys ( precious
alloys cannot be etched ).
The fragile nature of the resin tags engaging the
etched metal surface are liable to thermo cycling.
(DEBONDING& FAILURE)
Etched metals
Porous metal coating
Firing of fine particles of st.st. powder to the
metal surface provides the followings;
The presence of large area for retention with
resin cement and this technique can be used
with both noble alloys and base metal alloys
Powder
metallurgy
Sand-blasting Technique
Application of 50-250µ aluminum oxide to the
alloy surface by sandblasting technique for 30
sec. then washed in ultrasonic bath of detergent
agent followed by distilled water gives the
followings; - clean the alloy surface from any
greasy material ,increase surface area available
for cement , increase the wet ability of the alloy
due to increased surface energy leading to good
bonding with panavia resin cement.
Advantages of sandblasting technique
No need for special equipment.
The treated framework possess high bond
strength with tooth surface.
The procedure can be done intraorally during
the appointment of final cementing.
If the procedures completed as mentioned ,no
errors are detected and it takes no time.
Techniques to increase chemical bonding between
alloy surface and the cement.
A- Interfacial bonding (intermediate surface for
↑bonding with the cement).(NOBLE
ALLOYES )
B-Adhesive bonding (it depends on reactive
groups of the resin cements to bond directly on
the oxide layer on the alloy surface.)
1-Silicoater Technique
The surface of the alloy is sandblasted with 50-250µ Al2O3 for 10-15sec. With 4 bars pressure.
This will insures removal of 100µ of the metal surface then it is coated with a silicate SiO-C layer through a pyrolytic reaction in the silicoater unit.
The cements bonds very well with the alloys treated with this method (precious & non precious alloys).
2-Rocatec System
Abrasion of the metal surface with 120µ alumina
particles followed by abrasion with alumina
contains silicate particles .
This will deposits a layer rich in silica on the
surface that make a chemical bond with the
silane (a layer applied to bond the cement to the
tooth st. &to the restoration).
silane
Silicate rich
surface
cement
silane
3-Tin plating technique
Tin plating electrolytically deposits a layer of tin
metal on the alloy surface ,this layer is
chemically bonded to both the alloy and the
resin cement.
This method can improve bond strength of the
precious alloys with resin cement.
The cement bonds to 0.2-0.4µ of tin oxide on
the surface.
4-Sputtering (ion coating surface treatment)
The technique includes ion coating of the surface using a special machine called a sputtering unite in which ions strike a target electrode , causing emission of atoms from the electrode that will react with the oxygen in the chamber of the unit and deposited on the metal surface.
Ion coating can be used with precious &non precious alloys.
5-Lasers
Lasers are used to modify the surface topography of the alloy producing a surface with micro irregularities & scratches that enhance bonding with cements.
More over it causes some elements oxides to be concentrated on the surface of the alloy that aid in the chemical bonding to resin cement.
If curing of composite is done by laser , the bond strength is improved very much.
The metal framework should
be painted first with a material
that enhance laser beam
absorption.
6-Application of liquid Ga-Sn alloy (adlloy)
This method includes the modification of surface alloy by a liquid Ga-Sn alloy that improves the bond with 4-META adhesive cement.
The technique consists of application of 90%Ga 10%Sn mixture at room temperature.
Advantages include increase in bond strength of precious alloys with cement & no need for any special equipment.
7- Plasma coating : by the help of laser beam , a
plasma coat is precipitate on the metal surface ,
improving bond with cements (Pulsed Laser
Deposition Technique).
8- The use of metal primers on the sand blasted
metal surface capable of enhancement of bond
with resin cements.
Methods of adhesive bonding
1-Heating the alloys: this cause concentration of copper on the surface of the precious alloys due to heating leading to improved bonding with 4-META resin cement.
Single heating :the alloy is heated in furnace for 3-5min. At 400°C when the color changed the alloy is removed to cool at room temp.
Double heating: at 800°Cfor one hour the washed in dist.water then heating at 650°Cfor 10 min. then permit to cool.
2- Immersion in oxidizing solution: the solution
consists of 3%wt aqueous sulfuric acid with 1%
wt potassium permanganate .at room
temperature for 2min. Develops superior
bonding if combined with sandblasting with
alumina.
3-Immersion in conc. Nitric acid : nickel
chromium alloys develops a thin oxide layer that
bonds strongly with 4-META.
Bonding procedure
Patterns of etching:
•Type I : preferential
removal of enamel prism
cores.
•Type II: preferential
removal of prism
peripheries.
•Type III : not related to
prism morphology.
ETCHING OF ENAMEL
Etching:
Objectives:
1. Removal of the smear
layer.
2. Demineralization of the
superficial dentin matrix.
3. To uncover peri-tubular
and inter-tubular dentin.
Etching of enamel then priming
dentin then application of resin
cement.
Methods:
• Chemically:
a) Acids: Phosphoric acid
30-40% for 15 sec. was
found to be the most
effective acid for etching
of enamel and dentin.
b) Laser (inferior to etching
by acids)
Step by step procedure:
1-Clean the teeth with pumice
&water, then isolate the teeth with
rubber dam
2- enamel etching.
3-rinsing then drying .
4-priming (if dentine is exposed ).5-
application of Panavia cement(or
any suitable resin cement) (opaque
&tooth colored if it is anterior
bridge) on the inner surface of the
casting.6-seat the casting firmly
under pressure for 30-60sec.(time for
setting) then apply an oxygen guard
at the margins to ensure setting at
the margins, then light cure.
oxygaurd
Superior esthetics.
Thank you
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