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