Precision attachments

Fixed prosthodondics

1. Presented By: Stephanie Chahrouk

2. Historical Background
Definition
Precision: Quality or state of being precise
Attachment: Mechanical device for the fixation, retention and stabilization of dental prosthesis.
INTRODUCTION
• The desire to balance between functional stability and cosmetic appeal in
partial dentures gave rise to the development of Precision Attachments
• Precision Attachments have always been surrounded by an aura of mystery.
• The use of Precision Attachments for partial denture retention is
• • A practice builder for the better class of dentistry
• • It helps to elevate the general standard of partial denture prosthetics.
• The precision attachment is sometimes said to be a connecting link between fixed and
removable partial denture as it incorporates features common to both types of
construction.
Winder
• “Winders design” Screw joint retention
Parr (1886)
• Extracoronal socket attachment
Stair
• Telescopic abutment restoration
Ash (1912)
• Split bar attachment system

3. PrecisionAttachment (GPT-8) :
• A retainer consisting of a metal receptacle (matrix) and a closely fitting part (patrix);
the matrix is usually contained within normal or expanded contours of the crown on the
abutment tooth and the patrix is attached to a pontic or the removable partial denture
framework.
• An interlocking device, one component of which is fixed to an abutment or abutments, and
the other is integrated into a removable prosthesis to stabilize and/or retain it.
Mechanical device – Direct retainer
• They are designed to replace occlusal rest, bracing arm, and retaining arm of the conventional
clasp retained partial denture.
• They function to retain, support and stabilize the removable partial denture.

4. CLASSIFICATION OFATTACHMENTS
1. Based on method of fabrication and the tolerance of fit

2. According to their relationship to the abutment teeth
a. Intr-acoronal (Internal attachment)

b. Extr-acoronal (External attachment)
Male attachments
•Patrix Flange insert key fitting part
Female attachments
•Matrix Slot crypt keyway Receptacle
Precisionattachment(prefabricated
types)
-Semiprecisionattachment(custom
made/laboratorymadetypes)-
Prefabricatedwax/plastic/nylon
patterns

6. 3. Based on stiffness of the resulting joint
a. Rigid attachments


b. Resilient attachments (Non rigid)

4. Based on geometric configuration and design of the attachment.
a. Key and Keyway
b. Interlocks
c. Ball and socket
d. Bar and clip / sleeve
e. Hinge
f. Telescopic
g. Push button
h. Latch
i. Screw units

7. Classification used in literature:
M.C. Mensor (1973)
Classification according to shape, design and primary area of utilization of attachment.

Gerardo Beccera and others (1987)
Intra-dental attachments
- Frictional
- Magnetic
Extra-dental attachments
- Cantilever attachment
- Bar attachment
ADVANTAGES
Improved esthetics and elevated psychological acceptance

8. Mechanical advantage
 Direct the forces along the long axis of the teeth / more apically
 Force application closer to the fulcrum of the tooth
 Reduces Non axial loading
 Decreases Torquing forces
 Rotational movement of the abutment
 In Distal extension base cases – “Broken stress philosophy”
 Reduced stress to the abutment
 Stress free rotational/vertical movements
 Cross arch load transfer and prosthesis stabilization
 Compared to conventional clasp retained partial denture
 Less liable to fracture than clasp
 Less bulky and more esthetics
 Better retention and stability
 Less food stagnation
DISADVANTAGES
 Complexity of design, procedures for fabrication & clinical treatment
 Minimum occlusogingival abutment height (4-6mm)
 To incorporate attachment without overcontouring
 Enough length of parallel contact
 Anatomy of the tooth – Limited faciolingual tooth width (incisor and canine areas)
 Expensive
 Complexity of laboratory and clinical procedure
 Attachment maintenance (repair or periodic replacement)
 Wearing of attachment components
 Require high technical expertise – Dentist and laboratory technician

 Requires aggressive tooth preparation
 Cooperation and manual dexterity on the part of the patient
 Difficult to insert and remove
 Visually or manually challenged patient
 Increase demand on oral hygiene performance

9. Removable Prosthodontics
 As a retainer in a removable tooth supported partial denture
 4 large well rounded abutments are available
 For esthetic concern in the anterior part of the mouth
 Stress Breakers
 Free end saddles/Distal Extension Base cases (DEB)
 When cantilevered pontic is to be used as abutment
 For movable joints in sectional dentures
 Periodontal involvement of the tooth
 Contraindicates rigid FPDs
 Most efficient bilateral bracing and support are essential
 Divergent abutment teeth with high survey lines – parallel path of placement.
 As a retainers in tooth supported over denture
Fixed Prosthodontics
 As a connector in fixed partial denture construction (long span bridges)

 To overcome alignment problems where abutments have differing path of withdrawal.
IMPLANT PROSTHODONTICS
 Implant supported over denture
 They are used for connection between the tooth and the implant

10. CONTRAINDICATIONS OF PRECISION ATTACHMENTS
 Poor periodontal support.
 Poor crown to root ratio
 Poor oral hygiene habits
 Abnormally high carious rate
 Inadequate space / room to employ the attachment
 Compromised endodontic and restorative conditions

SELECTION OF THE ABUTMENT TEETH
Factors :
Condition of abutment teeth
Number of the abutment teeth
Location of the abutment teeth
Periodontal condition
– Crown root ratio
– Periodontal support
Pulpal status
– Vitality of the pulp
– Size of the pulpchamber
REQUIREMENTS FOR THE ABUTMENT TEETH
Axial space requirement
Sufficient clinical crown length – for minimum of 4mm attachment

Maximum
attachment length
6-7 mm
Minimum
attachment length
4mm
Inadequate
attachment length
< 4mm
Buccolingual space
requirement
Adequate space
between the pulp
and the normal
contour of the tooth

11.  Full crown retainers
 Intracoronal attachments
Ideal Contours
More retentive / rigid Ideal contours
Caries protection
 Partial coverage retainers
 Kennedys Cl III partial denture
 Splinted abutment teeth
Most vulnerable
Inadequate retention
Marginal leakage
 Inlays / onlays / pin ledges
 Not used for intracoronal attachments
Lack of retention
Marginal caries
Less life
Selection of the attachments
 Intracoronal vs Extracoronal
 Resilient vs Non resilient
EM attachment gauge (Matsuo (1970))

75 mm in length
Red  3-4 mm
Yellow 5-6 mm
Black 7-8 mm

12. 1. Precision attachment (prefabricated type)
2. Semiprecision attachments (custom made)
Intracoronal precision attachment (Dr. Herman E.S Chayes)



Conventional attachment T shaped attachments
Modern attachment H shaped attachments

13. Frictional : Preiskel group I
Retention – Surface area contact
Function of the length
– Controlled by height of clinical crown
– Intermaxillary space available
Function of cross sectional dimensions
Mechanical : Preiskel group II
Auxillary mechanical retentive features
Ex. Spring loaded plunger / clips

Passive Attachment:
Matrix: Simple channels closes at one end to provide stop
Matrix: Solid slide
Channels of passive attachment may be round / elliptical slides

DEPENDING ON ARTICULAR RETENTION
Passive attachment Active attachmentLocked precision attachment Omega Beyeler

14. ACTIVE ATTACHMENT:
I. Active friction grip attachment

II. Active snap grip attachments

Locked precision attachment
I. Attachments bolted by means of a sliding bolt or latch
II. Pinned or screwed together
Mc Collum attachment :
H shaped attachment
Single adjustment slot

Retention  expanding the adjustment slot

15. Stern attachment
Two adjustment slots

Stern Gold latch retained

Crismani attachment :
Available as Rigid / Resilient
Rigid crismani attachment
Frictional grip
Mechanical Spring clip

16. Semiprecision attachments
Semiprecision rest – intracoronal rest seat and resilient lingual arm.
“Laboratory fabricated rigid metalic extension (patrix) of a fixed or removable
dental prosthesis that fits into a slot type key way (matrix) in a cast restoration
allowing some movement between the component”.
Gillete (1923):
The first semiprecision attachment
Rectangular deep rest with buccal and lingual wrought clasps arms
Ira D Zinner (1979):
Locking semiprecision attachment
Non locking semiprecision attachment
Louis blatter fein (1969) : Four aspects of rest seat preparation
Occlusal form / outline form – controls amount of rotation
Proximal form / side walls – lateral force control

The angle of the proximal wall with the gingival floor
Circular (Rigid –locking type) Dove tail (Rigid –locking type)
Rectangular Resilient Mortice Some resiliency (Non-locking type)
Parallel outline Tapering outline

17. Gingival floor form: serves the function of reciprocation


Advantages:
 Versatility for clinical situations – employing various rest seat outline forms.
 Variation in tooth size and shapes are easily accommodated.
 Better crown contour compared to prefabricated type
Disadvantages:
 Long term wear is more – softness of alloy used.
 No standardization of sizing : Lack of interchangeability of male and female
attachment.
 Greater degree of laboratory skill and attention in detail.






Flat
Inclined
•Mortice occlusal
Channeled
•Rectangular occlusal form

18. EXTRA-CORONAL ATTACHMENTS
1. Introduced by Henry R. Boos (1900)
2. Modified by F Ewing Roach (1908)
Application: Kennedy‟s class I and class II
Boitel (1978)
Rigid attachments
Resilient attachments
Bar attachments

Advantages:
 No alteration of contour of the abutment crown
 Can be used in short abutment teeth
 Greater freedom in the design
 Ease of insertion and removal
Disadvantages (Wolf RE 1980):
 Lack of occlusal stability
 Bulky
 Rebasing problems
 Improper control of force distribution
 Encroachment on the gingival papilla – use of mini attachment

EXTRACORONALATTACHMENT
Rigid attachments Hinged attachments (Stress breaking
action)
Resilient attachments ERA
O-ring

19. ROLE OF ATTACHMENTS AS STRESS BREAKER
Broken stress philosophy

Mensor  stress can only be selected, altered or blocked
“Stress director”
Shohet (1969) Kratochvil (1981)
Low intensity forces on abutment teeth in contrast to rigid attachments.
Rationale of stress breaker  movement should be strictly only to displaceable tissue
Disadvantages of stress director:
 More complex, increased wear and breakage
 Increased bone resorption and trauma
 Occlusal contacts difficult to maintain
 Spring like device  tendency to fatigue

Rigid system
Non-rigid system
•Stress breaker Broken

20. References:
Removable Partial Dentures by Olcay Sakar editor