Direct retainers Part II

Direct retainers Part II

Direct retainers Part IIPrecision attachments

Dr. Akshi Gvalani

P.G. Dept of Prosthodontics Terna Dental College, Nerul, Navi Mumbai

The renaissance of attachment usage came about in the late 1950s with the work of Steiger and Boitell followed by the first compilations of representative attachment systems.

Precision/Semiprecision RPD is the treatment modality that can facilitate both an aesthetic and a functional replacement of missing teeth and oral structuresDEFINITIONPrecision quality or state of being precise Attachment Mechanical device for the fixation, retention and stabilization of dental prosthesis. PRECISION ATTACHMENT ( GPT-8)A retainer consisting of a metal receptacle (matrix) and a closely fitting part (patrix); the matrix is usually contained within the normal or expanded contours of the crown on the abutment tooth/dental implant and the patrix is attached to a pontic or the removable dental prosthesis framework.

SYNONYMS OF ATTACHMENTS INTERNAL ATTACHMENTS FRICTIONAL ATTACHMENTS PARALLEL ATTACHMENTS SLOTTED ATTACHMENTS KEY AND KEY WAY ATTACHMENTS

Patrix Matrix

Flange Slot

Insert Crypt

Key Keyway

Fitting part Receptacle

HISTORICAL BACKGROUNDWinder Winders designScrew joint retentionFirst unilateral fixed detachable type of RPD

Parr (1886)Extracoronal socket attachment

Stair (1886)Telescopic abutment restoration

Ash (1912) Split bar attachment system

Late 19th century :Dr. Herman ES Chayes T shaped Precision Attachment (1906) H shaped Chayes Attachment (1912)

First attachment to be available in the market

CLASSIFICATION OF ATTACHMENTS Based on method of fabrication and the tolerance of fitPrecision attachment (prefabricated types)Semiprecision attachment (custom made / laboratory made types) Prefabricated wax / plastic / nylon patterns JOEL M ZAHLER ( 1980 ) The term SEMI PRECISION is misnomer as when properly made, the laboratory fabricated attachment is just as precise as the prefabricated version.

According to their relationship to the abutment teeth

I. Intracoronal (Internal attachment) : attachment resides within the body/normal contours of the abutment teeth

II. Extracoronal (External attachment) : attachment resides outside the normal contours of the abutment crown/teeth

Based on stiffness of the resulting joint Rigid attachments

Resilient attachments (Non rigid) RIGID ATTACHMENT Metal to metal contact of the patrix and matrix restrict the relative movement between the abutment and prosthesis during the functional loading. Theoretically allow no movement of their component parts during function. Usually used in bounded saddle situations where the abutment teeth fully support the restoration and attachment, soft tissue does not give any support. RESILIENT ATTACHMENTS Attachments are designed to permit movement of the denture base during functional loading Functional movement of the prosthesis may be restricted to defined vertical, horizontal and or rotational path Theoretically minimizing the amount of force being transferred to the abutment teeth. Hinged motion Allowing movement along one plane. Rotary motion Allowing movement along many planes. Based on geometric configuration and design of the attachment

Key and Keyway Interlocks Ball and socket Bar and clip / sleeve Hinge Telescopic

M.C. Mensor (1973) Classification according to shape, design and primary area of utilization of attachment.IntracoronalTelescopeAuxiliary

Extracoronal(Pressure buttons)Screw units

Bar attachmentBar connectors

(Bar joints and bar units)Bolts

Stabilizers

Balances

Interlocks

Bacerra and Macantee(1987)

ADVANTAGES Improved esthetics and elevated psychological acceptance Mechanical Advantage ( in intracoronal attachment) Direct the forces along the long axis of the teeth more apically Force application closer to the fulcrum of the tooth In Distal extension base cases Broken stress philosophy Reduced stress to the abutment Stress free rotational/vertical movements

Cross arch load transfer / force transmission and prosthesis stabilization may also be improved - particularly with rigid precision attachments Lateral forces on the abutment during the insertion and removal are eliminated and more axial force during functions are achieved. 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, complex principles and procedures for fabrication and clinical treatment. Abutment must be crowned Precise and structurally demanding tooth preparation Encroachment on the root canal space in attempt to prepare abutment to receive attachments. Minimum abutment occlusogingival height ( 4-6 mm )

In order to facilitate acceptable emergence profile. To incorporate attachment components without over contour. Shorted abutment may yield over contoured coronal restorations and reduced frictional / binding retention of the attachment. Expensive Complexity of laboratory and clinical procedure Attachment maintenance (repair or periodic replacement) Wearing of attachment components - because of friction between metal parts overtime and may require repair or replacement Requires high technical expertise for successful fabrication experience and knowledge on the part of dentist and laboratory technician are essential. Cooperation and manual dexterity on the part of the patient Difficult to insert and remove Increase demand on oral hygiene performance

INDICATION / APPLICATIONSRemovable Prosthodontics As a retainer in a removable tooth supported partial denture For 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 Divergent abutment teeth with high survey lines difficult to get parallel path of placementAs a retainers in tooth supported over denture

Fixed ProsthodonticsAs a connector in fixed partial denture construction (long span bridges)

To overcome alignment problems where abutments have differing path of withdrawalThe existence of pier abutment : which promote a fulcrum like situation that can cause the weakest of the terminal abutment to fail.

Implant prosthodontics Implant supported over denture They are used for connection between the tooth and the implant

CONTRAINDICATIONSPoor periodontal supportPoor crown to root ratio Poor oral hygiene habits Abnormally high carious rate Inadequate space / room to employ the attachment Compromised endodontic and restorative conditionsDistal extension conditions Senescent / handicapped individuals

Studies have also demonstrated that precision-attachment partials last longer, wear less, need less adjustments, look better, work better, less destructive, protect abutment teeth, and are easier to clean

Rates of unsuccessful treatment for clasp retained cast RPDs range from 3% to 40% with mean being 26% (Frank et al, 1998). Patients seek treatment with cast RPDs for the purpose of improving appearance and masticatory function. It has been suggested that compliance improves when the prosthesis meets the aesthetic requirements of the patient (Mazurat & Mazurat, 2003).Treatment planning Six important questions 1. Is the patient healthy ?2. Is the prosthesis necessary ?3. Is the patient suitable for the prosthesis?4. How large is the span ?5. What structures support the prosthesis ?6. How is the prosthesis made ?

SELECTION OF THE ABUTMENT TEETHFactors : Sound abutment teeth Number of the abutment teeth Periodontal condition Crown root ratio Periodontal support Pulpal status Vitality of the pulp Size of the pulp chamberRequirements for the abutment teeth Occlusogingival length minimum of 4 mm vertical space is required so that there is adequate space. Maximum Minimum Inadequate

Buccolingual space requirementPlacement of attachments in the incisors can be difficult because or limited faciolingual width. Adequate space between pulp and normal tooth contour is necessary for the intracoronal component of an internal attachment.

1. Selection of the type of retainer2. Selection of the attachment :

Selection is based on some factors: Crown root ratio. Clinical crown length/height the length of the attachment is the main criteria in choosing the attachment, rather than the width. Vertical space available. Number of abutments used for support. Location of the abutment / strongest abutment. Quality of the bone of the residual ridge. Cost. Maintenance factors.

Selection of the attachment : Intracoronal Vs Extracoronal

Size and shape of the abutment teeth Intracoronal attachment - more teeth preparation and tooth reduction If intracoronal attachments are used where there is insufficient space, the abutment retainer will be over contoured on the proximal surface resulting in restoration that can create periodontal problems. In case the space is adequate intracoronal attachment is preferred as they direct the forces along the long axis of abutment teeth. Though extracoronal attachments are employed in areas of inadequate space they can create areas which may be difficult to clean leading to maintenance problems. The lever arm associated with extracoronal attachment may not direct all force along the long axis of teeth.

Resilient Vs Non resilient Major differences of philosophy regarding the use of resilient or non resilient attachment system occurs when dealing with distal extension edentulous situation. Theoretically, resilient attachment allows the functional forces to be directed to the tissues and alveolar ridge and the non-resilient attachment primarily directs the vertical functional forces to the abutment teeth. Realistically, there is some sharing of functional loads in both systems.ATTACHMENT SELECTION In 1971, 126 attachments were listed and classified by Dr. Merrill Mensor; this is called as E. M. attachment selector.

It has 5 charts giving specification as to the type of attachment.It utilizes a colour coded millimeter attachment gauge to define the vertical clearance available in the edentulous regions of occluded casts for attachment selection. Red designates 3 to 4 mm, yellow designates 5 to 6 mm and black designates 7 to 8 mm.

INTRACORONAL ATTACHMENTSIntracoronal attachment were introduced in the late nineteenth century with substantial contribution from Dr. Herman ES Chayes. Precision attachment (prefabricated type) Semiprecision attachments (custom made)

Intracoronal precision attachment Two component a matrix and patrix Matrix (female) is waxed into the crown or bonded into a preparation in the tooth. Patrix (male) is attached to the framework usually by soldering Machined to close tolerance (0.001 inch average). Axial space requirement Average dimension of the intracoronal attachment is just over 1.5mm and allowing for a minimum of 0.5mm of metal in the crown internal to the matrix. Minimum of 2mm of reduction in the area of attachment is essential to keep the final unit within normal contours. The tooth must have sufficient clinical crown length to accept a matrix with a minimum vertical height of 3mm. Greater the vertical length of the attachment complex, the greater the potential retention and stability that can be expected. The width of the matrix in buccolingual direction will be in the range of 3mm. Prefabricated intracoronal attachment Modern attachment utilize an H shaped flange which is stronger and has nearly double the frictional surface area of the earlier T-shaped flanges. Atleast two but sometimes three or four of the attachments are included in the denture and they have to be aligned so that the all the roots (and hence the flanges) are parallel to each other to ensure insertion and removal.

Types of intracoronal attachment :Depending on articular retention retention types between the matrix and patrix. Passive attachment Active attachment Active friction grip attachment Active snap grip attachment Locked precision attachment

PASSIVE ATTACHMENT :Matrix : Simple channels closed at one end to provide stop Patrix : Solid slide Channels of passive attachment may be round/elliptical slides

ACTIVE ATTACHMENT Active friction grip attachmentIncorporate the adjustable spring mechanism for added retention. Simplest form is split patrix, so that part of it forms a leaf spring which can be opened to compensate for wear to give retention.Function by forcing the part of the patrix against the matrix thus increasing the area of contact and the effort required to separate them. Friction grip attachments are often little larger than the bigger passive attachments and are therefore suitable for use in the anterior and premolar regions of the mouth.

Active snap grip attachmentsIn snap grip attachments, the active element consists of a spring loaded plunger, a split ring or a U spring which engages in a prepared pit or groove. Active snap grip attachments are among the largest attachments and hence can usually only be accommodated in molar retainers.

LOCKED PRECISION ATTACHMENTThey are either bolted by means of a sliding bolt or latch, or may be pinned or screwed together when fully articulated.

SEMIPRECISION ATTACHMENTS

Definition: 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. - GPT 8First semi precision attachment was constructed by Gillete in 1923. It had buccal and lingual wrought clasps arms with a rectangular deep rest. These semi precision attachment, almost always created in the dental laboratory either in the wax or by milling the completed casting. Deep rest seats can be fabricated in various out line forms to control the amount of rotation around the horizontal axis and direction of movement of the resultant partial denture.Outline form controls the rotationSide walls lateral force transmission Flat gingival floor occlusal force transmission and Retention provided by the frictional resistance between the rest and the rest seat.According to Louis Blatterfein (1969): In designing of a semiprecision attachment 4 aspects of rest seat preparation may be taken into consideration Occlusal form Proximal form Gingival floor form Proximal surface placement

Occlusal form Four type of deep rest occlusal outline forms- Controls the amount of rotation of attachment Circular Dovetail Rectangular MortiseProximal form : Lateral force controlled Controls the rotation around longitudinal axis in distal extension RPD . According to Blatterfrin the angle the proximal / lateral wall makes with gingival floor determines the rigidity of the retainer. Parallel TaperingGingival floor form The gingival floor form controls and serves the function of reciprocation. Flat gingival floor provides reciprocation.

Inclined gingival floor is indicated for added reciprocation, usually indicated in mortise occlusal form.

Channeled gingival floor : Used with rectangular occlusal outline form (nonlocking occlusal outline).

In 1979 Ira D Wisner discussed about two basic types of semiprecision attachment Locking Non lockingLocking type : Locking type of attachment do not allow for rotation and hence can be considered as rigid Locking type of internal attachment are not used with distal extension removable partial denture because of inherent excessive leverages most often associated with themNon locking type : Non locking type allows some movement and is useful in distal extension conditions. Non locking type of internal attachments in conjunction with sound prosthodontic principles can be advantageously used in many instances in Class I and Class II partially edentulous situation. Neurohr Willian No. 2 mandrel with channeled gingival floor rectangular occlusal outline (1930) Thompson Dowel rest (1949) Thompson Morris J

Advantages of custom made attachment (semi precision attachment) : Offers far greater adaptability to a wide variety of clinical situations . By employing rest seats of various outline forms amount of rotation and direction of movement can be controlled. Variation in tooth size and shapes are most easily accommodated. It allows the technician to achieve a far better crown contour in the critical gingival area than is possible with the prefabricated precision attachmentDisadvantages : Long term wear is more compared to prefabricated because of softness of alloy used in their fabrication. Prefabricated attachments are made of alloys which are harder and more resistant to wear than the alloys which are available to the lab technician No standardization of sizing : Lack of interchangiability of male and female attachment Repair and replacement of custom attachments are more difficult as composed to prefabricated parts. Greater degree of laboratory skill and attention in detail is required

EXTRACORONAL ATTACHMENTS Introduced by Henry R. Boos (1900)Modified by F .Ewing Roach (1908)Application Kennedys class I and class II

Boitel (1978) Rigid attachments Resilient attachments Bar attachments Rigid attachment : do not allow any rotation of the partial denture in function Hinged attachment : Offers a stress breaking action to the distal extension bases Resilient attachment ERA : Permit limited amount of movement of the denture baseAdvantages : 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 Rebasing problems Improper control of force distribution Encroachment on the gingival papilla ( use of mini attachment )

RIGID EXTRACORONAL ATTACHMENTS Roach attachment (ball and tube attachment)Oldest attachment Patrix round ball Matrix - tube

Pin and tube attachment The simplest Patrix - pin Matrix tube

Stabilex attachment Two retention pinsDisadvantage is increased length

Extracoronal resilient attachment

Colour coded capsMost flexible White > Orange > Blue > Gray Most rigid

Two types of ERA Standard Reduce vertical (ERA RV) male part is 0.5mm shorterVertical resiliency of 0.4mm Universal joint hinge action O Ring attachment Patrix - post with the groove or undercut. Matrix O-ring synthetic polymer gaskets + encapsulator O-ring are made up of Silicone Nitrile Fluorocarbon Ethylene propylene Advantages of O-ring Different degrees of retention Ease in changing the attachment Wide range of movement Low cost

HINGED EXTRA CORONAL ATTACHMENT Dalbo / Dallabona attachmentPatrix Matrix

Dalbo stress breakerRotational and Vertical movement

Ceka attachmentDeveloped by Karl Cluytens (1951)Two types- Ceka NV attachment- Ceka revaxMatrix metal ring retainer Patrix Attachment pin (split metal post)

Functional aspect : Mark E, Waltz 1973 Support Bracing Retention

Insertion and removalReduces frictional wear

ROLE OF ATTACHMENTS AS STRESS BREAKER Broken stress philosophy Mensor (1972) stress can only be selected, altered or blocked Stress director Rationale of stress breaker movement should be strictly only to displaceable tissueDisadvantages of stress director : Increased bone resorption and trauma Occlusal contacts difficult to maintain Loss of cross arch stabilisation Spring like device tendency to fatigue More complex, costly to make difficult to repairAUXILLARY ATTACHMENTS Screw and tube attachment Key and keyway / interlocks Presso Matic or Ipsco clip Bar connectors Attachments for sectional dentures / bolts Screw and tube attachment Indications : To overcome alignment problems

Connecting one restoration of fixed partial denture to another Allowing the removal of long span fixed partial denture for repair and examination of abutment. ATTACHMENT USED FOR SECTIONAL DENTURES Two part dentures : One part - chrome cobalt base Second part - removable acrylic flange with teeth Advantage of superior esthetics and improved retention Method of union : Physical interference : Bolt retained prosthesis Frictional resistance : Split post retained prosthesis SECTIONAL DESIGNS Individual sections / separate sections : uses mesial and distal surface of the abutment teeth as guiding planes.

Hinged sections : Buccal and lingual path of insertion

Direct clasp retention in the construction of a removable restoration is indicated(1) when the general hygiene promises to be good ;(2) when the remaining teeth have no periodontal involvement and are properly distributed for clasping; (3) when the abutment teeth have the necessary convexity and lend themselves to proper clasping ; (4) when the denture can be expected to render many years of service.

Internal precision attachments are indicated: (1) when few remaining teeth are present; (2) when the hygiene promises to be poor; (3) when the abutment teeth are overfilled or broken down, yet are serviceable if they are restored by full coverage ;(4) when splinting of teeth is indicated to aid in their preservation(5) when the economic status of the patient is such as to permit their use.

ConclusionRestoring and maintaining function and health of the partially edentulous mouth is one of the most complex and exacting services the dentist is required to perform. It requires a knowledge of biomechanical factors, vision, judgment, originality, resourcefulness and, above all, a will to do what the conscience dictates to be in the best interest of the patient

ReferencesPrecision attachments Gareth Jenkins.Stewart KL, Rudd KD, Kuebkar WA. Clinical Removable Partial Prosthodontics. 2nd ed.St. Louis, Missouri: CV Mosby; 1986 Miller EL, Grasso JE. Removable Partial Prosthodontics. Baltimore, U.S.A: Williams and Wilkins; 1979Preiskel HW. Precision Attachments in Dentistry. 3rd ed. London: Henry Kimpton; 1979