CHAPTER 5: MANDIBULAR MAJOR CONNECTORS

components of a typical removable partial denture

rests

direct retainers

major connectors

minor connectors

one or more bases

indirect retainers (if the prosthesis has distal extension bases)

stabilizing / reciprocal components (as parts of a clasp assembly)

when a prosthesis that can be removed from the mouth is used

prosthesis should extend to both sides of the arch for optimal stability

cross-arch tooth contact at a distance from functional force achieves optimal resistance

transfer of functional forces of occlusion from denture base to supporting teeth and tissues is crucial

rigid major connector is most effective in joining the function-receiving prosthesis to selected arch regions

major connector

designated for proper shape, thickness, and location

ensures unified and effective partial denture components

comparable to the frame of an automobile or the foundation of a building

provides cross-arch stability to resist displacement by functional stresses

connects prosthesis parts on one side of the arch with those on the opposite side

margins adjacent to gingival tissue should be far enough from tissue to avoid impingement

minimum of 4mm below the gingival margin

recommended location of the superior border of a lingual bar connector

—the limiting factor is the height of the moving tissue in the floor of the mouth

maxillary arch

the borders of the major connector may be placed well away from gingival tissue in this arch because no moving tissue is present in the palate as in the floor of the mouth

2 reasons why palate is well suited for placement of the connector

an adequate deep blood supply

presence of firm submucosal connective tissue

—however, when soft tissue covering the midline of the palate is less displaceable than the tissue covering the residual ridge, varying amounts of relief under the connectors must be provided to avoid impingement of tissue

chief functions of a major connector

minimization of torque to individual teeth

unification of the major parts of the prosthesis

distribution of the applied force throughout the arch to selected teeth and tissue

cross-arch stability

effectively distributes forces throughout the arch

the principle of leverage is connected with this component part

it limits movement possibilities by acting as a counteracting lever

acts to reduce the load to any one area while effectively controlling prosthesis movement

becomes more important in situations associated with high potential for greater prosthesis movement (e.g., distal extensions)

consequences of a flexible connector

detrimental to the comfort of the patient

jeopardizes the supporting oral structures

manifestation of a failure major connector to provide rigidity

injury to residual ridges

impingement of underlying tissue

traumatic damage to periodontal support of the abutment teeth

guidelines for the location & design of major connectors

should be free of movable tissue

impingement of gingival tissue should be avoided

bony and soft tissue prominences should be avoided during placement and removal

should be located and relieved to prevent impingement of tissue that occurs because the distal extension denture rotates in function

relief should be provided beneath a major connector to prevent its settling into areas of possible interference, such as inoperable tori or elevated median palatal sutures

directly proportional

the amount of relief required is __ to the difference in displaceability of the tissue covering the midline of the palate and the tissue covering the residual ridges

gingival tissue

must have an unrestricted superficial blood supply to remain healthy

2 ways to ensure maximum freedom for gingival tissue

palatal major connector should be placed a minimum of 6mm away from and parallel to the gingival margins

minor connectors that must cross gingival tissue should do so abruptly, joining the major connector at nearly a right angle

areas where palatal connectors require no relief

palatal torus

prominent median palatal suture area

intimate contact between the connector & the supporting tissue

this contact adds much to the support, stability, and retention of the denture

—except for gingival areas, intimacy of contact elsewhere in the palate is not detrimental to the health of the tissue if rests are provided on abutment teeth to prevent tissue-ward movement

anterior palatal strap

there will be irregular in outline as they follow the contours between the rugae

should be located as far as possible posteriorly to avoid interference with the tongue in the area of the rugae

should be uniformly thin and its anterior border should be located to follow the contours between the crests of the rugae

a useful rule applied to MC and throughout partial denture design

to try to avoid adding any part of the denture framework to an already convex surface

characteristics of MC contributing to health & well-being

contribute to prosthesis support

cover no more tissue than necessary

do not interfere with or irritation to the tongue

made from an alloy compatible with oral tissue

do not alter the natural contour of the lingual surface

do not contribute to food particle retention or trapping

provide cross-arch stability through broad stress distribution

have support from other framework elements to minimize rotation tendencies

do not impinge on oral tissue during restoration placement, removal, or rotation

6 types of mandibular major connectors

labial bar

lingual bar

linguoplate

sublingual bar

cingulum bar (continuous bar)

lingual bar with cingulum bar

lingual bar

additional bulk may be needed for rigidity

inferior border slightly rounded to prevent lingual tissue impingement

made of reinforced, 6-gauge, half-pear–shaped wax or similar plastic pattern

half-pear shape connector located above moving tissue but below gingival tissue

farther inferior border from adjacent teeth reduces impingement on gingival tissue

superior border tapered towards gingival tissue, with greatest bulk at inferior border

inferior border located as far as possible to avoid tongue interference and food trapping

lingual bar with cingulum bar

considered when a linguoplate is the major connector of choice but the axial alignment of the anterior teeth is such that excessive blockout of interproximal undercuts must be made

linguoplate

sublingual bar

cingulum bar

these major connectors are preferred if less than 8 mm exists between gingival margins and the movable floor of the mouth

relief

provided for soft tissue under all portions of the mandibular major connector and at any location where the framework crosses the marginal gingiva

superior border of a lingual bar connector

should be tapered toward the gingival tissue superiorly, with its greatest bulk at the inferior border, resulting in a contour that has a half-pear shape

inferior border of the lingual bar

framework should be slightly rounded when polished

round border prevents impingement on lingual tissue during inferior denture rotation

bar should be positioned to avoid impingement on mouth floor tissue during normal activities

lowering lingual bar distance from adjacent teeth's lingual gingival crevices helps avoid impingement

In addition, the more inferiorly a lingual bar can be located, the farther the superior border of the bar can be placed from the lingual gingival crevices of adjacent teeth, thereby avoiding impingement on the gingival tissue

2 clinically acceptable methods used to determine mouth floor height

measurement of mouth floor height using periodontal probe

• less variable and more clinically acceptable

• patient's tongue tip lightly touches upper lip vermilion border

• records allow transfer to diagnostic and master casts.

• ensuring a rather advantageous location of the inferior border of the major connector

use of individualized impression tray with lingual borders 3mm short of elevated floor

• use of impression material for accurate molding as patient licks lips

individualized / custom tray

may be used for the same purpose if a stock tray causes impingement on this functional position

linguoplate

should not serve as indirect retainers; definite rests must be provided

the upper border should follow the natural curve of the supracingular surfaces of the teeth

results from a rectangular space bounded by the lingual bar, anterior tooth contacts, and the cingula

should be thin and contoured to follow the contours of the teeth and embrasures; should not be above the middle third of the lingual surface

all gingival crevices and deep embrasures should be blocked out parallel to the placement path to avoid gingival irritation and wedging effect between the teeth

linguoplate & cingulum bar

these connectors ideally should have a terminal rest at each end, regardless of the need for indirect retention

upper border of linguoplate

should follow the natural curvature of the supracingular surfaces of the teeth

should not be located above the middle third of the lingual surface, except to cover interproximal spaces to the contact points.

apron of linguoplate

closely adapted to the teeth extending into non-undercut interproximal embrasures, resulting in a scalloped form

this form benefits from some anterior teeth acting together to help resist horizontal rotational tendencies of the prosthesis, especially if the posterior ridge form does not resist such movement

uses of apron

to cover areas that would be irritating to the tongue

to avoid gingival irritation / entrapment of food debris

indication of linguoplate

class I situations

high lingual frenum

limited space for a lingual bar

future replacement of incisor teeth

stabilizing periodontally weakened teeth

steps in designing mn major connectors

outline the basal seat areas on the diagnostic cast

outline the inferior border of the major connector

outline the superior border of the major connector

connect the basal seat area to the inferior and superior borders of the major connector

add minor connectors to retain the acrylic resin denture base material

sublingual bar

similar to lingual bar, but more inferior and posterior

can be used in lieu of lingual plate if lingual frenum doesn't interfere or in presence of an anterior lingual undercut

used when mouth floor height doesn't allow superior border placement at least 4mm below the free gingival margin

contraindications of sublingual bar

interfering lingual tori

high attachment of a lingual frenum

interference with elevation of the floor of the mouth during functional movements

cingulum bar (continuous bar)

can be added to lingual bar or used independently

located on or slightly above the cingula of the anterior teeth

may be more esthetically acceptable than a linguoplate when wide diastemata exist between the lower anterior teeth

suitable for linguoplate connectors where axial alignment of anterior teeth requires excessive blockout of interproximal undercuts

labial bar

lingually inclined teeth may need crowns reshaping

if a mandibular torus interferes with lingual bar placement, it should be removed unless surgery is contraindicated

used when extreme lingual inclination of lower premolar and inferior teeth rarely prevents the use of a lingual bar major connector

swing-lock design

connected by hinge and latch

consists of labial bar connected to major connector

incorporated with hinged continuous labial bar concept

can be used to ensure that all remaining teeth share in stabilization and retention of the prosthesis

indications of swing-lock design

missing key abutments — can be used when all remaining teeth are used for retention and stability

unfavorable soft tissue contours — the hinged continuous labial bar concept can accommodate these contours

teeth with questionable prognoses — the loss of a tooth would not compromise retention and stability to such a degree

unfavorable tooth contours — can be used when existing tooth contours or excessive labial inclinations prevent conventional clasp designs

contraindications of hinged labial bar concept

presence of a shallow buccal or labial vestibule or a high frenal attachment

poor oral hygiene or lack of motivation for plaque control by the patient — most obvious

—any of these factors would prevent the proper placement of components of the Swing-Lock partial denture

support

provided by multiple rests on the remaining natural teeth

gained by:

• using rests

• well-fitting denture bases

• minor connectors arising from the labial bar

stabilization / reciprocation

supplemented by the labial bar with its retentive struts

provided by a linguoplate that contacts the remaining teeth

retention

obtained on terminal abutments

provided by a bar type of retentive clasp with arms projecting from the labial or buccal bar and contacting the infrabulge areas on the labial surfaces of the teeth.

linguoplate pattern

continuous (cingulum) pattern

sublingual bar pattern

lingual bar major connector [illustration]

palatal major connector [illustration]

sublingual bar major connector [illustration]

metal lingual bar major connector [illustration]

linguoplate major connector [illustration]

lingual bar with cingulum bar [illustration]

cingulum bar major connector [illustration]

labial bar major connector [illustration]

single palatal bar

labial bar major connector class III mod 1 [illustration]