Bio mechanical considerations in complete denture prosthesis-cha/dental courseskra

BIO-MECHANICAL CONSIDERATIONS INBIO-MECHANICAL CONSIDERATIONS IN
COMPLETE DENTURE PROSTHESISCOMPLETE DENTURE PROSTHESIS
INDIAN DENTAL ACADEMYINDIAN DENTAL ACADEMY
Leader in Continuing Dental EducationLeader in Continuing Dental Education
www.indiandentalacademy.comwww.indiandentalacademy.com

INTRODUCTIONINTRODUCTION
 Complete denture prosthesis is aComplete denture prosthesis is a
mechanical object in a biologicalmechanical object in a biological
enviroinment.enviroinment.
 The mechanical and biologicalThe mechanical and biological
considerations that contribute to itsconsiderations that contribute to its
optimal performance are discussedoptimal performance are discussed
here.here.
 They areThey are
1.1. residual alveolar ridgeresidual alveolar ridge
2.2. retentionretention
3.3. stabilitystability
4.4. supportsupport
5.5. estheticsesthetics

ESTHETICSESTHETICS
 It is one of the prime concerns of theIt is one of the prime concerns of the
patient in complete denture treatment.patient in complete denture treatment.
 Thicker denture flanges are preferred inThicker denture flanges are preferred in
long term edentulous patients to give thelong term edentulous patients to give the
required mouthfullness.required mouthfullness.
 It normally restores the estheticIt normally restores the esthetic
natural display of teeth and gums, whilenatural display of teeth and gums, while
smiling, laughing, talking,etc.smiling, laughing, talking,etc.
 it also restores lower facial height,it also restores lower facial height,
lip, and cheek fullness.lip, and cheek fullness.

RESIDUAL ALVEOLAR RIDGERESIDUAL ALVEOLAR RIDGE
(formation)(formation)
 Following the loss of teeth, the emptyFollowing the loss of teeth, the empty
socket fills clot and is gradually replacedsocket fills clot and is gradually replaced
with new bone.with new bone.
 The bone around the socket margin alsoThe bone around the socket margin also
reorganizes.reorganizes.
 The mucoperiosteum gradually heals andThe mucoperiosteum gradually heals and
covers the healing socket.covers the healing socket.
 The remodeling process results in aThe remodeling process results in a
rounded ridge like structure known asrounded ridge like structure known as
Residual alveolar ridgeResidual alveolar ridge

Six orders of residual ridgeSix orders of residual ridge
formform
 A system of six orders of residual ridgeA system of six orders of residual ridge
form was proposed by atwoodDAform was proposed by atwoodDA
a) Order I - Pre extractiona) Order I - Pre extraction
b) Order II - Post extractionb) Order II - Post extraction
c) Order III - High, well roundedc) Order III - High, well rounded
d) Order IV - Knife edged) Order IV - Knife edge
e) Order V - Low, well roundede) Order V - Low, well rounded
f) Order VI - Depressedf) Order VI - Depressed

Resorption of RRRResorption of RRR
 It does not end with the remodeling of theIt does not end with the remodeling of the
socket, the process continues resulting insocket, the process continues resulting in
a gradual reduction in size of the ridge.a gradual reduction in size of the ridge.
 In some individuals, the resorption rate isIn some individuals, the resorption rate is
too rapid that well made denturestoo rapid that well made dentures
becomes loose (or) ill fitting in a shortbecomes loose (or) ill fitting in a short
period of time.period of time.
 The problems which are faced by theThe problems which are faced by the
patient due to this factor are not only thepatient due to this factor are not only the
financial cost but also the no of visits,financial cost but also the no of visits,
discomfort, pain and etc.. caused by loosediscomfort, pain and etc.. caused by loose
(or) ill fitting dentures.(or) ill fitting dentures.

Etiogenesis of RRREtiogenesis of RRR
 There are two schools of thought. TheyThere are two schools of thought. They
areare
i)It is a multifactorial, bio mechanicali)It is a multifactorial, bio mechanical
disease that results from a combinationdisease that results from a combination
of anatomic, metabolic and mechanicalof anatomic, metabolic and mechanical
determinants.determinants.
ii)The other group contends that is aii)The other group contends that is a
normal physiologic process which actsnormal physiologic process which acts
as a result of the loss of periodontalas a result of the loss of periodontal
structures and stimulation it provides tostructures and stimulation it provides to
the alveolar bone.the alveolar bone.
 The rate of the condition varies fromThe rate of the condition varies from
individual to individualindividual to individual

Pattern of resorptionPattern of resorption
 The pattern is different in maxilla andThe pattern is different in maxilla and
mandible. The ridge resorbs downward andmandible. The ridge resorbs downward and
outward in the mandible, whereas upwards andoutward in the mandible, whereas upwards and
inwards in maxilla.inwards in maxilla.
The end result is that over a period of time,The end result is that over a period of time,
the maxillary arch becomes progressivelythe maxillary arch becomes progressively
smaller, whereas mandibular becomes wider.smaller, whereas mandibular becomes wider.
It occurs more rapidly in the first 6 monthsIt occurs more rapidly in the first 6 months
after extraction of teeth and at a slower pace tillafter extraction of teeth and at a slower pace till
12 months.12 months.
It can be precipitated by certain systemicIt can be precipitated by certain systemic
diseases (or) ill-fitting dentures.diseases (or) ill-fitting dentures.

Factors causing RRRFactors causing RRR
 The RRR is a multi-factorial, bioThe RRR is a multi-factorial, bio
mechanical disease that results from amechanical disease that results from a
combination of anatomic, metabolic andcombination of anatomic, metabolic and
mechanical determinants.mechanical determinants.
i) Anatomic factorsi) Anatomic factors
ii) Metabolic factorsii) Metabolic factors
iii) Mechanical factors.iii) Mechanical factors.

Anatomic factorsAnatomic factors
RRR α Anatomical factorsRRR α Anatomical factors
 It is postulated that RRR varies with theIt is postulated that RRR varies with the
quantity and quality of alveolar ridgequantity and quality of alveolar ridge
bone.bone.
 Large well rounded ridges and broadLarge well rounded ridges and broad
palates would seen to be favourablepalates would seen to be favourable
anatomic factors.anatomic factors.
 Another factor to consider is the density ofAnother factor to consider is the density of
ridge.ridge.

Metabolic factorsMetabolic factors
RRR α Bone resorption factorsRRR α Bone resorption factors
Bone formation factorsBone formation factors
 Endotoxins from dental plaque, osteoclastEndotoxins from dental plaque, osteoclast
activating factor (OAF), prostaglandins,activating factor (OAF), prostaglandins,
human gingival bone-resorptionhuman gingival bone-resorption
stimulating factors and others could playstimulating factors and others could play
some important role in RRR.some important role in RRR.
 Other possible local bone resorptionOther possible local bone resorption
factors could be related to trauma, whichfactors could be related to trauma, which
leads to increased (or) decreasedleads to increased (or) decreased
vascularity and changes in oxygenvascularity and changes in oxygen
tension.tension.

Mechanical factorsMechanical factors
RRRRRR αα Forces (masticatory orForces (masticatory or
nonmasticatory)nonmasticatory)
 The amount of force applied to the boneThe amount of force applied to the bone
may be affected inversely by themay be affected inversely by the
“damping effect”“damping effect” or energyor energy
absorption.absorption.
RRRRRR αα 11
damping effectdamping effect


 Since the overlying mucoperiosteum variesSince the overlying mucoperiosteum varies
in its visco elastic properties from patientin its visco elastic properties from patient
to patient and from maxilla to mandible, ifto patient and from maxilla to mandible, if
energy absorption qualities may influencesenergy absorption qualities may influences
the rate of RRR.the rate of RRR.
 A correlation exists between the year’s ofA correlation exists between the year’s of
denture wearing and the severity ofdenture wearing and the severity of
atrophy. This kind of severity is moreatrophy. This kind of severity is more
important in day and night wearer’s ofimportant in day and night wearer’s of
denture than in day wearers.denture than in day wearers.
 Swallowing generates forces that are littleSwallowing generates forces that are little
higher than the average chewing forces inhigher than the average chewing forces in
the complete denture wearersthe complete denture wearers

RETENTIONRETENTION
 It is a “quality inherent in the prosthesisIt is a “quality inherent in the prosthesis
which resists the force of gravity,which resists the force of gravity,
adhesiveness of foods and the forcesadhesiveness of foods and the forces
associated with the opening of jaws”associated with the opening of jaws”
 The factors that affect retention areThe factors that affect retention are
i) Anatomical factorsi) Anatomical factors
ii) physiological factorsii) physiological factors
iii) physical factorsiii) physical factors
iv) mechanical factorsiv) mechanical factors
v) muscular factorsv) muscular factors

Anatomic factorsAnatomic factors
 Size of the denture bearing areaSize of the denture bearing area
Retention increases with in size of the↑Retention increases with in size of the↑
denture bearing areadenture bearing area
MAXILLAMAXILLA - 24cm²- 24cm²
MANDIBLEMANDIBLE - 14cm²- 14cm²
 Quality of the denture bearing areaQuality of the denture bearing area
 influenced by displaceability of tissuesinfluenced by displaceability of tissues
Tissues displaced during impressionTissues displaced during impression
making leads to tissue rebound duringmaking leads to tissue rebound during
denture use, leading to loss of retention.denture use, leading to loss of retention.www.indiandentalacademy.comwww.indiandentalacademy.com

Physiological factorsPhysiological factors
 SalivaSaliva::
The viscosity of saliva determinesThe viscosity of saliva determines
retention.retention.
Thick and ropy saliva gets accumulatedThick and ropy saliva gets accumulated
between the tissue surface of the denturebetween the tissue surface of the denture
and palate leading to the loss of retentionand palate leading to the loss of retention
An excessive flow of saliva frequentlyAn excessive flow of saliva frequently
accompanies the insertion of newaccompanies the insertion of new
dentures. This is a reaction to a newdentures. This is a reaction to a new
stimulus.stimulus.

Physical factorsPhysical factors
1.1. AdhesionAdhesion
2.2. CohesionCohesion
3.3. Interfacial surface tensionInterfacial surface tension
4.4. CapillarityCapillarity
5.5. Atmospheric pressure & PeripheralAtmospheric pressure & Peripheral
sealseal

AdhesionAdhesion
““It is the physical attraction of unlikeIt is the physical attraction of unlike
molecules to one another”molecules to one another”
 A thin film of saliva which is formedA thin film of saliva which is formed
between the denture and the tissuebetween the denture and the tissue
surface, helps to hold the denture to thesurface, helps to hold the denture to the
mucosamucosa
 The amount of adhesion present isThe amount of adhesion present is
proportional to the denture base areaproportional to the denture base area

CohesionCohesion
““It is the physical attraction of likeIt is the physical attraction of like
molecules for each other”molecules for each other”
 The effectiveness of these forces increasesThe effectiveness of these forces increases
with the denture bearing areawith the denture bearing area
 Watery serous saliva can form a thinnerWatery serous saliva can form a thinner
film and is more cohesive than thickfilm and is more cohesive than thick
mucous saliva.mucous saliva.

Interfacial surface tensionInterfacial surface tension
““The tension (or) resistance toThe tension (or) resistance to
separation possessed by the filmseparation possessed by the film
of liquid between two wellof liquid between two well
adapted surfaces”adapted surfaces”
 It plays a major role in the retentionIt plays a major role in the retention
of a maxillary denture.of a maxillary denture.
 It is totally dependant on theIt is totally dependant on the
presence of air at the margins ofpresence of air at the margins of
liquid and solid contact.liquid and solid contact.

To obtain more InterfacialTo obtain more Interfacial
surface tension…surface tension…
 Saliva should be thin and even.Saliva should be thin and even.
 Perfect adaptation should be presentPerfect adaptation should be present
between the tissues and denture base.between the tissues and denture base.
 The denture base should cover a largeThe denture base should cover a large
area.area.

capillaritycapillarity
 This is a quality (or) state, because ofThis is a quality (or) state, because of
surface tension causes elevation (or)surface tension causes elevation (or)
depression of the liquid that is contactdepression of the liquid that is contact
with the solid.with the solid.
 When there is close adaptation betweenWhen there is close adaptation between
the denture and the mucosa, the thin filmthe denture and the mucosa, the thin film
of saliva tends to flow and increase itsof saliva tends to flow and increase its
surface contact there by increasing thesurface contact there by increasing the

peripheral sealperipheral seal
 Peripheral seal is the area of contactPeripheral seal is the area of contact
between the peripheral border’s of thebetween the peripheral border’s of the
denture and the resilient limitingdenture and the resilient limiting
structures.structures.
prevents air entry between the dentureprevents air entry between the denture
surface and the soft tissue.surface and the soft tissue.
 Hence a low pressure is maintained withinHence a low pressure is maintained within
the space between the denture and softthe space between the denture and soft
tissues.tissues.

Atmospheric pressureAtmospheric pressure

WhenWhen displacing forces act on thedisplacing forces act on the
denture a partial vacuum is produceddenture a partial vacuum is produced
between the denture and the softbetween the denture and the soft
tissue, which aids in retention.tissue, which aids in retention.
this is called the natural suction ofthis is called the natural suction of
aa denture.denture.
hence, atmospheric pressure ishence, atmospheric pressure is
referredreferred to as emergencyto as emergency
retentive force.retentive force.

Mechanical factorsMechanical factors
 UndercutsUndercuts
 Retentive springsRetentive springs
 Magnetic forcesMagnetic forces
 Denture adhesivesDenture adhesives
 Suction chambers and discsSuction chambers and discs

undercutsundercuts
 Unilateral undercuts aid in retention whileUnilateral undercuts aid in retention while
bilateral will interfere with denturebilateral will interfere with denture
insertion and require surgical correctioninsertion and require surgical correction

Magnetic forcesMagnetic forces
 Intra mucosal magnets aid in increasingIntra mucosal magnets aid in increasing
retention of highly resorbed ridgesretention of highly resorbed ridges

Denture adhesivesDenture adhesives

They are available as creams (or)They are available as creams (or) gels (or)gels (or)
powder’s.powder’s.
 They should be coated on tissue surfaceThey should be coated on tissue surface
before wearing the denture.before wearing the denture.

Suction chambers and suctionSuction chambers and suction
discsdiscs

TheThe suction chambers creates an area ofsuction chambers creates an area of
negative pressure, which increasesnegative pressure, which increases
 They are avoided now due to their potencyThey are avoided now due to their potency
for creating palatal hyperplasiafor creating palatal hyperplasia

Muscular factorsMuscular factors
 There is a balance between the forcesThere is a balance between the forces
acting from the buccal musculature andacting from the buccal musculature and
the tongue.the tongue.
this balance is obtained in the neutralthis balance is obtained in the neutral
zonezone
 Hence the artificial teeth should beHence the artificial teeth should be
arranged in the neutral zone to achievearranged in the neutral zone to achieve
better retention.better retention.

STABILITYSTABILITY
 It is defined as the “The quality of aIt is defined as the “The quality of a
denture to be firm, steady, ordenture to be firm, steady, or
constant, to resist displacement byconstant, to resist displacement by
functional stresses and not to befunctional stresses and not to be
subject to change of position whensubject to change of position when
forces are applied.forces are applied.
 It is the ability of the denture toIt is the ability of the denture to
withstand horizontal forces.withstand horizontal forces.

Factors affecting stabilityFactors affecting stability
 Vertical height of the residual ridgeVertical height of the residual ridge
 Quality of soft tissue covering theQuality of soft tissue covering the
ridgeridge
 Quality of the impressionQuality of the impression
 Occlusion rimsOcclusion rims
 Arrangement of teethArrangement of teeth
 Contour of the polished surfacesContour of the polished surfaces

Vertical height of residual ridgeVertical height of residual ridge
 It should have sufficient vertical height toIt should have sufficient vertical height to
obtain good stabilityobtain good stability
 Highly resorbed ridges offer least stabilityHighly resorbed ridges offer least stability

Quality of soft tissue covering theQuality of soft tissue covering the
ridgeridge
 The ridge should provide a firm soft tissueThe ridge should provide a firm soft tissue
base with adequate submucosa to offerbase with adequate submucosa to offer
good stabilitygood stability
 Flabby tissues with excessive submucosaFlabby tissues with excessive submucosa
offer poor stability.offer poor stability.

Quality of the impressionQuality of the impression
 An impression should be as accurate asAn impression should be as accurate as
possible.possible.
 The impression surface should be smoothThe impression surface should be smooth
and duplicate all the details accurately.and duplicate all the details accurately.
 It should be devoid of voids and any roughIt should be devoid of voids and any rough
surfacessurfaces
 Should not warp on removalShould not warp on removal
 Should be dimensionally stable and theShould be dimensionally stable and the
cast should be poured as soon as possible.cast should be poured as soon as possible.

Occlusal planeOcclusal plane
 Should be oriented parallel to the ridge.Should be oriented parallel to the ridge.
 If the occlusal plane is inclined, then theIf the occlusal plane is inclined, then the
sliding forces may act on the denture,sliding forces may act on the denture,
reduce its stability.reduce its stability.
 The occlusal plane should divide theThe occlusal plane should divide the
interarch space equally.interarch space equally.

Teeth arrangementTeeth arrangement
 Balanced occlusion facilities the evenBalanced occlusion facilities the even
distribution of forces across the denture.distribution of forces across the denture.
 The teeth in the denture should beThe teeth in the denture should be
arranged in the neutral zone.arranged in the neutral zone.

Contour of the polished surfaceContour of the polished surface
 The polished surfaces of the dentureThe polished surfaces of the denture
should be harmonious with the oralshould be harmonious with the oral
structures.structures.
 They should not interfere with the actionThey should not interfere with the action
of the oral musculatureof the oral musculature..

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