2nd dental students

3. RETENTION FORM
 Def:
The quality of a preparation that prevents theThe quality of a preparation that prevents the
restoration from being dislodged by that forcesrestoration from being dislodged by that forces
parallel to the path of placement.parallel to the path of placement.

4. Retention formRetention form
1.Magnitude of the dislodging forces1.Magnitude of the dislodging forces
2.Geometry of the tooth preparation2.Geometry of the tooth preparation
3. Roughness of the fitting surface of the3. Roughness of the fitting surface of the
restorationrestoration
4.Materials being cemented4.Materials being cemented
5.type of luting cement5.type of luting cement
6.Film thickness of the luting agent6.Film thickness of the luting agent

5.  1. Magnitude of the
Dislodging Forces.
The greatest removal forces
generally arise when sticky
food is eaten.
Magnitude of the dislodging
forces depends on
 the stickiness of the food
 the surface area of the
restoration
 the surface texture of the
restoration
Retention formRetention form
1.Magnitude of the dislodging forces1.Magnitude of the dislodging forces
2.Geometry of the tooth preparation2.Geometry of the tooth preparation
3. Roughness of the fitting surface of the3. Roughness of the fitting surface of the
restorationrestoration
4.Materials being cemented4.Materials being cemented
5.type of luting cement5.type of luting cement
6.Film thickness of the luting agent6.Film thickness of the luting agent

6. 2.Geometry of tooth preparation
-Taper.
-Surface area.
-Type of preparation
-Stress concentration.
Retention formRetention form
1.Magnitude of the dislodging forces1.Magnitude of the dislodging forces
2.Geometry of the tooth preparation2.Geometry of the tooth preparation
3. Roughness of the fitting surface of the restoration3. Roughness of the fitting surface of the restoration
4.Materials being cemented4.Materials being cemented
5.type of luting cement5.type of luting cement
6.Film thickness of the luting agent6.Film thickness of the luting agent

7.  a) Taper: Is theIs the
convergence of twoconvergence of two
opposing external walls ofopposing external walls of
a tooth preparation whena tooth preparation when
viewed from given plane.viewed from given plane.
 Parallel walls→ maximumParallel walls→ maximum
retention “difficult toretention “difficult to
prepare with currentprepare with current
techniques andtechniques and
instrumentation”.instrumentation”.
2.Geometry of tooth preparation
-Taper.
-Surface area.
-Type of preparation
-Stress concentration.

9. UndercutsUndercuts

10. Convergence angleConvergence angle
Angle between opposing axial wall of tooth.Angle between opposing axial wall of tooth.
The optimal degree of taper should be 6°.The optimal degree of taper should be 6°.
The angle between the hands of a clock showin
12:01 is 5½ degrees.

15. √√ XX

16. Prep. in the mouth is viewed through aPrep. in the mouth is viewed through a
mouth mirror using one eyemouth mirror using one eye

17.  Limiting number of paths of insertionLimiting number of paths of insertion
path of withdrawal and insertion:path of withdrawal and insertion: it is the directionit is the direction
through which the restoration could be precisely seatedthrough which the restoration could be precisely seated
on the prepared teeth.on the prepared teeth.

18. path of withdrawal and insertion of a prep must parallel thepath of withdrawal and insertion of a prep must parallel the
adjacent proximal contactsadjacent proximal contacts

19. b) Surface area:b) Surface area:
2.Geometry of tooth preparation
-Taper.
-Surface area.
-Type of preparation
-Stress concentration.

21. 2.Geometry of tooth preparation
-Taper.
-Surface area.
-Type of preparation
-Stress concentration.
c) Type of preparation:
The retention of complete crown is more than
double that of partial coverage restoration.

23.  d) Stress concentrationd) Stress concentration
Sharp line anglesSharp line angles
→ ↑→ ↑ stressstress
→ ↑→ ↑ failurefailure
2.Geometry of tooth preparation
-Taper.
-Surface area.
-Type of preparation
-Stress concentration.

25. Retention formRetention form
 1.Magnitude of the dislodging forces
 2.Geometry of the tooth preparation
 3. Roughness of the fitting surface of the restoration
 4.Materials being cemented
 5.type of luting cement
 6.Film thickness of the luting agent
Retention formRetention form
 3. Roughness of the
fitting surface of the
restoration
Rough surface (restoration)
→more retentive than
smooth surface.

28. 4.Materials being cemented
The more reactive the alloy is,The more reactive the alloy is,
the more adhesion to thethe more adhesion to the
selected cement.selected cement.
 Base metal alloys > noble alloys.Base metal alloys > noble alloys.
Retention formRetention form
 1.Magnitude of the dislodging forces
 2.Geometry of the tooth preparation
 3. Roughness of the fitting surface of the
restoration
 4.Materials being cemented
 5.type of luting cement
 6.Film thickness of the luting agent

29. -core materials:
the cement adhere better to amalgam
>composite resin > cast gold.

30.  5.Type of luting cement
Resin cement > conventionalResin cement > conventional
Retention formRetention form
 1.Magnitude of the dislodging forces
 2.Geometry of the tooth preparation
 3. Roughness of the fitting surface of the restoration
 4.Materials being cemented
 5.type of luting cement
 6.Film thickness of the luting agent
Adhesive resin > glass ionomer > polycarboxylate-
zinc phosphate > zinc oxide-eugenol.

32. Retention formRetention form
 1.Magnitude of the dislodging forces
 2.Geometry of the tooth preparation
 3. Roughness of the fitting surface of the restoration
 4.Materials being cemented
 5.type of luting cement
 6.Film thickness of the luting agent
6.Film thickness of the luting agent
Its effect uncertain

33. Resistance formResistance form
 DefDef.. it is the features of the tooth preparation thatit is the features of the tooth preparation that
enhance the stability of a restoration and resistenhance the stability of a restoration and resist
dislodgement along an axis other than the path ofdislodgement along an axis other than the path of
withdrawal and insertion. (apical, oblique andwithdrawal and insertion. (apical, oblique and
horizontal direction).horizontal direction).

34. Resistance formResistance form
1. Magnitude and direction of the of1. Magnitude and direction of the of
the dislodging force.the dislodging force.
2. Geometry of tooth preparation.2. Geometry of tooth preparation.
3. Physical properties of the luting3. Physical properties of the luting
cement.cement.
1. Magnitude and direction of the1. Magnitude and direction of the
dislodging force.dislodging force.
--Normal occlusion→ biting forces ,well distributed andNormal occlusion→ biting forces ,well distributed and
axially directed → greater resistanceaxially directed → greater resistance..
--Biting habits (pipe smoking-bruxism) → large obliqueBiting habits (pipe smoking-bruxism) → large oblique
force →lower resistanceforce →lower resistance..

35. 2. Geometry of2. Geometry of
tooth preparation.tooth preparation.
Tooth preparation must beTooth preparation must be
shaped so that particular areasshaped so that particular areas
(resistance areas) of the axial(resistance areas) of the axial
wall prevent rotation of thewall prevent rotation of the
crowncrown
 1. Taper1. Taper
Resistance formResistance form
1. Magnitude and direction of the1. Magnitude and direction of the
of the dislodging force.of the dislodging force.
2. Geometry of tooth preparation.2. Geometry of tooth preparation.
3. Physical properties of the luting3. Physical properties of the luting
cement.cement.

36.  2. Diameter2. Diameter
Small (premolar) > large (molar).Small (premolar) > large (molar).

37.  3. Height:3. Height:
Long > short.Long > short.

38.  4. Preparation type:4. Preparation type:
Complete coverage > Partial coverage (asComplete coverage > Partial coverage (as
no buccal resisting areas)no buccal resisting areas)

39.  Luting agent:Luting agent:
Adhesive resin > Glass ionomer > ZincAdhesive resin > Glass ionomer > Zinc
phosphate > Zn polycarboxylate > Zincphosphate > Zn polycarboxylate > Zinc
oxide-eugenoloxide-eugenol
Resistance formResistance form
1. Magnitude and direction of1. Magnitude and direction of
the of the dislodging force.the of the dislodging force.
2. Geometry of tooth2. Geometry of tooth
preparation.preparation.
3. Physical properties of the3. Physical properties of the
luting cement.luting cement.

40. 3.Preventing
deformation of
the restoration
 A restoration must haveA restoration must have
sufficient strength tosufficient strength to
prevent permanentprevent permanent
deformation duringdeformation during
function. Otherwise, itfunction. Otherwise, it
will fail.will fail.
Mechanical principles
1.Providing retention form
2.Providing resistance form
3.Preventing deformation of the
restoration

41. Deformation may be a result of :Deformation may be a result of :
 1. Inappropriate alloy selection.1. Inappropriate alloy selection.
 2. Inadequate tooth preparation.2. Inadequate tooth preparation.
 3. Poor margin design.3. Poor margin design.
 4. Poor metal-ceramic framework design.4. Poor metal-ceramic framework design.

42. 1. Alloy selection1. Alloy selection
 Type I and Type II gold alloys are too softType I and Type II gold alloys are too soft
for crowns and fixed partial dentures.for crowns and fixed partial dentures.
 Type III or Type IV gold alloys are harderType III or Type IV gold alloys are harder
 Metal ceramic alloy with high noble metalMetal ceramic alloy with high noble metal
content have hardness equal tocontent have hardness equal to Type IVType IV
gold alloy.gold alloy.
 Ni-Cr alloys are harder.Ni-Cr alloys are harder.

43. 2. Adequate tooth reduction2. Adequate tooth reduction
 There should be aThere should be a
minimum alloy thicknessminimum alloy thickness
of about 1.5 mm overof about 1.5 mm over
centric cuspscentric cusps
1 mm over non centric1 mm over non centric
cuspcusp

44.  Occlusal reduction should be as uniform,Occlusal reduction should be as uniform,
following the cuspal planes of the teeth thusfollowing the cuspal planes of the teeth thus
will give rigidity to the crown because of thewill give rigidity to the crown because of the
"corrugated effect"" of the planes."corrugated effect"" of the planes.

45.  The supraerupted tooth may needThe supraerupted tooth may need
considerably more than 1.5 mm ofconsiderably more than 1.5 mm of
reduction to result in adequate clearancereduction to result in adequate clearance

46. 3. Margin design3. Margin design
 Distortion of the restorationDistortion of the restoration
margin is prevented by:margin is prevented by:
 1.Sufficient tooth reduction1.Sufficient tooth reduction
that provide sufficient roomthat provide sufficient room
for metal at the margin as infor metal at the margin as in
case of a chamfercase of a chamfer
preparation.preparation.

47.  2.The grooves and ledges incorporated in a2.The grooves and ledges incorporated in a
partial coverage restoration provide essentialpartial coverage restoration provide essential
strengthening for the casting, particularly anstrengthening for the casting, particularly an
anterior pinledge retainer.anterior pinledge retainer.

48. 4. Metal-ceramic framework design.4. Metal-ceramic framework design.
Proper framework design allows:Proper framework design allows:
 a. Even thickness of porcelain veneer.a. Even thickness of porcelain veneer.
 b. Proper porcelain metal interfaceb. Proper porcelain metal interface
framework design to allow distinct margin.framework design to allow distinct margin.

49.  c. Good connector designc. Good connector design
 d. Optimally placed occlusal contact:d. Optimally placed occlusal contact:
The centric stops can be located on either
porcelain or metal, at least 1.5 mm away from
the junction

50. Esthetic considerationsEsthetic considerations
 Determination of patient expectations andDetermination of patient expectations and
needs.needs.

51. Esthetic restorations include:Esthetic restorations include:
Metal-ceramic restorationsMetal-ceramic restorations
Partial veneer crownsPartial veneer crowns
All –ceramic restorationAll –ceramic restoration

52. Metal –ceramic restorationsMetal –ceramic restorations

1- Facial surfacereduction 1-1.3mm1- Facial surfacereduction 1-1.3mm
LowerincisorsLowerincisors → pulp exposure→ pulp exposure
OrOr
→→ less than ideal estheticless than ideal esthetic

53. Metal –ceramic restorationsMetal –ceramic restorations
1- Facialsurfacereduction1- Facialsurfacereduction
2- Incisal reduction2- Incisal reduction
(2mm)(2mm) Incisal edgewithno metalIncisal edgewithno metal
backingbacking→ increase esthetic→ increase esthetic
3- Proximal reduction3- Proximal reduction

54.  Metal –ceramic restorationsMetal –ceramic restorations
 4- Labial margin4- Labial margin
placementplacement
High lip line →High lip line →
subgingival finishing linesubgingival finishing line

55.  Partial coverage restorationsPartial coverage restorations
 1- Proximalmargin1- Proximalmargin
Mesial → just buccal to the proximal contactMesial → just buccal to the proximal contact

56.  Partial coverage restorationsPartial coverage restorations
 1- Proximalmargin1- Proximalmargin
DistalDistal
→→ further buccally as it is less visible to allfurther buccally as it is less visible to all
proper preparation, finishing and access toproper preparation, finishing and access to
oral hygieneoral hygiene

57.  Partial coverage restorationsPartial coverage restorations
1- Proximalmargin1- Proximalmargin
2- Facialmargin2- Facialmargin
Maxillary: just beyondtheoccluso-faciallineangleMaxillary: just beyondtheoccluso-faciallineangle
short bevel to prevent enamelchipping.short bevel to prevent enamelchipping.

58.  Mandibular: facial chamfer as appearanceMandibular: facial chamfer as appearance
is impaired by the occlusalis impaired by the occlusal
reduction.reduction.

59.  All –ceramic restorationAll –ceramic restoration
High esthetic but less conservative (1-1.2mm)High esthetic but less conservative (1-1.2mm)