1. Essential and fundamental factors involved in crown & bridge
嘉泉醫大 吉病院 齒醫學 敎室
主任敎授 : 金 滿 龍

2. Considering factors of fixed partial denture
Biologic phase factor
Physiologic phase factors
Engineering phase factor
Mechanical phase factors
Esthetic phase factor
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3. A. Biologic requirement
Pulps of these teeth ; remove the pathogenesis
Hard & soft investing tissue
Design : inter-proximal embrasure area, location of sub-gingival margin, materials, solder joint, pontic areas, retainer
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4. B. Physiologic requirement
Anatomic details characteristic of natural teeth
Functional occlusion; inter-maxillary relationship, harmony and balance of occlusion
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5. C. Engineering & mechanical esthetic requirement
Good construction
Comprehensive knowledge of properties of material
Oral tissues will accept the restorations biologically
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6. Requirements for success of a fixed partial denture
Thorough examination
Favorable occlusion
Careful selection and designing of retainers
Incorporating into the restoration those anatomic details characteristic of natural teeth
Applies conform to the laws of nature
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7. Requirements for success of a fixed partial denture
Thorough examination
Proper selection of most desirable type or method
To preserve the remaining teeth – primary purpose
Masticatory function, phonetics improvement of esthetics – 2nd purpose
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8. Requirements for success of a fixed partial denture
Favorable occlusion
To note the discrepancies of jaw relationships, tooth to tooth position
Understanding of centric occlusion
To seek & balance between occlusal stress and tissue
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9. Requirements for success of a fixed partial denture
Careful selection and designing of retainers
Ideal retainer
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10. IDEAL RETAINER
One that requires the least amount of destruction to the abutment(최소한의 삭제)
One that least destroys the outline form of the tooth
Least amount of marginal line
Finished about its periphery with great accuracy

11. IDEAL RETAINER
Positioned margin at less susceptible to caries or recurrence of caries
Rigidity – withstand the requisite load
Functional adaptation and protect the tooth against its fracture
Least destroys the cervical marginal ridge

12. IDEAL RETAINER
Preparation can be made without trauma to the pulp or surrounding tissue
Accurate complement to the lost tooth structure
Cleansable
esthetic

13. “Weak point in a bridge is the cement lute”
Dental cements are not adherent, and do not bond to the retainer or to the tooth. Cements hold a bridge in place by mechanical locking. If the stress in the cement lute are too high, the cement will break and the bridge will become loose. To design bridge retainer – transmits the functional forces to the cement lute as compressive force and not tensile or shear forces.

14. Requirements for success of a fixed partial denture
Incorporating into the restoration those anatomic details characteristic of natural teeth
Ridge and groove increase the sharpness and shearing action of teeth
Reduce friction by keeping the contacting area to a minimum
Reducing the load trasmitted to the abutment teeth
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15. Requirements for success of a fixed partial denture
Applies conform to the laws of nature
Proper selection of dental materials
Correct abutment preparation
Good technical procedure
Application of the basic laws of mechanics & engineering
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16. Application of the basic laws of mechanics & engineering
Lack of sufficient rigidity ; solution – correct shape, form, thickness
Consideration of the stresses of occlusion
The alignment of the abutment teeth
Physical aspect of the tooth itself
Size & shape of crown
Number of root shape, length
Bone height
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17. Application of the basic laws of mechanics & engineering
Consideration of the stresses of occlusion
The ratio of bone support to the length of the tooth
Ante’s law; combine peri-cemental area area abutment teeth = missing teeth
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18. Application of the basic laws of mechanics & engineering
Consideration of the stresses of occlusion
Crown to root ratio ; 1:2, minimum 1:1
Length of span to be replaced ; long or short
Contact and alignment of adjacent teeth
Long axis relationship; maximum deviation 25-30’
Structure of the supporting bone such as thickness pattern and density ; trabecular – uniform, the bone can withstand the load of proper function
Arch form; restoration involving anterior teeth(fig)
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19. Arch form ; restoration involving anterior teeth
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20. Application of the basic laws of mechanics & engineering
Consideration of the stresses of occlusion
The greatest leverage occurs when four maxillary incisors are replaced in a narrow tapered arch. The presence of a single incisor will considerably shorten the lever arm.
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21. Application of the basic laws of mechanics & engineering
Consideration of the stresses of occlusion
Pontics
1st consideration is strength
2nd consideration is anatomic form.
3rd consideration is esthetics
The tissue – contacting surface of the pontic should be convex in form, smooth, make minimal contact, free of pressure, within the area of the immovable mucosa of the ridge.
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22. Application of the basic laws of mechanics & engineering
Consideration of the stresses of occlusion
Midline
Pulp - health
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23. Engineering principles
It is impossible to guess at the forces to which such a structure is exposed. (strains, stress, torque, equilibrium)
One must make use of principles of mechanics acceptable to engineering practice.
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25. A. Dimension Deflection of bar
It must not be too long for the number of retainers.
The retainers must have adequate retention.
Lateral occlusal forces should not be excessive in order to ovoid displacement of the restoration from its abutment.
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26. Engineering principles
Metal (hardness): type4 – increase the load
Bending stress – middle portion
Loading carrying capacity; type4 (80000N) type3 (40000N)
3 unit bridge type 3, 6 unite type 4 (same thickness)
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27. Engineering principles
Soldered joint ; deep occlusogingivally
Where bending movement are large, joints should be located as far as possible from the center of the bridge span.
Dental bridge의 load-carrying capacities에 관계되는 factors
The loads that are to come up the bridge
The form and shape of structure “I beam”
The ability of the material
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28. Engineering principles
Equilibrium : How do we obtain the important condition of a bridge in equilibrium?
The walls of abutment preparations are parallel or converge 2’ and not over 5’
The walls of the abutment teeth are surveyed to obtain this parallelism.
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29. Engineering principles
The strength of the cement bond is determined by following factors.
Strength of the cement in compression, tension, shear
The number and size of the interlocking keys
The areas of the bond between opposing walls
The taper of cavity preparation
Tolerance or closeness of fit between the casting & the tooth
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30. Salient facts Abutment casting must be rigid.
Dowel & crown : effective coupling between the attachment casting and the tooth
Heavy sections of attachment casting
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31. Salient facts
Physical properties of the tooth and the restorative material shall be properly met.
Cavity preparation should be shallow but extensive
Pitch in the cavity walls is essential.
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32. Important factors in influencing retention of fixed partial denture
Correct tooth selection, design and preparation to accept the proper retainer
Accurate construction and fit of the retainer
Correct tooth form and function
Adequate strength of gold alloy
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33. “The looser fitting casting gave high values after cementation then those obtained from tight casting
Tight casting – irregular cement thickness
Loose casting – regular cement thickness
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34. Another important finding was that the retention values of un-cemented casting gave no indication of the retention values obtained after cementation.
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35. Retainers Partial veneer crowns Full veneer crowns 0110
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36. Partial veneer crown are ideal.
Guides for coronal contours
Embrasure forms are pre-established.
Adequate amounts of attached gingival
Adequate vestibular depth
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37. Full veneer crown
Clinical crown and the anatomical crown are dissimilar.
Need of splinting for mechanical retention
Reshaping of coronal forms
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38. Types of abutment preparation
Inlay
¾ crown
Pin-ledge crown
Full veneer crown
Half-crown or mesial version of veneer crown
7/8 crown
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39. Types of abutment preparation
Inlay : less retention – MO.DO,MOD
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40. Inlay bridge
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41. ¾ crown Caries index – low
Maximum retention with a minimum sacrifice of tooth structure
Its retention depends upon the staple formed by the mesial and distal coverage grooves.
Pin in the region of the cingulum
Linguo-incisal portion – sufficient thickness
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42. Pin –ledge crown Dowels are cast instead of using metal wire.
Dowel hole must be slightly larger for good impression.
Cautious in its preparation
Retention - tripodism
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43. Pin –ledge crown Co-factors of this type retainer
Length of span
Masticatory forces
Amount of torque torsion bending
Failure : because of margins the “open up”. Resistance can be increased to this by grooving adjustment to the margin for increased bulk, by keeping the margin away for the area of stress in occlusion
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44. Full veneer crown Most retentive of all the retainer
Extremely short or extensively decayed teeth
Gingival decay is prevalent.
Marginal gingival health
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45. Half crown or mesial version of the veneer crown
Teeth that are tilted mesially.
Always keep margins away from all stressful situation ; avoid placing margins
Abutment preparation should always protected
Maintain the proper mesio-distal relation
Prevent sensitive cavities
Maintain proper relation of occluding teeth
Prevent chipping of delicate margin
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46. Tooth form and function
Contact area : plus contact – arch may be shifted; cause some mal-occlusion, minus contact – food impaction; discomfort, periodontal disease, recurrent decay
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47. Tooth form and function
Occlusal surfaces : cusp fossae, grooves, ridge excessive occlusal contact – pulpal involvement (periodontal disturbance)
Occlusal width : 50-60% / diameter
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48. Occlusal elements Definite cusp, ridges, grooves
Occlusal table 50-60% on diameter
Each cusp has a primary ridge with a smaller supplementary ridge on each side.
Each primary ridge is at least twice as wide as each supplementary ridge.
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49. Occlusal elements Primary and supplementary ridges are biconvex.
The lingual surfaces of anterior teeth have a definite concave surface.
Incisal edge of anterior teeth are rounded.
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50. Stress of occlusion in unworn teeth fall very near the long axis.
On worn teeth stress are spread over wide and more dangerous area.
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51. Arrows illustrate escape of food in all directions from the contacting point (small contact point)
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52. OCCLUSAL TABLE
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53. OCCLUSAL TABLE
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54. Our occlusal surface designs and physiologic of restorations must be harmonious with biomechanical requirements.
Lack of attention to these requirements and basic tails will cause damage to the oral mechanism.
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55. Thank you for your attention