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s10-finals-Biomechanical considerations Flashcards

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1
Q

What are the three primary types of forces acting on implants?

A

Compressive, tensile, and shear.

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2
Q

Which force type is most destructive to bone-implant interfaces?

A

Shear forces (65% weaker than compression).

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3
Q

Define stress in biomechanical terms.

A

Force distributed over a surface (F/A).

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4
Q

How does strain differ from stress?

A

Strain is deformation; stress is force distribution.

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5
Q

Why is bone strongest under compressive forces?

A

Trabecular alignment resists pushing forces better.

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6
Q

What is the modulus of elasticity?

A

Stiffness; resistance to elastic deformation.

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7
Q

How does load duration impact implant failure?

A

Cyclic loading → fatigue failure (e.g., bruxism).

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8
Q

What is a moment arm in implant dentistry?

A

Lever effect (e.g., crown height = vertical lever).

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9
Q

Where is bite force highest in the jaw?

A

Molar region (~200 lbs vs. 25-35 lbs in incisors).

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10
Q

What magnification factor increases implant stress?

A

Cantilevers (force × length).

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11
Q

How does implant diameter reduce stress?

A

↑ diameter → ↑ surface area → ↓ stress (F/A).

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12
Q

Why is length less critical than diameter for stress?

A

Only first 8-10mm of length bears load.

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13
Q

Name two thread designs that reduce shear stress.

A

Square threads, power threads.

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14
Q

What surface treatment improves osseointegration?

A

Sandblasting + acid etching (micro/nano roughness).

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15
Q

How does splinting implants help biomechanics?

A

Distributes load across multiple implants.

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16
Q

What is the ideal implant angulation for load?

A

Parallel to occlusal forces (axial loading).

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17
Q

Why avoid angled abutments?

A

Transverse forces → ↑ shear stress.

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18
Q

What is Misch D1 bone?

A

Dense cortical (e.g., anterior mandible).

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19
Q

Which bone type heals fastest but is weakest?

A

D4 (fine trabecular, posterior maxilla).

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20
Q

How does D4 bone affect implant planning?

A

Requires wider implants to compensate for low density.

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21
Q

What is Division A bone volume?

A

≥5mm width, ≥12mm height, ideal for implants.

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22
Q

What is the minimum bone width needed for implants?

A

0.5mm around implant.

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23
Q

Define osteointegration.

A

Direct bone-to-implant contact (bio-inert titanium).

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24
Q

What is Wolff’s Law?

A

Bone remodels under load (↑ density where stressed).

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25
How does crown height space (CHS) increase risk?
↑ vertical cantilever → ↑ bending moments.
26
What CHS is needed for removable prostheses?
≥12mm (for denture teeth + acrylic base).
27
Why reduce occlusal table width?
↓ bucco-lingual moment arm → ↓ off-axis loads.
28
When is metal preferred over acrylic prostheses?
For better load distribution in long-span bridges.
29
What cuspal inclination minimizes shear?
Flat angles (axial forces).
30
What connection type reduces screw loosening?
Internal hexagon or conical connections.
31
What is the primary risk of excessive crown height space?
Crestal bone loss, screw loosening, or implant fracture.
32
How does reducing occlusal table width improve biomechanics?
Decreases moment arm and off-axis loading.
33
Why are metal prostheses better than acrylic for load distribution?
Metal has higher stiffness and reduces bending overload.
34
What is the ideal cuspal angle for implant crowns?
Minimal angles (flat anatomy) to direct forces axially.
35
When would you use porcelain-fused-to-metal over all-ceramic?
For bruxers - metal substructure better absorbs eccentric forces.
36
What's the minimum distance between two adjacent implants?
1.5mm to maintain blood supply and bone viability.
37
How does tripod implant placement help?
Creates stability by distributing forces in three dimensions.
38
What is the maximum recommended cantilever length?
2.5 times the anteroposterior (A-P) spread.
39
Why is progressive loading important?
Allows bone to adapt gradually to functional forces.
40
What diet is recommended during early loading?
Soft diet to minimize excessive forces.
41
How does bruxism affect implant treatment planning?
Requires more implants, splinted prostheses, and durable materials.
42
What are three ways to reduce stress in D4 bone?
Increase implant number, diameter, and splint implants.
43
When is immediate loading contraindicated?
In poor bone quality (D3/D4) or unstable primary stability.
44
What's the difference between early and delayed loading?
Early: 2-3 weeks; Delayed: 3-8 months post-surgery.
45
Why avoid wide occlusal tables in implant prostheses?
Increases faciolingual tipping forces.
46
What prosthetic complication is most common with bruxism?
Screw loosening or prosthesis fracture.
47
How does implant thread depth affect stability?
Deeper threads increase initial stability in soft bone.
48
What's the benefit of platform switching?
Reduces crestal bone loss by shifting stress inward.
49
When would you use a removable overdenture vs fixed prosthesis?
Overdentures for severe bone loss or financial constraints.
50
What's the primary cause of early implant failure?
Poor primary stability or surgical trauma.
51
How does bone density affect healing time?
D1: longest (3-6 months); D4: fastest (6-8 weeks).
52
What's the key biomechanical advantage of tilted implants?
Allows longer implants in atrophic bone while reducing cantilevers.
53
Why is the first molar implant most prone to failure?
Highest occlusal forces and often placed in poorer bone.
54
What's the "A-P spread" and why is it important?
Distance between most anterior and posterior implants - determines safe cantilever length.
55
How does smoking affect implant biomechanics?
Reduces bone density and impairs osseointegration.
56
What's the primary advantage of zirconia abutments?
Better esthetics and lower plaque accumulation.
57
When would you recommend a bar-retained overdenture?
For completely edentulous patients needing stability.
58
What's the main disadvantage of acrylic provisional prostheses?
Higher risk of bending overload on supporting implants.
59
How often should implant occlusion be checked?
Every 6 months, especially for bruxers.
60
What radiographic sign indicates biomechanical overload?
Progressive crestal bone loss (>0.2mm/year after first year).
61
How would you treat a bruxer needing full-arch implants?
Use 6+ splinted implants with metal prosthesis and flat occlusion.
62
What's your protocol for a failed implant due to overload?
Remove, graft, then place wider diameter implant with progressive loading.
63
How do you calculate safe cantilever length?
Measure A-P spread between implants → cantilever ≤ 2.5x this distance.
64
Why might a tilted implant survive better than a vertical one in atrophic maxilla?
Longer implant engages more bone, reduces cantilever needs.
65
When would you choose a zygomatic implant?
Severe maxillary atrophy where conventional implants lack bone support.
66
How do you adjust occlusion for an implant-supported bridge?
Light contacts in centric, no working/non-working interferences.
67
What's your solution for recurrent screw loosening?
Check for overload, switch to conical connection, or use torque-limiting device.
68
How does diabetes affect implant biomechanics?
Delays osseointegration → require longer healing and progressive loading.
69
What's the biomechanical risk of "all-on-4"?
Distal cantilevers may overload anterior implants if not balanced.
70
How would you manage a fractured implant abutment?
Replace with stronger material (titanium vs. zirconia) and check occlusion.
71
Why avoid cantilevers in D4 bone?
Low density can't resist bending moments → crestal bone loss.
72
What's your approach for a fractured implant body?
Remove and graft; place new implant with wider diameter.
73
How do you prevent overload in immediate loading?
Use provisional prosthesis with soft diet and no eccentric contacts.
74
What's the key difference in planning mandibular vs. maxillary full-arch cases?
Maxilla has softer bone (D3/D4) → often needs more implants.
75
How does osseodensification improve biomechanics?
Compresses bone → increases density and primary stability.
76
When would you use a hybrid prosthesis?
For full-arch cases needing lip support and easy maintenance.
77
What's the risk of over-contouring an implant crown?
Increases plaque retention and lateral forces on the implant.
78
How do you test implant stability clinically?
Percussion sound, reverse torque test (20 Ncm), or ISQ values.
79
Why is titanium better than PEEK for implant prostheses?
Higher modulus of elasticity better mimics bone stiffness.
80
What's your strategy for a patient with parafunctional habits?
Night guard, acrylic prosthesis, and additional implants.
81
How does bone remodeling affect long-term implant success?
Bone adapts to loads (Wolff's Law) but excessive strain → resorption.
82
What's the role of finite element analysis in implant planning?
Simulates stress distribution to optimize implant position/size.
83
How do you manage a loose implant with no infection?
Evaluate overload → splint to adjacent implants or reduce cantilever.
84
What's the minimum ISQ value for immediate loading?
≥70 (varies by system).
85
Why is the anterior mandible ideal for implants?
D1/D2 bone density provides excellent primary stability.
86
How do you handle a fractured prosthetic screw?
Retrieve with ultrasonic or screw extractor, then replace.
87
What's the biomechanical advantage of a cross-arch splint?
Distributes forces across multiple implants → reduces individual load.
88
How does implant micro-motion affect healing?
>50-100μm inhibits osseointegration → need stable fixation.
89
What's your final check before delivering an implant prosthesis?
Verify passive fit, occlusion, and patient hygiene access.
90
How do you educate patients on implant maintenance?
Annual radiographs, professional cleanings, and no hard foods

Implantology (8 decks)

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