This document discusses biomechanical considerations for dental implants including load-bearing capacity, implant failure mechanisms, and treatment planning strategies. Key points include: osseointegrated implants can withstand anticipated loads if placed properly; excessive or nonaxial loads can lead to bone loss and failure; treatment planning aims to distribute loads across multiple implants placed in optimal positions and angles to avoid overload; and implant-retained overdentures are generally preferable to fixed prostheses for edentulous patients.

1. BIOMECHANICS, TREATMENT
PLANING, AND PROSTHETIC
CONSIDERATIONS
Chapter 76

2. Biomechanical considerations
• Osseointegrated implant provide predictable
means of replacing missing teeth
• Load-bearing capacity of implants > anticipated
loads during function
• If applied loads > load-bearing capacity
Failure : Mechanical, Biologic

3. • Implant failure
• Mechanical failure : screw
loosening, bend, fracture of
the implants
• Biologic failure : resorption-
remodeling response of bone
around implants 
Progressive bone loss
Biomechanical considerations

4. • Teeth are suspended within the supporting
alveolar bone by periodontal ligament
Physiologic movement
Teeth movement: orthodontic
Implant- VS Tooth-retained restoration
Excessive forces

5. • Osseointegrated dental implants : direct
contact with alveolar bone
No periodontal ligament
Destructive alveolar bone
Implant- VS Tooth-retained restoration
Excessive forces

6. Load-bearing capacity
• The bone appositional index : percentage of
bone-to-implant contact
• Several factors influence load-bearing capacity
• Number and size of implant
• Angulations of implant position
• Quality of the bone-to-implant interface

7. Load-bearing capacity
• Posterior maxilla : less dense
trabecular, thin cortical plate
layer
poor bone quality
• Anterior mandible : dense
trabecular, thick cortical plate
layer

8. • Surface modification : altered
microtopography achieve higher bone
apposition index
• Lack of bone height ≠ long implant -> reduce
bone-to-implant contact
Use of short, wide implants
Increase load-bearing capacity
Load-bearing capacity

9. Angulation and arrangement
• Angulation of implants in relation to the plane
of occlusion and the direction of the occlusal
load
• Axial loads are well-tolerated
• Implant at an angle of 20 degrees or more -
>resorptive remodeling response of bone

10. • Nonaxial loads concentrated stresses around
the neck of the implant
Angulation and arrangement

11. Mechanism of implant failure
• Excessive occlusal loads
• Load resulting in microdamage: fracture, cracks, and
delaminations
• Resorption-remodeling response of bone
• Loss of bone at the bone-to-implant interface as a
result of remodeling
• Vicious cycle of continues loading, additional
microdamage, and bone loss progressing to implant
failure

12. • Distal cantilivered pontics were used to
replaced missing maxillary posterior teeth
Nonaxial occlusal forces
Angulation and arrangement

13. • Distal angulation and the
curve of Spee
Nonaxial loads
Angulation and arrangement

14. Treatment planing with dental implants
• Anterior-posterior (A-P)
implant spread
• Distance from the middle
of the most anterior
implant to the distal edge
of the most posterior
implant

15. Edentulous maxilla
• Implant-supported prosthesis : provide
stability comfort and restore confidence
• Poor ridge form with a marginally stable
conventional maxillary denture : 2 or 4 implants
provide greater stability and security of a maxillary
denture in function

16. Edentulous maxilla
• Implant-supported prosthesis : provide stability
comfort and restore confidence
• Lack of posterior support with an intact mandibular
anterior dentition : Combination syndrome “Hammer and
anvi”

17. • Implant-supported prosthesis : provide
stability comfort and restore confidence
• Palatal coverage is not tolerated
Minimum of four implants with
adequate A-P spread
Edentulous maxilla

18. • Implant-assisted maxillary overdenture is
preferred over an implant-supported fixed
prosthesis -> labial flange can provide lip
support
Edentulous maxilla

19. Edentulous mandible
• Mandibular complete denture is more
problematic especially for pt with severely
atrophic mandibular ridge
• Two-implant-assisted overdenture ->
treatment of choice

20. • Implant-supported fixed prosthesis
• 4,5, or 6 implants arranged in an appropriate arc
of curvature with at least 1 cm of A-P spread
• distal extension cantilevers up to twice the A-P
spread
Edentulous mandible

21. Partially edentulous patients
• Multiple tooth sites
• The number of implants used will influence the
load-bearing capacity
• Posterior maxilla : one implant for every missing
tooth
• Posterior mandible : three-unit bridge supported
by two implants is widely accepted

22. • Single tooth sites
Partially edentulous patients

23. • Implant: Adequate number, size and position
to sustain the occlusal loads
• Residual ridge and site permits : wide
diameter implants should be used for molar
replacement
Strategies to avoid implant overload

24. Strategies to avoid implant overload
• Place implants perpendicular to the occlusal plane
• Place implants in tooth positions
• Use an implant for each unit being replaced
• Avoid the use of cantilevers in linear configurations
• Avoid connecting implants to teeth

25. Strategies to avoid implant overload
• If connecting implants to teeth, use a rigid
attachment
• Control occlusal factors such as cusp angles and
width of occlusal table
• Restore anterior guidance if possible

26. • Occlusal design
• Limit the width of occlusal table
• Flattening the cusp angles
• Avoid Cantilevered restoration
Strategies to avoid implant overload

27. • Connecting implant to teeth
• Keep implant-supported restorations separate
from natural teeth
• Implants and teeth function differently
• Connect with the rigid system
Strategies to avoid implant overload

28. Conclusions
• The biomechanics must be factored into the
planning at the beginning of any implant
treatment
• To achieve long-term, predictable success