Why should we be concerned with implant biomechanics when we develop a plan of treatment?  Because if we are not, we risk implant overload and implant loss, implant fracture, as well as prosthesis failures such as screw loosening, screw fractures.  The clinician must be aware of the load bearing capacity of osseointegrated implants in a variety of applications and be aware of the factors which influence the magnitude of forces delivered to the implants if long term predictable results are to be achieved.  This program will discuss the impact of implant length, diameter, angulation and arrangement on treatment planning as well as the occlusal factors that effect the magnitude of forces delivered to the implants.

Implant Dentistry – Biomechanics and Treatment Planning — Course Transcript

1. 8a. Biomechanics and Treatment Planning John Beumer III DDS, MSDivision of Advanced Prosthodontics, Biomaterials and Hospital Dentistry, UCLAThis program of instruction is protected by copyright ©. No portion ofthis program of instruction may be reproduced, recorded or transferredby any means electronic, digital, photographic, mechanical etc., or byany information storage or retrieval system, without prior permission.
2. Implant Biomechanics and Treatment PlanningWhy should we be concerned withimplant biomechanics when we developa plan of treatment? Because if we are not, we risk implant overload and prosthesis failures such as fracture and screw loosening.Implant overload can lead to bone loss around implants and eventually implant failure.
3. Is it possible to overload the bone anchoring an osseointegrated implant?Bone is a dynamic structure. Excessive loads lead to aresorptive remodeling response ! Hoshaw et al (1994) observed a resorptive remodeling of the bone around implants subjected to excessive axial loads (300N). Bone loss was observed at the crest around the neck of the implant and in the zone of bone adjacent to the body of the implant ! Brunski et al, 2000 J Oral Maxillofac Implants – Consensus ! Isador’s studies (1996, 1997) using a monkey model presented data that was consistent with the hypothesis proposed by Hoshaw and her colleagues. ! Recent studies by Myamoto et al (1998, 2000, 2008) have reconfirmed Hoshaw and Brunski’s original hypothesis
4. Do the new surfaces reduce the risk Courtesy C Stanford of Implant Overload?v  Excessive occlusal loadsv  Resulting microdamage (fractures, cracks, and delaminations)v  Resorption remodeling response of bonev  Increased porosity of bone in the interface zone secondary to remodelingv  Vicious cycle of continued loading, more microdamage, more porosity until failure
5. Implant Biomechanics! What is the load bearing capacity of osseointegrated implant supported restorations?! Is the load carrying capacity of implant prostheses influenced by the quality of the bone sites?! What factors control the magnitude of the loads that are delivered through the implant into the surrounding bone?! What loads should implant borne restorations be designed to resist?
6. Implant Biomechanics Karnak The Great Wall Pont de GardYou must over engineer your implant restorations, particularlywhen restoring posterior quadrants with linear configurations inorder achieve predictable long term results.
7. Implant BiomechanicsLOAD BEARING CAPACITY ANTICIPATED LOAD1. Quality of bone site (Affected by)2. Quality of bone !   Occlusal factors Cusp angles implant interface Width of occlusal table3. Implant microsurfaces Guidance type !   Machined vs Anterior guidance microrough vs Group function nano-enhanced !   Cantilever forces surfaces Connection to natural4. Implant dentition !   Number and Size of occlusal table Arrangement Cantilevered prostheses Linear vs Curvilinear !   Parafunctional habits !   Length and diameter (bruxism) !   Angulation !   Brachycephalics
8. Load bearing capacity Implant number and arrangementl  Both the number and arrangement of implants affect the load carrying capacity of any particular implant supported restoration.l  Curvilinear arrangements carry withstand more load than linear arrangements
9. Load bearing capacity Linear vs CurvilinearCurvilinear arrangements have thegreatest load bearing capacity.
10. Load bearing capacity Linear vs Curvilinearv  Curvilinear arrangements such as seen in this patient are very predictablev  This PFM fixed prosthesis is 8 years post insertion. Occlusion: Group function
11. Load bearing capacity Linear vs CurvilinearLinear configurations restoring the cuspid region, such as thepatient on the right, are unpredictable, whereas curvilinear implantarrangements such as shown on the left are very predictable. Predictable Not predictable
12. Load bearing capacity Linear vs Curvilinearv  The central incisor sites were the most favorable implant sites. Therefore: ! They were extracted and implants placed into these sitesv  Result: ! More favorable biomechanics and predictability Courtesy Dr. R. Faulkner
13. Load bearing capacity Linear vs Curvilinear v  Centrals extracted ! Note the horizontal dimension of the central incisor sites v  Implants inserted Courtesy Dr. R. Faulkner
14. Load bearing capacity Linear vs Curvilinear Courtesy Dr. R. Faulkner
15. Load bearing capacity Linear vs Curvilinearv  Completedprosthesisv  Biomechanics are favorable Courtesy Dr. R. Faulkner
16. Load bearing capacity Implant number and arrangementv  Anterior – Posterior Spread In the edentulous mandible, curvilinear arrangements such as this one have the greatest load bearing capacity. The cantilever length can be double the A-P spread but not exceeding 20 mm.
17. Load bearing capacity Cantilever length relative to A-P spreadRelatively linear arrangementscombined with excessivecantilever length such as shownhere are able to withstand lessocclusal load.v  Result •  Mechanical failures •  Implant overload A-P In this patient the result Spread was recurrent fractures of the prosthesis retaining screws.
18. Excessive Cantilever forces Implant Overload and Resorptive Remodelingl  If cantilevers are excessive however, they can lead to implant overload and provoke a resorptive remodeling response of bone around the distal implants. In this patient a fixed edentulous bridge similar to the one shown previously, was fabricated for this patient. However, the cantilever extensions were in excess of 30 mm. Note the bone loss around the distal implants particularly on the patient’s left. Eventually this implant fractured.
19. Maxilla vs MandibleCourtesy Dr. C. Stanford The size and shape of the trabeculae is different in the mandible as compared to the mandible and may be one of the reasons why the load carrying capacity of implant supported prostheses restoring posterior quadrants in the mandible appears to be superior to those in the maxilla.
20. Number of Implants per Unit Posterior Maxilla When restoring posterior quadrants with implants we are forced to use linear arrangements by anatomic necessity. Therefore in most instances: !  One implant for each dental unit. !  At least three where possible in extension areas.*The third implantdramatically improves thebiomechanics of therestoration One dental unit = premolar
21. Number of Implants per Unit Posterior Maxilla Curvilinear arrangements are favored over linear arrangements from a biomechanical perspective. However, when restoring posterior quadrants with implants we are forced to use linear arrangements by anatomic necessity. Therefore in most instances:!  One implant foreach dental unit.!  At least threewhere possible in *The third implant dramatically improvesextension areas. the biomechanics of the restoration
22. Number of Implants per Unit Posterior Maxilla The distal implants failed 30 months after loading in both these patients because of implant overload.
23. Number of Implants per Unit Posterior Maxilla These implants failed 66 months after loading because of implant overload.Group function was used to restore this patient. Result: Another problem:excessive lateral forces !   Application of Cusp angles too steep !   Implant failure and the occlusion was tripodized
24. Number of Implants per Unit Posterior Maxilla Space allowed only two implants to be placed in this patient. However, note anterior guidance.Design the occlusion to minimize the delivery of nonaxial forces
25. Number of Implants per Unit Posterior MaxillaOnly two implants were placed.Note anterior guidance
26. Bone Augmentation – Horizontal Deficiencies !  Grafting bone defects with horizontal deficiencies has been relatively predictable, particularly in the anterior region. !   However, these implants are usually exposed to minimal loads. In most patients the graft serves to restore bone and soft tissue contours in order to enhance the final esthetic result and idealize implant position. !  Fixation of the graft is easy to accomplish !  The blood supply to graft is usually quite good
27. Bone Augmentation – Vertical Defects Grafting vertical defects by adding bone on top of the alveolar ridge, as shown here, is much less predictable particularly in the posterior quadrants. Problems: !  Tension on the wound secondary to closure of tissue flaps !  Poor blood supply !  Difficulty in achieving fixation Result: !  Relapse (resorption) rate is 75%
28. Sinus Lift and Graft Sinus membrane Bone graft Bone of the residual allveolar ridgeAdvantages over only grafts Resorption probably less than 25%Challenge Elevate the sinus membrane without perforation
29. Sinus Lift and Graft !  This procedure has been reasonably predictable although no good long term followup studies are available. !  Sources of graft material include chin, ramus, and iliac crest sometimes mixed with bone substitutes. !  Best results with respect to implant success rates appear to obtained when there is at least 4-5 mm of residual ridge.
30. Sinus Lift and GraftThis patient was restored following a sinus liftand graft. Autogenous chin bone was used.She is 10 years post treatment and doing well.Note: Best results achieved when there is 4-5 mmof normal bone over the sinus before the procedure
31. Sinus Lift and Graft This patient was restored following a bilateral sinus lift and graft. Freeze dried bone was used to graft the left maxillary sinus. The implants placed in this graft failed 18 months following delivery of the implant supported fixed partial denture.
32. Distraction OsteogenesisThis procedure has been used successfully in other sites,particularly the anterior maxilla and the mandibular body. Itsusefulness in the posterior maxilla is probably limited. Therelapse (resorption) rate is about 25% (Moy et al, 2005) Osteotomy Distracted site bone Distraction Distraction apparatus apparatus
33. *Removable Partial Dentures*Removable partial dentures properly designed and fabricatedprovide the patient with masticatory function equivalent to thatobtained with an implant supported fixed partial dentures(Kapur, et al, 1992) and this service should be offered to thepatient before grafting is considered.
34. Number of Implants per Unit Posterior MandibleTwo is sufficient for most patientsWhy? The trabecular bone is more dense resulting in better bone anchorage
35. Number of Implants per Unit Posterior Mandible Three are recommended when:v  There is bone over the nerve for only short implantsv  Bone quality is poorv  When restoring four dental units
36. Number of Implants per Unit Posterior Mandible Three implants were used to restore four units in this patient
37. Posterior Mandible – Limiting Factors v  Inferior alveolar nerve(arrow) v  Insufficient bone over the nerve to permit placement of a 10 mm or longer implant v  Uni-cortical anchorage (arrow)
38. Posterior Mandible – Limiting FactorsMany patients such as this one, present with moderateto severe resorption precluding placement of implantsunless the inferior alveolar nerve displaced.
39. Displacement of the Inferior Alveolar Nerve!  This procedure enables placement of implants of sufficient length withbicortical anchorage.!  Although the risk of nerve injury is relatively small the morbiditiesassociated with injury may be severe.!   Therefore, these issues must be thoroughly discussed with the patientbefore proceeding with the procedure.
40. Crestal AugmentationAugmentation of vertical defects in posterior mandibular quadrants with freeautogenous bone grafts (A) has been unpredictable. Following surgery therelapse rate is about 75% and further bone loss is also seen after loading (B).Why? a) Tension on the wound upon closure b) Poor blood supply c) Difficulty is achieving proper fixation of the graft A B Presently, distraction osteogenesis is the only reasonably predictable method for enhancing this site vertically.
41. Use of Short Wide Diameter Implants in the Posterior MandibleThis practice has not been predictable. The short implantsare particularly prone to occlusal overload and bone loss. Thisis a 5 year followup x-ray of two 6 mm diameter implants.
42. If implants of adequate length cannot be used, consider removable partial denturesMastication efficiency of distal extension RPD’s isequivalent to implant supported fixed partial dentures.
43. Connecting Implants to Natural Dentition Semiprecision vs rigid attachments
44. Linear configurationsOver engineer your cases !   When in doubt add the 3rd implant in posterior quadrant cases. !   Minimize the length and width of the occlusal table
45. Over-engineer your linear quadrant cases v When in doubt re: the quality of the implant site bone, history of parafunction etc., add the third implant v Minimize the width of the occlusal table
46. Over-engineer your linear quadrant casesHowever there is a flaw in he design of thiscase. What is it?Note: The buccal-lingual dimension is excessivev Minimize the width of the occlusal surfaces. They shouldbe no wider than a premolar
47. Staggered vs linear configuration in posterior quadrants Straight line implant configuration 1.5 mm 1.5 mm 1.5 mm Staggered implant configurationThis has been studied using a photoelastic modelby Itoh, et al, 2003
48. Staggered vs linear configuration Is it biomechanically more favorable? Straight line implant configuration 1.5 mm 1.5 mm 1.5 mmv Yes, particularly with specificchewing cycles. Nonlineararrangements resist lateral forces Staggered implant configurationmore effectivelyv Is the improvement clinicallysignificant? This is unknown Itoh and Caputo, et al 2003
49. Staggered vs linear configuration Is it feasible in the posterior quadrants? Straight line implant configuration 1.5 mm 1.5 mm 1.5 mmProbably not. Inthe posteriorquadrants you can’t get enough Staggered implant configurationstagger to make much of adifference biomechanically. Itoh and Caputo, et al 2003
50. Implants in Compromised SitesCan we use shorter implants? ! Posterior maxilla ! Posterior mandible over the inferior alveolar nerve in partially edentulous patients ! Craniofacial application Theoretically perhaps. However we need well designed clinical outcome studies to determine predictability
51. Length and diameter of ImplantsAvoid the use of implants less than 10 mm in length and4mm in diameter when restoring posterior quadrants. v Short implants, such as this 7 mm screw shaped implant, demonstrate unfavorable stress distribution patterns as seen in this study performed with finite element analysis. Longer implants distribute stresses more favorably. v Given the bone anchorage achieved with modern surfaces, failures are most likely to occur in theCho et al, 1993 trabecular bone
52. Length and diameter of Implants•  Two year followup data from Moy and Sze,’93•  Note the high failure rates with the 7 mm and 10 mm implants in the posterior maxilla.
53. Implant length vs diameter Does increasing the diameter compensate for the lack of sufficient length? Using a photoelastic model, Caputo et al, 2002 attempted to determine whether increasing the diameter of the implant or increasing the length of the implant had a significant impact on stress distribution. They concluded that:
54. Implant length vs diameter !  Most equitable load transfer with axially directed loads. !  Under comparable loading conditions, the stresses transferred by the wide diameter implant were only slightly lower than the same length narrow implant. !  For implants tested, increased length was more important than diameter in Axial Buccal Lingual load load stress reduction. loadCaputo et al,2002
55. Implant length vs widthThese data appear to have clinical significance. In our clinicalexperience length is more important than width. Short widediameter implants appear to be susceptible to overload when usedin linear configurations such as shown here. 2 years 5 yearsCho,In Ho et al, 1992
56. Ideal Implant Diameter 4-5 mm in diameter!  Less than 4 mm the rate of implant fracture is unacceptably high ! Implants   3.75 mm in diameter have a 5-7% fracture rate!  More than 5 mm the higher the failure rate. ! Implants   6 mm in diameter have a 20% failure rate !  Implants 4-5 mm in diameter have a less than 5% failure rate
57. Implant Angulation – Posterior vs Anteriorv  Implants in the posterior quadrants should be placed so that occlusal loads can be directed axially in the posterior quadrants.v  In the anterior region, anatomic necessity precludes implant placement perpendicular to the occlusal plane. However, the forces used to incise the bolus are only about ¼ of those used posteriorly to masticate the bolus. For this and other reasons implant overload is rarely seen in the anterior regions.
58. Implant angulationv  Nonaxial loads result in load magnification. Kinni et al (1987), using photoelastic analysis and Cho et al (1993), using finite element analysis, demonstrated that nonaxial loads concentrated potentially clinically significant stresses around the neck and at the tip of the implant. Cho,In Ho et al, 1992
59. Biomechanics – Partially Edentulous Patients Nonaxial loads and implant overload in posterior quadrantsv  Because of the curve of Spee and the distal angulation of the implants, the occlusal loads (arrow) are nonaxial. Note the bone loss around the implants. Linear configurations in the posterior region, such as in this patient, are particularly vulnerable to the effects of nonaxial loading, particularly brachycephalic individuals.
60. Cantilever forcesCantilever forces are potentially detrimental particularly whenapplied to implants with a linear configuration and single implantsplaced in posterior quadrants.!  The longer thecantilever the greater theload magnification andthe more stressconcentrated in the boneanchoring neck of thedistal implant.!  Note the dramaticincrease in stressesassociated with the 20mm cantilever asopposed to the 5 mmone.
61. Cantilever forces Cantilever sectionThey are well tolerated whenimplant supportedrestorations are used torestore the edentulousmandible, so long as:l  The cantilevered section is within a reasonable limitl  The implants are arranged in a reasonable arc of curvature.l  Rigid frameworks with cross arch stabilization are used
62. Excessive Cantilever forces Implant Overload and Resorptive Remodelingl  If they are excessive however, they can lead to implant overload and provoke a resorptive remodeling response of bone around the distal implants. In this patient a fixed edentulous bridge similar to the one shown previously, was fabricated for this patient. However, the cantilever extensions were in excess of 30 mm. Note the bone loss around the distal implants particularly on the patient’s left. Eventually this implant fractured.
63. Excessive Cantilever forces Implant Overload and Resorptive Remodeling Case ReportThis tissue bar uses nonresilient attachments in the distal with along cantilever anteriorly and is therefore an implant supporteddesign. The implants were exposed to tipping forces magnifyingthe occlusal loads, in turn leading to a resorptive remodelingresponse of the bone around the implants and eventually loss ofthe implants.
64. Excessive Cantilever forces Implant Overload and Resorptive Remodeling Cantilever Cantilever Overlay Dentures in Edentulous Maxilla!  During the eighties, tissue bar designs using four implants, such as theone above, were commonly used at UCLA to retain overlay dentures. Haderbar attachments were used anteriorly and in the extension areas.!   Such designs result in most of the posterior occlusal forces borne by theimplants and therefore are implant supported.!  The followup data (collected by the author from his private patients)indicated significant bone loss and implant failures of the distal implants asshown in the following table.
65. Excessive Cantilever forces Implant Overload and Resorptive Remodeling Cantilever Cantilever Overlay Dentures in Edentulous MaxillaFour implanted supported overlay dentures with nonresilient(Hader) attachments (arrows) and distal cantilevers Patients # Implants Followup Failures Position Time of of failed failure implants 10 40 5-12 yrs. 4 all distal 39-73 mths. ***Failures were attributed to implant overload, with its resultant loss of bone around the implants
66. Cantilever forces Implant Overload and Resorptive Remodeling l  Implant Assisted Design – 4 implantsWhen implant tissue bars with resilient attachmentsconnected to the distal portion of the bar (ERA type inthis patient) were used in the maxilla the failures afterloading were completely eliminated.
67. Cantilevers and Linear Configurations in Posterior Quadrants Mesial and distal cantileversl  They are particularly detrimental and are therefore contraindicated when using linear configurations to restore posterior quadrants. They cause load magnification and overload the bone around the implant adjacent to the cantilever.
68. Cantilevers – Implant Overloadl  Note the bone loss around the dental implants adjacent to the cantilever. Restorations designed in this fashion have a poor prognosis.
69. Cantilevers – Implant Overload
70. Avoid buccal, lingual and cantilevers The occlusal tables are excessively wide in this case. Buccal and lingual cantilever forces may lead in selected patients to: Prosthesis failures • Porcelain fractures • Screw fractures Implant overload and bone loss
71. Occlusal Anatomy and Biomechanics v  Narrow occlusal tableGoal: Reduce the buccal – lingual cantilever effect
72. Avoid buccal and lingual cantileversThe occlusal table must be narrowedto avoid buccal and lingual cantilevers.Molars should be no wider thanpremolars as shown in these twoexamples.
73. Solitary implants restoring single molars – Cantilever effect A BWhen the food bolus is applied to the marginal ridge (B), therestoration is easily tipped because the crown is supported bysuch a narrow platform.Result: Cantilever forces lead to screw loosening, implantfracture and overload the bone anchoring the implant.
74. Solitary implants restoring single molars Cantilever effectFracture Implant fractured after 30 months of function
75. Single tooth restorations in the molar region – Cantilever effect Mesial cantilever 4 mm diameter implantThis implant was too short and too narrow towithstand occlusal loads and bone loss caused bythe resorptive remodeling response led to its loss.
76. Single Tooth Restorations Distal Extension Defects
77. Distal Extension Defects
78. Restoration of single molar sites – Solutions Eliminate the cantilever by using !   Wide diameter !   Multiple implants In this patient a wide diameter implant was used to restore the first molar.
79. Restoration of single molar sitesIn this patient, two 4 mm diameter implant were used torestore the first molar. The width of the occlusal table waslimited to the width of thenatural premolar,thereby elimating anypossible buccal orlingual cantilevers. Custom abutment Lingual set screw
80. Restoration of single molar sitesNote:!   Hygiene access for proxy brush!   Note width of occlusal table
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