Occlusal forms, cusp angles used for implant supported fixed partial dentures, occlusal schemes for patients with posterior quadrants are discussed in some detail.  The use of custom abutments when restoring miss-angled or malpositioned abutments is also described in this program of instruction.  Other topics addressed are connecting implants to natural dentition, use of implant in patients presenting with chronic bruxism, restoration of the cuspid region.  A summary is also presented which outlines strategies to avoid implant overload and mechanical failures in partially edentulous patient restored with dental implants.

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8b.biomechanics and treatment planning — Course Transcript

  • 1. 8b. Biomechanics and Treatment Planning (cont’d) 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. Custom abutments and the width of Note the buccal angulation of the implants. Custom abutments can be used to minimize the width of the occlusal table.
  • 3. Custom abutments and the width of the occlusal table*Note lingualset screwchannels
  • 4. Custom AbutmentsFinal prosthesis with ideal occlusal width.
  • 5. Misalignment of Implants – Custom abutments The implants placed in the right mandible were inclined towards the lingual
  • 6. Misalignment of Implants – Custom abutmentsThis technique permits the clinician to control two key occlusal factors –width of the occlusal table, and the cusp angles. Result: Reduced loadmagnification and less chance of implant overload.
  • 7. Misalignment of Implants – Custom Note width of the occlusal table*Note size of the embrasuresbetween the implants and theimplants and the dentition.
  • 8. Connecting Implants to Natural DentitionHow do you minimize cantilever forces?Semiprecision (nonrigid) vs rigid attachments
  • 9. Connecting Implants toto anterior abutment Natural DentitionPosterior implant attached Loads applied in the pontic areaRigid attachment Nonrigid attachment Nishimura et al, 1999
  • 10. Connecting Implants to Natural DentitionRigid vs non rigid attachments No difference as long as the nonrigid (semi- precision) attachments remain fully seated
  • 11. Semi-precision Attachments Problems v Intrusion of the natural tooth leading to: v Cantilever affect v Load magnification v Resorptive remodeling response v Bone loss (arrows)Semi-precisionattachment
  • 12. Semi-precision attachments Intrusion of the natural tooth abutment predisposes toThis phenomenon leads to load magnification and in selectedpatients, bone loss around the implant adjacent to the cantilever.
  • 13. Semi-precision attachments Intrusion of the natural tooth abutmentl Eleven years after delivery the patient noticed the premolar began to intrude. Exam revealed that the screw retaining the molar had become loose, hence the rotation of this crown.
  • 14. Rigid Attachments* Screw retained tube lock attachment*Shared support
  • 15. Rigid Attachments*Screw retained tube lock attachment*Shared support
  • 16. Rigid Attachment Systems* Cement retained with copings*Shared support
  • 17. Occlusal Anatomy and Biomechanics • Narrow occlusal table • Flat cusp angles • Lingualize or buccalize
  • 18. Occlusal Anatomy and Biomechanics v Narrow occlusal tableGoal: Reduce the cantilever effect
  • 19. Diagnostic WaxupThe prosthesis dictates the number and position ofthe implants. Therefore, a diagnostic waxup shouldbe performed on even the simplest of cases. Implants should be placed in tooth positions Implants should be placed so that occlusal loads can be directed axially Proximal positions should be avoided
  • 20. Implant Placement v Perpendicular to the occlusal plane v Tooth positions v Avoid proximal positions v Screw access channel should exit in the central fossa
  • 21. Advantages of Proper Implant Positioning l Proper emergence profiles can be developed l Space available interproximally for hygiene access (arrow) l Control of occlusal anatomy (narrowed occlusal table and flat cusp angles) l Occlusal loads delivered axially l Abutment selection simplified
  • 22. Magnitude of the occlusal load is controlled by: v Biting forces during normal function v Biting forces during para-function v Buccal-lingual width of occlusal table* v Cusp angles* v Presence and length of cantilevers* v Angulation of the implants relative to the occlusal plane**Factors controlled by the clinician.
  • 23. Strategies to Avoid Implant Overload and Mechanical Failures Edentulous patients – Implant Supported Restorations* v Avoid excessive cantilever length in implant supported* restorations ( limited to 2 times A-P spread in the mandible and ½ times A-P spread in the maxilla). v When planning for implant supported restorations place adequate numbers of implants (minimum number – 4 in the mandible, 6 in the maxilla).When these conditions cannot be met overlay dentures withimplant assisted tissue bar designs* are recommended.*In an implant supported prosthesis all the forces of occlusion areborn by the implants whereas in an implant assisted prosthesis,the occlusal forces are shared between the implants and thedenture bearing areas.
  • 24. Strategies to Avoid Implant Overload and Mechanical FailuresPosterior quadrants of partially edentulous patients v Place implants perpendicular to the occlusal plane (Note that the occlusal plane is not flat – Curve of Wilson, Curve of Spee) v When in doubt, always add the third implant v Avoid use of cantilevers in linear configurations v If required to attach to natural dentition, do so with a rigid attachment system v Control the occlusal factors (cusp angles, width of the occlusal table) v Avoid use of short implants (less than 10 mm) v Avoid use of implant diameters of less than 4 mmWhen these conditions cannot be met conventionalremovable partial dentures are recommended
  • 25. Pertinent Dental History FindingsBruxismChronic bruxism predisposes to: a) Implant fractures b) Fracture of retaining screws c) Implant overload with resorption of bone around the implant Note: The 3.75 mm diameter screw shaped implant is particularly prone to fracture in such patients.
  • 26. Bruxism – Case Report This is a five year followup x-ray of a patient with an implant supported fixed partial denture. The patient was a heavy bruxer. Six months later he presented with significant bone loss around both implants.Closer exam revealedboth implants to befractured .
  • 27. Bruxism -Case Report This patient did well with this implant supported fixed partial denture for more than four years (note 4 year followup x-ray).However, soon thereafter, theanterior implant fractured, thebridge was removed and atrephine used to remove theimplant.
  • 28. Implant FracturesvThe 3.75 mm diameter screw shaped implant is particularlyprone to fracture* when used to support fixed partial dentures inposterior quadrants of partially dentulous patients. Note thedifference between the 4 mm implant on the right and the 3.75mm implant on the left. .vThe thickness of the wall of the 3.75 mmscrew shaped implant is only .4 mm.vFracture rate for the 3.75 mm diameterscrew shaped implant has been reportedto be as high as 7% in 5 year followupstudies. We therefore recommend that implants of at least 4 mm in diameter be used in posterior quadrants. 3.75 mm
  • 29. Strategies for the Moderate Bruxer a) Use a wider diameter implant b) Add the third implant c) Narrow the occlusal table d) Flatten the cusp angles
  • 30. Strategies for the Moderate Bruxer Use of Wide Body Implants – 5 mm Five mm diameter implants were used in this patient. The risk of implant fracture, retaining screw fracture and screw loosening is almost eliminated. However, surgical placement is more difficult and the implants are still subject to occlusal overload in the chronic bruxer.
  • 31. Restoration of the Cuspid Region Less predictable a) Lateral forces b) Linear configurations
  • 32. Restoration of the Cuspid Region Patient presented with partial anodontia. The lateral incisors, cuspids and premolars were missing. Linear configurations restoring the cuspid region, such as the one in this patient, are unpredictable
  • 33. Restoring the Cuspid RegionCurvilinear arrangements such as in this patientare more capable of withstanding lateral forces.
  • 34. Load bearing capacity Linear vs Curvilinear v The central incisor sites were the most favorable implant sites. Therefore: They were extracted and implants placed into these sites v Result: More favorable biomechanicsCourtesy Dr. R. Faulkner and predictability
  • 35. Implants in the Maxillary Cuspid Region Mutually Protected Occlusion (Group Function) Patient in right working position. Note lateral guidance is provided by the premolars and the central incisor.Result: Lateral forces onthe implants areminimized. Courtesy Dr. M. Hamada
  • 36. Anterior Guidance with Centric Only ContactNote: The cusp Result: Lateralangles are flat forces on theand the occlusal implants aretables are minimizednarrow
  • 37. Anterior Guidance with Centric Only Contact Issues v Linear configuration v Posterior implants in poor quality bone v Posterior implants shorter than desired (10 mm)
  • 38. Anterior Guidance with Centric Only Contact Solution v Anterior guidance with remaining anterior dentition v Note buccal lingual dimension of occlusal tables (premolar sized) v Posterior implant used for addition support and stability v Note proxy brush access
  • 39. Anterior Guidance with Centric Only Contact
  • 40. Implants in the Maxillary Cuspid RegionMutually Protected Occlusion (Group Function) Issues v Insufficient number for the corner of the arch v Linear configuration with anterior cantilever v Slight labial-buccal angulation
  • 41. Implants in the Maxillary Cuspid RegionMutually Protected Occlusion (Group Function) Angulation v Addressed with milled customized abutments milled to a three degree taper
  • 42. Implants in the Maxillary Cuspid Region Mutually Protected Occlusion (Group Function) v Finished prosthesis v Note the hygiene access v Retention is by lingual set screws
  • 43. Implants in the Maxillary Cuspid RegionMutually Protected Occlusion (Group Function) v Guidance in the left working position is accomplished by the central incisor and the maxillary molars. The teeth restored with implants are not in contact during excursion v Lateral forces on the implants are minimized and the risk overload is diminished. v Remember, parafunctional habits are the most destructive
  • 44. Restoring the Cuspids: Mutually Protected Occlusion (Group Function) Patient in right and left working position. Note lateral guidance is provided by the premolars and the central incisor. Result: Lateral forces on the implants are minimized.Right working Left working
  • 45. Restoring the corner of the arch : Mutually protected occlusion Group function was used to distribute lateral loads as widely as possible in order to reduce the risk of implant overload
  • 46. Restoration of the Cuspid Region Errors made in this patient: a) Insufficient number of implants b) Connection with natural dentition made with semi- precision attachment
  • 47. Strategies to Avoid Implant Complications Posterior quadrants of partially edentulous patientsPlace implantsperpendicular to theocclusal plane (Note thatthe occlusal plane is notflat – Curve of Wilson,Curve of Spee)Place implants in toothpositionsWhen in doubt,always add the thirdimplantAvoid use of cantilevers inlinear configurations
  • 48. Strategies to Avoid Implant Complications Posterior quadrants of partially edentulous patients If required to attach tonatural dentition, do so with arigid attachment system Control the occlusal factors(cusp angles, width of theocclusal table) Avoid use ofshort implants(less than 10 mm Restore anterior guidance
  • 49. When these conditions cannot be met conventional removable partialMastication efficiency of distal extensionRPD’s is equivalent to implant supported fixedpartial dentures.
  • 50. v Visit ffofr.org for hundreds of additional lectures on Complete Dentures, Implant Dentistry, Removable Partial Dentures, Esthetic Dentistry and Maxillofacial Prosthetics.v The lectures are free.v Our objective is to create the best and most comprehensive online programs of instruction in Prosthodontics