Tilting of Posterior Implants for Improved Prosthesis Support

Purpose:

• Modified for implant placement in posterior region of jaw to increase A-P spread and reduce cantilever length in complete-arch prosthesis without the need for additional surgery.

Intro:

• Common considerations for tilting implants
  • Anatomical limitations (sinus, mental nerve/anterior loop, atrophic ridge, arch form)
  • Reduce cantilever by improving load distribution (via A-P spread)
  • Improved cortical anchorage and primary stability of implants
• Why tilting implants?
  • Implant support moved posteriorly
  • Increased implant length
  • Follows dense bony structures for increased primary stability

Materials and Methods:

• ​25 Consecutive mandibular patients (10 males, 15 females, mean age 63.1)
• 22 Consecutive maxillary patients (10 males, 12 females, mean age 61.2)
• Follow-up of bilaterally placed, tilted posterior implants
  • 36 tilted implants mandible with average of 40 months follow-up
  • 40 tilted implants maxilla with average of 53 months follow-up
• No grafting or transpositioning of alveolar nerve
• Surgical technique
  • Local anesthetics
  • Flap with subperiosteal dissection
  • Mandibular implants 25-35° distally and follow dense bony structure of anterior wall of mental loop
  • Maxillary implants angle 30-35° distally and follow anterior sinus wall
  • Post-operative antibiotics + Chlorhexidine rinse
  • Abutments placed 3 months post-implant placement in mandible and 6 months for maxilla
• Prosthodontics treatment
  • Prosthodontist placed standard or angulated abutments (Estheti-Cone abutment, Nobel BioWare)
  • Partial prostheses fabricated with PFM (precious metal)
  • Complete arch prostheses fabricated with titanium framework with acrylic teeth
• Follow-up
  • Prostheses removed and implant stability determined by prosthodontist
  • Radiographs taken to confirm integration and marginal bone loss subsequent of prostheses delivery
  • Stable and functional implants, but bone loss = "surviving"
  • Success rates excluded these surviving implants
• Implant Load Assessment
  • Strain gauge technique described by Glantz et al
  • 3 gauges mounted on lateral surface of strain gauge abutments replacing prostheses abutments
  • Maximum bite force onto special bite fork for measurements
  • Implant and prosthesis reconstruction theoretically simulated with bite force measurement
  • Compared values of actual bite force and theoretical bite force

Results:

• Success rate
  • Mandibular = 100%, tilted or non-tilted
  • Maxillary
    • 95.7% tilted implants (1 lost between 2-3 years, Survival after 5 years for 2 implants)
    • 92.5% non-tilted implants
      • 2 lost at 1-2 years
      • 3 lost at 3-4 years
      • 1 lost at 4-5 years
      • Survival after 5 years for 5 implants
    • Survival after 5 years based on bone loss criteria
      • 2 tilted
      • 5 non-tilted
• Complications
  • Suture dehiscence in 4 mandibular and 3 maxillary cases where cover screws visible
    • Careful hygiene
  • Paresthesias of mental nerves seen in 4 sides during 1st 2-3 weeks post-placement
  • Prosthetically, tilted implants were less accessible
  • No specific prosthetic complications
  • Difficult maintenance initially, primarily distal portion of the mouth regardless of tilted or non-tilted

Discussion:

• Clinical results show that tilting implants prove to be biologically and biomechanically advantageous compared to cantilevered implants with inadequate A-P spread
• 3 Key advantages
  • Longer implants in native bone, which improves primary stability of implants by more cortical/dense bone involved
  • Accommodating anatomical limitations for atrophic ridge, nerve, and sinus
  • A-P spread for favorable load distribution and support