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Prosthodontics

How do you manage implant therapy?

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This summary is based on the article published in the Dental Clinics of North America: Prosthodontic Management of Implant Therapy (January 2014)

Ghadeer Thalji, DDS, PhD, Matthew Bryington, DMD, MSb, Ingeborg J. De Kok, DDS, MSc, Lyndon F. Cooper, DDS, PhDc,

Key Messages

  • When considering implant prosthodontic treatment for rehabilitation of the partially or fully edentulous patient, the clinician has several choices to choose from including, but not limited to:
    •  Use of fixed or removable prostheses
    •  Use of individual attachments or bars for retention of removable overdentures
    •  Use of screw-retained or cement-retained prostheses
    •  Use of stock versus custom abutments
    •  Different restorative and abutment materials
  • Implant-supported restorations can be screw-retained, cement-retained, or a combination of both, whereby a metal superstructure is screwed to the implants and crowns are individually cemented to the metal frame. Each treatment modality has advantages and disadvantages.
  • Survival of zirconia abutments may be influenced by:
    • Manufacturing methods, and clinical and laboratory handling
    • The abutment wall thickness; a minimum wall thickness of 0.5 mm has been recommended
    • Implant-abutment connection
    • Aging of materials (low-temperature degradation)
    • Implant location
  • The use of computer-aided design/computer-assisted manufacture technologies for the manufacture of implant superstructures has proved to be advantageous in the quality of materials, precision of the milled superstructures, and passive fit.
  • Maintenance and recall evaluations are an essential component of implant therapy. The longevity of implant restorations is limited by their biological and prosthetic maintenance requirements.

Highlights

The 2-implant–supported overdenture is the minimum standard of care for the edentulous mandible. (1)

Maxillary removable overdentures may be considered as a satisfactory treatment option for patients with complaints about the retention and stability of their dentures. (2) (3) Advantages: hygiene access and providing proper lip support for patients with insufficient alveolar bone volume.

Maxillary and  mandibular removable overdentures are typically fabricated with acrylic resin prosthetic teeth processed on a rigid acrylic resin base that may be reinforced with a metal frame, often used for the maxillary overdentures with a horseshoe-shaped design. (4)

In a systematic review assessing differences between splinted and unsplinted oral implants for implant-retained overdentures. Stoumpis and Kohal (5) reported no differences in implant survival rates or peri-implant outcome between splinted and unsplinted designs, although the bar-supported overdentures have been shown to need less prosthetic maintenance. The observed greater peri-implant mucosal inflammation beneath bar-retained overdentures indicates another important, yet manageable issue when bars are required.

Cement-Retained and Screw-Retained Prostheses 

The use of screw-retained restorations provides clinicians with the accessibility of retrieving these restorations if needed for repairs, hygiene, and abutment-screw tightening. (6) 

If implants are improperly positioned, screw-access holes may compromise aesthetics and occlusion because of the wear of restorative materials used to cover the screw-access channel. (7) A possible complication of screw-retained prostheses is porcelain fracture at the screw-access channel resulting from unsupported porcelain. (8) 

Cement-retained restorations may offer aesthetic advantages when access holes are visible facially and occlusally. These restorations may be simpler to fabricate, and provide easier insertion in posterior areas of the mouth for patients with limited jaw openings.

For an implant-supported fixed-denture prosthesis (FDP), the potential for achieving a passive fit is higher with cement-retained
restorations. (9) (10) 

Elements that are important for the retention of the cementretained restorations are essentially the same as those for natural teeth; including taper of axial walls, surface area, height of the abutment, roughness of the surface, and type of cement. (11)

The main drawbacks of cement-retained restorations are difficult retrievability and retention of excess cement, especially when the restoration margins are placed subgingivally or the implants are deeply placed. Diligence in cement removal at time of cementation is critical. 

Residue can cause peri-implant inflammation associated with swelling, soreness, deeper probing depths, bleeding and/or exudation on probing, with radiographic evidence of peri-implant bone loss, and may eventually result in implant loss. (12) A prospective endoscopic clinical study showed that excess cement was associated with signs of peri-implant disease in the majority of cases investigated (81%). (13) 

Selection of Abutments

The main principles for selecting the appropriate abutment should be aimed to allow
for:

  • A proper biological response of the tissues
  • Provision of the retention and resistance forms essential for cement-retained restorations
  • Mechanical strength adequate enough to tolerate fatigue and loading
  • Accurate fit with their mating implants
  • Achievement of an adequate aesthetic result using the proper emergence profile and abutment material

Available clinical data presume that metal abutments made of titanium represent a ‘benchmark’ with few technical complications the exception being loosening of the abutment screw. (14) One limitation often encountered with the use of metal abutments is the gray discoloration of the peri-implant mucosa in patients with thin tissue biotype. (15) 

Framework and Bar Fabrication

Several longitudinal clinical studies demonstrated that poorly fitting frameworks could be one of the primary causes of screw loosening or fracture, abutment fractures, and even implant fracture. (16) (17) (18) 

Maintenance

Recommendations by the American Academy of Periodontology suggest that evaluations of implants at recalls should include (19):

  • Oral hygiene status
  • Clinical appearance of peri-implant tissues
  • Bleeding on probing and/or presence of exudate
  • Pocket probing depths
  • Radiographic appearance of peri-implant alveolar bone and its levels related to the implant-abutment junctions
  • Stability of the prostheses; screw loosening or cement failure
  • Assessment of the prostheses for presence of fractures
  • Occlusal assessment
  • Denture teeth wear
  • Patient comfort and function

 

References

  1. Feine JS, Carlsson GE, Awad MA, et al. The McGill consensus statement on overdentures. Mandibular two-implant overdentures as first choice standard of care for edentulous patients. Montreal, Quebec, May 24-25, 2002. Int J Oral Maxillofac Implants 2002;17(4):601–2.
  2. Naert I, Gizani S, van Steenberghe D. Rigidly splinted implants in the resorbed maxilla to retain a hinging overdenture: a series of clinical reports for up to 4 years. J Prosthet Dent 1998;79(2):156–64.
  3. Zembic A, Wismeijer D. Patient-reported outcomes of maxillary implantsupported overdentures compared with conventional dentures. Clin Oral Implants Res 2013. [Epub ahead of print].
  4. Bryant SR, MacDonald-Jankowski D, Kim K. Does the type of implant prosthesis affect outcomes for the completely edentulous arch? Int J Oral Maxillofac Implants 2007;22(Suppl):117–39.
  5. Stoumpis C, Kohal RJ. To splint or not to splint oral implants in the implantsupported overdenture therapy? A systematic literature review. J Oral Rehabil 2011;38(11):857–69.
  6. Nissan J, Narobai D, Gross O, et al. Long-term outcome of cemented versus screw-retained implant-supported partial restorations. Int J Oral Maxillofac Implants 2011;26(5):1102–7.
  7. Chee W, Felton DA, Johnson PF, et al. Cemented versus screw-retained implant prostheses: which is better? Int J Oral Maxillofac Implants 1999; 14(1):137–41.
  8. Hebel KS, Gajjar RC. Cement-retained versus screw-retained implant restorations: achieving optimal occlusion and esthetics in implant dentistry. J Prosthet Dent 1997;77(1):28–35.
  9. Michalakis KX, Hirayama H, Garefis PD. Cement-retained versus screw-retained implant restorations: a critical review. Int J Oral Maxillofac Implants 2003;18(5):719–28.
  10. Karl M, Taylor TD, Wichmann MG, et al. In vivo stress behavior in cemented and screw-retained five-unit implant FPDs. J Prosthodont 2006;15(1):20–4.
  11. Emms M, Tredwin CJ, Setchell DJ, et al. The effects of abutment wall height, platform size, and screw access channel filling method on resistance to dislodgement of cement-retained, implant-supported restorations. J Prosthodont 2007; 16(1):3–9.
  12. Gapski R, Neugeboren N, Pomeranz AZ, et al. Endosseous implant failure influenced by crown cementation: a clinical case report. Int J Oral Maxillofac Implants 2008;23(5):943–6.
  13. Wilson TG Jr. The positive relationship between excess cement and peri-implant disease: a prospective clinical endoscopic study. J Periodontol 2009;80(9): 1388–92. 
  14. Pjetursson BE, Bragger U, Lang NP, et al. Comparison of survival and complication rates of tooth-supported fixed dental prostheses (FDPs) and implantsupported FDPs and single crowns (SCs). Clin Oral Implants Res 2007; 18(Suppl 3):97–113.
  15. Jung RE, Sailer I, Hammerle CH, et al. In vitro color changes of soft tissues caused by restorative materials. Int J Periodontics Restorative Dent 2007; 27(3):251–7.
  16. Jemt T, Book K, Linden B, et al. Failures and complications in 92 consecutively inserted overdentures supported by Branemark implants in severely resorbed edentulous maxillae: a study from prosthetic treatment to first annual check-up. Int J Oral Maxillofac Implants 1992;7(2):162–7.
  17. Naert I, Quirynen M, van Steenberghe D, et al. A study of 589 consecutive implants supporting complete fixed prostheses. Part II: prosthetic aspects. J Prosthet Dent 1992;68(6):949–56. 
  18. Zarb GA, Schmitt A. The longitudinal clinical effectiveness of osseointegrated dental implants: the Toronto study. Part III: problems and complications encountered. J Prosthet Dent 1990;64(2):185–94.
  19. Parameter on placement and management of the dental implant. American Academy of Periodontology. J Periodontol 2000;71(Suppl 5):870–2.

 

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