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Complications with Acrylic Hybrids: The Case for BruxZir® Solid Zirconia

Shreya Shah, BDS, M.S., Research Associate

article by Shreya Shah, BDS, M.S., Research Associate

The implant-supported fixed hybrid denture has significantly elevated the quality of care for the fully edentulous patient. This restoration consists of an acrylic base, denture teeth, and a metallic framework through which prosthetic screws are used to attach the prosthesis to implants positioned around the edentulous arch. The hybrid denture provides very high levels of stability, comfort and function, and consistently outperforms traditional complete dentures and removable implant overdentures in scientific studies.1-4 In addition to reporting higher rates of satisfaction with treatment, patients who receive fixed full-arch implant restorations experience a greater increase in oral health-related quality of life and lower levels of psychological discomfort.5,6

After decades of use as the fixed implant prosthesis of choice for edentulous patients, however, research has shown that this type of prosthesis is vulnerable to an assortment of prosthetic complications, including fracture, dislodging of the denture teeth and acrylic wear.7 The advent of the monolithic zirconia-based restoration as a superior, more durable treatment option has addressed many of these concerns.8,9 Although full-arch zirconia restorations have typically included veneering porcelain, the entire body of the BruxZir® Full-Arch Implant Prosthesis, including the gingival areas and the prosthetic teeth, is milled from the same block of solid zirconia. As outlined below, this unique monolithic construction and absence of veneering material affords the durability needed to avoid the prosthetic complications that have been shown in the scientific literature to compromise screw-retained hybrid dentures.

“When I provide my edentulous patients with a fixed implant restoration, they’re getting the best treatment available. They’re also making a big investment in their dental health and are understandably upset when they need to bring their hybrid denture in for a repair. If you’re like me and you stand by your work, you have no choice but to cover the cost of repairing or replacing the prosthesis, to say nothing of the time this costs me and my patients.

I wish that I never did any acrylic hybrids, but unfortunately, I did a bunch; BruxZir full-arch restorations have only been available for a few years. The acrylic cases all have a common problem: They break. Or the teeth pop off and I have to use my chair time to bond another one on. Now instead of repairing the hybrids, I’m replacing them with BruxZir. It’s worth it to know I’m providing a long-lasting solution and I won’t be seeing the patient come in with a broken prosthesis.”

— Jack A. Hahn, DDS

Chipping, Cracks and Scratches

The problem: Hybrid dentures are susceptible to chipping, cracks and scratches that encourage the accumulation of plaque, food and debris (Figs. 1a–1f). In one clinical study comparing fixed metal-acrylic veneer appliances with metal-ceramic appliances, acrylic-based restorations demonstrated substantially higher concentrations of plaque after five years of use.10 Damage to the acrylic resin is the most common prosthetic complication for acrylic hybrids.11 In addition to requiring repairs, even minor cracks create areas where biofilm and debris can accumulate, which leads to soft- and hard-tissue inflammation.

The solution: With a flexural strength of 1465 MPa, BruxZir Solid Zirconia provides substantially higher resistance to chips and cracks than acrylic hybrid dentures. Research has also shown that the zirconia material is highly resistant to plaque formation.12,13 While the high porosity of acrylic material fosters bacterial growth, the lack of porosity in BruxZir Solid Zirconia inhibits it.

Fracture of the Acrylic Hybrid Prosthesis

The problem: The acrylic body of the screw-retained hybrid denture is vulnerable to fractures and commonly requires multiple repairs or replacements during the life of the restoration (Figs. 2a–4c). In one long-term study, patients had to have their prosthesis replaced an average of 2.27 times over a 20-year period.14 Fractures to the acrylic base are among the most common reasons for repair. For example, in a prospective study, 18 out of 24 patients required replacement of the acrylic base of their prosthesis within two years of delivery.15

The acrylic body of the screw-retained hybrid denture is vulnerable to fractures and commonly requires multiple repairs or replacements during the life of the restoration.

The solution: With the exception of the titanium copings that connect the restoration to the implants, the entirety of the BruxZir Full-Arch Implant Prosthesis is fabricated from the same durable material. Combined with the high fracture toughness (KIc value) of BruxZir Solid Zirconia, which reflects the material’s ability to absorb the energy responsible for crack propagation, this uniform construction prevents the wear and breakage that have been shown to compromise the acrylic of hybrid dentures on a recurring basis.

Debonding or Fracture of the Prosthetic Teeth

The problem: The prosthetic teeth of the hybrid denture commonly need to be replaced or repaired after becoming dislodged or cracked due to the considerable functional forces a fixed implant prosthesis must endure (Figs. 5a–6c). In a 10-year cohort study, an average of 4.7 repairs per prosthesis were required due to complications with the acrylic resin teeth, including rebonding of the prosthetic teeth, replacement of denture teeth, and repair of tooth fractures.16 Forty percent of patients participating in a separate two-year study required replacement of at least one acrylic resin tooth within two years of prosthetic delivery.15

The solution: The mechanical properties and high flexural strength of BruxZir Solid Zirconia allow the material to be milled into layers both thin and thick without compromising strength. Rather than being bonded to the body of the prosthesis in the manner of a hybrid denture, the teeth of the BruxZir Full-Arch Implant Prosthesis are milled as part of the overall restoration. As a result, the teeth enjoy the same durability as the body of the prosthesis, eliminating concerns of debonding or fracture.

The mechanical properties and high flexural strength of BruxZir Solid Zirconia allow the material to be milled into layers both thin and thick without compromising strength.

Conclusion

Although the implant-supported hybrid denture has restored function, stability and quality of life for countless edentulous patients, prosthetic complications have been a source of frustration to patients and practitioners alike. With its one-piece construction made possible by advancements in material science and dental CAD/CAM technology, the BruxZir Full-Arch Implant Prosthesis is a strong, esthetic restoration without the drawbacks of acrylic hybrid dentures.

References

  1. Turkyilmaz I, Company AM, McGlumphy EA. Should edentulous patients be constrained to removable complete dentures? The use of dental implants to improve the quality of life for edentulous patients. Gerodontology. 2010 Mar;27(1):3-10.
  2. Martín-Ares M, Barona-Dorado C, Guisado-Moya B, Martínez-Rodríguez N, Cortés-Bretón-Brinkmann J, Martínez-González JM. Prosthetic hygiene and functional efficacy in completely edentulous patients: satisfaction and quality of life during a 5-year follow-up. Clin Oral Implants Res. 2016 Dec;27(12):1500-5.
  3. De Kok IJ, Chang KH, Lu TS, Cooper LF. Comparison of three-implant-supported fixed dentures and two-implant-retained overdentures in the edentulous mandible: a pilot study of treatment efficacy and patient satisfaction. Int J Oral Maxillofac Implants. 2011 Mar-Apr;26(2):415-26.
  4. Allen F, McMillan A. Food selection and perceptions of chewing ability following provision of implant and conventional prostheses in complete denture wearers. Clin Oral Implants Res. 2002 Jun;13(3):320-6.
  5. Preciado A, Del Río J, Lynch CD, Castillo-Oyagüe R. Impact of various screwed implant prostheses on oral health-related quality of life as measured with the QoLIP-10 and OHIP-14 scales: a cross-sectional study. J Dent. 2013 Dec;41(12):1196-207.
  6. Brennan M, Houston F, O’Sullivan M, O’Connell B. Patient satisfaction and oral health-related quality of life outcomes of implant overdentures and fixed complete dentures. Int J Oral Maxillofac Implants. 2010 Jul-Aug;25(4):791-800.
  7. Bozini T, Petridis H, Garefis K, Garefis P. A meta-analysis of prosthodontic complication rates of implant-supported fixed dental prostheses in edentulous patients after an observation period of at least 5 years. Int J Oral Maxillofac Implants. 2011 Mar-Apr;26(2):304-18.
  8. Larsson C, Vult Von Steyern P. Implant-supported full-arch zirconia-based mandibular fixed dental prostheses. Eight-year results from a clinical pilot study. Acta Odontol Scand. 2013 Sep;71(5):1118-22.
  9. Pozzi A, Holst S, Fabbri G, Tallarico M. Clinical reliability of CAD/CAM cross-arch zirconia bridges on immediately loaded implants placed with computer-assisted/template-guided surgery: a retrospective study with a follow-up between 3 and 5 years. Clin Implant Dent Relat Res. 2015 Jan;17 Suppl 1:e86-96.
  10. Baucic I, Baucic M, Stipetic J, Komar D, Mehulic K, Bozic D, Klaic B, Celebic A. Screening of fixed prosthodontic dentures after five years of use in relation to material and construction. Coll Antropol. 2002 Dec;26(2):673-9.
  11. Jemt T, Johansson J. Implant treatment in the edentulous maxillae: a 15-year follow-up study on 76 consecutive patients provided with fixed prostheses. Clin Implant Dent Relat Res. 2006;8(2):61-9.
  12. Kim YS, Ko Y, Kye SB, Yang SM. Human gingival fibroblast (HGF-1) attachment and proliferation on several abutment materials with various colors. Int J Oral Maxillofac Implants. 2014 Jul-Aug;29(4):969-75.
  13. Glauser R, Sailer I, Wohlwend A, Studer S, Schibli M, Schärer P. Experimental zirconia abutments for implant-supported single-tooth restorations in esthetically demanding regions: 4-year results of a prospective clinical study. Int J Prosthodont. 2004 May-Jun;17(3):285-90.
  14. Attard NJ, Zarb GA. Long-term treatment outcomes in edentulous patients with implant-fixed prostheses: the Toronto study. Int J Prosthodont. 2004 Jul-Aug;17(4):417-24.
  15. Krennmair S, Seemann R, Weinländer M, Krennmair G, Piehslinger E. Immediately loaded distally cantilevered fixed mandibular prostheses supported by four implants placed in both in fresh extraction and healed sites: 2-year results from a prospective study. Eur J Oral Implantol. 2014 Summer;7(2):173-84.
  16. Fischer K, Stenberg T. Prospective 10-year cohort study based on a randomized controlled trial (RCT) on implant-supported full-arch maxillary prostheses. Part 1: sandblasted and acid-etched implants and mucosal tissue. Clin Implant Dent Relat Res. 2012 Dec;14(6):808-15.
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