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JADA Specialty Scan - Prosthodontics
Prosthodontics - A Quarterly Newsletter on Dental SpecialtiesJADA Specialty Scan

Zirconia survivability as prosthetic biomaterial

Researchers evaluated the survival outcomes of 1-piece complete arch fixed implant-supported prostheses (CAFIPs) fabricated by a large U.S.-based dental laboratory and determined that monolithic zirconia, the biomaterial in the investigated CAFIPs, is an excellent choice of material. They published their results online July 6 in The Journal of Prosthetic Dentistry.

In writing about their study, researchers discussed how CAFIPs conventionally have been fabricated with a metal framework and acrylic resin for artificial teeth and gingiva or with metal-composite resin or metal-ceramic biomaterials.

They discussed zirconia as an emergent alternative biomaterial for CAFIPs and cited 2 recent systematic reviews that summarized some of the material’s promising aspects and less desirable characteristics. Advantages identified for clinicians and patients included reduced laboratory costs; good dental and gingival esthetics; superior strength, durability, wear characteristics, biocompatibility and fit; availability of a digital file for future replication; reduced plaque accumulation; and favorable soft-tissue response.

Disadvantages included inability to repair framework fractures; difficulty in adjusting and polishing; low tolerance of minor inaccuracies in the impression, resulting in fractures during insertion; and minimal long-term scientific data for clinical outcomes.

This 5-year retrospective study used practice-based evidence in the form of warranty data from the dental laboratory that fabricated all of the prostheses involved in the study. All of the prostheses were made of the same kind of zirconia. Each prosthesis was predominantly monolithic zirconia, screw-retained, and had veneered porcelain restricted to the gingival region. The researchers collected and assessed data from the dental laboratory’s database for all zirconia prostheses from January 1, 2012, to December 31, 2016. They recorded how many prostheses were returned to the laboratory to be remade or adjusted under the warranty.

In evaluating the large sample database of 2,039 prostheses from the dental laboratory during the study period, researchers determined that 319 had a minimum of 3 years of clinical service, and 69 had a minimum of 4 years of clinical service. They identified 6 reported fractures, resulting in a first-year interval survival rate of 99.8% and a 5-year cumulative survival rate of 99.3%. In addition, 6 prostheses (0.29%) were returned to the laboratory owing to technical complications caused by debonding of the titanium cylinder, and 3 (0.14%) were returned owing to fracture of the titanium cylinder (0.14%). 
However, no prostheses were returned to the laboratory owing to chipping of the veneered gingival porcelain (an outcome determined at a rate of 14.7% in a previous literature analysis of 12 clinical studies on prosthetic use of monolithic zirconia). The laboratory successfully addressed all technical complications and returned the prostheses to clinicians without further returns.

In conclusion, researchers determined that the 1-piece zirconia CAFIP with veneered porcelain restricted to the gingival region has excellent short-term survival outcomes, a low rate of technical complications, and is an acceptable choice in the fixed implant rehabilitation of edentulous patients.

Read the original article here.


Consulting Editor: Donald A. Curtis, DMD, FACP
Diplomate, American Board of Prosthodontics
Professor, University of California San Francisco


Implant failure rate and surgical experience

Brazilian and Swedish investigators questioned whether a correlation exists between surgeons’ experiences and dental implant survival. They published results of their systematic review in the July/August issue of The International Journal of Prosthodontics.

The systematic review, performed in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses statement and registered in the International Prospective Register of Systematic Reviews, drew on dental literature found through MEDLINE (PubMed), Embase, Scopus, and the Cochrane Library database searches. Researchers searched publications from their inception to May 20, 2016, using keywords with Boolean operators to combine terms.

Their population, intervention, comparison, outcomes framework question was “Are the survival rates of dental implants placed by experienced surgeons similar to those placed by inexperienced surgeons?”

“Few studies have associated implant failure with individual characteristics of the surgeon, such as clinical training and expertise, and contradictory observations have been reported,” the researchers wrote.

Eight studies, gleaned from 599 studies, ultimately met researchers’ criteria for inclusion in their systematic review. One study was a prospective clinical trial, and 7 were retrospective cohorts. None was a randomized controlled clinical trial.

The referenced literature deemed experienced surgeons as those who were specialists in oral and maxillofacial surgery, periodontology, or prosthodontics with surgical training in implantology; clinicians with more than 5 years of clinical experience in implant dentistry; or clinicians who had placed more than 50 implants. Implant survival in the studies meant no implant loss, no mobility, no pain or discomfort, and the absence of detectable bone loss.

Researchers conducted 2 meta-analyses to different definitions of experienced surgeons. The first meta-analysis addressed definitions in 4 retrospective comparative studies that defined experienced surgeons as specialists in oral and maxillofacial surgery, periodontology, or prosthodontics with surgical training in the implant field. In evaluating failure in these studies, researchers found that the experience of the surgeon did not significantly affect the implant failure rate (P = .54), with an odds ratio of 1.24 (95% confidence interval [CI], 0.62 to 2.48).

The second meta-analysis compared definitions from 2 retrospective studies that defined experienced surgeons as professionals that had placed more than 50 implants. Using a fixed meta-analysis, the researchers determined that the experience of the surgeon significantly affected the implant failure rates (P = .0005), with an odds ratio of 2.18 (95% CI, 1.40 to 3.39).

The researchers concluded that when defining surgical experience by the number of implants placed as opposed to surgical experience as based on dental specialization implant failure was significantly affected. They also concluded that further standardized prospective studies with control groups of confounding factors are needed to clarify the role of surgical expertise on implant survival rates.

Read the original article here.

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Prevalence, compared mechanisms of peri-implant diseases

A European critical review published January 1 in Journal of Dental Research summarized evidence from the literature that illustrates the prevalence of peri-implant diseases and that compares and contrasts peri-implant and periodontal diseases, particularly relative to their pathogenic mechanisms.

The researchers encountered various studies with an inconsistent range of peri-implant disease prevalence, citing 1 systematic review with meta-analysis that reported peri-implant mucositis at 43% (range, 19% to 65%) and peri-implantitis at 22% (range, 1% to 47%). They also cited cross-sectional studies (not included in the systematic review) reporting other disparate prevalence of peri-implantitis.

“Clearly, these outcomes indicate a wide range in the prevalence of peri-implant diseases, making it difficult to globally estimate the magnitude of the disease,” the researchers wrote. “These inadequacies may rely on methodological inconsistencies and shortcomings of the reported studies.”

Different approaches to case definitions in studies elucidate the lack of consensus as to peri-implant disease prevalence, the researchers found. For instance, some studies used baseline radiographs to arrive at criteria to define peri-implantitis while others did not. Also, some studies reported only implant-based data and lacked patient-level outcomes. Other disparate reporting variables affecting determination of peri-implant disease prevalence include time of implant function and limited sample sizes (from universities or private clinics) rather than large, randomly selected population samples.

In the aspect of their critical review comparing and contrasting peri-implant diseases and periodontal diseases, researchers focused on how peri-implant mucositis and peri-implantitis and their counterparts affect natural teeth, gingivitis, and periodontitis. They analyzed both animal and human studies that considered host response to experimental biofilm accumulation around implants or natural teeth. They also compared pathogenesis of the corresponding diseases.

They reached a number of conclusions and described several clinical implications. Regarding the prevalence of peri-implant diseases, they deemed the wide-ranging reported figures controversial and pointed to differences in case definitions for making comparisons among the studies they cited difficult.

In the peri-mucositis versus gingivitis animal studies, they found more severe lesions in animal peri-implants compared with animal periodontal soft tissue related to the experimental plaque accumulation around implants. Humans also had stronger inflammatory responses to experimental plaque accumulation around implants than around natural teeth.

In the experimental peri-implantitis versus periodontitis sites, they found tissue destruction faster and greater at the peri-implantitis sites. Also, they wrote, despite similarities in etiology and clinical features, lesions in human peri-implantitis and periodontitis were histopathologically distinct entities.

Ultimately, the researchers determined these results indicate a need for the early diagnosis, management, and treatment of peri-implant diseases.

Read the original article here.


Narrow-body implant deformity, peri-implant bone loss

An experimental pilot study published September 19, 2016, in The International Journal of Oral & Maxillofacial Implants demonstrated a relationship between load application and deformity of the implant shoulder and displacement of the abutment in narrow-diameter implants.

“Narrow implants have become popular as they minimize the need of bone augmentation,” researchers wrote. They focused their study on narrow-diameter implants from 2 manufacturers. The implants were made of commercially pure titanium or titanium zirconia alloy with a conical implant-abutment connection.

Stable peri-implant bone level associated with healthy peri-implant tissue is key to the success of dental implants. Researchers noted a lack of long-term data on the clinical performance of narrow-diameter implants with a conical implant abutment connection in relation to bone outcomes. “The etiology of peri-implant bone loss is still not understood, but it is assumed to be of a multi-factorial genesis, among which an overload of the peri-implant bone is discussed,” researchers wrote. Also, they noted, the mode of force transmission is not known.

To visualize the mode of force transmission in narrow-diameter implants with different implant abutment designs and material properties and to quantify the displacement of the abutment on loading—the key aim of their study—the researchers used synchrotron radiography with absorption and inline x-ray phase contrast and tomography to assess prepared samples before and during loading. The samples were 4 narrow-diameter implants with diameters of 3 millimeters and 3.3 mm, 2 each from 2 separate manufacturers. “The incremental forces applied were 125 and 250 [newton] at an angle of 30 degrees to the implant axis onto the steel ball,” researchers wrote.

Results included increases in the outer and inner diameters of the samples during the 250-N force application and after loading. The samples also changed diameter at the implant shoulder with regard to the load applied, and the test yielded an intrusion of the abutment into the implant body during load application. In addition, plastic deformation at the implant shoulder occurred under force application of 250 N in a 30-degree angle in all of the implants examined. Researchers noted that the deformation of the implant shoulder persists after the load is removed.

In discussion of the study's relationship to bone outcomes, researchers wrote that micromovement within the implant could be visualized through use of synchrotron radiation. With it, they visualized the extent of movement per load applied and gained further insights into the strength and properties of implant and abutment materials and their roles. The visualization also allowed corroboration that overload of the implant at the implant shoulder could be responsible for peri-implant bone loss that had been demonstrated in the animal experiments in the literature.

Read the original article here.

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JADA+ Specialty Scans and JADA+ Scans

JADA+ Specialty Scans and JADA+ Scans are quarterly newsletters updating dentists on the latest research in selected specialties and disciplines in dentistry. ADA Publishing and the consulting editors from the represented specialties and disciplines aggregate and summarize research from previously published materials, each item attributed to its publication of origin. JADA+ Scan specialties and disciplines include endodontics, oral pathology, orthodontics, pediatric dentistry, periodontics, prosthodontics, radiology, cosmetic/esthetic and osseointegration. The ADA has engaged the specialty organizations in these areas as well as its own Science Institute and Division of Legal Affairs to assist with these newsletters. View past issues here.

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