Retaining implant prostheses
The March/April 2015 issue of The International Journal of Prosthodontics includes an analysis of prosthodontic maintenance and complications in screw- and cement-retained implant prostheses.
One of the major reported advantages of screw-retained implants is retrievability. They allow the clinician easy access for providing prosthodontic maintenance, such as tightening loose screws or repairing chipped porcelain. However, researchers note anecdotal reports that screw retention may result in more of these types of maintenance issues than cement retention.
Finding a lack of evidence-based guidelines to assist the dentist, “It appears that the choice of retention in implant prostheses still mainly depends on the individual’s preference and experience,” scientists in New Zealand and Canada said as they conducted a systematic review. They searched several databases, through Dec. 31, 2013, including: Medline, EMBASE, PubMed and Cochrane databases for studies on fixed implant prostheses using screws or cement, types of screws and methods of preloading, as well as different luting cements in correlation with prosthodontic maintenance and complications findings. They included additional studies found in reference lists and manual and online searches.
Scientists found the lack of standardized criteria in reporting prosthodontic maintenance/complications made comparing data difficult and precluded a comparison of prosthodontic outcomes between screw- and cement-retained fixed implant prostheses.
Of 1,432 studies identified through database searches, 62 were eligible and included in the systematic review. Six were randomized controlled trials. None included an equivalent number of screw- and cement-retained single implant crowns for comparison. Studies used different types of screws and only a few reported the preloading procedure for the prosthetic screws.
Studies involving cement-retained implant prostheses used a range of dental cements, however some did not specify the type used. Screw loosening, porcelain fracture, loss of retention and esthetic concerns were among issues reported. Some studies focused on specific regions in the mouth. The number of participants and implants varied greatly among the studies.
Only two studies stated standardized criteria for reporting data.
Common types of maintenance/complications included screw loosening (crowns or abutments), luting cement loss, veneering or porcelain fracture and esthetic concerns.
Authors noted the positive impact of the evolution in mechanics of prosthetic screws. “Application of the correct torque is translated into a preload, producing a clamping force and preventing a one-sided lift-off of the abutment. This positive impact on maintenance events is clearly evident in the newer studies, although it may still be argued that cement retention is a viable option for single implant crowns.”
Read the original article.
Consulting Editor: Lars O. Bouma, DDS
Diplomate, American Board of Prosthodontics
Rehabilitating the posterior maxilla
Researchers described a viable treatment option for implant rehabilitation of the posterior maxilla when bone quality and quantity are compromised in the March 2015 issue of The Journal of Prosthetic Dentistry.
They considered the case of a 65-year-old woman referred to a private clinic for prosthetic treatment of a recently edentulous area in the upper right quadrant. The patient sought to reestablish lost function and esthetics with a fixed prosthesis, to minimize the time period without teeth and to avoid a removable prosthesis.
An intraoral examination showed that she recently lost the first premolar and first molar. Preoperative radiography revealed bone loss associated with the extracted teeth and extensive coronal pneumatization at the maxillary sinus near the second premolar.
The treatment team considered two options. The patient chose immediate fixed prosthesis over delayed. It would be supported by one anterior axial implant and one posterior tilted fixture placed with an intrasinus insertion.
“Compared to implant placement with an osteotome technique, the trans-sinus technique allows a longer fixture in the molar area where higher mastication forces occur,” the treatment team reported. “Additionally, in contrast with a graftless approach using short implants and prosthetic extensions, the trans-sinus implant requires limited or no cantilever.”
In addition to the clinical report, authors provided a new classification protocol for the immediate treatment of the posterior maxilla based on the available bone.
Read the original article.
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Monolithic zirconia: A case report
Monolithic zirconia restorations are increasingly used because they produce better esthetics than metal ceramic prostheses. They are also associated with lower chipping rates than zirconia ceramic.
However, according to a team of South Korean scientists publishing in the February 2015 issue of The Journal of Prosthetic Dentistry, few clinical studies report on the outcomes of monolithic zirconia ceramic restorations. They reported on complications associated with such prosthesis in a 79-year-old man.
After the patient expressed concerns with a loose mandibular complete removable dental prosthesis, clinicians provided four dental implants and a screw-retained monolithic zirconia prosthesis. The patient also received a maxillary complete removable dental prosthesis over four anterior roots.
Researchers followed up with the patient at one, three, six, 12 and 18 months after treatment. At 12 months, he reported no discomfort. At 18 months, scientists found that all of the zirconia cylinders were fractured and the contacting abutment surfaces had lost structural integrity.
In view of its predictable results and long-term clinical success, clinicians replaced the damaged abutments and provided a CAD/CAM (computer-aided design and computer-aided manufacturing) prosthesis made of a titanium framework with denture teeth. The patient did not report any problems at the six-month follow-up.
“Because of its excellent mechanical and biocompatible properties, monolithic zirconia ceramic is an attractive choice for ISCFDPs [implant-supported complete fixed dental prostheses],” authors said in discussion.
“However, prosthetic failure was encountered with this treatment.”
Among conclusions, authors cautioned that clinicians should thoroughly evaluate the accuracy of the prosthesis, stress accumulation around zirconia ceramic cylinders and cantilever length to prevent failure.
Read the original article.
Prize winning posters were awarded at the 33rd International Congress of the Italian Academy of Prosthodontic Dentistry.
Poster topics were wide-ranging with winners including an investigation on survival rate and long-term behavior of CAD/CAM hybrid ceramic restorations (Frieburg, Germany) and an evaluation of digital impression techniques on marginal accuracy of single crowns (Padova, Italy).
First prize was awarded to a team investigating whether there is a correlation between the dynamics of mandibular lateral translation during symmetric movements in patients exhibiting different skeletal classes. Scientists hailed from Pontedera, Italy; Vienna, Austria; and Yokosuka, Japan.
The conference was held Nov. 20-22, 2014, in Bologna, Italy.
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What is Specialty Scan?
This is one in a series of quarterly newsletters updating dentists on selected specialties in dentistry. Information presented is aggregated and summarized from previously published materials, each item attributed to its publication of origin. This issue of JADA Specialty Scan focuses on prosthodontics, the second in the series on this topic for 2015. Other Specialty Scan issues are devoted to endodontics, orthodontics, oral and maxillofacial pathology, oral and maxillofacial radiology, pediatric dentistry and periodontics. 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. We welcome your feedback on this and all Specialty Scan issues.
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