Zirconia restorations and performance
Zirconia can be a reliable material to enhance esthetics, biocompatibility, performance and efficiency in fixed prosthodontics, according to research published in the May-June 2015 issue of The International Journal of Periodontics and Restorative Dentistry.
Scientists said their study found promising performance results for monolithic zirconia and minimally veneered zirconia using digital milling protocols on both teeth and implants in a wide variety of clinical applications, indicating a new paradigm is possible in fixed prosthodontics that allows for the use of an advanced high-strength ceramic (zirconia). They called for more studies to establish the treatment modality as a possible new benchmark in restorative dentistry.
A well-known material with high strength and excellent biocompatibility in both dentistry and medicine, zirconia ceramics are used for such restorations as implants, implant abutments and frameworks for fixed partial dentures.
However, previous studies showed breakage of the veneering feldspathic ceramic and substrate occurred frequently compared with bilayered metal restorations, particularly when used in the posterior.
“Historically, restoring patients with advanced wear of function with bilayered ceramics on both teeth and implants has been challenging without the prescription of a protective acrylic appliance or full-metal occlusion to prevent damage,” authors said.
Nevertheless, recent clinical reports and studies have shown reliable results for restorations using monolithic and minimally veneered zirconia. Such findings motivated the scientists to evaluate them by monitoring fracture, cracking and chipping of the zirconia structure and/or the minimally veneered feldspathic ceramic.
Employing a consecutive case series that included 1,022 restorative units and 238 patients between the ages of 16 and 92 — mean age of 61.9 years — the scientists observed no failures of the zirconia restorations after an observation time of up to 68 months.
The dental restorations as described in the study required a milling protocol. “Previously milling with analog machinery made this a tedious and time-consuming process. As CNC [computer numerical controlled] machinery and associated software became available, it allowed for an increase in the time efficiency of producing zirconia restorations.”
Authors said the new digital protocols for milling zirconia also provided a collateral benefit in the ability to create surgical guides, provisional restorations and prototype restorations.
Read the original article.
Consulting Editor: Lars O. Bouma, DDS
Diplomate, American Board of Prosthodontics
Retention force and overdenture success
The advantages of two-implant-retained mandibular overdentures when compared with conventional dentures are established. Better stability, better chewing ability and greater bone preservation, particularly in the mandible, are key improvements.
Although patients report a strong preference for greater retention in their dentures, scientists in Turkey found no studies on the influence of retention forces from two-implant-retained mandibular overdentures on patient satisfaction and quality of life. Considering the increasing popularity of this treatment, they deemed it valuable to analyze how this factor affects long-term treatment success.
To evaluate, scientists conducted a retrospective study of patients wearing two-implant-retained mandibular overdentures and published their findings in the March-April 2015 issue of the International Journal of Oral and Maxillofacial Implants.
They studied 98 edentulous patients — 31 women and 24 men — who were rehabilitated with mandibular overdentures, as well as maxillary complete dentures. Patients included in the study wore the two-implant-retained mandibular overdenture for exactly two years without prior maintenance procedures.
Researchers measured and recorded momentary retention forces for each patient and assessed their satisfaction by analyzing a questionnaire with patients’ reports of general comfort, retention, chewing, speech, ease of hygiene maintenance, esthetics and pain. To assess quality of life, scientists administered the Turkish-language OHIP-14, which covers the same domains as the original OHIP and measures oral health-related quality of life within seven domains: functional limitation, physical pain, psychological discomfort, physical disability, psychologic disability, social disability and handicap.
Among primary results, scientists detected no significant association between momentary retention forces and patient satisfaction. However, higher momentary retention forces were associated with significantly lower social disability and handicap domain scores on the OHIP-14.
“Present results show that after an adaptation period, the patients were usually satisfied with their two-implant-retained mandibular overdentures even if the retention was lost,” authors said. They surmised that this outcome may be due to patients’ sense of security with their prosthesis because of initial retention, as well as the effect of the abutments on the stability even if the retention was lost. (The literature shows that after six to 12 months of use, the retention force values decrease to approximately 10 to 30 percent, and sufficient stabilization of the overdentures occurs even if the attachment systems provide lower retention forces.)
“On the other hand, it should be noted that higher momentary retention forces caused better quality of life scores in the social disability and handicap domains, indicating that the patients having more retentive overdentures had been less embarrassed and uncomfortable because of problems with their prostheses,” authors said.
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Screw retrieval after fracture
When the abutment screw from a cement-retained implant prosthesis fractures, it is customary for the clinician to perforate part of the crown to gain access to the fractured screw so it can be removed.
The problem with this procedure is that it can compromise the esthetics and mechanical properties of the restoration, thereby reducing its longevity. Screw loosening is a common and challenging prosthetic complication of cement-retained, implant-supported restorations that can eventually lead to screw fracture. Although the literature documents several techniques to locate the abutment’s screw access hole without causing irreversible damage to the restoration are reported about in the dental literature, scientists at Ohio State University found no studies about the debonding of a cemented crown from the abutment using heat treatment with a dental porcelain furnace. They described implementing the method in the case of a 62-year-old male who presented with an avulsed cement-retained, implant-supported ceramo-metal restoration in the April 2015 issue of the Journal of Prosthodontics.
After making the decision to replace the fractured screw and re-cement the previously used crown to the existing abutment, instead of perforating the crown to locate the screw access they debonded the cemented crown from the abutment using a porcelain furnace. Clinicians selected the temperature range based on findings of a previous study where average cement disintegration temperatures for zinc phosphate, dual-cure resin cement and glass ionomer cement were observed at approximately 306 to 363°C.
In discussion authors said the technique does not jeopardize the integrity and strength of the implant-supported restoration through grinding or other access hole location techniques when an abutment screw has completely fractured off. They acknowledged, however, that the clinical presentation of an avulsed implant-supported restoration does not represent the most common clinical occurrence.
They called for more research to understand and avoid the loosening of implant-supported cement-retained restorations and more conservative, harmless retrieval techniques of dental prostheses.
Read the original article.
Survival of teeth with cast post and cores
Finding a lack of data on the survival of cast post and core-treated teeth after more than 10 years, a team of scientists at Technical University, in Dresden, Germany, studied the treatment data of patients with such prosthetic needs between January 1992 and June 2011.
Scientists searched the database of the university hospital dental clinic for all cast post and core treatments using relevant treatment codes and then analyzed tooth survival. Survival curves for different tooth types, the status of different adjacent teeth and different prosthetic restorations were tested for statistical significance.
Results revealed that 717 teeth were restored with cast post and cores in 434 patients. The mean survival time before tooth extraction was 13.5 years. Five-year survival rates for teeth were 86.9% and 10-year survival rates were 75.7%.
In discussion, scientists said that although the survival time of teeth restored with cast post and cores seems to be short, the different preconditions of this type of restoration have to be considered.
“Restoring a tooth with a cast post and core is, in most patients, reserved for a severely damaged tooth,” authors said. “Often, the only other alternative is extracting the tooth. Therefore, the calculated clinical survival rates still justify the use of cast post and cores for the restoration of severely damaged teeth.”
Specific groups of teeth showed different survival times. For example, a significant decrease was found for canines (11.9 years) and premolars (13.4 years) versus molars (14.1 years). A reduced mean survival time of 10.6 years was found for treated teeth without any adjacent tooth compared with 13.8 years for treated teeth with one or two adjacent teeth. The largest reduction in survival time was found for teeth being used as an abutment for a double crown-retained removable partial dental prosthesis (9.8 years).
Among conclusions, authors said that within the limitations of this study, cast post and core-treated teeth achieved an acceptable mean survival time and alternatives like fiber reinforced resin posts do not yet have comparable scientific long-term data. “Because different factors may influence survival, considering these factors in treatment planning may increase the long-term success of these restorations.”
The full report is published in the July 2015 issue of The Journal of Prosthetic Dentistry.
Read the original article.
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Removable Partial Denture brochure from the ADA
Patients may need help understanding the benefits of partials, as well as getting used to life with the prosthodontic. The ADA offers an updated brochure to help fill the knowledge gap.
Removable Partial Dentures conveys the importance of replacing missing teeth and shows what partial dentures are. The brochure gives tips on getting used to partials, and eating and speaking with them. Patients are encouraged to visit their dentist for any necessary adjustments and repairs and are reminded that it’s key to maintain good hygiene for remaining natural teeth.
The eight-panel brochure is sold in packs of 50. Brochure contents can be viewed on this page. To order, call 1-800-947-4746 or go to adacatalog.org. A personalized version is also available. Readers who use the code 15407E before November 13 can save 15 percent on all ADA Catalog products.
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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 third in the series on this topic for 2015. Other Specialty Scan issues are devoted to endodontics, orthodontics, oral 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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