Cement thickness and crown retention
Cement thickness is a key factor influencing the retentive strength of cemented implant-retained crowns. Yet even as cemented restorations seem to be gaining popularity over those that are screw-retained, design variables in published studies make it difficult to draw definitive conclusions about the impact of cement thickness on crown retention.
Seeking a systematic approach for evaluating the influence of cement film thickness on crown retention, scientists in Germany conducted an invitro study using state-of-the-art techniques and centering the abutments in the crowns. They published their findings in the December 2013 issue of the Journal of Prosthodontics.
For their study, the scientists used 96 tapered titanium abutments and computer-aided designed crowns. Before cementing, they established preset cement film thicknesses of 15, 50, 80 or 110 micrometers (um.) They used glass ionomer, polycarboxylate and resin cements.
After a storage period of three days in demineralized water, researchers measured the retention of crowns using a universal testing machine.
They found a significant interaction between cement and cement film thickness, and cement film thicknesses were achieved with a high level of precision. For all cements, crown retention decreased significantly between a cement film thickness of 15 and 50 um.
Extensive literature already exists on how cement film thickness influences crown retention, but most of these studies are more than 20 years old and evaluate the influence of die spacers or platinum foils to compensate for casting inaccuracies, the authors noted.
“One of the main goals of the current study was to deliver a systematic approach to center the abutment in the crowns, as nearly identical disclosing silicone values comparing opposing sides and crowns of debonded specimens suggest,” the authors said. “The other important aim was to reliably provide researchers with a system to establish a precise cement film thickness to evaluate different cement characteristics.”
The results suggested that cement film thickness and choice of cement have a major influence on the retentive strength of cemented implant-retained crowns.
Consulting Editor: Lars O. Bouma, DDS
Diplomate, American Board
One step vs. two for prosthetic impressions
Accuracy in terms of an impression’s dimensional stability and digital reproduction is crucial to long-term success of a dental prosthesis. Proper manipulation of materials and the technique used to make an impression greatly influence accuracy.
Scientists at Tel Aviv University in Tel Aviv, Israel, found that while some investigators have demonstrated no significant difference in accuracy between the one-step impression technique and the putty-wash two-step technique, others have claimed that technique has a greater impact on accuracy than material.
To reconcile the matter, they conducted their own study evaluating the effect of two putty-wash impression techniques on the long-term accuracy and dimensional stability of a popular impression material—poly vinyl siloxane (PVS) —in the narrow space between the surface of the tooth and the gum. Their findings were published in the February 2014 issue of the Journal of Prosthodontics.
To investigate, scientists took impressions from a master cast to simulate molar crown preparation. A space around the abutment served as the gingival sulcus. Thirty impressions were taken using each of three materials, with 15 obtained using each technique (one-step and two-step). Scientists observed significant variances when different materials and impression techniques were used. Also significant was the interaction of material, time and technique. They found the two-step impression technique to be more accurate, with smaller discrepancies than the one-step technique.
“The results clearly showed that the two-step impression technique produced more stable impressions and smaller discrepancies than the one-step impression technique; however, if pouring is performed within two hours of taking the impression, both techniques were acceptable, as the discrepancies were small and positive,” the authors said.
Pouring of the impressions may be postponed up to 30 hours when using the two-step putty washing technique, the authors reported.
BruxZir Full-Arch Implant Prosthesis
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Decreasing the odds of peri-implant pathology
What factors influence the frequency of peri-implant pathology (P-iP)?
Researchers in Portugal explored that question and reported their findings in the January 2014 issue of the Journal of Prosthodontics.
Defined as “the term for inflammatory reactions with loss of supporting bone tissue surrounding the implant in function,” a recent literature review on the prevalence of P-iP revealed its occurrence in 12 to 43 percent of implant sites. The literature also showed that most published clinical studies focused on implant successes and failures, rather than on risk factors for P-iP, the authors said.
To investigate possible factors that may contribute to increased risk of the complication, the scientists conducted a retrospective study of 1,350 patients who had received dental implants at the Center for Implantology and Fixed Oral Rehabilitation-Lisbon, Portugal, between February 1998 and November 2006. The subjects consisted of 270 patients who had been diagnosed with peri-implant pathology and 1,080 who had not.
Between January and July of 2009, researchers examined the patients’ written records, radiographs, medical questionnaires and clinical diaries to evaluate the effect various factors may have had on the probability that a patient developed disease.
The independent variables they examined were:
- implant length
- implant diameter
- implant surface (machined, oxidized)
- presence of cantilevers
- type of abutment (straight; 17 degrees angulated, 30 degrees angulated)
- abutment height
- fracture of prosthetic reconstruction
- type of prosthetic reconstruction
- type of material used in the prosthesis
- loosening of prosthetic components
- passive misfit diagnosed within the previous year.
The results revealed specific risk factors, and scientists theorized that the cases of P-iP would have been reduced if exposure to certain variables had been removed. Included among them was passive misfit of the prosthesis, loosening of prosthetic components, fracture of components and implants with a machined surface.
Considering the factors associated with an increased risk of P-iP frequency, authors said in conclusion: “The hypothetical removal of the exposure of the majority of these variables could result in a drastic decrease in disease incidence. More studies with stronger designs should be performed to attest the causal relationship between these variables with peri-implant pathology.”
Titanium and allergic reactions
New research puts a question mark on conventional thinking that titanium (Ti) is unlikely to cause allergic reactions because of its superior corrosion resistance.
The incidence of allergic reactions attributed to titanium sensitization may increase with its overall medical use, research published in the Feb. 4, 2014 online edition of the Journal of Prosthodontics reported.
Scientists in Japan described the case of a 33-year-old woman referred for treatment following a 10-year history of eczema and itchy redness on her fingers. An allergy clinic conducted lymphocyte stimulation testing (LST), which has been demonstrated in the literature to be a reliable method for detecting metal sensitivity. The patient showed a rare, specific reaction to mercury, nickel and silver, but no reaction to other tested metals, including titanium.
After checking the composition of the patient’s 17 metal restorations, researchers removed all of those containing mercury or silver. The patient’s pruritus improved within two months. After waiting an additional month, researchers replaced the restorations with new ones made of titanium.
Nine months after placement of the Ti restorations, the patient developed cervical eczema. The condition gradually worsened. LST testing revealed a specific reaction to titanium, so the authors removed all titanium containing restorations and replaced them with autopolymerizing poly (methyl methacrylate) resin. The patient’s eczema resolved within three months and didn’t reoccur over more than five years of observation.
Earlier research uncovered Ti allergy because dermal inflammatory conditions ceased after removal of titanium. This current study, however, described a case of dermatitis associated with a positive LST reaction to titanium after insertion of titanium dental restorations.
In discussion, the authors noted that Ti ions dissolve in artificial bioliquids more than expected when the surface film is destroyed, and topical fluoride solutions can cause stress corrosion cracking.
“The present findings suggest that the patient had become sensitized by nine months after insertion of Ti, and the fact that complete remission was achieved after removal of the Ti strongly suggests that the cervical eczema was caused by an allergy to intraoral Ti,” the authors said.
They speculated that titanium restorations are likely to increase in frequency as a substitute for precious metal due to the belief that titanium is very stable.
“It seems likely that the incidence of allergic reactions caused by sensitization to titanium will increase in the future as use of medical titanium increases,” authors said. “The rare occurrence of such a response to titanium materials in clinical dentistry should therefore be further discussed and investigated.”
‘JADA Live’ to spotlight office design
The first “JADA Live” presentation for 2014 will focus on practice improvement through office design.
To help dentists make the most of their practice investment, the publishers of The Journal of the American Dental Association will bring “JADA Live—Advancing Your Practice Through Office Design” to the Fairmont Scottsdale Princess, Scottsdale, Ariz., Friday, June 13, from 9 a.m. to 5:30 p.m.
Dr. Mark Tholen, former CEO of T.H.E. Design, will break down the office design process and teach techniques aimed at boosting office efficiency. The seminar will include interaction with exhibitors and hands-on sessions with the latest in dental technology.
“JADA Live” participants will earn six units of continuing education credit with successful completion of the course. To register, visit http://jadalive.org or call 1-888-692-2631. Registration for the seminar is $315 for ADA members, $375 for nonmembers.
The first 100 dentists to register will receive, free of charge, the ADA’s bestselling new book, “The ADA Practical Guide to Dental Office Design,” which retails for $134.95.
ADA offers discount on implant brochure
All ADA Catalog products, including a brochure on the Single Tooth Implant, are available to dentists at a 15 percent discount through May 31, using the promo code 14324E.
Single Tooth Implant (W173) conveys the message that, while nothing replaces a natural tooth, dental implants come close. The brochure reviews the reasons to replace a missing tooth and illustrates the structure of a single tooth implant.
It also describes the benefits of implants, updated steps involved in placement and healing, who qualifies as a candidate for the procedure and the importance of good oral hygiene.
The six-panel brochure is available in packs of 50 to member dentists for $26; retail price is $39. Discounts also are available for higher quantities.
To preview the Single Tooth Implant brochure and other prosthodontic brochures from the ADA, visit adacatalog.org. Orders can be placed online at adacatalog.org of by calling the ADA Member Service Center at 1-800-947-4746.
BruxZir Screw-Retained Crowns
BruxZir Solid Zirconia is a strong, biocompatible, monolithic restorative material that delivers color and translucency similar to that of natural dentition. With a titanium segment that rests directly on the implant head, BruxZir Screw-Retained Crowns deliver strength and esthetics even in cases with minimal soft tissue.
BruxZir Solid Zirconia: Esthetics and durability combined
By Tarun Agarwal, DDS, PA
As clinicians strive to achieve the ideal balance between beauty and durability in implant cases, root resorption, difficulties during extraction, failed osseointegration and other complications can diminish the desired outcome, particularly in the anterior esthetic zone.
Consider the case of a female patient with a thin-tissue biotype in the esthetic zone, who was diagnosed with non-restorable root resorption on tooth No. 9. A Biomet 3i Certain tapered implant (BIOMET 3i, LLC; Palm Beach Gardens, Fla.) was delivered to host the restorative crown.
During healing, excessive recession occurred, rendering the esthetic results of an IPS e.max cement-retained crown (Ivoclar Vivadent; Amherst, N.Y.) unacceptable due to the visible grayness of the titanium abutment at the tissue line. The abutment could not be placed more apically.
To achieve the desired result, a BruxZir Solid Zirconia screw-retained crown (Glidewell Laboratories; Newport Beach, Calif.) was prescribed instead. The titanium segment of this monolithic restoration rests at the deepest possible point—on the implant head—giving the tissue vitality and delivering a pleasing esthetic result.
Figure 1: Unexpected recession during the healing phase caused the titanium margin of the implant, and subsequently the margin of the titanium abutment at the tissue line of the original IPS e.max crown, to show.
Figure 2: The BruxZir Solid Zirconia screw-retained crown. Note the minimal size of the required titanium segment.
Figure 3: Delivery of the BruxZir screw-retained crown and the final esthetically pleasing result with no visible grayness at the margin.
In situations similar to this, a clinician’s knowledge of the materials available to achieve a durable result while maintaining optimal esthetics, particularly in the anterior, is of paramount importance. BruxZir Solid Zirconia crew-retained crowns can help to maximize these qualities in cases that are anything but optimal.
To read Dr. Agarwal’s full article, visit www.chairsidemagazine.com.
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 is focused on prosthodontics, the second in the series on this topic for 2014. Other Specialty Scan issues are devoted to orthodontics, periodontics, endodontics and oral and maxillofacial radiology. The ADA has engaged the specialty organizations in these areas as well as its own divisions of Science and Legal to assist with these newsletters. We welcome your feedback on this and all Specialty Scan issues.
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