Jörg R. Strub

Fracture strength and survival rate of endodontically treated maxillary incisors with approximal cavities after restoration with different post and core systems: an in-vitro study

OBJECTIVES This study compared the fracture strength and survival rate of endodontically treated crowned maxillary incisors with approximal class III cavities and different core build-ups. METHODS Sixty-four caries free human maxillary central incisors were selected for standardized size and quality, endodontically treated and prepared with approximal cavities 3mm in diameter. Group 1 was restored with titanium posts, group 2 received zirconia posts, in group 3 the root canal was partially filled with a hybrid composite. In the control group, only the access opening was restored. All teeth were prepared for and restored with full cast metal alloy crowns and subsequently exposed to 1.2 million cycles in a computer-controlled chewing simulator with simultaneous thermocycling. In addition, the samples were loaded until fracture in a static testing device. RESULTS One specimen with composite reinforced root canal did not survive the dynamic load test. The following median fracture strengths in Newtons for the different groups were: titanium post 1038, zirconia 1057, composite resin 750, control (no post) 1171. The fracture load in group 3 (composite resin) was significantly lower (P<0.05) than in the other groups. CONCLUSIONS The reconstruction of endodontically treated single rooted teeth with approximal cavities can be successfully performed by closure of the endodontic and additional cavities with composite. Cementation of endodontic posts offers comparable but no advantageous fracture resistance. Enlargement of the root canal space after completion of endodontic treatment should be avoided and cannot be compensated for by injection of composite resin. Less catastrophic failures were observed without post reconstruction.

Shear bond strengths between different zirconia cores and veneering ceramics and their susceptibility to thermocycling.

OBJECTIVES The purpose of this study was to evaluate the shear bond strength between various commercial zirconia core and veneering ceramics, and to investigate the effect of thermocycling. METHODS The Schmitz-Schulmeyer test method was used to evaluate the core-veneer shear bond strength (SBS) of three zirconia core ceramics (Cercon Base, Vita In-Ceram YZ Cubes, DC-Zirkon) and their manufacturer recommended veneering ceramics (Cercon Ceram S, Vita VM9, IPS e.max Ceram). A metal ceramic system (Degudent U94, Vita VM13) was used as a control group for the three all-ceramic test groups (n = 30 specimens/group). Half of each group (n = 15) was thermocycled (5-55 degrees C, 20,000 cycles). Subsequently, all specimens were subjected to shear force in a universal testing machine. Fractured specimens were evaluated microscopically to determine the failure mode. RESULTS The initial mean SBS values in MPa+/-S.D. were 12.5+/-3.2 for Vita In-Ceram YZ Cubes/Vita VM9, 11.5+/-3.4 for DC-Zirkon/IPS e.max Ceram, and 9.4+/-3.2 for Cercon Base/Cercon Ceram S. After thermocycling mean SBS values of 11.5+/-1.7 MPa for DC-Zirkon/IPS e.max Ceram, 9.7+/-4.2 MPa for Vita In-Ceram YZ Cubes/Vita VM9, and 9.6+/-4.2 MPa for Cercon Base/Cercon Ceram S were observed. Neither the differences between the SBS values of the all-ceramic test groups nor the influence of thermocycling on all groups were statistically significant. Irrespective of thermocycling the metal ceramic control group (27.6+/-12.1 MPa, 26.4+/-13.4 MPa) exhibited significantly higher mean SBS than all three all-ceramic groups tested. The all-ceramic groups showed combined failure modes as cohesive in the veneering ceramic and adhesive at the interface, whereas the metal ceramic group showed predominately cohesive fractures. SIGNIFICANCE The results indicated that the SBS between zirconia core and veneering ceramics was not affected by thermocycling. None of the zirconia core and veneering ceramics could attain the high bond strength values of the metal ceramic combination.

Prosthetic outcome of cement-retained implant-supported fixed dental restorations: a systematic review.

The aim of the article is to assess the current literature in terms of the prosthetic outcome of cement-retained implant-supported fixed restorations, as well as to determine the type of cement that can be recommended for clinical application. A review of the literature published up to May 2010 was conducted to identify clinical studies about cement-retained implant-supported fixed restorations. The search strategy applied was a combination of MeSH terms and free text words, including the following keywords: implants, implant-supported fixed dental prostheses (FDPs), bridges, implant-supported single crowns (SCs), cement-retained, cement fixation, cement, cementation, cement failure, retention, and loss of retention, technical complications, mechanical complications, prosthetic complication, retrievability and maintenance. Thirty-two studies met the inclusion criteria. The studies were divided into two categories: 15 short-term clinical studies with an observation period of less than 5 years, and 17 long-term clinical studies with an observation period of 5 years and more. The most common technical complications of cement-retained implant-supported fixed restorations were loss of retention, chipping and abutment screw loosening. The results of the current review revealed no guidelines about cement or cementation procedures. It may be stated that despite the questionable retrievability of cement-retained implant-supported fixed restorations, this treatment modality is a reliable and effective option, especially for implant-supported SCs and short-span FDPs. The literature does not provide accurate information about the clinical outcome of cement-retained implant-supported fixed restorations nor about the ideal type of cement that facilitates stability and maintains retrievability. Standardised randomised clinical trials will provide valuable information to this issue.

BONDING TO ALUMINA CERAMIC IN RESTORATIVE DENTISTRY : CLINICAL RESULTS OVER UP TO 5 YEARS

OBJECTIVES The purpose of this clinical pilot study was to evaluate the resin bond to alumina ceramic in vivo when using a bonding method which had been shown to be successful in laboratory testing. METHODS Seventeen resin-bonded all-ceramic bridges and splints fabricated from a glass-infiltrated alumina ceramic were tribochemically silica coated and resin bonded to their abutment teeth. The patients were recalled every 6 months to evaluate the restorations with regard to function and possible failures. RESULTS Over a mean observation time of 3.8 +/- 1.6 years some ceramic fractures occurred. However, the resin bond between the teeth and the alumina ceramic always remained stable. CONCLUSIONS Silica coating of alumina ceramic resulted in a durable resin bond over up to 5 years.

Marginal adaptation of three different zirconium dioxide three-unit fixed dental prostheses

STATEMENT OF PROBLEM Marginal adaptation is important for the long-term success of dental restorations. Data on the marginal discrepancy of zirconia-based fixed dental prostheses made with different computer-aided design/computer-aided manufacturing technology is needed. PURPOSE The purpose of this study was to evaluate the marginal adaptation of different zirconia 3-unit fixed dental prostheses at different fabrication stages and after artificial aging. MATERIAL AND METHODS Twenty-four zirconia 3-unit fixed dental prostheses (DCS, Procera, and VITA YZ-Cerec; n=8) were fabricated using different manufacturing systems and conventionally cemented with glass ionomer cement on human teeth. Each group was aged in a masticatory simulator with thermal cycling. The marginal gaps were examined on epoxy replicas for frameworks and for restorations before and after cementation, and after masticatory simulation, at x 250 magnification. Marginal adaptation was assessed using geometric means of the marginal gap values with 95% confidence intervals. Differences between the manufacturing systems and the effect of artificial aging were tested using repeated-measures ANOVA and post hoc paired and unpaired t tests with Bonferroni-Holm correction (alpha=.05). RESULTS The geometric mean (95% confidence limits) marginal gap values (mum) for frameworks and for restorations before cementation, after cementation, and after masticatory simulation were, respectively: DCS: 86 (80-93), 86 (83-90), 86 (78-94), and 84 (79-90); Procera: 82 (74-89), 89 (81-97), 89 (84-95), and 88 (82-94); and VITA YZ-Cerec: 64 (57-72), 67 (61-77), 76 (71-82), and 78 (76-80). The repeated-measures ANOVA showed significant group and stage effects (P<.05). Group VITA YZ-Cerec showed significantly smaller marginal gap values than groups DCS and Procera at framework (P<.05) and before-cementation (P<.05) stages. The VITA YZ-Cerec group showed significantly smaller marginal gap values than the Procera group after cementation (P<.05). The marginal gap values between different stages were not significantly different for all groups (P>.05). CONCLUSIONS The marginal accuracy of zirconia fixed dental prostheses is influenced by manufacturing technique.

Fracture strength of all-porcelain, resinbonded bridges after testing in an artificial oral environment

Twenty all-porcelain In-Ceram bridges were resin bonded to natural teeth on a study model. Ten of the test specimens were fixed on abutments placed directly in resin, and 10 were supported by an artificial periodontal membrane. Incisal forces of physiological magnitude and direction were applied in three bridges of both groups (test samples) in an artificial oral environment (1250,000 cycles). The fracture strength of the six test and 14 control specimens was tested in a universal testing instrument and the rupture strength measured. There was no significant difference between the fracture strength of the test and control samples. The artificial periodontal membrane around the abutment teeth did not reduce the fracture strength of the In-Ceram bridges.

Prognosis of immediately loaded implants and their restorations: a systematic literature review

Immediate loading of oral implants has become popular because of the increasing demands of a shortened treatment time. This literature review evaluates the prognosis of immediately loaded implants and their restorations with immediate or delayed implant placement. Special attention was given to the impact of type of jaw, bone quality, implant length, time of implant placement and type of restoration. An electronic (PubMed) and a manual search in relevant journals were conducted until February 2012. Only publications in English, in peer-reviewed journals, were considered. Nine studies met the inclusion criteria: five studies dealt with fixed restorations, two studies with removable rehabilitation of edentulous jaws and two studies dealt with partially edentulous patients. Implant survival rates ranged from 95·8% to 100%, implant success rates in the treatment for the mandible from 79% to 100% and restoration survival rates for both jaws from 96·4% to 100%. Within the limits of this review, appropriate patient selection, primary implant stability, splinting of implants and the expertise of surgeons seem to be important for the prognosis of immediately loaded implants and their restorations. Good bone quality and use of long implants appear to play a role. However, careful interpretation is required because conclusions are based on articles with low level of evidence. While immediate loading of oral implants in the mandible shows encouraging and predictable results, further multicenter randomised controlled clinical trials with sufficient statistical power are needed to examine (i) the outcome of immediately loaded implants in the maxilla and (ii) the outcome of immediate loading of immediately placed implants.

Influence of design and mode of loading on the fracture strength of all-ceramic resin-bonded fixed partial dentures: An in vitro study in a dual-axis chewing simulator

STATEMENT OF PROBLEM In a clinical study, all-ceramic resin-bonded fixed partial dentures showed a high rate of fractures within the first years of service but remained in function as cantilevered restorations. No data are available on the fracture strength of such cantilevered restorations. PURPOSE This in vitro study evaluated the influence of design and mode of loading on the fracture strength of all-ceramic resin-bonded fixed partial dentures. MATERIAL AND METHODS Forty-eight frameworks were copy milled using the aluminum-oxide ceramic In-Ceram, glass-infiltrated, and circularly veneered with feldspathic porcelain to replace a maxillary incisor on a test cast. The airborne particle-abraded restorations were bonded to acid-etched human abutments using composite. Twenty-four restorations used a conventional 2-retainer design and another 24 restorations used a cantilevered single-retainer design. Subgroups of 8 specimens were subjected to a quasi-static load in the direction of the long axis of the abutments (0 degrees) or in an angle of 45 degrees. Additional subgroups were subjected to dynamic loading under 45 degrees with either 50 or 25 N in a dual-axis chewing simulator until fracture. RESULTS Mean fracture strengths, under 45-degree quasi-static loading, were between 134 and 174 N and under 0-degree loading about 233 N. Samples subjected to dynamic loading fractured after 25 to over 200,000 loading cycles. CONCLUSION Direction of loading exhibited a significant influence on the fracture strength, regardless of the retainer design. The applied dynamic loading force, regardless of the retainer design, had a significant influence on the loading cycles until fracture.

Influence of water storage and thermal cycling on the fracture strength of all-porcelain, resin-bonded fixed partial dentures

The purpose of this in vitro study was to evaluate the influence of water storage and thermal cycling on the fracture strength of two designs of all-porcelain, resin-bonded fixed partial dentures made with the glass-infiltrated alumina ceramic In-Ceram. Forty frameworks of In-Ceram ceramic veneered with Vitadur-N porcelain were made to replace an upper central incisor bonded to extracted natural teeth. In 20 of the restorations the pontic was veneered only labially with Vitadur-N porcelain and no proximal box preparations were made (design A). The other 20 restorations had additional box preparations proximal to the pontic and the In-Ceram ceramic pontic framework was shifted to the labial aspect and veneered circumferentially with Vitadur-N porcelain (design B). Subgroups of 10 restorations were stored for 7 days in thymol solution or alternatively for 150 days in artificial saliva with thermal cycling for 18,750 cycles between 5 degrees and 55 degrees C. Restorations with design B had a statistically significantly higher fracture strength than restorations with design A. Storage in artificial saliva with thermal cycling significantly reduced the fracture strength of the resin-bonded In-Ceram fixed partial dentures. Therefore, the long-term clinical behavior of resin-bonded In-Ceram fixed partial dentures must be evaluated before general clinical use can be recommended.

Influence of framework configuration on the marginal adaptation of zirconium dioxide ceramic anterior four-unit frameworks

Objective. To evaluate the influence of the framework configuration on the marginal adaptation of four-unit anterior fixed partial denture (FPD) frameworks made of partially sintered zirconium dioxide (ZrO2) ceramics. Material and methods. Forty-eight standardized partially sintered ZrO2 ceramic four-unit FPD frameworks were fabricated using three different CAD/CAM systems: Cercon Smart Ceramics (group CE), Vita YZ/Cerec In-Lab (group YZ/CL), and Xawex (group XA). Two different framework configurations (straight and curved) were manufactured for each group. The marginal adaptation of the frameworks was measured at 60 different points across the entire circumferential margin using a stereomicroscope. Marginal discrepancy values were compared between the two framework designs and between the three test groups using the t-test. The overall level of statistical significance was 5% after correcting the p-values using the Bonferroni–Holm method. Results. The following geometrical means of the marginal discrepancies were obtained for the curved/straight design: group CE, 120.0 μm/88.0 μm; group YZ/CL, 96.8 μm/86.5 μm; and group XA, 147.3 μm/113.4 μm. Significant differences were detected between the straight and curved designs for groups CE (p=0.001) and XA (p=0.003), but not for group YZ/CL (p=0.225). For both designs, the marginal discrepancies were significantly smaller in group YZ/CL than in group XA. For the curved design, the marginal discrepancies in group YZ/CL were also significantly smaller than those in group CE. Conclusions. Within the limitations of this study, the framework configuration influences the marginal adaptation of anterior four-unit FPD frameworks that are manufactured from partially sintered ZrO2 ceramics independently of CAD/CAM system.