Pascal Magne

New zirconia primer improves bond strength of resin-based cements

OBJECTIVE Various chemical interactions can be used to develop ceramic-resin bonding and specific approaches are available for zirconia ceramics. This study evaluated the effect of a new experimental primer, a mixture of organophosphate and carboxylic acid monomers, on the zirconia-to-resin shear bond strength (SBS). METHODS Forty Y-TZP blocks (15x4x2mm) were embedded in an acrylic resin base, polished, Al(2)O(3)-sandblasted and randomly divided into eight groups. Three different resin-based luting agents (BisCem, Duo-Link, Panavia F) were used to build 2.4mm-diameter cylinders (n=15) onto the zirconia surface with and without the new experimental zirconia primer. The new primer was also tested with Z100 restorative composite resin cylinders. In addition, Panavia was used with its own primer (Clearfil Ceramic Primer). SBS testing was carried out after 24h of storage in water. Scanning electron microscopy (SEM) was used to evaluate the zirconia surface topography and failure mode. RESULTS According to ANOVA and Tukey test (alpha=0.05), the association of the experimental primer with the restorative composite resin Z100 yielded the highest SBS (29.35MPa) followed by DuoLink with the new primer (26.68MPa). The groups that did not receive the experimental primer presented the lowest SBS values (from 5.95 to 9.79MPa). The failure mode was adhesive for the non-primed specimens and predominantly mixed in the primed groups. SIGNIFICANCE The use of the new zirconia experimental primer based on organophosphate/carboxylic acid monomers increased the bond strength of different resin-based luting agents including Z100 restorative material.

Immediate dentin sealing supports delayed restoration placement

STATEMENT OF PROBLEM Immediate dentin sealing (IDS) is a new approach in indirect restorations. Dentin is sealed immediately following tooth preparation, prior to impression making. It is not known whether it is still possible to obtain an efficient bond between the resin-coated dentin and the restoration after 2 to 4 months of placement of provisional restorations. PURPOSE The purpose of this study was to determine if there were differences in microtensile bond strength to human dentin using the IDS technique when comparing 2, 7, and 12 weeks of delay until restoration placement, using 2 different dentin bonding agents (DBAs). Previously published preliminary IDS data were included for comparison. MATERIAL AND METHODS Fifty freshly extracted human molars were obtained and divided into 10 groups. A 3-step etch-and-rinse DBA (Optibond FL) and a 2-step self-etching DBA (SE Bond) were used. For each DBA, the control (C) specimens were prepared using a direct immediate bonding technique and composite restoration (Z100). Preparation of the other specimens used an indirect approach without dentin prebonding (delayed dentin sealing, DDS) or with immediate dentin sealing (IDS), immediately following preparation. IDS teeth had provisional restorations (Tempfil inlay) placed for 2 weeks (IDS-2W), 7 weeks (IDS-7W), or 12 weeks (IDS-12W) before restoration placement. All teeth were prepared for a nontrimming microtensile bond strength test (MTBS) 24 hours after definitive restoration with composite overlays (Z100). Ten to 11 beams (0.9 x 0.9 x 11 mm) from each tooth were selected for testing. MTBS data obtained from the 10 experimental groups were analyzed with a 2-way analysis of variance (ANOVA, dentin bonding system, and sequence of application) with each tooth (mean MTBS from the 10-11 beams) used as a single measurement. The Tukey HSD post hoc test was used to detect pairwise differences among experimental groups (alpha=.05). Fractured beams were also analyzed under stereoscopic microscope (x 30) and SEM. RESULTS For both adhesives, the mean microtensile bond strengths of C and all IDS groups were not significantly different and exceeded 45 MPa. DDS groups exhibited lower bond strength than all others sequences (P<.001) with SE Bond at 1.81 MPa significantly lower (P=.026) than Optibond FL at 11.58 MPa. The highest mean microtensile bond strength values were found with Optibond FL at 7 weeks (66.59 MPa) and 12 weeks (59.11 MPa). These were significantly higher than SE Bond in the same conditions with values of 51.96 MPa and 45.76 MPa (P=.001 and P=.003), respectively. Failures in DDS groups were all interfacial and purely adhesive. Both C and IDS-2W groups demonstrated interfacial failure that was typically mixed with both areas of failed adhesive resin and areas of cohesively failed dentin while IDS-7W and IDS-12W failed consistently between the existing resin coating (used during IDS) and the overlaying composite resin. CONCLUSIONS When preparing teeth for indirect bonded restorations, IDS with a 3-step etch-rinse or a 2-step self-etching DBA (prior to impression making) results in microtensile bond strength similar to that obtained with a freshly placed adhesive. The bond strength is not affected by up to 12 weeks of elapsed time prior to placement of the definitive restoration.

Crack propensity of porcelain laminate veneers: A simulated operatory evaluation

STATEMENT OF PROBLEM Anterior teeth are especially subject to the thermal variations of ingested food and drinks. Postoperative cracks of porcelain laminates are considered a possible consequence of polymerization shrinkage, function, and thermocycling. PURPOSE This investigation was conducted to define the parameters associated with the development of cracks in porcelain veneers using cyclic thermal fatigue. MATERIAL AND METHODS Twenty-seven maxillary incisors were restored with porcelain laminate veneers and subjected to thermocycling (5 degrees C to 50 degrees C) for 1000 cycles. Ceramic cracks were reported for 11 of the 27 specimens. Teeth were sectioned and prepared for SEM analysis. Measurements of the ceramic and the luting composite thicknesses were performed for each specimen at different restoration locations (facial, incisal, and proximal). RESULTS No significant differences in the ceramic or the luting composite thicknesses were observed between cracked and uncracked specimens. However, significant differences were observed in the ratio of the ceramic and luting composite thicknesses. Most cracked samples exhibited a ratio at the facial location below 3.0 (2.6 +/- 0.35), whereas most noncracked specimens were above this value (3.9 +/- 0.19). Incisal and especially proximal measurements alone were not significantly different between cracked versus uncracked specimens. Ceramic was slightly thinner in the facial aspect than in the proximal aspect, which was also thinner than the incisal aspect. Composite in the facial aspect was thinner in the cervical area than in the incisal third of the tooth. CONCLUSIONS Significant cyclic temperature changes can induce the development of flaws in porcelain veneers. Control of tooth reduction and the application of die spacers during laboratory procedures undoubtedly represent key elements; a sufficient and even thickness of ceramic combined with a minimal thickness of luting composite will provide the restoration with a favorable configuration with regard to crack propensity, namely, a ceramic and luting composite thickness ratio above 3.

Wear of enamel and veneering ceramics after laboratory and chairside finishing procedures

PURPOSE This in vitro study compared the wear of enamel against 3 types of ceramics with high esthetic potential (designed for layering techniques): feldspathic porcelain (Creation), aluminous porcelain (Vitadur alpha), and low-fusing glass (Duceram-LFC). Laboratory finishing (glazing/polishing) and chairside polishing with a Dialite kit were simulated to compare their respective effects on wear. METHODS Tooth-material specimen pairs were placed in an artificial mouth using closed-loop servohydraulics. Constant masticatory parameters (13.5 N occlusal force, 0.62 mm lateral excursion; 0.23 second cuspal contact time) were maintained for 300, 000 cycles at a rate of 4 Hz. The occlusal surface of each pair was mapped and digitally recorded before and after each masticatory test. Quantitative changes were measured in terms of depth and volume of wear. Quantitative wear characteristics were assessed by SEM. RESULTS Significant differences were observed (2-factor ANOVA, P <.05). Duceram-LFC generated increased volume loss of enamel (0.197 mm(3)) compared with Creation (0.135 mm(3)) and Vitadur alpha (0.153 mm(3)). Creation exhibited the lowest ceramic wear and lowest combined volume loss (0.260 mm(3); the sum of the data for enamel and the opposing material) compared with Duceram-LFC (0.363 mm(3)) and Vitadur alpha (0.333 mm(3)). The most significant differences among materials were observed in volume loss, not in depth of wear. For all 3 ceramic systems, qualitative SEM evaluation revealed an abrasive type of wear. Wear characteristics of chairside polished specimens were similar to those of laboratory finished specimens (glazed and polished). CONCLUSION Duceram-LFC was the most abrasive ceramic for the antagonistic tooth. Creation ceramic was the least abrasive material and most resistant to wear. Defects, brittleness, and the possibly insufficient toughness of LFC may explain its increased abrasiveness. Laboratory and chairside finishing procedures generated similar results.

In vitro fatigue resistance of CAD/CAM composite resin and ceramic posterior occlusal veneers

STATEMENT OF PROBLEM Thin, bonded, posterior occlusal veneers constitute a conservative alternative to traditional complete coverage crowns. Information regarding selection of the appropriate material and its influence on fatigue resistance, which may affect the longevity of the restoration, is missing. PURPOSE The purpose of this study was to assess and compare the fatigue resistance of composite resin and ceramic posterior occlusal veneers. MATERIAL AND METHODS Thirty extracted molars received a standardized nonretentive tooth preparation (simulating advanced occlusal erosion), including removal of occlusal enamel, exposure of dentin, and immediate dentin sealing (Optibond FL). All teeth were restored with a 1.2-mm-thick occlusal veneer (Cerec 3 chairside CAD/CAM system). The restorations (n=10) were milled from leucite-reinforced and lithium disilicate ceramics (IPS Empress CAD and IPS e.max CAD, respectively) and a composite resin (Paradigm MZ100). The intaglio surfaces of the ceramic restorations were conditioned by hydrofluoric acid etching and silane. Airborne-particle abrasion and silane were used to condition the composite resin restorations. Preparations were airborne-particle abraded and etched. All restorations were bonded with preheated luting material and submitted to cyclic isometric loading at 5 Hz, starting with a load of 200 N (x5000 cycles), followed by stepwise loading of 400, 600, 800, 1000, 1200, and 1400 N at a maximum of 30,000 cycles each. The number of cycles at initial failure (first cracks) was recorded. Specimens were loaded for a maximum of 185,000 cycles. Groups were compared using the life table survival analysis (alpha=.016, Bonferroni method). RESULTS IPS Empress CAD failed at an average load of 900 N, with no specimen withstanding all 185,000 load cycles (survival 0%), while IPS e.max CAD and Paradigm MZ100 demonstrated survival rates of 30% and 100%, respectively. None of the specimens exhibited catastrophic failure, but only cracks limited to the restorative material. CONCLUSIONS Posterior occlusal veneers made of composite resin (Paradigm MZ100) had significantly higher fatigue resistance (P<.002) compared to IPS Empress CAD and IPS e.max CAD.

Novel-design ultra-thin CAD/CAM composite resin and ceramic occlusal veneers for the treatment of severe dental erosion

STATEMENT OF PROBLEM Ultra-thin bonded posterior occlusal veneers represent a conservative alternative to traditional inlays and complete coverage crowns for the treatment of severe erosive lesions. There is a lack of data regarding selection of the most appropriate material and its influence on fatigue resistance, which may affect restoration longevity. PURPOSE The purpose of this study was to assess the influence of CAD/CAM restorative material (ceramic vs. composite resin) on fatigue resistance of ultra-thin occlusal veneers. MATERIAL AND METHODS A standardized nonretentive tooth preparation (simulating advanced occlusal erosion) was applied to 40 extracted molars including removal of occlusal enamel, and immediate dentin sealing (Optibond FL). All teeth were restored with a 0.6 mm-thick occlusal veneer (Cerec3 chairside CAD/CAM system). Reinforced ceramics (Empress CAD and e.max CAD) and composite resins (Paradigm MZ100 and XR (experimental blocks)) were used to mill the restorations (n=10). The intaglio surfaces were HF-etched and silanated (reinforced ceramics) or airborne-particle abraded and silanated (composite resins). Preparations were airborne-particle abraded and etched before restoration insertion. All restorations were adhesively luted with preheated Filtek Z100. Cyclic isometric loading was applied at 5 Hz, beginning with a load of 200N (x5,000), followed by stages of 400, 600, 800, 1000, 1200 and 1,400N at a maximum of 30,000 cycles each. The number of cycles at initial failure (first cracks) was recorded. Specimens were loaded until catastrophic failure (lost restoration fragment) or to a maximum of 185,000 cycles. Groups were compared using the life table survival analysis (α=.008, Bonferroni-method). RESULTS Empress CAD and e.max CAD initially failed at an average load of 500N and 800N, respectively with no specimen withstanding all 185,000 load cycles (survival 0%); with MZ100 and XR the survival rate was 60% and 100%, respectively. CONCLUSIONS Both composite resins (MZ100 and XR) increased the fatigue resistance of ultra-thin occlusal veneers (P<.001) when compared to the ceramics evaluated (Empress CAD and e.max CAD).

Dental diamond burs made with a new technology.

STATEMENT OF PROBLEM Conventional diamond burs show several limitations such as the heterogeneity of grain shapes, the difficulty of automation during fabrication, the decrease of cutting effectiveness due to repeated sterilization, and short lifetime. An additional shortcoming may be represented by the potential release of Ni+2 ions from the metallic binder into the body fluids. PURPOSE This study investigated a new diamond rotative instrument made of a continuous diamond film obtained by chemical vapor deposition (CVD). This bur, characterized by a pure diamond cutting surface without metallic binder between crystals, was compared with a conventional diamond bur. MATERIAL AND METHODS Cutting tests were followed by SEM examination and electron microprobe analysis (EMA) to trace metallic residues both at the surface of the bur and the substrate. RESULTS EMA demonstrated that the metals Ni, Cr, Si, and Fe were present in the metallic binder matrix of the conventional bur and could be smeared on the surface of the substrate during cutting. SEM showed that significant loss of diamond particles occurred during cutting. On the other hand, no discrete particles sheared off the CVD bur. The smearing of the metallic binder cannot occur using the new bur. CONCLUSION The new CVD bur not only proves to be more efficient in its cutting ability and longevity, but also excludes the risk of metal contamination. This last aspect concerns both the pollution of the oral environment and the contamination of the ceramic during the laboratory manufacturing of dental restorations.

Thickness of CAD-CAM composite resin overlays influences fatigue resistance of endodontically-treated premolars

OBJECTIVES Evaluate the influence of composite resin CAD-CAM restoration thickness on the in vitro fatigue resistance and failure mode of overlay-type restoration in endodontically treated premolars. METHODS Thirty extracted premolars received root canal treatment followed by a standardized tooth preparation (1.5-, 2.5- or 3.5-mm cusp reduction, proximal gingival margins located 1.5mm below the CEJ, glass-ionomer base and immediately sealed dentin with Optibond FL). Restorations were milled using Cerec3 and FiltekMZ100 composite blocks. The intaglio surfaces of the overlays were sandblasted and silanated. Tooth preparations were sandblasted and etched before insertion of the restoration. All restorations were luted with Optibond FL and preheated FiltekZ100. A closed-loop servohydraulic unit was used for simulating cyclic isometric chewing at 5 Hz, starting with a load of 200 N (5000 cycles), followed by stages of 400, 600, 800, 1000, 1200 and 1400 N at a maximum of 30,000 cycles each. All samples were loaded until fracture or to a maximum of 185,000 cycles. Groups were compared using the Kaplan-Meier survival curves. RESULTS None of the restored premolars with the 1.5-mm cusp overlap restoration withstood all 185,000 loading cycles. With 2.5- and 3.5-mm cusp overlap, the survival rate was 30% and 40%, respectively. The rate of fracture below the CEJ was 60%, 60% and 30% for 1.5, 2.5 and 3.5 mm of cusp overlap, respectively. Survival of restored premolars with 2.5- and 3.5-mm cusp coverage was not significantly different (p=.23). SIGNIFICANCE Thick FiltekMZ100 composite resin onlays showed higher fatigue resistance than thin ones and may be associated with fractures that are less subgingival.

Fatigue resistance and crack propensity of large MOD composite resin restorations: Direct versus CAD/CAM inlays

OBJECTIVES To assess the influence of material/technique selection (direct vs. CAD/CAM inlays) for large MOD composite adhesive restorations and its effect on the crack propensity and in vitro accelerated fatigue resistance. METHODS A standardized MOD slot-type tooth preparation was applied to 32 extracted maxillary molars (5mm depth and 5mm bucco-palatal width) including immediately sealed dentin for the inlay group. Fifteen teeth were restored with direct composite resin restoration (Miris2) and 17 teeth received milled inlays using Paradigm MZ100 block in the CEREC machine. All inlays were adhesively luted with a light curing composite resin (Filtek Z100). Enamel shrinkage-induced cracks were tracked with photography and transillumination. Cyclic isometric chewing (5 Hz) was simulated, starting with a load of 200 N (5000 cycles), followed by stages of 400, 600, 800, 1000, 1200 and 1400 N at a maximum of 30,000 cycles each. Samples were loaded until fracture or to a maximum of 185,000 cycles. RESULTS Teeth restored with the direct technique fractured at an average load of 1213 N and two of them withstood all loading cycles (survival=13%); with inlays, the survival rate was 100%. Most failures with Miris2 occurred above the CEJ and were re-restorable (67%), but generated more shrinkage-induced cracks (47% of the specimen vs. 7% for inlays). SIGNIFICANCE CAD/CAM MZ100 inlays increased the accelerated fatigue resistance and decreased the crack propensity of large MOD restorations when compared to direct restorations. While both restorative techniques yielded excellent fatigue results at physiological masticatory loads, CAD/CAM inlays seem more indicated for high-load patients.

Diagnostic mock-ups as an objective tool for predictable outcomes with porcelain laminate veneers in esthetically demanding patients: A clinical report

This clinical report demonstrates how a clinician can objectively overcome some of the barriers associated with providing patients with predictable esthetics, in a mutually satisfactory manner. Two such barriers are identified and discussed. The first is related to psychology and patient attitude to treatment. The second is related to the actual clinical procedure. A direct mock-up technique is described which serves as an effective communication tool between the dentist, patient, and dental laboratory technician.