Daniel A. Givan

Fracture resistance and marginal discrepancy of porcelain laminate veneers influenced by preparation design and restorative material in vitro.

OBJECTIVES The purpose of this investigation is to evaluate marginal discrepancy and fracture resistance of two veneering materials using two preparation designs. METHODS Two veneer preparation designs (full and traditional) were restored with leucite-reinforced ceramic (ProCAD, Ivoclar Vivadent, Amherst, NY) milled by CAD/CAM (Cerec 3D milling system, Serona Dental Systems), and conventional sintered feldspathic porcelain (Noritake Super Porcelain EX3, Noritake Dental Supply Co). Forty-eight specimens were analysed with a sample size of n=12 per group. The thickness of each veneer was measured on four specific surfaces. Marginal discrepancy was evaluated with a replica technique and cross-sectional view using a digital microscope. The fracture resistance of veneers cemented on standardised composite resin dies was evaluated using a universal testing machine. Results were analysed with ANOVA, Tukey-Kramer post hoc testing, and linear regression. RESULTS The results of this investigation revealed no correlation between the thickness and marginal discrepancy of the veneers. The full preparation design with ProCAD and the traditional preparation design with feldspathic porcelain manifested smaller gap. Fracture resistance was decreased for the full preparation design with feldspathic porcelain. CONCLUSIONS In terms of marginal discrepancy and fracture resistance, the most favourable combination was a traditional veneer preparation design with conventional sintered feldspathic porcelain. For the full veneer preparation, a stronger ceramic material such as ProCAD is suggested.

Influence of surface treatment of yttrium-stabilized tetragonal zirconium oxides and cement type on crown retention after artificial aging

STATEMENT OF PROBLEM Information about the influence of zirconia crown surface treatment and cement type on the retention of zirconia crowns is limited. It is unclear whether zirconia crowns require surface treatment to enhance their retention. PURPOSE The purpose of this in vitro study was to evaluate the effect of surface treatment on the retention of zirconia crowns cemented with 3 different adhesive resin cements after artificial aging. MATERIAL AND METHODS Ninety extracted human molars were prepared for ceramic crowns (approximately 20-degree taper, approximately 4-mm axial length) and were divided into 3 groups (n=30). Computer-aided design and computer-aided manufacturing zirconia copings were fabricated. Three surface treatments were applied to the intaglio surface of the copings. The control group received no treatment, the second group was airborne-particle abraded with 50 μm Al2O3, and the third group was treated with 30 μm silica-modified Al2O3, The copings were luted with a self-etch (RelyX Unicem 2), a total-etch (Duo-Link), or a self-etch primer (Panavia F 2.0) adhesive cement. They were stored for 24 hours at 37°C before being artificially aged with 5000 (5°C-55°C) thermal cycles and 100,000 cycles of 70 N dynamic loading. Retention was measured on a universal testing machine under tension, with a crosshead speed of 0.5 mm/min. Statistical analysis was performed with 1-way and 2-way ANOVA. RESULTS Mean retention values ranged from 0.72 to 3.7 MPa. Surface treatment increased crown retention, but the difference was not statistically significant (P>.05), except for the Duo-Link cement group (P<.05). Analysis of the adhesives revealed that the Duo-Link cement resulted in significantly lower crown retention (P<.05) than the other 2 cements. CONCLUSION For zirconia crowns, retention seems to be dependent on cement type rather than surface treatment.

The Effect of Etching Technique on the Retention of Adhesively Cemented Prefabricated Dowels

PURPOSE To determine if etching technique influences the bond strength of resin cement to root canal dentin. MATERIALS AND METHODS Fifty-five extracted teeth were endodontically treated, dowel space prepared, and divided into five groups. Each group was treated with different etchant consistencies: acid gel, semi-gel, low-viscosity gel, liquid, and a self-etching primer. After dowel cementation, four sections were removed from each root and a push-out test was performed. RESULTS Significant effects were found for etching procedure and for location within the root canal. The apical segment produced the lowest bond strength. Self-etching primer showed the highest bond strength. CONCLUSIONS The consistency of etchant material influenced the bond strength of a prefabricated dowel in the canal.

Factors influencing the progression of noncarious cervical lesions: A 5-year prospective clinical evaluation

STATEMENT OF PROBLEM The etiology (chemical, friction, abfraction) of noncarious cervical lesion (NCCL) progression is poorly understood. PURPOSE The purpose of this 5-year prospective clinical trial was to measure the relationship between NCCLs and various etiologic factors. MATERIAL AND METHODS After review board approval, 29 participants with NCCLs were enrolled. Polyvinyl siloxane impressions were made of each NCCL, and casts were poured at baseline, 1, 2, and 5 years. The casts were scanned with a noncontact profilometer, and 1-, 2-, and 5-year scans were superimposed over baseline scans to measure volumetric change in NCCLs. T-scan and Fujifilm Prescale films were used to record relative and absolute occlusal forces on teeth with NCCLs at the 5-year recall. Participant diet, medical condition, toothbrushing, and adverse oral habit questionnaires were given at the 5-year recall. Occlusal analysis was completed on mounted casts to determine the presence of wear facets and group function. Volumetric lesion progression from 1 to 5 years was correlated to absolute and relative occlusal force using mixed model analysis. The Kruskall-Wallis and Mann-Whitney analyses compared lesion progression with diet, medical condition, toothbrushing, adverse oral habits, wear facets, and group function. RESULTS The NCCL progression rate over 5 years was 1.50 ±0.92 mm(3)/yr. The rate of progression of NCCLs was related to mean occlusal stress (P=.011) and relative occlusal force (P=.032) in maximum intercuspation position. No difference was seen in NCCL progression between participants with any other factors. CONCLUSION Heavy occlusal forces play a significant role in the progression of NCCLs.

Comparison of the Passivity between Cast Alloy and Laser-Welded Titanium Overdenture Bars

PURPOSE The purpose of this study was to investigate the fit of cast alloy overdenture and laser-welded titanium-alloy bars by measuring induced strain upon tightening of the bars on a master cast as well as a function of screw tightening sequence. MATERIALS AND METHODS Four implant analogs were secured into Type IV dental stone to simulate a mandibular edentulous patient cast, and two groups of four overdenture bars were fabricated. Group I was four cast alloy bars and Group II was four laser-welded titanium bars. The cast alloy bars included Au-Ag-Pd, Pd-Ag-Au, Au-Ag-Cu-Pd, and Ag-Pd-Cu-Au, while the laser-welded bars were all Ti-Al-V alloy. Bars were made from the same master cast, were torqued into place, and the total strain in the bars was measured through five strain gauges bonded to the bar between the implants. Each bar was placed and torqued 27 times to 30 Ncm per screw using three tightening sequences. Data were processed through a strain amplifier and analyzed by computer using StrainSmart software. Data were analyzed by ANOVA and Tukeys post hoc test. RESULTS Significant differences were found between alloy types. Laser-welded titanium bars tended to have lower strains than corresponding cast bars, although the Au-Ag-Pd bar was not significantly different. The magnitudes of total strain were the least when first tightening the ends of the bar. CONCLUSIONS The passivity of implant overdenture bars was evaluated using total strain of the bar when tightening. Selecting a high modulus of elasticity cast alloy or use of laser-welded bar design resulted in the lowest average strain magnitudes. While the effect of screw tightening sequence was minimal, tightening the distal ends first demonstrated the lowest strain, and hence the best passivity.

Two-year Randomized, Controlled Clinical Trial of a Flowable and Conventional Composite in Class I Restorations

OBJECTIVES This study evaluated the two-year clinical performance and volumetric wear of a flowable resin composite compared to a conventional highly filled composite resin in Class I restorations. METHODS AND MATERIALS In this single-center, single-blinded, comparator-controlled clinical study (Institutional Review Board approved), 120 carious teeth distributed in 60 patients were randomly assigned to four calibrated practitioners who placed occlusal restorations (n=60 flowable and n=60 conventional composite). Direct and indirect assessment at baseline, six months, one year, and two years occurred during which the modified Cvar and Ryge criteria were evaluated. Volumetric wear was determined by superimposition of profilometer scans of baseline and two-year casts. RESULTS At two years, there was no significant difference in anatomic form (p=0.80), color match (p=0.08), marginal adaptation (p=0.89), marginal discoloration (p=0.79), surface integrity (p=0.18), secondary caries (p=0.66), cold sensitivity (p=0.522), occlusal sensitivity (p=0.818), or volumetric wear (p=0.661) between materials. Both materials showed a decrease in all criteria except secondary caries (p=0.95) over time. Two-year mean volumetric wear was 3.16 ± 2.38 mm(3) for the flowable composite and 3.43 ± 2.50 mm(3) for the conventional composite. CONCLUSIONS The flowable and conventional composites used in this study have similar clinical efficacy after two years of service when placed as Class I occlusal restorations having isthmus widths less than one-half the intercuspal distance.

Sectional Impressions and Simplified Folding Complete Denture for Severe Microstomia

A patient presenting with severe microstomia (PDI Class IV) was unable to insert a maxillary complete denture. Sectional final impressions were made using two impression materials and an interlocking custom tray. A folding record base was used for maxillomandibular relationship records. A novel folding maxillary denture with a custom hinge and plunger attachment to lock the denture in the open position was fabricated. The patient was able to insert the collapsed denture, open it intraorally, and enjoy successful masticatory function.

Light-transmitting fiber optic posts: An in vitro evaluation

Statement of problem. The clinical challenge of adhering cement to intracanal dentin is transmitting light to the most apical parts of root canals to allow more efficient polymerization of the cement. Purpose. The purpose of this in vitro study was to compare the cement‐polymerizing ability, microstructure, and radiopacity of a new fiber optic post (iLumi fiber optic Post) with a clinically successful fiber post (DT Light Post). Material and methods. Polymerizing ability was compared using a modified depth‐of‐polymerization protocol. A split aluminum mold with a 12‐mm cylindrical hole (diameter=4.7 mm) was filled with light‐polymerized resin cement (Variolink Esthetic LC). Each fiber post (n=12) was positioned and light‐polymerized on the coronal end for 60 seconds with a light‐emitting diode polymerization light. Unpolymerized resin was dissolved with an organic solvent, and the weight and length of the polymerized resin cement were measured. Scanning electron microscopy was used to examine vertical and horizontal cross‐sections. The radiopacity values of both the posts and 5 additional reference posts were evaluated using an aluminum step wedge. Results. The weight and length of the polymerized resin cement were significantly greater (P<.05) with the fiber optic post, which scanning electron microscopy showed to have a higher density of parallel fibers. The iLumi post demonstrated greater radiopacity among the tested fiber posts and a titanium alloy post. Conclusions. The iLumi fiber optic posts have a unique structural fiber composition and excellent radiopacity and light‐transmitting ability that produce more complete polymerization of the resin cement than the DT Light posts.

Retentive Force of Zirconia Implant Crowns on Titanium Bases Following Different Surface Treatments.

PURPOSE Screw-retained zirconia implant crowns with an internal titanium base have favorable mechanical properties compared with single-piece zirconia implant crowns; however, the screw-retained implant crowns require adequate bonding between the zirconia crown and the titanium base. This study measured the retention between a titanium base and a full-contour zirconia implant crown following different surface treatments of their bonded surfaces. MATERIALS AND METHODS Full-contour screw-retained zirconia implant crowns were fabricated to fit a titanium base. The crowns were bonded to the titanium bases following one of four treatment protocols (n = 15 per protocol group): no surface treatment (Control), 10-methacryloyloxydecyl dihydrogen phosphate (MDP) primer on the intaglio of crown and exterior of base (MDP), alumina airborne-particle abrasion of the intaglio of crown and exterior of base (Alu), and alumina airborne-particle abrasion and an MDP primer on the intaglio of crown and exterior of base (Alu+MDP). All crowns were bonded to the base with resin cement. Specimens were stored in water for 24 hours at 37°C and then thermocycled in water, with a temperature range of 5°C to 55°C, for 15,000 cycles with a 15-second dwell time. Crowns were separated from the titanium bases using a universal testing machine. The four treatment protocols were compared using one-way analysis of variance (ANOVA), followed by Tukey post hoc tests (P < .05). Sectioned specimens were examined with scanning electron microscopy (SEM). RESULTS Retention forces for Control (737.8 ± 148.9 N) and MDP (804.1 ± 114.5 N) were significantly greater than Alu+MDP (595.5 ± 122.2 N), which was significantly greater than Alu (428.2 ± 93.8 N). Visual inspection of the debonded specimens showed that the majority of the cement remnants were seen on the external surface of the titanium bases. Microscopic examination of the interface between the crown and the unaltered base shows that the cement gap is approximately 13 μm at the crest of the microgrooves and 50 μm within the channel of the microgrooves. After airborne-particle abrasion, the microgrooves became significantly dulled, and the cement gap increased to 27 to 40 μm at the crest and 55 to 58 μm in the channels. CONCLUSION Airborne-particle abrasion of titanium bases that contain retentive microgrooves prior to bonding is contraindicated. Application of an MDP primer demonstrated limited improvement in the retention of the zirconia implant crowns.

A method of removing a splint material from a cast with minimal damage

Londono and Marafie Givan and AuClair Thin vacuum-formed materials are used for a variety of purposes in dentistry, including: as a matrix for provisional restorations, for vertical and horizontal space assessment, or as surgical guides for implant placement, crown lengthening, and other preprosthetic surgical procedures. A clinician may desire a set of unaltered casts for presentation purposes, and most methods to remove a vacuumformed matrix will result in scratching or otherwise marring the cast. A simple procedure to remove a matrix while minimizing damage to casts is presented. In this method, a mounted bristle brush or similar short-bristle rotary brush is used with light pressure and rapid rotation in a straight handpiece or laboratory motor to efficiently cut the splint material. Alternative methA method of removing a splint material from a cast with minimal damage