Clinical performance of chairside monolithic lithium disilicate glass-ceramic CAD-CAM crowns.

OBJECTIVES: To evaluate the clinical performance and the effect of various patient and provider-related factors on the longevity of chairside monolithic posterior lithium disilicate glass-ceramic (LDGC) computer-aided design (CAD)-computer-aided manufacturing (CAM) crowns provided by predoctoral students. MATERIALS AND METHODS: A sample of posterior LDGC CAD-CAM crowns was evaluated. Crown preparations were milled chairside using the CEREC Omnicam system and cemented with Rely-X Unicem or Calibra Universal resin cements. Clinical assessment of the crowns and supporting periodontal structures was performed using the modified California Dental Association (CDA) criteria. Intraoral photographs as well as radiographs were taken for further assessment by two evaluators. Kaplan-Meier survival analysis was performed. RESULTS: A total of 40 crowns were inserted in 32 patients and evaluated for 4 years. Three complications were observed (two-technical and one-biological). No chipping or fracture of crowns was observed. No significant association was found between age, sex, periodontal condition, tooth type, tooth vitality, cement type, and longevity. The 4-year cumulative survival and success rates were 95.0 and 92.3%, respectively. CONCLUSION: Chairside LDGC CAD-CAM crowns exhibited a high survival rate after 4 years in function and were shown to be a viable and reliable treatment option for posterior teeth. CLINICAL SIGNIFICANCE: The high survival rate of chairside CAD-CAM crowns observed in this study suggests the likelihood of predictable performance in the predoctoral setup.

New 3D technologies applied to assess the long-term clinical effects of misfit of the full jaw fixed prosthesis on dental implants.

OBJECTIVES: To assess implant:suprastructure misfit in patients with an edentulous jaw restored by an implant-retained fixed dental prosthesis (FDP) and its association with biologic and mechanical adverse events over an extensive period. MATERIAL AND METHODS: Thirty patients with an edentulous mandible treated with implant-supported prosthetics before 2000 were examined clinically in 2012. Each patient had received 4 to 6 implants to retain a FDP made from acrylic and three different metal alloys, that is, Ag-Pd, Pd-Ag, and Au type IV. The implant intra-oral locations were recorded digitally by use of an intra-oral scanner, and the intaglio surface of the detached FDP was recorded using a desktop scanner. The fit was estimated by digital matching of the STL files using industrial metrological software. The average misfit was correlated with the average marginal bone loss and the prevalence of screw loosening or fractures, using the patient as the statistical unit. RESULTS: Over an average of 19 years (range 12 to 32), 5 implants had been lost in 4 participants (96.7% implant survival) and 8 eight prostheses (26.7%) had been remade. Anaverage misfit was 150 µm (SD 35, range 95-232, CI 138-163). An average marginal bone loss of 2.2 mm (SD = 0.7) had occurred (range 0.6 to 5.8 mm) for individual implants. The correlation between framework misfit and marginal bone loss was weak (R² = 0.04) (P = 0.29). The prostheses with a history of screw-related adverse events showed average misfit of 169 µm (SD = 32) vs. those with no history of screw-related adverse events, that is, 134 µm (SD = 30) (P = 0.005, Student's t-test). Fourteen of the 30 participants had experienced at least one incidence of screw loosening or fracture of prosthetic or abutment screw(s) over the period of follow-up. The occurrence among the frameworks fabricated with different metal alloys did not differ (P > 0.05, Fisher's exact test). CONCLUSIONS: Combining STL files with best-fit algorithms to appraise misfit is feasible using metrological software. The effect of misfit between the superstructures on its supporting implants up to ~230 µm on the long-term clinical outcomes appears to be minor, apart from a slightly higher risk of screw-related adverse events.

Simulated occlusal adjustments and their effects on zirconia and antagonist artificial enamel.

PURPOSE: The aim of this study was to evaluate the effect of occlusal adjustments on the surface roughness of yttria-tetragonal zirconia polycrystal (Y-TZP) and wear of opposing artificial enamel. MATERIALS AND METHODS: Twenty-five Y-TZP slabs from each brand (Lava, 3M and Bruxzir, Glidewell Laboratories) with different surface conditions (Control polished - CPZ; Polished/ground - GRZ; Polished/ground/repolished - RPZ; Glazed - GZ; Porcelain-veneered - PVZ; n=5) were abraded (500,000 cycles, 80 N) against artificial enamel (6 mm diameter steatite). Y-TZP roughness (in µm) before and after chewing simulation (CS) and antagonist steatite volume loss (in mm3) were evaluated using a contact surface profilometer. Y-TZP roughness was analyzed by three-way analysis of variance (ANOVA) and teatite wear by two-way ANOVA and Tukey Honest Difference (HSD) (P=.05). RESULTS: There was no effect of Y-TZP brand on surface roughness (P=.216) and steatite loss (P=.064). A significant interaction effect (P<.001) between surface condition and CS on Y-TZP roughness was observed. GZ specimens showed higher roughness after CS (before CS - 3.7 ± 1.8 µm; after CS - 13.54 ± 3.11 µm), with partial removal of the glaze layer. Indenters abraded against CPZ (0.09 ± 0.03 mm3) were worn more than those abraded against PVZ (0.02 ± 0.01 mm3) and GZ (0.02 ± 0.01 mm3). Higher wear caused by direct abrasion against zirconia was confirmed by SEM. CONCLUSION: Polishing with an intraoral polishing system did not reduce the roughness of zirconia. Wear of the opposing artificial enamel was affected by the material on the surface rather than the finishing technique applied, indicating that polished zirconia is more deleterious to artificial enamel than are glazed and porcelain-veneered restorations.

Physical properties and cytotoxicity of antimicrobial dental resin adhesives containing dimethacrylate oligomers of Ciprofloxacin and Metronidazole.

OBJECTIVE: Antimicrobial oligomers synthesized from ciprofloxacin (CF) and metronidazole (MN) were investigated for their potential use in dental adhesives. METHODS: Susceptibility of the cariogenic bacterium Streptococcus mutans UA159 to CF, MN, and CF/MN combination was evaluated. Hydrolytic stability and drug release from the oligomers was studied in buffer and simulated human salivary esterase conditions. Cytotoxicity of films with 15wt% drug oligomers co-polymerized with commercial monomers were assessed using human gingival fibroblasts (HGFs). In-house adhesives were prepared and characterized for viscosity. Polymerized films were analysed for gel content and water swelling. Interfacial fracture toughness (KIC) of composites bonded to dentin by either a 2 or 3-step etch-and-rinse approach using the in-house formulated adhesives was measured. RESULTS: The respective minimum inhibitory concentration for CF and MN against S. mutans was 0.7 and 2400µg/mL, with the combination having an additive effect (0.35µg/mL CF with 1200µg/mL MN). Antibiotics were released upon hydrolysis of the oligomers. Films containing the drug oligomers were not cytotoxic against HGFs. Replacing 2-hydroxyethyl methacrylate with the drug oligomers increased the viscosity of the experimental adhesives, reduced gel content, and decreased swelling of films in water. Antimicrobial adhesives demonstrated bonding to dentin with interfacial KIC values comparable to the in-house control in the 2-step application, and with slightly lower KIC values in the 3-step approach. SIGNIFICANCE: The antimicrobial oligomers can be incorporated into dental adhesive systems using formulations that show comparable fracture toughness to commercial materials, and may provide a means to deliver local antimicrobial drug release at the marginal interface.

Benchmarking Outcomes in Implant Prosthodontics: Partial Fixed Dental Prostheses and Crowns Supported by Implants with a Turned Surface over 10 to 28 Years at the University of Toronto.

PURPOSE: The aim of this noninterventional, retrospective study was to benchmark the outcomes of patients with partial fixed prostheses supported by implants treated at the University of Toronto at least 10 years earlier. A study protocol for assessing outcomes on like patients developed at the University of Bern, Switzerland, was followed. MATERIALS AND METHODS: All patients who had received at least one implant before 2002 were considered eligible to be included in the study (n = 298). The treatment histories were recorded from the patient chart of the participants, or from the participants' dentists by consent. Calibrated clinicians examined the study participants clinically and radiologically and recorded peri-implant mucosal status and observable technical and mechanical failures. Past adverse events were identified in the patient charts. Independent assessors measured bone levels on digitized radiographs. Statistical analysis included descriptive statistics at implants, teeth, and study participant levels, respectively. RESULTS: Of the 298 eligible patients, 121 attended a clinical examination (41%), while 12 declined (4%). The 121 study participants had received 321 implants between 1983 and 2001. The implants showed a success rate of 88.9% and a survival rate of 94% after an average of 17.5 years (SD 5.2, range 10 to 28 years). Approximately 5% of the surviving implants showed signs, or were associated with a prior history, of peri-implantitis. The distance from the implant shoulder to the first bone contact varied from -3 mm to 7 mm (mean = 1.52 mm [SD 1.57], median = 2.2 mm). Approximately half of the study participants had experienced at least one defect of their superstructure, representing a 52% "success rate," while the survival rate was 70%. The majority were very satisfied or satisfied with the treatment (102/121). CONCLUSION: A high proportion (94%) of conventional machined Brånemark System implants placed between 1983 and 2001 remained in function after an average of 17.5 years. The original superstructures predominantly fabricated as prefabricated acrylic teeth and acrylic resin reinforced with a cast palladium-silver alloy core were still in place for 70% of the participants, and 48% of the superstructures had never undergone any form of repairs.

Intensity of quartz-tungsten-halogen light-curing units used in private practice in Toronto.

BACKGROUND: The authors conducted a study to determine light intensity and heat/glare measurements of quartztungsten-halogen (QTH) light polymerization units used in dental offices. METHODS: Research assistants visited 100 dental offices and assessed 214 QTH light units. They recorded each unit's model, age, service history, light intensity and heat/glare emissions. RESULTS: Mean light intensity was 526 milliwatts per square centimeter (120-1,000 mW/cm2), with 26 units having intensity less than 300 mW/cm2. The mean light unit age was 5.6 years. Light units older than three years had significantly lower output intensities than those that were one, two or three years old. The authors found a wide range of heat/glare measurements (3-300 mW/cm2), with 4.6 percent of the units having values greater than 50 mW/cm2, including three with values of more than 200 mW/cm2. The mean light intensity of units serviced in the preceding year was 539 mW/cm2; it was 418 mW/cm2 for units serviced from one to six years previously. CONCLUSIONS: Light intensity and heat/glare values varied among the 214 units; some units had values well outside the recommended levels. Each unit's age and service history significantly affected its intensity. An awareness campaign is needed to promote testing, repair or replacement of light polymerization units. Periodic testing of light polymerization units should be considered by regulatory bodies to ensure optimum quality of composite restorations. CLINICAL IMPLICATIONS: Light polymerization units in some private dental offices in Toronto had intensities that may result in composites restorations with inferior properties. Dentists need to regularly monitor the intensity of the light polymerization units and maintain the units to ensure quality composite restorations.

Efficacy of halogen photopolymerization units in private dental offices in Toronto.

PURPOSE: Light units used for polymerization of resin composites are subject to deterioration with age, and frequent maintenance is required to maintain optimal efficacy. This study examined the efficacy of quartz-tungsten-halogen light units in private dental offices in Toronto for polymerization of resin composites. MATERIALS AND METHODS: One hundred dental offices met all selection criteria and agreed to participate in the study. The light intensity was determined for a total of 214 light units. Disk-shaped specimens, 2.5 mm thick, were made from 2 resin composites (Charisma, Heraeus Kulzer; Point 4, Kerr Corp) and were subjected to photopolymerization: Charisma for 20 seconds (99 units) and Point 4 for 20 and 40 seconds (all 214 units). Knoop hardness values for the upper and lower surfaces of each specimen were determined, and relative hardness values (hardness of lower surface/hardness of upper surface x 100) were calculated. Data were analyzed using descriptive statistics, t-tests, 1-way analysis of variance, and simple and multiple linear regression (a = 0.05). RESULTS: The light intensity of the individual units varied widely, from 120 to 1,000 mW/cm2. Surface hardness and relative hardness were significantly (p < 0.05) and positively associated with light intensity, and wide ranges in surface hardness and relative hardness values were observed. Mean relative hardness ranged from 34.8% to 57.7%. CONCLUSIONS: Light polymerization units in private dental offices displayed a wide range in light intensity, and many had below-recommended levels. Of the resin composite specimens polymerized for 40 seconds with each of the 214 light units, only 10% reached the desired relative hardness of at least 80%. A positive linear relationship was found between light intensity and relative hardness. Increased exposure time resulted in a significant increase in relative hardness. Also, relative hardness was found to be dependent on the brand of composite material used. Dentists should regularly monitor the condition of light units and replace deteriorating parts.

Effect of salivary esterase on the integrity and fracture toughness of the dentin-resin interface.

Human Salivary Derived Esterases (HSDE) are part of the salivary group of enzymes which show strong degradative activity toward the breakdown of one of the most common monomers used in dental composites and adhesives, 2,2-[4(2-hydroxy 3-methacryloxypropoxy)-phenyl] propane (Bis-GMA), to form the degradation product 2,2-bis [4 (2,3-hydroxy-propoxy)phenyl] propane (Bis-HPPP). This study was aimed to evaluate the effects of HSDE on the biodegradation and fracture toughness of the adhesive resin-dentin interface. Adhesive resin (Scotchbond Multi Purposes), resin composite (Z250) and mini short-rod specimens, were either not incubated; or incubated in phosphate-buffered saline (PBS) or HSDE media for up to 180 days (37 degrees C, pH 7.0). The amount of Bis-HPPP was analyzed by high performance liquid chromatography and mini-SR specimens were tested for fracture toughness using universal testing machine following 30, 90, or 180-day incubation periods. Significantly higher amounts of Bis-HPPP were produced in HSDE than in PBS incubated specimens (p < 0.05). Non-incubated mini-SR specimens had the higher fracture-toughness values, while specimens incubated for 180-days in HSDE had the lowest fracture toughness (p < 0.05). This study suggests that biodegradation is an on-going clinically relevant process that progressively compromises the integrity of the critical resin restoration-adhesive interface, as well as the resin-composite component with time.