J.O. BURGESS’s research while affiliated with University of Alabama at Birmingham and other places

Objective To compare the ability of two calcium-releasing restorative materials to inhibit root dentin demineralization in an artificial caries model. Methods and Materials Preparations were made at the cementum–enamel junction of extracted human molars (40, n=10/material) and restored with two calcium-releasing materials (Experimental composite, Pulpdent Corporation and Cention N, Ivoclar Vivadent), a resin composite (Filtek Supreme Ultra, 3M Oral Care), and a resin-modified glass ionomer (RMGI) (Fuji II LC, GC). All materials (other than the RMGI) were used with an adhesive (Scotchbond Universal Adhesive, 3M Oral Care) in the self-etch mode, which was light cured for 10 seconds. All restorative materials were light cured in 2-mm increments for 20 seconds and then finished with a polishing disc. Teeth were incubated (37°C) for 24 hours in water. An acid-resistant varnish was painted onto the teeth around the restoration, leaving a 2-mm border of uncovered tooth. A demineralization solution composed of 0.1 M lactic acid, 3 mM Ca3(PO4)2, 0.1% thymol, and NaOH (to adjust pH=4.5), and a remineralization solution composed of 1.5 mM Ca, 0.9 mM P, and 20 mM Tris(hydroxymethyl)–aminomethane (pH=7.0) were prepared. Specimens were placed in the demineralization solution for 4 hours, followed by the remineralization solution for 20 hours and cycled daily for 30 days. The specimens were embedded, sectioned into 100-μm sections, and the interface between the restorative material and root dentin was viewed with polarized light microscopy. A line was drawn parallel with the zone of demineralization for each tooth. The area of “inhibition” (defined as the area external to the line) or “wall lesion” (defined as the area internal to the line) was measured with image evaluation software. Areas of inhibition were measured as positive values, and areas of wall lesions were measured as negative areas. Results A one-way analysis of variance (ANOVA) found significant differences between materials for “inhibition/wall lesion” areas in root dentin (p<0.001). Tukey post hoc analysis ranked materials (μm2, mean ±SD): Fuji II LC (5412±2754) > Cention N (2768±1576) and experimental composite (1484±1585) > Filtek Supreme Ultra (−1119±1029). Conclusion The experimental composite and Cention N materials (used with an adhesive) showed net areas of inhibition greater than a reference resin composite, albeit at a lower level than a reference RMGI material (used with no adhesive).

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. 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. 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. 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.

Objective: Recent studies confirmed that resin-modified glass ionomers (RMGIs) set on the basis of two competing mechanisms, an acid-base reaction and a light-activated resin polymerization. This study evaluated the effect of the setting mechanism on bond strength by measuring the shear bond strength of three RMGIs to dentin with and without light activation. Methods: Sixty human molars were ground to midcoronal dentin and randomly divided into six even groups: 1) Ketac Nano (KN), 2) KN without light cure (woLC), 3) Fuji Filling LC (FF), 4) FF woLC, 5) Fuji II LC (FII), and 6) FII woLC. The dentin surfaces of the specimens were conditioned/primed according to the manufacturers' instructions. A 1.54-mm diameter plastic tube was filled with RMGI material and affixed to the dentin surface. Groups 1, 3, and 5 were light cured for 20 seconds, and groups 2, 4, and 6 were immediately placed in a damp dark box with no light curing at 37°C for 24 hours. Shear bond strength testing was performed in an Instron device at 1 mm/min. Data were analyzed with a one-way analysis of variance (ANOVA) and Tukey/Kramer test (α=0.05). Results: Mean ± standard deviation shear bond strength values (MPa) are: 7.1 ± 4.2 (KN), 11.7 ± 3.9 (FF), 10.2 ± 3.2 (FF woLC), 12.5 ± 5.1 (FII), and 0.3 ± 0.4 (FII woLC). Two KN, all KN woLC, and seven FII woLC specimens debonded before testing. Tukey/Kramer analysis revealed no significant differences in bond strength between the three light-cured RMGIs. KN and FII showed significantly lower bond strength without light cure, but no significant difference was observed between FF and FF woLC. Conclusions: The results of this study strongly suggest that light activation is necessary to obtain optimal bond strength between RMGI and dentin. FF may contain components that chemically activate resin polymerization. Clinically, KN and FII need to be light cured after placement of these RMGIs.

OObjective: To compare the polymerization shrinkage of 9 commercially available highly filled composite materials. Methods: Polymerization shrinkage was determined as percent shrinkage using ACUVOL, Volumetric Shrinkage Analyzer (BISCO Dental, Schaumburg, IL). Specimens were placed on the rotating pedestal of ACUVOL in equal amounts forming a sphere and left undisturbed for 10 minutes to take their final shape. After 10 minutes, they were light cured (Elipar S10/3M ESPE/900mW/cm) following manufacturers' instructions. A2 Universal or A2 Dentin shades were used for testing except for 2 materials (Reflexsions and IPS Empress direct) which had enamel shades tested as well as dentin. Shrinkage values were recorded continuously for 10 minutes after curing and the final shrinkage value was recorded as percent shrinkage. Five values were taken for each material. The data were analyzed with ANOVA and Tukey/Kramer post-hoc tests (p=0.05). Results: Material (n=5) % Volume Shrinkage (MeanSD) Manufacturer Reflexsions XLS/Dentin 0.7 0.1 Bisco Dental GC Kalore 1.8 0.6 GC Corporation Estelite Sigma Quick 2.0 0.04 Tokuyama Dental IPS Empress Direct/Enamel 2.1 0.2 Ivoclar/Vivadent IPS Empress Direct/Dentin 2.5 0.1 Ivoclar/Vivadent Gradia Direct 2.6 0.1 GC America Venus Diamond 2.6 0.3 Heraeus Kulzer Herculite Ultra 2.9 0.3 Kerr Corp Reflexsions XP/Enamel 3.0 0.2 Bisco Dental Conclusions: Bisco Inc Reflexsions XLS had the lowest shrinkage (p<0.0001). Bisco Inc Reflexsions XP and Kerr Corporation Herculite Ultra appeared to have the highest percent shrinkage of this group.

Digital impressions may provide new paradigms for fixed prosthodontics, but the clinical efficacy is not well established. Objective: The purpose of this randomized, prospective double-blind clinical study was to evaluate the impression time, adjustment time, and marginal fit of all-ceramic crowns made by digital and conventional impression technique. Methods: Fifty patients, meeting inclusion/exclusion criteria, had a tooth prepared for an all-ceramic restoration (LAVA core, 3M Dental Corp; Noritake veneering porcelain, Noritake Dental) using dual cord retraction by 3 experienced, calibrated clinicians. Both a conventional one-step double phase impression (XLV & Monophase Aquasil, Dentsply Inc.) and a digital impression (Itero, Cadent Inc.) were completed in randomized order. Conventional and digital models were fabricated and crowns made on each model (n=100). At cementation, delivery and adjustment times were recorded, marginal fit was captured via intaglio impressions. The clinician selected the best crown which was cemented. Power analysis predicted 75% Power for this sample size for repeated measures ANOVA (p=0.05). Results: Mixed model ANOVA analyses were used for subject factors of (1) maxillary vs. mandibular, (2) anterior vs. posterior, (3) left vs. right; (4) preparation margin (subgingival/ supragingival/ epigingival); and (5) presence of bleeding. Digital Conventional Impression Time (min:sec) 8:40 4:23 Adjustment Time (min:sec) 5:03 4:00 Average Marginal Fit (m) 165.0 150.2 Selected for Cementation 27 23 Regarding time for impression and adjustment, analyses revealed a significant difference between the methods at the p < .001 level, although subject factors were not significant. No significant differences were found in marginal fit. Logistic regression did not show any significant effects on a clinician's choice of crown. Conclusion: Digital impressions performed as well as conventional impressions although the time required was significantly longer.

Objectives: Measure color change produced with three thicknesses of two ceramics with one total-etch resin-cement (Variolink II) compared to the original ceramic color. The null hypothesis is both ceramics covering the cured cement will have no color change at any thickness. Methods: ProCAD-100/I14 ceramic blocks were sectioned into three thicknesses: 0.59, 1.1, 2.1mm. Vita-Mark-II-A1C/I12 ceramic blocks were also sectioned into three thicknesses: 2.1, 1.05, 0.62mm. A thin layer (approximately 0.1 mm) of resin-cement (Variolink Veneer, shade-value +3) was applied to the ceramic and light cured for 30s (3M ESPE Elipar S10-1030mW/cm2). Color change was observed using a Konica-Minolta 700d Spectrophotometer at 0 and 90 using white and black backgrounds. L*a*b* values were recorded and ΔE calculated: ΔE=(ΔL*2+Δa*2+Δb*2)1/2. The cement thickness was measured using a .001 micrometer caliper. The cementing procedure was repeated until n≥5 for each ceramic material. Results: The ΔE values for white and black backgrounds are displayed below. The data were analyzed (General Linear Models) using SAS-9.3 to determine intergroup differences (p=0.05). There was no statistical significant difference in measurements made at 0and 90. Significant differences were observed when comparing ProCad-0.59 to ProCad-1.14, ProCad-0.59 to ProCad-2.1, and Vita-0.62 to Vita-1.05 (p<.05). Ceramic Ceramic Thickness (mm) Average Cement Thickness (mm) White-Background Average ΔE Black-Background Average ΔE ProCad 0.59 0.1350.0077 0.7710.175 5.1710.326 ProCad 1.14 0.1220.0032 0.5900.039 1.4350.142 ProCad 2.10 0.1340.0038 0.4290.106 1.0430.141 Vita MII 0.62 0.0980.0012 0.6490.195 3.8020.351 Vita MII 1.05 0.0910.0053 0.4660.099 1.6750.201 Vita MII 2.12 0.1210.0060 0.3050.132 0.7460.146 Conclusions: As ceramic thickness increased to 2 mm, the ΔE values decreased showing that the color of a 2mm thick ceramic is difficult to alter with a thin (120μm) thickness of cement. However, the color of 0.6-1mm thick ceramics can be altered with a resin cement. SUPPORTED BY NIDCR GRANT DEO17607.

Objectives: The purpose of this study was to evaluate the wear rates of provisional restorative materials by in vitro system. Methods: Disk specimens (3.0mm thick, 8.0mm diameter) were fabricated with tested materials including a chemical-polymerizing acrylic resin with TMPT filler (Provista, Sun Medical), two chemical-polymerizing acrylic resins (Metafast, Sun Medical and UnifastIII, GC), two photo-polymerizing acrylic resins (Unifast LC, GC and Hardbite, Yoshida), and two chemical-polymerizing composite resins (Protemp Plus, 3M ESPE and Luxatemp, DMG). The specimens were secured to brass cups with an auto-cured acrylic and fixed to the UAB wear simulator. Localized wear test was carried out using a hemispherical steel tip and a PMMA/water slurry with 75 N at 1.2 Hz for 100,000 cycles. Wear depths were measured using a non-contact profilometer (Proscan2000, Scantron Industrial). The data (n=5) were statistically analyzed with one-way ANOVA and Tukey's test (=0.05). Results: The results of the wear tests are presented in the table below. Groups with identical letters are not significantly different (p>0.05). Conclusion: The mean wear values of composite materials were significantly lower than all other materials except Provista. The mean wear value of Provista was significantly lower compared to other chemical-polymerizing acrylics. There were no significant differences among two photo-polymerizing acrylics and two chemical-polymerizing acrylics.

Objectives: A novel composite crown system with a fiber-reinforced composite (Metacolor Prime Art, Sun Medical) has recently been introduced. The purpose of this study was to evaluate the wear of the fiber-reinforced composite according to the change of thickness of the overlying indirect composite. Methods: Disk specimens (1.5mm thick, 8.0mm diameter) of various thicknesses (shown in the upper row of the table) of the indirect composite (Metacolor Prime Art, Sun Medical) were fabricated on top of fiber-reinforced composite (Jacket Opaque, Sun Medical). They were then cemented onto Ni-Cr alloy disks (REX4, Pentron) using a resin cement (C&B Metabond, Parkell). Those specimens were secured inside brass cups with an auto-cured acrylic and inserted into the UAB wear simulator. Localized wear was carried out using a hemispherical steel tip and a PMMA/water slurry for 200,000 cycles with 75 N of force at a 1.2 Hz loading frequency. Wear depths were measured using a non-contact profilometer (Proscan2000, Scantron Industrial). The data were statistically analyzed with one-way ANOVA and Tukey's test (a=0.05). Results: The results of the wear tests are presented in the table below. Conclusion: The wear of Metacolor Prime Art was influenced by the thickness of the overlayed indirect composite. When the thickness of indirect composite was 0.1 mm or less, the underlying fiber-reinforced composite was exposed and worn rapidly.

Retention of posts in root canals relies on the strength of cements and techniques of application. As cements develop, different techniques are introduced and employed with the objective of enhancing post retention. Objective: To determine push out strength of fiber posts cemented using five techniques. Materials and Methods: Roots of 50 freshly extracted first mandibular premolar teeth with no caries, cracks or defects were selected after x-ray exposure in bucco-lingual orientation. They were instrumented with an endodontic cordless hand piece using K-Flex files (#15 to #45). The canals were obturated using AH26 and gutta-percha. 10 mm post space was created by removing gutta-percha with a universal drill pack. Dentin was etched with 34% acid gel for 15 seconds and rinsed. Bonding was done either with XP Bond and Self Cure Activator or with Xeno IV and Self Cure Activator which were applied once or twice according to the study design. Post cementation was done either with Calibra or Fluorocore II. Light curing was done through fiber posts using Coltulux curing light (550mW/cm2). Curing times varied between 10, 15 and 20 seconds. The treated teeth were embedded in clear acrylic, sectioned using a low-speed Buehler cutting saw into coronal, middle and apical 2mm sections and stored in de-ionized water for 72 hours at 370C before testing using the INSTRON 5565 series. Results: Results were analyzed using ANOVA and Tukey/Kramer post-hoc tests. No significant differences were observed across the groups (p=.1039) however all three sections were significantly different (p<.0001) from each other (Coronal>Middle>Apical). Conclusion: Within this study's limits, the number of times a bonding agent was applied to canal walls and differences in curing time did not significantly influence bond strength. Fluorocore II core material provided bond strengths that were comparable to the cemented groups.