bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Stepped Light Intensity on Polymerization Force and Conversion in a Photoactivated Composite
Authors: BOUSCHLICHER MURRAY R. , RUEGGEBERG FREDERICK A. , BOYER DANIEL B.
Published: July 2007

Purpose: This study evaluated the effect of stepped light intensity on the polymerization shrinkage forces and degrees of conversion of a hybrid composite.

Materials and Methods: Composite specimens were bonded between two steel rods (5.00 mm diameter, 1.25 mm apart, configuration factor = 2) mounted in a universal testing machine using a constant displacement mode. Polymerization contraction force was recorded for 300 seconds under four light exposure conditions: group 1: 40 s × 800 mW/cm2; group 2: 10 s × 100 mW/cm2+ 30 s × 800 mW/cm2; group 3: 60 s × 800 mW/cm2; group 4: 10 s × 100 mW/cm2+ 50 s × 800 mW/cm2. Maximum curing force (N300s) and maximum force rate of the four groups were compared using one‐way analysis of variance (ANOVA) (α= 0.05) and the Tukey test. Degree of conversion in all groups was evaluated at two depths (top surface and 2 mm) using Fourier transform infrared spectroscopy (FTIR).

Results: Mean maximum shrinkage forces and standard deviations (SD) were: group 1, 177 N (SD = 23); group 2, 172 N (SD = 11); group 3, 213 N (SD = 15); group 4, 197 N (SD = 17). Mean maximum forces for stepped and standard groups with the same duration (1 and 2; 3 and 4) were not statistically different; means for groups 2 and 3 were statistically different. Maximum force rates were not significantly different (p= .1548). Force:time curves were S‐shaped. Specimens exposed to stepped curing exhibited longer delays before force was recorded. Mode of curing was shown not to contribute to overall cure, but both duration of cure and the depth (top surface vs. 2.00 mm) were significant with an interaction effect.

CLINICAL SIGNIFICANCE

Mean maximum shrinkage force and force rate exhibited during the first 300 seconds of polymerization were not influenced by using stepped light exposure. Degree of conversion was equivalent for exposures of similar total duration at 2‐mm depth. Mode of cure (stepped vs. continuous intensity) had no effect on degree of conversion.
Removal of Porcelain Veneers Aided by a Fluorescing Luting Cement
Authors: WHITEHEAD SHAUN A. , AYA ASIF , MACFARLANE TATIANA V. , WATTS DAVID C. , WILSON NAIRN H.F.
Published: July 2007

Purpose: Porcelain veneers are a safe and effective treatment modality for selected teeth that have poor esthetics. However, removal of porcelain veneers that have failed may be time‐consuming and involve considerable removal of sound tooth structure adjacent to the veneer. The aim of this study was to evaluate a novel method of porcelain laminate veneer removal by incorporating a fluorescent dye into the luting cement that allows the practitioner to visualize the cement on the tooth and remove the veneer without causing residual damage to the adjacent tooth substance.

Materials and Methods: Porcelain veneers were luted on extracted teeth with a luting cement modified with a fluorescing agent. Faculty teaching staff and final year dental undergraduates were asked to remove the veneers with the aid of a curing light to render the luting cement visible by fluorescing. They were then asked to compare the removal of comparable veneers without this visual aid and to complete a standard questionnaire. The depth of cure of the conventional and modified cements was measured using a penetrometer.

Results: Results of the questionnaire indicated that the operators found removing the veneer cemented with the modified (fluorescing) cement considerably easier than removing the veneer cemented with the conventional cement. Microscopy indicated that more damage was caused to the underlying tooth during removal of conventionally cemented veneers. The incorporation of the dye into the cement reduced the depth of cure from 4.238 mm (SD = 0.025) to 3.761 mm (SD = 0.096).

CLINICAL SIGNIFICANCE

The fluorescent cement was considered to be superior to conventional cements in its ease of visibility, and as a consequence, veneers cemented with the fluorescing cement are easier to remove. The fluorescing dye significantly reduced the depth of cure, but this may not be clinically significant, because of the small thickness of cement employed when luting adhesive restorations. The use of such fluorescing materials may not be restricted to a luting cement for veneers but may also be incorporated into bases and lining materials so they can be visualized on removal of tooth‐colored restorations, to prevent further tooth destruction.
Computer Imaging versus Conventional Esthetic Consultation: A Prospective Clinical Study
Authors: PAPASOTIRIOU OLGA S. , NATHANSON DAN , GOLDSTEIN RONALD E.
Published: July 2007

Computer imaging can be helpful in demonstrating to patients the potential outcome of esthetic dental procedures. The current clinical study assesses the effectiveness of computer imaging by comparing the reactions of patient and dentist to conventional consultations versus the use of computer imaging. The responses from 35 subjects show that computer imaging consultations are more effective in helping patients decide to accept treatment. Patient satisfaction was higher (93.75%) with computer consultations than with conventional methods (83.3%). Computer imaging consultations were easier to conduct but significantly (p < .05) more time consuming.

CLINICAL SIGNIFICANCE

This experiment confirms the role of computer imaging as an effective aid in esthetic dentistry consultations and treatment planning. Imaging facilitates communication between patient and practitioner and provides a more realistic view of anticipated treatment outcomes.
Effect of Camera Angulation on Adaptation of CAD/CAM Restorations
Authors: PARSELL DOUGLAS E. , ANDERSON BRANDON C. , LIVINGSTON HAROLD M. , RUDD JEREMY I. , TANKERSLEY JERRY D.
Published: July 2007

Purpose: A significant concern with computer‐assisted design/computer‐assisted manufacturing (CAD/CAM)‐produced prostheses is the accuracy of adaptation of the restoration to the preparation. The objective of this study is to determine the effect of operator‐controlled camera misalignment on restoration adaptation.

Materials and Methods: A CEREC 2 CAD/CAM unit (Sirona Dental Systems, Bensheim, Germany) was used to capture the optical impressions and machine the restorations. A Class I preparation was used as the standard preparation for optical impressions. Camera angles along the mesio‐distal and buccolingual alignment were varied from the ideal orientation. Occlusal marginal gaps and sample height, width, and length were measured and compared to preparation dimensions. For clinical correlation, clinicians were asked to take optical impressions of mesio‐occlusal preparations (Class II) on all four second molar sites, using a patient simulator. On the adjacent first molar occlusal surfaces, a preparation was machined such that camera angulation could be calculated from information taken from the optical impression. Degree of tilt and plane of tilt were compared to the optimum camera positions for those preparations.

Results: One‐way analysis of variance and Dunnett C post hoc testing (α= 0.01) revealed little significant degradation in fit with camera angulation. Only the apical length fit was significantly degraded by excessive angulation. The CEREC 2 CAD/CAM system was found to be relatively insensitive to operator‐induced errors attributable to camera misalignments of less than 5 degrees in either the buccolingual or the mesiodistal plane. The average camera tilt error generated by clinicians for all sites was 1.98 ± 1.17 degrees.

CLINICAL SIGNIFICANCE

It is unlikely that camera misalignment is a major source of error during the fabrication of simplistic CEREC 2 CAD/CAM restorations.
Effect of Alcoholic and Low‐pH Soft Drinks on Fluoride Release from Compomer
Authors: ABU‐BAKR NEAMAT H. , HAN LININ , OKAMOTO AKIRA , IWAKU MASAAKI
Published: July 2007

Purpose: The purpose of this study was to evaluate the amount of fluoride released from compomer restorative materials after immersion in various media.

Materials and Methods: In this test, four materials were used: three compomers (Dyract, Dentsply, Konstanz, Germany; Compoglass, Vivadent, Schaan, Principality of Liechtenstein; and Xeno, Sankins, Tochigi, Japan) and one resin‐modified glass ionomer cement (Fuji II LC, GC, Tokyo, Japan). There were four test solutions: one alcoholic (whiskey), two low‐pH drinks (Coca‐Cola, orange juice), and one deionized water. Over a period of 60 days, the tested specimens were immersed in the test solution for 3 hours every day, then kept in deionized water. The fluoride released was detected by using a fluoride ion selective electrode connected to a microprocessor ion analyzer. The fluoride ion concentration (ppm) of the test solutions and deionized water was recorded after 1, 2, 3, 4, 7, 30, and 60 days. Electron probe microanalysis was used for surface analysis of the fluoride released.

Results: When immersed in low‐pH soft drinks, compomer showed a significantly higher fluoride release than when immersed in deionized water (p <.0001). For specimens immersed in Coca‐Cola, the fluoride release levels (pg/cm2, mean ± SD) at 1, 7, and 60 days for Dyract (91.6 ± 1.8, 39.3 ± 3.1, 10.5 ± 0.9), Compoglass (129.5 ± 0.9, 66.5 ± 2.7, 19.0 ± 0.3), Fuji II LC (147.0 ± 4.2, 50.8 ± 3.1, 27.6 ± 3.0), and Xeno (73.6 ± 3.2, 27.3 ± 2.1, 6.6 ± 0.6) demonstrated the trend of significantly lower releases with time in water solution. Over a 60‐day period, materials immersed in 100% orange juice released the highest amount of fluoride, which could be attributable to the erosive effect of the medium. Materials immersed in deionized water released the least amount of fluoride. Among the tested compomers, Compoglass released the most fluoride.

CLINICAL SIGNIFICANCE

The results of this study indicate that, at low pH, compomer restorative materials tend to release more fluoride.
INTERNAL BLEACHING: PART I
Authors: Swift Edward J. , Trope Martin
Published: July 2007

Internal bleaching is a cost‐effective esthetic treatment for certain types of tooth discoloration. It is a safe procedure, but has occasionally been associated with external root resorption and tooth loss. It appears that the cause of this resorption is the caustic effect of 30% hydrogen peroxide on the cemen‐tum, especially when used with heat. This review analyzes several recent publications that explore the possibility of bleaching with less toxic formulations, while still maintaining bleaching effectiveness.
Bioactive Glass Granules for Regeneration of Human Periodontal Defects
Authors: ROSENBERG EDWIN S. , FOX GREGORY K. , COHEN CHARLES
Published: July 2007

Purpose: A comparative study which evaluated the effectiveness of bioactive glass granules of uniform size (300–335 μm) for the regenerative treatment of interproximal intrabony periodontal defects was conducted.

Materials and Methods: Twelve pairs of advanced periodontal lesions in 12 patients (6 males and 6 females) were treated in a split‐mouth design with open flap débridement in the control sites and open flap debridement with bioactive glass particles placed in the test sites.

Results: At 6 months post‐treatment, both treatment modalities demonstrated a gain in clinical attachment level (CAL), with the test sites having a significantly (p < .01) greater gain in CAL than the control sites. Reentry procedures were performed to assess the amount of hard tissue fill. The test sites demonstrated significantly (p < .001) more gain in hard tissue fill than the controls.

CLINICAL SIGNIFICANCE

The use of bioactive glass granules of uniform size in human interproximal intrabony periodontal defects resulted in significantly better hard tissue fill and clinical attachment gain than surgical debridement alone.
Color Stability of Compomer after Immersion in Various Media
Authors: ABU‐BAKR NEAMAT , HAN LINLIN , OKAMOTO AKIRA , IWAKU MASAAKI
Published: July 2007

Purpose:The purpose of this study was to evaluate the effect of various media on the color stability of compomer and to compare these results to those of other materials that could be used in similar clinical circumstances.

Materials and Methods:In this test, six materials (shade A2) were used: four compomers (Dyract, Compoglass F, Xeno, F2000), one composite resin (Clearfil AP‐X), and one resin‐modified glass ionomer cement (Fuji II LC). There were four test solutions: one alcoholic (whiskey), two low pH soft drinks (Coca Cola, orange juice), and deionized water as a control. A plastic ring mold (9‐mm diameter x 1‐mm height) was used to prepare 120 disk specimens. For 60 days, the test specimens were immersed in the various media daily for 3 hours then transferred to the deionized water. Color was measured by CIE L* a* b* relative to CIE source against a white background, using a colorimeter. Color change (Δ*) was calculated as Δ*= [(δ*)2+ (δ*)2+ (Δ*)2]1/2. Color changes (Δ*) were recorded after 1, 7, 30, and 60 days.

Results:The results indicated that compomer and resin‐modified glass ionomer were susceptible to discoloration in various solutions over an extended period of time. Composite resin showed minimal perceptible color change. Specimens immersed in whiskey showed a significantly high perceptible color change(p< .0001). Water caused no perceptible color changes.

CLINICAL SIGNIFICANCE

Compomer and resin‐modified glass ionomer materials are susceptible to discoloration by various media.
Evaluating Porcelain Color Match of Different Porcelain Shade‐Matching Systems
Authors: WEE ALVIN G. , RANG EDITH Y. , JOHNSTON WILLIAM M. , SEGHI ROBERT R.
Published: July 2007

Purpose: This in vitro study was designed to evaluate the new ShadeEye‐EX Chroma Meter and a new visual porcelain shade‐matching system (Vitapan 3‐D Master, Omega 900) in comparison to the traditionally used visual porcelain shade‐matching system (Vita Lumin Vacuum, VMK 68). Materials and Methods: Shade matches and porcelain fabrications on individualized shade tabs were carried out. The fabricated porcelain tabs were evaluated against the respective natural tooth using the United States Public Health Service (USPHS) criteria to determine clinically acceptable match. The tabs also were ranked according to the final‐color match to the corresponding natural tooth.

Results: The percentage of clinically acceptable color matches were as follows: Vita Lumin Vacuum (46.67%), ShadeEye‐EX (40%), and Vitapan 3‐D Master (56.67%). The generalized estimating equation (α= 0.5) showed no statistically significant difference between systems in obtaining a clinically acceptable match (p= .5729). The chi‐squared test (α= 0.5) showed no statistically significant difference between systems in terms of rank order (p= .5017). The two new systems do not produce color match that is better than the conventional visual porcelain shade‐matching system.

CLINICAL SIGNIFICANCE

Both the shade‐matching environment and communication between dentist and technician should be optimized with use of visual and instrumental shade‐matching systems.
Effect of Distance on the Power Density from Two Light Guides
Authors: PRICE RICHARD B. , DÉRAND TORE , SEDAROUS MARY , ANDREOU PANTELIS , LONEY ROBERT W.
Published: July 2007

Purpose: This study determined the effect of distance on the power density from standard and Turbo light guides (Demetron/Kerr, Danbury, Connecticut).

Materials and Methods: Power density was measured from 0 to 10 mm away from the tip of standard 8‐mm curved light guides and 13/8‐mm Turbo curved light guides. To determine the effect of distance on power density, a polynomial regression line was fitted. The Kolmogorov‐Smirnov (K‐S) statistic and the Wilcoxon rank sum (WR) tests were used to determine if there was a difference in the rate at which the power density decreased for the standard and Turbo light guides as the distance from the tip increased. Photographs of the light dispersion from each tip were also taken.

Results: At 0 mm, the mean (± SD) power density from the two standard light guides was 743 ± 6.1 mW/cm2 and from the four Turbo light guides was 1128 ± 22.1 mW/cm2. As the distance from the tip of the light‐guide tip increased, the power density decreased, but the rate of decrease was greater from the Turbo light guides than from the standard light guides. At 6 mm the power density from the standard light guides fell to 372 mW/cm2 (50% of the original value) and the power density from the Turbo light guides fell to 263 mW/cm2 (23% of the original value). Both the K‐S statistic and the WR sum test indicated that the distribution of light intensities was significantly different from the two light guides (WR p‐value = .0246, K‐S p‐value < .0001). The two estimated polynomials intersected at 3.66 mm, and the 95% prediction intervals intersected at about 2.8 and 4.8 mm. Therefore, beyond 5 mm away from the tip of the light guide, the standard light guides gave higher power density readings than the Turbo light guides. Photographs showed that the light dispersed at a wider angle from the Turbo light guides than from the standard light guide.

CLINICAL SIGNIFICANCE

The design of the light guide of a light curing unit affects light dispersion, power density, and ultimately the dentist's ability to properly cure composite. For these reasons, manufacturers should report the power density at the tip of the light guide and 6 mm from the tip of the light guide, since significant differences exist between light guide designs.
Polymerization Depths of Contemporary Light‐Curing Units Using Microhardness
Authors: RUEGGEBERG FREDERICK A. , ERGLE JANET W. , METTENBURG DONALD J.
Published: July 2007

Purpose: This research investigated composite depths of cure using a variety of light‐curing units and exposure protocols.

Materials and Methods: Composite (Herculite XRV, shade A2, Kerr, Orange, California) was exposed in opaque compules to conventional quartz tungsten halogen (QTH) units, soft‐start units, high‐intensity QTH and plasma arc (PAC) curing lights, and one argon laser. Cured compules were sonicated to remove uncured composite and were sectioned and polished along the long axis to expose cured composite. Knoop hardness was measured 0.5 mm from the irradiated, top surface and then at 1.0 mm and in 1.0‐mm increments until reliable readings could no longer be obtained. Hardness values were compared by analysis of variance at similar depths within a specific curing‐light classification, using the hardness of the standard 40‐second conventional QTH exposure as comparison (Dunnett's t‐test). Depth of cure was defined as the deepest hardness value found equivalent to that at 0.5‐mm depth for a specific curing light and scenario.

Results: Conventional QTH lights provided similar hardness profiles. At 2‐mm depth, use of a different unit or curing tip made no difference in hardness compared with the standard. At this depth, soft‐start (pulse‐delay and step‐cure) methods yielded hardness similar to that of the standard. High‐intensity QTH lights provided similar hardness at 2‐mm depth in 10 seconds to that of the standard 40‐second exposure. Plasma arc exposure for less than 10 seconds produced inferior hardness compared with the standard. A 10‐second PAC and a 5‐second laser exposure gave hardness at 2‐mm depth equivalent to that of the 40‐second standard. Depth of cure for almost all curing scenarios was not greater than 2 mm.

CLINICAL SIGNIFICANCE

Similar‐type conventional QTH lights with different tip diameter (8 and 12 mm) provide similar composite cure characteristics. Soft‐start techniques provide similar cure profiles to those achieved with conventional QTH technique when used according to manufacturer's recommendations. High‐intensity QTH units and the argon laser can reduce exposure time while providing composite with similar hardness to that of conventional QTH curing. Plasma arc exposure should be at least of 10 seconds duration to provide hardness equivalent to that achieved with conventional 40‐second QTH exposure. Even with consideration of high‐intensity curing units, composite increments should still be no greater than 2 mm to provide homogeneous hardness.
Learning to Smile: The Neuroanatomic Basis for Smile Training
Authors: TERRY DOUGLAS A. , PIRTLE PHILIP L.
Published: July 2007

This article demonstrates that although any layperson could recognize that the smile manifests mainly in the oral and periorbital regions, a comprehension of the neurologic and musculoskeletal elements lends the clinician insight into the many aspects of a smile. The neurologic control of a smile consists of a complex process involving many facets. As with any other complex neuromuscular activity, repetitions of the act can train the central nervous system, neural network, and muscular network in efficient performance of and correct musculoskeletal activation involved in the act itself. With functional knowledge of muscles dedicated to a pleasing full smile, together with a battery of easy and effortless exercises, the clinician is able to help the patient change behavior intended to camouflage perceived oral flaws. A patient needs reassurance that behind the guidance from the clinician lies medical evidence that such routine movement of muscles will indeed improve the smile. When asked why or how the exercise succeeds, the clinician can reassure the patient based on a working knowledge of the neurologic and muscular anatomy involved.

CLINICAL SIGNIFICANCE

A functional knowledge of muscles dedicated to a pleasing full smile, together with a battery of easy and effortless exercises, provides the clinician with the ability to assist the patient in altering years of behavior intended to camouflage perceived oral flaws.
Minimum Color Differences for Discriminating Mismatch between Composite and Tooth Color
Authors: RAGAIN JAMES C. , JOHNSTON WILLIAM M.
Published: July 2007

Purpose: The purpose of this study was to determine if there are differences between patients and dental professionals in their ability to identify small color differences (AE) in composite resin restorative materials in vitro and to determine the AE that would indicate acceptability of color match between a restoration and an adjacent tooth.

Materials and Methods: Subjects were asked to evaluate composite resin disks to distinguish acceptability of ΔE between disk pairs. Color difference discrimination of dental professionals groups D1 (dentists, n = 12) and D2 (dental auxiliaries, n =12) was compared to that of dental patient groups P1 (patients, n = 12) and P2 (scientists, n = 12). Each group was pretested for normal color vision. Color differences between a standard and restoration disks of composite were measured in Colour Measurement Committee (CMC) (1:1) color units. Data were analyzed by logistic regression, and results were used to calculate a probability level for minimal acceptance or rejection of ΔE for all observers. Mean 50:50 ΔE replacement points (RP) for each group were obtained and analyzed by analysis of variance, and the Tukey pairwise comparison test was applied (α= 0.05 for all statistical analyses).

Results: There were significant differences found between the experimental groups (p= .020). Group D2 (mean 50:50 ΔE RP = 1.78) proved to be more discriminating in accepting differences between tooth and composite resin restorative material color than group P1 (mean 50:50 AE RP = 2.69). The mean 50:50 ΔE RP for all subjects was 2.29 CMC (1:1) units.

CLINICAL SIGNIFICANCE

The ability to generate an excellent color match between a tooth‐colored restoration and the tooth is critical to esthetic success. This study demonstrates that patients are not as discriminating in their ability to identify small color differences between composite restorations and the tooth as are dental professionals. Dental auxiliaries proved to be more discriminating in accepting differences between tooth and composite resin restorative material color than were patients.
The Science of Communicating the Art of Esthetic Dentistry. Part III: Precise Shade Communication
Authors: DERBABIAN KRIKOR , MARZOLA RICCARDO , DONOVAN TERRY E. , ARCIDIACONO ALESSANDRO
Published: July 2007

Shade matching is inherently complex and involves understanding the science of color, determining the shade and surface characteristics of teeth, and communicating this information to the laboratory technician. The laboratory technician then has the difficult task of mimicking the selected shade and ultimately reproducing it in the final restoration.

CLINICAL SIGNIFICANCE

This article describes several methods of communicating and several tools that are available to the restorative dentist to achieve the esthetic results desired. By using these simple techniques, the dentist and laboratory technician are better able to communicate the shade and surface characteristics of teeth.
Comparison of Color of Resin Composites of White and Translucent Shades with Two Shade Guides
Authors: LEE YONG‐KEUN , LIM BUM‐SOON , KIM CHEOL‐WE , POWERS JOHN M.
Published: July 2007

Purpose: The purpose of this study was to compare the color of resin composites of white, translucent, and conventional shades with shade guides, based on the analysis of the color distribution of shade guides. The influence of color measuring mode, specular component included (SCI) or excluded (SCE), was also determined.

Materials and Methods: The labial portions of shade guide tabs (Vita and Chromascop) were polished flat with up to 2400‐grit SiC paper. Color coordinates were measured according to CIE L*a*b* color scale on a reflection spectrophotometer with both the SCE and SCI modes. The color coordinates of white, translucent, and conventional shades of two brands of resin composites were measured and compared with those of the shade guides.

Results: There was no logical order in the color distribution of the two shade guides. The color of white and translucent shades of resin composites was located on the low CIE a* and CIE b* value area. The CIE L*, a*, b* values of resin composite with the same color designations were different, depending on the brand of material. The color difference (AE*) of shade guides by the measuring mode (SCE vs. SCI) was between 3.2 and 6.5.

CLINICAL SIGNIFICANCE

A new systematic shade guide including the new white or translucent shades of resin composites should be made, based on the logical distribution of colors. The color difference caused by the color measuring mode should be considered in color measurement of esthetic restorative materials and in the design of the shade guide. Also, regardless of the brand of materials, there should be unification of shades for consistent clinical result.
Critical Appraisal
Authors: St.‐Georges Annie J. , Miguez Patricia A. , Swift Edward J.
Published: July 2007

Multiple studies on composite light‐curing have focused on the effects of polymerization contraction stresses on restoration margins. Those stresses can potentially cause debonding of restorations and gap formation if they exceed resin bond strengths to enamel and dentin. Such gaps may permit microleakage, resulting in postoperative sensitivity or clinical failure of the restorative treatment. The effects of polymerization shrinkage are dependent on the configuration of the cavity, properties of the restorative material, and the kinetics of polymerization shrinkage. This review analyzes several studies that have been published on the subject
Esthetic Considerations in Removable Prosthodontics
Authors: DONOVAN TERRY E. , DERBABIAN KRIKOR , KANEKO LESLIE , WRIGHT ROBERT
Published: July 2007

Patients requiring extensive replacement of teeth with removable prostheses are indeed esthetic orphans in many contemporary dental practices. Although the advent of successful osseointegration has dramatically reduced the need for removable prostheses, there are still many patients who for health, anatomic, psychological, or financial reasons are not candidates for implants. These patients deserve the same level of esthetic restorative dentistry as those who are restored with fixed prostheses. Clearly, the restorative dentist has the greatest flexibility from an esthetic standpoint with complete dentures. Soft and hard tissues can be replaced with contemporary characterized denture‐base materials, and a truly infinite variety of tooth forms, shades, and arrangements can be used to meet the expectations of the most demanding patient. For partially edentulous patients, the major problem is designing a removable partial denture that avoids the unsightly display associated with conventional clasp assemblies. There are strategies available to accomplish this effectively while establishing an environment for optimal periodontal health, and to minimize destructive stresses on the abutment teeth.

CLINICAL SIGNIFICANCE

This article discusses the procedures essential for providing an upscale, quality esthetic service with removable prostheses. Effective strategies to eliminate unsightly clasp assemblies with removable partial dentures are described.
Dental Color Standards: Shade Tab Arrangement
Authors: PARAVINA RADE D. , POWERS JOHN M. , FAY ROSE‐MARIE
Published: July 2007

Purpose: The aim of this study was to analyze the shade tab arrangement of two popular dental shade guides, suggest possible improvements, and propose clinical guidelines. Materials and Methods: Data were recorded using a colorimeter set to standard illuminant source C and CIE L*a*b* system. The manufacturers' shade tab arrangement as well as the possible improvements in the arrangement of shade tabs of Vitapan Classical and Vitapan 3‐D Master (Vita Zahnfabrik, Bad Säckingen, Germany) shade guides were examined by regression analysis. Results: Certain shortcomings in the manufacturers' arrangement of both color standards were observed. The Vitapan 3‐D Master arrangement was more consistent, but with a decrease in lightness, tab saturation decreased as well in four of its five groups. When Vitapan Classical and Vitapan 3‐D Master tabs were arranged according to ΔE* in relation to the lightest tab, r2 was 0.98 and 0.96, respectively. After dividing the total ΔE* range into four equal segments for the newly established Vitapan Classical guide, r2 was 0.91, 0.95, 0.68, and 0.94, respectively. Corresponding r2 values for Vitapan 3‐D Master were 0.96, 0.94, 0.90, 0.94, and 1.0.

CLINICAL SIGNIFICANCE

Total color difference in relation to the lightest tab, followed by the tab division into an adequate number of groups, is recommended as a possible and universally applicable mode of tab arrangement in dental color standards.
Critical Appraisal
Authors: Swift Edward J.
Published: July 2007

Early composite resins were unsuited for use in posterior teeth because of their poor wear resistance. However, wear resistance has improved dramatically, and composites are now commonly used in Class I and II restorations. Improvements in adhesive materials and techniques have contributed to the clinical success of posterior composite restorations. Unfortunately, even with those improvements, the gingival margin of a Class II composite restoration remains a difficult area to seal predictably and, therefore, represents a potential location for failure. Early recommendations for management of this critical area involved the use of special light‐activation methods or use of self‐cure composites. However, more recent approaches have involved the use of materials such as resin‐modified glass ionomers, compomers, and flowable resins. This “Critical Appraisal” addresses this important aspect of Class II posterior composite restorations.
Posterior Resin‐Based Composite Restorations: Clinical Recommendations for Optimal Success
Authors: RITTER ANDRE V.
Published: July 2007

Resin‐based composites are increasingly used for the restoration of defects in posterior teeth. This review describes, illustrates and discusses important clinical aspects of the posterior composite technique. A relatively new stratification concept oriented to the development of functional and anatomic restorations is proposed.
Blending Incremental and Stratified Layering Techniques to Produce an Esthetic Posterior Composite Resin Restoration with a Predictable Prognosis
Authors: KLAFF DAVID
Published: July 2007

Composite resin restorations play an ever‐increasing role as routine restorations in everyday clinical practice. However, the long‐term prognosis of these restorations is still widely debated and open to question. The restorative protocols are still evolving, whether for direct or indirect placement, and little evidence is available in the scientific literature as to the ideal choice of site, technique, and category for placement. This article discusses the problems encountered and suggests a clinical restorative protocol to optimize composite resin placement.
effects of sequential versus continuous irradiation of a light‐cured resin composite on shrinkage, viscosity, adhesion, and degree of polymerization
Authors: Koran P. , Kürschner R.
Published: July 2007

Objective: This in vitro study compar ed different properties of a resin composite using a two‐step light‐curing method and a conventional continuous curing approach.

Materials and Methods: Five different tests were performed on specimens of resin composite. Fifty‐five specimens of 3.5‐mm thickness were divided among 11 different test groups that varied in light‐curing protocols. Top and bottom surface hardness were measured after curing. Adhesion of composite to pretreated metal surfaces was tested using 36 specimens irradiated with four different curing methods. Linear and volumetric shrinkage of adhesion specimens were measured using a linometer. Measurements of viscosity were performed on 10 specimens during polymerization. Finally, the dynamics of polymerization during two‐step versus continuous light‐curing were evaluated by measuring the residual monomer concentration in each specimen after different irradiation.

Results: Surface hardness depended on the total dose of light delivered, but not on how the light was delivered. Concerning adhesion, the results indicated that marginal adhesion was weakened by fast polymerization and was improved with a low‐intensity pre‐polymerization period. The results of the shrinkage test indicated less shrinkage a t the beginning of the process with the lower intensity light. However, at completion of polymerization, the total shrinkage did not differ significantly between groups. Also, during the curing process, the same viscosity changes occurred in the resin composite regardless of the irradiation method used. Finally, by the 40‐second completion point, specimens made with either two‐step or continuous light‐curing had reached a similar 90% degree of polymerization.

Conclusions: With an adequate total irradiation dose, the properties of resin composite cured with a two‐step approach were as good as or better than those obtained using a conventional continuous curing method. Moreover, marginal adaptation was improved by two‐step polymerization, which could be explained by the ability of the material to flow during the early stages of the curing process.
REDUCED LIGHT ENERGY DENSITY DECREASES POST‐GEL CONTRACTON WHILE MAINTAINING DEGREE OF CONVERSION IN COMPOSITES
Authors: Sakaguchi R.L. , Berge H.X.
Published: July 2007

Objective: The purpose of this study was to evaluate the effects of curing‐light energy density on degree of conversion and polymerization contraction stress of a hybrid composite resin.

Materials and Methods: Specimens of Bisfil P (Bisco, Inc., Schaumburg, Illinois) were fabricated. The specimens were 5.4 mm in diameter by 1.7 mm in thickness. Five groups of six specimens were cured using different light‐intensity protocols. The control group had the highest light intensity, at 337 mW/cm2. Three groups were light‐cured with modified light intensities, which were 71%, 49%, and 34% of the control intensity. In these four groups, the composite was light‐cured for 40 seconds, with only the intensity of the light varying. In the fifth group, specimens were irradiated for 20 seconds with a reduced intensity (241 mW/cm2), followed by 20 seconds at high intensity (337 mW/cm2). A light guide was positioned at 7 mm from the top surface of each specimen during the polymerization. Linear polymerization contraction was measured using electrical strain gauges positioned at the bottom of the specimens. One day after curing, specimens were polished to 600‐grit, and chips were removed with a scalpel from the top and the bottom surfaces of each of the samples to evaluate the degree of conversion using Fourier transform infrared spectroscopy.

Results: The control group (337 mWlcm2) had the highest degree of conversion at top and bottom surfaces. The degree of conversion of the specimens cured with the two‐step method was not significantly different from the values of those cured at either higher or lower intensity for 40 seconds. The linear contraction strain for the specimens cured with the two‐step method was not significantly different from that of the sample cured at the lower intensity for 40 seconds. Also, the post‐gel contraction strain increased linearly as the intensity of the light increased.

Conclusions: The degree of conversion was more sensitive to changes in light intensity at the bottom of the composite than at the top. Also, strain was linearly related to light intensity (i.e., greater intensity = more strain). Finally, the specimens cured with the two‐step method showed a 21.8% reduction from the contraction strain predicted from a light energy density calculation.
Identification of the gene encoding a type 1 RNase H with an N‐terminal double‐stranded RNA binding domain from a psychrotrophic bacterium
Authors: Tadokoro Takashi , Chon Hyongi , Koga Yuichi , Takano Kazufumi , Kanaya Shigenori
Published: July 2007

The gene encoding a bacterial type 1 RNase H, termed RBD‐RNase HI, was cloned from the psychrotrophic bacterium Shewanella sp. SIB1, overproduced in Escherichia coli, and the recombinant protein was purified and biochemically characterized. SIB1 RBD‐RNase HI consists of 262 amino acid residues and shows amino acid sequence identities of 26% to SIB1 RNase HI, 17% to E. coli RNase HI, and 32% to human RNase H1. SIB1 RBD‐RNase HI has a double‐stranded RNA binding domain (RBD) at the N‐terminus, which is commonly present at the N‐termini of eukaryotic type 1 RNases H. Gel mobility shift assay indicated that this domain binds to an RNA/DNA hybrid in an isolated form, suggesting that this domain is involved in substrate binding. SIB1 RBD‐RNase HI exhibited the enzymatic activity both in vitro and in vivo. Its optimum pH and metal ion requirement were similar to those of SIB1 RNase HI, E. coli RNase HI, and human RNase H1. The specific activity of SIB1 RBD‐RNase HI was comparable to that of E. coli RNase HI and was much higher than those of SIB1 RNase HI and human RNase H1. SIB1 RBD‐RNase HI showed poor cleavage‐site specificity for oligomeric substrates. SIB1 RBD‐RNase HI was less stable than E. coli RNase HI but was as stable as human RNase H1. Database searches indicate that several bacteria and archaea contain an RBD‐RNase HI. This is the first report on the biochemical characterization of RBD‐RNase HI.
Dose reduction for cardiac CT using a registration‐based approach
Authors: Wierzbicki Marcin , Guiraudon Gérard M. , Jones Douglas L. , Peters Terry
Published: July 2007

Two reasons for the recent rise in radiation exposure from CT are increases in its clinical applicability and the desire to maintain high SNR while acquiring smaller voxels. To address this emerging dose problem, several strategies for reducing patient exposure have already been proposed. One method employed in cardiac imaging is ECG‐driven modulation of the tube current between 100% at one time point in the cardiac cycle and a reduced fraction at the remaining phases. In this paper, we describe how images obtained during such acquisition can be used to reconstruct 4D data of consistent high quality throughout the cardiac cycle. In our approach, we assume that the mid‐diastole (MD) phase is imaged with full dose. The MD image is then independently registered to lower dose images (lower SNR) at other frames, resulting in a set of transformations. Finally, the transformations are used to warp the MD frame through the cardiac cycle to generate the full 4D image. In addition, the transformations may be interpolated to increase the temporal sampling or to generate images at arbitrary time points. Our approach was validated using various data obtained with simulated and scanner‐implemented dose modulation. We determined that as little as 10% of the total dose was required to reproduce full quality images with a spatial error and an error in intensity values on the order of the image noise. Thus, our technique offers considerable dose reductions compared to standard imaging protocols, with minimal effects on the quality of the final data.
A strategy to correct for intrafraction target translation in conformal prostate radiotherapy: Simulation results
Authors: Keall P. J. , Lauve A. D. , Hagan M. P. , Siebers J. V.
Published: July 2007

A strategy is proposed in which intrafraction internal target translation is corrected for by repositioning the multileaf collimator position aperture to conform to the new target pose in the beam projection, and the beam monitor units are adjusted to account for the change in the geometric relationship between the target and the beam. The purpose of this study was to investigate the dosimetric stability of the prostate and critical structures in the presence of internal target translation using the dynamic compensation strategy. Twenty‐five previously treated prostate cancer patients were replanned using a four‐field conformal technique to deliver to 95% of the planning target volume (PTV). Internal translation was introduced by displacing the prostate PTV (no rotation or deformation was considered). Thirty‐six randomly selected isotropic displacements of magnitude 0.5, 1.0, 1.5 and were sampled for each patient, for a total of 3600 errors. Due to their anatomic relation to the prostate, the rectum and bladder contours were also moved with the same magnitude and direction as the prostate. The dynamic compensation strategy was used to correct each of these errors by conforming the beam apertures to the new target pose and adjusting the monitor units using inverse‐square and off‐axis factor corrections. The dynamic compensation strategy plans were then compared to the original treatment plans via dose‐volume histogram (DVH) analysis. Changes of more than 5% of the prescription dose were deemed clinically significant. Compared to the original treatment plans, the dynamic compensation strategy produced small discrepancies in isodose distributions and DVH analyses for all structures considered apart from the femoral heads. These differences increased with the magnitude of the internal motion. Coverage of the PTV was excellent: , , and were not increased or decreased by more than 5% of the prescription dose for any of the 3600 simulated internal motion shifts. Dose increases for adjacent organs at risk were rare. of the rectum and of the bladder were increased by more than 5% of the prescription dose in 9 and 1 instances of the 3600 sampled internal motion shifts, respectively. of the right femoral head increased by more than 5% of the prescription dose in 651 (18%) internal motion shifts, predominantly due to the projection of the lateral beams through the femoral head for anterior prostate motion. However, was not increased by more than 5% for any of the internal motion shifts. These data demonstrate the robustness of the proposed dynamic compensation strategy for correction of internal motion in conformal prostate radiotherapy, with minimal deviation from the original treatment plans even for errors exceeding those commonly encountered in the clinic. The compensation strategy could be performed automatically with appropriate enhancements to available delivery software.
Handling data redundancy in helical cone beam reconstruction with a cone‐angle‐based window function and its asymptotic approximation
Authors: Tang Xiangyang , Hsieh Jiang
Published: July 2007

A cone‐angle‐based window function is defined in this manuscript for image reconstruction using helical cone beam filtered backprojection (CB‐FBP) algorithms. Rather than defining the window boundaries in a two‐dimensional detector acquiring projection data for computed tomographic imaging, the cone‐angle‐based window function deals with data redundancy by selecting rays with the smallest cone angle relative to the reconstruction plane. To be computationally efficient, an asymptotic approximation of the cone‐angle‐based window function is also given and analyzed in this paper. The benefit of using such an asymptotic approximation also includes the avoidance of functional discontinuities that cause artifacts in reconstructed tomographic images. The cone‐angle‐based window function and its asymptotic approximation provide a way, equivalent to the Tam‐Danielsson‐window, for helical CB‐FBP reconstruction algorithms to deal with data redundancy, regardless of where the helical pitch is constant or dynamically variable during a scan. By taking the cone‐parallel geometry as an example, a computer simulation study is conducted to evaluate the proposed window function and its asymptotic approximation for helical CB‐FBP reconstruction algorithm to handle data redundancy. The computer simulated Forbild head and thorax phantoms are utilized in the performance evaluation, showing that the proposed cone‐angle‐based window function and its asymptotic approximation can deal with data redundancy very well in cone beam image reconstruction from projection data acquired along helical source trajectories. Moreover, a numerical study carried out in this paper reveals that the proposed cone‐angle‐based window function is actually equivalent to the Tam‐Danielsson‐window, and rigorous mathematical proofs are being investigated.
SU‐DD‐A3‐03: Improvement in the Daily Alignment of Mobile Lung Tumors Using Implanted Fiducials
Authors: Nelson C , Balter P , Choi B , Vedam S , Lindsay P , Kudchadker R , Briere T , Chang J , Morice R , Starkschall G
Published: July 2007

Purpose: The purpose of this work is to develop, validate, and implement a technique in which imaged‐guided patient setup using gated kV images of implanted fiducials can be implemented for mobile lung tumors. Method and Materials: Software for matching markers by comparing 2D images with projections of 3D CT data sets was validated by acquiring respiratory‐gated kV images of a phantom on a moving platform. The procedures were implemented for patients in our clinic who have mobile lung tumors with fiducials implanted in the periphery of the tumors. Treatment was delivered using respiratory gating, and cine images of each of the gated treatment fields were acquired each treatment to examine uncertainties in tumor location after gated image guided alignment. Results: For the phantom study, the 2D‐3D marker matching software is accurate to within 1 mm. This accuracy is limited by the ability to locate the fiducials in the CT images (slice thickness 2.5 mm). Setup errors were reduced from 4 to 1 and 6 to 2 mm in the LR and SI directions (p<0.001 f‐test) respectively for our first patient. Shifts larger than 7 mm (PTV margin used to account for setup uncertainties) were observed on 13 of the 33 fractions for our first patient. Similar results were obtained for the other fiducial patients. Conclusion: Large variations in daily tumor position were observed and corrected for by acquiring gated kV images using the fiducials in these images for daily alignment. Respiratory gating in conjunction with image guided patient setup (planar kV imaging) using fiducials implanted near mobile lung tumors is an effective method of accurately aligning tumors without acquiring higher‐dose volumetric CT scans. This technique can be implemented using both kV imaging and standard MV portal imaging.