Neutron skin of (208)pb from coherent pion photoproduction.

Information on the size and shape of the neutron skin on (208)Pb is extracted from coherent pion photoproduction cross sections measured using the Crystal Ball detector together with the Glasgow tagger at the MAMI electron beam facility. On exploitation of an interpolated fit of a theoretical model to the measured cross sections, the half-height radius and diffuseness of the neutron distribution are found to be c(n)=6.70±0.03(stat.) fm and a(n)=0.55±0.01(stat.)(-0.03)(+0.02)(sys.) fm, respectively, corresponding to a neutron skin thickness Δr(np)=0.15±0.03(stat.)(-0.03)(+0.01)(sys.) fm. The results give the first successful extraction of a neutron skin thickness with an electromagnetic probe and indicate that the skin of (208)Pb has a halo character. The measurement provides valuable new constraints on both the structure of nuclei and the equation of state for neutron-rich matter.

Photoproduction of π0 mesons off neutrons in the nucleon resonance region.

Precise angular distributions have been measured for the first time for the photoproduction of π0 mesons off neutrons bound in the deuteron. The effects from nuclear Fermi motion have been eliminated by a complete kinematic reconstruction of the final state. The influence of final-state-interaction effects has been estimated by a comparison of the reaction cross section for quasifree protons bound in the deuteron to the results for free protons and then applied as a correction to the quasifree neutron data. The experiment was performed at the tagged photon facility of the Mainz Microtron MAMI with the Crystal Ball and TAPS detector setup for incident photon energies between 0.45 and 1.4 GeV. The results are compared to the predictions from reaction models and partial-wave analyses based on data from other isospin channels. The model predictions show large discrepancies among each other and the present data will provide much tighter constraints. This is demonstrated by the results of a new analysis in the framework of the Bonn-Gatchina coupled-channel analysis which included the present data.

Measurement of the 1H(γ, p)π0 reaction using a novel nucleon spin polarimeter.

We report the first large-acceptance measurement of polarization transfer from a polarized photon beam to a recoiling nucleon. The measurement pioneers a novel polarimetry technique, which can be applied to many other nuclear and hadron physics experiments. The commissioning reaction of 1H(γ, p)π0 in the range 0.4

Measurement of Compton scattering from the deuteron and an improved extraction of the neutron electromagnetic polarizabilities.

The electromagnetic polarizabilities of the nucleon are fundamental properties that describe its response to external electric and magnetic fields. They can be extracted from Compton-scattering data-and have been, with good accuracy, in the case of the proton. In contradistinction, information for the neutron requires the use of Compton scattering from nuclear targets. Here, we report a new measurement of elastic photon scattering from deuterium using quasimonoenergetic tagged photons at the MAX IV Laboratory in Lund, Sweden. These first new data in more than a decade effectively double the world data set. Their energy range overlaps with previous experiments and extends it by 20 MeV to higher energies. An analysis using chiral effective field theory with dynamical Δ(1232) degrees of freedom shows the data are consistent with and within the world data set. After demonstrating that the fit is consistent with the Baldin sum rule, extracting values for the isoscalar nucleon polarizabilities, and combining them with a recent result for the proton, we obtain the neutron polarizabilities as αn=[11.55±1.25(stat)±0.2(BSR)±0.8(th)]×10(-4) fm(3) and ßn=[3.65∓1.25(stat)±0.2(BSR)∓0.8(th)]×10(-4) fm(3), with χ(2)=45.2 for 44 degrees of freedom.

Narrow structure in the excitation function of η photoproduction off the neutron.

The photoproduction of η mesons off nucleons bound in 2H and 3He has been measured in coincidence with recoil protons and recoil neutrons for incident photon energies from threshold up to 1.4 GeV. The experiments were performed at the Mainz MAMI accelerator, using the Glasgow tagged photon facility. Decay photons from the η→2γ and η→3π0 decays and the recoil nucleons were detected with an almost 4π electromagnetic calorimeter combining the Crystal Ball and TAPS detectors. The data from both targets are of excellent statistical quality and show a narrow structure in the excitation function of γn→nη. The results from the two measurements are consistent, taking into account the expected effects from nuclear Fermi motion. The best estimates for position and intrinsic width of the structure are W=(1670±5) MeV and Γ=(30±15) MeV. For the first time precise results for the angular dependence of this structure have been extracted.

Beam-helicity asymmetries in double-pion photoproduction off the proton.

Beam-helicity asymmetries have been measured at the MAMI accelerator in Mainz in the three isospin channels gamma[over -->]p-->pi(+)pi(0)n, gamma[over -->]p-->pi(0)pi(0)p, and gamma[over -->]p-->pi(+)pi(-)p. The circularly polarized photons, produced from bremsstrahlung of longitudinally polarized electrons, were tagged with the Glasgow magnetic spectrometer. Charged pions and the decay photons of pi(0) mesons were detected in a 4pi electromagnetic calorimeter which combined the Crystal Ball detector with the TAPS detector. The precisely measured asymmetries are very sensitive to details of the production processes and are thus key observables in the modeling of the reaction dynamics.

Incoherent neutral pion photoproduction on 12C.

We present the first detailed measurement of incoherent photoproduction of neutral pions to a discrete state of a residual nucleus. The 12C(gamma,pi(0))(12)C*(4.4 MeV) reaction has been studied with the Glasgow photon tagger at MAMI employing a new technique which uses the large solid angle Crystal Ball detector both as a pi(0) spectrometer and to detect decay photons from the excited residual nucleus. The technique has potential applications to a broad range of future nuclear measurements with the Crystal Ball and similar detector systems elsewhere. Such data are sensitive to the propagation of the Delta in the nuclear medium and will give the first information on matter transition form factors from measurements with an electromagnetic probe. The incoherent cross sections are compared to two theoretical predictions including a Delta-hole model.

Relationship between the standards of removable partial denture construction, clinical acceptability, and patient satisfaction.

STATEMENT OF PROBLEM: Little is known about the importance of published fabrication standards in determining the outcome of treatment with mandibular distal extension removable partial dentures in patients of community practices. PURPOSE: This study describes mandibular partial dentures worn by patients from King County, Wash., and examines the validity of standards of design and fabrication by relating the standards to measures of clinical acceptability and patient satisfaction. MATERIAL AND METHODS: Eighty-two people treated in private dental practices who responded to a mail survey about satisfaction with a partial denture were examined. Eight standards of fabrication, overall clinical acceptability of the prosthesis, and tissue health were evaluated clinically. Patient satisfaction was assessed by questionnaire. Associations between variables were assessed by contingency tables and odds ratios. RESULTS: Half the prostheses met 4 or fewer of the 8 standards, and these were responsible for nearly all the displacement of tissue by the framework. Forty-three percent of the dentures (35/82) were rated clinically acceptable. Of the remaining dentures, 38 could be made acceptable by modifications. The remaining 9 dentures needed replacement. Sixty-three percent of the patients examined were satisfied with the dentures. There was a relationship between tissue health and the fabrication standards related to rest form, base extension, stress distribution, and framework fit. This study found no relation between tissue health and other design or fabrication features. None of the standards were found to be related to patient satisfaction. CONCLUSION: This study found partial support for the validity of design/fabrication standards for removable partial dentures. The most important standards are rest form, base extension, and stress distribution. The standards appear to be unrelated to patient satisfaction.

Surgical template for completely edentulous patients.

Implant angulation is of utmost importance for fabrication of esthetic, hygienic, and functional prostheses, even in the treatment of completely edentulous patients. Most mandibular surgical templates are not reliable because of a lack of stability resulting either from severe resorption of the mandible or from the interference of mucoperiosteal flaps elevated during surgery. This article describes a technique for fabrication and surgical application of a stable template for the completely edentulous mandible. By combining the mandibular template with a maxillary duplicate denture, the problem of lack of stability can be overcome. A consistently reliable reference for implant placement in the edentulous mandible, specifically in relation to implant angulation (trajectory), can be obtained.

The swing-lock removable partial denture in clinical practice.

The authors of this article consider that the swing-lock partial denture has a useful place in contemporary clinical dental practice and offers many advantages compared with conventional removable partial dentures in terms of retention and stability, especially in the extremely compromised dentitions. Here they describe the concept of the swing-lock removable partial denture, together with the indications, contraindications, technical and clinical considerations.

Retention of ERA direct overdenture attachments before and after fatigue loading.

This in vitro study investigated the retention of the four different color-coded ERA attachments prior to and after various levels of fatigue loading (at baseline, at 500 cycles, and after every 500 cycles up to 5,500 cycles). Samples were placed in the Instron testing machine for determination of initial retentive values and then cycled in a specially designed fatigue machine and retested. The results of this study demonstrated that although there are four different retentive elements supplied by the manufacturer of the ERA system, there were only two significantly different groups; (1) the white attachments and (2) the orange, blue, and gray attachments (P < .05). After 500 cycles, there was a loss in retention of 60% for the white, 60% for the orange, 56% for the blue, and 54% for the gray. After 1,500 cycles there was no difference in retentive values for any of the four colored attachments (P < .05). Microscopic examination of worn specimens supported the findings of the fatigue testing.

Frictional resistance of removable partial dentures with retrofitted resin composite guide planes.

Frictional resistance to the dislodging forces of a removable partial denture with and without resin composite retrofitted guide planes was compared in vitro. Six master models of four natural teeth, each simulating a Kennedy Class III modification 1 arch, were used. Guide planes were prepared, and 18 cobalt-chromium removable partial denture frameworks without clasps were fabricated. Three resin composite materials were applied to the guide planes as retrofitting materials. Following this, the resistance to dislodgment of the removable partial denture framework was evaluated under cyclic dislodgment, and the resistance to dislodgment before and after resin composite retrofitted guide planes was compared. The dislodgment force was recorded every 500 cycles. Testing was concluded when the dislodging force value reached 50% of the initial value. There was a significant difference between the dislodging forces with and without retrofitted guide planes. Higher dislodging forces were recorded when resin composite retrofitted guide planes were used. Z100 was the most effective retrofitting material under cyclic dislodgment, and Heliomolar and Herculite XR performed similarly.

Influence of reinforcement design on the loss of marginal seal of provisional fixed partial dentures.

Loss of marginal cement seal, initial fracture, and stiffness of three four-unit provisional restorations were tested. Loss of marginal cement seal was monitored using strain gauges located occlusogingivally at the distal of the second molar abutment and the mesial of the first premolar abutment of a four-unit posterior fixed provisional restoration with two pontics. The provisional restorations were then placed in an Instron testing machine and loaded to initial fracture. Stiffness was calculated from the Instron recordings. The provisional designs were permachrome band-reinforced, wire-reinforced, and a nonreinforced control. Analysis showed: (1) the band-reinforced design withstood a significantly greater load before loss of cement seal (P< or =.05); (2) the band-reinforced design had a significantly higher stiffness (P< or =.05); and (3) there was no difference between the three designs for load at initial fracture. Within the same sample it was found that for both band- and wire-reinforced designs the premolar abutment lost the marginal cement seal at a significantly lower load than the molar (P< or =.05). For the control there was no significant difference for load at marginal cement seal loss between abutments.

A new procedure to reinforce fixed provisional restorations.

The typical unreinforced fixed partial denture provisional restoration commonly fails because of fractures and loss of cement retention. A procedure to reinforce the provisional restoration with a substructure of orthodontic band material has dramatically increased the longevity of this restoration. The procedure requires commonly available materials without a significant increase in cost or construction time.

The effect of dentin primer on the tensile bond strength to human enamel.

Four third-generation dentin bonding products (Scotchbond Multi-Purpose, Optibond, All-Bond 2, and Prisma Universal Bond 3) were tested to evaluate their tensile bond strength to enamel. Test enamel specimens were etched, primed, and polymerized according to each manufacturer's directions. Control specimens were treated identically except the primer application was eliminated. The results demonstrated that the dentin primer significantly increased the tensile bond strength of All-Bond 2, significantly decreased the tensile bond strength of Scotchbond Multi-Purpose and Optibond, and had no significant effect for Prisma Universal Bond 3. A one-way analysis of variance was run between the eight groups tested, and three significant subsets were found (P < .05). The subset with the highest mean tensile bond strengths consisted of Prisma Universal Bond 3 primed and nonprimed, All-Bond 2 primed, and Optibond nonprimed.

Accuracy of replacing three tapered transfer impression copings in two elastomeric impression materials.

The accuracy of replacing three manufacturers' (Dental Imaging Associates, Implant Innovations Inc, and Steri-Oss) tapered transfer impression copings into impressions made with two different materials (Impregum F and Extrude) was evaluated. Five operators replaced these copings into the elastomeric impression materials. The angular deviations (replacement error) of the copings between the control (original) position and the replaced position in the impressions were evaluated. It was found that no one coping could be replaced into the impressions accurately and consistently by all five operators. However, there were significant differences in replacement accuracy between the three copings. Lower angular deviations were found for the Steri-Oss and Dental Imaging Associates copings when compared to the Implant Innovations coping. There was no significant difference in replacement accuracy between the two impression materials.

The tooth-removable partial denture interface.

During the metal finishing phase of removable partial denture construction, metal is removed from all aspects of the casting. The amount removed from areas designed to contact prepared surfaces of abutments is critical to the resulting fit of the partial. Castings were evaluated before and during finishing procedures to measure metal loss at the tooth-removable partial denture interface. Finishing and fitting techniques for controlling the loss of metal are presented.

Dental students' self-assessed competence in geriatric dentistry.

This study measured the self-assessed confidence levels of four classes of dental students (n = 172) exposed to both didactic and clinical training regarding geriatric patients. It was found that after completing a two-term (20-week) didactic course in their junior year, and a five-week clinical course with geriatric patients in their senior year, dental students graduating from this university between 1987 and 1990 perceived significant improvements in their abilities to manage geriatric patients in all areas assessed, most notably in their treatment planning skills, in coordinating preventive dentistry programs, in referring patients to appropriate community resources, and in providing dental care in alternative settings. Greatest self-assessed improvements were exhibited between pre-didactic and post-didactic assessments, with a tendency to stabilize rather than improve after the clinical experience. Interestingly, this study found that the students' self-assessed changes between post-didactic training and post-clinical training were significant in only one area--their ability to manage the medical emergencies of elderly patients, including a patient's death in the dental chair. No differences were found between students who completed the clinical course early in their senior year with those who took it later; nor did differences emerge among the four classes. Clinical teaching in geriatrics may be an opportunity to practice skills and reinforce knowledge that has been gained in didactic courses, not necessarily a place to enhance perceived competence.

Evaluation of heat-cured resin bases following the addition of denture teeth using a second heat cure.

This study compared heat-cured acrylic resin denture baseplate distortions following a second heat cure used to add the denture teeth. The second heat cure was done with three different water-bath curing temperatures. The distortions were evaluated in three planes by use of a measuring microscope. Recorded distortions were not clinically significant.

In vitro two-body wear of inlay-onlay composite resin restoratives.

Inlay-onlay composite resin restorations have been introduced to the profession as alternatives to amalgam and direct composite resins. Two-body wear testing was performed on three inlay-onlay resins and one direct composite resins using a machine designed to produce sliding wear. The composite resins were opposed by human enamel, type III gold alloy, and porcelain. Of the investigated materials, the homogeneously microfilled inlay-onlay material showed significantly less wear. The direct composite resin showed significantly the greatest wear. The hybrid inlay-onlay resins showed intermediate wear. The hybrid inlay-onlay resins and the direct composite (small particle, heavily filled) resin created wear tracks in the opposing surfaces while the homogeneous microfill inlay-onlay resin did not. The depth of the observed wear tracks in the opposing surface was sufficiently substantial to warrant further investigation into the wear of materials that oppose composite resin restorations.