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Rigidity is a requirement of removable partial denture frameworks. Although commonly used by dentists, the U-shaped (horseshoe) maxillary major connector lacks the rigidity of other maxillary major connector designs.The purpose of this study was to determine the effects of changing width, thickness, and shape on the rigidity of U-shaped maxillary major connectors.Five nickel-chrome alloy frameworks were fabricated from the same master cast for each of 4 different U-shape removable partial denture designs. The designs were an 8-mm wide U-shaped strap with a 6-mm posterior strap (A-P strap), a 13-mm-wide U-shape strap (Wide), an 8-mm-wide U-shape strap that widened to 13 mm at the midline (Notch), and an 8-mm-wide U-shaped strap that was twice the thickness of the other straps (Thick). A fifth group of 5 frameworks was made by removing the posterior strap from the A-P strap frameworks (A strap). Two testing points were marked on each framework corresponding to the first premolar and second molar positions. The frameworks were mounted in a universal testing machine, and vertical (torsional) and horizontal (compressive) loads were applied using a 10-kN load cell at a cross-head speed of 2 mm/min until a deflection of 1 mm occurred. A force-deflection curve was generated for each test, and slope of the curves (N/mm) was compared with analysis of variance and Scheffe's F test (alpha=0.05).The Thick group was found to be significantly more rigid (P.05) than the other frameworks when torsional loads were applied to both the premolar (22.42 N/mm) and molar (10.88 N/mm) areas, and when a compressive load was applied to the premolar (232.85 N/mm) area. The A-P strap group was significantly more rigid (Por =.05) than the other designs when a compressive load was applied to the molar (69.56 N/mm) area. Both the Thick and A-P strap groups were significantly more rigid (P.05) than the Notch and A strap groups in all tests.Doubling the thickness of the anterior strap of a U-shaped maxillary major connector improved the rigidity of the framework to torsional loads. A posterior strap became more effective in maintaining framework rigidity to compressive forces as the length of the arch increased.

The mandibular position indicator (MPI) was used to compare condylar position between centric relation (CR) and centric occlusion (CO) for 107 patients before orthodontic treatment. The MPI data were examined to determine frequency, direction, and magnitude of CO-CR difference; and data were analyzed for possible correlation to the patient's Angle classification, ANB angular measurement, age, or gender. Only one patient (0.9%) had no measurable CO-CR difference in all three spatial planes. Six subjects (5.6%) showed a shift in condylar position in the transverse plane without a measurable difference in the sagittal plane. Twenty patients (18.7%) experienced a superoinferior (SI) or anteroposterior (AP) condylar displacement of at least 2.0 mm on one or both sides; 17 (15.9%) displayed a transverse shift at the level of the condyles of 0.5 mm or greater. No statistical difference was found between the 31 patients with Class I malocclusions and 72 patients with Class II malocclusions when comparing the amount or direction of CO-CR change. The amount of CO-CR difference was nearly identical for right and left sides with the amount of SI displacement (x = 0.84 mm) consistently greater than AP displacement (x = 0.61 mm). Only weak correlations were found between movements of right and left condyles. The average transverse CO-CR difference was 0.27 mm. Patient age, ANB angle, gender, or Angle classification cannot be used to predict frequency, magnitude, or direction of CO-CR changes at the level of the condyles.

The purpose of this study was to evaluate the mechanical and bond strength properties of a commercially available light-cured glass ionomer cement and of a chemically cured glass ionomer cement. Sixty recently extracted human molars were randomly divided into six equal groups, and the bond strengths of the two cement types were evaluated at 1 hour, 24 hours, and 7 days. Stainless steel lingual buttons were bonded to prepared enamel surfaces, and the samples were placed in a water bath at 37 degrees C until testing. The shear bond strength of each sample was determined with a universal testing instrument. The mechanical strength properties of the two cements were then evaluated. The transverse flexural strength, compressive strength, rigidity, and diametral tensile strength were tested for each cement at 1 hour, 24 hours, and 7 days. The results of the mechanical property strength tests were then compared with the results of the bond strength tests.(ABSTRACT TRUNCATED AT 250 WORDS)

Light-cured glass ionomers with an initial set of 20 seconds may produce higher initial bond strengths, as well as decreased sensitivity to moisture contamination and desiccation, than chemically cured glass ionomers making them attractive for use as orthodontic bonding agents. The purpose of this study was to determine and compare the shear bond strength of stainless steel orthodontic attachments to enamel with a light-cured glass ionomer (Zionomer) tested at 60 minutes and 24 hours, and a rapidly setting chemically cured glass ionomer (Ketac-Bond) tested at 60 minutes and 24 hours. Fifty-two recently extracted human premolars were randomly divided into four groups—1-hour and 24-hour light-cured glass ionomer groups and 1-hour and 24-hour chemically cured glass ionomer groups. Stainless steel lingual buttons were bonded to prepared enamel surfaces, and the samples were placed in a water bath at 37° C until ready for testing. The shear bond strength of each sample was determined with a universal testing instrument. Results from the study conclude: (1) The mean shear bond strength of the light-cured glass ionomer is greater than that of the chemically cured glass ionomer at 1 and 24 hours. (2) The mean shear bond strength of both glass ionomers increases from 1 to 24 hours. (3) The mean shear bond strength of the lightcured glass ionomer is not significantly different from 1 to 24 hours, but the shear bond strength of the chemically cured glass ionomer cement is different. The faster setting reaction of the light-cured glass ionomer and its higher initial and sustained bond strength make it more attractive for use as an orthodontic bonding agent.

The purpose of this study was to determine the sensitivity and the specificity of detecting the presence and extent of occlusal carious lesions using traditional examination techniques performed by three experienced restorative dentists and a laser fluorescence-measuring device (DIAGNOdent) on 100 extracted third maxillary and mandibular molars. The extracted teeth were selected to ensure presence of questionable occlusal caries and intact occlusal surfaces. The results revealed that the DIAGNOdent demonstrated a higher sensitivity (94%) compared to the clinicians' consensus (82%) but a lower specificity. This study also indicated that higher values of the DIAGNOdent do not appear to correlate well with the depth of the carious lesion in the dentin (r = 0.3809) as measured by a caries-detecting dye.

A survey of published prospective and retrospective studies examining the longevity of posterior resin-based composite and amalgam restorations confirms the need for clinical judgment in materials selection.

The purpose of this study was to compare 10% carbamide peroxide to the combination of sodium perborate and water as intracoronal bleaching agents. Forty-four extracted teeth were discolored in vitro. Bleaching agents were placed intracoronally to the level of the cemento-enamel junction for 12 days; solutions were replaced after four and eight days. Standardized slides were used to rank color changes; a colorimeter was used to quantify color change. After 12 days, 65% of the discolored teeth in the 10% carbamide peroxide group and 67% of the discolored teeth in the sodium perborate group had lightened to their original shade or lighter. While there was no statistical difference between the two treatments, sodium perborate was easier to use.

The radiopacity of intermediate restorative materials should be sufficient to enable the clinician to distinguish the material from normal and decalcified tooth structure. The purpose of this study was to determine the relative radiopacities of intermediate restorative materials, including a newly introduced high-viscosity, self-cured, condensable glass ionomer material. Radiographs were made of six intermediate restorative materials: two reinforced zinc oxide-eugenol materials (IRM and Zinroc), a conventional glass ionomer material (Ketac-fil), a synthetic resin material (Cavit), a eugenol-free zinc oxide material (Tempit), and a new, general-purpose, condensable glass ionomer material (Fuji IX-GP). Optical density was measured using a densitometer. The optical density of dentin and enamel were used for radiographic comparison. Statistical analysis revealed significant differences among materials: Cavit = IRM = TempitZinroc = Fuji IX-GPKetac-fil = enameldentin (whereindicates a statistical difference at por = 0.05). Although not as radiopaque as some other intermediate materials tested, the radiopacity of Fuji IX-GP appears sufficient to aid diagnosis.

New temporary dental restorative materials are an important military requirement. This study compares the critical properties of the currently used temporary material, reinforced zinc oxide-eugenol (ZOE), with those of a glass ionomer restorative material (GI), a high-viscosity modified glass ionomer material (MGI), and two resin-modified glass ionomer materials (RMGIs). Properties tested included compressive and tensile strength, rigidity, hardness, bond strength, working and setting times, and storage stability. Ranked results for compressive strength, rigidity, and hardness were MGIGIRMGIZOE; for tensile strength they were RMGIMGIGIZOE; and for storage stability they were ZOEMGIGIRMGI. Working and setting times were all within reasonable clinical limits, and bond strength was heavily dependent on tooth surface preparation. Although none of the materials tested met all of the ideal requirements, the high-viscosity glass ionomer material offers the most promise for military field use.

Statement of problem. A secure bond between resin and an alloy framework is necessary for clinical success in removable prosthodontics. Purpose. This study compared the shear bond strength of composite to metal with two commercially available chemical bonding systems: a silicoating system (Silicoater) and a nitrogenous heterocycle-acrylonitrile system (Kevloc). Material and methods. Fifty-two nickel-chromium cubes were cast and composite resin was bonded to the alloy surfaces according to manufacturer's directions. After storage at 35° C for 15 days, and thermocycling at 5° C and 55° C for 1200 cycles, the bonds were fractured in shear on a universal testing machine. Results. Mean bond strength for the silicoated sample was 10.93 MPa and for the heterocycle-acrylnitrate system 11.44 MPa. An unpaired t test revealed no difference between the groups ( p = 0.60). Visual inspection of the fracture surfaces revealed that failure was adhesive at the resin-to-metal surface in almost all the specimens. (J Prosthet Dent 1998;79:270-3.)

In this study, various luting agents were evaluated to determine their retentive strengths as they pertain to the CeraOne single-tooth implant system. Ten samples of five different luting agents (zinc oxide-eugenol, glass-ionomer cement, hybrid glass-ionomer cement, composite resin, and zinc phosphate) were tested for retentive strength of the CeraOne gold cylinder to the CeraOne abutment. Under the conditions of the experiment, zinc phosphate showed a mean retentive strength 164% greater than that of glass-ionomer cement and 49% greater than that of composite resin cement. Scanning electron micrographs were taken to evaluate the effect of various luting agents on marginal opening. The measurements revealed that zinc phosphate had the greatest marginal opening, although its mean value of 62 microns is within clinically acceptable limits.

Statement of problem. Studies have suggested that coating a temporary soft denture liner with a semiset methyl methacrylate resin extends the period of resiliency of the liner. Purpose. This study determined whether coating three temporary soft denture liners with two different denture surface sealants, followed by thermocycling, affected the resiliency of the liners. Material and methods. Thirty 20 × 12.5 mm cylindrical samples each of Lynal, Coe Soft, and Visco-Gel soft lining materials were prepared and divided into three groups of 10 uncoated samples, 10 Palaseal-coated samples, and 10 mono-poly coated samples. Samples were thermocycled from 5° C to 45° C for 500 cycles and then compressed 10 mm on an Instron universal testing machine. Resiliency was determined by measuring the energy absorbed by the soft liners when stressed to a specific yield point. Results. Two-way ANOVA indicated a significant difference among materials ( p = 0.0001) and among treatments ( p = 0.0001). One-way ANOVA of each material group revealed a significant difference among Lynal groups ( p = 0.0001) and a significant difference among Visco-Gel groups ( p = 0.030). Conclusions. Surface-coating Lynal samples with Palaseal or mono-poly and Visco-Gel samples with Palaseal significantly increased the resiliency of these samples in the laboratory when compared with uncoated samples. (J Prosthet Dent 1997;77:370-4.)

To evaluate the effectiveness of 3 cavity-preparation lining agents in reducing microleakage under amalgam restorations, the apices of 64 human molars were sealed with amalgam, and Class V preparations were placed. Following storage and thermocycling, the molars were placed in acid fuchsin for 24 hours, then sectioned longitudinally. Ranked data were used to score dye penetration. A Kruskal-Wallis statistical test was used to compare the three groups to the control. Teeth treated with glass ionomer cement showed a statistically significant increase (p = .0227) in dye penetration. Dye penetration increased when Amalgambond Plus and glass ionomer resin liner were placed under amalgam restorations. No difference in dye penetration was observed when Copalite was applied. Results of this study do not support routine use of these agents under amalgam restorations for control of microleakage.

pH affects the efficacy of local anesthetics by determining the percentage of the lipid-soluble base form of the anesthetic available for diffusion and penetration of the nerve sheath. The purpose of this study was to determine the relationship between pH and the concentrations of antioxidant and vasoconstrictor in dental local anesthetic solutions over real-time and after accelerated aging. Several batches of lidocaine and mepivacaine with vasoconstrictors were tested. Results showed that, immediately upon receipt from the manufacturers, three batches were below the USP pH limit (pH 3.3), and two batches contained less than the minimum limit of vasoconstrictors (90%). Real-time tests on batches that were within normal limits revealed that solutions were stable past 4 yr. Accelerated aging tests revealed a strong correlation between a decrease in pH and loss of antioxidants and vasoconstrictors. In conclusion, a quality batch of local anesthetic should remain efficacious long past the manufacturer's stated shelf life; a batch that is less than optimal, or one that is exposed to environmental stresses, will degrade rapidly, and efficacy may be affected by decreases in pH and loss of vasoconstrictor. pH may be an inexpensive, readily available screening test for efficacy of local anesthetics.

The adhesive monomer, Clearfil New Bond, was used to enhance the bond strength between orthodontic brackets and primary molars, premolars, and NiCr crowns. Twenty specimens of each had this dental adhesive applied according to the manufacturer's instructions in addition to a chemically cured composite material. The remaining specimens (20 each) were bonded without the adhesive monomer. Shear bond strengths were determined using a universal testing machine. Fracture sites were examined to determine the type of bond failure. All bond strengths were significantly increased with the addition of Clearfil New Bond (Por = 0.0001). The shear bond strength to NiCr crowns with the addition of the adhesive monomer was 7.76 kg. This is comparable to the shear bond strength observed for primary molars (8.66 kg) and premolars (8.65 kg) without adhesive monomer. The observed decrease in adhesive bond failures with the addition of Clearfil New Bond indicated a stronger shear bond strength between the tooth surface and the bracket base. Clearfil New Bond can significantly increase the shear bond strength of orthodontic brackets to both primary molars and premolars. Additionally, it was shown that orthodontic brackets can be successfully bonded to Ni-Cr crowns at strengths comparable to primary or permanent enamel.

A dental impression material must have sufficient strength to allow removal from a gingival sulcus without tearing; it must also have adequate elastic recovery. This study examined the tear energy, the permanent deformation upon extension, the energy absorbed to an estimated point of significant deformation, and the extent of permanent deformation at tear of polysulfide, polyether, and addition-reaction silicone impression materials. As expected, polysulfide material had a higher tear energy and strain at tear than either polyether or addition-reaction silicone materials. However, the more relevant clinical properties, such as energy absorbed per amount of deformation and tear at a point of minimal permanent deformation, favored the addition-reaction silicone material, followed by the polyether material.

Recent manufacturer recalls of local anesthetics have emphasized the problems with storage stability. This article reviews the principles of drug stability, mechanisms of degradation of commonly used vasoconstrictors, research on the stability of commercially produced local anesthetic preparations, and possible effects of the container-closure system. The review concludes with a list of practical and clinical suggestions on how to minimize storage stability problems with dental local anesthetics.

Postceramic soldering of collarless veneered retainers in which the porcelain margins were formed with a platinum foil matrix technique was investigated. The purpose of the study was to determine if removing the platinum foil matrix before or after indexing and soldering procedures would affect the porcelain margin integrity in fixed partial dentures. Prostheses were fabricated on a nickel-chromium laboratory model using both sequences. Six test cycles were performed. Each cycle included one soldering with matrix support and one without the matrix, for a total of 12 solderings. The fixed partial dentures were compared for degree of marginal seating with a measuring microscope and for configuration changes at the porcelain margins with scanning electron micrographs. In the microscopic analysis of marginal closure, soldering without foil matrix was statistically equal to soldering with foil in place. Removal of the platinum foil matrices prior to indexing provided for no further seating of the metal ceramic retainers. Evaluation by scanning electron microscopy demonstrated distinct configuration changes in the porcelain margins for the specimens soldered without matrix support.

The concept of interim or transitional dentures is appropriate to the treatment of older patients who are hospitalized or medically compromised. This paper briefly reviews the emotional and physiological needs of these patients, and illustrates a case in which an interim denture technique was beneficial.