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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.

Statement of problem. Storage stability, or shelf life, is a critical property of perishable dental materials. Purpose. The purpose of this investigation was to document changes in the properties of nonaqueous elastomeric impression materials over time and on exposure to various environmental conditions. Material and methods. Materials investigated included a polyether impression material, a polysulfide material (light, regular, and heavy consistencies), and an addition-reaction silicone material (light, regular, heavy, and putty consistencies). Tests included viscosity of individual pastes, elastic recovery, working and setting times, strain in compression, dimensional change, creep compliance, and tear energy. Means and standard deviations were calculated for each test interval. Statistical analysis included 2-way ANOVA (variables: time and storage condition) and comparison to baseline values using 1-way ANOVA (variable: time) and Scheffe's multiple comparison test ( P ≤.05) within each material, consistency, and test. Results. Results over 72 months revealed changes in viscosity, working/setting times, elastic recovery, and creep compliance. Separation of components was seen with polysulfide and addition silicone materials. Some batches of polysulfide base paste and polyether reactor paste solidified in the tube. Conclusion. Most batches of the materials and consistencies tested remained efficacious well past their designated shelf lives under a variety of storage and use conditions. Data for the addition-reaction silicone impression material changed little during the 72-month testing period; thus, the material may be considered relatively storage stable. Creep compliance was the most precise storage-stability indicator. The storage stability of perishable materials should be addressed in American Dental Association Specifications. (J Prosthet Dent 2001;85:73-81.)

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 = Tempit > Zinroc = Fuji IX-GP > Ketac-fil = enamel > dentin (where > indicates a statistical difference at p < or = 0.05). Although not as radiopaque as some other intermediate materials tested, the radiopacity of Fuji IX-GP appears sufficient to aid diagnosis.

Statement of problem. Mechanical properties are considered to be important to the clinical success of dental cements. Storage time of dental luting agents (dental cements) before use and at the manufacturer may have substantial effects on their properties. Purpose. This study observed and investigated the changes in the properties of water-based dental luting agents over time and on exposure to various, environmental conditions. Methods and material. Properties of zinc phosphate, zinc polycarboxylate, and glass-ionomer, luting agents were recorded at baseline and at intervals past 84 months, whereas the materials were exposed to controlled storage, conditions as well as various conditions typical of clinical situations. Tests included viscosity, diametral tensile strength, ultimate compressive strength, rigidity, hardness, and working/setting times. Results. Viscosity increased over 24 to 60 months for the acidic polymer liquids (zinc polycarboxylate and glass ionomer). Tensile and compressive strengths began to decrease after 36, months for all cements, most acutely for glass ionomer. Conclusion. Changes in critical properties, on aging may not be noticed by the clinican and yet may impact clinical success. These data emphasize the importance of storage stability for perishable dental materials and portend the need for standardized tests.

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 (RM-GIs). 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 MGI > GI > RMGI > ZOE; for tensile strength they were RMGI > MGI > GI > ZOE; and for storage stability they were ZOE > MGI > GI > RMGI. 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.

PURPOSE: Previous research has shown that dental gypsum casts may be effectively disinfected by the substitution of 10% of the gauging water with 5.25% solution of sodium hypochlorite. The purpose of this investigation was to determine the properties of gypsum produced from such a solution as opposed to tap water alone. MATERIALS AND METHODS: Tests included setting time, compressive strength, rigidity, diametral tensile strength, setting expansion, hardness, and detail reproduction. RESULTS: The addition of sodium hypochlorite to the gauging water resulted in a statistically significant increase in the compressive strength and rigidity, and a decrease in setting time (p < or = .5). All other properties remained unchanged. CONCLUSIONS: This substitution may be an effective and convenient method of disinfecting gypsum casts in the laboratory without adversely effecting physical and mechanical properties.

This study evaluated commercially available molded gray elastomeric ligatures from seven companies for force decay, dimensional change, and the relationship between ligature dimension and force. The initial wall thickness, inside diameter, outside diameter, and force levels of each ligature were measured. Three of four test groups of ligatures were stretched over stainless steel dowels with a circumference approximating that of a large orthodontic twin bracket. Test group 1 was kept at room temperature and humidity for 28 days and test group 2 in a synthetic saliva bath at 37 degrees C, pH 6.84 for 28 days. The residual forces and dimensional changes were measured. The third test group was placed in a synthetic saliva bath at 37 degrees C, pH 6.84, and force levels recorded at initial, 24 hours, 7 days, 14 days, and 28 days. The fourth test group of unstretched samples was placed in a synthetic saliva bath at 37 degrees C, pH 6.84 for 28 days to evaluate dimensional changes due solely to moisture sorption. The results for stretched samples in a simulated oral environment revealed the following: (1) Moisture and heat had a pronounced effect on force decay and permanent deformation, (2) a positive correlation existed between the wall thickness and force, (3) a negative correlation existed between the inside diameter and force, (4) a weak correlation existed between outside diameter and force, (5) the greatest force loss occurred in the first 24 hours and the decay pattern was similar for all ligatures tested, and (6) unstretched ligatures absorbed moisture in the range of 0.060% to 3.15%. The ligatures tested appear to be suitable for use during initial aligning and leveling. However, the rapid force loss and permanent deformation of these products may preclude their use for rotational and torque corrections.

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.

To define the nature and the extent of problems that can be related to the storage stability of perishable dental materials in the U.S. Army, questionnaires were sent to each U.S. Army Dental Corps Officer, supply NCO, and laboratory technician. Results reveal that two-thirds of dentists believe that the deterioration of perishable materials is a significant (28%) or occasional (39%) problem in their practice; the most common problem noted by dental clinicians is loss of efficacy of local anesthetics. One-half of clinicians and supply personnel report that they frequently receive perishable supplies at or near the expiration date.

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 most commonly used luting agents for fixed prosthodontics are water-based cements: zinc phosphate, zinc polycarboxylate, glass ionomer, and resin-modified glass ionomer. Properties were tested at baseline and after the cement liquids were allowed to evaporate for 10, 20, and 30 minutes. Viscosity, pH, contact angle, and surface tension were determined using the cement liquids only; tensile strength, hardness, film thickness, and working/setting times were determined after the cements had been mixed with the various liquids. pH decreased over 30 minutes, while viscosity, contact angle, and film thickness all increased, especially for the zinc polycarboxylate and glass ionomer cements. Changes in mechanical properties depended upon time and material.

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.

In an attempt to determine the age of perishable dental materials used at any one time in U.S. Army dental care facilities, a questionnaire was distributed to each U.S. Army Dental Activity supply point. Results reveal that almost half of commonly used perishable dental restorative materials are older than the expiration date, determined by the manufacturer's shelf-life, at the time of use. Materials used in OCONUS facilities are generally several months older than materials within CONUS facilities. Supply personnel could not determine the shelf-life of perishable restorative dental materials from package information in over 25% of all entries.

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.)

Statement of problem. Titanium and its alloys are more commonly used in prosthodontics and welding has become the most common modality for their joining. Studies on the welding of titanium and its alloys have not quantified this value, though its importance has been suggested. Purpose. This study compared the strength and properties of the joint achieved at various butt joint gaps by the arc-welding of cast Ti-6Al-4V alloy tensile bars in an argon atmosphere. Material and methods. Forty of 50 specimens were sectioned and welded at four gaps. All specimens underwent tensile testing to determine ultimate tensile strength and percentage elongation, then oxygen analysis and scanning electron microscopy. Results. As no more than 3 samples in any group of 10 actually fractured in the weld itself, a secondary analysis that involved fracture location was initiated. There were no differences in ultimate tensile strength or percentage elongation between specimens with weld gaps of 0.25, 0.50, 0.75, and 1.00 mm and the as-cast specimens. There were no differences in ultimate tensile strength between specimens fracturing in the weld and those fracturing in the gauge in welded specimens; however, as-cast specimens demonstrated a higher ultimate tensile strength than welded specimens that fractured in the weld. Specimens that fractured in the weld site demonstrated less ductility than those that fractured in the gauge in both welded and as-cast specimens, as confirmed by scanning electron microscopy examination. The weld wire showed an oxygen scavenging effect from the as-cast parent alloy. Conclusions. The effects of the joint gap were not significant, whereas the characteristics of the joint itself were, which displayed slightly lower strength and significantly lower ductility (and thus decreased toughness). The arc-welding of cast titanium alloy in argon atmosphere appears to be a reliable and efficient prosthodontic laboratory modality producing predictable results, although titanium casting and joining procedures must be closely controlled to minimize heat effects and oxygen contamination. (J Prosthet Dent 1998;79:291-7.)

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.

The properties of chemically cured and light-cured composite resins were recorded at baseline and at intervals over seven years, while the materials were exposed to controlled storage conditions as well as to various conditions typical of clinical situations. For chemically cured resins in clinical conditions, mechanical properties decreased, and working and setting times increased over four years; if refrigerated (controlled), properties remained constant past seven years. For light-cured resins, test results were constant over the entire seven-year test period regardless of storage conditions. An accelerated aging protocol was developed to allow for the evaluation of the relative storage stability of new and similar materials.

Statement of problem. Storage stability is a critical characteristic for perishable dental materials. Purpose. The purpose of this shelf-life study was to document changes in the properties of an alginate impression material on exposure to various environmental conditions for more than 78 months. Material and methods. Properties measured included recovery from deformation, strain in compression, compressive strength, tear strength, working time, and creep compliance. Results. Results revealed increases in strength and working time and a decrease in recovery from deformation at 30 to 50 months; strength and recovery then remained constant past 6 years, whereas working time and creep compliance decreased. Only the most stressful environmental conditions (heat and humidity) caused spontaneous failure of the material to set. Conclusions. We concluded that, under most storage conditions, properties of the alginate material tested remain within ADA specification limits well past manufacturer's designated shelf life. ADA specifications should require manufacturers to verify that the shelf life of each perishable material is based on valid data. An accelerated aging test was developed to simulate real-time property changes and to assist in evaluating similar materials. (J Prosthet Dent 1997;77:601-6.)

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.)

Three materials used for class 5 restorations (composite resin, glass ionomer, and resin-modified glass ionomer) were contoured, finished, and polished using seven methods: Matrix only, Sof-Lex disks, Composite Finishing System, Enhance Finishing/Polishing System. Two Striper MFS/MPS System. Two Striper MPS polish only, and contouring burs only. Results were quantified by surface roughness and gloss (reflectance). The glass-ionomer material was rougher and less reflective than composite resin; the smoothness and gloss of the resin-modified glass ionomer were between these two extremes. The original matrix smoothness and gloss could not be reproduced with any of the contour/finish/polish techniques tested on any of the three materials. The smoothest surfaces were achieved using a sequential series of rotary abrasive instruments.

This study evaluated the effect of heat treatment on 0.036" diameter stainless steel wire. Forty wires were bent into arch forms (20 experimental and 20 control). The arch width changes were measured and the forces generated were determined over an eight week period. Heat treatment resulted in immediate and significant expansion (p0.001) followed by stabilization of arch width. The control wires continued to expand throughout the study. The force generated by the control group and experimental group expansion was capable of producing tooth movement.

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.

New ceramic materials for restorative dentistry have been developed and introduced in recent years. This article reviews advantages and disadvantages of dental ceramics, concentrating on strength properties. Included are factors affecting the strength of dental ceramic materials and the most common mechanisms for increasing the strength of dental ceramics. The properties of presently available materials such as dispersion-strengthened ceramics, cast ceramics, and foil-reinforced materials are discussed. Current research efforts to improve the fracture resistance of ceramic restorative materials are reviewed. A description of methods to evaluate the strength of ceramics is included, as a caution concerning the interpretation of strength data reported in the literature.

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.

In an attempt to determine the age of perishable dental materials used at any one time in U.S. Army dental care facilities, a questionnaire was distributed to each U.S. Army Dental Activity supply point. Results reveal that almost half of commonly used perishable dental restorative materials are older than the expiration date, determined by the manufacturer's shelf-life, at the time of use. Materials used in OCONUS facilities are generally several months older than materials within CONUS facilities. Supply personnel could not determine the shelf-life of perishable restorative dental materials from package information in over 25% of all entries.

To define the nature and the extent of problems that can be related to the storage stability of perishable dental materials in the U.S. Army, questionnaires were sent to each U.S. Army Dental Corps Officer, supply NCO, and laboratory technician. Results reveal that two-thirds of dentists believe that the deterioration of perishable materials is a significant (28%) or occasional (39%) problem in their practice; the most common problem noted by dental clinicians is loss of efficacy of local anesthetics. One-half of clinicians and supply personnel report that they frequently receive perishable supplies at or near the expiration date.