Rap1 regulates hematopoietic stem cell survival and affects oncogenesis and response to chemotherapy

Increased levels and non-telomeric roles have been reported for shelterin proteins, including RAP1 in cancers. Herein using Rap1 null mice, we provide the genetic evidence that mammalian Rap1 plays a major role in hematopoietic stem cell survival, oncogenesis and response to chemotherapy. Strikingly, this function of RAP1 is independent of its association with the telomere or with its known partner TRF2. We show that RAP1 interacts with many members of the DNA damage response (DDR) pathway. RAP1 depleted cells show reduced interaction between XRCC4/DNA Ligase IV and DNA-PK, and are impaired in DNA Ligase IV recruitment to damaged chromatin for efficient repair. Consistent with its role in DNA damage repair, RAP1 loss decreases double-strand break repair via NHEJ in vivo, and consequently reduces B cell class switch recombination. Finally, we discover that RAP1 levels are predictive of the success of chemotherapy in breast and colon cancer.

Noncoding RNAs: Master Regulators of Inflammatory Signaling

Inflammatory signaling underlies many diseases, from arthritis to cancer. Our understanding of inflammation has thus far been limited to the world of proteins, because we are only just beginning to understand the role that noncoding RNAs (ncRNA) might play. It is now clear that ncRNA do not constitute transcriptional 'noise' but instead harbor physiological functions in controlling signaling pathways. In this review, we cover the newly discovered mechanisms and functions of ncRNAs in the regulation of inflammatory signaling. We also describe advances in experimental techniques allowing this field of research to take root. These findings have opened new avenues for putative therapeutic intervention in inflammatory diseases, which may be seen translated into clinical outcomes in the future.

In Vivo Role of INPP4B in Tumor and Metastasis Suppression through Regulation of PI3K-AKT Signaling at Endosomes

The phosphatases PTEN and INPP4B have been proposed to act as tumor suppressors by antagonizing PI3K-AKT signaling and are frequently dysregulated in human cancer. Although PTEN has been extensively studied, little is known about the underlying mechanisms by which INPP4B exerts its tumor-suppressive function and its role in tumorigenesis in vivo. Here, we show that a partial or complete loss of Inpp4b morphs benign thyroid adenoma lesions in Pten heterozygous mice into lethal and metastatic follicular-like thyroid cancer (FTC). Importantly, analyses of human thyroid cancer cell lines and specimens reveal INPP4B downregulation in FTC. Mechanistically, we find that INPP4B, but not PTEN, is enriched in the early endosomes of thyroid cancer cells, where it selectively inhibits AKT2 activation and in turn tumor proliferation and anchorage-independent growth. We therefore identify INPP4B as a novel tumor suppressor in FTC oncogenesis and metastasis through localized regulation of the PI3K-AKT pathway at the endosomes.

SIGNIFICANCE

Although both PTEN and INPP4B can inhibit PI3K-AKT signaling through their lipid phosphatase activities, here we demonstrate lack of an epistatic relationship between the two tumor suppressors. Instead, the qualitative regulation of PI3K-AKT2 signaling by INPP4B provides a mechanism for their cooperation in suppressing thyroid tumorigenesis and metastasis.

Fabrication of a new composite orthodontic archwire and validation by a bridging micromechanics model

A new technique based on tube shrinkage is proposed for the fabrication of composite archwires. Compared with a traditional pultrusion method, this new technique can avoid any fiber damage during the fabrication and can provide the archwire with a required curvature in its final clinical usage. The present paper focuses on the technique development and mechanical design and validation in terms of constituent materials by using a micromechanics bridging model. Prototype archwire has been fabricated using fiberglass and an epoxy matrix, with a wire diameter of 0.5mm and a 45% fiber volume fraction. Tensile and three-point bending tests have shown that the mechanical performance of the prototype composite archwire is comparable to that of a clinical Ni-Ti archwire. Another purpose of the present paper is to provide an efficient procedure for a critical design of composite archwires. For this to be possible, the ultimate load especially flexural load carrying ability of the composite archwire must be assessed from the knowledge of its constituent properties. However, difficulty exists in doing this, which comes from the fact that the failure of the utmost filament of the composite archwire subjected to initially the maximum bending stress does not imply its ultimate failure. Additional higher loads can still be applied and a progressive failure process is generated. In this paper, the circular archwire was discretized into a number of parallel laminae along its axis direction, and the bridging micromechanics model combined with the classical lamination theory has been applied to understand the progressive failure process with reasonable accuracy. Only the constituent fiber and matrix properties are required for this understanding. Nevertheless, the ultimate bending strength cannot be obtained only based on a stress failure criterion. This is because neither the first-ply nor the last-ply failure corresponds to the ultimate failure. An additional critical deflection (curvature) condition must be employed also. By using both the stress failure and the critical deflection conditions, the predicted load-deflection up to the ultimate failure agrees well with the measured data. Thereafter, different mechanical performances of composite archwires can be tailored before fabrication by choosing suitable constituent materials, their contents, and the archwire diameters. Several design examples have been shown in the paper.

Marginal gap formation of composites in dentine: effect of water storage

This study investigated the effects of water storage on the marginal adaptation of two composite resins (Spectrum TPH and Ariston AT), two polyacid-modified composite resins (Dyract AP and F2000) and a new PRG composite (Reactmer) to dentine over time. Two cylindrical dentine cavities (1.5 mm diameter and 1.5 mm deep) were prepared on the horizontally sectioned surfaces of freshly extracted teeth. In each tooth, one cavity was restored using composites with their respective bonding system and the other without the bonding system. The sample size for each material with/without bonding system was 6. The composites were placed in one increment, bulk-polymerized, immediately finished/polished with the Sof-lex discs system and fine polished on 30 microm silicon carbide/9 microm aluminium oxide lapping film discs in a microgrinding system. The specimens were then stored in distilled water at 37 degrees C and the maximum marginal gap width between the material and the dentine wall was determined at 24 h, 1 week, 2 weeks, 3 weeks and 4 weeks using a measurescope at x500 magnification. Results were subjected to statistical analysis using monva, anova/Scheffe's post hoc test and independent samples of t-test at significance level 0.05. At all time intervals, no significant difference in marginal gap formation was observed between materials. Where bonding systems were not used, a decrease in gap widths over time was observed with most materials but only Dyract AP exhibited a significant decrease. The latter was observed after 2 weeks storage in water. The use of bonding systems reduced dentine marginal gaps significantly and is therefore mandatory for all composites evaluated. Marginal gaps arising from polymerization contraction of conventional, polyacid-modified and PRG composites cannot be fully compensated by hydroscopic expansion. Clinical relevance Bonding systems are mandatory for all composites when bonding to dentin. In the event of a bond failure at placement, hygroscopic expansion of composites can reduce marginal gaps but not completely.

Effects of cyclic loading on occlusal contact area wear of composite restoratives

OBJECTIVES

To investigate the effects of cyclic loading on occlusal contact area (OCA) wear and the possible presence of fatigue wear mechanisms in four composite resins (Silux, Z100, Ariston and Surefil) using a reciprocal compression-sliding test apparatus.

METHODS

Six specimens were made for each composite material and the amalgam alloy (Dispersalloy) control. The wear specimens were subjected to wear testing at 20 MPa with artificial saliva as lubricant. Wear depth (microm) was measured using profilometry every 20,000 cycles up to 120,000 cycles. The worn specimens were subjected to SEM to determine the presence of fatigue wear mechanisms. Results were analyzed using ANOVA/Scheffe's test (P<0.05) and Pearson's Correlation (P<0.01).

RESULTS

Dispersalloy had the lowest wear at all cyclic intervals. For all materials, OCA wear increased with increased number of cycles. Although Dispersalloy, Ariston and Surefil experienced no significant increase in wear between each 20,000 cycles increment, a significant increase was observed with Silux. For Z100, a significant difference was observed only from 40,000 cycles onwards. Both Z100 and Dispersalloy exhibited fatigue wear after wear testing for 120,000 cycles. Cyclic loading resulted in deep and wide microcracks in Silux. Fatigue wear was not observed with Silux, Ariston and Surefil.

SIGNIFICANCE

The effects of cyclic loading on wear is material dependent. While some restorative materials exhibit fatigue wear, others exhibit deep microcrack formation with extended cyclic loading. The latter may precipitate catastrophic failure despite the low wear observed. Care should, therefore, be exercised when selecting materials for posterior stress-bearing areas.

Environmental damage and occlusal contact area wear of composite restoratives

The chemical environment is one aspect of the oral environment, which could have an appreciable influence on the in-vivo degradation of composite resins. The resin matrix can be softened and fillers constituents can be leached out when composites are exposed to certain chemicals/food-simulating liquids (FSLs). A reciprocal compression sliding wear device was used to study the effects of the chemical environment on occlusal contact area (OCA) wear of four composite restoratives (Silux Plus, Z100, Ariston pHc and Surefil). The effects of FSL on hardness was also investigated and correlated to wear. Thirty-six hardness/wear specimens of each material were made and stored in artificial saliva at 37 degrees C for 24 h. The specimens were then divided into six groups of six specimens and stored in the following FSL for 1 week at 37 degrees C: distilled water (W), 0.02 N citric acid (C), 0.02 N lactic acid (L), heptane (H) and 75-25% ethanol-water solution (E). Conditioning in artificial saliva (S) was used as control. After conditioning, the specimens were wear tested at 20 MPa contact stress against SS304 counter-bodies in the respective FSL/artificial saliva up to 20 000 cycles. Wear depth (lm, n=6) was measured using profilometry. Change in hardness (DeltaKHN, Knoop hardness number) was determined by microhardness testing pre- and post-conditioning. Results of statistical analyses (ANOVA/Scheffe's at significance level 0.05) of wear data were as follows: Silux - S, W > L, H, E and C, L > H; Z100 - S, W > all other mediums and E > H; Ariston - all other mediums > H; Surefil - W, C > S, L, H, E (> indicates significantly more wear). With the exception of Surefil, the greatest wear was observed with conditioning and wear testing in water. This ranged from 93.18 +/- 21.96 lm for Z100 to 31.43 +/- 2.80 lm for Surefil. For all materials, conditioning in heptane resulted in the least wear. This ranged from 8.9 +/- 2.2 microm for Ariston to 16.5 +/- 5.9 lm for Silux. The effects of the different FSL on OCA wear were material dependent. No correlation was observed between DeltaKHN and wear.

Influence of thermal cycling on OCA wear of composite restoratives

This study investigated the effects of thermal cycling on wear of four commercial composite resins (Silux, Z100, Ariston and Surefil). Specimens of each material were divided into three treatment groups comprising a control and two different thermal cycling regimes. Control specimens were stored in distilled water at 35 degrees C for 178 hours. Thermal cycled specimens were stored in distilled water at 35 degrees C for 173 hours and subjected to five hours (300 cycles) of a thermal cycling regime consisting of the cycle ABAC, where A and B represent the fixed temperatures of 35 degrees C (28 seconds) and 15 degrees C (two seconds) and C, depending on the treatment group, was either 45 degrees C or 60 degrees C (two seconds). All specimens were subsequently subjected to wear testing at 20 MPa contact stress against SS304 counterbodies with distilled water as the lubricant. Wear depth (microm; n=6) was measured using profilometry every 2,000 cycles up to 10,000 cycles. Results were analyzed using ANOVA/Scheffe's test (p<0.05). The effect of thermal cycling on wear was material-dependent. The wear of Silux and Z100 were not significantly affected by thermal cycling. Thermal cycling of Ariston at an upper temperature of 60 degrees C significantly decreased wear resistance. Thermal cycling affected only the early wear resistance of Surefil.

Mechanical properties of an improved visible light-cured resin-modified glass ionomer cement

This study investigates the mechanical properties (hardness, flexural strength and compressive strength) of a new light-cured resin-modified glass ionomer cement (Fuji II LC Improved). Effects of the increased powder:liquid ratio on mechanical properties and the correlation between different mechanical properties were also studied. Mechanical properties of the cement at manufacturer's recommended powder:liquid ratio (F), 2% (F2) and 4% (F4) increased powder weight were measured after one day, one week and one month storage in distilled water at 37 degrees C. Hardness testing (KHN; n = 5) was done with a digital microhardness tester (load = 500 g, dwell time = 15 seconds). Flexural and compressive strength testing (MPa; n = 5) were conducted based on ISO 4049 and BS6039, respectively. Results were analyzed using ANOVA/Scheffe's test (p < 0.05) and Pearson's correlation (p < 0.01). The maximum mechanical properties of Fuji II LC Improved were achieved at one week. The hardness, flexural and compressive strength at one week was significantly higher than at one day. A decrease in all mechanical properties was observed at one month. Mechanical properties were significantly affected by increased powder:liquid ratio. After one month storage, significance was as follows: Hardness--F, F2 > F4; Flexural strength--F4 > F, F2 and F > F2; Compressive strength--F, F2 > F4 and F2 > F. A significant very strong and negative correlation was observed between flexural and compressive strengths (r = 0.97).

Bond strengths of glass ionomer restoratives to primary vs permanent dentin

An in vitro experiment was conducted to evaluate the shear bond strength of a conventional GIC (glass ionomer cement) and a RMGIC (resin modified glass ionomer cement) when applied to dentin of primary and permanent teeth. Results show that the bond strength of the RMGIC was more than thrice that of the conventional GIC. Fracture analysis showed that the bond failures were cohesive in the cement.

Clinical evaluation and microstructural analysis of a direct placement gallium restorative alloy

OBJECTIVES

The objective of this study was to assess the clinical performance of a direct placement gallium alloy sealed with an established dentine adhesive system. In addition, microanalysis of a few gallium restorations that failed in clinical service was performed. Clinical factors such as pulpal sensitivity, fracture of the restoration and of the tooth, marginal deterioration, and tarnish were assessed.

METHODS

Sixty-five restorations of Galloy and 62 of Tytin (49 and 51 Class II restorations, respectively) were placed according to a predetermined scheme for randomisation in 37 patients by two operators using rubber dam isolation. For the Galloy restorations, the enamel and dentine were etched, and then sealed with PAAMA 2 dentine adhesive according to the manufacturer's instructions. After carving, PAAMA 2 was applied to the Galloy and light-cured. Cavity preparations for Tytin received no adhesive sealer. All restorations were polished at least 24 h post-operatively. Microstructural analysis of retrieved fragments of failed restorations was conducted using electron probe microanalysis.

RESULTS

At 1 year, only one Tytin restoration was found to have failed due to an isthmus fracture. The remaining restorations of Tytin were intact with no reported sensitivity. Of the 65 Galloy restorations placed, 28 had to be removed, including restorations in teeth, which were symptomatic, non-vital and/or fractured, and teeth with fractured restorations. Tarnish was present on many of the Galloy restorations. Retrieved fragments of failed Galloy restorations exhibited a dark surface at the pulpal wall interface and small cracks were observed in that surface. Internal cracks and extensive corrosion was observed using the microprobe. Gallium oxides and chlorides were identified as the predominant corrosion products.

CONCLUSIONS

The gallium alloy, Galloy, sealed with PAAMA 2 dentine adhesive system demonstrated a high clinical failure rate.

Investment strength as a function of time and temperature

OBJECTIVES

The purpose of this investigation was to evaluate and compare the compressive strength characteristics of selected investments and to determine if these change as a function of time and temperature after mixing.

METHODS

Two phosphate-bonded investments and one gypsum-bonded investment were selected and 288 cylindrical specimens were fabricated (n = 9). Baseline compressive strength values were determined for each material at room temperature and compressive strength measurements were made for all materials at 700 degrees C, and at 872 degrees C only for phosphate-bonded investments. Each material was tested at 2, 6, 12, and 24 h after mixing. Specimens were heated at 15 degrees C/min and heat soaked for 5 min in a burnout oven at the applicable testing temperature. They were transferred to a preheated chamber on an Instron testing machine and subjected to a compressive load at a crosshead speed of 2 mm/min until failure. The resulting strength data are presented in MN/m2.

RESULTS

The gypsum-bonded investment did not exhibit marked differences in strength as a function of either time or temperature. The phosphate-bonded investments, on the other hand, demonstrated considerable changes in compressive strength and differed in compressive strength characteristics at 700 degrees C and 872 degrees C respectively.

CONCLUSIONS

At elevated temperatures, all materials approximated peak strength 2 h after initial mixing. At room temperature, the phosphate-bonded investments in this study were not significantly stronger than the gypsum-bonded investment material. However, they exhibited increased compressive strength as a function of time and temperature that was considerably higher than that exhibited by the gypsum-bonded investments.

An evaluation of bond strengths of denture repair resins by a torsional method

Chemical cure resin materials are generally used in the repair of dentures. Different repair resins used may yield different results. The bond strength of three autopolymerizing resins were evaluated using a torsional test method. The results showed that Palapress and Caulk resins had a higher repair strength than Rapid Repair resin.

Shear bond strength of denture teeth to base: a comparative study

Fracture and debonding of plastic teeth from the denture base are common clinical problems. In this study, a shear, or peeling, load was applied to the tooth-denture base junction. The bond strength of a high-impact, heat-cured denture base to three commercial brands of denture teeth, Bioform, Dentacryl, and TNR, was assessed. Ninety-three percent of the specimens exhibited cohesive failure within the body of the tooth and not adhesive failure at the tooth-denture base junction. Some of the teeth exhibited brittle fracture while others underwent distortion on loading. Dentacryl displayed the highest cohesive bond strength, followed by Bioform and TNR.

Direct tooth-colored materials for noncarious lesions: a 3-year clinical report

One hundred fifty-nine noncarious cervical lesions were restored with glass-ionomer cement, resin composite used with a dentinal bonding agent, or the laminate (sandwich) restoration, which combines both these materials. These restorations were evaluated at baseline, 1 year, and 3 years for color match, cavosurface marginal discoloration, anatomic form, marginal adaptation, and retention. There was a general deterioration of the restorations with time. Lesions restored with resin composite and a dentinal bonding agent exhibited the highest percentage of lost restorations.

Clinical evaluation of tooth-colored materials in cervical lesions

PURPOSE

To determine the 18-month clinical performance of four tooth-colored restoratives in non-carious cervical lesions.

MATERIALS AND METHODS

Buccal abrasion lesions in 83 teeth were restored with each of the following materials: Fuji Cap II, Fuji II LC, APH/Universal Bond 3, Lite Fil II A/Imperva Bond. Baseline and an 18-month recall was carried out using the Ryge (USPHS) method for retention, color match, marginal adaptation, cavosurface marginal discoloration, anatomic form and secondary caries.

RESULTS

The USPHS results (% alfa) for the four products were, respectively: color match (9%, 48%, 57%, 55%), marginal discoloration (71%, 76%, 52%, 50%), marginal adaptation (24%, 24%, 33%, 15%), anatomic form (67%, 86%, 95%, 45%) and retention (100%, 95%, 100%, 65%). Results indicated that (1) Fuji Cap II exhibited a poor color match at baseline (2) Color matching of Fuji II LC was comparable to the resin composites and (3) seven Lite Fil II/Imperva Bond restorations (35%) were dislodged after 1 1/2 years.

Interocclusal distance in patients with different skeletal patterns

A pilot study was conducted to measure the interocclusal distance in patients with class I, II and III skeletal patterns. Ten patients were randomly selected for each skeletal pattern group. The measurements of interocclusal distance were obtained from lateral cephalometric radiographs of each patient. The results indicated that there was a significant difference (p < 0.05) between the interocclusal space of skeletal class II and class III patients.

The influence of temperature on the dimensional stability of poly (vinyl siloxane) impression materials

It may be desirable to extend the working time of poly(vinyl siloxane) impression materials when making a multiple-unit impression. Alteration of the base-catalyst ratio is not possible with automix systems, but chilling the impression material provides an alternative. This study evaluated the dimensional accuracy of chilled impression material and the effect on accuracy of reheating the impression to mouth temperature prior to pouring. Two brands of poly(vinyl siloxane) impression material were evaluated both after refrigeration and at room temperature. Impressions were poured at room temperature and reheated to mouth temperature prior to pouring. Gypsum dies were recovered and measured. Refrigeration had no statistically significant effect on dimensional accuracy. Reheating the impression had no clinically significant effect on accuracy.

Shear bond strength of orthodontic brackets using Panavia: an in-vitro study

In this study, Panavia (a phosphonated Bis-GMA resin which is known to develop very high bond strengths with resin-bonded bridges) is compared to a conventional no-mix orthodontic Bis-GMA bracket adhesive. Results showed that there was no statistically significant difference in the shear bond strengths between the two resins when used as adhesives for bonding orthodontic brackets. Coupled with the fact that Panavia requires an anaerobic environment for complete polymerization, its routine use as a bracket adhesive in direct bonding of orthodontic brackets is not indicated.

A comparison of shear bond strengths between new and recycled ceramic brackets

The recycling of 'used' ceramic brackets in the orthodontic surgery has been previously described. The present study investigated the shear bond strength of both recycled and new ceramic brackets. The mean shear bond strengths of the new and recycled ceramic brackets were 259.7 +/- 88.2 N and 187.2 +/- 60.8 N, respectively. Although significantly lower (P less than 0.01), the bond strength of recycled ceramic brackets appeared to be clinically adequate. There appeared to be little difference in the variation in bond strength between the new and recycled ceramic bracket group. Our results showed that the site of bond failure depended on the magnitude of bond strength. Scanning electron micrograph examination of the failure sites showed enamel fracture in one sample where the bond strength was extremely high.

Long-term dissolution of mercury from a non-mercury-releasing amalgam

The hazards of mercury from dental amalgams have long been recognized. This study examined the mercury release from a "non-mercury-releasing" dental amalgam, Composil, over a 104-week period. Four cylindrical specimens were incubated in 10 ml of purified water at 37 degrees C. The incubate was changed at the end of each 24-hour period and assayed for its mercury content at biweekly intervals. Mercury estimation was carried out using cold-vapor, atomic absorption spectrophotometry over a 104-week period. Results showed that the overall mean release of mercury was 43.5 +/- 3.2 micrograms/cm2/24 hr, and the amount of mercury released remained fairly constant during the duration of the experiment. This study showed that Composil releases mercury in quantities that far exceed those detected in other amalgam systems.

Thermal effect on the dissolution of mercury from two dental amalgams

Various factors affect dissolution of mercury from dental amalgams. In this study we examined the effect of temperature on the release of mercury from two dental amalgams, namely an admixed high-copper amalgam (Contour) and a new tin- and copper-free amalgam (Composil). Ten cylindrically-shaped specimens of each type of amalgam were used in this investigation, and were divided into two equal groups. The five specimens in each group were each incubated in 10 ml purified water at either 37 degrees C or 60 degrees C, with a change of water every 24 h over an 8-day period. The quantity of mercury released from each amalgam specimen during each incubation period was expressed as micrograms cm-2 24 h-1. The amount of mercury released was estimated by cold-vapour atomic spectrometry. The results demonstrate that specimens incubated at 60 degrees C released significantly larger amounts of mercury than specimens incubated at 37 degrees C for both types of amalgam. The release of mercury by Composil was significantly greater than that by Contour (P less than or equal to 0.0001) for both temperatures studied. Raising the incubation temperature caused a disproportionate increase in mercury release from Composil compared to Contour.

Significance of hydrogen ion concentration on the dissolution of mercury from dental amalgam

The potential risks of mercury dissolution from dental amalgam have long been recognized. This study examined the effect of hydrogen ion concentration on the release of mercury from two dental amalgams: an admixed high-copper amalgam and a new tin- and copper-free amalgam. Specimens of each type of amalgam were incubated citric acid buffer of pH 2.5 or pH 7.0. Results showed that, for both types of amalgam, specimens incubated at pH 2.5 released statistically significantly greater (P less than .0001) quantities of mercury than did specimens incubated at pH 7.0. Release of mercury from the tin- and copper-free amalgam was also statistically significantly greater (P less than .0001) than that of the higher-copper amalgam at both pH levels.

Mechanical properties of metal-ceramic alloys at high temperature

Four alloys used for the construction of porcelain-fused-to-metal restorations were tested at high temperatures (1000 degrees C) so that loss of properties could be ascertained. In addition, thin flat plates of metal (30 x 11 x 1 mm) with a 9-mm recess and a metal thickness of 0.35 mm were processed for porcelain application and distortion measured at 15 points along the surface prior to and following each firing cycle. Yield and ultimate tensile strengths and elongation were determined on specimens at room temperature and at 1000 degrees C. None of the alloys tested showed a great amount of distortion during the various firing cycles, yet they showed increased change with each successive heating. The greatest distortion occurred with Jelenko "O" alloy. When the mechanical properties were compared, there was a marked loss of both yield and ultimate strength values for each alloy (Jelenko "O"-Y.S., 95.64%, U.T.S., 96.22%; Olympia--Y.S., 95.08%, U.T.S., 96.76%; Tempo--Y.S., 91.23%, U.T.S., 93.46%; Biobond II--Y.S., 83.72%, U.T.S., 86.21%). Percent elongation increased by 272% with Biobond II and 370% with Jelenko "O", whereas Tempo and Olympia increased by 120 and 155%. It is apparent that the palladium-based alloy and the nickel-chromium-based alloy have higher mechanical properties at the temperature where porcelain will be applied.

Retention of denture adhesives--an in vitro study

Denture adhesives are being used by patients to aid the retention and stability of their dentures. A number of laboratory and clinical investigations have been conducted to study the effects of such adhesives. This study describes a simple in vitro method for measurement of their retentive effect and its relation to loss of adhesive. The results show that there is a reduction in the effectiveness of adhesives, and that there is also an increase in adhesive loss, with time. There appears to be a correlation between these two properties.

Flange design in removable partial dentures

Flange design is an important component in the success of removable partial dentures. There are a number of factors such as undercuts, state of residual ridge, aesthetics, etc. that would influence the design. All these factors are interrelated and must be considered together. Only then will the denture serve its function for aesthetics without compromising the health of the remaining supporting tissues. The importance of each factor and its relationship to others are discussed.

Comparison of release of mercury from three dental amalgams

Mercury release from dental amalgams has generated considerable concern in recent years and is the subject of this study. Specimens of one admixed high-copper amalgam (Contour), one lathe-cut low-copper amalgam (SDI), and a new tin- and copper-free amalgam claimed to be non-mercury-releasing (Composil) were evaluated for release of mercury when incubated in purified water at 37 degrees C. Measurement of mercury was done by cold-vapor atomic absorption spectrophotometry, and the amount released was expressed as micrograms/cm2/24 hr. Study was conducted over a four-week period. Results show that Contour and SDI released similar insignificant amounts (mean release of less than 0.1 microgram/cm2/24 hr) compared with Composil (mean release of 41.0 micrograms/cm2/24 hr). The difference in release by Composil compared with that by Contour and SDI is highly significant (P less than 0.001). The implications of chronic release of mercury from dental amalgams are discussed. Long-term release studies are in progress.

Dimensional stability of two impression materials

Elastomeric impression materials are widely used in dentistry to obtain accurate impressions. The most recent group of these materials is the additional polymerised silicones which have been shown to produce great accuracy. An auto-mixing system has been developed to provide ease of manupilation. The material is mixed as it is syringed through a mixing tip. The dimensional accuracy of the material mix by this system is compared to that of a hand mixed material. Results show that the dimensional accuracy of this new material is good and the system easy to use. The limitations of the material are also discussed.

Food breakdown patterns produced by human subjects possessing artificial and natural teeth

The abilities of thirty-two complete denture wearers and thirty-two dentate subjects to break down raw carrot particles were compared. The particle size distributions produced were broader in those subjects that broke down food rapidly per chew and, conversely, narrower in those that were slower. This did not appear to depend on dental status. An analysis of mastication as composed of two separable processes, one describing the means by which particles come to be broken (selection) and the other, the size distributions of a particle upon fracturing (breakage), indicated that both processes were variable. It is concluded that no qualitative differences in the manner by which the two groups reduce food is apparent. To support this, a small study on dentate subjects suggests the covering of the palatal mucosa with an acrylic plate does not affect masticatory performance.

Relationship between jaw movement and food breakdown in human mastication

Different quantities and sizes of peanuts were offered to six human subjects for mastication at two or three experimental sessions during which jaw movements and chewing cycle duration were measured. The amplitude of vertical movement and cycle duration depended on the position of a chew in a sequence of chews (masticatory sequence). Cycle duration also depended on the position of a given masticatory sequence during the first experimental session, the earlier sequences tending to be longer. Lateral jaw movements fluctuated about a reasonably constant value during a sequence and were unaffected by different food inputs. The amplitude of vertical movements increased markedly with an increase in food weight but was unaffected by change in the initial food particle size. These results were analyzed in the light of previous reports on the comminution of peanuts. It is hypothesized that observed jaw movements were unrelated to food particle size but that the amplitude of each vertical movement depended on the volume of food that was broken by the teeth during the next closing stroke. This food volume was provided and selected by bulk movements of the tongue during the preceding jaw opening.

The acid-etched fixed partial denture: a two-year report

A 2-year report on 10 acid-etched fixed partial dentures was presented. Similar to other studies, it indicates that the acid-etched fixed partial denture is a clinically acceptable restoration for properly selected patients.

Clinical performance and physical properties of twelve amalgam alloys

An assessment of the marginal failure rate of 1,041 restorations of twelve alloys was made at one year. In addition, physical property tests were conducted. A correlation was found between the clinical performance and creep (.79), flow (.62) and 24-hour compressive strength (.60).