C.L. Chew

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.

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/Scheffes test (P<0.05) and Pearsons 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.

Culturing and characterization of human periodontal ligament fibroblasts - a preliminary study

The periodontal ligament (PDL) is believed to harbour cells with the capacity to regenerate the periodontium consisting of the PDL layer and surrounding alveolar bone and cementum. Fibroblast, the predominant cell type, is implicated in PDL tissue regeneration and repair. In this study, PDL fibroblasts (PDLF) from healthy human premolar and molar explants were cultured and characterized in vitro. Protein expression profiles were analysed and compared to gingival fibroblasts (GF) and alveolar bone osteoblasts (OB). Alkaline phosphatase (ALP) expression was higher in all induced cultures. Western blotting showed that all three cell types expressed osteonectin (ON) and osteopontin (OPN). Conversely, bone sialoprotein (BSP II) was down-regulated in PDLF and GF upon induction. Von Kossa staining revealed mineralised matrix for all induced cultures. This study showed the response of PDLF in protein expression, and pointed to its potential application in periodontal regeneration.

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.

The effect of food texture on the replication of jaw movements in mastication

Abstract The effect of different food textures on the replication of jaw movements has been generally ignored. In this study, the jaw movements of 28 young male subjects were measured while they chewed two samples of three foods—pork luncheon meat, dried apple and roasted salted peanuts. Several parameters, that characterized each chewing cycle when viewed from a frontal projection, were measured, and the average value for each variable was calculated. Values for dried apple and pork luncheon meat did not differ significantly between trials. However, for the second trial with peanuts, the chewing cycle duration was shorter (the duration of the closing phase being less and the closing velocity greater). These changes may have been due to exercizing caution during the chewing of a hard food while gaining familiarity with its texture.

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 manufacturers 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.

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.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.

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.

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.