Can poly(acrylic) acid molecular weight mixtures improve the compressive fracture strength and elastic modulus of a glass-ionomer restorative?

Objectives

To optimize the compressive fracture strength (σ) and elastic modulus (E) of a glass-ionomer (GI) restorative using poly(acrylic) acid (PAA) weight average molecular weight (M_w) mixtures.

Methods

174 PAA solutions were prepared (four control PAA M_ws at three PAA concentrations (25, 35 and 45%) (n = 12) and six M_w mixtures (Groups A-F at nine blend ratios and three PAA concentrations (n = 162))). The viscosity (η) of each PAA solution was determined using a digital viscometer. The PAA solutions were hand-mixed with a commercial GI restorative powder (Ionofil Molar; Voco, Cuxhaven, Germany) and σ and E were determined using cylindrical (6 mm height, 4 mm diameter) specimens (n = 20) at 24 h. Data were analyzed using analyses of variance (ANOVA) (three-, two- and one-way) and regression analyses at p < 0.05.

Results

The three- and two-way ANOVAs highlighted significant effects of M_w mixture, blend ratio and PAA concentration (all p < 0.0001) on the η, σ and E data. Regression analyses showed significant increases in η, σ and E (p < 0.0001) with increasing M_w from Groups A to F. There was no significant effect of blend ratio on the σ data for Groups A (p = 0.178), D (p = 0.747) and F (p = 0.107) and on the E data (p > 0.083).

Significance

The current approach to improving the mechanical properties of GI restoratives using PAA M_w mixtures is encouraging, however, further manipulation of the GI restorative system by optimizing PAA M_w mixtures, blend ratios and PAA concentrations is required to elicit further improvements in σ and E without impacting upon the η of the PAA solution.     

Virulence factors of the oral spirochete Treponema denticola

There is compelling evidence that treponemes are involved in the etiology of several chronic diseases, including chronic periodontitis as well as other forms of periodontal disease. There are interesting parallels with other chronic diseases caused by treponemes that may indicate similar virulence characteristics. Chronic periodontitis is a polymicrobial disease, and recent animal studies indicate that co-infection of Treponema denticola with other periodontal pathogens can enhance alveolar bone resorption. The bacterium has a suite of molecular determinants that could enable it to cause tissue damage and subvert the host immune response. In addition to this, it has several non-classic virulence determinants that enable it to interact with other pathogenic bacteria and the host in ways that are likely to promote disease progression. Recent advances, especially in molecular-based methodologies, have greatly improved our knowledge of this bacterium and its role in disease.     

A calculation method for the range of occluding phase at the lower incisal point during chewing movements using the curved mesh diagram of mandibular excursion (CMDME)

The purpose of this study was to develop a method for calculating the range of the occluding phase in chewing movements. In this study, we defined 'range' as the distance of the movement at the lower incisal point while the mandible moves with tooth contact. First, mandibular excursions were measured using an opto-electronic movement analysis system, which can measure mandibular movement with six degrees-of-freedom at a sampling frequency of 100 Hz. With use of this measurement data, the curved mesh diagram of mandibular excursion (CMDME) previously reported was made. Then, chewing movements were measured using the same analysis system. The movements were separated into their component chewing cycles. Finally, we calculated the distance between each cycle and the CMDME. The occluding range of our subject was 0.4 mm at the closing phase and 3.4 mm at the opening phase. These results suggest that tooth contact occurs during chewing movement and demonstrate that the range of the occluding phase for the opening and closing phases of a subject can be calculated without morphological data from a dental cast.     

Histological study of periapical tissue healing in the rat molar after retrofilling with various materials

We histologically examined the effects on the periapical tissue of various dental filling materials applied as retrofillings in rats and compared them with those of amalgam. The 4-META-TBB resin Superbond and the light-cured composite resin produced the least severe inflammatory reaction, with the greatest amount of new bone. In these specimens, regeneration of a part of the periodontal ligament was also observed. These results indicate that these materials might be very biocompatible and thus foster the natural regeneration of the periapical tissue.     

Bite force, endurance and masseter muscle fatigue in healthy edentulous subjects and those with TMD

It is well known that bite force and EMG activity are considerably reduced in edentulous patients, but the susceptibility of their jaw-closing muscles to localized fatigue is less certain. This information is even less clear for edentulous subjects who have TMD. Eleven healthy edentulous subjects and 10 edentulous subjects with TMD participated in this study. Maximum bite force was measured first, with the transducer placed on the canine-first premolar region bilaterally, and then two rapid relaxations were made from a brief voluntary clench to 50% of maximum. A sustained voluntary clench of 50% of maximum was then maintained and endurance time was noted. EMG was recorded from both masseter muscles and the median frequency of the power spectrum of the EMG from 2 s at the beginning of the sustained clench and 2 s at the end was subsequently calculated. Two more rapid relaxations from brief clenches were performed immediately after the sustained clench. The mean maximum bite force in the healthy group was 115 N (SD +/-41) and in the TMD group was 75 N (SD +/-22), this difference being significant (P = 0.0013). The mean endurance time in the healthy group was 86 s (SD +/-51) and in the TMD group was 63 s (SD +/-20). The percentage change in the median frequency in the healthy group as a result of the sustained contraction was 6% (left) and 8.6% (right) and in the TMD group was 13.9% (left) and 12.8% (right). The percentage change in the mean relaxation half time for the healthy group was 28.5% and for the TMD group was 72%, a significant difference (P = 0.0046). It was apparent that the maximum bite force was low in edentulous subjects and was further reduced in edentulous TMD subjects; endurance time was reduced in TMD subjects; fatigue resistance of the masseter muscles was reduced in TMD subjects.     

固齿健周煎剂对老年小鼠的抗氧化作用

目的探讨中药固齿健周煎剂对老年小鼠的抗氧化作用。方法实验组为固齿健周煎剂灌胃的老年小鼠，对照组为灌胃等量自来水的青、老年小鼠。检测过氧化脂质、超氧化物歧化酶及过氧化氢酶。结果实验组与青、老年小鼠对照组比较差异均有显著性。结论固齿健周煎剂具有抗脂质过氧化的作用，可能对调节机体代谢功能、抗自由基损伤及恢复牙周组织健康有益