Histopathological evaluation of the effects of fiber reinforced acrylic resins on living tissues

Abstract

Objective. The aim of this study was the histopathological evaluation of the effects of the fiber reinforced acrylic resins on living tissues. Materials and methods. The study was performed on 21 rabbits. Three groups, each including seven subjects, were formed. There was no applied plate in the control group. For the second group, heat-polymerized acrylic resin plates were inserted. For the third group, heat-polymerized acrylic resin plates containing proportionally 5% chopped silanated E type glass fiber were inserted. Plates were fixed to the palatine bone of the rabbits with titanium screws. Before the implementation of the plates and 1 month after the plates were applied, soft tissue samples were taken from the buccal mucosa of the rabbits. Also, tissue samples were taken from the control group. All samples were evaluated histopathologically. Results. In the control group, only a focal atrophy was observed. In the acrylic group, large decomposition containing erythrocytes under the parahyperkeratotic region and micro-vesicle like spongiotic tissue reactions were observed. In the fiber reinforced acrylic group, widespread focal atrophy, bulgy look of the epithelium cells similar to apoptosis, over-distension and sub-corneal decomposition had been observed. In terms of atrophy and hyperkeratosis there were no statistically significant differences among groups. However, in respect to sub-corneal decomposition, there was a statistically significant difference in the fiber reinforced group (p < 0.01). Conclusions. The statistically significant difference in the sub-corneal decomposition of the fiber reinforced group had made us think that fiber edges had a traumatic effect on the reaction.     

Light-attenuating effect of dentin on the polymerization of light-activated restorative resins

The light-attenuating effect of dentin on the mechanical properties of light-activated composite resins was evaluated using a simple experimental filter. The filter was designed to simulate the light transmittance and light diffusion characteristics of 1.0-mm thick dentin. The depth of cure, surface hardness, and flexural strength for 13 shades of three light-activated restorative resins were examined. These resins were cured either using direct irradiation with a light source, or indirect irradiation through the filter. The attenuation of light intensity by 1.0-mm thick dentin reached 85-90% in the 400-550 nm wavelength region. For all materials, the values of depth of cure, surface hardness on the top and bottom surfaces, and flexural strength of specimens irradiated indirectly through the simulated 1.0-mm thick dentin filter decreased by 37-60%, 16-55%, 50-83%, and 44-82% in comparison with those by direct irradiation, respectively. Recovery from mechanical properties' reduction was achieved when materials were irradiated 1.5-4 times longer than the standard irradiation time.     

Critical soft tissue parameters of the zygomatic implant

AIM: Zygomatic implants have been introduced for the rehabilitation of patients with severe bone defects of the maxilla. The soft tissue aspects of the palatal emergence situation have not been described yet. The aim of this study was to evaluate the incidence and clinical impact of possible periimplant alterations of zygomatic implants. MATERIALS AND METHODS: From 1998 to 2001 all patients with zygomatic implants were included into this study (24 patients, 37 zygomatic implants). One implant was lost in the loading phase giving a survival rate of 97%. Fourteen patients with 20 zygomatic implants fulfilled the inclusion criteria and were all available for the recall examination. Thirteen zygomatic implants were inserted in cases of severe maxillary atrophy, seven in cases of tumour-resection of the maxilla. Clinical examination and microbial analysis using a DNA probe was performed. The implants had a mean time in situ of 598 days (min: 326, max: 914). RESULTS: Colonisation with periodontal pathogens was found at four of the 20 implants. A positive microbiologic result of the periimplant pocket and the maximum pocket probing depth were not statistically related. Nine of the 20 implants showed bleeding on probing, four of these had positive microbiologic results. At sites without bleeding on probing only negative microbiologic samples were found (p=0.026). The mean palatal and mesial probing depth was 1 mm deeper than at the vestibular and distal aspect. Thus at nine out of the 20 implants both, bleeding on probing and pocket probing depth >/=5 mm indicated soft tissue problems resulting in a success rate of only 55%. The patient's history (tumor versus atrophy) or smoking habits seemed not to have influence the situation. CONCLUSION: These soft tissue problems should be taken into account if zygomatic implants are considered as an alternative therapy option in the maxilla.     

The effect of cure rate on the mechanical properties of dental resins

OBJECTIVE: This study investigates the effect of cure rate on the mechanical properties of a common dimethacrylate dental resin formulation (75/25 wt% bis-GMA/TEGDMA). METHODS: The polymerization rate and final conversion of the exact specimens subsequently used for mechanical testing were monitored by near-infrared (near-IR) spectroscopy. The glass transition temperature (T(g)) and modulus, as a function of temperature, were determined by dynamic mechanical analysis (DMA). Iniferter initiating systems were used to create partially cured networks that did not contain any trapped radicals. By the elimination of trapped radicals from the system, the formed networks can be characterized as a function of both temperature and double bond conversion without inducing additional thermal cure during testing. RESULTS: Copolymer specimens were cured with UV and visible light initiating systems, UV light intensities that varied by over four orders of magnitude, and cure temperatures that differed by 60 degrees C. Even though the polymerization rates for these resins were vastly different, similar T(g) and modulus were measured for specimens cured to the same final double bond conversion. SIGNIFICANCE: This study shows that highly cross-linked dimethacrylate systems, such as bis-GMA/TEGDMA, exhibit similar network structure and properties as a function of double bond conversion, regardless of the method or rate of cure.     

The effect of cycling deflection on the injection-molded thermoplastic denture base resins

Objective. The aim of this study was to evaluate the effect of cycling deflection on the flexural behavior of injection-molded thermoplastic resins. Materials and methods. Six injection-molded thermoplastic resins (two polyamides, two polyesters, one polycarbonate, one polymethyl methacrylate) and, as a control, a conventional heat-polymerized denture based polymer of polymethyl methacrylate (PMMA) were used in this study. The cyclic constant magnitude (1.0 mm) of 5000 cycles was applied using a universal testing machine to demonstrate plasticization of the polymer. Loading was carried out in water at 23ºC with eight specimens per group (n = 8). Cycling load (N) and deformation (mm) were measured. Results. Force required to deflect the specimens during the first loading cycle and final loading cycle was statistically significantly different (p < 0.05) with one polyamide based polymer (Valplast) and PMMA based polymers (Acrytone and Acron). The other polyamide based polymer (LucitoneFRS), polyester based polymers (EstheShot and EstheShotBright) and polycarbonate based polymer (ReigningN) did not show significant differences (p > 0.05). None of the materials fractured during the loading test. One polyamide based polymer (Valplast) displayed the highest deformation and PMMA based polymers (Acrytone and Acron) exhibited the second highest deformation among the denture base materials. Conclusion. It can be concluded that there were considerable differences in the flexural behavior of denture base polymers. This may contribute to the fatigue resistance of the materials.     

Critical systemic and psychosocial considerations in management of trauma in the elderly

Traumatic injuries in the elderly are increasing commensurately with the activeness and healthiness of the lifestyles seen in our expanding geriatric population. Census data suggest that the elderly population will expand by 50% in future years and will represent a larger percentage of Americans by the year 2050. The annual occurrence of traumatic injuries in the elder cohort is reported to be as high as 29%. Perioperative management of acutely injured elderly patients is different from the care rendered to younger patients and is typically more complex. The purposes of this article are to (1) review factors related to aging that may have profound effects on the care and outcomes of senior citizens with craniofacial trauma, (2) consider the perioperative medical evaluation of the older patient, (3) discuss nutritional support and anesthetic management in the elderly, (4) discuss the unique physiological factors that may influence the treatment of craniofacial trauma in older patients, and (5) provide a rationale for facial trauma repair in the elderly that is influenced by the risk-benefit outcome of treatment planning decisions.     

The effect of glutaraldehyde base disinfectants on denture base resins

The effect of two alkaline glutaraldehyde base disinfectants on a heat-cured denture base resin was evaluated by the flexural strength, the repair flexural strength, and the surface morphology of the material that had been immersed up to 12 hours in the disinfecting solutions. The flexural strength of the material was not significantly affected by either disinfectant. The disinfectant with phenolic buffer caused surface pitting of the material after 10 minutes of immersion, and softening and swelling of the surface after 2 hours of immersion. No apparent surface change was observed with the regular alkaline formulation, however. Between the two repair resins, the autopolymerized resin yielded greater repair flexural strength than the light-cured repair resin. However, the repair flexural strength of autopolymerized resin seemed to be influenced by either disinfecting solution whereas the light-cured repair resin was not affected.     

The effect of photo-activated glazes on the microhardness of acrylic baseplate resins.

OBJECTIVE: A comparative investigation of acrylic denture base surface microhardness, induced through glazing with different photo-activated liquids. MATERIALS AND METHODS: Thermopolymerized acrylic resin Paladon 65 (Kulzer) was used for this study. The samples were mechanically thinned by silicon carbide grinding papers and finally, mechanically polished by alumina pastes. The samples were then glazed with Palaseal, Plaquit and Lightplast-Lack photo-activated liquids. Microhardness tests were carried out via a Zeiss optical microscope equipped with an Anton Paar microhardness tester fitted with a Knoop indenter. RESULTS: Microhardness testing performed on surfaces glazed by Plaquit, Lightplast-Lack, and Palaseal photo-activated liquids showed enhanced microhardness values compared to the mechanically polished acrylic resin denture base material. CONCLUSIONS: Comparative microhardness tests performed on acrylic base resin treated with photo-activated acrylic glazes showed that all increases the surface microhardness. The enhancement of surface microhardness of acrylic denture bases suggests that they are likely to resist wear during service.