Hygiene practices in removable prosthodontics: A systematic review.

OBJECTIVE: To systematically review the recent scientific evidence about the hygiene practices of removable prostheses relative to the effectiveness, colour and dimensional stability. This review aimed also to identify patients' attitudes and habits towards denture hygiene. METHODS: Three electronic databases (MEDLINE/PubMed, Scopus and Cochrane Library) were screened, in English language, between January 1995 and December 2016. A supplementary hand search in the reference list of the identified articles was also performed. Controlled clinical trials (CCTs) involving patients with no clinical signs of denture stomatitis along with a comprehensive aim to assess the effectiveness of hygiene interventions and their impact on prosthesis colour and dimensional stability were eligible for inclusion. RESULTS: Following a thorough screening of titles/abstracts/full texts and consideration of the defined inclusion criteria, 21 CCTs examined the effectiveness of the hygiene approaches, 3 evaluated the colour stability of dentures subjected to hygiene practices, 2 examined the dimensional stability of dentures following microwave disinfection and 30 studies registered patients' attitudes and habits towards denture hygiene. CONCLUSIONS: Combined application of different hygiene interventions, including brushing or ultrasound vibration in conjunction with chemical agents, leads to more effective outcomes (reduction in denture biofilm percentage and/or number of microorganisms' colony-forming units). The dimensional stability seems to be unaltered, but the number of clinical trials was limited. Critical concentrations of cleansing solutions along with the duration of their implementation influence the serviceability of dentures regarding colour stability. Brushing represents the most commonly applied hygiene practice, while denture wearers' attitudes are not complied with the recommended guidelines considering the reported frequency of hygiene practices and the continuous denture wear.

The effect of accelerated ageing on performance properties of addition type silicone biomaterials.

The UV-protection provided to addition type silicone elastomers by various colorants, such as conventional dry earth pigments, as well as the so called "functional or reactive" pigments, was investigated. Moreover, the effect of a UV light absorber and a silica filler was also explored. Under the experimental parameters of this work, the exposure of silicone to UV radiation resulted in some changes of the IR absorbance, thermal decomposition after 400 degrees C, T(g) and tensile properties, whereas the storage modulus of samples was not affected. The obtained spectroscopic data, as well as the results of TGA and storage modulus, were interpreted by assuming that chain scission takes place during aging, whereas the improvement of tensile strength allows the hypothesis of a post-curing process, initiated by UV radiation. Therefore, the increase of T(g) could partly be due to the above reason and, furthermore, to the contribution of a rearrangement of chain fragments within the free volume of the elastomeric material. Regarding the evaluation of various coloring agents used in this work, the obtained results show that dry pigments are more sensitive to accelerated ageing conditions in comparison with functional liquid pigments. Moreover, the hydrophobic character of silicone matrix is enhanced, with the addition of this type pigments because of the vinyl functional silanes groups present in their chemical structure. Finally, it should be noted that the incorporation of silica nanofiller did not seem to prevent the silicone elastomer from degradation upon UV irradiation, but showed a significant reinforcing effect.

Mechanical behavior of facial prosthetic elastomers after outdoor weathering.

OBJECTIVES: The degradation of maxillofacial prosthetic elastomers that occurs during physical weathering is usually responsible for the replacement of prostheses. In this study the mechanical behavior of 4 non-pigmented facial prosthetic elastomers, exposed to outdoor weathering for 1 year, was investigated. The hypothesis investigated was that irradiation time did not affect the properties measured. METHODS: The samples were exposed to solar radiation for 1 year in Thessaloniki (Greece). Three different types of polydimethyl siloxane (PDMS) and chlorinated polyethylene (CPE) samples were tested in this study. Mechanical tests (compressive-tensile) were performed using a universal type testing machine. Hardness tests were evaluated using a durometer tester. Simple mathematical models were developed to correlate the measured properties with irradiation time. The stress-strain data of compression and tensile tests were modeled using parameters such as maximum stress (sigma(max)), maximum strain (epsilon(max)), elasticity parameter (E), and non-linearity parameter (p), while the mathematical model used for hardness data involves initial hardness of materials (H(0)). RESULTS: Two of the silicone prosthetics (Elastomer 42, TechSil 25) seem to become harder and more brittle contrary to the other silicone (M 511) and chlorinated polyethylene (CPE) samples that become softer and more ductile. Duration of exposure increases these phenomena. CONCLUSION: The effect of irradiation time on the mechanical behavior was introduced through its effect on the models' parameters. The hypothesis was rejected since changes were observed in the model parameters.

The effect of artificial accelerated weathering on the mechanical properties of maxillofacial polymers PDMS and CPE.

The effect of UVA-UVB irradiation on the mechanical properties of three different industrial types of polydimethylsiloxane and chlorinated polyethylene samples, used in maxillofacial prostheses, was investigated in this study. Mechanical properties and thermal analysis are commonly used to determine the structural changes and mechanical strength. An aging chamber was used in order to simulate the solar radiation and assess natural aging. Compression and tensile tests were conducted on a Zwick testing machine. Durometer Shore A hardness measurements were carried out in a CV digital Shore A durometer according to ASTM D 2240. Glass transition temperature was evaluated with a differential scanning calorimeter. Simple mathematical models were developed to correlate the measured properties with irradiation time. The effect of UVA-UVB irradiation on compressive behavior affected model parameters. Significant deterioration seems to occur due to irradiation in samples.

Structural damages of maxillofacial biopolymers under solar aging.

Additional types of silicone biopolymers are widely used in maxillofacial prosthetics. Therefore, the knowledge of the solar radiation's effect on their structural stability is highly important. Four different industrially synthesized biomaterials were examined, called Episil Europe 1, Europe 2, Europe 3 and Africa 3, which were exposed to solar radiation (UVA, UVB) for eight different time periods (from 8 to 168 h). Structural damages due to irradiation exposure were investigated by mechanical tests (compression) and differential scanning calorimetry (DSC) methods. Simple mathematical models were developed, containing parameters with physical meaning such as maximum stress (sigma(max)), maximum strain (epsilon), elasticity parameter (E), and viscoelastic parameter (p), for the compression test, and melting temperature (T (m)) and Enthalpy in melting point (Heat) for DSC. With increasing irradiation time their maximum stress and strain decreased significantly, and the materials lost their elasticity and molecular stability. A decrement in their melting points and heats was observed as irradiation time was increasing. Finally, experimental results demonstrated that solar radiation has a severe effect on the structural stability of the examined biomaterials.

Gingival fibromatosis and significant tooth eruption delay in an 11-year-old male: a 30-month follow-up.

This case report describes the dental management of an unusual case of idiopathic gingival fibromatosis with multiple impacted primary teeth, and the absence of eruption of permanent teeth, in an 11-year-old boy and at the 30-month follow-up. The patient presented with severely enlarged gingival tissues affecting both arches and multiple retained and non-erupted primary teeth. He had already been subjected to localized gingivectomies at the ages of 7 and 9 years. He had no known syndrome and there was no family history of any similar disorder. The patient was treated under general anaesthesia to remove the excessive gingival tissues using apically positioned flaps. During the surgical procedure, over-retained and unerupted impacted primary teeth were extracted in order to facilitate the eruption of the permanent successors. Two years postoperatively, there was no recurrence of the gingival enlargement. Overdentures were then constructed because none of the permanent teeth had yet erupted. Furthermore, pre-eruptive coronal resorption was detected radiographically affecting the crown of the unerupted 36. Thirty months postoperatively, no recurrence of gingival enlargement was seen, but the permanent teeth had still not erupted.

Effect of individual shades on reliability and validity of observers in colour matching.

The effect of individual shades in shade guides, on the reliability and validity of measurements in a colour matching process is very important. Observer's agreement on shades and sensitivity/specificity of shades, can give us an estimate of shade's effect on observer's reliability and validity. In the present study, a group of 16 students, matched 15 shades of a Kulzer's guide and 10 human incisors to Kulzer's and/or Vita's shade tabs, in 4 different tests. The results showed shades I, B10, C40, A35 and A10 were those with the highest reliability and validity values. In conclusion, a) the matching process with shades of different materials was not accurate enough, b) some shades produce a more reliable and valid match than others and c) teeth are matched with relative difficulty.

Fracture force, deflection at fracture, and toughness of repaired denture resin subjected to microwave polymerization or reinforced with wire or glass fiber.

STATEMENT OF PROBLEM: The ultimate goal of denture repair is to restore the denture's original strength and avoid further fracture. The best materials and methods for repair have not been conclusively determined. PURPOSE: This study investigated the fracture force, deflection at fracture, and toughness of a heat-polymerized denture base material repaired with heat-polymerized resin, autopolymerized resin alone, or autopolymerized resin with glass fiber or wire reinforcement. MATERIAL AND METHODS: Eight groups were evaluated: 6 with autopolymerized resin repairs, 1 with heat-polymerized resin repairs, and a control group of intact specimens. The 6 autopolymerized resin groups included 1 group with no reinforcement, 1 treated with microwave irradiation after polymerization, 2 with monolayer or multilayer glass fiber reinforcement, and 2 with round or braided wire reinforcement. Each group consisted of 12 specimens. The experimental specimens were cut, and a 3-mm butt joint gap was repaired as indicated by the group assignment. A 3-point bending test was used to determine the fracture force, deflection at fracture, and toughness of the specimens. The data were analyzed with 1-way analysis of variance and the Tukey post-hoc test (alpha=.05). RESULTS: The fracture force (28.4 to 73.4 N), deflection (1.6 to 3.8 mm), and toughness (0.02 to 0.13 J) values for all repaired groups were significantly lower than those for the control group (82.79 N, 4.4 mm, and 0.16 J, respectively), with one exception: the mean fracture force of specimens reinforced with round wire (102.9 N). Failure mode was always adhesive, meaning that fracture occurred between the denture base and repair resin. CONCLUSION: Among the repair treatments tested, the most effective was microwave-irradiated, autopolymerized resin reinforced with round wire or monolayer glass fiber ribbon.

Candida albicans growth on thermal cycled materials for maxillofacial prostheses in vitro.

In the present study, the growth of a single isolate of Candida albicans on saliva-, serum-coated or protein free (uncoated), thermocycled (4-70 degrees C for 1 min, respectively; 0, 1000 and 10 000 times) 15 commercial maxillofacial materials was investigated, by monitoring pH changes in growth media. The inhibitory effect of the tissue conditioners on fungal growth was analysed using three parameters viz: (i) delay in the onset of the rapid decline in pH (ii) reduction in the rate of pH change and (iii) the pH minima reached. In the case of control materials (non-thermocycled and uncoated), significant antifungal effect was observed with two products. However, the antifungal effect of the materials was significantly reduced both by thermal cycling (Analysis of covariance [ANOVA]; P < 0.01) and a layer of protein coating (saliva, P < 0.05; serum, P < 0.01). When the interrelation between three parameters of fungal growth and the surface hydrophobicity of the materials were analysed, minimum pH of fungal growth on 10 000-thermocycled materials correlated well with the contact angles of the materials (Student t-test, P < 0.01), suggesting that thermocycling process reduced the unpolymerized components of the materials which showed the antifungal effects, resulted in that the cell growth depends on the surface hydrophobicity of the specimens. These results, taken together, suggest that the ageing of the materials and the biological fluids of the host enhanced the fungal growth on maxillofacial materials.

Wettability of visible light-curing denture lining materials.

PURPOSE: Wetting characteristics of denture lining materials indicate the degree of salivary lubricating effect, which promotes denture retention and patient comfort. This in vitro study investigated the wettability of ten commercially available visible light-cured denture lining materials. MATERIALS AND METHODS: Ten soft and hard visible light-curing materials, one autopolymerized hard lining material, and one autopolymerized denture base material were evaluated for wettability. Wettability was estimated by measuring the equilibrium and hysteresis contact angles using the dynamic contact angle analysis, or Wilhelmy, technique. RESULTS: The equilibrium contact angle ranged from 59.9 to 77.3 degrees, and contact angle hysteresis ranged from 14.7 to 30.6 degrees. CONCLUSION: Visible light-curing lining materials exhibit wetting properties similar to the conventional hard lining and denture base materials.

Candida albicans colonization on thermal cycled maxillofacial polymeric materials in vitro.

In the present study, the colonization of a single isolate of Candida albicans on saliva-, serum-coated or protein free (uncoated), thermocycled (4-70 degrees C for 1 min, respectively; 0, 1000 and 10 000 times) 15 commercial maxillofacial materials were investigated, by adenosine triphosphate (ATP) analysis. In the case of control specimens (not thermocycled and uncoated), the fungal colonization appeared to depend upon the type of commercial products used. Thus, the lowest colonization was observed with additional silicone materials, soft acrylic liners with visible light curing, except for one product, whereas visible light curing liners comprising of single paste or single gel exhibited the highest colonization capacity, and cold cured acrylic liners exhibited the intermediate. However, the fungal colonization on the materials was significantly promoted both by thermal cycling (ANOVA; P < 0.01) and a layer of protein coating (saliva, P < 0.01; serum, P < 0.01). When the inter-relation between the fungal colonization and the surface hydrophobicity of the materials were analysed, fungal colonization on 1000- and 10 000-thermocycled materials correlated well with the contact angles of the materials (Student's t-test, P < 0.01), being consistent with the thermodynamic theory. These results, taken together, suggest that the ageing of the materials and the biological fluids of the host promote yeast colonization on maxillofacial materials.

Influence of curing method, sealer, and water storage on the hardness of a soft lining material over time.

PURPOSE: The purpose of this study was to determine the hardness of plasticized acrylic resin soft lining materials over time when curing procedures were modified and when surface sealers were either used or omitted. MATERIALS AND METHODS: A chairside plasticized acrylic resin material and a heat processed plasticized resin material were made into disks 40 mm in diameter and 10 mm in thickness. Materials were cured by processing at an elevated temperature or at mouth temperature. Five samples were used with each processing method. Half of all samples were treated with a surface sealer, whereas the other samples received no surface treatment. After processing, the samples were immersed in 37 degrees C water for a total time of 1 year. Specimens were tested to determine hardness on a monthly basis. Testing was accomplished using a Shore A durometer. RESULTS: Hardness testing showed differences relative to material and to time after processing. The heat-processed plasticized resin material showed significantly higher Shore A hardness values than the chairside over the entire experimental period (p <.01). Increased hardness was seen for all materials over time, but this was more pronounced with plasticized acrylic resin in which the hardness increased from 28.4% to 115.8% depending on processing method and surface treatment. Surface treatment showed significant softening only when the samples were cured at simulated mouth temperature (p <.05). CONCLUSIONS: Processing method and time after processing have an effect on surface hardness of the tested materials, but neither of these effects is as profound as the initial choice of material. J Prosthodont 2001;10:42-45.

Irritation test of tissue adhesives for facial prostheses.

STATEMENT OF PROBLEM: Adhesives are commonly used to improve the retention of a facial prosthesis to the skin. Although no requirement exists for facial prosthetic adhesives, an adhesive should be nonirritating and nontoxic. PURPOSE: This study assessed the irritative potential of facial prosthetic adhesives by using an in vitro technique for detection of eye-irritating chemicals. MATERIAL AND METHODS: Ten adhesives were evaluated by the hens egg test chorioallantoic membrane method. Adhesives were applied to the chorioallantoic membrane in fertilized hen eggs, and the membrane examined by a photomacroscope for injury to the blood vessels. The average irritation score was calculated from the recorded times for the debut of hemorrhage, lysis, and coagulation, and the products were classified as being non, slight, moderate, or strong irritants, based on the irritation score. RESULTS: The predominant injury to the membrane was coagulation of blood vessels, and the exposure time needed to initiate the reaction was dependent on the composition of the product. Four products were classified as strong irritants, 1 as moderate, and the remaining 5 as slight or nonirritant. CONCLUSION: On the basis of a test for eye irritation, the irritant potential of tissue adhesives varied from non to severe. The most severe reactions were mainly seen in products containing the solvent ethyl acetate.

Physical properties of a silicone prosthetic elastomer stored in simulated skin secretions.

STATEMENT OF PROBLEM: Facial prostheses worn over an extended time are exposed to various environmental factors, including sebaceous oils (sebum) and perspiration. PURPOSE: This study investigated the physical properties of tensile strength and modulus, elongation, tear strength, hardness, weight, and color change, of a silicone facial elastomer after immersion for 6 months in simulated sebum and perspiration at 37 degrees C. MATERIAL AND METHODS: Specimens made of Episil silicone elastomer were immersed in simulated alkaline or acidic perspiration as well as in sebum. Tensile and tear tests were conducted according to ISO specifications no. 37 and 39, respectively, in a Monsanto testing machine. Shore A hardness measurements were run according to ASTM D 2240. Weight changes were followed at 5, 15, 30, and 180 days, and color changes were determined in the CIE LAB system using a tristimulus colorimeter. RESULTS: An improvement of mechanical properties for specimens immersed in acidic perspiration was attributed to facilitation of the propagation of cross-linking reaction during aging of the silicone samples. Some weight increase was observed for the specimens immersed into the aqueous solution, whereas for those immersed in sebum, weight loss was recorded, probably because of extraction of some compounds. In this latter case, the color change was lower than that corresponding to simulated perspiration. CONCLUSION: The silicone specimens aged for a period, which simulates 1.5 years of clinical service, showed minimal changes with respect to the properties studied.

Roughness of denture materials: a comparative study.

PURPOSE: Surface properties of denture materials are of clinical importance since they may affect plaque accumulation and staining. This in vitro study investigated the roughness of 20 commercially available denture materials. MATERIALS AND METHODS: Four denture base resins, nine hard lining materials, and seven soft denture lining materials were evaluated for roughness. Roughness measurements were made using a Mitutoyo Surftest SV-400, and the mean arithmetic roughness values (Ra) obtained were used for the comparisons. RESULTS: The overall Ra values ranged from 0.7 to 7.6 microns. The denture base materials group exhibited Ra values from 3.4 to 7.6 microns, whereas the hard liners were from 0.7 to 4.4 microns. The autopolymerized and visible light-cured soft liners presented Ra values from 0.7 to 3.5 microns, while the heat-cured soft liners ranged from 3.5 to 4.0 microns. CONCLUSION: The roughness exhibited by all of the materials tested (Ra values greater than 0.7 micron) indicates that there is a possibility for plaque accumulation, since 0.2 micron is considered the threshold below which no further bacterial adherence can be expected.

Curing efficiency of visible light- and dual-cured denture reliners.

PURPOSE: The purpose of this study was to evaluate the curing efficiency of 8 light- and dual-cured denture reliners. MATERIALS AND METHODS: The curing efficiency was measured with Fourier infrared micromultiple internal reflectance spectroscopy, calculating the percentage of remaining carbon double bonds on the top and bottom surfaces of each specimen immediately after exposure to the extraoral light-curing unit according to the manufacturer's instructions and after 1 week of storage in dark and dry conditions. Another group of specimens was photopolymerized initially through a denture base resin prior to the extraoral light-curing polymerization. Five specimens of each reliner were tested. RESULTS: The dual-cured reliners showed no statistically significant differences (P > 0.05) between top and bottom surfaces after immediate exposure to the light-curing unit. On the contrary, light-cured reliners revealed significant differences. The majority of the reliners showed reduction of the percentage of remaining carbon double bonds at both surfaces after 1 week of storage in dark and dry conditions. Photopolymerization of light-cured reliners through a denture base resin induced an increased amount of remaining carbon double bonds, whereas no effect was observed in dual-cured materials. CONCLUSION: Dual-cured denture liners exhibited distinct advantages over light-cured ones concerning the curing efficiency.

Color stability of facial silicone prosthetic polymers after outdoor weathering.

STATEMENT OF PROBLEM: Color deterioration of silicone prosthetic elastomers affects the life expectancy of facial prostheses in a service environment. PURPOSE: This study investigated the color stability of 3 nonpigmented silicone elastomers (Silskin 2000, Elastosil M3500, Ideal) exposed to outdoor weathering for 1 year. MATERIAL AND METHODS: A tristimulus colorimeter was used to evaluate the color differences (DeltaE*) of the silicone elastomers every 2 months. Ten disk-shaped specimens for each material were tested. Data were analyzed with a repeated measures ANOVA and Student-Newman-Keuls test at a significance level of alpha = .05. RESULTS: All silicone elastomers showed visually detectable, mean color differences (DeltaE* > 2.0), that ranged from 2.13 to 3.98. Silskin 2000 showed greater color differences (P <.05) compared with Elastosil M3500 and Ideal, which showed similar behavior (P >.05). CONCLUSION: Outdoor exposure of silicone facial elastomers for 1 year resulted in visually detectable color differences. Duration of exposure and silicone elastomer were significant factors that affected color stability. Silskin 2000 was significantly less color stable than Elastosil M3500 and Ideal, which were not statistically significantly different from each other.

Color stability of visible light-cured, hard direct denture reliners: an in vitro investigation.

PURPOSE: Previous studies have disclosed the unsatisfactory color stability of autopolymerizing, hard direct denture reliners (HDDR). The present study investigated the color stability of the newly introduced visible light-cured and dual-cured HDDRs. MATERIALS AND METHODS: Five HDDRs were evaluated after 1 hour, 1 day, 7 days, and 30 days of immersion in coffee, tea, and water. Color measurements were obtained with a tristimulus colorimeter, and color differences (delta E*) were calculated. RESULTS: After 30 days of immersion one visible light-cured material exhibited the highest delta E* value (17.8). The other materials showed acceptable color stability in water and coffee. However, tea strongly affected their color. CONCLUSION: Reliners, staining solutions, and immersion time are significant factors that affect color stability. After 7 days of immersion, all of the materials showed perceptible color differences. Tea exhibited higher staining capacity than coffee.

Wettability of silicone rubber maxillofacial prosthetic materials.

STATEMENT OF PROBLEM: Maxillofacial prosthetic materials that contact skin or mucosa should have good wettability. A material that is easily wetted will form a superior lubricating layer between the supporting tissues and, thus, reduce friction and patient discomfort. The surface energy of a maxillofacial prosthetic material will give an indication of the amount of energy available for adhesion and of the susceptibility of the material to bacterial adhesion. PURPOSE: This study evaluated the wettability and surface energies of a range of commercially available silicone rubber maxillofacial prosthetic materials. MATERIAL AND METHODS: Contact angles and surface energies were measured by using a dynamic contact angle measuring technique. Four commonly used silicone maxillofacial materials were tested and their properties compared with those of an acrylic resin denture base material and a widely used denture soft lining material. RESULTS: There were no significant differences in the wettability of the silicone rubber materials. All materials were significantly less wetted than the denture acrylic resin material. There were no significant differences in the surface energies of the silicone rubber materials, but all were significantly lower than denture acrylic resin material. CONCLUSIONS: The Cahn dynamic contact angle analyzer was a quick and reproducible method for determining the contact angles and surface energies of maxillofacial materials. Further work is needed to improve the wettability of silicone rubber materials used for maxillofacial prostheses, thus, reducing their potential to produce friction with tissues.

Mechanical properties of 2 new addition-vulcanizing silicone prosthetic elastomers.

PURPOSE: This study evaluated some mechanical properties of 2 newly introduced, addition-type silicone prosthetic elastomers (Cosmesil and Episil). MATERIALS AND METHODS: The properties evaluated were tensile strength, modulus at 100% elongation, elongation at break, tear strength, and hardness. The properties tested were selected because of their clinical significance for fabricating facial prostheses. RESULTS: Episil showed greater tensile strength (P = 0.0002), elastic modulus (P = 0.0001), hardness (P = 0.0002), and tear strength (P = 0.0004) than Cosmesil material. Cosmesil exhibited a higher elongation at break (P = 0.0002) than Episil. CONCLUSION: Cosmesil and Episil showed reasonable properties as facial prosthetic elastomers and neither was superior for all properties tested. Both materials showed favorable combinations of elongation at break and tear strength.