V P Lassila

University of Kuopio, Kuopio, Eastern Finland Province, Finland

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Publications (11)25.09 Total impact

  • P K Vallittu, A S Vallittu, V P Lassila
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    ABSTRACT: The aim of this study was to evaluate the attitudes of various groups of patients towards the appearance of their teeth. A questionnaire was used which consisted of six background variables and 13 attitudinal statements concerning the appearance of the teeth. The number of responses obtained was 254. Multiple regression analysis was undertaken to reveal any statistical associations between the answers to the statements and the background variables. According to the results, the appearance of the teeth was found to be more important to women than to men. For older patients, the appearance of teeth was not as important as for younger patients (r = -0.144, P = 0.012). Patients with limited education had a greater preference for white teeth than patients with a high level of education (r = 0.115, P = 0.037). The perception that very white teeth are beautiful decreased with increasing age (r = 0.112, P = 0.049), and younger patients expressed a greater preference for white teeth than older patients (r = 0.11, P = 0.50). This study suggests that various groups of patients have different attitudes towards the appearance of their teeth.
    Journal of Dentistry 10/1996; 24(5):335-8. · 3.20 Impact Factor
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    ABSTRACT: This study compares four different notch shapes made on the anterior margin of the palatal plates of heat-cured acrylic resin test specimens as well as the effect of self-cured acrylic resin repair on the fatigue resistance of dentures. The test specimens had the shape of an upper partial denture (n = 25). The fatigue test applied was a constant-force fatigue test at a force of 150 N. The stress concentrations during loading the replicas of the test specimens were determined in the field of a circular polarized light. The results showed that the fatigue resistance of the test specimens decreased dramatically (P = 0.002) when there was a notch at the anterior margin of the palatal plate in the test specimen. A 90 degree notch decreased the fatigue resistance most effectively. The test specimens repaired with self-cured acrylic resin were also weaker than the original unnotched test specimens. Examination of the replicas in the field of polarized light showed that stresses occurred only very close to the notch. The highest stress concentrations were detected in the test specimen with a 90 degree notch, i.e. the test specimens with the lowest fatigue resistance. The results of this study suggest that the shape of the anterior margin of the palatal plate in the acrylic resin-based partial denture plays an important role in the fatigue resistance of the dentures.
    Journal of Oral Rehabilitation 03/1996; 23(2):108-13. · 2.34 Impact Factor
  • P K Vallittu, H Vojtkova, V P Lassila
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    ABSTRACT: The impact strength of heat-cured acrylic resin test specimens that had been reinforced in various ways was compared in this study. Ten rectangular test specimens were fabricated for each test group. The strengtheners included 1.0-mm-diameter steel wire and continuous E-glass fibers. Both notched and unnotched test specimens were tested in a Charpy-type impact test. In a further analysis the concentration of glass fibers in the test specimens was determined and plotted against the impact strength of the test specimens. The results showed that, compared with the unreinforced specimens, both types of reinforcement increased the impact strength of the test specimens considerably (p < 0.001). There was no clear difference between the mean impact strength value of the test specimens reinforced with metal wire and that of the specimens reinforced with glass fiber. The correlation coefficient between the fiber concentration of the test specimens and their impact strength was 0.818 (p < 0.005). Specimens with fiber concentrations greater than 25 wt% yielded to the higher impact strength more readily than those with metal wire reinforcement did.
    Acta Odontologica Scandinavica 01/1996; 53(6):392-6. · 1.36 Impact Factor
  • Journal of Dentistry 01/1996; 24(5). · 3.20 Impact Factor
  • P K Vallittu, V P Lassila, R Lappalainen
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    ABSTRACT: This study investigated the transverse strength of repaired test specimens of heat-cured acrylic resin. The repair surfaces of the specimens were wetted with methyl methacrylate for various amounts of time before the autopolymerizing acrylic resin was applied to the joint space. A three-point loading test was used to determine the transverse strength of the test specimens, and the morphologic changes in the methyl methacrylate-wetted repair surface was analyzed by scanning electron microscopy. Visual inspection was used to determine whether the failures were adhesive or cohesive. The results revealed that repaired test specimens were weaker than those unrepaired (p < 0.001). The strength of the test specimens increased as the duration of methyl methacrylate wetting of the repair surfaces increased (p < 0.001). Furthermore, the number of adhesive failures was small if the repair surfaces were adequately wetted with methyl methacrylate. Scanning electron micrographs revealed that after 60- and 180-second wetting periods, the poly(methyl methacrylate) was noted to be dissolved with a smooth surface texture. This study suggests that proper wetting of the repair surface makes an important contribution to the strength of repaired acrylic resin.
    Journal of Prosthetic Dentistry 01/1995; 72(6):639-43. · 1.72 Impact Factor
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    ABSTRACT: In this study the fatigue life of heat-cured acrylic resin test specimens shaped as maxillary partial dentures was examined. Ten test specimens were prepared from polymethyl methacrylate and were tested by a constant force fatigue test at 150 N immersed in +37 degrees C water. The fatigue-fracture surfaces of the test specimens were compared with a one-bend fracture surface of the control specimen by scanning electron microscopy. The correlation coefficient between the number of loading cycles required to cause fatigue failure in the midline section was calculated as was the concentration of residual methyl methacrylate. Results revealed that the fatigue life of the test specimens varied greatly (483 x 10(3) +/- 371 x 10(3) cycles) and that the correlation between the number of loading cycles and the midline section was poor (r -0.455). The correlation coefficient between the number of loading cycles and the concentration of residual methyl methacrylate was r 0.476 and p > 0.5. The fatigue-fracture surface of the test specimens was smoother in texture on the tension side than on the one-bend fracture surface.
    Journal of Prosthetic Dentistry 09/1994; 72(3):289-95. · 1.72 Impact Factor
  • P K Vallittu, V P Lassila, R Lappalainen
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    ABSTRACT: This study tested the effect on the fracture resistance of acrylic resin test specimens when different amounts of fibers were incorporated in the resin matrix. The fibers used included glass, carbon, and aramid fibers, with 30 test specimens of each concentration of fibers. Transverse sections of the specimens were studied by scanning electron microscope to establish how the fibers behave in the polymerization process. The results indicated that an increase in the amount of fibers enhanced the fracture resistance of the test specimens (p < 0.001). The SEM micrographs of transverse sections of test polymerized specimens revealed void spaces of different sizes inside the fiber roving.
    Journal of Prosthetic Dentistry 06/1994; 71(6):607-12. · 1.72 Impact Factor
  • P K Vallittu, V P Lassila, R Lappalainen
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    ABSTRACT: The aims of this experiment were: 1) to test the effect of a high concentration of continuous glass fibers on the transverse strength of test specimens made of heat-cured acrylic resin; and 2) to determine the fatigue weakening of both unreinforced and continuous glass fiber-reinforced specimens of heat-cured acrylic resin shaped into upper complete dentures. A three-point loading test was used to determine the transverse strength of test specimens (n = 30 per group). The fatigue test was the constant deflection test (n = 10 per group). The results revealed that, compared to unreinforced specimens, continuous glass fibers at a concentration of 58 wt% enhanced the transverse strength of the test specimens up to 146% (p < 0.001) and increased the fatigue resistance (p < 0.001) during 5 x 10(5) loading cycles. This study suggests that by incorporating glass fibers into PMMA denture bases, the strength of the denture can be increased.
    Dental Materials 03/1994; 10(2):116-21. · 3.77 Impact Factor
  • P K Vallittu, V P Lassila, R Lappalainen
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    ABSTRACT: The number of damaged dentures and type of damage to removable dentures repaired in dental laboratories was investigated using a questionnaire sent to 24 dental laboratories in Finland. Eight variables were examined for each damaged denture. The results showed that the type of dentures most commonly needing repair was the complete upper denture (49%). The most frequent type of damage was breakdown of the acrylic base and loosening of an artificial tooth. The chi-square test established a statistical dependence (p < 0.005) between damaged dentures and their age. Damaged upper partial dentures most frequently had natural teeth or fixed prostheses as antagonist teeth. Damaged lower skeletal dentures and acrylic partial dentures had a complete denture as the antagonist (p < 0.05). Removable dentures made of acrylic resin material seemed to break despite strengtheners, such as clasp wire.
    Acta Odontologica Scandinavica 12/1993; 51(6):363-9. · 1.36 Impact Factor
  • P K Vallittu, V P Lassila
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    ABSTRACT: The aim of this study was to clarify the effect of the surface roughness of various metal wires on the fracture resistance of the acrylic test specimens. The number of test groups compared were 16, and there were 30 test specimens in each group. The investigation showed that the surface roughening of the metal wires used to reinforce acrylic resin denture base material increased the fracture resistance of the test specimens. The best results were achieved by sandblasting. The differences in resistance were also statistically significant.
    Journal of Oral Rehabilitation 08/1992; 19(4):385-91. · 2.34 Impact Factor
  • P K Vallittu, V P Lassila
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    ABSTRACT: The effect of different metal and fibre strengtheners on the fracture resistance of polymethylmethacrylate was tested. Different types of commonly used metal wire and glass fibre, as well as carbon and aramid fibres, were used as strengtheners in test specimens. There were 21 groups, and each group contained 12 test specimens. Each metal strengthener had a beneficial effect on the fracture resistance of the polymethylmethacrylate (P less than 0.001-0.01). Some fibres, which were silanized for better adhesion, also had strengthening properties.
    Journal of Oral Rehabilitation 06/1992; 19(3):225-30. · 2.34 Impact Factor