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PubMed2004

Morphologic comparison of two neutral zone impression techniques: a pilot study.

STATEMENT OF PROBLEM: Several studies have compared dentures fabricated using neutral zone and conventional techniques. However, studies comparing swallowing and phonetic techniques for assessing the location and shape of the neutral zone could not be identified in the literature. PURPOSE: The purpose of this pilot study was to compare the outline form of the phonetic and swallowing neutral zone impression techniques for the same subjects. MATERIAL AND METHODS: Nine denture wearers with advanced mandibular ridge resorption were included in this study. For each subject 2 trays were prepared in autopolymerizing acrylic resin. One method used phonetics and tissue conditioner to shape the neutral zone; the second method used swallowing and modeling plastic impression compound. The resulting neutral zone impressions were leveled to the same occlusal height by gently grinding the occlusal surface on sandpaper until it corresponded with landmarks (corners of the mouth, two thirds of the height of the retromolar pads, bilaterally) noted on the cast. The impression was inverted onto graph paper, and the contour was outlined with a lead pencil. One impression was made for each subject, for each technique. The buccal contours of both neutral zones coincided at the median line. The maximum distance between the zones was measured in a buccolingual direction in the anterior, premolar, and molar regions bilaterally. When the location of the phonetic neutral zone in relation compared to the swallowing neutral zone was buccally oriented, a plus score was given. When the phonetic neutral zone was lingually located, a minus score was given. When the 2 lines coincided, a score of 0 was given. Measurements were made from direct readings on the graph paper. Statistical analysis was performed using the Sign test (alpha=.05). RESULTS: Significant differences were noted buccally in the left molar (P =.031) and right molar (P =.003) regions and also in the left and right premolar regions (P =.007), where the swallowing neutral zone was found to be located buccal to the phonetic neutral zone. Significant differences were also noted lingually, in the right premolar region (P =.015), where the swallowing neutral zone was found to be located lingual to the phonetic neutral zone. There was no significant difference between the techniques for the anterior region. CONCLUSION: Within the limits of this study, the phonetic neutral zone appears to be narrower posteriorly compared to the swallowing neutral zone, thus limiting premolar and molar positioning.

Aged↗
PubMed2004

An evaluation of impression techniques for multiple internal connection implant prostheses.

STATEMENT OF PROBLEM: Movement of impression copings inside the impression material using an open-tray impression technique during clinical and laboratory phases may cause inaccuracy in transferring the 3-dimensional spatial orientation of implants intraorally to the definitive cast. Consequently the restoration may require corrective procedures. PURPOSE: This in vitro study evaluated the accuracy of 3 different impression techniques using polyether impression material to obtain a precise definitive cast for a multi-unit implant restoration with multiple internal connection implants. MATERIAL AND METHODS: A reference acrylic resin model with 4 internal connection implants (3i Implant Innovations) was fabricated. Forty-five medium-consistency polyether impressions (Impregum Penta) of this model were made with square impression copings using an open-tray technique. Three groups of 15 specimens each were made with different impression techniques: in the first group, nonmodified square impression copings were used (NM group); in the second group, square impression copings were used and joined together with autopolymerizing acrylic resin before the impression procedure (R [resin] group); and in the third group, square impression copings previously airborne-particle abraded and coated with the manufacturer-recommended impression adhesive were used (M [modified] group). Matching implant replicas were screwed into the square impression copings in the impressions. Impressions were poured with ADA type IV stone (New Fujirock). A single calibrated examiner blinded to the nature of the impression technique used examined all definitive casts to evaluate the positional accuracy (mum) of the implant replica heads using a profile projector (at original magnification x10). These measurements were compared to the measurements calculated on the reference resin model which served as control. Data were analyzed with a 1-way analysis of variance at alpha=.05, followed by the Student Newman-Keuls test (alpha=.05). RESULTS: The data obtained with the profile projector revealed significant differences within the 3 impression techniques ( P <.001). The Student Newman-Keuls procedure disclosed significant differences between the groups, with group R casts being significantly more accurate than group NM and group M casts ( P =.05). The mean distance (+/-SD) between the posterior implants compared to the reference acrylic resin model was 18.17 mum (+/- 6.4) greater for group R casts, 41.27 mum (+/- 8.4) greater for group M casts, and 46.21 mum (+/- 8.9) greater for group NM casts. Distances between the anterior implants were also greater than those recorded on the reference model. The distance was 15.23 mum (+/- 5.9) greater on group R casts, 38.17 mum (+/- 8.3) greater on group M casts, and 43.23 mum (+/- 8.7) greater on group NM casts. CONCLUSION: Within the limitations of this study, improved accuracy of the definitive cast was achieved when the square impression copings joined together with autopolymerizing acrylic resin were used to make an impression of multiple internal connection implants.

Acrylic Resins↗
PubMed2003

Evaluation of the accuracy of three techniques used for multiple implant abutment impressions.

STATEMENT OF PROBLEM: Movement of pick-up type impression copings inside the impression material during clinical and laboratory phases may cause inaccuracy in transferring the spatial position of implants from the oral cavity to the master cast. As a consequence, the laboratory technician may fabricate a restoration that requires corrective procedures. PURPOSE: This in vitro study evaluated the accuracy of 3 different impression techniques using polyether impression material to obtain a master cast for the fabrication of a prosthesis that would fit passively on multiple implants. MATERIAL AND METHODS: A machined metal model with 6 implants and abutments and a corresponding, passively fitting, matching metal template were fabricated. A total of 45 medium-consistency polyether impressions (Impregum Penta) of this model were made with pick-up type square impression copings. Three groups of 15 each were made with different impression techniques: in group 1, nonmodified square impression copings were used; in group 2, square impression copings were used and joined together with autopolymerizing acrylic resin before the impression procedure; and in group 3, square impression copings previously airborne particle-abraded and coated with the manufacturer-recommended impression adhesive were used. The matching metal template, which had been passively fit to the metal model so that it encountered no visually perceptible resistance or rocking on the abutments, was used as the control for evaluation of the accuracy of passive fit. A single calibrated and blinded examiner visually evaluated each cast. Positional accuracy of the abutments was numerically assessed with an optical scanner at original magnification x 10, which provided measurements to within 2 microm of the variations of the casts with respect to the horizontal distances between the 2 most posterior abutments and the 2 most anterior abutments. Data were analyzed with a 1-way analysis of variance at alpha=.05, followed by the Student Newman-Keuls method (P=.05). RESULTS: Visual examination of the casts from group 1 revealed discrepancies between 1 or more abutments and the metal template. Visual analysis of the master casts from groups 2 and 3 revealed close alignment of the metal template on all 6 abutments. One-way analysis of variance analyzed the numerical data obtained with the optical scanner and revealed significant differences among the 3 impression techniques (P<.001). The Newman-Keuls procedure disclosed significant differences between the groups, with group 2 and 3 casts being significantly more accurate than group 1 casts (P=.05). The distance between abutments 1 and 6 compared to the standard metal model was 33.83 microm (SD +/- 5.4) greater on group 2 casts, 31.72 microm (SD +/- 4.6) greater on group 3 casts, and 78.16 microm (SD +/- 22.14) greater on group 1 casts. Distances between the most anterior abutments were also greater than those recorded on the metal model. The distance was 31.42 microm (SD +/- 7.6) greater on group 2 casts, 30.34 microm (SD +/- 6.4) greater on group 3 casts, and 67.91 microm (SD +/- 15.34) greater on group 1 casts. CONCLUSION: Within the limitations of this study, improved accuracy of the master cast was achieved when the impression technique involved square impression copings joined together with autopolymerizing acrylic resin or square impression copings that had been airborne particle-abraded and adhesive-coated.

Air Abrasion, Dental↗
PubMed2002

Contamination level of alginate impressions arriving at a dental laboratory.

The contamination level of alginate impressions delivered to a large dental laboratory in Sweden was determined. One hundred and seven consecutive alginate impressions were included during 7 days. Samples were taken and transferred into sterile physiological saline and analysed microbiologically for colony-forming units (cfu) as well as nonhemolytic, alpha-hemolytic, and beta-hemolytic colonies. After sampling, the clinics were contacted and asked to fill in simple questionnaires about their routines of disinfecting impressions. The questionnaire study revealed that about half of the clinics had some kind of disinfection routine, while the others rinsed in running water only. Seventy-two percent of the impressions yielded growth of bacteria, with a median number of 1.3x10(2) cfu. Thirteen per cent of the samples yielded >10(3) cfu, with a maximum number of 3.4x10(4) cfu. The majority of isolates were non- and alpha-hemolytic bacteria. Growth was recorded in 61.3% of disinfected impressions, and the numbers of bacteria in disinfected and nondisinfected impressions were similar. These findings raise the question of whether impressions need to be disinfected or if proper handling and hygienic procedures are sufficient to block the possible route of infection.

Alginates↗
PubMed2002

In vitro study of transmission of bacteria from contaminated metal models to stone models via impressions.

The purpose of this study was to determine the risk of microbiological transmission into the dental laboratory via impressions and dental stone models. Metal master models were contaminated with Bacillus subtilis and Streptococcus sanguis. Impressions in alginate, polyvinylsiloxane, and polyether were used, and models were cast in two brands of dental stone. Samples were taken from the impression surfaces before and after casting, and sections from the stone models were taken by a technique developed for this study. After incubation, the numbers of colonies were counted and the numbers of colony-forming units per milliliter were calculated. The reductions were statistically significant but considered to be clinically insignificant. The conclusion is that even after severe contamination, the risks to dental laboratory personnel are minimal. "Normal" hygienic procedures are recommended instead of disinfection.

Alginates↗
PubMed1969

Accurate casts.

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Dental Impression Materials↗