STATEMENT OF PROBLEM: The selective pressure technique has been recommended for making impressions of maxillary edentulous residual ridges. Although various methods for making impressions have been reported, a definitive procedure has not been clearly elucidated. PURPOSE: This in vitro study evaluated changes in impression pressure produced by different types of relief space and escape holes in the impression tray for making an impression of a simulated maxillary edentulous arch. MATERIAL AND METHODS: Silicone impression material (Exadenture) and a maxillary edentulous acrylic cast were used. A miniature pressure sensor was embedded at the mid-palatal suture (point-P) and at the left first molar area on the edentulous ridge (point-R). Three types of tray relief were used: no spacer (NS), a 0.36-mm-thick sheet of wax (SS), or a 1.40-mm-thick base plate wax (BS). Four types of escape holes were made: no hole (NH), or escape holes of 0.5, 1.0, or 2.0 mm in diameter (05H, 10H, and 20H, respectively) in the area opposing point-P. Twelve trays were formed using these relief space and escape hole combinations. The cast and tray were attached to a rheometer for applying a continuous isotonic force of 5.0 kgf and compressive speed of 120 mm/min. Impressions were made and measurement of pressure (kPa) began immediately prior to compression and continued until the materials had polymerized for 2 minutes, with a sampling time of 5 Hz. Measurements were performed 5 times for each tray. The data were analyzed using 3-way analysis of variance and the Bonferroni test (alpha=.05). RESULTS: At initial pressure, the data obtained at point-P showed significantly higher values for NSNH, NS05H, SSNH, and SS05H (range: 22.29 +/- 1.58 kPa to 29.96 +/- 1.41 kPa) than those at point-R (range: 18.61 +/- 1.12 kPa to 22.71 +/- 2.11 kPa). At end pressure, the data obtained from NSNH at point P showed a significantly higher value (25.36 +/- 1.69 kPa) than that of point-R (15.36 +/- 0.99 kPa) (P<.001), whereas data from NS10H and NS20H at point-P showed a significantly lower value (6.32 +/- 0.84 kPa and 4.50 +/- 0.42 kPa) than at point-R (15.50 +/- 0.49 kPa and 14.98 +/- 0.88 kPa) (P<.001). The data obtained from SS05H, SS10H, and NS20H at point-P showed significantly lower values (range: 3.72 +/- 0.44 kPa to 9.10 +/- 0.26 kPa) than those at point-R (range: 13.40 +/- 1.31 kPa to 14.40 +/- 0.98 kPa). Moreover, the data obtained from BSNH, BS05H, BS10H, and BS20H at point-P showed significantly lower values (range: 3.24 +/- 1.96 kPa to 10.20 +/- 1.84 kPa) than those of point-R (range: 11.69 +/- 1.01 kPa to 14.04 +/- 2.08 kPa). CONCLUSION: For making impressions of an edentulous maxilla, the data suggest that a tray with an escape hole 1.0 mm or larger or a spacer thickness of base plate wax (1.40 mm) be used.
STATEMENT OF PROBLEM: The selective pressure technique has been recommended for making impressions of maxillary edentulous residual ridges. Although various methods for making impressions have been reported, a definitive procedure has not been clearly elucidated. PURPOSE: This in vitro study evaluated changes in impression pressure produced by different types of relief space and escape holes in the impression tray for making an impression of a simulated maxillary edentulous arch. MATERIAL AND METHODS:Silicone impression material (Exadenture) and a maxillary edentulous acrylic cast were used. A miniature pressure sensor was embedded at the mid-palatal suture (point-P) and at the left first molar area on the edentulous ridge (point-R). Three types of tray relief were used: no spacer (NS), a 0.36-mm-thick sheet of wax (SS), or a 1.40-mm-thick base plate wax (BS). Four types of escape holes were made: no hole (NH), or escape holes of 0.5, 1.0, or 2.0 mm in diameter (05H, 10H, and 20H, respectively) in the area opposing point-P. Twelve trays were formed using these relief space and escape hole combinations. The cast and tray were attached to a rheometer for applying a continuous isotonic force of 5.0 kgf and compressive speed of 120 mm/min. Impressions were made and measurement of pressure (kPa) began immediately prior to compression and continued until the materials had polymerized for 2 minutes, with a sampling time of 5 Hz. Measurements were performed 5 times for each tray. The data were analyzed using 3-way analysis of variance and the Bonferroni test (alpha=.05). RESULTS: At initial pressure, the data obtained at point-P showed significantly higher values for NSNH, NS05H, SSNH, and SS05H (range: 22.29 +/- 1.58 kPa to 29.96 +/- 1.41 kPa) than those at point-R (range: 18.61 +/- 1.12 kPa to 22.71 +/- 2.11 kPa). At end pressure, the data obtained from NSNH at point P showed a significantly higher value (25.36 +/- 1.69 kPa) than that of point-R (15.36 +/- 0.99 kPa) (P<.001), whereas data from NS10H and NS20H at point-P showed a significantly lower value (6.32 +/- 0.84 kPa and 4.50 +/- 0.42 kPa) than at point-R (15.50 +/- 0.49 kPa and 14.98 +/- 0.88 kPa) (P<.001). The data obtained from SS05H, SS10H, and NS20H at point-P showed significantly lower values (range: 3.72 +/- 0.44 kPa to 9.10 +/- 0.26 kPa) than those at point-R (range: 13.40 +/- 1.31 kPa to 14.40 +/- 0.98 kPa). Moreover, the data obtained from BSNH, BS05H, BS10H, and BS20H at point-P showed significantly lower values (range: 3.24 +/- 1.96 kPa to 10.20 +/- 1.84 kPa) than those of point-R (range: 11.69 +/- 1.01 kPa to 14.04 +/- 2.08 kPa). CONCLUSION: For making impressions of an edentulous maxilla, the data suggest that a tray with an escape hole 1.0 mm or larger or a spacer thickness of base plate wax (1.40 mm) be used.
Authors: Subash M Reddy; Chenthil Arun Mohan; D Vijitha; R Balasubramanian; A Satish; Mahendira Kumar Journal: J Indian Prosthodont Soc Date: 2012-10-30