Laurence Stein DDS
Medical Moderator
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DENTISTRY TOMORROW
Issue 1, Dec 1995 - PROSTHETICS
F. Musajo, P. Passi, G.B. Girardello, F. Rusca, S. Galassini
The influence of repeated pressure variations on the retentiveness of prosthetic crowns fixed with different cements.
Summary
A previous experiment demonstrated that repeated variations of the environmental pressure, such those of scuba divers, weaken the strenght of zinc phosphate cement.
In this work, the experiment was repeated, testing also two other resin cements, subjected to more severe pressure variations with a lesser tapering of preparations.
Metal cast crowns were cemented on 48 duplicated abutments, obtained by duplicating a single master preparation. Three cements were utilized: zinc phospate, Panavia Ex and Super Bond.
After the cementations, half of the samples were subjected to compression-decompression cycles in a hyperbaric chamber, until the pressure of 5 atm.
The force necessary to dislodge the crowns was then measured. Zinc phospate and Super Bond showed a statistically significant decrease in strenght, compared to the controls, while Panavia Ex showed a lesser weakening.
A comparison is made with the results obtained in the former experiment, in which the preparations had a tapering of 9°, instead of 6° as in this work. Great care should be taken about the retentiveness of dental preparations in scuba divers and airplane pilots, and the use of very strong cements seems to be advisable.
Introduction
Some disorders affecting the stomatognathic system can originate from pressure variations, caused by high altitude climbing and expecially by scuba diving (1).
An airplane pilot is subjected to a pressure of about 210 mmHg at 10,000m and 450 mmHg at 4,000m, when the pressure to ground level is equal to about 760 mmHg. But we must consider that most airplane cockpits are at least partially pressurized, so that great differences in pressure usually do not occur.
Scuba divers, indeed, are subjectd to strong variations of environmental pressure. A diver at a depth of 30m, which is not exceptional, must withstand a pressure which is four times that at surface. Another additional problem for scuba divers is the repeated exposition to quick variations in pressure, during immersion and emersion. Moreover, this problem can be worsened by the mechanical stimulation of posterior teeth, caused by clenching the mouthpiece (2).
Pulp necrosis and hyperemia were detected in teeth extracted from airplane pilots suffering of strong dental pain (3), and the same findings were present in the dental pulp of dogs experimentally subjected to simulated decompression at 15,000 m of altitude (4).
Pain for decompression occur above all in teeth which are carious or filled without a lining cement, or in teeth with infected root canals (5,6). Pulpar hyperemia from decompression is likely the main cause of pain (7), but it seems also that barodontalgia may dipend on an increase of the permeability of the dentinal tubuli, induced by pressure variations (8).
Some authors underlined the possible role of of microbubbles of air, which can be trapped in restorations, cements or root canals (9,10), and expand during decompression, causing compression of pulp and periodontium and related pain.
The effect of repeated pressure variation on the retention of prosthetic crowns, cemented with zinc oxyphosphate, was studied in a former work of us (11). The results indicated a remarkable weakening of the cement, after 15 cycles of simulated decompression at 3 atm.
In this second experiment, the effect of pressure variation was tested also on two other organic adhesive cements.
Materials and methods
48 duplicates in epoxy resin were made, utilizing an addition silicon from a single original model of a human molar prepared for a complete crown abutment (Fig.1).
The tapering angle of the vertical walls was controlled with a goniometer during preparation of the original abutment.
The form of the abutment was as follows:
* Vestibular height= 6 mm
* Lingual height= 4 mm
* Max. mesiodistal diameter= 7 mm
* Max. vestibulolingual diameter = 5.5 mm
* Tapering angle = 6 degrees
A crown was modelled in wax on each duplicate, and cast in a metal alloy# consisting of Au 30%, Ag 43.5%, Pd 13%, Cu 10%, other metals 3.5%.
Crowns were modelled with a loop on the occlusal face, to help dislodgement maneuvers (Fig. 2).
They were divided into three groups of 16 crowns, each of them was cemented with a different cement, carefully prepared and utilized according to manufacturer's instructions.
Care was taken during spatulation in order to avoid trapping of microbubbles of air.
The first group was fixed with zinc phosphate cement##, the second one with a BIS-GMA cement with inorganic filler (Panavia Ex*), and the third group with a BIS-GMA unfilled cement (Super Bond**).
After the set of cement, the specimens were immersed in saline solution to simulate the wet environment to which the film at the margin of casts is exposed in the mouth.
After two weeks, half of the specimens of each group, in open glass containers, were placed in a hyperbaric chamber and underwent the following compression-decompression cycles:
* 10 times at 5 atm for 5 minutes
* 10 times at 4 atm for 10 minutes
* 10 times at 3 atm for 25 minutes
* 5 times at 2 atm for 50 minutes
* 3 times at 1 atm for 200 minutes
These cycles were performed with a speed lower than 1 atm/min.
The day after, the force necessary to dislodge all the crowns was measured. For this aim, the base of the abutments was enclosed in a stone base, the crowns placed with the loop downward, and a metal wire was connected to the loop, with a container attached to the other end. Water was gradually added to the container, until the crown was dislodged.
Results
The force necessary to dislodge the crowns is reported in table one. Some specimens were discarded, owing to fracture of the abutment or the stone base.
The DATA tables will be posted in the next window.
DENTISTRY TOMORROW
Issue 1, Dec 1995 - PROSTHETICS
F. Musajo, P. Passi, G.B. Girardello, F. Rusca, S. Galassini
The influence of repeated pressure variations on the retentiveness of prosthetic crowns fixed with different cements.
Summary
A previous experiment demonstrated that repeated variations of the environmental pressure, such those of scuba divers, weaken the strenght of zinc phosphate cement.
In this work, the experiment was repeated, testing also two other resin cements, subjected to more severe pressure variations with a lesser tapering of preparations.
Metal cast crowns were cemented on 48 duplicated abutments, obtained by duplicating a single master preparation. Three cements were utilized: zinc phospate, Panavia Ex and Super Bond.
After the cementations, half of the samples were subjected to compression-decompression cycles in a hyperbaric chamber, until the pressure of 5 atm.
The force necessary to dislodge the crowns was then measured. Zinc phospate and Super Bond showed a statistically significant decrease in strenght, compared to the controls, while Panavia Ex showed a lesser weakening.
A comparison is made with the results obtained in the former experiment, in which the preparations had a tapering of 9°, instead of 6° as in this work. Great care should be taken about the retentiveness of dental preparations in scuba divers and airplane pilots, and the use of very strong cements seems to be advisable.
Introduction
Some disorders affecting the stomatognathic system can originate from pressure variations, caused by high altitude climbing and expecially by scuba diving (1).
An airplane pilot is subjected to a pressure of about 210 mmHg at 10,000m and 450 mmHg at 4,000m, when the pressure to ground level is equal to about 760 mmHg. But we must consider that most airplane cockpits are at least partially pressurized, so that great differences in pressure usually do not occur.
Scuba divers, indeed, are subjectd to strong variations of environmental pressure. A diver at a depth of 30m, which is not exceptional, must withstand a pressure which is four times that at surface. Another additional problem for scuba divers is the repeated exposition to quick variations in pressure, during immersion and emersion. Moreover, this problem can be worsened by the mechanical stimulation of posterior teeth, caused by clenching the mouthpiece (2).
Pulp necrosis and hyperemia were detected in teeth extracted from airplane pilots suffering of strong dental pain (3), and the same findings were present in the dental pulp of dogs experimentally subjected to simulated decompression at 15,000 m of altitude (4).
Pain for decompression occur above all in teeth which are carious or filled without a lining cement, or in teeth with infected root canals (5,6). Pulpar hyperemia from decompression is likely the main cause of pain (7), but it seems also that barodontalgia may dipend on an increase of the permeability of the dentinal tubuli, induced by pressure variations (8).
Some authors underlined the possible role of of microbubbles of air, which can be trapped in restorations, cements or root canals (9,10), and expand during decompression, causing compression of pulp and periodontium and related pain.
The effect of repeated pressure variation on the retention of prosthetic crowns, cemented with zinc oxyphosphate, was studied in a former work of us (11). The results indicated a remarkable weakening of the cement, after 15 cycles of simulated decompression at 3 atm.
In this second experiment, the effect of pressure variation was tested also on two other organic adhesive cements.
Materials and methods
48 duplicates in epoxy resin were made, utilizing an addition silicon from a single original model of a human molar prepared for a complete crown abutment (Fig.1).
The tapering angle of the vertical walls was controlled with a goniometer during preparation of the original abutment.
The form of the abutment was as follows:
* Vestibular height= 6 mm
* Lingual height= 4 mm
* Max. mesiodistal diameter= 7 mm
* Max. vestibulolingual diameter = 5.5 mm
* Tapering angle = 6 degrees
A crown was modelled in wax on each duplicate, and cast in a metal alloy# consisting of Au 30%, Ag 43.5%, Pd 13%, Cu 10%, other metals 3.5%.
Crowns were modelled with a loop on the occlusal face, to help dislodgement maneuvers (Fig. 2).
They were divided into three groups of 16 crowns, each of them was cemented with a different cement, carefully prepared and utilized according to manufacturer's instructions.
Care was taken during spatulation in order to avoid trapping of microbubbles of air.
The first group was fixed with zinc phosphate cement##, the second one with a BIS-GMA cement with inorganic filler (Panavia Ex*), and the third group with a BIS-GMA unfilled cement (Super Bond**).
After the set of cement, the specimens were immersed in saline solution to simulate the wet environment to which the film at the margin of casts is exposed in the mouth.
After two weeks, half of the specimens of each group, in open glass containers, were placed in a hyperbaric chamber and underwent the following compression-decompression cycles:
* 10 times at 5 atm for 5 minutes
* 10 times at 4 atm for 10 minutes
* 10 times at 3 atm for 25 minutes
* 5 times at 2 atm for 50 minutes
* 3 times at 1 atm for 200 minutes
These cycles were performed with a speed lower than 1 atm/min.
The day after, the force necessary to dislodge all the crowns was measured. For this aim, the base of the abutments was enclosed in a stone base, the crowns placed with the loop downward, and a metal wire was connected to the loop, with a container attached to the other end. Water was gradually added to the container, until the crown was dislodged.
Results
The force necessary to dislodge the crowns is reported in table one. Some specimens were discarded, owing to fracture of the abutment or the stone base.
The DATA tables will be posted in the next window.
