Journal of Medical Engineering & Technology
ISSN: 0309-1902 (Print) 1464-522X (Online) Journal homepage: http://www.tandfonline.com/loi/ijmt20
A simple method for determining the transparency of dental materials D. W. Cruickshanks-Boyd & E. H. Davies To cite this article: D. W. Cruickshanks-Boyd & E. H. Davies (1978) A simple method for determining the transparency of dental materials, Journal of Medical Engineering & Technology, 2:1, 28-29, DOI: 10.3109/03091907809161746 To link to this article: http://dx.doi.org/10.3109/03091907809161746
Published online: 09 Jul 2009.
Submit your article to this journal
View related articles
Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=ijmt20 Download by: [University of California Santa Barbara]
Date: 15 March 2016, At: 18:54
Short Communications A simple method for determining the transparency of dental materials
ing, previously abraded specimens were polished using Drdinary metal polish and using the normal dental laboratory procedure of pumice, followed by whiting and finally gloss. Transparency was determined as: I T = - x 100% where T is the percentage transparency, I is light intensity (in lux) falling on the photocell after passing through the
C
B
D. W. Cruickshanks-Boyd, BSc, AMICoI"
D
E. H. Davies, MIST Institute of Dental Surgery, University of London, London,
Downloaded by [University of California Santa Barbara] at 18:54 15 March 2016
UK. The optical properties of restorative dental materials are important both for aesthetic and, in certain cases, practical reasons. Anterior restorative materials, such as porcelain, composite resins and silicate cement must imitate as closely as possible the optical characteristics of adjacent tooth tissue. Acrylic resins used in the construction of artificial dentures are required to simulate the oral tissues. One of the most important optical characteristics of a material is the degree to which it allows the passage of light through it. Materials which allow little or no light to pass through them are referred to as opaque materials, and in the dental situation the opaque porcelain layer applied in the metal-ceramic technique is a typical example. Some materials permit the passage of light but they disperse it such that objects cannot be clearly seen through them. Such materials are translucent and dental examples are enamel, dentine, silicates and veneer porcelain. Materials which allow the passage of light in such a manner that little distortion takes place are referred to as transparent materials, and in the dental situation clear acrylic resin, used for the production of clear dental bases, is the primary example. The aim of this communication is to describe a simple technique for determining the transparency of dental materials. The apparatus is described, and the technique illustrated by its application to commercial acrylic sheet prepared to varying degrees of transparency.
I Experimental Technique The apparatus used to determine the transparency is illustrated diagrammatically in Figure 1. It consists of a light-tight box containing an adjustable light source, one fixed aperture (15 x 30 mm) and one removable 'aperture (15 x 30 mm), against which the specimen (20 x 40 mm) is held, and a photocell (EEL 18 lightmaster photocell and photometer, Evans Electroselenium Limited, Halstead, Essex). The peak response of Ihe photocell occurs at a wavelength of 580 nm, very similar to the peak response of the human eye. A photometer records the light intensity received by the photocell, giving a visual meter r,eadout directly in lux. The linearity of the photocell was determined by application of the inverse square law, and found to be good within the range tested, 200 to 1,000 lux (see Figure 2). The light box is so constructed that only light which passes through the specimen and apertures is monitored by the photocell. In order to evaluate the apparatus, acrylic sheet specimens were prepared to a kariety of transparent conditions, as given in Table 1. In order to produce a loss in transparency certain specimens were wet abraded using new silicon carbide paper. To illustrate the efficacy of polish28
A-Pholoc~ll
B- Circular
C-Fixed Apcrlure
D-
Removablm A#rlure(both 30xlSmm)
€-Specimen
F-
Light SourcdlWwatt par1 bulb)
Aporture(S0mrn DiJmeWr)
X- Adjustable DistJnce(mm)
Figure 1. Optical system for transparency test.
121110.
9. 8-
yo 7c X
x 6.
3 5.
4-
3. 2.
1.
; h : d ; 1 + 8 B i b D'2 x 10-3 cm D is the source to photocell distance Figure 2. Linearity of the photocell.
Journal of Medical Engineering and Technology
Table 1 Surface condition
As-received (clear)
rhickness Transparenc mm % 3 6
93.5 95.0
3 6
43.5 39.0
3 6
18.0 18.0
3 6
53.5
3 6
32.0 33.0
Repolished with laboratory procedure, one side previously abraded
3
92.0
Repolished with laboratory procedure, both sides previously abraded
3
90.0
one side previously abraded
6
94.5
Repolished with metal polish, both sides previously abraded
6
94.5
Abraded with grade 80 Sic paper, one side only
Abraded with grade 80 Sic paper, both sides
Abraded with grade 800 Sic paper, one side only
Downloaded by [University of California Santa Barbara] at 18:54 15 March 2016
Abraded with grade 800 Sic paper, both sides
50.5
specimen and I, is light intensity (in lux) falling on the photocell with no specimen in place. The results indicate the sensitivity of this apparatus to small losses in transparency. The as-received acrylic sheet specimens were approximately 94% transparent, that is, some 6% of light was lost by reflection at the air/acrylic interfaces. Very little light was lost by dispersion within the specimens, as indicated by the similar results obtained with 3 mm and 6 mm thick specimens. Abrading one or both surfaces to various finishes led to a drop in transparency to as low as 18%. Repolishing with metal polish produced a specimen with the same transparency as the original as-received material. Polishing with the normal laboratory procedure produced almost as good a surface, with only approximately 2% extra light being lost at each surface.
Conclusion The results indicate the sensitivity of the apparatus in determining the transparency of acrylic sheet. Currently the technique is being used to assess the clarity of rapidcure acrylic resin processed in the dental laboratory, to determine which factors influence the production of this clear material. It is envisaged that the apparatus could usefully be employed to determine the transparency of a wide range of dental materials.
Repolished with metal polish,
A simple isolated pre-amplifier for use in electrophysiology 5 Perry, BSc Department of Medical Electronics. tt. Bartholomew's HospStd, London. E.C.IA 7BE.
With the increasing use of computers in alectrophysio. logy, it is often necessary to provide many channels d nformation simultaneously. One such field, requiring nany isolated pre-amplifiers, is that of epicardial map. hg1s2, where signals are recorded from the surfam 3f the exposed heart in order to determine the detailed q u e n c e of ventricular excitation. When conventional nstmmentation amplifiers are used, problems of inpul )ffset voltage tolerance are often experienced. as the ;mall signals of interest can be superimposed upon arge and variable d.c. offsets. An amplifier has been leveloped which meets the requirement of adequate wrformance a t low cost. The design meets the usual quirements for an amplifier of this type, such as low ioise and good common mode rejection, and the tmplifier is capable of tolerating very large d.c. offsets, vithout saturating the input stages.
Jircuit description f i e circuit is basically that of the standard instrumentaion amplifier, used in many biomedical applications'. January, 1978
A major problem with this type of amplifier is preserving a good d.c. offset tolerance without sacrificing common mode rejection or increasing the noise level. Some designs have ,been used which make use of input coupling capacitors, thus blocking the d.c. component of the signal to the amplifier. The disadvantage of this circuit, as shown in Figure 1. is that it is necessary t o define the input time constant with a resistor (R), for each input amplifier (A1 and A2). This resistor must have a ,high value to give the high input impedance required. Therefore. to gain a good common mode rejection. it is necessary to match the input components quite closely. which is a time-consuming procedure, or to buy expensive 'high tolerance components.
O L+Vi
RL
ref.
I
Output to D i f f e r e n c e Amplifier
d
Input 2
Figure 1. Amplifier configuration with capacitive input coupling. 29
ISSN: 0309-1902 (Print) 1464-522X (Online) Journal homepage: http://www.tandfonline.com/loi/ijmt20
A simple method for determining the transparency of dental materials D. W. Cruickshanks-Boyd & E. H. Davies To cite this article: D. W. Cruickshanks-Boyd & E. H. Davies (1978) A simple method for determining the transparency of dental materials, Journal of Medical Engineering & Technology, 2:1, 28-29, DOI: 10.3109/03091907809161746 To link to this article: http://dx.doi.org/10.3109/03091907809161746
Published online: 09 Jul 2009.
Submit your article to this journal
View related articles
Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=ijmt20 Download by: [University of California Santa Barbara]
Date: 15 March 2016, At: 18:54
Short Communications A simple method for determining the transparency of dental materials
ing, previously abraded specimens were polished using Drdinary metal polish and using the normal dental laboratory procedure of pumice, followed by whiting and finally gloss. Transparency was determined as: I T = - x 100% where T is the percentage transparency, I is light intensity (in lux) falling on the photocell after passing through the
C
B
D. W. Cruickshanks-Boyd, BSc, AMICoI"
D
E. H. Davies, MIST Institute of Dental Surgery, University of London, London,
Downloaded by [University of California Santa Barbara] at 18:54 15 March 2016
UK. The optical properties of restorative dental materials are important both for aesthetic and, in certain cases, practical reasons. Anterior restorative materials, such as porcelain, composite resins and silicate cement must imitate as closely as possible the optical characteristics of adjacent tooth tissue. Acrylic resins used in the construction of artificial dentures are required to simulate the oral tissues. One of the most important optical characteristics of a material is the degree to which it allows the passage of light through it. Materials which allow little or no light to pass through them are referred to as opaque materials, and in the dental situation the opaque porcelain layer applied in the metal-ceramic technique is a typical example. Some materials permit the passage of light but they disperse it such that objects cannot be clearly seen through them. Such materials are translucent and dental examples are enamel, dentine, silicates and veneer porcelain. Materials which allow the passage of light in such a manner that little distortion takes place are referred to as transparent materials, and in the dental situation clear acrylic resin, used for the production of clear dental bases, is the primary example. The aim of this communication is to describe a simple technique for determining the transparency of dental materials. The apparatus is described, and the technique illustrated by its application to commercial acrylic sheet prepared to varying degrees of transparency.
I Experimental Technique The apparatus used to determine the transparency is illustrated diagrammatically in Figure 1. It consists of a light-tight box containing an adjustable light source, one fixed aperture (15 x 30 mm) and one removable 'aperture (15 x 30 mm), against which the specimen (20 x 40 mm) is held, and a photocell (EEL 18 lightmaster photocell and photometer, Evans Electroselenium Limited, Halstead, Essex). The peak response of Ihe photocell occurs at a wavelength of 580 nm, very similar to the peak response of the human eye. A photometer records the light intensity received by the photocell, giving a visual meter r,eadout directly in lux. The linearity of the photocell was determined by application of the inverse square law, and found to be good within the range tested, 200 to 1,000 lux (see Figure 2). The light box is so constructed that only light which passes through the specimen and apertures is monitored by the photocell. In order to evaluate the apparatus, acrylic sheet specimens were prepared to a kariety of transparent conditions, as given in Table 1. In order to produce a loss in transparency certain specimens were wet abraded using new silicon carbide paper. To illustrate the efficacy of polish28
A-Pholoc~ll
B- Circular
C-Fixed Apcrlure
D-
Removablm A#rlure(both 30xlSmm)
€-Specimen
F-
Light SourcdlWwatt par1 bulb)
Aporture(S0mrn DiJmeWr)
X- Adjustable DistJnce(mm)
Figure 1. Optical system for transparency test.
121110.
9. 8-
yo 7c X
x 6.
3 5.
4-
3. 2.
1.
; h : d ; 1 + 8 B i b D'2 x 10-3 cm D is the source to photocell distance Figure 2. Linearity of the photocell.
Journal of Medical Engineering and Technology
Table 1 Surface condition
As-received (clear)
rhickness Transparenc mm % 3 6
93.5 95.0
3 6
43.5 39.0
3 6
18.0 18.0
3 6
53.5
3 6
32.0 33.0
Repolished with laboratory procedure, one side previously abraded
3
92.0
Repolished with laboratory procedure, both sides previously abraded
3
90.0
one side previously abraded
6
94.5
Repolished with metal polish, both sides previously abraded
6
94.5
Abraded with grade 80 Sic paper, one side only
Abraded with grade 80 Sic paper, both sides
Abraded with grade 800 Sic paper, one side only
Downloaded by [University of California Santa Barbara] at 18:54 15 March 2016
Abraded with grade 800 Sic paper, both sides
50.5
specimen and I, is light intensity (in lux) falling on the photocell with no specimen in place. The results indicate the sensitivity of this apparatus to small losses in transparency. The as-received acrylic sheet specimens were approximately 94% transparent, that is, some 6% of light was lost by reflection at the air/acrylic interfaces. Very little light was lost by dispersion within the specimens, as indicated by the similar results obtained with 3 mm and 6 mm thick specimens. Abrading one or both surfaces to various finishes led to a drop in transparency to as low as 18%. Repolishing with metal polish produced a specimen with the same transparency as the original as-received material. Polishing with the normal laboratory procedure produced almost as good a surface, with only approximately 2% extra light being lost at each surface.
Conclusion The results indicate the sensitivity of the apparatus in determining the transparency of acrylic sheet. Currently the technique is being used to assess the clarity of rapidcure acrylic resin processed in the dental laboratory, to determine which factors influence the production of this clear material. It is envisaged that the apparatus could usefully be employed to determine the transparency of a wide range of dental materials.
Repolished with metal polish,
A simple isolated pre-amplifier for use in electrophysiology 5 Perry, BSc Department of Medical Electronics. tt. Bartholomew's HospStd, London. E.C.IA 7BE.
With the increasing use of computers in alectrophysio. logy, it is often necessary to provide many channels d nformation simultaneously. One such field, requiring nany isolated pre-amplifiers, is that of epicardial map. hg1s2, where signals are recorded from the surfam 3f the exposed heart in order to determine the detailed q u e n c e of ventricular excitation. When conventional nstmmentation amplifiers are used, problems of inpul )ffset voltage tolerance are often experienced. as the ;mall signals of interest can be superimposed upon arge and variable d.c. offsets. An amplifier has been leveloped which meets the requirement of adequate wrformance a t low cost. The design meets the usual quirements for an amplifier of this type, such as low ioise and good common mode rejection, and the tmplifier is capable of tolerating very large d.c. offsets, vithout saturating the input stages.
Jircuit description f i e circuit is basically that of the standard instrumentaion amplifier, used in many biomedical applications'. January, 1978
A major problem with this type of amplifier is preserving a good d.c. offset tolerance without sacrificing common mode rejection or increasing the noise level. Some designs have ,been used which make use of input coupling capacitors, thus blocking the d.c. component of the signal to the amplifier. The disadvantage of this circuit, as shown in Figure 1. is that it is necessary t o define the input time constant with a resistor (R), for each input amplifier (A1 and A2). This resistor must have a ,high value to give the high input impedance required. Therefore. to gain a good common mode rejection. it is necessary to match the input components quite closely. which is a time-consuming procedure, or to buy expensive 'high tolerance components.
O L+Vi
RL
ref.
I
Output to D i f f e r e n c e Amplifier
d
Input 2
Figure 1. Amplifier configuration with capacitive input coupling. 29
