Underpacking (use of too little material) can cause porosity in the denture base. Another cause could be if the student/technician packs the material at the "incorrect" stage. The stage which is preferable is when the material has reached the "dough stage". On polymerization there is an exothermic reaction. This causes the temperature of the resin to rise above 100°C. If the temperature increases before the polymerization process is completed gaseous monomer is formed.This causes gaseous porosity. Gaseous porosity can be avoided by rising the temperature in a slow and controlled fashion.
The vaporization of monomer when the temperature of the resin increases above the boiling point of the monomer (100.8) or very low molecular weight polymers Lack of homogenity, if the dough is not homogenous at the time of polimerization the portions containing more monomer will shrink more than the adjacent area. the shrinkage will result in voids making the resin appear white. Lastly lack of adequate pressure could cause porosity during polimerization or inadequate amount of dough in the mould during final closure causes bubbles making the resin lighter in colour.
To elaborate on Vera's comment about the lack of homogenity, the inadequate mixing of powder and liquid will cause some areas of the material to contain more monomer than others. During the polymerization process, these localized areas shrink more than other areas and cause porous voids in the denture base. Therefore correct powder to liquid ratios should be used to prevent this.
Results informs when polymerisation reaction occurs in the microwave few smaller polymer molecules will react with large molecules and try to pack and close together which obtain that material is smaller in volume than the starting components. The density of methyl methacrylate monomer is only 0.945g/cc at 200C, compared with 1.16 to 1.18g/cc for poly (methyl methacrylate). These values facts and these values can be obtained from any assessment. These values show an increase at density and decrease in volume of monomer. The main problem that occurs while dealing with polymer is the polymer shrinkage which bonding material to tooth structure reduces the potential for these gapes and which ultimately result micro leakage.
gaseous porosity: 1. shows a fine uniform bubbles, below the surface of the thicker sections of denture away from the source of the heat. 2. caused by too rapid heating. more exothermic heat reaction in the thicker sections. 3. surface of denture polymerizes first, trapping the gaseous monomer within. 4. porosity is often caused by the incorrect amount of monomer used.
contraction porosity: 1. can occur anywhere in the denture and the voids are irregular. 2. caused when the case is under-packed. 3. insufficient pressure applied during packing. 4. localized excess of monomer due to packing in the pre-dough stage.
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Underpacking (use of too little material) can cause porosity in the denture base.
ReplyDeleteAnother cause could be if the student/technician packs the material at the "incorrect" stage. The stage which is preferable is when the material has reached the "dough stage".
On polymerization there is an exothermic reaction.
This causes the temperature of the resin to rise above 100°C.
If the temperature increases before the polymerization process is completed gaseous monomer is formed.This causes gaseous porosity.
Gaseous porosity can be avoided by rising the temperature in a slow and controlled fashion.
The vaporization of monomer when the temperature of the resin increases above the boiling point of the monomer (100.8) or very low molecular weight polymers
ReplyDeleteLack of homogenity, if the dough is not homogenous at the time of polimerization the portions containing more monomer will shrink more than the adjacent area. the shrinkage will result in voids making the resin appear white.
Lastly lack of adequate pressure could cause porosity during polimerization or inadequate amount of dough in the mould during final closure causes bubbles making the resin lighter in colour.
Good JP, now elaborate on why underpacking causes porosity.
ReplyDeleteTo elaborate on Vera's comment about the lack of homogenity, the inadequate mixing of powder and liquid will cause some areas of the material to contain more monomer than others. During the polymerization process, these localized areas shrink more than other areas and cause porous voids in the denture base. Therefore correct powder to liquid ratios should be used to prevent this.
ReplyDeleteThis comment has been removed by a blog administrator.
DeleteResults informs when polymerisation reaction occurs in the microwave few smaller polymer molecules will react with large molecules and try to pack and close together which obtain that material is smaller in volume than the starting components. The density of methyl methacrylate monomer is only 0.945g/cc at 200C, compared with 1.16 to 1.18g/cc for poly (methyl methacrylate). These values facts and these values can be obtained from any assessment. These values show an increase at density and decrease in volume of monomer. The main problem that occurs while dealing with polymer is the polymer shrinkage which bonding material to tooth structure reduces the potential for these gapes and which ultimately result micro leakage.
ReplyDeletegaseous porosity:
ReplyDelete1. shows a fine uniform bubbles, below the surface of the thicker sections of denture away from the source of the heat.
2. caused by too rapid heating. more exothermic heat reaction in the thicker sections.
3. surface of denture polymerizes first, trapping the gaseous monomer within.
4. porosity is often caused by the incorrect amount of monomer used.
contraction porosity:
1. can occur anywhere in the denture and the voids are irregular.
2. caused when the case is under-packed.
3. insufficient pressure applied during packing.
4. localized excess of monomer due to packing in the pre-dough stage.
Hello friends. Today I want to talk about dental implants, dental implants in Cancun are very cheap and if you ask yourself how much do dental implants cost? prices are from 1200 usd. Do not wait any longer see Cancun vacation and returns with a whole new sonrissa
ReplyDeleteThe field of education is constantly changing and growing with technology. In this digital era, children grow up with computers from the time they are very young. In order to reach these children, educators need to adapt to technology in education and learn how to teach students using technological tools. have a peek here
ReplyDeleteBlogs on technology helps you stay updated in terms of the latest technology news, launch of gadgets, and many more. Subscribe to technology blogs and use information for your personal or professional use. mobile tracker free
ReplyDeleteParents battle with their kids with their use of tablets, mobile phones, TV, and streaming services. How can a parent balance a child's use of technology with education? spy cam
ReplyDeleteThe world has become a 'global village'. This oxymoron is because of the immense contribution of the internet and the way it has been able to successfully bring the globe together in a village like community. The term 'Global Village' was coined in 1970s by the great visionary Marshall McLuhan. This has been converted into reality by the growth of the internet technology and its continuing trend. Before delving deep into the stats, one can easily count the benefits of the internet in the field of transportation, communication, entertainment, medical science, education, research and development, logistics and many more. The growth of internet has been exemplary over the last couple of decades. It is already documented and speaks volume about how this technology has penetrated into the lives of the masses all over the globe. planning pod
ReplyDeleteMany people say that the business drives the technology whereas some people say that the technology drives the business. It is really unknown that which is really responsible for what and I must say that the emergence of the information technology has really made it even more complex. free xmind alternative
ReplyDeleteMillions of people use security devices to surveillance their home and office. A CCTV camera was introduced in the late 1940's, and now it has been so popular with the emerging technologies. For home security, these security cameras are considered as a necessity today. รับติดตั้งกล้องวงจรปิด
ReplyDeleteThanks for sharing nice information with us. i like your post and all you share with us is uptodate and quite informative, i would like to bookmark the page so i can come here again to read you, as you have done a wonderful job. Dental implants Corby
ReplyDelete