Lecture 11 Flashcards
what is the difference between getting a scan of the teeth in the past and now ?
past : impression with a polymer paste
now : 3D scanner, takes 1-2 min, can overlap it with x ray
how can we make a digital denture now ?
- scan, get a digital model of the mouth
- on the model, set up where the teeth go (AI does a lot now)
- denture can be 3D printed ; we can tailor the surface morphologies fo tissue integration or bacteria repelling
digital work flow of clear aligners and its accuracy limits. Why can we accept this uncertainety ?
- scan : resolution limits
- computer model : 50 microns
- 3D printing : 20-100 microns
- thermoform : 30-100 microns
Each of the aligners is misaligned by 0.2-0.3 mm to force the teeth to move. Thus we don’t have to care to much about the errors in accuracy.
why is thermoforming a polymer on top of a 3D model better than direct 3D printing of the aligner ?
safer because that way we don’t have to use plasticizers in the polymer. Direct printing is also slow on the large scale.
relationship between T and the resulting gap between aligner and teeth ?
we are in glass transition range.
By heating to 150 degrees, we can an optimized overlap (small gap volume). If we heat more, we would only increase the stress on the material and increase defects.
what new material can we use for aligners ? 2 advantages ?
use biopolymers :
- fatty acids as plasticizers in cellulose plastics
- use as drug delivery device (because biopolymers can take up water with functional molecules)
how does a stress relaxation test look like for a biopolymer taking up water ? what is necessary for aligners ?
strength starts high. Then it becomes softer as it takes up water. But it has a certain stability : there is always force left that can be used to move the teeth.
describe a few aspects of biofilm formation
- initial adhesion
- maturation : formation of EPS, like an oily matrix
- dispersion ; release of biomarkers
what is the advantage of natural antimicrobials over antibiotics ?
- more long term effect
- does not kill all the bacteria but stop them from growing incontrollably -> creates a balanced bacteria population
explain one result from biomarker data between a group wearing loaded aligners and the other wearing normal aligners
The aligners with the natural antimicrobials : reduction in inflammation markers. This means that there are less bacteria, the body is in less stress.
what is enamel and what is its structure ? properties ? one things that damages it ?
nanometer sized, elongated, directionally ordered hydroxyapatite crystals ; key-hole shaped parallel rods.
Very tough, less brittle.
Acidic things dissolve the enamel and make it porous.
dentin : structure at the micrometer and nanometer level
micro : dentinal tubules. they are aligned with where the highest force comes from. They show the growth tracks of the odontoblasts.
nano : collagen fibrous network that surrounds the tubules.
how can you image teeth ? for what kind of tissue is this technique not possible ?
X-rays : absorption and scattering (reciprocal space).
Cannot be done with living tissues (x-rays deadly to soft tissue). But teeth can be used easily post mortem !
what info can we get from scattering data ? what preparation step is required ?
- presence of nanostructures
- orientation and shape
- degree of anisotropy
- size and size distribution
Slicing is required (a fraction of a mm).
what can x-ray scattering not tell us ? How do you solve the problem ?
It can’t differentiate between where the enamel, dentin, pulp is.
-> histology in real space to get the boundaries, and then overlap with scatttering info (reciprocal space)
