Fabrication of a michigan splint. Lab steps
Today I witnessed an educational demo of the fabrication of a michigan splint from start to finish.
1) take alginate impressions of upper and lower. Make sure there are no tears and distortions and that the alginate hasn't come away from the tray at all as that will distort the tooth shapes of the cast
2) Pour the cast up in dental stone and trim. Don't remove bubbles as removal can be unpredictable and excessive removal of stone will result in high spots on the acryllic which though small can cause rocking of the final appliance as it will not fit closely to the fitting surface. When it will interfere with occlusion, you can use a sharp scalpel to trim it slightly.
3) Take a wax bite of the pt at the desired bite opening. a good estimate is 3mm anteriorly and 2mm posteriorly to allow for bulk of acryllic. The idea of a splint is to disocclude the teeth to avoid locking movements during grinding. the wax bite should cover all the teeth and have sufficient bulk. take the wax out of the mouth when it has cooled slightly, cool in water and retry it in.
4) Mount the casts with the wax bite on the articulator. The occlusal relationship will be correct in any articulator at the height of the desired occlusion because the wax bite you took correctly displays that relationship. any effort to increase or decrease the height even with a facebow may result in errors as the hinge axis doesn't exactly reproduce human movements so a new wax bite is needed or post processing grinding of the appliance is needed to adjust for descrepancies.
5) Build up a wax dam on the labial surfaces of the upper teeth with 2 small strips of wax running along the whole labial surfaces till halfway up the teeth (the coronal border of these will represent where the highest point of the acryllic will be) and a larger strip of wax attached to this flaring buccally covering vertically to at least past the occlusal surface of the lower teeth. The join can be reinforced by melting the wax on the join with the 2 smaller strips of wax. (NB: this method is for autopolymerising resins to produce the splint)
6) Apply separating medium to the upper and lower teeth and soak the non teeth areas in water till glossy
7) Build up the autopolymerising acryllic by sprinkling/squirting fine acryllic powder over the area that you want using the dam to contain it then covering this with liquid component. Colours can be incorporated here. Repeat this till your acryllic is built up to the top of the dam. When the acryllic is firmer but still soft, smoothen the top off with a wax knife and press the upper and lower models together to the required OVD (NB you can mark the inter occlusal distances on the casts with dividers to check when you are at the right OVD)
8) Put the apparatus into the processing machine for 20 mins
9)Trim the splint with a set of lab burs and discs and develop excursive movements e.g. canine guidance by reducing lower contacting surface except for canine area.
10) Polish the splint first wet with pumice then dry
11) Clean with liquid soap and a toothbrush
12) Check occlusion with bite paper and grind down high spots will there is all teeth contacting in CO.
1) take alginate impressions of upper and lower. Make sure there are no tears and distortions and that the alginate hasn't come away from the tray at all as that will distort the tooth shapes of the cast
2) Pour the cast up in dental stone and trim. Don't remove bubbles as removal can be unpredictable and excessive removal of stone will result in high spots on the acryllic which though small can cause rocking of the final appliance as it will not fit closely to the fitting surface. When it will interfere with occlusion, you can use a sharp scalpel to trim it slightly.
3) Take a wax bite of the pt at the desired bite opening. a good estimate is 3mm anteriorly and 2mm posteriorly to allow for bulk of acryllic. The idea of a splint is to disocclude the teeth to avoid locking movements during grinding. the wax bite should cover all the teeth and have sufficient bulk. take the wax out of the mouth when it has cooled slightly, cool in water and retry it in.
4) Mount the casts with the wax bite on the articulator. The occlusal relationship will be correct in any articulator at the height of the desired occlusion because the wax bite you took correctly displays that relationship. any effort to increase or decrease the height even with a facebow may result in errors as the hinge axis doesn't exactly reproduce human movements so a new wax bite is needed or post processing grinding of the appliance is needed to adjust for descrepancies.
5) Build up a wax dam on the labial surfaces of the upper teeth with 2 small strips of wax running along the whole labial surfaces till halfway up the teeth (the coronal border of these will represent where the highest point of the acryllic will be) and a larger strip of wax attached to this flaring buccally covering vertically to at least past the occlusal surface of the lower teeth. The join can be reinforced by melting the wax on the join with the 2 smaller strips of wax. (NB: this method is for autopolymerising resins to produce the splint)
6) Apply separating medium to the upper and lower teeth and soak the non teeth areas in water till glossy
7) Build up the autopolymerising acryllic by sprinkling/squirting fine acryllic powder over the area that you want using the dam to contain it then covering this with liquid component. Colours can be incorporated here. Repeat this till your acryllic is built up to the top of the dam. When the acryllic is firmer but still soft, smoothen the top off with a wax knife and press the upper and lower models together to the required OVD (NB you can mark the inter occlusal distances on the casts with dividers to check when you are at the right OVD)
8) Put the apparatus into the processing machine for 20 mins
9)Trim the splint with a set of lab burs and discs and develop excursive movements e.g. canine guidance by reducing lower contacting surface except for canine area.
10) Polish the splint first wet with pumice then dry
11) Clean with liquid soap and a toothbrush
12) Check occlusion with bite paper and grind down high spots will there is all teeth contacting in CO.
Nice post. I was checking constantly this blog and I am impressed.
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