Upload
others
View
6
Download
0
Embed Size (px)
Citation preview
Dental Implant Cement Flow
Simulations with STAR-CCM+ Sabine Goodwin
Missing teeth are replaced by implants
and crowns
It is now common place for dentists to
join crowns and implants using cement
(as opposed to using screws)
– Improved esthetics
– Cost-effective
– Reduced chair-time
Excess cement extrusion into the soft
tissue has been shown to cause long-
term peri-implant disease
Problem Description
Only very limited data is available on how to achieve optimal
cementation and avoid these health issues
Questions to ask :
– How much cement should be used?
– What type of cement should be used?
– Where should the cement be loaded in the crown?
– Can the implant shape be changed?
System control solution : consider the complete implant abutment,
cement and crown system
System Control Solution
STAR-CCM+ is well-positioned and can address these problems
– Understand cement flow patterns of the system
– Explore effects of
• Amount of cement
• Initial cement placement
• Speed of crown seating
– Re-design implant to retain excess cement within the implant abutment
Key features of STAR-CCM+ :
– 3D-CAD
– Overset Mesh
– Volume of Fluid (VOF) Multiphase Model
– Optimate Powered by HEEDS
Simulating the System
Non-Newtonian Properties of Cement
Source : http://portal.daledental.com/files/proddocs/11/RelyX%20ARC%20Technical%20Profile.pdf
Dental cements are non-Newtonian in nature
– Viscosity varies with shear rate
– RelyX™ cement is shear thinning (viscosity decreases with shear rate)
STAR-CCM+ offers several models for simulating non-Newtonian laminar liquids – Herschel-Bulkley model for Bingham
plastics is commonly used
– Input parameters for model were obtained through curve fitting of the RelyX™ cement viscosity vs. shear rate properties
Parameters for Herschel-Bulkley model provided by Nathanael Inkson (CD-adapco)
Implant and Crown Simulation Setup
Overset Mesh Approach – Polyhedral mesh
– Significant refinement to capture free surface and small gap at end position
– Background region for implant is stationary
– Overset region translates down to reflect motion of the crown
Initial cement loading – ½ toroid shape, 1 mm radius
– Located just above margin line
– Defined using a scalar array of volume fraction
Simulation – Transient solution
– VOF (air/cement)
– Laminar flow/Segregated solver
– Non-Newtonian fluid
– Spans 0.5 seconds from starting to ending position
Cross-sectional cut through implant, crown and cement system
100% Cement 100% Air
Animation of Implant Abutment & Crown System
Abutment modifications : Experimental Studies
0
0.05
0.1
0.15
Wei
ght
of
cem
ent
mg.
Closed Open IVA Abutment modification
Implant design : what are we looking for? – Minimal amount residual excess cement enters the
surrounding soft tissue results in reduced peri-implant disease
– Large contact area between cement/implant and crown results in greater retentive capability
– Crown/Implant margin needs to be sealed
Studies performed on three types of abutments : – Closed abutment
– Open abutment
– Internal vent abutment
In-vitro experimental study results : – Leaving screw access hole open improves cement
retention
– Internal vent abutment shows a better infill of the screw access hole
Abutment Modifications : STAR-CCM+
Simulations Open Abutment
– Screw access chamber is left open
• Provides a reservoir for excess cement to be retained inside abutment system
– Leads to :
• Less cement extrusion – Reduced peri-implant disease
– Easier and faster clean-up
• Improved retentive capabilities from increased contact area
Internal Vent Abutment
– Screw access chamber is left open
– Two additional round vents
• 2.5 mm below occlusal surface
• 180 degrees apart
• 1 mm in diameter
– Leads to :
• Further control over cement flow
• Improved retentive capabilities from increased contact area
Abutment Modifications : STAR-CCM+ Validation
100% Cement 100% Air
Closed Abutment Open Abutment Internal Vent Abutment
How much cement should be loaded?
~45 mm3 ~35 mm3 ~30 mm3
How much cement should be loaded?
Amount of cement : ~45 mm3 Amount of cement : ~35 mm3
What application technique should be used?
Cement loaded at crown margin :
• Vents fill up before the screw access hole.
• Overall flow of cement is smooth
• No cement leaves the system.
Cement loaded near occlusal surface:
• Screw access hole fills up first
• Cement is pushed with force
through the vents
• Results in an incomplete margin
seal
What application technique should be used?
Closed abutment with cement loaded
near occlusal surface
Close abutment with cement loaded
at crown margin
How fast should the crown be seated?
Slow : 1 second for seating Fast : .25 seconds for seating
STAR-CCM+ was used to investigate the problem of excess cement extrusion that leads to peri-implant disease
Simulation of the complete implant, cement & crown system showed: – Good comparison with experimental
studies : internal vent abutment is the best design
– Amount of cement loaded matters!
– Loading cement near the implant crown margin reduces residual excess cement
– Speed of seating of crown matters!
Future work – Continue current research
– Expand to other application such as cementation during hip replacements
Conclusion