Dental Implant Cement Flow Simulations with...

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

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0.1

0.15

Wei

ght

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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