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EFFECT OF OXYGEN INHIBITION ONCOMPOSITE REPAIR STRENGTH OVER TIME
A Study
published
in October
2006
INTRODUCTION
A composite..
0 A composite is a curing mixtures of monomers (Bis-GMA) and (TEGDMA)
0 After initiation they Form a three dimensional tetra functional network by radical polymerization of methacrylate c=c bonds
0 During the copolymerization reaction 30% of total amount of c=c bonds remain unreacted, and this quantity is correlated with the amount of Bis-GMA in the system
Oxygen effect
When Oxygen binds with free radicals
peroxy radicals which are much less reactive toward double bond
efficiency of initiation is reduced
inhibition of the polymerization
Effect of Oxygen Inhibition layer
Previous studies have shown that composite bonds even with absence of an oxygen inhibition layer
the amount of free and unreacted radicals that bond to another resin monomer is a crucial factor in direct composite repair.
Aim0 Is oxygen inhibition layer required for
repairing a pre-existing composite?
0 Determine the time required for free radicals within a polymerized composite to decay to the extent that there is a significant drop in composite repair strength.
Clinical Significance
Provides information on the optimal time period for refurbishing pre-existing aesthetic composite restoration without compromising the bond strength of the final restoration.
MATERIALS &
METHODS
10 direct anterior resin composite
slabs
CONTROL GROUP
(with O2)
EXPERIMENTAL GROUP(with N2 )
REF:Perdiga˜o J, Geraldeli S, Carmo ARP, Dutra HR. In vivo influence of residual moisture on microtensile bond strengths of one-bottle adhesives. J Esthet Restor Dent 2002
)A) Control Group
0polymerization occurred in the presence of oxygen.
0Two layers of bonding resin were applied to the flat surface of the composite slabs:
1st resin layer = light-cured for 20 s in atmospheric air.
2nd resin layer = light cured for 20 s in atmospheric air
After polymerization, the control group Stored in
atmospheric air in a dark room at 37C.
(B)Experimental Group
0 In the absence of oxygen
0 Two layers of bonding resin were applied to the flat surface of the composite slabs :
1st resin layer = light-cured for 20 s in atmospheric air .
2nd resin layer = light-cured in a N2 atmosphere to eliminate the oxygen inhibition layer.
0 The time employed for light-curing of the bonding resin within the chamber was increased from 20 to 40 s to compensate for the increased distance from the light source.
0 To ensure followed by conventional light-curing in atmospheric air for an additional 20 s.
0 both groups Stored in the dark room at 37 c .
TIME INTERVALS
1 h 1 dy 30 dy
14 dy2 h
Different shades were intentionally chosen for the ‘‘substrate’’ and for the ‘‘repairing material’’ to facilitate orientation of the ‘‘repairing interface’’ during microtensile bond strength evaluation .
RESULTS
RESULTS0 the atmosphere under which the adhesive
layer was curd did not significantly affect the composite repair strength .
0 the interaction between curing atmosphere and the time of composite repair significantly affected the composite repair strength.
0The composite repair strengths measured at 24 hrs were significantly higher than those at 14 days.
0The lowest strength record was at 30 days .
Tukey test
0 Interaction between curing atmosphere and the time of composite repair indicated that the highest strengths were recorded in specimens that ware repeated at 24 hrs after curing in the nitrogen chamber .
0 A significant inverse linear correlation existed between the composite repair strength and time of composite repair in specimens that were cured in nitrogen chamber .
0 The lower repair strengths were associated with occurrence of adhesive failure .
0 The strengths recorded for cohesive failures within the composites were slightly higher in specimens that were cured in side the nitrogen chamber .
DISCUSSION
0 Complete removal
and remaking not necessary or desirable.
0 Simple composite repair and refurbishing preserves tooth structure, and reduces the potentially harmful effects of tooth preparation on the dental pulp.
VARIABLES Affecting Composite Repair StrengthThey include:0 surface roughness of the
composite repair substrate0 the intermediary material
applied0 repairing material employed0 the timing of repair
REF:- Lucena-Martı´n C, Gonzalez-Lopez S, Navajas-Rodriguez de
Mondelo JM. 2001- Mitsaki-Matsou H, Karanika-Kouma A, Papadoyiannis Y,
Theodoridou-Pahine S. 1991
\COMPOSITE
/---------TOOTH
BONDCOMPOSI
TE
Investigating the effect of O2 inhibition on composite repair
strength!
1
0 a positive correlation exists between the presence of an oxygen-inhibited layer and composite repair strength is based on the principle of molecular interaction.
REF:- Truffier-Boutry D, Place E, Devaux J, Leloup G. 2003- Rueggeberg FA, Margeson DH. 1990
The oxygen-inhibited layer
1. Increases the contacting area
2. Allows co-polymerisation
Contrary to this hypothesis reported:
0 higher composite repair strengths when bonding to a composite surface without an oxygen-inhibited layer.
REF:Eliades GC, Caputo AA. The strength of layering technique in visible light-cured composites. J Prosthet Dent
Investigating the effect of O2 inhibition on composite repair
strength!
2
0 There is no change in the composite repair strength with time in the absence of an oxygen inhibition layer
Suh and colleagues!IN CONTROL GROUP:
0 No differences in shear & tensile bond strengths were observed when composites were repaired with or without an oxygen-inhibited layer.
0 Complete inter-diffusion of a thin oxygen-inhibited layer by a fresh composite overlay was speculated to be responsible for the improvement in composite repair strength.
REF:Suh BJ. Oxygen-inhibited layer in adhesion dentistry. J Esthet Restor Dent 2004
IN EXPERIMENTAL GROUP:
0 Time of repair ∞ 1Repair strength
second null hypothesis REJECTED!
REF:- Suh BJ, Feng L, Hayes K, Sharp L. 2003 - Suh BJ. J Esthet Restor Dent 2004
Suh and colleagues!
Study also proved:
0Presence of an oxygen inhibited layer does not significantly a affect bond strength if coupling is done in a certain time period (i.e. 2 weeks)
first null hypothesis REJECTED!
Suh and colleagues!
CONCLUDING(Within the limits of this study)
Composite repair
< or @14days = not compulsory to apply adhesive
due to the presence of incompletely decayed, active, residual free radicals within the cured composite or adhesive
> 2weeks = use of a resin activator is advisable
due to the minimal quantity of remaining active free radicals that reside within the bonding resin layer.
adequate bond strengths cannot be guaranteed!
…
LONGETIVITY OF REPAIRED RESTORATIONSA PRACTICE BASED STUDY
Why do we repair a failed restoration rather than
totally replacing it ?0The total replacement requires a larger
preparation than the previous one , risk of pulp injuries
0Repair is less expensive
0More gentle on the tooth substance ( less exhausting )
The problem is …0when the repair is advisable and when
replacement is a better choice.
0Total replacement has an advantage over repair that it has a better prognosis in terms of bond strength.
When do we repair a restoration ?
In case of:0Active caries0Bruxism 0 factors that affect the longevity of all
restorations
Aim Opdam et al.(2012) evaluate the influence of repaired restorations on restoration longevity
Technique 0 Etching the preparation with 38%
phosphoric acid
0 Rinsing
0 Applying etch and rinse adhesive system (Clearfil™ PhotoBond)
0 A hybrid composite (Clearfil™ PhotoPosterior and Clearfil™ AP-X)
To replace or repair ?Decision depends on :
0 the quality of the remaining restoration0The size of the restoration requiring repair 0The risk for complications0Procedural difficulty
Success was defined as : restoration remains in place and doesn’t
need any intervention
Survival was defined as : repaired restoration still functioning
without any further intervention
Results
0 Of the repaired restorations , 61% were still in service without further intervention after a mean observation time of 4.8 years
0 The most common reasons for repair and failure of repaired restorations were tooth fracture and caries
FILLING REPLACED REASONAmalgam 57% tooth fractureComposite 62% caries
Conclusion 0Repair can enhance the longevity of
dental restorations considerably
0The intervention preserves a restored tooth during lifetime by reducing the number of total interventions required !
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