tys shen ti od Flashcards
explain mechanism of retention for CR and AR. discuss cav prep designs to maximise performance of these 2 materials in clinical practice
CR is by micromechanical and chemical adhesion vs AR is purely mechanical adhesion
- elaborate on CR using both ENAMEL AND DENTINE
- in enamel, it is micromechnical vis resin tags & chemical bonding through primary (ionic, covalent) and secondary (hyddrogen) bonds
- in dentine, hybrid layer is a mix of both dentine and CR?
cavity prep
- CR is conservative prep as it does not require converging axial walls whereas AR requires mechanical interlocking and hence need convergent axial walls
discuss the impact of CR and its bonding systems in achieving the role of an ideal material in the oral envt
properties of an ideal material should be split into
1) biological
- biocompatible to pulp: monomers of CR can irritate pulp, need to be fully cured, then talk about factors of curing like depth, time of cure
- biocompatible in terms of perio: CR is polishable to achieve smooth surface and good marginal adaptation and hence less plaque acumulation, hence dont irritate perio tissues. the polishability is contributed by filler particle size because smaller bound nanoparticles are abraded off during polishing
- ability to achieve good marginal seal to arrest caries progression: can talk about adhesive bonding systms and how it can create micromech tag infiltration of resin into enamel
+ reduced polymerisation shrinkage when bulk fill CRs are developed (are higher flow, using UDMA as monomer) - conservative of tooth structure: reduced need for retention and resistance forms in cavity prep
2) mechanical
- sufficient strength to withstand occlusal forces: the combination of bisgma and fillers creates CR with improved mechanical properties
- wear resistance: higher filler content in CR can improve wear resistance and theres the advent of nanofilled CRs
- retention and resistance to dislodgement: CR is ok in this aspect because of adhesive bonding
- COTE: CR is higher than tooth, meaning that the material expands and contracts more with changes in temp. mismatch can lead to microleakage, debonding
3) aesthetic
- CR got different shades with different translucencies which can be matched to tooth structure
4) operator friendly
- easy to handle: viscosity controllers to make different stuff - flowable vs packable
- good working time: light cured polymerisation allows for control of setting reaction
- but it is technique snsitive!
what are the causes of microleakage due to properties of CR?
1) POLymerisation shrinkage due to contraction stresses due to polymerisation reaction
- components which affect this would be monomer (Bisgma in normal CR vs UDMA in bulk fill which contracts less), viscosity controllers with control flow (eg TEGDMA)
- TEGDMA is a low molecular weight monomer which is used as a diluent to make CR more flowable but tradeoff is high shrinkage
2) moisture sensitivity
- water sorption in the filler matrix interface will lead to microleakage
3) COTE
- of CR>enamel
- leads to differential expansion and contraction of material and tooth and thus marginal gap formation
- the COTE of CR can be decreased by increasing filler loading
working from first principles, write a critique of the resin infiltration technique with reference to remineralisation of the early proximal carious lesion
what is resin infiltration:
- etch surface, typically with 15% HCL to open up the enamel microporosities
- apply low viscosity resin like TEGDMA based infiltrants that penetrate the lesion body via capillary action
- light cure to arrest lesion by occluding pores and blocking diffusion pahtways for acids and nutrients
how we should mx early carious lesion:
- early caries involves subsurface enamel demineralisation beneath the intact surface.
- lesion is porous, because the loss of minerals create micropores
- but ultimately the lesion is non cavitated and so the goal is non invasive mx
so critique is lowkey like discussing how well the infiltration can work VS remineralising (via fluoride?)
1) RI arrests progression mechanically but does not regenerate. because it doesnt remin the enamel, there is no ion replenishment and hence enamel remains structurally compromised beneath the resin
2) the efficacy depends on whether the penetration of resin can reach the full extent of the lesion. while the resin does infiltrate deeper than fluoride or CPP-ACP can penetrate, the penetration is still limited in lesions with hypermineralised surface layer acting as a barrier, or in cases with incomplete etching or drying
3) RI is minimally invasive, but irreversible. so failure will lead to complex re treatment. vs remin which is a biologically driven process which can be repeated
4) ideal treatment should promote natural repair, which RI cannot do. on the other hand, remin agents can restore mineral density, rebuild crystal structure
5) but RI can provide a nice esthetic effect, helping to mask opacity of WSL
from your knowledge of pathogenesis of caries, how is it possible for caries to be arrested by merely placing a CR without caries removal?
Discuss what problems may arise from routinely treating all class I carious lesions this way
first talk about pathogenesis:
- bacteria in biofilm ferment carbs
- acid production causes breakdown of tooth structure
- tooth, diet, time, bacteria
therefore,
- when CR bonds to sound tooth structure, it seals off bacteria from oral envt and source of fermentable carbs is depleted
- kill bcteria
problems:
- this tx only feasible for small carious lesions where there is a clear margin of sound tooth structure for bondingof resto. if resto bonded to carious tooth structure then restoration-tooth bond will break down
- this tx cannot be rendered to patients who are expected to be non compliant. bc stringent follow up should be carried out to ensure sealants are retained, if not need replacement
- cannot be used for carious lesions which have extended into dentine because in dentine, caries progresses much more rapidly due to structural differences. dentine contains less mineral, and has dentinal tubules as pathway for ingress of bacteria.
- hence dentine got less resistance to acid breakdown. and these lesions require reduction of bacterial load by removing all or at least some infected dentine
- resto also compromised due to structurally undermined enamel, risk of enamel fracture
difference between infected and affected dentine?
and how this knowledge can be used when managing a tooth with deep carious lesion that has reversible pulpitis, so that need for RCT is minimised?
1) presence of bacteria
- infected has bacteria contamination vs affected got no bacteria present
2) reversibility
- infected dentine is irreversibly damaged with odontoblast processes being lost, collagen fibres denatured, cant remin
- affected is reversible and odontoblasts still present, collagen fibres can relink
3) zones
- infected consist of zone of destruction and bacterial penetration
- affected consists of zone of remin and sclerosis
4) sensation
- infected got no more sensation
- affected got sensation
5) hardness
- infected is soft, affected can be soft at times too
6) colour
- infected usually not discoloured
- affected may be discoloured
in pulpitic tooth
- can opt for VPT instead and leave some caries to seal with resto
- prevent carious pulp exposure
- allows continued root development
- can be done by distinguishin gbetween 2 layes of carious dentine - infected and affected
then talk about indirect pulp cap
and stepwise caries excavation
- interim resto placed for 6-9 months to allow remin of affected dentine and tertiary dentine formation
then ULTRACONSERVATIVE caries excavation
- some INFECTED caries is left behind to prevent pulp exposure and final restoration is placed with CaOH liner and GIC base
- basis is that cariogenic bacteria can be isolated from their source of nutrition by a well sealed restoration, and hence will die or remain quiescent
discuss possible factors that will influence the clinical outcome of resin infiltration technique
intro: success of this technique hinges on its ability to seal off the carious lesions
split into preop, op and postop
PREOP
- whether it is cavitated
- in incipient lesions without cavitation, it may suffice to apply fluoride to promote remineralisation
- bc placement of a restoration starts the tooth on a tooth death cycle and if the resto is not well sealed, microleakage can occur and lead to secondary caries
INTRA OP
1) poor access, esepcially in interprox areas
- can compromise adhesive bond, making it susceptible to marginal leakage
2) difficultly in ascertaining integrity of tooth surface for bonding
- if the area is not opend up for access, it will be difficult to evaluate the amount of caries and this has bearings on bond strength because if restoration is placed on carious tooth structure, it will compromise the adhesive bond strength
- can be improved by using SEPARATING bands which allows operator to visaulise caries
3) isolation
- talk about how hydrophobic CR is very moisture sensitive and fluid can cause microgaps in interface between tooth and resto
4) access for light curing. light may not penetrate through darker shades of CR as well, must be compensated by longer curing times
POSTOP (or rather SEE THIS AS PATIENT FACTORS)
1) Caries risk and OH
- oh affects longevity of any restoration placed
- increased risk with cariogenic diet
2) recalls
- whether or not patient is compliant, affects long term success of resto
what should we talk about when we say nanoleakage
talk about how there is always that possibility bc we cant ensure that adhesive has fully infiltrated the microporosities
considerations for selection of most suitable material to restore mesioocclusal cavity for #16
split into PATIENT, TOOTH, RESTORATION, OPERATOR
PATIENT:
1) medhx - any allergies to materials?
2) caries risk
- if high, consider AR over CR because Opdam 2007: CR failures are mostly due to secondary caries contributed by breakdown of margin vs AR failures are due to fracture
- Opdam 2012: In general, AR has better longevity, but if patient has low caries risk then CR has higher success
3) occlusion and parafunction?
- Opdam 2007: AR failures uuslaly due to fracture due to wedging effect of AR
4) financial ability
- direct > indirect
5) aesthetic conerns
- CR over AR for aesthetics bc can choose shade
- #16 mo may be seen, do SMILE ANALYSIS
TOOTH
1) Cavity size
- bigger restorations more likely to fail
- Opdam 2014: every additional surface increases failure rate by 30-40% bc of propensity to fracture
2) the shape of the cavity
- if wide isthmus, AR has wedging effect causing cuspal deflection, hence risk of cuspal fracture
- consider if the shape of the cavity will require excessive removal of tooth structure to create mechanical undercuts
3) quality of tooth structure for bonding
- CR may be a poor choice if there is enamel hypoplasia etc
4) look at opposing tooth
- if AR is on opposing then consider CR to avoid galvanic currents
MATERIAL FACTORS - further split into biological, mech and aesthetic
1) BIOLOGICAL
- which one can provide a good marginal seal?
- AR corrosion products might be self sealing
- CR bonding system depends on quality of peripheral tooth structure
- IRRITANT TO PULP! CR monomer might be, but wecan try to theorectically achieve complete polymerisation
2) MECHANICAL
- moisture sensitiivty
- wear resistance
Discuss the factors that may influence the retention of RMGIC and CR in the restoration of NCCL
firstly note that NCCL have poor retention and resistance form, rely on adhesive bonding for retention
FACTOR 1: tooth structure involved
Is it largely enamel or dentin
GIC bonding
- to HAP: via chemical adhesion via ion exchange layer
- to collagen of dentine: hydrogen bonding or metallic ion bridging
CR bonding
- to enamel is the best, via micromechanical retention through resin tags
- but unpredictable bonding to dentine due to variability of composition of dentine, dynamic nature of dentine, presence of odontoblasts, constant outward pressure from dentinal tubules
FACTOR 2: isolation
- problem of constant flow of fluid from GCF for NCCL
- CR more moisture sensitive
Factor 3:
- CR got polymerization shrinkage,
Cause contraction stresses at margins of CR restoration
Aetiology of NCCL
by Grippo et al 2011
3 main factors then all combined, is multifactorial
1) STRESS (abfraction)
- when occlusal loading causes deformation & tooth flexure at cervical region
- these lesions often seen at cervical region because cervical enamel dentine bond is weaker due to the absence of scalloping at DEJ
- presents as wedge shaped lesions with sharp margins
Causes:
A) endogenous
- para functional habits like bruxism or clenching
- occlusion: premature contacts/ eccentric loading
B) exogenous
- mastication of hard and resistant foods
- habits: biting objects like pencils, fingernails
2) FRICTION (wear)
- refers to abnormal wear of tooth structure by mechanical process
- presents as a wedge shaped lesion
Causes:
- toothbrush abrasion
(Force, technique, bristle stiffness)
- habits (fingernail biting)
- dental appliances eg partial denture clasps
3) BIOCORROSION (chemical, biochemical, electrochemical degradation of the organic matrix of dentine)
- via chemical exogenous and endogenous acids, proteolytic enzymes
- but then Grippo says that this erosion is not a chemical mechanism, but a physical mechanism causing wear by friction from movement of liquids
Presents as smooth, disc shaped lesion
Causes:
A) exogenous
- diet: consumption of acidic foods and drinks, pouching of acidic food
B) endogenous
- GERD
- bulimic habits
Based on the etiology of NCCL, how can a patient prevent it?
1) oral hygiene habits
- bass technique, not forceful scrubbing motion
- soft toothbrush, toothpaste with low abrasivity
- considering that NCCL is also contributed by erosion, avoid brushing teeth 30 mins after having a meal high in erosive foods
2) DIET
- if NCCLs are on buccal surface, can advise to cut down on acidic foods
- if NCCLs on palatal, suspect GERD
3) para functional habits
- suspect if got occlusal wear facets
- advise to adopt stress reducing lifestyle
Possible causes for tooth sensitive to cold after an AR was placed
Split into operative causes, endo, pros (occlusal) and perio
OPERATIVE CAUSES
1) deep cavity prep
- the deeper into dentine, the wider the dentinal tubules
- greater hydraulic conductance, more fluid movements and stretching of nerve fibres
2) lack of protective liner
- liner functions as a thermal barrier by sealing dentinal tubules
3) trauma to pulp during cavity prep
- heat from friction without adequate irrigation
- over drying of tooth
4) thermal conductivity from AR
5) incomplete caries removal
- persistence of bacteria and toxins which can continue to penetrate dentinal tubules and cause continued pulp inflammation
6) marginal breakdown of restoration because AR is not adhesive
- mecuroscopic expansion due to corrosion of amalgam can push restoration away from tooth surface
- but is unlikely in a short period of time
ENDO CAUSE - PULPTIIS
- pre existing pulpitis
- in inflamed pulps, there is sensitisation of and lowering threshold of nociceptors
- hence pain on stimuli
OCCLUSAL FORCES
1) cracked tooth
- AR especially got WEDGING effect, increase risk of tooth fracture, especially for wide isthmuses
2) hyperocclusion
- flexure of tooth cusps during occlusion causes dentine tubules to be exposed
PERIO
- exposure of dentine, root surface exposure
How do sensitive toothpastes help
Contain tubule occluding agents eg potassium nitrate, which decreases dentine permeability and helps to reduce symptoms of dentine hypersensitivity
How to test that the cause for hypersensitivity is dentine hypersensitivity
1) dry tooth with trip syringe
2) scratch exposed dentine surfaces with a probe
If patient experiences sensitivity, it is due to dehydration aka the removal of fluid from dentinal surfaces, resulting in outward flow of dentinal fluid, stretching of nerve fibres and pain
Discuss the use of GIC in luting and lining
LUTING
- cement for crowns, FUJICEM
- ortho brackets
Features of GIC that allow this
1) chemical adhesion to enamel and dentine is MOST IMPT
2) biocompatible
- but note that post cementation sensitivity can still occur if there was too thin a mix causing slow setting and prolonging low pH
3) sufficient mechanical strength
4) not very impt but got fluoride release
5) similar COTE to dentine
- impt because differential expansion and contraction can break luting layer and lead to marginal leakage
6) low solubility
- but it is still susceptibility to moisture contamination during setting reaction
LINING
- liner is VITREBOND
- act as barrier (thermal, chemical, electrical)
- apply over CaOH
- or used to block small undercuts in preps
FUJI II can also be used as base
Features:
1) biocompatible
- impt as it is placed close to pulp
2) fluoride release
3) mech strength sufficient
4) radiopaque so can see
