Restorative Dentistry Flashcards
1
Q
What chemicals are currently used to bleach teeth? (2)
A
- hydrogen peroxide
- carbamide peroxide
2
Q
What is the mode of action of the chemicals used to bleach teeth?
A
Carbamide peroxide is broken down into hydrogen peroxide and urea, so in both cases the bleaching is actually done by hydrogen peroxide. This is a very small molecule which penetrates enamel and dentine and dissociates into a superoxide ion and water. The superoxide ion is thought to bleach teeth by oxidising the pigments that are trapped in the stains
3
Q
What are the side effects/complications of vital bleaching? (5)
A
- sensitivity
- the bleaching possible fades over time and needs to be redone
- possibility of resorption of teeth, especially in those techniques that use heat to activate the hydrogen peroxide
- soft tissue chemical burns
- potential adverse effects on restorative materials
4
Q
When would vital bleaching not be indicated? (4)
A
- patients who have severe widespread discolouration of their teeth such as tetracycline staining or pitting hypoplasia
- adolescent patients with large pulp chambers
- teeth with large or defective restorations
- teeth with apical pathology
5
Q
What is microabrasion?
A
A technique where no more than the outer 100um of enamel is removed by using a combination of abrasion and erosion
6
Q
What material is used in microabrasion?
A
Hydrochloric acid is used in a slurry on the tooth, applied with a rubber cup over the enamel surface
7
Q
What are the indications for microabrasion?
A
Used mainly for discoloured spots rather than generalised discolouration, in particular fluorosis, brown mottling and idiopathic stains before veneer placement
8
Q
What are the advantages of veneer preparation before veneer placement? (3)
A
- the bond strength is greater when the tooth is prepared
- the emergence profile is better and results in better gingival health
- the tooth is not increased in size, which gives a better aesthetic outcome
9
Q
When would a veneer not be indicated? (4)
A
- if the patient was subject to abnormally heavy occlusion e.g. in the case of a patient with bruxism
- where the margins of the restoration would have to be placed below the gingival margin
- if the tooth had already received large restorations in which is may be more sensible to opt for a full coverage restoration rather than a veneer
- poor OH
10
Q
What are the stages involved in luting a veneer?
A
- the tooth to receive the veneer should be isolated and then cleaned with pumice. Care must be taken to ensure that there is no oil contaminating the pumice because this will affect the bond
- the veneer should not be tried on the model because stone will contaminate the fit surface of the veneer
- apply the appropriate silane coupling agent to the veneer and let it dry
- try the veneer on the tooth with a drop of water or in paste on the fit surface. This helps in terms of shade assessment
- carry out any adjustments of the fit and proximal contacts
- remove and try in paste with ethyl alcohol
- reapply silane coupling agent
- etch tooth and apply dentine bonding agent
- place unfilled resin on tooth and veneer
- apply filled resin lute to veneer and gently seat the veneer
- spot cure the incisal edge
- remove excess resin lute and floss the contacts
- cure completely
- carry out minimal finishing with a bur because this is best left until the resin has set which is 24hr later. When fully set a diamond finishing bur can be used along with finishing strips
11
Q
What changes may occur to the tooth structure as a result of endodontic treatment? (4)
A
- the preparation of the access cavity, leading to changes in the architecture, especially the lost of marginal ridge and occlusal isthmus
- changes in the property of dentine: collagen depletion with predisposition to fracture
- changes in proprioception, non vital teeth apparently have higher pain threshold
- the original insult, leading to need for endodontic treatment e.g caries, cracks trauma
12
Q
What is a ferrule?
A
A band of crown material that completely encircles the tooth and is between the dentine- core interface and the cervical crown margin
13
Q
Why are nayyar cores useful in posterior teeth?
A
Because amalgam can be packed 2-3mm into the canal orrifice, avoiding the need for a post and providing an orrifice seal
14
Q
Drugs can be delivered locally into periodontal pockets. However, they should not be used without root surface instrumentation at the site. Why?
A
Root surface instrumentation is needed because plaque and calculus in the pocket will decrease the ability of the drug to get into the tissues of the periodontal pocket
If deposits of plaque and calculus remain this will favour re- colonisation of the pocket by bacteria; the periodontal treatment and maintenance are therefore likely to be less effective or ineffective
15
Q
What are the indications for using drugs in periodontal pockets? (4)
A
- as an adjunct to drainage and root surface debridement in the management of a periodontal abscess
- for areas of resistant disease
- in the management of furcation involved teeth
- in the management of aggressive periodontitis
16
Q
What are the advantages of delivering drugs locally into periodontal pockets?
A
High levels of the drug can be delivered directly to the area where they are needed and can be maintained for a period of time in the gingival crevicular fluid. When drugs are given systemically, the concentrations rise and fall, whereas these spikes in concentration are not seen in the local drug delivery systems
There is also less likelihood of adverse effects from the drugs
17
Q
Name 6 drugs that can be delivered locally into periodontal pockets
A
- chlorohexidine
- tetracycline
- minocycline
- doxycycline
- metronidazole
- azithromycin
18
Q
Name the different categories of definitive tooth coloured crowns that can be used (3)
A
- metal ceramic/PFM
- all ceramic
- composite
19
Q
What are the main advantages of metal- ceramic crowns over composite and all ceramic crowns? (2)
A
- Laboratory studies have shown metal- ceramic restorations to be stronger
- the ability to have metal lingual and occlusal surfaces makes these types of restorations more conservative of tooth tissue
20
Q
What is the main disadvantage of metal ceramic crowns over composite and all ceramic crowns?
A
Metal- ceramic restorations are not translucent and often have a metal collar, which may be noticeable at the cervical margin. Therefore they may have inferior aesthetics
21
Q
Name 4 commercially available dental materials from which all ceramic restorations are made from
A
- leucite reinforced glass ceramic
- lithium dislocate reinforced glass ceramic
- feldspathic porcelain
- alumina
- zirconia
22
Q
Name two methods pf constructing an all ceramic monolithic crown
A
- CAD CAM
- lost wax hot pressing technique
23
Q
What are the differences between CAD CAM crowns (zirconia) and pressed (lithium disilicate) ? (4)
A
- CAD CAM is zirconia based whereas pressed is glass based
- CAD CAM has greater opacity whereas pressed is more translucent
- CAD CAM has higher strength whereas pressed has low strength
- CAD CAM strength is not influenced by type of cement used and zirconia cannot be etched whereas pressed must be etched and bonded with resin cement which increases the strength
24
Q
What non vital bleaching techniques are there? (4)
A
- walking bleach technique
- inside outside technique
- in surgery technique
- individual tooth bleaching trays
25
How do you do the walking bleach technique?
- the gutta percha is removed from a satisfactory root canal treated tooth to a level of 2-3mm below the epithelial attachment
- the cut face of the root canal GP is sealed with about 2-3mm of glass ionomer cement. It is important to get the barrier at the correct level to ensure that the whole of the crown is bleached but to prevent material seeping through dentine below the epithelial attachment as cervical resorption could occur
- the bleaching material is sealed in the cavity with a pledget of cotton wool and a temporary restoration placed
- the original technique used sodium perborate
- the patient is reviewed after 2-3 days and the procedure repeated until the desired colour is achieved
26
What is the inside outside bleaching technique?
- the first part of the technique is similar to the first two steps in the walking bleach technique
- the access cavity is then left open
- the patient applies bleaching solution into the access cavity and into a bleaching tray every 2 hours during the day time and also wears the bleaching tray overnight
- the bleaching solution used is usually 10% carbamide peroxide
27
What is the in surgery technique for bleaching?
- the tooth in question is isolated with a rubber dam
- the access cavity is opened
- hydrogen peroxide is placed in the access cavity
- activated with light or laser to speed up the activation of the free radicals
28
What is the recommended concentration of bleaching agent used?
Between 0.1% and 6% hydrogen peroxide is the recommended concentration
29
What is the difference between a craze, a crack and a fracture in a tooth?
- A craze is an area of weakness in tooth structure where further propagation will result in a crack. They can be identified with fibre optic illumination
- a crack is a definitive break in the continuity of the tooth structure which begins in the enamel or cementum but no separation is evident. They can be seen with fibre optic illumination or in good clinical light
- a fracture is when the tooth structure has separated into two or more distinct pieces and is visible clinically and radiographically
30
What is the mechanism which causes pain in a cracked tooth?
The movement of the cracked pieces of tooth cause movement of fluid in the dentinal tubules, which stimulates A delta pain fibres
31
What is the difference between a file and reamer?
A file has much tighter spirals along its length and produces a cutting action when it is withdrawn from the root canal whereas a reamer has looser spiral and is used by rotating and withdrawing
32
If there is evidence of serous fluid seeping into the canal what does this suggest?
It suggests inflammation of the periapical tissues is present
33
What techniques are available to obturate a root canal with gutta percha? (6)
- lateral condensation
- vertical condensation
- thermo mechanical condensation
- thermo plasticised GP
- single point techniques
- carrier based techniques
34
What is the difference between reattachment and new attachment?
Reattachment means the reunion of the connective tissue to a root surface that had been separated by either incision or an injury whereas the term new attachment means the union of connective tissue with a root surface that was previously pathogenically altered
35
What is guided tissue regeneration and why is it desirable in periodontal healing?
Using a membrane it is possible to guide the tissue regeneration to prevent epithelial cells from gaining access to the root surface and also preventing gingival connective tissue from contacting the root surface. It also creates a small space to allow stem cells from the periodontal ligament and alveolar bone to migrate, differentiate and hopefully repopulate the exposed root surface to form new attachment
36
What factors would be considered desirable when designing a material for GTR? (4)
- biocompatibility
- ease of clinical use
- impermeable to cells
- able to maintain the space created
- tissue integration
37
Which of the following material used in GTR are resorbable and which are non resorbable: collagen, polyactic acid, teflon?
Collagen and polyactic acid- resorbable
| Teflon- non resorbable
38
What measurement gives the most accurate assessment with regards to periodontal destruction and why?
The measurement of attachment loss from the CEJ to the base of the pocket, as it gives a true idea of how much connective tissue attachment loss from the root surface has been; also it is not influenced by false pocketing
39
How much pressure should be applied on the probe when carrying out periodontal probing?
0.25N
40
What factors may influence the results of periodontal probing? (4)
- Pressure applied to the probe and the angle it is inserted
- thickness of the probe
- the contour of the tooth
- the presence of calculus
41
What is the biological width?
The combined width of the attachment to the tooth from the most coronal aspect of the junctional epithelium to the most apical attachment of the gingival fibres at the level of the alveolar bone crest
42
Where is the free gingivae? Where is the attached gingivae?
The free gingivae extends from the most coronal aspect of the gingival contour to the free gingival groove
Apical to the free gingiva is the attached gingiva which extends from the free gingival groove to the mucogingival junction
43
What is the function of the gingival crevicular fluid? (3)
- it is an inflammatory exudate from the gingival crevicular tissues and forms part of the defence mechanism of the dento gingival junction as it carries antimicrobial factors into the crevice
- it is thought to wash debris such as dead epithelial cells and bacteria out of the crevice.
- it also carries polymorphonuclear leukocytes, macrophages, lysozyme and immunoglobulins into the crevice, which have an antimicrobial effect
44
Name 5 causes of intrinsic discolouration of vital teeth
- trauma resulting in pulpal death
- fluorosis
- tetracycline staining
- amelogenesis imperfecta
- dentinogenesis imperfecta
45
How would you remove extrinsic stains? (3)
- polishing the surfaces with pumice slurry and water or prophylaxis paste
- ultrasonic cleaners
- bleaching
46
What is primary dentine?
Primary dentine is formed before eruption or within 2-3 years after erupt and consists of mainly circumpulpal dentine. It also includes mantle dentine in the crown and the hyaline layer and granular layer in the root
47
What is secondary dentine?
Secondary dentine is the regular dentine that is formed during the life of the tooth and laid down in the floor and ceiling of the pulp chamber. It is physiological type of dentine after the full length of root has formed
48
What is tertiary dentine?
Tertiary dentine can be divided into reparative and reactionary dentine both of which are laid down in response to noxious stimuli. Reactionary dentine is laid down in response to to mild stimuli whereas reparative dentine is laid down directly beneath the path of injured dentinal tubules as a response to stronger stimuli and are irregular
49
Do internal and external resorption occur in vital teeth?
Internal resorption can occur only in vital teeth
| External resorption may occur on vital or non vital teeth
50
How does fluoride affect teeth before eruption? (2)
- teeth have more rounded cusps and shallower fissures
| - the crystal structure of the enamel if more regular and less acid soluble
51
What is the effect of fluoride after eruption? (4)
- decreases acid production by plaque bacteria
- prevents demineralisation and encourages remineralisation of early caries
- remineralised enamel is more resistant to further acid attacks
- thought to affect plaque and pellicle formation
52
What are the possible consequences of a fluoride overdose?
Dental effects- enamel fluorosis, mottling, pitting
| Toxic effects- gastrointestinal
53
What is the recommended fluoride concentration in the water supply for optimal caries prevention?
1ppm
54
What is the difference between reversible and irreversible pulpitis?
Reversible pulpitis is a sharp pain, set off by hot/cold things and sweet things. It is poorly localised and lasts for several seconds. Irreversible pulpitis is throbbing pain, set off by biting or spontaneously. It is well localised once the periodontal fibres are involved and lasts for hours
55
What type of nerve fibres are there in the pulp? (3)
- A-beta fibres are large fast conduction proprioceptive fibres
- A delta fibres are small sensory fibres
- C fibres are small unmyelinated sensory fibres
56
Patients have thermal sensitivity following placement of a restoration. One theory for this is thermal shock theory. However, another theory for thermal sensitivity is now more widely accepted- what is it called and what is it based on?
Theory of pulpal hydrodynamics
Fluid can move along dentinal tubules and when there is a gap between the restoration and the dentine, fluid will slowly flow outwards. A decrease in temperature leads to a sudden contraction in this fluid and consequently increased flow, which the patient will feel as pain
57
How can restorative techniques limit thermal sensitivity?
Aim is to seal the dentine and increase the integrity of the interface between the dentine and the restorative material
58
What are cavity sealers used for?
To prevent leakage at the interface of the restorative material and the cavity walls, and to provide a protective coating to the cavity walls
59
What are the types of cavity sealers?
Varnishes (e.g. a synthetic resin based material or a natural resin gum)
Adhesive sealers which also bond at the interface between the restorative material and cavity walls (e.g. glass ionomer luting cements)
60
What is microleakage?
The passage of bacteria, fluids, molecules or ions along the interface of a dental restoration and the wall of the cavity preparation
61
What are the consequences of micro leakage? (3)
- marginal discolouration of restorations
- secondary caries
- pulpal pathology
62
You are cutting a cavity in a vital upper first permanent molar. You have removed all the caries but then you create a small exposure of the pulp. How would you proceed?
What is this treatment called?
DIRECT PULP CAPPING
1. rubber dam
2. dry the cavity
3. place calcium hydroxide over the exposure
4. cover with cement/liner
5. restore as normal
6. inform the patient
7. arrange review
63
What are you hoping will happen when you do direct pulp capping? (2)
- a dentine bridge will form
| - the pulp will remain vital
64
Give 4 contraindications to pulp capping? (4)
- non vital tooth
- irreversible pulpitis
- evidence of periapical pathology
- large exposure
65
What restorative material is capable of adhesion to the tooth tissue without surface pretreatment?
Glass ionomer
66
How may adhesion be improved?
Using a polyalkenoic acid conditioner
67
How does glass ionomer bond?
Micro mechanical interlocking- hybridisation of the hydroxyapatite coated collagen fibril network
Chemical bonding- ionic bonds form between the carboxyl groups of the polyalkenoic acid and the calcium in the hydroxyapatite
68
What do you understand by the term smear layer?
When tooth tissue is cut, the debris is smeared over the tooth surface. This is called the smear layer and it contains any debris produced by reduction or instrumentation of dentine, enamel or cementum. It is calcific in nature and contaminant that precludes interaction of restorative materials with the underlying pure tooth tissue
69
Dentine an be treated with acid (or conditioned). What does this achieve?
Within dentine, acid treatment removes most of the hydroxyapatite and exposes a microporous network of collagen. The smear layer is altered or dissolved. The bonding that results its diffusion based and relies on the exposed collagen fibril scaffold being infiltrated by the resin
70
Why are primers needed during the process of creating an adhesive restoration?
The dentine surface after conditioning is difficult to wet with bonding agents. The primer increases the wet ability of the surface which allows the resin to spread and penetrate the tubular dentine. This improves the bonding of the subsequently applied adhesive resin
71
What do you understand by the term hybrid layer and where would you find it?
The hybrid layer is the area in which the resin of the adhesive system has interlocked with the collagen of the dentine, providing micro mechanical retention
72
What do dentine bonding agents do? (3)
- form resin tags in the dentinal tubules
- stabilise the hybrid layer
- form a link between the resin primer and restorative material
73
What are the indications for an apicectomy? (4)
- infection due to a lesion that requires a biopsy
- instrument stuck in canal with residual infection
- impossible to fill apical third of root canal due to anatomy or calcification
- perforation of the root
74
What is acid etching of enamel?
Application of a mild acid to the surface of enamel results in dissolution of about 10um of the surface organic component, leaving a microporous surface layer up to 50um deep. The surface is thus pitted, and the unfilled resin of the restorative material is able to flow into the irregularities to form resin tags that provide micro mechanical retention
75
What acid etch is commonly used and at what strength? In what form are etchants produced and what effect do the different forms have on working properties?
Phosphoric acid 30-40% is commonly used. Etchants come as gel or liquid, however, in the newer systems the etchant is combined with the dentine conditioner. The etch produced is the same with a gel or liquid but gels take twice as long to rinse away. Gels are less likely to drip onto areas where etching is not intended
76
What do you understand by the term "total etch technique" and which acid would you use for it?
The total etch technique involves using an acid to etch the enamel and condition the dentine at the same tie. Commonly used acids include phosphoric acid, nitric acid, maliec acid, oxalic acid and citric acid
77
Name 4 types of composite materials
- traditional composites
- microfilled resins
- hybrid composites
- small particle hybrid composites
78
What are the advantages and disadvantages of traditional composites?
Good mechanical properties
| Surface roughness- difficult to polish
79
What are the advantages and disadvantages of microfilmed resins?
Very good surface polish
| Poor wear resistance- unsuitable for load bearing areas- high contraction shrinkage
80
It is possible to bond amalgam to tooth structure. Give 4 potential advantages of this over non bonded restoration of amalgam
- decrease in micro leakage
- may limit the need for dentine pins
- may increase fracture resistance of restored teeth
- transmits and distributes force better
- there may be less postoperative sensitivity due to better sealing of the margins
81
What materials are commonly used for primary impressions for complete dentures? (3)
- alginate
- compound thermoplastic
- impression putty
82
What broad groups can hydrocolloid impression materials and synthetic elastomeric impression materials be divided into?
Hydrocolloids can be divided into: reversible (agar) and irreversible (alginate). Synthetic elastomeric impression materials can be divided into: elastomers, polysulphides, polyethers, silicones (addition cured/condensation cured)
83
What is a mucostatic impression?
A mucostatic impression is an impression taken with the mucosa in its resting state. It provides a good fit at rest and therefore good retention most of the time but when the patient chews the denture will tend to rock around the most incompressible areas, e.g. a palatine torus
84
What is a mucocompressive impression?
A mucocompressive impression is an impression taken when the denture bearing area is being subjected to compressive force. This results in a denture that is maximally stable during function but not at rest
85
What is a selective mucocompressive impression?
This is an impression taken with only certain areas of the denture bearing area being subjected to the compressive force
86
What factors may affect the RVD? (4)
- stress
- head posture
- pain
- age
- neuromuscular disorders
- bruxism
87
What is group function?
Group function means that during lateral excursion there is contact between several upper and lower teeth on the working side and no contacts on the non working side
88
What is canine guidance?
Canine guidance means that during lateral excursions there is contact between upper and lower canine teeth on the working side only and no contact on the non working side
89
What is balanced occlusion?
Balanced occlusion means simultaneous contacts between opposing artificial teeth on both sides of the dental arch
90
What kind of function/guidance/occlusion would you try to create in a complete denture case?
Balanced occlusion
91
What is the difference between balanced occlusion and balanced articulation?
Balanced articulation is simultaneous contact of opposing teeth in central and eccentric positions as the mandible moves, i.e. it is a dynamic relationship whereas balanced occlusion is a static situation
92
When trying to achieve the correct occlusion in a complete denture case what factors will affect the occlusion in protrusive movements? (4)
- incisor guidance angle
- cusp angles of the posterior teeth
- condylar guidance angles
- orientation of the occlusal plane
- prominence of the compensating curve
93
What do you understand by the term lateral compensating curve and how does it affect the set up of complete denture teeth
During lateral excursions the mandible does not move in a horizontal plane only. There are vertical components to the movement due to the condylar guidance angle and the incisor guidance angle. To achieve occlusion in lateral excursions when the mandible and lower denture carry out these tipping movements the upper teeth needs to be inclined buccal so that the occlusal planes of the teeth lie on a curve (viewed in the coronal plane). This is analogues to the monsoon curve in the natural dentition
94
Name 4 disadvantages of immediate dentures?
- denture may not fit after extraction
- will need relining/copying or remaking
- will not fit when the alveolus remodels
- unable to try in
- may need many visits for adjustment
95
What is meant by the term altered cast technique? Explain the theory behind it
When patient wears a denture with a free end saddle (FES) supported by both tooth and soft tissue there is a risk that when a load is applied to the saddle the underlying mucosa will compress and the saddle will move. The part of the denture supported by the teeth will only move as much as the periodontal ligament of the teeth moves and so this differential movement will cause the denture to rotate. To overcome this an impression of the FES area is taken with the mucosa compressed so that minimal displacement will occur with loading and this reduces the rotation effect. However, over compression of the soft tissues must be avoided as this can lead to either displacement of the denture when the tissues try to recover or to pressure necrosis of the mucosa
This technique of taking a special mucocompressive impression of the FES area is known as the altered cast technique. The idea is to compensate for the difference in degree of support offered by the mucosa and the teeth
96
What is the method for the altered cast technique? (4)
1. the denture framework has base plates attached to the FES area. These are relieved to allow about 2mm of space between them and the mucosa
2. an impression is taken of the FES area with the pressure applied only to the tooth supported part and of the denture and no pressure applied over the FES
3. The original working master cast is sectioned to remove the FES area
4. the denture framework is reseated on the cast and the FES impression area cast up
97
Name five muscles, the movements of which may affect the peripheral flanges of a complete denture
- geniohyoid
- orbicularis iris
- mentalis
- mylohyoid
- buccinator
- palatopharyngeus
- palatoglossus
98
Where is the posterior margin of an upper complete denture usually situated?
Anterior to the fovea palatinae
99
What is a post dam and what function does it form?
A post dam is a raised lip on the posterior border of the fit surface of an upper complete denture. It compresses the palatal soft tissue to form a border seal
100
What do you understand by the term neutral zone?
The area between the tongue, lips and cheeks where the displacing forces of the muscles is minimal. It is the ideal area into which a prosthesis should be placed to minimise displacing forces
101
What is meant by the term direct retainer in a partial denture?
Any element of a partial denture that provides resistance to movement of the denture away from the supporting tissues is a direct retainer
102
What are the advantages of using a crown down method for preparation of a root canal
Preparing the canal from the crown down gives better access. Flaring of the coronal part first removes restrictions and helps prevent instruments binding short of the working length. The coronal part is usually where most of the affected material is present. If this is removed and cleaned first it limits the possibility of spreading the infected material to the apical and periapical tissues. If you estimate the working length and then change the coronal part of the preparation it may inadvertently alter the length. Coronal preparation first allows irritants to gain access to more of the root canal system
103
What is the difference between an over denture and an onlay denture?
An over denture is a denture which derives its support from one or more abutment teeth by completely covering them beneath its fitting surface. An onlay denture is a partial denture that overlays the occlusal surface of all or some of the teeth. It is often used to increase the occlusal vertical dimension
104
What factors need to be considered in choosing and preparing the abutment teeth?
- The abutment should ideally be bilateral and symmetrical with a minimum of one tooth space between them
- order of preference, canine, molars, premolars, incisors
- healthy attached gingivae and periodontal support, minimal mobility
- dome root surface 2-4mm above gingival margin
- root canal treatment may be required
105
What is the definition of osseointegration?
A direct structural and functional union between ordered living bone and the surface of a load carrying implant
106
Give 3 patient related factors that may affect the success of implant placement
- oral hygiene
- periodontal disease
- previous radiotherapy
- smoking
- bisphosphonate medication and anti resorptive/ anti angiogenesis drug usage
107
What anatomical factors need to be considered with regard to implant placement?
- bone height
- bone width
- bone density or quality
- proximity of inferior dental nerve
- proximity of maxillary sinus
108
What would you see clinically if an implant has failed?
- mobility
- pain
- ongoing marginal bone loss
- soft tissue infection
- peri implantitis
109
What are the constituents of dental amalgam? (5)
- silver
- tin
- copper
- zinc
- mercury
110
With amalgam what are the y, y1, y2 phases and what is their importance?
y phase= Ag3Sn
y1 phase= Ag2Hg3
y2 phase= Sn7Hg
The y2 phase is the weakest part of the amalgam- it has the lowest tensile strength and is the softest of the phases. If the amount of y2 phase can be limited in the final dental amalgam the resulting amalgam will be stronger
111
What do you understand by the terms lathe cut particles and spherical particles? What is the significance of the different types?
Lathe cut alloy is made by chipping off pieces from a solid ingot of alloy. This results in particles of different shapes and sizes. Spherical particles are made by melting the ingredients of the alloy together and spraying them into an inert atmosphere. The droplets then solidify into spherical pellets that are regular in shape and can be more closely packed together. this results in increased strength of the amalgam
112
Why is it common practice to overfill a cavity and then carve it down?
When amalgam is condensed mercury rises to the surface of the restoration. To try to minimise the residual mercury left in the restoration it is usual to overfill the preparation and the excess mercury rich amalgam can be carved away leaving the lower mercury containing amalgam which has a greater strength and better longevity
113
What are dental ceramics made out of?
feldspar, silica (quartz) and kaolin
114
What are the three technical stages in producing a porcelain jacket crowns?
1. the first stage is compaction. This powder is mixed with water and applied to the die so as to remove as much water as possible and compact the material such that there is a higher density of particles which minimises firing shrinkage
2. the next stage is firing. The crown is heated in a furnace to allow the molten glass to flow between the powder particles and fill the voids
3. the last stage is glazing, which is done to produce smooth and impervious outer layer
115
Give one advantage and disadvantage of porcelain jacket crowns
Advantages:
- excellent aesthetics
- low thermal conductivity
- high resistance to wear
- glazed surface resists plaque accumulation
Disadvantages:
- poor strength and very brittle so often fracture
- firing shrinkage so must be overbuilt
116
How has the main disadvantage of porcelain jacket crowns been overcome?
By fusing the porcelain to metal to produce metal ceramic restorations, by making reinforced ceramic core systems and by creating resin bonded ceramics
117
What does CAD CAM mean in connection with ceramic restorations?
Computer assisted/aided design, computer assisted/aided manufacture
118
Give 3 requirements of a metal ceramic alloy
- high bond strength to the ceramic
- no adverse reaction with the ceramic
- melting temperature must be greater than the firing temperature of the ceramic
- accurate fit
- biocompatible
- no corrosion
- easy to use and cast
- high elastic modulus
- low cost
119
What are the uses of dental cements? (3)
- luting agents
- cavity linings and bases
- temporary restorations
120
Name 2 luting agents
- modified zinc phosphate
- zinc oxide and eugenol
- zinc polycarboxylate, glass ionomer, resin modified glass ionomer, compomers, resin cements
121
Name 2 cavity linings and bases
- calcium hydroxide
| - zinc oxide and eugenol
122
Name 2 temporary restorations
- zinc oxide and eugenol
| - glass ionomer
123
Which zinc based cement bonds to tooth substance?
Zinc polycarboxylate
124
How should zinc polycarboxylate be mixed and why?
On a glass slab as it must not be mixed on anything that absorbs water, also on a glass slab can be cooled and this will increase working time
125
Which cement should not be used under composite restorations and why?
Zinc oxide and eugenol as the eugenol is thought to interfere with the proper setting of the composite material
126
Which material is used for pulp capping and why?
Calcium hydroxide as it is extremely alkaline (pH 11) which helps with the formation of reparative dentine. It is also antibacterial and has a long duration of action
127
Which cement is thought to reduce sensitivity of a deep restoration?
Zinc oxide and eugenol is thought to reduce sensitivity due to the obtundant and analgesic properties of the eugenol
128
What would you need to check prior to advising placement of veneers? (4)
- is the discolouration enough to warrant treatment or is it so severe that it will not be masked
- the patients smile line
- is there enough crown present to support the veneer?
- any occlusal restrictions
- any parafunctional activities
- is there an alternative option
129
What is the long term prognosis of veneers and what would you warn the patient about?
May require replacement in the long term (approx 4 years for composite veneers) as a result of:
- risk of chipping of incisal edge
- debunking
- need to keep good gingival health
130
What is the thickness of veneers?
0.5-0.7mm
131
What is the function of a post and core?
Provides support and retention for the restoration and distributes stresses along the root
132
What is important to check prior to the placement of a post and why?
The condition of the orthograde root filling and the apical condition as the placement of the post will make it difficult to redo the root canal filling so if necessary repeat orthograde root canal treatment
133
What is the ideal length of the post?
Ideal length is at least the length of the crown; approximately two thirds of the canal length; and the apical seal must not be distributed so at least 4mm of well condensed gutta percha should be left
134
Give the classifications of a post and core system (3)
- prefabricated or custom made
- parallel sided or tapered
- threaded, smooth or serated
135
What are the ideal characteristics of a post? (4)
- have adequate length
- be as parallel as possible
- have a roughened or serrated surface
- not rotate in the root canal
136
What measures can be taken to avoid post perforation? (3)
- avoid large diameter post in small tapered roots, instead used tapered post and cement passively
- avoid long posts in curved roots
- avoid threaded post which will increase internal stress within root canal
137
How would you manage a post perforation?
Depends on the location of the perforation. If it is in the coronal third try to incorporate into the design of the post crown, e.g. diaphragm post and core preparation. For a minimal preparation in the middle third seal the perforation and reposition the post
For a perforation in the apical two thirds use a surgical approach to try and reduce the exposed post and seal the perforation. If attempting repair of perforations, the use of MTA would be preferable
Due to the poor long term prognosis, extraction and implant placement may be favoured
138
What features affect the retention and resistance form of the crown preparation? Give 3 for each form
Retention relies on the height, diameter and taper of the preparation. It will also be increased by the placement of boxes, grooves, pins and surface texture
Resistance relies on taper preparation, height to diameter ratio, correctly aligned and positioned grooves and boxes
139
What are the advantages of a partial coverage crown? ()
- preservation of tooth structure
- less pulpal damage
- margins more likely to be supra gingival
- remaining tooth substance can act as a guide for the technician
140
If the gingival recession continues on the lower left lateral incisor what other option may you consider? (4)
- lateral pedicle graft
- double papilla flap
- coronally repositioned flap
- free gingival graft to provide a wider and functional zone of attached gingivae
- thin acrylic gingival veneer/stent
141
Give six clinical features of necrotising ulcerative gingivitis
- painful yellowish white ulcer
- initially involve the interdental papillae
- spread to involve the labial and lingual marginal gingivae
- metallic taste
- regional lymphadenopathy
- fever
- malaise
- poor oral hygiene
- sensation of teeth being wedged apart
142
What organisms are implicated in ANUG?
Fuso spirochetaal organisms (borellia vincentii, fusobacterium fusiformis) and gram negative anaerobes including porphyromonas, treponema species, selenomonaos species and prevotella species
143
What are the risk factors for ANUG?
- poor OH
- pre existing gingivitis
- smoking
- stress
- malnourishment
- HIV
