First Midterm Flashcards
1
Q
What are Carious Lesions?
A
- caused by bacterial infection that attacks the tooth structure
- the diseased tissues needs to be removed
- need to have a precise cavity prep
2
Q
What are non-carious lesions?
A
loss of tooth structure that’s caused by mechanical or chemical factors such as attrition, abrasion, erosion, and abfraction
3
Q
What is the Goal of a restorative dentist?
A
to carefully remove the diseased tissue in a precise manner (cavity prep) and replace the missing part with a restorative material (restoration).
4
Q
What is a cavity prep?
A
the mechanical alteration to remove the diseased tooth structure.
5
Q
What is restoration?
A
dental material used to restore back function and morphology of the missing part of the tooth structure.
6
Q
What is direct restoration?
A
dental material placed in a soft state directly in cavity prep to restore contour before it sets hard.
7
Q
What is indirect restoration?
A
a restoration fabricate outside the oral cavity then cemented or bonded to the tooth
8
Q
What’s a handpiece?
A
a device that holds and delivers power to rotating instruments to perform tooth preps
9
Q
What are the 2 types of handpieces? Describe them
A
1) air driven - for many years has been the mainstay for cutting teeth
2) electric - increasingly popular, quite, cuts with higher torque, higher power and less stalling - so a smoother cut
10
Q
tell me about the Slow speed handpiece
A
- <12,000 rpm (Revolutions per minute)
- no water coolants
- less efficient, more controlled removal
11
Q
What are the uses of the slow hand piece?
A
- controlled removal - deep caries excavation in close proximity to pulp
- cleaning external surface of teeth (coronal polishing)
- finishing and polishing procedures (whether it’s a restoration or a prep)
12
Q
Speed of medium hand piece
A
12,000- 20,000 rpm
- it’s not used
13
Q
tell me about the high speed hand piece
A
> 200,000 rmp
- generated considerable amount of heat so needs water coolants
- has the most cutting efficiency - less vibration and pressure leading to less patient discomfort
- uses: teet prep and removal of old restorations
14
Q
What does the dental unit delivery system consist of?
A
1) air syringe
2) hand piece control button
3) light for high speed hand piece
15
Q
What does the delivery tubing system in the control panel consist of?
A
- the 4 hole connector line
- the large nut which goes with the high speed
- the small nut that goes with the slow speed
16
Q
What is the anatomy of the high speed hand piece?
A
Has a head, an attachment (contrangled), shaft, and a coupler
17
Q
What is the one chuck mechanism of the head?
A
push button friction grip head holds friction grip type rotary instruments.
18
Q
What’s the coupler?
A
attached the hand piece to the delivery unit and supplies air and water to the hand piece.
the 4 hole line received the hand piece coupler. It’s fixed or movable (360 swivel)
19
Q
What are the slow speed attachments?
A
- slow speed motor
- nose cone/straight attachment (only used for extra oral procedures like trimming down casts/crown)
- contra-angled attachment (used inside the mouth/intraoral)
20
Q
What bur goes with the straight hand piece?
A
A long shank type or straight bur. These are used for extra oral procedures like finishing a crown.
21
Q
What type of head attachments can go on the contrangled slow speed head?
A
The latch type (like swing latch, push button latch, or spring latch) or friction grip (push button type or bur tool type)
22
Q
What does the latch type (RA) head accept?
A
It only accepts latch end burs. Latch end burs are larger in diameter than the friction grip burs.
23
Q
What does the friction grip head accept?
A
It uses friction grip type burs which are smaller in diameter and have shorter shanks than latch-type. The burs can be attached on to the head via two mechanisms.
1) first is the push button where friction is generated from an internal spring assembly. You just push a button to put in/take out the bur from the head.
2) second is the bur tool type where a special tool is using force to overcome and generate friction - need a bur changing wrench to take bur out of the head
24
Q
What the 3 main components of rotary instruments (so like a bur)?
A
- head
- neck
- shank (the end of this part can be friction or latch)
25
Tell me what the head component of rotary instruments is
It is the working part of the instrument. It consists of either blades or abrasive particulates surfaces and can come in many shapes and sizes.
26
What are the 3 types of rotary instruments?
1) blades instruments (intraoral)
2) diamond (abrasive) instruments (crown preps)
3) other abrasives
27
What are the components of the shank?
1) It can be a straight/long shank (nose cone).
2) It can be used for the latch design (slow speed contrangled latch type) or 3) for the friction grip design (slow speed contrangle friction grip head and high speed)
28
What are the components of the neck?
It's not too bulky so it doesn't interfere with the operator's visibility. but it's also not too narrow to become a weak link between the head and shank.
29
What are bladed instruments (burs) used for?
1) excavating (cutting/drilling - cavity prep)
| 2) finishing
30
What are the number of blades in bladed instruments - specifically in excavating burs and finishing burs?
1) excavating/cutting burs:
- had 6 or 8 blades
2) finishing burs:
- has 10-20 blades
- has coded colors for the number of blades
* 10-12 blades - red
* 16-20 blades = yellow
* 30 blades = white
31
Is it better to have more blades or less blades?
the greater the number of blades the smoother the finish
32
What are bladed instruments made of?
Carbide
- the blades are made of Tungsten carbide whose blanks ground to the desired shaped. They are stronger and harder than stainless steel but brittle. I
- The tungsten carbide head is attached to the steel neck and shank by welding and brazing.
- the bladed instruments are used for intracoronal preps
33
What are diamond instruments made of?
Diamonds (obviously) for abrasive cutting
- It's a metal blank on which small diamond particles are held together within a softer matrix. Basically a long piece of metal and small particles of diamonds are wrapped around the whole thing.
- diamond instruments are used for extracoronal preps like crown preps
34
What are the shank colors for the degree of abrasiveness in diamond instruments?
- yellow = superfine
- red = fine
- blue = medium
- green = coarse
- black = super coarse
It gets more abrasive as we go down the list.
35
What level of abrasiveness of diamond instruments will we use?
medium (blue) and coarse (green)
36
What are the different types of bladed head designs (dental burs)?
round, inverted cone, pear-shaped, straight-fissure, and tapered fissure
37
What are some pear shaped burs and their dimensions?
330
- length (height of head): 1.5 mm
- taper: 8 deg
- diameter: 0.8 mm
- gives us convergent walls
245
- length: 3.0 mm
- taper: 4 deg
- diameter: 0.8 mm
38
What is the working head of a bur called (attached to the neck)?
the proximal head
39
What is the part of the head called that's at the end (the tip of the bur)?
the distal end
40
Plain cylindrical fissure burs
55-59 (designates 200 series for rounded corners)
| we use the 57 bur which gives us parallel walls
41
Plain tapered fissure burs
169-172
diameter: 1 mm
- gives us divergent walls
- is tapered down at the distal end
42
What are some other variable head designs of burs?
1) end cutting = designate a 900 (only the end of the head carries the cutting blades)
- ex) 956 - we use this to smooth the floor
2) cross cut = designate a 500 before the bur number. Also 700 version.
43
What are some mechanisms of cutting?
1) brittle fracture - use abrasive cutting (diamond burs) with these materials
2) ductile fracture - this can be cut by bladed cutting
teeth can undergo both brittle and ductile fractures.
44
What is brittle fracture?
- brittle material fractures by crack formation upon tensile loading.
- Enamel is brittle because it needs the lead amount of energy to break (it's like chinaware - if you just drop it it will break)
- abrasive cutting (diamond burs): used for brittle fractures because it's more efficient with them (micro cracks) and also because it doesn't deform. so used for extracoronal preps like on the surface of teeth.
45
What is ductile fracture?
- is the plastic deformation of the material by shearing.
- it absorbs energy first, starts to deform, and then breaks.
- bladed cutting is used with these materials because it's more efficient and it cuts by shearing layers of tooth structure (like a veg. peeler). It's recommend for intracoronal preps. It's also efficient to cut pulp.
- dentin is ductile
46
Blade Design - what is rake face?
The surface of blade that forms the chip (the first surface to touch the tooth). The surface of blade towards the direction of cutting.
47
Blade design - what is clearance face?
the surface that clears the chips away from the direction of cutting.
48
Blade Design - where is the edge angle?
It's the angle between the rake and clearance surfaces.
49
Blade design - where's the rake angle?
It's the angle between the radial line and rake face.
50
Blade design - where's the clearance angle?
It's the angle that provides clearance between the cutting edge and the tooth surface.
51
Blade angle: What is the positive rake angle?
It's when the radius (from the cutting edge to axis of bur) is ahead of the rake face and when the blade is behind the perpendicular.
- it has a higher cutting efficiency because sharper but can also break very easily too.
- larger chips are produced and the chip space is small so the chip space gets clogged.
52
Blade angle: What's the negative rake angle?
- it's when the rake face is ahead of the radius (from the cutting edge to axis of bur).
- it has a decrease cutting efficiency but cutting edge is spared (less liable to fracture) since carbide burs are brittle.
- smaller chips are produced so there is no clogging of the chip space.
- this angle also lasts longer then the positive rake angle so we use this rake angle.
53
Blade angles: What is the clearance angle?
- the angle that provides the clearance between the tooth structure and the cutting edge.
- purpose:
* prevents blade from rubbing on the tooth surface
* bigger (wider) the clearance angle, the less friction there will be, dulling will be minimized so the life of the bur will be lengthened/
54
Hazards of cutting instruments
Patients: vibration and heat generation that may lead to pulpal trauma and discomfort to the patient so water coolants are used.
Clinician: bur heads are placed on the control away from you. Scalpels need to be covered at all time. Need to wear masks to prevent breathing in aerosolized particles and need to wear safety glasses.
55
What are the basic components of the hand instruments?
1) handle
2) shank: connects the handle to the working end, straight or angled, rigid or flexible.
3) working end: nib/point (non cutting instruments) or blade (cutting instruments)
- hand instruments are double ended if there are working ends on both ends.
56
Hand instruments: what are examination instruments?
These are non-cutting instruments that examine teeth, soft tissue and hard tissue for defects, caries, etc.
ex) mirror, explorer, perio probe
57
Hand instruments: what are hand cutting instruments?
refine the walls of the tooth prep to receive the restoration
58
hand instruments: what are restorative instruments?
are non cutting instruments that insert dental material in the cavity prep and carve back the tooth contour
59
hand instruments: what are accessory instruments?
Aid to complete the procedure like scissors, pluckers, etc.
60
Examination instrument: Mirror
- used in the non-dominant hand
- reflects light
- for indirect vision
- retraction of lips, cheeks and tongue for access
- protection of soft tissue: tongue, floor of the mouth
61
Examination instrument: Explorer
- pointed tip to enhance tactile sensation for caries detection
- ex) shepherds hook # 23, pigtail/cowhorn #2, and inter proximal explorer #17
62
Examination instrument: perio probe
- measures cavity depth or distance from one tooth to another
- there are no 4 and 6 markings on the probe
- just 1,2,3,5,7,8,9,10
63
What are hand cutting instruments composed of?
The blade is compose of carbon steel (carbon is harder than stainless steel)
The handle is composed of stainless steel (chromium is corrosion resistant and retain the shine)
64
What are the components of hand cutting instruments?
1) handle: has 2 codes on there
- first is the instrument formula (I.D formula)
- second is the manufacturer's serial number
2) shank: connects handle to the blade
3) blade: working part of the instrument and is beveled to create the cutting edge.
65
Bevels of the blade of a cutting instruments
blade can have a primary cutting edge which is at the tip of the blade and secondary cutting edges which is on the sides of the blades.
66
shanks of cutting instruments
the shank can be straight, mono-angled (one bend), bin angles (or bi-angled) (which as 2 bends) and triple angle (3 bends)
67
Principles in shank design
balance: concentration of the force onto the blade without the rotation of the instrument
if the tip of the angle makes a straight line down the middle of the instrument, then the instrument is in balance (ex: bi-angle).
If the tip doesn't make a straight line with the handle of the instrument (like mono angle) then the shank is out of the balance and will have more torque and rotation.
68
Black's instrument formula
The basic instrument formula consists of 3 numbers:
1) the first number is the width of the blade in tenth of a mm
- the width of the tip of the blade
- 10 = 1 mm, if it says 10, it actually means 1 mm
2) the second number is the length o the blade in mm
- 7 mm = 7
3) the third number is the angulation of the blade to the long axis of the handle. It is expressed in 100th (not in 360 deg) of a circle and is always less then 50 deg.
69
Black's instrument formula - the four number formula
The 2nd number in the 4 number formula indicates the primary cutting edge relative to the long axis of handle. It is also greater then 50 deg.
- first number is the width of blade (0.1 mm)
- the second number is the primary cutting edge angle which is always greater then 50 deg.
- the third number is the blade length in mm
- the fourth number is the angle of the blade
70
What are restorative instruments?
insert and carve the restorative material
| ex) carrier, condenser/plugger, anatomical/acorn burnisher
71
What are accessory instruments?
accessory instruments:
- ex) articulating paper holder (miller forceps) and scissors
accessory equipment:
- amalgam well
72
What are identification bands?
Are colored rubber bands that can be put around instruments to easily ID them
73
Bevels Method of Use: direct cutting
- force applied by bevel is perpendicular to cutting edge
- instrument is held parallel to the wall being planed at all time
- the cutting edge is in contact with the wall being planed
- this is an example of an enamel hatched - 8/9 hatchet
74
Bevels Method of use: lateral cutting
indirect cutting/lateral cutting/scrapping: force is exerted parallel to the cutting edge
- motion: from the beveled to the non-beveled (pointy) side or away from the bevel
- an example of this is an enamel hatchet (8/9 [is doubled ended]: which do both direct and indirect cutting) and the gingival margin trimmer
75
What are part of the chisel family?
enamel hatchet and gingival margin trimmer
76
chisel family: gingival margin trimmer
- the blade is curved and not milled in a single plane: curved blade accentuates the lateral cutting
- the cutting edge makes an angle to the long axis of the blade
- in lateral cutting (indirect cutting), the force is applied parallel ( // ) to the cutting edge.
- this has four numbers on the handle
77
What instruments are part of the excavator family?
ordinary hatchet, hoes (pull), angle former, and spoon
78
What are dental caries?
A multofactorial infectious disease that attacks teeth by certain bacteria if the conditions are permissible causing destruction (deminiarlization/dissolution) of the tooth. Time, bacteria, and carbs cause caries.
79
Stages of caries:
1) incipient (reversible):
able to remineralize. the caries is only the enamel and hasn't passed he DEJ yet
2) small (operative 1):
- it's now passed the DEJ and is just into the dentin. You call these small lesions
3) moderate:
- caries is half way through the dentin
4) extensive:
- caries is very close to the pulp
- have to do direct/indirect pulp therapy
80
location of caries - pit and fissure
- caries in the fossa (pit) or groove (fissure)
- pits and fissures on the occlusal surfaces of posterior teeth, buccal and lingual surfaces of molars, lingual surfaces of maxillary anterior teeth
81
location of caries - smooth surface caries
- on the surfaces that are "pit and fissure" free
| - happen on the proximal surfaces - messiah and distal sides
82
location of caries - root surface caries
- more in elderly, follows an advanced gingival recession
83
what are active caries?
- are still going on
- rampant (acute): rapidly invading, softer lesions, affects multiple teeth, no chance for remineralization.
* ex): nursing bottle caries, radiation caries, meth mouth
- chronic (slowly progressive): slow, long standing, dark in color and so there is a good chance of remineralization in early stages (reverse the demineralization process)
* see this in clinic more
84
What are arrested caries
- caries that have stopped progressing, not showing any further progression
- usually on root surface
- smooth and polished like surface
85
What are recurent/secondary caries?
Caries that still exist after a restoration.
| - all of the caries weren't taken out properly before the tooth was restored.
86
GV Black's Class 1
pits and fissures of : occlusal surfaces of premolars and molars; buccal or lingual pits/fissures of the molar; lingual pit near the cingulum of the max incisors
87
GV Black's class II
- involving the proximal surfaces (mesial and distal) of premolars and molars - not anteriors (like a drop box)
88
GV Black's Class III
proximal (mesial and distal) surfaces of incisors and canines
89
GV Black's Class IV
proximal surfaces of incisors and canine, but also will involve the incisal edge.
- a lot of these caries can be trauma like chips/fractures
90
GV Black's Class V
gingival third (the area near the gingiva) of the facial or lingual surfaces of any tooth and maybe a little to distal or mesial surfaces. Some also go to the root surface .
91
GV Black's Class VI
involve the incisal edges of anterior teeth and the cusp tips of posterior teeth. Carious lesions are rare.
92
Class prep designs
according to GV Black the location of the lesion dictates the design of the cavity prep
93
What are the fundamental concepts for all tooth preps?
1) removal of dental caries
2) removal of weak tooth structure to provide well supported sound hard tissue
3) pulp protection
94
What is a line angle?
junction of two surfaces
95
what are point angles?
junction of three surfaces
96
The cavity walls
According to the proximity to the external surface:
1) external wall - extend to the outer tooth surface
2) internal wall - don't extent to the outer tooth surface
According to the angulation from the long axis:
1) axial walls: parallel to the long axis
- axial/buccal/lingual walls
2) perpendicular walls
- gingival/pulpal floors
97
What's an isthmus?
- in a class I prep: narrowest portion of a cavity prep
| - in a class II prep: a portion of the cavity connecting an occlusal portion and proximal portion together
98
What's a dovetail?
- in class I cavity preps, isthmus connects the 2 dovetails
| - dovetail design includes each marginal fossa and the developmental grooves around the marginal pits
99
What's a cavosurface margin?
junction between the external walls of the cavity prep and the uncut tooth surface.
100
Basic principles of cavity prep - 1) outline form
- the shape of the cavity prep, perimeter of the tooth prep in width, length, and depth
- factors governing outline form:
* conservation of tooth structure: preservation of the remaining tooth structure - minimal extension of the outline form
* location and extent of the carious lesion: the entire carious area should be removed and any weak enamel. placing the margins (cavosurface margin) on sound strong tooth structure and unsupported enamel is removed.
* position of pit and fissure dictate the outline
101
Basic principles of cavity prep - 2) resistance form
- design features of cavity prep allowing the remaining tooth structure and the restoration to withstand forces that are principally directed towards the long axis of the tooth. If it's fractured, it's not resistant.
102
Basic principles of cavity prep - 2) resistance forms: primary resistance
1) removal of undermined surface enamel: cavosurface margin shouldn't terminate on unsupported or undermined enamel to prevent it's fracture
2) flat pupal floor:
- cup shaped cavity: rotation of the restoration (micro movements) results in a wedging effect on the supporting dentin bridge. Can lead to shearing.
- box shaped cavity: plural floor is perpendicular to the long axis of the tooth
3) cavity prep depth: adequate depth to provide enough thickness of amalgam to prevent its fracture under load b/c to handle mastication. minimum amalgam thickness to withstand forces - 1.5 mm - have to go beyond the DEJ.
4) well defined rounded internal lines and point angles:
placing line angles to delineate the walls. sharp line angles aren't recommended in any restoration. sharp line angles act as stress concentrations areas.
5) type of restorative material: amalgams have low edge strength, thus amalgam margin is of prime importance. Want the cavosurface angle to be at 80-90 deg - reinforcement of the amalgam restoration at the margin by painting an angle of 80-90 deg. Cavosurface margin has to establish a 90 deg (butt-joint margin) amalgam margin.
103
Basic principles of cavity prep - 3) retention form
- design features of the cavity prep that prevent dislodgment of the restoration by lifting or tipping forces
- amalgam doesn't bond to tooth structure thus increasing the surface area of the walls that contacts the amalgam (increased friction)
- making opposing walls parallel or slightly converging toward the occlusal
104
Basic principles of cavity prep - 4) convenience form
- sufficient access to the cavity, to facilitate visibility and instrumentation of the cavity prep and the insertion of the restorative material
- visibility: for complete removal of decay
- access the prep for instrumentation
- insertion fo the restorative material: the diameter of the small end ( 1.0 mm) of the smaller condenser should fit passively into the prepared cavity.
105
Basic principles of cavity prep - 5) finishing
- finishing the cavosurface margin (enamel margin) to prevent jagged or rough outline
- to achieve the best marginal seal
106
Basic principles of cavity prep - 6) debridement
- this is the final step before the cavity prep receives the restoration
- rinsing the cavity is done with air/water spray syringe and high suction evacuation
- to remove debris and wash away dentinal shavings (smear layer)
- free the cavity from moisture (blood and saliva)
107
Rules of Conservation of tooth structure
- Two cavities shouldn't be united unless the separating ridge is less than 0.5 mm
1) don't extend into the oblique ridge of max molars unless it's undermined by caries
2) don't extend into transverse ridge of hand 1st premolar unless it is undermined by caries
- cavity outline should extend around the cusps (conservative approach)
- shape: flowing curves around triangular ridges
- isthmus width: shouldn't exceed 1/3 intercuspal distance
- minimal extension of the buccal and lingual walls and into triangular ridges (from the central groove to the cusp tip)
- minimal extension into the marginal ridges (include the mesial and distal pits)
- depth of cavity prep should be 0.2-0.5 mm into dentin/ 1.5-2.0 mm on ivorine teeth in total
108
Drilling around the buccal and lingual walls
Around the central groove area
- the 2 opposing walls converge occlusally
-the occlusal convergence of the 2 opposing walls provide the primary retention form
- the walls take the shape of the 330 bur
- keep the bur angulation with the long axis of the tooth
don't over converge by tilting the bur
109
buccolingual extension
- minimal extension of the buccal and lingual walls - minimal extension from the central groove to the cusp tip (conservation of the triangular ridges)
- isthmus area is usually narrower than at the dovetail
110
proximal walls: mesial and distal walls
diverge the mesial and distal walls slightly toward the occlusal to follow the direction of the enamel rods w/o involving the marginal ridge (conserve the marginal ridge)
111
proximal walls: mesiodistal extension
- 1.6 mm of tooth structure should be left between cavosurface margin and the proximal contact area (conservation of marginal ridge)
- if cavosurface margin is past the crest of the marginal ridge then you are too extended
112
pulpal depth
- adequate depth: resistance force
- clinicald depth is 0.2-0.5 mm beyond DEJ
- in the typodont from the cavosurface margin to the plural floor = 1.5 mm at the fossa and 1.75 - 2.00 mm at the ridges
113
cavosurfave margine
- 90 deg/ 100 deg
- not sharp , no irregularities
- flowing curves , not abrupt change in the direction
114
Pattern to label line and point angles
```
axial = 1
mesial =2
distal = 3
facial = 4
lingual =5
occlusal/incisal = 6
gingival = 7
pulpal = 8
```
115
bur orientation for mand 1st premolar
line is slanted pointing not directly down but tilted down towards the buccal
116
When doing a class I prep with extension
the axial depth should be 1.0-1.2 mm with a 245 bur
117
Outline Form
- removal of caries and defects
- extensions of the margins on the sound enamel
- preservation of sound tooth structures
118
resistance form
- minimizes fracture potential of the tooth and restoration
| - that means we need adequate thickness of the amalgam restoration to withstand the occlusal forces
119
how wide should isthmus be?
1 -1.25 mm
120
retention form
- cavity prep should have adequate retention features to prevent dislodgment of the restoration
- right angulation of walls and flat plural floor
121
convenience form
- cavity prep should be large enough to permit visualization and proper instrumentation
122
common errors: over-extension
- marginal ridge
- wide and long grooves
- wide isthmus
123
common errors: under extension
- not extended enough in the grooves
| - narrow isthmus and grooves
124
common errors: B & L Walls
- incorrect wall angulation
- too much converging B and L walls
- diverging B and L walls
125
common errors: M & D walls
- too much diverging M & D walls and in grooves
| - irregular walls (not flat but rough)
126
common errors: floor
- too deep
- too shallow
- uneven
- rough
127
common errors: cavosurface margin
- rough
| - sharp
128
buccal and lingual walls
-ideal: convergent occlusal or straight
provide retention to amalgam against displacement and lifting forces
-ideal is when bur is parallel to the long axis of the tooth it's going to make walls convergent and the line angles rounded ( 330)
-over convergent - undercuts near floor, chances of poorly condense amalgam near the axiopulpal line angle and excessive reduction of the sound dentin
- if divergent occlusally - excess reduction towards the triangular ridges and compromised retention form against lifting and tipping forces during mastication - occlusal forces
129
proximal walls: M and D walls
- ideal: slightly divergent to follow the enamel rods
- common errors: too much divergence - ends up having thin marginal ridge. not including pits in the prep.
- thin marginal ridges problem: makes tooth weak against the occlusal forces to support the restoration. fracture or crack on the marginal ridge results in failure of the restoration.
- divergent mesial and distal walls shouldn't have more then a 6-8 deg angulation.
130
Pulpal depth
- depth of 1.5-1.75 mm is considered ideal for the thickness of the amalgam restoration
- 1.5 mm near fossa (mesial/distal triangular fossa and central fossa)
- 1.75 near the triangular ridges
- problem - shallow preps lead to inadequate thickness affects resistance form
- deep depth problem: leads to unnecessary removal of health dentin and increases the chance of approaching pulp horns or even exposure of pulp
131
Line angles
- ideal: slightly rounded and well defined line angles. provides resistance against occlusal forces.
- any sharp angle leads to concentration of the stress
132
Pulpal Wall
- ideal pulpal floor: flat/even plural floor, provides a strong and stable base/floor, contributes to occlusal forces along with the long axis of the tooth.
- common error: uneven distribution of the forces and micromovement of the restoration affects the longevity of the restoration and tooth
133
cavosurface margin
- ideal: strong enamel margin
- errors: undermines enamel margin and rough and sharp margin
- problem: weak enamel, microfracture of the tooth/restoration, leakage of saliva through cracks, development of secondary caries, and fracture of the restoration
134
slot
is a modification from class II if there is still adjacent tooth but no occlusal pits and fissure caries we can still do occlusal approach going through the marginal ridge but sparing the central groove area.
135
box clearance
- ideal: 0.2-0.3 mm buccal, lingual
- ideal 0.5 gingivally
- 1/3 of explorer top
- very tip of pig tail
136
Axial Wall in drop box
- shape follows the external proximal wall - convex or straight
- height of axial wall is 1-1.5 mm
- depth of axial wall is 1-1.2 mm
- axiopulpal line angle is rounded, not sharp
