Access Cavity Preparation Posteriors

ACCESS CAVITY
PREPARATION
POSTERIORS
GUIDED BY-
Dr. SANDEEP METGUD
Dr. DEEPALI AGRAWAL
DONE BY-
Dr. RAMSUNDAR HAZRA
Ist Year PG
DEPT. OF CONSERVATIVE
DENTISTRY AND ENDODONTICS
2

“Of all the phases of anatomic study in the
human system, One of the most complex
is the Pulp cavity morphology.”
-M.T. Barrett
3

CONTENTS
• INTRODUCTION
• COMPONENTS OF ROOT CANAL SYSTEM
• ROOT CANAL ANATOMY
• STUDIES ON ROOT CANAL MORPHOLOGY
• PRINCIPLES OF ACCESS CAVITY PREP
• OBJECTIVES AND GUIDELINES FOR
ACCESS CAVITY PREPARATION
• POSTERIOR ACCESS CAVITY
PREPARATION
4

CONTENTS
• MORPHOLOGY AND ACCESS CAVITY
PREPARATION OF INDIVIDUAL TEETH
• PROCEDURAL ERRORS
• CONCLUSIONS
• REFERENCES
5

INTRODUCTION
• Endodontic disease and apical periodontitis
has a microbial pathogenesis.
• Root canal treatment is performed to treat
endodontic disease by eradicating Bacteria
from the root canal space.
• A thorough knowledge of tooth morphology,
careful interpretation of angled radiographs
and adequate access to and exploration of
tooth’s interior are prerequisites for treatment.
6

INTRODUCTION
• The main objectives of RCT are thorough
cleaning and shaping of all pulp spaces and
complete obturation of these spaces with an
inert filling material.
• Optimal endodontic result is difficult to
achieve if the access is not properly prepared.
• Understanding of complexity and anatomy of
root canal system .
7

COMPONENTS OF ROOT
CANAL SYSTEM
• The entire space in the dentin where the pulp
is housed is called the root canal system.
• Outline corresponds to external contour of the
tooth.
8

COMPONENTS OF ROOT
CANAL SYSTEM
• Nearly all root canals are curved, particularly
in a faciolingual direction.
• A Curvature may be gradual, sharp near the
apex or double S-shaped.
• In most cases number of root canals
corresponds to the number of roots.
• An oval root may have more than one canal.
9

COMPONENTS OF ROOT
CANAL SYSTEM
• A curvature of 20 degree in a narrow root canal
may be difficult or even impossible with endodontic
instruments.
• A curvature of 30 degree in a wide canal may be
negotiated.
• Success in negotiating a narrow, curved canal
depends on-
1. Degree of curvature
2. Size and constriction of root canal
3. Size and flexibility of instrument blade
4. Skill of operator 10

COMPONENTS OF ROOT
CANAL SYSTEM
• Accessory canals, or lateral canals, are lateral
branching of the main root canal generally
occurring in the apical third or furcation area
of a root.
• Distinction between an accessory and lateral
canal is that a lateral canal is an accessory
canal that branches to the lateral surface of the
root and may be visible on a radiograph.
11

COMPONENTS OF ROOT
CANAL SYSTEM
• Accessory canals may occur in the bifurcation or
trifurcation of multirooted teeth.
• Vertucci and Williams called these Furcation
canals.
• According to SEM findings, Diameter of furcation
openings in Mandibular Molars varies from 4 to
720µm.
• Mandibular teeth have a higher incidence of
foramina involving both pulp chamber floor and the
furcation surface (56%) than do maxillary teeth
(48%). 13

ROOT CANAL ANATOMY
• From early work of Hess and Zurcher to the
most recent studies on anatomic compexities
of the root canal system, it has been
established that a root with a tapering canal
and a single foramen is the exception rather
than the rule.
• Investigators have shown multiple foramina,
additional canals, fins, delta, intercanal
connections, loops, C-shaped, furcation and
lateral canals in most teeth. 15

ROOT CANAL ANATOMY
MULTIPLE PRESENCE OF ISTHMUSES,
FINS AND IRREGULAR ROOT CANAL
ANATOMY ARE EVIDENT
16

ROOT CANAL ANATOMY
• The pulp canal system is complex and canals may
branch, divide and rejoin.
• Weine categorized the root canal systems into four
basic types-
a)Type I- Single canal from pulp chamber to apex
b)Type II- Two canals leaving from the chamber and
merging to form a single canal short of the apex.
c) Type III- Two separate and distinct canals from
chamber to apex.
d)Type IV- One canal leaving the chamber and
dividing into two separate and distinct canals. 17

ROOT CANAL ANATOMY
• Vertucci et al, using cleared teeth in which the
root canal systems had been stained with
hematoxylin dye, found a much more complex
canal system.
• They identified eight pulp space configurations.
• The only teeth that showed all eight possible
configurations was the maxillary second
premolar.
18

STUDIES ON ROOT CANAL
MORPHOLOGY
19

STUDIES ON ROOT CANAL
MORPHOLOGY
• Specific types of canal morphology appear to
occur in different racial groups.
• Compared with White patients, Black patients
have a higher number of extra canals in both
the mandibular 1st
premolar (32.8% v/s 13.7%)
and 2nd
premolar (7.8% v/s 2.8%).
• Higher incidence of single rooted and C-
shaped mandibular 2nd
molars in Asians
compared with other populations.
20

CORONAL ACCESS CAVITY
• The principles of preparation of coronal and
radicular canal spaces can be divided into two
distinct steps-
A)Preparation of coronal access cavity.
B)Radicular canal shaping.
21

• The objective of coronal access cavity is to
provide a smooth free-flowing tapered
channel from the orifice to the apex that
allows instruments, irrigants, and medicaments
to attempt cleaning and shaping of the entire
length and circumference of the canal, with as
minimal a loss of structural integrity to the
tooth as possible.
(Ingle’s Endodontics 6)
22

PRINCIPLES OF ENDODONTIC CAVITY
PREARATION
• Slightly modifying Black’s principles, a list of
principles of endodontic cavity preparation may be
established.
 ENDODONTIC CORONAL CAVITY PREP-
I. OUTLINE FORM.
II.CONVENIENCE FORM.
III.REMOVAL OF REMAINING CARIOUS DENTIN.
IV. TOILET OF THE CAVITY.
23

PRINCIPLES OF ENDODONTIC CAVITY
PREARATION
 ENDODONTIC RADICULAR CAVITY PREP-
I. OUTLINE FORM.
II.CONVENIENCE FORM.
III.TOILET OF THE CAVITY.
IV. RETENTION FORM.
V. RESISTANCE FORM.
A similar approach to coronal preparation was
suggested by Pucci in 1944.
24

PRINCIPLE I- OUTLINE FORM
• Must be correctly shaped and positioned to establish
complete access for instrumentation from cavity
margin to apical foramen.
• External outline form evolves from the internal
anatomy of the tooth established by pulp.
• To achieve optimal preparation, three factors of
internal anatomy must be considered:
1. The size of the pulp chamber.
2. The shape of the pulp chamber
3. The number of the individual root canals, their
curvature and their position. 25

PRINCIPLE II- CONVENIENCE FORM
• In Endodontics, convenience form makes more
convenient and accurate the preparation as well as
filling of the root canal.
• Four important benefits are gained through
convenience form modifications-
1. Unobstructed access to the canal orifice.
2. Direct access to the Apical foramen.
3. Cavity expansion to accommodate filling techniques.
4. Complete authority over the enlarging instrument.
27

• Luebke has made the important point that an
entire wall need not be extended in the event
that instrument impingement occurs due to a
severely curved root or an extra canal.
• In extending only that portion of the wall
needed to free the instrument , a clover-leaf
appearance may evolve as the outline form.
• Hence, Luebke has termed this a ‘Shamrock
preparation’.
28

• Failure to properly modify the access cavity
outline by extending the convenience form
will ultimately lead to failure by either root
perforation , ‘ledge’ or ‘shelf’formation
within the canal, instrument breakage, or the
incorrect shape of the completed canal
preparation often termed ‘zipping’ or apical
transportation.
29

PRINCIPLE III- REMOVAL OF THE
REMAINING CARIOUS DENTIN AND
DEFECTIVE RESTORATIONS
• Caries and defective restorations remaining in
an endodontic cavity preparation must be
removed for three reasons-
1.To eliminate mechanically as many bacteria as
possible from the interior of the tooth.
2.To eliminate the discolored tooth structure,
that may ultimately lead to staining the crown.
3.To eliminate the possibility of any bacteria-
laden saliva leaking into the prepared cavity. 31

PRINCIPLE IV- TOILET OF THE CAVITY
• All the caries, debris, and necrotic material must be
removed from the chamber before the radicular
preparation is begun.
• Calcified or metallic debris left in chamber may act
as an obstruction during canal enlargement.
• Soft debris might increase the bacterial population in
the canal.
• Coronal debris may stain the crown.
• Round burs, endodontic spoon excavator and
irrigation with sodium hypochlorite aids in debris
removal and for cleansing the chamber.
32

PRINCIPLE IV- TOILET OF THE CAVITY
• The chamber may finally be wiped out with
cotton and a careful flush of air will eliminate
the remaining debris.
• Air must never be aimed down the canals-
Emphysema of the oral tissues has been
produced by a blast of air escaping out the
apex.
• Toilet of the cavity makes up a significant
portion of the radicular preparation.
33

GENERAL PRINCIPLES
• ‘Do No Harm’
• Confirmation of etiology of pulpal pathosis.
• Assessment of Restorability.
• Straight Line Access.
• Three Dimensional position of teeth in jaws.
• External root surface as a guide.
34

‘DO NO HARM’
• No practitioner performs treatment with the
intent to harm.
• To minimize the frequency of harm, learning
and awareness should be lifelong objectives.
• ‘A mindful practice’ is the objective that
continuously monitors and reevaluates results
and techniques over time.
35

CONFIRMATION OF ETIOLOGY
OF PULPAL PATHOSIS
• Confirm the etiology of pulpal breakdown
assessed during diagnosis.
• Etiological factors are Bacterial
contamination (via caries, coronal leakage
under restorations, fractures) And Trauma
(eg- resorption, thermal, mechanical,
physical).
• Clinically, Microleakage and cracks is
extremely subtle and difficult to detect.
36

ASSESSMENT OF
RESTORABILITY
• Once root canal treatment has been diagnosed,
another major objective is to check the
restorability of the tooth prior to RCT.
• Operator should search for presence of cracks,
height, and thickness of the remaining dentinal
walls for ferrule effect, the relationship of the
remaining coronal tooth margins relative to
osseous crest, root length, location of furcation
and position of the tooth in the arch.
37

STRAIGHT LINE ACCESS
• To prepare the Apical third of the canal
circumferentially, a straight path for the
cutting instrument from the orifice to the apex
is imperative.
• As the curvature of the canal increases, a
file that enters into the canal is deflected at
its tip by the force exerted by the dentin.
• Eventually, the file will cut the dentin rather
than bend.
38

• The term ‘ Straight Line Access’ describes a
preparation that provides a straight or
outwardly flared, unimpeded path from the
occlusal surface to the apex.
• The diameter of the apical preparation also
affects the access preparation.
• In order to avoid stripping on the furcal
surface or transporting the apex, one must
achieve SLA beforehand.
39

• Radiographically, canal curvature in the
mesiodistal plane can be directly observed.
• Cunningham and Senia demonstrated that
canals possess a 3D curvature.
• To obtain an SLA, sometimes the tooth
structure must be removed more on the buccal
or the lingual surface than just on the mesial or
the distal surface.
40

• SLA involves selective removal of the outer
canal tooth structure to protect the furcal
surface.
• The ‘Anticurvature’ filing involves cutting
only on the outward stroke away from the
furcal surface but is not effective beyond
curvatures.
• GG Burs, Stiffer NiTi rotaries have significant
laterally cutting ability.
41

THREE DIMENSIONAL POSITION
OF TEETH IN JAWS
• True three dimensional position that teeth hold
in each jaw cannot be assessed accurately by
clinically or radiographically.
• Lingual and mesial inclination of the
mandibular molars, Mesial inclination of the
maxillary molars and the labial inclination of
all the incisors.
• Bur must be angled to mimic these inclinations
in both mesiodistal and buccolingual planes.
42

EXTERNAL ROOT SURFACE
AS A GUIDE
• External root anatomy is determined by the
internal pulp.
• As the long axis of the tooth cannot be seen in
the clinical setting the next best guide is the
external root surface.
• Acosta and Trugeda found the pulp chamber
in the center of the tooth, closely matching
its outer contour and maintaining the same
distance from all the surfaces.
43

EXTERNAL ROOT SURFACE
AS A GUIDE
• In a study involving 500 Pulp chambers
Krasner and Rankow found that the CEJ
was the most important anatomic landmark
for determining the location of pulp chambers
and root canal orifices.
• These authors proposed five guidelines of
laws of pulp chamber anatomy to help
clinicians determine the number and location
of orifices on the chamber floor.
44

• LAW OF CENTRALITY-
The floor of the pulp chamber is always
located in the center of the tooth at the level of
the CEJ.
• LAW OF CONCENTRICITY-
The walls of the pulp chamber are always
concentric to the external surface of the tooth
at the level of the CEJ, that is, the external root
surface anatomy reflects the internal pulp
chamber anatomy.
45

• LAW OF THE CEJ-
The distance from the external surface of the
clinical crown to the wall of the pulp chamber
is the same throughout the circumference of
the tooth at the level of the CEJ- the CEJ is the
most consistent repeatable landmark for
locating the position of the pulp chamber.
46

• LAW OF SYMMETRY 1-
Except for the maxillary molars, the orifices
of the canals are equidistant from a line drawn
in a mesial-distal direction, through the pulp
chamber floor.
• LAW OF SYMMETRY 2-
Except for the maxillary molars, the orifices
of the canals lie on a line perpendicular to a
line drawn in a mesial-distal direction across
the center of the floor of the pulp chamber.
47

• LAW OF COLOR CHANGE-
The color of the pulp chamber floor is always darker
than the walls.
• LAW OF ORIFICE LOCATION 1-
The orifices of the root canals are always located at
the junction of the walls and the floor.
The orifices of the root canals are located at the
angles in the floor-wall junction.
The orifices of the root canals are located at the
terminus of the root developmental fusion lines. 48

• More than 95% of the teeth Krasner and Rankow
examined conformed to these laws. Slightly fewer
than 5% of mandibular 2nd
and 3rd
molars did not
conform because of occurrence of C-shaped
anatomy.
49

CLINICAL ARMAMENTARIUM
• The preparation of an access cavity requires
the following equipment-
 Magnification and illumination
 Handpieces
 Burs
 Endodontic explorer(DG-16, DE-17)
 Endodontic operative spoon
 #17 Explorer
 Ultrasonic unit and tips
50

OBJECTIVES OF ACCESS
CAVITY PREPARATION
1. To penetrate through the occlusal surface.
2. To find the Pulp Chamber.
3. To ‘Unroof’ the dentin that covers the pulp
chamber.
4. To obtain uniform contact of the file with the
access cavity wall.
5. To obtain SLA.
(By Ingle’s Endodontics 6)
51

GUIDELINES
• Removal of caries and Permanent restoration-
 Caries typically is removed early, before the pulp
chamber is entered.
 Defective permanent restorations must be
removed entirely to prevent coronal leakage from
contaminating pulp chamber, the root canals or
both.
 Management of intact permanent restorations
when reccurent caries is not present requires some
judgement.
52

GUIDELINES
The clinician may want to retain the proximal
portion of Class II restoration that extends
subgingivally to aid in rubber dam isolation.
 Often clinicians decide to perform endodontic
therapy through intact crowns rather than
removing or replacing them.
 The clinician can enhance visibility by
beveling the crown’s cavosurface margins and
making all axial walls glassy smooth.
53

GUIDELINES
• Initial External Outline Form-
 The removal of caries and existing
restorations often accomplishes this step.
 The pulp chamber of posterior teeth is
positioned in the center of the tooth at the level
of the CEJ.
 An access starting location must be
determined.
54

GUIDELINES
In maxillary premolars this point is on the
central groove between the cusp tips.
 The crowns of mandibular premolars are tilted
lingually relative to their roots.
55

GUIDELINES
• To determine the starting location for molar access
cavity preparations, establish the mesial and distal
boundary limitations.
• Evaluation of Bite-wing radiographs is an accurate
method.
• The mesial boundary for both the maxillary and
mandibular molars is a line connecting the mesial cusp
tips.
• Distal boundary for maxillary molars-The Oblique
Ridge
• For Mandibular molars- a line connecting the buccal
and lingual grooves. 57

GUIDELINES
• Penetration through enamel into the dentin
(approx. 1mm) is performed using #2 round
bur for premolars and #4 round bur for molars.
• Premolar shape is oval and widest
buccolingually.
• Molar shape is triangular (for three canals) or
rhomboid (for four canals) and widest
buccolingually for Max. Molars and
mesiodistally for Man. Molars.
59

GUIDELINES
• Penetration of the Pulp Chamber Roof-
The clinician changes the angle of penetration
from perpendicular to the occlusal table to an
angle appropriate for penetration through the
roof of the pulp chamber.
In premolars- angle is parallel to the long axis of
the roots both in MD and BL direction.
In molars- Penetration angle should be toward
the largest canal, because the pulp chamber
space is large just occlusal to the orifice of this
canal. 60

GUIDELINES
In Maxillary molars- Penetration angle is toward the
palatal orifice.
In Mandibular molars- Penetration angle is towards
the distal orifice.
If the drop-in effect is not felt at this depth, carefully
evaluate the angle of penetration before drilling
deeper.
In multirooted posterior teeth, guard against lateral
and furcation perforations.
Aggressive probing with endodontic explorer can
help locate the pulp chamber.
61

GUIDELINES
• Complete Roof Removal-
 A round bur, tapered fissure bur, or a safety tip
diamond or carbide bur is used to remove the roof
of the pulp chamber completely, including all
pulp horns.
In vital cases pulp tissue hemorrhage can impair
the clinician’s ability to see the internal anatomy.
The coronal pulp should be amputated at the
orifice level with an endodontic spoon and
chamber irrigated copiously with sodium
hypochlorite. 62

GUIDELINES
 If hemorrhage continues, a tentative canal
length can be established measuring the preop
radiograph.
A small broach coated with chelating agent
then can be introduced into the canal and
rotated, which amputates the radicular pulp at
a more apical level, followed by irrigation.
 The goal is to funnel the corners of the access
cavity directly into the orifices.
63

GUIDELINES
• Identification of all canal orifices-
In posterior teeth with multiple canals, the canal
orifices play an important role in determining the
final extensions of the external outline form of the
access cavity.
 Ideally, the orifices are located at the corners of
the final preparation to facilitate the shaping and
cleaning process.
 Internally, acccess cavity should have all orifices
positioned entirely on the pulp floor and should
not extend into an axial wall. 65

GUIDELINES
• Removal of the Cervical Dentin Bulges and Orifice
and Coronal Flaring-
In posterior teeth the internal impediments are the
cervical dentin bulges and the natural coronal canal
constriction.
The cervical bulges are shelves of dentin that
frequently overhang orifices in posterior teeth,
restricting access into root canals and accentuating
existing canal curvatures.
 These bulges can be removed with safety tip
diamond or carbide burs or GG Burs. (Fig 7-53, C,D)
67

GUIDELINES
• Straight line Access Determination-
Straight line access is paramount to successful
shaping.
 Files must have unimpeded access to the
apical foramen or the first point of canal
curvature to perform properly during shaping
and cleaning.
69

GUIDELINES
• Visual Inspection of the Access Cavity-
 The clinician should inspect and evaluate the
access cavity using appropriate magnification
and illumination.
 The axial walls at their junction with the
orifice must be inspected for grooves that
might indicate an additional canal.
 The orifice and coronal canal must be
evaluated for a bifurcation.
70

GUIDELINES
• Refinement and Smoothening of the
Restorative Margins-
 In both temporary and interim permanent
restorations, the restorative margins should be
refined and smoothed to minimize the
potential for coronal leakage.
 The final permanent restoration of choice for
posterior teeth that have undergone root canal
therapy is a crown or onlay.
72

MORPHOLOGY AND ACCESS
CAVITY PREPARATIONS FOR
INDIVIDUAL POSTERIOR TEETH
73

MAXILLARY FIRST PREMOLARS
• ANATOMY AND MORPHOLOGY-
 From the occlusal aspect the tooth resembles
roughly a hexagonal structure, and it is much
broader BL than MD.
 As more of the buccal cusp is seen the access
preparation is angled buccally into the cervical
area.
 There is a well-defined developmental groove in
the enamel of MMR that runs into the central
groove on the occlusal table. 74

It must be assumed that at least two canals are
present, and the third canal is shown to exist in
high enough numbers that the access
preparation must be designed to search for
it(either MB or DB).
 When three canals are present, the pulp
chamber morphology resembles that of a
maxillary molar, and they are termed as ‘Mini-
Molars’
MAXILLARY FIRST
PREMOLARS
75

MAXILLARY FIRST PREMOLARS
• CLINICAL-
The point of entry is centrally in the fossa,
aiming at the center point at the CEJ.
 The outline is an elongated slot and can
extend almost to the cusp tips depending on
the angle.
 If three canals are found, the orientation is
very similar to that of the maxillary molar.
77

MAXILLARY SECOND PREMOLAR
 The occlusal table is very similar to that of
the first premolar, presenting without a
depression in the mesial root surface.
 It has a more rounded crown form and has a
single root.
 The incidence of two canals is significantly
less but when present they are not spaced so
far apart from each other.
79

MAXILLARY FIRST MOLAR
 It is the largest tooth in volume and one of the
most complex in root and canal anatomy.
 It has four well defined cusps and a supplemental
cusp of carabelli of the mesiolingual cusp.
 From occlusal view, it has roughly rhomboidal
outline.
 The oblique ridge crosses the occlusal surface
from the ridge of the DB cusp to the distal ridge
of the ML cusp. 82

 The palatal canal orifice is centered palatally.
 Distobuccal orifice is near the obtuse angle of the
pulp chamber floor.
 The main mesiobuccal canal orifice (MB-1) is
buccal and mesial to the distobuccal orifice and is
positioned within the acute angle of the pulp
chamber.
 The second mesiobuccal canal orifice (MB-2) is
located palatal and mesial to the MB-1.
 A line drawn to connect the three main canal orifices
forms a triangle, known as the Molar Triangle.
83

The three individual roots of the Maxillary first
molar form a tripod.
The palatal root is the longest, has the largest
diameter, and generally offers the easiest access.
It can contain 1,2,3 root canals.
 Palatal root often curves buccally at the apical
one-third.
 From its orifice, the palatal canal is flat, ribbon
like and wider in a MD direction.
The distobuccal root is conical and may have
one or two canals. 84

 The mesiobuccal root has generated more
research and clinical investigation than any
other root in the mouth.
 It may have 1,2 or 3 root canals.
 A single mesiobuccal canal is oval and wider
buccolingually; two or three canals are more
circular.
 A concavity exists on the distal aspect of the
MB root, which makes the wall very thin. 87

• The DOM has been used to study the location
and pathway of the MB-2 canal in maxillary
first and second molars.
• The canal is generally located mesial to or
directly on a line between the MB-1 and
palatal orifices, within 3.5mm palatally and
2mm mesially of the MB-1 orifice.
• Not all MB-2 orifices lead to a true canal.
• A true MB-2 orifice was present only 84% of
molars in which a second orifice was identified.89

• Negotiation of MB-2 canal often is difficult.
• A ledge of dentin covers its orifice, the orifice has a
mesiobuccal inclination on the pulp floor, and the
canal’s pathway often takes one or two abrupt
curves in the coronal part of the root.
• Most of these obstructions can be eliminated by
troughing or counter-sinking with ultrasonic tips
mesially and apically along the mesiobuccal pulpal
groove.
• Troughing may need to be 0.5 to 3mm deep.
91

• Because Maxillary 1st
Molars always has four
canals, access cavity has a rhomboid shape.
• Access cavity should not extend into the
Mesial Marginal Ridge.
• Distally, the preparation can invade the mesial
portion of oblique ridge.
• The buccal wall should be parallel to a line
connecting the MB-1 and DB orifices and not
to the buccal surface of the tooth.
93

MAXILLARY SECOND MOLAR
• Coronally, the maxillary second molar closely
resembles the Maxillary first molar.
• The distinguish morphologic feature of the
maxillary second molar is that its three roots
are grouped closer together and are
sometimes fused.
• 2nd
molar usually has one canal in each root;
however it may have two or three mesiobuccal
canals, one or two distobuccal canals, or two
palatal canals. 96

• The three main orifices (MB,DB,P) usually
form a flat triangle and sometimes almost a
straight line.
• The mesiobuccal canal orifice is located more
to the buccal and mesial than in the first molar.
• The distobuccal orifice approaches the
midpoint between the MB and palatal orifices.
• The palatal orifices is located at the most
palatal aspect of the root.
99

• The floor of the pulp chamber is markedly
convex, which gives the canal orifices a slight
funnel shape.
• When four canals are present, the access
cavity preparation has a rhomboidal shape.
• If only three canals are present, it is a
rounded triangle with the base to the buccal.
100

MAXILLARY THIRD MOLAR
• Loss of Maxillary 1st
molar and 2nd
molar often
is the reason the 3rd
molar must be considered
as a strategic abutment.
• Fully functioning mandibular 3rd
molar in an
arch that has sufficient room for full eruption
and oral hygiene.
• Can have one to four roots and one to six
canals, and C-shaped canals also can occur.
• 3rd
molar usually has three roots and three root
canals. 102

MAXILLARY THIRD MOLAR
• The access cavity form for the 3rd
molar can
vary greatly.
• Because the tooth typically has one to three
canals, the access preparation can be anything
from an oval that is widest in the BL
dimension to a rounded triangle similar to
Maxillary 2nd
Molar.
104

MANDIBULAR FIRST PREMOLAR
• As a group, Mandibular premolars are very
difficult to treat.
• Extreme variations in root canal morphology.
• The root canal system is wider BL than MD.
• Two pulp horns are present: a large pointed
buccal horn and a small, rounded lingual horn.
• At the cervical line, the root and canal are
oval; this shape tends to become round as the
canal approaches the middle of the root.
106

• If two canals are present, they tend to be
round from the pulp chamber to their
foramen.
• In another anatomic variation, a single broad
root canal may bifurcate into two separate
root canals.
• The lingual inclination of the crown tends to
direct files buccally, making location of a
lingual canal orifice more difficult.
• Extend the lingual wall of access cavity107

• The oval external outline form typically is
wider MD than its maxillary counterpart,
making it more oval and less slot shaped.
• Because of the lingual inclination of the
crown, buccal extension can nearly approach
the tip of the buccal cusp to achieve SLA.
• Lingual extension barely invades the poorly
developed lingual cusp incline.
109

MANDIBULAR SECOND PREMOLAR
• The mandibular 2nd
premolar is similar to the 1st
premolar with the following differences-
• Pulp chamber is wider BuccoLingually.
• Separation of pulp chamber and root canal
normally is distinguishable.
• Canal Morpholgy variations: Two, three and
four canals and a lingually tipped crown.
111

MANDIBULAR SECOND PREMOLAR
• The access cavity form varies on at least two
ways in its external anatomy.
• First, because the crown typically has a
smaller lingual inclination, less extension up
the buccal cusp incline is required to achieve
SLA.
• Second, the lingual half of the tooth is more
fully developed, therefore the lingual access
extension typically is halfway up the lingual
cusp incline. 113

MANDIBULAR FIRST MOLAR
• Earliest permanent posterior tooth to erupt,
most often requires RCT.
• It is often extensively restored, and it is
subjected to heavy occlusal stress. Therefore
the pulp chamber frequently has receded or
calcified.
• The tooth usually has two roots, but
occassionally it has three, with two or three
canals in the mesial root and one, two or three
canals in the distal root. 115

• The canals in the mesial root are the MB and
ML canals; a middle mesial (MM) canals
sometime is present in the developmental
groove between the MB and ML canals.
• The incidence of MM canals ranges from 1%
to 15%.
• Orifices to all canals are loacted in the mesial
two-thirds of the crown, and the pulp chamber
floor is roughly trapezoid or rhomboid.
116

• The presence of two separate distal roots is rare
but does occur; in such cases DL root is smaller
than DB root and more curved.
• The mesial roots, the wider of the two, curves
mesially from the cervical line to the middle third
of the root and then angles distally to the apex.
• The buccal and lingual surfaces are convex
throughout their length, whereas the distal surface
of mesial root and mesial surface of distal root
have a root concavity, which makes the dentin
wall thin. 117

• The mesial canal orifices are usually well
separated within the main pulp chamber and
connected by a developmental groove.
• The MB orifice is under the MB cusp whereas
the ML orifice is found just lingual to the
central groove.
• An MM canal orifice is present in the groove
between the MB and ML orifices.
120

• If three root canals are present in this tooth,
each is oval in the cervical and middle thirds
of the root and round in the apical third.
• If two canals are present in the distal root,
they usually are more round than oval for
their entire length.
• The mesial root canals usually are curved,
with the greatest curvature in the MB canal.
121

• Multiple accessory foramina are located in the
furcation of the mandibular molars.
• The access cavity typically is trapezoid or
rhomboid regardless of the number of canals
present.
• Mesially, the access need not invade the marginal
ridge.
• Distal extension must allow SLA to the distal
canals.
• Buccal wall forms a straight connection between
MB and DB orifices, and lingual wall connects
the ML and DL orifices without bowing.
122

MANDIBULAR SECOND MOLAR
• It is somewhat smaller coronally than the 1st
molar and tends to be more symmetric.
• Proximity of its roots; the two roots often
sweep distally in a gradual curve, with the
apices close togther.
• Studies shows 100% of the specimens showed
curvature in both lingual and mesiodistal
views.
124

• The pulp chamber and canal orifices generally
are not as large as those of the first molar.
• May have one, two, three or four root canals.
• The two mesial orifices are located closer
together.
• The apices of this tooth are very close to the
mandibular canal; not to allow instruments or
filing material to invade this space, because
paresthesia may result.
126

• May have one to six canals, although the most
prevalent configurations are two, three and
four canals.
• When three canals are present, the access
cavity is very similar to that for the mandibular
1st
molar.
• Distal orifice is less often ribbon shaped BL.
• For a two canal 2nd
molar, access cavity is
rectangular, wide MD and narrow BL.
• Single canal-Oval and lined up in the center. 128

• Four types of pulp floor were found in Mandibular
second molars-
 Type I- A peninsula like floor with continuous C-
shaped orifce.
 Type II- A buccal, striplike dentin connection
between the peninsula-like floor and the buccal wall
of the pulp chamber that separates the C-shaped
groove into mesial and distal orifices.
 Type III- Only one mesial, strip like dentin
connection exists between the peninsula like floor
and the M wall, which separates the C-shaped groove
into a small ML orifice and a large MB-D orifice.
 Type IV- Non C-shaped floors. 129

THREE TYPES OF C-SHAPED CANAL
SYSTEMS IN MAND. 2ND
MOLAR
130

MANDIBULAR THIRD MOLAR
• It is anatomically unpredictable and must be
evaluated on the basis of its root formation.
• Fused, short, severely curved, or malformed
roots often support well-formed crowns.
• May have one to four roots and one to six
canals.
• C-shaped canals can occur.
• Anatomy is very unpredictable; access cavity
can take any of several shapes. 133

MANDIBULAR THIRD MOLAR
• Three or more canals- Rounded
triangle/Rhomboid shape.
• Two canals- Rectangular shape.
• Single canal- Oval shape.
• Most of these teeth are endodontically treated
successfully; however, long term prognosis is
determined by the root surface volume in
contact with bone.
• Benefit of treatment v/s Prognosis. 134

TEETH WITH C-SHAPED
ROOT CANAL SYSTEMS
• The C-shaped root canal system was first
reported in 1979.
• Most C-shaped canals occur in the Mandibular
second molar, but they also have been reported
in the mandibular 1st
molar, Maxillary 1st
and 2nd
molar, Mandibular 1st
premolar.
• C-shaped mandibular molars are so named
because of the cross-sectional morphology of
their roots and root canals.
137

TEETH WITH C-SHAPED
ROOT CANAL SYSTEMS
• Instead of having several discrete orifices, the
pulp chamber of a molar with a C-shaped root
canal system is a single, ribbon-shaped orifice
with an arc of 180 degrees or more.
• It starts at the mesiolingual line angle and
sweeps around either to the buccal or the
lingual to end at the distal aspect of the pulp
chamber.
138

TEETH WITH C-SHAPED
ROOT CANAL SYSTEMS
• Below the orifice, the root structure can show
a wide range of anatomic variations:
Single, ribbonlike, C-shaped canal from orifice
to apex.
 Three or more distinct canals below the usual
C-shaped orifice.(More Common type)
• Fortunately, Molars with a single swath of
canal are the exception rather than the rule.
139

TEETH WITH C-SHAPED
ROOT CANAL SYSTEMS
• The main cause for C-shaped roots and canals
is the failure of Hertwig’s epithelial root
sheath to fuse on either the buccal or lingual
root surface.
• The original classification has been modified
and has produced a more detailed description
of C-shaped root canal morphology.
140

• Category I (C1): The shape is an uninterrupted
C with no separation or divison.
• Category II (C2): The canal shape resembles a
semicolon resulting from a discontinuation of
the C outline, but either angle α or β should be
no less than 60 degrees.
• Category III (C3): Two or three separate canals
and both angles α and β, are less than 60
degrees.
• Category IV (C4): Only one round or oval
canal is in the cross-section.
• Category V (C5): No canal lumen is observed.142

CONCLUSION
ERRORS IN ACCESS CAVITY PREPARATION
• Successful endodontic treatment originates
from a well designed and executed access
preparation.
• The opposite is also true; errors during root
canal treatment can often be traced back to a
problem originating from an inadequate access
preparation.
• Errors generally stem from two access cavity
characteristics: underextension and
overextension. 144

“ The journey of a thousand miles begins
with a single small step.”
- Lao Tzu
149

Access Cavity Preparation Posteriors

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