Preclinical conservative dentistry involves students gaining expertise in restorative procedures by practicing on plaster tooth models and extracted teeth before treating patients. It covers tooth preparation classifications, defining features like cavosurface angles and walls, and the steps of tooth preparation including outline form, resistance/retention forms, removal of carious dentin, and finishing preparation walls. The goal is to develop student confidence and skills in restorative techniques before clinical work.

1. Introduction to Preclinical
Conservative Dentistry

3. Definition
• Operative dentistry is art and science of dentistry which deals with
diagnosis, treatment and prognosis of defects of the teeth which do
not require full coverage restorations for correction. Such treatment
should result in the restoration of proper form, function and esthetics
while maintaining the physiologic integrity of the teeth in harmonious
relationship with the adjacent hard and soft tissues, all of which
should enhance the general health and welfare of the patient”

6. • Basic purpose of preclinical conservative dentistry is to make the
students to gain expertise for restorative procedures before handling
the patient. This develops confidence in the student before they
manage the patient.

7. • To have knowledge about anatomy of teeth
• To gain expertise for restorative procedures before handling the
patient in simulated clinical conditions
• To gain expertise for restorative procedures before handling the
patient by performing restorative procedures in simulated clinical
conditions
• To gain expertise for manipulation of different dental materials
• To have knowledge of different instruments used in restorative
dentistry
• To understand the fundamentals of tooth preparation.

8. Armamentarium

9. Tooth Preparations on Plaster Models
• Before going for tooth preparation on typhodonts or extracted teeth,
it is advisable to practice on plaster models.
• These plaster models are prepared by pouring plaster of paris in
readymade tooth moulds

11. Tooth preparation
• Tooth preparation is the mechanical alteration of a defective, injured
or diseased tooth in order to best receive a restorative material which
will re-establish the healthy state of the tooth including esthetic
correction when indicated along with normal form and function.

12. • Tooth preparation is done for
• Treatment of carious tooth
• Treatment of old and defective restorations
• Treatment of malformed and fractured tooth
• Aesthetic correction

13. Classification GV Black

14. • Class I: Pit and fissure preparations occur on the occlusal surfaces of
premolars and molars, the occlusal two-third of buccal and lingual surface
of molars and lingual surface of incisors
• Class II: Preparations on the proximal surface of premolars and molars are
class II
• Class III: Preparations on the proximal surface of anterior teeth and not
involving the incisal angles are class III
• Class IV: Preparations on the proximal surface of anterior teeth also
involving the incisal angle falls under class IV
• Class V: Preparations on gingival third of facial and lingual or palatal
surfaces of all teeth came under Class V

20. • Class VI: Preparations on incisal edges of anterior and cusp tips of
posterior teeth without involving any other surface

21. DEFINITIONS
• Simple Tooth Preparation
• A tooth preparation involving only one tooth surface is termed simple
preparation for example, occlusal preparation.

22. • Compound Tooth Preparation
• A tooth preparation involving two surfaces is termed as compound
tooth preparation , for example, mesio-occlusal or disto-occlusal
preparation

23. • Complex Tooth Preparation
• A tooth preparation involving more than two surfaces is called as
complex tooth preparation for example, MOD preparation.

24. Walls
• Internal Wall
• It is a wall in the preparation, which is not extended to the external
tooth surface
• External Wall
• An external wall is a wall in the prepared tooth that extends to the
external tooth surface

25. • Pulpal Wall
• A pulpal wall is an internal wall that is towards the pulp and covering
the pulp
• Axial Wall
• It is an internal wall which is parallel to the long axis of the tooth

26. • Cavosurface Angle Margin
• Cavosurface angle is formed by the junction of a prepared tooth
surface wall and external surface of the tooth . The acute junction is
referred to as preparation margin or cavosurface margin

27. • Line Angle
• It is a junction of two surfaces of different orientations along the line.
Its name is derived from the involved surfaces.
• Point Angle
• It is a junction of three plane surfaces or three line angles of different
orientations. Its name is derived from its involved surfaces or line
angles.

28. • NUMBER OF LINE AND POINT ANGLES
• Number of line angles and point angles in different tooth
preparations are enumerated as
Table 8.1 ̈Number of line angles and point angles in different tooth preparation designs
Type of tooth preparation Line angles Point angles
Class I 8 4
Class II 11 6
Class III 6 3
Class IV 11 6
Class V 8 4

31. • Steps in Tooth Preparation
• Stage I: Initial tooth preparation steps
• – Outline form and initial depth
• – Primary resistance form
• – Primary retention form
• – Convenience form.
.

32. • Stage II: Final tooth preparation steps
• infected dentin and/or old restorative material, if
• indicated
• – Pulp protection, if indicated
• – Secondary resistance and retention form
• – Procedures for finishing the external walls of the
• tooth preparation
• – Final procedures: Cleaning, inspecting and sealing.
• Under special conditions these sequences can be changed

33. INITIAL STAGE
Outline Form and Initial Depth
• Outline form means:
• Placing the margins in a position that they will occupy in the final
tooth preparation
• maintaining the initial depth in .2 to .8mm into dentin
• Extend the cavity margins to sound tooth structure and remove all
unsupported enamel. Include all susceptible fissures in the outline
form. This phenomenon of 'Extension for Prevention' was first
suggested by Marshall Ebb and was later adopted by Black.

34. • Two cavities having less than 0.5 mm of sound tooth structure
between them should be joined.
• Cavity margins should not terminate in high stress areas, such as cusp
heights or ridge crests.
• Extend the margins to allow sufficient access for cavity refinement,
restoration placement and finishing procedures.

36. Resistance and Retention Forms
• 'Resistance form' may be defined as that shape and configuration of
the cavity that best enables both the restoration and the tooth to
withstand occlusal forces without fracture.
• The resistance form is in direct relation to the degree of exposure of
the restoration to the occlusal forces.

37. • There are some fundamental factors, which are to be followed in
obtaining resistance form, which are as follows:
• a. The cavity should be prepared as a box with a flat floor. Flat floor
resists the occlusal stresses, being at right angle to such forces

38. • Cusps and ridges should not be undermined. When a fissure is cut,
the cavity margin should extent to 1/3rd the distance from the central
groove to cusp tip.
• Weakened tooth structure should be enveloped or included in cavity
form
• Roundening of line angles avoids stresses directly on to the tooth,
thereby resistance to fracture is increased. The sharp line angles lead
to poor resistance form

39. • The minimal thickness of amalgam and cast gold to resist fracture is
approximately 1.5 mm, though little more depth is required for
amalgam to achieve the requisite bulk.

40. • Retention form' may be defined as the shape and configuration of the
cavity that enables the restoration to be retained in that cavity under
all types of tipping and tilting stresses.
• For silver amalgam, the retention form is achieved by:
• Converging the walls occlusally (both for class I and class II cavities)
• Marginal ridge is to be conserved
• Slight undercuts can be given in the dentin
• Occlusal Dovetail Prepration

42. • Convenience Form
• Definition
• The convenience form is that form which facilitates and provides
adequate visibility, accessibility and ease of operation during
preparation and restoration of the tooth.

43. • features of Convenience Form
• Sufficent extension of distal facial mesial and lingual walls to gain
adequate access to the deeper portion of the prepration
• Cavosurface margins of the restoration should be related to the
selected restorative material for the
• This is the form of the cavity, which visualizes lesion more clearly. The
shape of the cavity is modified so as to have proper access to the
lesion, better manipulation during restoration and finally for better
finishing and polishing. This form is required mostly in proximal
cavities.

44. Final tooth preparation steps
• Removal of Remaining Carious Dentin
• Elimination of any infected carious tooth structure or faulty
restoration left in the cavity preparation is the fourth principle. case
soft and infected caries should be left over the pulp. Such residual
caries leads to pulpal inflammation and subsequently slow death of
pulp.

46. • Pulp Protection
• Pulp protection is a very important step in adapting the preparation
for final restoration although actually it is not a step of tooth
preparation.
• When remaining dentin thickness is less, pulpal injury can occur
because of heat production, high speed burs with less effective
coolants, irritating restorative materials, galvanic currents due to
restoration of dissimilar metals, excessive masticatory forces
transmitted through restorative materials to the dentin and ingress of
microorganisms and their noxious products through microleakage.

48. • Secondary Resistance and Retention Forms
• Grooves and Coves
• Coves are small conical depressions prepared in healthy dentin to
provide additional retention. These are normally prepared in the
proximal walls of class II preparations at the axiofacial and axiolingual
line angles, thus reducing proximal displacement of the restoration.

49. • Slot or Internal Box
• dentin to increase the surface area. These are prepared in occlusal
box, buccoaxial, linguoaxial and gingival walls

50. • Locks
• Locks are usually prepared for class II amalgam restorations for
increasing resistance and retention form

51. • Pins
• Different pins of various size and shape to provide additional
retention in amalgam, composite and cast restorations.

52. • Skirts
• Skirts are prepared for providing additional retention in cast
restorations. They increase the total surface area of the preparation.

53. • Amalgapins
• Amalgapins are vertical posts of amalgam anchored in dentin. Dentin
chamber is prepared by using inverted cone bur in the gingival floor

54. • Finishing the External Walls of the Tooth Preparation
• Finishing of a tooth preparation walls is further development of a
specific cavosurface design and degree of smoothness which
produces maximum effectiveness of the restorative material being
used.
• It helps to provide
• Better marginal seal b/w tooth and restoration

55. • Final Procedures: Cleaning, Inspecting and Sealing
• Final step in tooth preparation is cleansing of the preparation. This
includes the removal of debris, drying of the preparation, and final
inspection before placing restorative materials.
• It is achieved by
• Cleaning the prepared tooth surface using warm water
• alcohol free disinfectant: Use of mild disinfectant in tooth preparation
serves the purpose of disinfection.