Dental Cavity Preparation Techniques

Cavity Preparation (I-V)

• Students and listeners are reminded that lecture/seminar information cannot be copied, recorded, or distributed without the author's consent.

• Preparation rules and recommendations exist for each cavity class (I-V), with different restorative materials used.

  • Composite resin
  • Amalgam
  • GIC

• Initial teeth preparation skills are practiced on phantom teeth. This simulates experience with real teeth, allowing practice of cutting enamel and dentine, and composite bonding techniques

• Natural teeth need cleaning and placing in sodium hypochlorite 0.5% for preparation.

• The teeth are placed in hermetically sealed containers, and solution should be changed every two weeks.

• Cavities on models are prepared following recommendations and theoretical rules of resistance for restoring the tooth.

• In clinical practice, cavity shape may differ from models, based on caries spread and previous restorations.

• The models depict the process clearly, and theoretical recommendations are followed during preparation.

• There are different types of cavity preparations.

  • Conventional preparation (retention form, special requirements)
  • Conventional with bevels (amalgam restoration replaced by composite).
  • Modified preparation (for composite resins)
  • Minimally invasive preparation (biomimetic restorative technique)

• Rules for establishing outline form include.

  • Extending margins until sound enamel is reached
  • Avoiding margin on cusp heights or ridge crests
  • Minimizing reduction in cases of grooves extending more than one-third of cusp tip distance

• The theoretical recommendations for preparation are to ensure a consistent structure as cavities can be imagined in the models.

• Typical outlines for preparation should be rounded without sharp angles, keeping two occlusal cavities separate unless necessary, and preserving the transverse ridge between cusps. Extending the outline must consider efficient access for restorative work.

• outlines are further described on buccal and palatal surfaces.

• If the marginal ridge does not meet the 1.5 mm standard, class II preparation is considered.

• The depth must be minimal 1.5 mm if amalgam needed, for support when there's load from opposing tooth.

• The preparation width should not exceed ⅓ of the distance between facial and lingual cusp tips to avoid fracture.

• A correct bur position is essential, enabling preparation of parallel or converging walls.

• Retention is achieved through a slight convergence of axial walls.

• Cavity excavation requires a low-speed round carbide bur, with hard dentin left if the cavity is deep.

• Enamel margins are prepared at a 90° angle to enamel rods with sound dentin underneath.

• Unsupported enamel is not resistant.

• Class I preparation is to be as narrow as possible without enamel beveling in the occlusal fissure area, with the removal of unsupported enamel. General preparation requirements are similar to amalgam preparation but not relying on retention form.

• Small cavities with masticatory forces result in small fillings, with increased longevity compared to large fillings

• Cavity preparations for resin composite materials differ from amalgam preparations with different outlines and no retention form.

• Class II preparation involves occlusal and proximal preparation, or slot, with the removal of the lesion from caries or old restorations from the occlusal surface. (slots are usually preferable)

• Initial Class II cuts are made through the marginal ridge with a narrow bur; widen the slot faciolingually to remove the dentin and thinning of the proximal enamel.

• Proximal surfaces of adjacent teeth may be damaged during Class II preparation. Using hand instruments to prevent damage is crucial, along with planning fractured margins.

• Wedges are placed to separate teeth and prevent damage.

• Slot widening is directed faciolingually until caries-free areas are reached.

• The final cavity outline is determined after removing carious structures, providing a minimum of 0.5 mm margin separation from the adjacent tooth for amalgam, extending to the contact area

• The gingival margin is ideally placed supragingivally, with as much healthy enamel preserved as possible

• Unsupported or demineralized enamel is removed with a gingival margin trimmer or bur.

• Occlusal part preparations should be limited to the demineralized area following a conservative outline to save as much structure as possible, with ridges and cusps maintained.

• To resist amalgam fracture the occlusal/interproximal box junction is beveled and cavities are 1.5mm deep. Caries in the fissures extending preparation into the occlusal surface increases retention. The width buccolingually should not exceed 1/3 the distance between the tips of the facial and lingual cusps.

• Faciolingual width of preparation should not exceed a third of the distance between the facial and lingual cusps to avoid fracturing. Cavity excavation of soft dentin follows.

• Retention forms that include occlusal fissure cavities increase retention using walls that converge occlusally and a gingival wall directed axially.

• Secondary retention grooves in the slot preparation are 0.5mm wide and 0.5mm deep and oriented parallel to the DEJ. This is usually done in low-speed situations.

• Large cavities use an alternative restoration to avoid fractures, minimizing the occlusal surface to 2.5mm following its anatomy, including all cusps and covering with amalgam.

• Tissue-saving preparations with pear shapes are used in Class 2 composite restorations to preserve more tissue and have a more conservative outline.

• Step-by-step use of burs for preparation are further explored in image sequences (Class I).

• Clinical example is to place rubber dam, wedge, and metal strip prior to cavity preparation.

• Separating teeth using a WedgeGuard (e.g., Palodent) or a retaining ring facilitates interproximal protection during preparation.

• Enamel preparation on buccal or lingual walls can be beveled for composite restorations.

• Enamel on the gingival wall, if not close to the cervical line, can be beveled for improved composite adaptation and sealing.

• Enamel bevels for Class II (composite) include bevels on buccal and lingual/gingival walls. Adequate enamel may not be present on gingival walls.

• Proximal lesion excavation, with refining preparation and an inverse bevel, enhances enamel rod exposure and gingival margin adhesion.

• Final composite resin preparation stages are described with images.

• Class III cavities are beneath the contact point, often in the middle of the proximal surface. Class III preparation follows a similar outline to Class II, using a facial or lingual approach as appropriate. A rounded form and maintaining sound structure away from adjacent teeth is a key concern.

• Caries extending to dentin cementum requires extra preparation to prevent microleakage, using 0.5-0.7mm depth grooves away from the surface of the root (technically difficult). An adhesive composite restoration is recommended in this type of preparation.

• Enamel bevels for Class III (using glass ionomer cement) do not require grooves or bevels.

• Class IV preparation (fractures or caries spreading to incisal edges) requires sufficient enamel width and preparation at 45-degree angles to allow for retention.

• In the cases of caries, the margins of Class III caries extending to incisoral edges, is prepared with wider bevels onto the vestibular and palatal sides as well.

• Class V preparation has a rounded outline, limited to the demineralized area, shaped as kidney shapes (premolars) or sausage shapes (molars).

• Grooves may be placed to reduce microleakage on gingival walls but doing so is technically difficult and does not retain all healthy dentin.

• Class V for composite preparation prepares with enamel bevel occlusally and then uses acid-etch retention in enamel.

• Minimal preparation is needed for Glass Ionomer cements.

• Summary highlights various considerations for different cavity classes (Class I composite preparation, Class II composite, Class III-IV, Class V for GIC). Key factors include faciolingual width limits, preserving marginal ridges, ensuring adequate enamel width, and appropriate bevels considerations based on whether for Amalgam/Composite or glass-ionomer cements.

Sequence of Burs

• Key anatomical burs and instruments related to cavity preparation are also visually presented.

This quiz focuses on essential techniques and principles of dental cavity preparation. Explore the types of restorative materials and various considerations for effective tooth preparation, including minimally invasive approaches and cavity outline formation. Test your understanding of best practices in dental skill development.