Nicholas Yik Tao TsangBDS II, Class of 2013, HKU

Step 1: occlusal preparation The critical requirements of this step

are:1.Ensure conservation of as much tooth structure as possible2.Creating a retention form that will hold the restoration material3.Creating depth of 1.5mm to 2.0mm in order to retain amalgam restoration

Procedure: Using a 330 bur on a high speed handpiece, an occlusal cavity is prepared on the occlusal surface of the 36. The preparation does not cross the midline of the tooth for req. 1.; its most central aspect has a dove-tail for enhancing req. 2; the distal aspect is 1.4mm in width, while isthmus at the midpoint of preparation is approximately 0.8mm for req. 1.

Fig. 1: Occlusal preparation

The first step in my preparation involves creating a occlusal cavity preparation.

midlinedove-tailisthmus

Step 1: occlusal preparationPurpose of requirements:

1.The purpose of ensuring conservation of tooth structure is in line with the more modern approaches of conservative dentistry that only carious structure should be removed, as to maintain the overall integrity of the tooth. By creating an occlusal preparation with a width of 1.4mm at the most distal aspect and 0.8mm at the isthmus, minimal amount of tooth structure is removed while providing adequate space for condensers (i.e. Mortonson) to pack amalgam restoration into the preparation in this idealized situation.2.Since amalgam restoration does not have any chemical retentive factors (unless bonded amalgam), retention in the physical sense, in the form of a dove-tail, must be created. Also, the 330 bur is wider in diameter at the tip, therefore, the pulpal floor of the preparation is wider (shown in Fig. 8) than the outline form that can be seen in the picture. This creates a slight undercut that acts as a retentive factor for the amalgam restoration.3.A 1.5 to 2.0 mm deep preparation (shown in Fig. 3 and Fig. 4) is for adequate physical retention of amalgam restoration.

Step 2: mesial extensionThis step in my preparation involves extending the occlusal preparation mesially, to the edge of the marginal ridge

Fig. 2: Occlusal preparation with mesial extension

The clinical requirements of this step are:1.Ensure conservation of as much tooth structure as possible and creation of a retentive form2.Create a reverse S shape to ensure breaking of contact point while minimizing mesio-buccal cusp

Procedure: Using a 330 bur with a high speed handpiece, the occlusal preparation is extended to the mesial marginal edge. The width of the mesial extension is approximately 2.5mm, to ensure enough retentive factor due to increased occlusal force at the marginal ridge, while not too wide to conserve sound tooth structure. The reverse S outline is created at the buccal and lingual aspects of the extension to ensure req. 2.

Reverse S

Evaluation of depth

Fig. 3: Periodontal probe is positioned in the mesial extension

Fig. 4: Periodontal probe is positioned in the mesial extension

From Fig. 3 and Fig 4, the height of the occlusal cavity is shown to be approximately 2.0mm, which satisfies the clinical requirement in step 1: occlusal preparation that depth of the occlusal preparation should 1.5 to 2.0mm to ensure adequate retention of amalgam restoration.

Step 3: mesial boxThis step in my preparation involves creating a mesial box from the mesial extension

Fig. 5: Mesial box is created at the mesial extension

The clinical requirements of this step are:1.Create a box that is 3.0 to 4.0 mm in depth2.Create a slight undercut at buccal and lingual wall of mesial box3.Ensure that the axial wall is parallel to the mesial edge

Procedure: Switching to a 256 bur, the mesial extension is deepened apically to form a mesial box. First, two holes of optimal depth are created at the buccal and lingual ends of the mesial extension, and from there, the tooth structure in between is removed. This procedure is my personal preference because the 256 bur is longer and wider than the 330 bur, thereby allowing me to gain access apically easier. Remaining unsupported enamel is thereafter removed. The walls and gingival floor of the box is finished with hatchets and gingival margin trimmers.

Evaluation of depth

Fig. 6: Periodontal probe placed on gingival floor of mesial box reveals a depth of 3.0mm

Fig. 7: After removal of unsupported enamel, periodontal probe shows the gingival floor is 3.0mm deep

Fig. 8: Periodontal probe is place on the floor of the occlusal preparation to show it is 2.0mm deepNote that in Fig. 7 and Fig. 8, the buccal and lingual walls of the

mesial box as well as the walls of the occlusal preparation are slightly undercut, which are there to provide adequate retention factors for the amalgam restoration.

Undercuts

Step 4: applying matrix bandThis step involves applying a matrix band for amalgam insertion

The clinical requirements of this step are:1.Ensure a tight fit of the matrix band around the tooth to be restored2.Ensure proper adaptation of the matrix band to the mesial box

Procedure: Using a Tofflemire matrix retainer , a Tofflemire universal matrix band is placed on the tooth and tightened into place to ensure req. 1. A wooden wedge is then positioned into the interproximal space between the 35 and 36 to adequate adapt the universal matrix band onto the mesial box.

Fig. 9: An universal matrix band tightened around 36 using a matrix retainer, with wooden wedge

Step 5: amalgam insertionThis step involves inserting the amalgam restoration material into the prepared cavity.

The clinical requirements of this step are:1.Ensure amalgam is tightly packed into the cavity2.Ensure marginal ridge of restoration remains intact

Procedure: Amalgam restoration material is prepared and is first inserted into the gingival floor of the mesial box up to the point of the floor of the occlusal preparation. A Mortonson condenser is used to pack the amalgam into place. Then the remainder of the cavity is filled, to a point of excess.

Fig. 10: Amalgam is inserted and packed into the prepared cavity

Step 6: carving amalgamThis step is to burnish the amalgam to adapt properly with the cavity walls, while carving it to produce grooves and cuspal features similar to those found of a sound tooth.

Fig. 11: Top view of amalgam restoration

Fig. 12: Off-angled top view of amalgam restoration

The clinical requirements of this step are:1.Ensure the marginal ridge is intact after burnishing and carving2.Ensure grooves and cuspal features are similar to that on sound tooth.

Procedure: A ball burnisher 155 is first used to adapt the restoration with the cavity walls. Then, a Hollenbach carver is used to carve the required cuspal features and grooves.

Step 7: polishing amalgamThis step

involves polishing the amalgam to create a smooth and lustrous finish.The clinical requirements of this step are:1.Ensuring all scratches and roughness on restoration’s surfaces are gone to eliminate plaque retentive areas.

Procedure: After a wait of 24 hours, the amalgam is polished using a slow speed handpiece with an amalgam polishing kit. Tungsten-carbide burs are first used to reshape the cusps and define the grooves. Then, abrasive burs, from coarse to fine, are used to gradually reduce scratches. Finally, plastic burs are used to achieve the shiny brilliance. Sandpaper strips, coarse to fine, are used to polish the interproximal area.

Fig. 13: Amalgam restoration after polish

Fig. 14: Amalgam restoration after polish

Reflection:Major problems in preparation:• In order to protect the 35 from damage when creating the mesial box, a Tofflemire universal matrix was placed around it. This caused a visual impairment because the part of the matrix would obscure the mesial marginal ridge from direct view. To go around this, I had to use indirect vision with a mirror, combined with tactile sense of my bur to create the mesial box. This was difficult because water spray would quickly cover the mirror and I had to rely on mainly tactile sense. However, the difficulty reduces with practice as I found more adequate positions for the mirror with less water spray and my tactile sense improved.• Adaptation of the matrix band to the tooth was rather difficult because even when tightened fully, the matrix band does not perfectly adapt to the mesial box of the cavity preparation such that all edges of box are touching the matrix band. Manually contouring a curve into the matrix band with a ball burnisher helped slightly, but still did not perfectly adapt the matrix band to the tooth. This resulted in excess amalgam at the interproximal region that had to be gradually removed by abrasive amalgam polishing strips.• If grooves have been cut into the amalgam using tungsten-carbide burs, the plastic polishing burs may not be narrow enough to reach the entire depth of the groove, making this area difficult to polish completely. A periodonotal probe was therefore used to access and burnish the grooves.

Reflection:Other points to note:•During the creation of the mesial box in step 3, I switched to using a 256 bur because its larger diameter and longer length provides easier access when deepening the mesial extension to required depth.•Using sandpaper abrasive strips to polish the amalgam at the interproximal area can be quite a tedious process, as it requires both manual dexterity and many back-and-forth repetitions of all the strips of different roughness. In fact, 3 different strips were used – one was very coarse and is metallic, and is intended for polishing amalgam, while the other two were coarse and fine strips are intended for polishing composite resin. I chose to use the strips for composite resin as well because they are finer than the metallic strip for amalgam, and thus can give me a smoother finish.

•Conclusion: Overall, my class II preparation went fairly smoothly besides the two difficulties listed above. I believe with more practice, I can develop more speed and accuracy in performing similar cavity restorations in the future.

References

Kidd, E., Smith, B., Watson, T. (2003). Pickard’s Manual of Operative Dentistry (8th ed.). United States: Oxford University Press.

Summitt, J., Robbins, J., Schwartz, R. (2000). Fundamentals of Operative Dentistry (2nd ed.). Singapore: Quintessence Publishing.