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Self-Learning, Self Assessment 2007 (February 01, 2007)

February 1, 2007
by Oral Health


The SLSA program is based on current, referenced literature and consists of 40 questions, answers, rationales and references. Answers appear in the following issue at the end of each quiz.

Dentists who complete the 15 question quiz in the November, 2007 issue of Oral Health may be eligible to receive continuing education points. The names and license numbers of all who complete the quiz will be forwarded to their respective provincial licensing authorities.

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QUESTION 5

A single implant is required to replace a maxillary central incisor lost in an accident. Which of the following requires assessment?

1. Pattern of bone loss at the site.

2. Alveolar bone volume.

3. Gingival thickness.

4. Periodontal status.

A. 1, 2, 3

B. 1 and 3

C. 2 and 4

D. 4 only

E. All of the above

Rationale

After traumatic loss of a tooth, evaluation of the bone pattern in the area is essential since with accidental tooth loss the facial plate of bone is often unevenly resorbed. There must be sufficient bone and soft tissue volume to allow the implant to be positioned for a predictable esthetic outcome. The periodontal status has to provide optimal health. A thick periodontal tissue biotype with thick, flattened osseous plates gives resistance to recession and is therefore to be preferred to thin gingiva. Coupled with radiographic examination, the osseous contour and gingival thickness should be evaluated under local anaesthesia by measuring to the periosteum with an endodontic probe and a rubber marker. In determining the optimal tooth position for function and esthetics a diagnostic set up with a denture tooth should be made with a suitable wax-up of hard and soft tissue contours. A vacuum formed matrix of this diagnostic aid will help in surgical placement of the implant. It is important to determine whether the patient can open the mouth 35mm or more to allow the surgeon sufficient drilling access in placing the implant in the anterior maxilla. The single tooth implant requires adequate interproximal bone. A 4mm diameter implant requires 8mm of space, i.e. 2mm of bone on either side of the implant. There must also be at least 1mm of facial and lingual cortical bone. Implant length is recommended at 12-16mm. Where bone and or gingival thickness is inadequate, bone or gingival grafting must be considered.

REFERENCES

1.Stanford, C.M.: Application of oral implants to the general dental practice. JADA 136:1092-1100, 2005.

2.Misch, C.E., D’Alessio, R., Misch-Dietsh, F.: Maxillary partial anodontia and implant dentistry. Oral Health, August 45-57. 2005.

QUESTION 6

A posterior crossbite in the primary dentition should be corrected as soon as possible.

A unilateral posterior crossbite in the primary dentition due to functional displacement of the mandible should be corrected as soon as possible.

A. The first statement is true, the second is false.

B. The first statement is false, the second is true.

C. Both statements are true.

D. Both statements are false.

Rationale

Posterior cross bites in the primary dentition commonly arise as a result of a narrow maxilla caused by genetics, environmental influences or a combination of both. Significant maxillary constriction is associated with sucking habits continuing beyond 24 months of age. Nasal obstruction causing mouth breathing also leads to posterior crossbite.

Up to 45% of posterior crossbites in the primary dentition are self-correcting and there is no evidence to support routine correction of crossbites at this stage as opposed to treatment in the mixed dentition. However, a crossbite in the primary dentition with a functional displacement of the mandible requires immediate attention since the lack of correction can lead to long-term detrimental consequences. These include TMJ dysfunction and abnormal facial esthetics. Selective grinding of premature contacts of the primary teeth is a clinically proven treatment for posterior crossbite correction, but some treatment may require symmetric expansion of the maxillary arch, removal of occlusal interferences and elimination of the shift. Early diagnosis of unilateral crossbites is essential to achieve the benefits of treatment.

REFERENCES

1.Malandris, M., Mahoney, E.K.: Etiology, diagnosis and treatment of Posterior Crossbite in the primary dentition. Oral Health, January 27-45, 2005.

2.Kennedy, D.B., Osepchook, M.: Unilateral Posterior Crossbite with Mandibular Shift: A Review. J Can Dent Assoc 71:569-573, 2005.

QUESTION 7

In endodontics, underfilling of the root canal will occur as a result of

1. incomplete instrumentation.

2. inaccurate measurement of the working length.

3. poor irrigation of the canal.

4. ledge formation in the canal.

A. 1,2,3

B. 1 and 3

C. 2 and 4

D. 4 only

E. All of the above

Rationale

Procedural errors in endodontics are not in themselves a direct cause of treatment failure. Instead it is the presence of pathogens in the incompletely treated canal system that is to blame. Studies have shown that although factors such as pulpal and periradicular status, underfilling, overfilling, root perforations, and ledge formation affect the prognosis, only two factors — root canal infection and preoperative periradicular lesions have a direct impact on outcomes. Underfilling often occurs as a result of incomplete instrumentation or from the creation of a ledge during the mechanical phase. Incomplete instrumentation will occur because of inaccurate measurement of the working length or from poor irrigation leading to canal blockage by dentin filings. Ledge formation is mainly the result of inadequate straight- line access to the apical portion of the canal, and from poor irrigation and lubrication. It also results from skipping the sequential file sizes and packing of debris into the apical portion of the canal. Studies indicate that teeth with underfillings have a poorer prognosis (68% success) compared to teeth with flush fillings (94% success) and overfillings (70% success).

REFERENCE

Lin, L.M., Rosenberg, P.A., Lin, J.: Do procedural errors cause endodontic treatment failure? JADA136:187-193, 2005.

QUESTION 8

Patients often express concern about mercury being released from their amalgam restorations. How long would it take to release all the combined mercury of a typical amalgam?

A. 16.8 years

B. 168 years

C. 1680 years

D. 16800 years

Ratlonale

It would require 1680 years to release all the combined mercury of a typical amalgam restoration weighing 0.65 g. Only 0.534 g of mercury vapour is released per day from an amalgam surface. Guidelines set for young children and women of childbearing age indicate that the maximal permissible level is 300 g /day. To reach the maximum exposure limit, an individual would have to have 490 amalgam surfaces in the mouth, which is a practical impossibility.

Concern has also been expressed regarding waste dental amalgam’s contribution to environmental pollution. This, however, is minimal. At least 50% of environmental mercury comes from the evaporation of the oceans, erosion of rocks, release from trees and other sources. Man-made mercury accounts for the rest with 42% of environmental pollution caused by the combustion of solid fuels. There is a potential for increased amounts of mercury entering the water systems as a result of acid rain eroding mercury from rocks. Discarded amalgam is small in proportion and furthermore is in the inorganic form that requires conversion into the more dangerous organic form before it can enter biologic tissues. Inorganic mercury can be collected in sludge and can be converted to the organic form by bacteria. Such mercury can be consumed by plankton, which, eaten by fish, can be consumed by humans. Mercury in dental amalgams should not be a co
ncern for patients and dentally related sources contribute very little to mercury contamination of the environment.

REFERENCE

Jones, D.W.: Putting dental mercury pollution in perspective. Br Dent J 197:175-177, 2004.

Answers to SLSA Questions 1-4, January 2007 issue:

1. B

2. A

3. D

4. C


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