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, 2006 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.
QUESTION 29
When restoring an endodontically treated tooth with a post and core, which of the following is the suggested minimum thickness of sound dentin to surround the post?
A. 0.5mm
B. 1mm
C. 2mm
D. 3mm
Rationale
A recent review examined the various factors related to post and core selection. Radiographic evaluation of the canal anatomy will allow for appropriate post selection in both length and width. Preservation of tooth structure, leaving as much residual dentin as possible, is advocated to reduce risk of fracture. It is suggested that the post be surrounded by a minimum of 1mm of sound dentin. Shear stress on a post-core restored tooth is the most detrimental of the stresses induced. An increase in post length, with the diameter kept to a minimum, will reduce shear stress and preserve tooth structure.
Post designs are classified by shape, i.e., parallel, tapered, or parallel-tapered combination. Posts are either active or passive: the former engage the dentin with threads, the latter depend on cement for retention.
Reference
Fernandes, A.S., Sharat, S., Continho, I. Factors determining post selection: A literature review. J Prosthet Dent. 90:556-562, 2003.
QUESTION 30
Cavity preparation by the ER, Cr:YSGG laser results in
1. a smooth surface on dentin.
2. no smear layer.
3. pulpitis.
4. an excellent bonding surface.
A. 1, 2, 3
B. 1 and 3
C. 2 and 4
D. 4 only
E. All of the above
Rationale
All laser energy, regardless of wave length, is either absorbed by tissue, reflected by tissue, scattered within tissue, or transmitted directly through tissue. It is the combination of these factors that determines the effectiveness of the laser.
Laser wavelength works along with what is called a “waveform” to influence the tissue effect. Laser energy is delivered in two waveforms-continuous and pulsed. Continuous wave lasers deliver large amounts of energy, whereas pulsed lasers provide smaller amounts to a tissue in interrupted bursts. Although at least five lasers are identified for use in dentistry, the recent development of the Er, Cr:YSGG laser appears the most superior for practice. It has multiple applications and therefore has economics on its side.
With a pulsed waveform, the Er, Cr:YSGG laser has a wavelength of 2.78m. It can be used for enamel etching, caries removal, cavity preparation, bone cutting with no burning and root canal preparation. The laser produces a rough surface on both enamel and dentin. No smear layer is left, providing an excellent bonding surface. It is not harmful to the pulp and there is no need to administer local anaesthesia. It is used with a water spray and because its interaction with tissue is influenced by variations in the air-to-water ratio of the spray it can also be used on soft tissue. Another point of interest is that melting the enamel increases resistance to demineralization.
REFERENCES
1.Dederich, D.N. and Bushick, R.D. Lasers in dentistry: Separating science from hype. JADA 135:204-212, 2004.
2.Jacobson, B., Berger, J., Kravitz, R., et al. Laser pediatric Class II composites utilizing no anaesthesia. J Clin Pediatr Dent. 28:99-102, 2004.
QUESTION 31
In prosthodontics, the material of choice for a provisional restoration is
A. composite resin.
B. polymethyl methacrylate.
C. vinyl ethyl methacrylate.
D. ethyl methacrylate.
Rationale
A recent review of provisional restorative care in prosthodontics identifies polymethyl methacrylate as the material of choice. It has superior marginal accuracy when compared to vinyl ethyl methylacrylate. Also of note is the improved marginal fit when indirectly fabricated. Retention of polymethyl methacrylate crowns was found to be 20% better when compared to composite materials.
In colour stability, polymethyl methacrylate was superior to ethyl and vinyl-ethyl methacrylate-an important property for esthetics. The physical strength, density and hardness of methyl methacrylate can be greatly improved by heat polymerization or by use of a pressure vessel with air and water. This produces a durable temporary restoration.
REFERENCE
Burns, D.R., Beck, D.A., Nelson, S.K. A review of selected dental literature on contemporary provisional fixed prosthodontic treatment: Report of the Committee on Research in fixed prosthodontics of the Academy of Fixed Prosthodontics. J Prosthet Dent. 90:474-497, 2003.
QUESTION 32
Experimentally, it has been shown that mastication can be associated with
1. better learning ability.
2. improved memory.
3. control of body weight.
4. release of histamine from the satiety control centre.
A. 1, 2, 3
B. 1 and 3
C. 2 and 4
D. 4 only
E. All of the above
Rationale
Maintaining masticatory ability has essential benefits not only related to the digestion of food, but also to physical and mental well-being. Mastication stimulates the flow of saliva. Saliva not only lubricates food and contains digestive enzymes, but also contains compounds that help maintain the health of oral tissues and protect the body against pathogens. It has also been demonstrated that the act of mastication increases blood flow within the brain and stimulates central neural activity. Loss of masticatory ability may be associated with emotional and physical health complications.
In the experimental animal, it has been shown that mastication results in an increased release of histamine from the satiety control centre of the brain. This release is associated with better learning ability and improved memory, and has, as well, an effect on control of body weight. Studies have shown that senior citizens who have good chewing ability with their own teeth manage much better than their counterparts who are without teeth or who wear dentures. Dentists have a responsibility to instruct their patients on the importance of good oral health and mastication in the maintenance of their general health.
REFERENCES
1.Nakata, M. Masticatory function and its effect on general health. Int Dent J. 48:540-548, 1998.
2.FDI Statement, General Assembly, 2003.
Answers to July 2006 SLSA questions:
25. C26. A27. E28. E
