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Week of November 6, 2002

Title: The effect of preflaring on the rates of separation for .04 taper nickel titanium rotary instruments

Author: Roland, David et al.

Journal: JOE, vol. 28, no. 7, pages 543-545

Reviewed by: Andrew Schoelch, D.D.S.

Purpose:   To compare the separation rates of .04 taper nickel titanium (NiTi ) instruments, using the manufacturer’s recommended technique, with a combination of passive step-back technique and rotary NiTi instruments

Materials and Methods:

- Extracted maxillary and mandibular molars were used (18 to 25 mm in clinical length)

- Mesial roots of mandibular molars and buccal roots of maxillary molars were included

- Roots had to have a 20 to 30 degree curvature

- Group A

-teeth were hand instrumented to a size 3(.167) Series 29 instrument followed by crown down prep to size 4(.216) rotary

- Group B

-teeth were hand instrumented to a size 2(.129) Series 29 instrument followed by crown down prep to size 4(.216) rotary

- Rotary instruments were used until they separated or 20 times

Results: Preflaring canals to a larger size showed less instrument separation

Conclusion:  Canals should be preflared to prevent separation of instruments

Title:  Efficiency of hand and rotary instruments in shaping oval root canals

Authors:  Roland Weiger et al

Journal:  Journal of Endodontics, 28(8): 580-583, 2002

Reviewed by:  Donna Salin, D.M.D.

Purpose:  To determine the efficiency of hand and rotary instruments in shaping oval root canals.

Materials and Methods:

· 75 oval canals were used.

· The apical third of all canals was prepared with rotary LightSpeed instruments either to size 52.5 (mandibular incisors) or to size 57.5 (distal root of mandibular molars).

· The middle third was shaped using 1 of 3 techniques:

o Shaped with Hedstrom hand files using a circumferential technique.

o Shaped with 6% taper rotary Hero files in a circumferential filing movement.

o Shaped with rotary LightSpeed instruments in a step-back technique.

· The teeth were sectioned at two levels in the middle third of the root.

· An assembly technique allowed comparing the canal outline before and after instrumentation.

· The ratio of prepared to unprepared canal outline was calculated for each section.

Results: Preparation of dentin walls in the middle third of the root canal was insufficient with all instrumentation techniques. The Hero file group showed the highest prepared/unprepared ratio with a mean of 0.58 compared with 0.56 in the Hedstrom group. Both preparation methods provided significantly better results than the LightSpeed technique with a mean of 0.42.

Discussion: The results may be attributed to the combined filing and rotation movements with which the Hero files were used. Also, the cutting efficiency of the Hero files and hand Hedstrom files were accentuated through the increased stiffness compared with the LightSpeed instruments, allowing lateral pressure to be exerted on the root canal walls. Also, the small design of the Hero files at their tips may access recesses or fins present in the root canals.

Title: The effect of rotational speed and the curvature of root canals on the breakage of rotary endodontic instruments

Author: Zelada, Gabriela et. al.

Journal: JOE, vol. 28(7):540, July 2002

Reviewer: Alison Morrison, D.M.D.

Purpose: The purpose of this investigation was to evaluate the effect of rotational speed and curvature of root canals in the breakage of nickel titanium (NiTi) instruments, and to assess whether they really are factors that increase the breakage.

Materials and Methods: 120 canals from extracted molars were used. Mesiodistal and buccolingual direction radiographs were taken of all the teeth and the angle and the radius of the curvature of each root canal was ascertained. The teeth were divided into two groups of 60. Canal curvature and radius of curvature were used to determine the sharpness of each curve.

• Group A had an angle of curvature less than 30 degrees  
• Group B had an angle of curvature greater than 30 degrees.
  
  Each group was then further divided into 3 subgroups of 20 canals each. Subgroup 1, 2, and 3 used 150, 250, 350 RPM respectively. Standard safety measures were used to avoid breakage. Group A files were used a maximum of 20 times and Group B files were discarded after 12 uses.

Results: File breakage occurred in 12.5% of all the instrumented canals. All breakage occurred in Group B canals with a curvature of greater than 30 degrees. No file breakage occurred in group A canals. The files that were used with rotational speeds of 250 and 350 RPM broke more frequently than those used at 150 RPM. The files that broke were #25 and #30 .04 taper and less frequently #20, #25, #30 .06 taper. The majority of breakage occurred between the first and sixth uses of each file. All separations occurred without any visible sign of a deformation.

Conclusion: Speed of rotation and the curvature of the root canals contribute to an increased risk of breakage of rotary instruments. The resistance of files differs depending on whether the canals are relatively straight or slightly curved, or if the curvature is pronounced and acute.

Title: Antimicrobial efficacy of various root canal preparation techniques: an in vitro comparative study.

Author: Pataky, L. et al.

Journal: JOE, vol. 28 (8): 603, Aug 2002

Reviewer: Alison Byrne, D.M.D.

Purpose: To compare the eventual differences in the cleaning efficacy of the standardized (reamer) method and step-back technique using various instruments (traditional K-file and K-file NiTiflex)

Materials and Methods: 40 intact human maxillary premolars extracted for orthodontic reasons were used. After pulpectomy, crowns of the teeth were removed and the teeth were autoclaved . Root canals were then flushed with enterococcus faecalis suspension and incubated at 37 degrees Celsius for 24 hours. The teeth were divided into 5 groups: 

• preparation with k-files (step-back technique, group 1) 
• k-NiTiflex files (step-back technique, group 2)
• k-reamer (standardization technique, group 3)
• irrigation only (group 4)
• no treatment (group 5).
  
  Before and after treatment, samples were taken for culture. At the evaluation of cultures, post infection samples were first compared among groups, then intra-group comparisons were performed.

Results: In all of the tooth groups with mechanical preparation, there was a considerable reduction in bacterial population compared with groups 4 and 5. No differences were seen among the instrumented groups.

Discussion: In this study, there were no differences among the efficacy of files made of traditional metals or nickel-titanium alloy. This was because maxillary premolars were were used which rarely have severely curved roots. Therefore the benefits of nickel-titanium alloy k-type files, such as flexibility and elastic memory were limited. Although instrumentation yielded marked reductions in bacteria, a total absence of bacteria could not be achieved by mechanical preparation, thus confirming the necessity for chemical irrigants.

Title: Displacement of the contents of dentinal tubules and sensory transduction in the intradental nerves of the cat.

Author: Andrews, D. and Matthews, B.

Journal: J. Physiology 529.3: 791-802, 2000.

Reviewer: Brett Strong, D.D.S.

Purpose: To test the hypothesis that fluid flow through dentinal tubules is part of the mechanism involved in the transduction of pain producing stimuli.

Materials and Methods:

1. in vivo: 1 mm tip of mandibular canine removed on anesthetized adult cats. Dentin etched to open tubules. Capillary glass tip connected to an acrylic cap was sealed on tooth and hydrostatic pressure applied to dentin which was measured by observing droplets of milk fat in water and confirmed with an attached low compliance , differential pressure transducer. Tooth was encased in a 30^o C air jacket to maintain constant external temperature. Positive and negative hydrostatic pressure in the range of +/- 500 mmHg were then applied to the exposed dentin in 50 mmHg steps. The ipsilateral inferior alveolar nerve was exposed and single A type pressure sensitive nerve filaments were isolated to record action potentials during pressure stimuli.
2. in vivo test #2: M&M same as above with the following exceptions. Neural recordings were made when applying hot, cold, osmotic, hydrostatic pressure, mechanical and drying stimuli to the tip of the canine. Area of exposed dentin was determined by measuring the average diameter of the tip under a microscope. Pulpal blood flow measurements taken with a laser-Doppler flow meter. In vitro: Exposed root sections of tooth were used to determine fluid flow during stimulation of the crown.

Results:

• In all preparations a continuous outflow of fluid was recorded.
• Estimated tubules opened ranged from 14675-28098 (mean 22490).
• The number of action potentials during repeated application of pressure stimuli always declined during experiment. This decline was permanent and probably due to odontoblastic death.
• Microscopic examination showed little damage to pulp of odontoblasts. Structures were displaced slightly into tubules.
• No change in pulpal blood flow was seen.
• Cold and hot stimulated nerve fibers, but heat response was only evoked at limit of testing ranges.
• Mechanical stimulation showed irregular neuronal discharge.
• In vitro: Heating, Positive pressure, Mechanical stimuli caused inward flow.  Cooling, Negative pressure, and Osmotic stimulation caused outward flow.
• 10/17 isolated A-fibers responded to negative pressure only (outward fluid flow). The remaining 7/17 responded to both outward/inward fluid flow. All units were more sensitive to negative hydrostatic pressure. During negative pressure there was always an increasing discharge frequency with increasing pressure.
• All data points demonstrated the same basic curve with respect to neuronal stimulation.

Discussion: The relationship between hydrodynamic pressure, fluid flow, and neuronal discharge was clearly indicated. In addition, the fact that multiple stimuli evoked discharge of pulpal A-fibers also lends strong support to the hydrodynamic hypothesis. Cold produced a response at much lower fluid flow thresholds probably because thermal stimuli creates fluid outflow from tubules which need not be as exposed as those which also respond to different stimuli, mechanical for example. Although fluid flow was implicated in causing dentinal discomfort through stimulation of myelinated A-fibers, it is not yet clear if dentin sensitivity is only invoked by pressure receptors, or if other components such as cell death/ displacement are needed simultaneously.

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Week of November 20, 2002

Title: Assessment of post-traumatic PDL cells viability by a novel collagenase assay

Author: Pileggi, R. and et. al.

Journal: Dental Traumatology, vol. 18(4):186, August 2002.

Reviewer: Michael Moreno, D.M.D.

Purpose: To investigate the efficacy of a potentially faster method utilizing dispase and collagenase enzymes to quantify the number of viable PDL cells after a simulated avulsion injury and to determine which storage medium maintains the greatest number of viable PDL cells after 30 minutes of dry time followed by storage for 45 minutes in commonly accepted media.

Materials and Methods: Thirty-three freshly extracted human teeth were used in this study. Following extraction, the coronal three millimeters of PDL was scraped with a curette and rinsed with distilled water to remove damaged cells. The teeth were divided into six groups. They were stored dry for 30 minutes.

• Four groups were then immersed in one of either Hank’s balanced salt solution, milk, saline, or water.
• One of the six groups was used as a positive control, and was immediately treated with dispase and collagenase.
• The last group was used as a negative control, and was bench dried for eight hours followed by treatment in dispase and collagenase.
  
  After enzymatic treatment, the teeth were centrifuged for five minutes at 800 rpm and the cells were labeled with 0.4% Trypan Blue. The number of viable and nonviable cells were counted under light microscopy with a hemocytometer and analyzed with an ANOVA and a post hoc Scheffe’s test.

Results: The teeth stored in milk showed the highest number of viable PDL cells followed by Hank’s solution, saline, and water. However, no statistically significant difference was found in the number of viable cells among saline, milk, and HBSS after a 30-minute dry time.

Conclusion: Milk is comparable to saline and HBSS for storage of avulsed teeth when dry time does not exceed 30 minutes. The collagenase and dispase assay appears to be a valid method for evaluating PDL cell vitality.

Title: Effects of temperature, storage time and media on periodontal and pulpal healing after replantation of incisors in monkeys

Author: O.schwartz, F.M. Andreasen, J.O. Andreasen

Journal: Dental Traumatology 2002; 18:190-195

Reviewed by: S. Shin, D.M.D.

Purpose: To investigate the healing patterns after replantation of mature teeth following saline, saliva or dry storage at a range of temperatures from -18 to 37° C in order to reveal optimal storage conditions for the avulsed teeth or the teeth to be transplanted.

Materials and Methods: Mandibular lateral incisors of green vervet monkeys with mature root formation were extracted and kept in dry storage at 22, 4 and -18° C; in saline at 37, 22, 4 and -18°C; in saliva (i.e. in the buccal vestibule) at 37°C for either 60 and 120 min prior to replantation. The animals were sacrificed 8 weeks after replantation and the replanted teeth examined histometrically. The following histological parameters were registered for each tooth: normal PDL, surface resorption, inflammatory resorption, replacement resorption (ankylosis), downgrowth of pocket epithelium, periapical inflammatory changes, and the extent of vital pulp.

Results: A total of 125 replanted teeth were examined. 

• Storage in saliva at 37°C showed a similar amount of normal PDL compared to saline storage for both 60 and 120 min. 
• Saline storage for 60 or 120 min showed no difference in the extent of normal PDL when storage was compared at 37, 22 and 4°C. 
• Storage at -18°C resulted in significantly less normal PDL than storage at other temperatures. 
• Dry storage for 60 min showed significantly less root resorption at 4°C compared to 22°C.  
• Dry storage at -18°C showed significantly less normal PDL than storage at 4°C. 
• When the dry storage period was extended to 120min, no difference was found between 22.4 and -18°C.

Discussion: It is concluded that the temperature (above 0°C) of the storage medium is of importance only for dry storage and in such a situation only for shorter extra-alveolar periods, i.e. for 60-min storage and not for 120-min, where extensive destruction of the PDL always takes place. It is suggested that the temperature effect of 4°C could be related to less evaporation from the PDL cells or a strict temperature effect upon cell metabolism. Pulp healing in all the cases was limited to the entrance of the pulp canal, and no significant pattern was found between storage media, time and temperature.

The present experiments indicate that avulsed teeth can be stored in either saliva or saline. With saline storage, benefits will occur from deviations from temperature. Dry storage under all circumstances is very harmful to the PDL and should be avoided.

Title: Autotransplantation of teeth: requirements for predictable success

Author: Tsukiboshi, M.

Journal: Dental Traumatology 2002; 18: 157-180.

Reviewed by: Fernando Meza, D.M.D.

Purpose: To summarize the biologic principles, and surgical technique required for successful autotransplantation of teeth.

Discussion: 

• Successful PDL healing is expected if mechanical damage to the PDL of donor teeth during extraction is minimal, and if placement into recipient socket is immediate. 
• Artificially formed sockets have lower prognosis and longer healing time. 
• Healing of a damaged root surface is dependent on size of defect. A small defect will undergo cemental healing where cells forming new cementum and PDL cover the damaged root. A larger defect will undergo replacement resorption (ankylosis) where cells forming bone will cover the damaged root and induce root resorption followed by bone apposition. 
• The PDL cells of a transplanted tooth are able to induce bone production by differentiation into osteoblasts. 
• The use of bone graft materials is generally unnecessary.
• Pulp regeneration is expected to occur in teeth with incomplete root formation. Blood vessels and replacement cells will eventually occupy the pulp space. The teeth will usually react positively to sensitivity testing in 6 months. Pulp-canal obliteration is inevitable. Continuation of root development is expected in an immature donor tooth with preservation of Hertwig’s epithelial root sheath around the apices. 
• Since no additional root development is a potential outcome, maximally formed roots with a radiographic apex opening of 1 mm to allow pulp regeneration is optimal. Transplantation of fully formed teeth require RCT to ensure success since pulp regeneration is not possible.
• Cases must be carefully examined taking into account anatomic shape of donor teeth and recipient sites, stage of root development, recipient socket modifications, and potential damage of the donor tooth at removal. 
• Immediate transplantation into recipient site is preferable, but can be initiated within 2 to 6 weeks after extraction of tooth at recipient site. If RCT is required for the donor tooth, it may be completed prior to transplantation or 2 weeks following transplantation. 
• The surgical procedure sequence for autotransplantation is as follows: 
  
  1-premedication with antibiotics 1 hour prior
  2-disinfection and local anesthesia of surgical sites
  3-extraction of recipient site tooth
  4-extraction of donor tooth (the anatomy and PDL condition are carefully examined, the tooth can be placed back into the socket, or stored in Hank’s balanced salt solution if extra-oral time is anticipated) 
  5-donor tooth is measured
  6-reciepient site is prepared larger than donor tooth with round burs at low speed and cooling with saline 7-try-in and adjustment of donor tooth into recipient site 
  8-trimming and suturing of flap to ensure tight closure
  9-positioning and splinting of donor tooth
  10-occlusal adjustment
  11-post-op radiograph
  12-surgical dressing to protect against infection during the initial 2-3 days of wound healing
  13-dressing removal 3-4 days
  14-suture removal 4-5 days post op
  15-splint removal 6 weeks post-op. 
  
  Root canal treatment of transplanted teeth should be initiated for inflammatory root resorption, (or any other signs of infection), and 2 weeks post-op for teeth with fully formed roots where pulpal regeneration is not expected. Apexification of transplanted teeth is indicated in younger patients with failed pulp regeneration and an open apex. The 6 year follow-up period resulted in a 90% survival and 82% success rate for conventional autotransplantation. A 75% survival and 60% success rate for transplants into artificially formed sockets was observed.

Conclusion: Autotransplantation should be included as a treatment option given its high level of success and significant savings in time and cost compared to implants.

Title: The effect of fish oil on bone resorption following pulp exposure in rats.

Authors: Indahyani, DE, et al.

Journal: Dental Traumatology. 18: 206-211, 2002.

Reviewed by: Brett Strong, D.D.S.

Purpose: To determine whether treatment with fish oil may alter periapical bone resorption following pulpal exposure in rats.

Materials and Methods:

· Fish oil was dispensed to rats once a day in an oral gavage dose.

· Treated rats were divided into three groups (0.5mL, 1.0mL, and 2.0mL) of nine rats each.

· Negative and positive control rats were fish oil-untreated animals.

· In treated rats, and the positive control group, the pulp chamber of the left first maxillary molar was exposed from the occlusal surface with a round bur. (0.06mm diameter).

· The rats were prepared for histomorphometric evaluation on days 1, 7, and 14. They were stained with tartrate-resistant acid phosphatase followed by methyl green. The number of preosteoclasts and osteoclasts was counted per mm of bone surface.

Results:

· The number of preosteoclasts and osteoclasts in the rats orally dosed with 0.5mL, 1.0mL, or 2.0 mL of fish oil for 14 days was significantly lower than those in the positive control group over the same time period. Also, no statistical difference between the number of osteoclasts in the negative control and those taking one or two mL of fish oil a day could be seen at day 14.

· The number of periapical preosteoclasts in the animals treated with one or two mLs of fish oil a day steadily decreased over the 14 day trial and was not statistically different than the negative control at day 14.

· A decrease in bone resorption was seen in all of the treated groups at day 14, and the one and two mL groups exhibited the same levels of bone resorption as the negative control group on day 14.

Discussion:  The data clearly shows that the ingestion of fish oil decreases the production of preosteoclasts and osteoclasts and therefore decreases bone resorption in periapical inflammatory processes. However, nobody knows why the observed therapeutic effect happens. The current theory is that fish oil alters the effective concentration(s) of the cytokines PGE₂, IL-1, or TNFa on preosteoclasts and/or osteoclasts. The problem is that while there is a lot of evidence that these cytokines have significant effect on bone formation and absorption, nobody yet understands exactly how they interact. This study does strongly suggest that fish oil works faster and more effectively when taken at a higher dose; however, I am not sure that at the doses taken this information is of clinical relevance. For example, if a 2mL/kg dose is needed for treatment than a 50kg human would have to ingest 0.1 liters of fish oil a day to inhibit bone resorption. Further elucidation of the pathways of bone resorption and the cytokines effecting them, in addition to isolation of the effective chemical(s) in fish oil must occur before practical clinical application can or should become a reality.

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Created: September 20, 2000 Revised: URL:

Roy H. Stevens, DDS, MS; Wanda Gordon, D.M.D. - Comments to author:	wgordon@dental.temple.edu
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