Molecular characterization of young and mature odontoblasts

The odontoblast is the secretory cell responsible for primary, secondary and tertiary reactionary dentinogenesis. We provide evidence that the changes in secretory activity of odontoblasts reflect differential transcriptional control and that common regulatory processes may exist between dentine and bone.

INTRODUCTION

Based on the hypothesis that differential dentine secretion (primary and secondary dentinogenesis) is associated with changes in the transcriptional control within the cell, we have investigated the transcriptome of odontoblasts at young and mature stages and subsequently used this information to identify key regulatory intracellular pathways involved in this process.

MATERIALS AND METHODS

We used microarray analysis to compare the transcriptome of early stage (primary dentinogenesis) and late stage (secondary dentinogenesis) odontoblasts from 30 month old bovine teeth. Secondarily, we used post-array sqRT-PCR to confirm the differential expression of 23 genes in both populations of odontoblasts. Finally, immunohistochemistry was performed on bovine and murine tissues with antibodies to DMP1 and anti-phospho p38 proteins.

RESULTS

DMP-1 and osteocalcin gene expression were up-regulated in the mature odontoblasts, whereas collagen I, DSPP, TGF-beta1 and TGF-beta1R gene expression were down-regulated. Microarray analysis highlighted 574 differentially regulated genes (fold change>2 - p<0.05). This study supports further existing similarities between pulp cells and bone cells. Using post-array Sq-RT-PCR we characterized transcript levels of genes involved in the p38 MAP kinase pathway (PTPRR, NTRKK2, MAPK13, MAP2K6, MKK3). Differential p38 gene activation was confirmed by immunohistochemistry for p38 protein in murine teeth. Finally, immunohistochemistry for DMP1 indicated that odontoblasts involved in primary and secondary dentinogenesis may coexist in the same tooth.

CONCLUSION

As established in bone cells, the transcriptome of the odontoblast was shown here to evolve with their stage and functional maturity. Identification of the involved signalling pathways, as highlighted for p38, will enable the deciphering of physiology and pathology of mineralised tissue formation.

Root canal retreatment

Root canal therapy is not always successful and an increasing number of patients are requesting retreatment to address intra-radicular infection. The armamentarium available to assist the dentist, some of which is described in this article, has never been greater.

CLINICAL RELEVANCE

This paper discusses the causes of failure and reviews many of the techniques available to the practitioner to tackle the problem.

Comparison of operative procedure variables on pulpal viability in an ex vivo model

AIM

To measure and compare the responses of pulp tissue to cavity preparation and restoration variables using a novel tooth slice culture model.

METHODOLOGY

Experimental cavities (265) were continuously cut, under carefully controlled conditions, into the dentine of the labial aspect of 28-day-old Wistar rat incisors, and slices of these teeth maintained in organ culture for up to 2 weeks. The experimental variables examined were: the preparation method, remaining dentine thickness, coolant, drill speed, conditioning with EDTA and filling materials. The reactions of the dentine-pulp complex to the experimental variables were measured using pathohistometric analysis and the correlations between variables were determined using analysis of variance statistical tests.

RESULTS

In rank order of surgically induced restorative pulpal injury, from the most to the least injurious were: remaining dentine thickness, absence of coolant during cavity preparation, bur speed, cavity conditioning treatments and the filling material.

CONCLUSIONS

To reduce pulp injury and to promote pulpal repair activity, the correct use of appropriate materials are important. However, of relatively greater importance is the operative technique adopted, the need to avoid the excess removal of dentine and to minimize trauma during preparation.

A new insight into the oscillation characteristics of endosonic files used in dentistry

The aim of this study was to assess the oscillation characteristics of unconstrained endosonic files using a scanning laser vibrometer (SLV). Factors investigated included file vibration frequency and node/antinode location as well as the variation in file displacement amplitude due to increasing generator power setting. A 30 kHz Mini Piezon generator (Electro-Medical Systems, Switzerland) was used in conjunction with a #15 and #35 K-file. Each file was fixed in position with the long axis of the file perpendicular to the SLV camera head. The laser from the SLV was scanned over the length of the oscillating file for generator power settings 1 to 5 (minimum to half power). Measurements were repeated ten times. The fundamental vibration frequency for both files was 27.50 kHz. Scans of each file showed the positions of nodes/anti-nodes along the file length. The #15 file demonstrated no significant variation in its mean maximum displacement amplitude with increasing generator power, except at power setting 5, where a decrease in displacement amplitude was observed. The #35 file showed a general increase in mean maximum displacement amplitude with increasing power setting, except at power setting 4 where a 65% decrease in displacement amplitude occurred. In conclusion, scanning laser vibrometry is an effective method for assessing endosonic file vibration characteristics. The SLV was able to demonstrate that (unloaded) file vibration displacement amplitude does not increase linearly with increasing generator power. Further work is being performed on a greater variety of files and generators. Vibration characteristics of files under various loads and varying degrees of constraint should also be investigated.

Odontoblast morphology and dental repair

OBJECTIVES

To investigate the changes in morphology and activity of pulp odontoblasts in response to cavity restoration variables and patient factors.

METHODS

Class V non exposed cavities were prepared in the intact 1st or 2nd premolar teeth of 27 patients, aged between 9 and 17 years-old. Following tooth extraction, the area of reactionary dentine and the area of the odontoblasts were measured using computerised histomorphometry.

RESULTS

The cytoplasm to nucleus ratio of the odontoblasts was found to increase beneath cut dentinal tubules, following the secretion of reactionary dentine. However, none of the patient or preparation variables were found to be correlated with changes in the odontoblast cytoplasm to nucleus ratio.

CONCLUSIONS

Morphological changes in human odontoblasts is directly related to their capacity to repair dentine injuries and provide pulp protection. Changes in odontoblast morphology reflect secretory activity.

A pilot investigation of operator variability during intra-oral light curing

OBJECTIVE

To test the hypothesis that operator experience influences the efficacy of light curing in a typical posterior intra-oral location. To investigate whether short cure cycles affect performance.

DESIGN

A cross-sectional single-centre study designed to assess the efficacy of experienced and inexperienced operators when undertaking simulated intra-oral curing.

SETTING

An in vitro laboratory based investigation conducted in a dental school during 2001.

MATERIALS AND METHODS

A computer-based technique was used to monitor light intensity in a clinical simulation. Dentists and student operators were tested for their ability to cure a posterior restoration effectively. Relative light intensity was assessed against time for each operator and test run.

RESULTS

Experienced (qualified) operators produced more effective and consistent cure results than less experienced undergraduate students. Operator performance was not affected by variations in irradiation time.

CONCLUSIONS

This cross-sectional pilot investigation demonstrates that operator experience is a factor in successful clinical photo-curing of posterior restorations. Stable and accurate light guide positioning are required throughout the entire irradiation cycle to optimise intra-oral cure of light-activated restorations. Further investigations are planned to assess the potential of this novel method of assessment for use as a routine teaching aid in clinical practice.

Evaluation of smear layer removal by EDTAC and sodium hypochlorite with ultrasonic agitation

AIM

To evaluate smear layer removal by different irrigating solutions under ultrasonic agitation.

METHODOLOGY

Twenty recently extracted mandibular incisors with a single root canal were divided into four equal groups. Three groups were instrumented using the modified double-flared technique, the fourth remained unprepared. Each group was irrigated with either distilled water, 1.0% sodium hypochlorite alone or associated with 15% EDTAC between each file size. The final group was not instrumented but irrigated with 1.0% sodium hypochlorite and 15% EDTAC. A size 15 file energised by ultrasound was used with small amplitude filing movements against the canal walls in all groups. The teeth were split longitudinally and the roots measured to provide three sections of the same size (cervical, middle and apical). Samples were examined under the scanning electron microscope and assessed for the amount of smear layer by three independent and calibrated examiners. The scoring system ranged from 1 (no smear layer) to 4 (all areas covered by smear layer). Due to the non-parametric nature of the data, Friedman's test was used for statistical analysis.

RESULTS

Canal walls were covered with smear layer in the group irrigated with 1% sodium hypochlorite alone and the group irrigated with distilled water. Canals irrigated with 1.0% sodium hypochlorite associated with 15% EDTAC had less smear layer throughout the canal (P < 0.001). There were no statistical differences for the amount of smear layer found on the cervical, middle and apical thirds when each group was analysed separately.

CONCLUSIONS

Under ultrasonic agitation, sodium hypochlorite associated with EDTAC removed the smear layer from root canal walls, whereas irrigation with distilled water or 1.0% sodium hypochlorite alone did not remove smear layer.

Effect of exposure intensity and post-cure temperature storage on hardness of contemporary photo-activated composites

OBJECTIVES

The effect of variation in post-exposure storage temperature (18 vs. 37 degrees C) and light intensity (200 vs. 500mW/cm(2)) on micro-hardness of seven light-activated resin composite materials, cured with a Prismetics Mk II (Dentsply) light activation unit, were studied.

METHODS

Hardness values at the upper and lower surfaces of 2mm thick disc shaped specimens of seven light-cured resin composite materials (Herculite XRV and Prodigy/Kerr, Z100 and Silux Plus/3M, TPH/Dentsply, Pertac-Hybrid/Espe, and Charisma/Kulzer), which had been stored dry, were determined 24h after irradiation with a Prismetics Mk II (Dentsply) light activation unit.

RESULTS

Hardness values varied with product, surface, storage temperature, and curing light intensity. In no case did the hardness at the lower surface equal that of the upper surface, and the combination of 500mW/cm(2) intensity and 37 degrees C storage produced the best hardness results at the lower surface.

CONCLUSIONS

Material composition had a significant influence on surface hardness. Only one of the seven products (TPH) produced a mean hardness values at the lower surface >80% of the maximum mean upper surface hardness obtained for the corresponding product at 500mW/cm(2) intensity/37 degrees C storage temperature when subjected to all four test regimes. Despite optimum post-cure storage conditions, 200mW/cm(2) intensity curing for 40s will not produce acceptable hardness at the lower surface of 2mm increments of the majority of products tested.

The influence of sample dimensions on hydroxyl ion release from calcium hydroxide products

The purpose of this study was to compare the rate of hydroxyl ion release from commercially available setting and non-setting calcium hydroxide products. The rate of hydroxyl ion release is important, as this has been suggested to be the main factor in the therapeutic activity of these products. In total, hydroxyl ion release was measured from 1104 samples of Dycal, Life, Calasept and Hypocal in solution using in vitro titration. The rate of hydroxyl ion release was measured for up to 14 days, using two sizes of sample surface area. The dimensions of the exposed sample surface area was found to be an important physical constraint to the hydroxyl ion release from non-setting calcium hydroxide products, whereas this was not found to be the case with setting products. The range in hydroxide activity between products was found to be 298%. In rank order of hydroxide ion release, from the most to the least active was: Hypocal, Calasept, Life and Dycal. The differences in the rate of hydroxyl ion release from these products may have some implications for their clinical applications. It is suggested that in cases where the oral healing responses have been poorer than expected, the size and seal of prepared cavities could have negatively influenced the therapeutic release of hydroxyl ions from non-setting calcium hydroxide products.

Tooth slice organ culture for cytotoxicity assessment of dental materials

The purpose of this work was to develop a tooth slice organ culture method to assess the response of the cells of the dental pulp to commonly used dental materials and products. Wistar rat tooth slices were grown in culture for two and ten days in the presence of dental materials. After culture, the tooth tissues were processed and the responses of the pulpal cells were analysed histomorphometrically. Cytotoxic cell destruction was observed following the direct application of test materials to tooth slices (n = 298) after 10 days in culture (MANOVA, P = 0.0001), whilst the restoration of prepared deep dentine cavities (n = 30), with test products, did not result in a significant amount of pulpal injury (MANOVA, P = 0.287). In rank order of causing pulpal injury, the test materials from the most to the least cell destructive, was; Salicylic acid. Calcium hydroxide, Kalzinol zinc oxide eugenol, high-mercury Amalgam, Prime & Bond, Dycal, Barium sulphate, Hypocal, Scotchbond, Calasept, Life and One-step. Tooth slice organ culture, provided a cytotoxicity screening method for dental materials, bearing a closer physiological resemblance to the clinical situation than cell culture screening methods. Tooth slice culturing may have the potential to replace some types of in vivo animal experimentation, as there is a clear need to reduce this form of testing.

An in vitro investigation into the cutting action of ultrasonic radicular access preparation instruments

The aim of this study was to investigate the dentine cutting action of a CT4 and SJ4 radicular preparation inserts (Excellence in Endodontics/Analytic Technology, Orange, CA, USA) used in a Piezon Master 400 ultrasonic handpiece (Electro Medical Systems SA, Nyon, Switzerland). Calibration of the ultrasonic inserts was carried out at minimum, medium and maximum power settings using light microscopic measurement of the tip displacement amplitudes (x120 mag). Polished dentine samples were instrumented, at monitored loads, at the three chosen power settings, to produce uniform dentine cuts. The resultant dentine debris was collected for SEM analysis, and comparison with that produced by rotary instruments. The depth of dentine cut was measured at x30 magnification. Fracture of the SJ4 insert was noted at medium power setting. Results revealed a significant increase in both displacement amplitude and depth of dentine cut with power setting (ANOVA P < 0.001). Dentine chip size increased with power, and differed in structure and appearance from those produced by rotary instruments. In conclusion, ultrasonic cutting is influenced significantly by power setting, and dentine chip formation is fundamentally different to rotary instrumentation.

Ultrastructural localisation of TGF-beta exposure in dentine by chemical treatment

Transforming growth factor-beta (TGF-beta) sequestered in dentine matrix has an important role in dental tissue repair after injury and its exposure at sites of injury may stimulate tertiary dentinogenesis. This study aimed to investigate the expression of TGF-beta isoforms in mature human dentine matrix and the ability of chemical treatments to expose TGF-beta on the cut surface of dentine using gold immunolabelling and subsequent scanning electron microscopy examination. TGF-beta1 was the only isoform that could be detected in human dentine and the nature of the chemical treatment of the tissue influenced its detection. EDTA treatment provided good exposure of TGF-beta1 on the dentine surface, whilst citric acid and sodium hypochlorite treatments revealed lesser amounts of this isoform. Only minimal staining for TGF-beta1 was observed in samples treated with phosphate-buffered saline. TGF-beta2 and -beta3 could not be detected in the specimens with any of the treatments. This study suggests that TGF-beta1 is the only TGF-beta isoform expressed by human odontoblasts to be sequestered in dentine implying that differences in isoform-extracellular matrix interactions may exist. Information on chemical treatment of tissue specimens for immunostaining may provide a useful basis for selection of tissue preparation techniques for clinical restorative treatment procedures to facilitate TGF-beta mediated reparative processes at sites of dental injury.

Human odontoblast cell numbers after dental injury

OBJECTIVES

The purpose of this study was to measure the changes in odontoblast cell numbers in response to cavity restoration variables and patient factors, and the effect these factors have on dental repair by tertiary dentinogenesis. The number of vital odontoblasts is a critical factor for pulpal repair following restorative surgery, and yet little information is available on these cell numbers.

METHODS

Class V non-exposed cavities were prepared in the buccal surface of intact first or second premolar teeth of 27 patients, between 9 and 17 years of age. Following tooth extraction (28-163 days) the area of reactionary dentine and the area of the odontoblasts were measured histomorphometrically.

RESULTS

Patient factors, as well as cavity preparation and restoration variables, had little effect on the numbers of odontoblasts per pulpal unit area. However, the age of the patient did appear to have an effect on the reactionary dentine secretory capacity of odontoblasts per unit area, and on the relative number of odontoblasts beneath cut dentinal tubules.

CONCLUSIONS

Odontoblast cell numbers were maintained following the preparation of cavities cut into dentine with a 0.5mm residual dentine thickness. The repair capacity of the pulp-dentine complex would appear to be age dependent, this may explain differences in the success of various restorative treatments between patients.

Cleaning efficacy of two apical preparation regimens following shaping with hand files of greater taper

AIM

The aim of this investigation was to assess canal cleaning following shaping with hand files of greater taper.

METHODOLOGY

Thirty mesial canals and 30 distal canals in mandibular molars were prepared with .08 and .10 hand files of greater taper, respectively. Following initial preparation, 0.02 instruments were used incrementally shorter in a stepback manner. In half the canals instrumentation was performed to size 35 1 mm short of the canal terminus. In the other half the series was continued through to size 60 using stepback increments of half to one millimetre as appropriate (foramen size was maintained at size 20 in all groups). Sodium hypochlorite (4.5%) and REDTA (17%) were used as irrigants for all groups. Cleaning efficacy was evaluated by scoring the amount of remaining debris using a light microscope (x50) and calibrated eyepiece micrometer (range 0-3).

RESULTS

Canals stepped back through to a size 60 were significantly cleaner than those instrumented to a size 35 only (Mann-Whitney P < 0.05).

CONCLUSION

Refining the apical region of canal preparation by stepping back through to a size 60 reduced remaining debris following shaping with files of greater taper.

Postoperative pulpal and repair responses

BACKGROUND

Each year in the United States, the success of 10 million surgically restored carious lesions depends on a favorable tertiary dentin repair response to preparation, restoration and patient factor variables. The authors investigated the relationship between these variables and dentinal response.

METHODS

Standardized rectangular Class V restoration preparations were cut into the buccal dentin of intact first or second premolars of 27 patients without exposing the pulp and were restored. The patients were between 9 and 17 years of age. The treated teeth were scheduled for extraction for orthodontic reasons. After tooth extraction, the tertiary dentin was analyzed histomorphometrically.

RESULTS

The area of tertiary reactionary dentin was found to be correlated using linear regression analysis of variance with restoration residual dentin thickness (P = .0024), age of the patient (P = .0045), restoration floor surface area (P = .0266) and restoration width (P = .0415). The authors did not find a correlation with the premolar position (P = .0594), sex of the patient (P = .650), pulpal inflammatory reaction (P = .613) or the time elapsed since surgery (P = .531). Restoration with zinc oxide eugenol was found to negatively influence tertiary dentin matrix secretion (post hoc analysis of variance, P = .030).

CONCLUSIONS

The age of a patient at treatment, the choice of restorative material and the size of the restoration preparation are all factors that can positively or negatively affect the pulpal repair response.

CLINICAL IMPLICATIONS

Age of the patient affects dentin repair capacity and may be a factor in treatment planning decisions. Minimizing the cutting of dentin, especially the width and base of the preparation, reduces the probability of recurrent pulpal complications.

The periodontal-endodontic interface

The periodontal tissues and the pulp-dentine complex form an intimate continuum through which pathological changes of either one may lead to infection of the other, and whose management can be fraught with diagnostic and therapeutic difficulty. The purpose of this review paper is to explain the nature of that relationship and to provide pointers which may assist in the diagnostic process and thus enable appropriate management from the outset. Traditional classifications of lesions affecting the periodontal-endodontic complex have caused confusion by attempting to form diagnoses which indicate the putative primary source of infection. We would suggest that the origin of the infection is irrelevant to the management process, and that what is important is whether either, or indeed both, of the tissues are viable or not. Successful therapy will only result from the establishment of an accurate diagnosis, and forming such a diagnosis requires a methodical multi-staged approach.

Protection against Helicobacter pylori infection by intestinal immunisation with a 50/52-kDa subunit protein

A mouse model of Helicobacter pylori infection was used to evaluate the vaccine antigen potential of the citrate synthase homologue protein purified from the H. pylori NCTC 11637 strain. Mice were immunised with the protein by intra-Peyer's patch immunisation. This route gives maximal intestinal immunisation and was used to screen oral vaccine candidate antigens without the added complication of simultaneously testing oral delivery systems. Two weeks post-immunisation mice were infected with Sydney strain H. pylori and 4 weeks after infection the mice were killed and the level of H. pylori infection in the stomach determined. Pre-immunisation with the 50/52-kDa protein led to a 84-91% reduction in H. pylori infection compared to unimmunised controls.

Seating of composite inlays with ultrasonic vibration

The use of vibration enables the clinician to use high-viscosity luting agents when seating composite inlays and allows quick and efficient placement of the inlay. The film of composite luting agent is achieved in a much shorter time and with lower loads by ultrasonic vibration than using manual methods. In order to achieve a thin lute, the vibrations of the ultrasonic scaler must be directed perpendicular to the surface of the inlay.

The external and internal anatomy of human mandibular canine teeth with two roots

This study investigated the internal anatomy of 65 human mandibular canines with two well-defined roots. The teeth were decalcified and injected with gelatin coloured with india ink. Diaphanization was carried out using clear resin to allow permanent preservation. It was found that all mandibular canines with two roots had two root canals. Lateral canals were found in 68.9% of teeth and 19.7% had lateral canals at the bifurcation. The results of the external measurements (cusp tip to root apex) showed that the average buccal root length was 23.0 mm and the average lingual root length was 22.7 mm. The maximum and minimum buccal lengths were 26.7 mm and 17.9 mm respectively and the maximum and minimum lingual lengths were 27.2 mm and 17.1 mm respectively. The buccal root was the larger of the two in 47.7% of teeth and 43.1% had roots of equal size. The lingual root was larger than the buccal root in 9.2% of cases. Clinicians should be aware of the anatomical variation that exists for mandibular canines.

An in vitro evaluation of canal preparation using Profile .04 and .06 taper instruments

A model system involving a double radiographic exposure technique was developed in order to evaluate maintenance of the original canal path of curved root canals. The mesiobuccal roots of 30 maxillary molars were prepared using one of three techniques (n = 10 in each group). One group was instrumented using rotary Profile .04 tapers and a second group was prepared using orifice openers, rotary Profile .04 and .06 tapers. The final group was prepared using Profile hand files .02 taper and Gates-Glidden drills. Canal transportation was evaluated in the apical, middle and coronal regions from the double-exposed radiographs. Canal shape was determined by the ease with which a D11T spreader passed to within 1 mm of the working length. Time of instrumentation was also recorded. The results showed no significant difference between the techniques in canal transportation in the apical, middle or coronal regions (P > 0.05). It was significantly easier to place the D11T spreader in the .06 taper group (P < 0.05). Canal preparation was significantly quicker in the .04 taper group (P < 0.05). In conclusion, the use of .06 taper files improved canal shape and did not increase transportation. The additional file changes, however, increased the instrumentation time.

An in vitro investigation of coronal leakage with three gutta-percha backfilling techniques

The aim of this study was to compare the backfilling capabilities of System B, Obtura II and Alphaseal. Forty-six lower premolar teeth were prepared chemomechanically and allocated to four experimental and two control groups. Ten were obturated using lateral condensation as a standard and 30 were obturated in the apical third using the System B. The latter 30 teeth were then backfilled using one of three techniques, System B, Obtura II or Alphaseal (n = 10 in each group). The remaining six teeth served as controls. Roots were radiographed from the proximal in order to evaluate voids and then placed in India ink for 65 h prior to being demineralized and rendered transparent, coronal leakage was quantified by linear measurement of ink penetration. No significant difference was found between the four groups with respect to the presence of voids radiographically (P < 0.05). The difference in leakage between the System B and Obtura II groups was not significant (P > 0.05). Both System B and Obtura II leaked significantly less than Alphaseal and lateral condensation (P < 0.001).

Surface integrity of composite inlays following ultrasonic vibration

PURPOSE

To assess the effect of ultrasonic vibration on the surface integrity of a resin composite inlay.

MATERIALS AND METHODS

Ultrasonic vibration in the form of a scaling tip oriented either parallel or perpendicular to the surface was applied to 2 mm thick, 10 mm wide composite discs and the experiment was repeated with the probe oriented perpendicular using composite or rubber shields. The indentations produced were measured using a form Talysurf profilometer. The surfaces of the discs were also observed using scanning electron microscopy. Five discs were used for each experiment.

RESULTS

Both parallel and perpendicular orientations produced an indentation with a scattering of composite debris. A significant increase in the depth of indentation occurred if the vibrations of the ultrasonic scaler were oriented parallel to the composite surface (Two sample t- test, P < 0.01). The presence of a composite shield significantly reduced (Mann-Whitney, P < 0.05) the depth of indentation but produced roughening of the surface with impaction of material from the shield onto the surface. The rubber shield, however, polished the surface significantly smoother than the control specimens (Mann-Whitney, P < 0.05). Microscope slide separation was used to measure the thickness of composite luting agent following vibration with an ultrasonic scaling tip with and without a protective sleeve. There was a significantly thinner film of luting agent when an unsleeved scaler was used (ANOVA, P < 0.001). Although an unguarded tip oriented perpendicular to the surface appears to result in the best energy transfer for a thin layer of composite luting agent, it does, however, create minimal surface damage.

Cutting ability of Heliosonic, Rispisonic, and Shaper files

The aim of this study was to investigate the cutting ability of the Heliosonic, Rispisonic, and Shaper files supplied with the MM 1500 sonic handpiece. A model system was used and the following variables evaluated; file type (Heliosonic, Rispisonic or Shaper), power (air inlet ring opening of half, three quarters or fully open), width (15, 25 or 35), and load (25, 50 or 100 grams). A 3(4) full factorial analysis with two replications was performed. A new file with water irrigation was used for each cut. The substrate used was 1 mm thick sections of bovine bone. The differences between the variables were significant (ANOVA, p < 0.001). The most significant variable to affect cutting was load, followed by file type, power, and width. It is suggested that operators should select the file type for use appropriately and press the file against the root canal wall for optimum cutting.

A comparison of dentine removal using safety or conventional Hedstrom files

Mandibular molars (n = 20) were divided and the mesial roots mounted in an acrylic mould which allowed them to be removed, sectioned horizontally and then reassembled. The furcal root canal wall thickness 7 mm from the apex was measured prior to instrumentation. The roots were allocated to two groups (n = 10). One group was instrumented using the step back technique with safety Hedstroms in one canal and conventional Hedstrom files in the other canal. The second group was instrumented using a crown down approach (using files and Gates Glidden drills to provide early radicular access). The furcal root canal wall thickness was then remeasured and the amount of dentine removed calculated. The results showed that the safety Hedstrom file removed less dentine from the furcal region of the canal compared to the conventional Hedstrom file. This however was not statistically significant (Paired t test, n = 10, p > 0.05). The amount of dentine removed using the crown down technique was significantly greater than that using the step back technique (Two sample t, n = 20, p < 0.01). In conclusion, less dentine was removed from the furcal region with safety Hedstrom files compared to conventional Hedstrom files; however, Gates Glidden drills removed more dentine than either type of hard file.

Incidence of root face alteration after ultrasonic retrograde cavity preparation

PROBLEM

Ultrasonic root end preparation is now a recognized clinical procedure. Advantages claimed include improved access to the surgical site (because of reduced root end bevel), and faster more conservative preparation of the root end cavity. However, cracking of the root face has been reported after preparation.

OBJECTIVES

The aim of this study was to determine the incidence of root end cracking at varying ultrasonic power levels with a replica technique and scanning electron microscopy.

STUDY DESIGN

The root canals of 55 single-rooted teeth were prepared to size 40 apically and obturated with laterally condensed gutta perch and sealer. Root ends were resected at 90 degrees 3 mm from the apex. Class 1 cavities (n = 5) were prepared with retro tips in a Neosonic handpiece with different power settings. Time of preparation and load applied were constant. Another experimental group (n = 5) was prepared with a no. 1 rotary bur. A replica technique with addition-cured silicone impression material and epoxy resin was used to prevent drying artefacts. Specimens were viewed under scanning electron microscope for alterations of the root face.

RESULTS

Results showed no root face cracking across the full range of instrument power settings, although chipping of the retrograde cavity margins was observed. No cracking was noted in bur-prepared teeth.

Analysis of the surface cut by sonic files

The purpose of this investigation was to compare 3D profilometry and SEM analysis of a polished surface of bovine bone instrumented by sonic files. Two situations where investigated, i) no operator assisted movement, ii) operator assisted movement. Heliosonic, Rispisonic and Shaper files were investigated at full power setting and an interfacial load of 100 grams. The specimens were subjected to analysis using a 3D Form Talysurf prior to being sputter coated with gold and viewed under an SEM. The 3D surface analysis was found to be complimentary to SEM evaluation in that each provided additional information to the other. 3D analysis proved to be excellent for showing the topographical nature of the cut surface and gave a better indication of depth than the SEM. Debris was however more apparent on SEM evaluation. Each file showed distinctive characteristics in the shape that was cut. The cutting appeared to be as a result of abrasion with no operator assisted movement and was as a result of the longitudinal file action. However when movement was superimposed on this action continuous chip formation was apparent especially for the Rispisonic and Shaper files.

Intra-canal cutting ability of MM1500 files

The aims of this study were to develop a model system capable of monitoring lateral forces during root canal preparation and to measure the cutting ability of files activated by the MM1500 sonic handpiece. Forces were monitored by a calibrated model system which utilized a combination of spring steel beams fitted with strain gauges, these were interfaced through two strain gauge amplifiers to an x-y recorder. Single rooted canine teeth (n = 36; 32 experimental, four control) were mounted in a two-part acrylic mould (which was an integral part of the model system) prior to sectioning horizontally 11 mm from the tooth apex. A 2(4) full factorial experiment with two replications was performed. Four variables were selected for evaluation, load (50 and 100 g), power (air inlet ring half or fully open), file type (Heliosonic or Shaper) and stroke rate (1 or 2 cycles per second). A new file (size 25) was used for 1 min in each canal with water irrigation. The control group was not instrumented. The cross-sectional root canal area was measured before and after instrumentation using image analysis and increase in area was used as an indication of cutting ability. The results showed that the increase in load, power and the Shaper file all produced a significant increase in cutting ability (ANOVA, P < 0.001). However, stroke rate was not found to have a significant effect (P > 0.05). None of the interactions between the variables were significant and there was no significant difference in the control group (P > 0.05). In conclusion, this work has developed a model system to monitor lateral forces and has shown that instrument design and operator usage affect dentine removal from a root canal wall.

Factors affecting the wear of sonic files

The aim of this study was to investigate factors affecting the wear and cutting ability of sonic files. A model system was used and the following variables evaluated, file type; Heliosonic, Rispisonic or Shaper, load; 25, 50 or 100 grams and length of time in use; new, 30 or 60 seconds. A 3(3) full factorial analysis with two replications into the effect of the above variables on the cutting ability of the Heliosonic, Rispisonic and Shaper files powered by the MM1500 sonic instrument was performed. A new file size 25 (Heliosonic and Shaper) or No 3 (Rispisonic) was used for each cut together with water irrigation and the substrate used was 1 mm thick sections of bovine bone. All variables had a significant effect on cutting (ANOVA. p < 0.001). However examination of the F values showed that the most significant variable was load, followed by file type, and time. The most significant interaction was between file type and load followed by time and file type. The interaction between time and load was not significant (p > 0.05). The Rispisonic file was most susceptible to wear during use especially at higher loads and the Heliosonic file cut least. It is suggested that the Shaper file is the better design of the three with respect to cutting ability and wear with use.

Breakage of ultrasonic root-end preparation tips

Modified ultrasonic tips are used to prepare rootend cavities during endodontic surgery. The purpose of this study was to determine whether such tips are prone to breakage during use. Ten different tip designs were driven by an ultrasonic unit at maximum power. Multirooted teeth were instrumented, the apex removed, and the tooth was placed horizontally on a pan balance. The apex was instrumented by each ultrasonic tip in turn for 15 min, with the load being increased by 100 g every 5 min. Those tips with curvatures of 70 degrees or greater fractured within the first 5-min loading period. Breakage occurred approximately 2 to 3 mm from the end and always at a bend. Scanning electron microscopy revealed that the fractures were brittle in nature, with little change in the remaining section. Two tips bent: one isthmus preparation tip and one silver point removal tip. All the other designs were deemed satisfactory after experimentation. This study shows that fracture of ultrasonic tips can occur and is related to the degree of bending.

Factors affecting the cutting ability of sonic files

The aim of this study was to investigate the cutting ability of sonic files. A model system was developed and the following variables evaluated: file type. Heliosonic or Shaper; file length, 21 or 29 mm; power, air inlet ring opening of half or fully open; stroke length, 2 or 4 mm; stroke rate, one or two cycles per second; and load 50 or 100 g. A 2(6) full-factorial analysis with two replications into the effect of the above variables on the cutting ability of the MM1500 sonic instrument was performed. A new size 25 file was used for each cut, together with water irrigation, and the substrate used was 1-mm thick sections of bovine bone. The differences between the variables were significant (ANOVA, P < 0.001). However, examination of the F-values showed that the most significant variable to affect cutting was load, followed by power, file type, stroke length and stroke rate, with the least significant variable being file length. The most significant interaction was between rate and length of stroke. An increase in stroke rate from one to two cycles per second at a stroke length of 2 mm produced an increase in cutting for both the Heliosonic and Shaper files. However, at the longer stroke length of 4 mm, the same increase in rate resulted in a decrease in cutting for the Shaper files. Therefore, it is suggested that operators should press the file against the canal wall and move it slowly to maximise cutting.

Taper and stiffness of sonic endodontic files

The aims of this investigation were to measure the thickness and taper of the different files (Heliosonic 15-40. Shaper 15-40 and Rispisonic 1-6) supplied with the MM1500 sonic instrument and relate this to their stiffness. The diameter of the files (n = 5 for each file type) was measured at 2 mm intervals using light microscopy and a calibrated graticule (mag x 120). A model system was developed for the stiffness testing. The file was held 3 mm from its tip and the load in g required to produce a 45 degrees deflection of the file was recorded. Measurements of file diameter showed that the width of the Heliosonic and Shaper increased in a linear manner and that the file taper was the same for increasing file sizes in accordance with ISO recommendations. The Rispisonic files however showed differing widths and degrees of taper which were not consistent with ISO standards. The stiffness testing results showed the Heliosonic files to be less flexible than the Rispisonic and Shaper files for all sizes (ANOVA, p < 0.001). The differences in stiffness of the Heliosonic, Shaper and Rispisonic files were due to the variation in cross sectional area of metal. In conclusion sonic endodontic files do not have the same taper and stiffness.

Cutting characteristics of a sonic root-end preparation instrument

The aim of this study was to investigate the cutting ability of retro tips powered by a sonic handpiece (MM 1500, Micro Mega, Prodonta, Geneva, Switzerland). Two levels of the following variables were evaluated in this study: a) power setting with the an inlet ring half or fully open, b) orientation of tip perpendicular or parallel to the long axis of the handpiece, c) length of tip 2 or 3 min, d) loading of 25 or 50 grams, e) tip size 35 or 55. The substrate used was 1 mm thick sections of bovine bone and load was controlled by using a load cell interfaced with a transducer meter. Instrumentation time was fixed at 10 seconds with water irrigation. A 2(5) full factorial analysis was performed with two replications making a total of 64 experimental units. The resultant depth of cut was measured using a stereo microscope at x50 magnification. Analysis of the data indicated that all variables had a significant effect on cutting (ANOVA p < 0.05). The most significant factor was power, followed by tip length tip orientation, width and load. An increase in loading resulted in tip constraint and a reduction of cutting at the lower power setting. In conclusion sonically activated retro tips were found to cut satisfactorily with instrument air inlet ring opening/power having the main effect.

Sonic instruments in root canal therapy

Although hand instrumentation is considered the most acceptable method of preparing root canals, sonic instruments may be useful additions to the endodontic armamentarium. Sonic instrumentation may be incorporated as an adjunct to traditional techniques for shaping the root canal. The use of such instruments may assist the practitioner during root canal treatment in general practice.

Applying composite luting agent ultrasonically: a successful alternative

The authors conducted research to determine if sonic vibration affected the viscosity of a composite luting agent. They found that using either an ultrasonic or a sonic scaler can thin composite resin. The thickness of the lute is similar to that resulting from manual loading methods, but it is obtained in much shorter time periods and with lower loads.

Tunnel restorations: a long-term pilot study over a minimum of five years

OBJECTIVES

The purpose of this study was to investigate the long-term performance of tunnel restorations.

METHODS

Thirty-three glass polyalkenoate (ionomer) or cermet restorations were placed in the premolar or first molar teeth of 25 patients. Conservative amalgam control restorations were the means of treatment in 14 similar teeth of the same group. Review as to performance consisted of a regular clinical and radiographic examination and the criteria for failure were recurrent caries, fracture of the marginal ridge or gross loss of restorative material.

RESULTS

After 3 years all types of restoration were satisfactory. By approximately 5 years one-quarter of the glass ionomer and 10% of the cermet restorations had failed. All the failures after any period of service could be replaced by conservative amalgam fillings. None of the controls required replacement.

CONCLUSION

While tunnel restorations employing glass ionomer material and the cermet variant do enjoy a degree of success, this preliminary work suggests that small restorations of dental amalgam are more successful in the long term.

Cutting ability of an ultrasonic retrograde cavity preparation instrument

The aim of this study was to investigate the cutting ability of a working ultrasonic instrument designed for surgical endodontic use (Neosonic, Amadent Corp, Cherry Hill, NJ, USA). Three designs of tip, designated CT 1 to CT 3 were calibrated by measuring their displacement amplitudes in air using light microscopy over a range of power settings. Extracted teeth were sectioned longitudinally and polished to produce a smooth dentine surface onto which the tips were applied for 1 minute over the above range of power settings at a load of approximately 20 g. The depth of cut in the dentine surface was measured using a two dimensional surface profilometry technique. Results showed that a raising of the power setting produced an increase in displacement amplitude and cutting ability for all tip designs. This increase was linear, with minimal cutting occurring at lower power settings. In conclusion the ultrasonic tips could be successfully used to remove dentine, and medium to high power settings optimised their efficiency.

An in vitro investigation into the cutting ability of ultrasonic K files

Endosonic files vary in their oscillation when operated in air with the greatest displacement at the unconstrained tip. It was the aim of this study to investigate how files of different lengths and sizes varied in their ability to cut dentine. Single rooted teeth were sectioned to produce 1 mm dentine discs. These were positioned on a plastic block connected to a load transducer. Endosonic K-files (#15 to 25) were used to cut the disc for 10 s using operator assisted movement. The files contacted the disc at the following points along their length; apical (3 mm from tip), middle (8 mm from tip) and coronal (13 mm from tip) under applied loads of 30 and 50 g. The depth of cut produced by each file was measured using light microscopy. The #15 and #25 were similar in their pattern of dentine removal. The #20 file produced a large variation in its cutting ability and was also susceptible to fracture. The tip of the files was prone to constraint at higher loading with the thicker part of the file producing more cutting. It was concluded that the pattern of dentine removal of endosonic files was affected by the amount of load applied. The displacement amplitudes of endosonic files in air would not appear to be a good indicator of file cutting ability.

Effect of air inlet ring opening on sonic handpiece performance

This study investigated the effect of air inlet ring opening on the oscillatory pattern of the MM 1500 sonic handpiece and files. The oscillatory pattern of the driver head and files in air and under load was determined microscopically. The results showed that a critical opening of the air inlet ring was necessary to elicit oscillation of the driver head and sonic file. The driver oscillated in an elliptical manner, the displacement of which varied with air inlet ring opening. When operated in air the file exhibited an elliptical movement which was influenced by different design, length and thickness. This action was constrained under load and replaced by a longitudinal action of the same dimension for all files which appeared to have an efficient cutting action. This work shows that air inlet ring opening increases oscillation of the driver head once a critical opening has been reached and that clinical loading does not constrain the cutting action of the file.

Variability of sonic scaling tip movement

The sonic scaler operates at frequencies of 2 to 6 kHz and is powered by pressurised air from the dental unit. Variables likely to affect how these instruments perform include the air pressure input and load applied by the operator. Other variables include the brand of scaler used and the clinical technique of the operator. The aim of this study was to investigate differences in instrument performance within a dental teaching hospital. Light microscopy was used to measure the displacement amplitudes in air of 32 Sonic scalers which were in regular clinical use in three departments (Periodontal Unit, Restorative Unit and School of Hygiene). During operation, the air pressure was kept at a constant 2.8 kg cm-2 and measurements were made on each instrument with three scaling tips (universal, sickle and periodontal). The periodontal scaling tip exhibited the greatest vibration although this was not significant (p > 0.1). There was a significant difference in performance between the different clinical environments where the scalers were used (p < 0.01). 4 new sonic scaling instruments made by different manufacturers were selected for displacement amplitude measurements. One brand of sonic scaler demonstrated a significantly greater displacement amplitude in comparative measurements between instruments (p < 0.01). This study demonstrated differences in the oscillation of sonic scalers which should be recognised by clinicians when using these instruments, since they may influence clinical performance.

Site-specific alkaline phosphatase levels in gingival crevicular fluid in health and gingivitis: cross-sectional studies

Using a recently developed chemiluminescent assay enabling alkaline phosphatase (ALP) quantification in nanolitre volumes of gingival crevicular fluid (GCF), we have investigated GCF ALP levels in health and in the presence of gingivitis. In gingival health, there was a site-specific pattern of ALP concentration with higher enzyme concentrations around the upper and lower anterior teeth. Furthermore, clinically normal sites that had been subjected to different levels of plaque control produced significantly different ALP levels, (p < 0.03). This indicates that biochemical components of GCF may be used to measure subclinical inflammatory status. The ratio of GCF to serum ALP varied from 6:1 to 11:1, suggesting that a major source of the enzyme is through local production. The main cross-sectional study of 30 patients with gingivitis (276 sites) demonstrated that total GCF ALP levels, collected over a 30-s sampling time were higher for a gingival index of 1 than of 0 (p < 0.014). There was no significant relationship between total GCF ALP and plaque levels of the enzyme, and analysis of plaque within the study group demonstrated very low levels of ALP, indicating that the enzyme is likely to be largely derived from the periodontal tissues. The ratio of GCF ALP levels to those of saliva within individuals was 530:1, thereby eliminating saliva contamination as a risk, when total GCF ALP is being measured.

An in vitro investigation of Thermafil obturation at different temperatures

The apical leakage of lower premolars obturated with Thermafil at three different temperatures was investigated in vitro. The temperatures were determined after calibration of the Thermaprep oven. The root canals of 35 extracted teeth were prepared chemomechanically and divided into three groups of 10 each with a control group of five. The root canals of the experimental group were obturated using plastic Thermafil obturators at three different temperatures 144, 120 and 100 degrees C with the controls being obturated using laterally condensed gutta percha. The teeth were suspended in indian ink for 28 days prior to being cleared and the degree of apical leakage assessed. The results showed no significant difference (p > 0.05) in the apical leakage of the teeth obturated with Thermafil compared to laterally condensed gutta percha. There was a trend towards less leakage in the teeth obturated with Thermafil at the lower temperatures, this, however, was not significant (p > 0.05).