Growth factor release from dentine matrix by pulp-capping agents promotes pulp tissue repair-associated events.

AIM: To characterize growth factor release from dentine by pulp-capping agents and to determine the effects of liberated dentine extracellular matrix (dECM) components on pulp cells in the key wound healing processes of migration and cell growth. METHODOLOGY: Powdered human dentine was exposed to solutions of calcium hydroxide, white and grey mineral trioxide aggregate (MTA) (ProRoot, (Dentsply Tulsa, Tulsa, OK, USA) over 14 days. The solubilized dECM components were dialysed and lyophilized and characterized using multiplex quantitative ELISA. Following dECM component extraction dentine was analysed using Fourier-transformed infrared spectroscopy (FTIR). Primary rat dental pulp cells (RDPCs) were exposed to dECM components (0.1-100 µg mL-1 ) released by calcium hydroxide, white and grey MTA, and cell growth and chemotactic responses were assessed. Statistical differences between the experimental and control groups were determined using one-way anova. RESULTS: A broad range of growth factors, many not previously reported in dentine, were liberated by these pulp-capping agents, including SCF, M-CSF, GM-CSF, IGFBP-1, NGF and GDNF. White and grey MTA liberated more growth factors than calcium hydroxide. FTIR analysis of dentine exposed to pulp-capping agents showed partial depletion of amide bands I, II and III, with little alteration in phosphate peaks compared to untreated dentine. dECM components released by white and grey MTA induced significantly more cell growth at low-to-moderate concentrations (P â‰¦ 0.05) examined in this study and significantly enhanced cell chemotaxis at all concentrations compared with controls (P â‰¦ 0.05). CONCLUSIONS: White and grey MTA solubilize a broad range of bioactive molecules from dentine, which can induce proliferation and chemotaxis in pulp cells.

Should pulp chamber pulpotomy be seen as a permanent treatment? Some preliminary thoughts.

AIM: To investigate the benefits of pulpotomy (to the level of the floor of the pulp chamber) as an endodontic treatment for teeth with vital pulps. METHODOLOGY: Seventeen patients, aged 7-54 years (mean of 37.2 year), were treated by pulpotomy and filling with ProRoot MTA(®) in premolar or molar teeth with vital pulps and without clinical evidence of irreversible pulpitis. The patients were then followed up for 12 to 24 months and the teeth then assessed by clinical and radiographic examination. Statistical analysis was performed with Kaplan-Meier survival probability statistics to estimate the survival of the treated teeth. RESULTS: At 24 months, the survival rate without any complementary treatment was estimated to be 82%. Two of the 17 treated teeth required root canal treatment for pain control and one for prosthetic reasons. CONCLUSIONS: Under the conditions of this study, pulpotomy offered a viable alternative to root canal treatment for teeth with vital pulps in the short term. However, there is insufficient clinical evidence to consider this technique for the treatment of every permanent tooth. Nevertheless, it should be considered as a potential alternative approach to be further developed for future applications.

Dentin-pulp complex regeneration: from lab to clinic.

Dentistry is entering an exciting era in which many of the advances in biotechnology offer opportunities for exploitation in novel and more effective therapies. Pulp healing is complex and dependent on the extent of injury, among many other factors. Many of the molecular and cellular processes involved in these healing events recapitulate developmental processes. The regulation of odontoblast activity is clearly central to pulp healing, and an understanding of the mechanisms involved in these processes is necessary to enable laboratory studies to be translated to clinic application. Transcriptome analysis has identified changes in many odontoblast genes during the life-cycle of this cell and its responses to injurious challenge. The p38 MAPKinase pathway appears to be central to the transcriptional control of odontoblasts and may provide a key target for therapeutic intervention. The many recent advances in knowledge of pulpal stem cells and molecular signaling molecules within the tooth, now provide exciting opportunities for clinical translation to novel therapies. Such translation will require the partnership of researchers and skilled clinicians who can effectively apply advances in knowledge to appropriate clinical cases and develop novel therapies which can be realistically introduced into the clinic.

Ten-year outcome of root fillings in the General Dental Services in England and Wales.

AIM: To consider the survival of root canal treatment provided within the General Dental Services in England and Wales, with failure being defined as re-treating of a root canal, apical surgery or extraction. METHODS: A data set was established consisting of patients, 18 years or older, whose birthdays were included within a set of randomly selected dates and whose restoration records contained the placement of one or more direct restorations or crowns in courses of treatment between September 1990 and January 2002. The history of each root canal-treated tooth was consulted, and the next date for an intervention on the root canal of the tooth, defined as a re-treatment, apical surgery or extraction, was obtained. Thus, a data set was created of root canal-treated teeth, with the dates of root canal filling placement and the dates, if any, of re-intervention. RESULTS: Data for over 80,000 different adult patients were analysed, and a total of 30,843 root canal-treated teeth identified from the data over a period of 11 years. The proportion surviving without further treatment of the root canal was estimated at 74% within an observation time of up to 10 years, with survival being strongly correlated with the characteristics of the patient, including age and treatment history, with older patients having root canal treatment with earlier re-intervention than those of younger patients. CONCLUSION: Within the data set analysed, an estimated 74% of root canal-treated teeth pass through 10 years without re-treatment, apical surgery or extraction.

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.

Root canal retreatment.

UNLABELLED: 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.

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.

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.

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.

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.

Effect of precurving on the performance of endosonic K files.

This study compared the performance of precurved and straight endosonic files. Size 15, 20, and 25 endosonic K files were precurved to different degrees (20 to 90 degrees) and the resultant oscillatory pattern showed no significant difference compared with corresponding straight files. Endovue blocks were prepared with either a #15, 20, or 25 endosonic file which was either straight or precurved. Those blocks prepared with precurved files had a continuous taper while blocks prepared with straight files had constrictions along their lengths. Finally, a curved root of a human natural tooth had windows prepared along its length so that the oscillatory pattern of the file could be observed. The precurved file oscillated more freely than a straight file as observed by the presence of antinodes along the file and the accumulation of dentin chips within the canal. The results of this study suggest that it is advantageous to precurve endosonic files before using them in curved canals.

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.

Effect of precurving endosonic files on the amount of debris and smear layer remaining in curved root canals.

Endosonic files are prone to constraint; this reduces their efficiency, particularly in the apical third and in curved root canals. Precurving the file may reduce constraint, thereby improving the file's ability to debride. This investigation was undertaken to compare both straight and precurved endosonic files as to debris and smear layer removal. Thirty-six curved root canals were randomly allocated into six groups. Each group was prepared using a step-down technique, then instrumented with either a straight or precurved endosonic file of size 15, 20, or 25. The tooth roots were split and examined under the scanning electron microscope. Blind examinations were made for debris and smear layer removal and evaluation scores were analyzed using a log linear approach. The root canals instrumented with the precurved files had a significantly lower debris score than those prepared with straight files. Precurving did not affect smear layer removal. In conclusion, precurving of files decreased the amount of debris but did not affect smear layer removal.

Cleaning of oval canals using ultrasonic or sonic instrumentation.

This study investigated the effect of direction of file oscillation on the amount of debris and smear remaining within oval canals. Sixty-five lower premolars were allocated to six experimental groups (n = 10) and one control group (n = 5). Canals were prepared using Gates Glidden burs and hand instruments. Preparations were completed using either an ultrasonic size 15 K file or a sonic size 15 shaper file. Three preparation techniques were used: (a) file oscillation toward oval recesses within the canal, (b) file oscillation at right angles to the recesses, and (c) rotational movement of handpiece. Canals were examined under the scanning electron microscope and blindly scored for debris and smear layer. Log linear analysis revealed no significant difference (p > 0.05) between sonic or ultrasonic instrumentation as to debris or smear layer remaining. File oscillation directed toward oval recesses left the least amount of debris (p < 0.05). Smear layer remained unaffected by all techniques.

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.

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.

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.

Ultrasound in dentistry. Part 2--Periodontology and endodontics.

Ultrasound in the kHz frequency range is used widely in clinical dentistry. The most common uses are in the fields of periodontology and endodontics. The ultrasonic scaler works by the vibratory chipping action of the oscillating tip and is assisted by the presence of cavitational activity in the associated cooling water. When assessing clinical studies it is often difficult to interpret results from different workers due to the lack of standardization of the ultrasonic scaler. Operators should be aware of the oscillatory pattern of different instruments. Endosonics utilizes an ultrasonically oscillating endodontic file to clean and shape the root canal prior to obturation. The cleaning ability of such files is assisted by the occurrence of acoustic microstreaming forces. The endosonic file is prone to constraint when it contacts the canal wall which alters its oscillatory pattern. Clinical techniques should be modified to reduce this problem.

Thermal changes and cure depths associated with a high intensity light activation unit.

OBJECTIVES: The objectives of this study were to evaluate the thermal emission and curing characteristics of a high intensity halogen light (Astralis 10-Ivoclar Vivadent, Schaan. Leichtenstein) alone and on curing a conventional and a fast-curing micro-hybrid composite. METHODS: A bead thermistor was placed in the base of a standard model cavity. The cavity was irradiated using the light unit whilst empty, and when filled with either composite. Temperature rises were recorded using the light in four different output modes. Further samples were prepared to assess depth of cure via a digital penetrometer, light transmission using a computer-based radiometer, and microhardness with a Wallace hardness tester. RESULTS: Mean peak temperature rises recorded during polymerisation of the composites ranged from 6.9 degrees C for the product InTen-S cured with the Adhesive programme (Adh) to 11.0 degrees C for the product Tetric Ceram HB cured with the High Power (HI P) programme. A significantly greater depth of cure was obtained for InTen-S in line with the greater light transmission obtained for this material. DISCUSSION: The very high thermal emission characteristics reported in a recently published investigation for this light unit were not confirmed. CONCLUSIONS: As the extent of thermal trauma that can be tolerated by the dental pulp is unknown consideration should be given to the choice of light activation unit and curing programme when polymerising light activated resin based restorations in deep cavities close to the pulp.

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.