Investigation of the effect of a proprietary dental waterline disinfectant on shear bond strengths of Panavia 21 to enamel and dentine.

This study investigated the effect of 'Alpron mint', a dental unit waterline disinfectant, on shear bond strengths between 'Panavia 21' resin based cement and tooth tissue. Eighty-eight human premolar tooth specimens were prepared in either enamel (N=44) or dentine (N=44). Half the specimens within each group were irrigated with an Alpron mint solution and the other half with distilled water (control) prior to application of Panavia 21 resin luting cement. There was no significant difference in shear bond strengths for both enamel and dentine with Alpron mint irrigation compared with distilled water (P = 0.245).

Assessment of the amount of remaining coronal dentine in root-treated teeth.

OBJECTIVES: There is currently no standardised technique to measure the amount of coronal dentine remaining in a root-treated tooth after crown preparation. The aim of this study was to develop a method of measuring remaining coronal dentine in root-treated teeth and to propose an index for grading tooth restorability. METHODS: The study recruited 20 patients who had completed molar endodontic treatment at the Eastman Dental Hospital and had been prescribed an amalgam coronal-radicular core with a full coverage cast restoration. Using a series of interlocking special trays and impressions, a method was devised to produce a cast of the amount of remaining dentine coronal to the finish line after crown preparation. This cast was scanned using a laser profilometer and the volume of remaining dentine was calculated. A tooth restorability index (TRI) was developed to assess the strategic value of the remaining dentine. The TRI allowed scores of 0-3 in each sextant with a maximum score of 18 per tooth. RESULTS: Twenty teeth were scored by three examiners and the TRI scores varied from 2 to 13. The volume of coronal dentine varied from 61.73 to 232.22 mm(3). CONCLUSIONS: A tooth restorability index has been devised to assess the strategic value of remaining dentine. A Kappa statistic was calculated to produce values of 0.584, 0.688 and 0.720, giving moderate-good agreement between the examiners.

Root canal obturation by ultrasonic condensation of gutta-percha. Part II: an in vitro investigation of the quality of obturation.

AIM: To compare the quality of root canal obturation using ultrasonic or cold condensation of gutta-percha and to determine the effect of power setting and activation time on the quality of obturation using the former technique. METHODOLOGY: An extracted human maxillary canine was used in an in vitro split tooth model to allow repeated obturation of the same root canal system using an ultrasonic device to thermocompact gutta-percha without sealer. After each obturation, the root filling was removed from the tooth to allow evaluation of its quality and for the tooth to be re-obturated. The influence of combinations (n = 10 per combination) of power setting (1, 3, 5) and activation times (4, 10, 15 s) was tested on the quality of root filling, assessed by measuring the voids within the body of the root filling as well as at the surface. Image analysis was used to quantify the voids within the body of the root filling. Cold lateral condensation of gutta-percha served as a control. RESULTS: Both surface and cross-sectional analyses revealed that different power setting and activation time combinations produced significantly fewer voids than cold lateral condensation (P < 0.05) at the apical, mid-root and coronal levels. CONCLUSIONS: Taking surface and cross-sectional analysis together only power setting 5 and activation times of 10 and 15 s consistently produced ultrasonically thermocompacted root canal fillings with fewer voids than cold lateral condensation without sealer.

Ultrasonic condensation of gutta-percha: the effect of power setting and activation time on temperature rise at the root surface - an in vitro study.

AIM: To determine the effect of power setting and duration of activation on the temperature rise at the root surface during root canal obturation by ultrasonic condensation of gutta-percha. METHODOLOGY: A human maxillary canine was used in an in vitro split tooth model to allow repeated obturation of the root canal system using an ultrasonic device to thermocompact gutta-percha. Combinations of power settings (1, 3 and 5) and durations of activation (4, 10 and 15 s) were used to test their effect on temperature rise at the root surface using eight K-type thermocouples at the mid-root and apical levels. At the end of each obturation, the tooth was disassembled to remove the gutta-percha in preparation for the next obturation (n = 10 for each combination). Multiple linear regression models were used to investigate the effects of power setting, duration of activation and thermocouple location on the maximum temperature rise recorded. RESULTS: Only one combination of power setting (5) and duration of activation (15 s) resulted in temperature rise in excess of 10 degrees C. The maximum temperature rise at the mid-root level was significantly (P < 0.001) greater than that recorded apically. It is also significantly affected by the combination of power setting and duration of activation. CONCLUSIONS: Temperature rises at the root surface during ultrasonic condensation of gutta-percha in excess of 10 degrees C were evident in only one combination of power (5) and time (15 s) settings at the mid-root level.

Prevalence of and factors affecting post-obturation pain in patients undergoing root canal treatment.

AIM: This longitudinal, prospective study (1) investigated the prevalence of post-obturation pain after root canal treatment and (2) evaluated the influence of factors affecting the pain experience. METHODOLOGY: Twenty practitioners, comprising general dental practitioners, MSc graduates and Endodontists, participated in this study. The patient sample (n = 415) was derived from consecutive patients attending the practitioners' surgeries for root canal treatment on a single tooth. Demographic, medical history, preoperative and intra-operative data as well as pain experience on day 1 and day 2 after root canal obturation were recorded. Intensity of pain experienced was recorded on a visual analogue scale (VAS) of 0-5. The data were analysed using logistic regression models. RESULTS: The prevalence of post-obturation pain within 48 h after treatment was 40.2% (n = 167) but less than 12% of patients experienced severe pain (VAS 4 or 5) on either day 1 or day 2. The factors that significantly influenced post-obturation pain experience were: gender (OR = 0.434, P < 0.001), tooth type (OR = 1.733, P = 0.007), size of periapical lesion (OR = 0.493, P = 0.004), history of post-preparation pain (OR = 4.110, P = <0.001) or generalized swelling (OR = 3.435, P = 0.005) and number of treatment visits (OR = 2.604, P < 0.001). CONCLUSIONS: The prevalence of post-obturation pain was high (40.2%). The important prognostic determinants of post-obturation pain were female, molar tooth, size of periapical lesion smaller than 3 mm, history of post-preparation pain or generalized swelling and single-visit treatment.

Prevalence of and factors affecting postpreparation pain in patients undergoing two-visit root canal treatment.

AIM: This longitudinal, prospective study (i) investigated the prevalence of postpreparation pain during root canal treatment and (ii) evaluated the influence of factors affecting the pain experience. METHODOLOGY: Twenty practitioners, comprising general dental practitioners, MSc graduates and endodontists, participated in this study. The patient sample (n=272) was derived from consecutive patients attending the practitioners' surgeries for a two-visit root canal treatment on a single tooth. Demographic, medical history, preoperative and intraoperative data as well as pain experience on days 1 and 2 after root canal preparation were recorded. Intensity of pain experienced was recorded on a visual analogue scale (VAS) of 0-5. The data were analysed using logistic regression models. RESULTS: The prevalence of postpreparation pain within 48 h after treatment was 64.7% (n=176), but less than 10% of patients experienced severe pain (VAS 4 or 5) on either day 1 or day 2. The presence of preoperative pain (OR=2.841, P<0.001), tooth type (OR=2.008, P=0.009), systemic steroid therapy for other medical reasons (OR=0.181, P=0.023) and preoperative swelling (OR=2.433, P=0.040) were the only factors to significantly influence postpreparation pain experience. CONCLUSIONS: The prevalence of postpreparation pain was high, and the important prognostic determinants were presence of preoperative pain, tooth type, systemic steroid therapy and preoperative swelling.

Clinical evaluation of a carbon fibre reinforced carbon endodontic post.

This study reports a prospective clinical trial comparing a carbon fibre reinforced carbon (CFRC) endodontic post with a conventional prefabricated post. Twenty-seven single rooted maxillary anterior teeth in 18 patients (nine males and nine females; age range 18-60 years) were restored either with a CFRC post or a wrought precious alloy control. Cast type III gold alloy cores were used in conjunction with both post groups. The CRFC posts (n = 16) were cemented with a composite luting agent and the conventional posts (control) were cemented with zinc phosphate. Four failures were recorded in the CFRC post group at 24, 29, 56 and 87 months, compared with one failure in the control group at 84 months. These results suggest that post-retained crowns utilizing a CFRC material and a composite resin luting agent do not perform as well as conventional wrought precious alloy posts.

A laboratory investigation of the accuracy of two impression techniques for single-tooth implants.

PURPOSE: This laboratory study investigated the accuracy of four implant impression procedures using two impression techniques and two different materials. MATERIALS AND METHODS: A master model was used to produce 40 different stone casts incorporating laboratory implant or abutment analogues from the different combinations of two impression techniques (the repositioning impression coping technique at the implant level and the pickup impression technique at the abutment level) and materials (President polyvinyl siloxane and Impregum F polyether). Variations in the resulting working casts were measured using the Reflex Microscope to derive distances and angles from the three-dimensional coordinates of optical targets that were attached to a test coping placed on the implant analogue and on a reference device positioned on the occlusal surfaces of the casts. RESULTS: The results showed greater variations in analogue position with the repositioning impression technique than with the pickup technique. The rotational errors were large enough to be of clinical concern. No significant differences were found between polyvinyl siloxane and polyether impression materials for the two tested types of impression techniques. CONCLUSION: The repositioning impression technique at the implant level can produce less predictable results than the pickup technique at the abutment level. The choice of impression material made no significant difference.

Effect of Nd:YAG radiation at millisecond pulse duration on dentine crater depth.

BACKGROUND AND OBJECTIVE: The effect of laser parameters on laser-dentine interaction has not been explored fully. This in vitro study investigated the effect on dentine crater depth of Nd:YAG laser radiation with varying repetition rates, total delivered energy, and dentine site either dyed or undyed. STUDY DESIGN/MATERIALS AND METHODS: One hundred forty-four caries-free third molars were sectioned transversely to provide 288 upper and lower cut surfaces. The upper surfaces were dyed (IR5). These upper and lower cut surfaces were exposed to an Nd:YAG laser with a 7 millisecond (msec) pulse duration, pulse repetition rates (RR) of 2. 5, 5.4, and 10.5 Hz, and four total energies (2.28, 2.64, 3.6, 4.2 joules). Dentine crater depth was measured by using a Reflex microscope. Results were statistically analysed with analysis of variance. RESULTS: Crater depth increased with increase in total delivered energy and in dyed and inner dentine sites (P<0.0001) but decreased with increasing repetition rate (P< 0.0001). CONCLUSIONS: Increasing energy, dyed, and inner dentine sites produced deeper craters.

A comparison of thermocouple and infrared thermographic analysis of temperature rise on the root surface during the continuous wave of condensation technique.

AIM: This study was designed to use two methods of temperature measurement to analyse and quantify the in vitro root surface temperature changes during the initial stage of the continuous wave technique of obturation of 17 single-rooted premolar teeth with standard canal preparations. METHODOLOGY: A model was designed to allow simultaneous temperature measurement with both thermocouples and an infrared thermal imaging system. Two thermocouples were placed on the root surface, one coronally and the other near the root apex. A series of thermal images were recorded by an infrared thermal imaging camera during the downpack procedure. RESULTS: The mean temperature rises on the root surface, as measured by the two thermocouples, averaged 13.9 degrees C over the period of study, whilst the infrared thermal imaging system measured an average rise of 28.4 degrees C at the same sites. Temperatures at the more apical point were higher than those measured coronally. After the first wave of condensation, the second activation of the plugger in the canal prior to its removal always resulted in a secondary rise in temperature. The thermal imaging system detected areas of greater temperature change distant from the two selected thermocouple sites. CONCLUSIONS: The continuous wave technique of obturation may result in high temperatures on the external root surface. Infrared thermography is a useful device for mapping patterns of temperature change over a large area.

Surface strains induced by measured loads on teeth in vivo: a methodological study.

Visual feedback enabled three subjects to apply predetermined near-axial loads to the incisal edge of an intact maxillary central incisor. In two subjects, principal strains and orientations developed on the labial surface of the intact incisor were resolved from strains recorded with a multiple element strain gauge. Load application was accurate and precise enough to allow resolution of strains induced by target loads of 10 to 50 N. Axially orientated compressive labial surface strains were induced by measured loads. The method could be used to validate bench-top stress analyses and investigate the effects of restoration on the structural integrity of teeth.

A retrospective study of 50 treatments using an appliance to produce localised occlusal space by relative axial tooth movement.

This paper describes the use of 50 appliances which have been used to produce a localised occlusal space prior to the restoration of teeth. These were provided for 45 patients aged 19 to 69 years at the Eastman Dental Hospital London between 1981 and 1994. The concept is similar to that described by Dahl, the space being produced by the teeth in contact with the appliance being intruded and those out of contact over erupting. Many of the appliances however differed from those originally described by Dahl.

Conventional crown and bridgework.

The restoration of worn teeth with crowns requires a number of strategies to create space for retentive, resistant and durable castings.

An in vitro investigation of the temperature rises produced in dentine by Nd:YAG laser light with and without water cooling.

Infrared lasers are reported to have thermal side effects which may damage pulp tissue. This study investigated the thermal effects of the pulsed Nd:YAG laser. Prepared, extracted teeth were measured prior to irradiation. Temperature was recorded using a thermocouple/data logging system. Laser irradiation was carried out with or without water spray for an exposure time of ten seconds. Results indicated that dry irradiation produced unacceptable temperature rises with dentine thicknesses used. Wet irradiation produced a significantly lower temperature rise. It was concluded that the Nd:YAG laser produced thermal effects which could potentially cause pulpal trauma. A water coolant was effective in reducing these thermal effects, but the temperature rise achieved whilst using water coolant may still cause pulpal damage.

How long do routine dental restorations last? A systematic review.

OBJECTIVE: To conduct a systematic review of the literature on the longevity of routine dental restorations in permanent posterior teeth, and to identify and examine factors influencing its variability. METHOD: Accepted guidelines were followed. An advisory group oversaw the project. Simple Class I and Class II amalgam, composite resin, glass ionomer and cast gold restorations were covered. Comprehensive searching of electronic databases, hand-searching, and location of 'grey' literature, generated 124 research reports. Those considered relevant were assessed for validity and quality according to agreed criteria. The analysis was descriptive. RESULTS: Eight of 58 relevant research reports were categorised, according to agreed criteria, as being of satisfactory validity and quality. They suggested that 50% of all restorations last 10 to 20 years, although both higher and lower median survival times were reported. The findings were supported by the totality of studies reviewed. However, variability was substantial. Restoration type, materials, the patient, the operator, the practice environment and type of care system appeared to influence longevity. CONCLUSIONS: Many studies were imperfect in design. Those considered to be the most appropriate for analysis were too limited to undertake a formal statistical exploration. Therefore there remains a need for definitive randomised controlled trials of restoration longevity, of sound design and adequate power, employing standardised assessments and appropriate methods of analysis.

Die relief, seating methods and fit of full crowns.

This study investigated the influence of different frequencies of vibration supplied by an electropneumatic condenser on the seating rate and vertical discrepancy of full crowns with four different internal configurations: A) unrelieved; B) four layers of die spacer; C) eight layers of die spacer and D) unrelieved but vented occlusally. Crowns were luted with zinc phosphate cement under a static 5 Kg load alone and with three frequencies of vibration. The seating process was monitored electronically to determine seating rate and final fit. Venting and die relief enhanced seating under static load. Vibration increased the seating rate and reduced vertical discrepancy of groups B to D crowns compared to group A crowns. Medium frequency vibration with group C and D crowns gave the smallest vertical discrepancies. Vibration did not improve the final seating of group A crowns. This suggests that vibration is only effective when an escapeway of some kind is provided.

An in vitro evaluation of a carbon fiber-based post and core system.

STATEMENT OF PROBLEM: A self-contained post and core system, Composipost, comprising an epoxy-based carbon fiber post, a composite core material, and a low viscosity Bis-GMA bonding resin, has recently been marketed for the restoration of pulpless teeth. PURPOSE: This study compared the in vitro performance and the failure characteristics of the Composipost system against existing post and core combinations. MATERIAL AND METHODS: Using extracted human teeth, three post and core test groups and one control group were then tested to failure with an obliquely applied compressive load at 130 degrees in a Hounsfield testing-machine with a crosshead speed of 5 cm/minute. RESULTS: The mean stress values at failure (MNm.2) with standard deviations for each group were as follows: Composipost system 8.89, SD 2.40; stainless steel post and composite core 14.18, SD 3.49; cast gold alloy post and gold alloy core 15.25, SD 4.07; and endodontically treated tooth only 24.84 SD 4.58. CONCLUSION: The specimens restored with the Composipost system exhibited inferior strength properties in comparison to the other post and core systems tested (p < 0.01). Teeth without post and core foundations tested significantly stronger than the other comparison groups (p < 0.01).

In vitro measurement of cuspal strain and displacement in composite restored teeth.

OBJECTIVES: This study was carried out to measure changes in cuspal strain and displacement occurring during placement and polymerization of bonded composite restorations in extracted human teeth in vitro. METHODS: Strains were measured using electrical resistance strain gauges bonded to the buccal and lingual cusps of each specimen and cuspal displacement was recorded with a linear variable differential transformer. Mesio-occluso-distal cavities of two types were prepared in lower molar teeth. Following enamel acid etching and application of a dentine adhesion promoter, specimens were restored incrementally with a light curing posterior composite material. RESULTS: It was shown that the shrinkage of a composite material during polymerization generated stresses which resulted in tensile strains on the tooth surface. Strains of up to 882 microns/m were recorded and a maximum cusp displacement of 14 microns was also measured. These strains were reduced but not eliminated by preparation and restoration a mesio-distal slot running the full length and depth of the restoration. Statistical analysis revealed significantly higher strains and displacement produced on the buccal cusps of teeth that had a reduced cusp width (P < 0.001). CONCLUSIONS: The in vitro restoration of posterior teeth with a bonded composite material generates polymerization stresses which can be recorded as tensile strains and displacements on the tooth surface. Strains measured during composite placement were greater when the remaining cusp width was less. A stress relief procedure resulted in a decrease in cuspal strain and displacement of approximately 30-40%.

The application of thermoelastic analysis to study stresses in human teeth.

The aims of this investigation were to use a full-field thermoelastic technique to study the stress distribution on human teeth subjected to dynamic loads and derive a value for the thermoelastic constant for human enamel. Surface stresses were observed on extracted intact human molar teeth subjected to a load of 200 N cycled at 20 Hz. Measurements were repeated for the same teeth following mesio-occluso-distal cavity preparation and restoration with amalgam and adhesively bonded composite restorations. A value for the thermoelastic constant for human enamel (Km) of 2.25 X 10(-12)m2/N was calculated from physical coefficients in the literature. Unprepared specimens exhibited a comparable magnitude and distribution of stresses to those seen when teeth were restored with adhesively bonded composite restorations. Higher stresses were observed on prepared teeth and there was little change following restoration with amalgam. It can be concluded that a full-field thermoelastic stress analysis technique can be successfully applied to study teeth subjected to axial dynamic loads in vitro and that the resultant stresses are greater in prepared teeth than those restored with bonded composite materials.