David C. Attrill

Thermal effects of the Er:YAG laser on a simulated dental pulp: a quantitative evaluation of the effects of a water spray

OBJECTIVES To quantify the temperature increments in a simulated dental pulp following irradiation with an Er:YAG laser, and to compare those increments when the laser is applied with and without water spray. METHODS Two cavities were prepared on either the buccal or lingual aspect of sound extracted teeth using the laser. One cavity was prepared with water spray, the other without and the order of preparation randomised. Identical preparation parameters were used for both cavities. Temperature increments were measured in the pulp chamber using a calibrated thermocouple and a novel pulp simulant. RESULTS Maximum increments were 4.0 degrees C (water) and 24.7 degrees C (no water). Water was shown to be highly significant in reducing the overall temperature increments in all cases (p<0.001; paired t-test). None of the samples prepared up to a maximum of 135 J cumulative energy prepared with water spray exceeded that threshold at which pulpal damage can be considered to occur. Only 25% of those prepared without water spray remained below this threshold. DISCUSSION Extrapolation of the figures suggests probably tolerable limits of continuous laser irradiation with water in excess to 160 J. With the incorporation of small breaks in the continuity of laser irradiation that occur in the in vivo situation, the cumulative energy dose tolerated by the pulp should far exceed these figures. CONCLUSIONS The Er:YAG laser must be used in conjunction with water during cavity preparation. As such it should be considered as an effective tool for clinical use based on predicted pulpal responses to thermal stimuli.

Diagnostics: occlusal caries detection in primary teeth: a comparison of DIAGNOdent with conventional methods

Objective To compare the accuracy and repeatability of three diagnostic systems (DIAGNOdent, visual and radiographic) for occlusal caries diagnosis in primary molars.Design Two examiner, in vitro, blinded study. Histological gold standard.Materials and methods 58 occlusal surfaces of primary molars examined in turn by two examiners using each of three diagnostic systems (DIAGNOdent, visual and radiographic). These results were compared with a histological gold standard. Sensitivity and specificity were calculated for each diagnostic system at a range of thresholds. Inter- and intra- examiner repeatability were calculated for each diagnostic system using the kappa statistic.Main outcome measures Sensitivity, specificity, inter and intra examiner repeatability for each diagnostic system.Results The highest sensitivity values were provided by DIAGNOdent (0.77 and 0.80, examiners 1 and 2 respectively) however this was offset by a lower specificity (0.82 and 0.85) than all other systems with the exception of examiner 1 at V1 visual threshold. The DIAGNOdent gave the highest values of kappa for intra- and inter- examiner repeatability with the exception of intra-examiner repeatability for examiner 2 where visual diagnosis had the highest value of kappa.Conclusion The DIAGNOdent was the most accurate system tested for the detection of occlusal dentine caries in primary molars. The performance of the DIAGNOdent systems was not statistically significantly better than that achieved using visual examination for non-cavitated teeth (V1 and V2 threshold). DIAGNOdent may prove useful as a predictive clinical tool, however with appropriate training visual examination may offer similar results without the need for additional equipment.

Toothbrushing Habits and Caries Experience

dental caries is strongly influenced by the way it is used. Recent studies [Chesters et al., 1992; Sjögren and Birkhed, 1993; O’Mullane et al., 1997] have reported that both brushing frequency and mouthrinsing after using toothpaste have an important effect on anticaries benefits. The aim of this study was to confirm the association between reported toothbrushing and rinsing behaviour and caries experience in adolescents from Manchester, UK. A total of 2,888 adolescents in the Manchester area, aged 15–16 years, who had used a toothpaste containing 1,000 ppm F during the previous 3 years participated. The caries experience of each individual was determined at the dentinal level using the visual criteria described by Downer [1975] and the diagnosis of approximal lesions was supplemented with fibre-optic transillumination (FOTI). Under supervision each participant completed a questionnaire which requested information on the frequency of brushing, amount of toothpaste used and rinsing behaviour. Independent sample t tests were used to compare mean DMFT values between different groups. A forward stepwise multiple regression model was fitted to DMFT, with the three toothbrushing variables for potential inclusion in the model. A probability of entry into the model was set at 0.05 and for exclusion 0.10. Short Communication

Er:YAG (λ=2.94 µm) Laser Etching of Dental Enamel as an Alternative to Acid Etching

Abstract.Acid etching is widely used in clinical dentistry to facilitate the mechanical retention of resin-based materials to teeth, in particular enamel surfaces. Several laser systems have been developed with the aim of modifying dental hard tissues and the Er:YAG (λ=2.94 µm) laser may offer a possible alternative to the acid etching technique.This study compares the shear bond strengths of composite beads attached to sound enamel surfaces prepared using either (a) no etching (negative control), (b) acid etching (positive control) or (c) Er:YAG laser etching, either with or without water, at one of three fluences: 15 J/cm2, 18 J/cm2 or 24 J/cm2. A histological appraisal was also conducted using environmental scanning electron microscopy (ESEM) techniques.The mean shear bond strength for acid-etched enamel was 16.6 MPa (SD 4.4, n=10), whereas the best laser-etched mean bond strength obtained was 11.5 MPa (SD 4.1, n=11) using a fluence of 24 J/cm2 with water. These values were significantly greater than those obtained for the negative control (no etching) of 4.4 MPa (SD 0.9, n=8). There was a significant positive correlation between the etching fluence and the shear bond strength, but pitting of the enamel surface at fluences above 25 J/cm2 limited the maximum fluence for etching purposes. Although Er:YAG laser etching enhanced the retention of a resin-based material to an enamel surface when compared to a negative control, the mean shear bond strengths were significantly lower than those obtained using conventional acid etching. The optimal laser etching parameters in this study were shown to be 24 J/cm2 in conjunction with water.

Effects of a surface water film on the interaction of Er:YAG radiation with dental hard tissues in vitro

ABSTRACT: Aims:To quantify the effects of Er:YAG laser radiation on simulated pulpal temperature changes when laser energy is applied in conjunction with and without a surface water film. Materials and Methods:Sound extracted premolar teeth stored in neutral buffered formalin prior to experimentation were used. Debris was removed from the pulp chamber and a simulant pulpal tissue introduced. A calibrated digital thermal probe was placed in the pulp chamber and recordings made at 0.5 second intervals prior to, during and following laser radiation.Each tooth was subjected to laser radiation, with and without water present, using identical lasing parameters ina paired study design. Teeth were mounted on a fixed speed translation stage and moved back and forth acrossthe beam plane producing slots through enamel into the inner third of dentine. The free running Er:YAG laser operated at 2.94jtm with an overall macropulse duration of 200j.ts and wasfocused using an 85mm CaF2 lens. Lasing parameters were either 2, 4 or 8Hz for durations of up to 300s.

Dentine ablation dependency on incident Er:YAG (2.94-um) laser irradiation conditions

Ablative etch rates within human dentine using an Er:YAG laser have been measured with and without the application of additional water to the sample surface. Projection imaging techniques were found to be useful from both diagnostic and clinical aspects. Well-defined, spatially uniform laser pulses allow accurate determination of ablation threshold fluences as well as fluence-dependent effective absorption coefficients and material removal efficiencies. Etch rate dependency on sample water content is consistent with a thermal ablation mechanism. A model which accounts for this behavior, in view of the temporal pulse structure of the free-running Er:YAG laser, is put forward. The clinical implications of these results are also discussed.