Clinical lasers are of two types; soft lasers are essentially an aid to healing with relatively few rigorous studies available to support their use. Surgical hard lasers, however, can cut both hard and soft tissues and replace the scalpel and drill in many areas. From initial experiments with the ruby laser most clinicians are using Argon, CO2 and now NdYAG systems. The first dental laser based on a NdYAG engine provides handpieces of similar size to conventional instrumentation and, being fed by a fibre-optic 'cable', has the flexibility for intra-oral use that the CO2 lasers, widely used in oral surgery, lack. Furthermore, extensive clinical investigation has demonstrated their safety in clinical practice and the fact that procedures can usually be performed without a local anaesthetic is obviously seen as a considerable advantage by patients. Sterilising as it cuts, the NdYAG laser promises to find uses not only in caries removal and soft tissue surgery, but also in endodontics and gingival curettage.

Laser irradiation produces bactericidal effects which may be of use in dentistry. The aims of this study were to investigate the effect of pulsed NdYAG laser irradiation on bacteria in a laboratory model, in the presence and absence of a black dye, Suomi ink. The experiments were carried out in small capillary tubes containing a measured volume of Enterococcus faecalis broth culture. This model simulated the number of organisms that could be expected to occur in an infected root canal. Laser irradiation was delivered from a NdYAG laser via a 320-microns fibre. Powers of 0.3 to 3.0 W were used for 20 to 60 s. Controls received no irradiation. The effect of the black dye was investigated by the addition of a fixed volume to the culture before lasering. The treatments were evaluated for bactericidal effect by comparing the number of viable bacteria remaining in the irradiated and the control specimens. At energy doses of 54 J and above, without black dye, a reduction of 10,000-fold or greater occurred. A similar reduction was achieved at energies above 25 J when black dye was added. These results indicate the energy levels which should be investigated to assess the potential role of the NdYAG laser in endodontics.

Eighteen per cent of all patients have some degree of sensitivity and a range of therapies has been devised to alleviate this condition. An electronic monitoring machine was constructed which allowed for air stream, directed at a patient's tooth, to be started by the clinician and halted by the patient when the sensation of pain in the tooth became too unpleasant to tolerate. The time for which the patient could tolerate the air flow was electronically measured in units of 1/50th second. By measuring the patient's reaction time on each visit and correcting the readings obtained for 'tooth pain time' using these figures, a quantitative measure of sensitivity change is achieved. Using this system, a clinical trial has been conducted to test the efficacy of the NdYAG dental laser. The 30 patients treated had an average tooth pain time initially of 1.2 seconds. Following laser treatment patients were recalled at 3, 7 and 14 days. At the 2-week review, this figure had increased to 7.8 seconds, which was found to be statistically significant. Control (unlased) teeth demonstrated an average improvement of only 1.7 seconds (not statistically significant). Patients' subjective assessment of sensitivity pain on a 0-10 scale averaged 8.0 before treatment. This reduced to 3.7 after treatment. Treatment of this condition can thus be performed easily and painlessly with a predictable response and considerable patient satisfaction.

Previous studies have shown that the inclusion of certain enzymes in mouthrinses and dentifrices will reduce plaque and gingivitis scores. The enzymes that are most effective clinically have, as their active ingredients, amyloglucosidase and glucose oxidase. These produce hydrogen peroxide from dietary fermentable carbohydrates which in turn converts thiocyanate to hypothiocyanite in the presence of salivary lactoperoxidase. The resultant hypothiocyanite acts as a bacterial inhibitor by interfering with cell metabolism; thus, there is a reduction in plaque accumulation and therefore in gingival inflammation. Pilot studies have compared over a short period the action of the trial dentifrice with enzymes and fluoride at 1100 ppm, using as controls the paste without enzymes but with fluoride and a commercial fluoride paste. There was an expected reduction in all scores with all products due to the mechanical removal of plaque, but a significantly greater reduction in gingivitis was noted in the paste with enzymes. This study is of longer duration with many more subjects. Baseline data include plaque and gingival indices and Periotron readings for crevicular fluid. The trial is of a double-blind non-crossover study design using a split-mouth technique. One side of the mouth is given a prophylaxis and the subject given one of the 3 test pastes to use. Readings were repeated every 2 weeks for 3 months. The results show a significant reduction in gingivitis scores in the enzyme-containing dentifrice group.

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