Among the many clinical uses of the latest type of Erbium all tissue lasers is the ability to prepare cavities and cut enamel, dentine and composite. Historically lasers used for these applications have been associated with adverse thermal effects and relatively slow rates of cutting. These problems have now been successfully overcome: by use of an appropriate wavelength (2780-2940nm) the Erbium lasers cut by virtue of the expansive power of water rather than by heat coagulation or carbonisation. By exposing the target tissue to a laser wavelength that activates the water and hydroxyl groups present the tissue is efficiently broken apart. The schematic in the figure illustrates this process which is described technically as ablation. Once exposed to the laser the water and hydroxyl element of the tissue becomes highly agitated such that there is a volumetric increase of 1600x in a fiftieth of a second. The exploding pockets of water drive the tissue apart without any significant thermal damage to the tissues. In fact research shows as opposed to the laser irradiated tissues being heated up there is actually a degree of local cooling, and there is significantly less local heat generated than a conventional turbine. The Erbium lasers also incorporate a water spray which provides additional water for the laser to target in tissues with a low water content such as enamel; this water spray also acts as a coolant so there is no charring or any adverse thermal effects. This is a significant advance over earlier generations of lasers which were associated with considerable heat generation resulting in poor clinical results.
There are many clinical benefits to using an Erbium laser to cut dental tissues not the least of which is the ability to cut many cavities without a local anaesthetic. In part this is due to the absence of vibration as the laser is a non-contact cutting instrument. Also the zone of destruction is tightly confined as the laser beam is highly focussed, so the trauma to the adjacent vital tissues is minimal. In addition, the laser has a profound physiological effect on the pulpal tissues which has an analgesic effect. The typical patient experiences at most slight cold sensitivity which is probably due to the coolant water spray. There are limitations to what can be reasonably achieved without a local anaesthetic and success relies on a proper understanding of how best to operate the laser. Due to differences in the technical profile of the machine the Waterlase MD is the best Erbium laser to use as it achieves peak power for the shortest duration at the optimum wavelength (2780nm). In consequence, sensitivity is less frequently a problem in comparison to the other machines on the market. Even in inexperienced hands at least half of all small to medium sized cavity preparations can be comfortably achieved without LA with the Waterlase MD and with training and practise this rises easily to 80 per cent. Many patients intensively dislike the drill and/ or an injection and practices that have incorporated the laser attract many new patients and are growing despite the current recession.
Lasers do not cut through amalgam or other metals and a further limitation is they do not ablate glass ionomers. They do however have a high affinity for composites and this offers a big advantage over conventional rotary instruments as the composite goes white as it is denatured and as a result it is easy to see the boundary between where an old composite remains and the sound tooth tissue begins. I find this especially useful when removing old luting cement in veneer re-treatment cases and I use the laser to take the old veneers off. I can preserve the maximum amount of underlying sound enamel and also be sure I have removed all of the old cement so I have an optimum bond site for the replacement restorations. I find this application particularly useful when removing old fibre glass and composite periodontal splints, removing residual luting cements and orthodontic brackets.
The lasered tooth tissue is an ideal bonding site as the dentine is left without a smear layer and any enamel is pristine clean. Providing the cut surfaces are finished at the correct settings there are no issues with sub-surface cracking. By comparison when one applies a turbine to a tooth there is very considerable trauma to the tissues caused by mechanical vibration. If a burr is blunt or there is any wear in the handpiece cartridge the drilled tooth surfaces can be thermally damaged and micro-fractured. This can result in a cusp fracture at the time of cavity preparation which is a complication which most experienced practitioners will have experienced at one time or another. Laser cut tooth surfaces avoid these problems and as a result there is little if any post treatment sensitivity plus the mechanical integrity of the tooth is not accidentally compromised.
The Waterlase MD is an all tissue laser so amongst the many advantages of using it in restorative dentistry is the ability to switch applications between cutting hard and soft tissues. Cavities often extend sub-gingivally or there may be hypertrophic tissue to remove. At a touch of a button the laser can be reset into soft tissue settings which allow the rapid effective and highly accurate removal of any soft tissues that are in the way. These cut tissues do not bleed so it is possible to complete bonding procedures without any contamination. If more extensive crown lengthening surgery is required it is easily achieved with the minimum amount of fuss. As a matter of routine I use a Cerec 3D in my practice and I frequently find myself switching between cavity preparation and crown lengthening, all with the same laser tip; I merely switch settings between hard and soft tissues. In crown and bridge work it is convenient to trough the gingival sulcus prior to taking impressions. This saves a lot of time as it is not necessary to use retraction cords to obtain clear margins on the impressions. In this application the laser is used to create a trough in the gingival sulcus allowing the flow of the impression materials to clearly demarcate preparation margins. Post treatment the lasered gingival tissues heal without any recession.
One obstacle to the uptake of lasers by dentists for restorative work has been the speed of the cuts as historically the drill has been faster. The latest generation of lasers however now cuts as fast as a conventional turbine and it is even possible to cut crown preparations if desired. A striking case example of this can be found on the Biolase website at www.biolase.com/clinical.php where a case is presented of a full mouth reconstruction by Mark Colonna: 28 units of full ceramic crowns prepared and fitted all on the same day using lasers and CADCAM, without a local anaesthetic. Of course this called for a high degree of operator skill. There is also the issue of operator preference as at the end of the day the laser is merely a tool and most experienced clinicians prefer to stick to the more familiar armamentarium out of habit. Faced with a patient who is severely medically compromised and unable to have a local anaesthetic or is a drill and needle phobe the possibility of using the laser as an alternative is there if desired, and a lot can be achieved as is admirably demonstrated by the case previously described.
The clinical experience of cutting tissues with a laser is entirely different to the standard turbine as there is no physical contact with the target tissue. It is advisable to use high powered loupes and to have appropriate training to achieve good consistent results. This is a mature technology with a considerable body of clinical experience particularly from the US where there are currently over 3,500 Waterlase MD units in practices today. As a mature practitioner I am very comfortable using the standard turbine due to its familiarity for restorative treatment and my clinical preference is to use the laser more for its outstanding surgical applications. However this is a patient and market led revolution and without doubt the restorative applications of the all tissue Erbium lasers will become a common feature of clinical practice in the UK.
For more information visit www.henryschein.co.uk or www.biolase.com