Surgical laser use in implantology and endodontics

Key Points

• Laser use in implantology has been historically controversial.

• The development of a range of laser wavelengths has shown the adjunctive use of lasers to be more beneficial, both in the healthy and diseased implant case.

• Laser use in endodontics has advocated benefits in all stages of treatment. However, some are based on anecdote or innovation.

• The greater investigation into all wavelengths has centred on the anti-bacterial action of laser light energy.

Key Points

Lasers in dentistry

• 1 Introduction, history of lasers and laser light production

• 2 Laser-tissue interaction

• 3 Low-level laser use in dentistry

• 4 Lasers and soft tissue: 'loose' soft tissue surgery

• 5 Lasers and soft tissue: 'fixed' soft tissue surgery

• 6 Lasers and soft tissue: periodontal therapy

• 7 Surgical laser use in implantology and endodontics

• 8 Surgical lasers and hard dental tissue

• 9 Laser regulation and safety in general dental practice

Abstract

The use of surgical lasers has been advocated to aid in the placement and second stage recovery of dental implants, together with soft tissue contouring. In addition, laser use has been suggested as an aid in decontamination of the implant surface in cases of peri-implantitis. In endodontics, the association of laser energy with dentine hypersensitivity, bacteriocidal action and pulp-capping, has led to a growing number of reports as to its beneficial use, together with claims of morphological changes in the canal wall, to enhance endodontic treatment success.

The use of lasers in implantology

Surgical lasers can be used in a variety of ways with regard to implantology, ranging from placement, second stage recovery and gingival management, through to the treatment of peri-implantitis. Within this range of usage, dependant on wavelength employed, exists the ablation of target tissue and the ability to reduce bacterial contamination.

Whilst there is a general acceptance that lasers are capable of accurate cutting of materials and tissue, there is no evidence-based advocacy as to the use of any laser wavelength in producing a fully-prepared osteotomy site for the placement of root-form dental implants. However, there are anecdotal reports of the use of erbium YAG and erbium YSGG lasers to establish a controlled incision of overlying gingival tissue and to initiate a breach of the cortical bone plate, prior to the use of conventional implant drills. Such techniques, although intrinsically correctly based on predictable laser-tissue interaction, run the risk of scepticism amongst practitioners more allied to a conventional surgical approach to implant placement.

The fundamental controversy?

With all other predisposing factors addressed, the fundamental key to success in implant placement is the apposition of normal healing bone onto the implant surface. The preparation of the osteotomy site demands a technique whereby the local temperature does not exceed 47°C.¹ Inasmuch as the prime interaction in laser use results in the conversion of incident electromagnetic energy into heat energy, any therapeutic use of lasers in implant dentistry must address this fact. Added to this, once in place, the possibility of implant surface damage arising from incident laser light must be avoided.

The first dental laser, the Nd:YAG (1,064 nm) offered advantages of soft tissue ablation, haemostasis and bacterial control. However, the free-running pulsed emission mode can give rise to peak power values per pulse of >1,000 Watts. Research into the use of this laser as an adjunctive to implantology, drew conclusions that the penetrating and high peak heat energy effects produced during soft tissue and peri-implant treatment, caused damage to both the implant surface and surrounding bone.^2,3,4 This led to a general deprecation of laser use in connection with implants, which remained for several years.

With the further development of other laser wavelengths, investigations were carried out to establish whether these newer lasers would cause damage. The general parameters would include the emission mode of the laser (continuous wave (CW), gated pulsed (GP) or free-running pulsed (FRP)), the nature of the target tissue and type of laser-tissue interaction. Other investigations centred around the material used in implant manufacture, its reflectivity, whether the titanium was coated and, generally, the conductive effects of heat through the implant into surrounding bone. Of prime concern is the potential damage to the implant surface and the escalation of heat effects beyond the 47°C threshold in adjacent bone.

Titanium as a metal exhibits reflectivity to incident light energy. With regard to the wavelengths of current lasers, the reflectivity is lowest in the range 780-900 nm, rising as the wavelength increases towards 10,600 nm (CO₂ laser emission).⁵ This would suggest that shorter wavelengths are most damaging, as the low reflectivity would allow greater heat effects to build up, and is in keeping with studies carried out with the Nd:YAG laser. However, there is evidence to suggest that the diode wavelength group, delivered in low power CW values (1-2 Watts average power), cause minimal damage to the implant² or surrounding bone.^6,7 This is explained by the fact that the Nd:YAG, Er,Cr:YSGG and Er:YAG emission modes (FRP), result in high peak power values and heat production (>several hundred °C). Despite the damaging effects of carbon dioxide laser light on bone, several studies have borne out the high reflectivity of titanium to this wavelength, in reporting low thermal effects on the metal surface^{8,9,10,11,12,13,14} and non-damaging effects on the metal composition.¹⁶

Soft tissue management associated with implants

Based on laser-tissue interaction characteristics, all laser wavelengths are suitable for the second stage recovery of implants, provided care is exercised to avoid contact with the implant body (Figs 1, 2, 3, 4, 5, 6, 7, 8). The ablation of soft tissue leads to precise and predictable healing and often this procedure can be carried out using topical anaesthesia.

Figure 1

Implant cover screw access obtained using diode (810 nm) laser

Figure 2

Healing cap in place

Figure 3

Soft tissue healing at 10 days

Figure 4

Implants uncovered using Er:YAG (2,940 nm) laser without water spray

Figure 5

Healing at one week

Figure 6

Second stage recovery using CO₂ laser (10,600 nm)

Figure 7

Laser use complete

Figure 8

Healing at 10 days

Suggested energy levels of one to two Watts (CW diode), 150 mJ/15 pps (Nd:YAG), 200-250 mJ/10 pps (erbium group) and one to two Watts (CO₂), appear to be appropriate in removing gingival tissue overlying the implant cover screw. The prime advantages of laser use in this procedure would be haemostasis, facilitating easier visual access to the cover screw, production of a protective coagulum as an aid to healing and patient comfort during and after treatment.

Minor surgical correction of the gingival margin can be carried out, to assist adequate implant exposure or to establish the correct emergence profile of the trans-mucosal element (Figs 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19).

Figure 9

Two implants uncovered with scalpel–assisted flap. Poor tissue contour due to early loss of sutures

Figure 10

Excess soft tissue being removed using CO₂ (10,600 nm) laser. Note use of damp gauze to prevent distant damage

Figure 11

Immediate post-laser exposure of healing caps and re-contouring of soft tissue outline

Figure 12

Soft tissue healing at two weeks

Figure 13

Transmucosal elements in place at three implant sites in the UR posterior region

Figure 14

Diode (810 nm) laser used to contour soft tissue around TMEs

Figure 15

Immediately post-laser surgery with provisional crowns in place

Figure 16

Finished result at five months

Figure 17

Laboratory made acrylic copings fitted to implant abutments to aid in protecting implant neck from thermal energy. Nd:YAG (1,064 nm) laser

Figure 18

Immediately post-laser surgery

Figure 19

Peri-implant soft tissue contour at one month

As with gingivoplasty around natural teeth, a near-excision approach can be adopted with final detachment of the discard with a sharp curette; alternatively, laboratory-made acrylic copings can be fitted.

Laser use in peri-implantitis

As with conventional treatment approaches, assessment must be made as to the causative factors associated with the condition (infection, occlusion, implant overloading and other local, systemic and life-style factors), and whether the implant is essentially saveable.

Peri-implantitis is recognised as a rapidly progressive failure of osseo-integration,¹⁷ in which the production of bacterial toxins precipitates inflammatory change and bone loss.¹⁸ The development of peri-implantitis is not restricted to any one type of implant design or construction^19,20 and is cited as one of the greater causes of implant loss.^21,22 Inasmuch as mechanical debridement together with chemical decontamination (eg chlorhexidine digluconate, citric acid) of the exposed implant surface, with or without site-specific antibiotics, has proved somewhat effective, the possibility to remove bacterial colonisation with an appropriate laser wavelength might well be seen as an added benefit.^{23,24,25,26,27,28,29,30,31,32} In spite of the risks inherent in using a micro-second pulsed laser, studies by Kreisler et al., using an Er:YAG laser (60-120 mJ/10 pps – 0.6-1.2 W), and Miller, using an Er,Cr:YSGG laser with similar energy parameters, found bacterial kills >99%, without reported damaging effects on the implant surface.^33,34

Meticulous attention must be given to curettage of granulation tissue; a laser wavelength that is non-injurious to bone (eg erbium group plus water) can be used to remove this tissue, although careful use of a diode laser, avoiding heat effects (a water spray can be used) and restricting its use to fragmentation and ablation, can be employed. The ability of laser energy in bacterial decontamination appears to place its use above that of other modalities (Figs 20, 21, 22, 23).

Figure 20

Peri-implantitis resulting in labial and interstitial bone loss in 21/1 region (figure courtesy of Professor G. Romanos, New York University, New York, USA)

Figure 21

Following removal of granulation tissue, diode (810 nm) laser used to remove bacteria from implant surfaces (figure courtesy of Professor G. Romanos, New York University, New York, USA)

Figure 22

Post-surgery healing at three months, with new coronal restorations (figure courtesy of Professor G. Romanos, New York University, New York, USA)

Figure 23

Pre-surgery (left) and three months (right) radiographs, following open flap debridement and bone grafting (figure courtesy of Professor G. Romanos, New York University, New York, USA)

However, there is less evidence of beneficial use where the implant is coated with a ceramic or hydroxyapatite; this may be mostly due to the micro-complex surface irregularities, which have been shown to harbour bacteria and foreign ions in a failing situation.^35,36

Lasers and endodontics

All current dental laser wavelengths have been used in a wide range of endodontic treatments, either to aid the preparation stages or obturation techniques of root canal therapy or to alleviate low-grade pulpal injury.^37,38

The areas of endodontics where laser use has been investigated include the following:

• Direct pulp capping

• Removal of pulpal tissue

• Access/shaping of canal walls and morphological changes in structure

• Bacterial decontamination

• Sealing with or removal of gutta percha obturation material

• Root dentine (cervical) desensitisation.

As with laser use in the debridement of the periodontal pocket, it should be remembered that non-visual access places a potential limit on the control exercised by the operator in using laser energy within the root canal. In addition, laser use should be adjunctive to good clinical practice if benefits are to be maximised. Wherever laser use is indicated, it is recommended that this should be evidence-based and, if deemed appropriate, complementary to all other treatment measures that might be considered. Table 1 lists the procedures that have been advocated and investigated in the field of endodontics and the current commercially available laser wavelengths that are applicable.

Table 1 Laser wavelengths and their possible application in endodontics

Pulp capping and pulpotomy

The consideration for pulp capping and/or pulpotomy using a laser should complement contemporary protocols for such action. Vital pulp exposure (arising from caries or trauma) and subsequent local action, leading to preservation of vital tissue, is contentious in the permanent dentition and success rates are low. It is suggested that permanent teeth with open apices or deciduous teeth offer better chances of pulp reparation.^39,40 However, the use of laser energy to aid haemostasis and remove bacterial contamination in order that a reparative dentine bridge could form can offer increased chances of a successful resolution.^41,42,43

In a study of 83 patients with 93 teeth treated through a pulp capping procedure, Santucci reported survival rates over 54 months of 43% in teeth treated with calcium hydroxide/resin cement, as opposed to 90% in those teeth treated with Nd:YAG laser and a similar capping cement.⁴⁴ Moritz et al. (260 teeth treated, 130 study/130 control), reported a tooth vitality two-year survival rate of 93% (control 66%), using a super-pulsed CO₂ laser under similar conditions.⁴⁵

Laser technique involving the exposed vital pulp should be carried out under rubber dam, to prevent contamination with salivary bacteria. Minimal energy levels (1-2 W average power) per wavelength should be employed to provide haemostasis and sterilise the cut surface. A calcium hydroxide dressing should be applied directly, prior to completion of cavity restoration.

Access/shaping of canal walls and morphological changes in structure

The accepted interaction of the Er:YAG and Er,Cr:YSGG lasers with dental hard tissue makes these wavelengths ideal for removal of dentine overlying the pulp chamber.⁴⁶ The benefit of non-tactile stimulation can aid this procedure in teeth that are tender to percussion and where anaesthesia is incomplete or insufficient.

Within the confines of the root canal, the use of laser wavelengths without water cooling can lead to a potential high rise in temperature. Risks associated include melting/cracking of dentine walls and trans-apical irradiation of the tooth socket.⁴⁷ With short infrared and CO₂ lasers, if benefit is to be obtained, power levels of 0.75-1.5 W should be considered maximal. With water-assisted erbium lasers, power values of 150-250 mJ/4-8 pps are considered suitable, but it is essential to allow water to reach the ablation site, in order to prevent over-heating and cavitation of canal walls.^48,49,50

In order to address the end-on emission of laser light from the delivery system, modified intra-canal instruments have been developed^51,52 and pre-trial experimental devices to produce non-axial laser light propagation along optic fibres have been investigated (Figs 24, 25, 26).

Figure 24

Endodontic laser tip for use with Er:YAG laser

Figure 25

Laser tip being used in root canal. Laser energy is reflected off inclined surfaces and through gaps in spiral to exit at 90° to the axis

Figure 26

'Micro-probe' insert for use with CO₂ laser

With mechanical canal preparation, a smear layer is often produced, which can harbour bacteria. Most laser wavelengths will remove the smear layer and can be used in conjunction with irrigants and chelating agents such as NaOCl or EDTA. The Nd:YAG laser has been extensively investigated, but many reports have been made regarding melting and carbonisation.^53,54,55,56 It is considered that the erbium group of laser wavelengths is best placed to achieve this, without causing damaging temperature rise.⁵⁷

Bacterial decontamination

Peri-radicular lesions are diseases either primarily or secondarily caused by micro-organisms. Conventional treatments suggest the combination of mechanical debridement and chemical anti-bacterial agents.^58,59

As discussed previously, the anti-bacterial action of laser light is a major benefit of this treatment modality, although in complex canal systems, the use of NaOCl or H₂O₂ has been shown to be more effective.^60,61,62 The fine (200-320 μm) diameters of quartz optic fibres associated with diode and Nd:YAG lasers has enabled these wavelengths to be easily used in bacterial decontamination of the root canal (Figs 27, 28, 29, 30, 31, 32, 33, 34, 35).^63,64,65

Figure 27

320 μm diameter quartz fibre for use with diode (810-980 nm) and Nd:YAG (1,064 nm) lasers. A canula is usually fitted onto the fibre. Size comparable with #30 endodontic file. Fibre length can be measured in the same way as hand files

Figure 28

Fibre with HeNe aiming beam being introduced into extracted root canal

Figure 29

Optic fibre inserted to two millimetres short of working length. Note 'fluorescence' effect of light through tubular dentine. Invisible laser light is thought to behave in a similar manner

Figure 30

200 μm diameter fibre in clinical use in endodontics

Figure 31

Measurement of fibre length

Figure 32

Buccal swelling associated with acute periapical abscess, LR 6

Figure 33

'No touch' incision of swelling using CO₂ (10,600 nm) laser

Figure 34

Aspiration of pus. Note absence of bleeding along incision line

Figure 35

Lesion at two weeks, following root canal therapy

Of the current lasers available, the CO₂ wavelength would appear least successful in effecting bacterial decontamination⁶⁶ and the effectiveness of laser use appears to depend on fluence values and direct access.⁶⁷ In addition, some concern has been expressed that the plume produced during laser action might allow bacterial contamination to spread.^68,69 As with laser bacterial action in other clinical sites, sub-ablative energy levels should be employed for all wavelengths.

Comparative studies on two common bacterial pathogens, Escherichia coli and E. faecalis have shown that the more complex cell wall of the latter can reduce the effectiveness of laser action. One study by Schoop et al. concluded that diode 810 nm and erbium YAG were better placed to ablate significant numbers of E. faecalis organisms.⁷⁰ Curiously, in another study by Jha investigating the Er,Cr:YSGG laser, no beneficial bacteriocidal effect could be demonstrated, with either lasers or rotary instrumentation.⁷¹ As was reported in the paper on LLLT (BDJ 2007; 202: 131–138), some studies have been carried out, both in vitro and in vivo, into the use of photo-activated disinfection in eliminating intra-canal pathogenic species.^72,73,74 In common with studies on many areas of bacterial populations in dentistry, inclusion/exclusion criteria remain significant in determining outcome and can make direct comparison difficult.

Sealing with or removal of gutta percha obturation material

A number of studies have been carried out to establish the usefulness of lasers in the softening and obturation of gutta percha in the root canal (Fig. 36).^{75,76,77,78,79} However, the development of thermoplastic materials and instruments for such purposes has rendered such application comparatively time consuming and expensive.⁴⁷

Figure 36

Nd:YAG laser being used to section gutta percha points

Dentine hypersensitivity

In the absence of any other aetiological factors, 'true' dentine hypersensitivity can be due to gingival recession or toothbrush abrasion and may cause pulpal stimulation through dynamic changes in the intra-tubular proteinaceous fluid.⁸⁰ Laser–mediated treatment of exposed dentine has been either to address the patency of tubular openings, causing closure of tubule openings to a depth of several microns, or to coagulate the tubular contents.^81,82,83 Kimura, in a review of the literature from 1985-2000, ranged the effectiveness of lasers in the treatment of dentine hypersensitivity from 5-100%, dependant upon wavelength and fluence.⁸⁴ The most commonly explored lasers are the low-level diode (HeNe 633 nm, GaAlAs 810 nm) group and moderate power diode and Nd:YAG.^{85,86,87,88,89,90} Of these, the use of the Nd:YAG wavelength appears to be more successful. The effectiveness of the low-level group has been proposed through a biostimulatory effect and the higher powered lasers through heat-welding of tubule openings. The erbium group are thought to cause coagulation of tubular contents. Notwithstanding, some studies have called the success of laser use in treating sensitivity into question.⁹¹

Energy levels when using hard lasers must be sufficiently low in order to avoid pulpal damage (shorter wavelengths), or tissue ablation (longer wavelengths) and should be of an order of 0.3-0.5 W average power.

Conclusion

The use of lasers in implantology and endodontics has prompted controversy, due either to the essential photothermal action of high powered lasers and its potential for collateral thermal damage, or to the risks associated with 'blind' techniques. The considerable number of investigations carried out into the many permutations of laser wavelengths and target sites has allowed a refinement of criteria and a balanced approach to the claimed success, or otherwise, of laser use. Anecdotal claims as to the effectiveness of this modality continue to drive the need for critical evaluation.