8 Lasers in Fixed Prosthetic and Cosmetic Reconstruction

James C. Downs, DMD , Robert A. Convissar, DDS , Eugenia Anagnostaki, DDS , Grace Sun, DDS

This chapter describes the clinical applications of laser dentistry with respect to soft tissue and hard tissue alterations for prosthetic and cosmetic reconstruction. Clinical advantages of laser use clearly benefit both dentist and patient. A clear field of vision resulting from excellent hemostasis and moisture control allows the dentist to perform all procedures with precision. Major advantages of laser use include reduced intraoral bleeding, much less postoperative pain, and remarkably less swelling compared with conventional techniques such as electrosurgery.

The procedural techniques routinely encountered during fixed prosthetic and cosmetic reconstruction include the following:

Troughing for impression taking

Hard and soft tissue crown lengthening

Emergence profile creation

Ovate pontic design

Melanin depigmentation

Laser bleaching

Before each of these procedures is discussed, the role of various laser wavelengths and biologic width in cosmetic and prosthetic reconstruction is reviewed.

Laser Wavelengths for Cosmetic/Prosthetic Procedures

Carbon Dioxide Lasers

The CO₂ wavelength of 10,600 nm is delivered through an articulated arm or waveguide that terminates at a handpiece. Most CO₂ laser manufacturers have multiple handpieces with different angles (straight and contra-angle) and different focal points to perform different procedures (e.g., vaporization, coagulation, tissue modification).

Oral soft tissue is 90% to 97% water. The CO₂ wavelength is highly absorbed by water, more so than any other soft tissue laser wavelength. CO₂ lasers are therefore the most efficient lasers because they are best absorbed by soft tissue. Soft tissue excision or incision surgery is accomplished at 100° C, at which vaporization of intracellular and extracellular water causes ablation of biological tissue.¹

The mode of operation for CO₂ lasers historically has been a continuous wave, which means energy is emitted constantly for as long as the laser is activated. Mechanical and electrical controls can produce a chopped, gated, “superfast,” or ultrafast pulse of this continuous wave, which minimizes the heat transferred to the tissue. This in turn reduces thermal damage to the target and surrounding tissue.

Erbium Lasers

The erbium-doped yttrium-aluminum-garnet (Er:YAG) wavelength is 2940 nm and the erbium, chromium–doped yttrium-scandium-gallium-garnet (Er,Cr:YSGG) 2780 nm. Erbium laser wavelengths are transmitted through semiflexible hollow waveguides, low-OH⁻ fiberoptic cables, or articulated arms. All the delivery methods terminate in a handpiece that may use sapphire or quartz tips to transmit the energy to the target tissue. These wavelengths are highly absorbed by the OH⁻ radical and thus work well in hard tissue, targeting the OH⁻ in hydroxyapatite. The erbium lasers can also cut soft tissue, but with much less hemostatic ability than soft tissue lasers.²

Erbium lasers are safe when ablating tooth decay and working close to the pulp. Because this laser wavelength penetration is not significant in depth, patients may not need anesthesia. Erbium laser cavity preparation is less traumatic to the tooth’s pulpal tissues than techniques that involve rotary bur drilling. The vibration and heat produced by rotary instruments, which are the main reasons for discomfort during procedures, do not occur with the erbium wavelengths.³

One disadvantage compared with conventional techniques is diminished bond strength, particularly tensile strength, when etching with erbium lasers.⁴ Another disadvantage is that erbium wavelengths cannot remove gold or metal crowns, vitreous porcelain, or amalgam restorations (see Chapter 11).

Diode Lasers

Diode lasers deliver wavelengths at 810 to 1064 nm. Diode lasers are compact and portable solid-state units. They are used strictly for soft tissue procedures and penetrate 2 to 3 mm or more into soft tissue, depending on the wavelength and tissue biotype. Diode lasers are absorbed by pigmented structures, making them ideal for cutting melanotic soft tissues and providing hemostasis.⁵

The usefulness of the diode laser can be greatly expanded by proper carbonization of the fiber tip. This allows for vaporization with limited peripheral damage to nonpigmented tissue.⁶

Neodymium:Yag Laser

The Nd:YAG wavelength of 1064 nm delivered in a free-running mode can be used for numerous soft tissue procedures. Similar to the diode and CO₂ lasers, the advantages of the Nd:YAG laser are a relatively bloodless surgical field, minimal swelling, reduced surgical time, excellent coagulation, and in most cases, reduced or no postoperative pain.⁷

The main disadvantage of the Nd:YAG laser is the depth of penetration into the target tissue. The Nd:YAG wavelength penetrates deeply into tissue because it is poorly absorbed by water, the main component of gingival tissue. The clinician must be alert to the risk of unnecessary collateral tissue damage, particularly to the underlying bone or pulpal tissues. Tissue vaporization is slower than with other, better-absorbed laser wavelengths (e.g., CO₂). Applications of a topical photo-absorbing dye can shorten the lag time for absorption of the laser energy.⁸ Nd:YAG laser light directed at the clinical crown or root surface of the tooth is a concern. Heating of the pulp may be of sufficient magnitude to cause pulpal inflammation and possibly irreversible damage to pulpal tissue.⁹ This would occur only if incorrect laser parameters were used. This highlights the critical role of proper laser training when performing laser-enhanced prosthetic and cosmetic dentistry (see Chapter 16).

Biologic Width

Biologic width is defined as the combined height of connective tissue and epithelium that isolates the bone from the oral cavity. It is the distance from the most apical extent of a dental restoration to the osseous crest necessary to maintain periodontal health ¹⁰ (Figure 8-1).

FIGURE 8-1 • The tooth is attached to the surrounding gingival tissue and alveolar bone by fibrous attachments. The gingival fibers run from the cementum into the gingiva immediately apical to the junctional epithelium attachment, and the periodontal ligament fibers run from the cementum into the adjacent cortex of the alveolar bone.

(Modified from Rose LF, Mealey BL: Periodontics: medicine, surgery, and implants, St Louis, 2004, Mosby.)

The biologic width distance is approximately 2 mm, with about 1 mm of the 2 mm composed of the connective tissue attachment and 1 mm consisting of the junctional epithelium. Because it is impossible to restore a tooth perfectly to the precise coronal edge of the junctional epithelium, the 1 mm of depth of the sulcus can be added to the biologic width to establish a margin of safety.¹⁰

This distance is important to consider when fabricating dental restorations, because the dentist must respect the natural architecture of the gingival attachment to avoid complications. The problem is not the restoration but rather bacteria, which will always find shelter in the interface between the restorative margin and the tooth structure. When restorative procedures do not take these considerations into account and violate biologic width parameters, the following three possible issues may arise ¹⁰ (Figure 8-2):

Pocketing develops, with progressive periodontal soft tissue loss.

Gingival recession and localized bone loss occur, most dramatically in cases with thin labiobuccal bone.

Localized gingival hyperplasia develops, with bone loss.

FIGURE 8-2 • A, Biologic width impingement in the anterior segment. Note localized gingival hyperplasia, redness, and inflammation surrounding the porcelain veneers. B, Photograph of site 2 weeks after correction of biologic width using an erbium laser in a closed-flap procedure to establish new bone level.

Soft Tissue Troughing With and Without Gingivoplasty

The gingival trough is defined as the narrow space between the free margin of the gingival epithelium and the adjacent enamel of a tooth.¹¹ At times, permanent alteration of the gingival contours around a tooth or teeth is necessary to ensure a superior, long-lasting cosmetic restoration. The outcome of a direct or indirect restoration is related to the dentist’s ability to control the surgical site. In controlling the site for delivery of a superior restoration, lasers provide the following functions:

1. Enable the dentist to access and visualize the operative site and all the margins clearly, especially when the margins are subgingival.

2. Create a blood-free environment and achieve hemostasis if necessary.

3. Control saliva and contamination of the field.

4. Ensure “sterility” of the field, leading to superior gingival health around the margins.

5. Control the soft tissue contours for a harmonious esthetic and functional relationship between the soft tissues of the periodontium and the restored hard tissues of the teeth and underlying bone.

These steps are essential for the fabrication of precise impressions, for digital scanning, or for direct placement of restorative materials. The displacement of gingival tissue is critical for finalizing tooth preparation and impression taking or restorative material placement.¹² A common challenge to the dentist is placement of the preparation “finish line” at or below the crest of the gingiva so that the margin does not show. Retraction of the gingival tissues can be performed mechanically with the retraction cord impregnated with medicaments for hemostasis. Packing of retraction cord around the circumference of the tooth to reflect the gingiva away from the tooth and to absorb crevicular fluids is the conventional technique used to record the finished preparation margin or to complete placement of the direct restorative material.

Conventional Techniques

A technique widely used for gingival retraction is a double-cord technique for subgingival reflection of tissue. Removing the second (top) retraction cord before injecting the impression material or creating an optical impression allows for complete capture of the finish line. This time-consuming technique has its disadvantages, including potential injury to the periodontal ligament if excessive force is used; difficulty in removing the retraction cord without creating bleeding, and postoperative discomfort.¹³

Another conventional gingival troughing technique, electrosurgery or radiosurgery, allows for contouring of gingival tissues and hemorrhage control. Healing after electrosurgery can produce a delayed wound-healing response, asymmetrical gingival heights, crestal bony recession, and moderate postoperative discomfort.¹⁴ In a study of electrosurgical gingival troughing with a fully rectified current on rhesus monkeys, Wilhelmsen et al.¹⁵ showed statistically significant recession of the gingival margin along with apical migration of the junctional epithelium. Deep soft tissue resections close to bone repeatedly produced gingival recession, bone sequestration and necrosis, loss of bone height, furcation involvement, and tooth mobility. Electrosurgery (or radiotherapy) is contraindicated around dental implants¹⁶ and must not be used in patients with pacemakers, with previous radiation to the jaws, with poorly controlled (or uncontrolled) diabetes, or with blood dyscrasias, immunodeficiencies, or other diseases that cause delayed or poor healing.¹⁰

Scalpel techniques are primarily used to resect tissue to provide access and visualization of the target site. Scalpel incision surgery may result in gingival attachment loss with apical repositioning, exposure of sensitive root surface to the oral environment, asymmetrical gingival margins, and the postoperative pain and discomfort typically associated with periodontal surgery.¹⁷

Laser Troughing

In contrast to conventional techniques, laser troughing allows for clear, clean visualization of gingival margins. Most lasers are excellent coagulation devices, with minimal to no bleeding. Unlike blade or electrosurgical techniques, laser gingival troughing with a laser gingivectomy can be performed at the same appointment as impression taking. The patient saves a trip to the office, greatly reducing valuable chair time. The ease with which necrotic tissue debris is removed from around the preparation finish line simplifies impression taking. Retraction cord is not necessary for reflection around the tooth or teeth; no placement or removal of cord from multiple pockets is required when taking impressions of multiple teeth or a full arch. Laser treatment causes no recession or repositioning of the gingival margin.¹⁸ Laser troughing promotes an ideal environment for current impression scanning devices.

Dentists who practice laser surgery and laser gingival troughing have reported high patient acceptance and comfort. Neill’s survey ¹⁹ on patient comfort after laser gingival troughing revealed that 3 hours after treatment, patients were comfortable, with half “extremely” comfortable. The overall pain rating was 1.9 (scale of 0.0-10.0), indicating patients experienced minimal to no pain.

Laser vaporization of fibrotic tissue around crown margins is extremely fast, with virtually no bleeding, swelling, or postoperative pain. There is predictable stability of the gingival tissue on healing, with the additional benefit of elimination of pathogens from the periodontal pocket.²⁰^,²¹

Slightly different techniques are used for each wavelength. The laser dentist must learn the specific procedure and follow the specific protocols for the particular device employed.

Clinical TIP

Clinical Tip: The new laser dentist should never start with procedures in the esthetic zone. Start gingival troughing with molars, where the tissue is slightly thicker. Once you become proficient with molars, work your way more anteriorly until you have confidence to perform this procedure in the esthetic zone. New laser users should always start with power settings at the lower end of suggested parameters until they become experienced with the modality of treatment. Thermal tissue damage in the anterior region could potentially result in undesirable gingival contours.

Erbium lasers use thin tips made of sapphire or quartz for troughing. When using erbium lasers on soft tissue, the water spray is usually turned off. This aids in hemostasis. CO₂ lasers have thin hollow metal tips for troughing. The Nd:YAG and diode lasers use optical fibers that come in various diameters to perform gingival troughing.