March 1, 2006
by Ron Goodlin, DDS
The days of GV Black’s “extension for prevention” have long passed us by, and the watchword now is “Enamel is sacred”. Of course this has only become a possibility due to the development of modern techniques and materials.
The reduction of enamel from the surface of the tooth has been shown to weaken the entire tooth complex. The more tooth structure removed the greater the risk of fracture of the tooth regardless of the type of restorative material which is placed to repair the tooth loss.1
It has been long recognized that the flex characteristics of the dentin and the brittle nature of the overlying enamel create a rigid structure which gives the tooth its’ inherent strength. Evidence has concluded that with increased force or decreased structural integrity, teeth are more prone to abfraction lesions2 and fractures3 (Fig. 1).
In anterior teeth the greater the amount of enamel that is removed, such as in the case of a an aggressive veneer preparation, the higher the risk of fracture because of the decrease in the holding power of the enamel to prevent dentinal flexion4 (Fig. 2).
It has been researched thoroughly and the results show that there is always a stronger bond to enamel than dentin. So it becomes our responsibility as practitioners to maintain the integrity of the tooth to maximize the enamel remaining so that our restorations are bonded to the tooth in a stronger manner.
In posterior teeth structural integrity is lost due to the removal of enamel and the placement of a restoration, regardless of which type. This will result in an increased risk of fracture when the tooth is placed under occlusal load5 (Fig. 3). The resultant fracture does not necessarily manifest itself as a physically evident broken tooth, but often will be manifested as “Cracked Tooth Syndrome”. The resulting internal crack proliferating over time until the tooth becomes endodontically compromised or the tooth in fact splits.6
It has long been believed by this author, that teeth can only take so much trauma during their lifetime. This trauma is accumulative. We know that some patients have a lower threshold level, and other patients will have a higher threshold level. Once the threshold has been reached, “the straw that broke the camels’ back” syndrome takes over and the tooth dies, pulpal necrosis being the result.
Pulpal trauma can come in the form of chemical, bacterial or mechanical means. Mechanical pressure on the dental complex from bruxism, or biting into a hard object creating a moment of traumatic incident or bruising can be enough to reach the maximum traumatic threshold.
Cutting into the tooth using burs which create microfractures, heat buildup, odontoblastic injury, dessication of dentin, vibration which creates shock waves to the pulp, pulp exposure, and bruising can be enough to cause pulpal death from a variety of these factors.8
The deleterious effects of the handpiece on the tooth along with the creation of the smear layer can result in problems with bonding and microleakage. The toxic effects of restorative materials themselves on the pulpal tissue has been well researched.9,10
Bacterial trauma from decay, or infiltration from perio disease reaching open dentinal tubules or a micro-fracture that has opened to the surface resulting in bacterial infiltration can result in the threshold being reached and the bacterial trauma results in pulpal necrosis.11
It is evident therefore, that we must treat the teeth in a compassionate and gentle manner, and it is in the interest of the patient to use the most prudent means possible to reduce and eliminate where possible all forms of trauma to the dentition. This can vary from providing our patients with equilibration and an occlusal bite splint to reduce the effects of traumatic occlusion and bruxism, to early caries detection and removal of that decay by using kinder and gentler methods to reduce the risk of pulpal trauma.
MINIMALLY INVASIVE TECHNIQUES
In clinical practice, as soon as we cut into a tooth we have sentenced that tooth to a lifetime of being repaired, replaced and treated with progressively aggressive and costly techniques. Our goal must be to minimize the structural tooth loss during the restorative process (Fig. 4). When treating our patients in clinical practice, it has become easy to use your MInD (minimally invasive dentistry) techniques, for the early detection, removal of decay, and its’ repair, in a manner which will minimize the compromise of the structural integrity of the tooth and reduce the trauma inflicted by iatrogenic sources in the process.12
Early detection of caries
In years gone by, we were taught that amalgam had to be larger to be strong, the tooth prep as championed by GV Black, had to incorporate retention and resistance form to prevent the amalgam restoration from falling out or breaking. Extension for prevention to include all the pits, fissures and grooves of the tooth should be included in the prep to prevent further decay. We all seemed to be concerned about this, so when confronted with a small carious lesion, we would mark OBS (observe) or W (watch) on the chart, until the lesion became large enough that morally we would feel it warranted to remove hefty amounts of tooth structure. In essence we would be watching the cavity get bigger over time.
Laser caries detection using “DIAGNOdent” (Kavo) (Fig. 5) to quantify the amount of organic material in the pits and fissures allow us to differentiate between stain and decay. This early detection allows the practitioner to easily remove the decay before it has compromised the tooth due to increased dentinal decay proliferation and the resulting undermining of healthy enamel and structural compromise.
This newer method of Laser Fluorescence Detection of Dental Caries along with the newer dental materials, allow us to detect decay earlier, without having to rely only on the method of tactile, visual, or radiographic detection techniques which have been shown to be unable to detect carious activity as early as the laser diagnostic procedure.13,14 The early detection will allow us to remove the decay without compromising the structural integrity of the tooth and to restore that tooth with a long lasting, aesthetic and functional material.
One must be very careful however as this method of treatment may not yet be recognized as a standard of care as is evidenced by the case of the Examining Board of Wisconsin vs. a dentist who is alleged to have found 13 carious lesions using the DIAGNOdent laser and the patient sought a second opinion from another dentist who used traditional means of caries detection. The Board found the dentist guilty of misconduct and his license was revoked.17
It must remain the clinical duty of the practitioner to assess all of the detection modalities before making a decision as to the treatment plan which will be presented to the patient. During the consultation, the practitioner must inform the patient of the results of the diagnostic tests and what they mean, and then allow the patient to decide if they wish to proceed with treatment. This informed consent must be established before any form of treatment may commence.
Magnification is one of those magical innovations that have allowed us to improve our dentistry by being able to see on a magnified basis. This allows us to detect lesions sooner, get a clearer picture of the problem and allow us to perform our dentistry in a more highly skilled manner, and in a more ergonomic way so as to prevent fatigue and muscle strain to the practitioner.15,16 Magnification can be in the form of loupes or the more advanced use of microscopes chairside18,19 (Fig. 6).
Caries indicating dye is an old standby that still works well in clinical practice to make sure all the decay has been removed from the tooth before placing your restorative materials.
The use of air abrasion has
become a standard of care for the removal of areas of decay in pits and fissures. The benefits of micro-abrading the interior of crowns before cementation to remove surface contaminants has been long recognized as a tremendous improvement to the bonding criteria (Fig.7). The use of air abrasion technology (Sunrise) removes the decay and only very small amounts of intact enamel and dentin, thus minimizing the loss of tooth structure and the maximization of tooth structure.20
Hard tissue laser
The advent of lasers in dentistry has enabled the practitioner to safely and easily removed decayed areas of tooth with minimal tooth loss and with the lack of smear layer to allow us to bond our restorative material with higher bond strengths and decreased marginal leakage (Fig. 8). The microfractures and smear layer created when using conventional handpieces and burs directly diminish the abilitiy to bond to the tooth requiring acid etching of the tooth before bonding. It is argued that there is a much greater risk of technique sensitivity resulting in highly variable bond strengths.21,22
A group of dentists from the Toronto Academy of Cosmetic Dentistry attended the laboratories of Ivoclar corporation in Buffalo, NY. Approximately 50 dentists took part in the study where under strict laboratory conditions, we were all given identically prepared teeth and we were to acid etch, rinse, place dentin bonding agent to the tooth and bond material to it. An “instron” machine was used to measure the bond strength of all 50 teeth. The results varied from a bond strength of 0 to a bond strength of 80 megapascals. This study clearly shows the high degree of variability under identical circumstances, leading one to conclude that the technique sensitivity of acid etching and bonding is of major concern in clinical practice.
By eliminating the development of the smear layer (Fig. 9) and hence the need to acid etch, bonding technique is simplified and the bond strengths and marginal integrity of the restorations should improve.
When confronted with a tooth that shows mottled or hyper-calcified spots on the enamel, the clinician can use a micro-abrasion technique to remove the majority of the discoloration (in most cases) so that the tooth can be spared from an enamel-ectomy, the cutting into the enamel to remove the spot, and the subsequent replacement with a bonded composite resin which will in time, stain, decay and discolor and need to be replaced adding extra trauma to the tooth. In most cases the improvement is sufficient that most patients are satisfied and their aesthetic concern is not noticeable from a social distance. In some cases however additional treatment may be required to mask the discoloration in the form of a composite restoration or a veneer (Fig. 10).
The use of a 6% hydrochloric acid slurry in pumice (Opalustre by Ultradent) is used in a prophy cup applied to the affected teeth over a course of 3-5 minute intervals. The procedure can be repeated 2-3 times. It is important to not allow the frictional heat to build up on the tooth which could cause pulpal hyperaemia. The patient is instructed to tell the dentist if the tooth is at all uncomfortable during the procedure.
During the process if the slurry begins to dry out, simply by dipping the prophy cup into a dappen dish of water and reapplying, the slurry will become wetter and decrease the risk of heat buildup. It is strongly recommended that a stringent regimen of sealing all exposed gingival and oral tissues using liquid dam as used in the Zoom II bleaching protocol be used to prevent any extraneous material or splatter from coming into contact with the oral tissues or skin (Fig. 11).
In some areas the use of Hydrochloric acid or Hydrofluoric acid (routinely used in the repair of fractured porcelain) in any form is considered to be not within the standards of care. The practitioner should check with their governing body to make sure this mode of treatment is considered to be an acceptable treatment.
If the treatment does not result in a satisfactory conclusion for the patient, then the patient must be made aware that progressing to the next step will involve the removal of tooth structure, that this restoration will need to be replaced over time and depending on the size of the aesthetic defect may compromise the structural integrity of the tooth. Once the patient has been informed of the options and risks involved, they can confidently make a decision as to which treatment path they wish to proceed.
In many cases the use of minor tooth re-contouring techniques enable the practitioner to improve the aesthetics of the case without having to resort to placement of full veneers, thus minimizing treatment for the patient and maintaining tooth structure in the process.
The success of modern implant prosthetics have allowed us to recommend an implant as a first option to patients with missing teeth (Fig. 12). This option precludes the need to cut down healthy enamel on the teeth adjacent to the edentulous site thereby preserving healthy tooth structure which is our ultimate goal.
The use of orthodontics should be a mainstay of the general practitioner. Even if the general dentist is not comfortable in minor orthodontic procedures, eliciting the help of the local orthodontist to help will be welcomed by both patient and practitioner. Every ortho case does not necessarily have to be a full ortho case. When confronted with a situation where the use of minor orthodontics will result in a decrease in the amount of restorative treatment in the form of removal of tooth structure, then this should be the first choice presented to the patient (Fig. 13).
In cases of a bridge or implant to replace a tooth and the adjacent teeth have drifted or opposing teeth have over-erupted. In the case of anterior crowding where veneers are the final option, even some minor ortho first can align the teeth so that the amount of tooth structure removed is minimized and the tooth structure is not compromised to the same degree. This will result in a minimally invasive prep that will maintain tooth structure, be less invasive to the pulp and will result in a stronger restoration less resistant to fracture bond failure.
Many perio-restorative situations can be improved before the restoration is placed by some minor orthodontics, such as the eruption of a broken tooth to bring the perio complex down to maintain papilla heights and gingival heights of contour before restoration or placement of implants (Fig. 14). The use of ortho to control the problem of a congenitally missing lateral, where ridge preservation is optimized by using ortho to move the cuspid into its appropriate arch position before restoration using an implant or bridge is paramount in the successful aesthetic conclusion.23
Reduction stents and diagnostic mock ups
By preparing a diagnostic wax up of aesthetic cases we can determine the end result before we begin the treatment process. This will allow the clinician to analyze the case and pre-determine how to minimize the loss of tooth structure during preparation. This may come in the form of some minor orthodontics before beginning the active restorative treatment phase.
The use of a reduction stent and reduction temporaries is a mainstay technique in the rationale of minimally invasive dentistry. The sequence has been described in other articles,24 but basically involves, making a stent of the diagnostic mock up. Then using this in the mouth to ensure the arch form has been reduced to fit within the wax up parameters. Then using the stent a set of temporaries are created and applied to the non-prepared teeth which have been minimally reduced to conform to the arch form only.
In the case of a crooked tooth, the portion of the tooth which is rotated behind the arch form will have a high degree of material thickness applied over top, while the portion of the tooth which is at the arch form perimeter will have no temporary m
aterial covering it. Now by prepping into these provisional an ideal prep as if they are the real teeth, certain areas of the actual tooth will be prepped and other areas of the actual tooth will not be touched. After the ideal prep is created in the temporaries, the remaining temporary material is flicked off the teeth and final touches to the preps are finished. Impressions are taken. This technique allows the practitioner to prepare the teeth in the most minimally invasive manner in order to achieve the desired aesthetic results (Figs. 15a-15h).
Perio and perio restorative
The use of minimally invasive techniques such as closed flap crown lengthening using laser and the debridement and sterilization of deep pockets using lasers have greatly improved the process of these periodontal procedures, cutting down both procedure and healing times while giving all the advantages of the previous therapies of deep scaling curettage and osseous recontouring with flap exposure of the areas.
Impression taking is made easier with tissue control achieved with laser. A trough created around the tooth without bleeding allows the impression materials to flow below the preparation margin for an easier and more accurate impression. It is a much faster and easier procedure than packing cord or using other astringents, both for the practitioner and the patient (Fig. 16).
Treatment of root senstivity
Whereas the previous regimen was topical application of fluorides and desensitizers, followed if necessary by acid etching and placing dentin bonding agents or cutting into the exposed root and placing a restorative material of choice, can now be reduced to a 30 second application of laser energy to occlude any exposed tubules rendering the tooth virtually sensitivity free within minutes (Fig. 17).
The new techniques, materials and methods in Dentistry provide us with the ability to provide better and longer lasting care for our patients by using the concepts of minimally invasive dentistry. By reducing the trauma to the tooth by earlier detection of caries, using kinder and more gentle methods of caries removal, the use of reduction stents and orthodontics to minimize the loss of tooth structure during the treatment phase, the use of implants to eliminate the need to cut down virgin teeth adjacent to a missing tooth, and the maintenance of tooth structure so as to not compromise the structural integrity of the tooth allows us to provide a better service to our patients. These new methods and materials would most certainly meet with GV Black’s whole hearted approval.
Dr. Goodlin is an accredited member of the American Academy of Cosmetic Dentistry and a Fellow of the Academy of General Dentistry. He has a practice limited to cosmetics in Aurora, ON, Canada, and maintains his dental licenses in Ontario, Florida and Texas.
Oral Health welcomes this original article.
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