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MOD RESTORATIONS

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drmithila's picture
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 Working in Tight Spaces With Rotating Instruments: Informed Consent

Another important item to mention here is that we are simply dealing with rotating instruments in a very small and confined space. This carries with it an associated risk for human error. Accidents do happen, even though we all we try to the best of our abilities to be careful and not damage adjacent teeth. This risk should be noted in an informed consent to the patient before any restorative procedure. Yes, we do mean that seriously. A patient should have an informed consent for every single procedure that is done on them, just like they do for every procedure that is done in a physician's office or in a hospital. There are certainly risks and benefits to every procedure that we do, and it is our duty to properly inform the patient of what could happen, even when it is a remote possibility. Feel free to visit commonsensedentistry.com to download current informed consent form for dental procedures.

Magnification
There are numerous ways to prevent damage to adjacent teeth during teeth preparation, especially for restorative procedures. The absolute first requirement for any dental restorative procedures these days would be the use of magnification glasses, surgical telescopes, or surgical microscopes. Magnification glasses will help somewhat, but they do not allow the clinician to see all the details that are required for proper teeth preparation. Surgical microscopes, with their ability to literally almost take you on a journey down the endodontic canal, are an incredible advancement. Unfortunately, for most general dental restorative practices, they are cost prohibitive at this time. Generally, the best choice for everyday magnification use in general dentistry is the surgical telescope. 
There are a number of manufacturers who provide some excellent surgical telescopes (such as Orascoptic, Designs for Vision, SurgiTel, and others). There are a myriad of features and designs, and every dental practitioner should do their due diligence when deciding which surgical telescope is best for them and their practice. What is the bottom line? The use of magnification is required as the absolute minimum step to take to prevent damage to adjacent teeth during teeth preparation procedures.

 

Preventing Soft-Tissue and Osseous Damage in the Interproximal Zone 
A major operative risk, as the preparation design approaches the gingival area, is possible trauma to both the soft tissue and the osseous structures. This can often result in the damage or even loss of the gingival papilla. When this type of trauma occurs, many times the end result can be an aesthetic restoration with good margins, but the patient may now experience a food trap between the teeth because of loss of the interproximal gingival structure. This so-called "black triangle" effect is one of the most frustrating aesthetic and functional complaints to dentists due to the lack of adequate treatments for this challenge. While there are new and successful techniques available which we have developed using laser biostimulation (with a diode laser such as Picasso [AMD Lasers]) and dermal filler materials, the best way to prevent this problem from happening is to place a physical barrier that will protect the tissue and bone.

Placing an Interproximal Barrier 
Another way to prevent damage to adjacent teeth during preparation is by placing a physical barrier between the teeth. The most common way to do this in the past was to create this "barrier" with a tofflemire matrix band. The advantage of using a tofflemire band, or any appropriately thick metal strip for that matter, was the ability to at least absorb minor scratches and damage. In addition, it also gave the operator some "warning" to pull away from the interproximal area.
Today, metal matrix bands are often not regularly found in dental offices, especially if the dental office does not currently use amalgam. Furthermore, one must consider that the matrix band metal is a flimsy, soft metal that does not allow for much protection. Metal matrix bands also encircle the entire tooth, and many times the operator does not have a clear path of sight into the interproximal area that is being prepared. In addition, other matrix systems used today cannot double as protection for the adjacent tooth, primarily because they are made from clear matrices and will shred upon first contact with a rotating carbide bur or high-speed diamond.
Another choice that has been available for some time now is the use of a metal shield that was especially designed for this purpose, the InterGuard protective interproximal shield (Ultradent Products). These disposable shields (available in 4.0 and 5.5 mm vertical heights to accommodate varying teeth) do not encircle the tooth, and are adequately thick/tough enough to help protect the adjacent tooth from iatrogenic damage during preparation. If you are not using a rubber dam, or the shields are not adequately wedged properly and continually supervised using a high volume evacuation tip, the manufacturer advises that the clinician thread an ample length of floss through the hole provided in the side of the shield. The floss allows the clinician or assistant to easily retrieve an accidentally loose interproximal shield, thus preventing the patient from accidentally swallowing or aspirating it. (Note: The floss should be of a length to hang no less than 7 inches outside of mouth.) 
In the clinical case example that follows, we will introduce a new and novel multipurpose, single-product option that was designed to help the clinician prevent interproximal and soft tissue damage during restorative preparation, while fulfilling all of the requirements of MID.

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drmithila's picture
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MOD RESTORATIONS
Figure 1. Preoperative photo of the failing composite resin restoration in tooth No. 30.
Figure 2. Protection (Wedge Guard [Triodent Corporation]) of the gingiva and adjacent tooth was placed before the preparation began.
Figure 3. Bur marks that were observed in the metal (distal) demonstrated damage that may have otherwise occurred on the adjacent tooth surface during preparation.
Figure 4. Initial removal of the protection shield.

 

Figure 5. Completed removal.
Figure 6. A sectional matrix (V3 Ring Sectional Matrix System [Triodent]) was placed.
Figure 7. Composite resin (KALORE [GC America]) placed in the cavity preparation; the sectional matrices were removed.
Figure 8. The final restoration; completed with no damage to the adjacent tooth or the gingival structures. (Note: The wave wedges were kept in place until after all of the finishing was completed to facilitate proper interproximal finishing.)
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MOD RESTORATIONS

It is observed clinically that some years after MOD restoration of molar and premolar teeth, cuspal failures commonly occur. The period between restoration and failure is usually from eight to fifteen years. Evidence has been found, both from observations of fractured cusps and from a mathematical model of an idealized molar tooth, that allows a clear description of the mechanism of these slow failures. Suggested changes in clinical practice are recommended if such failures are to be prevented in the future.

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MOD RESTORATIONS

The use of an mesial-occlusal-distal (MOD) restoration in repairing a large carious lesion depends on many factors. Biomechanical performance is one of the most important. It has been recognized that resistance to restoration failure is not solely a biological concern (e.g. toxicity), but that the cavity shape, dimensions, and the state of stress must all be taken into account. In the present study, a newly developed auto-mesh program was used to generate 30 three-dimensional (3D) finite element (FE) models simulating the biomechanics for multiple factorial design of the MOD gold restoration in a maxillary second premolar. Stress levels were related to individual design factors (e.g. pulpal wall depth [P], isthmus width [W] and interaxial thickness [T]) and to their interactions under the worst physiological scenario: a concentrated bite force acting on lingual cusp with debonded interfaces between cavity walls and restorations. The results showed that enlarging the volume of the MOD cavity significantly increased stresses in enamel but did not intentionally affect stresses in dentin. The alternation of individual design parameters significantly changed the peak stresses (P < 0·05). For all three parameters, except for the width, the peak stress increased as the cavity dimension increased. Stress elevation rate (termed as ‘volumetric stress rate’– stress elevation by increasing one unit volume of the restored materials) was different among three design factors. Depth was the most critical factor governing the stress elevation in enamel (1·76 MPa mm−3) while length (interaxial thickness) was the most important parameter in dentin (0·49 MPa mm−3). Width was the least compromising factor to the remaining tooth, 0·32 MPa mm−3 for enamel and −0·23 MPa mm−3 for dentin. The findings, at its core, did not fully agree with the traditional concept that the preservation of tooth substances will reduce risk of tooth fracture. This study leaves open possibility for the structural optimization of the MOD restoration.

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