Fall 2000 Presentation Summary:

The key to successful orthodontic/restorative treatment is to set sound restorative goals prior to orthodontic treatment. To do this, the orthodontist needs to know how restorative choices are influenced by occlusion and tooth position.

Restorative Options

Dr. Kinzer explained that in restorative decision making, his goals are (1) conservation of tooth structure, (2) pleasing esthetics, and (3) longevity of the restoration. In planning treatments, he starts with the most conservative restoration, and then, with the goal of conserving tooth structure, he looks for reasons not to do the restoration.

Procedures from most conservative to least conservative are: veneers, bonded all-ceramic crowns, cemented all-ceramic crowns, and finally, metal ceramic crowns.

Veneers

Veneers are the most conservative restoration, and Dr. Kinzer feels they are the restoration of choice when the following criteria can be met:

• 3 mm or less unsupported porcelain extension (2 mm in bruxers)
• 50% of the remaining preparation is in enamel (strength is achieved through enamel bonding)
• No significant change in shade is needed

Bonded All-Ceramic Crowns (Porcelain Jacket, Empress, OPC)

The next choice is a bonded all-ceramic crown. These restorations use micromechanical adhesion for resistance and retention, and must be bonded for strength. Indications for this restoration are:

• Area of high esthetic need
• Occlusion that can be managed
• Normal dentin - if dentin is sclerotic or bond strength is questionable, this restoration is contraindicated
• Non-bruxer-due to the elastic modulus of dentin, teeth flex causing ceramic fracture in bruxers

Cemented All-Ceramic Crowns (In Ceram, In Ceram Spinell, Procera, Empress 2)

The strength of these restorations is inherent in the traditional resistance and retention form of the tooth preparation. They have a significantly higher strength than the bonded restorations, but less than metal ceramics. Indications and advantages are:

• Very esthetic regardless of tooth preparation color, higher opacity
• Cement does not rely on bonding for strength Contraindication and disadvantages:
• History of parafunction (history of bruxing)
• Special equipment is necessary for fabrication

Metal Ceramic Crowns

Advantages:

• Strength and durability
• Bonding is not necessary
• Excellent esthetics when done properly, however esthetics are dependent upon laboratory quality

Management of Small Malformed Teeth

The most common situation where management of small teeth occurs is retained primary teeth and "peg-shaped" lateral incisors. Dr. Kinzer's discussion primarily focused on the diminutive lateral incisor. Questions that arise are: How much space is necessary? Where should the tooth be positioned? and When should the restoration be placed?

How to Determine the Correct Space

1. Mimic the contralateral tooth if present and normal in shape.

2. Golden Proportion - the established ratio of central incisor:lateral incisor:canine of 1.618:1.0: 0.618 as viewed from the frontal aspect of a patient is difficult to utilize. This is not a linear measurement, but rather a 2-dimensional representation of a 3-dimensional object and, thus, not practical for clinical use.

3. Esthetics and Occlusion: Place central incisors in most favorable esthetic position, place canines where they need to be to provide disclusion, and then evaluate whatever space is left for the lateral incisor.

• Range of lateral incisor width: 5.0 mm to 7.0 mm (generally about two-thirds width of the central incisor)
• If the available space is too small you may consider stripping the centrals if Width:Length (W:L) proportions allow. W:L ratios of 80-85 % are best, however 65-85% can be acceptable.
• If the available space is too large, evaluate the W:L proportion and amount of overjet present for possible orthodontic retraction (may be in conjunction with stripping of the lower anterior) or restoration to broaden adjacent teeth.

Where to Position the Small Lateral Incisor

Mesial-Distal: Dr. Kinzer advises positioning the lateral incisor nearer to the central. Generally the emergence profile on the mesial is flat, on the distal more convex. Positioning the lateral closer to the central gives better contour to the papilla in the more esthetic area. Extra space is easier to hide on the distal.

Buccal - Lingual: The decision to position the lateral on the center of the ridge, or more labial, or lingual depends upon the planned final restoration, a veneer or a crown.

For example:

If a crown is the restoration of choice:

Position: Center of ridge or more facial, leaving 1.0 mm space between the palatal surface and lower incisors

Advantage: Less preparation of the palatal surface

If a veneer is to be used:

Position: More lingually so that the palatal aspect of the tooth is in occlusal contact

Advantage: Less preparation of the facial surface is necessary, more enamel is available for bonding

Incisal-Gingival: Level gingival margins such that the gingival margin of the lateral incisor is to 1 mm more incisal than the centrals or canines. Gingival margins are even more critical in cases with canine substitution. Dr. Kinzer recommends extruding the canines to at least the same gingival height level as the centrals with equilibration in order to achieve a more esthetic result.

Sequence of Treatment

Ideally, the build up should be done before orthodontic treatment, but this is often impossible because of poor spacing. The sequence Dr. Kinzer recommends is opening space for composite bonding to approximate the final tooth shape, followed by completion of orthodontic treatment. If more than one tooth requires restoration for alteration in mesial-distal dimension, a diagnostic set up is indicated.

Management of the Interdental Space

An open gingival embrasure is judged to be unesthetic by orthodontists if it is greater than 2 mm, according to a study by Kokich Jr., et al. In the same study, dentists and lay people determined an open gingival embrasure of 3 mm or more to be less attractive.

The papilla acts as a "fluid filled sac" with a constant volume. Its final shape is influenced by the adjacent teeth, the contact point, the bone level, and the attachment length. Dr. Kinzer reviewed a study (Tarnow, et al) that showed that if the distance from the contact point to the crest of the bone is 3-5mm, papilla is present 100% of the time. If this distance is 6mm, papilla is present 56% of the time, and only 27% of the time
if the distance is 7 mm.

Interdental Space Concerns: a "Tooth" Problem or a "Tissue" Problem?

Dr. Kinzer recommends the following evaluation sequence in diagnosing the cause of an interproximal black space. First, evaluate the papilla height relative to the adjacent papilla. If the papilla are at the same level, the cause of the black space is most likely a tooth problem, such as root angulation or tooth shape. Second, evaluate the radiograph for root divergence. As the roots diverge, the volume of the gingival embrasure increases. If roots are parallel, then tooth shape is the more likely cause. Use radiographs to also evaluate interproximal bone loss, which can cause true tissue problems occur due to interproximal bone loss. If bone levels are equal, then probe the sulcus. If probing depth is less than the probing depths of the adjacent teeth, then the cause can either be due to an increased volume of interdental space (teeth) or a regenerative problem (tissue).

The options for correction of the interproximal tissue problems include surgery, orthodontics, or restorative treatment. Surgical augmentation with soft tissue or bone grafting is not a predictable option. The goal of decreasing the gingival embrasure is best addressed with orthodontics or restorative treatment. If roots are divergent, orthodontic treatment to parallel roots will decrease the volume of the gingival embrasure. If the problem is due to tooth shape, and the width:length ratio is >0.8 and there is adequate overjet, orthdontic treatment in conjunction with stripping can be done to reduce the gingival embrasure volume. If the width:length ratio or amount of overjet does not allow stripping, or if the patient does not wish to under go orthodontic treatment, an option is to restore the teeth with a composite, veneer, or crown. Regardless of the restoration chosen, it must be carried subgingivally to avoid leaving an overhang.

Treatment Alternatives for Single Tooth Replacement

The goals for single tooth replacement are conservation, function, esthetics and longevity. Dr. Kinzer advises that the most conservative treatment option be chosen to replace a single tooth, as long as it meets these goals. Bonded Bridges (metallic or non-metallic) have the advantage that the adjacent teeth need less reduction. The failure rate is variable, and ranges from 54% over 11 months to 10% over 11 years. Indications for bonded bridges are:

• adequate surface area available for retention
• normal overjet/overbite relationship
• favorable inter-incisal angle (incisors more upright to direct occlusal forces vertically through the long axis of the tooth, delivering a "shear" load, rather than a "tensile" load with proclined incisors
• no tooth mobility present
• teeth are thick and non-translucent in order to mask any metal Cantilevered Bridges are generally used to replace lateral incisors. They are more predictable than bonded bridges, and can be used with full-coverage or partial-coverage retainers. It is necessary that the pontic be in disclusion in all excursive movements to prevent failure. They are not indicated in patients with parafunctional habits (bruxers). Conventional Bridges are indicated when adjacent teeth need full coverage. They can be used in any occlusal scheme, including situations with tooth mobility. Failure rate varies from 20% over three years to 3% over 23 years.

Implants

Dr. Kinzer believes that implants are the standard of care in meeting the goals of long-term, maintenance free, functional and esthetic single tooth replacement. Implants differ from natural teeth in that they lack a periodontal ligament, and as such lose the benefits that the PDL provides (adaptation to occlusal overloading, shock absorption, and proprioceptive inhibition). The goal in successful implant placement is to decrease the occlusal load because implants lack the ability of natural tooth adaptation.

Implant failure can be due to lack of integration occurring shortly after first stage surgery, most likely due to surgical factors such as contamination or overheating of the bone. Loss of integration occurs following placement of the restoration (provisional or final) and is due to excessive occlusal force or peri-implantitis. Structural failure is the most common cause of implant failure. This ranges from porcelain fracture, loosening or fracture of abutment screws to fracture of the implant body, and is almost always due to occlusion. The key to avoiding structural failure, according to Dr. Kinzer, is the ability to control lateral occlusal forces.

Implant Treatment Planning

Patient selection is critical to implant success. The predictability for implant success depends to some degree on the patient history. Implant success is greater is a tooth was lost due to caries, and decreases as loss occurs from trauma, periodontitis, or occlusion in that order.

Occlusal history and management is very important in implant treatment planning. Occlusal management for patients with no history of parafunction is similar to natural teeth. Patients with parafunction, as demonstrated with the presence of wear, mobility and fractured teeth are at higher risk for implant failure. The key to developing the overall implant treatment plan is to diagnose the etiology of the parafunction. There are two categories of parafunction according to Dr. Kinzer: those caused by occlusal factors and those influenced by the central nervous system (CNS).

To diagnose the cause of parafunction, first identify any occlusal findings such as CR-CO or balancing interferences that may trigger parafunction. (Dr. Kinzer notes that the presence of occlusal interferences, however, does not indicate that they are responsible for parafunctional habits.) Then, two to three month trial occlusal splint therapy can be used to eliminate existing occlusal interferences. If wear facets are not present, it can be assumed that occlusal therapy to eliminate interferences will alter parafunction. However, if facets are still present, it can be assumed that the etiology of the parafunction is CNS influenced.

CNS parafunction can be vertical (a small range of mandibular motion resulting in wear on the palatal functional surfaces of the mandibular teeth), or horizontal (wear occurs of incisal edges and buccal cusps of maxillary teeth). The treatment goal is to get the teeth out of the way of the parafunctional movements. In a vertical bruxer, an increased vertical overlap is more acceptable given the limited range of parafunctional motion. However, in the horizontal bruxer minimal vertical overlap is required to allow the least resistance with mandibular movement. The lower the contact angle between the implant and opposing tooth, the less stress occurs during para-function. The contact angle increases with greater horizontal and vertical overlap, therefore establishing minimal overjet/overbite occlusion, which is preferred.

Implant Site Development

The goal in implant site development is to have enough bone present so that the implant can be placed in the ideal position. Surgical bone grafting can provide additional ridge width, but has limited predictability in providing vertical ridge height. Orthodontics extrusion (if a tooth is still present) or bodily tooth movement can also be used to improve bony contours. Although this requires a longer treatment time, development of alveolar ridge height is more predictable.

Gingival Considerations

Gingival form generally follows the underlying bony form. The gingival of a natural anterior tooth follows the ~3mm scallop from facial to interproximal, resulting in an esthetic gingival form. The challenge with flat headed implants is the lack of facial-interproximal bone scallop, and thus lack of gingival scallop. With multiple implants, it is extremely difficult to obtain a normal gingival scallop. Two adjacent implants in an esthetic area are a concern due to the flat gingival architecture. For this reason, Dr. Kinzer recommends using orthodontics to create single tooth implant sites whenever possible. For example, if there is a two-tooth pontic space, bodily movement of a tooth into the middle of the site to create two one-tooth implant sites adjacent to natural teeth will result in an esthetically more favorable gingival embrasure.

Space Requirements

Coronal:

• Generally want 1.0 mm space between implant and tooth for adequate papilla
• Conventional 3.75 mm implant has 4.0 mm platform, so 6 mm space is necessary

Inter-Radicular:

• Generally, at least .75 mm is required between the implant and adjacent tooth
• For a maxillary lateral incisor, the goal in 4.5-5.0 mm of inter-radicular space using a 3.25 mm diameter implant
• Root divergence is necessary to facilitate implant placement

Interim Restoration (following completion of orthodontic treatment and awaiting implant placement)
A removable retainer with a pontic tooth is good for short-term use, having the advantage of being quick and inexpensive. The retainer should be designed with rests on the cingulum of the adjacent teeth to prevent pressure on the tissue, and contoured for adequate papilla development. If implant placement is not planned for four to five years, a resin-bonded bridge may be a better interim restoration choice.

Summary of the Orthodontist's Role in Implant Treatment Planning

1. Whenever possible, position teeth and design occlusion so that the natural teeth provide guidance in eccentric movements. Group function (central, lateral, 1st premolar) is recommended if canine implants are to be placed.

2. If parafunction is CNS and horizontal in nature, provide a dental relationship with minimal overbite and overjet relationship, either through orthodontics alone, or in combination with orthognathic surgery.

3. In a multiple tooth implant site, position natural teeth to provide single tooth implant sites rather than adjacent implants for improved gingival architecture.

4. Provide adequate coronal and inter-radicular space and root divergence for implant placement.

5. Orthodontically extrude or move teeth to improve bony site for implant placement.

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