MANAGEMENT OF BADLY BROKEN TEETH ********************************************************************* INTRODUCTION
EVALATION OF REMAINING TOOTH STRUCTURE
FEATURES SPECIFIC TO MATERIALS
INTRODUCTION: Nothing is more challenging than providing a sound restoration to a grossly destructed tooth. A mutilation can occur due to caries, trauma, extensive restorative procedures or even developmental malformations. Such compromised teeth prevent the use of traditional preparation designs as it is often necessary to compensate for inadequate length, missing cusps and in extreme cases, even a missing clinical crown. Modifications of the preparation designs and the proper choice of the restorative material can be a test of the operator’s ingenuity, knowledge and skill.
MANAGEMENT: The management of these compromised teeth has to follow an organized and systematic approach 1. A general preliminary evaluation regarding the tooth’s strategic importance, position in the arch, oral hygiene, caries rate, patient interest etc. should be made. sometimes, it is better to go ahead with an extraction instead of wasting precious time and energy on an elaborate procedure on a tooth having a questionable prognosis. 2. Next an evaluation of the condition of the pulp and periodontal tissues is made. If the tooth has not suffered a pulpal exposure, is asymptomatic, responds normally to vitality tests, displays no radiographic periapical changes and has adequate coronal structure for retention and resistance forms, every effort is made to maintain the vitality of the pulp. However, if pulpal condition is doubtful or if even small exposure has occurred, the tooth should be endodontically treated. The patient should also be forwarned regarding the need of an international root canal treatment if during the course of the treatment it is felt that a RCT is needed. A periodontal evaluation is also warranted to check for sub-gingival extensive and health of the supporting tissues. At times periodontal surgeries are required to attain adequate crown height / expose the gingival extent of the destruction.
This is followed by initial outline form and removal of caries, undermined
enamel, weakened tooth structure and old restorations (Protective liners and bases are placed wherever required). 4.
The tooth is then re-evaluated for its reconstructability. If it can be restored, a
final preparation design is decided upon. If it is felt that an intra-radicular retention will help, then an intentional RCT is done to be followed later via a post and core. If this also is not possible, then an extraction is the only alternative.
EVALUATION OF THE REMAINING TOOTH STRUCTURE: Now, once a decision is made that the tooth can be vitaly restored, the next critical step is to evaluate the remaining tooth structure. It is important to form a mental image of the restorative design, material and technique before starting any procedure. Certain points to be kept in mind during this are: 1. Stress patterns on the tooth: The stress concentration areas of the posterior tooth are: o the ridges (including marginal, transverse and oblique) o the cusps with their inclines o the clinical crown root junction For an anterior tooth it is the o lingual ridges and concavity o incisal angle o cervical areas. Every effort should be made to leave these undisturbed if uninvolved. Also remember that: ďƒ˜ stresses are maximum at the IInd premolar and Ist molar region ďƒ˜ upper teeth resist stresses better than the lowers ďƒ˜ stresses are the least in teeth opposing a bridge pontic, denture, inclined tooth / space. 2. Cariogenic evaluation: Is basically done to decide which areas of remaining tooth structure needs to be further involved. Defects / decalcifications can be restored separately rather than
involving them in the main design. Of course, this totally depends on their size and location. 3. Craze lines: Should be detected, as they can be precursors for partial or complete tooth fracture. Craze lines should be involved into the preparation design if they are more than 5-6 in number. 4. Proximal drifting: Can occur as a result of long-term loss of the mesio- distal dimension of the tooth. establishing proper contacts, contours and occlusion can be difficult. Here 3 options are then available to us: Either restoring the tooth to a reduced dimension such as making a bicuspid of a tricuspid pre-molar. This is applicable only for minimally drifted teeth The other option is to regain the lost space orthodontically using coiled springs, separators or even an over-contoured temporary restoration. If space loss results in root to root contact, then the tooth should be extracted or hemisected if it is multi- rooted 5. The gingival seat: Location is an important factor to bear in mind. Based on different extensions of the destruction relative to the periodontal apparatus, 4 locations are possible : •
Supragingival = Regular procedures are carried out unless a hyperplastic gingival tissue or polyp is present warranting on excision.
Subgingival but suprabony = a gingivectomy may suffice or else a full thickness muco-gingival flap is raised and re-attached apical to the destruction.
Infrabony but sufficient bone support present = A minor osteotomy may be needed
Infrabony but osteotomy is not feasible = Here an intentional extrusion can be attempted to expose the apical extent of the gingival seat using orthodontic brackets and elastics. Periodic occlusal adjustments will be needed.
All these procedures seem very elaborate a fancy but in reality may not be feasible at all and even if done can cause further problems like furcation exposures, undercut formation, loosening of teeth, improper crown:root ratio etc. The pros and cons of each procedure should be measured carefully before implementation.
MECHANICAL CONSIDERATIONS: Once these evaluations are completed, some thought should given to the mechanical considerations which influence the amount and type of retentive and resistance modes which have to be applied and also the kind of restorative material to be used. •
If >50% of coronal structures is sound, then sufficient retention is achieved by supplemental retentive features. Anything lesser calls for RCT + Post & Core.
Regarding the cusps: Here 3 ratios are important: 1.
< 1/3 – ½
Destruction width Intercuspal distance
If this ratio is
retentive features are required like grooves /
> ½ -1
Cusp width If it is > 2 then cusp reduction and capping is mandatory as the cusp becomes very weak. Ideally a function cusp is reduced by 1.5mm and a non-functional cusp by 1mm 3.
Surrounding wall If this is lesser, then both retention and resistance forms are compromised. Regarding ridges: Leave them intact as far as possible. A thickness of even 0.5mm is adequate if not occlusally involved. If in contact, then 1.5-2mm thickness is mandatory. Anything lesser should be cut across. Ridge length = 1 should be achieved Ridge Width
Preparation depth: Pulpally, axially and gingivally should be considered not only for then biologic importance but also to decide whether they need to be stepped for enhancing resistance. Junction between clinical crown and root should be observed. If intact, leave it undisturbed but if involved, place retention modes in the root rather than the crown. Crown root ratio: Ideally, it should be 1:3. If this is > 1:3, stresses get concentrated on the tooth rather than dissipating onto the PD tissues. This can be reduced by occlusal reduction & decreasing incline steepness Considerations should also be given to occlusal abnormalities such as crossbites, deep bite, tilting, rotation etc and also to any paranormal habits like bruxism. A decision has to be taken regarding whether such abnormalities need to be orthodontically corrected prior to the completion of the restorative procedures. Also note if the tooth is going to be used as an abutment for an FPD.
PREPARATION MODIFICATIONS: The basic concepts of cavity preparation and the conventional cavity form should be firmly fixed in the operators mind. Every feature has a definite purpose and if conditions prevent their incorporation, then same other geometric feature must be improvised to fill its role. This is the principle of substitution. No â€œcorrectâ€? or ideal preparation exists; only guidelines to select a material and execute a design can be followed. Most modifications consist of squaring the walls and adding auxiliary features for retention and resistance forms. As this requires further cutting of an already weakened tooth, bear two points in mind: 1. Do not involve the vital core, which comprises of the pulp plus 1mm of surrounding dentin. No retentive feature should be deeper than 1.5mm cervically / occlusally . 2. Do not reduce a remaining wall of dentin to a thickness less than its height to get added retention.
Defects can be converted into retentive features if not very extensive. The walls of the remaining defects can be shaped to remove undercuts and provide vertical walls One or a combination of the following can be utilized to get added retention and resistance forms: 1. Grooves: Are placed usually vertical axial walls at 1mm depth and width. They can be also be placed internally at line angles of oversize boxes to enhance their resistance form 2. Slots: are basically grooves whose length is in a horizontal plane. They are 0.5mm in depth and about 1-4um in length and are placed 0.5mm axial to DEJ 3. Coves and locks: Are smaller slots and grooves respectively. They are never used alone but always with pins / slots 4. Convert classical grooves to box forms: When the destruction occurs beyond the outline of a standard groove form, the situation calls for a conversion to a box form. Ideally > 180o of sound tooth should be presented between the 2 retentive features to prevent tooth fracture. Thoughtful location will help over- come such problems 5. Sloping surface orientation: On brood sloping surfaces left after cusp fracture, it is better to form multiple small steps instead of one long and broad single step which would weaken the tooth and jeopardize pulpal health. 6. Pinholes and pins: Are probably the only retention features that do not require existing vertical supragingival tooth structures for their placement. They can be used in 2 ways. ď‚§
Pinholes parallel to path of insertion where the pins are an integral part of the cast restoration. These pins aid in enhancing retention of over tapered preparations
Non-parallel pinholes and pins aid in retaining a core of amalgam / composite over which a cast restoration is fabricated.
There are 3 types of pins : Cemented Threaded Friction lock Regardless of the type of pin which is used, it should be surrounded by 0.5mm of dentin. Hence, it is contraindicated in small, thin teeth. Some general rules to be followed while placing pins are: Place them as close to the line angles as possible within 0.5mm from DEJ and 0.5mm from axial wall. This allows for sufficient dentin bulk for stress distribution, adequate space for amalgam condensation and prevention of crazing or fracture of enamel. Threaded pins need to be placed at a depth of only 2mm while cemented need about 4mm. Both should extend 2mm into the restorations. Place them as far from the fulcrum of the anticipated tipping motion. Safest locations are the line angles and tooth corners while the least desirable is in the middle of the tooth especially over furcation and external concavities. Always examine radiographs carefully before starting pinhole preparation. A drill can also be placed in the gingival sulcus in the estimated direction of the hole to get an idea of the outer surface in area of pinhole. Briefly, the procedure involves making a pilot hole or a dimple with a no. ¼ bur followed by, preferably, a depth limiting twist drill to drill a channel up to 2mm. A slightly larger diameter self- threading pin is then twisted into this channel using a hand wrench / latch type HP. The excess length of pin is removed with a 169L bur placed perpendicular to the pin, in a brushing motion to prevent unscrewing the pin. Self shearing pins are also available. If they need to be bent, it should be done with a pin bending tool. All these features mentioned are applicable to the posterior restorative materials used in such situations such as amalgam, composites and cast alloy onlays and full coverage crowns. Certain newer, esthetic alternatives are the
ceramic and indirect composite onlays. For anteriors, restorations have to be tooth coloured unless they are to be used as foundations of porcelain fused to metal cast restorations.
FEATURES SPECIFIC TO PARTICULAR MATERIALS: 1. AMALGAM: Amalgapins are simply amalgam filled dentin holes. The hole diameter of 0.8mm and depth of 1.5-2mm is created by #330 bur. Amalgapins cause lesser stress on the dentin and thus, can be placed close to the DEJ. Bonded Amalgam: Utilized bonding systems such as 4-META and MDP. The advantage of these is the more conservative design, better retention, fracture resistance and a better marginal seal. Matrix for a complex amalgam restoration includes -
Convoluted band for sub-gingival extensions.
Spot-welded matrices which help to close the gap near the retainer-band junction and provides a closed system.
Copper-band matrix : these are especially useful when additional height is needed
2. CAST ALLOYS INLAYS AND ONLAY These provide high strength to the tooth by their enveloping pattern. For inlays and onlays, added retention is achieved by preparing skirts, collars, extended secondary flares, reverse flares and over angulated- bevels. Wax patterns are fabricated on dies and the casting is luted using Zn PO 4 or Type I GIC cement. The margins of the casting should be accurate to prevent any microleakage, which would be detrimental to such a compromised tooth.
3. COMPOSITE: As a posterior restorative material can be used as a permanent restoration but preferable should be used as a foundation for a stronger cast crown. Retention here mainly is via micro-mechanical bonding but secondary retentive features may be provided as the ones mentioned before. Additionally, wider bevels can be given to provide more surface area for etching. Preparations are definitely more conservative than either amalgam or cast restorations. After etching and priming, a suitable matrix is provided. It is very difficult to develop proper contact points with composite. Some matrix systems include: -
The toffelmire with thin Dixieland bands
Auto matrix with Mylar strips
The segmental matrix such as the palodent and composi â€“ tight
The composite can be placed in 4 ways -
Bulk curing / trans-tooth curing
Open sandwich method with a F releasing material like RMGIC at the gingival seat.
Directed shrinkage technique using a chemically cured resin at the gingival seat
4. Esthetic indirect restoration including CERAMIC AND INDIRECT COMPOSITES are relatively new in their use as inlays and onlays. As they are luted with adhesive cements, additional strength is provided to the completed restoration. Indirect composites are less likely to fracture and are easily repairable. Ceramics are more esthetic and strong but tend to wear out the opposing tooth. 5. FULL COVERAGE CROWNS may be indicated for -
Teeth with extensive decay
Extensive restorations / wear
Short clinical crowns
Abutment teeth for FPD
These can be all metal, ceramic metal or all ceramic.
Now all these restoration placement require proper isolation in most cases, especially if there are sub-gingival extensions or if the restorative materials is composite. Isolation also can be quite problematic due to inadequate tooth structures or weakened tooth clamp placement. certain techniques and clamps for isolation are. ⇒ Clamp with apically inclined jaws ⇒ Tiger clamps with serrated jaws ⇒ Silker- Glickman or S-G clamp with anterior extensions ⇒ Split dam technique ⇒ Customized clamps wherein the jaws of certain clamps can be slightly ground to accommodate a broken down tooth.
1. Over tapered axial wall
Increase retention by placing a beveled shoulder; increase resistance by placing grooves.
2. Short axial wall
Multiple grooves/ a combination of groove and box/ pins will enhance retention
3. Overextended box form
Place grooves/locks at their line angles
4. Undercuts in axial wall
Should be filled with cement before proceeding with preparations
5. Fractured cusps, sloping surfaces
Convert into multiple steps; reduce cusps for cusp capping
6. 1 missing cusp
Create a box adjacent to cusp/ place grooves in tooth surrounding missing cusp/ place pin-hole in area of missing cusp
7. 2/ more missing cusps
Pin retained core
8. Partial cusp loss
Cusp capping; skirts, reverse secondary flares, exaggerated bevels
9. Loss of crown-root junction
CONCLUSION: Time and again you would have come across a case sheet reporting of a grossly destructed tooth or caries extending onto the root but patient insists on Rx. Donâ€™t look down upon such cases. Take it up as a challenge as advances in technique and restorative materials today has made saving the most hopeless of teeth possible. By combining the right attitude with dedication, knowledge and skill, you will definitely attain results that would be a truly rewarding experience.
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