Tooth assessment for crowning

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TOOTH ASSESSMENT FOR CROWNING

Dr. Bahjat Abu HamdanConsultant Prosthodontist.

Introduction.

Functional disability of a Pt. is increased by increasing the MT number.

Tooth ability to withstand normal function is decreased with the loss of tooth sound tissues.

Successfully saving a badly damaged tooth requires a thoughtful combination of many aspects of dental treatment.

In the questionable and strategic teeth, think how to replace before extraction.

A thorough background in the principles and techniques of restorative dentistry are required.

Introduction.

In the treatment planning and evaluation for tooth crowning , which is the topic of the lecture, as in any other treatment planning, there is one principle that should be kept in mind: treatment simplification.

The restorative dentist, or prosthodontist, is the one who should manage the sequencing and referral to other specialist. Because he is the one who will finish the treatment.

Based on the collected data (x Ray, study models and clinical Exam.) evaluation of each case could be done properly.

Introduction.

1. Overview of restoration requirements will be exposed. 2. Assessment of a tooth in question will be divided into A. patient-level risk factors B. Pulpal/endodontic status. C. Periodontal/occlusal assessment. D. Evaluation of the remaining tooth structures. 1. Build up of the crown. 2. The cervical metallic collar ( the ferrule). 3. Margin location. 4. Evaluation of short teeth. 5. Crown lengthening.

1.Restoration requirements.

All the requirements for tooth crowning are done for sound and vital teeth which :

Have Sound bone and periodontal tissue. Normal anatomy of the crown . Have normal 3D position in the dental

arch; So that a compromised tooth needs to be

evaluated based on biologic ,mechanic , functional and aesthetic principles before being ready for crowning.

1.Restoration Requirements.

Common errors

1. Over Reduced / Under Reduced 2. Over Tapered / Under Tapered 3. Sharp Angles / Corners 4. Undefined Margin 5. Irregular Margin 6. Margin Position 7. Marred Adjacent Tooth 8. Contact Unbroken 9. Functional Cusp Bevel location

2.A.Patient-level risk factors

Behavioral risk factors Compromised or poor oral hygiene Cariogenic diet Low exposure to fluoride Parafunctional habits Ability and willingness to adhere to a

long-term maintenance protocol SmokingThese facotors affect the prognosis of

the case.

2.B.Tooth evaluation, Pulpal/endodontic status

The loss of structural integrity associated with the access preparation, rather than changes in dentin, that lead to tooth fracture.

Prior to core build-up, an assessment should be made of the pulpal status of the tooth in question. If the pulp is exposed or there are signs/symptoms of irreversible pulpitis, endodontic treatment should be performed.

In the case of an ET tooth, the quality of the treatment should be assessed clinically and by the x ray.


• Existing ET treated teeth need to be assessed carefully for the following:

Good apical seal and lesion free. No sensitivity to pressure. No exudate. No fistula. No apical sensitivity. No active inflammation.


Unacceptable ET should be retreated in spite of the lack of any symptom, others believe that a free symptom short RCT done 6 month ago is different from that one done 6 years ago.

Posting procedures require the removal of the RCF which will disturb the state of the delicate balance between the poor ET and the body defense mechanism causing flare up

Today, ET results are reproducible, and predictable therefore the restoration procedures can commence in 2-3 weeks following the completion of the ET .

2.C. Periodontal/occlusal assessment

Periodontal and gingival tissues should be sound and bleeding free. Evaluation should be done after excavation of carious tooth tissues. The gingival tissue represent the biologic width which should never be violated by the restoration.

Teeth considered questionable were those with deep probing depths, furcation involvement, bone loss, and mobility.


It is beneficial to restore teeth to the physiologic occlusal plane and that over-erupted and tilted teeth can potentially prevent normal tooth contact during function and therefore require treatment.

In partly edentulous patients, such teeth may create a problem when restoring the opposing arch.

The scope of potential treatment ranges from enameloplasty or orthodontic treatment to extraction of severely tilted or over-erupted teeth.


Moderate cases may require a partial or a full-coverage restoration.

However, some cases may require a combination of endodontic treatment, crown-lengthening surgery, and a restoration to achieve a functional tooth that lies correctly within the occlusal plane.

In case of posterior mesially or lingually inclined teeth, its better to adjust it by orthodontic procedure otherwise it may need endo-treatment or using a partial crown.

Redistribution of the spaces to have normal size of the replaced teeth for esthetic reason is mandatory.


Due to the round section of their roots, upper central position can be corrected(to certain limits) if its rotated, in labial or in lingual position (no skeletal malocc)

In the young patients, with proximal caries, drift is more significant. Crowning of these teeth may affect the adjacent ones. However, 1/4 to 1/3 mm touch does not cause any problem. (don’t perforate the enamel).

Severe attrition caused by bruxism may affect little or at all the vertical dimension, because the eruption of the teeth compensates the loss of tooth tissues. Eruption done with the alveolar bone.

2.D.Evaluation of the remaining tooth structures.

In a 20-year retrospective study analysis of 1638 ET posterior teeth restored with amalgam without cusp coverage, fracture was a significant problem. Maxillary bicuspids with MOD restorations showed the lowest survival rate overall.

After 3 years period, the failure of resin-restored and amalgam restored ET teeth was similar.


The clinical longevity of ET posterior teeth (molars and bicuspids) is significantly improved with coronal coverage.

The amount of remaining tooth structure was a significant factor in tooth survival.

Aqualina et al found that ET teeth without crowns failed at a 6 times greater rate than crowned teeth.

The presence of a crown was more important than the type of foundation restoration, although it was noted that teeth with posts have decreased resistance to fracture.

2.D.Evaluation of the remaining tooth structures

1.Build up of the crownRoutine use of crown on ET may not be

necessary if the marginal ridge are intact Cuspal deflection increased with increasing

cavity size in mandibular molars, and it was greatest after endodontic access.

they concluded that cuspal coverage is important so as to minimize the danger of marginal leakage and cuspal fracture in ET teeth.

Stress distribution before and after roof removal of the pulp chamber


1.Build up of the crown A compromised tooth needs to be evaluated

up to the amount of the lost tooth tissues and the functional stresses to withstand.

If the remaining sound tissues are less than 50%, an additional means to retain the core is needed using a post in the root canal.

However, preparation of a post space adds a certain degree of risk to a restorative procedure, that may be root perforation, also it may increases the chance of root fracture.

a radiograph of fractured maxillary second

premolar with a metallic

prefabricated post

Post space preparation involves risk .

An unnecessary post was placed in this largely intact mandibular

molar. Perforation occurred resulting in eventual loss of the

tooth. .

Vertical root fracture was revealed after tooth extraction.


1.Build up of the crown For these reasons, posts should only be used when

other options are not available to retain a core. The need for a post varies greatly between the anterior and posterior teeth.

If an ET anterior tooth is to receive a crown, a post often is indicated. However, at least, 1mm of sound tissues after prep is necessary, build up could be done by LCC and prefabricated post if the tooth is thick enough , otherwise a casting post and core is indicated to withstand the occlusal forces.

2.D.Evauation of the remaining tooth structuresl.

1.Build up of the crown Unless the destruction of coronal tooth

structure is extensive(more than 50%) a post is not needed , the pulp chamber and canals provide adequate retention for a core buildup .

Molars resist primarily vertical forces. The post to be placed in the largest, straightest canal.

1. palatal canal in the Maxillary molars .2. distal canal in the Mandibular molars.3. Post should not extend more than 7mm into

the root apical to the orifice of the root canal.

Screw post and post in the mesial should be avoided


1.Build up of the crownPremolars are usually bulkier than anterior

teeth, but often are single-rooted teeth with relatively small pulp chambers.

For these reasons, they require posts more often than molars. Premolars are more likely than molars to be subjected to lateral forces during mastication. It is important to alleviate the lateral stresses . So that the canine will take over the lateral stresses.


1.Build up of the crown molars have more tooth substance and

a larger pulp chamber to retain a core buildup.

In general, parallel post are more retentive than

tapered post, and threaded posts are more retentive than cemented ones.

The use GG drills and P-reamers should precede the instrument use of any post drills that come with the prefabricated post kit.

Intra-radicular build up without post for molar teeth


1.Build up of the crownIMPORTANT PRINCIPLES FOR POSTS Retention and Resistance Retention is influenced the post’s length,

diameter and taper, the luting cement used and whether a post is active or passive.

Parallel posts are more retentive than tapered posts.

Diameter is less important than the other factors listed.

Resistance refers to the ability of the post and tooth to withstand lateral and rotational forces.


1. Build up of the crownAcceptable guidelines for determining thepost length include the following: the post length should be equal to the clinicalcrown length. the post length should be equal to 1/2 to 2/3 of

the length of the remaining root. the post should extend to 1/2 length ofthe root that is supported by bone. It is accepted widely that the post diameter makes

little difference in the retention of the post.


No matter how the length of the post is but 4-5 mm of gutta-percha is necessary to ensure an adequate apical seal.

Vertucci: FJ. Root Canal Anatomy of the human teeth 1984. Lateral Root Canal Occur:

73.5% in the apical third. 11.4% in the middle third. 6.2% in the cervical third. A root always contains a root canal even

though when is not visible in the X ray and is difficult to locate and negotiate.

Factors influencing retention of posts

Force in kg.

0 5 10 15 20 25 30

Unitek tapered 5 mm

Unitek tapered 8 mm

Whaledent parallel 5 mm

Whaledent parallel 8 mm

Manipulation of cement during post placement

Factors influencing resistance of posts


1. build up of the crown. Resistance is influenced by the remaining tooth

structure, the post’s length and rigidity, the presence of anti rotation features, and the presence of a ferrule.

A restoration lacking resistance form is not likely to be a long-term success, regardless of the retentiveness of the post.

Minimal enlargement of the post space means the post must be made of a strong material that can withstand functional and parafunctional forces.

Post maximum diameter 1/3 of the root section.

Use the GG drills and P reamers

This cast post and core had adequate length for retention, but

failed because of the lack of resistance form.

Post and crown loosened from

maxillary canine a few months

after placement. Both thecore/prefabricated post

and the crown came off (a).Clinical photograph shows

the absence of cervical tooth

structure ( no ferrule) for resistance

of the crown


2.The Ferrule Effect The “ferrule effect” is important to long-term

success when a post is used. A ferrule is defined as a vertical band of tooth structure at the gingival aspect of a crown preparation. It adds some retention, but primarily provides resistance and enhance longevity.

studies have shown maximum beneficial effects from a ferrule with 1.5 to 2 mm or more of vertical tooth structure. Crown lengthening and forced eruption are used to expose the tooth sound tissue.

Force distribution W/WO using ferrule

Crown ferrules increase the tooth’s resistance to fracture.

Variation in bite force by location

Corrosion due to leakage and to defect in the structure

corrosion

Dissimilar metals and alloys have different electric potentials. When two or more come into contact with one another a galvanic couple is created. One metal acts as an anode and the other as a cathode. There is a potential difference between the two dissimilar metals which causes an accelerated attack on the anode. The anode metal dissolves into the electrolyte and deposition is formed on the cathode metal.

http://en.wikipedia.org/wiki/Electrode_potential

Corrosion

Corrosion can be defined as the graded degradation of materials by chemical or electrochemical attack. This phenomenon is of concern particularly when metallic implants, metallic/silver fillings, or orthodontic appliances are placed in the hostile electrolytic environment provided by the human mouth. Corrosion can severely limit the fatigue life and ultimate strength of dental materials leading to mechanical failure.


2. Ferrule effect: wide posts in severely compromised teeth with little or no residual crown structure will fail for a variety of reasons but typically by catastrophic root fracture.

Without adequate circumferential tooth structure, occlusal forces are directed internally down the root creating a wedge effect and the high likelihood of root fracture. Also incomplete ferrule which does not include the tooth filling in the cervical area may result in recurrent caries.

Crowned maxillary bicuspid with extra wide, tapered

cast post and minimal ferrule showing typical

verticalroot fracture

Crown Lengthening (To expose sound tooth structure)

(Force Eruption

Crown Lengthening (To expose sound tooth structure) (Forced

Eruption)


3.Margin locationSupragingivalequiginguvalSubgingival; presence of caries or tooth fracture Increase retention of preparation Esthetic


BW. Violations can be corrected by either surgically removing bone away from proximity to the restoration margin, or orthodontically extruding the tooth and thus moving the margin away from the bone, or both.


Biological width: It is the sum of the supracrestal

fibers, the junctional epithelium, and the gingival sulcus and has a proposed minimal dimension of 3 mm


3. Margin location. Rules Can be used to place margins.Sulcus probes 1.5mm or less : margin could

be placed 0.5 mm below the gingival tissueSulcus probes more than 1.5 mm, margin can

be placed in half the depth of the sulcus.If the sulcus is greater than 2 mm

gingivectomy could be performed to lengthen the tooth and create 1.5 sulcus. Then the pt. can be treated as per the first rule.


4. Evaluation of short teeth. must be established. Restorative assessment

should include: 1. Consideration of the arch position of the tooth. 2. Strategic value of the tooth. 3. Periodontal considerations. 4. Crown-to-root ratio. 5. Inter arch space occlusion. 6. Endodontic treatment feasibility. 7. Esthetics. 8.Supraerupted opposed teeth.


4. Evaluation of short teeth. The restoration of teeth with SCC has included the

following techniques: 1. Alteration of tooth preparation design and

placement of auxillary retention and resistance form features.

2. Placement of foundation restorations. 3. Surgical crown lengthening 4. Orthodontic eruption. 5. ET and overlay removable partial dentures. 6.Pulp chamber crown, and adjustment of the

opposed tooth to the physiologic occlusal plane and lower anterior teeth in deep overbite.


5. crown lengthening Crown-lengthening surgery is designed to increase

the clinical crown length. To preserve biologic width. and prevent attachment loss, restorative margins should be at least 3-4 mm from crestal bone.

Sub gingival restorative margins should be properly contoured an adequate band of keratinized tissue is mandatory.

Consider the benefits of periodontal surgery and orthodontic extrusion in improving the restorability conditions of the damaged teeth with strong roots in the alveolar bone.


5.Indication of crown lengthening; Inadequate clinical crown for retention due to

extensive caries , sub gingival caries or tooth fracture, root perforation, or root resorption within the cervical 1/3rd of the root in teeth with adequate periodontal attachment.

Short clinical crown. Placement of sub gingival restorative margins. Unequal, excessive or unaesthetic gingival level

for esthetics. Violation of biologic width.


5.Contraindication of crown lengthening. 1. Teeth with deep carious lesions or fractures. 2. With restorable teeth, crown lengthening is

contraindicated when there is an unfavorable crown-root .

3. Exposure of furcation introduces potential periodontal breakdown and puts prognosis of the tooth in question.

4. Crown lengthening on a single anterior tooth causes uneven gingival contour, which is esthetically unpleasing smile line .

5. Patients with debilitating systemic diseases or poor plaque control may compromise the healing potential and are contraindicated for surgery.

THANKS FOR YOUR ATTENTION

Tooth assessment for crowning

Health & Medicine

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