CURRENT THEORIESCURRENT THEORIES OF OF

CROWN CONTOURCROWN CONTOUR,,MARGIN PLACEMENTMARGIN PLACEMENT,,

AND AND PONTIC DESIGNPONTIC DESIGN

CURTIS M. BECKERCURTIS M. BECKER WAYNE B. KALDAHL WAYNE B. KALDAHL

JPD FEB 2005, VOL 93, NO 2, PAGE:107-115JPD FEB 2005, VOL 93, NO 2, PAGE:107-115

One of the prime goals of One of the prime goals of restorative therapy is to restorative therapy is to establish a establish a physiologic physiologic periodontal climateperiodontal climate and and facilitate the maintenance of facilitate the maintenance of periodontal health. periodontal health.

Crown contourCrown contour, , margin margin placementplacement, and , and pontic designpontic design all affect periodontal health. all affect periodontal health. This article This article reviews reviews the current the current theories of all three of these.theories of all three of these.

CROWN CONTOUR

The contours for full and partial coverage restorations play a supportive role in establishing a favorable periodontal climate. Three prominent theories of crown contour have evolved:

(1) Gingival Protection,(2) Muscle Actions, (3) Access For Oral Hygiene.

GINGIVAL PROTECTION THEORY

Advocates : contourscontours of cast restorations be designed to protect the marginal gingiva from mechanical injury.

Double deflecting contours have been advocated by some authors, allegedly to protect the marginal gingiva from mechanical injury.

The concept of protecting the gingiva has been with dentistry for many years. A number of dental anatomy textbooks, periodontology textbooks, and respected clinicians advocate the concept of gingival protection with little or no supporting scientific evidence. Statements in support of gingival protection appear to be primarily empirical.

Wheeler has stated, “The gingiva is apt to be stripped or pushed apically through lack of protection and consequent overstimulation.’’ The axiom of gingival protection has become so ingrained in the dental literature and teaching that for years this concept was seldom challenged.

Some dentists and laboratory personnel apparently have reasoned that, if a little gingival protection is good, then more is better. This theory and the increased use of full coverage veneer crowns have produced an era of overcontoured restorations.

Wheeler has remarked that, when molars have curvatures in excess of normal, the gingiva will be over protected and will suffer from lack of proper stimulation

Wheeler’s warning was based on “protection” of the gingiva.

The gingival protection theory has been defended primarily on the basis of three elements: Protection of gingival margins, Gingival stimulation, and Self-cleansing contours.

This concept implies that undercontouring of the clinical crown will cause deflection of masticated food onto the gingival margin, forcing it into the sulcus, thus initiating gingivitis.

This concept may have originated from the observation that interproximal food impaction occasionally can initiate acute inflammation.

PROTECTION OF GINGIVAL PROTECTION OF GINGIVAL MARGINSMARGINS

However, numerous studies have demonstrated a cause and effect relationship between plaque and gingivitis, and in comparison, the interrelationship of periodontal disease and food impaction appears slight.

Many authors have reported situations where crowns of temporary fixed partial dentures have been lost or removed for long periods of time with no apparent ill effects to the surrounding gingiva.

Schluger et.al, stated, in discussing crown contours, “ The so called protective cervical bulge that hypothetically protects the human gingival crevice protects nothing but the microbial plaque.’’

Koivumaa and Wennstrom studied the histologic effects of crown contour on human gingiva. They found that there was an increase in inflammation adjacent to bulbous artificial crowns but the properly contoured artificial crowns exhibited no such increase at the adjacent gingiva.

PerelPerel, in studying dogs, cut Class , in studying dogs, cut Class V preparations 0.5 mm above the V preparations 0.5 mm above the buccogingival crest. He then buccogingival crest. He then overcontoured some restorations overcontoured some restorations and undercontoured other and undercontoured other restorations. After 9 weeks, he restorations. After 9 weeks, he found found no clinical or histologic no clinical or histologic changes with the undercontoured changes with the undercontoured restorationsrestorations; ;

but with the but with the overcontoured overcontoured restorations, he reported evidence of restorations, he reported evidence of inflammation and hyperplasia both inflammation and hyperplasia both clinically and histologicallyclinically and histologically. Thus, . Thus, there appears to be no evidence to there appears to be no evidence to support crown contours designed to support crown contours designed to ‘‘‘‘protect gingival margins.protect gingival margins.’’’’

GINGIVAL STIMULATIONGINGIVAL STIMULATION

This concept reasons that, as food is masticated, it will pass over the gingiva, stimulating it and causing increased keratinization of the epithelium. The keratinized epithelium would be more resistant to periodontal breakdown.

Several authors have shown that the gingival margin is not in the path of masticated food. Even if the food passing over the teeth were to increase keratinization (there is little evidence to back this assumption)

this stimulation would only occur at the buccal and lingual surfaces, leaving the interproximal tissues without proper stimulation. It appears that, under normal circumstances, the mechanics of mastication has very little effect on gingival health.

This concept This concept assertsasserts that, as food that, as food passes over the tooth during passes over the tooth during mastication, the tooth will be mastication, the tooth will be cleansedcleansed. While certain . While certain prominent buccal and lingual prominent buccal and lingual surfaces of teeth do not surfaces of teeth do not accumulate plaque even in accumulate plaque even in neglected mouths. neglected mouths.

SELF-CLEANSING CONTOURS

Numerous Numerous authors authors have shown have shown that that mastication does not mastication does not remove plaque at the gingival remove plaque at the gingival marginsmargins of teeth. Neither does of teeth. Neither does mastication have any effect on mastication have any effect on the the progress of gingivitisprogress of gingivitis..

Thus self-cleansing crown contours apparently are non-existent at the gingival margins of the teeth

MUSCLE ACTION THEORYMUSCLE ACTION THEORY

MorrisMorris was one of the first to was one of the first to question the rationale of the question the rationale of the gingival protection theory. He gingival protection theory. He and others have suggested that and others have suggested that overcontouring prevents the overcontouring prevents the normal cleansing actionnormal cleansing action of the of the musculature and allows food to musculature and allows food to stagnatestagnate in the overprotected in the overprotected sulcus.sulcus.

LindheLindhe and and WicenWicen, , LoeLoe, and others , and others have all demonstrated that, in the have all demonstrated that, in the absenceabsence of oral hygiene, “ of oral hygiene, “self-self-cleansingcleansing’’ mechanisms ’’ mechanisms do nothingdo nothing to prevent gingivitis. Even if there to prevent gingivitis. Even if there were some cleansing of the buccal were some cleansing of the buccal and lingual surfaces from muscle and lingual surfaces from muscle action, action, interproximal cleansing interproximal cleansing still would be impossiblestill would be impossible..

Some Some proponentsproponents of the of the gingival protection theory also gingival protection theory also concur with the muscle action concur with the muscle action theory These authors strive for theory These authors strive for an an intermediate design of crown intermediate design of crown contourcontour which allows for both which allows for both gingival protection and gingival protection and muscular action.muscular action.

THEORY OF ACCESS FOR ORAL HYGIENETHEORY OF ACCESS FOR ORAL HYGIENE

This theory is based on the concept This theory is based on the concept that that plaqueplaque is the is the prime etiologic prime etiologic factorfactor in caries and in caries and gingivitisgingivitis. Thus . Thus crown contour should crown contour should facilitatefacilitate plaque plaque removalremoval, not hinder it . , not hinder it . When crowns were overcontoured When crowns were overcontoured experimentally, experimentally, 64.3%64.3% of the test of the test sites demonstrated an increase in sites demonstrated an increase in periodontal inflammation. This was periodontal inflammation. This was attributed to attributed to decreased accessdecreased access for for oral hygiene.oral hygiene.

The The four guidelinesfour guidelines to contouring to contouring crowns with emphasis on access crowns with emphasis on access for oral hygiene will be described.for oral hygiene will be described.

Buccal and lingual contoursBuccal and lingual contoursFLAT, FLAT, NOT FAT !NOT FAT !

Numerous Numerous authors’authors’ have have demonstrated that plaque retention demonstrated that plaque retention on the buccal and lingual surfaces on the buccal and lingual surfaces occurs primarily at the occurs primarily at the infrabulgeinfrabulge of of the tooth. the tooth. Reduction Reduction oror elimination elimination of of the infrabulge would reduce plaque the infrabulge would reduce plaque retention. retention.

PerelPerel demonstrated that in actuality demonstrated that in actuality undercontouring may undercontouring may promote promote gingival health. gingival health. Ramjford etRamjford et..al,al, and and an increasing number of other an increasing number of other authorsauthors have come to the realization have come to the realization that that overcontouring is a greater overcontouring is a greater periodontal hazardperiodontal hazard than than undercontouringundercontouring..

OPEN EMBRASURESOPEN EMBRASURES If plaque is a primary etiologic If plaque is a primary etiologic

factor in gingivitis, then every factor in gingivitis, then every effort should be made to effort should be made to allow allow easy accesseasy access to the interproximal to the interproximal area for plaque control. area for plaque control. Open Open embrasureembrasure spaces will allow for spaces will allow for this easy access.this easy access.

An An overcontoured embrasureovercontoured embrasure will will reduce the space intended for the reduce the space intended for the gingival papilla. The result is a gingival papilla. The result is a broadening of the col area, broadening of the col area, causing causing pressurepressure and and irritationirritation on on the papilla. This alsothe papilla. This also inhibits inhibits effective oral hygiene. effective oral hygiene.

Several Several authors authors have suggested have suggested or implied that an or implied that an interproximal interproximal spacespace that is that is slightly larger than slightly larger than normalnormal may be desirable since it may be desirable since it provides adequate room for the provides adequate room for the gingival papilla and is a more gingival papilla and is a more accessible area to clean.accessible area to clean.

Some authors have reported the Some authors have reported the fear of creating an environment fear of creating an environment which promotes “which promotes “lateral food lateral food impactionimpaction’’ when open embrasures ’’ when open embrasures are employed. are employed. Townsend Townsend has has observed that, even with grossly observed that, even with grossly undercontoured, open embrasure undercontoured, open embrasure spaces, lateral food impaction spaces, lateral food impaction rarely occurs rarely occurs as long asas long as interproximal tooth contacts are interproximal tooth contacts are properly maintainedproperly maintained..

Several Several authorsauthors have demonstrated have demonstrated that the most effective method of that the most effective method of interproximal plaque control in interproximal plaque control in gingival recession is the use of an gingival recession is the use of an interproximal brushinterproximal brush. When the . When the interproximal brush is used, the interproximal brush is used, the space between two adjacent space between two adjacent proximal surfaces must be proximal surfaces must be wide wide enoughenough to allow it to pass through it to allow it to pass through it with relative ease.with relative ease.

LOCATION OF CONTACT AREASLOCATION OF CONTACT AREASContacts should be highContacts should be high ((directed incisallydirected incisally))

and buccal in relation to the central fossa and buccal in relation to the central fossa ((exceptexcept between maxillary first and second between maxillary first and second molars)molars)

Several Several authors authors have demonstrated have demonstrated that the contact areas on natural that the contact areas on natural teeth occur at the teeth occur at the incisal one thirdincisal one third of the tooth. Many agree that of the tooth. Many agree that natural teeth are natural teeth are straightstraight or or slightly slightly concaveconcave interproximally from the interproximally from the CEJ to the contact area. This tends CEJ to the contact area. This tends to open the embrasure, particularly to open the embrasure, particularly if the contact area is if the contact area is highhigh (in the (in the incisal direction). incisal direction).

Many Many authorsauthors have pointed out have pointed out that the contact area of all teeth, that the contact area of all teeth, except except between the maxillary between the maxillary first and second molars, should first and second molars, should be buccal to the central fossa. be buccal to the central fossa. This creates a This creates a large lingual large lingual embrasure for optimum healthembrasure for optimum health of of the lingual papilla. the lingual papilla.

HazenHazen and and Osborne Osborne have warned of have warned of the consequences of an the consequences of an ““oversizedoversized’’ ’’ colcol resulting from resulting from broad (buccolingual) contacts. The broad (buccolingual) contacts. The colcol is a is a nonkeratinized areanonkeratinized area which which is thought to be more susceptible is thought to be more susceptible to plaque. The broad contact to plaque. The broad contact produces a larger col, thereby produces a larger col, thereby leading to increased chance of leading to increased chance of inflammation. inflammation. Ramjford Ramjford recommends placement of contact recommends placement of contact areas as areas as far occlusallyfar occlusally as possible as possible to facilitate access for to facilitate access for interproximal plaque control.interproximal plaque control.

FURCATIONS INVOLVEMENTFURCATIONS INVOLVEMENT

Furcations that have been exposed Furcations that have been exposed owing to loss of periodontal owing to loss of periodontal attachment should be “attachment should be “flutedfluted” or ” or ““barreled out.barreled out.””

The concept of fluting into molar furcations The concept of fluting into molar furcations is based on the desire to eliminate “is based on the desire to eliminate “plaque plaque trapstraps’’ and facilitate plaque control. ’’ and facilitate plaque control. Yuodelis et.al,Yuodelis et.al, in discussing molar in discussing molar furcations, that the final restoration furcations, that the final restoration should should notnot follow the anatomy of the original follow the anatomy of the original clinical crownclinical crown

but should be an but should be an extension extension of the contours of of the contours of the periodontally exposed roots. When this the periodontally exposed roots. When this approach is properly executed, the approach is properly executed, the triangular regiontriangular region that is created by the roots that is created by the roots and the cervicular bulge is and the cervicular bulge is eliminatedeliminated..

This This triangular regiontriangular region is the most difficult is the most difficult area to maintain in a plaque-free condition area to maintain in a plaque-free condition with conventional brushing techniques. We with conventional brushing techniques. We have found that by have found that by recontouring recontouring the the furcation to furcation to eliminate the triangleeliminate the triangle, plaque , plaque control with normal brushing is greatly control with normal brushing is greatly facilitated. facilitated.

MARGIN PLACEMENTMARGIN PLACEMENT

The concept of subgingival margins The concept of subgingival margins is a natural out growth of is a natural out growth of G.V. G.V. Black’sBlack’s “ “extension for preventionextension for prevention” ” and the “and the “caries-free zonecaries-free zone.’’.’’

Locations for marginal placement for Locations for marginal placement for cast restorations have included: cast restorations have included:

(1)(1)The base of the gingival crevice The base of the gingival crevice

(2) Half the distance between the (2) Half the distance between the base of the gingival crevice and base of the gingival crevice and the gingival margin the gingival margin

(3) slightly below the gingival margin(3) slightly below the gingival margin

(4) The crest of the gingival margin ; (4) The crest of the gingival margin ; andand

(5) (5) SupragingivallySupragingivally. .

With each of these margin locations, With each of these margin locations, the authors have reported clinically the authors have reported clinically healthy periodontal tissues when healthy periodontal tissues when quality restorations were combined quality restorations were combined with effective plaque control.with effective plaque control.

As early as As early as 19411941, , OrbanOrban proposed proposed supragingival margins for improved supragingival margins for improved periodontal healthperiodontal health. . OrbanOrban and and other other researchersresearchers discovered that discovered that the “the “caries freecaries free” or “” or “cleanclean” ” subgingival zone, which had been subgingival zone, which had been observed previously on extracted observed previously on extracted teeth, was nothing more than the teeth, was nothing more than the location of the epithelial location of the epithelial attachmentattachment. .

This epithelial attachment will This epithelial attachment will not not attach to the margin of a attach to the margin of a cast restoration. Thus the cast restoration. Thus the concept of routine subgingival concept of routine subgingival margins was questioned as more margins was questioned as more scientific evidence appeared.scientific evidence appeared.

PlaquePlaque accumulation, accumulation, inflammationinflammation, , and and gingivitisgingivitis are reported to occur are reported to occur more frequently in teeth with more frequently in teeth with subgingivalsubgingival crown margins than in crown margins than in those with supragingival margins.’ those with supragingival margins.’ Oral hygiene instructions do not Oral hygiene instructions do not seem to alter this pattern. seem to alter this pattern.

ChristensenChristensen has demonstrated has demonstrated that the that the visually accessible visually accessible margin (supragingival)margin (supragingival) can be, can be, and is, fitted more accurately and is, fitted more accurately than the than the visually inaccessible visually inaccessible margin (subgingival)margin (subgingival)

Based on these and other Based on these and other findings, subgingival findings, subgingival margins should be margins should be avoided avoided exceptexcept for the following specific for the following specific situations:situations:

(1) Esthetic demands(1) Esthetic demands

(2) Caries removal (2) Caries removal

(3) Subgingival tooth fracture(3) Subgingival tooth fracture

(4) To cover existing subgingival (4) To cover existing subgingival restorationsrestorations

(5) To gain needed crown length, (5) To gain needed crown length, and and

(6) To provide a more favorable (6) To provide a more favorable crown contour (that is, furcation crown contour (that is, furcation involvement)involvement)

PONTIC DESIGNPONTIC DESIGN

The design of pontics for fixed The design of pontics for fixed partial dentures has been partial dentures has been clouded clouded by empirical judgment. by empirical judgment. The so called “The so called “sanitary ponticsanitary pontic” is ” is not new to dentistry. The “not new to dentistry. The “bullet-bullet-shapedshaped’’ pontic has been ’’ pontic has been advocated by some authors as a advocated by some authors as a desirable design to reduce food desirable design to reduce food accumulation. accumulation.

Nearly all authors agree that the Nearly all authors agree that the

“ “ridge-lapridge-lap’’ pontic is ’’ pontic is undesirable undesirable from from the point of view of the point of view of tissue healthtissue health..

Numerous Numerous investigatorsinvestigators have have reported that inflammation of reported that inflammation of the edentulous mucosa adjacent the edentulous mucosa adjacent to pontics is probably a to pontics is probably a responseresponse to plaque to plaque accumulation on the surface of accumulation on the surface of the pontics. Many authors feel the pontics. Many authors feel that that glazed porcelainglazed porcelain is the is the material of choice for contact material of choice for contact against the edentulous ridge. against the edentulous ridge.

Other Other investigators investigators have shown have shown that there is that there is nono clinical or clinical or histologic difference in the histologic difference in the response of the mucosa to response of the mucosa to pontics pontics properly constructedproperly constructed of of cast gold, acrylic resin, or glazed cast gold, acrylic resin, or glazed or unglazed porcelain.or unglazed porcelain.

Stein’sStein’s classic article on classic article on pontic pontic designdesign was largely responsible was largely responsible for a change in philosophy from a for a change in philosophy from a ““sanitarysanitary” or “” or “bullet-shapedbullet-shaped’’ ’’ design to what is now commonly design to what is now commonly called a “called a “modified ridge-lapmodified ridge-lap” ” design. design.

The The modified ridge-lapmodified ridge-lap design in design in the the posterior regionposterior region

and the and the ridge lap facingridge lap facing design in the anterior design in the anterior regionregion

offer offer minimal tissue contactminimal tissue contact, , acceptable cosmetic valueacceptable cosmetic value, , proper cheek supportproper cheek support, and , and accessibility for adequate oral accessibility for adequate oral hygienehygiene. It has now been . It has now been established that the established that the designdesign of of the pontic may be the most the pontic may be the most important factor in preventing important factor in preventing inflammatory reactions, inflammatory reactions, not the not the materialmaterial used in the pontic. used in the pontic.

In addition to In addition to properly designingproperly designing the undersurface of pontics, it is the undersurface of pontics, it is imperative to imperative to open embrasure open embrasure spacesspaces adjacent to abutments to adjacent to abutments to allow roomallow room for interproximal for interproximal tissue and tissue and accessaccess for oral for oral hygiene.hygiene.

The occlusal surface should not be The occlusal surface should not be narrowed arbitrarily since this may narrowed arbitrarily since this may create a food impaction and/or create a food impaction and/or plaque retention situation similar to plaque retention situation similar to that of mal posed teeththat of mal posed teeth

The embrasure space between The embrasure space between two adjacent pontics usually is two adjacent pontics usually is closedclosed to provide to provide added strengthadded strength, , reduce foodreduce food and and plaque retentionplaque retention, , and and facilitate oral hygiene facilitate oral hygiene proceduresprocedures under pontic areas. under pontic areas.

Basic Basic guidelines guidelines for the for the ACCESS FOR ACCESS FOR ORAL HYGIENE THEORYORAL HYGIENE THEORY of of crown crown contour, margin placement, and contour, margin placement, and pontic designpontic design can be applied to can be applied to nearly allnearly all fixed restorative fixed restorative procedures. These guidelines apply procedures. These guidelines apply to full porcelain coverage to full porcelain coverage restorations.restorations.

precisionprecision attachmentsattachments

andand coping reconstructionscoping reconstructions

Occasionally tooth preparations must be Occasionally tooth preparations must be modified to allow for the added bulk needed for modified to allow for the added bulk needed for attachments, occlusal porcelain, and copingsattachments, occlusal porcelain, and copings

IF PROPER IF PROPER TOOTH REDUCTIONTOOTH REDUCTION IS IS ACHIEVED, PHYSIOLOGIC CROWN ACHIEVED, PHYSIOLOGIC CROWN CONTOURS CAN BE DEVELOPED EASILY, CONTOURS CAN BE DEVELOPED EASILY, REGARDLESSREGARDLESS OF THE PROSTHESIS BEING OF THE PROSTHESIS BEING USEDUSED

SUMMARYSUMMARY

Crown contoursCrown contours which promote which promote favorable tissue responsefavorable tissue response follow follow these guidelines :these guidelines :

Buccal and lingual contours are Buccal and lingual contours are flat.flat.

Embrasure spaces should be Embrasure spaces should be open.open.

Contacts should be Contacts should be highhigh ( (incisal one incisal one thirdthird) and ) and buccalbuccal to the central fossa to the central fossa ((exceptexcept between first and second molars) between first and second molars)

Furcations should be “Furcations should be “fflutedluted” or ” or ““barreled outbarreled out””

Margins should be Margins should be supra gingivalsupra gingival where possiblewhere possible

The The pontic designpontic design of of choice is the “ choice is the “ modified modified ridge-lapridge-lap” for posterior ” for posterior spacesspaces

and the “ridge-lap” facing for anterior spaces.

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