Emergence profiles in natural tooth contour. Part II: Clinical considerations

Hurney &I. Croll, D.D.S.

;4.w l’.)rl , N.\‘.

Selection of the straight emergence profile in designing artificial crowns for teeth has been shown to improve the effectiveness of oral hygiene near the gingival sulcus. The axial profile of teeth can be viewed as a series of straight lines with

curved transitions. Reproduction of these geometric patterns facilitates fabrication of restorations that appear natural. (J PROSTHET DENT 1990;374-9.)

P art, I of this study confirmed the straight emer- gence profile as the norm in naturally occurring axiogingi- val tooth contour.’ Observations supporting a straight emergence profile as the normally occurring tooth mor- phology approximating the gingival sulcus, based on pho- tographic measurements, are a departure from traditional

concepts.’ The existence of a protective convexity in I he gingival one third of a tooth presented by Wheeler3, 4 and others” implied a continuous curved surface in the gingival third. The curved profile concept, although unsupported by photographic evidence, has been classically taught to dental students and laboratory technicians by using line drawings in technical manuals and atlases. The curved transition of axial tooth contour at the height of contour is not always located in the gingival one third.

Presented before the American Academy of Crown and Bridge Prosthodontics, Chicago, Ill.

10/l/10954

Interpreting emergence profiles as geometric shapes can provide guidelines for oral hygiene, restoration design, and tooth preparation. A straight line and a curve meet at only one point, the tangent seen in the left example in Fig. 1, A. Conversely, a straight line and a flat emergence profile can be adapted to one another, demonstrated in the right example in Fig. 1, A. The emergence profile affects the convenience and effectiveness of oral hygiene procedures designed to remove bacterial plaque from natural and re- stored tooth surfaces. Toothbrush bristles and tooth picks used in conjunction with handles such as the Perio-aid (Marquis Dental Mfg. Co., Denver, Colo.) device are straight in profile. In Fig. 1, B, the appropriate relationship

of the oral hygiene device to the emergence profile is dem- onstrated.

Restorations designed and placed with straight emer- gence profiles in the gingival one third provide the patients with a shape that is accessible and facilitates oral hygiene recommended by Eissmann et al.fi and others.‘. s This same rationale is applicable in the convex tissue-facing surface

Fig. 1. A, Straight oral hygiene appliance and straight-curved emergence profile. The curve and straight line meet only at tangent in left illustration. B, Convenient adaptation of oral hygiene appliance and emergence profile of canine. Note relationship of this angle to emergence profile of premolars posterior to canine.

374 APHIL VOLUME63 NUMBER4

EMERGENCE PROFILES IN NATURAL TOOTH CONTOUR: II

Fig. 2. A, Sectioned diagnostic cast of mandibular incisors demonstrates convexity on lingual surface of mandibular incisors. Example on left has lingual convexity below gingi- val tissue. Example on right has convexity above gingival tissue with tooth extruded and gingival recession creating niche difficult to keep clean. B, Area on lingual surface of man- dibular incisors with bacterial plaque and calculus accumulation below lingually convex emergence profile. Fig. 3. A, Straight emergence profile selected for lingual surface of mandibular anterior restoration to facilitate oral hygiene. 3, Completed restorations with straight gingival emergence profiles lingually and open embrasure form below contact area to facilitate oral hygiene from lingual surface.

of the modified ridgelap pontic, recommended by Stein,g with optimal contact of the dental floss, improving oral hy- giene. A straight emergence profile will enable effective reaching to the depth of the sulcus in close contact with the surface of the restoration. This is especially desirable on the surface of the tooth beyond the cavosurface margin, to facilitate removal of the accumulated microbial plaque. If the emergence profile of a restoration is convex in the gin- gival one third, it is possible, but inconvenient, to remove the bacterial plaque on the tooth surface contacting the gingival sulcus below the point of tangency.

The lingual surfaces of mandibular incisors provide an example where a convex emergence profile in the gingival third is cornman. The section thri~ugh the central incisor on the left side of Rg. 2, A illustrates a mandibular incisor with its convexity located subgingivally. The mandibular incisor on the right aide of Fig. 2, A with a lingual convexity located

above the free gingival margin demonstrates the niche be- tween the height of contour fingually and the root surface. In Fig. 2, B the calculus and bacterial plaque accumulated on this surface are evident because it is inconvenient for patients to maintain. A modification of the natural tooth can create a surface that is more easily maintained by the patient. Specifically, the lingual surface of mandibular in- cisors may be restored with a straight erne~e~~ profile.

If the dentist chooses to extend the contact area between anterior teeth from the incisal embrasure to the level of the gingival papilla for esthetics, the lingual embrasure must be wide enough for access to the gingival tiesue under the contact area from the lingual surface (Fig. 3). When viewed from the facial surface, rn~d~b~ ineisom have straight interproximal emergence profiles that begin at the end of a long contact area and extend to the cementoenamel junction (Fig. 4). If restorations follow this pattern, they

THE JOURNAL OF PROSTHETIC DENTISTRY 315

CROLL

3 76 APRIL1990 VOLUME63 NUME

See opposite page for legends.

ma.4

EMERGENCE PROFILES IN NATURAL TOOTH CONTOUR: II

Fig. 7. Mandibular canine, anatomic crown with concavity on distal surface.

Fig. 8. Emergence angle is +15 degrees in relationship to long axis of tooth.

can be esthetic and allow convenient interproximal thread- ing of dental floss (Fig. 5).

Sectioned diagnostic casts reveal a flat facial emergence profile in mandibular anterior teeth extending to a point midway on the facial surface when viewed from the inter- proximal aspect (Fig. 6). Similar to the maxillary canine, the mandibular canine has a concavity below the contact area of its distal surface (Fig. 7).

Tooth preparations must be perceptively designed to accommodate dimensional requirements of restorative ma- terials within the limits of the emergence profile. “Depth cut” controlled shoulder preparations with a hollow-ground bevel are an approach that meets these requirements. The emergence angle (Fig. 8) made by the emergence profileand the long axis of the tooth is +15 degrees. On the basis of mathematical axioms, KuwatarO concluded that if the path of insertion was parallel to the long axis of the tooth, all metal ceramic restorations with cavosurface bevel angles less than 35 degrees with the path of insertion should have metal collars to prevent overcontouring and opaque expo- sure.

LABORATORY APPLICATIONS

If adequate space has been created for the restorative materials during tooth preparation, retainers of fixed par- tial dentures can be made with suitable emergence profiles. Several waxing instruments have a flat surface to create a flat profile in the marginal area of the wax pattern. The convex side of the waxing instruments can develop concave contours in the wax pattern such as the distal surfaces of maxillary canines and mesial surfaces of the premolars (Fig. 9). Mounted grinding wheels and sandpaper disks have flat cutting profiles that can machine straight emer- gence profiles and finish restorations during fabrication.

Clinically, the facial and lingual surfaces of restorations can be easily evaluated for straight emergence profile with a periodontal probe. Fig. 10 demonstrates restorations with suitable facial emergence profiles. Interproximally, radio- graphs provide the best picture to establish that the desired emergence profile and adaptation between the restoration and root have been accomplished (Fig. 11). The overall axial profile of many dental forms are viewed as a series of straight lines with curved transitions. Reproduction of

Fig. 4. A, Interproximal emergence profile of mandibular incisor extending from long contact area to CEJ, anatomic crown facial surface. B, Relationship of natural anterior teeth-contact areas and gingival tissue. Fig. 6. A, Mandibular anterior teeth with long contact area and straight emergence pro- file. B, Mandibular anterior teeth with long contact area and straight emergence profile on pontic of mandibular lateral incisor. Fig. 6. A, Mandibular incisor,sectioned diagnostic cast. B, Mandibular canine, sectioned diagnostic cast. C, Mandibular canine anatomic crown with gingival overlay.

TEE JOURNAL OF PROSTHETIC DENTISTRY 377

378

Fig. 9. A, Flat waxing instrument creates straight emergence profile in wax pattern. B, Convex waxing instrument develops concave shape in wax pattern.

Fig. 10. A, Desired emergence profiles and emergence angles. B, Suitable emergence profiles and emergence angles.

Fig. 11. A, Radiograph of natural interproximal emergence profiles. B, Completed metal ceramic restorations seen radiographically with straight interproximal emergence profiles.

APRIL 1990 VOLUME 63 NUMBER 4

EMERGENCE PROFILES IN NATURAL TOOTH CONTOUR: II

these geometric patterns creates restorations that appear natural.

SUMMARY

Photographic data reveal that most normally occurring emergence profiles are straight. Because one objective of a dental restoration is accurate replacement of missing tooth structure with a reliable anatomic model, reproduction of the appropriate emergence profile is essential. Selection of a straight emergence profile for designing dental restora- tions facilitates the convenience and effectiveness of oral hygiene procedures approximating the gingival sulcus.

I thank Dr. R. Sheldon Stein of Boston, Mass. for suggesting the subject for this research while I was a postdoctoral student in Prosthodontics at Tufts University, School of Dental Medicine from 1970-72.

REFERENCES

1. Croll BM. Emergence profiles in natural tooth contour. Part I. Photo- graphic observations. J PROSTHET DENT 1989;62:4-10.

2. Tjan AHL, Freed H, Miller GD. Current controversies in axial contour design. J PROSTHET DENT 1980;44:536-9.

3. Wheeler RC. Dental anatomy and physiology. 3rd ed. Philadelphia: WB Saunders, 1963;75-84.

4. Wheeler RC. Complete crown form and the periodontium. J PROSTHET

DENT 1961;11:722-34. 5. Amsterdam M, Fox L. Provisional splinting-principles and technics.

Dent Clin North Am 1959;3:73-99. 6. Eissmann HF. Radke RA, Noble WH. Physiologic design criteria for

fixed dental restorations. Dent Clin North Am 1971;15:543-75.

7. Youdelis RA, Weaver JD, Sapkos S. Facial and lingual contours of ar-

tificial complete crown restorations and their effect on the peridontium. J PROSTHET DENT 1973;29:61-73.

8. Burch JG. Developing crown contours in restorations. Dent Clin North

Am 1971;14:611-8. 9. Stein RS. Pontic-residual ridge relationship: a research report. J PROS-

THET DENT 1966;16:251-85. 10. Kuwata M. Color atlas of ceramo-metal technology. St Louis: Ishiyaku

EuroAmerica, 1986;235-50.

Reprint requests to: DR. BURNEY M. CROLL 901 LEXINGTON AVE. NEW YORK, NY 10021

TAR JOURNAL OF PROSTHETIC DENTISTRY 379