Emergence Profile In Natural Tooth Contour 6th4t

Emergence profiles considerations Hurney ;4.w

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Selection of the straight emergence profile in deg 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.)

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art, I of this study confirmed the straight emergence profile as the norm in naturally occurring axiogingival tooth contour.’ Observations ing a straight emergence profile as the normally occurring tooth morphology approximating the gingival sulcus, based on photographic 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 uned 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 restored 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 demonstrated. Restorations designed and placed with straight emergence 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

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

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Fig. 2. A, Sectioned diagnostic cast of mandibular incisors demonstrates convexity on lingual surface of mandibular incisors. Example on left has lingual convexity below gingival tissue. Example on right has convexity above gingival tissue with tooth extruded and gingival recessioncreating niche difficult to keep clean.B, Area on lingual surface of mandibular incisorswith bacterial plaque and calculus accumulation below lingually convex emergenceprofile. Fig. 3. A, Straight emergenceprofile selectedfor lingual surface of mandibular anterior restoration to facilitate oral hygiene. 3, Completed restorations with straight gingival emergenceprofiles lingually and openembrasureform below area to facilitate oral hygiene from lingual surface. of the modified ridgelap pontic, recommendedby Stein,g with optimal of the dental floss,improving oral hygiene. A straight emergenceprofile will enable effective reachingto the depth of the sulcusin close with the surface of the restoration. This is especially desirable on the surface of the tooth beyond the cavosurfacemargin, to facilitate removal of the accumulatedmicrobial plaque. If the emergenceprofile of a restoration is convex in the gingival one third, it is possible,but inconvenient, to remove the bacterial plaque on the tooth surface ing the gingival sulcusbelow the point of tangency. The lingual surfacesof mandibular incisors provide an example where a convex emergenceprofile in the gingival third is cornman.The sectionthri~ughthe central incisor on the left sideof Rg. 2, A illustrates a mandibular incisor with its convexity located subgingivally. The mandibular incisor on the right aideof Fig. 2, A with a lingual convexity located

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above the free gingival margin demonstratesthe niche between the height of contour fingually and the root surface. In Fig. 2, B the calculus and bacterial plaque accumulated on this surface are evident becauseit 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 incisorsmay be restored with a straight erne~e~~ profile. If the dentist choosesto extend the areabetween anterior teeth from the incisal embrasureto the level of the gingival papilla for esthetics,the lingual embrasuremust be wide enoughfor accessto the gingival tiesue under the areafrom the lingual surface(Fig. 3). When viewed from the facial surface, rn~d~b~ ineisomhave straight interproximal emergenceprofiles that begin at the end of a long area and extend to the cementoenamel junction (Fig. 4). If restorations follow this pattern, they

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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 threading 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 interproximal aspect (Fig. 6). Similar to the maxillary canine, the mandibular canine has a concavity below the area of its distal surface (Fig. 7). Tooth preparations must be perceptively designed to accommodate dimensional requirements of restorative materials 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 exposure.

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If adequate space has been created for the restorative materials during tooth preparation, retainers of fixed partial 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 emergence 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, radiographs 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 area to CEJ, anatomic crown facial surface. B, Relationship of natural anterior teeth- areas and gingival tissue. Fig. 6. A, Mandibular anterior teeth with long area and straight emergence profile. B, Mandibular anterior teeth with long 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

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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. 378

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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 deg dental restorations 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 graphic observations.

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profiles in natural tooth contour. J PROSTHET DENT 1989;62:4-10.

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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 artificial 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 PROSTHET DENT 1966;16:251-85. 10. Kuwata M. Color atlas of ceramo-metal technology. St Louis: Ishiyaku EuroAmerica, 1986;235-50.

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