How Proper Function Dictates Restorative Success
Repairing functional challenges in an esthetically pleasing smile
Tyler Wynne, DDS | William P.D. Wynne, DDS
In pursuit of satisfying patients’ esthetic demands, harmonious function of the stomatognathic system must not be overlooked. A visually pleasing smile may be temporarily gratifying for a patient; however, if precise restorative parameters are not followed, the equilibrium between hard and soft tissues may be affected, resulting in speech, masticatory, neuromuscular, and deglutition impairment. Stability must be the underlying goal in all decisions regarding tooth placement.1
The patient in this case presented with complaints about his recently placed eight maxillary porcelain restorations—six veneers (teeth Nos. 5, 7, 8, 9, 10, and 12) and two full-coverage crowns (teeth Nos. 6 and 11). His comments focused more on a functional than esthetic concern as he reported having difficulty closing his lips over his new teeth and slight interference with his speech. Figure 1 and Figure 2 show a smile that appeared to be esthetically acceptable with healthy gingival tissues and satisfactory hue, value, and chroma of the restorations. Based solely upon the patient’s photographs, there are no changes the authors would make. Fortunately, this meticulous patient had kept an original pre-treatment model of his teeth prior to preparation for his current restorations.
Diagnosis and Treatment Planning
To evaluate the changes that were made, a model of the patient’s maxillary arch was fabricated to capture the contours of the existing restorations by placing a Sil-Tech® Putty (Ivoclar Vivadent, www.ivoclarvivadent.com) matrix over his new front teeth and original posterior teeth. When the matrix was placed over the model of his original teeth, there was quite a discrepancy (Figure 3). The new restorations were built out facially 3 to 4 mm farther than his original teeth and they were 4 mm longer than his original teeth. It is no wonder he could not close his lips over his new front teeth. The technical term for this problem is violation of lip closure pattern or violation of envelope of function. As teeth erupt, the outward pressure of the tongue and inward pressure of the lips and buccinator-orbicularis oris muscle bands influence their horizontal position and inclination until the opposing forces are equal.2 This concept is referred to as the neutral zone. Therefore, any violation of moving teeth outside of this neutral zone defined by the musculature will result in increased pressure against the muscle upon which the tooth intrudes.2,3
Since neutral zone forces develop through muscular contraction during the various functions of chewing, speaking, and swallowing, they vary in magnitude and direction in different individuals.4 In a normal eruption pattern, the gingival half of the maxillary incisors forms a straight line with the alveolar crest, and as the mouth closes, the incisal half falls behind the vermillion border of the lower lip (Figure 4). This patient’s maxillary incisal edges did not fall behind the lower lip, but rather compressed into the lip (Figure 5). Ideally, the maxillary incisal edge should lightly contact the inner vermillion border when speaking words that begin with the letters “F” and “V”; however, phonetics were impaired due to the excessive vertical length of the restorations that intruded the lower inner vermillion border. A permissive anterior guidance, in which vertical and horizontal overlap are altered so that anterior esthetic change is accomplished within the patient’s envelope of function, is essential for functionally successful restorations.5 An unfavorable anterior guidance with overcontoured maxillary restorations may produce abnormal and potentially pathologic functional movements of the condyles.6,7 According to Dawson, the position of the upper incisal edges is critically important to determine whether an anterior guidance is in harmony with an ideal envelope of function or is interfering with it.2 Determination of precisely correct incisal edges is the second most important decision a dentist must make regarding occlusion, with centric relation being the most important.2 Both dental and gingival esthetics act together to provide a balanced smile; a defect in the surrounding tissues cannot be compensated by the quality of the dental restoration and vice versa.8 Therefore, other issues to address included the need for crown lengthening on teeth Nos. 5 and 12 to achieve a more balanced gingival zenith.