Stereophotogrammetric Evaluation of Tooth-Induced Labial Protrusion Riccardo Rosati, DDS, PhD,1 Marcio De Menezes, DDS, MSc, PhD,1,2 Ana Maria Bettoni Rodrigues da Silva, DDS, MSc, PhD,1,3 Alberto Rossetti, DDS, PhD,1 Giuseppe C. Lanza Attisano, DDS,1 & Chiarella Sforza, MD, PhD1 1
Functional Anatomy Research Center (FARC), Laboratorio di Anatomia Funzionale dell’Apparato Stomatognatico (LAFAS), Dipartimento di Scienze Biomediche per la Salute, Facolta` di Medicina e Chirurgia, Universita` degli Studi di Milano, Milan, Italy 2 Professor of Operative Dentistry, Course of Dentistry, School of Health Science, State University of Amazonas, Brazil 3 ˜ Preto, University of Sao ˜ Paulo, Postdoctoral Program in Restorative Dentistry, Department of Restorative Dentistry, Faculty of Dentistry of Ribeirao Brazil
Keywords 3D; lips; stereophotogrammetry; prosthesis; orthodontics. Correspondence Chiarella Sforza, Dipartimento di Scienze Biomediche per la Salute, Universita` degli Studi di Milano, via Mangiagalli 31, 20133 Milano, Italy. E-mail: [email protected] The authors deny any conflicts of interest. Accepted September 15, 2013 doi: 10.1111/jopr.12135
Abstract Purpose: To better manage dental treatment outcome, a previsualization of desired appearances can be used to understand patients’ wishes. A deeper comprehension of labial modifications related to hard-tissue movements is advantageous. The purpose of the study was to evaluate tooth restoration-induced labial displacements in three dimensions. Materials and Methods: In a group of 20 healthy Caucasian individuals, simulations of vestibular translations of maxillary anterior crowns were obtained by placing an acrylic resin veneer on the labial surfaces of maxillary incisors and canines. Threedimensional stereophotogrammetric acquisitions were made to evaluate soft-tissue changes induced by the simulations. Linear dislocation of selected landmarks and labial surfaces were quantified using dedicated software. Results: All paired and two midline labial landmarks had significant displacements, ranging from 13% (Subnasale landmark) to 103% (left Cheilion landmark) of veneer thickness (2 mm thick). A significant positive correlation was obtained between the lower lip displacement and overjet values. Conclusions: The vestibular shift of maxillary incisors and canines affect both upper and lower vermilion areas, without involving cutaneous perilabial landmarks.
Patient requests for esthetic teeth are increasing.1 Different treatment options have been proposed to change the appearances of anterior teeth. In fact, unesthetic dentitions could be caused by displaced soft and hard tissues, altered dento-enamel structures, or both.2 For many years, the most predictable and durable esthetic improvement of anterior tooth appearance was obtained by fabricating ceramic full crowns. This approach is invasive because it requires the removal of large amounts of healthy tooth structure. In addition, pulpal and periodontal complications secondary to tooth preparation have been reported.3 In some cases, dental esthetic discrepancies could also be treated by orthodontic,4 surgical, and/or adjunctive therapies.5 However, orthodontic or surgical solutions may be rejected by patients, leaving only prosthetic solutions to solve the problem.6 Regardless of the chosen treatment, all procedures should be performed after careful planning, with the most accurate possible predictions of the proposed soft-tissue results.2,3,7,8 Several preoperative clinical procedures exist to visualize, study, and
modify esthetic outcomes, and to share this information with patients. In the case of prosthetic treatments, a previsualization of desired appearances can be used to illustrate the proposed treatment outcomes with the help of composite mock-ups9 or with interim prostheses. These predictions should be documented and measured to provide quantitative records of the proposed treatments. Photographic assessments are currently used, but they cannot completely satisfy the estimation because of their 2-D nature and to some difficulties in quantifying the results.7,10 In orthodontics and maxillofacial surgery, a previsualization of possible treatment outcomes could be difficult because of hard-tissue movements, which affect the resulting profile. The overlying soft-tissue adaptation to the “new” hard-tissue morphology determines facial appearances and profiles.11-13 Several computer programs, such as Quick Ceph, DentoFacial Planner, and Computer-Assisted Simulation System, have been proposed for predicting soft-tissue modifications. The larger
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area of error found in predictions through these software programs was in the lower lip area.14,15 In addition to the radiographic protocols,16 several noninvasive instruments have been used to measure soft-tissue facial morphology. Optical, noncontact instruments (laser scanners, stereophotogrammetric digitizers, three-dimensional [3-D] range cameras), and contact instruments (electromagnetic and electromechanic digitizers) are currently being used in dentistry and in maxillofacial and esthetic surgery.7,10,17-28 To better manage treatment outcome visualization, a better comprehension of labial modifications related to hard-tissue changes is desired. The aim of the current investigation was to evaluate the immediate effect of an induced dental displacement on perioral soft tissues using a 3-D noninvasive instrument. The null hypothesis was that a simulated dental movement did not cause soft-tissue (labial) changes (i.e., labial displacement should be zero). In the alternative hypothesis, labial displacement was significantly different from zero.
Materials and methods Study design
A simulation of labial changes associated with maxillary anterior crown restorations was obtained by placing acrylic resin veneers on the labial surfaces of the maxillary incisors and canines. 3-D stereophotogrammetric acquisitions were made to evaluate soft-tissue modifications induced by the restorations. Linear movement of selected landmarks and labial surfaces were quantified using dedicated software. Participants
A group of 20 healthy Caucasian participants, 11 women and 9 men, age range from 21 to 49 years (mean age 25.78 ± 6.42), was recruited for this study. Inclusion criteria were the following: 1. 2. 3. 4. 5. 6.
No congenital diseases or deformities No history of cosmetic surgery Molar and canine Angle Class I Overjet and overbite ranging from 1 to 5 mm No dental prosthetic rehabilitations No active orthodontic treatment at the time of the study.
All participants were informed about the procedures and gave written consent to the investigation, according to the principles outlined in the Declaration of Helsinki. For each participant, overjet and overbite were measured using periodontal probes. Experimental procedures
Veneers: Alginate impressions (Tropicalgin; Zhermack SpA, Badia Polesine, Italy) were made to produce casts of both dental arches using type 3 dental stone (Elite model; Zhermack SpA; Fig 1A). One- and 2-mm thick individual “one-piece acrylic resin veneers,” which extended from the maxillary left canine to the maxillary right canine, were made for each participant through the following steps: 2
1. Veneers were waxed to the desired thicknesses (Figs 1B and C). 2. Wax pattern impressions were developed using an extrahard silicone (Hard Mask; Techim Group S.r.L., Milan, Italy; Fig 1D); the wax was then removed. R ; Peri3. Dental casts were covered with separator (Unifol dent, Bagno a Ripoli, Italy); autopolymerizing resin (Pattern Resin, GC America, Alsip, IL) was packed using the silicone index. 4. The veneers were separated from the stone casts and measured with a thickness gauge along the vertical axis of each crown. Any excess resin was removed with polishing burs, allowing flattening and smoothening of the surfaces (Fig 1E). All laboratory procedures were accomplished by the same technician to avoid interindividual variability. To evaluate effects of vestibular changes, no tooth preparations were performed; to avoid modifications of the vertical dimension of the teeth, no incisal overlap was added.29 Facial measurements: On the facial surface of all participants, 13 anthropometric landmarks were identified and marked using black eyeliner, as follows:21,27 1. Midline landmarks: N, Nasion; Prn, Pronasale; Sn, Subnasale; Ls, Labiale Superius; Sto, Stomion; Li, Labiale Inferius; Sl, Sublabiale; Pg, Pogonion. 2. Paired landmarks (right and left): Ftr , Ftl , Frontotemporale; Cphr , Cphl , Crista Philtri; Chr , Chl , Cheilion. Reproducibility of landmark positioning has already been tested and found to be satisfactory.21 A 3-D stereophotogrammetry instrument was used (Vectra 3D; Canfield Scientific, Fairfield, NJ) to evaluate facial softtissue morphology. The system recorded a set of four 2-D images of a given participant’s head. The images were processed into one 3-D reconstruction. The acquisition process required less than 1 millisecond, and the 3-D offline elaboration lasted approximately 1 minute; it was noninvasive.20 The accuracy and reproducibility of the system was previously investigated demonstrating that it could assess the coordinates of facial landmarks with satisfactory precision and reproducibility.20 Landmark digitization was performed on the 3-D reconstructions using the marks made on the participants’ skin before each acquisition: indirect digital landmark identification was avoided, as it has been reported to be less precise,19 especially in the perilabial region.28 Two sets of acquisitions were taken for each participant, one in natural condition, defined as “baseline surface” (B), and one wearing the experimental veneers, called “veneer surface” (V). The acquisitions were taken in centric occlusion; the participants were invited to look straight into a mirror mounted at eye level at a 150 cm distance to facilitate their natural head position. The “V surface” was obtained immediately after wearing the experimental veneers, and no modifications of the cutaneous marks were made. To avoid position-related artifacts, both surface acquisitions of each participant were fused to compare them: preliminary alignment was performed overlapping four facial landmarks (Tr, N, Ftr , and Ftl ). Subsequently, corresponding surfaces were
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Figure 1 Labial-displacing veneer fabrication procedure: (A) cast of dental arch using a type 3 dental stone, (B) and (C) the veneers were molded using laboratory wax, (D) an impression of the planned veneers was developed using an extra-hard silicone, (E) autopolymerizing resin was packed using the silicone mask, then any resin excess was removed with polishing burs.
Figure 2 Overlap of baseline and veneer-modified stereophotogrammetric facial reconstruction; lateral perspective showing labial and perilabial midline landmarks: Sn, Subnasale; Ls, Labiale Superius; Li, Labiale Inferius; Sl, Sublabiale; Pg, Pogonion.
overlapped using a selected area identified on the forehead and nose. This area was the most stable and reliable in aligning different 3-D photographs.25,26 Dedicated software (VAM, version 2.8.3; Canfield Scientific) was used to evaluate modifications on the labial and perilabial regions of the two 3-D reconstructions. Nine linear measurements were performed to assess the movement of labial and perilabial landmarks after positioning of the veneers; linear distances between homologous landmarks were used to measure the single point displacements. Chosen landmarks were Subnasale, Labiale superius, Labiale inferius, Sublabiale, Pogonion, right and left Cheilion, right and left Crista Philtri (Figs 2 and 3). A surface-distance tool was used to evaluate average distances between matched B and V surfaces: in the superior lip, the area among Subnasale, right and left Cheilion was selected; in the inferior lip, the area among Pogonion, right and left Cheilion was chosen (Fig 4).
Figure 3 Overlap of baseline and veneer-modified stereophotogrammetric facial reconstruction; horizontal perspective showing labial and perilabial paired landmarks: Cph, Crista Philtri; Ch, Cheilion (l-left, r-right).
Figure 4 Overlap of baseline and veneer-modified stereophotogrammetric facial reconstruction; a surface-distance tool was used to evaluate average distances in the labial and perilabial areas.
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Table 1 Method error between repeated measurements with the same veneer (acquisition error) and with two veneers (manufacturing error)
1 mm thick veneers Student’s t-test MAD (mm) TEM (mm) REM (%) 2 mm thick veneers Student’s t-test MAD (mm) TEM (mm) REM (%)
Acquisition error
Manufacturing error
< 0.001 0.4 0.4 34
< 0.05 0.5 0.5 46
N.S. 0.3 0.3 21
N.S. 0.4 0.3 23
MAD: mean absolute difference; TEM: technical error of measurement; REM: relative error of measurement; N.S.: not significant (p > 0.05).
Data were analyzed using paired Student’s t-tests. Pearson correlations were separately computed between each facial landmark displacement and overjet and overbite values; the significance was set at 5% for all analyses. Procedure repeatability: All procedures were performed with two veneers (1- and 2-mm thick). Protocol repeatability was tested on five participants comparing linear distances obtained from two acquisitions. To estimate the error caused by the veneer production procedures (manufacturing-related error), the same participants were evaluated twice while wearing two veneers of the same thickness. Acquisition-related error was also checked by acquiring five participants twice while wearing the same veneer in two different times. Manufacturing- and acquisition-related errors were separately measured for 1- and 2-mm thick veneers. A descriptive statistical analysis (mean and standard deviation) was computed for all linear distances. Mean absolute difference (MAD, mean of the absolute differences between the values of two sets of measurements), technical error of measurement (TEM), and relative error of measurement (REM) were calculated for all distances to estimate the method error.26,30 Paired Student’s t-tests were performed to identify systematic errors (p < 0.05).
Results Method error results are reported in Table 1. Acquisitionand manufacturing-related errors gave significant differences in repeated acquisitions with 1-mm thick veneers. REM index showed a measurement error ranging from 34% to 46% of the measured value. Repeated acquisitions of facial morphology with 2-mm thick veneers showed no significant differences, with a measurement error between 21% and 23% of the measured value. Soft-tissue facial modifications with 1-mm thick veneers were not reproducible; therefore, in Table 2, only the data obtained with the 2-mm thick veneers are reported. When the participants wore the 2-mm thick veneers, all paired and two midline labial landmarks had significant displacements (Table 2), ranging from 13% (Sn landmark) to 103% (left Cheilion landmark) of veneer thickness. Significant movements were also found for both lip areas. A large interindividual 4
Table 2 Landmark movements wearing a 2-mm thick veneer (% of veneers thickness) in 20 healthy young adults
Linear distances Sn Ls Li Sl Pg Chr Chl Cphr Cphl Average surface distances Superior lip Inferior lip
Mean
SD
Student’s t
13 38 63 18 25 100 103 39 39
37 71 64 65 72 89 111 70 71
N.S. < 0.05 < 0.001 N.S. N.S. < 0.001 < 0.001 < 0.05 < 0.05
19 34
20 37
< 0.001 < 0.001
Paired Student’s t-test; N.S.: not significant (p > 0.05).
variability was observed in all analyses, with standard deviation values similar to or even greater than the relevant mean. In the 20 analyzed participants, the mean overjet was 3 mm (SD, 1 mm), and the mean overbite was 3.2 mm (SD, 1.3 mm). A significant positive correlation (y = 0.621x − 0.714; R2 = 0.25) was obtained between Labiale Inferius displacement and overjet values.
Discussion In total prosthetic reconstructions, the starting point for tooth positioning is usually the incisal edge of maxillary central incisors. This step is decisive not only for the esthetic point of view, but also in developing the posterior functional areas. In fact, an inaccurate positioning of anterior teeth could determine an imprecise location of maxillary premolars and molars, and, subsequently, the relation to the mandibular dental arch could be erroneous.31 Moreover, in edentulous patients, the determination of maxillary incisor position is a critical step that should be performed considering all possible factors, including the soft-tissue responses. In this study, we tested veneers of two different thicknesses, but the 1-mm thick veneers gave irreproducible soft-tissue movements. The error was large both with different veneers of the same thickness (manufacturing-related error), and with the same veneer at different times (acquisition-related error). For the 2-mm thick veneers, the average method error was 22% of measured value, corresponding to an average TEM of 0.3 mm. All further tests were therefore performed only with 2-mm thick veneers. Overall, the biological response to dental movement was very variable, and interindividual variability in lip movements, because of the artificial dental modifications, was great; the standard deviations of the labial displacement was between 20% and 111% of the veneer thickness. The 22% mean REM was obtained without changing landmark position on the skin.10,20 In repeated stereophotogrammetric acquisitions, Aldridge et al18 reported that 11 linear measurements out of 190 had an error because of landmark identification and imaging greater
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than 5% of the total observed variance. Six of these 11 distances involved perilabial landmarks. Facial mimicry could change lip position, potentially altering the relative locations of landmarks placed on these structures more than those of landmarks in other facial areas.23-25 In this study, the landmark digitization error was greatly reduced using the same skin-signed landmarks. Aldridge et al18 measured distances between landmarks identified in different times; in the present investigation the displacement of the same skin-signed landmark was evaluated, providing small distances, more susceptible to acquisition errors.21 On average, the ratio of soft- to hard-tissue movement was between 38% and 103%. These values are in accordance with literature results, even if no direct comparisons can be made. Indeed, all previous investigations assessed 2-D movements measured on lateral cephalograms, they considered different landmarks, and had patients who received actual treatments and not simulations. In particular, surgical patients submitted to maxillary advancement with a Le Fort I osteotomy were analyzed by Chew et al,12 Ewing and Ross,16 and Louis et al,8 while orthodontic patients were measured by Yogosawa.32 Chew et al12 reported a soft-tissue movement between 66% and 106% of hard-tissue advancement. Ewing and Ross16 described soft-tissue movements ranging from 40% to 90% of maxillary advancement. Louis et al8 found a soft-tohard shifting ratio between 16% and 80%. Yogosawa32 described a 40% ratio for the upper lip and a 70% ratio for the lower lip. In all these studies, the supporting hard-tissue movements were greater than the 2-mm dental advancement of the current investigation, with surgical modifications between 3.5 and 11.5 mm. Indeed, according to Ewing and Ross,16 ratios should not be calculated for surgical movements smaller than 4 mm, and soft-tissue movements may be not linear.12 When wearing a 2-mm thick veneer, all landmarks placed on lip vermilion surfaces were moved significantly by the artificial dental changes. The movements in the paired landmarks were symmetrical. Only three cutaneous landmarks, the farthest from the vermilion area (Sn, Sl, and Pg), did not change their positions significantly. When analyzing individual landmark movements, right and left Cheilion were the most displaced (average movement: 102%). Cheilion is located in a critical area, at the border between skin and mucosa, at the conjunction of two different structures: lower and upper lip. Technical reproduction complexity and facial expression bias could modify measurements in these landmarks. The significant movements observed in the inferior lip depended on the relative positions between teeth and labial soft tissues. In healthy young adults, from 14% to 50% of the maxillary incisor and canine clinical crowns have been found to be below the labial commissure.33 The lower lip landmark Labiale inferius moved approximately twice more than the corresponding landmark in the upper lip (Ls), showing the strong influence of maxillary incisor and canine movements on the lower lip.10,32 Moseling and Woods13 obtained similar results when analyzing orthodontic patients: the lower part of the face was more affected by dental and skeletal variations than its middle part. They found that incisor position and angulation had a larger role on the lower lip position than on the upper lip position. Indeed, a positive linear correlation between overjet and Labiale
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inferius displacement was found: a larger overjet corresponded to a larger influence of maxillary teeth on the inferior lip. Patients with a small overjet may have a smaller Labiale inferius displacement because of the maxillary incisor advancing. Among the limitations of the current investigation, a lack of labial thickness evaluation occurred. In fact, before altering the facial-lingual position of the tooth, the clinician should classify the lips as full, medium, or thin, because thick lips seem to be less affected by restoration thickness or by orthodontic movements.6,11 Also, the current data were obtained only in healthy young adults of Caucasian origin. Labial response may be different in patients with previous labial surgery,16 of different age,22,34,35 or of another ethnic group.11 Furthermore, we assessed only the immediate effect of the veneer, and we cannot predict labial movements during an adaptation period: this process may be also age-related.36,37 Future investigations should analyze the time course of soft-tissue displacements. Even if several significant soft-tissue modifications were found, interindividual variability in landmark movements was large, as already reported in the literature,13,16 preventing suggestion of a uniform set of peri-labial changes. Considering its lack of invasiveness and the rapidity of execution, the method could be used to assess patients before prosthetic or orthodontic treatments, thus recording and quantifying the effect of interim prostheses or simulations of dental movements in three dimensions.10
Conclusion The stereophotogrammetric protocol was suitable for defining the soft-tissue changes with hard-tissue movements of at least 2 mm. Previous studies that reported smaller soft-tissue displacements than hard-tissue movements were confirmed, highlighting the importance of the soft-tissue compensation after changes of the supporting structures. Maxillary incisors’ and canines’ vestibular shift affected both upper and lower vermilion areas, without involving cutaneous perilabial landmarks.
References 1. Bloom DR, Padayachy JN: Aesthetic changes with four anterior units. Br Dent J 2006;200:135-138 2. Bidra AS: Three-dimensional esthetic analysis in treatment planning for implant-supported fixed prosthesis in the edentulous maxilla: review of the esthetics literature. J Esthet Restor Dent 2011;23:219-236 3. Peumans M, Van Meerbeek B, Lambrechts P, et al: Porcelain veneers: a review of the literature. J Dent 2000;28:163-177 4. Curry FT: Porcelain veneers: adjunct or alternative to orthodontic therapy. J Esthet Dent 1998;10:67-64 5. T¨urkaslan S, Ulusoy KU: Esthetic rehabilitation of crowded maxillary anterior teeth utilizing ceramic veneers: a case report. Cases J 2009;29:8329 6. Javaheri D: Considerations for planning esthetic treatment with veneers involving no or minimal preparation. J Am Dent Assoc 2007;138:331-337 7. Holberg C, Heine AK, Geis P, et al: Three-dimensional soft tissue prediction using finite elements. Part II: clinical application. J Orofac Orthop 2005;66:122-134
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8. Louis P, Austin RB, Waite PD, et al: Soft tissue changes of the upper lip associated with maxillary advancement in obstructive sleep apnea patients. J Oral Maxillofac Surg 2001;59:151156 9. G¨urel G: Porcelain laminate veneers: minimal tooth preparation by design. Dent Clin North Am 2007;51:419-431 10. Tartaglia GM, Dolci C, Sidequersky FV, et al: Soft tissue facial morphometry before and after total oral rehabilitation with implant-supported prostheses. J Craniofac Surg 2012;23:16101614 11. Brock RA 2nd, Taylor RW, Buschang PH, et al: Ethnic differences in upper lip response to incisor retraction. Am J Orthod Dentofacial Orthop 2005;127:683-691 12. Chew MT, Sandham A, Wong HB: Evaluation of the linearity of soft- to hard-tissue movement after orthognathic surgery. Am J Orthod Dentofacial Orthop 2008;134:665-670 13. Moseling KP, Woods MG: Lip curve changes in females with premolar extraction or nonextraction treatment. Angle Orthod 2004;74:51-62 14. Kaipatur NR, Flores-Mir C: Accuracy of computer programs in predicting orthognathic surgery soft tissue response. J Oral Maxillofac Surg 2009;67:751-759 15. Jayaratne YS, Zwahlen RA, Lo J, et al: Facial soft tissue response to anterior segmental osteotomies: a systematic review. Int J Oral Maxillofac Surg 2010;39:1050-1058 16. Ewing M, Ross RB: Soft tissue response to orthognathic surgery in persons with unilateral cleft lip and palate. Cleft Palate Craniofac J 1993;30:320-327 17. Kamashita Y, Kamada Y, Kawahata N, et al: Influence of lip support on the soft-tissue profile of complete denture wearers. J Oral Rehabil 2006;33:102-109 18. Aldridge K, Boyadjiev SA, Capone GT, et al: Precision and error of three-dimensional phenotypic measures acquired from 3dMD photogrammetric images. Am J Med Genet A 2005;138:247253 19. Aynechi N, Larson BE, Leon-Salazar V, et al: Accuracy and precision of a 3D anthropometric facial analysis with and without landmark labeling before image acquisition. Angle Orthod 2011;81:245-252 20. De Menezes M, Rosati R, Ferrario VF, et al: Accuracy and reproducibility of a 3-dimensional stereophotogrammetric imaging system. J Oral Maxillofac Surg 2010;68:2129-2135 21. Ferrario VF, Sforza C, Poggio CE, et al: Preliminary evaluation of an electromagnetic three-dimensional digitizer in facial anthropometry. Cleft Palate Craniofac J 1998;35: 9-15 22. Holberg C, Schwenzer K, Rudzki-Janson I: Three-dimensional soft tissue prediction using finite elements. Part I: implementation of a new procedure. J Orofac Orthop 2005;66:110-121
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23. L¨ubbers H-T, Medinger L, Kruse AL, et al: The influence of involuntary facial movements on craniofacial anthropometry: a survey using a three-dimensional photographic system. Br J Oral Maxillofac Surg 2012;50:171-175 24. Maal TJ, van Loon B, Plooij JM, et al: Registration of 3-dimensional facial photographs for clinical use. J Oral Maxillofac Surg 2010;68:2391-2401 25. Maal TJ, Verhamme LM, van Loon B, et al: Variation of the face in rest using 3D stereophotogrammetry. Int J Oral Maxillofac Surg 2011;40:1252-1257 26. Rosati R, De Menezes M, Rossetti A, et al: Digital dental cast placement in 3-dimensional, full-face reconstruction: a technical evaluation. Am J Orthod Dentofacial Orthop 2010;138:84-88 27. Sforza C, Ferrario VF: Soft-tissue facial anthropometry in three dimensions: from anatomical landmarks to digital morphology in research, clinics and forensic anthropololgy. J Anthropol Sci 2006;84:97-124 28. Wong JY, Oh AK, Ohta E, et al: Validity and reliability of craniofacial anthropometric measurement of 3D digital photogrammetric images. Cleft Palate Craniofac J 2008;45:232-239 29. Stappert CFJ, Ozden U, Gerds T: Longevity and failure load of ceramic veneers with different preparation designs after exposure to masticatory simulation. J Prosthet Dent 2005;94:132-139 30. Weinberg SM, Scott NM, Neiswanger K, et al: Digital threedimensional photogrammetry: Evaluation of anthropometric precision and accuracy using a Genex 3D camera system. Cleft Palate Craniofac J 2004;41:507-518 31. Spear F: Too much tooth, not enough tooth: making decisions about anterior tooth position. J Am Dent Assoc 2010;141:93-96 32. Yogosawa F: Predicting soft tissue profile changes concurrent with orthodontic treatment. Angle Orthod 1990;60:199-206 33. Rosati R, De Menezes M, Rossetti A, et al: Three-dimensional analysis of dentolabial relationships: effect of age and sex in healthy dentitions. Int J Oral Maxillofac Surg 2012;41:1344-1349 34. De Menezes M, Rosati R, Baga I, et al: Three-dimensional analysis of labial morphology: effect of sex and age. Int J Oral Maxillofac Surg 2011;40:856-861 35. Iblher N, Kloepper J, Penna V, et al: Changes in the aging upper lip-a photomorphometric and MRI-based study (on a quest to find the right rejuvenation approach). J Plast Reconstr Aesthet Surg 2008;61:1170-1176 36. Desai S, Upadhyay M, Nanda R: Dynamic smile analysis: changes with age. Am J Orthod Dentofacial Orthop 2009;136:310-e1-310.e10. 37. Van der Geld P, Oosterveld P, Kuijpers-Jagtman AM: Age-related changes of the dental aesthetic zone at rest and during spontaneous smiling and speech. Eur J Orthod 2008;30:366-373
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Functional Anatomy Research Center (FARC), Laboratorio di Anatomia Funzionale dell’Apparato Stomatognatico (LAFAS), Dipartimento di Scienze Biomediche per la Salute, Facolta` di Medicina e Chirurgia, Universita` degli Studi di Milano, Milan, Italy 2 Professor of Operative Dentistry, Course of Dentistry, School of Health Science, State University of Amazonas, Brazil 3 ˜ Preto, University of Sao ˜ Paulo, Postdoctoral Program in Restorative Dentistry, Department of Restorative Dentistry, Faculty of Dentistry of Ribeirao Brazil
Keywords 3D; lips; stereophotogrammetry; prosthesis; orthodontics. Correspondence Chiarella Sforza, Dipartimento di Scienze Biomediche per la Salute, Universita` degli Studi di Milano, via Mangiagalli 31, 20133 Milano, Italy. E-mail: [email protected] The authors deny any conflicts of interest. Accepted September 15, 2013 doi: 10.1111/jopr.12135
Abstract Purpose: To better manage dental treatment outcome, a previsualization of desired appearances can be used to understand patients’ wishes. A deeper comprehension of labial modifications related to hard-tissue movements is advantageous. The purpose of the study was to evaluate tooth restoration-induced labial displacements in three dimensions. Materials and Methods: In a group of 20 healthy Caucasian individuals, simulations of vestibular translations of maxillary anterior crowns were obtained by placing an acrylic resin veneer on the labial surfaces of maxillary incisors and canines. Threedimensional stereophotogrammetric acquisitions were made to evaluate soft-tissue changes induced by the simulations. Linear dislocation of selected landmarks and labial surfaces were quantified using dedicated software. Results: All paired and two midline labial landmarks had significant displacements, ranging from 13% (Subnasale landmark) to 103% (left Cheilion landmark) of veneer thickness (2 mm thick). A significant positive correlation was obtained between the lower lip displacement and overjet values. Conclusions: The vestibular shift of maxillary incisors and canines affect both upper and lower vermilion areas, without involving cutaneous perilabial landmarks.
Patient requests for esthetic teeth are increasing.1 Different treatment options have been proposed to change the appearances of anterior teeth. In fact, unesthetic dentitions could be caused by displaced soft and hard tissues, altered dento-enamel structures, or both.2 For many years, the most predictable and durable esthetic improvement of anterior tooth appearance was obtained by fabricating ceramic full crowns. This approach is invasive because it requires the removal of large amounts of healthy tooth structure. In addition, pulpal and periodontal complications secondary to tooth preparation have been reported.3 In some cases, dental esthetic discrepancies could also be treated by orthodontic,4 surgical, and/or adjunctive therapies.5 However, orthodontic or surgical solutions may be rejected by patients, leaving only prosthetic solutions to solve the problem.6 Regardless of the chosen treatment, all procedures should be performed after careful planning, with the most accurate possible predictions of the proposed soft-tissue results.2,3,7,8 Several preoperative clinical procedures exist to visualize, study, and
modify esthetic outcomes, and to share this information with patients. In the case of prosthetic treatments, a previsualization of desired appearances can be used to illustrate the proposed treatment outcomes with the help of composite mock-ups9 or with interim prostheses. These predictions should be documented and measured to provide quantitative records of the proposed treatments. Photographic assessments are currently used, but they cannot completely satisfy the estimation because of their 2-D nature and to some difficulties in quantifying the results.7,10 In orthodontics and maxillofacial surgery, a previsualization of possible treatment outcomes could be difficult because of hard-tissue movements, which affect the resulting profile. The overlying soft-tissue adaptation to the “new” hard-tissue morphology determines facial appearances and profiles.11-13 Several computer programs, such as Quick Ceph, DentoFacial Planner, and Computer-Assisted Simulation System, have been proposed for predicting soft-tissue modifications. The larger
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area of error found in predictions through these software programs was in the lower lip area.14,15 In addition to the radiographic protocols,16 several noninvasive instruments have been used to measure soft-tissue facial morphology. Optical, noncontact instruments (laser scanners, stereophotogrammetric digitizers, three-dimensional [3-D] range cameras), and contact instruments (electromagnetic and electromechanic digitizers) are currently being used in dentistry and in maxillofacial and esthetic surgery.7,10,17-28 To better manage treatment outcome visualization, a better comprehension of labial modifications related to hard-tissue changes is desired. The aim of the current investigation was to evaluate the immediate effect of an induced dental displacement on perioral soft tissues using a 3-D noninvasive instrument. The null hypothesis was that a simulated dental movement did not cause soft-tissue (labial) changes (i.e., labial displacement should be zero). In the alternative hypothesis, labial displacement was significantly different from zero.
Materials and methods Study design
A simulation of labial changes associated with maxillary anterior crown restorations was obtained by placing acrylic resin veneers on the labial surfaces of the maxillary incisors and canines. 3-D stereophotogrammetric acquisitions were made to evaluate soft-tissue modifications induced by the restorations. Linear movement of selected landmarks and labial surfaces were quantified using dedicated software. Participants
A group of 20 healthy Caucasian participants, 11 women and 9 men, age range from 21 to 49 years (mean age 25.78 ± 6.42), was recruited for this study. Inclusion criteria were the following: 1. 2. 3. 4. 5. 6.
No congenital diseases or deformities No history of cosmetic surgery Molar and canine Angle Class I Overjet and overbite ranging from 1 to 5 mm No dental prosthetic rehabilitations No active orthodontic treatment at the time of the study.
All participants were informed about the procedures and gave written consent to the investigation, according to the principles outlined in the Declaration of Helsinki. For each participant, overjet and overbite were measured using periodontal probes. Experimental procedures
Veneers: Alginate impressions (Tropicalgin; Zhermack SpA, Badia Polesine, Italy) were made to produce casts of both dental arches using type 3 dental stone (Elite model; Zhermack SpA; Fig 1A). One- and 2-mm thick individual “one-piece acrylic resin veneers,” which extended from the maxillary left canine to the maxillary right canine, were made for each participant through the following steps: 2
1. Veneers were waxed to the desired thicknesses (Figs 1B and C). 2. Wax pattern impressions were developed using an extrahard silicone (Hard Mask; Techim Group S.r.L., Milan, Italy; Fig 1D); the wax was then removed. R ; Peri3. Dental casts were covered with separator (Unifol dent, Bagno a Ripoli, Italy); autopolymerizing resin (Pattern Resin, GC America, Alsip, IL) was packed using the silicone index. 4. The veneers were separated from the stone casts and measured with a thickness gauge along the vertical axis of each crown. Any excess resin was removed with polishing burs, allowing flattening and smoothening of the surfaces (Fig 1E). All laboratory procedures were accomplished by the same technician to avoid interindividual variability. To evaluate effects of vestibular changes, no tooth preparations were performed; to avoid modifications of the vertical dimension of the teeth, no incisal overlap was added.29 Facial measurements: On the facial surface of all participants, 13 anthropometric landmarks were identified and marked using black eyeliner, as follows:21,27 1. Midline landmarks: N, Nasion; Prn, Pronasale; Sn, Subnasale; Ls, Labiale Superius; Sto, Stomion; Li, Labiale Inferius; Sl, Sublabiale; Pg, Pogonion. 2. Paired landmarks (right and left): Ftr , Ftl , Frontotemporale; Cphr , Cphl , Crista Philtri; Chr , Chl , Cheilion. Reproducibility of landmark positioning has already been tested and found to be satisfactory.21 A 3-D stereophotogrammetry instrument was used (Vectra 3D; Canfield Scientific, Fairfield, NJ) to evaluate facial softtissue morphology. The system recorded a set of four 2-D images of a given participant’s head. The images were processed into one 3-D reconstruction. The acquisition process required less than 1 millisecond, and the 3-D offline elaboration lasted approximately 1 minute; it was noninvasive.20 The accuracy and reproducibility of the system was previously investigated demonstrating that it could assess the coordinates of facial landmarks with satisfactory precision and reproducibility.20 Landmark digitization was performed on the 3-D reconstructions using the marks made on the participants’ skin before each acquisition: indirect digital landmark identification was avoided, as it has been reported to be less precise,19 especially in the perilabial region.28 Two sets of acquisitions were taken for each participant, one in natural condition, defined as “baseline surface” (B), and one wearing the experimental veneers, called “veneer surface” (V). The acquisitions were taken in centric occlusion; the participants were invited to look straight into a mirror mounted at eye level at a 150 cm distance to facilitate their natural head position. The “V surface” was obtained immediately after wearing the experimental veneers, and no modifications of the cutaneous marks were made. To avoid position-related artifacts, both surface acquisitions of each participant were fused to compare them: preliminary alignment was performed overlapping four facial landmarks (Tr, N, Ftr , and Ftl ). Subsequently, corresponding surfaces were
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Morphological Evaluation of Soft Tissue Modification
Figure 1 Labial-displacing veneer fabrication procedure: (A) cast of dental arch using a type 3 dental stone, (B) and (C) the veneers were molded using laboratory wax, (D) an impression of the planned veneers was developed using an extra-hard silicone, (E) autopolymerizing resin was packed using the silicone mask, then any resin excess was removed with polishing burs.
Figure 2 Overlap of baseline and veneer-modified stereophotogrammetric facial reconstruction; lateral perspective showing labial and perilabial midline landmarks: Sn, Subnasale; Ls, Labiale Superius; Li, Labiale Inferius; Sl, Sublabiale; Pg, Pogonion.
overlapped using a selected area identified on the forehead and nose. This area was the most stable and reliable in aligning different 3-D photographs.25,26 Dedicated software (VAM, version 2.8.3; Canfield Scientific) was used to evaluate modifications on the labial and perilabial regions of the two 3-D reconstructions. Nine linear measurements were performed to assess the movement of labial and perilabial landmarks after positioning of the veneers; linear distances between homologous landmarks were used to measure the single point displacements. Chosen landmarks were Subnasale, Labiale superius, Labiale inferius, Sublabiale, Pogonion, right and left Cheilion, right and left Crista Philtri (Figs 2 and 3). A surface-distance tool was used to evaluate average distances between matched B and V surfaces: in the superior lip, the area among Subnasale, right and left Cheilion was selected; in the inferior lip, the area among Pogonion, right and left Cheilion was chosen (Fig 4).
Figure 3 Overlap of baseline and veneer-modified stereophotogrammetric facial reconstruction; horizontal perspective showing labial and perilabial paired landmarks: Cph, Crista Philtri; Ch, Cheilion (l-left, r-right).
Figure 4 Overlap of baseline and veneer-modified stereophotogrammetric facial reconstruction; a surface-distance tool was used to evaluate average distances in the labial and perilabial areas.
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Table 1 Method error between repeated measurements with the same veneer (acquisition error) and with two veneers (manufacturing error)
1 mm thick veneers Student’s t-test MAD (mm) TEM (mm) REM (%) 2 mm thick veneers Student’s t-test MAD (mm) TEM (mm) REM (%)
Acquisition error
Manufacturing error
< 0.001 0.4 0.4 34
< 0.05 0.5 0.5 46
N.S. 0.3 0.3 21
N.S. 0.4 0.3 23
MAD: mean absolute difference; TEM: technical error of measurement; REM: relative error of measurement; N.S.: not significant (p > 0.05).
Data were analyzed using paired Student’s t-tests. Pearson correlations were separately computed between each facial landmark displacement and overjet and overbite values; the significance was set at 5% for all analyses. Procedure repeatability: All procedures were performed with two veneers (1- and 2-mm thick). Protocol repeatability was tested on five participants comparing linear distances obtained from two acquisitions. To estimate the error caused by the veneer production procedures (manufacturing-related error), the same participants were evaluated twice while wearing two veneers of the same thickness. Acquisition-related error was also checked by acquiring five participants twice while wearing the same veneer in two different times. Manufacturing- and acquisition-related errors were separately measured for 1- and 2-mm thick veneers. A descriptive statistical analysis (mean and standard deviation) was computed for all linear distances. Mean absolute difference (MAD, mean of the absolute differences between the values of two sets of measurements), technical error of measurement (TEM), and relative error of measurement (REM) were calculated for all distances to estimate the method error.26,30 Paired Student’s t-tests were performed to identify systematic errors (p < 0.05).
Results Method error results are reported in Table 1. Acquisitionand manufacturing-related errors gave significant differences in repeated acquisitions with 1-mm thick veneers. REM index showed a measurement error ranging from 34% to 46% of the measured value. Repeated acquisitions of facial morphology with 2-mm thick veneers showed no significant differences, with a measurement error between 21% and 23% of the measured value. Soft-tissue facial modifications with 1-mm thick veneers were not reproducible; therefore, in Table 2, only the data obtained with the 2-mm thick veneers are reported. When the participants wore the 2-mm thick veneers, all paired and two midline labial landmarks had significant displacements (Table 2), ranging from 13% (Sn landmark) to 103% (left Cheilion landmark) of veneer thickness. Significant movements were also found for both lip areas. A large interindividual 4
Table 2 Landmark movements wearing a 2-mm thick veneer (% of veneers thickness) in 20 healthy young adults
Linear distances Sn Ls Li Sl Pg Chr Chl Cphr Cphl Average surface distances Superior lip Inferior lip
Mean
SD
Student’s t
13 38 63 18 25 100 103 39 39
37 71 64 65 72 89 111 70 71
N.S. < 0.05 < 0.001 N.S. N.S. < 0.001 < 0.001 < 0.05 < 0.05
19 34
20 37
< 0.001 < 0.001
Paired Student’s t-test; N.S.: not significant (p > 0.05).
variability was observed in all analyses, with standard deviation values similar to or even greater than the relevant mean. In the 20 analyzed participants, the mean overjet was 3 mm (SD, 1 mm), and the mean overbite was 3.2 mm (SD, 1.3 mm). A significant positive correlation (y = 0.621x − 0.714; R2 = 0.25) was obtained between Labiale Inferius displacement and overjet values.
Discussion In total prosthetic reconstructions, the starting point for tooth positioning is usually the incisal edge of maxillary central incisors. This step is decisive not only for the esthetic point of view, but also in developing the posterior functional areas. In fact, an inaccurate positioning of anterior teeth could determine an imprecise location of maxillary premolars and molars, and, subsequently, the relation to the mandibular dental arch could be erroneous.31 Moreover, in edentulous patients, the determination of maxillary incisor position is a critical step that should be performed considering all possible factors, including the soft-tissue responses. In this study, we tested veneers of two different thicknesses, but the 1-mm thick veneers gave irreproducible soft-tissue movements. The error was large both with different veneers of the same thickness (manufacturing-related error), and with the same veneer at different times (acquisition-related error). For the 2-mm thick veneers, the average method error was 22% of measured value, corresponding to an average TEM of 0.3 mm. All further tests were therefore performed only with 2-mm thick veneers. Overall, the biological response to dental movement was very variable, and interindividual variability in lip movements, because of the artificial dental modifications, was great; the standard deviations of the labial displacement was between 20% and 111% of the veneer thickness. The 22% mean REM was obtained without changing landmark position on the skin.10,20 In repeated stereophotogrammetric acquisitions, Aldridge et al18 reported that 11 linear measurements out of 190 had an error because of landmark identification and imaging greater
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than 5% of the total observed variance. Six of these 11 distances involved perilabial landmarks. Facial mimicry could change lip position, potentially altering the relative locations of landmarks placed on these structures more than those of landmarks in other facial areas.23-25 In this study, the landmark digitization error was greatly reduced using the same skin-signed landmarks. Aldridge et al18 measured distances between landmarks identified in different times; in the present investigation the displacement of the same skin-signed landmark was evaluated, providing small distances, more susceptible to acquisition errors.21 On average, the ratio of soft- to hard-tissue movement was between 38% and 103%. These values are in accordance with literature results, even if no direct comparisons can be made. Indeed, all previous investigations assessed 2-D movements measured on lateral cephalograms, they considered different landmarks, and had patients who received actual treatments and not simulations. In particular, surgical patients submitted to maxillary advancement with a Le Fort I osteotomy were analyzed by Chew et al,12 Ewing and Ross,16 and Louis et al,8 while orthodontic patients were measured by Yogosawa.32 Chew et al12 reported a soft-tissue movement between 66% and 106% of hard-tissue advancement. Ewing and Ross16 described soft-tissue movements ranging from 40% to 90% of maxillary advancement. Louis et al8 found a soft-tohard shifting ratio between 16% and 80%. Yogosawa32 described a 40% ratio for the upper lip and a 70% ratio for the lower lip. In all these studies, the supporting hard-tissue movements were greater than the 2-mm dental advancement of the current investigation, with surgical modifications between 3.5 and 11.5 mm. Indeed, according to Ewing and Ross,16 ratios should not be calculated for surgical movements smaller than 4 mm, and soft-tissue movements may be not linear.12 When wearing a 2-mm thick veneer, all landmarks placed on lip vermilion surfaces were moved significantly by the artificial dental changes. The movements in the paired landmarks were symmetrical. Only three cutaneous landmarks, the farthest from the vermilion area (Sn, Sl, and Pg), did not change their positions significantly. When analyzing individual landmark movements, right and left Cheilion were the most displaced (average movement: 102%). Cheilion is located in a critical area, at the border between skin and mucosa, at the conjunction of two different structures: lower and upper lip. Technical reproduction complexity and facial expression bias could modify measurements in these landmarks. The significant movements observed in the inferior lip depended on the relative positions between teeth and labial soft tissues. In healthy young adults, from 14% to 50% of the maxillary incisor and canine clinical crowns have been found to be below the labial commissure.33 The lower lip landmark Labiale inferius moved approximately twice more than the corresponding landmark in the upper lip (Ls), showing the strong influence of maxillary incisor and canine movements on the lower lip.10,32 Moseling and Woods13 obtained similar results when analyzing orthodontic patients: the lower part of the face was more affected by dental and skeletal variations than its middle part. They found that incisor position and angulation had a larger role on the lower lip position than on the upper lip position. Indeed, a positive linear correlation between overjet and Labiale
Morphological Evaluation of Soft Tissue Modification
inferius displacement was found: a larger overjet corresponded to a larger influence of maxillary teeth on the inferior lip. Patients with a small overjet may have a smaller Labiale inferius displacement because of the maxillary incisor advancing. Among the limitations of the current investigation, a lack of labial thickness evaluation occurred. In fact, before altering the facial-lingual position of the tooth, the clinician should classify the lips as full, medium, or thin, because thick lips seem to be less affected by restoration thickness or by orthodontic movements.6,11 Also, the current data were obtained only in healthy young adults of Caucasian origin. Labial response may be different in patients with previous labial surgery,16 of different age,22,34,35 or of another ethnic group.11 Furthermore, we assessed only the immediate effect of the veneer, and we cannot predict labial movements during an adaptation period: this process may be also age-related.36,37 Future investigations should analyze the time course of soft-tissue displacements. Even if several significant soft-tissue modifications were found, interindividual variability in landmark movements was large, as already reported in the literature,13,16 preventing suggestion of a uniform set of peri-labial changes. Considering its lack of invasiveness and the rapidity of execution, the method could be used to assess patients before prosthetic or orthodontic treatments, thus recording and quantifying the effect of interim prostheses or simulations of dental movements in three dimensions.10
Conclusion The stereophotogrammetric protocol was suitable for defining the soft-tissue changes with hard-tissue movements of at least 2 mm. Previous studies that reported smaller soft-tissue displacements than hard-tissue movements were confirmed, highlighting the importance of the soft-tissue compensation after changes of the supporting structures. Maxillary incisors’ and canines’ vestibular shift affected both upper and lower vermilion areas, without involving cutaneous perilabial landmarks.
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