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Three-Dimensional Evaluation of Alveolar Bone and Soft Tissue Dimensions of Maxillary Central Incisors for Immediate Implant Placement: A Cone-Beam Computed Tomography Assisted Analysis Mohit G. Kheur, MDS,* Nidhi R. Kantharia, BDS,† Supriya M. Kheur, MDS,‡ Aneesha Acharya, MDS,§ and Bach Le, DDS, MDk
he high predictability and success of osseointegration with immediate implant placement have led to a shift in the focus toward achieving ideal long-term esthetics with periimplant bone and tissue architecture. One of the keys to the esthetic illusion of a natural tooth is to create the ideal emergence profile. A critical element of the emergence profile is the nature of soft tissue surrounding the tooth or implant.1 Periimplant soft tissue characteristics are influenced by 3 major factorsd3-dimensional implant position,2 adequate support of labial bone
T
*Professor and Post Graduate Guide, Department of Prosthodontics, M.A. Rangoonwala College of Dental Sciences and Research Centre, Pune, India. †Post Graduate Student, Department of Prosthodontics, M.A. Rangoonwala College of Dental Sciences and Research Centre, Pune, India. ‡Professor and Head of Department, Department of Oral Pathology and Microbiology, Dr. D. Y. Patil Dental College and Hospital, Pune, India. §MPhil Candidate, Oral Rehabilitation, Faculty of Dentistry, University of Hong Kong, Hong Kong; Professor, Department of Periodontology, Dr. D. Y. Patil Dental College and Hospital, Pune, India. kClinical Associate Professor, Department of Oral & Maxillofacial Surgery, The Herman Ostrow School of Dentistry of USC, Los Angeles County/USC Medical Center, Los Angeles, CA.
Reprint requests and correspondence to: Mohit G. Kheur, MDS, Department of Prosthodontics, M.A. Rangoonwala College of Dental Sciences and Research Centre, Camp, Pune 411001, India, Phone: +91 9890350037, Fax: +912026430962, E-mail: [email protected] ISSN 1056-6163/15/00000-001 Implant Dentistry Volume 0 Number 0 Copyright © 2015 Wolters Kluwer Health, Inc. All rights reserved. DOI: 10.1097/ID.0000000000000259
Introduction: This study explored the relationship between the thickness of bone and soft tissue along the labial and palatal aspect of maxillary central incisors. The influence of overall socket width, labiopalatal positioning of the incisor on the bone, and soft tissue thickness were also investigated. Materials and Methods: This study used cone-beam computed tomography of 150 patients to determine labial, palatal soft and hard tissue thickness, labiopalatal (B-P) socket width and corelated the same to the labiopalatal positioning of maxillary central incisors. Results: Mean (SD) thicknesses of the labial soft tissue at cervical (C), midroot (M), and apical (A) locations and the corresponding bone thicknesses were 1.07 (0.28), 0.987 (0.27), 1.240 (0.41), and 0.928
(0.39), 0.894 (0.52), 1.57 (0.88), respectively. Similarly, palatal soft tissue and bone thicknesses at locations C, M, A were 1.807 (0.66), 1.557 (0.62), 1.639 (0.66), and 1.679 (0.62), 3.439 (1.28), 6.038 (1.63), respectively. Mean (SD) thicknesses of the B-P socket width at location C was 8.047 (0.963). Conclusions: There is a positive correlation between the labial and palatal bone and corresponding soft tissue thickness, between thickness of the labial bone and the labiopalatal thickness of the alveolar socket. No correlation was observed between the thickness of the labial cortical bone and the labiopalatal positioning of the tooth. (Implant Dent 2015;0:1–9) Key Words: labial bone thickness, palatal bone thickness, labiopalatal inclination
over the labial surface of an implant,3,4 and the periodontal tissue biotype.5 The term “gingival biotypes” was introduced by Seibert and Lindhe6 in 1989. It was later divided into thick and thin, based on the thickness of soft
tissue overlying the bone.7 A thick flat biotype has been shown to be associated with more predictable esthetic results than a thin biotype. A thick biotype is more likely to respond to injury and consequent inflammation
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Fig. 1. Sagittal section showing soft tissue outline (marked in red), bone outline (marked in yellow), and root surface outline (marked in white). Measurements recorded at positions “C,” “M,” and “A.”
Fig. 2. Sagittal section showing labial cortical thickness marked in blue at point C and the labiopalatal thickness marked in orange.
Fig. 3. Sagittal section showing line marked in yellow connecting point A (subspinale) of the maxilla to pogonion (Pog) of the mandible. Line marked in red passes through the incisal edge of the maxillary central incisor. Line marked in green depicts the perpendicular distance between the 2.
by pocket formation instead of recession, whereas a thin biotype is more likely to result in a recession.8 Buser2 stated that an adequate bone volume provides support to supracrestal soft
tissue, thereby producing desirable esthetic results. A minimum 2 mm thickness of labial cortical bone is deemed critical to prevent periimplant recession.2,9–11
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An understanding of the 3dimensional alveolar bone and its associated soft tissue anatomy around maxillary anterior teeth is critical for successful dental implant treatment, especially immediate implant placement. Previous studies evaluating labial bone and soft tissue thickness in the anterior maxilla have been performed on cadaver skulls or using medical and spiral computed tomography (CT) technology.12,13 Studies correlating supporting labial bone to its overlying soft tissue have reported conflicting results.1,13–15 A study performed by Cook et al14 reported a significant association between a thin biotype with a thin labial plate and narrow keratinized tissue width. Fu et al13 also showed a moderate correlation between gingival thickness and the underlying bone in a human cadaver study, whereas Han et al16 found no association between bone thickness and soft tissue thickness in a human cadaver study. La Rocca et al1 also found no correlation between bone thickness and soft tissue thickness in a human study using CT. Cadaver studies have limitations in their assessment of soft tissue parameters due to lack of hydration of tissues and subsequent shrinkage, which make their findings difficult to correlate with live human studies.17 No study has been reported so far, which identifies the correlation of soft tissue with the underlying bone in the dentate anterior maxilla in a large clinical sample. In addition, the influence of palatal socket wall characteristics and tooth angulations on soft tissue profile has never been studied. Tooth angulation and palatal wall thickness can influence the ability to place an immediate implant and has ramification on the definitive prosthetic design. Kan et al18 reported on the sagittal root position (SRP) of the tooth in relationship to its osseous housing; however, their study does not report its correlation to bone and soft tissue thickness. This study used cone-beam computed tomography (CBCT) data of patients to evaluate the relationship between the labial and palatal bone thickness and its overlying soft tissues. Alveolar ridge
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Table 1. Mean Labial and Palatal Bone Thickness and Corresponding Soft Tissue Thickness at 3 Points C, M, and A Labial Bone Thickness (n ¼ 150) (Mean 6 SD)
Labial Soft Tissue Thickness (n ¼ 150) (Mean 6 SD)
Palatal Bone Thickness (n ¼ 150) (Mean 6 SD)
Palatal Soft Tissue Thickness (n ¼ 150) (Mean 6 SD)
0.928 6 0.388 0.894 6 0.520 1.570 6 0.882
1.07 6 0.28 0.987 6 0.268 1.240 6 0.41
1.679 6 0.617 3.439 6 1.28 6.038 6 1.63
1.807 6 0.656 1.557 6 0.624 1.639 6 0.666
Points C M A
Table 2. Correlation Between Bone Thickness and Corresponding Soft Tissue Thickness at Point C at Labial and Palatal Aspect Location Labial aspect Palatal aspect
Karl Pearson Correlation Coefficient (r) Value
Student t Test Value
P
Significance
0.4955
33.989
,0.001
High
0.1128
24.540
,0.01
High
Table 3. Correlation Between Labial Bone Thickness With Palatal Bone Thickness and B-P Thickness of Alveolar Crest at Point C
Correlation of labial bone thickness to palatal bone thickness at point C Correlation of labial bone thickness to B-P alveolar thickness at point C
Karl Pearson Correlation Coefficient (r) Value
Student t Test Value
P
Significance
−0.03715
20.653
,0.001
High
0.2227
30.087
,0.001
High
Fig. 4. Scatter plot showing correlation between labial bone thickness and labial soft tissue thickness at point C. The plot depicts a moderate correlation of the labial bone thickness with the overlying labial soft tissue thickness at point C. The regression equation established was labial bone thickness ¼ 0.1933 + 0.6866 labial soft tissue thickness.
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dimensions and tooth position within the alveolus were also evaluated. The influence of the labiopalatal positioning of central incisors on the bone and its soft tissue profile were also studied. The hypothesis formulated that, for maxillary central incisors, thickness of soft tissue is associated to that of underlying labial and palatal bone and that the labiopalatal inclination of the tooth affects the overlying labial soft tissue thickness.
MATERIALS
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METHODS
The study was conducted at M.A. Rangoonwala College of Dental Sciences and Research Centre, Pune, Maharashtra, India. Patients included were those who required a CBCT scan (i-CAT unit; Imaging Sciences International Inc., Hatfield, PA) for the purpose of future implant therapy or orthodontic treatment. Teeth that were periodontally compromised were excluded from the study because of its potential influence on the thickness of labial cortical bone and the corresponding overlying soft tissue. In addition to this, teeth that were prosthetically rehabilitated or carious were also excluded. A sample size of 150 was estimated to provide 80% power to detect a small to moderate correlation (Pearson r ¼ 0.2) when a ¼ 0.05 and 150 CBCT scans of maxilla meeting the inclusion criteria of this study were analyzed. The CBCT examination was outlined using i-CAT unit (Imaging Sciences International, Inc., Hatfield, PA) at 120 kVp and 18.66 mA with the voxel size of 0.250 mm, grayscale of 14 bits while the field of view varied according to the patient requirements. The CBCT images were analyzed using Invivo 5.1 BV Anatomage on HD monitor with resolution of 1920 3 1080 pixels (Sync Master 60 Hz, Viewsonic Electronics Co, Ltd, Korea). The data for measuring the thickness of labial cortical bone and its adjacent soft tissue were reconstructed with 0.25 mm slices aimed to pass through the center of the respective root of the tooth, perpendicular to the alveolar ridge. The long axis of the root subsequently dictated the vertical orientation of the slice. To
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Fig. 5. Scatter plot showing correlation between palatal bone thickness and palatal soft tissue thickness at point C. The plot depicts a significant correlation of the palatal bone thickness with the overlying palatal soft tissue thickness at point C. The regression equation established was palatal bone thickness ¼ 1.4870 + 0.1060 palatal soft tissue thickness.
perform the measurements, sagittal scans obtained from the reconstructed data demonstrating the entire root, the cementoenamel junction (CEJ) of the root being examined, along with the supporting bone and gingival tissue were displayed with the largest
zooming factor possible, appropriate contrast and brightness, for the respective images. The thickness of the cortical bone and the adjoining soft tissue were measured perpendicular to the long axis of the tooth both along the labial and
Fig. 6. Scatter plot showing correlation between labial bone thickness and palatal bone thickness at point C. The plot depicts a significant correlation of the labial bone thickness with the corresponding palatal bone thickness at point C. The regression equation established was labial bone thickness ¼ 0.9670 − 0.0233 palatal bone thickness.
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palatal cortical plate at 3 particular locations for all the teeth being examined (3 mm apical to CEJ denoted as “C,” at the midroot region denoted as “M,” and at the apex of the root denoted as “A”) (Fig. 1). The total labiopalatal (denoted as “B-P”) thickness of the alveolar crest was also measured perpendicular to the long axis of the tooth at the point C, so as to gather correlation between the labial cortical bone thickness and B-P thickness at the point “C” (Fig. 2). The data for assessing the position of the maxillary central incisors with reference to a fixed reproducible reference line was collected using linear measurements using Down’s analysis (the linear distance between the maxillary central incisal edge and the A-pogonion (Pog) line). These data were reconstructed with 1.50 mm slices aimed to pass through the center of the incisive papilla perpendicular to the alveolar ridge. The long axis of the roots subsequently dictated the vertical orientation of the slice. To perform the measurements, sagittal scans from the reconstructed data demonstrating the point A (subspinale) of the maxilla, the entire root of the examined tooth, the entire crown of the examined tooth, and the pogonion on the mandible were displayed with the largest zooming factor possible for the respective images. The position of maxillary central incisor was analyzed according to the range of measurements as defined by Down’s analysis (2.7 6 1.8 mm) by measuring the perpendicular distance between the incisal edge of central incisor and the A-Pog line (Fig. 3). All measurements were completed by a single examiner who was blinded to the clinical findings and follow-up of the participating patients. Statistical analysis of the data collected was performed using a statistical software package (SYSTAT, version 12.0, Bangalore, India). A percentage of the number of teeth having labial soft tissue thickness ,1 and $1 mm at the point “C,” mean, and SD values were calculated for the labial and palatal cortical bone thickness and the soft tissue thickness at the 3 positions “C,” “M,” and “A.” The Karl Pearson correlation coefficients
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and the SD of the thickness of labial bone and the corresponding soft tissue at point C for all the 3 groups were compared. For assessing the difference in the thickness of the labial cortical bone with the varying position of the teeth, Student t test was applied.
RESULTS
Fig. 7. Scatter plot showing correlation between labial bone thickness and B-P thickness at point C. The plot depicts a significant correlation of the labial bone thickness with the B-P thickness at point C. The regression equation established was labial bone thickness ¼ 0.2053 + 0.0898 B-P thickness at point C.
Table 4. Mean Thickness of Labial Soft Tissue and the Thickness of Corresponding Labial Bone at Point C of Teeth Showing Different Inclinations Inclination Normal (n ¼ 46) Forwardly placed (n ¼ 95) Backwardly placed (n ¼ 9)
Labial Soft Tissue Thickness (Mean 6 SD)
Labial Bone Thickness (Mean 6 SD)
1.51 6 0.29 1.087 6 0.24 1.24 6 0.67
0.92 6 0.25 0.92 6 0.26 0.827 6 0.16
Table 5. Comparison of the Results for Bone Thickness Between the 3 Groups of Different Positions of Teeth Comparison For normal vs proclined For normal vs retroclined For proclined vs retroclined
t
P
Significance
0.6849 0.53 0.059
.0.05 .0.05 .0.05
Not significant Not significant Not significant
(r) were used to assess the following relationships: 1. Relationship between the thickness of labial cortical bone and the corresponding labial soft tissue at point “C” 2. Relationship between the thickness of palatal cortical bone and the corresponding palatal soft tissue at point “C” 3. Relationship between the thickness of labial cortical bone and
the thickness of the palatal cortical bone at point “C” 4. Relationship between the thickness of labial cortical bone and the B-P thickness of the alveolar crest at point “C” For further statistical analysis, the teeth were pooled into 3 groups according to their position related to A-Pog line as (1) normally positioned, (2) forwardly positioned, and (3) backwardly positioned using Down’s analysis. The mean
The central incisors of 150 individuals were assessed. The difference between the right and left central incisors was analyzed using the oneway analysis of variance. No significant difference was obtained between these 2. Hence, measurement of either of the centrals was considered as the same group. The gingival biotype was considered thin if the measurement was ,1.0 mm and thick if the measurement was $1.0 mm. The majority of the examined teeth exhibited a thick biotype ($1.0 mm; 65.34%), whereas the remaining (34.66%) presented with thin biotype The mean thickness with SD of labial bone for all analyzed teeth was 0.928 (60.388) mm at point C; 0.894 (60.520) mm at point M, and 1.570 (60.882) mm at point A (Table 1). The mean thickness of soft tissue corresponding to the labial bone was 1.07 (60.28) mm at point C, 0.987 (60.268) mm at point M, and 1.240 (60.41) mm at point A (Table 1). The mean thickness with SD of the palatal bone for all analyzed teeth was 1.679 (60.617) mm at point C, 3.439 (61.28) mm at point M, and 6.038 (61.63) mm at point A (Table 1). The mean thickness of soft tissue corresponding to the palatal bone was 1.807 (60.656) mm at point C, 1.557 (60.624) mm at point M, and 1.639 (60.666) mm at point A (Table 1). The mean thickness with SD of the B-P alveolar crest width for all the analyzed teeth was 8.047 (60.963) mm at point C. The Karl Pearson correlation coefficients (r) determined the following significant relationships (P , 0.001): thickness of labial cortical bone and corresponding soft tissue at point C (moderately correlated; r ¼ 0.4955), thickness of palatal bone and palatal soft tissue thickness at point C (r ¼ 0.1128), labial bone thickness and palatal bone thickness at
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point C (r ¼ −0.03715), bone thickness and B-P thickness of alveolar crest at point C (r ¼ 0.22270), and were all significantly correlated (Tables 2 and 3). Scatter plots and regression equations were also created (Figs. 4–7). For further statistical analysis, the teeth were pooled into 3 groups according to their position related to A-Pog line as (1) normally positioned, (2) forwardly positioned, and (3) backwardly positioned using Down’s analysis. The mean and the SD of the thickness of labial soft tissue at point C was 1.51 (60.29) mm for normally inclined teeth, 1.087 (60.24) mm for forwardly inclined teeth, and 1.24 (60.67) mm for backwardly inclined teeth (Table 4). The mean and the SD of the thickness of labial bone at point C was 0.92 (60.25) mm for normally inclined teeth, 0.92 (60.26) mm for forwardly inclined teeth, and 0.827 (60.16) mm for backwardly inclined teeth (Table 4). There was no significant difference found between mean values of labial bone thickness with changing positions of the teeth (ie, P . 0.05) (Table 5). Thickness of palatal bone at point A of teeth showing different inclinations for normal versus proclined was significantly different (Table 5).
DISCUSSION CBCT has been regarded as a reliable technique for quantitative assessment of the thickness of labial bone in natural teeth with high precision of submillimeter accuracy for linear measurements.15,16,19–23 In addition, it offers better quality image at low radiation exposure when compared with conventional CT.24–26 It is a suitable noninvasive technique available for assessing the thickness of soft tissue and the underlying bone.27 The accuracy of CBCT in measuring soft tissue depth measurements has been demonstrated.28 Maxillary central incisors form an area of great esthetic significance and were therefore the focus of this study. Much consideration has been given to the thickness of the gingiva and its importance in implant dentistry.29 The thinner biotype is more prone to recession and loss of interdental papilla.30–33
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In a retrospective analysis of 42 singletooth implants placed in the esthetic zone, a significant change in crown height due to marginal tissue recession of approximately 1 mm was noted.34 Thin tissue biotypes showed slightly greater recession than thick tissue biotypes. Not only is the thin tissue biotype more prone to recession, but it is also more susceptible to poor esthetic outcome.30–32 Jung et al35 used photospectrometry to show that soft tissue thickness of greater than 2 mm is ideal to achieve a natural esthetic outcome without tissue discoloration from the underlying abutment. Evidence also suggests that thick soft tissue may be protective against crestal bone loss.36 Linkevicius et al reported that implants with greater than 2.5 mm of periimplant soft tissue thickness experienced a mean of 0.26 mm crestal bone loss compared with 1.45 mm of crestal bone loss seen at those sites with less than 2 mm of periimplant soft tissue thickness. Careful treatment planning is therefore needed for patients with thinner biotypes when considering immediate implant therapy. Soft tissue thickness has been measured using different methods over the years including periodontal probe,16 endodontic files,1,37 spiral CT,37 and others. Soft tissue CBCT is an accurate, convenient, and painless technique for obtaining a 3-dimensional overview of the soft tissue along with its supporting bone.13,37–40 Gingival tissue thickness has been measured at points ranging 1 to 3 mm apical in relation to the bone crest14 or gingival margin.1,41 Fu13 assessed the soft tissue thickness 2 mm apical to the bone crest with a caliper (0.5 mm; range, 0.1–1.2 mm) and compared it with the measurements obtained from the CBCT scans (0.57 mm; range, 0.2–1.86 mm) and found no significant difference among them. La Rocca1 measured the mean thickness of soft tissue on the labial aspect of the upper anterior teeth at a point 1 mm apical to the depth of the sulcus and measured it to be 1.10 mm (range, 0.1–2.50 mm). In this study, the mean thickness of the labial soft tissue was assessed using a CBCT at 3 different positions; 3 mm apical to CEJ (C), midroot (M), and apical root position
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(A) and was found to be 1.07 (60.28) mm, 0.987 (60.268) mm, and 1.240 (60.41) mm, respectively. These values are in agreement with those reported by these previous studies.13,37–40 Gingival contour is dictated by the contour of the underlying bone and the shape of the tooth.42 Labial bone thickness is also considered a crucial parameter for treatment planning immediate implant placement. Ferrus et al identified factors that influence ridge alterations at the buccal aspects of extraction sites after immediate implant placement. A series of measurements of the extraction sites were made immediate after implant placement and at reentry. The degree of horizontal gap fill and postextraction bone crest remodeling was more favorable in sites where labial bone thickness exceeds 1 mm.4 Teeth with thin or dehisced labial wall are at risk of midfacial gingival recession after immediate implant placement. This is especially true in patients that have a thin biotype. A recent study found that the thickness of labial crestal soft tissue around maxillary implants can be influenced by the underlying bone.27 Le and Borzabadi-Farahani28 found a correlation between labial crestal soft tissue thickness and underlying labial bone thickness, indicating that soft tissue thickness can be heavily influenced by the labial bone thickness. In other words, the thicker the bone, the thicker the crestal labial soft tissue around implants and vice versa. Labial bone thickness lower than 2 mm has been indicated for hard tissue bone augmentation to develop an esthetically pleasing soft tissue profile.9,10,43,44 The labial bone thickness of the central incisors have been reported with the highest percentage of thin walls among all the anterior teeth.21 The mean thicknesses of labial bone measured in this study at the specific positions are relatively higher than those reported by previous authors.1,14,21,30 Smaller sample size, different subject ethnicity, and cadaver measurements may account for these noted differences. Owing to the thickness and dense cortication, palatal mucosa with its supporting bone is considered to be a favorable foundation for the placement of an implant.21 In the present sample, palatal bone thickness
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IMPLANT DENTISTRY / VOLUME 0, NUMBER 0 2015 of the examined teeth presented with thick palatal bone [87.33% with thickness $1 mm (at point C)], whereas only 12.66% showed thin palatal bone [thickness ,1 mm (at point C)]. Our findings are in agreement with those of Kan et al,18 which reported the majority of maxillary anterior teeth are positioned against the labial cortical plate (approximately 81%), allowing a considerable amount of bone on the palatal aspect for immediate implant placement. Kan et al18 classified the relationships of the SRP of maxillary teeth to their alveolar housings using CBCT analysis. Their proposed classification of the SRP is Class I (root against labial cortex; incidence 81%), Class II (root centered in alveolar housing; incidence 6.5%), Class III (root against palatal cortex; incidence 0.7%), and Class IV (root against labial housing; incidence 11.7%). The authors proposed objective guidelines for planning immediate implant placements and provisionalization based on the classification of SRP: Class I SRPs being favorable, Class IV being contraindicated, and Class II and Class III SRPs being technique sensitive. The results of the bony dimensions determined in this study were in agreement with those of Braut et al22 and Hyunh-Ba et al.45 Braut et al22 used CBCT data to analyze the thickness of the labial bone wall in anterior teeth. The majority of the examined teeth exhibited a thin facial bone wall (,1 mm; 62.9%). A thick bone wall ($ 1 mm) was found in only 11.4% of all examined teeth. Huynh-Ba et al45 analyzed the thickness of labial bone walls of anterior teeth at extraction sites. Their results showed that a majority of anterior teeth (87%) had thickness less than 1 mm, whereas only 2.6% had thickness more than 2 mm. These measurements were manually made using calipers. In this study, 36.7% of patients had labial bone thickness $1 mm, whereas the majority of patients (63%) had labial bone thickness ,1 mm. A significant moderate correlation (r ¼ 0.496) was shown between the soft tissue thickness and the underlying bone thickness by Fu et al.13 They showed a small correlation (r ¼ 0.1128) between overlying soft tissue and bone at the
palatal aspect.15 The results of this study are not in agreement with the study of La Rocca et al1 who found no correlation between the crestal bone thickness and the thickness of the overlying gingiva. This difference between the results of the 2 studies could be attributed to the differences in the study protocols followed because the study of La Rocca1 used transgingival probing to measure gingival thickness rather than CBCT analysis. A positive correlation of the labial bone thickness to the labiopalatal bone width was noted in this study. Socket dimensions have been shown to influence wound healing, with more bone loss in the narrower sockets and those with thinner labial wall thickness.18,39 Although the thickness of the palatal cortical plate is greater compared with the labial cortical plate in the anterior maxilla,15 this finding may highlight that wider sockets tend to associate with thicker labial cortices and may indicate advantages in socket healing potential. In a controlled animal study on immediate implants, Vignoletti et al46 concluded socket dimensions influence wound healing of implants placed into fresh extraction sockets, with more bone loss in the narrower sockets. No study has reported the influence of the labiopalatal positioning of anterior teeth on the labial bone thickness. In this study, no differences in the thickness of the labial cortical bone between varying labiopalatal tooth positioning of the teeth were evident. However, proclined teeth (64%) had significantly lower thickness of palatal bone at the apex than normally positioned teeth (30%). This finding may have prognostic implications for immediate implant placement where the amount of palatal bone available for implant anchorage is critical. In a study examining the SRP of maxillary anterior teeth, Wang H et al47 concluded most teeth have their roots angled out in close proximity to the labial plate. They measured the inclination of teeth by describing the angle made by the tooth long axis against the alveolar ridge long axis. Similarly Kan et al18 reported that 81% of the teeth in their sample had the root in close proximity
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to the labial cortical plate. This study used Down’s analysis to determine the labiopalatal positioning of the teeth. The results of the studies by Hui-ming Wang et al, Kan et al,18 and this study further underline the need for proper diagnosis and especially radiographic analysis using CBCT before tooth extraction. This would help to determine the appropriate implant dimensions, angulations, and the need for auxiliary procedures such as bone augmentation, to achieve adequate hard tissue contours around the implant and ensure a predictable esthetic outcome. In immediate implant placement, teeth with proclined inclination may necessitate placement with a labial angulation or risk perforation of the apex. Implant angulation may dictate restoration design (screw-retained vs cement-retained) and has been shown to be correlated with soft tissue thickness. Le et al48 studied the association between crestal labial soft tissue thickness and buccolingual angulation of the implant. The buccolingual angulation was recorded as being cingulum, incisal, or labial based on the position of the screw access hole on provisional restorations. A significant association was observed between crestal labial soft tissue thickness and implant buccolingual angulation when implant labial bone thickness at crestal level was less than 2 mm (P , 0.01). They concluded that implants with labial angulations carry a higher risk of soft-tissue complications when the crestal implant labial bone thickness is less than 2 mm.
CONCLUSIONS Within the limitations of this study, it can be concluded that a significant correlation exists between the labial and palatal cortical bone thickness and the thickness of corresponding soft tissue. Similarly, there is a significant corelation between thickness of the labial bone and the labiopalatal thickness of the alveolar socket width. No relationship was observed between the thickness of the labial cortical bone and the labiopalatal inclination of the associated tooth. These findings have implications in treatment planning of immediate implant therapy.
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DISCLOSURE The authors claim to have no financial interest, either directly or indirectly, in the products or information listed in the article.
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cone-beam CT. J Adv Prosthodont. 2010;2:92–96. 13. Fu JH, Yeh CY, Chan HL, et al. Tissue biotype and its relation to the underlying bone morphology. J Periodontol. 2010; 81:569–574. 14. Cook DR, Mealey BL, Verrett RG, et al. Relationship between clinical periodontal biotype and labial plate thickness: An in vivo study. Int J Periodontics Restorative Dent. 2011;31:345–354. 15. Maynard JG Jr, Wilson RD. Diagnosis and management of mucogingival problems in children. Dent Clin North Am. 1980;24:683–703. 16. Han JY, Jung GU. Labial and lingual/palatal bone thickness of maxillary and mandibular anteriors in human cadavers in Koreans. J Periodontal Implant Sci. 2011;41:60–66. 17. Fourie Z, Damstra J, Gerrits PO, et al. Accuracy and reliability of facial soft tissue depth measurements using cone beam computer tomography. Forensic Sci Int. 2010;199:9–14. 18. Kan JY, Roe P, Rungcharassaeng K, et al. Classification of sagittal root position in relation to the anterior maxillary osseous housing for immediate implant placement: A cone beam computed tomography study. Int J Oral Maxillofac Implants. 2011;26:873–876. 19. Loubele M, Van Assche N, Carpentier K, et al. Comparative localized linear accuracy of small-field cone-beam CT and multislice CT for alveolar bone measurements. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2008;105: 512–518. 20. Timock AM, Cook V, McDonald T, et al. Accuracy and reliability of buccal bone height and thickness measurements from cone-beam computed tomography imaging. Am J Orthod Dentofacial Orthop. 2011;140:734–744. 21. Januário AL, Duarte WR, Barriviera M, et al. Dimension of the facial bone wall in the anterior maxilla: A conebeam computed tomography study. Clin Oral Implants Res. 2011;22:1168–1171. 22. Braut V, Bornstein MM, Belser U, et al. Thickness of the anterior maxillary facial bone wall-a retrospective radiographic study using cone beam computed tomography. Int J Periodontics Restorative Dent. 2011;31:125–131. 23. Nowzari H, Molayem S, Chiu CH, et al. Cone beam computed tomographic measurement of maxillary central incisors to determine prevalence of facial alveolar bone width $2mm. Clin Implant Dent Relat Res. 2012;14:595–602. 24. De Vos W, Casselman J, Swennen GR. Cone-beam computerized tomography (CBCT) imaging of the oral and maxillofacial region: A systemic review
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of the literature. Int J Oral Maxillofac Surg. 2009;38:609–625. 25. Scarfe WC, Farman AG, Levin MD, et al. Essentials of maxillofacial cone beam computed tomography. Alpha Omegan. 2010;103:62–67. 26. Behneke A, Burwinkel M, Knierim K, et al. Accuracy assessment of cone beam computed tomography-derived laboratory-based surgical templates on partially edentulous patients. Clin Oral Implants Res. 2012;23:137–143. 27. Kim KD, Ruprecht A, Wang G, et al. Accuracy of facial soft tissue thickness measurements in personal computer-based multiplanar reconstructed computed tomographic images. Forensic Sci Int. 2005;155:28–34. 28. Le BT, Borzabadi-Farahani A. Labial bone thickness in area of anterior maxillary implants associated with crestal labial soft tissue thickness. Implant Dent. 2012;21:406–410. 29. Kois JC. Predictable single tooth peri-implant esthetics: Five diagnostic keys. Compend Contin Educ Dent. 2001; 22:199–206; quiz 208. 30. De Rouck T, Eghbali R, Collys K, et al. The gingival biotype revisited: Transparency of the periodontal probe through the gingival margin as a method to discriminate thin from thick gingiva. J Clin Periodontol. 2009;36:428–433. 31. Müller HP, Eger T, Schorb A. Gingival dimensions after root coverage with free connective tissue grafts. J Clin Periodontol. 1998;25:424–430. 32. Hämmerle CH, Chen ST, Wilson TG Jr. Consensus statements and recommended clinical procedures regarding the placement of implants in extraction sockets. Int J Oral Maxillofac Implants. 2004; 19:26–28. 33. Chen ST, Darby IB, Reynolds EC, et al. Immediate implant placement postextraction without flap elevation. J Periodontol. 2009;80:163–172. 34. Evans CD, Chen ST. Esthetic outcomes of immediate implant placements. Clin Oral Implants Res. 2008;19:73–80. 35. Jung RE, Sailer I, Hämmerle CH, et al. In vitro color changes of soft tissues caused by restorative materials. Int J Periodontics Restorative Dent. 2007;27:251– 257. 36. Linkevicius T, Apse P, Grybauskas S, et al. The influence of soft tissue thickness on crestal bone changes around implants: A 1 year prospective controlled clinical trial. Int J Oral Maxillofac Implants. 2009;24: 712–719. 37. Ueno D, Sato J, Igarashi C, et al. Accuracy of oral mucosal thickness measurements using spiral computed tomography. J Periodontol. 2011;82: 829–836.
Copyright Ó 2015 Wolters Kluwer Health, Inc. Unauthorized reproduction of this article is prohibited.
IMPLANT DENTISTRY / VOLUME 0, NUMBER 0 2015 38. Ronay V, Sahrmann P, Bindl A, et al. Current status and perspectives of mucogingival soft tissue measurement methods. J Esthet Restor Dent. 2011;23:146–156. 39. Misch KA, Yi ES, Sarment DP. Accuracy of cone beam computed tomography for periodontal defect measurements. J Periodontol. 2006;77:1261–1266. 40. Benavides E, Rios HF, Ganz SD, et al. Use of cone beam computed tomography in implant dentistry: The International Congress of Oral Implantologists consensus report. Implant Dent. 2012;21:78–86. 41. Müller HP, Schaller N, Eger T, et al. Thickness of masticatory mucosa. J Clin Periodontol. 2000;27:431–436. 42. Ochsenbein C, Ross S. A concept of osseous surgery and its clinical applications.
In: Ward HL, Chas C, eds. A Periodontal Point of View: A Practical Expression of Current Problems Integrating Basic Science With Clinical Data. Springfield, IL: Charles C Thomas Publishing Co.; 1973: 276–323. 43. Lee A, Fu JH, Wang HL. Soft tissue biotype affects implant success. Implant Dent. 2011;20:e38–e47. 44. Le B, Burstein J. Esthetic grafting for small volume hard and soft tissue contour defects for implant site development. Implant Dent. 2008;17:136–141. 45. Huynh-Ba G, Pjetursson BE, Sanz M, et al. Analysis of the socket bone wall dimensions in the upper maxilla in relation to immediate implant placement. Clin Oral Implants Res. 2010;21:37–42.
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46. Vignoletti F, de Sanctis M, Berglundh T, et al. Early healing of implants placed into fresh extraction sockets: An experimental study in the beagle dog. II: Ridge alterations. J Clin Periodontol. 2009;36:688–697. 47. Wang HM, Shen JW, Yu MF, et al. Analysis of facial bone wall dimensions and sagittal root position in the maxillary esthetic zone: A retrospective study using cone beam computed tomography. Int J Oral Maxillofac Implants. 2014;29:1123–1129. 48. Le BT, Borzabadi-Farahani A, Pluemsakunthai W. Is buccolingual angulation of maxillary anterior implants associated with the crestal labial soft tissue thickness? Int J Oral Maxillofac Surg. 2014;43:874–878.
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1
Three-Dimensional Evaluation of Alveolar Bone and Soft Tissue Dimensions of Maxillary Central Incisors for Immediate Implant Placement: A Cone-Beam Computed Tomography Assisted Analysis Mohit G. Kheur, MDS,* Nidhi R. Kantharia, BDS,† Supriya M. Kheur, MDS,‡ Aneesha Acharya, MDS,§ and Bach Le, DDS, MDk
he high predictability and success of osseointegration with immediate implant placement have led to a shift in the focus toward achieving ideal long-term esthetics with periimplant bone and tissue architecture. One of the keys to the esthetic illusion of a natural tooth is to create the ideal emergence profile. A critical element of the emergence profile is the nature of soft tissue surrounding the tooth or implant.1 Periimplant soft tissue characteristics are influenced by 3 major factorsd3-dimensional implant position,2 adequate support of labial bone
T
*Professor and Post Graduate Guide, Department of Prosthodontics, M.A. Rangoonwala College of Dental Sciences and Research Centre, Pune, India. †Post Graduate Student, Department of Prosthodontics, M.A. Rangoonwala College of Dental Sciences and Research Centre, Pune, India. ‡Professor and Head of Department, Department of Oral Pathology and Microbiology, Dr. D. Y. Patil Dental College and Hospital, Pune, India. §MPhil Candidate, Oral Rehabilitation, Faculty of Dentistry, University of Hong Kong, Hong Kong; Professor, Department of Periodontology, Dr. D. Y. Patil Dental College and Hospital, Pune, India. kClinical Associate Professor, Department of Oral & Maxillofacial Surgery, The Herman Ostrow School of Dentistry of USC, Los Angeles County/USC Medical Center, Los Angeles, CA.
Reprint requests and correspondence to: Mohit G. Kheur, MDS, Department of Prosthodontics, M.A. Rangoonwala College of Dental Sciences and Research Centre, Camp, Pune 411001, India, Phone: +91 9890350037, Fax: +912026430962, E-mail: [email protected] ISSN 1056-6163/15/00000-001 Implant Dentistry Volume 0 Number 0 Copyright © 2015 Wolters Kluwer Health, Inc. All rights reserved. DOI: 10.1097/ID.0000000000000259
Introduction: This study explored the relationship between the thickness of bone and soft tissue along the labial and palatal aspect of maxillary central incisors. The influence of overall socket width, labiopalatal positioning of the incisor on the bone, and soft tissue thickness were also investigated. Materials and Methods: This study used cone-beam computed tomography of 150 patients to determine labial, palatal soft and hard tissue thickness, labiopalatal (B-P) socket width and corelated the same to the labiopalatal positioning of maxillary central incisors. Results: Mean (SD) thicknesses of the labial soft tissue at cervical (C), midroot (M), and apical (A) locations and the corresponding bone thicknesses were 1.07 (0.28), 0.987 (0.27), 1.240 (0.41), and 0.928
(0.39), 0.894 (0.52), 1.57 (0.88), respectively. Similarly, palatal soft tissue and bone thicknesses at locations C, M, A were 1.807 (0.66), 1.557 (0.62), 1.639 (0.66), and 1.679 (0.62), 3.439 (1.28), 6.038 (1.63), respectively. Mean (SD) thicknesses of the B-P socket width at location C was 8.047 (0.963). Conclusions: There is a positive correlation between the labial and palatal bone and corresponding soft tissue thickness, between thickness of the labial bone and the labiopalatal thickness of the alveolar socket. No correlation was observed between the thickness of the labial cortical bone and the labiopalatal positioning of the tooth. (Implant Dent 2015;0:1–9) Key Words: labial bone thickness, palatal bone thickness, labiopalatal inclination
over the labial surface of an implant,3,4 and the periodontal tissue biotype.5 The term “gingival biotypes” was introduced by Seibert and Lindhe6 in 1989. It was later divided into thick and thin, based on the thickness of soft
tissue overlying the bone.7 A thick flat biotype has been shown to be associated with more predictable esthetic results than a thin biotype. A thick biotype is more likely to respond to injury and consequent inflammation
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Fig. 1. Sagittal section showing soft tissue outline (marked in red), bone outline (marked in yellow), and root surface outline (marked in white). Measurements recorded at positions “C,” “M,” and “A.”
Fig. 2. Sagittal section showing labial cortical thickness marked in blue at point C and the labiopalatal thickness marked in orange.
Fig. 3. Sagittal section showing line marked in yellow connecting point A (subspinale) of the maxilla to pogonion (Pog) of the mandible. Line marked in red passes through the incisal edge of the maxillary central incisor. Line marked in green depicts the perpendicular distance between the 2.
by pocket formation instead of recession, whereas a thin biotype is more likely to result in a recession.8 Buser2 stated that an adequate bone volume provides support to supracrestal soft
tissue, thereby producing desirable esthetic results. A minimum 2 mm thickness of labial cortical bone is deemed critical to prevent periimplant recession.2,9–11
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An understanding of the 3dimensional alveolar bone and its associated soft tissue anatomy around maxillary anterior teeth is critical for successful dental implant treatment, especially immediate implant placement. Previous studies evaluating labial bone and soft tissue thickness in the anterior maxilla have been performed on cadaver skulls or using medical and spiral computed tomography (CT) technology.12,13 Studies correlating supporting labial bone to its overlying soft tissue have reported conflicting results.1,13–15 A study performed by Cook et al14 reported a significant association between a thin biotype with a thin labial plate and narrow keratinized tissue width. Fu et al13 also showed a moderate correlation between gingival thickness and the underlying bone in a human cadaver study, whereas Han et al16 found no association between bone thickness and soft tissue thickness in a human cadaver study. La Rocca et al1 also found no correlation between bone thickness and soft tissue thickness in a human study using CT. Cadaver studies have limitations in their assessment of soft tissue parameters due to lack of hydration of tissues and subsequent shrinkage, which make their findings difficult to correlate with live human studies.17 No study has been reported so far, which identifies the correlation of soft tissue with the underlying bone in the dentate anterior maxilla in a large clinical sample. In addition, the influence of palatal socket wall characteristics and tooth angulations on soft tissue profile has never been studied. Tooth angulation and palatal wall thickness can influence the ability to place an immediate implant and has ramification on the definitive prosthetic design. Kan et al18 reported on the sagittal root position (SRP) of the tooth in relationship to its osseous housing; however, their study does not report its correlation to bone and soft tissue thickness. This study used cone-beam computed tomography (CBCT) data of patients to evaluate the relationship between the labial and palatal bone thickness and its overlying soft tissues. Alveolar ridge
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Table 1. Mean Labial and Palatal Bone Thickness and Corresponding Soft Tissue Thickness at 3 Points C, M, and A Labial Bone Thickness (n ¼ 150) (Mean 6 SD)
Labial Soft Tissue Thickness (n ¼ 150) (Mean 6 SD)
Palatal Bone Thickness (n ¼ 150) (Mean 6 SD)
Palatal Soft Tissue Thickness (n ¼ 150) (Mean 6 SD)
0.928 6 0.388 0.894 6 0.520 1.570 6 0.882
1.07 6 0.28 0.987 6 0.268 1.240 6 0.41
1.679 6 0.617 3.439 6 1.28 6.038 6 1.63
1.807 6 0.656 1.557 6 0.624 1.639 6 0.666
Points C M A
Table 2. Correlation Between Bone Thickness and Corresponding Soft Tissue Thickness at Point C at Labial and Palatal Aspect Location Labial aspect Palatal aspect
Karl Pearson Correlation Coefficient (r) Value
Student t Test Value
P
Significance
0.4955
33.989
,0.001
High
0.1128
24.540
,0.01
High
Table 3. Correlation Between Labial Bone Thickness With Palatal Bone Thickness and B-P Thickness of Alveolar Crest at Point C
Correlation of labial bone thickness to palatal bone thickness at point C Correlation of labial bone thickness to B-P alveolar thickness at point C
Karl Pearson Correlation Coefficient (r) Value
Student t Test Value
P
Significance
−0.03715
20.653
,0.001
High
0.2227
30.087
,0.001
High
Fig. 4. Scatter plot showing correlation between labial bone thickness and labial soft tissue thickness at point C. The plot depicts a moderate correlation of the labial bone thickness with the overlying labial soft tissue thickness at point C. The regression equation established was labial bone thickness ¼ 0.1933 + 0.6866 labial soft tissue thickness.
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dimensions and tooth position within the alveolus were also evaluated. The influence of the labiopalatal positioning of central incisors on the bone and its soft tissue profile were also studied. The hypothesis formulated that, for maxillary central incisors, thickness of soft tissue is associated to that of underlying labial and palatal bone and that the labiopalatal inclination of the tooth affects the overlying labial soft tissue thickness.
MATERIALS
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METHODS
The study was conducted at M.A. Rangoonwala College of Dental Sciences and Research Centre, Pune, Maharashtra, India. Patients included were those who required a CBCT scan (i-CAT unit; Imaging Sciences International Inc., Hatfield, PA) for the purpose of future implant therapy or orthodontic treatment. Teeth that were periodontally compromised were excluded from the study because of its potential influence on the thickness of labial cortical bone and the corresponding overlying soft tissue. In addition to this, teeth that were prosthetically rehabilitated or carious were also excluded. A sample size of 150 was estimated to provide 80% power to detect a small to moderate correlation (Pearson r ¼ 0.2) when a ¼ 0.05 and 150 CBCT scans of maxilla meeting the inclusion criteria of this study were analyzed. The CBCT examination was outlined using i-CAT unit (Imaging Sciences International, Inc., Hatfield, PA) at 120 kVp and 18.66 mA with the voxel size of 0.250 mm, grayscale of 14 bits while the field of view varied according to the patient requirements. The CBCT images were analyzed using Invivo 5.1 BV Anatomage on HD monitor with resolution of 1920 3 1080 pixels (Sync Master 60 Hz, Viewsonic Electronics Co, Ltd, Korea). The data for measuring the thickness of labial cortical bone and its adjacent soft tissue were reconstructed with 0.25 mm slices aimed to pass through the center of the respective root of the tooth, perpendicular to the alveolar ridge. The long axis of the root subsequently dictated the vertical orientation of the slice. To
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Fig. 5. Scatter plot showing correlation between palatal bone thickness and palatal soft tissue thickness at point C. The plot depicts a significant correlation of the palatal bone thickness with the overlying palatal soft tissue thickness at point C. The regression equation established was palatal bone thickness ¼ 1.4870 + 0.1060 palatal soft tissue thickness.
perform the measurements, sagittal scans obtained from the reconstructed data demonstrating the entire root, the cementoenamel junction (CEJ) of the root being examined, along with the supporting bone and gingival tissue were displayed with the largest
zooming factor possible, appropriate contrast and brightness, for the respective images. The thickness of the cortical bone and the adjoining soft tissue were measured perpendicular to the long axis of the tooth both along the labial and
Fig. 6. Scatter plot showing correlation between labial bone thickness and palatal bone thickness at point C. The plot depicts a significant correlation of the labial bone thickness with the corresponding palatal bone thickness at point C. The regression equation established was labial bone thickness ¼ 0.9670 − 0.0233 palatal bone thickness.
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palatal cortical plate at 3 particular locations for all the teeth being examined (3 mm apical to CEJ denoted as “C,” at the midroot region denoted as “M,” and at the apex of the root denoted as “A”) (Fig. 1). The total labiopalatal (denoted as “B-P”) thickness of the alveolar crest was also measured perpendicular to the long axis of the tooth at the point C, so as to gather correlation between the labial cortical bone thickness and B-P thickness at the point “C” (Fig. 2). The data for assessing the position of the maxillary central incisors with reference to a fixed reproducible reference line was collected using linear measurements using Down’s analysis (the linear distance between the maxillary central incisal edge and the A-pogonion (Pog) line). These data were reconstructed with 1.50 mm slices aimed to pass through the center of the incisive papilla perpendicular to the alveolar ridge. The long axis of the roots subsequently dictated the vertical orientation of the slice. To perform the measurements, sagittal scans from the reconstructed data demonstrating the point A (subspinale) of the maxilla, the entire root of the examined tooth, the entire crown of the examined tooth, and the pogonion on the mandible were displayed with the largest zooming factor possible for the respective images. The position of maxillary central incisor was analyzed according to the range of measurements as defined by Down’s analysis (2.7 6 1.8 mm) by measuring the perpendicular distance between the incisal edge of central incisor and the A-Pog line (Fig. 3). All measurements were completed by a single examiner who was blinded to the clinical findings and follow-up of the participating patients. Statistical analysis of the data collected was performed using a statistical software package (SYSTAT, version 12.0, Bangalore, India). A percentage of the number of teeth having labial soft tissue thickness ,1 and $1 mm at the point “C,” mean, and SD values were calculated for the labial and palatal cortical bone thickness and the soft tissue thickness at the 3 positions “C,” “M,” and “A.” The Karl Pearson correlation coefficients
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and the SD of the thickness of labial bone and the corresponding soft tissue at point C for all the 3 groups were compared. For assessing the difference in the thickness of the labial cortical bone with the varying position of the teeth, Student t test was applied.
RESULTS
Fig. 7. Scatter plot showing correlation between labial bone thickness and B-P thickness at point C. The plot depicts a significant correlation of the labial bone thickness with the B-P thickness at point C. The regression equation established was labial bone thickness ¼ 0.2053 + 0.0898 B-P thickness at point C.
Table 4. Mean Thickness of Labial Soft Tissue and the Thickness of Corresponding Labial Bone at Point C of Teeth Showing Different Inclinations Inclination Normal (n ¼ 46) Forwardly placed (n ¼ 95) Backwardly placed (n ¼ 9)
Labial Soft Tissue Thickness (Mean 6 SD)
Labial Bone Thickness (Mean 6 SD)
1.51 6 0.29 1.087 6 0.24 1.24 6 0.67
0.92 6 0.25 0.92 6 0.26 0.827 6 0.16
Table 5. Comparison of the Results for Bone Thickness Between the 3 Groups of Different Positions of Teeth Comparison For normal vs proclined For normal vs retroclined For proclined vs retroclined
t
P
Significance
0.6849 0.53 0.059
.0.05 .0.05 .0.05
Not significant Not significant Not significant
(r) were used to assess the following relationships: 1. Relationship between the thickness of labial cortical bone and the corresponding labial soft tissue at point “C” 2. Relationship between the thickness of palatal cortical bone and the corresponding palatal soft tissue at point “C” 3. Relationship between the thickness of labial cortical bone and
the thickness of the palatal cortical bone at point “C” 4. Relationship between the thickness of labial cortical bone and the B-P thickness of the alveolar crest at point “C” For further statistical analysis, the teeth were pooled into 3 groups according to their position related to A-Pog line as (1) normally positioned, (2) forwardly positioned, and (3) backwardly positioned using Down’s analysis. The mean
The central incisors of 150 individuals were assessed. The difference between the right and left central incisors was analyzed using the oneway analysis of variance. No significant difference was obtained between these 2. Hence, measurement of either of the centrals was considered as the same group. The gingival biotype was considered thin if the measurement was ,1.0 mm and thick if the measurement was $1.0 mm. The majority of the examined teeth exhibited a thick biotype ($1.0 mm; 65.34%), whereas the remaining (34.66%) presented with thin biotype The mean thickness with SD of labial bone for all analyzed teeth was 0.928 (60.388) mm at point C; 0.894 (60.520) mm at point M, and 1.570 (60.882) mm at point A (Table 1). The mean thickness of soft tissue corresponding to the labial bone was 1.07 (60.28) mm at point C, 0.987 (60.268) mm at point M, and 1.240 (60.41) mm at point A (Table 1). The mean thickness with SD of the palatal bone for all analyzed teeth was 1.679 (60.617) mm at point C, 3.439 (61.28) mm at point M, and 6.038 (61.63) mm at point A (Table 1). The mean thickness of soft tissue corresponding to the palatal bone was 1.807 (60.656) mm at point C, 1.557 (60.624) mm at point M, and 1.639 (60.666) mm at point A (Table 1). The mean thickness with SD of the B-P alveolar crest width for all the analyzed teeth was 8.047 (60.963) mm at point C. The Karl Pearson correlation coefficients (r) determined the following significant relationships (P , 0.001): thickness of labial cortical bone and corresponding soft tissue at point C (moderately correlated; r ¼ 0.4955), thickness of palatal bone and palatal soft tissue thickness at point C (r ¼ 0.1128), labial bone thickness and palatal bone thickness at
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point C (r ¼ −0.03715), bone thickness and B-P thickness of alveolar crest at point C (r ¼ 0.22270), and were all significantly correlated (Tables 2 and 3). Scatter plots and regression equations were also created (Figs. 4–7). For further statistical analysis, the teeth were pooled into 3 groups according to their position related to A-Pog line as (1) normally positioned, (2) forwardly positioned, and (3) backwardly positioned using Down’s analysis. The mean and the SD of the thickness of labial soft tissue at point C was 1.51 (60.29) mm for normally inclined teeth, 1.087 (60.24) mm for forwardly inclined teeth, and 1.24 (60.67) mm for backwardly inclined teeth (Table 4). The mean and the SD of the thickness of labial bone at point C was 0.92 (60.25) mm for normally inclined teeth, 0.92 (60.26) mm for forwardly inclined teeth, and 0.827 (60.16) mm for backwardly inclined teeth (Table 4). There was no significant difference found between mean values of labial bone thickness with changing positions of the teeth (ie, P . 0.05) (Table 5). Thickness of palatal bone at point A of teeth showing different inclinations for normal versus proclined was significantly different (Table 5).
DISCUSSION CBCT has been regarded as a reliable technique for quantitative assessment of the thickness of labial bone in natural teeth with high precision of submillimeter accuracy for linear measurements.15,16,19–23 In addition, it offers better quality image at low radiation exposure when compared with conventional CT.24–26 It is a suitable noninvasive technique available for assessing the thickness of soft tissue and the underlying bone.27 The accuracy of CBCT in measuring soft tissue depth measurements has been demonstrated.28 Maxillary central incisors form an area of great esthetic significance and were therefore the focus of this study. Much consideration has been given to the thickness of the gingiva and its importance in implant dentistry.29 The thinner biotype is more prone to recession and loss of interdental papilla.30–33
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In a retrospective analysis of 42 singletooth implants placed in the esthetic zone, a significant change in crown height due to marginal tissue recession of approximately 1 mm was noted.34 Thin tissue biotypes showed slightly greater recession than thick tissue biotypes. Not only is the thin tissue biotype more prone to recession, but it is also more susceptible to poor esthetic outcome.30–32 Jung et al35 used photospectrometry to show that soft tissue thickness of greater than 2 mm is ideal to achieve a natural esthetic outcome without tissue discoloration from the underlying abutment. Evidence also suggests that thick soft tissue may be protective against crestal bone loss.36 Linkevicius et al reported that implants with greater than 2.5 mm of periimplant soft tissue thickness experienced a mean of 0.26 mm crestal bone loss compared with 1.45 mm of crestal bone loss seen at those sites with less than 2 mm of periimplant soft tissue thickness. Careful treatment planning is therefore needed for patients with thinner biotypes when considering immediate implant therapy. Soft tissue thickness has been measured using different methods over the years including periodontal probe,16 endodontic files,1,37 spiral CT,37 and others. Soft tissue CBCT is an accurate, convenient, and painless technique for obtaining a 3-dimensional overview of the soft tissue along with its supporting bone.13,37–40 Gingival tissue thickness has been measured at points ranging 1 to 3 mm apical in relation to the bone crest14 or gingival margin.1,41 Fu13 assessed the soft tissue thickness 2 mm apical to the bone crest with a caliper (0.5 mm; range, 0.1–1.2 mm) and compared it with the measurements obtained from the CBCT scans (0.57 mm; range, 0.2–1.86 mm) and found no significant difference among them. La Rocca1 measured the mean thickness of soft tissue on the labial aspect of the upper anterior teeth at a point 1 mm apical to the depth of the sulcus and measured it to be 1.10 mm (range, 0.1–2.50 mm). In this study, the mean thickness of the labial soft tissue was assessed using a CBCT at 3 different positions; 3 mm apical to CEJ (C), midroot (M), and apical root position
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(A) and was found to be 1.07 (60.28) mm, 0.987 (60.268) mm, and 1.240 (60.41) mm, respectively. These values are in agreement with those reported by these previous studies.13,37–40 Gingival contour is dictated by the contour of the underlying bone and the shape of the tooth.42 Labial bone thickness is also considered a crucial parameter for treatment planning immediate implant placement. Ferrus et al identified factors that influence ridge alterations at the buccal aspects of extraction sites after immediate implant placement. A series of measurements of the extraction sites were made immediate after implant placement and at reentry. The degree of horizontal gap fill and postextraction bone crest remodeling was more favorable in sites where labial bone thickness exceeds 1 mm.4 Teeth with thin or dehisced labial wall are at risk of midfacial gingival recession after immediate implant placement. This is especially true in patients that have a thin biotype. A recent study found that the thickness of labial crestal soft tissue around maxillary implants can be influenced by the underlying bone.27 Le and Borzabadi-Farahani28 found a correlation between labial crestal soft tissue thickness and underlying labial bone thickness, indicating that soft tissue thickness can be heavily influenced by the labial bone thickness. In other words, the thicker the bone, the thicker the crestal labial soft tissue around implants and vice versa. Labial bone thickness lower than 2 mm has been indicated for hard tissue bone augmentation to develop an esthetically pleasing soft tissue profile.9,10,43,44 The labial bone thickness of the central incisors have been reported with the highest percentage of thin walls among all the anterior teeth.21 The mean thicknesses of labial bone measured in this study at the specific positions are relatively higher than those reported by previous authors.1,14,21,30 Smaller sample size, different subject ethnicity, and cadaver measurements may account for these noted differences. Owing to the thickness and dense cortication, palatal mucosa with its supporting bone is considered to be a favorable foundation for the placement of an implant.21 In the present sample, palatal bone thickness
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IMPLANT DENTISTRY / VOLUME 0, NUMBER 0 2015 of the examined teeth presented with thick palatal bone [87.33% with thickness $1 mm (at point C)], whereas only 12.66% showed thin palatal bone [thickness ,1 mm (at point C)]. Our findings are in agreement with those of Kan et al,18 which reported the majority of maxillary anterior teeth are positioned against the labial cortical plate (approximately 81%), allowing a considerable amount of bone on the palatal aspect for immediate implant placement. Kan et al18 classified the relationships of the SRP of maxillary teeth to their alveolar housings using CBCT analysis. Their proposed classification of the SRP is Class I (root against labial cortex; incidence 81%), Class II (root centered in alveolar housing; incidence 6.5%), Class III (root against palatal cortex; incidence 0.7%), and Class IV (root against labial housing; incidence 11.7%). The authors proposed objective guidelines for planning immediate implant placements and provisionalization based on the classification of SRP: Class I SRPs being favorable, Class IV being contraindicated, and Class II and Class III SRPs being technique sensitive. The results of the bony dimensions determined in this study were in agreement with those of Braut et al22 and Hyunh-Ba et al.45 Braut et al22 used CBCT data to analyze the thickness of the labial bone wall in anterior teeth. The majority of the examined teeth exhibited a thin facial bone wall (,1 mm; 62.9%). A thick bone wall ($ 1 mm) was found in only 11.4% of all examined teeth. Huynh-Ba et al45 analyzed the thickness of labial bone walls of anterior teeth at extraction sites. Their results showed that a majority of anterior teeth (87%) had thickness less than 1 mm, whereas only 2.6% had thickness more than 2 mm. These measurements were manually made using calipers. In this study, 36.7% of patients had labial bone thickness $1 mm, whereas the majority of patients (63%) had labial bone thickness ,1 mm. A significant moderate correlation (r ¼ 0.496) was shown between the soft tissue thickness and the underlying bone thickness by Fu et al.13 They showed a small correlation (r ¼ 0.1128) between overlying soft tissue and bone at the
palatal aspect.15 The results of this study are not in agreement with the study of La Rocca et al1 who found no correlation between the crestal bone thickness and the thickness of the overlying gingiva. This difference between the results of the 2 studies could be attributed to the differences in the study protocols followed because the study of La Rocca1 used transgingival probing to measure gingival thickness rather than CBCT analysis. A positive correlation of the labial bone thickness to the labiopalatal bone width was noted in this study. Socket dimensions have been shown to influence wound healing, with more bone loss in the narrower sockets and those with thinner labial wall thickness.18,39 Although the thickness of the palatal cortical plate is greater compared with the labial cortical plate in the anterior maxilla,15 this finding may highlight that wider sockets tend to associate with thicker labial cortices and may indicate advantages in socket healing potential. In a controlled animal study on immediate implants, Vignoletti et al46 concluded socket dimensions influence wound healing of implants placed into fresh extraction sockets, with more bone loss in the narrower sockets. No study has reported the influence of the labiopalatal positioning of anterior teeth on the labial bone thickness. In this study, no differences in the thickness of the labial cortical bone between varying labiopalatal tooth positioning of the teeth were evident. However, proclined teeth (64%) had significantly lower thickness of palatal bone at the apex than normally positioned teeth (30%). This finding may have prognostic implications for immediate implant placement where the amount of palatal bone available for implant anchorage is critical. In a study examining the SRP of maxillary anterior teeth, Wang H et al47 concluded most teeth have their roots angled out in close proximity to the labial plate. They measured the inclination of teeth by describing the angle made by the tooth long axis against the alveolar ridge long axis. Similarly Kan et al18 reported that 81% of the teeth in their sample had the root in close proximity
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to the labial cortical plate. This study used Down’s analysis to determine the labiopalatal positioning of the teeth. The results of the studies by Hui-ming Wang et al, Kan et al,18 and this study further underline the need for proper diagnosis and especially radiographic analysis using CBCT before tooth extraction. This would help to determine the appropriate implant dimensions, angulations, and the need for auxiliary procedures such as bone augmentation, to achieve adequate hard tissue contours around the implant and ensure a predictable esthetic outcome. In immediate implant placement, teeth with proclined inclination may necessitate placement with a labial angulation or risk perforation of the apex. Implant angulation may dictate restoration design (screw-retained vs cement-retained) and has been shown to be correlated with soft tissue thickness. Le et al48 studied the association between crestal labial soft tissue thickness and buccolingual angulation of the implant. The buccolingual angulation was recorded as being cingulum, incisal, or labial based on the position of the screw access hole on provisional restorations. A significant association was observed between crestal labial soft tissue thickness and implant buccolingual angulation when implant labial bone thickness at crestal level was less than 2 mm (P , 0.01). They concluded that implants with labial angulations carry a higher risk of soft-tissue complications when the crestal implant labial bone thickness is less than 2 mm.
CONCLUSIONS Within the limitations of this study, it can be concluded that a significant correlation exists between the labial and palatal cortical bone thickness and the thickness of corresponding soft tissue. Similarly, there is a significant corelation between thickness of the labial bone and the labiopalatal thickness of the alveolar socket width. No relationship was observed between the thickness of the labial cortical bone and the labiopalatal inclination of the associated tooth. These findings have implications in treatment planning of immediate implant therapy.
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THREE-DIMENSIONAL EVALUATION
DISCLOSURE The authors claim to have no financial interest, either directly or indirectly, in the products or information listed in the article.
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