Estimation of soft- and hard-tissue thickness at implant sites.

INTRODUCTION: Anchorage control is a critical consideration when planning treatment for patients with dental and skeletal malocclusions. To obtain sufficient stability of implants, the thickness of the soft tissue and the cortical-bone in the placement site must be considered; so as to provide an anatomical map in order to assist the clinician in the placement of the implants.
OBJECTIVE: The aim of this study is to evaluate the thickness of soft- and hard-tissue.
MATERIALS AND METHODS: To measure soft tissue and cortical-bone thicknesses, 12 maxillary cross-sectional specimens were obtained from the cadavers, which were made at three maxillary mid-palatal suture areas: The interdental area between the first and second premolars (Group 1), the second premolar and the first molar (Group 2), and the first and second molars (Group 3). Sectioned samples along with reference rulers were digitally scanned. Scanned images were calibrated and measurements were made with image-analysis software. We measured the thickness of soft and hard-tissues at five sectional areas parallel to the buccopalatal cementoenamel junction (CEJ) line at 2-mm intervals and also thickness of soft tissue at the six landmarks including the incisive papilla (IP) on the palate. The line perpendicular to the occlusal plane was made and measurement was taken at 4-mm intervals from the closest five points to IP.
RESULTS: (1) Group 1:6 mm from CEJ in buccal side and 2 mm from CEJ in palatal side. (2) Group 2:8 mm from CEJ in buccal side and 4 mm from CEJ in palatal side. (3) Group 3:8 mm from CEJ in buccal side and 8 mm from CEJ in palatal side.
CONCLUSIONS: The best site for placement of implant is with thinnest soft tissue and thickest hard tissue, which is in the middle from CEJ in buccal side and closest from CEJ in palatal side in Group 1 and faraway from CEJ in buccal side and closest from CEJ in palatal side in Group 2 and faraway from CEJ in buccal side and faraway from CEJ in palatal side in Group 3.

Anchorage control is a critical consideration when planning treatment for patients with dental and skeletal malocclusions. The use of endosseous implants for absolute orthodontic anchorage has been the focus of many studies. Gainsforth and Higley,[1] placed vitallium screws in the jaw bones of dogs in 1945. Roberts et al.,[2] used titanium screws as orthodontic implants in dog mandibles. Turley et al.,[3] Shapiro and Kokich,[4] and Schweizer et al.,[5] in their study have reported the use of endosseous implants in orthodontics, and Block and Hoffman,[6] used onplants. When skeletal anchorage is stable, biocompatible, and free from site specificity, it can be used effectively without patient compliance. Several systems such as miniplates, miniscrews, and microscrews can satisfy these criteria, which can be placed in different positions: the inferior ridge of the piriform aperture, the maxillary alveolar bone, the infrazygomatic crest, the palatal alveolar bone, the maxillary tuberosity, the hard palate, and the mid-palatal suture area.

Potential complications with miniscrews in orthodontics are soft tissue irritation at the site of insertion, risk of infection, and premature loosening of the screw. The stability of implant increases with the quality of the bone.

For this reason, it is very important to know the thickness of soft and hard-tissue at implant placement sites. Several studies have been conducted on the sites of implant placement using different methods.

In this study, buccopalatal cross-sectional samples from interdental areas of the posterior teeth and mid-palatal suture areas of cadavers were evaluated. This information will assist the clinician in placement of orthodontic implants.

Materials and Methods

To measure the soft and hard-tissue thickness of the areas mostly interested by miniscrews insertion, such as buccopalatal interdental bone and maxillary mid-palatal suture, 12 cadavers were selected with all maxillary premolars and molars still intact. To measure the incisal areas, 12 cadavers with intact maxillary occlusal planes (at least incisors and first molars remaining) were selected. Cross-sectional specimens were made at three areas: The interdental area between the first and second premolars (Group 1), the interdental area between the second premolar and the first molar (Group 2), and the interdental area between the first and second molars (Group 3). The thickness of soft and hard-tissues were measured at five sectional areas parallel to the buccopalatal cementoenamel junction (CEJ) line at 2 mm intervals [Figure 1] for each group.

Figure 1

Measurement of the thickness of the soft- and hard-tissues on the buccal side and palatal side of the sectioned specimen on parallel lines drawn 2, 4, 6, 8, and 10 mm, from cementoenamel junction

Outer point of the buccal side of the sectioned specimen on a parallel line drawn 2 mm superior to the CEJ line

Outer point of the buccal side of the sectioned specimen on a parallel line drawn 4 mm superior to the CEJ line

Outer point of the buccal side of the sectioned specimen on a parallel line drawn 6 mm superior to the CEJ line

Outer point of the buccal side of the sectioned specimen on a parallel line drawn 8 mm superior to the CEJ line

Outer point of the buccal side of the sectioned specimen on a parallel line drawn 10 mm superior to the CEJ line

Outer point of the palatal side of the sectioned specimen on a parallel line drawn 2 mm superior to the CEJ line

Outer point of the palatal side of the sectioned specimen on a parallel line drawn 4 mm superior to the CEJ line

Outer point of the palatal side of the sectioned specimen on a parallel line drawn 6 mm superior to the CEJ line

Outer point of the palatal side of the sectioned specimen on a parallel line drawn 8 mm superior to the CEJ line

Outer point of the palatal side of the sectioned specimen on a parallel line drawn 10 mm superior to the CEJ line.

The thickness of soft tissue were also measured at 6 landmarks mentioned below, including the incisive papilla (IP) on the palate, which meet with the line perpendicular to the occlusal plane and passing through closest five points from the IP at 4-mm intervals [Figure 2].

Figure 2

Measurement of the thickness of the soft tissue at six points on the palate of the sectioned specimen, which were drawn at 4-mm intervals from the incisive papilla and perpendicular to the occlusal plane

Outer point of the sectioned specimen at the IP of the palate

Outer point of the sectioned specimen contacted with a parallel line drawn 4 mm posterior to the line passing through IP perpendicular to the occlusal plane

Outer point of the sectioned specimen contacted with a parallel line drawn 8 mm posterior to the line passing through IP perpendicular to the occlusal plane

Outer point of the sectioned specimen contacted with a parallel line drawn 12 mm posterior to the line passing through IP perpendicular to the occlusal plane

Outer point of the sectioned specimen contacted with a parallel line drawn 16 mm posterior to the line passing through IP perpendicular to the occlusal plane

Outer point of the sectioned specimen contacted with a parallel line drawn 20 mm posterior to the line passing through IP perpendicular to the occlusal plane.

The specimens were sectioned with a jewelers saw. Sectioned samples along with reference rulers were digitally scanned (Umax flatbed scanner [UMAX. 48 Bit True Color Depth]). Scanned images were calibrated and measurements were made with image-analysis software (Autocad 2004 [Autocad is the Industry Software that Sets the Standard in Cad Design.).

Results

Group 1

The buccal soft tissue is thickest at 10 mm (1.73742) and thinnest at 4 mm (1.50317) from the CEJ

The palatal soft tissue is thickest at 8 mm (3.14033) and thinnest at 2 mm (2.44308) from the CEJ

The buccal hard tissue is thickest at 10 mm (1.43733) and thinnest at 2 mm (1.25350) from the CEJ

The palatal hard tissue is thickest at 2 mm (1.55575) and thinnest at 10 mm (1.36567) from the CEJ.

Buccal side

The hard tissue is thickest at 10 mm (1.43733) and soft tissue at 10 mm (1.73742) from the CEJ

The soft tissue is the thinnest at 4 mm (1.50317) and hard tissue at 4 mm (1.28233) from the CEJ

Average thickness of soft tissue at 6 mm is (1.62042) and hard tissue at 6 mm is (1.39650) from CEJ.

Palatal side

The hard tissue is thickest at 2 mm (1.55575) and soft tissue at 2 mm (2.44308) from the CEJ

The soft tissue is the thinnest at 2 mm (2.44308) and hard tissue at 2 mm (1.55575) from the CEJ

Average thickness of soft tissue at 6 mm is (3.00008) and hard tissue at 6 mm is (1.47767) from CEJ [Table 1].

Table 1

Comparison of measurements (in mm) of sectioned specimens in Group 1

Group 2

The buccal soft tissue is thickest at 10 mm (2.04292) and thinnest at 4 mm (1.85242) from the CEJ

The palatal soft tissue is thickest at 10 mm (3.37350) and thinnest at 2 mm (2.75925) from the CEJ

The buccal hard tissue is thickest at 8 mm (1.58342) and thinnest at 6 mm (1.49608) from the CEJ

The palatal hard tissue is thickest at 4 mm (1.70542) and thinnest at 2 mm (1.53958) from the CEJ.

The hard tissue is thickest at 8 mm (1.58342) and soft tissue at 8 mm (1.86558) from the CEJ

The soft tissue is the thinnest at 4 mm (1.85242) and hard tissue at 4 mm (1.54075) from the CEJ

Average thickness of soft tissue at 6 mm is (1.96000) and hard tissue at 2 mm is (1.51608) from CEJ.

The hard tissue is thickest at 4 mm (1.70542) and soft tissue at 4 mm (2.84675) from the CEJ

The soft tissue is thinnest at 2 mm (2.75925) and hard tissue at 2 mm (1.53958) from the CEJ

Average thickness of soft tissue at 6 mm is (3.12100) and hard tissue at 6 mm is (1.67742) from CEJ [Table 2].

Table 2

Comparison of measurements (in mm) of sectioned specimens in Group 2

Group 3

The buccal soft tissue is thickest at 2 mm (2.0055) and thinnest at 6 mm (1.5177) from the CEJ

The palatal soft tissue is thickest at 10 mm (3.05708) and thinnest at 6 mm (2.48025) from the CEJ

The buccal hard tissue is thickest at 8 mm (1.61108) and thinnest at 2 mm (1.53433) from the CEJ

The palatal hard tissue is thickest at 2 mm (1.5494) and thinnest at 6 mm (1.3058) from the CEJ.

The hard tissue is thickest at 8 mm (1.61108) and soft tissue at 8 mm (1.6779) from the CEJ

The soft tissue is the thinnest at 6 mm (1.5177) and hard tissue at 6 mm (1.54778) from the CEJ

Average thickness of soft tissue at 4 mm is (1.7431) and hard tissue at 6 mm is (1.54778) from the CEJ [Table 3].

Table 3

Comparison of measurements (in mm) of sectioned specimens in Group 3

The hard tissue is thickest at 2 mm (1.5494) and soft tissue at 2 mm (2.69117) from the CEJ

The soft tissue is thinnest at 6 mm (2.48025) and hard tissue at 6 mm (1.3058) from the CEJ

Average thickness of soft tissue at 8 mm is (2.66167) and hard tissue at 10 mm is (1.4190) from CEJ. Measurement of thickness of soft tissue at 6 landmarks (on the IP and at 4-mm intervals from the IP) showed that the soft tissue is thickest at 12 mm (1.92079) and thinnest at 20 mm (1.65256) from IP [Table 4].

Table 4

Measurements (in mm) in sectioned specimens at mid-palatal suture area

Discussion

Orthodontic anchorage is the ability to limit the movement of some teeth while achieving the desired movement of other teeth. For this reason, orthodontists have been searching for the most appropriate methods and appliances to achieve this goal. The age old problem in orthodontics is essentially the application of Newton's third law of motion: for every action, there is an equal and opposite reaction. Orthodontists often have inadequate mechanical systems with which to control anchorage, which leads to a loss of anchorage in the reactive unit and thus incomplete correction of intra- and inter-arch alignment problems. Moreover, in an attempt to overcome these limitations, clinicians often incorporate bulky acrylic appliances or extraoral appliances, which when combined with the ever challenging problem of uncooperative patients, are often a futile attempt at best. Hence, to overcome these problems microimplants had been introduced. The stability of these microimplants depends on the placement site, thickness of the bone and soft tissue. Thinnest soft tissue and thickest bone area is ideal for implant placement. Different methods have been used to measure the thickness.

Poggio et al.,[7] conducted a study using the volumetric tomographic images of 25 maxillae and 25 mandibles taken with the NewTom System T (Newtom is a Radiographic Methoid Used in Other Study by a Different Authors Mentioned in my Reference). In the maxilla, the greatest amount of mesiodistal bone was on the palatal side between the second premolar and the first molar. The lowest amount of bone was in the tuberosity. The greatest thickness of bone in the buccopalatal dimension was between the first and second molars, whereas the lowest was found in the tuberosity. Schnelle et al.,[8] conducted a study using panoramic radiographs. Bone stock for placement of screws was found to exist primarily in the maxillary (mesial to first molars) and mandibular (mesial and distal to first molars) posterior regions. Typically, adequate bone was located more than halfway down the root length, which is likely to be covered by movable mucosa. King et al.,[9] conducted a study using Cone beam computed tomographic scans. Vertical bone depth was measured at nine unilateral locations in the PP of each subject. They found a significant variability in the bone thickness among locations and among subjects. Male subjects had significantly greater mean bone thickness in six of the nine locations measured, showing a mean of 1.22 mm more vertical bone than females showed at these locations. Costa et al.,[10] conducted a study using volumetric computed tomography for bone depth and needle with a rubber stop for mucosal depth. The results indicate that bone thickness will allow temporary anchorage devices (TADs) 10 mm in length only in the symphysis, retromolar, and palatal premaxillary regions. TADs 6-8 mm in length can be placed in the incisive fossa, in the upper and lower canine fossae. A direct study was conducted by Kim et al.,[11] using cadavers. Their results indicated that in all groups, buccal soft tissues were thickest closest to and far away from the CEJ and thinnest in the middle. Palatal soft tissue thickness increased gradually from the CEJ toward the apical region in all groups. Buccal cortical-bone was thickest closest and far away from the CEJ and thinnest in the middle in Groups 1 and 2. In Group 3, unlike Groups 1 and 2, thickness was greatest at the middle. Palatal cortical-bone thickness was greatest 6 mm apical to the CEJ in Groups 1 and 3, and 2 mm apical to the CEJ in Group 2. Along the mid-palatal suture, palatal mucosa remained uniformly 1 mm thick posterior to the IP. However, in our study, we found different findings with regard to hard- and soft-tissue thickness at the various sites, and these differences may be attributed to racial differences between the two populations.

According to our study, the best site for placement of implant considering the thinnest soft tissue and thickest hard tissue is

Group 1: 6 mm from CEJ in buccal side and 2 mm from CEJ in palatal side

Group 2: 8 mm from CEJ in buccal side and 4 mm from CEJ in palatal side

Group 3: 8 mm from CEJ in buccal side and 8 mm from CEJ in palatal side.

Conclusion

Implant passes through the soft tissue and bone, and therefore the thickness of the soft tissue and cortical-bone at the surgical site are critical factors for success of the implant.

In terms of soft- and hard-tissues, thin soft tissue is more advantageous because the likelihood of inflammation is lower. The stability of miniscrew implants depends on the quality and quantity of the cortical-bone. The main objective of an orthodontic screw is to gain maximum retention by placing the screw in an area with the thinnest soft tissue and the thickest cortical-bone. Surgical placement of miniscrew implants for orthodontic anchorage in the maxillary molar region requires consideration of the placement site and angle based on anatomical characteristics. The best site for placement of implant is with thinnest soft tissue and thickest hard tissue, which is in the middle from CEJ in buccal side and closest from CEJ in palatal side in Group 1 and faraway from CEJ in buccal side and closest from CEJ in palatal side in Group 2 and faraway from CEJ in buccal side and faraway from CEJ in palatal side in Group 3.