The Orthodontics Professors
the latest in contemporary & evidence-based orthodontics
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By WILLIAM R. PROFFIT, DDS, PhD
At the Case-Western Reserve Dept. of Orthodontics, cone-beam CT images were used to evaluate the shape and location of the mandibular buccal shelf below the molars in white (European descent) patients as possible sites for skeletal anchorage. The cortical bone at this location has been used by orthodontists working with Asian patients, and excellent success (93%) with bone screws there has been presented.(1)
The objectives in this study were to:
Cone-beam CT images for 30 adolescent white patients who had CBCT’s as part of their diagnostic evaluation were used to obtain a detailed view of the mandible in the first and second molar region (Figures 1 and 2). Cortical shelf thickness and the width of the buccal shelf bone were measured at the distal of the first molar and at the mesial and distal of the second molar. Then, the position of the mandibular nerve at these locations was established and its distance from a visual screw placed vertically was measured.
The data showed that cortical bone thickness was greatest below the disto-buccal cusp of the second molar (8.1 + 1.3 mm), and that although this also was the point of greatest proximity to the mandibular neurovascular bundle (5.5 + 1.6 mm), this amount of clearance would provide adequate safety. Based on these measures, the authors recommended a 10 mm anchorage screw with a 5 mm screw head extension in this location. Locations below the first molar, not the second molar, have been recommended for Asian patients. Whether this recommendation is related to a clinically significant difference in mandibular anatomy between the two racial groups is not known.
WHAT THE PROFESSOR THINKS
Alveolar bone screws have proved to be acceptable as anchorage for minor tooth movement but disappointing as anchorage for major tooth movement. For example, two clinical trials of a Nance lingual arch vs. alveolar bone screws for maxillary incisor retraction found no advantage with the bone screws—the two anchorage types were equally ineffective.
It has become clear that cortical bone of the palate does offer almost perfect anchorage for intrusion, retraction and protraction of maxillary dental segments or the whole maxillary dental arch(2), and palatal anchorage now is preferred.
Is the cortical bone of the buccal shelf of the mandible equally superior to mandibular alveolar bone? The existing data from Asian patients certainly indicates that for them, it is. This report for white adolescents shows that:
Based on these points, it is reasonable to expect bone anchors in the buccal shelf to be more stable than bone screws in the mandibular alveolus. However, there are no studies yet with high-quality outcome data for white patients to be certain that this is correct.
Should American clinicians now start using bone screws into the mandibular buccal shelf for white as well as Asian patients when movement of mandibular segments or the whole mandibular arch is needed?
On balance, I would say yes.
Article Reviewed: Elshebiny T, Palomo JM, Baumgartel S. Anatomic assessment of the mandibular buccal shelf for miniscrew insertion in white patients. Am J Orthod Dentofac Orthop 2018; 153:505-511 (Apr).
By TATE H. JACKSON and TUNG T. NGUYEN
The use of skeletal anchorage for true orthopedic effect in growing Class III patients has now been well documented. Might the same strategy, using skeletal plates in both the maxilla and mandible, be effective to modify mandibular growth in Class II patients? A recent publication provides some initial evidence that it might.
28 growing children (age 11.83 +/- 0.83 years) with an ANB of 5 or greater, an OJ of 5mm or greater, and a ½ cusp Class II buccal relationship or greater were all treated with a standardized protocol by a single orthodontist.
Each patient first went through alignment with fixed appliances for an average of 7 months before miniplates were placed in the anterior maxilla (2 just distal to the lateral incisors) and posterior mandible (2 just distal to the first molar).
A cephalometric radiograph was taken after alignment and just before orthopedic traction began. Patients were instructed to wear intermaxillary elastics to the bone plates full-time beginning 20 days after plate fixation. The plates were ultimately loaded with ~450g on each side, and orthopedic traction was carried out for an average of 9 months. Another cephalometric radiograph was taken once each patient had a Class I molar and canine relationship and 1-3mm of OJ.
Cephalometric superimposition of the pre-orthopedic and post-orthopedic radiographs were compared to non-treated Class II controls from another recent study matched based on age, race, observational period, gender, and skeletal maturity.
Compared to controls, patients with Class II bone plates showed a significant:
WHAT THE PROFESSORS THINK
This study represents a nice initial approach to a topic for which randomized controlled data might be very difficult to obtain. The use of cephalometric radiographs following alignment and then immediately after orthopedic traction was a clever way to help account for potentially confounding tooth movement as a part of Class II correction.
Using a well-matched control group of untreated Class II patients from a cohort who were apparently followed recently strengthens the data – despite the fact that 2D cephalometric analysis has limitations.
It is key to note that the orthopedic effects reported (most importantly, mandibular elongation/forward-positioning) are not only larger than those described in meta-analyses with the use of more traditional appliances such as a Herbst or Twin-Block, but also that the 95%CI range is small (3.15-4.51).
Of further clinical importance are the rotational mandibular changes and the overall combination of ANB and OJ reduction, with an accompanying increase in OB and uprighting of the incisors. Together, these changes suggest an absence of the dentoalveolar side-effects seen with functional appliances.
What’s the bottom line for clinicians?
Bone anchors, not surprisingly, show great promise for true orthopedic correction of Class II skeletal relationships, through a combination of elongation/forward-positioning of the mandible, as well as maxillary restraint.
The use of skeletal plates for growth modification in Class II patients should be considered when:
Article Reviewed: Al-Dumanini et. al. A novel approach for treatment of skeletal Class II malocclusion: Miniplates-based skeletal anchorage. Am J Orthod Dentofac Orthop 153:239-47. 2018
BY WILLIAM R. PROFFIT, DDS, PHD
This study at the University of Melbourne, Australia, provides new data for the prevalence of enamel damage from debonding brackets, and relates such damage to the type of bracket, the type of adhesive, and the surface preparation of the enamel for bonding. Four groups of brackets and bonding techniques were examined. All brackets were GAC Innovation – either the metal “R” version or the ceramic “C” version. All brackets were bonded and removed in the setting of 5 private orthodontic practices. 437 total brackets from anterior teeth were analyzed.
The four in-vivo bracket and bonding protocol combinations were:
Debonding was accomplished for metal brackets with a debonding instrument (444-761 bracket lifter from Unitek) and for ceramic brackets with a debonding plier. Only maxillary canine to canine brackets were collected. The back of each bracket was visualized with scanning electron microscopy at 60 x magnification. An elemental map was made using dispersive x-ray spectrometry to detect calcium, phosphorus, aluminum, and silicon. Calcium and Phosphorus together indicated the presence of enamel that had sheared from the tooth. Areas of bonding material and enamel were mapped, the amount of bonding material was categorized, and bracket fracture was tabulated.
WHAT THE PROFESSOR THINKS
This is a particularly interesting study because it analyzes data from patients treated across several orthodontics clinics, rather than just from laboratory testing. Despite some limitations, clinical orthodontists can use the following points to help inform their practice:
Article Reviewed: Cochrane NJ, Lo TWG, Adams GG, Schneider PM. Quantitative analysis of enamel on debonded orthodontic brackets. Am J Orthod Dentofac Orthop 152:312-319, 2017.
Lessons Learned from 75 BAMP Cases – Part III of Our Series on Management of Class III Malocclusion using Bone Anchors
BY TUNG T. NGUYEN, DMD, MS
In two previous posts (BAMP Part I and BAMP Part II), we have:
The purpose of this post is to share practical information learned from our clinical care of patients. Failures are rarely discussed at meeting or in publications, yet we often learn more from our failures than from our successes. It is these failures that keep us humble and allows us to grow as clinicians.
The following article will highlight some of the potential complications encountered in the BAMP treatment and summarize our current philosophy on the use of BAMP.
Expect some failures
When we started using the BAMP protocol in 2005, our 6-month plate failure rate was 30-35%. The maxillary plates tended to fail more than the mandibular plates, primarily due to bone thickness and quality. With surgical refinements such as the use of pilot holes in the maxilla, the use of the Y-shape plates, localized CBCT to assess infrazygomatic crest bone thickness, and in some cases delaying treatment for a year or more, our plate failure rate has decreased to 10-15%.
Our first instinct upon encountering a loose plate is to send the patient back to the surgeon and have it replaced. While experience has shown that replaced plates tend to be more stable due to callus formation at the surgical site, re-operating carries an additional financial cost, as well as psychological anxiety to the patients and doubt from the parents that the procedure might not work. If the plate is loose at 4 weeks post-op, test it by taking a ligature director or scaler and pushing on the plate in a distal direction. Our experience has shown that plates with up to 2mm of mobility have a chance of healing. Load these plates with ¾” 2oz elastics. The light forces will help promote boney remodeling and healing around the surgical site. If the patient cannot tolerate the light elastics, bond a button to the closest tooth and secure the anchor to the button with a ligature tie and recall in 6-8 weeks. This ligature helps to limit the mobility of the loose plate and allows the site to heal. Typically, the mobility of the plate will decrease, and you can start traction force with a ¼” 2oz elastic and progress to stronger elastics at 6-week intervals. Bone plates tend to fail more under the following conditions:
we often have the mindset that if 250g of force is good for orthopedic traction, then 500g is better. After all, reverse pull face masks are often loaded with 500-800g of force. The reality is that heavy forces are often detrimental with BAMP cases. The plates are designed to flex a little to adapt to shape changes that occur with growth of the zygoma and maxilla – and therefore the plates can only resist 400-500 of force. We have seen plate breakage when they are loaded with 500g or more. Orthopedic traction is not correlated most closely to the magnitude of the force, but rather to continuous force application. Based on our experience, we can obtain effective orthopedic maxillary protraction with only 250g of force connecting two bone plates (i.e. 250g of force per side).
Retain until cessation of growth
When we started the BAMP protocol in 2005, we would remove the plates after 1 year of treatment or when adequate positive overjet was obtained. The rational for removal at this time was that bone would occasionally grow over the head of the screws making removal difficult. However, we neglected an important concept. Class III mandibular prognathic patients tend to have mandibular growth into late adolescence.1 Our current treatment protocol is to overcorrect to 3-4mm overjet. Patients are instructed to wear 250g elastics (2 x ¼” 4oz on each side) elastics at night and are recalled at 6-month intervals. If the overjet is decreasing, patients are instructed to wear elastics full time. In the rare instances that overjet increases, patients are instructed to only wear elastics every other night or decrease the force level to 125g (¼” 4oz). The plates are then removed at 18 year of age in conjunction with 3rd molar extractions to minimize the amount of surgery.
Applications of BAMP
Craniofacial cleft patients often have a Class III skeletal malocclusion. Recent studies have shown that BAMP is effective for protracting the maxilla and restraining mandibular growth in these patients.2-3 While effective maxillary protraction decreases after the age of the 14, our long-term study shows BAMP is still effective at restraining mandibular growth into late adolescence. One of our recent applications is using BAMP in older patients (>14 years of age) to reduce the severity of the surgical movement or reduce the need for 2-jaw surgery.
Our Treatment Philosophy for Class III patients
When Class III malocclusion is detected early, Reverse Pull Headgear (RPHG) has been shown to be effective at reducing the need for orthognathic surgery.4 After 10 years of age, the effects of RPHG are primarily dentoalveolar with a higher relapse rate.5 From age 11-14, BAMP has been shown to be effective at protracting the maxilla and restraining mandibular growth.6-7 After 15 years of age, orthognathic surgery is the treatment of choice, especially if the severity of the malocclusion is large. BAMP can be used to reduce the serverity of the malocclusion and reduce the amount of surgical movement. To Summarize:
Tate H. Jackson, DDS, MS