Phenotype Modification Therapy (PhMT) was the overall topic of the Best Evidence Consensus 2019. What does the term “phenotype” mean?
Dr. Kao: Phenotype means what you see, but it’s also based on genetic factors. Asians for example have shorter roots and a different crown-to-root ratio. Their tissues are overall thinner compared to Caucasians, and they have more bone dehiscenses. They have different phenotypes. Minor gum disease, bone loss or attachment loss may have a greater impact in these patients.
And “phenotype modification” then means to change a thin phenotype into a thicker one?
Dr. Kao: Yes. Because in case of implant placement or orthodontic treatment, patients with a thin phenotype, for example thin buccal bone or thin soft tissues, are more prone to developing gingival recessions. These patients will benefit if we change the conditions and modify their phenotype to achieve sustainable results.
Prof. Kornman: I agree. Phenotype Modification Therapy is about recognizing patients’ individual situations and helping them before problems occur. We see this as an important area to focus on for the future.
The starting point for the BEC is to determine where there is a true clinical need. If there is a need, how are clinicians managing those needs today? The BEC process produces summaries of evidence and clinical experiences that are currently available to help increase confidence in certain specific clinical applications. We are certainly broadening the ability of our clinicians to help more patients live well longer.
You discussed several indications, where PhMT could benefit patients. Which indications were these?
Dr. Kao: We focused on the tissues around teeth1, around implants2, in the context of orthodontic treatment3. The main questions were: When is it beneficial to thicken soft tissues, to create more keratinized tissue or to thicken the bone? For example, in the context of implant placement: Is there a benefi tin thickening the soft tissue in addition to augmenting the bone?
These three topics were discussed at the AAP Best Evidence Consensus 2019
One reason could be that the peri-implant mucosa is more vulnerable than the gingiva around a tooth. Is this the case?
Dr. Kao: Yes, the tissues around an implant are more susceptible to tissue damage or tissue loss than around teeth. There are no Sharpey’s fibers and cementum. The connective tissue contains fewer blood vessels and fi broblasts. Literature shows that the bony housing in the front area is very thin in most patients.1 With time and age, this is one of the most predictable areas for gum recession, even around teeth. With an implant the risk is even higher, independent of how well an implant has been placed. So, there are good reasons to better prepare the ridge before placing an implant.
What did the consensus group conclude with regards to soft tissue around implants?
Dr. Kao: Dr. Guo-Hao Lin and colleagues prepared a meta-analysis on the significance of surgically modify ing soft tissue phenotype around fi xed dental prostheses. One of the conclusions was that increasing soft tissue thickness and the amount of keratinized tissue may be beneficial for providing more favorable peri-implant tissue health.1 And in the consensus statement it is stated that phenotype modification therapy around fixed dental prostheses can improve esthetics, e.g., create a more harmonious soft tissue architecture and decrease show-through of restorations, abutments and implants, and that it also improves comfort, hygiene and maintenance.4
The third topic was phenotype modification in the context of orthodontics. Why is there a need to modify?
Dr. Kao: Literature shows that 20-35% of patients develop facial gingival recession two to fi ve years after orthodontic treatment. 3 This is dependent on the phenotype, but also on the cranial and facial arrangement. If bone and soft tissue are thin, recessions will develop very soon after orthodontic treatment. If the bone is thin, but the tissue is thick, recessions will be visible only years later.
How is phenotype modification done in this context? Which method was discussed in the systematic review and during the meeting?
Dr. Kao: For most orthodontic treatments, there is usually adequate volume of bone and soft tissue. Where there are concerns for gingival recession, clinicians can proactively “thicken” the gingiva with grafting procedures. When the orthodontic treatment planning and analysis indicate the required orthodontic movements would be beyond the bony and soft tissue envelop, surgically facilitated orthodontic therapy, SFOT, periodontally accelerated osteogenic orthodontics, PAOO, and corticotomy-assisted orthodontic therapy, CAOT , are the most common procedures. They involve corticotomy surgery and decortication of the dentoalveolar complex with or without particulate bone grafting. The goal is to enable faster tooth movement and widen the jaw bone. Chin-Wei Wang et al. focused on these techniques in their meta-analysis on the question: Is periodontal phenotypic modifi cation therapy benefi cial for patients receiving orthodontic treatment?3
What do they conclude from the literature?
Dr. Kao: Treatments such as SFOT, PAOO and CAOT may shorten treatment time and accelerate tooth movement. But they also supported an increased scope of tooth movement. They achieved thicker hard tissue dimensions and reduced dehiscence defects. And finally, they enhanced post-orthodontic stability of the mandibular anterior teeth—a typical area with very thin bony envelops—and had a potential to reduce the level of orthodontic relapse over a 10-year follow-up period.4
Few studies have been published in this field so far. What was the experience in the consensus group?
Dr. Kao: Three of us have treated a total of 1,500 cases with these techniques. So, we shared our documentation and notes. What are the materials we used? What was the sequence of events? What were the watch-out points, the diagnostic tools we needed? What have we tried that did not work? In about 90 percent of content the three of us came up with the same strategy. On the other 10% we disagreed. But that’s okay. It shows us where there is some clinical flexibility.
Did the consensus group conclude that PhMT is beneficial in the context of orthodontic treatment?
Dr. Kao: Yes, the consensus group concluded that Phenotype Modificaing tion Therapy should be pursued prior to orthodontic treatment in patients with thin phenotype when the necessary orthodontic tooth movement would compromise the bony housing.4
And there will be situations in which both bone and soft tissue augmentation are necessary.
Are orthodontists aware of these developments?
Dr. Kao: Yes, orthodontists nowadays have computer modelling systems based on CBCT data, where they plan how much they are going to move the teeth and what this will mean for the bony
housing. So, we can together plan how to protect the envelope and prevent longterm complications with an interceptive thickening of the gum and bone.4
Is this interdisciplinary work also a source of error?
Dr. Kao: Collaboration is certainly beneficial and the way to go for the future. Dr. George Mandelaris is currently preparto Modificaing a paper on how this interdisciplinary work between orthodontists, periodontists and possibly also oral surgeons can be organized most efficiently.
Is there also a broader collaboration planned between periodontal and orthodontic societies?
Dr. Kao: The AAP and the American Orthodontic Association are both very interested in collaboration. We have a joint conference set for 2021, and we are currently thinking about teaming
up for an e-learning platform. This will definitely help to disseminate this kind of information to a broader population.