Newsletter

Building a Healthy Foundation for Dental Implants

Our article topic in this issue is achieving dental implant stability through guided bone regeneration. I wanted to take a look at the historical perspective of ‘where we've been’ and share some updates on where we are today. I hope you find this article informative and helpful as you work with your patients.

Today's dental implants are the recommendation of choice for a healthy patient with one or more missing teeth. Over the last 20 years, changes in the design and composition of the dental implant (surface, type, platform, coating), have decreased healing times and broadened restorative options. The expanding application and understanding of bone regeneration procedures continues to make implant restorations feasible for most replacement scenarios. (1)

Prosthodontist Dr. Marco Brindis presented ‘A Hopeless Tooth is Not a Useless Tooth’ at our October 26th RRSC meeting.

Osseointegration as the Goal

The road to successful osseointegration of dental implants is based on a series of small decisions. While we all strive to ‘begin with the end in mind’ the analysis, planning and patient collaboration in implant dentistry is a thoughtful process from the moment the decision is made to extract a tooth. (2)

How much bone do we need?

Implant site assessment is based on several interdependent factors; at the top of the list are bone height/width and the necessary implant length/diameter and crown-to-implant ratio for restorative success. (3)

• Generally, a minimum implant length (and bone height) needed to achieve a favorable outcome is 8-10 mm, with a recommended 2mm margin from landmarks such as the mandibular canal, etc. (3)
• Bone width is defined as the “distance between the buccal and lingual plates, measured at the crest”. (3)

Increasing the diameter of the implant reduces stress on the crestal bone; with that, each 1mm increase in implant diameter expands the necessary surface area by 20-30%. (3) Often bone width presents as the greater challenge over bone height in implant placement.

With implant selection, an oversized implant can impede blood flow and inhibit bone growth (as revealed by studies surrounding peri-implantitis in larger implants). (4) Balancing all the necessary criteria to accomplish osseointegration is key.

Guided Bone Regeneration Materials

The regenerative functions that bone grafting materials serve are 1) to provide a framework for continued growth (osteoconduction) or 2) to stimulate osteoblast cell growth (osteoinduction).

Most dental bone graft materials are bioresorbable and do not normally cause an antigen-antibody reaction. (5) In a 2015 survey of 100 patients on the use of bone grafts in dental treatments, Fernandez et al. reported that the highest rates of patient refusal occurred with allograft and xenograft. (6) The primary reason for rejection were concerns over disease transmission. The highest acceptance occurred with autogenous grafts, followed by alloplastic grafts. (5) In my practice we find that patients are generally accepting of allograft materials.

The term ‘guided bone regeneration’ (GBR) infers the use of a barrier membrane to assist with holding the graft in place, or, to help stabilize a blood clot. (3,7)

Resorbable membranes are collagen-based and are often used to assist in clinical management of tissue or grafting materials.(8) Nonresorbable membranes are available, however they do require a second surgery to remove them. Both have been found to be equally effective. (8)

Our February 8th RRSC meeting featured hands-on instruction by Dr. Matthew Nejad ‘Advanced Adhesion Minimally Invasive Dentistry’

Dental Implant Stability

In 2017, Tettamanti et. al. cited primary implant stability as the main determinant of successful osseointegration. Bone quality/quantity and load, in addition to other health, tissue condition and technique factors influence primary implant stability at the time of placement. (9)

Implants Immediately after Extraction and Immediate Load Implants
Generally, immediate implant placement is more likely considered in anterior cases, stemming from the patient's esthetic concerns and the clinician's desire for clinical control of healing esthetics and prosthesis support.

Immediate implant placement is a popular and constantly evolving area of study. Current research is supportive of immediate implant placement at the time of extraction. One mention in the literature is a controlled study by Sabir et. al., in which 12 patients age 20-50 showed a 100% success rate of implant survival (all in anterior sites) at 30 months post-placement. (10)

Immediate load implants require careful case selection as they are at a higher risk of failure and complications than delayed implants. (9) Beyond esthetics, there is motivation for further research and development, as evidence supports that immediate placement of dental implants can assist with preservation of alveolar bone. (10)

All-on-Four and Full Arch Implant Restorations

All-on-four and full-arch implant restorations are also a growing area of practice that has tremendous patient appeal.

The documented success of short/long implants and angling techniques to avoid anatomical structures (sinus, inferior alveolar canal, etc.) has pushed full-arch rehabilitation for the edentulous patient to the forefront of dentistry. And, as we know, the results can be life changing for the long-term denture patient. (11)

Bone Graft Procedures

Socket Grafting
We have all been there. A patient has a painful toothache in a non-restorable tooth. While it may not be the ideal time to introduce the concept of a bone graft and dental implant, we know that making the case for the bone graft is important while the opportunity exists.

Sometimes, however, the graft itself presents a challenge, especially when the level of horizontal and/or vertical bone loss is substantial. The question of ‘now’ vs. ‘later’ is a good one. After a tooth is extracted, the body's healing processes go to work. The healing cycle, from 1) blood clot, 2) granulation tissue, 3) collagen to 4) initial bone formation generally takes about 4-6 weeks. The epithelium stays active throughout this process and finishes the job to cover the extraction site. (8)

There are restorative challenges inherit to the natural healing process:

• Bone resorption is inevitable due to the loss of normal mechanical bone strain. (12)
• Agarwal et. al. reports that “the rate of post-extraction bone loss is rapid in the first 6 months, followed by gradual modeling and remodeling of the remaining bone with approximately 40% of the alveolar height and 60% of alveolar width lost in the first 6 months”. (13)
• Simultaneous epithelium growth can actually impede bone regeneration as it fills the open space. (12)
• The physiological healing response to tooth extraction does not necessarily create an esthetically pleasing or stable site for a dental implant, especially in the esthetic region. (13,15)
• Bone loss or bone defects can occur for a wide variety of reasons, including: periodontal disease, systemic medical illness or medications, bruxism/clenching and issues with occlusion, as well as genetics. (5) Histology alone adds a wide range of healing considerations.

Clearly, the answer to ‘graft or not to graft’ lies within the difficulty to predict if the extraction site will be suitable for prosthesis placement if we just let nature take its course without intervention. Socket preservation is a preventive measure intended to avoid “alveolar bone and soft tissue collapse, which would cause unacceptable prosthesis esthetics.” (13)

While most peer research supports the practice of socket grafting to offset bone resorption and promote regeneration following a tooth extraction, comparable studies have shown that “bone generation can occur without socket grafting in extraction sockets with intact bony walls”. (8) Granted, this is a judgment call that might not be possible until after the tooth is removed.

If placement of a dental implant is an acceptable recommendation, generally both the patient and the provider would prefer to minimize surgical time and healing time by placing bone graft materials at the time of extraction. Bone, however, tends to be imperfect, even before the disruption of an extraction. (7)

Ridge Preservation
In 1988, periodontist and author E.S. Cohen defined the term socket preservation as a “surgical procedure in which graft material or a scaffold is placed in a fresh extraction socket to preserve the alveolar ridge for a future prosthesis”. (13) This was expanded in 2007 to delineate socket preservation as “specifically for the treatment of fresh extraction sockets with intact buccal bone walls” and ridge preservation in circumstances with “deficient buccal bone walls”.(13) The distinction came about because the buccal bone wall is “believed to have a relevant influence on bone healing”. (13)

Alveolar ridge preservation (ARP) generally involves a flap elevation procedure and placement of a bone graft with the goal of shoring up the midbuccal or midlingual height at the wall of the implant. Timing varies; depending on the extent of the bone deficiency, ARP can be performed in conjunction with the extraction, post-healing or at implant placement. (9)

Sinus lift procedures are frequently used to address vertical bone deficiency in pre-implant preparation of the maxillary posterior. The surgery itself includes gaining access to the sinus cavity, after which the sinus membrane is gently detached and lifted to create an area for placement of the bone graft.

While it is possible to place a dental implant immediately following the sinus lift procedure, Bortoluzzi et. al. concluded that greater success occurs with patients that have higher residual bone heights (>4mm). (14) Delayed placement with a healing period of approximately 6 months is the alternative.

Looking Ahead
Implant manufacturers and biologics companies are hot on the heels of solutions to provide both the clinician and patient with predictable outcomes and minimal surgery with shorter healing times.

And, interestingly, in the not-so-distant future, stem-cell research points to the possible implantation of tooth buds in sockets to regrow teeth or placement of a cellular scaffold in the socket to maintain the bone. (13)

Tissue Repair and Regeneration in Periodontics

While the first order of business in managing a patient's periodontal health is to eliminate infection and disease, the question of “how do we replace what has been lost?” is one that is pondered daily in our profession. The study of the periodontal repair and regeneration of soft tissue and bone has seen major changes over the last twenty years; surgical techniques have been taken to a new level through the development of regenerative products designed and tested specifically for the oral tissues.

CASE EXAMPLES: In Case Examples 1 and 2, these patients present with vertical intrabony defects. Assuming that all other oral health needs are stable and well-managed, the challenge becomes the inherent difficulties in repairing and rebuilding the bone, periodontal ligament and soft tissue to prevent further damage and tooth loss while also attempting to regenerate the lost alveolar bone, PDL and cementum.

Guided Bone Regeneration (GBR) and Guided Tissue Regeneration (GTR):

We would agree that the treatment plan for these situations would likely include periodontal surgery for access and root surface debridement to reduce bacterial levels and promote healing. In these cases, each of the treating periodontists employed Guided Tissue Regeneration (GTR) surgical procedures to facilitate the growth of bone and fill the defect.

Beyond the surgery itself, GBR and GTR typically involve the use of membranes (filters), bone and tissue grafts or tissue-stimulating proteins that are designed to interact with the body's natural healing and regenerative processes. The strategic objective of these products is to retard the downgrowth of gingival tissues, provide space maintenance, and promote new cementum, alveolar bone, and periodontal ligament cells.

Where Repair and Regeneration Overlap

In dental practice, we address one patient at a time. When we achieve results as in the examples provided, we would describe these as successful outcomes and probably not argue “what is repair vs. regeneration”? In the scientific arena, analysts would tell us that the only way to verify “regeneration” would be to obtain tissue samples followed by histological studies. Katz describes guided tissue regeneration as verified by through histological analysis as a form of repair termed “new attachment” (2013). So, the claim that we can “grow tissue” is perhaps better stated that we can “repair loss of tissue and bone”. Semantics, maybe, but also an indication of how wide and vast this area of research has become.

Who are Candidates for Guided Tissue Regeneration Procedures?

Patients that would likely benefit from regenerative periodontal surgical procedures are those that present with vertical bony defects evident on radiographs and localized deep probing depths. As with any dental treatment, healthy patients have a better treatment prognosis than those with systemic medical conditions, but certainly this will vary on a case by case basis. Also, smokers have much less predictable regenerative results than do non-smokers. A combined radiographic and clinical examination is needed to determine potential sites for regeneration; however, sites that are potential candidates are usually confirmed intrasurgically when the defect can be fully visualized.

How are Regenerative Procedures Different from Conventional Treatment?

In comparison, surgical bone and tissue regenerative procedures are closely related to soft tissue grafting procedures for addressing gingival recession, but are generally more invasive and require longer healing times.

Post-surgical healing is also different - in traditional surgical and non-surgical therapy, tissue response and growth is limited to the most apical portion of the defect along the root surface. A positive response to regenerative periodontal surgery will stimulate differential tissue response, which increases bone levels, clinical Attachment levels and reduces pocket probing depths. Humphrey states, “the use of regenerative periodontal procedures that include bone graft materials and membranes generally produce greater intrabony bone defect fill than flap debridement alone” (2014).

The Future of Periodontal Regeneration

Future efforts in the study of regeneration will likely focus on controlling this process to create predictable outcomes. As we continue to manage the oral health of our aging “baby boomer” population, the demand for services that help patients keep their teeth and support an enjoyable quality of life will continue to inspire researchers and practitioners alike in this area of practice.