Implant-enhanced removable partial denture treatment - dental implants by jizhen1947



Implant-enhanced removable
partial denture treatment
John F Carpenter presents a case report illustrating the retrofit of an existing
removable partial denture with implants

             e are all familiar with the science
             and great success of implant           Education aims and objectives
             osseointegration. A multitude of       The aim of this article is to introduce the clinical use of the implant-
articles and lectures have demonstrated the         enhanced removable partial denture (IERPD).
merits of fixed implant prosthodontics for the          The reader will:
partially edentulous patient. There is, however,    • Have an appreciation of the advantages and disadvantages of
a paucity of studies discussing the utilisation     this treatment modality
of implants with removable partial dentures         • Learn about its clinical suitability through a case study
(Mijiritsky E, 2007).                               • Understand that while simple in theory, IERPD requires a
    This article describes one of these often-      comprehensive understanding of implant therapy and a mastery of
neglected patients who is partially edentulous      removable prosthodontics.
and does not desire a fixed prosthodontic              Implant Dentistry Today subscribers can answer the CPD questions
solution. Treatment of this type of patient         on page xx to earn one hour of verifiable CPD from reading this article.
has been a major growth area of my practice.
Demographic studies show a population growth
in ageing baby boomers who have maintained         A, Ostry L, 2002; Douglass CW, Watson AJ,                  months of additional time needed for bone
many of their own teeth (Douglass CW, Shih         2002; Wöstmann B et al, 2005). Years ago,                  augmentation to heal.
                                                   this age group was often fully edentulous but                  Removable partial dentures (RPD) can be
                                                   is now partially edentulous.                               greatly enhanced by the addition of implants.
            Dr Carpenter graduated from                The advantages of a fixed implant                      Many of the problems with conventional RPDs
            Boston College with a Bachelor’s       restoration are numerous and patients often                can be overcome with the placement of one or
            and then a Master’s degree in          perceive them as actual body parts. However,               more strategically positioned implants. These
            chemistry. He obtained his             the disadvantages of the construction of a                 enhanced RPDs have been called implant-
            Doctorate of Dental Medicine           fixed implant restoration option include                   assisted removable partial dentures (IARPD)
            from Tufts University in               anatomical challenges, such as proximity                   (Schneid T, Mattie P, 2008), implant-retained
Massachusetts and completed a residency            to vital structures and lack of bone. While                partial overdentures (IRPOD) (Chikunov I,
at Brookdale Hospital in New York City. Dr         many of these challenges can be overcome,                                  ,
                                                                                                              doan P, Vahidi F 2008) and implant-supported
Carpenter has been practising dentistry in
                                                   not all patients are willing, for example, to              removable partial dentures (ISRPD) (Ohkubo
New Windsor in New York State since 1983.
Throughout his career, he has understood           undergo additional surgeries to grow bone.                 C et al, 2008). There are many advantages
the importance of continuing education,            Bioengineering challenges of fixed implant                 to implant-enhanced RPD (IERPD) versus
allowing him to treat his patients with            restorations often preclude their use. In cases            conventional RPD (see Table 1 overleaf).
the most advanced dentistry available. Dr          of excessive interocclusal space, a removable                  A major advantage of implant-enhanced
Carpenter has been involved with dental            restoration puts less stress on the implant                RPD as compared to a fixed implant restoration
implantology since 1982, with the goal             abutments and is often more aesthetic; a                   is that separate bone augmentation surgery is
of helping his patients to achieve optimal         removable partial denture can make use of the              rarely needed. A small ‘island of bone’ is all
dental health for a lifetime. Dr Carpenter has     acrylic denture base to support and enhance                that is required to anchor the implant fixture.
received a Fellowship from the International
                                                   facial aesthetics in a non-surgical manner.                Forces on the implant fixtures are much less
Congress of Oral Implantologists. He has
also received the Academy of General                   It has been my experience when discussing              in an IERPD situation compared to a fixed
Dentistry’s Fellowship and Mastership              the option of fixed implant restorations                   implant restoration. Multiple long, wide and
awards. Dr Carpenter frequently lectures           requiring extensive bone grafting that the                 exactly placed implant fixtures are required
at various continuing education meetings           patient often asks for alternative treatment               to support fixed implant restorations. Often,
and has published articles on advanced             options. Patients often choose the less                    only one or two small implants are necessary
treatment techniques and procedures. His           challenging removable option. Many reasons                 to help enhance a RPD.
special interests include dental implants,         exist, including the following:                                The only contraindications I have found to
complex restorations and cosmetics. He is          1. Financial limitations                                   an implant-enhanced RPD are:
a member of multiple dental organisations,
                                                   2. Emotionally, patients are often unable to               1. A patient who is unwilling to wear any kind
including the International Congress of
Oral Implantologists, the Academy of               commit to additional surgery with associated               of removable prosthesis
Osseointegration, and the International            morbidity                                                  2. Patients who oppose any surgical procedure
Association for Orthodontics.                      3. Patients’ unwillingness to commit to the six            to place an implant or whose medical condition

June 2010 	                                                                                                                            Implant	dentistry today xx

prevents them from receiving elective implant
placement.                                             Table 1: Advantages of an implant-enhanced removable
                                                       partial denture versus conventional removable partial denture
Case presentation
Pre-operative assessment
A 65-year-old male patient presented for his           • Improved comfort and confidence
three-month recall visit. Although the patient
                                                       • Patients who were formerly unable to wear a conventional RPD are often
had no complaints, clinical examination                able to wear an enhanced RPD
revealed an increase in mobility of teeth UR4
and UL4. These teeth are the abutments for             • Enhanced retention, support and stability
his maxillary removable partial denture (RPD).         • Improved aesthetics if clasps can be eliminated
This Kennedy Class I RPD had been made 10
                                                       • Preservation of bone
years previously, and replaced UR7, UR6, UR5,
UL5, UL6 and UL7 (Figures 1, 2 and 3). The             • Better distribution of forces and elimination of damaging leverage to
teeth are stained from chlorhexidine rinse but         natural abutment teeth
are, for the most part, plaque-free.                   • Psychological advantage to patient of preserving compromised natural
    His remaining dentition, although                  teeth that are not suitable to use as abutments to support an RPD
periodontally compromised, had remained                • An increase in chewing force
stable excepting one incident over the past
10 years. The UR7 was a compromised tooth              • A contingency plan where implant placement may be staged and this
                                                       prosthesis can be used as an interim option
when the partial was first constructed, but was
maintained since it offered some additional
retention and stability. After four years, UR7
required extraction and a tooth was added to
the existing RPD (Figure 4). This converted
the partial from a Kennedy Class II design with
a tripodal configuration of clasps to a Kennedy
Class I design with a bilateral configuration of
clasps. Kennedy Class I is the least desirable
RPD and placed increased leverage forces on
the abutments at UR4 and UL4 (Figures 5 and
                                                    Figure 1: Facial view of patient with retractors           Figure 2: Occlusal view of patient without partial
    The patient understood the situation and
requested something be done to prevent the
loss of teeth UR4 and UL4. He wished to
maintain his natural dentition for as long as
possible and was quite happy with his existing
partial. It is important to note that the patient
was on a fixed income. Aesthetics, such as the
display of clasps, was not a concern for him
(Figure 1).
    Several treatment options were discussed
and it was mutually decided that advanced
bone grafting and fixed implant options would
not be entertained. Financially and emotionally,    Figure 3: Occlusal view of patient with existing partial   Figure 4: Existing Kennedy Clasp I RPD showing where
he was interested in less challenging treatment     in place                                                   UR7 was added
options. Construction of a new partial
would do little to improve the forces on the
compromised abutments.                              for its major connector (Figure 3). This                   available just distal of the UR4 and UL4 to
    I felt that since he was so happy and           distributes occlusal forces over a broad area,             place implants (Figure 6)
functioning well with his existing partial, there   in much the same way a snowshoe functions.                 3. Interocclusal space analysis – treatment
was no need to complicate things. A careful         All clasps, rests and guide planes were intact             using attachments to connect a partial denture
examination of his mouth and existing partial       and functioning well. A reline had previously              to implants is quite space-sensitive. A careful
was undertaken to see if implants could be          been performed one year earlier so poor tissue             assessment of interocclusal space was done
placed and whether they would enhance his           fit was not contributing to movement of the                (Figure 7). Using a Boley gauge, a space of
existing partial.                                   natural teeth abutments                                    6.5mm was recorded. For strength, 2mm of
    The following three areas were evaluated to     2. Radiographic analysis: extreme bone loss                acrylic should cover the attachment; therefore,
assist in making this decision:                     posteriorly and the pneumatisation of the                  the remaining 4.5mm of space was available for
1. Partial design analysis: the existing RPD        maxillary sinus was noted. Even with this                  the attachment. This is sufficient for multiple
was quite sound, utilising full palatal coverage    severe bone loss, two ‘islands of bone’ were               implant attachment systems.

xx Implant	dentistry today                                                                                                                                  June 2010

Figure 5: Lateral view demonstrating leverage forces   Figure 6: Radiograph displaying ‘islands of bone’       Figure 7: Boley gauge measuring existing interocclusal
                                                       available in the UR5 and UL5 areas                      space available

Figure 8: Intra-oral view of healing collars           Figure 9: Panoramic radiograph with implants in place   Figure 10: Locator abutments

   Based on these findings, it was decided             Retrofit of existing partial (RPD)                      place. Light cure the intaglio surface and fill any
to place two implant fixtures and retrofit             The decision to use locator attachments was             voids to ensure the housings are secure. The
his existing RPD with implant attachments.             based on its low profile, allowing sufficient           locator tool is then used to remove the black
This would enhance his partial and mitigate            acrylic to cover the attachment housings for            processing parts and insert the appropriate
destructive torquing forces on his abutment            maximum strength. This was quite important              retentive males. In this situation, blue males
teeth. An additional benefit was to provide            since natural teeth oppose the attachment and           (1.5lbs of retention) were used (Figure 15).
a contingency plan for the future. If anterior         the patient exhibited evidence of bruxism.                  At the three-month recall, natural teeth
teeth are lost, implants could be added and            The gold-plated female locator abutment                 abutments UR4 and UL4 displayed much
an implant bar-retained overdenture could be           (Figure 10) was selected and torqued into               less mobility and an improved prognosis was
constructed.                                           place. Adequate interocclusal space is obvious          noted.
                                                       (Figure 11). Metal housings were snapped on
Implant placement                                      and were ready to be picked up into the RPD             Discussion and conclusion
A surgical guide was first constructed. This           (Figure 12). Relief of the partial denture was          Implant-enhanced removable partial denture
guide took into consideration the normal               accomplished to allow for passive fit over the          (IERPD) treatment, while simple in theory,
concerns of spacing and 3D orientation of              attachment housings (Figure 13). Note the               requires a comprehensive understanding of
the implant fixtures. A surgical guide for             metal mesh still present around the relieved            implant therapy and a mastery of removable
an implant-enhanced RPD must also take                 area, providing reinforcement and acrylic               prosthodontics. First, a proper pre-operative
into consideration the path of insertion and           fracture prevention.                                    clinical assessment and evaluation of dental
removal of the RPD. Every effort must be made              To connect the attachment to the RPD,               anatomy, including intra- and inter-arch
to keep the implant fixture parallel to this           Zest light-cured composite was used. After the          spaces, should be performed. A good
path. This will prevent wear of the attachment         application of a bonding agent, the composite           understanding of RPD design concepts (Daher
components and minimise the use of angled              was injected through a hole in the side of the          T, Hall D, Goodacre C, 2006; Phoenix R, Cagna
implant abutments or some other compensating           RPD (Figure 14). The flowable composite was             D, DeFreest C, 2008) and the biomechanical
feature. This is best accomplished using a             light cured as the partial was firmly held in the       capability of implants, teeth and RPDs are
dental laboratory surveyor with mounted                rest seats and guide planes.                            necessary to execute this therapy.
diagnostic models.                                         The patient should never close and clench               IERPD is a space-sensitive treatment.
   Two ScrewPlant implant fixtures were                when processing the attachment into the RPD.            Interocclusal space must be carefully
placed (4.7 x 8mm and 4.7 x 10mm) (Figures             It is best to use one’s fingers pressing firmly         assessed prior to treatment. Insufficient
8 and 9). Since it was necessary for the patient       on the metal rest seats. This will prevent over-        space could prevent implant utilisation or
to wear his partial during osseointegration,           compression of the soft tissue and the creation         result in inadequate bulk of acrylic over the
the partial denture was relieved generously in         of a dislodging force that may cause the RPD            attachment. Acrylic requires bulk for strength;
this area and soft relined. After five months of       to pop loose.                                           if this is not achieved, the unfortunate result
healing, the partial was attached to the implant           The partial denture is removed with both            will be continuous repairs for the life of the
using Zest locator attachments.                        metal housings and black processing males in            prosthesis.

June 2010 	                                                                                                                                Implant	dentistry today xx

Figure 11: Lateral view displaying sufficient      Figure 12: Attachment housings ready to be               Figure 13: Necessary space created for attachments
interocclusal space for attachments                incorporated into RPD

Figure 14: Injecting flowable composite            Figure 15: Intaglio view of retrofitted RPD with metal   Figure 16: Damaging leverage forces to this patient’s
                                                   housing and one blue male attachment                     natural teeth from his conventional Kennedy Class I
                                                                                                            RPD. Pathologic mobility of abutment teeth was noted

    When retrofitting an existing RPD with             The addition of implants to this patient’s
implants, be sure that there are no design         RPD improved the biomechanics of the
flaws and the RPD fits well. It would be best to   partial. These implants mitigated damaging
construct a new RPD if there are any problems.     leverage forces to his natural abutment teeth
Design principles for an IERPD should be           and mobility was decreased (Figure 17).
consistent with those of a conventional RPD.       Additional benefits to this patient included
The partial should be well reinforced with         improved comfort, retention, support and
metal around the location of the implant           stability, bone preservation, maintenance of
attachments. This will prevent one of the major    existing teeth and RPD, contingency planning
complications – the fracture of acrylic around     for the future, and cost effectiveness.
the implant attachment housing.
    As discussed in this case presentation, this   References                                               Figure 17: By adding implants, an implant-enhanced
                                                                                                            RPD was created. This neutralised the unfavourable
patient’s major problem was the increased          Chikunov I, Doan P, Vahidi F (2008) Implant-             torquing forces of the conventional partial
mobility of RPD abutment teeth UR4 and             retained partial overdenture with resilient
UL4. By adding two implants, it was possible       attachments. J Prosthet Dent 17: 141-148
to improve the biomechanics of his existing        Daher T, Hall D, Goodacre C (2006) Designing
RPD. A conventional RPD distributes chewing        successful removable partial dentures.                   extension removable partial dentures: in vivo
force between natural teeth abutments and          Compendium 27: 186-193                                   assessment. Int J Oral Maxillofac Implants 23:
soft tissues. An IERPD distributes the force       Douglass CW, Shih A, Ostry L (2002) Will                 1095-1101
among natural teeth abutments, soft tissues        there be a need for complete dentures in                 Phoenix R, Cagna D, DeFreest C (2008)
and implants. By adding an implant to a RPD,       the United States in 2020? J Prosthet Dent               Mechanical principles associated with
the retention, support and stability of the RPD    87: 5-8                                                  removable partial dentures. In: Stewart’s
are all enhanced.                                  Douglass CW, Watson AJ (2002) Future needs               Clinical Removable Partial Prosthodontics. 4th
    A review of the oral biomechanics shows        for fixed and removable partial dentures in the          ed, p95-117. Quintessence, Illinois
that healthy teeth may be vertically displaced     United States. J Prosthet Dent 87: 9-14                  Schneid T, Mattie P (2008) Implant-assisted
0.08mm to 0.28mm under load (Misch C,              Mijiritsky E (2007) Implants in conjunction              removable partial dentures. In: Stewart’s
2008). In contrast, healthy soft tissue covering   with removable partial dentures: a literature            Clinical Removable Partial Prosthodontics. 4th
ridges can be displaced 1.0mm and if flabby,       review. Implant Dentistry 16: 146-152                    ed, p259-277. Quintessence, Illinois
soft tissue exists, this number is much higher.    Misch C (2008) Contemporary implant dentistry.           Wöstmann B, Budtz-Jø0rgensen E, Jepson N
The significant difference between teeth and       3rd ed, p259. Mosby, St Louis                            et al (2005) Indications for removable partial
ridge mobility can lead to the pathologic          Ohkubo C, Kobayashi M, Suzuki Y et al                    dentures: a literature review. Int J Prosthodon
mobility of abutment teeth (Figure 16).            (2008) Effect of implant support on distal-              18: 139-45 I

xx Implant	dentistry today                                                                                                                             June 2010

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