A Systematic Review on Prosthodontic Rehabilitation of Hemimandibulectomy Defects

Restoration of hemimandibulectomy defects following tumour extirpation to restore oral function is a herculean task for practitioners. Prosthetic treatment alternatives available for rehabilitation of acquired hemimandibulectomy defects according to mandibular reconstruction type and extent (Cantor-Curtis classification) are unclear. This systematic review aims to assess the spectrum of prosthodontic rehabilitation approaches with regard to reconstruction type and extent of mandibular surgical defects. The databases incorporated for literature search were Google Scholar and Medline (PubMed). Relevant search terms for hemimandibulectomy and reconstruction with prosthetic rehabilitation were used. Two reviewers independently assessed the articles using eligibility criteria; published case reports and case series in the English language and depicting prosthodontic treatment modality of patients greater than 15 years were included. A total of 202 records were identified from the database search of which 19 duplicates were removed. The remaining articles were assessed for eligibility, and 55 articles (comprising 58 cases) were finally included in the study. This review revealed various prosthetic alternatives ranging from guide flange, twin occlusion, palatal ramp, conventional to hybrid partial and complete dentures to implant-supported prosthesis including a few innovative prosthetic approaches. This systematic review provides a plethora of prosthodontic rehabilitation approaches according to the extent of hemimandibular surgical defect and type of reconstruction. This will facilitate practitioners and prosthodontists in sequential treatment planning and management of hemimandibulectomy cases in their routine practice.


Introduction And Background
Surgical excision of various malignant or benign tumours like ameloblastoma, osteosarcoma and various injuries of the maxilla and/or mandible has resulted in partial or total maxillofacial defects involving hard and soft tissues.These conditions deteriorate oral function, aesthetics and comfort leading to impaired quality of life.Due to extensive surgical resection, the surface area required for adequate retention of the prosthesis is remarkably reduced.The radiotherapy adjunct with surgery further deteriorates the loadbearing capacity of the underlying denture-supporting tissue, and thus, the prosthodontic rehabilitation of these patients becomes an uphill task.Various classifications of hemimandibulectomy defects based on the nature and extent of mandible resection are available, but the Cantor and Curtis (CC) classification devised in the 1970s was widely observed in the majority of the articles studied.This system classifies defects based on remaining structures into six classes [1].
Restoration of the hemimandibular defect is a multidisciplinary approach involving an onco-surgeon, oral maxillofacial surgeon, prosthodontist, speech therapist, physiotherapist, etc. Treatment varies according to the type of mandibular reconstruction (hard tissue graft; fibula, iliac, etc. or soft tissue graft; pectoralis major myocutaneous flaps, etc.).Various prosthetic options are available including implant-supported prosthesis, endoprosthesis, guiding flange, twin occlusion prosthesis, etc. to improve a patient's mastication, speech, aesthetics and lifestyle [2].Despite these treatment recommendations, the ideal prosthetic rehabilitation of patients diagnosed with hemimandibulectomy is challenging and indecisive among practitioners.A review of the literature regarding functional outcomes related to prosthetic treatment after hemimandibulectomy has been performed previously, but a published systematic review on this topic is lacking.The present systematic review was a comprehensive review of prosthetic treatment approaches in hemimandibulectomy patients, and the purpose of the systematic review was to give treatment recommendations according to the type of mandibular reconstruction and the extent of the defect on the available evidence.

Methodology Review Protocol
The systematic literature search was performed according to the Preferred Reporting Items for Systematic Reviews and Meta-analysis (PRISMA) guidelines [3] and was registered at the International Prospective Register of Systematic Reviews (PROSPERO-CRD42021264928).

Literature Search Strategy
An initial search was conducted on June 30, 2021, by using electronic databases of Medline (PubMed) and Google Scholar by two independent researchers (SK and SS) for published articles from January 1, 2010, to June 30, 2021, as per inclusion criteria.The database Medline (PubMed) was searched with the following keywords for Medical Subject Headings (MeSH) terms: "hemimandibulectomy", "rehabilitation", "prosthetic" and combinations of these keywords were used for Google Scholar with appropriate filters (Table 1).

Screening and Selection
All published case reports and case series on human subjects having hemimandibulectomy defects, fulfilling the inclusion criteria and depicting a type of prosthetic rehabilitation were considered.Only full-text articles published in the English language were included.Original research, clinical trials, laboratory studies, animal studies, editorials, questionnaire studies and reviews were excluded.Titles and abstracts were screened (HD and SK) according to the inclusion criteria, and those with unclear methodology were included in the fulltext assessment (Table 2).

Risk of Bias Assessment
Quality assessment of all the relevant studies included in the present review was performed by two reviewers (HD and BS) according to the Joanna Briggs Institute (JBI, Adelaide, Australia) [4].This JBI critical appraisal tool comprises eight questions for case reports and 10 questions for case series that assess specific domains to determine the potential risk of bias and could be answered with 'yes', 'no' or 'unclear'(Supplementary Appendix 1).Reports scoring less than four questions out of eight as 'yes' (<50% JBI) in case reports and less than five answers as 'yes' out of 10 questions in case series were denoted as high risk of bias and were excluded.Any disagreements between reviewers were discussed and resolved by consensus.If no consensus could be reached, a third reviewer (RJ) gave a binding verdict.The risk of bias in individual studies was determined with the following cut-offs: low risk of bias if 70% of answers scored yes, moderate risk if 50% to 69% of questions scored yes and high risk of bias if yes scores were below 50% and were excluded [5].

Data Extraction
The relevant studies obtained following screening were categorised into two groups: case reports and case series.Two reviewers (HD and SK) accomplished data extraction individually, while AJ checked the data: author name, year of publication, JBI score, age, gender, extent of defect (CC classification), name and type of prosthesis in both arches, reconstruction type (if any), surgical scarring, radiotherapy, follow-up period and adverse effect.

Study Characteristics
The initial literature search from the selected databases revealed 202 records from which 19 duplicates were identified and removed.After the screening of titles and abstracts, 55 articles (58 cases) with moderate to low risk of bias were finally included after quality assessment (Figure 1).3, 4) .

Post-prosthetic Follow-Up
Post-prosthetic recall visits were reported in 48 cases with duration ranging between 48 hours to four years (n=9; < 1 month, n=27; 1 month to 1 year, n=4 ; >1 year).Recall visit without duration was noted in eight cases, while follow-up was not reported among 10 cases.

Discussion
Prosthodontic rehabilitation of hemimandibulectomy defects is a challenging task including multiple procedures with an interdisciplinary approach towards restoring function and patient satisfaction.Prosthetic rehabilitation post-resection with radiotherapy poses challenges in implant placement due to the risk of radiation-induced osteoradionecrosis at the bone level.Dental implant placement within 12 months following radiotherapy corresponds with a 34% increased risk of failure and thus recommends placement after one year of irradiation.Radiation dose greater than 5,000 cGy increases the implant failure rate to 33% [9].A case of class I defect exhibiting marginal mandibulectomy was successfully rehabilitated using a single-piece smooth surface cortically anchored implant-supported fixed partial denture placed in native bone.These implants are the preferred choice in post-radiotherapy cases, as they do not require active biologic osseointegration (immediate loading is possible), transmit occlusal forces at the cortical bone, reduce the risk of infection, devoid of micro gap junctions resulting in the least plaque accumulation causing peri-implantitis and no abutment screw loosening/fracture as compared to two-piece implants [7].

Prosthetic Alternatives According to
Removable CPD or CD with extracoronal semi-precision attachments is a cost-effective and less invasive treatment alternative where dental implants are not feasible [48,49].
Segmental mandibulectomy distal to the canine (CC class II) devoid of hard tissue reconstruction leaves the patient with no option of chewing due to mandibular deviation towards the resected side exhibiting rotation and angular path of jaw closure.This is aggravated in edentate arches due to the generation of unilateral occlusal forces during mastication resulting in dislodgement of maxillary denture; therefore, implantsupported overdenture adjunct with MRP has overcome these problems and has proved to be a boon in completely edentate patients.The abnormal jaw relations along with the angular path of closure favoured the use of monoplane teeth adjunct with neutrocentric concept are advisable to achieve a non-restrictive occlusion.The maxillary ramp stabilizes the prosthesis, limits the mandibular deviation and provides a broad occlusal table for ease in mastication [8,9].If implants are not practical, removable MGFP/MRP are advisable where the mandible can be manipulated to correct the deviation followed by definitive prosthesis [20,21,28,29,32,34,37,41,[53][54][55][56][57][58][59][60].In individuals where mandibular deviation correction was not possible manually as mostly seen following radiotherapy and scar formation, a twin occlusion (palatal row for occlusion and buccal row for cheek support) has proved to be beneficial in achieving mastication and aesthetics [11,14,15,17,19].
A class III segmental resection extending to the midline elicits increased mandibular deviation with marked facial disfigurement, decreased masticatory function, diminished speech and altered occlusion with condylar rotation resulting in anterior open bite thereby complicating the treatment prognosis.Early initiation of post-resection jaw exercises helps to loosen the scar contracture and improve the maxillomandibular relationship [2].Intermaxillary fixation may also minimise deviation but complicates feeding.Acrylic MGFP is a cost-effective alternative with the added advantage of periodic adjustment over metal guide flange [24-26,30, . The acrylic flange during sequential adjustment becomes thin and weak; hence, reinforcing with 'W'-shaped wrought wire is an innovative approach to overcome this drawback [23].The twin occlusion prosthesis as given in class II situation is indicated in class II defects [16,18].In completely edentate individuals, the definitive treatment of choice is similar to class II defect.Flexible dentures (Valplast) are indicated in reduced mouth opening with mandibular deviation situations which facilitates easy insertion and removal.It comprised monoplane occlusion (minimises stress and improves stability) along with acetal resin clasp to enhance retention and aesthetics [52].
Class IV defect involves the resection of the lateral aspect of the mandible augmented to maintain pseudo articulation of bone and soft tissue in the region of the ascending ramus.It presents with facial asymmetry, mandibular deviation and improper occlusion due to the depressor muscle action of the normal side.Various treatment modalities have been proposed to reduce post-surgical mandibular deviation (e.g.mandibular guidance therapy, intermaxillary fixation, resection guidance restorations).A similar challenging situation with limited interarch distance causing occlusal interference by the buccal flange of MGFP on the nonresected side has been resolved by using an MRP in relation to the non-defect side and MGFP on the defect side to establish bilateral guidance.This unique combination of prosthesis reduces the deviation and retrains the individual to achieve proper occlusion by neuromuscular reprogramming activity [27].
Authors have suggested immediate mandibular reconstruction post-resection with vascularised free flaps to prevent implant placement complications post-radiotherapy [9] and improve both facial symmetry and masticatory efficiency.Implant prosthesis is the treatment of choice for a reconstructed mandible, but an extensive period of more than one year is required for the healing of osseous graft and osseointegration of implants (in irradiation).During this initial healing phase, early prosthodontic intervention by MGFP and maxillary stabilisation prosthesis serve the purpose of reducing the mandibular deviation, preventing extrusion of the maxillary teeth and improving the masticatory efficiency.In cases where implants are not feasible, an interim MGFP/MRP followed by CPD is an effective, economic alternative [45,46].A modified swing lock CPD with the flexible arc of the acetal labial bar has been used by authors which supersede the conventional complex design with enhanced aesthetics along with retention and stability [43].Mandibular deviation and anterior open bite in a complex class IV defect (along with radical neck dissection and base of the tongue) can be corrected with MGFP subsequently followed by a definitive prosthesis.In some patients, the correction of mandibular rotation with a guidance appliance cannot be accomplished adequately; therefore, to compensate for the residual open bite, an overlay RPD provides optimum occlusion bilaterally improving the patient's form and function [51].
The present systematic review had limitations as it was restricted only to Medline by means of PubMed and Google Scholar; so, the literature published on other databases and languages apart from English may have been omitted despite meeting all our inclusion criteria.Randomised controlled trials (RCT) were scarce in our search on the particular topic; therefore, the next level of evidence (i.e.case reports and series) was included; therefore, authors are urged to perform extensive RCTs on similar topics.Post-prosthesis observation duration was a deficit in many studies, while few reported short-term (less than one month) follow-up; therefore, future studies with long-term follow-up data are recommended for assessing the prosthesis longevity.Several data were lacking from the reviewed literature including CC classification, reconstruction type and scarring which decreases the article quality limiting us to deduce a strong correlation among the type of prosthesis to be selected for a particular situation.

Conclusions
This study suggests that the first line of treatment following surgical resection includes hard tissue graft reconstruction along with interim guidance and definitive implant prosthesis (after one year in case of irradiation).In cases of CC classes II, III, IV and V defects associated with mandibular deviation where occlusion can be attained manually, MGFP/MRP would be the preferred treatment modality followed by a definitive prosthesis.In mandibular-deviated cases where occlusion is not achievable manually, a twin occlusion prosthesis is recommended.
In spite of certain limitations, this review highlights numerous prosthetic approaches according to the extent of hemimandibular defect and type of reconstruction in a snapshot.Adequate patient adaptation with minor complications in few which when corrected revealed favourable results.This study will guide the clinicians during treatment planning of hemimandibulectomy patients.

JBI critical appraisal checklist for case series
Reviewer ____________________________________ Date____________________________ Author _____________________________________ Year_________ Record Number________

FIGURE 1 :
FIGURE 1: PRISMA flow diagram depicting the literature selection process PRISMA: Preferred Reporting Items for Systematic Review and Meta-analysis; JBI: Joanna Briggs Institute.

1 . 2 .□ 3 . 4 . 5 . 6 .
Were the patient's demographic characteristics clearly described?Was the patient's history clearly described and presented as a timeline?□ □ □ Was the current clinical condition of the patient on presentation clearly described?Were diagnostic tests or assessment methods and the results clearly described?Was the intervention(s) or treatment procedure(s) clearly described?Was the post-intervention clinical condition clearly described?

TABLE 1 : Systematic search strategy
MEDLINE: Medical Literature Analysis and Retrieval System Online; MeSH: Medical Subject Headings.

TABLE 2 : Inclusion and exclusion criteria
TMJ: temporomandibular joint.
Were there clear criteria for inclusion in the case series?□□ □ □2.Was the condition measured in a standard, reliable way for all participants included in the case series?